Smoothelin-like 1 deletion enhances myogenic reactivity of mesenteric arteries with alterations in PKC and myosin phosphatase signaling

Abstract

The role of the smoothelin-like 1 (SMTNL1) protein in mediating vascular smooth muscle contractile responses to intraluminal pressure was examined in resistance vessels. Mesenteric arterioles from wild type (WT) and SMTNL1 global knock-out (KO) mice were examined with pressure myography. SMTNL1 deletion was associated with enhanced myogenic tone in vessels isolated from male, but not female, mice. Intraluminal pressures greater than 40 mmHg generated statistically significant differences in myogenic reactivity between WT and KO vessels. No overt morphological differences were recorded for vessels dissected from KO animals, but SMTNL1 deletion was associated with loss of myosin phosphatase-targeting protein MYPT1 and increase in the myosin phosphatase inhibitor protein CPI-17. Additionally, we observed altered contractile responses of isolated arteries from SMTNL1 KO mice to phenylephrine, KCl-dependent membrane depolarization and phorbol 12,13-dibutyrate (PDBu). Using pharmacological approaches, myogenic responses of both WT and KO vessels were equally affected by Rho-associated kinase (ROCK) inhibition; however, augmented protein kinase C (PKC) signaling was found to contribute to the increased myogenic reactivity of SMTNL1 KO vessels across the 60–120 mmHg pressure range. Based on these findings, we conclude that deletion of SMTNL1 contributes to enhancement of pressure-induced contractility of mesenteric resistance vessels by influencing the activity of myosin phosphatase.

Enhanced diastolic dysfunction but preserved systolic function after acute pressure overload in the absence of smoothelin-like 1 protein

“…Previous reports have revealed important impacts for SMTNL1 on cardiovascular performance; therefore, we characterized the structural and functional phenotype of the heart in the absence of SMTNL1, at baseline and under cardiac stress with pressure overload induced by constrictive banding of the aorta. The results of our study reveal that SMTNL1 plays a critical role in modulating cardiac functionality in addition to its previously reported impacts on vascular performance (Turner et al, 2014; Turner et al, 2019; Wooldridge et al, 2008; Lontay et al, 2010).…”

“…In this regard, male Smtnl1 -/- mice exhibited longer time to fatigue and greater distances run than male WT littermates when subjected to a forced-running exercise program. SMTNL1 deletion was also associated with enhanced myogenic reactivity of vessels isolated from male, but not female, mice (Turner et al, 2019). The augmented pressure-induced contractility of mesenteric resistance vessels from Smtnl1 -/- mice was linked to changes in protein kinase C signaling and the activity of myosin phosphatase.…”

“…The findings stress the importance of SMTNL1 deletion in advancing adverse cardiac responses to a hyperconstrictive vasculature. The splanchnic mesentery receives 10-40% of the cardiac output depending on digestion status (Harper and Chandler, 2016; Sun et al, 1992), and male Smtnl1 -/- mice possess significantly enhanced vasoconstriction of the mesenteric arteries that would contribute to elevated systemic vascular resistance (Turner et al, 2019). However, an earlier characterization of the Smtnl1 -/- animals is in disagreement since it did not reveal any alteration in peripheral blood pressure (Wooldridge et al, 2008).…”

“…The systemic vascular resistance of the Smtnl1 -/- mice with TAC-burden further increased in comparison to the WT but not the Smtnl1 -/- mice in the Sham-operated group, showing that only the WT mice did trend to develop a higher vascular resistance upon pressure overload. This implies that the Smtnl1 -/- animals were more adapted to withstand the acute pressure overload inflicted by the aortic banding than their WT counterparts, presumably due to the inherent presence of enhanced myogenic reactivity of the microvasculature (Turner & MacDonald, 2014; Turner et al, 2019). Interestingly, PKG-Iα is reported to inhibit cardiac remodeling in TAC-challenged hearts (Blanton et al 2012).…”

“…On the other hand, pressure myography experiments performed ex vivo on isolated resistance vessels such as cerebral and mesenteric arteries found vessels from male but not female KO mice to display enhanced myogenic reactivity in response to increasing luminal pressure (10-120 mmHg) while vessels from wild-type mice developed normal autoregulatory constrictions (Turner and MacDonald, 2014; Turner et al, 2019). No overt structural alterations were observed for vessels isolated from KO mice, and augmented PKC signaling acting on Ca 2+ -sensitizing mechanisms of smooth muscle contraction (i.e., myosin light chain phosphatase (MLCP) and the C-kinase potentiated inhibitor of myosin phosphatase (CPI-17)) were associated with enhanced myogenic reactivity of vessels in the absence of SMTNL1 (Turner et al, 2019). This finding was consistent with previous reports that revealed SMTNL1 to regulate myosin phosphatase activity through direct interaction with the myosin phosphatase-targeting subunit 1 (MYPT1) of MLCP (Borman et al, 2009; Lontay et al, 2010) and through transcriptional/translational effects on the expression levels of MYPT1 (Lontay et al, 2010).…”