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Oxidative stress has been implicated in the etiology of age-related muscle loss (sarcopenia). However, the underlying mechanisms by which oxidative stress contributes to sarcopenia have not been thoroughly investigated. To directly examine the role of chronic oxidative stress in vivo, we used a mouse model that lacks the antioxidant enzyme CuZnSOD (Sod1). Sod1(-/-) mice are characterized by high levels of oxidative damage and an acceleration of sarcopenia. In the present study, we demonstrate that muscle atrophy in Sod1(-/-) mice is accompanied by a progressive decline in mitochondrial bioenergetic function and an elevation of mitochondrial generation of reactive oxygen species. In addition, Sod1(-/-) muscle exhibits a more rapid induction of mitochondrial-mediated apoptosis and loss of myonuclei. Furthermore, aged Sod1(-/-) mice show a striking increase in muscle mitochondrial content near the neuromuscular junctions (NMJs). Despite the increase in content, the function of mitochondria is significantly impaired, with increased denervated NMJs and fragmentation of acetylcholine receptors. As a consequence, contractile force in aged Sod1(-/-) muscles is greatly diminished. Collectively, we show that Sod1(-/-) mice display characteristics of normal aging muscle in an accelerated manner and propose that the superoxide-induced NMJ degeneration and mitochondrial dysfunction are potential mechanisms of sarcopenia.

Summary paragraph Entamoeba histolytica is the causative agent of amoebiasis, a potentially fatal diarrheal disease in the developing world. The parasite was named “histolytica” for its ability to destroy host tissues, which is most likely driven by direct killing of human cells. The mechanism of human cell killing has been unclear, though the accepted model was that the parasites use secreted toxic effectors to kill cells prior to ingestion1. Here we report the surprising discovery that amoebae kill by biting off and ingesting distinct pieces of living human cells, resulting in intracellular calcium elevation and eventual cell death. After cell killing, amoebae detach and cease ingestion. Ingestion of bites is required for cell killing, and also contributes to invasion of intestinal tissue. The internalization of bites of living human cells is reminiscent of trogocytosis (Greek trogo–, nibble) observed between immune cells2–6, but amoebic trogocytosis differs since it results in death. The ingestion of live cell material and the rejection of corpses illuminate a stark contrast to the established model of dead cell clearance in multicellular organisms7. These findings change the paradigm for tissue destruction in amoebiasis and suggest an ancient origin of trogocytosis as a form of intercellular exchange.

The mechanisms of action of dietary fish oil (FO) on osteoporosis are not fully understood. This study showed FO decreased bone loss in ovariectomized mice because of inhibition of osteoclastogenesis. This finding supports a beneficial effect of FO on the attenuation of osteoporosis.Introduction: Consumption of fish or n-3 fatty acids protects against cardiovascular and autoimmune disorders. Beneficial effects on bone mineral density have also been reported in rats and humans, but the precise mechanisms involved have not been described. Methods: Sham and ovariectomized (OVX) mice were fed diets containing either 5% corn oil (CO) or 5% fish oil (FO). Bone mineral density was analyzed by DXA. The serum lipid profile was analyzed by gas chromatography. Receptor activator of NF-B ligand (RANKL) expression and cytokine production in activated T-cells were analyzed by flow cytometry and ELISA, respectively. Osteoclasts were generated by culturing bone marrow (BM) cells with 1,25(OH) 2 D 3 . NF-B activation in BM macrophages was measured by an electrophoretic mobility shift assay. Results and Conclusion: Plasma lipid C16:1n6, C20:5n3, and C22:6n3 were significantly increased and C20:4n6 and C18:2n6 decreased in FO-fed mice. Significantly increased bone mineral density loss (20% in distal left femur and 22.6% in lumbar vertebrae) was observed in OVX mice fed CO, whereas FO-fed mice showed only 10% and no change, respectively. Bone mineral density loss was correlated with increased RANKL expression in activated CD4 ϩ T-cells from CO-fed OVX mice, but there was no change in FO-fed mice. Selected n-3 fatty acids (docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA]) added in vitro caused a significant decrease in TRACP activity and TRACP ϩ multinuclear cell formation from BM cells compared with selected n-6 fatty acids (linoleic acid [LA] and arachidonic acid [AA]). DHA and EPA also inhibited BM macrophage NF-B activation induced by RANKL in vitro. TNF-␣, interleukin (IL)-2, and interferon (IFN)-␥ concentrations from both sham and OVX FO-fed mice were decreased in the culture medium of splenocytes, and interleukin-6 was decreased in sham-operated FO-fed mice. In conclusion, inhibition of osteoclast generation and activation may be one of the mechanisms by which dietary n-3 fatty acids reduce bone loss in OVX mice.

SummarySarcopenia, the loss of skeletal muscle mass and function during aging, is a major contributor to disability and frailty in the elderly. Previous studies found a protective effect of reduced histone deacetylase activity in models of neurogenic muscle atrophy. Because loss of muscle mass during aging is associated with loss of motor neuron innervation, we investigated the potential for the histone deacetylase (HDAC) inhibitor butyrate to modulate age‐related muscle loss. Consistent with previous studies, we found significant loss of hindlimb muscle mass in 26‐month‐old C57Bl/6 female mice fed a control diet. Butyrate treatment starting at 16 months of age wholly or partially protected against muscle atrophy in hindlimb muscles. Butyrate increased muscle fiber cross‐sectional area and prevented intramuscular fat accumulation in the old mice. In addition to the protective effect on muscle mass, butyrate reduced fat mass and improved glucose metabolism in 26‐month‐old mice as determined by a glucose tolerance test. Furthermore, butyrate increased markers of mitochondrial biogenesis in skeletal muscle and whole‐body oxygen consumption without affecting activity. The increase in mass in butyrate‐treated mice was not due to reduced ubiquitin‐mediated proteasomal degradation. However, butyrate reduced markers of oxidative stress and apoptosis and altered antioxidant enzyme activity. Our data is the first to show a beneficial effect of butyrate on muscle mass during aging and suggests HDACs contribute to age‐related muscle atrophy and may be effective targets for intervention in sarcopenia and age‐related metabolic disease.

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