Transcriptional Upregulation of α ₂ δ-1 Elevates Arterial Smooth Muscle Cell Voltage-Dependent Ca ²⁺ Channel Surface Expression and Cerebrovascular Constriction in Genetic Hypertension

Abstract

A hallmark of hypertension is an increase in arterial myocyte voltage-dependent Ca2+ (CaV1.2) currents that induces pathological vasoconstriction. CaV1.2 channels are heteromeric complexes comprising a pore forming CaV1.2α1 with auxiliary α2δ and β subunits. Molecular mechanisms that elevate CaV1.2 currents during hypertension and the potential contribution of CaV1.2 auxiliary subunits are unclear. Here, we investigated the pathological significance of α2δ subunits in vasoconstriction associated with hypertension. Age-dependent development of hypertension in spontaneously hypertensive rats (SHR) was associated with an unequal elevation in α2δ-1 and CaV1.2α1 mRNA and protein in cerebral artery myocytes, with α2δ-1 increasing more than CaV1.2α1. Other α2δ isoforms did not emerge in hypertension. Myocytes and arteries of hypertensive SHR displayed higher surface-localized α2δ-1 and CaV1.2α1 proteins, surface α2δ-1 to CaV1.2α1 ratio (α2δ-1:CaV1.2α1), CaV1.2 current-density and non-inactivating current, and pressure- and - depolarization-induced vasoconstriction than those of Wistar-Kyoto controls. Pregabalin, an α2δ-1 ligand, did not alter α2δ-1 or CaV1.2α1 total protein, but normalized α2δ-1 and CaV1.2α1 surface expression, surface α2δ-1:CaV1.2α1, CaV1.2 current-density and inactivation, and vasoconstriction in myocytes and arteries of hypertensive rats to control levels. Genetic hypertension is associated with an elevation in α2δ-1 expression that promotes surface trafficking of CaV1.2 channels in cerebral artery myocytes. This leads to an increase in CaV1.2 current-density and a reduction in current inactivation that induces vasoconstriction. Data also suggest that α2δ-1 targeting is a novel strategy that may be used to reverse pathological CaV1.2 channel trafficking to induce cerebrovascular dilation in hypertension.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

“…Both are also subject to alternative splicing (195, 209). Vascular SMCs express β 2 (283), β 3 (745, 1038, 1039), α 2 δ 1 (87, 88, 283) and α 2 δ 3 (283) isoforms of these accessory subunits.…”

“…The δ subunits are postranscriptionally modified with a glycophosphatidylinositol membrane anchor, tethering these proteins to the membrane in association with the α 1 -pore-forming subunit (209). Cerebrovascular SMCs express α 2 δ 1 subunits that are essential for trafficking and targeting Ca V 1.2 VGCCs to the plasma membrane (87, 88). Vascular SMCs also express β2 (283) and/or β3 subunits (745) that increase the stability of the channel proteins by inhibiting their degradation, and which mediate upregulation of the channels by angiotensin II.…”

Calcium Channels in Vascular Smooth Muscle

“…In cerebral VSM, α 2 δ is a crucial regulator of LTCC function as illustrated by decreased Ca 2+ influx via LTCCs and vasodilation following α 2 δ1 knockdown (Bannister et al, 2009). Furthermore, increased α 2 δ1 mRNA and protein were observed in cerebral VSM from spontaneously hypertensive rats (Bannister et al, 2012). These data, and the β subunit data discussed earlier, suggest that increased α 2 δ1 and β3 expression enhances LTCC expression and function, thus contributing to augmented vasoconstriction during hypertension.…”

Identification of Glycosylation Sites Essential for Surface Expression of the CaVα2δ1 Subunit and Modulation of the Cardiac CaV1.2 Channel Activity

“…Regulation of the L-type Ca 2ϩ current has profound physiological significance. Indeed, alterations in density or the activation/inactivation gating of L-type Ca 2ϩ channels have been implicated in a variety of cardiovascular diseases (3,4), including cardiac arrhythmias such as atrial fibrillation (5)(6)(7)(8), heart failure (9, 10), and ischemic heart disease (10). The molecular mechanisms underlying changes in the activity of the L-type Ca 2ϩ channel remain under study for most pathologies.…”