Taurine might be acting as a trophic factor in the retina by modulating phosphorylation of cellular proteins

Protein phosphorylation is involved in the regeneration of the nervous system. Taurine modulates the phosphorylation of specific proteins in the retina, and also increases outgrowth from ganglion cells. In order to test the possible role of protein phosphorylation on the outgrowth from the retina and on the trophic effect of taurine, in vitro studies were performed in the presence of phorbol and nonphorbol protein kinase C activators, the protein kinase C inhibitor tamoxifen, and phosphatase inhibitors. After crush of the optic nerve, explants of the goldfish retina were cultured and the outgrowth was evaluated by measuring the length and the density of neurites. The activation of protein kinase C decreased the outgrowth from the explants and impaired the stimulatory effect of taurine. Phosphatase inhibitors produced a similar effect on basal and taurine-modulated outgrowth. In certain concentrations, some of these drugs did not affect the emission of neurites in the absence of taurine, but decreased the effect of the amino acid. Tamoxifen also reduced the outgrowth, probably acting at other cellular levels or indicating that the regulation of outgrowth by phosphorylation is a complex and dual process. The response to the drugs, evaluated by length or density of fibers, was not the same, since rate of outgrowth was more affected than density, which suggests that both parameters are modulated at differential stages or sensitivities to the tested agents.