Small Molecules that Protect Mitochondrial Function from Metabolic Stress Decelerate Loss of Photoreceptor Cells in Murine Retinal Degeneration Models

Abstract

One feature common to many of the pathways implicated in retinal degeneration is increased metabolic stress leading to impaired mitochondrial function. We found that exposure of cells to calcium ionophores or oxidants as metabolic stressors diminish maximal mitochondrial capacity. A library of 50,000 structurally diverse "drug-like" molecules was screened for protection against loss of calcium-induced loss of mitochondrial capacity in 661W rod-derived cells and C6 glioblastomas. Initial protective hits were then tested for protection against IBMX-induced loss of mitochondrial capacity as measured via respirometry. Molecules that protected mitochondria were then evaluated for protection of rod photoreceptor cells in retinal explants from rd1 mice. Two of the molecules attenuated loss of photoreceptor cells in the rd1 model. In the 661W cells, exposure to calcium ionophore or tert-butylhydroperoxide caused mitochondrial fragmentation that was blocked with the both compounds. Our studies have identified molecules that protect mitochondria and attenuate loss of photoreceptors in models of retinal degeneration suggesting that they could be good leads for development of therapeutic drugs for treatment of a wide variety of retinal dystrophies.

Large-scale phenotypic drug screen identifies neuroprotectants in zebrafish and mouse models of retinitis pigmentosa

“…In rd1 mice, photoreceptor degeneration begins around P10 and progresses rapidly. By P21, only a single row of photoreceptor cells remain in the outer nuclear layer (ONL; Tansley, 1951) making it an excellent system for screening potential neuroprotectants (Beeson et al, 2016). Here, retinal explants from P10 rd1 mice were isolated and cultured ex vivo (Bandyopadhyay and Rohrer, 2010).…”

Newly Identified Chemicals Preserve Mitochondrial Capacity and Decelerate Loss of Photoreceptor Cells in Murine Retinal Degeneration Models

“…61 The pharmacological target of CB11 is not clear. Based on our previous data presented at the RD2014 meeting, 46 CB11 was found to both protect against mitochondrial fission by decreasing Drp1, a GTPase that is a member of the dynamin superfamily of proteins and involved in mitochondrial fission, and increasing Mfn2, a GTPase embedded in the mitochondrial outer membrane and involved in mitochondrial fusion. Work is being conducted to identify the target of CB11 in mitochondrial dynamics.…”

“…A preliminary excerpt was published previously as part of a conference proceeding. 46 Following this strategy, the main results of the current study are: (1) utilizing the 661W cone photoreceptorderived cells and MTT and maximal oxygen consumption assays, 6 compounds from the 50,000 compound Chem-Bridge library protected against dysregulated energy metabolism triggered by calcium stress; (2) a pharmacophore, uniquely describing common features of CB11 and CB12 was identified; (3) CB11 was found to slow the progression of photoreceptor cell loss in the rd1 mouse organ culture; (4) CB11 was also tested in the S334ter rhodopsin rat retina organ culture, confirming efficacy across species and genetic phenotypes underlying degeneration; (5) Preliminary bioavailability of CB11 in the pig retina suggests that pharmacological concentrations can be achieved upon eye drop application; and (6) CB11 efficacy was confirmed in the light-induced retinal degeneration model in the Balb/c mouse.…”

In vivo genome editing rescues photoreceptor degeneration via a Cas9/RecA-mediated homology-directed repair pathway

“…Thus, rd1 mice are a suitable model for advancing therapeutic treatments for RP disease (6)(7)(8). Several strategies have been developed for rescuing photoreceptor degeneration in rd1 mice, such as small-fragment target homologous replacement in germ lines (9), adeno-associated virus (AAV) vectors for gene complementation (6), or small molecules for promoting cell survival (10). However, each of these methods demonstrates substantial shortcomings such as limited efficiency or no gene correction for lasting phenotypic rescue.…”