Abstract 11616: Obstructive Sleep Apnea Disrupts Endothelial Cellular Cholesterol Trafficking

Abstract

Introduction: Obstructive sleep apnea (OSA), a highly prevalent disorder, triples cardiovascular risk. Our previous studies showed that intermittent hypoxia (IH), the hallmark of OSA, triggers endothelial cell (EC) inflammation by reducing protection against complement activity, which is cholesterol-dependent. We assessed whether IH promotes accumulation of cellular cholesterol in ECs in OSA patients and investigated the underlying mechanisms. Methods: We used ECs collected from OSA patients and cultured human umbilical vein ECs (HUVECs) exposed to IH (alternating 30 min 21% O 2 for normoxia/30 min 2% O 2 for hypoxia for 8 h). Results: Levels of free, cellular cholesterol were increased and the presence of lipid droplets was reduced in ECs from OSA patients compared with OSA-free controls as well as in HUVECs exposed to IH compared with normoxia. Cholesterol uptake and synthesis were similar in normoxia and IH. In contrast, co-localization of free cholesterol and late endosome/lysosome (LE/LY) was increased in IH compared with normoxia, suggesting impaired trafficking of free cholesterol from LE/LY to endoplasmic reticulum (ER) in IH. Immunoglobulin binding protein (BiP), a marker of ER stress, was upregulated in ECs of OSA patients compared with controls. IH-induced ER stress reduced interaction between LE/LY-bound oxysterol binding protein-related protein-1L (ORP1L) and ER-bound VAMP-associated protein-B (VAPB), which is required for cholesterol trafficking from LE/LY to ER. After screening ER-associated degradation machinery components for potential binding to VAPB in IH, we identified Derlin1 as a ligand that binds increasingly to VAPB in IH thereby potentially reducing interaction between ORP1L and VAPB. In OSA patients, ORP1L-VAPB interaction was reduced whereas Derlin1-VAPB was increased and positive airway pressure, a standard therapy for OSA, reversed these changes. Conclusions: IH induces ER stress that disrupts cholesterol trafficking from LE/LY to ER leading to accumulation of free cholesterol in ECs, which underlies impaired endothelial protection against complement and endothelial inflammation that may increase cardiovascular risk in OSA.