Smooth muscle-selective CPI-17 expression increases vascular smooth muscle contraction and blood pressure.
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Recent data revealed that protein kinase C-potentiated myosin phosphatase inhibitor of 17 kDa (CPI-17), a myosin phosphatase inhibitory protein preferentially expressed in smooth muscle, is upregulated/activated in several diseases but whether this CPI-17 increase plays a causal role in pathologically enhanced vascular smooth muscle contractility and blood pressure remains unclear. To address this possibility, we generated a smooth muscle-specific CPI-17 transgenic mouse model (CPI-17-Tg) and demonstrated that the CPI-17 transgene was selectively expressed in smooth muscle-enriched tissues, including mesenteric arteries. The isometric contractions in the isolated second-order branch of mesenteric artery helical strips from CPI-17-Tg mice were significantly enhanced compared with controls in response to phenylephrine, U-46619, serotonin, ANG II, high potassium, and calcium. The perfusion pressure increases in isolated perfused mesenteric vascular beds in response to norepinephrine were also enhanced in CPI-17-Tg mice. The hypercontractility was associated with increased phosphorylation of CPI-17 and 20-kDa myosin light chain under basal and stimulated conditions. Surprisingly, the protein levels of rho kinase 2 and protein kinase Cα/δ were significantly increased in CPI-17-Tg mouse mesenteric arteries. Radiotelemetry measurements demonstrated that blood pressure was significantly increased in CPI-17-Tg mice. However, no vascular remodeling was detected by morphometric analysis. Taken together, our results demonstrate that increased CPI-17 expression in smooth muscle promotes vascular smooth muscle contractility and increases blood pressure, implicating a pathological significant role of CPI-17 upregulation. protein kinase c-potentiated myosin phosphatase inhibitor of 17 kDa (CPI-17), a myosin phosphatase inhibitory protein, is predominantly expressed in mature smooth muscle, with especially high levels in arteries (8, 38). Under physiological conditions, CPI-17 plays a critical role in regulating smooth muscle contraction (16, 17, 20). It is established that the reversible phosphorylation of CPI-17 at Thr38 regulates its activity (8, 34). Phosphorylated CPI-17 directly binds to myosin phosphatase, inhibits its activity, and consequently causes the accumulation of phosphorylated 20-kDa myosin light chain (MLC20) and smooth muscle contraction (7). In isolated enzyme systems, multiple kinases have been demonstrated to phosphorylate CPI-17 (7). In mature vascular smooth muscle tissue, rho kinase (ROCK) 2 is believed to be primarily responsible for slow, sustained CPI-17 phosphorylation, whereas protein kinase C (PKC) is believed to be mainly responsible for fast CPI-17 phosphorylation (6). Recently, accumulating evidence indicated that, in addition to reversible phosphorylation, the expression levels of CPI-17 are altered under various pathological conditions. CPI-17 mRNA or protein is increased in airway smooth muscle in antigen-induced airway hyperresponsive rats (33), in the bladder detrusor muscle of alloxan-induced type 1 diabetic rabbits (3), and in the aorta of type 2 diabetic db/db mice (40). CPI-17 protein is diminished in intestinal smooth muscle during intestinal inflammation (29) and in the neointima of wire-injured rat aorta (15). CPI-17 upregulation is often associated with increased smooth muscle contractility, whereas CPI-17 downregulation is often associated with decreased smooth muscle contractility. Together, these data implicate a role for CPI-17 expression levels in the alteration of smooth muscle contractility under various disease conditions. Moreover, we have demonstrated that CPI-17 upregulation/activation in the type 2 diabetic db/db vasculature is associated with a significant blood pressure increase (36), further suggesting a possible role for CPI-17 activation/upregualtion in increasing blood pressure. However, in addition to CPI-17, numerous alterations are present in smooth muscle under such pathological conditions. Consequently, it is unclear whether increased CPI-17 expression contributes to these observed changes in smooth muscle contractility and blood pressure. To address this issue, we have generated a smooth muscle-specific CPI-17 transgenic mouse model (CPI-17-Tg). Using this model and a combination of physiological, pharmacological, and biochemical approaches, the current study tests the hypothesis that CPI-17 upregulation in vascular smooth muscle increases both vascular smooth muscle contractility and blood pressure.
Su, Wen; Xie, Zhongwen; Liu, Shu; Calderon, Lindsay; Guo, Zhenheng; and Gong, Ming C., "Smooth muscle-selective CPI-17 expression increases vascular smooth muscle contraction and blood pressure." (2013). EKU Faculty and Staff Scholarship. 538.
American Journal of Physiology: Heart and Circulatory Physiology