Proteoglycans in Articular Cartilage and Their Contribution to Chondral Injury and Repair Mechanisms

Abstract

Proteoglycans are vital components of the extracellular matrix in articular cartilage, providing biomechanical properties crucial for its proper functioning. They are key players in chondral diseases, specifically in the degradation of the extracellular matrix. Evaluating proteoglycan molecules can serve as a biomarker for joint degradation in osteoarthritis patients, as well as assessing the quality of repaired tissue following different treatment strategies for chondral injuries. Despite ongoing research, understanding osteoarthritis and cartilage repair remains unclear, making the identification of key molecules essential for early diagnosis and effective treatment. This review offers an overview of proteoglycans as primary molecules in articular cartilage. It describes the various types of proteoglycans present in both healthy and damaged cartilage, highlighting their roles. Additionally, the review emphasizes the importance of assessing proteoglycans to evaluate the quality of repaired articular tissue. It concludes by providing a visual and narrative description of aggrecan distribution and presence in healthy cartilage. Proteoglycans, such as aggrecan, biglycan, decorin, perlecan, and versican, significantly contribute to maintaining the health of articular cartilage and the cartilage repair process. Therefore, studying these proteoglycans is vital for early diagnosis, evaluating the quality of repaired cartilage, and assessing treatment effectiveness.

Keywords: articular cartilage; biomarkers; chondral injury; extracellular matrix; proteoglycans.

Figure 1

Aggrecan and PG aggregates structure. (A) Aggrecan, a hybrid PG consisting of a protein core with three lobular regions, keratan sulfate, and chondroitin sulfate. (B) PG aggregates composed of a central hyaluronan filament with numerous aggrecan molecules bound together. Modified from Roughley et al. [17].

Figure 2

Immunohistochemical staining of aggrecan in healthy sheep articular cartilage [38]. (A) Lower magnification image depicting the cartilage and underlying bone. (B) Higher magnification image revealing intricate details of all cartilage areas. The adivin-biotin-complex method was used for the immunohistochemistry. Enzymatic pre-treatment with hyaluronidase was used. The primary antibody used was anti-aggrecan (ab3778, Abcam, Cambride, UK) at 1/100 dilution in PBS containing 10% normal goat serum.