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Background/Aims: Myoblasts and muscle satellite cells have the potential to transdifferentiate into adipocytes or adipocyte-like cells. Previous studies suggest that mitogen-activated protein kinase (MAPK) is critical to adipogenic trans-differentiation of muscle cells. ERK1/2, P38 and JNK are three major MAPK family members; their activation and regulatory functions during adipogenic trans-differentiation of myoblasts are investigated. Methods: C2C12 myoblasts were cultured and induced for adipogenic trans-differentiation. Activation patterns of MAPKs were assayed using protein microarray and Western blot. Three specific MAPK blockers, U0126, SB20358 and SP600125, were used to block ERK1/2, P38 and JNK during trans-differentiation. Cellular adipogenesis was measured using staining and morphological observations of cells and expression changes in adipogenic genes. Results: Inhibitors reduced phosphorylation of corresponding MAPK and produced unique cellular effects. Suppressing P38 promoted adipogenic trans-differentiation and intensified adipolytic metabolism in differentiated cells. However, inhibition of ERK1/2 had the opposite effects on adipogenesis and no effect on adipolysis. Blocking JNK weakly blocked trans-differentiation but stimulated adipolysis and induced apoptosis. Conclusion: Three MAPKs participate in the regulation of myoblast adipogenic trans-differentiation by controlling adipogenic and adipolysis metabolism.

Pancreatic lipase plays a key role in intestinal digestion of feed fat, and is often deficient in young animals such as weaning piglets. The objective of this study was to express and characterize a partial codon optimized porcine pancreatic lipase (opPPL). A 537 bp cDNA fragment encoding N-terminus amino acid residue of the mature porcine pancreatic lipase was synthesized according to the codon bias of Pichia pastoris and ligated to the full-length porcine pancreatic lipase cDNA fragment. The codon optimized PPL was cloned into the pPICZαA (Invitrogen, Beijing, China) vector. After the resultant opPPL/pPICZαΑ plasmid was transformed into P.pastoris, the over-expressed extracellular opPPL containing a His-tag to the C terminus was purified using Ni Sepharose affinity column (GE Healthcare, Piscataway, NJ, USA), and was characterized against the native enzyme (commercial PPL from porcine pancreas, Sigma). The opPPL exhibited a molecular mass of approximately 52 kDa, and showed optimal temperature (40°C), optimal pH (8.0), Km (0.041 mM), and Vmax (2.008 µmol.mg protein −1.min−1) similar to those of the commercial enzyme with p-NPP as the substrate. The recombinant enzyme was stable at 60°C, but lost 80% (P<0.05) of its activity after exposure to heat ≥60°C for 20 min. The codon optimization increased opPPL yield for ca 4 folds (146 mg.L−1 vs 36 mg.L−1) and total enzyme activity increased about 5 folds (1900 IU.L−1 vs 367 IU.L−1) compared with those native naPPL/pPICZαΑ tranformant. Comparison of gene copies and mRNA profiles between the two strains indicated the increased rePPL yields may partly be ascribed to the increased protein translational efficiency after codon optimization. In conclusion, we successfully optimized 5-terminal of porcine pancreatic lipase encoding gene and over-expressed the gene in P. pastoris as an extracellular, functional enzyme. The recombination enzyme demonstrates a potential for future use as an animal feed additive for animal improvement.

No abstract

Background/Aims: Muscle cells are able to trans-differentiate into adipocytes with adipogenesis induction. MicroRNAs (miRNAs), a class of small non-coding RNAs, widely participate in the regulation of growth and development of cells. However, the expression and regulatory role of miRNAs in the trans-differentiation of muscle cell are largely unknown. Methods: C2C12 myoblasts were inducted to adipogenesis trans-differentiation and microarrays were used to assay the changes of expression profile of miRNAs. MiR-199a, a miRNA showed significant change in the trans-differentiation, was selected for the subsequent function study via over- expression and knock down. Results: Dozens of miRNAs showed different changes followed the adipogenesis trans-differentiation of C2C12 cells. In which, miR-199a was decreased in the adipogenic cells and miR-199a over-expression inhibited the trans-differentiation and decreased lipid accumulation in the cells. Moreover, Fatty acid transport protein 1 (Fatp1), a major regulator of trans-membrane transportation and the oxidative metabolism of free fatty acids, was showed to be a target of miR-199a by computational and luciferase reporter assays. Additionally, Fatp1 knock-down by small interfering RNA had similar inhibitory effects on the trans-differentiation in C2C12 cells. Conclusion: Our study reveals an important role for miR-199a in the regulation of adipogenic trans-differentiation in muscle cells via suppression of Fatp1 gene.