Abstract 101: Transforming Growth Factor-Beta-Receptor Antagonist Blocks the Cardiac Fibrosis and Remodeling in Guanylyl Cyclase/Natriuretic Peptide Receptor-A Gene-Disrupted Mice

Abstract

Targeted-disruption of guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) gene ( Npr1 ) exhibits hypertension and provokes congestive heart failure in mice; however, the underlying mechanisms are not well clear. The objective of this study was to determine whether transforming growth factor-beta receptor (TGF-βR) antagonist, GW788388 inhibits the development of cardiac fibrosis and remodeling in Npr1 gene-disrupted mice. The adult male (16-20 weeks) Npr1 null mutant ( Npr1 -/- , 0-copy), heterozygous ( Npr1 +/- , 1-copy), and wild-type ( Npr1 +/+ , 2-copy) mice were orally administered with TGF-βR antagonist, GW788388 (1 mg/kg/day) for 28 days. The expression of cardiac fibrotic markers was analyzed using real-time PCR and Western blot. Heart weight-to-body weight (HW/BW) ratios were determined and heart functions were measured by echocardiographic analysis. The Npr1 -/- mice showed markedly increased cardiac fibrosis and HW/BW ratio with increased expression of collagen-1α (3.5-fold), monocyte chemoattractant protein (4-fold), connective tissue growth factor (CTGF, 5-fold), α-smooth muscle actin (α-SMA, 4-fold), TGF-βRI (4-fold), TGF-βRII (3.5-fold) and SMAD proteins (SMAD-2, 5-fold; SMAD-3, 3-fold) compared with Npr1 +/+ mice. The expression of phosphorylated extracellular-regulated kinase (pERK1/2) was also up-regulated by 68% ( P <0.001) in Npr1 -/- mice. The treatment of Npr1 -/- mice with GW788388 prevented the development of cardiac fibrosis and down-regulated the expression of fibrotic markers and SMAD proteins by 70-75% ( P <0.001) compared to vehicle-treated mice. In contrast, the expression of pERK1/2 proteins was unaffected in GW7885388-treated mice excluding the involvement of non-genomic pathway. The left ventricular dimensions (systole and diastole) and fractional shortening were significantly ( P <0.001) improved in the drug-treated Npr1 -/- mice. The results suggest that the cardiac fibrosis, remodeling, and dysfunction in Npr1 -/- mice are regulated through TGF-βR-mediated SMAD-dependent canonical pathway. The findings will be important for the development of new molecular therapeutic targets for the treatment of cardiac fibrosis, remodeling, and dysfunction in humans.