TGFβ inducible early gene‐1 (TIEG1) and cardiac hypertrophy: Discovery and characterization of a novel signaling pathway

Cellular mechanisms causing cardiac hypertrophy are currently under intense investigation. We report a novel finding in the TGFbeta inducible early gene (TIEG) null mouse implicating TIEG1 in cardiac hypertrophy. The TIEG(-/-) knock-out mouse was studied. Male mice age 4-16 months were characterized (N = 86 total) using echocardiography, transcript profiling by gene microarray, and immunohistochemistry localized upregulated genes for determination of cellular mechanism. The female mice (N = 40) did not develop hypertrophy or fibrosis. The TIEG(-/-) knock-out mouse developed features of cardiac hypertrophy including asymmetric septal hypertrophy, an increase in ventricular size at age 16 months, an increase (214%) in mouse heart/weight body weight ratio TIEG(-/-), and an increase in wall thickness in TIEG(-/-) mice of (1.85 +/- 0.21 mm), compared to the control (1.13 +/- 0.15 mm, P < 0.04). Masson Trichrome staining demonstrated evidence of myocyte disarray and myofibroblast fibrosis. Microarray analysis of the left ventricles demonstrated that TIEG(-/-) heart tissues expressed a 13.81-fold increase in pituitary tumor-transforming gene-1 (Pttg1). An increase in Pttg1 and histone H3 protein levels were confirmed in the TIEG(-/-) mice hearts tissues. We present evidence implicating TIEG and possibly its target gene, Pttg1, in the development of cardiac hypertrophy in the TIEG null mouse.