Sirtuin 6 inhibition protects against glucocorticoid-induced skeletal muscle atrophy by regulating IGF/PI3K/AKT signaling.

Chronic activation of stress hormones such as glucocorticoids leads to skeletal muscle wasting in mammals. However, the molecular events that mediate glucocorticoid-induced muscle wasting are not well understood. Here, we show that SIRT6, a chromatin-associated deacetylase indirectly regulates glucocorticoid-induced muscle wasting by modulating IGF/PI3K/AKT signaling. Our results show that SIRT6 levels are increased during glucocorticoid-induced reduction of myotube size and during skeletal muscle atrophy in mice. Notably, overexpression of SIRT6 spontaneously decreases the size of primary myotubes in a cell-autonomous manner. On the other hand, SIRT6 depletion increases the diameter of myotubes and protects them against glucocorticoid-induced reduction in myotube size, which is associated with enhanced protein synthesis and repression of atrogenes. In line with this, we find that muscle-specific SIRT6 deficient mice are resistant to glucocorticoid-induced muscle wasting. Mechanistically, we find that SIRT6 deficiency hyperactivates IGF/PI3K/AKT signaling through c-Jun transcription factor-mediated increase in IGF2 expression. The increased activation, in turn, leads to nuclear exclusion and transcriptional repression of the FoxO transcription factor, a key activator of muscle atrophy. Further, we find that pharmacological inhibition of SIRT6 protects against glucocorticoid-induced muscle wasting in mice by regulating IGF/PI3K/AKT signaling implicating the role of SIRT6 in glucocorticoid-induced muscle atrophy.

Development of a less toxic dichloroacetate analogue by docking and descriptor analysis.

Dichloroacetate (DCA) is a synthetic compound that promotes the activity of pyruvate dehydrogenase (PDH) by inhibiting its repressor protein called pyruvate dehydrogenase kinase (PDHK). The activation of PDH leads to a reduction in ambient cellular lactate concentrations both in vitro and in vivo which contributes to the therapeutic use of DCA in the treatment of systemic lactic acidosis in humans. The therapeutic potential of DCA is now being explored in disorders that are accompanied by elevations of lactate concentration such as in hypoxic cancer cells. Yet conflicting evidence regarding its mutagenic potential has been a major setback in its clinical trials. Hence, docking and descriptor analysis of halogen substituted DCA analogues were performed to find out a drug candidate with less toxicity and better binding affinity than DCA. The Docking analysis was carried out using human PDHK isozyme 2, the physiological receptor for DCA. Bromo(iodo)acetate and Diiodoacetate were found out to be the plausible analogues of DCA from this study.