Cartilage-derived morphogenetic proteins and cartilage morphogenesis

Doublecortin may play a role in defining chondrocyte phenotype

Embryonic development of articular cartilage has not been well understood and the role of doublecortin (DCX) in determination of chondrocyte phenotype is unknown. Here, we use a DCX promoter-driven eGFP reporter mouse model to study the dynamic gene expression profiles in mouse embryonic handplates at E12.5 to E13.5 when the condensed mesenchymal cells differentiate into either endochondral chondrocytes or joint interzone cells. Illumina microarray analysis identified a variety of genes that were expressed differentially in the different regions of mouse handplate. The unique expression patterns of many genes were revealed. Cytl1 and 3110032G18RIK were highly expressed in the proximal region of E12.5 handplate and the carpal region of E13.5 handplate, whereas Olfr538, Kctd15, and Cited1 were highly expressed in the distal region of E12.5 and the metacarpal region of E13.5 handplates. There was an increasing gradient of Hrc expression in the proximal to distal direction in E13.5 handplate. Furthermore, when human DCX protein was expressed in human adipose stem cells, collagen II was decreased while aggrecan, matrilin 2, and GDF5 were increased during the 14-day pellet culture. These findings suggest that DCX may play a role in defining chondrocyte phenotype.

Distinct patterns of gene expression in the superficial, middle and deep zones of bovine articular cartilage

Hyaline articular cartilage will not heal spontaneously, and lesions in hyaline articular cartilage often result in degenerative joint disease. Considerable progress has been made with respect to the responsive stem cells, inductive signals and extracellular scaffolding required for the optimal regeneration of cartilage. However, many challenges remain, such as topographic differences in the functional zones of articular cartilage. We hypothesized that a distinct set of differentially expressed genes define the surface, middle and deep zones of hyaline articular cartilage. Microarray analysis of bovine articular cartilage from the superficial and middle zones revealed 52 genes differentially expressed ≥ 10-fold and 114 additional genes differentially expressed ≥ five-fold. However, no genes were identified with a ≥ five-fold difference in expression when comparing articular cartilage from the middle and deep zones. There are distinct, differential gene expression patterns in the superficial and middle zones of hyaline articular cartilage that highlight the functional differences between these zones. This investigation has implications for the tissue engineering and regeneration of hyaline articular cartilage.

Bone morphogenetic proteins in tissue engineering: the road from the laboratory to the clinic, part I (basic concepts)

Discovered in 1965, bone morphogenetic proteins (BMPs) are a group of cytokines from the transforming growth factor-beta (TGFbeta) superfamily with significant roles in bone and cartilage formation. BMPs are used as powerful osteoinductive components of diverse tissue-engineering products for the healing of bone. Several BMPs with different physiological roles have been identified in humans. The purpose of this review is to cover the biological function of the main members of BMP family, the latest research on BMPs signalling pathways and advances in the production of recombinant BMPs for tissue engineering purposes.

The interface of functional biotribology and regenerative medicine in synovial joints

Biotribology is the science of biological surfaces in sliding contact encompassing the concepts of friction, wear, and lubrication of interacting surfaces. This bioscience field has emerged from the classical field of tribology and is of paramount importance to the normal function of numerous tissues, including articular cartilage, blood vessels, heart, tendons, ligaments, and skin. Surprisingly, relatively little attention has been given to the restoration of surface characteristics in the fields of tissue engineering and regenerative medicine-the science of design and manufacture of new tissues for the functional restoration of impaired or diseased organs that depend on inductive signals, responding stem cells, and extracellular matrix scaffolding. Analogous to ancient civilizations (c. 3000 B.C.) that introduced wheeled vehicles, sledges for transporting heavy blocks, and lubricants, modern biotribologists must aim to restore surface characteristics to regenerated tissues and develop novel biomaterials with optimal tribological properties. The objective of this article is to highlight the significance of functional biotribology in the physiology of body surfaces and provide a comprehensive overview of unresolved issues and controversies as it relates to regenerative medicine. Specific attention is placed on the molecular basis of lubrication, mechanical and biochemical regulation of lubricating molecules, and the need to study wear processes in articular cartilage, especially in light of degenerative diseases, such as osteoarthritis. Surface engineering of replacement tissues exhibiting low friction and high wear resistance is examined using articular cartilage as an illustrative model system.

Gene expression profiling of mouse articular and growth plate cartilage

Articular cartilage is recalcitrant to repair and regeneration. Tissue engineering and regenerative medicine are potential strategies to treat the damage to articular cartilage. A thorough understanding of the gene expression profiles in articular cartilage and growth plate chondrocytes will be an important prerequisite for tissue engineering of cartilage. Regeneration is a recapitulation of embryonic development and morphogenesis. We used laser capture microdissection to capture the surface articular chondrocytes and the resting zone chondrocytes of growth plate from 14-day-old C57BL/6J mice. Total RNA was individually purified, pooled, and amplified by two rounds of in vitro transcription. Labeled cRNA probes were analyzed using the Affymetrix GeneChip Mouse Genome 430 2.0 Array. We identified 107 genes that were highly expressed by the surface articular chondrocytes and 130 genes that were highly expressed by the resting zone chondrocytes of growth plate (> or = fivefold). The expression of major matrix proteins aggrecan and collagen II were similar, while several morphogens and growth factors were differentially expressed by the surface articular chondrocytes and the resting zone chondrocytes of growth plate. The results of this investigation will be of use in the evaluation of tissue engineered cartilage.

Limb bud progenitor cells induce differentiation of pluripotent embryonic stem cells into chondrogenic lineage

Pluripotent embryonic stem (ES) cells are the most versatile cells, with the potential to differentiate into all types of cells. However, the cellular and molecular mechanisms responsible for their differentiation into specific lineages have not been elucidated. Recent studies in human ES cells have challenged the scientific community to focus research on the basic mechanisms of stem cell differentiation for their potential applications in regenerative medicine and cell-based therapies. The majority of studies thus far have focused on cells that are already committed to specific lineages. The current studies were designed to establish a system for investigating the mechanisms of cell fate determination starting from undifferentiated ES cells, to gain insight into events during the normally inaccessible period of development. Here we demonstrate that pluripotent ES cells can be programmed to differentiate into chondrocytes, the cartilage-producing cells, by co-culture with progenitor cells from the limb buds of the developing embryo. Almost 60%-80% of the cells exhibited phenotypic characteristics of mature chondrocytes and expressed genes such as sox9, collagen type II, and proteoglycans, which was accompanied by a decrease in ES cell-specific transcription factor Oct-4. Collagen type II, which is expressed in two different forms during chondrogenic differentiation due to the alternate splicing of mRNA, was also properly regulated. The studies presented here suggest that the signals produced by progenitor cells from the developing embryo can induce lineage-specific differentiation. The system described here may serve as an in vitro model to study the mechanisms of cell fate determination by stem cells.

Bone growth factors in maxillofacial skeletal reconstruction

A literature review was performed to survey the available information on the potential of bone growth factors in skeletal reconstruction in the maxillofacial area. The aim of this review was to characterize the biological and developmental nature of the growth factors considered, their molecular level of activity and their osteogenic potential in craniofacial bone repair and reconstruction. A total of 231 references were selected for evaluation by the content of the abstracts. All growth factors considered have a fundamental role in growth and development. In postnatal skeletal regeneration, PDGF plays an important role in inducing proliferation of undifferentiated mesenchymal cells. It is an important mediator for bone healing and remodelling during trauma and infection. It can enhance bone regeneration in conjunction with other growth factors but is unlikely to provide entirely osteogenic properties itself. IGFs have an important role in general growth and maintenance of the body skeleton. The effect of local application of IGFs alone in craniofacial skeletal defects has not yet shown a clear potential for enhancement of bone regeneration in the reported dosages. The combination of IGF-I with PDGF has been effective in promoting bone regeneration in dentoalveolar defects around implants or after periodontal bone loss. TGFbeta alone in skeletal reconstruction appears to be associated with uncertain results. The presence of committed cells is required for enhancement of bone formation by TGFbeta. It has a biphasic effect, which suppresses proliferation and osteoblastic differentiation at high concentrations. BMPs, BMP2, BMP4 and BMP7 in particular, appear to be the most effective growth factors in terms of osteogenesis and osseous defect repair. Efficacy of BMPs for defect repair is strongly dependent on the type of carrier and has been subject to unknown factors in clinical feasibility trials resulting in ambiguous results. The current lack of clinical data may prolong the period until this factor is introduced into routine clinical application. PRP is supposed to increase proliferation of undifferentiated mesenchymal cells and to enhance angiogenesis. There is little scientific evidence about the benefit of PRP in skeletal reconstructive and preprosthetic surgery yet and it is unlikely that peri-implant bone healing or regeneration of local bone into alloplastic material by the application of PRP alone will be significantly enhanced.

Articular cartilage repair: basic science and clinical progress. A review of the current status and prospects

OBJECTIVE

To review the basic scientific status of repair in articular cartilage tissue and to assess the efficiency of current clinical therapies instigated for the treatment of structural lesions generated therein as a result of trauma or during the course of various diseases, notably osteoarthritis (OA). Current scientific trends and possible directions for the future will also be discussed.

DESIGN

A systematic and critical analysis is undertaken, beginning with a description of the spontaneous repair responses in different types of lesion. Surgical interventions aimed at inducing repair without the use of active biologics will then be considered, followed by those involving active biologics and those drawing on autogenic and allogeneic tissue transplantation principles. Cell transplantation approaches, in particular novel tissue engineering concepts, will be critically presented. These will include growth-factor-based biological treatments and gene transfection protocols. A number of technical problems associated with repair interventions, such as tissue integration, tissue retention and the role of mechanical factors, will also be analysed.

RESULTS

A critical analysis of the literature reveals the existence of many novel and very promising biologically-based approaches for the induction of articular cartilage repair, the vast majority of which are still at an experimental phase of development. But prospective, double-blinded clinical trials comparing currently practiced surgical treatments have, unfortunately, not been undertaken.

CONCLUSION

The existence of many new and encouraging biological approaches to cartilage repair justifies the future investment of time and money in this research area, particularly given the extremely high socio-economic importance of such therapeutic strategies in the prevention and treatment of these common joint diseases and traumas. Clinical epidemiological and prospective trials are, moreover, urgently needed for an objective, scientific appraisal of current therapies and future novel approaches.

Growth factors and cartilage repair

Growth factors are obvious tools to enhance cartilage repair. Understanding of reactivities in normal and arthritic cartilage and potential side effects on other compartments in the joint will help to identify possibilities and limitations. Growth factor responses have been evaluated in normal and diseased murine knees. The main cartilage anabolic factor, insulinlike growth factor-1, shows great safety, but has little contribution in diseased cartilage because of insulinlike growth factor nonresponsiveness of arthritic chondrocytes. Transforming growth factor-beta can overrule interleukin-1 catabolic effects and can enhance cartilage repair in arthritic tissue, unlike bone morphogenetic protein-2 that only is capable of enhancing chondrocyte proteoglycan synthesis in the absence of interleukin-1. Transforming growth factor-beta and bone morphogenetic protein-2 induce chondrophyte formation at the margins of the joint. Studies with scavenging transforming growth factor beta soluble receptor identified endogenous transforming growth factor-beta involvement in spontaneous cartilage repair and chondrophyte and subsequent osteophyte formation in arthritic conditions. Osteophyte induction may hamper intraarticular transforming growth factor-beta application in the joint and warrants targeted growth factor application to cartilage lesion sites only.