NF-KB CANONICAL PATHWAY DELETION ALLEVIATES ATHEROGENETIC EFFECT OF INTERMITTENT HYPOXIA INDUCED MACROPHAGE FOAM-CELL FORMATION
Abdull Massri, Toshihiro Imamura, Dan Zhou.
University of California, San Diego, La Jolla, CA.
Obstructive sleep apnea syndrome (OSAS) is a common sleeping disorder characterized by intermittent hypoxia (IH). Clinical studies revealed an independent relationship between OSAS and atherosclerosis. Furthermore, the predisposition to atherosclerosis in OSAS patients has been shown to be due to the NF-kappa B (NF-kB) pathway activation. The hallmark of atherosclerotic lesions is lipid-laden macrophages known as foam cells; however, the contribution of IH to foam-cell formation is not yet fully understood. We hypothesize that IH induces macrophage foam-cell formation through the activation of the NF-kB pathway. Myeloid restricted IKK-beta deleted mice were employed to down regulate the NF-kB canonical pathway in macrophages. Peritoneal macrophages were incubated with low-density lipoprotein and simultaneously were exposed to either IH or normoxia for 24 hours. After exposure, foam-cell formation was assessed by quantification of intracellular cholesterol. Nuclear protein was extracted for western blotting to quantify the expression of phosphorylated p65 as NF-kB pathway activity. IH significantly increased total cholesterol in wild-type macrophages (63.4 ± 3.3 μg/mg of cellular protein) in comparison to normoxia (51.2 ± 1.6). Intriguingly, this increase of intracellular cholesterol in response to IH exposure was significantly reduced in the IKK-beta deleted macrophages (IH 52.4 ± 1.1; normoxia 50.0 ± 1.6). This suggests that NF-kB pathway regulated gene expression is integral to IH-induced foam-cell formation. Indeed, we found that p65 expression in normoxia was increased 2-fold in response to IH, but this effect was alleviated by the IKK-beta deletion. Canonical NF-kB pathway plays a critical role in IH-induced macrophage foam cell formation.