Maintenance of adrenergic vascular tone by MMP transactivation of the EGFR requires PI3K and mitochondrial ATP synthesis.

AIMS: G-protein-coupled receptors (GPCRs) modulate vascular tone, at least in part, via matrix metalloproteinase (MMP) transactivation of the epidermal growth factor receptor (EGFR). We previously have identified novel signalling pathways downstream of the EGFR suggestive of mitogen-activated protein kinase and mitochondrial redox control of vascular tone. In the present study, we examined whether MMP modulation of vascular tone involves phosphoinositide 3-kinase (PI3K) and mitochondrial ATP synthesis. METHODS AND
RESULTS: To determine whether PI3K is required for the maintenance of adrenergic vascular tone, we first constricted rat small mesenteric arteries with phenylephrine (PE) and then perfused with PI3K inhibitors, LY294002 and wortmannin, both of which produced a dose-dependent vasodilatation. Next, to investigate whether MMPs modulate PI3K activity, we cultured rat aortic vascular smooth muscle cells (VSMCs) and stimulated them with GPCR agonists such as PE and angiotensin II. Inhibition of MMPs (by GM6001) or EGFR (by AG1478) or suppressing the expression of MMP-2 or MMP-7 or the EGFR by small interfering RNA blunted the PI3K phosphorylation of Akt induced by PE. Further, in VSMCs, PI3K inhibitors reduced the PE-induced increase in ATP synthesis and glucose transporter-4 translocation, an effect that was also observed with MMP and the EGFR inhibitors. Further, the PE-induced increase in ATP synthesis activated MMP-7 by mechanisms involving purinergic (P2X) receptors and calcium.
CONCLUSION: These data suggest that the maintenance of adrenergic vascular tone by the MMP-EGFR pathway requires PI3K activation and ATP synthesis. Further, our data support the view that elevated levels of GPCR agonists exaggerate the MMP transactivation of EGFR response and contribute to enhanced vascular tone and development of cardiovascular disease such as hypertension.