Docosahexaenoic acid ameliorates photoreceptor death in the rd mouse during early development in vitro

MIRANDA GE; ROTSTEIN NP; POLITI LE

Buenos Aires, Argentina

Congreso; ICER; 2006

ISER

Docosahexaenoic acid ameliorates photoreceptor death in the rd mouse during early development in vitro Miranda, Gisela, Rotstein, Nora and Politi, Luis. Instituto de Investigaciones Bioquímicas,  Universidad Nacional del Sur-CONICET, Bahía Blanca, Buenos Aires, Argentina. E-mail: gmiranda@criba.edu.ar   Apoptosis of photoreceptors is the hallmark of many degenerative diseases of the retina. In spite of extensive research, diseases such as retinitis pigmentosa, have still no cure. In the rd mouse, one of the best characterized animal model for this disease, the progressive death of photoreceptors during the first month of postnatal life leads to blindness. In this and other animal models of the disease, retina degeneration is associated with lower levels of docosahexaenoic acid (DHA) in the retina, and particularly in rod outer segments. Findings showing that the extent of the loss of DHA, the major polyunsaturated fatty acid in the retina, correlates with the severity of degeneration led to the hypothesis that photoreceptor degeneration might be slowed or prevented by DHA supplementation. However, evidence concerning a role for DHA in preventing photoreceptor degeneration is contradictory. Previous work in our laboratory has established that DHA prevents apoptosis and promotes differentiation of rat retina photoreceptors during their early development in vitro and also during oxidative stress. We have now investigated whether DHA would have a similar neuroprotective effect on the survival and differentiation of rd mouse photoreceptors in vitro. Pure neuronal cultures were obtained from rd mice retinas and incubated for different times in vitro in a chemically defined medium, supplemented with or without 6.7 µM DHA. We then evaluated the percentage of photoreceptors having apoptotic nuclei, showing mitochondrial membrane depolarization or expressing opsin. After 4 days in vitro, apoptotic photoreceptors were less than 30% of total photoreceptors, and this percentage was the same in cultures with or without DHA. Apoptosis of photoreceptors increased to about 60% by day 7 in cultures lacking DHA; however, supplementation with DHA significantly decreased photoreceptor apoptosis. In addition, while at day 4, the percentage of photoreceptors preserving their mitochondrial membrane potential was the same in both experimental conditions, this percentage decreased in rd cultures lacking DHA at day 7, consistent with the increase in photoreceptor apoptosis; however, DHA addition prevented mitochondrial membrane depolarization in photoreceptors at this culture time. DHA supplementation also induced an increase in opsin expression compared with control rd mouse photoreceptors, increase that was already evident after 4 days in vitro. These results suggest that DHA ameliorates the apoptosis of rd mouse photoreceptors at early culture times, a protection that is related to the preservation of mitochondrial membrane potential, and simultaneously promotes the differentiation of these neurons.