The Influence Of Intramuscular Fat Deposit And Gene Expression Of ACC/HSL And PPARγ With The Supplemetation Of Vitamin A In Beef Cattle

Three experiments were conducted both in vivo and in vitro to investigate the regulation of vitamin A (VA) on intramuscular fat (IMF) content and genes expression of Acetyl-coA carboxylase (ACC), a rate-limiting enzyme for long chain fatty acid synthesis, and Hormone sensitive lipase (HSL), a key enzyme in the degradation of triacylglycerol, and Peroxisome proliferators activated receptorγ(PPARγ), a key nuclear receptor regulating adipocyte differentiation of beef cattle. In experiment 1, 16 crossbred beef cattle (Limousin×Luxi), 12 months old and weighing about 350kg, were randomly allotted to four treatments with four steers per group for VA supplementation containing 0, 50%, 100%, 200% of 2200 IU/kgDM respectively, the standard of the nutrient requirements of beef cattle. The treatment without additional VA is the control. All were weighed monthly. Twelve steers were chosen from four treatments with three per group and slaughtered in 18 months of age. The IMF content of longissimus dorsi and gluteus medius muscle samples taken from the carcasses were determined immediately. The result showed that weight gain of the 50% VA treatment is higher than the control and the others (P<0.05); The highest supplemetation of VA had the lowest IMF content in longissimus dorsi comparing with the control (P<0.05); The IMF content was decreasing with additional increasing VA. In experiment 2, the total RNA was isolated from the longissimus dorsi and gluteus medius muscle samples collected in experiment 1. Relative Real-time RT-PCR by SYBR greenⅠdye was used to mensurate the relative mRNA level of the treatments. The relative mRNA level of HSL in 200% VA treatment is lower than the control (P<0.05). All of the three treatments with different VA had much fewer transcription of mRNA than the control (P<0.05). Genes of ACC, HSL, PPARγwere down-expressing with addition of VA . In in vitro experiment, subcutaneous preadipocytes were cultured in the free-serum DMEM/F12 containing 0, 5, 25, 100μg/dL retinoic acid (RA), and the same conduct both of retinol (RO) and retinyl palmitate (RP) were done. The adipocytes were collected in the 10th differentiation day and total RNA was isolated. The mRNA level of ACC/HSL/PPARγwere determined by relative Real-time RT-PCR. The result showed that the adipocytes differentiation were suppressed, and the total number of adipose dripping also decreasing in vitamin A condition; The relative mRNA levels of ACC of adipocytes with 25 or 100μg/dL VA were significantly lower than the control without VA (P<0.01). HSL gene expression of the treatment with 25, 100μg/dL RA or RO decreased (P<0.01) comparing with the control. However, it was not affected by RP (P>0.05). All of treatments with VA had much lower PPARγmRNA level than the control (P<0.01), and the RA treatment was restrained much more. All genes transcription decreased as the vitamin A concentration increased. RA inhibite PPARγexpression more effectively and concomitantly cause a greater inhibition of gene expression of lipometabolism, including ACC and HSL, then control adipocytes differentiation indirectly. Maybe VA suppress gene expression of ACC/HSL directly, then change the equilibrium of adipose metabolism, finally affect the deposit of IMF in beef cattle.