Retinal ganglion cell axons undergo degeneration prior to cell body loss in the pathogenesis of glaucoma. Prior to degeneration, retinal ganglion cell axons demonstrate metabolic dysfunction, including ATP decreases that correlate with high intraocular pressure. This metabolic dysfunction could be a result of changes in axonal mitochondria or alterations in the provision of energy substrates from glia to axons. A critical question for therapeutic development is whether the metabolic dysfunction is intrinsic to the retinal ganglion cell axon. The long-term goal of this work is to determine the onset, progression and mechanisms of retinal ganglion axon dysfunction so that crucial intervention points for developing glaucoma therapies can be defined and prioritized. The overall objective of this proposal is to examine the causes of energy availability failure in early glaucoma and place those causes in context with structural pathology. The central hypothesis of this work is that the mechanism of metabolic dysfunction is shared by the RGC axon mitochondria and optic nerve glia. This hypothesis has been formulated from preliminary data gathered in the applicant's laboratory that suggests deficits in mitochondrial recycling, low glycogen stores and lactate transporters in glaucomatous optic nerve. The rationale for this proposed work is that investigating the source of metabolic dysfunction in glaucomatous optic nerve will identify new therapeutic targets in a disease that has no mechanism-based interventions. Guided by strong preliminary data, this hypothesis will be tested by the following specific aims: 1) determine whether mitochondria underlie the metabolic vulnerability of glaucoma by investigating ROS production and mitochondria quality control; 2) by establishing the relationship between mitochondrial respiration and degeneration; and 3) by determining how glia drive metabolic vulnerability through energy store levels and mobilization, lactate transporter expression and distribution, and metabolic enzyme activity. Overall, this work will determine the contribution of energy availability to glaucoma pathogenesis by analyzing how mitochondrial and glial-related energy substrates and delivery mechanisms are altered in optic neuropathy. Confirmation will occur through manipulation of mitochondrial quality control, reactive oxygen species levels, and energy stores to the nerve, and quantifying the resultant decrease in axon degeneration. The approach is innovative because it departs from the general perspective that energy availability and utilization are tangential to optic neuropathy. Critical intervention points to halt optic neuropathy will emerge from this analysis. For this reason, the proposed research is significant, but also because it will provide insight into the role of energy in axon degeneration generally.
The proposed research is relevant to public health because it will define and prioritize the crucial intervention points in retinal ganglion cell axon degeneratin, as well as examine the utility of limiting mitochondrial dysfunction as a glaucoma therapy. The proposed research is thus relevant to the mission of the NIH to reduce illness by developing fundamental knowledge for the cause and cure of human disease.
| Harun-Or-Rashid, Mohammad; Pappenhagen, Nate; Palmer, Peter G et al. (2018) Structural and Functional Rescue of Chronic Metabolically Stressed Optic Nerves through Respiration. J Neurosci 38:5122-5139 |
| Pappenhagen, Nate; Inman, Denise M (2018) Changes in ganglioside GM1 expression in glaucomic retina. J Neurosci Res 96:1627-1630 |
| Inman, Denise M; Harun-Or-Rashid, Mohammad (2017) Metabolic Vulnerability in the Neurodegenerative Disease Glaucoma. Front Neurosci 11:146 |
