Heparin-binding growth factors are crucial for the formation of human epidermis, but little is known about the role of heparan sulfate proteoglycans in this process. Here we investigated the role of the heparan sulfate proteoglycan, perlecan, in the formation of human epidermis, by utilizing in vitro engineered human skin. By disrupting perlecan expression either in the dermis or the epidermis, we found that epidermally derived perlecan is essential for epidermal formation. Perlecan-deficient keratinocytes formed a strikingly thin and poorly organized epidermis because of premature apoptosis and failure to complete their stratification program. Exogenous perlecan fully restored epidermal formation. Perlecan deposition in the basement membrane zone correlated with formation of multilayered epidermis. Perlecan deficiency, however, had no effect on the lining and deposition of major basement membrane components as was evident by a continuous linear staining of laminin and collagen IV. Similarly, perlecan deficiency did not affect the distribution of ␤1 integrin. Addition of the perlecan ligand, fibroblast growth factor 7, protected perlecan-deficient keratinocytes from cell death and improved the thickness of the epidermis. Taken together, our results revealed novel roles for perlecan in epidermal formation. Perlecan regulates both the survival and terminal differentiation steps of keratinocytes. Our results suggested a model whereby perlecan regulates these processes via controlling the bioavailability of perlecan-binding soluble factors involved in epidermal morphogenesis.Skin is the largest organ of the body. It serves as a shield against microorganism invasion and UV radiation, prevents dehydration, regulates body temperature, and is a part of the immune system (1). It consists of two distinct tissues, epidermis and dermis that are separated by a basement membrane (BM). 4 The dermis is a dense collagen-rich connective tissue that provides the support and nourishment to the overlying epidermis. It is mainly composed of fibroblasts that synthesize and secrete the various extracellular matrix (ECM) components (2). The epidermis is made primarily of keratinocytes that form a stratified squamous epithelium. It consists of multiple layers exhibiting distinct morphology and function. From the innermost to the outermost layers, they are the basal, spinous, granular, and cornified strata (3). Throughout adult life, the epidermis undergoes continuous self-renewal through proliferation of the basal cells, the only cells of the epidermis with the ability to proliferate. The keratinocytes undergo terminal differentiation as they leave the basal layer and move upward through the suprabasal layers toward the tissue surface, where they die and are sloughed off (3). This process makes the skin an excellent model system to study the coordinated regulation of cell proliferation, cell differentiation, and cell death. The formation of the mature epidermis is regulated by cross-talk with the adjacent connective tissue through a netw...

HS (heparan sulphate) proteoglycans bind secreted signalling proteins, including FGFs (fibroblast growth factors) through their HS side chains. Such chains contain a wealth of differentially sulphated saccharide epitopes. Whereas specific HS structures are commonly believed to modulate FGF-binding and activity, selective binding of defined HS epitopes to FGFs has generally not been demonstrated. In the present paper, we have identified a series of sulphated HS octasaccharide epitopes, derived from authentic HS or from biosynthetic libraries that bind with graded affinities to FGF4, FGF7 and FGF8b. These HS species, along with previously identified oligosaccharides that interact with FGF1 and FGF2, constitute the first comprehensive survey of FGF-binding HS epitopes based on carbohydrate sequence analysis. Unexpectedly, our results demonstrate that selective modulation of FGF activity cannot be explained in terms of binding of individual FGFs to specific HS target epitopes. Instead, different FGFs bind to identical HS epitopes with similar relative affinities and low selectivity, such that the strength of these interactions increases with increasing saccharide charge density. We conclude that FGFs show extensive sharing of binding sites in HS. This conclusion challenges the current notion of specificity in HS-FGF interactions, and instead suggests that a set of common HS motifs mediates cellular targeting of different FGFs.

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