Cardiac-specific LIM protein FHL2 modifies the hypertrophic response to beta-adrenergic stimulation

Background-A deficiency of muscle LIM protein results in dilated cardiomyop athy, but the function of other LIM proteins in the heart has not been asse ssed previously. We have characterized the expression and function of FHL2, a heart-specific member of the LIM domain gene family. Methods and Results-Expression of FHL2 mRNA and protein was examined by Nor thern blot, in situ hybridization, and Western blot analyses of fetal and a dult mice. FHL2 transcripts are present at embryonic day (E) 7.5 within the cardiac crescent in a pattern that resembles that of Nkx2.5 mRNA. During l ater stages of cardiac development and in adult animals, FHL2 expression is localized to the myocardium and absent from endocardium, cardiac cushion, outflow tract, or coronary vasculature. The gene encoding FHL2 was disrupte d by homologous recombination, and knockout mice devoid of FHL2 were found to undergo normal cardiovascular development. In the absence of FHL2, howev er, cardiac hypertrophy resulting from chronic infusion of isoproterenol is exaggerated (59% versus 20% increase in heart weight/body weight in FHL nu ll versus wild-type mice; P < 0.01). Conclusions-FHL2 is an early marker of cardiogenic cells and a cardiac-spec ific LIM protein in the adult. FHL2 is not required for normal cardiac deve lopment but modifies the hypertrophic response to P-adrenergic stimulation.