Mechanical stretch potentiates angiotensin II-induced proliferation in spontaneously hypertensive rat vascular smooth muscle cells

Abstract

Angiotensin II (AngII) stimulates vascular smooth muscle cell (VSMC) proliferation; however, the effect of AngII on cell proliferation in the presence of mechanical force is not clear. We investigated the mechanism of AngII-induced cell proliferation mediated by mechanical stretch in VSMCs of both normotensive and hypertensive rats. VSMCs obtained from the thoracic aortas of 8-week-old Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were stretched by a Flex culture system. Mechanical stretch significantly upregulated protein expression of AngII type 1 (AT 1 ) receptor, epidermal growth factor (EGF) receptor and mitogen-activated protein kinase phosphatase-1 in both SHR and WKY VSMCs; however, there was no significant difference in these changes between the cells from SHR and WKY. Mechanical stretch attenuated AngII-induced phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, ERK kinase (MEK) and EGF receptor; it also attenuated [ 3 H] thymidine incorporation and cell proliferation in VSMC of WKY. In contrast, the effects of AngII were augmented by mechanical stretch in VSMC of SHR. AngII-induced ERK 1/2 phosphorylation and cell proliferation in SHR were inhibited by pretreatment with an AT 1 receptor blocker, candesartan and an inhibitor of MEK, PD98059. Moreover, pretreatment with an EGF receptor tyrosine kinase inhibitor, AG1478, also blocked upregulation of AngII-induced ERK 1/2 phosphorylation induced by stretch in SHR VSMCs. This study demonstrates that mechanical stretch augments SHR VSMC proliferation through an AT 1 /EGF receptor/ERK-dependent pathway. These findings may provide new insights into the signaling mechanisms whereby AngII exerts its growth-promoting effects on vasculature in a hypertensive state.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli

“…Mechanical stretch potentiates AngII-induced VSMCs proliferation in spontaneously hypertensive rat through an AT 1 receptor/ EGFR/ERK-dependent pathway. These findings may provide new insights into growth-promoting mechanisms in vasculature in a hypertensive state (Liu et al, 2010). Mechanical stretch triggered an AT 1 receptordependent conformational change in b-arrestin similar to that induced by a b-arrestin-biased ligand (Rakesh et al, 2010).…”

Role of pro renin receptor in Ang II-mediated EGF receptor transactivation

“…Previous studies showed that Ang II levels in the cell lysate are elevated in human podocytes and HEK293 cells by prorenin stimulation (17, 18). Furthermore, EGF receptor is transactivated via the activation of AT 1 receptor induced by Ang II in VSMCs and HEK293 cells (15, 16, 31). …”

“…The supernatant was filtered on Amicon Ultra devises (10 kDa cut-off; Millipore). We measured Ang II concentration by radioimmunoassay using specific antibody for Ang II, monoiodinated 125 I-labeled Ang II, and Ang II standard as previously described (15, 28). In brief, each lyophilized antiserum was diluted sufficiently to yield a specific binding rate after incubation with a 9,000 cpm label for 48 hours at 4°C.…”

“…Several tyrosine residues in EGF receptor play a regulatory role in mediating the intracellular signaling pathway (14). In VSMCs, Ang II phosphorylates at both Tyr992 and Tyr1068 sites of EGF receptor which activates c-Src and ERK 1/2 (15, 16). Different phosphorylation sites of EGF receptor may induce activation of different downstream signaling pathways.…”

Inverse agonism: the classic concept of GPCRs revisited [Review]

“…That report showed that the synergy is at least partly caused by augmented AT1 receptor expression and is inhibited by ARB. Even in that case, the main action of ARB may be due to its antagonist activity, although inverse agonist activity would have some effect against the overactivity of AT1 receptor due to augmented expression [49,50].…”