Combined Treatment Targeting Ca2+ Store Mediated Ca2+ Release and Store-operated Calcium Entry Reduces Secondary Axonal Degeneration and Improves Functional Outcome After SCI

Store-operated calcium entry (SOCE) is crucial for cellular processes, including cellular calcium homeostasis and signaling. However, uncontrolled activation of SOCE is implicated in neurological disorders and CNS trauma, but underlying mechanisms remain unclear. We hypothesized that inhibiting SOCE enhances neurological recovery following contusive spinal cord injury (SCI). To investigate key SOCE effectors, stromal interaction molecules (STIM) and Orai channels on neurological recovery following spinal cord injury (SCI), we utilized male and female conditional neuronal Stim1KO mice to investigate the role of neuronal STIM1 in SCI outcome following a mild (30 kdyn) contusion at T13. To investigate Ca2+ store mediated Ca2+ store depletion, and SOCE-mediated refilling in SCI outcome, we inhibited the IPR with 2-APB, and uncoupled STIM/Orai activation with DPB162-AE, respectively. Intravital microscopy demonstrated that neuron specific Stim1KO increased axonal survival post-SCI. Likewise, pharmaceutical uncoupling of STIM1/Orai activation, alone or combined with IPR inhibition, enhanced axon survival 24 h after T13 contusion in male and female Thy1YFP+ mice. Behavioral evaluation of female C57BL/6 J mice revealed that DPB162-AE, alone or combined with 2-APB, improved neurological recovery 4-6 weeks following a moderate (50 kdyn) T9 contusion. Immunohistochemical analysis showed that combined treatment improves axonal sparing, increases astrogliosis, and reduces microglia/macrophage density at the injury epicenter 6 weeks post-SCI. These findings reveal a novel role for neuronal STIM1 in "bystander" secondary axonal degeneration, and introduce STIM/Orai functional uncoupler DPB162-AE, combined with IPR inhibitor 2-APB, as a novel therapeutic approach for improving neurological recovery following SCI.