STIM Protein-NMDA2 Receptor Interaction Decreases NMDA-Dependent Calcium Levels in Cortical Neurons

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.