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

Abstract

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.

Effects of zinc ex vivo on taurine uptake in goldfish retinal cells

“…In addition, taurine does not counteract the inhibitory effect of 1 µM zinc [16], which may be due to inhibition of taurine transport. This conclusion is consistent with the fact that the trophic effect of the taurine is dependent on its intracellular levels [42,43]. Zinc deficiency alters taurine levels in goldfish retina, its trophic effect and increases taurine uptake [40].…”

Neuroprotective Mechanisms of Taurine against Ischemic Stroke

“…In the CNS it plays a role in: neuromodulation [55,56,57], osmoregulation [33,58], the maintenance of calcium homeostasis [59,60,61,62,63], membrane stabilization [64], anti-oxidation [65,66], anti-inflammation [67,68] and neuroprotection [59,69,70,71,72,73] and is also seen as a trophic factor during CNS development [40,74]. Its neuroprotective effect is observed against l -glutamate induced excitotoxicity whereby it counteracts the glutamate-induced increase of intracellular calcium through L-, P/Q-, N-type voltage-gated calcium channels (VGCCs) and the N -methyl- d -aspartate (NMDA) receptor, thus preventing glutamate-induce membrane depolarization [59,69].…”

Taurine and Zinc Modulate Outgrowth from Goldfish Retinal Explants

“…The regeneration of goldfish retinal explants is stimulated by taurine, increasing neuritic outgrowth from retinal explants after crushing the optic nerve by its in vitro presence, and by the intraocular administration during the degeneration-regeneration period after the lesion (2). This process is related to an increase in calcium fluxes (6), and to a modification of phosphorylation of retinal proteins (7).…”