Resumo

TRPV1 channels are involved in retinal signaling. In this study, we analyzed the colocalization of TRPV1 receptors with several proteins, including endothelial, microglial and neuronal cell markers in the early postnatal retina. We also studied the effects of TRPV1 blocking in retinal explants on cellular proliferation, cell cycle and apoptosis. The expression of the neuronal markers calbindin, calretinin and parvalbumin was also analyzed. Albino male rats (Rattus norvegicus) with 3 days of life (P3) were used in this study. Immunohistochemistry demonstrated that TRPV1-expressing cells in the ganglion cell layer and the inner nuclear layer (INL) are mainly calretinin-positive neurons, and very few cells in INL were positive for both TRPV1 and parvalbumin. TRPV1 receptor is also expressed by retinal astrocytes, as well as by microglial and endothelial cells. Retinal explants were treated in vitro for 12 and 24 hours with capsazepine (CPZ; 1 µM), a TRPV1 antagonist. TUNEL labeling indicated that TRPV1 blocking reduced cell apoptosis in the inner nuclear layers of the retina (40.0% +/- 10.0 of control values; p < 0.05). The expression of two markers of cell cycle, Ki-67 and PCNA, was analyzed by means of immunohistochemistry and immunoblotting, respectively, and their content was not changed after TRPV1 blocking. The expression of calbindin and parvalbumin was not changed either. However, calretinin protein levels were diminished after 24 hours of CPZ treatment (50.1% +/- 7.9 of control values; p<0.05). Several P3 rats also received single-daily doses of CPZ (40mg/Kg; IP) for three days, and were kept for 2 months. Their retinas were prepared for immunoblotting analysis. Intriguingly, calbindin and parvalbumin protein levels were upregulated (220.1% +/- 42.3, and 261% +/- 27.6 of control values, respectively; p < 0.05), while calretinin protein levels were similar to controls. The expression of two markers of retinal astrocytes and Müller cells, GFAP and vimentin, respectively, was not changed in this tissue. Our results indicate that TRPV1 channels play a role in the control of the early apoptosis that occur during retinal development. Moreover, given that CPZ treatment alters the expression of several neuronal markers in the developing and adult retina, it seems that TRPV1 function might be important for retinal neuronal maturation and differentiation.