Ozanimod, an S1PR1 ligand, attenuates hypoxia plus glucose deprivation-induced autophagic flux and phenotypic switching in human brain VSM cells

Abstract

Vascular smooth muscle (VSM) cell phenotypic expression and autophagic state are dynamic responses to stress. Vascular pathologies, such as hypoxemia and ischemic injury, induce a synthetic VSM phenotype and autophagic flux resulting in a loss of vascular integrity and VSM cell death respectfully. Both clinical pilot and experimental stroke studies demonstrate that sphingosine-1-phosphate receptor (S1PR) modulation improves stroke outcome; however, specific mechanisms associated with a beneficial outcome at the level of the cerebrovasculature have not been clearly elucidated. We hypothesized that ozanimod, a selective S1PR type 1 ligand, will attenuate VSM synthetic phenotypic expression and autophagic flux in primary human brain VSM cells following acute hypoxia plus glucose deprivation (HGD; in vitro ischemic-like injury) exposure. Cells were treated with ozanimod and exposed to normoxia or HGD. Crystal violet staining, standard immunoblotting, and immunocytochemical labeling techniques assessed cellular morphology, vacuolization, phenotype, and autophagic state. We observed that HGD temporally decreased VSM cell viability and concomitantly increased vacuolization, both of which ozanimod reversed. HGD induced a simultaneous elevation and reduction in levels of pro- and antiautophagic proteins respectfully, and ozanimod attenuated this response. Protein levels of VSM phenotypic biomarkers, smoothelin and SM22, were decreased following HGD. Furthermore, we observed an HGD-induced epithelioid and synthetic morphological appearance accompanied by disorganized cytoskeletal filaments, which was rescued by ozanimod. Thus, we conclude that ozanimod, a selective S1PR1 ligand, protects against acute HGD-induced phenotypic switching and promotes cell survival, in part, by attenuating HGD-induced autophagic flux thus improving vascular patency in response to acute ischemia-like injury.