Year: 2012
Type: book-chapter
Abstract: IntroductionOsteoarthritis (OA), a degenerative joint disease, increases in prevalence with age, and affects majority of individuals over the age of 65.OA frequently affects several joints including the hands, knees, hips and spine, and is a leading cause of impaired mobility in the elderly.The major clinical symptoms include chronic pain, joint instability, stiffness and radiographic joint space narrowing (Felson, 2006;Goldring & Goldring, 2007).During OA development, articular chondrocytes undergo hypertrophy leading to extracellular matrix degradation, articular cartilage breakdown and osteophyte formation in the margins of the articular cartilage (Felson, 2006; Goldring & Goldrig, 2007).The precise signaling pathways which are involved in the degradation of cartilage matrix and development of OA are poorly understood and there are currently no effective interventions to decelerate the progression of OA or retard the irreversible degradation of cartilage except for total joint replacement surgery (Krasnokutsky et al., 2007).In this chapter, we will summarize important molecular mechanisms related to OA pathogenesis and provide new insights into potential molecular targets for the prevention and treatment of OA. Characteristics of articular cartilageThe skeleton is an organ composed of two distinct tissues: bone and cartilage.Bones are rigid mineralized organs formed in a variety of shapes.Normal articular cartilage, emerging during the postnatal stage as a permanent tissue distinct from the growth plate cartilage, is an extremely smooth, hard and white tissue that lines the surface of all the diathrodial joints.Articular cartilage facilitates interactions between two bones in a joint with a low coefficient of friction.Water, type II collagen (Col2), and proteoglycans are the principle components of articular cartilage.Of the wet mass, 65%~80% of cartilage is water, 10%~20% is Col2, and 4%~7% is aggrecan.Other collagens and proteoglycans such as types V, VI, IX, X, XI, XII, XIV collagens (Eyre et al., 2002) and decorin, biglycan, fibromodulin, lumican, epiphycan, and www.intechopen.comPrinciples of Osteoarthritis -Its Definition, Character, Derivation and Modality-Related Recognition 322 perlecan (Knudson & Knudson, 2001) also contribute a small part (less than 5%) of the normal cartilage composition.The articular chondrocyte is the only cell type in articular cartilage and as such is the major player in cartilage development and maintenance.During articular cartilage development, articular chondrocytes establish the cartilage matrix by synthesizing and depositing collagens and proteoglycans.The collagen/proteoglycan matrix consists of a highly dense meshwork of collagen fibrils including the major collagen type II (Col2) and minor collagen types IX, and XI embedded in gel-like negatively-charged proteoglycans (Kannu et al., 2009).This hydrated architecture of the matrix provides the articular cartilage with tensile and resilient strength which allows joints to maintain proper biomechanical function (Iozzo, 2000).As articular cartilage matures, articular chondrocytes maintain the cartilage by synthesizing matrix components (Col2 and proteoglycans) and matrix degrading enzymes with minimal turnover of cells and matrix.The existing collagen network becomes cross-linked, and articular cartilage matures into a permanent tissue with the ability to absorb and respond to mechanical stress (Verzijl et al., 2000).Under normal conditions, articular chondrocytes become arrested at a pre-hypertrophic stage of differentiation, thereby persisting throughout postnatal life to maintain normal articular cartilage structure (Pacifici et al., 2005).
Source: InTech eBooks
DOI: 10.5772/27835
Authors: Jie Shen, Meina Wang, Hongting Jin, Erik Sampson, Di Che
Language: English
Subfield: Rheumatology
Field: Medicine
Domain: Health Sciences
Open Access status: hybrid
OpenAlex ID: W1593976265