Siramesine Attenuates Early Brain Injury Through the TMEM97/NPC1 Pathway After Experimental Subarachnoid Hemorrhage in Rats

The occurrence of oxidative stress and apoptosis is closely associated with early brain injury (EBI) following subarachnoid hemorrhage (SAH). Currently, there is a lack of effective therapeutic targets or specific pharmacological agents to counteract oxidative stress and cell death after SAH. Our study demonstrates that the TMEM97/NPC1 signaling pathway plays a significant role in EBI in rats with SAH. TMEM97 protein expression in rat brain tissue progressively decreased after SAH, reaching its lowest level at 24 h. Immunofluorescence double-staining further confirmed a notable reduction in TMEM97-positive neurons at 24 h post-SAH. Treatment with Siramesine, a reported TMEM97 activator, was observed to ameliorate both short-term and long-term neurological deficits in SAH rats. The administration was also associated with a reduction in oxidative stress and suppression of neuronal apoptosis. At the molecular level, Siramesine treatment correlated with upregulation of TMEM97, NPC1, DJ-1, and the anti-apoptotic protein Bcl-2, alongside downregulation of the mitochondrial fission protein Drp1, the oxidative stress-related protein Romo-1, and the pro-apoptotic protein Bax. Notably, the protective effects of Siramesine were significantly, though not completely, attenuated by co-administration of the TMEM97 inhibitor SM-21 or by NPC1 siRNA. The partial nature of this reversal, particularly with the TMEM97 antagonist SM-21, indicates that while TMEM97 activation constitutes a significant component of Siramesine's mechanism, it is unlikely to be the sole contributor to its full neuroprotective effect. Collectively, these results suggest that the TMEM97/NPC1 pathway is involved in the neuroprotective actions of Siramesine, while also implying the potential engagement of additional, complementary mechanisms. This study provides a foundation for future preclinical investigations aimed at further elucidating this complex mechanism.