Elevated Myocardial Na+/H+ Exchanger Elicits the Expression of Genes that Lead to Cardiac Hypertrophy

In myocardial disease, elevated expression and activity of Na+/H+ exchanger isoform 1 (NHE1) is detrimental. To better understand the involvement of NHE1, transgenic mice with elevated heart-specific NHE1 expression were studied. N-line mice expressed wild-type NHE1 and K-line mice expressed activated NHE1. Cardiac morphology, interstitial fibrosis and cardiac function were examined by histological staining and echocardiography. Differences in gene expression between the N- or K-line and non-transgenic littermates were probed using genechips. We found that NHE1 K-line hearts (but not N-line) developed hypertrophy, including elevated heart weight to body weight and increased cross sectional area of the cardiomyocytes, interstitial fibrosis, as well as depressed cardiac function. N-line transgenic hearts had modest changes in gene expression (50 up-regulations and 99 down-regulations, P<0.05), whereas K-line hearts had a very strong transcriptional response (640 up-regulations and 677 down-regulations, P<0.05). In addition, the magnitude of expression alterations was much higher in K-line than in N-line transgenic mice. The most significant changes in gene expression were involved in cardiac hypertrophy, cardiac necrosis/cell death and cardiac infarction. Secreted phosphoprotein 1 signaling pathways were up-regulated while peroxisome proliferative activated receptor gamma signaling was down-regulated in K-line mice. Our study shows that expression of activated NHE1 elicits specific pathways of gene activation in the myocardium that lead to cardiac hypertrophy, cell death and infarction. Alterations on gene expression profiles were determined in the hearts of transgenic mice carrying either a wild-type NHE1 gene (N-line) or a constitutively active NHE1 mutant gene (K-line).