Bone remodeling is a continuous process that maintains the homeostasis of the skeletal system, and it depends on the homeostasis between bone-forming osteoblasts and bone-absorbing osteoclasts. A large number of studies have confirmed that the Smad signaling pathway is essential for the regulation of osteoblastic and osteoclastic differentiation during skeletal development, bone formation and bone homeostasis, suggesting a close relationship between Smad signaling and bone remodeling. It is known that Smads proteins are pivotal intracellular effectors for the members of the transforming growth factor-β (TGF-β) and bone morphogenetic proteins (BMP), acting as transcription factors. Smad mediates the signal transduction in TGF-β and BMP signaling pathway that affects both osteoblast and osteoclast functions, and therefore plays a critical role in the regulation of bone remodeling. Increasing studies have demonstrated that a number of Smad signaling regulators have potential functions in bone remodeling. Therefore, targeting Smad dependent TGF-β and BMP signaling pathway might be a novel and promising therapeutic strategy against osteoporosis. This article aims to review recent advances in this field, summarizing the influence of Smad on osteoblast and osteoclast function, together with Smad signaling regulators in bone remodeling. This will facilitate the understanding of Smad signaling pathway in bone biology and shed new light on the modulation and potential treatment for osteoporosis.
Satisfactory repair of damaged articular cartilage is still a challenge, while tissue engineering provides a promising strategy. Collagen-based hydrogels have been widely applied in cartilage tissue engineering due to their biocompatibility. In this study, type I collagen and type II collagen were selected to prepare physically crosslinked composite hydrogels by self-assembly of collagen, and the effects of their physicochemical properties on chondrocyte phenotype maintenance and extracellular matrix (ECM) secretion were investigated. First, the microstructure of hydrogels was observed by a scanning electron microscope, and the compressive modulus was measured by a dynamic mechanical analyzer. Then, chondrocytes were encapsulated in hydrogels and detected by Live/Dead staining. The secretion of ECM was qualitatively estimated by histological staining and quantitatively analyzed by sulfated glycosaminoglycans and DNA content detection. Finally, cartilage-specific gene expression was analyzed by quantitative real-time polymerase chain reaction analysis. The results showed that the microstructure and mechanical property of hydrogels were relevant to the composition of composite hydrogels. The compressive modulus of hydrogels improved with the increase of type I collagen content in the hydrogels. Chondrocytes could maintain their round or oval morphology and secrete cartilage-specific ECM in the four groups of hydrogels, but higher the compressive modulus of composite hydrogels, the more ECM secretion of chondrocytes.
In recent years, research on wound healing has become increasingly in-depth, but therapeutic effects are still not satisfactory. Occasionally, pathological tissue repair occurs. Influencing factors have been proposed, but finding the turning point between normal and pathological tissue repair is difficult. Therefore, we focused our attention on the most basic level of tissue repair: fibroblasts. Fibroblasts were once considered terminally differentiated cells that represent a single cell type, and their heterogeneity was not studied until recently. We believe that subpopulations of fibroblasts play different roles in tissue repair, resulting in different repair results, such as the formation of normal scars in physiological tissue repair and fibrosis or ulcers in pathological tissue repair. It is also proposed that scarless healing can be achieved by regulating fibroblast subpopulations.
We report the fabrication and post-functionalization of a highly stretchable hydrogel tube and its potential application as an artificial blood vessel.
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