Effects of α-lipoic acid on muscle fiber type composition and meat quality of tan sheep and underlying regulatory mechanism

The objective of this study was to investigate the influence of dietary supplementation with α-lipoic acid on muscle fiber properties, meat quality, and the regulation mechanism of biceps femoris from Tan sheep. Two groups were divided to randomly select the 12 healthy sheep aged 4 months with an initial body weight of (20.64±1.15) kg. The control group was fed with the basic diet, and the α-lipoic acid group was supplemented with α-lipoic acid at 600 mg/kg, according to the diet of the control. The pre-feeding and formal periods were set as 7 and 60 days, respectively. After that, the selected sheep were transport into the abattoir for slaughter, where the entire biceps femoris muscle from the right side was immediately dissected and weighed within 10 min postmortem. The muscle samples were prepared and then chilled in the air at 4 °C to determine the meat quality of Tan sheep. Moreover, the other muscle samples (stored at -80°C) were collected to determine the muscle fiber properties, energy metabolic enzyme activity, and muscle fiber type-related genes. The results showed that the dietary supplementation with α-lipoic acid significantly increased the average daily gain (ADG) (P<0.01), while decreasing the feed conversion ratio (FCR) (P<0.01), b* value (P<0.01), shear force value (P<0.01), and water loss rate (P<0.05) of biceps femoris from Tan sheep. The muscle fiber showed that the dietary supplementation with α-lipoic acid increased the ratio of type IIA muscle fibers (P<0.05), but decreased the ratio of type IIB muscle fibers (P<0.01). There was a significant increase in the enzyme activity of creatine kinase (CK) (P<0.01) and succinate dehydrogenase (SDH) (P<0.05) in the biceps femoris from Tan sheep under the dietary α-Lipoic acid supplementation, whereas a significant decrease was found in the lactic dehydrogenase (LDH) (P<0.01). In addition, the dietary supplementation with α-lipoic acid significantly increased the mRNA expression of adenosine 5'-monophosphate-activated protein kinase α2 (AMPKα2) (P<0.01), peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α) (P<0.01), myocyte enhancer factor 2C (MEF2C) (P<0.05), and the nuclear respiratory factor 1 (NRF1) (P<0.05), particularly to significantly activate the AMPK enzyme activity (P<0.01) in biceps femoris from Tan sheep. In conclusion, the dietary α-lipoic acid supplementation can be expected to enhance the mitochondrial biogenesis and muscle oxidative metabolism in biceps femoris from Tan sheep, leading to an increase in the mRNA expression of AMPKα2, PGC1α, MEF2C, and NRF1 via the AMPK-SIRT1-PGC-1α signaling pathway. The dietary α-Lipoic acid supplementation can induce the transformation of muscle fiber types, thereby improving the meat quality of Tan sheep.