Neuronal Store-Operated Ca2+ Entry (nSOCE) plays an essential role in refilling endoplasmic reticulum Ca2+ stores and is critical for Ca2+-dependent neuronal processes. SOCE sensors, STIM1 and STIM2, can activate Orai, TRP channels and AMPA receptors, and inhibit voltage-gated channels in the plasma membrane. However, the link between STIM, SOCE, and NMDA receptors, another key cellular entry point for Ca2+ contributing to synaptic plasticity and excitotoxicity, remains unclear. Using Ca2+ imaging, we demonstrated that thapsigargin-induced nSOCE was inhibited in rat cortical neurons following NMDAR inhibitors. Blocking nSOCE by its inhibitor SKF96365 enhanced NMDA-driven [Ca2+]i. Modulating STIM protein level through overexpression or shRNA inhibited or activated NMDA-evoked [Ca2+]i, respectively. Using proximity ligation assays, immunofluorescence, and co-immunoprecipitation methods, we discovered that thapsigargin-dependent effects required interactions between STIMs and the NMDAR2 subunits. Since STIMs modulate NMDAR-mediated Ca2+ levels, we propose targeting this mechanism as a novel therapeutic strategy against neuropathological conditions that feature NMDA-induced Ca2+ overload as a diagnostic criterion.
Keywords: Ca2+ homeostasis; NMDA receptor; STIM proteins; endoplasmic reticulum (ER); neuronal store-operated calcium entry (nSOCE); neurons; organellar Ca2+; plasma membrane (PM).