Distribution of type VI collagen in chondrocyte microenvironment: Study of chondrons isolated from human normal and degenerative articular cartilage and cultured chondrocytes

The chondron is the microanatomical unit composed of a chondrocyte and its pericellular microenvironment (PCME), including the pericellular matrix and capsule. In the present study, we extracted chondrons from human articular cartilages and investigated the relationship between the distribution of the matrix molecules, including type VI collagen, and the degeneration of articular cartilage. We also investigated the effects of interleukin-1β (IL-1β) and transforming growth factor β-1(TGF-β₁) on the distribution of type VI collagen in cultured chondrocytes. Chondrons were extracted by low-speed homogenization from cartilage pieces obtained from forensic autopsies and from patients with knee osteoarthritis (OA) undergoing total knee arthroplasty. Cartilage sections were classified into three groups (normal, slight degeneration, and moderate degeneration) based on the degree of degeneration according to Mankin's score. Extracted chondrons were immunostained, and the distribution of the matrix molecules, including type VI collagen, was investigated using a confocal laser scanning microscope (CLSM). The chondrocytes isolated by enzymic treatment were subjected to three-dimensional culture in agarose gel and then treated with IL-1β or TGF-β₁. The distribution of newly synthesized type VI collagen in agarose gel was also investigated using the CLSM. Type VI collagen was localized specifically within the PCME of chondrons. The volume ratio of PCME to chondrocyte (P/C ratio) was significantly higher in the moderate degeneration group than in the other two groups. The accumulation of type VI collagen around a chondrocyte was obviously increased by the addition of TGF-β₁. The P/C ratio significantly increased as the severity of the OA progressed, suggesting that type VI collagen distributed specifically in the PCME was playing a protective role for chondrocytes by maintaining the pericellular microenvironment in OA.