Opposing effects of 25‐hydroxy‐ and 1α,25‐dihydroxy‐vitamin D₃ on pro‐cachectic cytokine‐and cancer conditioned medium‐induced atrophy in C2C12 myotubes

Abstract

Aim: Loss of skeletal muscle is one of the main features of cancer cachexia. Vitamin D (VD) deficiency is associated with impairment of muscle mass and performance and is highly prevalent in cachectic patients; therefore, VD supplementation has been proposed to counteract cancer cachexia-associated muscle loss. However, in both cachectic cancer patients and tumour-bearing animals, VD supplementation led to disappointing results, urging the need for a better understanding of VD activity on skeletal muscle. Methods: Cancer-associated muscle wasting was reproduced in vitro by treating C2C12 myotubes with cancer cell conditioned medium, a combination of TNF-α and IFNγ or IL-6 pro-cachectic cytokines. The biological effects and mechanisms of action of 1,25-dihydroxy VD (1,25 VD) and its precursor 25-hydroxy VD (25 VD) on myotubes were explored. Results: We demonstrated that only 25 VD was able to protect from atrophy by activating Akt signalling, inducing protein synthesis, and stimulating the autophagic flux, while 1,25 VD had an atrophic activity per se, increasing FoxO3 levels, inducing the expression of atrogenes, and blocking the autophagic flux. Furthermore, we showed that the contrasting activities of these VD metabolites on C2C12 myotubes depend on a differential induction of VD-24-hydroxylase and transformation of VD metabolites in pro-atrophic 24-hydroxylated products, as silencing of VD-24-hydroxylase reduced the atrophic activity of 1,25 VD. Conclusions: Altogether these data might explain the lack of efficacy of VD treatment in vivo for the protection of muscle mass in cancer. K E Y W O R D Satrogenes, autophagy, cancer cachexia, Cyp24a1 24-hydroxylase, Cyp27b1 1α-hydroxylase, skeletal muscle atrophy 2 of 10 | SUSTOVA eT Al.

Effects of conditioned media from murine lung cancer cells and human tumor cells on cultured myotubes

“…A common model used to test for effects of tumor-derived factors on skeletal muscle involves treating cultured muscle cells with conditioned media (CM) from cancer/tumor cells (11,22,54,60,61). CM experiments provide a focused model to examine the direct effects of tumor/cancer cell-derived factors on skeletal muscle.…”

Metabolic Remodeling in Skeletal Muscle Atrophy as a Therapeutic Target

“…However, contrasting activities of vitamin D have been reported in muscle cell lines and in tumor-bearing animals [ 180 , 213 ]. For instance, both pro- and anti-atrophic effects have been reported for two vitamin D metabolites on C2C12 myotubes upon addition of cancer cell-conditioned medium [ 215 ], discouraging the use of this treatment in vivo for rescuing cancer cachexia. Similarly, tumor-bearing rats treated with vitamin D displayed an impairment in the muscle regenerative program and any beneficial effect in counteracting muscle wasting [ 216 ].…”

Environment and exposure

“…Sustova et al, in a recently published study, examined the role of adequate vitamin D generation in cachexia patients, with relevant implications for therapeutic substitution. 13 Among all more or less adverse environmental conditions studied, insufficient oxygen availability has been the most prominent topic, affecting several different pathophysiologic mechanisms.…”

“…Ultraviolet light, to humans, is the most relevant form of radiation on a daily basis, which may be both a blessing and a curse. Sustova et al, in a recently published study, examined the role of adequate vitamin D generation in cachexia patients, with relevant implications for therapeutic substitution 13 …”