CD44 and hyaluronan expression in human cutaneous scar fibroblasts

Fibrotic disorders of skin and other organs are typically associated with an abnormal accumulation of extracellular matrix. This study focuses on a matrix constituent, hyaluronan-which is known to be altered in fibrotic disorders of skin- and on CD44, a cell adhesion molecule and putative receptor for hyaluronan. Tissue samples were obtained from biopsies of human normal skin, normal cutaneous scar; and hypertrophic cutaneous scar. After culturing, cells were studied by single- and double-labeling immunohistochemistry using the two anti-CD44 monoclonal antibodies, BU-52 and J173, and a biotinylated hyaluronan binding complex probe, b-HABR. Certain cultures were pretreated with Streptomyces hyaluronidase to assess the dependency of CD44 expression on the presence of endogenous hyaluronan. CD44 expression, both in the presence and the absence of exogenous hyaluronan, was quantitated by radioimmunobinding assay. Overall glycosaminoglycan synthesis and identification of hyaluronan were accomplished by precursor incorporation assays and by quantitative cellulose acetate electrophoresis. CD44 was found to be a normal human adult fibroblastic antigen whose expression is markedly increased for hypertrophic scar fibroblasts compared with normal skin fibroblasts. Although hyaluronan was found to be the predominant glycosaminoglycan constituent of the pericellular matrix for these fibroblasts, CD44 attachment to the cell surface is neither mediated by hyaluronan nor is the presence of hyaluronan a prerequisite for CD44 expression. Exogenous hyaluronan induced a decline in measurable CD44 expression for normal skin fibroblasts but not for hypertrophic scar fibroblasts. These observations are compatible with current understanding of the way cells manage the hyaluronan economy of the extracellular matrix and emphasize phenotypic heterogeneities between fibroblasts derived from normal versus scar tissues.