Cigarette smoke extract causes endothelial nitric oxide synthase dysfunction through stimulation of ubiquitin proteasome system

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Cigarette smoking (CS) is a major risk factor for endothelial dysfunction (ED), a prognostic predictor for the risk of future cardiovascular events. Endothelial nitric oxide synthase (eNOS) dysfunction has been linked to CS‐induced ED; however, the exact mechanism is not fully understood. This study reports the role of the ubiquitin proteasome system (UPS) in CS‐ induced eNOS dysfunction and ED. Exposure of bovine aortic endothelial cells (BAECs) to cigarette smoke extract (CSE) resulted in a concentration‐dependent decrease in nitric oxide (NO) production, accompanied by an increase in superoxide generation and formation of 4‐hydroxy‐2‐nonenal protein adducts. CSE depleted tetrahydrobiopterin (BH4). total biopterin, and decreased the expression of eNOS and guanosine triphosphate cyclohydrolase‐1 (GTPCH‐1). More importantly, exposure of BAECs to CSE led to accumulation of ubiqutinylated protein and increased the 26S proteasomal activity in a concentration‐and time‐dependent manner. Pre‐treatment of BAECs with MG132, an inhibitor of 26S proteasome, restored the levels of eNOS, BH4, GTPCH‐1, and enhanced NO production in BAECs following CS exposure. Our data reveal that CS‐induced stimulation of the UPS resulted in degradation of eNOS and GTPCH‐1 that led to eNOS dysfunction and uncoupling. Thus, controlled interference with the UPS pathway could be a novel modality in the prevention of CS‐induced ED. (NIH # HL38324 to JLZ; Egyptian government)