Role of the Osteocyte in Musculoskeletal Disease

Deletion of FNDC5/irisin modifies murine osteocyte function in a sex-specific manner

Irisin, released from exercised muscle, has been shown to have beneficial effects on numerous tissues but its effects on bone are unclear. We found significant sex and genotype differences in bone from wildtype (WT) mice compared to mice lacking Fndc5 (knockout [KO]), with and without calcium deficiency. Despite their bone being indistinguishable from WT females, KO female mice were partially protected from osteocytic osteolysis and osteoclastic bone resorption when allowed to lactate or when placed on a low-calcium diet. Male KO mice have more but weaker bone compared to WT males, and when challenged with a low-calcium diet lost more bone than WT males. To begin to understand responsible molecular mechanisms, osteocyte transcriptomics was performed. Osteocytes from WT females had greater expression of genes associated with osteocytic osteolysis and osteoclastic bone resorption compared to WT males which had greater expression of genes associated with steroid and fatty acid metabolism. Few differences were observed between female KO and WT osteocytes, but with a low-calcium diet, the KO females had lower expression of genes responsible for osteocytic osteolysis and osteoclastic resorption than the WT females. Male KO osteocytes had lower expression of genes associated with steroid and fatty acid metabolism, but higher expression of genes associated with bone resorption compared to male WT. In conclusion, irisin plays a critical role in the development of the male but not the female skeleton and protects male but not female bone from calcium deficiency. We propose irisin ensures the survival of offspring by targeting the osteocyte to provide calcium in lactating females, a novel function for this myokine.

Deletion of FNDC5/Irisin modifies murine osteocyte function in a sex-specific manner

Irisin, released from exercised muscle, has been shown to have beneficial effects on numerous tissues but its effects on bone are unclear. We found significant sex and genotype differences in bone from wildtype (WT) mice compared to mice lacking Fndc5 (KO), with and without calcium deficiency. Despite their bone being indistinguishable from WT females, KO female mice were partially protected from osteocytic osteolysis and osteoclastic bone resorption when allowed to lactate or when placed on a low-calcium diet. Male KO mice have more but weaker bone compared to WT males, and when challenged with a low-calcium diet lost more bone than WT males. To begin to understand responsible molecular mechanisms, osteocyte transcriptomics was performed. Osteocytes from WT females had greater expression of genes associated with osteocytic osteolysis and osteoclastic bone resorption compared to WT males which had greater expression of genes associated with steroid and fatty acid metabolism. Few differences were observed between female KO and WT osteocytes, but with a low calcium diet, the KO females had lower expression of genes responsible for osteocytic osteolysis and osteoclastic resorption than the WT females. Male KO osteocytes had lower expression of genes associated with steroid and fatty acid metabolism, but higher expression of genes associated with bone resorption compared to male WT. In conclusion, irisin plays a critical role in the development of the male but not the female skeleton and protects male but not female bone from calcium deficiency. We propose irisin ensures the survival of offspring by targeting the osteocyte to provide calcium in lactating females, a novel function for this myokine.

Aerobic training and vitamin E administration ameliorates cardiac apoptosis markers in rats exposed to methamphetamine

Methamphetamine (MA) abuse is related to risks to the cardiovascular system. The present study aimed to compare the effects of moderate-intensity aerobic training (MIAT) and vitamin E (Vit.E) supplementation on markers of cardiac apoptosis following MA exposure. Fifty-four rats were randomly divided into six groups. CON group did not receive MA, while the others received MA alone or in combination with MIAT, Vit. E, MIAT+Vit E, or paraffin (PAR). These groups received MA incrementally for 23 consecutive days. Vit.E and MIAT+Vit.E groups received vitamin E three times a week for six weeks. MIAT and MIAT+Vit.E groups exercised for 25-40 min. Immunohistochemical and gene expression analyses were performed on the heart tissues. Bax and TGF-β expression was significantly higher, while Bcl-2 and VEGF expression was significantly lower in the MA and PAR groups than in the other groups (p < 0.05). Bcl-2 and VEGF expression was higher, and Bax and TGF-β expression was significantly lower in the MIAT and MIAT+Vit.E groups than in the other groups (p < 0.05). In Vit.E treated groups, Bax and TGF-β expression were lower, and VEGF was higher than that in the MA and PAR groups, but higher than those in the CON, MIAT and MIAT+Vit.E groups. MA increased the expression of Bax and TGF-β, and decreased the expression of Bcl-2 and VEGF, suggesting increased cardiac apoptosis. In contrast, MIAT and Vit.E decreased the expression of Bax and TGF-β, suggesting a reduction in cardiac apoptosis induced by MA.