Funding

VDRC will be offering Pilot and Feasibility (P&F) Awards for 2022 in the following areas:

 

 

 

 


Introducing the 2021 P&F Awardees:

 

Rafael Arrojo e Drigo, PhD

photo

P&F

Department of Molecular Physiology & Biophysics

 

The molecular signature of long-lived beta cells in the developing pancreas

Diabetes is caused by the functional collapse of insulin-producing beta cells in the islet of Langerhans in the pancreas. Beta cell function is supported via paracrine signaling pathways from neighboring alpha and delta cells. Most alpha, beta and all delta cells in the healthy pancreas can be as old as cortical neurons and are classified as long-lived cells. During diabetes, beta cells become dysfunctional and/or lose their maturation via unknown mechanisms that are enhanced by aging and diabetes. Our recent study has linked the onset of islet cell longevity to early stages of postnatal life in mice between post-natal days 21 and 45 (P21 and P45, respectively). Further, data from our lab indicate that 25% of alpha and beta cells become long-lived and likely are functionally and transcriptionally mature prior to weaning at P21 – a time point that has been thought to be critical for functional maturation of all beta cells. This data suggests that a significant sub-set of beta cells makes the critical decision towards becoming a long-lived cell at a very early point in post-natal life and before all metabolic signaling cues associated with adulthood and sexual maturation are active. However, it is currently unknown what cellular adaptations and molecular pathways are associated with the early life onset of beta cell longevity. This project will establish the longevity and molecular signatures of beta cells at different post-natal developmental time points in the mouse pancreas through utilization of high-resolution single cell transcriptional sequencing and isotope tissue mapping. These profiling technologies are complementary and are expected to reveal the connection between beta cell transcriptome and epigenetic architecture and age during the critical window of time when beta cell longevity is determined. Understanding the pathways activated by maturing beta cells and associated with long-term maintenance of cell function and health will lead to new methods to promote and preserve beta cell function in diabetic patients.

 

Jamey Young, PhD

photo

P&F

Department of Chemical & Biomolecular Engineering

 

In vivo 2H/13C flux analysis to assess LXR activation as a strategy to inhibit NASH pathogenesis

Despite the fact that non-alcoholic fatty liver disease (NAFLD) affects nearly 30% of the US population, there is currently no approved pharmaceutical treatment to inhibit progression of NAFLD to its more severe stage of nonalcoholic steatohepatitis (NASH). Recent studies using isotope tracers to assess in vivo metabolism of human subjects and mouse models have uncovered that citric acid cycle flux is nearly 2-fold higher in NAFLD compared to controls, which was hypothesized to promote oxidative stress associated with NASH development. The liver X receptors (LXRs) are key regulators of cholesterol and fatty acid homeostasis in liver. When activated, LXRs induce a series of genes that are involved in fatty acid synthesis, absorption, transport and excretion. Activation of LXR has the potential to modulate membrane phospholipid (PL) composition, improve hypercholesterolemia, induce anti-inflammatory effects, regulate endoplasmic reticulum stress and increase insulin sensitivity, but may potentially increase liver hypertriglyceridemia. GW3965 is a selective, orally active non-steroidal agonist for the LXRs. It was shown to induce the expression of LXR target genes, modulate cellular PL composition and blunt the induction of downstream, unfolded protein response signaling pathways in primary mouse hepatocytes. However, the effects of LXR activation on in vivo liver metabolic fluxes during NASH development are not well understood. The overall objective of this proposal is to apply 2H/13C metabolic flux analysis (MFA) and molecular profiling to assess responses to pharmacologic LXR activation designed to inhibit progression from NAFLD to NASH in vivo. We hypothesize that even though LXR activation may worsen liver steatosis, it will reduce metabolic dysregulation by improving membrane fluidity and fatty acid trafficking through augmenting PL and cholesterol composition of the ER and mitochondrial membranes. This in turn may prevent overactivation of mitochondrial metabolic pathways and oxidative tissue injury leading to NASH. These studies will use a melanocortin-4 receptor knockout (MC4R-/-) mouse model that has been previously shown to rapidly and spontaneously develop characteristics of human NASH upon Western diet feeding. To enable a more comprehensive analysis of in vivo fluxes, we will apply a recently developed mass spectrometry (MS)-based MFA approach that explicitly accounts for Cori cycling between hepatic and extrahepatic compartments in order to relax several constraining assumptions of previous models. We also expect to utilize LC-MS based analysis of glycolytic intermediates to build more detailed models and further understand metabolic changes during NASH pathogenesis.

 

Richard O'Brien, PhD

photo

Discovery

Department of Molecular Physiology & Biophysics

 

Developing and performing a high throughput screen for ZnT8 inhibitors

Genome-wide association studies (GWAS) have shown that the ‘T’ allele of the rs13266634 nonsynonymous single nucleotide polymorphism (SNP) in the SLC30A8 gene, which encodes the zinc transporter ZnT8, decreases susceptibility to type 2 diabetes (T2D). The ‘T’ allele changes ZnT8 amino acid 325 from an arginine to a tryptophan resulting in decreased ZnT8 activity. Similarly, SLC30A8 haploinsufficiency is markedly protective against the development of T2D. The SLC30A8 gene is predominantly expressed in pancreatic islet beta cells and both the rs13266634 ‘T’ allele and haploinsufficiency are associated with improved glucose-stimulated insulin secretion (GSIS). Reduced SLC30A8 expression also protects beta cells from both endoplasmic reticulum-associated and cytokine-mediated stress. These observations strongly suggest that ZnT8 inhibitors may prevent T2D through actions on beta cell function and clearly justify efforts to identify such compounds.

We have created a bacterial-based assay that enables us to quantitate ZnT8 activity in intact cells. This assay is based on the ability of ZnT8 to enhance the inhibitory effect of cadmium chloride on bacterial cell growth. The goal of Aim 1 is to compare two common inducible bacterial protein expression systems, in which ZnT8 expression is controlled by either isopropyl b-D-1-thiogalactopyranoside (IPTG) or L-arabinose, to identify one that is optimal for the induction of ZnT8 expression for use in a high-throughput screen (HTS). The goal of Aim 2 is to then use the optimized assay to perform a HTS using Vanderbilt’s HTS screening facility and compound libraries to identify compounds that affect bacterial growth specifically through an action on ZnT8. We hypothesize that that our novel ZnT8 transport assay will lead to the identification of ZnT8 inhibitors.

 


 

Read more about previous P&F Award recipients below.

 

  •  

    photo

    Sheila Collins, PhD

    Department of Medicine (Cardiovascular Medicine)

     

    Modulating Gbγ–SNARE interaction for adipose tissue metabolism and energy expenditure

    Obesity is now an epidemic in the United States – more than 40% of the population obese or severely obese (2016 data from CDC). The associated risk for type 2 diabetes, cardiovascular disease, hypertension, and certain cancers continue to escalate. Given that this epidemic is driven by an overall positive energy balance, and since current pharmacological treatments for obesity are largely ineffective, agents acting through peripheral mechanisms to increase energy expenditure (EE) should be particularly valuable. We have discovered a mechanism that is unexpectedly effective at increasing energy expenditure (EE) and improving glucose homeostasis. Disabling the GBγ-mediated inhibition of hormone and neurotransmitter secretion through its interaction with the exocytotic fusion machinery has led to metabolic phenotypes of enhanced insulin action, protection against diet-induced obesity (DIO) despite similar food intake, and increased brown adipose tissue (BAT) thermogenesis and ‘beiging’/’browning’ in adipose tissue. Our long-term goal is to understand the signaling mechanisms that control body fat metabolism and its consequences for glucose/insulin homeostasis and cardiovascular disease.

    P&F

     

    photo

    Danielle Dean, PhD

    Department of Medicine (Endocrinology, Diabetes & Metabolism)

     

    Glucagon resistance in obesity

    Glucagon and its partner insulin are dually linked in both their secretion from islet cells and action in the liver. Glucagon signaling increases hepatic glucose output, and hyperglucagonemia is partly responsible for the hyperglycemia in diabetes making glucagon an attractive target for therapeutic intervention. Interrupting glucagon signaling lowers blood glucose, but also results hyperglucagonemia and alpha cell hyperplasia. Our investigation of the mechanism for alpha cell proliferation led to the description describe a conserved liver-alpha cell axis where glucagon is a critical regulator of amino acid homeostasis. In return, amino acids regulate alpha cell function and proliferation. New evidence suggests that dysfunction of the axis in humans may result in the hyperglucagonemia observed in diabetes. This proposal outlines important but often overlooked roles for glucagon that extend beyond glycemia and investigating its role in ureagenesis/amino acid homeostasis. We propose that hyperaminoacidemia observed in the obese and diabetic states are due to dysregulation of the liver-alpha cell axis. We will leverage transcriptomics from liver of obese mice with mouse clamping studies to understand if glucagon resistance is a feature of the obese liver and will form the basis for future funding applications.

    P&F

     

    photo

    Dawn Newcomb, PhD

    Department of Allergy, Pulmonary, and Critical Care Medicine

     

    Obesity and estrogen signaling upregulate Th17 cell metabolism in asthma

    Obese women have the highest prevalence of severe, uncontrolled asthma leading to increased asthma- related morbidity, exacerbations, and health care costs.1 New therapeutic options are critically needed for patients, particularly obese women, with severe asthma. Asthma is not a uniform disease with mild to severe phenotypes that is driven by increase airway inflammation, mucus production, and airway hyperreactivity. Milder phenotypes of asthma have increased airway eosinophils and CD4+ Th2 cell cytokine production where more severe phenotypes of asthma, that do not respond well to corticosteroids, have increased airway neutrophils and IL17-producing T cells (Th17). T cell metabolism plays a critical role to in T cell differentiation and inflammation, thereby influencing airway inflammation in asthma. Dr. Rathmell’s laboratory (co-I on this application) showed glutamine metabolism is critical for Th17 cell differentiation and allergen-induced airway inflammation in a mouse model. Glutamine is metabolized to glutamate by glutaminase (GLS), and GLS inhibition with CB839 impaired development of Th17 cells and protected against lung inflammation in a mouse model of neutrophilic asthma. Preliminary data for this application showed 1) patients with severe asthma have increased Th17 cells and glutamine metabolism compared to healthy controls, 2) Women with severe asthma have increased Th17 cells compared to men with severe asthma, 3) high fat diet (HFD, 45%) fed female, but not male, mice had increased frequencies of Th17 cells, and 4) 17β-estrogen signaling through estrogen receptor alpha (ER-α) increased Th17 cell differentiation, IL-17A production, and Th17 cell metabolism. However, it remains unclear if ER-α signaling and obesity alter T cell glutamine metabolism for preferential differentiation of Th17 cells and IL-17A production.  Based on these data, we hypothesize that obesity and ER-α signaling increase glutamine metabolism in activated T cells, leading to increased Th17 cell differentiation and IL-17A production in severe asthma. To test our hypothesis, we have assembled an impressive team of experts and utilize many of Vanderbilt University Medical Center’s core facilities and propose the following aims: (Aim 1) Test if T cells from healthy and severe asthma human donors that are normal weight or obese have different regulation of glutamine metabolism that may be targeted. (Aim 2) Determine if ER-α signaling enhances glutamine metabolism in T cells in obese female mice.

    P&F

  •  

    photo

    Sheila Collins, PhD

    Department of Medicine (Cardiovascular Medicine)

     

    Augmentation of natriuretic peptide signaling: developing a screen for the inhibition of a novel receptor heterodimer

    The ‘second messenger’ signaling molecule cyclic guanosine monophosphate (cGMP) is a well-established therapeutic target for lowering blood pressure, being exemplified by nitrovasodilators (such as nitroglycerin, isosorbide dinitrate, etc.) and PDE5 inhibitors (such as sildenafil and tadalafil). Nitrovasodilators activate the so-called soluble guanylate cyclases (sGCs), and the resulting cGMP can then activate protein kinase G (PKG). The other important class of blood pressure lowering GCs are the membrane-bound, ‘particulate’ GCs. The major receptor in this class is NP receptor-A (NPRA; also called GC-A). It binds the cardiac peptide hormones atrial natriuretic peptide (ANP1-28) and B-type natriuretic peptide (BNP1-32). Upon ANP/BNP binding to the homodimeric NPRA, the intracellular domains that form the GC generate cGMP. NPs also bind to NP receptor-C (NPRC), another homodimeric receptor that lacks GC activity; rather, it is referred to as the ‘NP clearance receptor’, because it has been shown to endocytose the NPs, contributing to their removal from circulation. Despite the important physiology of the cardiac NPs, unlike the nitrates and sGCs there are no small molecules which can activate or augment NPRA, and this is a limiting factor in the clinical utilization of this arm of the cGMP producing pathway.

    In addition to lowering blood pressure, ANP and BNP are also important regulators of fuel metabolism. They activate adipocyte lipolysis as well as the amount and activity of brown adipocytes (Collins, 2014), and skeletal muscle fatty acid oxidation (Engeli et al., 2012). We and others have shown that the level of NPRC is dynamically regulated, and the relative ratio of NPRA to NPRC dictates the signaling strength through NPRA (Bordicchia et al., 2012; Kuhn et al., 2004; Wu et al., 2017).

    The Scientific Premise of this project is that, contrary to the conventional view of NP receptors functioning as homodimers, these receptor proteins also form heterodimers that cannot produce cGMP. Therefore, this finding represents a paradigm-shifting new mechanism, with clear implications for better understanding the biology of these receptors and screening for compounds that can specifically block heterodimer formation, to thus improve NPRA signaling.

    The central hypothesis is that the formation of an NPRA:NPRC heterodimer is a major mechanism by which NPRC inhibits NP-cGMP signaling. This is a somewhat heretical concept because it challenges the ‘competition for ligand’ model, which is the universally accepted mechanism for how NPRC can blunt hormone binding to NPRA and cGMP levels. The objective of this application is to work with the Vanderbilt Institute of Chemical Biology to generate receptor-FRET pairs of NPRA and NPRC to develop an assay that can be used to screen for molecules that will disrupt heterodimer formation, possibly enhancing NPRA activity.

    Discovery

     

     

    photo

    Todd Graham, PhD

    Department of Biological Sciences

     

    Influence of Atp10a and Atp10d on diet induced obesity and insulin resistance

    Nearly 40% of US adults and 19% of US children are clinically obese with Hispanic and non-Hispanic black populations being particularly overrepresented. This growing obesity epidemic leads to increased incidences of type 2 diabetes, heart disease, stroke and some cancers. At least 10% of the US population has diabetes with most of these cases being type 2 diabetes. In addition to the personal trauma associated with obesity-related diseases, annual costs of treatment are estimated to be $147 billion per year in the US (2008 dollars) (https://www.cdc.gov/obesityhttps://www.cdc.gov/diabetes). It is essential to gain a better understanding of underlying genetic risk factors for obesity and type 2 diabetes in order to manage and ultimately resolve this major public health problem. ATP10A and ATP10D have been linked to diet-induced obesity and insulin resistance in mice and humans, but how these type IV P-type ATPases (P4-ATPases) contribute to metabolic disease is unknown. Recent studies indicate ATP10A and ATP10D transport specific sphingolipid species across the plasma membrane of cultured cells. However, the physiological consequences of this lipid transport activity are poorly understood. For example, existing mouse models are inadequate to determine if Atp10a/10d deficiency is sufficient to cause insulin resistance and dyslipidemia in mice fed a high fat diet. Therefore, new murine models bearing precise deletions or mutations have been generated. The current pilot and feasibility study proposes to test whether these Atp10a and Atp10d deficient mice display diet-induced obesity, insulin resistance and dyslipidemia (perturbations on serum lipid profiles) when fed a high fat diet.

    P&F

     

    photo

    Hassane Mchaourab, PhD

    Department of Molecular Physiology & Biophysics

     

    Biophysical analysis of G6PC1, a key factor driving elevated hepatic glucose production in diabetes

    Glucose-6-phosphatase is a multi-component enzyme system located in the endoplasmic reticulu that plays a critical role in maintaining interprandial blood glucose homeostasis. Mediating the terminal ste of gluconeogenesis and glycogenolysis in the liver, the membrane-bound catalytic subunit, G6PC1, work in concert with accessory transport proteins to catalyze the hydrolysis of glucose-6-phosphate to glucos and inorganic phosphate. Previous studies have suggested that dysregulation of G6PC1 gene expressio contributes to elevated hepatic glucose production (HGP) associated with diabetes. Furthermore, mutations in G6PC1 that compromise activity lead to severe hypoglycemia, forming the clinical basis of glycogen storage disease (GSD). Importantly, the lack of high-resolution structural models precludes a complet understanding of G6PC1 function and impairment. The major bottleneck for a detailed structural analysis of G6PC1 is the absence of efficient heterologous expression and purification strategies that isolate the enzyme in a functional form. This proposal describes logical, time-tested approaches to express and purif G6PC1 for functional and biophysical experiments, which sets the stage for detailed structural analysis by crystallography and/or cryo-electron microscopy. The methodology employs a small-scale screenin approach utilizing the highly sensitive technique of fluorescence detection size exclusion chromatograph to rapidly identify optimal gene constructs and expression conditions, which will inform large-scal expression and purification protocols from insect cells to obtain milligram quantities of wild type and mutan G6PC1. Global structural properties of purified G6PC1 determined from a suite of biophysical tools will be correlated with in vitro hydrolase activity. The results of this work will support progress toward a detailed description of the structural basis of G6PC1 activity and the relationship to disease-associated mutations.

    P&F

  •  

    photo

    Rachel Bonami, PhD

    Department of Medicine (Rheumatology & Immunology)

     

    Interrogating the molecular origins of B lymphocyte autoimmunity for insulin

    Patients who present with two or more islet autoantibodies have an 80% likelihood of symptomatic type 1 diabetes (T1D) onset within 20 years. Islet autoantibodies are produced by autoreactive B lymphocytes that defy normal immune regulation to differentiate into antibody-secreting cells. Our preliminary data in T1D prone non-obese diabetic mice suggest that whereas most islet-reactive B lymphocytes are capable of driving beta cell attack through autoantigen presentation to T cells, only a minority successfully differentiate further into autoantibody-secreting cells. Furthermore, insulin-reactive antibodies predict disease risk, yet little is known about insulin-binding B lymphocytes in human T1D patients. This proposal seeks to interrogate this critical, understudied population of antigen-presenting B lymphocytes in human pre-symptomatic and new-onset T1D subjects to improve our understanding of how the disease process unfolds and facilitate the development of new immune-targeted therapeutic strategies. We hypothesize that B lymphocyte transcriptional and repertoire perturbations exist in the T1D prodrome that correlate with early disease stages. The following aims will test this hypothesis: Aim 1: To transcriptionally identify aberrant B lymphocyte population states in pre-symptomatic T1D patients and correlate immunoglobulin repertoire shifts at the single cell level, and Aim 2: To elucidate how the anti-insulin B lymphocyte repertoire evolves during the pre-symptomatic period ofT1D. The proposed aims will employ cutting-edge technologies possessed by few other institutions to advance the T1D field by identifying BCR repertoire shifts and dysregulated pathways by which B lymphocytes escape normal immune control, as well as by tracking the evolution of anti-insulin responses in pre-symptomatic and new-onset T1D patients. These studies will generate paired, single cell transcriptomic and B cell receptor (BCR) repertoire data amongst pre-symptomatic T1D and islet autoantibody-negative controls to synergistically enhance our understanding of how autoreactive B lymphocytes breach normal immune regulation barriers to enter the circulating repertoire of patients to drive T1D (Aim 1). BCR repertoire data, including V gene usage and mutation analysis, along with antibody isotype and affinity studies will be conducted to capture and characterize insulin-binding B lymphocytes as hybridomas from pre-symptomatic vs. new onset T1D patient PBMC (Aim 2). These studies hold potential to identify new biomarkers of early disease stages and enhance our knowledge about how B lymphocyte islet autoimmunity develops to drive beta cell attack.

    P&F

     

    photo

    Sean Davies, PhD

    Department of Pharmacology

     

    Discovery Award

    Abstract

    Discovery

     

    photo

    Ayush Giri, MS, PhD

    Department of Obstetrics and Gynecology

     

    Discovery Award

    Abstract

    Discovery

     

    photo

    Erkan Karakas, PhD

    Department of Molecular Physiology & Biophysics

     

    Structural characterization of inositol-1,4,5-triphosphate receptors

    Mitochondria are dynamic and complex organelles that are essential for a wide range of metabolic and signaling processes. Mitochondrial dysfunction is strongly associated with a growing number of metabolic and neurodegenerative diseases and cancer. A crucial regulator of mitochondrial functions is mitochondrial Ca2+ influx, which relies on synapse-like contact sites with the endoplasmic reticulum (ER). Sustained Ca2+ transfer into mitochondria at these contact sites is necessary to maintain synthesis of ATP and mitochondrial substrates, whereas excessive or reduced Ca2+ transfer leads to initiation of apoptotic cell death or autophagy, respectively. Recent studies link aberrant Ca2+ signaling at ER-mitochondria contact sites to the onset and progression o many metabolic diseases including diabetes-2 and obesity related illnesses. Despite recent identification of components of the Ca2+ transfer machinery at ER-mitochondria contact sites and their emergence as potential therapeutic targets, the molecular mechanisms underlying regulation of mitochondrial Ca2+ influx is poorly understood, hampering development of tools to fine tune Ca2+ flux in diseased states. One of the long-term goals of my research program is to uncover the molecular mechanisms underlying the activity and regulation of inosito1-1,4,5-triphosphate receptors (IP3Rs), the key regulator of Ca2+ transfer into mitochondria, using cutting edge structural biological methods including X-ray crystallography and cryo-electron microscopy (cryo-EM) together with biophysical, biochemical and functional methods. The aim of this proposal is to i) perform identification and biochemical, pharmacological and structural characterization of IP3R domains that can be expressed as isolated entities, and ii) express and purify intact recombinant IP3R suitable for the subsequent structural and functional analysis. These studies will facilitate the necessary tools to address more specific questions regarding to IP3R activity and regulation and would pave the path for discovery of novel tools to control the receptor activity in diabetes and obesity as well as other diseases where aberrant IP3R activity is involved.

    P&F

     

    photo

    Ethan Lippmann, PhD

    Department of Chemical & Biomolecular Engineering

     

    Mechanisms of leptin transport across the human blood-brain barrier

    Novel strategies are needed to treat obesity and its associated metabolic detriments. This research proposal seeks to clarify the mechanisms by which leptin, an integral hormone that regulates energy utilization and metabolism, is transported through the blood-ˇbrain barrier (BBB) and into the brain where it exerts its primary effects. Paradoxically, obese individuals have increased levels of leptin in the bloodstream, but leptin transport across the BBB is reduced. The mechanisms behind this so-ˇcalled “peripheral leptin resistance” are unknown, mainly because the receptors and transporters that shuttle leptin across the BBB are also unknown. We hypothesize that if this leptin transport machinery is properly characterized, it can be directly manipulated to increase leptin brain uptake in obese individuals, thereby providing a novel route for treating obesity and obesity-ˇrelated behaviors. To identify this leptin transport machinery, we will utilize: (1) robust human brain endothelial cell sources that appropriately mimic BBB behavior, and (2) cutting-ˇedge targeted and high throughput CRISPR techniques. Aim 1 will assess leptin uptake in BBB endothelial cells derived from human induced pluripotent stem cells (iPSCs) after treatment with a library of small molecule agonists. After identification of compounds that increase leptin uptake, RNA sequencing will be conducted to profile upregulated genes that are potentially responsible for this increase. Gene knockouts will then be generated in the iPSC-ˇderived BBB model to validate their role in leptin transport. Aim 2 will assess leptin uptake in an immortalized BBB endothelial cell line after it is transduced with a genome-ˇwide CRISPR activation library, such that every cell overexpresses a single gene. Positive selection and RNA sequencing will be used to determine genes whose upregulation consequently increases leptin uptake. The relevance of each gene for leptin transport will then be confirmed in the iPSC-ˇderived BBB model. The combination of targeted and high throughput assays maximizes the odds of success for identifying novel contributors and regulators of leptin transport into the brain. This work is expected to have an important positive impact on the field of obesity research by providing insight into a central metabolic question that has remained unanswered for over 20 years. Furthermore, outcomes from this research will motivate exciting in vivo studies to validate the identified mechanisms, as well as create immediate opportunities for drug screening campaigns to specifically target the leptin transport machinery.

    P&F

     

    photo

    Dolly Padovani-Claudio, MD, PhD

    Department of Opthamology & Visual Sciences

     

    The CXCL8:CXCR1/2 axis as a biomarker and therapeutic target for diabetic retinopathy

    Diabetic Retinopathy (DR), a microvascular complication of Diabetes Mellitus, is the leading cause of blindness in working age adults.This work will explore the effects of manipulating the CXCL8:CXCR1/2 chemokine signaling system to reduce pathologic retinal angiogenesis in models of DR. It will also explore correlations between genetic variants in the CXCL8:CXCR1/2 chemokine signaling system and DR susceptibility, progression, and response to VEGF inhibitors (the gold standard drugs used to treat retinal angiogenesis in DR).

    Discovery

     

    photo

    Maulik Patel, PhD

    Department of Biological Sciences

     

    Mechanisms underlying metabolic regulation of mutant mitochondrial genome dynamics

    Mitochondrial dysfunction underlies a variety of metabolic diseases, as well as age-related decline in health. Common sources of mitochondrial dysfunction include mutations in the mitochondrial genome (mtDNA), a small circular chromosome that encodes several genes essential for mitochondrial respiration. Mutant mtDNA (ΔmtDNA) has been implicated in a number of diseases characterized by metabolic dysfunction, including obesity and diabetes. However, ΔmtDNA do not follow the inheritance patterns that are typical of the nuclear genome, making it difficult to predict the risk of developing a ΔmtDNA-associated disease and highlighting the importance of investigating the cellular mechanisms governing the propagation of ΔmtDNA. We have preliminarily found metabolic signals, namely insulin signaling and the ability to metabolize glucose, to be important regulators of ΔmtDNA proliferation in a Caenorhabditis elegans model of mitochondrial disease. Specifically, insulin signaling promotes the proliferation of ΔmtDNA while glycolysis inhibition suppresses it. While these findings are consistent with previous reporting that energy metabolism is an important regulator of mitochondrial networks, the underlying mechanisms are not known. We propose to follow up on these exciting findings by investigating the role of insulin signaling, as well as the utilization of dietary nutrients, on the maintenance and propagation of a pathogenic deletion-bearing mitochondrial genome in the simple animal model, C. elegans. Specifically, our first aim seeks to characterize the downstream mechanisms by which insulin signaling modulates ΔmtDNA levels. Our second aim will characterize the mechanisms underlying the shift in ΔmtDNA levels upon altered utilization of dietary nutrients. This study will yield key insights on the mechanisms governing the propagation of disease causing mutations in mtDNA, as well as provide a framework for further research on the potential usage of nutritional and metabolic interventions in combating diseases associated with mitochondrial mutations.

    P&F

  •  

    photo

    David Jacobson, PhD

    Department of Molecular Physiology & Biophysics

     

    Discovery Award

    The overall objective of this study is to identify selective activators and inhibitors of the two-pore-domain potassium channel, TALK-1. TALK-1 channels are key regulators of pancreatic beta-cell electrical excitability, Ca2+ homeostasis and insulin secretion. KCNK16 the gene that codes for TALK-1 is the most abundant K+ channel transcript of the islet and TALK-1 is the most islet-restricted ion channel. Moreover, a mutation in KCNK16 results in neonatal diabetes and a nonsynonymous polymorphism in KCNK16 causes an increased predisposition for type-2 diabetes. However, our understanding of the role(s) of TALK-1 channel in human islets remains obscure due to a lack of specific and potent pharmacology. Therefore, this project will utilize a robust thallium (Tl+) based fluorescent assay in a high throughput screen (HTS) to identify pharmacological probes of the human TALK-1 channel. The assay will be performed on a tetracycline inducible TALK-1 cell line, which was selected for based on its performance in the Tl+ assay. The TALK-1 Tl+ assay was validated with primary screens of two small molecule libraries including the Spectrum Collection (~2320 molecules) and a bioactive lipid library (~928 molecules), which identified a small cohort of activators and inhibitors of TALK-1. The primary screens were utilized to optimize the Tl+ assay for use with the TALK-1 cell line in a large HTS. Building on these preliminary studies, this proposal plans to perform a HTS on the human TALK-1 channel with 35,000 structurally diverse small molecules from the Vanderbilt HTS small molecule library. This will be accomplished using 1. A Tl+ flux based HTS, which will be followed by 2. Secondary assays utilizing Tl+ flux, electrophysiology and Ca2+ imaging to support rapid hit-to-lead progression. This will be followed by assays to determine the mechanism of action of TALK-1 regulation including TALK-1 in single channel inside out membrane patches as well as inhibition of G-protein-coupled receptor signaling, and finally 3.Molecular regulators of TALK-1 activity identified in this HTS will be utilized to test the influence of TALK-1 channels on human and mouse islet cell electrical activity, Ca2+ homeostasis and insulin secretion.

    Discovery

     

    photo

    Anne Kenworthy, PhD

    Department of Molecular Physiology & Biophysics

     

    Discovery Award

    Macroautophagy (hereafter referred to as autophagy) is an intracellular catabolic pathway involved in recycling of cellular components. The normal functioning of a variety of cell types important in both diabetes and obesity, including pancreatic beta cells and adipocytes, depends heavily on autophagy. Thus, it is critically important to understand the mechanisms that underlie this process. MAP1LC3B (LC3) is one of the central proteins involved in autophagy, playing essential roles in both the formation of autophagosomes as well as the capturing cargo for degradation by autophagy. Emerging evidence suggests nuclear forms of LC3 are also important in autophagy. However, the functions of nuclear LC3 are still largely unexplored and little information is currently available regarding LC3’s interacting partners in the nucleus. Work from our group has shown that in the nucleus, LC3 is contained within ~1000 kDa complexes. We also identified an initial list of candidate LC3-interacting proteins using mass spectrometry. These studies have revealed a number of intriguing candidate interacting partners of nuclear LC3, including ribosomal subunits and tubulin. These findings lead us to hypothesize that additional functions of nuclear LC3 remain to be discovered, and that the identification of bona fide nuclear LC3 interacting proteins could provide new insights into how autophagy maintains cellular and organismal homeostasis. Here, we propose to leverage and expand on our initial findings by i) determining how the nuclear LC3 interactome is physiologically regulated and ii) validating key interacting partners of nuclear LC3 and exploring the functional significance of their interactions. These studies will thus set the stage for obtaining external funding for future work focused on identifying new functions of nuclear LC3. Ultimately, these studies should provide a framework that will inform our understanding of how autophagy functions as a general regulator of metabolism and how this pathway can be exploited to help prevent and treat diabetes and obesity.

    Discovery

     

    photo

    Rolanda Lister, MD

    Department of Obstetrics and Gynecology

     

    Intrauterine program-ming of diabetes induced cardiac embryopathy

    I hypothesize that maternal hyperglycemia induces changes in DNA methylation in the developing heart thus increasing the risk of congenital heart defects due to abnormal mRNA expression of cardiac important genes. I have three specific aims to test this hypothesis. Aim 1: To analyze the cardiac phenotypes of embryos born to dams with hyperglycemia compared with pups of euglycemic pregnancies. Aim 2: To identify methylationsensitive DNA loci within developing fetal hearts that are more vulnerable to maternal hyperglycemia using a high-resolution genome-wide cytosine methylation profiling assay. Aim 3: To juxtapose differential mRNA expression in developing fetal hearts with changes in genome wide DNA methylation.

    Research strategy: Diabetes will be induced in standard 8 week old CD-1 WT female mice with a one time intraperitoneal injection of 150 mg/kg of streptozotocin (STZ). Histological analysis of fetal cardiac morphology will be performed on the hearts of the hyperglycemic and the euglycemic pups at day E16.5. We will extract the hearts at different timepoints and use genome wide cytosine methylation profiling to delineate the difference between pups of hyperglycemic mothers versus controls. We will then juxtapose differential mRNA expression. With this information, we can then in the future obtain gene candidates that may be the targets for intervention.

    Expected Results: We anticipate that maternal diabetes will alter DNA methylation of specific genes related to cardiac development. We believe that by sequencing the entire genome of the extracted DNA after creating our library following the modified HELP-tagging assay and sequence, we will identify candidate genes that are implicated in dysregulation of the methylation patterns that ultimately predispose these embryos to congenitally acquired cardiac lesions.

    P&F

     

  • photo

    Nathan Bingham, MD, PhD

    Department of Pediatrics

     

    Mitigation of hypothalamic inflammation via ablation of microglial NF-kB

    Rodents fed a high-fat diet (HFD), upregulate proinflammatory cytokines within the mediobasal hypothalamus (MBH), an important center of neuronal control of appetite and metabolism. This metabolically-induced inflammation, or ‘metaflammation,’ contributes to central leptin resistance, increased caloric intake, and obesity. These results run contrary to a large body of work that has identified hypothalamic inflammatory signaling as a mediator of the sickness-induced cachexia response triggered in response to classic inflammatory stimuli such as injury, infection, cancer, or autoimmunity.

    As the innate immune cells of the CNS, microglia have been implicated as potential effector cells of both metabolic and classical inflammatory stimuli within the hypothalamus. Here, we propose strategies for defining the role of microglial NF-kB signalling, a key molecular of the microglial inflammatory response, in the development of hypothalamic inflammation. We have developed an inducible Cre-Lox mouse line to ablate NF-kB signaling specifically in microglia. Study of these mice will provide a better understanding of the mechanisms whereby microglia contribute to hypothalamic inflammation and could uncover novel targets for the treatment of diet-induced obesity and cachexia.

    P&F

     

    photo

    Raymond Blind, PhD

    Department of Medicine (Division of Diabetes, Endocrinology & Metabolism)

     

    Novel anti-diabetic therapeutics by nuclear receptor competitive displacement

    The exogenous plant phospholipid DLPC was recently found to activate the nuclear receptor NR5A2 and have dramatic anti-diabetic effects in the mouse liver. DLPC is thought to activate NR5A2 the same way all nuclear receptors are thought to be activated - as an allosteric switch. However, we recently discovered that NR5A2 can act as scaffod for endogenous phospholipid ligands, and these phospholipids themselves mediate new interactions. This new paradigm suggests that past drug screening platforms that searched for allosteric modulators of NR5A2 were misguided, explaining why those efforts failed. Here, we propose a new type of nuclear receptor screen designed to detect endogenous phospholipid competitive displacement, not allostery. This screen is ready for anti-diabetic therapeutic development as all the in vivo models, used to validate DLPC in vivo, are ready and await a new DLPC-like molecule. The NR5A2 target is exceptionally well validated, and the novel nature of our screen, based on new mechanistic information, suggests our new screen has an excellent chance to lead to novel & pharmacologically tractable DLPC-like anti-diabetes therapeutics.

    Discovery

     

    photo

    Justin Gregory, MD

    Department of Pediatrics

     

    Peripheral insulin delivery's contribution to insulin resistance in type 1 diabetes

    The goal of this pilot and feasibility proposal is to determine the pathophysiologic mechanisms underpinning insulin resistance (IR) in type 1 diabetes (T1DM), a consistent but under-recognized problem in this condition and a major predisposing factor to macrovascular disease, the leading cause of death in these patients. My research will test the hypothesis that IR in T1DM is predominantly a consequence of iatrogenic hyperinsulinemia in the peripheral circulation (as opposed to an effect of chronic hyperglycemia, as is commonly thought). I will test this hypothesis using a novel cross-sectional study design evaluating IR in 3 groups: subjects with T1DM, glucokinase mutations, and non-diabetic controls. I will utilize the hyperinsulinemic, euglycemic clamp to exploit key metabolic differences between these 3 groups and determine the etiology of T1DM IR at whole-body and tissue-specific levels. These studies will increase our understanding of IR in T1DM and how novel therapeutic approaches could alleviate this obstacle to optimal cardiovascular health for patients who live with this condition.

    P&F

     

    photo

    Carrie Grueter, PhD

    Department of Anesthesiology

     

    DGAT1 as a central regulator of diet-induced obesity

    Evidence indicates an essential role for the central nervous system (CNS), particularly lipid-sensing neurons in the hypothalamus, in the regulation of whole-body energy balance. It is suggested that different classes of lipids are used by lipid-sensing neurons, not as nutrients, but as cellular messengers which relay information regarding whole-body energy status. Even though the enzymes responsible for TG synthesis, acyl-CoA:diacylglycerol acyltransferase-1 and -2 (DGAT-1 and -2), are expressed in the brain and are known to regulate of whole-body EB, their function in the CNS has yet to be investigated. The long-term objective of my research program is to understand the physiological relevance(s) of intracellular TG and how it impacts CNS processes. The overall objectives for this proposal, which will establish the platform for achieving my long-term goal, are 1) to identify the neuroanatomical expression and distribution of Dgat1, 2) to elucidate the impact of central DGAT1 on the regulation of whole-body energy balance. I hypothesize that intracellular TG metabolism in the CNS, mediated by DGAT1, impacts lipid-sensing in the brain and thus regulates of whole-body energy balance. The rationale for this proposal is that identification of specific cell-types and lipid messengers mediated by DGAT1 in the CNS will provide mechanistic insight into how and where intracellular TG metabolism impacts the regulation of whole-body energy balance. These data will open the door for discovery of new therapeutic approaches for the prevention and treatment of obesity, type 2 diabetes and mechanistically related disorders such as depression and anxiety.

    P&F

  • photo

    David Aronoff, MD

    Department of Medicine (Division of Infectious Diseases)

     

    Placental inflammation in gestational diabetes

    Gestational diabetes mellitus (GDM) impacts up to 1 in 10 pregnancies in the US and significantly increases the risk of complications, including infant macrosomia, neonatal hypoglycemia, preeclampsia, premature labor, and Cesarean delivery. It also increases the risk of postpartum complications in both mother and child including late onset diabetes and cardiovascular disease. Causal mechanisms explaining how GDM predisposes to these adverse outcomes are poorly defined, but the placenta is increasingly appreciated to be a target organ of diabetes. This proposal addresses a potential cause of exaggerated placental inflammation in GDM related to increased iron accumulation by macrophages within this vital organ. Placental macrophages (PMs) play an important role in normal placental development and govern maternal-fetal tolerance and tissue inflammatory tone. Notably, PM numbers increase and they take on a more pro-inflammatory phenotype in GDM. We recently found that healthy human PMs accumulate iron through undefined mechanisms. Using a mouse model of GDM, we also found increased tissue iron staining and greater macrophage infiltration in diseased placentae, along with increased fetal resorption (fewer live pups). A potential explanation for increased placental iron in GDM is the previously described higher expression of the hemoglobin-haptoglobin receptor (CD163) by PMs affected by GDM. Thus, our central hypothesis is that PMs exhibit an exaggerated proinflammatory phenotype in GDM, related to an increased accumulation of intracellular iron and enhanced CD163 expression.

    This proposal brings together a new multidisciplinary team of investigators to test our hypothesis through three specific aims: In Aim 1 we will characterize the cellular immunophenotype of the mouse placenta in GDM, with a special focus on PMs, CD163 expression, and intracellular iron storage. Immunophenotyping studies in a robust mouse model of GDM will assess leukocyte phenotypes including macrophages (both M1 and M2 subtypes), CD4+ cells, CD8+ cells, NK cells (NK1.1+ or CD335+), and neutrophils (Neu7/4+). Tissue inflammation will be assessed by histology and flow cytometry and macrophage expression of CD163 and accumulation of iron will be assessed. In Aim 2 we will determine the cellular inflammatory phenotype of human placental tissues affected by GDM using archived tissue specimens linked to clinical meta-data from the electronic medical record, with a special focus on PMs, CD163 expression, and intracellular iron storage. Case and control placentae will be analyzed histologically for inflammation. Macrophage abundance, polarization, and iron accumulation will be determined by specific tissue immunostaining (and iron staining). These studies will help validate a mouse model of GDM using human tissues, while advancing our understanding of the impact that GDM has on placental biology. They will also provide critical preliminary data for externally-supported grants that can expand institutional efforts to prevent and treat GDM.

    P&F

     

    photo

    Leslie Crofford, MD

    Department of Medicine (Division of Rheumatology & Immunology)

     

    Microsomal PGE synthase-1 deficiency in obesity and metabolic syndrome

    Patients with chronic inflammatory diseases, including rheumatoid arthritis (RA), have an increased prevalence of obesity and metabolic syndrome (MetS).  Little is known about the phenotype of adipose tissue (AT) in patients with RA.  It is also unknown if experimental inflammatory arthritis stimulates changes in AT and metabolic derangement.  An important characteristic of inflammation in both arthritis and AT is activation of the prostaglandin (PG) biosynthetic pathway characterized by markedly increased expression of cyclooxygenase -2 and microsomal PGE synthase-1 (mPGES-1).  In inflamed tissues, expression of PGE2 increases disproportionately to other PGs because of coordinated regulation of these two biosynthetic enzymes.  When mPGES-1 is genetically deleted in mice (KO), PG synthesis is shunted toward other terminal PG in a cell and tissue specific manner.  In adipose tissues, shunting is towards alternate species that may lead to changes in AT phenotype, specifically in the capacity to develop brown-in-white or brite adipocytes.  Increased brown/brite adipocyte activity is inversely associated with obesity, age, and type II diabetes.  Our preliminary data demonstrate that mPGES-1 KO mice are resistant to weight gain when being fed a high-fat (HF) diet.  In addition, we showed that mPGES-1 KO mice exhibit markedly increased expression of UCP-1 mRNA, the marker of brite adipocytes, in white AT and increased energy expenditure.  Thus, our preliminary data suggests that mPGES KO mice could be resistant to arthritis-induced MetS due to their ability to promote “browning” of white AT.  In this pilot project, we will test the hypotheses that (1) mPGES-1 deficiency reduces weight gain by stimulating brite adipocyte phenotype during HF feeding, (2) inflammatory arthritis increases AT inflammation and induces MetS, and (3) mPGES-1 deficiency blocks arthritis-associated changes in AT and MetS.  This will be accomplished by determining the effect of mPGES-1 deficiency on differentiation to the brite adipocyte phenotype, obesity, and energy metabolism during HF feeding and determining if a murine model of RA increases inflammation in AT and alters energy metabolism and test whether the AT phenotype in mPGES-1 deficient mice is modulated by arthritis.

    P&F

     

    photo

    Takamune Takahashi, MD, PhD

    Department of Medicine (Division of Nephrology)

     

    Assessment of diabetic nephropathy using a magnetization transfer MRI technique

    Diabetic nephropathy (DN) is a major diabetic complication that determines the morbidity and mortality of the diabetic patients. Although clinical indicators or risk factors of this disease have been described, the currently available tests do not reliably assess its severity or progression in individual patients, making it difficult to do the targeted and intensified treatment to high-risk patients. Renal fibrosis is a hallmark of progressive DN; therefore, it is critical to evaluate the presence and extent of renal fibrosis in the diabetic kidney to treat the patients as well as to predict their long-term outcome. However, the current clinical tests lack the sensitivity and specificity to measure renal fibrosis in diabetic kidney. Although renal biopsy can diagnose fibrosis, it is invasive and prone to sampling errors, and does not reliably measure renal fibrosis in the affected kidney. Thus, a non-invasive test that better evaluate renal fibrosis would greatly improve the assessment of this disease. In recent decade, a variety of magnetic resonance imaging (MRI) methods have been developed and applied to human disease including cancer and brain disorders. These techniques have enabled us to assess the pathological changes in disease organ at molecular and cellular levels. Magnetization transfer (MT) imaging is a MRI technique that evaluates large and immobile macromolecules distributed within the tissue and could provide a means to evaluate the pathological events that are accompanied by the changes of macromolecular components, such as fibrosis and apoptosis. However, this method is poorly applied to kidney disease including DN. Therefore, here we will evaluate the utility of MT imaging in measuring renal fibrosis in diabetic kidney using a mouse model of progressive DN (db/db eNOS -/- mice). The aims of this study are: 1) To optimize and establish the MT protocol for mouse kidney imaging; 2) To examine the correlation between MT data and histological or biochemical measures of renal fibrosis. Thus, this application explores a new MRI test to assess renal fibrosis in DN. Given the fact that this MRI technique can be translated to clinics, the present work should efficiently improve the outcome of the DN patients.

    P&F

  • photo

    Heidi Hamm, PhD

    Department of Pharmacology

     

    Role of a2A adrenergic receptors and Gbg-SNARE interaction in impaired insulin secretion in T2D

    One of the earliest and most important pathophysiological signs of type 2 diabetes (T2D) is impaired insulin release. A number of therapies used in the clinic, such as GLP1- agonists and DPP-4 inhibitors, act to enhance insulin release from the beta cell. Gi/o-coupled G-protein coupled receptors (GPCRs) inhibit insulin release. One mechanism through which these receptors inhibit insulin release is through liberating G protein βγ subunits. We have demonstrated that Gβγ can directly inhibit exocytosis at a point distal to Ca2+ entry by binding to soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It has been shown that beta cell α2A adrenergic receptors (α2AAR) profoundly inhibit insulin release by this mechanism. This proposal aims to investigate the role of the α2AAR in the inhibition of insulin release in animal models of T2D. We hypothesize that overactive inhibition of insulin secretion by Gi/o coupled GPCRs is a part of the impaired insulin secretion in the pathogenesis of T2D. In Aim 1, we will test whether α2AARmediated inhibition is enhanced in islets isolated from animal models of T2D. In Aim 2, we will test whether small molecule inhibitors of the Gβγ-SNARE interaction are able to overcome the inhibitory effect of α2AAR agonists upon insulin release. Finally, in Aim 3, we will determine whether the inhibitors synergize with α2AAR antagonists or compounds that enhance insulin secretion such as sulfonylureas, agonists of Gs or Gqcoupled receptors (e.g. GLP-1 agonists). These studies should allow us to evaluate both the role of α2A adrenergic receptor-mediated inhibitory signaling and the Gβγ-SNARE interaction in impaired insulin secretion in T2D.

    P&F

     

  • photo

    Jerod Denton, PhD

    Department of Anesthesiology

     

    Development of small-molecule Kir4.2 modulators for treatment of type 2 diabetes

    Type 2 Diabetes Mellitus (T2DM) imposes a substantial burden on society through increased healthcare costs, loss of productivity, and reduced quality of life. The number of diagnosed T2DM patients is projected to increase dramatically in the coming decades. Therefore, developing improved treatment strategies will be essential to lessen the economic and societal impact of T2DM. KCNJ15, which encodes the inward rectifier potassium (Kir) channel Kir4.2, was recently identified as a T2DM susceptibility gene. Kir4.2 is expressed in glucose-responsive, insulin-secreting beta-cells of the pancreas, where recent studies suggest that its up-regulation in T2DM leads to diminished glucose-induced insulin secretion. Importantly, siRNA-mediated knock-down of Kir4.2 expression in vivo increases insulin secretion and lowers blood glucose in diabetic mice. Taken together, these studies raise important questions regarding the physiology of Kir4.2 in beta cells and suggest the intriguing possibility that Kir4.2 represents a novel drug target for T2DM. There are currently no specific pharmacological modulators of Kir4.2. Therefore, the goal of this proposal is to develop, validate, and implement a high-throughput screening (HTS) assay to enable the discovery of the first small-molecule probes of Kir4.2 function. In Aim 1, the investigators will develop a thallium flux-based fluorescence assay to monitor Kir4.2 activity in a 384-well plate format. The robustness of the assay will be determined by meeting a series of performance benchmarks and running a pilot screen of 3,655 compounds in the Vanderbilt HTS center. In Aim 2, the investigators will perform a 30,000 compound screen (15,000 compounds each in funding years 1 and 2) of the Vanderbilt Institute of Chemical Biology Library. The potency and selectivity of Kir4.2 modulators will be characterized in Aim 3 using a panel of established high-throughput thallium flux assays for 9 different Kir channels. These assays dramatically shorten the time from hit discovery in a primary screen to lead compound identification and optimization. The successful outcome of the proposed work will be the development of pre-clinical tool compounds for exploring the physiology of Kir4.2 in beta cells and its therapeutic potential in T2DM.

    P&F

     

    photo

    Kasey Vickers, PhD

    Department of Medicine (Cardiovascular Medicine)

     

    Mechanisms and consequences of HDL microRNA communication in diabetes

    We have previously reported that HDL transports and delivers beta-cell specific miRNAs to recipient hepatocytes. Therefore, we aim to determine if beta cells export specific miRNAs to HDL to be delivered to the liver as part of a novel endocrine-like communication network. Furthermore, we aim to determine if this cell-to-cell communication is altered in hyperglycemia and corrected by Colesevelam treatment, a diabetes drug that has been found to improve beat cell function and insulin secretion. Results from this pilot and feasibility study will provide a foundation of basic understanding into a new paradigm of cell communication that likely contributes to systemic glucose homeostasis. Extracellular RNA and HDL-mediated intercellular communication has tremendous applicability to many diseases. As new investigator to Vanderbilt, I have a strong interest in expanding my research program to include diabetes, and have a significant interest in a research career in diabetes. Nevertheless, my investigation into diabetes is just beginning; therefore, this award will provide the necessary funds to obtain sufficient data for individual grant support in the field of diabetes.

    P&F

     

    photo

    Danny Winder, PhD

    Department of Molecular Physiology & Biophysics

     

    BNST CRF and maintenance of weight loss

    Maintenance of diet-induced weight loss is a major problem in the treatment of type II diabetes. Animal model studies have suggested an important role for corticotropin releasing factor (CRF) neurons in the bed nucleus of the stria terminalis (BNST) in stress-reward interactions, and more recently in feeding behavior. In particular, CRF signaling within the BNST produces anorexia. Recent studies demonstrate that caloric restriction in mice produces a profound decrease in CRF levels in the BNST that persists even after a return to ad libitum feeding.

    This may represent the removal of an important brake on stress-induced feeding behavior that contributes to diet relapse. Currently, however, very little is understood regarding the CRF system in the BNST. We have recently successfully utilized a genetic reporter strategy to isolate CRF neurons within the BNST for morphological and electrophysiological analysis. Here, we propose to use optogenetic and fluorescent-reporterbased animal models to determine inputs and outputs of CRF neurons in the BNST, to determine the specific inputs to the BNST that are opposingly regulated by CRF and orexin, and to examine the long-term impact of caloric restriction on the excitability of BNST CRF neurons and neuropeptide function in the region. The successful completion of these studies will delineate a microcircuit potentially involved in diet relapse and set the stage for 1) further ex vivo studies testing for means of controlling this circuit and 2) in vivo analysis of the impact of activation and inhibition of this circuit on feeding behavior.

    P&F

  • photo

    David Jacobson, PhD

    Department of Molecular Physiology & Biophysics

     

    Two pore-domain potassium channels: Pancreatic islet expression and function

    Pancreatic islet hormone secretion is imperative to maintaining glucose homeostasis and becomes perturbed in 7.8% of the United States population that develops diabetes. Thus, identifying the mechanisms that regulate islet hormone secretion may reveal new therapeutic targets for treating diabetes. Glucose stimulated insulin secretion results from calcium entry that occurs due to beta-cell membrane potential depolarization, which activates voltage dependent calcium channels (VDCCs). The activity of two-pore domain potassium (K2P) channels regulates the membrane potential in neurons, which influences calcium entry and electrical activity. However, a role of K2P channels in regulating the pancreatic β-cell membrane potential is unknown. We have determined that K2P channels are expressed in pancreatic islet cells where their currents modulate the membrane potential and influence glucose stimulated calcium influx. Therefore, this project plans to test the hypothesis that K2P channels modulate the membrane potential of mouse and human islet cells regulating calcium influx and hormone secretion. The specific objectives are to: A. Define the K2P channels of mouse and human islet cells, B. Identify the biophysical regulation of islet K2P channels and their influence on membrane potential and hormone secretion, and C. Characterize the pharmacology of islet K2P channels and utilize this pharmacology to address the influence of K2P channels on human and mouse islet cell electrical activity and hormone secretion. These goals will significantly contribute to our understanding of the ion channels that influence islet hormone secretion and provide important insights of potential therapeutic targets relevant to diabetes.

    P&F

     

    photo

    Anne Kenworthy, PhD

    Department of Molecular Physiology & Biophysics

     

    Small molecule modulators of the Y4 receptor for treatment of obesity

    Pancreatic beta cells faced a variety of ongoing stresses that lead to the accumulation of damaged proteins and organelles. Recent evidence indicates that a housekeeping process known as autophagy plays a critical role in clearing these damaged components, as genetic disruption of autophagy in pancreatic beta cells leads to beta cell dysfunction and loss of beta cell mass in mice. In addition, ubiquitinated protein aggregates accumulate in stressed beta cells, suggesting that a form of autophagy known as selective autophagy becomes compromised in response to conditions that lead to beta cell stress. However, very little is known about the molecular mechanisms that lead to the formation of these potentially toxic protein aggregates, what steps in selective autophagy are rate limiting for their clearance, or how their presence impacts beta cell function under conditions where selective autophagy fails. As a first step toward addressing these questions, in this pilot project we will test the hypothesis that selective autophagy is responsible for the clearance of both cytoplasmic and nuclear protein aggregates that form in response to beta cell stress, and that failure of this process is associated with beta cell dysfunction. To do so, we will utilize a combination of live cell imaging and immunocytochemical approaches to 1) test the hypothesis that two key components of the selective autophagy pathway, LC3 and p62, cooperate to remove ubiquitinated protein aggregates from the nucleus as well as the cytoplasm, and that this pathway functions to clear aggregates formed in response to oxidative stress in pancreatic beta cells in vitro and 2) determine if the accumulation of cytoplasmic and nuclear ubiquitinated protein aggregates is a general characteristic of mouse models of beta cell dysfunction and human islets from type 2 diabetics. In addition to testing a novel role for selective autophagy in nuclear quality control, these pilot studies will enable us to develop model systems to study how selective autophagy contributes to beta cell homeostasis, determine how this process becomes compromised in type 2 diabetes, and identify steps in this pathway that could serve as potential targets for therapeutic intervention in order to prevent or reverse beta cell damage in humans.

    P&F

     

    photo

    Jens Meiler, PhD

    Department of Chemistry

    photo

    Dave Weaver, PhD

    Department of Pharmacology

     

    Small molecule modulators of the Y4 receptor for treatment of obesity

    The 375 amino acid G-protein coupled receptor (GPCR) neuropeptide Y4 receptor (Y4) is expressed both in the periphery, including the gastrointestinal tract, and in the central nervous system. The Y4 subtype is the only receptor of the Y-receptor family with a very high affinity for the 36-residue pancreatic polypeptide (PP). Selective small molecule modulators of this receptor would not only be valuable probe molecules to study its pharmacology, they also present attractive strategies for treatment of obesity. In fact, variants of PP are currently in phase II clinical trials for treatment of obesity (TM30339, 7TM Pharma). However, as PP is a peptide, issues of stability and bioavailability remain. The development of subtype-selective orthosteric ligands has failed in the past hampering development of effective probe molecules and therapeutics6. It is the objective of the present study to identify small molecule allosteric modulators of Y4 as tools for pharmacological research and to test their potential in a therapeutic strategy. We argue that allosteric modulators of GPCRs have a higher chance to be selective as allosteric binding sites tend to be evolutionary less conserved between subtypes. The therapeutic potential of allosteric modulators is further increased by their ability to fine-tune the receptor instead of turning it entirely on or off. Side effects are reduced not only through subtype selectivity but also as the therapeutic acts only at times when the receptor is engaged by its native ligand. It is the central hypothesis of the present proposal that identification of small molecule allosteric modulators selective to Y4 will allow the development of probe molecules to study subtype-selective pharmacology and can seed drug discovery programs in obesity. Preliminary data demonstrate the adaptation of an Y4 functional assay for high-throughput screening (HTS). A pilot screen of 2,000 compounds of the Spectrum Collection (MicroSource) yielded several hit compounds. Among those, Niclosamide displayed a robust, selective allosteric potentiation with an EC50-value of 410 nM. Cell lines for orthogonal GIRK-based assay for hit validation and to establish the initial selectivity profile through testing allosteric modulation of Y1/2/5 have been established.

    P&F