All-trans retinoic acid and chromium regulate physiological changes through altering gene and protein expression in bovine muscle and adipose cells.



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The precursor of vitamin A, carotene, is rich in forage based diets for beef cattle. The inhibitory effects of vitamin A during differentiation of adipocytes have attracted beef producers who want to increase marbling of steak. Furthermore, dietary chromium (Cr) has been used as a feed additive for beef cattle for last few decades. Chromium increases insulin sensitivity of muscle and adipose cells and enhances glucose uptake. To identify the effects of vitamin A, especially all-trans retinoic acid (ATRA), on bovine adipose cells and muscle cells, primary cell cultures were prepared with bovine satellite cells (BSC), intramuscular (IM) preadipocytes, and subcutaneous (SC) preadipocytes isolated from 19 and 24-mo-old beef cattle. Cultured cells were incubated with different doses of ATRA and harvested after 96 h of differentiation. Addition of retinoic acid to bovine IM adipocytes decreased (P < 0.01) expression of PPARγ, a key regulator of adipogenesis. Expression of PPARγ also linearly decreased (P < 0.01) levels of ATRA increased in subcutaneous adipocytes. Expression of SMAD3 linearly increased with ATRA both in IM (P < 0.01) and SC (P = 0.01). Different from bovine adipocytes, ATRA increased (P <0.01) expression of PPARδ in BSC, which is associated with oxidative metabolism in skeletal muscle. It is also found that the expression of LPL (P < 0.01) was upregulated by ATRA. Addition of ATRA on BSC also altered gene expression of myosin heavy chains. Expression of MHC I, which is associated with oxidative, slow twitch muscle fiber types, increased (P < 0.01) with ATRA. Conversely, ATRA downregulated the expression of fast twitch types, MHC IIA (P = 0.04) and IIX (P = 0.02). To determine the effects of Cr source on gene and protein expression of bovine adipocytes, various doses of chromium acetate (CrAc) were added to differentiation media of IM and SC adipose cells isolated from 16-mo-old steer. After 96h of incubation, cells were harvested and used for used for gene expression, protein level, and morphological analysis. Protein level of PPARγ was upregulated by 10µM of CrAc in IM but not in SC. Increased doses of CrAc, resulted in a decreased (P < 0.01) pAMPKα to AMPKα protein level ratio in IM but not SC adipocytes (P = 0.94).



retinoic acid, chromium acetate