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3. Ebook Principles of osteoarthritis – Its definition, character, derivation and modality-related recognition: Part 2

Part 2 book “Principles of osteoarthritis – Its definition, character, derivation and modality-related recognition” has contents: Cartilage extracellular matrix integrity and oa, biochemical mediators in volved in cartilage degradation and the induction of pain in osteoarthritis, proteases and cartila ge degradation in osteoarthritis, anion channels in osteoart hritic chondrocytes, and other contents. | Part 5 Metabolic 14 Cartilage Extracellular Matrix Integrity and OA Chathuraka T. Jayasuriya and Qian Chen Alpert Medical School of Brown Universit, Rhode Island Hospital United States of America 1. Introduction Articular cartilage tissue is mostly composed of extracellular matrix (ECM) in which a sparse population of cells (chondrocytes) reside. These cells produce both anabolic and catabolic factors that perpetuate a homeostatic process of ECM breakdown and repair termed cartilage turnover. This balance between tissue anabolism and catabolism is characteristic of normal articular cartilage. However, during osteoarthritis (OA), this process is disrupted due to disregulation of chondrocyte function. Although articular cartilage is anatomically classified as a single tissue type, it is divided into four zones defined by their physiological position relative to the joint surface. Likewise, the populations of chondrocytes housed within these zones and their respective ECMs often differ from one another in both appearance and organization. The calcified zone lies directly on top of the subchondral bone, which the cartilage tissue shields from physical forces. This zone contains a very small population of chondrocytes that are slowly being replaced by bone forming cells (osteoblasts) continuously throughout life. When compared to other cartilage zones, the calcified zone ECM is highly mineralized and contains the sparsest chondrocyte population. Osteoblasts from the neighboring subchondral bone secrete bone morphogenic factor (BMPs), and other factors such as stromal cell derived factor 1 (SDF-1) which promote chondrocyte hypertrophy and mineralization. The deep zone cartilage layer lies directly above the calcified zone and contains small vertical aggregates of chondrocytes embedded within a uniquely organized ECM which histologically resemble columnar structures. The middle zone is by far the largest layer containing round bodied chondrocytes and a well hydrated .