[Mstn knockdown promotes intramuscular fatty acid metabolism by β oxidation via the up-regulation of Cpt1b]

Myostatin (Mstn) is known as growth/differentiation factor-8 (GDF-8). Knockout or knockdown of Mstn gene promotes muscle development and reduces fat content. Here we prepared Mstn knockdown mice by RNA interference, then the morphology of the skeletal muscle, the content of triglyceride (TG), the content and composition of fatty acids in the skeletal muscle were detected. The expression of Mstn reduced in muscle of Mstn knockdown mice compared to the controls. The cross sectional areas of the skeletal muscle myofibers were significantly larger while the content of TG was less than that of the controls, and the ratios of n-3/n-6 and unsat/sat in the knockdown mice increased significantly. Subsequently, we detected the expression of genes associated with fatty acid metabolism. The expression of the genes associated with lipolysis and fatty acid transportation were up-regulated, while the genes associated with fatty acid synthesis were down-regulated. Of these genes, the up-regulation of a gene associated with β oxidation, Cpt1b, was up-regulated remarkably. We further detected the enzyme activity of CPT1 in skeletal muscle and obtained the same results with gene expression. Moreover, chromatin immunoprecipitation assay was performed and we found that SMAD3, a transcription factor downstream of Mstn, directly binds to the promoter of Cpt1b gene. These results showed that knockdown of Mstn up-regulated the expression of Cpt1b through the binding of SMAD3 to the promoter of Cpt1b, then promoted the β oxidation metabolism of intramuscular fatty acids.

Leptin decreases BC cell susceptibility to NK lysis via PGC1A pathway

Large prospective studies established a link between obesity and breast cancer (BC) development. Yet, the mechanisms underlying this association are not fully understood. Among the diverse adipocytokine secreted by hypertrophic adipose tissue, leptin is emerging as a key candidate molecule linking obesity and cancer, since it promotes proliferation and invasiveness of tumors. However, the potential implication of leptin on tumor escape mechanisms remains unknown. This study aims to explore the effect of leptin on tumor resistance to NK lysis and the underlying mechanism. We found that leptin promotes both BC resistance to NK92-mediated lysis and β oxidation on MCF-7, by the up-regulation of a master regulator of mitochondrial biogenesis, the peroxisome proliferator activated receptor coactivator-1 α (PGC1A). Using adenoviral approaches, we show that acute elevation of PGC1A enhances the fatty acid oxidation pathway and decreases the susceptibility of BC cells to NK92-mediated lysis. Importantly, we identified the involvement of PGC1A and leptin in the regulation of hypoxia inducible factor-1 alpha (HIF1A) expression by tumor cells. We further demonstrate that basal BC cells MDA-MB-231 and BT-20 exhibit an increased PGC1A mRNA level and an enhanced oxidative phosphorylation activity; in comparison with luminal BC cells MCF7 and MDA-361, which are associated with more resistance NK92 lysis. Altogether, our results demonstrate for the first time how leptin could promote tumor resistance to immune attacks. Reagents blocking leptin or PGC1A activity might aid in developing new therapeutic strategies to limit tumor development in obese BC patients.