Expression of beta1 integrins during periosteal chondrogenesis

Osteogenic and Chondrogenic Potential of Periosteum-Derived Mesenchymal Stromal Cells: Do They Hold the Key to the Future?

The periosteum, with its outer fibrous and inner cambium layer, lies in a dynamic environment with a niche of pluripotent stem cells for their reparative needs. The inner cambium layer is rich in mesenchymal progenitors, osteogenic progenitors, osteoblasts, and fibroblasts in a scant collagen matrix environment. Their role in union and remodeling of fracture is well known. However, the periosteum as a source of mesenchymal stem cells has not been explored in detail. Moreover, with the continuous expansion of techniques, newer insights have been acquired into the roles and regulation of these periosteal cells. From a therapeutic standpoint, the periosteum as a source of tissue engineering has gained much attraction. Apart from its role in bone repair, analysis of the bone-forming potential of periosteum-derived stem cells is lacking. Hence, this article elucidates the role of the periosteum as a potential source of mesenchymal stem cells along with their capacity for osteogenic and chondrogenic differentiation for therapeutic application in the future.

Polycaprolactone Triol-Citrate Scaffolds Enriched with Human Platelet Releasates Promote Chondrogenic Phenotype and Cartilage Extracellular Matrix Formation

In this paper we report the differentiating properties of platelet-rich plasma releasates (PRPr) on human chondrocytes within elastomeric polycaprolactone triol-citrate (PCLT-CA) porous scaffold. Human-derived chondrocyte cellular content of glycosaminoglycans (GAGs) and total collagen were determined after seeding into PCLT-CA scaffold enriched with PRPr cells. Immunostaining and real time PCR was applied to evaluate the expression levels of chondrogenic and extracellular gene markers. Seeding of chondrocytes into PCLT-CA scaffold enriched with PRPr showed significant increase in total collagen and GAGs production compared with chondrocytes grown within control scaffold without PRPr cells. The mRNA levels of collagen II and SOX9 increased significantly while the upregulation in Cartilage Oligomeric Matrix Protein (COMP) expression was statistically insignificant. We also report the reduction of the expression levels of collagen I and III in chondrocytes as a consequence of proximity to PRPr cells within the scaffold. Interestingly, the pre-loading of PRPr caused an increase of expression levels of following extracellular matrix (ECM) proteins: fibronectin, laminin and integrin β over the period of 3 days. Overall, our results introduce the PCLT-CA elastomeric scaffold as a new system for cartilage tissue engineering. The method of PRPr cells loading prior to chondrocyte culture could be considered as a potential environment for cartilage tissue engineering as the differentiation and ECM formation is enhanced significantly.

Phytoestrogen (Daidzein) Promotes Chondrogenic Phenotype of Human Chondrocytes in 2D and 3D Culture Systems

Clinical investigations have shown a significant relationship between osteoarthritis (OA) and estrogens levels in menopausal women. Therefore, treatment with exogenous estrogens has been shown to decrease the risk of OA. However, the effect estrogen has not been clearly demonstrated in the chondrocytes using phytoestrogens, which lack the specific side-effects of estrogens, may provide an alternative therapy. This study was designed to examine the possible effects of phytoestrogen (daidzein) on human chondrocyte phenotype and extracellular matrix formation. Phytoestrogens which lack the specific side-effects of estrogens may provide beneficial effect without causing hormone based side effect. Human chondrocytes cells were cultured in 2D (flask) and 3D (PCL-CA scaffold) systems. Daidzein cytotoxic effect was determined by MTT assay. Chondrocyte cellular content of glycosaminoglycans (GAGs), total collagen and chondrogenic gene expression were determined in both culture systems after treatment with daidzein. Daidzein showed time-dependent and dose-independent effects on chondrocyte bioactivity. The compound at low doses showed significant (p < 0.05) increase in total collagen and GAGs production at similar levels in 2D and 3D culture environment. The mRNA levels of Collagen II and Sox9 were increased significantly (p < 0.01) after the treatment while the upregulation in COMP expression was statistically insignificant (p > 0.05). The expression levels of Fibronectin, Laminin and Integrin β1 were significantly increased especially in 3D culture system. This study was illustrated the potential positive effects of daidzein on maintenance of human chondrocyte phenotype and extracellular matrix formation suggesting an attractive and viable alternative therapy for OA.

Two non-coding RNAs, MicroRNA-101 and HOTTIP contribute cartilage integrity by epigenetic and homeotic regulation of integrin-α1

Non-coding RNAs have been less studied in cartilage development and destruction regulated by sophisticated molecular events despite their considerable theranostic potential. In this study, we identified significant down-regulation of mR-101 and up-regulation of lncRNA, HOTTIP in the processes of endochondral ossification and osteoarthritic progression. In wing mesenchymal cells, up-expression of miR-101 by TGF-β3 treatment is targeting DNMT-3B and thereby altered the methylation of integrin-α1 addressed as a positive regulator of endochondral ossification in this study. In like manner, down-regulation of miR-101 also coordinately up-regulated DNMT-3B, down-regulated integrin-α1, and resulted in cartilage destruction. In an OA animal model, introduction of lentiviruses that encoded miR-101 or integrin-α1 successfully reduced cartilage destruction. In like manner, long non-coding RNA (lncRNA), HOTTIP, a known regulator for HoxA genes, was highly up-regulated and concurrent down-regulation of HoxA13 displayed the suppression of integrin-α1 in OA chondrocytes. In conclusion, two non-coding RNAs, miR-101 and HOTTIP regulate cartilage development and destruction by modulating integrin-α1 either epigenetically by DNMT-3B or transcriptionally by HoxA13 and data further suggest that these non-coding RNAs could be a potent predictive biomarker for OA as well as a therapeutic target for preventing cartilage-related diseases.

The use of a vascularised periosteal patch onlay graft in the management of nonunion of the proximal scaphoid

We describe the use of a vascularised periosteal patch onlay graft based on the 1,2 intercompartmental supraretinacular artery in the management of 11 patients (ten men, one woman) with chronic nonunion involving the proximal third of the scaphoid. The mean age of the patients was 31 years (21 to 45) with the dominant hand affected in eight. Six of the patients were smokers and three had undergone previous surgery to the scaphoid. All of the proximal fragments were avascular. The presence of union was assessed using longitudinal axis CT.

Only three patients progressed to union of the scaphoid and four required a salvage operation for a symptomatic nonunion. The remaining four patients with a persistent nonunion are asymptomatic with low pain scores, good grip strength and a functional range of wrist movement.

Although this technique has potential technical advantages over vascularised pedicled bone grafting, the rate of union has been disappointing and we do not recommend it as a method of treatment.

Major biological obstacles for persistent cell-based regeneration of articular cartilage

Hyaline articular cartilage, the load-bearing tissue of the joint, has very limited repair and regeneration capacities. The lack of efficient treatment modalities for large chondral defects has motivated attempts to engineer cartilage constructs in vitro by combining cells, scaffold materials and environmental factors, including growth factors, signaling molecules, and physical influences. Despite promising experimental approaches, however, none of the current cartilage repair strategies has generated long lasting hyaline cartilage replacement tissue that meets the functional demands placed upon this tissue in vivo. The reasons for this are diverse and can ultimately result in matrix degradation, differentiation or integration insufficiencies, or loss of the transplanted cells and tissues. This article aims to systematically review the different causes that lead to these impairments, including the lack of appropriate differentiation factors, hypertrophy, senescence, apoptosis, necrosis, inflammation, and mechanical stress. The current conceptual basis of the major biological obstacles for persistent cell-based regeneration of articular cartilage is discussed, as well as future trends to overcome these limitations.

Temporal evolution of mechanical properties of skeletal tissue regeneration in rabbits: an experimental study

Various mathematical models represent the effects of local mechanical environment on the regulation of skeletal regeneration. Their relevance relies on an accurate description of the evolving mechanical properties of the regenerating tissue. The object of this study was to develop an experimental model which made it possible to characterize the temporal evolution of the structural and mechanical properties during unloaded enchondral osteogenesis in the New Zealand rabbit, a standard animal model for studies of osteogenesis and chondrogenesis. A 25 mm segment of tibial diaphysis was removed sub-periosteally from rabbits. The defect was repaired by the preserved periosteum. An external fixator was applied to prevent mechanical loading during osteogenesis. The regenerated skeletal tissues were studied by CT scan, histology and mechanical tests. The traction tests between 7 and 21 days post-surgery were done on formaldehyde-fixated tissue allowing to obtain force/displacement curves. The viscoelastic properties of the regenerating skeletal tissues were visualized throughout the repair process.

The healing potential of the periosteum molecular aspects

The presence of pluripotential mesenchymal cells in the under surface of the periosteum in combination with growth factors regularly produced or released after injury, provide this unique tissue with an important role in the healing of bone and cartilage. The periosteum contributes in the secondary callus formation with cells and growth factors and should always be preserved and protected when surgery is performed for the management of a fracture. The current evidence about the cellular interactions, the stimulants and the signalling pathways related to osteogenesis and chondrogenesis is described. An essential knowledge of the basics related to the contribution of the periosteum in the healing of fractures, osteotomies, during the process of distraction osteogenesis and in some degree in the repair of cartilagenous defects, provides the surgeons with a better insight to understand the upcoming "biological" interventions in the management of skeletal injuries.

The role of very late antigen-1 in immune-mediated inflammation

The alpha1beta1 integrin, also known as "very late antigen" (VLA)-1, is normally expressed on mesenchymal cells, some epithelial cells, activated T cells, and macrophages, and interacts, via the I-domain of the extracellular domain of the alpha1 subunit, with collagen molecules in the extracellular matrix (ECM). By "outside-in" transmembranal signaling to the interior of the cell, it mediates adhesion, migration, proliferation, remodeling of the ECM, and cytokine secretion by endothelial cells, mesangial cells, fibroblasts, and immunocytes. Importantly, its expressions and functions are enhanced by inflammatory cytokines including interferon (IFN)gamma and tumor necrosis factor (TNF)alpha, thus augmenting angiogenesis and fibrosis linked, in particular, to inflammation. Moreover, within the immune system, VLA-1 marks effector memory CD4+ and CD8+ T cells that are retained in extralymphatic tissues by interactions of the integrin with collagen and produce high levels of IFNgamma. Thus, immune-mediated inflammation in vivo is inhibited by blockade of the VLA-1-collagen interaction in experimental animal models of arthritis, colitis, nephritis, and graft versus host disease (GVHD), suggesting that inhibiting the interaction of the alpha1 I-domain with its ligands or modulating "outside-in" signaling by VLA-1 would be a useful approach in the human diseases simulated by these experimental models.

Accelerated, aging-dependent development of osteoarthritis in alpha1 integrin-deficient mice

OBJECTIVE

Cell-matrix interactions regulate chondrocyte differentiation and survival. The alpha1beta1 integrin is a major collagen receptor that is expressed on chondrocytes. Mice with targeted inactivation of the integrin alpha1 gene (alpha1-KO mice) provide a model that can be used to address the role of cell-matrix interactions in cartilage homeostasis and osteoarthritis (OA) pathogenesis.

METHODS

Knee joints from alpha1-KO and wild-type (WT) BALB/c mice were harvested at ages 4-15 months. Knee joint sections were examined for inflammation, cartilage degradation, and loss of glycosaminoglycans (by Safranin O staining). Immunohistochemistry was performed to detect the distribution of alpha1 integrin, matrix metalloproteinases (MMPs), and chondrocyte apoptosis.

RESULTS

In WT mice, the alpha1 integrin subunit was detected in hypertrophic chondrocytes in the growth plate and in a subpopulation of cells in the deep zone of articular cartilage. There was a marked increase in alpha1-positive chondrocytes in the superficial and upper mid-zones in OA-affected areas in joints from old WT mice. The alpha1-KO mice showed more severe cartilage degradation, glycosaminoglycan depletion, and synovial hyperplasia as compared with the WT mice. MMP-2 and MMP-3 expression was increased in the OA-affected areas. In cartilage from alpha1-KO mice, the cellularity was reduced and the frequency of apoptotic cells was increased. These results suggest that the alpha1 integrin subunit is involved in the early remodeling process in OA cartilage.

CONCLUSION

Deficiency in the alpha1 integrin subunit is associated with an earlier deregulation of cartilage homeostasis and an accelerated, aging-dependent development of OA.

Induction of CD-RAP mRNA during periosteal chondrogenesis

Induction of chondrogenesis and maintenance of the chondrocyte phenotype are critical events for autologous periosteal transplantation, which is a viable approach for cartilage repair. Cartilage-derived retinoic acid-sensitive protein (CD-RAP) is a recently discovered protein that is mainly produced in cartilage. During development, CD-RAP expression starts at the beginning of chondrogenesis and continues throughout cartilage maturation. In order to investigate the involvement of CD-RAP during periosteal chondrogenesis we have determined the nucleotide sequence of the rabbit CD-RAP mRNA and utilized this information to evaluate the temporal and spatial expression pattern of CD-RAP at the mRNA level during chondrogenesis. When the periosteal explants were cultured under chondrogenic conditions, the expression of CD-RAP was induced, as shown by a 40-fold increase in CD-RAP mRNA between days 7 and 10. The temporal expression pattern of CD-RAP closely mimicked that of collagen type IIB mRNA. Also, the CD-RAP mRNA was localized to the matrix forming chondrocytes in the cambium layer of the periosteum by in situ hybridization as indicated by colocalization with collagen type II mRNA and positive safranin O staining. These data suggest a regulatory role of CD-RAP in periosteal chondrogenesis, which is potentially important for both cartilage repair and fracture healing via callus formation.