Cu–Zn superoxide dismutase activates muscarinic acetylcholine M1 receptor pathway in neuroblastoma cells

Muscarinic receptors (mAChRs) control several neuronal functions and are widely expressed in the central nervous system (CNS): M1 subtype represents the predominant mAChR in the CNS.Previously, we showed that antioxidant enzyme Cu–Zn superoxide dismutase (SOD1) is secreted by many cellular lines and specifically interacts with cell surface membrane of human neuroblastoma SK-N-BE cells thus activating phospholipase C (PLC) transduction pathway and increasing intracellular calcium concentration ([Ca2 +]i). In addition, we demonstrated that a small amount of SOD1 is contained in large core dense vesicles and that it is secreted in response to depolarization induced by elevated extracellular K+ concentration. In the present study, we investigated the involvement of muscarinic M1 receptors in SOD1-induced activation of PLC transduction pathway. We showed that, in SK-N-BE cells, SOD1 was able to activate muscarinic M1 receptor producing a phosphorylation of ERK 1/2 and Akt in dose- and time-dependent manner. Interestingly, in the presence of the M1 antagonist pirenzepine, ERK 1/2 and Akt phosphorylation induced by SOD1 was remarkably prevented. This effect was mimicked by knocking-down M1 receptor using two sequences of RNA silencing (siRNA). At functional level, siRNAs against M1 receptor were able to prevent the increase in [Ca2 +]i induced by SOD1. The same inhibitory effect on [Ca2 +]i changes was produced by the M1 antagonist pirenzepine. Collectively, the results of this study demonstrated that SOD1 could activate a transductional pathway through the involvement of M1 muscarinic receptor.