Differential modulation of growth and phenotypic expression of chondrocytes in sparse and confluent cultures by growth factors in cartilage

Osteochondral lesions of the talus: size, age, and predictors of outcomes

In this article, our research on osteochondral lesions of the talus (OLTs) is summarized, the orthopedic literature is reviewed, and the direction of future research and treatment trends are discussed. Our research has explored the role of lesion size, significance of marrow edema, relationship of patient age, importance of lesion containment, and role of a stable cartilage lesion cap in the prognosis and outcomes of these lesions. We have identified smaller sized lesions, younger patients and contained lesions as independent predictors of success for the operative treatment of OLTs. Our data should facilitate the development of a more comprehensive treatment algorithm to more accurately predict success in operative management of these lesions.

New era in health care: tissue engineering

Tissue engineering is a rapidly expanding field, which applies the principles and methods of physical sciences, life sciences and engineering to understand physiological and pathological systems and to modify and create cells and tissues for therapeutic applications. It has emerged as a rapidly expanding ‘interdisciplinary field’ that is a significant potential alternative wherein tissue and organ failure is addressed by implanting natural, synthetic, or semi synthetic tissue or organ mimics that grow into the required functionality or that are fully functional from the start. This review presents in a comprehensive manner the various considerations for the reconstruction of various tissues and organs as well as the various applications of this young emerging field in different disciplines.

Tissue engineering: orthopedic applications

Because of an aging population and increased occurrence of sports-related injuries, musculoskeletal disorders have become one of the major health concerns in the United States. Current treatments, although fairly successful, do not provide the optimum therapy. These treatments typically rely on donor tissues obtained either from the patient or from another source. The former raises the issue of supply, whereas the latter poses the risk of rejection and disease transfer. This has prompted orthopedic surgeons and scientists to look for viable alternatives. In recent years, tissue engineering has gained increasing support as a method to treat orthopedic disorders. Because it uses principles of engineering, biology, and chemistry, tissue engineering may provide a more effective approach to the treatment of musculoskeletal disorders than traditional methods. This chapter presents a review of current methods and new tissue-engineering techniques for the treatment of disorders affecting bone, ligament, and cartilage.

Tissue-engineered cartilage using serially passaged articular chondrocytes. Chondrocytes in alginate, combined in vivo with a synthetic (E210) or biologic biodegradable carrier (DBM)

In vitro multiplication of isolated autologous chondrocytes is required to obtain an adequate number of cells to generate neo-cartilage, but is known to induce cell-dedifferentiation. The aim of this study was to investigate whether multiplied chondrocytes can be used to generate neo-cartilage in vivo. Adult bovine articular chondrocytes, of various differentiation stages, were suspended in alginate at densities of 10 or 50 million/ml, either directly after isolation (P0) or after multiplication in monolayer for one (P1) or three passages (P3). Alginate with cells was seeded in demineralized bovine bone matrix (DBM) or a fleece of polylactic/polyglycolic acid (E210) and implanted in nude mice for 8 weeks. The newly formed tissue was evaluated by Alcian Blue and immunohistochemical staining for collagen type-II and type-I. Structural homogeneity of the tissue, composed of freshly isolated as well as serially passaged cells, was found to be enhanced by high-density seeding (50 million/ml) and the use of E210 as a carrier. The percentage of collagen type-II positive staining P3-cells was generally higher when E210 was used as a carrier. Furthermore, seeding P3-chondrocytes at the highest density (50 million/ml) enhanced collagen type-II expression. This study shows promising possibilities to generate structurally regular neo-cartilage using multiplied chondrocytes in alginate in combination with a fleece of polylactic/polyglycolic acid.

Immunohistochemical profile of basic fibroblast growth factor and heparan sulphate in adult rat mandibular condylar cartilage

Basic fibroblast growth factor (bFGF) and heparan sulphate (HS) were detected immunohistochemically in mandibular condylar cartilage, and the findings compared with those on epiphyseal articular cartilage. In the condylar cartilage, both bFGF and HS were localized in chondrocytes throughout the various zones including the fibrous, proliferative, mature-cell and hypertrophic zones: bFGF immunostaining was most significant in the proliferative and mature-cell zones, while intense staining for HS was found mainly in the hypertrophic zone. Immunoreaction for bFGF was detected in the nuclei of chondrocytes, whereas HS staining was observed in the cytoplasm. In articular cartilage, only chondrocytes beneath the superficial zone (intermediate zone) demonstrated both bFGF and HS immunoreactivities. Chondrocytes in the deeper calcifying region of the articular cartilage did not immunoreact for either bFGF or HS. These findings suggest that, in contrast to the epiphyseal articular cartilage, a continuous bFGF-mediated remodelling of cells and matrix takes place in mandibular condylar cartilage during the process of endochondral ossification.

Exogenous fibroblast growth factors-1 and -2 do not accelerate fracture healing in the rabbit

Both fibroblast growth factors-1 (acidic FGF) and -2 (basic FGF) increase the proliferation of osteoblasts and chondrocytes in vitro and FGF-2 stimulates angiogenesis and bone formation in vivo. To test their effects on rabbit tibial fracture-healing under stable and unstable mechanical conditions, 3 micrograms of either FGF-1 or FGF-2 was injected around rabbit tibial fractures on day 4 after fracture. Neither growth factor had a significant effect on either the size of, or the amounts of bone and cartilage in, the 10-day callus irrespective of the mechanical conditions under which the fracture was healing. The 10-day FGF-2-treated calluses were, however, more mature than FGF-1-treated calluses because the cartilage was separated from the periosteum by bone and endochondral ossification had progressed further. In conclusion, the application of FGF-1 or FGF-2 to normally healing fractures of the rabbit tibia does not have a significant effect on the rate of healing.

Responsiveness of articular cartilage from normal and inflamed mouse knee joints to various growth factors

OBJECTIVE

Disturbed anabolic signalling might contribute to the decreased chondrocyte proteoglycan (PG) synthesis during joint inflammation. Articular cartilage obtained from mouse knee joints with experimentally-induced arthritis exhibits a state of nonresponsiveness towards stimulation of chondrocyte PG synthesis by insulin-like growth factor-1 (IGF-1). Investigations were carried out on the role of other growth factors apart from IGF-1 on regulation of chondrocyte PG synthesis under pathological conditions, that is, during repair after IL-1 exposure as well as during early and later arthritis.

METHODS

Mouse patellae were obtained from normal knee joints and joints injected with IL-1 or zymosan. The patellae were cultured with basic fibroblast growth factor [bFGF], platelet-derived growth factor [PDGF], epidermal growth factor [EGF] or transforming growth factor beta [TGF beta] for 24 hours in the presence or absence of IGF-1. Chondrocyte PG synthesis was measured by 35S-sulphate incorporation.

RESULTS

In normal cartilage none of the tested growth factors elicited stimulatory effects on the chondrocyte PG synthesis as caused by IGF-1. EGF and TGF beta even caused significant inhibition of chondrocyte PG synthesis. Combination of bFGF or PDGF with IGF-1 exerted significant additional stimulation of the 35S-sulphate incorporation. IL-1 exposed cartilage displayed reactivity to IGF-1 as well as to the other growth factors similar to control cartilage. Cartilage obtained from joints with experimentally-induced arthritis exhibited a state of nonresponsiveness towards all individually tested growth factors as well as growth factor combinations.

CONCLUSION

Arthritis causes nonresponsiveness to stimulation of chondrocyte PG synthesis by the tested growth factors, which might be caused by a general receptor function defect.

Studies of chondrogenesis in rotating systems

A great deal of energy has been exerted over the years researching methods for regenerating and repairing bone and cartilage. Several techniques, especially bone implants and grafts, show great promise for providing a remedy for many skeletal disorders and chondrodystrophies. The bioreactor (rotating-wall vessel, RWV) is a cell culture system that creates a nurturing environment conducive to cell aggregation. Chondrocyte cultures have been studied as implants for repair and replacement of damaged and missing bone and cartilage since 1965 [Chesterman and Smith, J Bone Joint Surg 50B:184-197, 1965]. The ability to use large, tissue-like cartilage aggregates grown in the RWV would be of great clinical significance in treating skeletal disorders. In addition, the RWV may provide a superior method for studying chondrogenesis and chondrogenic mutations. Because the RWV is also reported to simulate many of the conditions of microgravity it is a very useful ground-based tool for studying how cell systems will react to microgravity.

Bone morphogenetic proteins (BMP-2 and BMP-3) promote growth and expression of the differentiated phenotype of rabbit chondrocytes and osteoblastic MC3T3-E1 cells in vitro

We studied the effects of highly purified bone morphogenetic protein 2 and 3 (BMP-2 and -3) on growth plate chondrocytes and osteoblastic cells in vitro and compared to TGF-beta. A mixture of BMP-2 and 3 (BMPs) strongly stimulated DNA synthesis of chondrocytes in the presence of fibroblast growth factor (FGF). BMPs induced rapid maturation of chondrocytes at a growing stage: BMPs transformed the cells into rounded cells and induced marked accumulation of cartilage matrix; TGF-beta slightly reduced matrix accumulation and changed cell morphology into spindle-like in the presence of FGF. Moreover, exposure of chondrocytes to BMPs resulted in a dramatic increase of the putative approximately 80 kD PTH receptors expressed on the cell surface. In multilayered chondrocytes at the calcifying stage, BMPs stimulated alkaline phosphatase (ALPase) activity but TGF-beta inhibited it. In osteoblastic MC3T3-E1 cells, BMPs were found to be the most potent stimulator of ALPase activity thus far described: ALPase in the cells treated with approximately 100 ng/ml of BMPs reached 5- to 20-fold over the basal, whereas TGF-beta inhibited expression of ALPase activity in these cells. The stimulatory action of BMPs overrode the inhibition of ALPase activity by TGF-beta when the cells were incubated with TGF-beta and BMPs. BMPs also upregulated expression of the approximately 80 kD PTH receptor on the cells. These results suggest that BMPs have unique biologic activities in vitro that lead to growth and phenotypic expression of cells playing a critical role in endochondral bone formation.

Molecular cloning of a new class of cartilage-specific matrix, chondromodulin-I, which stimulates growth of cultured chondrocytes

Here we report the structure and bioactivity of 25 kDa glycoprotein (chondromodulin-I) as a tissue-specific functional matrix component identified and cloned for the first time. Chondromodulin-I purified from fetal bovine cartilage markedly stimulated DNA synthesis of cultured growth-plate chondrocytes in the presence of basic fibroblast growth factor (FGF). Bovine chondromodulin-I cDNA revealed that the mature protein consists of 121 amino acids with three possible glycosylation sites and is coded as the C-terminal part of a larger precursor. On northern blot analysis, expression of chondromodulin-I mRNA was observed only in cartilage.