Research Interests:

Our laboratory is focused on studying two major aspects of retinal degeneration: (1) fundamental cellular and molecular processes that govern neurodegeneration in the retina, whether caused by angiogenesis, aging, oxidative stress or light damage, and (2) endogeneous mechanisms of neuroprotection in the eye. Some of the major diseases that cause catastrophic loss of vision do so as a result of the abnormal growth of blood vessels in the retina and choroid, which ultimately results in death of photoreceptors, the underlying cause of blindness. Our laboratory has had a long standing interest in the mechanisms by which an endogenous retinal molecule, pigment epithelial derived factor (PEDF), protects retinal neurons and blocks the growth of new blood vessels. We have identified and isolated this 50 kDa protein from conditioned medium obtained from primary cultures of human RPE cells (Fig 1), characterized its genomic structure, identified and refined its map location (Fig 2), analyzed its expression in most human and mouse tissues (Fig 3), and defined its conservation and relatedness in phylogeny (Fig 4). Fig2. Localization of the human PEDF gene: 17p13.1 Chr17 radiation-reduced somatic cell hybrid panel. Tombran-Tink J, Pawar H, Swaroop A, Radriguez I, Chader G. Genomics 19 (2) 266-272, 1994 ___figure_4___ More importantly, we have shown that PEDF is an effective differentiation and protective factor for retinal neurons. It protects photoreceptors from damage caused by light (Fig 5), H2O2, RPE detachment, and the rd and rds mutation. These protective actions are not limited to the retina but have also been observed in hippocampal neurons, cerebellar granule cells, and spinal cord motor neurons. We have also shown that it is a potent neurite outgrowth and cell differentiation factor (Fig 6). In progress we now have clear studies indicating that PEDF and a specific N-terminal PEDF peptide protect retinal ganglion cells from ischemic injury. In addition, we have shown that the expression of PEDF decreases in senescent RPE cells, which may reflect increased susceptibility of the retina to vascularization in aging individuals. Fig5. PEDF protects rat photoreceptors from degeneration after exposure to constant bright light. A,C,E: Exposure of eyes to 3,10,14 days of constant light after intravitreal injection of 1 ug PEDF. B,D,F: Controls. 3,10,14 days constant exposure after injection with PBS. Fig6. PEDF induces differentiation in human Y79 retinablastoma cells. Left untreated controlls. Right cultures treated with 50 ng/ml PEDF. One objective in our lab is to define more clearly the functional domains of PEDF and to understand how these regions protect the retina from such a wide range of neurodegenerative insults. A second objective is to determine whether there is a common neuroprotective mechanism in the retina shared by other well-characterized neurotrophic factors, such as BDNF and CNTF, which also offer strong protection to photoreceptors in the presence of similar insults. A third objective is to identify whether there are other neuroprotective factors in the retina. To achieve these goals, we specifically ask the questions: How does PEDF protect retinal neurons from such completely different insults? Does it trigger a common survival pathway that is applicable to both photoreceptor and ganglion cells? are its actions fine-tuned to each target cell or to each degenerative stimuli? Does PEDF trigger the same mechanisms in normal and pathological conditions? Do PEDF and other neurotrophic factors interact with a common neuroprotective pathway in the retina? or do they signal through specific pathways which then allow neuroprotective cross talk that ultimately trigger key downstream junctional molecules that alter the fate of the cells? Is there a group of endogenous neuroprotective factors in the eye? Do they work in concert? These questions have already led us to design experiments that define basic signaling strategies used by PEDF in both retinal and endothelial cells. We have found that the PEDF interacts with three principal pathways: MAPK, Akt/PI3K, and caspases (Fig 7). Our experiments systematically combine innovative cell cultures, in vivo and in vitro models of angiogenesis and retinal degeneration with modern investigative tools including gene arrays, proteomics, and bioinformatics to explore the spectrum of molecular changes induced by PEDF under stress conditions. We are also determining whether the entire spectrum of molecular changes induced by PEDF during protection of the retina or apoptosis in endothelial cells is the same as those of selected bioactive PEDF fragments. We have identified two unique domains of PEDF that are not homologous with other members of the serpin gene family (Fig 8). We are assessing the neuroprotective and antiangiogenic potential of these peptides in both basic scientific and clinical contexts. From these analyses, we hope to gain a better understanding of general principles that govern neuroprotection in the retina and of those aspects unique to a given protective factor, neurodegenerative insult, or cell type. Such knowledge may uncover novel selective cellular and molecular targets that will foster the design, optimization, and implementation of more effective combinatorial strategies to reduce the impact of stress on the retina. From the basic observations in our lab, we conclude that there are strong inherent cellular and molecular responses of the retina to neurodegenerative stimuli and that these may be less active with aging. Successful treatments for retinal degeneration are likely to be more powerful when operating in concert with endogenous biologic mechanisms and will have the fewest negative sequelae.

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