TGFB1 and osteoporosis: The proteins of the AFI axis are part of the TGF-β superfamily, and the AFI axis plays an important role in regulating reproductive function, tissue development, insulin sensitivity (energy supply), muscle wasting, and osteoporosis (Bouzoni et al., 2022; Perakakis et al., 2019; Perakakis et al., 2018a; Perakakis et al., 2018b).