Janus effect of glucocorticoids on differentiation of muscle fibro/adipogenic progenitors

Abstract

Muscle resident fibro-adipogenic progenitors (FAPs), support muscle regeneration by releasing cytokines that stimulate the differentiation of myogenic stem cells. However, in non-physiological contexts (myopathies, atrophy and aging) FAPs cause fibrotic and fat infiltrations that impair muscle function. We set out to perform a fluorescence microscopy-based screening to identify compounds that perturb the differentiation trajectories of these multipotent stem cells. From a primary screening of 1120 FDA/EMA approved drugs, we identified 34 compounds as potential inhibitors of adipogenic differentiation of FAPs isolated from the murine model (mdx) of Duchenne muscular dystrophy (DMD). To our surprise we found the hit list enriched for the glucocorticoid chemical class (GCs). Glucorticoids are often described as drugs that promote adipogenesis in vitro and in vivo. To shed light on conflicting reports we further characterized by different approaches three GCs identified in our screening focusing on budesonide a potent inhibitor of adipogenesis. We found that, similarly to dexamethasone, budesonide inhibits adipogenesis induced by insulin on subconfuent FAPs. However, both drugs have a proadipogenic impact when the adipogenic mix contains factors that increase the concentration of cAMP. By gene expression analysis we observed that treatment with glucocorticoids induces the transcription of Gilz/Tsc22d3, an inhibitor of the adipogenic master regulator PPARγ, only in antiadipogenic conditions. Finally, we noticed that alongside their anti-adipogenic effect, GCs promote terminal differentiation of satellite cells. Both the pro-adipogenic and pro-myogenic effects are mediated by the glucocorticoid receptor as they are not observed in the presence of receptor inhibitor. Steroid administration currently represents the standard treatment of DMD patients, the rationale being based on their antiinflammatory effects. The findings presented here offer new insights on additional glucocorticoid effects on muscle stem cells that may affect muscle homeostasis and physiology.

Adipogenesis of skeletal muscle fibro/adipogenic progenitors is affected by the WNT5a/GSK3/β-catenin axis

“…To identify crucial hubs affecting FAP adipogenesis, we applied a fluorescence microscopy-based screening [46] of a small molecule library targeting the mouse kinome. FAPs were purified as CD45 − /CD31 − /ITGA7 − /SCA1 + from the hind limbs of mdx mice and cultured in pro-adipogenic condition (1 μg/ml insulin) for 7 days [31,47] (Fig.…”

Fibro-adipogenic progenitors in skeletal muscle homeostasis, regeneration and diseases

“…A similar increase in adipogenesis was also observed in vivo following daily injection of prednisone, another glucocorticoid, in dystrophic mice [ 114 ]. Recent findings also suggest that glucocorticoids can have pro- or anti-adipogenic effects on FAPs depending on the type of glucocorticoids used and on the culture conditions [ 115 ]. For instance, glucocorticoids such as halcinonide and clobetasol have no effect on adipogenesis, while budesonide has anti-adipogenic effect in vitro [ 115 ].…”

“…Recent findings also suggest that glucocorticoids can have pro- or anti-adipogenic effects on FAPs depending on the type of glucocorticoids used and on the culture conditions [ 115 ]. For instance, glucocorticoids such as halcinonide and clobetasol have no effect on adipogenesis, while budesonide has anti-adipogenic effect in vitro [ 115 ]. This anti-adipogenic effect of budesonide was only observed when FAPs were actively proliferating in vitro .…”

“…This anti-adipogenic effect of budesonide was only observed when FAPs were actively proliferating in vitro . Conversely, budesonide has a pro-adipogenic effect when FAPs are confluent and are incubated in adipogenic induction medium [ 115 ]. Overall, while glucocorticoids preserve muscle function by reducing inflammation, there is room for improvement to develop therapeutic drugs targeting FAPs, directly or indirectly, to promote their beneficial effects (e.g.…”

Promoting endogenous repair of skeletal muscle using regenerative biomaterials

“…[37][38][39][40] In fact, certain drugs have been found to enhance FAP apoptosis 204 as well as alter their differentiation. 205 One can imagine incorporating these agents into biomaterials to actively decrease fibrosis and adipogenesis after severe injury. Some of the biggest issues still to overcome include the large variability in geometry of injured muscle and scalability as most studies are currently being performed in small animals which require smaller amounts of material.…”