Transforming growth factor-beta2 (TGF-β2) is recognized as a versatile cytokine that plays a vital role in regulation of joint development, homeostasis, and diseases, but its role as a biological mechanism is understood far less than that of its counterpart, TGF-β1. Cartilage as a load-resisting structure in vertebrates however displays a fragile performance when any tissue disturbance occurs, due to its lack of blood vessels, nerves, and lymphatics. Recent reports have indicated that TGF-β2 is involved in the physiological processes of chondrocytes such as proliferation, differentiation, migration, and apoptosis, and the pathological progress of cartilage such as osteoarthritis (OA) and rheumatoid arthritis (RA). TGF-β2 also shows its potent capacity in the repair of cartilage defects by recruiting autologous mesenchymal stem cells and promoting secretion of other growth factor clusters. In addition, some pioneering studies have already considered it as a potential target in the treatment of OA and RA. This article aims to summarize the current progress of TGF-β2 in cartilage development and diseases, which might provide new cues for remodelling of cartilage defect and intervention of cartilage diseases

Background

Treatment of cartilage defects requires in vitro expansion of human articular chondrocytes (HACs) for autologous chondrocyte implantation (ACI). During standard expansion culture (i.e. plasma osmolarity, 280 mOsm) chondrocytes inevitably lose their specific phenotype (i.e. collagen type II (COL2) expression). This de-differentiation makes them inappropriate for ACI. Physiological osmolarity (i.e. 380 mOsm) improves COL2 expression in vitro, but the underlying reason is unknown. However, an accepted key regulator of chondrocyte differentiation, transforming growth factor beta (TGFβ), is known to stimulate COL2 production. In this study we aimed to elucidate if TGFβ signaling could potentially be driving the COL2 expression under physiological culture conditions.

Aims. Developmental dysplasia of the hip (DDH) is a complex musculoskeletal disease that occurs mostly in children. This study aimed to investigate the molecular changes in the hip joint capsule of patients with DDH. Methods. High-throughput sequencing was used to identify genes that were differentially expressed in hip joint capsules between healthy controls and DDH patients. Biological assays including cell cycle, viability, apoptosis, immunofluorescence, reverse transcription polymerase chain reaction (RT-PCR), and western blotting were performed to determine the roles of the differentially expressed genes in DDH pathology. Results. More than 1,000 genes were differentially expressed in hip joint capsules between healthy controls and DDH. Both gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that extracellular matrix (ECM) modifications, muscle system processes, and cell proliferation were markedly influenced by the differentially expressed genes. Expression of Collagen Type I Alpha 1 Chain (COL1A1), COL3A1, matrix metalloproteinase-1 (MMP1), MMP3, MMP9, and MMP13 was downregulated in DDH, with the loss of collagen fibres in the joint capsule. Expression of transforming growth factor beta 1 (TGF-β1) was downregulated, while that of TGF-β2, Mothers against decapentaplegic homolog 3 (SMAD3), and WNT11 were upregulated in DDH, and alpha smooth muscle actin (αSMA), a key myofibroblast marker, showed marginal increase. In vitro studies showed that fibroblast proliferation was suppressed in DDH, which was associated with cell cycle arrest in G0/G1 and G2/M phases. Cell cycle regulators including Cyclin B1 (CCNB1), Cyclin E2 (CCNE2), Cyclin A2 (CCNA2), Cyclin-dependent kinase 1 (CDK1), E2F1, cell division cycle 6 (CDC6), and CDC7 were downregulated in DDH. Conclusion. DDH is associated with the loss of collagen fibres and fibroblasts, which may cause loose joint capsule formation. However, the degree of differentiation of fibroblasts to myofibroblasts needs further study. Cite this article: Bone Joint Res 2021;10(9):558–570

Introduction. In vitro expansion of human articular chondrocytes (HACs) is required for cell-based strategies to treat cartilage defects. We have earlier shown that culturing HACs at increased osmolarity (i.e., 380 mOsm), as compared to plasma osmolarity (i.e., 280 mOsm), increases collagen type II (COL2A1) expression in vitro. Our earlier results showed that knockdown of TGF-β2, a prototypic member of the TGF-β superfamily and an accepted key regulator of chondrocyte differentiation, resulted in increased COL2A1 production. BMPs are members of the TGF-β superfamily which are known to be involved in the regulation of COL2A1 expression. In this study, we aimed to elucidate the role of BMP signaling, in the upregulation of COL2 production upon TGF-β2 knockdown (KD) under hyperosmotic culture conditions. Methods. HACs from five OA patients (passage 1) were cultured in cytokine-free medium, under 280 or 380 mOsm respectively, under standard 2D in vitro conditions. TGF-β2 knockdown (KD) by siRNA was performed in the presence or absence of the established bone morphogenetic protein (BMP) type I receptor (BMPRI) inhibitor dorsomorphin (10 μM). Expression of COL2A1 was evaluated by qRT-PCR. Results. Culturing HACs at 380 mOsm increased COL2A1 mRNA expression. Addition of dorsomorphin decreased COL2A1 mRNA expression at both 280 and 380 mOsm, but its expression was still significantly higher at 380 mOsm. In hyperosmotic 380 mOsm culture conditions, TGF-β2 KD further increased COL2A1 mRNA expression, while addition of dorsomorphin under these conditions abrogated this effect. Still, expression of COL2A1 mRNA levels remained higher as compared to 280 mOsm. Conclusion. This study confirms that BMP signalling is involved in the expression of the single best accepted key chondrocyte marker, COL2A1, in osteoarthritic HACs. However, inhibition of BMP signalling could not abrogate the increase in COL2A1 expression under hyperosmotic culture conditions. Our data suggest an inverse regulation of TGF-β2 and COL2A1, under these conditions, which may largely be dependent on increased BMPRI-mediated cell signaling. Our findings further suggest that hyperosmotic culture improves COL2A1 expression by means that are independent of TGF-β- and BMPRI-signaling. Further elucidation of the molecular network underlying this observation is ongoing

The structure and extracellular matrix composition of the interface are complex and allow for a gradual mechanical stress transfer between tendons and bone. In this study, biphasic silk fibroin scaffolds designed to mimic the gradient in collagen molecule alignment present at the interface. The scaffolds had two different pore alignments: anisotropic at the tendon side and isotropic at the bone side. Total porosity ranged from 50–80% and the majority of pores were <100–300 µm. Young's modulus varied from 689–1322 kPa. In addition, human adMSC were cultured on the scaffolds to evaluate the effect of pore morphology on cell proliferation and gene expression. Biphasic scaffolds supported cell attachment and influenced cytoskeleton organization depending on pore alignment. In addition, the gene expression of tendon, enthesis and cartilage markers significantly changed in each region of the scaffolds. We functionalized those scaffolds with heparin and explored their ability to deliver TGF-β2 and GDF5. TGF-β2 and pore anisotropy synergistically increased the expression of tendon/ligament markers and collagen I protein content. The combined delivery of TGF-β2 and GDF5 enhanced the expression of cartilage markers and collagen II protein content on substrates with isotropic porosity, whereas enthesis markers were enhanced in areas of mixed anisotropic/isotropic porosity

Adult chondrocytes experience a hypoxic environment in vivo. Culturing chondrocytes under oxygen tension that more closely resembles the in vivo situation, i.e. hypoxic conditions, has been shown to have positive effects on matrix synthesis. During redifferentiation of expanded chondrocytes, hypoxia increased collagen type II expression. However, the mechanism by which hypoxia enhances redifferentiation is still incompletely elucidated. We employed micro-bioreactor technology to elucidate the contribution of TGF-β superfamily ligands to the chondrocyte differentiation process under hypoxic conditions in vitro. Dedifferentiated chondrocytes in alginate were cultured for 48 hours under hypoxic (1% pO2) or normoxic (20%) conditions, using specialized bioreactor technology. Gene expression of chondrocyte-specific markers (SOX9, COL2A1, COL1A1, AGC1 and MMP13) as well as established hypoxia-controlled genes (GDF1-, PHD3, HAS2, VEGF, COX2) and components of the TGF-β superfamily signaling pathways were analyzed by qPCR and protein expression after 48 hours in combination with TGF-β superfamily ligand-specific siRNA as well as selected TGF-β superfamily receptor inhibitors. Hypoxic culture showed robust upregulation of the selected hypoxia-specific marker genes. In addition, well-established chondrocyte-specific markers like SOX9 and collagen type II were upregulated. TGF-β isoforms were selectively upregulated under hypoxia on both mRNA and protein level. In addition, both Activin receptor-like kinases, ALK1 and ALK5, were upregulated under hypoxia, while respective type II and III receptors were unresponsive. The hypoxia-induced COL2 expression was abrogated by TGF-β2 siRNA, as was ALK5 inhibition. Our data strongly indicates that TGF-β superfamily signaling pathways are involved in chondrocyte redifferentiation under low oxygen tension in vitro

Aims

The lack of disease-modifying treatments for osteoarthritis (OA) is linked to a shortage of suitable biomarkers. This study combines multi-molecule synovial fluid analysis with machine learning to produce an accurate diagnostic biomarker model for end-stage knee OA (esOA).

Objectives

Many in vitro studies have investigated the mechanism by which mechanical signals are transduced into biological signals that regulate bone homeostasis via periodontal ligament fibroblasts during orthodontic treatment, but the results have not been systematically reviewed. This review aims to do this, considering the parameters of various in vitro mechanical loading approaches and their effects on osteogenic and osteoclastogenic properties of periodontal ligament fibroblasts.

Objectives

The biomembrane (induced membrane) formed around polymethylmethacrylate (PMMA) spacers has value in clinical applications for bone defect reconstruction. Few studies have evaluated its cellular, molecular or stem cell features. Our objective was to characterise induced membrane morphology, molecular features and osteogenic stem cell characteristics.