MATRIX CATABOLISM IN ABNORMAL SCARRING--CD44, HYALURONAN

University Of California Los Angeles, Los Angeles CA

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Abstract

Hypertrophic scarring and keloid formation are serious derangements in the healing of cutaneous orofacial wounds after traumatic injury. They are defined almost exclusively on the basis of an abnormal accumulation of extracellular matrix and they disproportionately afflict certain minority populations, most particularly African-Americans. The long-term objectives of this work are to determine why extracellular matrix accumulates in hypertrophic scars and keloids and to establish how such accumulation can be prevented. The project focuses on hyaluronan, a ubiquitous component of human connective tissue matrix and one that is known to accumulate in hypertrophic scars and keloids. Abnormal hyaluronan accumulation in scars and other fibrotic disorders is believed to occur because of a disequilibrium between production and breakdown. The cause is unknown; however, previous work suggests that fibroblasts, and possibly microvascular endothelial cells, are responsible for binding, internalizing, and degrading hyaluronan. If this is true, a difference in the capacity of cells from normal versus abnormal tissues to degrade hyaluronan could be a key element in understanding how accumulation of extracellular matrix occurs and where the specific derangement resides. The proposed work will be the first to test directly whether CD44--a known cell surface receptor for hyaluronan in other human systems--acts as a hyaluronan receptor for cells derived from human skin and scar. Further, it will establish whether CD44 is altered, either quantitatively or qualitatively, as a function of the normalcy of the tissue of origin. The specific aims of this project are: (1) To establish whether fibroblastic CD44 is a cell surface receptor for hyaluronan. (2) To determine whether expression of CD44 differs for fibroblasts derived from normal human tissues (normal skin and normal scar) versus abnormal tissues (hypertrophic scars and keloids); and, to establish whether the binding affinity of CD44 for hyaluronan is altered as a function of the tissue of origin (normal versus abnormal). (3) To extend preliminary data by confirming that CD44 is expressed by the microvascular endothelium of skin and scar tissues and to establish whether such expression is altered as a function of the tissue of origin (normal versus abnormal). Thus, the experimental plan will assess two variables: CD44 expression and CD44 function and it will establish whether either or both variables are altered as a function of the normalcy of the tissue of origin. Most of the work will focus on fibroblasts; however, preliminary work on endothelial CD44 will be confirmed and extended. Methodologically, CD44 expression will be assessed by immunologic measures of CD44 antigen and by molecular measures of CD44 gene expression. CD44 function will be assessed by the capacity of anti-CD44 monoclonal antibodies (mAbs) to block binding of CD44's native ligand (hyaluronan), and by direct studies of binding between hyaluronan and purified CD44 in solution.