Immunohistochemistry in the study of normal and osteoarthritic articular cartilage

Precise Lubrication and Protection of Cartilage Damage by Targeting Hydrogel Microsphere

Osteoarthritis (OA) is a degenerative bone and joint disease characterized by decreased cartilage lubrication, leading to continuous wear and ultimately irreversible damage. This situation is particularly challenging for early-stage OA, as current bio-lubricants lack precise targeting for small inflammatory lesions. In this work, an antibody-mediated targeting hydrogel microspheres (HMS) is developed to precisely lubricate the local injury site of cartilage and prevent the progression of early OA. Anti-Collagen type I (Anti-Col1) is an antibody that targets cartilage injury sites in early OA stages. It is anchored on a HMS matrix made of Gelatin methacrylate (GelMA) and poly (sulfobetaine methacrylate) (PSBMA) to create targeted HMS (T-G/S HMS). The T-G/S HMS's high hydrophilicity, along with the dynamic interaction between its surficial Anti-Col1 and the Col1 on cartilage injury site, ensures its precise and effective lubrication of early OA lesions. Consequently, injecting T-G/S HMS into rats with early OA significantly slows disease progression and reduces symptoms. In conclusion, the developed injectable targeted lubricating HMS and the precisely targeted lubrication strategy represent a promising, convenient technique for treating OA, particularly for slowing the early-stage OA progression.

Evaluation of histological scoring systems for tissue-engineered, repaired and osteoarthritic cartilage

OBJECTIVE

Regeneration of hyaline cartilage has been the focus of an increasing number of research groups around the world. One of the most important outcome measures in evaluation of its success is the histological quality of cartilaginous tissue. Currently, a variety of histological scoring systems is used to describe the quality of osteoarthritic, in vivo repaired or in vitro engineered tissue. This review aims to provide an overview of past and currently used histological scoring systems, in an effort to aid cartilage researchers in choosing adequate and validated cartilage histological scoring systems.

METHODS

Histological scoring systems for analysis of osteoarthritic, tissue engineered and in vivo repaired cartilage were reviewed. The chronological development as well as the validity and practical applicability of the scoring systems is evaluated.

RESULTS

The Histological-Histochemical Grading System (HHGS) or a HHGS-related score is most often used for evaluation of osteoarthritic cartilage, however the Osteoarthritis Research Society International (OARSI) Osteoarthritis Cartilage Histopathology Assessment System seems a valid alternative. The O'Driscoll score and the International Cartilage Repair Society (ICRS) II score may be used for in vivo repaired cartilage. The 'Bern score' seems most adequate for evaluation of in vitro engineered cartilage.

CONCLUSION

A great variety of histological scoring systems exists for analysis of osteoarthritic or normal, in vivo repaired or tissue-engineered cartilage, but only few have been validated. Use of these validated scores may considerably improve exchange of information necessary for advances in the field of cartilage regeneration.

Osteoarthritis cartilage histopathology: grading and staging

OBJECTIVE

Current osteoarthritis (OA) histopathology assessment methods have difficulties in their utility for early disease, as well as their reproducibility and validity. Our objective was to devise a more useful method to assess OA histopathology that would have wide application for clinical and experimental OA assessment and would become recognized as the standard method.

DESIGN

An OARSI Working Group deliberated on principles, standards and features for an OA cartilage pathology assessment system. Using current knowledge of the pathophysiology of OA morphologic features, a proposed system was presented at OARSI 2000. Subsequently, this was widely circulated for comments amongst experts in OA pathology.

RESULTS

An OA cartilage pathology assessment system based on six grades, which reflect depth of the lesion and four stages reflecting extent of OA over the joint surface was developed.

CONCLUSIONS

The OARSI cartilage OA histopathology grading system appears consistent and simple to apply. Further studies are required to confirm the system's utility.

Topographic and zonal distribution of tenascin in human articular cartilage from femoral heads: normal versus mild and severe osteoarthritis

OBJECTIVE

The extracellular matrix glycoprotein tenascin (TN) is upregulated in articular cartilage with severe osteoarthritis (OA). This study gives a detailed description of TN expression in areas of articular cartilage from femoral heads with mild OA showing structural lesions and in structurally normal areas of the same femoral heads compared with normal cartilage and cartilage with severe OA.

METHODS

Immunohistochemical evaluation was performed on cryosections stained with antibodies against TN. Sections were selected as follows: from each macroscopically normal femoral head (n=6) a normal central and peripheral biopsy; from each femoral head with macroscopically mild OA (n=8) a central biopsy that showed structural lesions and a peripheral normal biopsy; from each femoral head with severe OA (n=9) a central and a peripheral biopsy with structural lesions. Central biopsies represent load bearing areas, whereas peripheral biopsies are non-load bearing.

RESULTS

Central cartilage with mild OA contains significantly higher levels of TN in the superficial zone than structurally normal, peripheral cartilage from the same femoral heads. Normal cartilage and cartilage with severe OA do not display this topographic variation. Central cartilage with mild OA shows significantly higher levels of TN than normal, central cartilage. Peripheral, normal cartilage with mild OA shows significantly less TN than peripheral cartilage with severe OA.

CONCLUSIONS

In femoral heads with mild OA, TN is accumulated in areas displaying structural damage. This proposes mild OA to be a localized disorder. Extreme caution is necessary for sampling of articular cartilage, especially from joints with mild OA.

Collagen-binding I domain integrins--what do they do?

Collagens are the most abundant proteins in the mammalian body and it is well recognized that collagens fulfill an important structural role in the extracellular matrix in a number of tissues. Inactivation of the collagen alpha 1(I) gene in mice results in embryonic lethality and collagen mutations in humans cause defects leading to disease. Integrins constitute a major group of receptors for extracellular matrix components, including collagens. Currently four collagen-binding I domain-containing integrins are known, namely alpha 1 beta 1, alpha 2 beta 1, alpha 10 beta 1 and alpha 11 beta 1. Unlike the undisputed role of collagens as structural elements, the biological importance of integrin mediated cell-collagen interactions is far from clear. This is in part due to the limited information available on the most recent additions of the integrin family, alpha 10 beta 1 and alpha 11 beta 1. Future studies using gene inactivation of individual and multiple integrin genes will allow testing of the hypothesis that collagen-binding integrins have redundant functions but will also shed light on their importance in pathological conditions. In this review we will describe what is currently known about the collagen-binding integrins and discuss their biological functions.

Histochemical studies of the extracellular matrix of human articular cartilage--a review

OBJECTIVE

This paper reviews the histochemistry of the extracellular matrix of human articular cartilage. No systematic review of histochemical knowledge and techniques in the study of articular cartilage has been published previously.

METHODS AND RESULTS

Literature was searched in the Winspirs Medline database from 1960 to 2000. Only techniques applicable for bright field or polarization microscopy were considered. Unless otherwise noted, all applies to hyaline cartilage. The most widely used fixatives are adequate for routine staining of proteins, but proteoglycan fixation is problematic, and no one fixative can be recommended. Proteoglycan can be stained reliably but it is problematic that, at low substrate concentrations, these methods are not stoichiometric. Collagen can be stained efficiently, although attempts to differentiate collagen types have not been successful.

CONCLUSIONS

Detailed studies of fixation and staining procedures should be carried out and standards for cartilage sampling, handling and evaluation agreed upon if results from different laboratories are to be compared.

Studies on YKL-40 in knee joints of patients with rheumatoid arthritis and osteoarthritis. Involvement of YKL-40 in the joint pathology

OBJECTIVE

The presence of YKL-40 (human cartilage glycoprotein 39) in synovium, cartilage and synovial fluid (SF) from knee joints of patients with rheumatoid arthritis and osteoarthritis (OA) were related to histopathological changes in synovium and cartilage and to serum YKL-40 and other biochemical markers.

METHODS

The localization of YKL-40 in synovium and cartilage was determined by immunohistochemistry. Synovial inflammation was estimated histologically and by magnetic resonance imaging (MRI). Biochemical markers of inflammation, neutrophil activation and cartilage metabolism were analysed. YKL-40 concentrations in serum and SF were determined by RIA and ELISA.

RESULTS

In the synovium YKL-40 positive cells were found in lining and stromal cells (macrophages) and the number of YKL-40 positive cells was related to the degree of synovitis. In arthritic cartilage, YKL-40 was located to chondrocytes. YKL-40 levels in SF were higher in RA patients with moderate/severe or none/slight synovitis of the knee joint compared to OA patients with moderate/severe or none/slight synovitis. SF YKL-40 correlated with the synovial membrane and the joint effusion volumes determined by magnetic resonance imaging (MRI) and with other biochemical markers of intercellular matrix metabolism. SF YKL-40 was higher than serum YKL-40, and a relationship existed between the YKL-40 levels in SF and serum. Intraarticular glucocorticoid injection was followed by clinical remission and a decrease in serum YKL-40, which increased again at clinical relapse.

CONCLUSIONS

YKL-40 in SF is derived from cells in the inflamed synovium, chondrocytes and SF neutrophils. Joint derived YKL-40 influences serum YKL-40. YKL-40 may be involved in the pathophysiology of the arthritic processes and reflect local disease activity.

Altered electrophysiological responses to mechanical stimulation and abnormal signalling through alpha5beta1 integrin in chondrocytes from osteoarthritic cartilage

OBJECTIVE

To establish whether chondrocytes from normal and osteoarthritic human articular cartilage recognize and respond to pressure induced mechanical strain in a similar manner.

DESIGN

Chondrocytes, extracted from macroscopically normal and osteoarthritic human articular cartilage obtained from knee joints at autopsy, were grown in monolayer culture and subjected to cyclical pressure-induced strain (PIS) in the absence or presence of anti-integrin antibodies, agents known to block ion channels and inhibitors of key molecules involved in the integrin-associated signalling pathways. The response of the cells to mechanical stimulation was assessed by measuring changes in membrane potential.

RESULTS

Unlike chondrocytes from normal articular cartilage, which showed a membrane hyperpolarization response to PIS, chondrocytes from osteoarthritic cartilage responded by membrane depolarization. The mechanotransduction pathway involves alpha5beta1 integrins, stretch-activated ion channels, tyrosine kinases and phospholipase C but the actin cytoskeleton and protein kinase C, which are important in the membrane hyperpolarization response in normal chondrocytes, are not necessary for membrane depolarization in osteoarthritic chondrocytes in response to PIS.

CONCLUSION

Chondrocytes derived from osteoarthritic cartilage show a different signalling pathway via alpha5beta1 integrin in response to mechanical stimulation which may be of importance in the production of phenotypic changes recognized to be present in diseased cartilage.

Microscopic and histochemical manifestations of hyaline cartilage dynamics

Structure and function of hyaline cartilages has been the focus of many correlative studies for over a hundred years. Much of what is known regarding dynamics and function of cartilage constituents has been derived or inferred from biochemical and electron microscopic investigations. Here we show that in conjunction with ultrastructural, and high-magnification transmission light and polarization microscopy, the well-developed histochemical methods are indispensable for the analysis of cartilage dynamics. Microscopically demonstrable aspects of cartilage dynamics include, but are not limited to, formation of the intracellular liquid crystals, phase transitions of the extracellular matrix and tubular connections between chondrocytes. The role of the interchondrocytic liquid crystals is considered in terms of the tensegrity hypothesis and non-apoptotic cell death. Phase transitions of the extracellular matrix are discussed in terms of self-alignment of chondrons, matrix guidance pathways and cartilage growth in the absence of mitosis. The possible role of nonenzymatic glycation reactions in cartilage dynamics is also reviewed.