Studies on mechanisms underlying accumulation of intramuscular fat in porcine muscle

为了阐明低赖氨酸日粮促进猪肌内脂肪积累的机理，本研究进行了两个试验，第一个试验将6周龄猪分为低赖氨酸组和对照组。低赖氨酸组饲喂低赖氨酸日粮，对照组饲喂对照日粮。这些猪被给予这些饮食一周或三周。测定背最长肌和菱形肌中脂肪形成相关基因mRNA的丰度。在低赖氨酸组中，PPARγ和SREBP-1c mRNA的丰度较高。PGC-1α基因表达在低赖氨酸组也较高。此外，我们通过肌肉切片的油红-O染色评估肌内脂肪（IMF）的量。肌内脂肪含量菱形肌高于背最长肌。这种较高量的IMF似乎与菱形肌的较高氧化能力有关。此外，货币基金组织的数量也在增加， ...更多信息 低赖氨酸日粮仅对菱形肌有抑制作用。实验二研究了培养液中赖氨酸水平对3 T3-L1脂肪细胞分化的影响。培养基中低水平的赖氨酸抑制了3 T3-L1脂肪细胞中三酰甘油的积累，从而抑制了脂肪细胞的分化。反应呈剂量依赖性。我们检测了3 T3-L1脂肪细胞中脂肪形成相关转录因子C/EBPα、C/EBPβ、C/EBPσ和PPARγ的mRNA丰度。虽然C/EBPβ和C/EBPσ的mRNA丰度不受培养基中赖氨酸水平的影响，但C/EBPα和PPARγ的mRNA丰度在诱导分化后6和8天降低。脂肪酸合成酶的活性和mRNA丰度在诱导后4天已经较低。结论：低水平赖氨酸可抑制3 T3-L1脂肪细胞的分化，这种抑制作用是通过抑制脂肪形成相关转录因子C/EBPα和PPARγ的表达而实现的。少

We conducted two experiments in order to elucidate underlying mechanisms of promoted accumulation of intramuscular fat in porcine muscle induced by low lysine diet feeding.In the first experiment, 6 week old pigs were assigned to low lysine group or control group. Pigs of the low lysine group were given a low lysine diet while pigs of the control group given a control diet. The pigs were given these diets for one or three weeks. Abundances of mRNA of adipogenesis related genes in longissimus dorsi and rhomboideus muscles were determined. Abundances of PPARγ and SREBP-1c mRNAs were higher in the low lysine group. Gene expression of PGC-1α was also higher in the low lysine group. Further, we assessed amount of intramuscular fat (IMF) by Oil Red-O staining of muscle sections. The amount of IMF was higher in rhomboideus muscle than in longissimus dorsi muscle. This higher amount of IMF seems to relate to higher oxidative capacity of rhomboideus muscle. Further, the amount of IMF was increa … More sed by low lysine diet only in rhomboideus muscle. From these results, we conclude that adipogenesis related genes play a role in promoting accumulation of intramuscular fat in porcine muscle by low lysine diet.In the second experiment, influences of lysine levels in culture media on differentiation of 3T3-L1 adipocytes were studied. Accumulation of triacylglycerol in 3T3-L1 adipocytes, thus differentiation of the adipocytes, was inhibited by low levels of lysine in culture media. The response was dose dependent. We determined abundances of mRNA of adipogenesis related transcription factors, C/EBPα, C/EBPβ, C/EBPσ and PPARγ in 3T3-L1 adipocutes. Although abundances of mRNA of C/EBPβ and C/EBPσ were not affected by levels of lysine in culture media, those of C/EBPα and PPARγ were lower at 6 and 8 days after induction of differentiation. Activities and mRNA abundances of fatty acid synthase were lower already at 4 days after the induction. We conclude that low level of lysine in culture medium inhibits differentiation of 3T3-L1 adipocyte and that this inhibition is mediated by suppressed expression of major adipogenesis related transcription factors, C/EBPα and PPARγ. Less