Knockdown of STIM1 inhibits 6-hydroxydopamine-induced oxidative stress through attenuating calcium-dependent ER stress and mitochondrial dysfunction in undifferentiated PC12 cells

Stromal interaction molecule (STIM) proteins are parts of elaborate eukaryotic Ca2+ signaling systems and are considered to be important players in regulating neuronal Ca2+ homeostasis under normal ageing and pathological conditions. Here, we investigated the potential role of STIM1 in 6-hydroxydopamine (6-OHDA)-induced toxicity in undiff erentiated PC12 cell lines. Cells exposed to 6-OHDA demonstrated alterations in the generation of reactive oxygen species (ROS) in a Ca2+-dependent manner. Downregulation of STIM1 expression by specifi c small interfering RNA (siRNA) attenuated apoptotic cell death, reduced intracellular ROS production, and partially prevented the impaired endogenous antioxidant enzyme activities after 6-OHDA treatment. Furthermore, STIM1 knockdown signifi cantly attenuated 6-OHDA-induced intracellular Ca2+ overload by inhibiting endogenous store-operated calcium entry (SOCE). The eff ect of STIM1 siNRA on SOCE was related to orai1 and L-type Ca2+ channels, but not to transient receptor potential canonical type 1 (TRPC1) channel. In addition, silencing of STIM1 increased the Ca2+ buffering capacity of the endoplasmic reticulum (ER) in 6-OHDA-injured cells. ER vacuoles formed from the destruction of ER structural integrity and activation of ER-related apoptotic factors (CHOP and Caspase-12) were partially prevented by STIM1 knockdown. Moreover, STIM1 knockdown attenuated 6-OHDA-induced mitochondrial Ca2+ uptake and mitochondrial dysfunction, including the collapse of mitochondrial membrane potential (MMP) and the decrease of ATP generation. Taken together, our data provide the fi rst evidence that inhibition of STIM1-meditated intracellular Ca2+ dyshomeostasis protects undiff erentiated PC12 cells against 6-OHDA toxicity and indicate that STIM1 may be responsible for neuronal oxidative stress induced by ER stress and mitochondrial dysfunction in PD.