Differential roles of caveolin-1 in ouabain-induced Na⁺/K⁺-ATPase cardiac signaling and contractility

Abstract

Binding of ouabain to cardiac Na/K-ATPase initiates cell signaling and causes contractility in cardiomyocytes. It is widely accepted that caveolins, structural proteins of caveolae, have been implicated in signal transduction. It is known that caveolae play a role in Na/K-ATPase functions. Regulation of caveolin-1 in ouabain-mediated cardiac signaling and contractility has never been reported. The aim of this study is to compare ouabain-induced cardiac signaling and contractility in wild-type (WT) and caveolin-1 knockout (cav-1 KO) mice. In contrast with WT cardiomyocytes, ouabain-induced signaling e.g., activation of phosphoinositide 3-kinase-α/Akt and extracellular signal-regulated kinases (ERK)1/2, and hypertrophic growth were significantly reduced in cav-1 KO cardiomyocytes. Interactions of the Na/K-ATPase α-subunit with caveolin-3 and the Na/K-ATPase α-subunit with PI3K-α were also decreased in cav-1 KO cardiomyocytes. The results from cav-1 KO mouse embryonic fibroblasts also proved that cav-1 significantly attenuated ouabain-induced ERK1/2 activation without alteration in protein and cholesterol distribution in caveolae/lipid rafts. Intriguingly, the effect of ouabain induced positive inotropy in vivo (via transient infusion of ouabain, 0.48 nmol/g body wt) was not attenuated in cav-1 KO mice. Furthermore, ouabain (1-100 μM) induced dose-dependent contractility in isolated working hearts from WT and cav-1 KO mice. The effects of ouabain on contractility between WT and cav-1 KO mice were not significantly different. These results demonstrated differential roles of cav-1 in the regulation of ouabain signaling and contractility. Signaling by ouabain, in contrast to contractility, may be a redundant property of Na/K-ATPase.

Downregulation of TGF-β Receptor-2 Expression and Signaling through Inhibition of Na/K-ATPase

“…On the other hand, increasing evidence suggests that cardiac glycosides may promote cell growth signaling through Src, EGFR, ERK and PI3K in caveolae [23–31]. Even though these caveolae-mediated signaling events may be dissociated from the pump activity of Na + /K + ATPase [32–34], it is possible that these signaling events may also contribute to the downregulation of TGFβR2 expression by ouabain. Understanding the mechanism by which cardiac glycosides downregulate TGFβR2 expression is our current goal.…”

“…Interestingly, the signaling role of Na + /K + ATPase was reported to be associated with caveolae, where significant amounts of Src, EGFR, ERK1/2 and α1/2-subuntis of Na + /K + -ATPase have been detected [30,31]. However, this signaling role of caveolae seems to be dissociated from the Na + /K + pump activity and from regulation of cardiac contractility by Na + /K + ATPase [32–34]. …”

The Redox-Sensitive Na/K-ATPase Signaling in Uremic Cardiomyopathy

“…Comparing wild-type (WT) mice with caveolin-1 knockout (cav-1 KO) mice, depletion of caveolin-1 does not affect the total or plasma membrane abundance of Na/K-ATPase α1 isoform in cardiac fibroblasts [66], adult cardiomyocytes, and left ventricle lysates [67]. In isolated cardiac fibroblasts, depletion of caveolin-1 increases the Na/K-ATPase ion-exchange activity as well as basal activities of Src and ERK1/2, but it also suppresses ouabain-induced signal transduction, growth, and collagen production [66].…”

“…In isolated cardiac fibroblasts, depletion of caveolin-1 increases the Na/K-ATPase ion-exchange activity as well as basal activities of Src and ERK1/2, but it also suppresses ouabain-induced signal transduction, growth, and collagen production [66]. In isolated adult cardiomyocytes, the ouabain-stimulated activation of phosphoinositide 3-kinase (PI3K)-α/Akt and ERK1/2, interaction of Na/K-ATPase with caveolin-3 and PI3K-α, and hypertrophic growth were significantly reduced in cav-1 KO mice, compared to WT mice [67]. Interestingly, in both WT and cav-1 KO mice, the transient infusion of ouabain induces similar positive inotropy in vivo, and ouabain also causes similar dose-dependent contractility in isolated working hearts [67].…”

“…In isolated adult cardiomyocytes, the ouabain-stimulated activation of phosphoinositide 3-kinase (PI3K)-α/Akt and ERK1/2, interaction of Na/K-ATPase with caveolin-3 and PI3K-α, and hypertrophic growth were significantly reduced in cav-1 KO mice, compared to WT mice [67]. Interestingly, in both WT and cav-1 KO mice, the transient infusion of ouabain induces similar positive inotropy in vivo, and ouabain also causes similar dose-dependent contractility in isolated working hearts [67]. The data suggest differential roles of cav-1 in the regulation of ouabain signaling and contractility.…”