Activation of PERK branch of ER stress mediates homocysteine-induced BK(Ca) channel dysfunction in coronary artery via FoxO3a-dependent regulation of atrogin-1

The molecular mechanism of endoplasmic reticulum (ER) stress in vascular pathophysiology remains inadequately understood. We studied the role of ER stress in homocysteine-induced impairment of coronary dilator function, with uncovering the molecular basis of the effect of ER stress on smooth muscle large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels. The vasodilatory function of BK(Ca) channels was studied in a myograph using endothelium-denuded porcine small coronary arteries. Primary cultured porcine coronary artery smooth muscle cells were used for mRNA and protein measurements and current recording of BK(Ca) channels. Homocysteine inhibited vasorelaxant response to the BK(Ca)channel opener NS1619, lowered BK(Ca) β1 subunit protein level and suppressed BK(Ca) current. Inhibition of ER stress restored BK(Ca) β1 protein level and NS1619-evoked vasorelaxation. Selective blockade of the PKR-like ER kinase (PERK) yielded similarly efficient restoration of BK(Ca) β1, preserving BK(Ca) current and BK(Ca)-mediated vasorelaxation. The restoration of BK(Ca) β1 by PERK inhibition was associated with reduced atrogin-1 expression and decreased nuclear localization of forkhead box O transcription factor 3a (FoxO3a). Silencing of atrogin-1 prevented homocysteine-induced BK(Ca) β1 loss and silencing of FoxO3a prevented atrogin-1 upregulation induced by homocysteine, accompanied by preservation of BK(Ca) β1 protein level and BK(Ca) current. ER stress mediates homocysteine-induced BK(Ca) channel inhibition in coronary arteries. Activation of FoxO3a by PERK branch underlies the ER stress-mediated BK(Ca) inhibition through a mechanism involving ubiquitin ligase-enhanced degradation of the channel β1 subunit.