P90 Ribosomal S6 Kinase Contributes To Na+/H+ Exchanger Isoform1 (Nhe1) Induced Cardiac Hypertrophy In H9C2 Cardiomyoblasts

Cardiovascular diseases are the leading cause of death worldwide. One in three cases of heart failure is due to dilated cardiomyopathy. The Na+/H+ exchanger isoform 1 (NHE1), a multifunctional protein and the key pH regulator in the heart, has been demonstrated to be increased in this condition. We have previously demonstrated that elevated NHE1 activity induced cardiac hypertrophy in vivo. Furthermore, the overexpression of active NHE1 elicited modulation of gene expression in cardiomyocytes including an upregulation of myocardial osteopontin (OPN) expression. To determine the role of OPN in inducing NHE1-mediated cardiomyocyte hypertrophy, double transgenic mice expressing active NHE1 and OPN knockout were generated and assessed by echocardiography and the cardiac phenotype. Our studies showed that hearts expressing active NHE1 exhibited cardiac remodeling indicated by increased systolic and diastolic left ventricular internal diameter and increased ventricular volume. Moreover, these hearts demonstrated impaired function with decreased fractional shortening and ejection fraction. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) mRNA was upregulated, and there was an increase in heart cell cross-sectional area confirming the cardiac hypertrophic effect. Moreover, NHE1 transgenic mice also showed increased collagen deposition, upregulation of CD44 and phosphorylation of p90 ribosomal s6 kinase (RSK), effects that were regressed in OPN knockout mice. In conclusion, we developed an interesting comparative model of active NHE1 transgenic mouse lines which express a dilated hypertrophic phenotype expressing CD44 and phosphorylated RSK, effects which were regressed in absence of OPN.

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Abstract 190: Disruption of P90 Ribosomal S6 Kinase Binding 3 to Muscle A-kinase Anchoring Protein In Vivo Via Adeno-associated Virus Expression of a Competing Peptide Attenuates Pressure Overload-induced Cardiac Hypertrophy

Circulation Research ◽

10.1161/res.115.suppl_1.190 ◽

2014 ◽

Vol 115 (suppl_1) ◽

Author(s):

CATHERINE L PASSARIELLO ◽

Michael D Kritzer ◽

Hrishikesh Thakur ◽

Michael Sanders ◽

Jinliang Li ◽

...

Keyword(s):

Cardiac Hypertrophy ◽

Cardiac Myocyte ◽

Troponin T ◽

Pressure Overload ◽

Compensatory Response ◽

S6 Kinase ◽

Anchoring Protein ◽

P90 Ribosomal S6 Kinase ◽

Ribosomal S6 Kinase

RATIONALE: Cardiac myocyte hypertrophy is the main compensatory response to chronic stress in the heart. p90 ribosomal S6 kinase (RSK) family members are effectors for extracellular signal-regulated kinases that induce myocyte growth. RSK3 contains a unique N-terminal domain that mediates RSK3 binding to the muscle A-kinase anchoring protein (mAKAPβ) scaffold. We have previously published that disruption of RSK3-mAKAPβ complexes using a competing peptide inhibited the phenylephrine-induced hypertrophy of neonatal ventricular myocytes in vitro. In vivo, RSK3 gene deletion in mice attenuated the concentric cardiac hypertrophy induced by pressure overload. We hypothesize that RSK3 anchoring to mAKAPβ in myocytes is required for cardiac hypertrophy in vivo. METHODS AND RESULTS: Adeno-associated viruses (AAV) are gene therapy vectors in development for the treatment of human diseases owing to their nonpathogenic capability for transducing non-dividing cells and their long-term transgene expression. We have used a recombinant AAV2/9 vector to express a mAKAPβ RSK3-binding domain (RBD)-GFP fusion protein under the control of the cardiac myocyte-specific cardiac troponin T promoter. 3 day-old C57BL/6 mice were injected intraperitoneally with either AAV-RBD-GFP or AAV-GFP control virus. At 8 weeks of age mice were subjected to transverse aortic constriction to induce pressure overload (TAC) for two weeks. Cardiac hypertrophy was attenuated in mice injected with the AAV-RBD-GFP virus (biventricular weight indexed to tibial length (mg/mm): 7.7, 8.6, and 9.2 for AAV-RBD, AAV-GFP and non-injected TAC cohorts, respectively; p<0.05 vs. both controls). Echocardiography both corroborated the inhibition of hypertrophy and revealed no deleterious effect on cardiac function attributable to the AAV-RBD-GFP vector. CONCLUSIONS: Anchored RSK3 regulates pathologic myocyte growth. AAV can successfully deliver a competing peptide inhibiting pathological hypertrophy and should be investigated further as a prevention and/or treatment for heart failure.

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p90 ribosomal S6 kinase 3 contributes to cardiac insufficiency in α-tropomyosin Glu180Gly transgenic mice

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00237.2013 ◽

2013 ◽

Vol 305 (7) ◽

pp. H1010-H1019 ◽

Cited By ~ 10

Author(s):

Catherine L. Passariello ◽

Marjorie Gayanilo ◽

Michael D. Kritzer ◽

Hrishikesh Thakur ◽

Zoharit Cozacov ◽

...

Keyword(s):

Heart Failure ◽

Transgenic Mice ◽

Cardiac Function ◽

Interstitial Fibrosis ◽

Cardiac Insufficiency ◽

S6 Kinase ◽

Transgenic Expression ◽

P90 Ribosomal S6 Kinase ◽

Ribosomal S6 Kinase

Myocardial interstitial fibrosis is an important contributor to the development of heart failure. Type 3 p90 ribosomal S6 kinase (RSK3) was recently shown to be required for concentric myocyte hypertrophy under in vivo pathological conditions. However, the role of RSK family members in myocardial fibrosis remains uninvestigated. Transgenic expression of α-tropomyosin containing a Glu180Gly mutation (TM180) in mice of a mixed C57BL/6:FVB/N background induces a cardiomyopathy characterized by a small left ventricle, interstitial fibrosis, and diminished systolic and diastolic function. Using this mouse model, we now show that RSK3 is required for the induction of interstitial fibrosis in vivo. TM180 transgenic mice were crossed to RSK3 constitutive knockout ( RSK3−/−) mice. Although RSK3 knockout did not affect myocyte growth, the decreased cardiac function and mild pulmonary edema associated with the TM180 transgene were attenuated by RSK3 knockout. The improved cardiac function was consistent with reduced interstitial fibrosis in the TM180; RSK3−/− mice as shown by histology and gene expression analysis, including the decreased expression of collagens. The specific inhibition of RSK3 should be considered as a potential novel therapeutic strategy for improving cardiac function and the prevention of sudden cardiac death in diseases in which interstitial fibrosis contributes to the development of heart failure.

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