Extracellular signal regulated kinase and SMAD signaling both mediate the angiotensin II driven progression towards overt heart failure in homozygous TGR(mRen2)27

Angiotensin (Ang) II is a key player in left ventricular (LV) remodeling and cardiac fibrosis. Its effects are thought to be transferred at least in part by mitogen-activated protein kinases (MAPK), transforming growth factor (TGF) beta(1), and the Smad pathway. In this study we sought to elucidate whether Ang II related effects on LV dysfunction and fibrosis in vivo are mediated via MAPK or rather via Smad stimulation. We treated homozygous REN2 rats (7-11 weeks) with placebo, Ang II type 1 (AT(1)) receptor blocker or tyrphostin A46 (TYR), an inhibitor of epidermal growth factor receptor tyrosine kinase that blocks extracellular signal-regulated kinase (ERK) activity. REN2 rats had LV hypertrophy (LVH) and LV dysfunction that progressed to heart failure between 10 and 13 weeks. Blood pressure normalized over time. Renin, N-terminal atrial natriuretic peptide (N-ANP), and ERK were activated while p38 MAPK was not. Treatment with AT(1) receptor blockade prevented LVH and fight ventricular hypertrophy, normalized systolic and diastolic dP/dt, N-ANP levels, and reduced collagen apposition. Similarly, TYR reduced LVH, NANP levels, and collagen apposition. Myocardial ERK activation did not depend on AT, receptor signaling as it was not affected by AT(1) receptor blockade. TYR abolished myocardial ERK activity. Smad2 activation was inhibited by AT(1) receptor blockade but was unaltered by TYR. Ang II induced LV remodeling and fibrosis are dependent on both ERK and Smad2 activation. This process is prevented by both AT(1) receptor blockade and TYR, and therefore inhibition of either pathway is equally efficacious in restoring LV function and architecture.