Muscle‐Specific Over‐Expression of the NAD + ‐Dependent Nuclear Sirtuin SIRT6, Suppresses Cancer‐Associated Cachexia

Involuntary loss of muscle mass, termed as cachexia, is associated with many terminal diseases. Almost 30% of cancer patients succumb to death due to cachexia rather than to the primary disease itself. Earlier we had observed that mice deficient for SIRT6, a chromatin‐associated lysine deacylase had reduced muscle mass and degenerative changes in their muscles, such as induction of fibrosis and infiltration of inflammatory cells. We have reported that SIRT6 down‐regulated myostatin (Mstn) expression, a major negative regulator of muscle growth and differentiation, by attenuating NF‐κB binding to Mstn promoter. The present study was undertaken to explore the possibility whether muscle‐specific overexpression of SIRT6 could have dual benefit in suppressing cancer‐associated cachexia as well as retarding tumor growth. Methods Immunoblotting, RT‐qPCR, histology, plasma cytokine profiling and ELISA assays were carried out to assess effect of SIRT6 overexpression in tumor‐induced muscle samples. Results We generated Rosa26‐Fl‐STOP‐SIRT6‐Flag mice and crossed them with Myl1 tm1(cre)Sjb mice to obtain skeletal muscle‐specific overexpression of SIRT6. Two‐month old control (SIRT6‐endogenous) and SIRT6 muscle‐specific overexpresser male mice were injected, subcutaneously, with B16F10 mouse melanoma cells. After 14 days, when tumor dimensions reached 2 cm in control mice, gastrocnemius muscles were harvested for further analysis. Skeletal muscle‐specific overexpression of SIRT6 was confirmed by immuno‐blotting. Skeletal muscle‐specific overexpression of SIRT6 reduced tumor volume significantly (40% reduction, n=7, p<0.01) and increased muscle mass by five‐fold in the melanoma‐challenged male mice, compared to tumor‐bearing controls (n=10). Mstn protein expression was reduced significantly (p<0.001) with SIRT6 overexpression in muscles. H&E staining of the gastrocnemius muscle revealed that SIRT6 overexpression aided in maintaining the cross‐sectional diameter of muscle fibers in tumor‐bearing mice. We also observed that plasma insulin levels, which were downregulated in control tumor‐bearing mice, were upregulated significantly (p<0.005) by skeletal muscle‐specific overexpression of SIRT6. Our results indicate that muscle‐specific overexpression of SIRT6 influences multiple targets to suppress tumor growth as well as associated muscle loss. It normalizes insulin secretion by down‐regulating WNT4, a canonical Wnt signaling inhibitor, as well as CXCL10, an interferon‐inducible circulating inflammatory chemokine, both reported to be negative regulators of beta‐cell function. Conclusions Insulin supplementation is shown to slow down tumor growth, and cancer‐induced muscle wasting. Our results indicate that moderate overexpression of SIRT6 protects mice from developing cancer‐cachexia in two ways: by impeding tumor growth and attenuating tumor‐induced muscle degeneration. Therefore, SIRT6 could be a novel target for drug design. Support or Funding Information RO1 HL‐136712 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .