Intramuscular fat, as one of the most important palatability attribute of beef carcase, is the primary determinant of beef quality. The research of adipogenesis mechanism would provide new insight into intramuscular fatty deposition. Here, the role of microRNA-378 was investigated during bovine adipogenic differentiation. It was revealed that miR-378 expression exists variably in bovine major tissue and organs by RT-qPCR. It was predicted that miR-378 targets CaMKK2, as an AMPKα kinase, by DIANA Tools. For better research, primary preadipocytes with stable transfection for up-/down-regulated expression of miR-378 were constructed by lentiviral vectors with GFP gene. The analyses of qPCR showed that <i>PPARγ</i> and <i>adiponectin</i> mRNA levels increased, but <i>C/EBPβ, pref-1</i> and <i>CaMKK2</i> mRNA levels decreased during adipogenic differentiation. When miR-378 was overexpressed, preadipocytes proliferation became slower, there are more cellular lipid droplets, and <i>PPARγ</i> and <i>C/EBPβ</i> mRNA levels were higher, but <i>pref-1, adiponectin</i> and <i>CaMKK2</i> were lower than control groups. Luciferase assay and western blot analysis validated that miR-378 binds the nucleotide sites of the 3'- untranslated region of <i>CaMKK2</i>, which inhibits the mRNA and protein expression of <i>CaMKK2</i>. These findings suggest that miR-378 promotes adipogenic differentiation in bovine intramuscular preadipocytes by targeting <i>CaMKK2</i> via AMPK signalling pathway.
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