Vascular Biology of the Retina

Dr. Penn’s research program focuses on translational science: work that directly relates to developing new treatments for eye disease.  His work places an emphasis on precisely targeted drug therapies and novel mechanisms of drug delivery to the eye.  Basic scientists in his lab work closely with clinician scientists to seek a better understanding of the clinical manifestations of eye disease, so that clues regarding the fundamental cellular and molecular processes that drive these diseases can be unraveled.  Penn’s research team seeks to identify specific molecules or signaling pathways that contribute to disease progression and to develop novel inhibitors of those molecules or pathways for pre-clinical and, ultimately, clinical testing in the eye.  To this end, Penn’s program is primarily focused on three general research areas, see Current Research Projects.

Drug target discovery for diabetic retinopathy

The advent of a class of new and highly effective drugs recently approved by the FDA for diabetic retinopathy (DR), called anti-VEGF drugs, has radically changed how diabetics are treated for eye disease.  These drugs show great effectiveness in slowing or halting late stage DR, but at later stages irreparable damage has already occurred in the retina from which there can be no recovery.  Unfortunately, there are no existing therapies that address the early stages of DR, when progression of pathology is predictable but no irreversible damage has yet occurred.  Penn’s team seeks to address these early stages of disease with new therapies, and the team has expended great effort to identify pathogenic molecules that signal DR onset and might be targeted with new drugs to stop DR before irreversible damage occurs in the retina.  In diabetics, elevated glucose and high levels of damaging lipid molecules flow through the circulation.  Over time, this causes an insult to blood vessels, and the capillaries of the retina are among the most susceptible to this insult.  In early stage DR, the primary pathogenic feature is inflammation of retinal capillaries.  This inflammation causes the capillaries to become leaky and/or occluded, and causes the death of cells that normally support their health.  As DR progresses, the retinal capillary cells undergo changes in response to inflammation that ultimately cause them to become sick and eventually die.  This, in turn, may cause new retinal capillaries to grow abnormally, extending into the vitreous cavity of the eye where they do not belong.  Growth of these abnormal retinal capillaries has serious vision threatening consequences, such as vitreous hemorrhage and/or scarring.

There are four ongoing projects in the Penn lab that are aimed at blocking the inflammation that causes death of the retinal capillary cells and, subsequently, abnormal retinal blood vessel growth.  These projects involve using drugs that alter the protein composition of the capillary cells and/or block chemical signals in these cells, making them resistant to DR-related disease processes.  All four projects focus on the therapeutic value of inhibiting specific transcription factors – proteins that respond to disease stimuli and facilitate the pathogenic responses of cells.  The specific transcription factors under study are: 1) peroxisome proliferator-activated receptor-beta (PPAR-b), 2) nuclear factor of activated T-cells (NFAT), 3) nuclear factor kappa-light-chain-enhancer of activated B-cells (NFkB); and 4) the Drosophila seven in absentia (Siah-1) / glyceraldehyde phosphate dehydrogenase (GAPDH) transcriptional complex.  All but one of these targets (NFkB) is completely novel in the context of DR, demonstrating the innovative nature of Penn’s research.  Publications detailing Penn’s early successes in these areas of investigation have recently appeared in: the Journal of Clinical Investigation, the New England Journal of Medicine, Nature Scientific Reports, the Journal of Biological Chemistry, and PLoS One.


Retinal imaging and nanoparticle therapies for eye disease

Technologies for imaging the retina in pre-clinical models and patients have been significantly improved through advances in instrumentation, enabling high-resolution imaging of tissue structure.  Furthermore, decades of basic research (like the studies described above) have identified a number of molecular biomarkers that may be used to assess susceptibility to retinal disease, monitor disease progression, or follow response to therapy, as well as to dissect molecular mechanisms in pre-clinical studies.  Our ongoing research is focused on the development of molecular imaging technologies, including both optical imaging and optical coherence tomography (OCT), in combination with nano-scale engineering, to identify molecular targets for early disease-detection and treatment.  The goal of this work is to build upon advances in imaging instrumentation and biomarker identification in order to develop technologies for in vivo molecular imaging of the retina.  Our primary strategy is based on “hairpin functionalized gold nanoparticles” (hAuNP), which are biocompatible gold nanospheres engineered to enter living tissues and fluoresce upon association with targeted messenger RNA (mRNA) or microRNA sequences.  Recently published studies and our own preliminary work demonstrate that hAuNP are capable of specifically targeting multiple distinct RNA sequences in mammalian cells and in retinal capillaries, without adverse effects on cell function.  We are utilizing these optical imaging techniques and nanotechnology-based approaches for diagnosis and drug delivery in pre-clinical models of diabetic retinopathy, retinopathy of prematurity, retinal vein occlusion and age-related macular degeneration.  These are all highly prevalent eye conditions that can lead to irreversible vision loss.  In preliminary pre-clinical experiments, hAuNP were used to image disease-relevant biomarkers in relevant cultured retinal cells, and also to work out the biodistribution and safety profiles in rodent eyes.  Currently, hAuNP are being evaluated further in a reliable, pre-clinical model of age-related macular degeneration in order to establish the utility of longitudinal, multiplexed RNA imaging.  We are investigating the identification of a number of molecular targets using this strategy, while we are also working on the development of new molecular imaging contrast agents.  These studies will set the framework for molecular imaging of RNA and other molecular biomarkers in multiple animal models of eye disease, and will facilitate clinical translation of these technologies for early detection and staging of disease in patients.


Vanderbilt Ophthalmic Contract Research Organization

For three decades the Penn lab has partnered with drug companies to develop new therapeutic agents to treat eye disease.  Recently, the lab developed a research service arm, called the Vanderbilt Ophthalmic Contract Research Organization (VO-CRO), to facilitate this relationship.  VO-CRO is dedicated to producing the highest quality pre-clinical data to evaluate these new therapeutic strategies. VO-CRO offers several experimental platforms that combine state-of-the-art technology with unparalleled expertise in ophthalmic disease modeling.  These platforms facilitate evaluation of the effectiveness of putative therapeutic strategies in clinically relevant models, and extend to assessment of both structure and function of eye tissues. VO-CRO capabilities include, but are not limited to: in vitro screening for drug target identification/verification and for mechanistic studies of drug mechanisms-of-action; in vivo rodent modeling of ocular pathologies; highly accurate evaluation of drug efficacy; macroscopic and microscopic longitudinal morphological phenotyping; and longitudinal evaluation of retinal function and visual acuity.  The VO-CRO research team specializes in models of oxygen-induced retinopathy, various diabetes models leading to diabetic retinopathy, retinal vein occlusion and laser-induced choroidal neovascularization, along with numerous tissue-based and cell culture techniques.  Currently, VO-CRO is working in close partnership with several drug companies to develop and test novel therapeutics for eye disease.  This close partnership between VO-CRO and the drug industry allows Penn’s lab to expand its reach well beyond what is possible for a traditional academic laboratory.  The VO-CRO website can be found here.



John S. Penn, PhD




Dolly A, Padovani-Claudio, MD, PhD


Inhibitors of the IL-8 receptor, CXCR1/2 are clinically approved drugs, however they have yet to be tested in diabetic retinopathy. IL-8 is elevated in the vitreous of patients with diabetic retinopathy and possesses both inflammatory and angiogenic activities. Therefore, the goal of Dr. Padovani-Claudio's project is to determine whether CXCR1/2 inhibitors will be effective in pre-clinical models of diabetic retinopathy with the goal of quickly translating these therapeutics to the clinic.


 Imam Uddin, PhD


Dr. Uddin is a new investigator and his research is focused on the development of molecular imaging technologies including optical imaging, optical coherence tomography (OCT) and nano-scale engineering to identify molecular targets for early disease-detection and treatments in ophthalmology, vascular medicine and oncology. Dr. Uddin is currently using optical imaging techniques and nanotechnology-based approaches for diagnosis and drug delivery in preclinical models of diabetic retinopathy (DR), retinopathy of prematurity (ROP), retinal vein occlusion (RVO) and age-related macular degeneration (AMD).


Graduate Students

Meredith Giblin

MeredithGiblin photo.jpg

Meredith's thesis focuses on an early event in the pathology of diabetic retinopathy, basement membrane thickening. The basement membrane surrounding retinal blood vessels becomes thicker early in DR. The mechanisms underlying basement membrane thickening as well as how it is contributing to the pathological cascade are currently unclear. Meredith focuses on the role of a transcription factor, NFAT, in control of matrix expression in the retinal vasculature in hopes of identifying a novel, early therapeutic target.



Gary McCollum, PhD; Senior Scientist



Rong Yang, MD; RA III



​Grace Griffith; RA I


Tyler Kilburn; RA I


Nolan Beatty; RA I


Angie Mudrick; Sr. Administrative Assistant


Undergraduate Students

Charlie DeYoung

Veronica Hamilton

Natalie Schmidt


Hartnett M.E., Penn J.S. (2012) Mechanisms and management of retinopathy of prematurity. N Engl J Med. 367(26):2515-26.

Capozzi M.E., Gordon A.Y., Penn J.S., Jayagopal A. (2013) Molecular Imaging of Retinal Disease. J Ocul Pharmacol Ther. 29(2):275-86. 74.

McCollum, G.W., Savage, S., Penn, J.S. (2013) Peroxisome Proliferator-Activated Receptor-β/δ Regulates Angiogenic Cell Behaviors and Oxygen-Induced Retinopathy.  Invest. Ophthalmol. Vis. Sci. Jun 19;54(6):4197-207.

Barnett, J.M., Penn, J.S., Jayagopal, A. (2013) Imaging of endothelial progenitor cell subpopulations in angiogenesis using quantum dot nanocrystals. Methods in Molecular Biology: Nanomedicine Protocols. 1026:45-56.

Chavala, S.H., Kim, Y., Tudisco, L., Cicatiello, V., Milde, T., Kerur, N., Claros, N., Yanni, S., Guaiquil, V.H., Penn, J.S., Rafii, S., De Falco, S., Lee, T.C. and Ambati, J.  (2013) Nutlin-3 suppresses retinal angiogenesis through p53 and hypoxia inducible factor-1 alpha. J Clin Invest. 123(10):4170-81.

Watkins, W.M., McCollum, G.W., Penn, J.S. and Morrison, D.G. (2013) Hypoxia-induced expression of VEGF splice variants and protein in four retinal cell types. Exp. Eye Res. 116:240-246.

Bretz, C.A., Savage, S.R., Capozzi, M.E. and Penn, J.S. (2013) The role of the NFAT signaling pathway in retinal neovascularization. Invest Ophthalmol. Vis. Sci. 54:(10)7020-7.

Capozzi, M.E., McCollum, G.W. and Penn, J.S. (2014) The Role of Cytochrome P450 Epoxygenases in Retinal Angiogenesis. Invest Ophthalmol Vis Sci. 55(7):4253-60.

Madamanchi, A., Capozzi, M.E., Geng, L., Li, Z., Friedman, R.D., Dickeson, S.K., Penn, J.S., and Zutter, M.M. (2014) Mitigation of oxygen-induced retinopathy in α2β1 integrin-deficient mice. Invest Ophthalmol Vis Sci. 55(7):4338-47.

Barnett, J.M., Suarez, S., McCollum, G.W., Penn, J.S. (2014) Endoglin promotes angiogenesis in cell- and animal-based models of retinal neovascularization. Invest Ophthalmol Vis Sci. 55(10):6490-8.

Suarez S., McCollum G.W., Bretz C.A., Yang R., Capozzi M.E., Penn J.S. (2014) Modulation of VEGF-induced retinal vascular permeability by peroxisome proliferator-activated receptor-β/δ. Invest Ophthalmol Vis Sci. 55(12):8232-40.

Savage, S.R., Bretz, C.A., Penn, J.S. (2015) RNA-seq reveals a role for NFAT-signaling in human retinal microvascular endothelial cells treated with TNFα. PLoS One. 2015 Jan 24;10(1):e0116941.

Savage, S.R., McCollum, G.W., Yang, R., Penn, J.S. (2015) RNA-seq identifies a role for the PPARβ/δ inverse agonist GSK0660 in the regulation of TNFα-induced cytokine signaling in retinal endothelial cells. Mol. Vis. 2015 May 20; 21:568-76.

Bretz, C.A., Savage, S.R., Capozzi, M.E., Suarez, S., Penn, J.S. (2015) NFAT isoforms play distinct roles in TNFα-induced retinal leukostasis. Nature Sci. Rep. 5, 14963; doi: 10.1038/srep14963.

Suarez, S., McCollum, G.W., Jayagopal, A., Penn, J.S. (2015) High glucose-induced retinal pericyte apoptosis depends on association of GAPDH and Siah1. J. Biol. Chem. 2015 Nov 20;290(47):28311-20.

Xu, L., Ruan, G., Dai, H., Liu, A.C., Penn, J.S. and McMahon, D.G. (2016) Mammalian retinal Müller cells have circadian clock function. Mol. Vis. Mar 24, 2016; 22:275-283.

Uddin, M.I., Evans, S.M., Craft, J.R., Capozzi, M.E., McCollum, G.W., Yang, R., Marnett, L.J., Uddin, M.J., Jayagopal, A. and Penn, J.S. (2016) In vivo imaging of retinal hypoxia in a model of oxygen-induced retinopathy. Nature Sci. Rep. (In press).