Expression of enzymes and transcription factors involved in n-3 long chain PUFA biosynthesis in limousin bull tissues.

The current low consumption of n-3 long chain polyunsaturated fatty acids (n-3 LCPUFA) led scientists to wonder about the possible enrichment of human food, including meats such as beef, with n-3 LCPUFA. However, their biosynthesis from dietary n-3 PUFA seems limited in mammalian tissues implying that a better understanding of the molecular mechanisms responsible for this down regulation is needed. This study aimed at identifying and comparing the limiting steps of n-3 LCPUFA synthesis in liver, intermuscular adipose tissue (IM-AT) and semitendinosus muscle (ST) from six Limousin bulls. Tissue FA composition was analysed by GLC and mRNA abundance of enzymes and transcription factors involved in n-3 LCPUFA synthesis was assessed by RT-qPCR. In liver, mRNA encoding proteins involved in n-3 LCPUFA synthesis were present in agreement with the significant high content of n-3 LCPUFA (8.4 mol% of total FA, 257 mg/100 g of fresh tissue) in this organ. In IM-AT, these mRNA were all present, but at a tenfold lower intensity than in liver in agreement with the low contents of n-3 LCPUFA in this tissue. In ST muscle, these mRNA were all present except elongase 5 mRNA which was only present as trace, the corresponding protein being undetectable, probably inducing a break of n-3 LCPUFA synthesis from 18:4n-3. In conclusion, Limousin bull ST muscle seemed unable to synthesize n-3 LCPUFA. However, the presence of 20:5n-3 (EPA) and 22:5n-3 (DPAn-3) in muscle raised the question of the origin of these n-3 LCPUFA.