Introduction: Muscle atrophy observed in several physio-pathological situations has harmful consequences for the patients and results from an imbalance between protein synthesis and proteolysis. With no proven treatment of muscle atrophy, there is still a need to develop efficient strategies. Activation of the transcription factor 4 (ATF4) is involved in muscle atrophy through the overexpression of some atrogenes, i.e. genes whose mRNA levels are regulated during muscle atrophy. However, ATF4 also controls the transcription of genes involved in muscle homeostasis maintenance (1), and a controlled activation of the eIF2alpha/ATF4 pathway before a stressful event preserved organ function (2).

Aim: Here, we explored whether such a controlled activation of ATF4 before induction of atrophy may preserve muscle function.

Method: For that purpose, mice were treated with the pharmacological molecule halofuginone (0.25mg/kg, 3 times a week) for 3 weeks, before inducing muscle atrophy by hindlimb suspension for 3 or 7 days. Data were analyzed by ANOVA and were considered statistically different between groups for p-values below 0.05.

Results: Firstly, we reported that periodic activation of ATF4-regulated atrogenes (Gadd45a, Cdkn1a, and Eif4ebp1) by halofuginone was not associated with muscle atrophy in untreated and treated healthy mice (6 mice/group). Secondly, the atrophy induced by hindlimb suspension was reduced in halofuginone-treated mice compared to untreated ones, although the induction of the ATF4 pathway by hindlimb suspension was identical in halofuginone treated and untreated mice (8-19 mice/group). We further showed that transforming growth factor-β (TGF-β) signaling was inhibited, while bone morphogenetic protein (BMP) signaling was promoted in halofuginone-treated healthy mice compared to untreated ones (5-8 mice/group). In addition, halofuginone treatment also slightly preserved protein synthesis during hindlimb suspension (5-8 mice/group). Finally, ATF4-regulated atrogenes were also induced in the atrophy-resistant muscles of hibernating compared to active brown bears (6 bears/group), in which we previously also reported concurrent TGF-β inhibition and BMP maintenance during hibernation (3).

Conclusions: Overall, we show that ATF4-induced atrogenes can be uncoupled from muscle atrophy. Our data also indicate that halofuginone can control the TGF-β/BMP balance toward muscle mass maintenance. Whether halofuginone-induced BMP signaling can counteract the effect of ATF4-induced atrogenes needs to be further investigated and may open a new avenue to fight muscle atrophy. Finally, our study opens the way for further studies to identify well-tolerated chemical compounds in humans that enable fine-tuning of the TGF-β/BMP balance and could be used to preserve muscle mass during catabolic situations.