Castonguay, R. | Search bioRxiv

bioRxiv2023

Myostatin is a major endocrine driver of follicle-stimulating hormone synthesis

Myostatin is a paracrine myokine that regulates muscle mass in a variety of species, including humans. Here, we report a functional role for myostatin as an endocrine hormone directly promoting pituitary follicle-stimulating hormone (FSH) synthesis and thereby ovarian function. Previously, this FSH-stimulating role was attributed to other members of the transforming growth factor {beta} family, the activins. The results both challenge activins eponymous role in FSH synthesis and establish an endocrine axis between skeletal muscle and the pituitary gland. The data also suggest that efforts to antagonize myostatin to treat muscle wasting disorders may have unintended consequences on fertility. One-Sentence SummaryHormone synthesis and reproduction depend on crosstalk between skeletal muscle and the pituitary gland.

physiology↗

bioRxiv2022

The orphan ligand, Activin C, signals through activin receptor-like kinase 7

Activin ligands are formed from two disulfide-linked inhibin {beta} subunit chains. They exist as homodimeric proteins, as in the case of activin A (ActA; Inh{beta}A/Inh{beta}A) or activin C (ActC; Inh{beta}C/Inh{beta}C), or as heterodimers, as with activin AC (ActAC; Inh{beta}A:Inh{beta}C). While the biological functions of ActA and activin B (ActB) have been well-characterized, little is known about the biological function of ActC or ActAC. One thought is that the Inh{beta}C chain functions to interfere with ActA production by forming less active ActAC heterodimers. Here, we assessed and characterized the signaling capacity of ligands containing the Inh{beta}C chain. ActC and ActAC activated SMAD2/3-dependent signaling via the type I receptor, activin receptor-like kinase 7 (ALK7). Relative to ActA and ActB, ActC exhibited lower affinity for the cognate activin type II receptors and was resistant to neutralization by the extracellular antagonist, follistatin. In mature adipocytes, which exhibit high ALK7 expression, ActC elicited a SMAD2/3 response similar to ActB, which can also signal via ALK7. Collectively, these results establish that ActC and ActAC are active ligands that exhibit a distinct signaling receptor and antagonist profile compared to other activins.

biochemistry↗