Maturational differences in superficial and deep zone articular chondrocytes

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Abstract
To examine whether differences in chondrocytes from skeletally immature versus adult individuals are important in cartilage healing, repair, or tissue engineering, superficial zone chondrocytes (SZC, from within 100 μm of the articular surface) and deep zone chondrocytes (DZC, from 30%–45% of the deepest un-mineralized part of articular cartilage) were harvested from immature (1–4 months) and young adult (18–36 months) steers and compared. Cell size, matrix gene expression and protein levels, integrin levels, and chemotactic ability were measured in cells maintained in micromass culture for up to 7 days. Regardless of age, SZC were smaller, had a lower type II to type I collagen gene expression ratio, and higher gene expression of SZ proteins than their DZC counterparts. Regardless of zone, chondrocytes from immature steers had higher levels of Sox 9 and type II collagen gene expression. Over 7 days in culture, the SZC of immature steers had the highest rate of proliferation. Phenotypically, the SZC of immature and adult steers were more stable than their respective DZC. Cell surface α5 and α2 integrin subunit levels were higher in the SZC of immature than of adult steers, whereas β1 integrin subunit levels were similar. Both immature and adult SZC were capable of chemotaxis in response to fetal bovine serum or basic fibroblast growth factor. Our data indicate that articular chondrocytes vary in the different zones of cartilage and with the age of the donor. These differences may be important for cartilage growth, tissue engineering, and/or repair.

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