Implications of α v β 3 Integrin Signaling in the Regulation of Ca 2+ Waves and Myogenic Tone in Cerebral Arteries

Abstract

The myogenic response is central to blood flow regulation in the brain. Its induction is tied to elevated cytosolic [Ca(2+)], a response primarily driven by voltage-gated Ca(2+) channels and secondarily by Ca(2+) wave production. Although the signaling events leading to the former are well studied, those driving Ca(2+) waves remain uncertain. We postulated that αvβ3 integrin signaling is integral to the generation of pressure-induced Ca(2+) waves and cerebral arterial tone. This hypothesis was tested in rat cerebral arteries using the synergistic strengths of pressure myography, rapid Ca(2+) imaging, and Western blot analysis. GRGDSP, a peptide that preferentially blocks αvβ3 integrin, attenuated myogenic tone, indicating the modest role for sarcoplasmic reticulum Ca(2+) release in myogenic tone generation. The RGD peptide was subsequently shown to impair Ca(2+) wave generation and myosin light chain 20 (MLC20) phosphorylation, the latter of which was attributed to the modulation of MLC kinase and MLC phosphatase via MYPT1-T855 phosphorylation. Subsequent experiments revealed that elevated pressure enhanced phospholipase Cγ1 phosphorylation in an RGD-dependent manner and that phospholipase C inhibition attenuated Ca(2+) wave generation. Direct inhibition of inositol 1, 4, 5-triphosphate receptors also impaired Ca(2+) wave generation, myogenic tone, and MLC20 phosphorylation, partly through the T-855 phosphorylation site of MYPT1. Our investigation reveals a hitherto unknown role for αvβ3 integrin as a cerebral arterial pressure sensor. The membrane receptor facilitates Ca(2+) wave generation through a signaling cascade, involving phospholipase Cγ1, inositol 1,3,4 triphosphate production, and inositol 1, 4, 5-triphosphate receptor activation. These discrete asynchronous Ca(2+) events facilitate MLC20 phosphorylation and, in part, myogenic tone by influencing both MLC kinase and MLC phosphatase activity.