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Chondrocyte hypertrophy is a significant factor in cartilage development, yet the molecular mechanism for cell volume expand during the process is remains unclear. In the present study, the relationship between Swell1, a cell volume regulated anion channel, and chondrocyte hypertrophy was explored. The results reveal that the spatiotemporal expression of Swell1 was similar with the development process of hypertrophic chondrocytes in condyles. Through Col10a1 mediated knock out of Swell1 in hypertrophy chondrocytes, we found that there are less obvious boundary between different condylar cartilage layers in which increased hypertrophic chondrocytes were scattered in all three cartilage layers. The cortical bone mass and bone mineral density in the subchondral bone significantly increased. Additionally, knock out of Swell1 could increase the expression of OCN in the femur condyle. Based on the aforementioned findings, a conclusion could be drawn that Swell1 is a significant factor in chondrocyte hypertrophy during the condylar osteochondral development process, and there was some difference between the mandibular and femur condyles, which will provide some new clues for understanding the development of cartilage and related diseases.

Mesenchymal stem cell-derived exosomes (MSC-exos), with its inherent capacity to modulate cellular behavior, are emerging as a novel cell-free therapy for bone regeneration. Herein, focusing on practical applying problems, the osteoinductivity of MSC-exos produced by different stem cell sources (rBMSCs/rASCs) and culture conditions (osteoinductive/common) were systematically compared to screen out an optimized osteogenic exosome (BMSC-OI-exo). Via bioinformatic analyses by miRNA microarray and in vitro pathway verification by gene silencing and miRNA transfection, we first revealed that the osteoinductivity of BMSC-OI-exo was attributed to multi-component exosomal miRNAs (let-7a-5p, let-7c-5p, miR-328a-5p and miR-31a-5p). These miRNAs targeted Acvr2b/Acvr1 and regulated the competitive balance of Bmpr2/Acvr2b toward Bmpr-elicited Smad1/5/9 phosphorylation. On these bases, lyophilized delivery of BMSC-OI-exo on hierarchical mesoporous bioactive glass (MBG) scaffold was developed to realize bioactivity maintenance and sustained release by entrapment in the surface microporosity of the scaffold. In a rat cranial defect model, the loading of BMSC-OI-exo efficiently enhanced the bone forming capacity of the scaffold and induced rapid initiation of bone regeneration. This paper could provide empirical bases of MSC-exo-based therapy for bone regeneration and theoretical bases of MSC-exo-induced osteogenesis mechanism. The BMSC-OI-exo-loaded MBG scaffold developed here represented a promising bone repairing strategy for future clinical application.

Defects of either articular cartilage or subchondral bone would destroy the structural integrity and functionality of the joint. Reconstruction of osteochondral defects requires difunctional scaffolds that simultaneously induce cartilage and subchondral bone morphogenesis, however, high-performance cartilage reconstructive scaffolds remain a considerable challenge. In this study, a solvent-free urethane crosslinking and spontaneous pore-forming procedure under room temperature was proposed and optimized to produce PEGylated poly(glycerol sebacate) (PEGS) scaffolds with controllable crosslinking degrees and hierarchical macro-/micro-porosities. Based on the economical and feasible preparative approach, the viscoelastic PEGS-12h with low crosslinking degree was demonstrated to significantly stimulate chondrogenic differentiation, maintain chondrocyte phenotype and enhance cartilage matrix secretion compared to elastic polymer with high crosslinking degree, emphasizing the importance of matrix viscoelasticity in cartilage regeneration. On this basis, the viscoelastic low-crosslinked PEGS-12h was combined with the well-acknowledged osteoinductive mesoporous bioactive glass (MBG) to construct a difunctional PEGS/MBG bilayer scaffold, and evaluated in a full-thickness osteochondral defect model in vivo. The PEGS/MBG bilayer scaffold successfully reconstructed well-integrated articular hyaline cartilage and its subchondral bone in 12 weeks, exhibiting extraordinary regenerative efficiency. The results indicated that the viscoelastic PEGS scaffold and PEGS/MBG bilayer scaffold proposed in this study made an excellent candidate for cartilage and osteochondral regeneration, and was expected for clinical translation in the future.