Genistein affects osteoblastic MC3T3-E1 cells both through estrogen receptor and BMP-Smad signaling pathways

Many epidemiological studies show that genistein intake is effective for maintaining bone mineral density (BMD). Because the reason for the efficacy of genistein as a bone protective agent in vivo remains unclear, we investigated the mechanisms underlying the effects of genistein on BMD in relation to BMP-Smad signaling systems. When osteoblastic MC3T3-E1 cells were exposed to 1 μM genistein, they increased in number. Combined administrations of 1 μM genistein and 1 μM of ICI 182,780 inhibited the increase in cell numbers. Alkaline phosphatase (ALP) and Alizarin red staining showed high activities, indicating that genistein might promote estrogenic differentiation of MC3T3-E1 cells. Moreover, ELISA determined that production of osteoprotegerin (OPG), which is expressed by osteoblasts, was higher when 1 μM genistein was added to the medium than in controls. In contrast, when 10 ng/mL of noggin was administered in the medium, OPG production was inhibited. In order to clarify the underlying mechanism, we investigated the BMP-Smad signaling pathway. When genistein was added to the medium, it induced gene expression of BMP-4. Immunofluorescence staining showed that genistein induced phosphorylation of Smad 1/5, a downstream molecule of BMP. When noggin, which binds to BMP and blocks BMP signaling, was added to the medium, phosphorylation of Smad 1/5 was reduced. These results indicate that genistein may regulate bone metabolism through the BMP-Smad signaling pathway as well as through the estrogen receptor pathway

Chronic Stress Induces Type 2b Skeletal Muscle Atrophy via the Inhibition of mTORC1 Signaling in Mice

Chronic stress induces psychological and physiological changes that may have negative sequelae for health and well-being. In this study, the skeletal muscles of male C57BL/6 mice subjected to repetitive water-immersion restraint stress to model chronic stress were examined. In chronically stressed mice, serum corticosterone levels significantly increased, whereas thymus volume and bone mineral density decreased. Further, body weight, skeletal muscle mass, and grip strength were significantly decreased. Histochemical analysis of the soleus muscles revealed a significant decrease in the cross-sectional area of type 2b muscle fibers. Although type 2a fibers also tended to decrease, chronic stress had no impact on type 1 muscle fibers. Chronic stress increased the expression of REDD1, FoxO1, FoxO3, KLF15, Atrogin1, and FKBP5, but did not affect the expression of myostatin or myogenin. In contrast, chronic stress resulted in a decrease in p-S6 and p-4E-BP1 levels in the soleus muscle. Taken together, these results indicate that chronic stress promotes muscle atrophy by inhibiting mammalian targets of rapamycin complex 1 activity due to the upregulation of its inhibitor, REDD1