Coffee is a widely consumed beverage worldwide and is believed to help prevent the occurrence of various chronic diseases. However, the effect of coffee on skeletal muscle hypertrophy, differentiation and the mechanisms of action responsible have remained unclear. To investigate the effect of coffee on skeletal muscle hypertrophy, mice were fed a normal diet or a normal diet supplemented with 0.3% coffee or 1% coffee. Coffee supplementation was observed to increase skeletal muscle hypertrophy, while simultaneously upregulating protein expression of total MHC, MHC2A, and MHC2B in quadricep muscle. Myostatin expression was also attenuated, and IGF1 was upregulated with subsequent phosphorylation of Akt and mTOR, while AMPK phosphorylation was attenuated. Coffee also increased the grip strength and PGC-1α protein expression, and decreased the expressions of TGF-β and myostatin in tricep muscle. Coffee activated the MKK3/6-p38 pathway and upregulated PGC-1α, which may play a role in promoting myogenic differentiation and myogenin expression in C2C12 cells. These results suggest that coffee increases skeletal muscle function and hypertrophy by regulating the TGF-β/myostatin - Akt - mTORC1.

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Mitochondrial dysfunction is associated with insulin resistance. Although chicoric acid (CA) is known to have beneficial effects on insulin sensitivity, the involvement of mitochondrial function has not been elucidated yet. Here, we investigated the effect of CA on insulin resistance and mitochondrial dysfunction. In palmitate-induced insulin-resistant C2C12 myotubes, CA improved impaired glucose uptake and insulin signaling pathways, along with enhanced mitochondrial membrane potential and oxygen consumption. CA treatment in diet-induced obese mice ameliorated glucose tolerance and increased insulin sensitivity. CA treatment also recovered the dysregulated expression of glucose metabolism-related genes in the high-fat-fed mice. CA significantly increased the mitochondrial DNA content, citrate synthase, and ATP content, as well as the expression of genes related to mitochondrial biogenesis and oxidative phosphorylation in the liver and skeletal muscle in high-fat- fed obese mice. These findings suggested that CA attenuates insulin resistance and promotes insulin sensitivity by enhancing mitochondrial function.

Gliadin is a major protein component of gluten and causes gluten toxicity through intestinal stress. We previously showed that gliadin intake induces oxidative stress in the intestine and reduces fertility in a Caenorhabditis elegans model. To elucidate the possible link between intestinal stress and reproduction, changes in the intestine and germ cells of C. elegans after gliadin intake were examined at the molecular level. Gliadin intake increased reactive oxygen species (ROS) production in the intestine, decreased intestinal F-actin levels, and increased germ cell apoptosis. These gliadin-triggered effects were suppressed by antioxidant treatment. These results suggest that ROS production in the intestine induced by gliadin intake causes disruption of intestinal integrity and increases germ cell apoptosis. Gliadin-induced germ cell apoptosis (GIGA) was suppressed by depletion of cep-1, ced-13, egl-1, or mpk-1. However, HUS-1 was not activated, suggesting that GIGA is activated through the mitogen-activated protein kinase (MAPK) pathway and is CEP-1-dependent but is a separate pathway from that controlling the DNA damage response. Taken together, our results suggest that gliadin causes intestinal barrier disruption through ROS production and interacts with the germ cells to reduce fertility through GIGA.