Retinoic Acid Alters Expression of Key Genes during Differentiation of Bovine Intramuscular Preadipocytes

Abstract Text:

Retinoic acid has been shown to be important in regulating mammalian tissue development, such as, proper bone formation, growth, energy metabolism, and cell differentiation. Retinoic acid has been reported to be a potent inhibitor of adipocyte differentiation by binding to the retinoic acid receptor (RAR) or retinoid X receptor (RXR). The objective was to determine the effect of RAR agonist (retinoic acid) and RAR antagonist (LE540) on gene expression during differentiation of bovine intramuscular preadipocytes. Intramuscular (IM) adipose tissue was collected between the 10^th and 13^th rib from longissimus muscle and cultured in growth media consisting of DMEM, 10% fetal bovine serum, and antibiotics at 37^oC under a humidified atmosphere of 95% O₂ and 5% CO₂. Upon reaching confluence, the growth medium was replaced by a differentiation medium consisting of DMEM and 10 μg/mL insulin, 25 nM hydrocortisone, 10 μM oleic acid, 5 μM ciglitizone, and antibiotics with treatments The treatments were: 1)control, 2)10 μM all-trans retinoic acid (RA), and 3)10 μM LE540 (synthetic RA antagonist; Waco Co.). Real-Time RT-PCR was used to measure the quantity of C/EBPβ, PPARγ, SCD, and SMAD3 mRNA relative to the quantity of ribosomal protein subunit 9 (RPS9) mRNA in total RNA isolated from cultured bovine IM adipocyte cultures. Addition of RA reduced (P < 0.05) PPARγ and SCD mRNA levels compared to control IM adipocytes. However, addition of LE 540 increased expression of PPARγ and SCD mRNA (P < 0.05) levels in bovine IM adipocytes. Relative level of C/EBPβ mRNA was inhibited (P < 0.05) by LE540 during differentiation. Results of this study indicated that retinoic acid inhibits bovine IM preadipocyte differentiation by down regulation of PPARγ or SCD.  However, treatment of RAR antagonist induces adiopogenic gene expressions during IM preadipocyte differentiation.

Keywords: bovine intramuscular adipose cell, marbling, retinoic acid