Modulation of Proteoglycan and Collagen Profiles in Human Dermal Fibroblasts by High Density Micromass Culture and Treatment with Lactic Acid Suggests Change to a Chondrogenic Phenotype

Abstract

Cartilage formation during embryonic development and in fracture healing in adult animals involves chondrogenic differentiation of mesenchymal precursors. Here we describe an in vitro model whereby human dermal fibroblasts, considered to be restricted to a fibroblast lineage, are apparently redirected toward a chondrogenic phenotype by high density micromass culture in the presence of lactic acid. Micromass cultures treated with 40 mM lactate exhibited increased levels of Alcian blue staining and sulfate incorporation, indicative of elevated sulfated glycosaminoglycan synthesis. Northern analysis revealed an up-regulation of chondroitin sulfate proteoglycan 1 (aggrecan) and transforming growth factor-β1 mRNA and a decrease in type I collagen expression. Type II collagen was detected by reverse transcription-PCR only in experimental cultures. Although the observed changes in biosynthesis and gene expression were consistent with differentiating chondrocytes. the cells displayed an elongated. fibroblast-like morphology. These findings suggest that dermal fibroblasts may be committed to differentiate along a chondrogenic paths as by to in vitro culture under specific forcing conditions.