Neuroprotective effects of methyl 3,4 dihydroxybenzoate in a mouse model of retinitis pigmentosa

Retinitis pigmentosa is a photoreceptor-degenerative disease that is currently untreatable and eventually causes blindness. Methyl 3,4 dihydroxybenzoate (MDHB) is a small molecule that exerts neuroprotective effects in vitro. The present study tests whether MDHB protects the retina of rd10 mice, a model of retinitis pigmentosa. MDHB or an equal volume of vehicle was intraperitoneally injected in rd10 mice daily from postnatal day 12 (P12) to P26. Retinal morphology was evaluated by immunostaining, and retinal function by electroretinogram (ERG) and by visual behavior. TUNEL, Iba1, GFAP staining and western blotting were applied to explore the neuroprotective mechanism of MDHB in retina. MDHB treatment significantly promoted photoreceptor survival and preserved cone morphology compared to the untreated animals. The visual behavior and ERG responses were also greatly enhanced in MDHB-treated rd10 mice. Mechanistically, following MDHB treatment, the number of TUNEL-positive cells was decreased in rd10 retina, and the expression of brain-derived neurotrophic factor (BDNF) protein and phosphorylated tropomyosin-related kinase B (TrkB) receptor were increased. Furthermore, blocking TrkB using the antagonist ANA-12 prevented the protective effect of MDHB on photoreceptor survival and structure. MDHB treatment also inhibited microglial activation and Muller cell gliosis in rd10 retina. In conclusion, MDHB treatment delays retinal degeneration in rd10 mice and preserves retinal structure and functions. These effects are likely mediated by the BDNF-TrkB pathway. Due to its neurotrophic effects and ability to reduce reactive gliosis, MDHB may be useful to treat degenerative diseases in retina and brain.