Low level electrical stimulation has been shown to have neuroprotective effects on retinal dystrophy. Subretinal electrical stimulation (SES) from a subretinally implanted microphotodiode array, delays photoreceptor loss and transiently preserves retinal function in the Royal College of Surgeons (RCS) rat model of hereditary retinal degeneration. In addition, SES induces selective expression of fibroblast growth factor 2 (Fgf2), the gene for a potent, neuroprotective growth factor. This study seeks to determine (1) the in vivo effect of SES on retinal FGF2 expression at the cellular level, (2) the extent to which FGF2 is necessary for the observed neuroprotection, and (3) if the neuroprotection from SES can act synergistically with intravitreal administration of CNTF (ciliary neurotrophic factor). Thus, we propose to test the following hypotheses: Hypothesis 1) Messenger RNA for FGF2 and downstream markers of FGF2 signaling are greatest in close proximity to the electric field provided by SES and originate in M|ller cells. This hypothesis will be tested by mRNA in situ hybridizations, western blots, and immunohistochemistry to compare SES-treated RCS rats to sham-implanted controls. Hypothesis 2) The FGF2 molecule is necessary for SES neuroprotection. This hypothesis will be tested by inhibiting the FGF2 receptor, FGFR1 (fibroblast growth factor receptor 1) and assessing retinal morphology (photoreceptor cell counts) and function (ERG). Hypothesis 3) SES and intravitreal administration of CNTF act synergistically to achieve a greater neuroprotective effect than either treatment alone. We will test this hypothesis through functional (ERG), morphological (photoreceptor cell counts), apoptotic (TUNEL assay) assessments, as well as quantification of phototransduction proteins and their cognate mRNAs. It is envisaged that low level electrical stimulation can effectively be applied to provide therapeutic neuroprotection to eyes of individuals with a retinopathy or glaucoma. Results from the proposed experiments will directly address potential roadblocks to translating this therapy into clinical use by defining the mechanism, duration, and spatial reach of neuroprotection from SES. Furthermore, these studies will provide evidence of whether combination therapies are needed to optimize SES therapy.
Narrative: This project will contribute to the development of a neuroprotective treatment for retinal degenerations with the ultimate goal of preserving visual function in patients with RP and AMD. By addressing the mechanism of neuroprotection from subretinal electrical stimulation, the duration of the effect, the spatial reach of the effect within the retina, and whether it can be used to augment another neuroprotective treatment, this project seeks information that is critical to creating a viable neuroprotective clinical treatment. Such information will guide improvements to devices and stimulation paradigms to slow the progression of retinal cell death. This goal is consistent with VA RR&D program goals to advance rehabilitation health care for veterans through the development of treatments for vision loss. With the possibility that electrical stimulation can also preserve retinal ganglion cell function, this intervention may be effective in glaucoma, as well as RP and AMD, diseases found in 70% of the patients in the VA Blind Rehabilitation Center.