PARP1 modulates BBB function via regulating NLRC5 in cerebral endothelial cells during ischemic stroke

Ischemic stroke (IS) is one of the major causes of morbidity and mortality worldwide. Blood-brain barrier (BBB) dysfunction acts as an important alteration after IS, however, the underlying pathophysiological mechanisms remain incompletely delineated. Endothelial cells are the primary constituents of BBB. In this study, we demonstrated that NOD-like receptor family CARD domain containing 5 (NLRC5) was markedly decreased in brain endothelial cells after IS and the Adeno-Associated Virus Serotype 9 (AAV9)-inducted endothelial cell-specific knockdown of NLRC5 further aggravates BBB dysfunction, neurological function, delays cerebral blood flow recovery and promotes neuroinflammation. Immunoprecipitation-mass spectrometry and co-immunoprecipitation demonstrate the interaction between NLRC5 and Poly (ADP-ribose) polymerase 1 (PARP1), which resulted in the downregulation of NLRC5. Mechanistically, PARP1-mediated PARylation of NLRC5 enhanced its ubiquitination, thereby promoted NLRC5 proteasomal degradation. By using PJ34, a specific inhibitor of PARP1, IS induced BBB dysfunction was alleviated. Collectively, our study provided a novel mechanistic insight into how PARP1 impacts BBB function in IS and identified PARP1 inhibitor as a promising therapeutic strategy for IS.