Coralie Fontaine

Skeletal muscle stem cells (MuSC) are the guardians of muscle regeneration, sustaining tissue integrity through a delicate balance of quiescence, activation, and lineage commitment. While numerous molecular cues have been implicated in regulating these processes, the influence of androgen receptor (AR) signaling, an essential hormonal pathway for male muscle physiology, has remained largely unexplored. Here, we show that AR expression defines quiescent MuSC and acts as a safeguard of their dormancy. Integrated multiomic analyses reveal a redistribution of AR binding from quiescence-maintenance loci to regulatory elements driving activation and metabolic reprogramming during repair. Loss of AR in young adult mice disrupts this balance, precipitating premature cell-cycle entry, skewed division modalities, depletion of the stem cell reservoir, and destabilization of the niche. These defects converge with hallmarks of aging-associated androgen decline, while androgen supplementation restores regenerative competence. Together, our findings establish AR signaling as a pivotal determinant of MuSC fate and a cornerstone of skeletal muscle homeostasis.

SUMMARY: Skeletal muscle stem cells (MuSC) are the guardians of muscle regeneration, sustaining tissue integrity through a delicate balance of quiescence, activation, and lineage commitment. While numerous molecular cues have been implicated in regulating these processes, the influence of androgen receptor (AR) signaling, an essential hormonal pathway for male muscle physiology, has remained largely unexplored. Here, we show that AR expression defines quiescent MuSC and acts as a safeguard of their dormancy. Integrated multi-omic analyses reveal a redistribution of AR binding from quiescence-maintenance loci to regulatory elements driving activation and metabolic reprogramming during repair. Loss of AR in young adult mice disrupts this balance, precipitating premature cell-cycle entry, skewed division modalities, depletion of the stem cell reservoir, and destabilization of the niche. These defects converge with hallmarks of aging-associated androgen decline, while androgen supplementation restores regenerative competence. Together, our findings establish AR signaling as a pivotal determinant of MuSC fate and a cornerstone of skeletal muscle homeostasis.

Growth Differentiation Factor 15 (GDF15) is recognized as a biomarker of cardiovascular disease, but its role in atherosclerosis remains unclear. Here, we investigated the role of GDF15 in atherosclerosis by crossing GDF15-deficient mice with LDLr^-/- mice. Male GDF15^-/- LDLr^-/- mice fed a Western diet developed less atherosclerotic lesions than littermate controls despite exhibiting a pro-obesogenic phenotype, whereas GDF15 deficiency did not affect metabolism or lesion development in females. Plasma GDF15 levels were higher in male LDLr^-/- mice than in females but were comparable to those measured in ovariectomized LDLr^-/- females. Importantly, ovariectomy in females induced metabolic and vascular phenotypes similar to those of GDF15^-/- LDLr^-/- males, while gonadectomy in males had no effect, emphasizing the role of female steroid hormones in GDF15-related sexual dimorphism. These findings highlight the sex-specific effects of GDF15 on metabolism and atherosclerosis, underscoring the importance of sex and hormonal status in cardiometabolic disease management.

Les maladies cardiovasculaires (MCV) sont souvent perçues comme étant principalement masculines, alors qu’elles représentent la première cause de mortalité chez les femmes. Bien que les effets bénéfiques des œstrogènes soient bien établis chez les organismes jeunes, la question de savoir si les œstrogènes exogènes peuvent prolonger la protection contre les MCV après le début de la ménopause n’est toujours pas résolue. Cette revue décrit les études sur les effets des œstrogènes sur les artères, en mettant l’accent sur l’impact du vieillissement sur l’endothélium. Nous aborderons également l’impact de l’âge sur l’expression et la signalisation des récepteurs des œstrogènes (ER), avant d’exposer le progrès des connaissances sur les mécanismes d’action d’ERα afin d’optimiser le traitement hormonal de la ménopause.

The main estrogen, 17β-estradiol (E2), exerts several beneficial vascular actions through estrogen receptor α (ERα) in endothelial cells. However, the impact of other natural estrogens such as estriol (E3) and estetrol (E4) on arteries remains poorly described. In the present study, we report the effects of E3 and E4 on endothelial healing after carotid artery injuries in vivo. After endovascular injury, which preserves smooth muscle cells (SMCs), E2, E3, and E4 equally stimulated reendothelialization. By contrast, only E2 and E3 accelerated endothelial healing after perivascular injury that destroys both endothelial cells and SMCs, suggesting an important role of this latter cell type in E4’s action, which was confirmed using Cre/lox mice inactivating ERα in SMCs. In addition, E4 mediated its effects independently of ERα membrane-initiated signaling, in contrast with E2. Consistently, RNA sequencing analysis revealed that transcriptomic and cellular signatures in response to E4 profoundly differed from those of E2. Thus, whereas acceleration of endothelial healing by estrogens had been viewed as entirely dependent on endothelial ERα, these results highlight the very specific pharmacological profile of the natural estrogen E4, revealing the importance of dialogue between SMCs and endothelial cells in its arterial protection.

Flow-mediated dilation (FMD) of resistance arteries is essential for tissue perfusion but it decreases with ageing. As estrogen receptor alpha (Erα encoded by Esr1), and more precisely membrane ERα, plays an important role in FMD in young mice in a ligand-independent fashion, we evaluated its influence on this arteriolar function in ageing. We first confirmed that in young (6-month-old) mice, FMD of mesenteric resistance arteries was reduced in Esr1−/− (lacking ERα) and C451A-ERα (lacking membrane ERα). In old (24-month-old) mice, FMD was reduced in WT mice compared to young mice, whereas it was not further decreased in Esr1−/− and C451A-ERα mice. Markers of oxidative stress were similarly increased in old WT and C451A-ERα mice. Reduction in oxidative stress with superoxide dismutase plus catalase or Mito-tempo, which reduces mitochondrial superoxide restored FMD to a normal control level in young C451A-ERα mice as well as in old WT mice and old C451A-ERα mice. Estradiol-mediated dilation was absent in old WT mice. We conclude that oxidative stress is a key event in the decline of FMD, and that an early defect in membrane ERα recapitulates phenotypically and functionally ageing of these resistance arteries. The loss of this function could take part in vascular ageing.