Co-Overexpression of C/EBP Beta and C/EBP Delta Genes Induces Lipid Synthesis in Bovine Fibroblasts

Although fat is unpopular in many countries, being considered unhealthy, and while appropriate fat deposition in the muscle of beef cattle can improve meat tenderness and palatability, marbling beef is very popular and expensive, especially in the orient. However, little is known about the molecular mechanisms of fat deposition in bovine muscle. In mouse 3T3-L1 preadipocyte, differentiation led to the expression of C/EBPβ and C/EBPδ simultaneously increasing. In the very early stage, the cell activates other genes, such as PPARγ and C/EBPα, and adipocytes start differentiating. Therefore if both C/EBPβ and C/EBPδ are overexpressed simultaneously in the fibroblasts, the question is whether this can induce lipid synthesis in fibroblasts. These are the main issues of this study, in which we have constructed adenovirus overexpression vectors carrying bovine C/EBPβ and C/EBPδ genes, which are also packaged and amplified the corresponding C/EBPβ+δ adenovirus to co-infect primary bovine fibroblasts, using empty adenovirus as control. Bovine fibroblasts treated with C/EBPβ+δ adenovirus undergo adipogenesis and accumulate lipid droplets soon after treatment. RT-PCR showed the expression patterns of 3 recognized transcriptional regulators, PPARγ, C/EBPα and SREBP1 are distinctive. PPARγ was suppressed in the initial stage, and significantly increased later on; C/EBPα had sharp ups and downs in the middle stage, whereas there were no significant changes (but slightly lower than control) in SREBP1 expression. LPL and ACCα were significantly upregulated throughout the differentiation. FAS increased in the initial 4 days before returning to normal. Considering the fibroblasts lipid droplet and gene expression occurring together, we speculated that the regulatory mechanism in bovine fibroblast adipogenesis is different from that in adipocytes. Simultaneously overexpressed C/EBPβ and C/EBPδ can activate PPARγ and C/EBPα gene expression, but they are not essential for inducing lipid droplets in bovine fibroblasts.