Studies on mechanisms underlying accumulation of intramuscular fat in porcine muscle

2006 Fiscal Year Final Research Report Summary

• Project/Area Number: 17580249
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Applied animal science
• Research Institution: National Agricultural Research Organization
• Principal Investigator: KATSUMATA Masaya National Agricultural Research Organization, National Institute of Livestock and Grassland Science, Molecular Nutrition Research team, Chief Researcher (60355683)
• Project Period (FY): 2005 – 2006
• Keywords: intramuscular fat / pig / lysine / adipogenesis / adipocyte

Research Abstract

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 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.