Biphasic effects of transforming growth factor β on bone morphogenetic protein–induced osteoblast differentiation

Abstract

Bone morphogenetic proteins (BMPs) exert an important role in skeletal development, adult bone homeostasis, and fracture healing and have demonstrated clinical utility for bone regeneration. However, BMPs fall short as regenerative agents because high doses need to be used to obtain therapeutic effects. Determining the molecular mechanisms controlling BMP-induced bone formation may lead to the development of more effective BMP-based therapies. To identify kinases mediating BMP-induced osteoblast differentiation, we performed an siRNA screen to find kinases modulating BMP-6-induced alkaline phosphatase (ALP) activity. Surprisingly, although transforming growth factor b (TGF-b) generally is considered to antagonize BMP-induced osteoblast differentiation, C2C12 cells transfected with siRNAs targeting TGF-b receptors displayed reduced BMP-6-induced ALP activity. Furthermore, pharmacologic inhibitors blocking the TGF-b type I receptor impaired BMP-induced ALP activity in KS483 and C2C12 cells and mineralization of KS483 cells. Consistently, costimulation with BMPs and TGF-b further increased expression of osteoblast-specific genes, ALP activity, and mineralization of KS483 cells and primary mesenchymal stem cells compared with BMPs alone. The stimulatory and inhibitory effects of TGF-b were found to depend on timing and duration of the costimulation. TGF-b inhibited BMP-induced activation of a BMP-Smaddependent luciferase reporter, suggesting that the stimulatory effect of TGF-b is not due to increased BMP-Smad activity. TGF-b also inhibited the BMP-induced expression of the BMP antagonist noggin and prolonged BMP activity. In conclusion, TGF-b, besides acting as an inhibitor, also can, by dampening the noggin-mediated negative-feedback loop, enhance BMP-induced osteoblast differentiation, which might be beneficial in fracture healing. ß

Nano-biphasic calcium phosphate/polyvinyl alcohol composites with enhanced bioactivity for bone repair via low-temperature three-dimensional printing and loading with platelet-rich fibrin

“…61 TGF mainly recruits osteoblast precursors. 62 While some other researchers have tried to release single growth factors from scaffolds, the process of bone regeneration requires multiple growth factors working together to promote the activity of osteogenic-related cells. 63,64 The prolonged release of growth factors from PRF may provide proliferation and differentiation stimuli for BMSCs to promote bone formation.…”

Delayed Expression of Circulating TGF-β1 and BMP-2 Levels in Human Nonunion Long Bone Fracture Healing

“…Further studies showed biphasic effects of TGF-β on BMP in which TGF-β1, in addition to its action as an inhibitor, could enhance osteoblast differentiation induced by BMP through reducing the negative feedback loop mediated by noggin 26 . This might be useful in improving fracture healing.…”

Synergistic effect of BMP9 and TGF-β in the proliferation and differentiation of osteoblasts

“…The TGF-b-Smad signaling pathway is the most important intracellular signal transduction medium. Smad 2/3 can activate a large number of target genes such as collagen I, cell cycle regulator p15, and p21, among others (De Gorter et al, 2011), as well as cause cell gathering and osteogenesis (Bharadwaj et al, 2013;Gao et al, 2013;Knight and Hankenson, 2013). In this study, though single application of TGF-b failed to result in MSC transformation, strengthened late-stage osteogenesis and cell proliferation abilities were observed under combined use of TGF-b.…”