Contractile regulatory proteins tropomyosin and troponin-T as indicators of the modulatory role of retinoic acid.
Retinoic acid (RA), the active metabolite of vitamin A, plays a significant role in regulating cardiac form and function throughout the life of the organism. Both cardiac morphogenesis and myocardial differentiation are affected by alterations in RA homeostasis. In order to test the effect of all-trans RA and 13-cis RA on cardiomyocyte differentiation, we studied the level and the subcellular compartmentalization of alpha-tropomyosin and troponin-T proteins in cultures of chick embryo cardiomyocytes obtained from Hamburger and Hamilton's (HH) stage 22, 32 and 40 embryos. The retinoids increased the levels of alpha-tropomyosin and troponin-T in the cytoplasmic and cytoskeletal fractions of cells at all three stages of development. The greatest increases in alpha-tropomyosin occurred in the cytoplasmic fraction in HH22 cells cultured for 24 h with all-trans RA or 13-cis RA, whereas the greatest increases in troponin-T were found in the cytoplasmic fraction of HH32 cells exposed to retinoids for 24 h. In cultures treated for 48 h with retinoids, the levels of alpha-tropomyosin and troponin-T showed significant increases in the cytoplasmic compartment of cells treated in HH32-with respect to the control values. These findings are further evidence that RA plays a modulating role in the formation and reorganization of sarcomeric proteins during the process of cardiomyocyte maturation.