Mechanisms of regulation of intramuscular fat deposition in porcine muscle by dietary lysine content

Feeding a low-lysine diet to pigs promotes the deposition of intramuscular fat (IMF). However, the mechanisms underlying fat accumulation and marbling in porcine muscle remain unclear. As such, the aim of this study was to elucidate the manner in which dietary lysine regulates IMF deposition in finishing pigs. Low dietary lysine levels increased the volume but not the number of intramuscular adipocytes in the longissimus dorsi muscle. This observation indicates that lipogenesis in already existing adipocytes plays a pivotal role in IMF accumulation, as opposed to the differentiation of preadipocytes into mature adipocytes. We also found that a low-threonine diet did not affect IMF content in either longissimus dorsi or rhomboideus muscle. Thus, dietary shortages among the various indispensable amino acids may differentially influence IMF deposition. Furthermore, insulin signaling and triacylglyceride levels were enhanced in cultured adipocytes by cellular exposure to low vs. high concentrations of lysine, suggesting that insulin might similarly contribute to the nutritional modulation of IMF deposition in vivo.