Abstract
Abstract: :
Purpose: Ciliary neurotrophic factor (CNTF) has been found to be a potent neuroprotectant for photoreceptors in the rodent retina. It appears to act by stimulating the JAK–STAT signaling pathway in Müller cells, but the regulation of the pathway is not well studied. In the present study, we have examined some temporal aspects of CNTF action on Müller cells Methods: The retinal Müller cell line, rMC–1, was treated with CNTF for different time periods, ranging from 15 min to 5 hr. Subsequently, cell extracts were analysed by western blotting using a phosphorylated–STAT3 (pSTAT3)–specific antibody. In other experiments, cells were first treated with CNTF for 5 hr and later exposed to Leukemia inhibitory factor (LIF), a cytokine closely related to CNTF. Results: In Müller cell cultures exposed to CNTF, there was a rapid accumulation of pSTAT3 by 15 min. Subsequently, the level of pSTAT3 declined and returned to baseline by 60 min. The level of pSTAT did not change even after a prolonged time period (5 hr) of CNTF exposure. Moreover, CNTF addition at this time had no effect pSTAT3 level. Similarly, in rMC1 cultures treated for 5 hr with CNTF, addition of LIF did not change pSTAT3 level. When rMC1 cultures were treated for 5 hr with LIF and exposed to CNTF, there was no change in the pSTAT3 level. Conclusions: CNTF treatment results in immediate activation of the JAK–STAT pathway, which subsequently levels off possibly due to negative control of the pSTAT3 level. In addition, long–term exposure to CNTF desensitizes Müller cells resulting in heterologous regulation. Supported by NIH grant EY–13125.