Ablation of p21-activated kinase-1 in mice promotes isoproterenol-induced cardiac hypertrophy in association with activation of Erk1/2 and inhibition of protein phosphatase 2A

Abstract

Rationale Earlier investigations in our lab indicated an anti-adrenergic effect induced by activation of p21-activated kinase (Pak-1) and protein phosphatase 2A (PP2A). Objective Our objective was to test the hypothesis that Pak-1/PP2A is a signaling cascade controlling stress-induced cardiac growth. We determined the effects of ablation of the Pak-1 gene on the response of the myocardium to chronic stress of isoproterenol (ISO) administration. Methods and Results Wild-type (WT) and Pak-1-knockout (Pak-1-KO) mice were randomized into six groups to receive either ISO, saline (CTRL), or ISO and FR180204, a selective inhibitor of Erk1/2. Echocardiography revealed that hearts of the Pak-1-KO/ISO group had increased LV fractional shortening, reduced LV chamber volume in diastole and systole, increased cardiac hypertrophy, and enhanced transmitral early filling deceleration time, compared to all other groups. The changes were associated with an increase in relative Erk1/2 activation in Pak-1-KO/ISO mice versus all other groups. ISO-induced cardiac hypertrophy and Erk1/2 activation in Pak-1-KO/ISO were attenuated when the selective Erk1/2 inhibitor FR180204 was administered. Immunoprecipitation showed an association between Pak-1, PP2A, and Erk1/2. Cardiac myocytes infected with an adenoviral vector expressing constitutively active Pak-1 showed a repression of Erk1/2 activation. p38 MAPK phosphorylation was decreased in Pak-1-KO/ISO and Pak-1-KO/CTRL mice compared to WT. Levels of phosphorylated PP2A were increased in ISO-treated Pak-1-KO mice, indicating reduced phosphatase activity. Maximum Ca2+-activated tension in detergent-extracted bundles of papillary fibers from ISO-treated Pak-1-KO mice was higher than in all other groups. Analysis of cTnI phosphorylation indicated that compared to WT, ISO-induced phosphorylation of cTnI was blunted in Pak-1-KO mice. Conclusions Active Pak-1 is a natural inhibitor of Erk1/2 and a novel anti-hypertrophic signaling molecule upstream of PP2A.

Signaling effectors underlying pathologic growth and remodeling of the heart

“…A number of these MAPKKKs modulate cardiac hypertrophy and heart failure, such as TAK1, PAK1, ASK1, and MEKK1 (117)(118)(119)(120)(121)(122)(123). However, these are less tangible targets since there are currently no drugs available with high specificity toward any of these.…”

Angiotensin‐Converting Enzyme 3 (ACE3) Protects Against Pressure Overload‐Induced Cardiac Hypertrophy

“…Since we have validated the protective roles of ACE3 in response to Ang II‐ and pressure overload‐induced cardiac hypertrophy, it has significance to test whether ACE3 can also affect other types of cardiac hypertrophy, such as the adrenergic receptor‐induced cardiac hypertrophy. Among the multiple signaling pathways that activated by the adrenergic receptors, a large body of evidence has showed the essential roles of the ERK1/2 signaling during different adrenergic receptor‐induced hypertrophic response 25, 26. As we have demonstrated the anti‐hypertrophic effects of ACE3 are mainly depend on inhibition of the MEK‐ERK1/2 signaling, it is likely that ACE3 can also function as a negative regulator in adrenergic receptor‐induced hypertrophy.…”

p21-activated kinase improves cardiac contractility during ischemia-reperfusion concomitant with changes in troponin-T and myosin light chain 2 phosphorylation

“…Mice with Pak-1 gene disruption at both alleles were created in SV129 background and have been described previously (14,26). Pak1-KO mice were previously rederived in FVB background and genotyped to confirm the deletion of the Pak1 gene, and the levels of protein expression of Pak1, Pak2, and Pak3 (two less abundant protein isoforms of Pak1 in the heart) were measured in the left ventricle cardiac tissue lysate by Western immunoblotting (27). Additionally, hemodynamic parameters were previously assessed by echocardiography, which demonstrated no morphometric and hemodynamic differences between Pak1-KO mice and WT controls (27).…”

“…Pak1-KO mice were previously rederived in FVB background and genotyped to confirm the deletion of the Pak1 gene, and the levels of protein expression of Pak1, Pak2, and Pak3 (two less abundant protein isoforms of Pak1 in the heart) were measured in the left ventricle cardiac tissue lysate by Western immunoblotting (27). Additionally, hemodynamic parameters were previously assessed by echocardiography, which demonstrated no morphometric and hemodynamic differences between Pak1-KO mice and WT controls (27). In the current study, young adult (16.2 Ϯ 0.3 wk) female mice were used for acquisition of functional and Western immunoblotting analysis.…”

“…On the other hand, Pak1 has been implicated to be an upstream mediator of c-Jun NH 2 -terminal kinase (JNK) (19,20), which is activated during myocardial I/R and leads to cardiomyocyte death (3). However, a recent study found no differences in JNK 1/2/3 phosphorylation in cardiac tissue due to Pak1 during baseline conditions (27). One particular prior study found Pak1 to prevent I/R-associated arrhythmias (4).…”