MTOR and osteoporosis: MacFarlane et al. (2017) proposed that TGF-β is a multifunctional cytokine closely related to bone metabolism and a potential marker to measure osteoporosis. Zhang et al. (2019) showed that TGF-β1 promoted the survival, osteogenic differentiation, and migration of osteoblasts through the PI3K/AKT/mTOR/S6 kinase 1 signaling pathway.