Cardiac Gq receptors and calcineurin activation are not required for the hypertrophic response to mechanical left ventricular pressure overload

Abstract

RationaleGq-coupled receptors are thought to play a critical role in the induction of left ventricular hypertrophy (LVH) secondary to pressure overload, although mechano-sensitive channel activation by a variety of mechanisms has also been proposed, and the relative importance of calcineurin- and calmodulin kinase II (CaMKII)-dependent hypertrophic pathways remains controversial.ObjectiveTo determine the mechanisms regulating the induction of LVH in response to mechanical pressure overload.Methods and ResultsTransgenic mice with cardiac-targeted inhibition of Gq-coupled receptors (GqI mice) and their non-transgenic littermates (NTL) were subjected to neurohumoral stimulation (continuous, subcutaneous angiotensin II (AngII) infusion for 14 days) or mechanical pressure overload (transverse aortic arch constriction (TAC) for 21 days) to induce LVH. Candidate signalling pathway activation was examined. As expected, LVH observed in NTL mice with AngII infusion was attenuated in heterozygous (GqI+/-) mice and absent in homozygous (GqI-/-) mice. In contrast, LVH due to TAC was unaltered by either heterozygous or homozygous Gq inhibition. Gene expression of atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP) and α-skeletal actin (α-SA) was increased 48 hours after AngII infusion or TAC in NTL mice; in GqI mice, the increases in ANP, BNP and α-SA in response to AngII were completely absent, as expected, but all three increased after TAC. Increased nuclear translocation of nuclear factor of activated T-cells c4 (NFATc4), indicating calcineurin pathway activation, occurred in NTL mice with AngII infusion but not TAC, and was prevented in GqI mice infused with AngII. Nuclear and cytoplasmic CaMKIIδ levels increased in both NTL and GqI mice after TAC but not AngII infusion, with increased cytoplasmic phospho- and total histone deacetylase 4 (HDAC4) and increased nuclear myocyte enhancer factor 2 (MEF2) levels.ConclusionCardiac Gq receptors and calcineurin activation are required for neurohumorally mediated LVH but are not required for LVH induced by mechanical pressure overload (TAC); the latter is mediated by activation of the CaMKII-HDAC4-MEF2 pathway.

Piezo1 is the cardiac mechanosensor that initiates the hypertrophic response to pressure overload

“…As expected, α-MHC-MCM +/mice exhibited strong activation of the CaMKII-HDAC4-MEF2 hypertrophic signalling pathway 2 days after TAC (Fig. 5), consistent with our previous ndings in TAC-induced hypertrophy 6,7 . The hallmark of this activation is increased levels of both total and activated CaMKII, which is auto-phosphorylated at threonine 287 (p-CaMKII) 20,21 , and the resultant increase in the cytoplasmic to nuclear ratio of HDAC4 (p < 0.01), indicating nuclear export of HDAC4, with consequent de-repression of MEF2A (p < 0.001, Fig.…”

“…Cardiomyocyte-speci c deletion of Piezo1 is associated with activation of the calcineurin-NFAT hypertrophic signaling pathway in response to pressure overload As expected, α-MHC-MCM +/mice exhibited no evidence of activation of the calcineurin-NFAT hypertrophic signalling pathway 2 days after TAC (Fig. 6), consistent with our previous ndings in TAC-induced hypertrophy 6,7 . One explanation for this nding is that pressure overload activates CaMKII and activated CaMKII inhibits calcineurin activation 22 .…”

“…Early markers of LVH induction in WT and Piezo1 P1-tdT/P1-tdT mice Consistent with the early induction of hypertrophic signalling after TAC 6,7 , gene expression of atrial natriuretic peptide (ANP, Nppa), brain natriuretic peptide (BNP, Nppb) and α-skeletal actin (α-SA, Acta1) was increased signi cantly 48 hours after TAC, preceding the development of signi cant LVH (supplementary Table 1), in both whole LV tissue and isolated LV cardiomyocytes, with no signi cant differences between WTLs and Piezo1 P1-tdT/P1-tdT hearts (Table 2). The increased expression of these genes in whole LV tissue and isolated LV cardiomyocytes persisted 14 days after TAC in WTLs and Piezo1 P1-tdT/P1-tdT mice (Table 2).…”

“…We reported previously that calcineurin activation was not required for the hypertrophic response to pressure overload with TAC, which was associated with activation of the CaMKII-HDAC4-MEF2 pathway 6 . In the present study, we found that cardiomyocyte-speci c deletion of Piezo1 prevented any activation of the CaMKII-HDAC4-MEF2 signalling pathway secondary to TAC, and reduced the amount of LVH developed after TAC by approximately 60%.…”

“…As previously described 6,7 , male mice were subjected to TAC to induce pressure overload. Mice were anesthetized with 5% iso urane and ventilated at 120 breaths/min (Harvard Apparatus Rodent Ventilator).…”