Investigating The Roles That G Protein-Coupled Receptor Kinase 2 Plays in Arterial Smooth Muscle Proliferation
2019-12-06T09:03:46Z (GMT) by
Vascular smooth muscle cell (VSMC) proliferation plays a key role in the development of hypertensive vascular remodelling, a process strongly associated with increased circulating vasoconstrictor concentrations such as angiotensin-II (AngII), endothelin-1 (ET1) and uridine-5'-triphosphate (UTP), leading to continuous activation of their cognate Gαq-coupled/G protein-coupled receptors (GPCR). Furthermore, hypertension is associated with elevated G protein coupled receptor kinase 2 (GRK2) expression in arterial smooth muscle cells, which negatively regulates Gαq/GPCR signalling. Indeed, GRK2 has been shown to play a key role in cell growth and development of the cardiovascular system, and the regulation of cell cycle progression. Therefore this study aimed to investigate the potential roles that GRK2 plays in VSMC proliferation, and in particular on two signalling pathways that have been implicated in this process: mitogen activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)/Akt. Initial studies indicated that inhibition of MAPK/ERK and PI3K/Akt prevented VMSC growth stimulated by ET1 and AngII, while UTP did not stimulate proliferation. Similarly, GRK2 depletion or catalytic inhibition prevented ET1/AngII-stimulated VSMC proliferation. Furthermore, prolonged ET1 and AngII-stimulated ERK signalling was dependent on GRK2 expression and catalytic activity, whereas these treatments enhanced UTP-stimulated signals. Moreover, ET1-stimulated ERK signals were arrestin3-dependent, whilst AngII signals were arrestin2-dependent. Conversely, GRK2 expression but not its catalytic activity was essential to facilitate ET1 and AngII-stimulated PI3K/Akt signals, whereas UTP signals were unaffected. Interestingly, ET1/AngII-stimulated PI3K/Akt signalling was arrestin-independent. Similarly, ET1/AngII signalling to the Akt target GSK3 was ablated following GRK2 knockdown. Collectively, these data highlight two different molecular mechanisms underlying GRK2-mediated regulation of VSMC proliferation; with ERK-stimulated growth being dependent on GRK2 kinase activity and arrestin recruitment, and the other presumably utilizing GRK2 as a PI3K scaffold to facilitate efficient PI3K/Akt/GSK3 signalling. Thus, increased GRK2 expression in hypertension could be an underlying factor promoting long-term proliferative pathways and consequently, contribute to VSMC proliferation, vascular wall thickening, and hypertensive vascular remodelling.