Regulation of the SIRT1 signaling pathway in NMDA-induced Excitotoxicity

•NMDA induced a downregulation of SIRT1 at the mRNA and protein level. Furthermore, NMDA triggered an increase in HuR phosphorylation.•Functionally, the decrease in SIRT1 results in cell damage while inhibition of HuR phosphorylation promotes cell survival upon NMDA treatment via an increased expression of SIRT1.•Inhibition of PKC activity can reverse the NMDA-induced effects probably due to a reduction in HuR phosphorylation by PKC.•BAPTA-AM, an intracellular calcium, was able to reverse the NMDA-induced insults probably by an inhibition of PKC-dependent HuR phophorylation.•The Ca2+-PKC-HuR-SIRT1 pathway may be the access point to affect SIRT1 expression and functional regulation in the NMDA excitotoxicity model. Silent Information Regulator 1 (SIRT1), an NAD+-dependent deacetylase, contributes to the neuroprotective effect. However, intracellular signaling pathways that affect SIRT1 function remain unknown. It is well known that N-methyl-D-aspartate (NMDA) receptor activation induces calcium influx which then activates PKC, and SIRT1 is a mRNA target for HuR protein. We hypothesize that Ca2+-PKC-HuR-SIRT1 pathway modulates SIRT1 function. The present study is to investigate the potential pathway of SIRT1 in the SH-SY5Y cell line as an in vitro model of NMDA-induced neurotoxicity. The results showed that: (1) SIRT1 levels were downregulated in NMDA model; (2) NMDA induced an increase in serine phosphorylation of HuR, while inhibition of serine phosphorylation of HuR increased SIRT1 levels, promoting cell survival; (3) PKC inhibitor (Gö 6976) reversed NMDA insults and also suppressed serine phosphorylation of HuR; (4) 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid (BAPTA-AM), an intracellular calcium chelator, fully reversed NMDA insults and also inhibited PKC activity evoked by NMDA. These results indicate that intracellular elevated Ca2+ activates PKC, which phosphorylates HuR and then promotes SIRT1 mRNA decay and subsequent neuronal death in NMDA model. Therefore, the study suggests that inhibition of Ca2+-PKC-HuR-SIRT1 pathway could be an effective strategy for preventing certain neurological diseases related to NMDA excitotoxicity.