Enhancement of adipogenesis and fibrogenesis in skeletal muscle of Wagyu compared with Angus cattle

Intramuscular fat and collagen content are major factors affecting beef quality, but mechanisms regulating intramuscular adipose and connective tissue deposition are far from clear. Japanese Wagyu cattle are well known for their extremely high marbling. The objective of this study was to evaluate intramuscular fat (IMF) and collagen deposition in the muscle of Wagyu compared with Angus cattle. Animals were managed under the same condition and slaughtered at an averaging 585 +/- 12.1 kg of BW. Samples of sternomandibularis muscle were collected from Wagyu (n = 3) and Angus (n = 3) for molecular and histological investigations of adipogenesis and fibrogenesis. With exception of C/EBP beta (P = 0.2864), the expression of the adipogenic markers C/EBP alpha (P = 0.008), PPAR gamma (P = 0.028), and zip finger protein 423 (Zfp423; P = 0.047) in Wagyu were greater than in Angus muscle, which was consistent with greater IMF deposition in Wagyu (P < 0.05). In addition, more adipocytes and preadipocytes were detected intramuscularly in Wagyu cattle. Similarly, fibrogenesis was also enhanced in Wagyu, with a greater expression of fibroblast growth factor (FGF)-2 (P = 0.028), FGF receptor 1 (P = 0.030), transforming growth factor (TGF)-beta (P = 0.028), collagen I (P = 0.012), and collagen III (P = 0.025). Similarly, Wagyu muscle had greater collagen content (P = 0.002) and decreased collagen solubility (P = 0.005). In addition, muscle fiber diameter was larger (P < 0.0001) in Wagyu than in Angus cattle. These results clearly show that both IMF and collagen contents are enhanced in Wagyu cattle and more adipogenic cells are detected in Wagyu muscle, indicating intramuscular adipogenesis is enhanced in Wagyu compared with Angus muscle.