Histomorphological and proliferative characterization of developing periosteal neochondrocytes in vitro

Role of the fibroblast growth factor 19 in the skeletal system

Fibroblast growth factor family (FGFs) is a kind of cytokine that plays an important role in growth, development, metabolism and disease. During bone development, multiple FGFs and fibroblast growth factor receptors (FGFRs) play important roles. Previous reports have elucidated the great importance of FGF1, 2, 4, 6, 7, 8, 9, 10, and 18 in bone development, and FGF21 and 23 in bone homeostasis and bone regulation. FGF19 was initially found in the human foetal brain, and its gene location is related to osteoporosis pseudoglioma syndrome. Presently, gene chip detection has repeatedly found that FGF19 shows spatiotemporal specificity of gene expression in bone development and bone-related diseases, as well as differences in the protein level, indicating that FGF19 affects the skeletal system. Considering the current insufficient understanding of FGF19 and its potential function in the skeletal system, this review aims to introduce the background of FGF19 in bone, summarise the research progress of FGF19 in the skeletal system, and discuss the role and therapeutic potential of FGF19 in bone development and bone-related diseases.

Bevacizumab as a potential anti-angiogenic therapy in schistosomiasis: A double-edged, but adjustable weapon

AIM

Investigating the anti-angiogenic effect of bevacizumab on chronic schistosomiasis mansoni in a trial to hinder the Schistosome-induced angiogenesis and porto-systemic shunting complications.

METHODS

The immunohistochemical expression of CD34, VEGF-R1, PCNA and α-SMA (angiogenesis markers) was analysed in the lung, liver and gastrointestinal junctions of chronic S mansoni infected mice after intraperitoneal injection of bevacizumab. The effect of prolonged administration of bevacizumab with praziquantel was also assessed through parasitic load, protective index, granuloma and fibrous tissue evaluation.

RESULTS

A regression in the vascular activity and microvascular density was observed in the infected mice after receiving bevacizumab. They had a significantly less VEGF-R1, PCNA, CD-34 and α-SMA expression in comparison to the infected untreated mice. The least tissue egg count was reported in mice received bevacizumab for 6 weeks (Mean = 27 120). However, they had persistent liver granulomas, and massively amalgamated fibrosis. Interestingly, the least faecal egg and tissue worms counts (Mean = 112, 13.4), and the highest protection index (39.26) were reported in mice received bevacizumab for 3 weeks, with marked granuloma, and fibrous tissue resolution.

CONCLUSIONS

Bevacizumab has a promising protective effect against the Schistosoma-induced angiogenesis. As an adjuvant to praziquantel, it is important to adjust the appropriate duration of administration that achieves the best schistosomicidal effect without impeding granuloma and fibrous tissue resolution.

Paeoniflorin in experimental BALB/c mansoniasis: A novel anti-angiogenic therapy

Chronic hepatic schistosomiasis causes portal hypertension, fibrosis and lethal hepatosplenic complications. Previous studies focused mainly on schistosomicidal drugs and neglected the therapeutic approaches against the vascular complications after portal hypertension. Investigating a novel anti-angiogenic therapy is an urgent. The current study is to evaluate the performance of Paeoniflorin (PAE) as an anti-angiogenic therapy, being a powerful anti-fibrotic, compared to artemether (ART) and praziqantel (PZQ) in schistosomiasis mansoni BALB/c mice. Thirty two laboratory bred male BALB/c Swiss albino mice. The mice were classified into four groups (8 mice each), control infected (CI), PZQ (300 mg/kg/12 h), ART (0.1 ml/mg/d) and PAE (50 mg/kg/d) treated groups for one month. All mice groups were sacrificed 15 weeks post infection for assessment of the drugs' efficacy by parasitological, histopathological and immunohistochemical studies. Our results in PAE group showed marked reduction in the mean egg count/gram stool, worm burden, egg count/gram liver tissue, granuloma diameter and pro-angiogenic factors as vascular endothelial growth factor (VEGF), Proliferating cell nuclear antigen (PCNA), alpha-smooth muscle actin (α-SMA) and CD34; conversely, there was an augmentation of the tissue inhibitor metalloproteinases-2 (TIMP-2) as an anti-angiogenic expression that was exceeded ART and PZQ treated groups compared to CI group (p˂0.001). Conclusively, PAE has an anti-angiogenic impact with no vascular proliferative activity or recanalization, no micro-vessel density (MVD) changes, granuloma resolution and fibrosis regression. PAE is predicted to be a potential therapy for chronic hepatic diseases associated with fibrosis and angiogenesis, hopeful in protecting from advanced serious complications; cancer and metastasis.

Novel Technique for Suspension Culture of Autologous Chondrocytes Improves Cell Proliferation and Tissue Architecture

We have developed a new and simple method of chondrocyte suspension culture using a spinner bottle with rotation of the matrices. We compared the characteristics of chondrocytes cultured by this method with those grown in standard monolayer cultures. We also determined the optimal nutritional medium for suspension cultures. Periosteum explants seeded with chondrocytes were grown in monolayer and suspension cultures under three conditions: in medium with no additive (control), with 10% fetal bovine serum (FBS), or with 10% autologous serum (AS). After culturing, the explants were harvested, processed for histology, and stained with hematoxylin-eosin or TUNEL, or immunostained for type I, II, and III collagen, and Ki-67 antigen. In monolayer cultures, the attachment of the chondrocytes to the periosteum was weak and the superficial layer consisted of fibrotic tissue and few nucleated cells. Collagen type II staining was strong, but types I and III were weak. Among the suspension cultures the AS group produced the thickest layer of chondrocytes with the fewest apoptotic cells. The superficial layer of cartilage in these cultures stained positive for type I and III collagen and Ki-67 antigen. Among the suspension cultures, total chondroitin and chondroitin-4 sulfate (C-4S) concentration was highest in the AS group, while prostaglandin E2 (PGE2) was highest in the FBS group. In summary, our new method of suspension culture of periosteal explants using rotational matrices combined with AS nutritional media was the most effective method for maintaining the bond between the chondrocyte layer and periosteum, as well as the production of type I and III collagen in the superficial layer.

Articular cartilage repair: Current needs, methods and research directions

Articular cartilage is a highly specialized tissue whose remarkable properties of deformability, resistance to mechanical loading, and low-friction gliding are essential to joint function. Due to its role as a cushion in bone articulation, articular cartilage is subject to many types of damaging insults, including decades of wear and tear, and acute joint injuries. However, this built-for-life tissue has a very poor intrinsic ability in adulthood to durably heal defects created by damaging insults. Consequently, articular cartilage progressively deteriorates and is eventually eroded, exposing the subchondral bone to the joint space, triggering inflammation and osteophyte development, and generating severe pain and joint incapacitation. The disease is called osteoarthritis (OA) and is today the leading cause of pain and disability in the human population. Researchers and clinicians have worked for decades to develop strategies to treat OA and restore joint function, but they are still far from being able to offer patients effective preventive or restorative treatments. Novel ideas, knowledge and technologies that nurture hope for major new breakthroughs are therefore sought. In this review, we first outline the composition, structure, and functional properties of normal human adult articular cartilage, as a reference for tissue conservation and regenerative strategies. We then describe current options that have been used clinically and in pre-clinical trials to treat osteoarthritic patients, and we discuss the benefits and inadequacies of these treatment options. Next, we review research efforts that are currently ongoing to try and achieve durable repair of functional cartilage tissue. Methods include engineering of tissue implants and we discuss the needs and options for tissue scaffolds, cell sources, and growth and differentiation factors to generate de novo or repair bona fide articular cartilage.

FGFR2 mutation confers a less drastic gain of function in mesenchymal stem cells than in fibroblasts

Gain-of-function mutations in FGFR2 cause Apert syndrome (AS), a disease characterized by craniosynostosis and limb bone defects both due to abnormalities in bone differentiation and remodeling. Although the periosteum is an important cell source for bone remodeling, its role in craniosynostosis remains poorly characterized. We hypothesized that periosteal mesenchymal stem cells (MSCs) and fibroblasts from AS patients have abnormal cell phenotypes that contribute to the recurrent fusion of the coronal sutures. MSCs and fibroblasts were obtained from the periostea of 3 AS patients (S252W) and 3 control individuals (WT). We evaluated the proliferation, migration, and osteogenic differentiation of these cells. Interestingly, S252W mutation had opposite effects on different cell types: S252W MSCs proliferated less than WT MSCs, while S252W fibroblasts proliferated more than WT fibroblasts. Under restrictive media conditions, only S252W fibroblasts showed enhanced migration. The presence of S252W mutation increased in vitro and in vivo osteogenic differentiation in both studied cell types, though the difference compared to WT cells was more pronounced in S252W fibroblasts. This osteogenic differentiation was reversed through inhibition of JNK. We demonstrated that S252W fibroblasts can induce osteogenic differentiation in periosteal MSCs but not in MSCs from another tissue. MSCs and fibroblasts responded differently to the pathogenic effects of the FGFR2^S252W mutation. We propose that cells from the periosteum have a more important role in the premature fusion of cranial sutures than previously thought and that molecules in JNK pathway are strong candidates for the treatment of AS patients.

Long-term histologic changes and effects of perichondrium preservation of auricular cartilage grafted in rabbit tympanic bullae

INTRODUCTION

This study evaluated the long-term histologic changes of grafted auricular cartilage in rabbit tympanic bullae.

MATERIALS AND METHODS

Auricular cartilage with or without perichondrium was prepared and cut into small pieces to obliterate the rabbit tympanic bullae. The histologic changes of the grafted cartilage in both groups were compared 20 months after surgery.

RESULTS

Remarkable spongy bony trabeculae of mature lamellar bone with red bone marrow formation were observed in the perichondrium-preserved group. Parts of the grafted cartilage pieces were invaded and replaced by bone and bone marrow. The grafted cartilage pieces grossly maintained their original polygonal shapes, and no osteochondral tissue regeneration was observed in the perichondrium-removed group. The viable chondrocyte ratios were 46.21 ± 5.58 versus 27.80 ± 4.81%, and the minimal resorption ratios were 10.31 ± 3.27 versus 2.98 ± 1.48% in the perichondrium-preserved (n = 14) and -removed groups (n = 12, p < 0.05). The tissue ratios were cartilage: 38.18 ± 8.76 versus 52.97 ± 9.30%; lamellar bone: 18.49 ± 5.31 versus 0.82 ± 0.43%; bone marrow: 20.72 ± 6.27 versus 0.00 ± 0.00%; fibrous tissue: 10.13 ± 2.74 versus 5.81 ± 2.20%, and adipose tissue: 12.01 ± 4.48 versus 40.70 ± 7.83% in the perichondrium-preserved and -removed groups. The differences were all statistically significant (p < 0.05).

CONCLUSION

A space-filling mass effect with minimal resorption of the cartilage pieces was observed in the perichondrium-removed group. In addition to this mass effect, the progenitor cells in the preserved perichondrium allowed active bone tissue regeneration and cartilage resorption in the perichondrium-preserved group.

Short-term effects of perichondrium preservation on chondrocyte survival and chondrogenesis of auricular cartilage grafted in rabbit tympanic bullae

INTRODUCTION

Obliteration of the mastoid cavities with auricular cartilage is a frequently used method to minimize the open cavity problem in cholesteatoma surgery. However, the method of cartilage preparation and histopathologic changes of the grafted cartilage in patients receiving mastoid obliteration are rarely reported. Hence, the authors developed rabbit tympanic bulla obliteration with auricular cartilage as an animal model and studied the effects of perichondrium preservation on the grafted cartilage.

MATERIALS AND METHODS

Auricular cartilage with or without perichondrium was prepared and cut into small pieces to obliterate rabbit tympanic bullae. Four weeks after surgery, the viable chondrocyte ratio indicated by the number of viable chondrocytes divided by the total number of chondrocytes, the microvascular density shown by CD31-labeled vessels, and the chondrogenesis ratio represented by the ratio of the cross-sectional areas of the newly formed cartilage and the originally grafted cartilage were calculated and compared.

RESULTS

The viable chondrocyte ratio was 49.21 +/- 10.17% in the perichondrium-preserved group (n = 12) and 35.46 +/- 3.96% in the perichondrium-removed group (n = 12, p = 0.001). The CD31 microvascular density was significantly higher in the perichondrium-preserved group than in the perichondrium-removed group (167.77 +/- 15.83 vs. 77.17 +/- 19.67 microvessels/mm(2), p < 0.001). The chondrogenesis ratios were 27.58 +/- 12.44% in the perichondrium-preserved group and 0.45 +/- 0.63% in the perichondrium-removed group (p < 0.001).

CONCLUSION

Obliteration of tympanic bullae with perichondrium-preserved cartilage results in faster restoration of circulation, higher survival of chondrocytes and more cartilage regeneration than with perichondrium-removed cartilage.

Effect of indenter size on elastic modulus of cartilage measured by indentation

Our preliminary indentation experiments showed that the equilibrium elastic modulus of murine tibial cartilage increased with decreasing indenter size: flat-ended 60 deg conical tips with end diameters of 15 microm and 90 microm gave 1.50+/-0.82 MPa (mean+/-standard deviation) and 0.55+/-0.11 MPa, respectively (p<0.01). The goal of this paper is to determine if the dependence on tip size is an inherent feature of the equilibrium elastic modulus of cartilage as measured by indentation. Since modulus values from nonindentation tests are not available for comparison for murine cartilage, bovine cartilage was used. Flat-ended conical or cylindrical tips with end diameters ranging from 5 microm to 4 mm were used to measure the equilibrium elastic modulus of bovine patellar cartilage. The same tips were used to test urethane rubber for comparison. The equilibrium modulus of the bovine patellar cartilage increased monotonically with decreasing tip size. The modulus obtained from the 2 mm and 4 mm tips (0.63+/-0.21 MPa) agreed with values reported in the literature; however, the modulus measured by the 90 microm tip was over two and a half times larger than the value obtained from the 1000 microm tip. In contrast, the elastic modulus of urethane rubber obtained using the same 5 microm-4 mm tips was independent of tip size. The equilibrium elastic modulus of bovine patellar cartilage measured by indentation depends on tip size. This appears to be an inherent feature of indentation of cartilage, perhaps due to its inhomogeneous structure.

Ingénierie tissulaire du cartilage : état des lieux et perspectives

Lesions of the articular cartilage have a large variety of causes among which traumatic damage, osteoarthritis and osteochondritis dissecans are the most frequent. Returning damaged cartilage in articular joints back to a functionally normal state has been a major challenge for orthopaedic surgeons. This interest results in large part because cartilage defects cannot adequately heal themselves. Current techniques used in orthopaedic practice to repair cartilage give variable and unpredictable results. Bone marrow stimulation techniques such as abrasion arthroplasty, drilling and microfracture produce mostly fibrocartilage. Autologous osteochondral transplant systems (mosaicplasty) have shown encouraging results. Autologous chondrocyte transplantation has led to a hyaline articular cartilage repair but little is known about the predictability and reliability of the procedure. The rapidly emerging field of tissue engineering promises creation of viable substitutes for failing cartilage tissue. Current tissue engineering approaches are mainly focused on the restoration of pathologically altered tissue structure based on the transplantation of cells in combination with supportive matrices and molecules. Among natural and synthetic matrices, collagen and polysaccharidic biomaterials have been extensively used with promising results. Recently, interest has switched to the use of mesenchymal stem cells instead of chondrocytes. Tissue engineering offers the possibility to treat localised cartilage lesions. Genetic engineering techniques using genetically modified chondrocytes offer also the opportunity to treat diffuse cartilage lesions occurring in osteoarthritis or inflammatory joint diseases. Electroporation is specially a reliable and inexpensive technique that shares with electrochemotherapy an ability to target the chondrocytes despite the barrier effect of the extracellular matrix without viral vectors. The authors review recent research achievements and highlight the potential clinical applications of new technologies in the treatment of patients with cartilage injuries.

Histochemical evidence of the initial chondrogenesis and osteogenesis in the periosteum of a rib fractured model: implications of osteocyte involvement in periosteal chondrogenesis

We have examined cellular events at the early stages of periosteal chondrogenesis and osteogenesis induced by bone fracture, using a well-standardized rib fracture model of the mouse. The initial cellular event was recognized as considerable proliferation in the deeper layer referred to as the "cambium layer" of the periosteum, as evidenced by numerous proliferating cell nuclear antigen-positive cells. The periosteal cartilage and bone were then regenerated directly from the region of the most-differentiated cell, i.e., mature osteoblasts of the cambium layer both close to and distant from the fracture site. Therefore, periosteal osteoblasts appeared to have the potential to differentiate into chondrogenic and osteoblastic lineages. CD31-positive blood vessels were uniformly localized along the periosteum that was regenerating cartilage and bone, being therefore indicative of less influence on the initiation of osteochondrogenesis. In contrast, however, the regenerated periosteal cartilage or bone extended from the cortical bones included dead or living osteocytes, respectively. Empty lacunae and lacunae embedded with amorphous materials were found close to the regenerated cartilage, while intact osteocytes persisted adjacent to the regenerated bone. The embedded lacunae with amorphous materials would render the tissue fluid, nutrients, oxygen, and several secretory factors such as dentin matrix protein-1 impossible to be delivered to the periosteal osteoblasts that interconnect osteocytes via gap junctions. Our study thus provides two major clues on initial cellular events in response to bone fracture: the potentiality of periosteal osteoblastic differentiation into a chondrogenic lineage, and a putative involvement of osteocytes in periosteal cartilage and bone regeneration.

Animal models for cartilage reconstruction

Animal models are widely used to develop and evaluate tissue-engineering techniques for the reconstruction of damaged human articular cartilage. For the purpose of this review, these model systems will include in vitro culture of animal cells and explants, heterotopic models of chondrogenesis, and articular cartilage defect models. The objectives for these preclinical studies are to engineer articular cartilage for the functional restoration of a joint surface that appears anatomically, histologically, biologically, biochemically, and mechanically to resemble the original joint surface. While no animal model permits direct application to humans, each is capable of yielding principles on which decisions can be made that might eventually translate into a human application. Clearly, the use of animal models has and will continue to play a significant role in the advancement of this field. Each animal model has specific advantages and disadvantages. The key issue in the selection of an appropriate animal model is to match the model to the question being investigated and the hypothesis to be tested. The purpose of this review is to discuss issues regarding animal model selection, the benefits and limitations of these model systems, scaffold selection with emphasis on polymers, and evaluation of the tissue-engineered articular cartilage.

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.

Combined effects of insulin-like growth factor-1 and transforming growth factor-beta1 on periosteal mesenchymal cells during chondrogenesis in vitro

OBJECTIVE

Periosteum contains undifferentiated mesenchymal stem cells that have both chondrogenic and osteogenic potential, and has been used to repair articular cartilage defects. During this process, the role of growth factors that stimulate the periosteal mesenchymal cells toward chondrogenesis to regenerate articular cartilage and maintain its phenotype is not yet fully understood. In this study, we examined the effects of insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta1 (TGF-beta1), alone and in combination, on periosteal chondrogenesis using an in vitro organ culture model.

METHODS

Periosteal explants from the medial proximal tibia of 2-month-old rabbits were cultured in agarose under serum free conditions for up to 6 weeks. After culture the explants were weighed, assayed for cartilage production via Safranin O staining and histomorphometry, assessed for proliferation via proliferative cell nuclear antigen (PCNA) immunostaining, and assessed for type II collagen mRNA expression via in situ hybridization.

RESULTS

IGF-1 significantly increased chondrogenesis in a dose-dependent manner when administered continuously throughout the culture period. Continuous IGF-1, in combination with TGF-beta1 for the first 2 days, further enhanced overall total cartilage growth. Immunohistochemistry for PCNA revealed that combining IGF-1 with TGF-beta1 gave the strongest proliferative stimulus early during chondrogenesis. In situ hybridization for type II collagen showed that continuous IGF-1 maintained type II collagen mRNA expression throughout the cambium layer from 2 to 6 weeks.

CONCLUSION

The results of this study demonstrate that IGF-1 and TGF-beta1 can act in combination to regulate proliferation and differentiation of periosteal mesenchymal cells during chondrogenesis.

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.

The spatiotemporal expression of TGF-beta1 and its receptors during periosteal chondrogenesis in vitro

Transforming growth factor-beta1 (TGF-beta1) has been shown to stimulate chondrogenesis in periosteal explants cultured in agarose suspension. TGF-betas exert their cellular effects through a heteromeric cell membrane receptor complex consisting of TGF-beta type I and type II receptors. In this study, the spatial and temporal expressions of the type I receptor (TbetaR-I), type II receptor (TbetaR-II) and endogenous TGF-beta1 in periosteal explants cultured in vitro were examined using reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry. The temporal changes in the expression of the TbetaR-I and TbetaR-II mRNAs correlated with that of TGF-beta1. Exogenous administration of TGF-beta1 upregulated the expression of both receptors and of the TGF-beta1 ligand in a biphasic pattern. The earlier peak of upregulation was observed at 7 days in culture. A later peak of upregulation was seen at 42 days, at which time cartilage formation reached a maximum. Immunohistochemical studies demonstrated co-localization of TbetaR-I and TbetaR-II simultaneously among the same cells expressing TGF-beta1. TGF-beta1 treatment increased the expression of TGF-beta1, TbetaR-I and TbetaR-II in mesenchymal cells in the cambium layer at 7 days in culture. Small round chondrocytes showed widely distributed immunoreactivity of TGF-beta1, TbetaR-I and TbetaR-II in the 42-day explants treated with TGF-beta1. These observations support the hypothesis that TGF-beta1 regulates the initiation and formation of cartilage during periosteal chondrogenesis.

The role of periosteum in cartilage repair

Periosteum, which can be grown in cell and whole tissue cultures, may meet one or more of the three prerequisites for tissue engineered cartilage repair. Periosteum contains pluripotential mesenchymal stem cells with the potential to form either cartilage or bone. Because it can be transplanted as a whole tissue, it can serve as its own scaffold or a matrix onto which other cells and/or growth factors can be adhered. Finally, it produces bioactive factors that are known to be chondrogenic. The chondrocyte precursor cells reside in the cambium layer. These vary in total density and volume with age and in different donor sites. The advantages of whole tissue periosteal transplants for cartilage repair include the fact that this tissue meets the three primary requirements for tissue engineering: a source of cells, a scaffold for delivering and retaining them, and a source of local growth factors. Many growth factors that regulate chondrocytes and cartilage development are synthesized by periosteum in conditions conducive to chondrogenesis. These include transforming growth factor-beta 1, insulinlike growth factor-1, growth and differentiation factor-5, bone morphogenetic protein-2, integrins, and the receptors for these molecules. By additional study of the molecular events in periosteal chondrogenesis, it may be possible to optimize its capacity for articular cartilage repair.