Downregulation of RTN1-C attenuates MPP+-induced neuronal injury through inhibition of mGluR5 pathway in SN4741 cells

Reticulons (RTNs) are a group of membrane-bound proteins that are dominantly localized to the endoplasmic reticulum (ER). RTN1-C, one isoform of RTNs highly expressed in the brain, has been shown to mediate neuronal injury in cerebral ischemia models. The aim of this study was to investigate the role of RTN1-C in an in vitro model of Parkinson's disease (PD) mimicked by 1-methyl-4-phenylpyridinium (MPP+) treatment in SN4741 cells. We found that MPP+ significantly increased the expression of RTN1-C, with no effect on RTN1-A and RTN1-B. Downregulation of RTN1-C using siRNA (Si-RTN1-C) markedly increased cell viability and inhibited apoptosis induced by MPP+ treatment. The results of western blot showed that downregulation of RTN1-C inhibited the surface expression of metabotropic glutamate receptor 5 (mGluR5) but had no effect on mGluR1. The protective effects of Si-RTN1-C were partially prevented by activating mGluR5, not mGluRl. In addition, the results of Ca2+ imaging showed that downregulation of RTN1-C attenuated intracellular Ca2+ release induced by MPP+, which could be nullified by activation of mGluR5 pathway. In conclusion, our data suggest that downregulation of RTN1-C protects SN4741 cells against MPP+ through mGluR5-mediated preservation of Ca2+ homeostasis. Therefore, RTN1-C might represent a therapeutic target for the treatment of neuronal injury in experimental PD models.