Superficial and deep zone articular chondrocytes exhibit differences in actin polymerization status and actin-associated molecules .

Objective: The actin cytoskeleton regulates cell shape and plays a role in regulating chondrocyte phenotype. Most studies investigating regulation of the chondrocyte phenotype by the actin cytoskeleton use chondrocytes isolated from full-thickness (FT) cartilage, which has a heterogeneous cell population. Superficial zone chondrocytes (SZC) have an elongated morphology and account for 10-20% of chondrocytes, while the remaining chondrocytes in the deeper zones appear more rounded.

CDC42 regulates the expression of superficial zone molecules in part through the actin cytoskeleton and myocardin-related transcription factor-A.

Osteoarthritis (OA) is a degenerative disease that initially manifests as loss of the superficial zone (SZ) of articular cartilage. SZ chondrocytes (SZC) differ in morphology from other chondrocytes as they are elongated and oriented parallel to the tissue surface. Proteoglycan 4 (PRG4) and tenascin C (TNC) are molecules expressed by SZC, which have been shown to be chondroprotective.