The roles of tenascin in cartilage development and function remain unclear. Based on the observation that tenascin is particularly abundant at the epiphyseal extremities of developing cartilaginous models of long bones in chick and mouse embryo, we tested the hypothesis that tenascin is involved in articular cartilage development. Immunofluorescence analysis revealed that tenascin was first localized in the cell condensation region of Day 4 chick embryo limb buds, where the cartilaginous models form. With further development, tenascin gene expression became indeed restricted to the articular cap of the models. Tenascin persisted in the articular cartilage of postnatal chickens but appeared to decrease with age. The protein was also abundant in embryonic and adult tracheal cartilage rings which, like articular cartilage, persist throughout postnatal life. Similar patterns of tenascin expression were seen in mouse. Using monoclonal antibodies to avian tenascin variants, we found that the bulk of articular cartilage contained the shortest tenascin variant (Tn190), whereas the largest variant (Tn230) was present in tissues associated or interacting with articular cartilage (ligaments and meniscus). The protein and its mRNA, however, were undetectable in growth plate cartilage undergoing maturation and endochondral ossification. This inverse correlation between chondrocyte maturation and tenascin production was corroborated by the finding that tenascin gene expression decreased markedly during maturation of chondrocytes in culture and during formation of a secondary ossification center within the articular cap in vivo. Thus, tenascin is intimately associated with the development of articular cartilage and other permanent cartilages whereas absence or reduced amounts of this matrix protein characterize transient cartilages which undergo maturation and are replaced by bone.0 1993 Wiley-Liss, Inc.

Keloids are wounding‐induced fibroproliferative human tumor‐like skin scars of complex genetic makeup and poorly defined pathogenesis. To reveal dynamic epigenetic and transcriptome changes of keloid fibroblasts, we performed RNA‐seq and ATAC‐seq analysis on an early passage keloid fibroblast cell strain and its paired normal control fibroblasts. This keloid strain produced keloid‐like scars in a plasma clot‐based skin equivalent humanized keloid animal model. RNA‐seq analysis reveals gene ontology terms including hepatic fibrosis, Wnt‐β‐catenin, TGF‐β, regulation of epithelial‐mesenchymal transition (EMT), STAT3 and adherens junction. ATAC‐seq analysis suggests STAT3 signalling is the most significantly enriched gene ontology term in keloid fibroblasts, followed by Wnt signalling (Wnt5) and regulation of the EMT pathway. Immunohistochemistry confirms that STAT3 (Tyr705 phospho‐STAT3) is activated and β‐catenin is up‐regulated in the dermis of keloid clinical specimens and keloid skin equivalent implants from the humanized mouse model. A non‐linear dose‐response of cucurbitacin I, a selective JAK2/STAT3 inhibitor, in collagen type I expression of keloid‐derived plasma clot‐based skin equivalents implicates a likely role of STAT3 signalling in keloid pathogenesis. This work also demonstrates the utility of the recently established humanized keloid mouse model in exploring the mechanism of keloid formation.

We studied the roles of protein kinase A (PKA) activation and cyclic AMP response element binding protein (CREB) phosphorylation in chondrogenesis using serum-free chicken limb bud micromass cultures as a model system. We showed the following points: 1) in micromass cultures, activation of PKA enhances chondrogenesis and increases the phosphorylation of CREB; 2) BMP-2, a chondrogenic stimulator, increases PKA activity and the level of phosphorylated CREB (P-CREB); 3) H8, a PKA inhibitor, inhibits chondrogenesis; 4) the chondrogenic activities of BMP-2 and cAMP are suppressed by H8; and 5) long-term TPA treatment (a protein kinase C (PKC) modulator) inhibits chondrogenesis and decreases the levels of CREB and P-CREB. These results suggest that activation of PKA is a physiological event during chondrogenesis that is involved in the chondrogenic effects of both BMP-2 and cyclic AMP (cAMP)-dependent pathways.