Differential regulation of p38 mitogen-activated protein kinase mediates gender-dependent catecholamine-induced hypertrophy.

OBJECTIVE: Exogenous catecholamine exposure has been associated with p38 mitogen-activated protein kinase (MAPK) and cardiac hypertrophy. In this study, we investigated the regulation of p38 MAPK in cardiac remodeling elicited by endogenous adrenergic mechanisms. METHODS: Transgenic male and female mice with fourfold phospholamban (PLB) overexpression exhibited enhanced circulating norepinephrine (NE), as a physiological compensatory mechanism to attenuate PLB's inhibitory effects. This enhanced noradrenergic state resulted in left ventricular hypertrophy/dilatation and depressed function. RESULTS: Male transgenics exhibited ventricular hypertrophy and mortality at 15 months, concurrent with cardiac p38 MAPK activation. Female transgenics, despite similar contractile dysfunction, displayed a temporal delay in p38 activation, hypertrophy, and mortality (22 months), which was associated with sustained cardiac levels of MAP Kinase Phosphatase-1 (MKP-1), a potent inhibitor of p38. At 22 months, decreases in cardiac MKP-1 were accompanied by increased levels of p38 activation. In vitro studies indicated that preincubation with 17-beta-estradiol induced high MKP-1 levels, which precluded NE-induced p38 activation. CONCLUSION: These findings suggest that norepinephrine-induced hypertrophy is linked closely with p38 MAP kinase activation, which can be endogenously modulated through estrogen-responsive regulation of MKP-1 expression.

Combined phospholamban ablation and SERCA1a overexpression result in a new hyperdynamic cardiac state.

OBJECTIVE: Phospholamban ablation or ectopic expression of SERCA1a in the heart results in significant increases in cardiac contractile parameters. The aim of the present study was to determine whether a combination of these two genetic manipulations may lead to further augmentation of cardiac function. METHODS: Transgenic mice with cardiac specific overexpression of SERCA1a were mated with phospholamban deficient mice to generate a model with SERCA1a overexpression in the phospholamban null background (SERCA1(OE)/PLB(KO)). The cardiac phenotype was characterized using quantitative immunoblotting, sarcoplasmic reticulum calcium uptake and single myocyte mechanics and calcium kinetics. RESULTS: Quantitative immunoblotting revealed an increase of 1.8-fold in total SERCA level, while SERCA2 was decreased to 50% of wild types. Isolated myocytes indicated increases in the maximal rates of contraction by 195 and 125%, the maximal rates of relaxation by 200 and 124%, while the time for 80% decay of the Ca(2+)-transient was decreased to 43 and 75%, in SERCA1(OE)/PLB(KO) hearts, compared to SERCA1a overexpressors and phospholamban knockouts, respectively. These mechanical alterations reflected parallel alterations in V(max) and EC(50) for Ca(2+) of the sarcoplasmic reticulum Ca(2+) transport system. Furthermore, there were no significant cardiac histological or pathological alterations, and the myocyte contractile parameters remained enhanced, up to 12 months of age. CONCLUSIONS: These findings suggest that a combination of SERCA1a overexpression and phospholamban ablation results in further enhancement of myocyte contractility over each individual alteration.

Hypertrophy and functional alterations in hyperdynamic phospholamban-knockout mouse hearts under chronic aortic stenosis.

OBJECTIVE: To determine whether the hyperdynamic phospholamban-knockout hearts are capable of withstanding a chronic aortic stenosis. METHODS: The transverse section of the aorta was banded in phospholamban-knockout and their isogenic wild-type mice, which were followed with echocardiography in parallel, along with sham-operated mice, before and at 2.5, 5 and 10 weeks after surgery. RESULTS: Cardiac decompensation was evidenced by the presence of lung congestion in some banded knockouts and wild-types, giving rise to a subset of non-failing and failing hearts within each group. The incidence of heart failure was not genotype-dependent but rather associated with higher heart rates before surgery. The development of left ventricular hypertrophy was similar between knockouts and wild-types and longitudinal assessment of end-diastolic dimension indicated progressive increases after banding, with a greater dilation in failing mice. Fractional shortening was reduced in failing knockouts and wild-types to a similar degree, with an earlier onset in the knockouts. In addition, fractional shortening was decreased in non-failing knockouts but not wild-types. Ejection times shortened after aortic banding particularly for failing hearts. Assessment of the SR Ca(2+)-ATPase protein levels indicated similar downregulation for failing knockouts and wild-types, while the phospholamban levels were not significantly altered in wild-types. CONCLUSION: The hyperdynamic phospholamban-knockout hearts are able to compensate against a sustained aortic stenosis similar to wild-types.