Retinoic acid-inducible gene-I aggravates neuroinflammation in early brain injury after subarachnoid hemorrhage through mediating brain microvascular endothelial cell pyroptosis

Retinoic acid-inducible gene-I (RIG-I) is an immune signal that promotes inflammatory responses and plays an important role in endothelial cell-mediated inflammation. Currently, no studies have investigated the role of RIG-I in early brain injury (EBI) after subarachnoid hemorrhage (SAH). In this research, an in vivo SAH model was established in Sprague Dawley (SD) rats through carotid artery puncture, while oxyhemoglobin (OxyHb) was used to stimulate brain microvascular endothelial cells (BMVECs) to generate an in vitro SAH model. The results showed that RIG-I was activated and expressed in BMVECs in both in vivo and in vitro. To explore how RIG-I is involved in the EBI, small interfering RNA was used to downregulate its expression. Compared with SAH rats, RIG-I knockdown rats had better short-term and long-term neurological recovery after SAH, milder brain edema and neurodegeneration, and weaker blood-brain barrier disruption and neuroinflammation. Furthermore, RIG-I knockdown attenuated SAH-induced BMVECs pyroptosis. In OxyHb-stimulated BMVECs, RIG-I knockdown reduced the cellular dysfunction and inflammation. To determine the mechanism of RIG-I in BMVECs pyroptosis, co-immunoprecipitation was used to verify the direct binding of RIG-I to caspase-1, and RIG-I knockdown could reduce Oxy-Hb-induced BMVECs pyroptosis, while caspase-1 inhibitor VX-765 can alleviate the tight junction loss, inflammation and pyroptosis exacerbated by RIG-I agonist. In addition, RIG-I levels in the cerebrospinal fluid of SAH patients were higher than those in controls and correlated with the levels of pyroptosis, inflammatory factors and clinical outcomes. In summary, the results demonstrated that RIG-I aggravates neuroinflammation after SAH by promoting caspase-1-mediated BMVECs pyroptosis.