Maternal obesity induces epigenetic modifications to facilitate Zfp423 expression and enhance adipogenic differentiation in fetal mice.

Maternal obesity (MO) predisposes offspring to obesity and type 2 diabetes despite poorly defined mechanisms. Zfp423 is the key transcription factor committing cells to the adipogenic lineage, with exceptionally dense CpG sites in its promoter. We hypothesized that MO enhances adipogenic differentiation during fetal development through inducing epigenetic changes in the Zfp423 promoter and elevating its expression. Female mice were subjected to a control (Con) or obesogenic (OB) diet for 2 months, mated, and maintained on their diets during pregnancy. Fetal tissue was harvested at embryonic day 14.5 (E14.5), when the early adipogenic commitment is initiated. The Zfp423 expression was 3.6-fold higher and DNA methylation in the Zfp423 promoter was lower in OB compared with Con. Correspondingly, repressive histone methylation (H3K27me3) was lower in the Zfp423 promoter of OB fetal tissue, accompanied by reduced binding of enhancer of zeste 2 (EZH2). Gain- and loss-of-function analysis showed that Zfp423 regulates early adipogenic differentiation in fetal progenitor cells. In summary, MO enhanced Zfp423 expression and adipogenic differentiation during fetal development, at least partially through reducing DNA methylation in the Zfp423 promoter, which is expected to durably elevate adipogenic differentiation of progenitor cells in adult tissue, programming adiposity and metabolic dysfunction later in life.

AMP-activated protein kinase stimulates myostatin expression in C2C12 cells.

AMP-activated protein kinase (AMPK) is a master regulator of energy metabolism in skeletal muscle; AMPK induces muscle protein degradation but the underlying mechanisms are unclear. Myostatin is a powerful negative regulator of skeletal muscle mass and growth in mammalian species. We hypothesized that AMPK stimulates myostatin expression, which provides an explanation for the negative role of AMPK in muscle growth. The objective of this study is to demonstrate that AMPK stimulates myostatin expression using C2C12 cells as a model. Activation of AMPK by 5-aminoimidazole-4-carboxamide-1-ß-d-riboruranoside (AICAR) dramatically increased the mRNA expression and protein content of myostatin in C2C12 myotubes, and to a lesser degree in myoblasts. Metformin, another AMPK activator, also stimulated myostatin expression at low concentrations. In addition, ectopic expression of AMPK wild-type α subunit (enhancing AMPK activity) and AMPK K45R mutant (knockdown AMPK activity) enhanced and reduced myostatin expression, respectively. These results indicate that AMPK stimulates myostatin expression in C2C12 cells, providing an explanation for the negative effect of AMPK on muscle growth.