Delayed Recovery of Skeletal Muscle Mass following Hindlimb Immobilization in mTOR Heterozygous Mice

The present study addressed the hypothesis that reducing mTOR, as seen in mTOR heterozygous (+/−) mice, would exaggerate the changes in protein synthesis and degradation observed during hindlimb immobilization as well as impair normal muscle regrowth during the recovery period. Atrophy was produced by unilateral hindlimb immobilization and data compared to the contralateral gastrocnemius. In wild-type (WT) mice, the gradual loss of muscle mass plateaued by day 7. This response was associated with a reduction in basal protein synthesis and development of leucine resistance. Proteasome activity was consistently elevated, but atrogin-1 and MuRF1 mRNAs were only transiently increased returning to basal values by day 7. When assessed 7 days after immobilization, the decreased muscle mass and protein synthesis and increased proteasome activity did not differ between WT and mTOR+/− mice. Moreover, the muscle inflammatory cytokine response did not differ between groups. After 10 days of recovery, WT mice showed no decrement in muscle mass, and this accretion resulted from a sustained increase in protein synthesis and a normalization of proteasome activity. In contrast, mTOR+/− mice failed to fully replete muscle mass at this time, a defect caused by the lack of a compensatory increase in protein synthesis. The delayed muscle regrowth of the previously immobilized muscle in the mTOR+/− mice was associated with a decreased raptor•4EBP1 and increased raptor•Deptor binding. Slowed regrowth was also associated with a sustained inflammatory response (e.g., increased TNFα and CD45 mRNA) during the recovery period and a failure of IGF-I to increase as in WT mice. These data suggest mTOR is relatively more important in regulating the accretion of muscle mass during recovery than the loss of muscle during the atrophy phase, and that protein synthesis is more sensitive than degradation to the reduction in mTOR during muscle regrowth

Water Extract from the Leaves of Withania somnifera Protect RA Differentiated C6 and IMR-32 Cells against Glutamate-Induced Excitotoxicity

Glutamate neurotoxicity has been implicated in stroke, head trauma, multiple sclerosis and neurodegenerative disorders. Search for herbal remedies that may possibly act as therapeutic agents is an active area of research to combat these diseases. The present study was designed to investigate the neuroprotective role of Withania somnifera (Ashwagandha), also known as Indian ginseng, against glutamate induced toxicity in the retinoic acid differentiated rat glioma (C6) and human neuroblastoma (IMR-32) cells. The neuroprotective activity of the Ashwagandha leaves derived water extract (ASH-WEX) was evaluated. Cell viability and the expression of glial and neuronal cell differentiation markers was examined in glutamate challenged differentiated cells with and without the presence of ASH-WEX. We demonstrate that RA-differentiated C6 and IMR-32 cells, when exposed to glutamate, undergo loss of neural network and cell death that was accompanied by increase in the stress protein HSP70. ASH-WEX pre-treatment inhibited glutamate-induced cell death and was able to revert glutamate-induced changes in HSP70 to a large extent. Furthermore, the analysis on the neuronal plasticity marker NCAM (Neural cell adhesion molecule) and its polysialylated form, PSA-NCAM revealed that ASH-WEX has therapeutic potential for prevention of neurodegeneration associated with glutamate-induced excitotoxicty

Insulin-like growth factor 1 signaling regulates cytosolic sialidase Neu2 expression during myoblast differentiation and hypertrophy.

Cytosolic sialidase (neuraminidase 2; Neu2) is an enzyme whose expression increases during myoblast differentiation. Here we show that insulin-like growth factor 1 (IGF1)-induced hypertrophy of myoblasts notably increases Neu2 synthesis by activation of the phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (P13K/AKT/mTOR) pathway, whereas the proliferative effect mediated by activation of the extracellular regulated kinase 1/2 (ERK1/2) pathway negatively contributed to Neu2 activity. Accordingly, the differentiation L6MLC/IGF-1 cell line, in which the forced postmitotic expression of insulin-like growth factor 1 stimulates a dramatic hypertrophy, was accompanied by a stronger Neu2 increase. Indeed, the hypertrophy induced by transfection of a constitutively activated form of AKT was able to induce high Neu2 activity in C2C12 cells, whereas the transfection of a kinase-inactive form of AKT prevented myotube formation, triggering Neu2 downregulation. Neu2 expression was strictly correlated with IGF-1 signaling also in C2 myoblasts overexpressing the insulin-like growth factor 1 binding protein 5 and therefore not responding to endogenously produced insulin-like growth factor 1. Although Neu2-transfected myoblasts exhibited stronger differentiation, we demonstrated that Neu2 overexpression does not override the block of differentiation mediated by PI3 kinase and mTOR inhibitors. Finally, Neu2 overexpression did not modify the ganglioside pattern of C2C12 cells, suggesting that glycoproteins might be the target of Neu2 activity. Taken together, our data demonstrate that IGF-1-induced differentiation and hypertrophy are driven, at least in part, by Neu2 upregulation and further support the significant role of cytosolic sialidase in myoblasts

Growth Inhibition and Compensation in Response to Neonatal Hypoxia in Rats

BackgroundHypoxia is an important disease mechanism in prematurity, childhood asthma and obesity. In children, hypoxia results in chronic inflammation.MethodsWe investigated the effects of hypoxia (Hx) (12% O2) during postnatal day 2 to 20 in rats. Control groups were normoxic (Nc), and normoxic growth restricted (14 pup liters) (Gr).ResultsHypoxia decreased growth similar Gr. Hx increased plasma TNFα and IL-6 and decreased IGF-I and VEGF. Hypoxia resulted in right ventricular (RV) hypertrophy but disproportionate decrements in limb skeletal muscle (SM) growth. miR206 was depressed in the hypertrophied RV of Hx rats while increased in growth retarded SM. Hx resulted in a decreased RV mRNA for myostatin but had no effect on SM myostatin. The mRNA for hypoxia sensitive factors such as HIFα was depressed in the RV of Hx rats suggesting negative feedback.ConclusionThe results indicate that Hx induces a proinflammatory state that depresses growth regulating mechanisms and that tissues critical for survival, such as the heart, can escape from this general regulatory program to sustain life. This study identifies accessible biomarkers for evaluating the impact of interventions designed to mitigate the long-term deleterious consequences of hypoxia that all too often occur in babies born prematurely