Vascular smooth muscle cell (VSMC) phenotype switching is a term that describes a shift from contractile to synthetic cells. In physiological conditions VSMCs exist as contractile cells, regulating vascular tone. In response to injury, VSMCs become synthetic: they lose expression of contractility-related genes and proliferate, migrate, secrete extracellular vesicles (EVs) and extracellular matrix-related proteins to repair the damage. Phenotype switching has been shown to be involved in many vascular pathologies, such as atherosclerosis, calcification and aneurysm formation. The exact mechanisms inducing VSMC phenotype changes are not well understood, and were the aim of this study. 
		In a qPCR gene expression screen, we found that Nox5 mRNA expression was higher in synthetic VSMCs than contractile. Lentiviral overexpression of Nox5 in VSMCs induced hallmarks of the synthetic phenotype: decreased expression of contractile markers p-MLC and CNN1 measured by western blot and increased EV release. Conversely, Nox5 downregulation with siRNA increased expression of contractile markers CNN1, p-MLC and SM22α. 
	Since Nox5 is a reactive oxygen species (ROS) producing enzyme we investigated whether ROS can regulate VSMC phenotype. Nox5 overexpression resulted in increased ROS production by VSMCs and treating VSMCs with H2O2 downregulated expression of p-MLC and increased ROS production. 
	Additionally, in a transcriptomics analysis Nox5 expression positively correlated with MLC, SMTN, αSMA and negatively correlated with MYH11 and CNN1, suggesting expression in phenotypically modulated VSMCs in human atherosclerotic plaques. By immunohistochemistry, elevated Nox5 expression was observed in VSMCs that lost expression of CNN1 in human coronary arteries.
		In conclusion, Nox5 can induce phenotype changes in VSMCs via ROS. Nox5 is therefore a potential target to modulate vascular remodeling.

02 - NOX5 REGULATES VASCULAR SMOOTH MUSCLE CELL PHENOTYPE