Hypercholesterolemia‐Induced Loss of Flow‐Induced Vasodilation and Lesion Formation in Apolipoprotein E–Deficient Mice Critically Depend on Inwardly Rectifying K ⁺ Channels

Abstract

BackgroundHypercholesterolemia‐induced decreased availability of nitric oxide (NO) is a major factor in cardiovascular disease. We previously established that cholesterol suppresses endothelial inwardly rectifying K+ (Kir) channels and that Kir2.1 is an upstream mediator of flow‐induced NO production. Therefore, we tested the hypothesis that suppression of Kir2.1 is responsible for hypercholesterolemia‐induced inhibition of flow‐induced NO production and flow‐induced vasodilation (FIV). We also tested the role of Kir2.1 in the development of atherosclerotic lesions.Methods and ResultsKir2.1 currents are significantly suppressed in microvascular endothelial cells exposed to acetylated–low‐density lipoprotein or isolated from apolipoprotein E–deficient (Apoe −/−) mice and rescued by cholesterol depletion. Genetic deficiency of Kir2.1 on the background of hypercholesterolemic Apoe −/−mice, Kir2.1 +/− /Apoe −/− exhibit the same blunted FIV and flow‐induced NO response as Apoe −/−or Kir2.1 +/− alone, but while FIV in Apoe −/− mice can be rescued by cholesterol depletion, in Kir2.1 +/− /Apoe −/− mice cholesterol depletion has no effect on FIV. Endothelial‐specific overexpression of Kir2.1 in arteries from Apoe −/− and Kir2.1 +/− /Apoe −/− mice results in full rescue of FIV and NO production in Apoe −/− mice with and without the addition of a high‐fat diet. Conversely, endothelial‐specific expression of dominant‐negative Kir2.1 results in the opposite effect. Kir2.1 +/− /Apoe −/−mice also show increased lesion formation, particularly in the atheroresistant area of descending aorta.ConclusionsWe conclude that hypercholesterolemia‐induced reduction in FIV is largely attributable to cholesterol suppression of Kir2.1 function via the loss of flow‐induced NO production, whereas the stages downstream of flow‐induced Kir2.1 activation appear to be mostly intact. Kir2.1 channels also have an atheroprotective role.

Regulation of Kir2.1 Function Under Shear Stress and Cholesterol Loading

“…The contribution of the impairment of the K + channel in hypercholesterolemia‐induced EC dysfunction has been suggested, but the exact mechanism remains unclear. Fancher et al have nicely shown the crucial role of Kir2.1 in cholesterol loading–induced EC dysfunction and atherosclerosis formation both in vitro and in vivo . The role of ion channels as part of mechanosensory pathways has attracted substantial attention .…”

“…In this issue of Journal of the American Heart Association (JAHA), Fancher et al have assessed the functional role of cholesterol-mediated Kir2.1 channel suppression in a model of hypercholesterolemia by performing patch clamp analyses on isolated mouse ECs. 10 The authors presented experimental evidence demonstrating that Kir2.1 suppression is a contributing factor in the impairment of shear stress-mediated NO bioavailability and EC-dependent vasodilation induced by hypercholesterolemia. When loading ECs isolated from the resistance arteries with cholesterol using modified lowdensity lipoproteins, the shear stress-mediated increase of Kir2.1 current was inhibited.…”

“…Fancher et al have nicely shown the crucial role of Kir2.1 in cholesterol loading-induced EC dysfunction and atherosclerosis formation both in vitro and in vivo. 10 The role of ion channels as part of mechanosensory pathways has attracted substantial attention. 22 These findings provide us with a novel mechanism of hypercholesterolemia-induced vascular dysfunction and support the importance of endothelial Kir2.1 channels as a novel target for combating this disease.…”

Structural Determinants of Cholesterol Recognition in Helical Integral Membrane Proteins

“…For example, CLR seems to preferentially bind to the inactive state of rhodopsin (23,24) or to inhibit the conductance of the Ca 2+ -sensitive K + channels (BK) (25,26). CLR binding also suppresses the endothelial Kir2.1 channel that impairs flow-induced vasodilation and augments the development of atherosclerosis (27,28).…”

Membrane Lipid-KIR2.x Channel Interactions Enable Hemodynamic Sensing in Cerebral Arteries

“…Pathophysiological events that reduce membrane PIP 2 content could also render the endothelium insensitive to flow regulation, an example being this lipid’s stark drop with advancing Alzheimer’s disease (Arancio, 2008). Alternatively, dyslipidemia where plasma cholesterol rises, could if membrane lipids change accordingly, push endothelial K IR channels to reside in a preferred silent state and insensitive to flow activation (Fancher et al, 2018).…”