JDP2 overexpression provokes cardiac dysfunction in mice.

The transcriptional regulator JDP2 (Jun dimerization protein 2) has been identified as a prognostic marker for patients to develop heart failure after myocardial infarction. We now performed in vivo studies on JDP2-overexpressing mice, to clarify the impact of JDP2 on heart failure progression. Therefore, during birth up to the age of 4 weeks cardiac-specific JDP2 overexpression was prevented by doxycycline feeding in transgenic mice. Then, JDP2 overexpression was started. Already after 1 week, cardiac function, determined by echocardiography, decreased which was also resembled on the cardiomyocyte level. After 5 weeks blood pressure declined, ejection fraction and cardiac output was reduced and left ventricular dilatation developed. Heart weight/body weight, and mRNA expression of ANP, inflammatory marker genes, collagen and fibronectin increased. Collagen 1 protein expression increased, and fibrosis developed. As an additional sign of elevated extracellular matrix remodeling, matrix metalloproteinase 2 activity increased in JDP2 mice. Thus, JDP2 overexpression is deleterious to heart function in vivo. It can be concluded that JDP2 overexpression provokes cardiac dysfunction in adult mice that is accompanied by hypertrophy and fibrosis. Thus, induction of JDP2 is a maladaptive response contributing to heart failure development.

Inhibition of the Na+/H+ exchanger attenuates the deterioration of ventricular function during pacing-induced heart failure in rabbits.

AIMS: Inhibition of the Na+/H+-exchanger (NHE) preserves myocardial morphology and function in rat and mouse models of hypertrophy and failure. The mechanism(s) involved in such cardioprotective effects remain(s) unclear, but might involve blockade of increased protein kinase activity as observed in untreated hearts. METHODS AND RESULTS: We investigated the functional, morphological and biochemical consequences of NHE-inhibition with BIIB722 in rabbits with pacing-induced heart failure (HF). In sham rabbits treated with placebo (n = 9) or BIIB722 (30 mg/kg/day po, n = 9), LV end-diastolic diameter (LVEDD) and systolic fractional shortening (FS, %) remained unchanged. In HF rabbits (n = 9), LVEDD increased and FS decreased from 31.5 +/- 1.4 to 8.1 +/- 0.9 (p < 0.05) at 3 weeks of LV pacing (400 bpm). Apoptosis, fibrosis and myocyte cross-sectional area as well as p38MAPK phosphorylation and iNOS protein expression were significantly increased in HF compared to sham rabbits. The activity of the 90 kDa NHE-kinase was greater in HF than in sham rabbits. In HF rabbits receiving BIIB722 prior to (18.1 +/- 2.2, n = 9) or following 1 week (15.5 +/- 1.6, n = 7) of pacing, FS at 3 weeks was better preserved than in untreated HF rabbits (p < 0.05). Apoptosis, fibrosis, myocyte cross-sectional area, p38MAPK phosphorylation and iNOS protein expression were significantly reduced in HF rabbits receiving BIIB722. CONCLUSION: NHE-inhibition attenuates the functional, morphological and biochemical derangements of pacing-induced HF in rabbits.