Effects of inhibin on activin A-Induced glucose metabolism in rat hepatocytes

Effect of physical training on liver expression of activin A and follistatin in a nonalcoholic fatty liver disease model in rats

Nonalcoholic fatty liver disease (NAFLD) is characterized by fat accumulation in the liver and is associated with obesity and insulin resistance. Activin A is a member of the transforming growth factor beta (TGF)-β superfamily and inhibits hepatocyte growth. Follistatin antagonizes the biological actions of activin. Exercise is an important therapeutic strategy to reduce the metabolic effects of obesity. We evaluated the pattern of activin A and follistatin liver expression in obese rats subjected to swimming exercise. Control rats (C) and high-fat (HF) diet-fed rats were randomly assigned to a swimming training group (C-Swim and HF-Swim) or a sedentary group (C-Sed and HF-Sed). Activin βA subunit mRNA expression was significantly higher in HF-Swim than in HF-Sed rats. Follistatin mRNA expression was significantly lower in C-Swim and HF-Swim than in either C-Sed or HF-Sed animals. There was no evidence of steatosis or inflammation in C rats. In contrast, in HF animals the severity of steatosis ranged from grade 1 to grade 3. The extent of liver parenchyma damage was less in HF-Swim animals, with the severity of steatosis ranging from grade 0 to grade 1. These data showed that exercise may reduce the deleterious effects of a high-fat diet on the liver, suggesting that the local expression of activin-follistatin may be involved.

Activin A regulates growth and acute phase proteins in the human liver cell line, HepG2

Activin, and its binding protein, follistatin, are up-regulated by mediators of inflammation, and recent studies have demonstrated that activin A can block the activity of the key inflammatory cytokine, interleukin-6 (IL-6). These findings thereby implicate activin and follistatin in the control of the inflammatory cascade. In this study, interactions between interleukin-1beta (IL-1beta), IL-6 and activin were examined the human liver cell line, HepG2, for their effect on cell proliferation and the production of the acute phase proteins, haptoglobin and alpha1-acid glycoprotein (alpha1-AGP). IL-1beta and activin A, but not IL-6, inhibited the proliferation of HepG2 cells. Activin A together with IL-1beta caused a greater inhibition of proliferation than either factor alone, and the inhibitory effects of activin A were blocked by the addition of follistatin to the cultures. Activin A alone inhibited the production of haptoglobin but did not affect alpha1-AGP concentrations. However, activin A suppressed the stimulatory effects of IL-6 on the production of both haptoglobin and alpha1-AGP. Production of follistatin by HepG2 cells was stimulated by activin A, but was inhibited by both IL-1beta and IL-6, indicating a complex regulatory loop is operable to modulate the effects of activin A during inflammation. Taken together, these data suggest that activin A interacts with IL-1beta and IL-6 to regulate and coordinate the production of acute phase proteins during an inflammatory episode.

Follistatin: a multifunctional regulatory protein

Follistatin was first described in 1987 as a follicle-stimulating hormone inhibiting substance present in ovarian follicular fluid. We now know that this effect of follistatin is only one of its many properties in a number of reproductive and nonreproductive systems. A majority of these functions are facilitated through the affinity of follistatin for activin, where activin's effects are neutralized through its binding to follistatin. As such, the interplay between follistatin and activin represents a powerful regulatory mechanism that impinges on a variety of cellular processes within the body. In this review we focus on the biochemical characteristics of follistatin and its interaction with activin and discuss the emerging role of these proteins as potent tissue regulators in the gonad, pituitary gland, pregnancy membranes, vasculature, and liver. Consideration is also given to the larger family of proteins that contain follistatin-like modules, in particular with regard to their functional and structural implications.