Hyaluronan synthesized in the epidermis has an exceptionally short half-life, indicative of its catabolism by epidermal keratinocytes. An intracellular pool of endogenously synthesized hyaluronan, from 1 to 20 fg/cell, inversely related to cell density, was observed in cultured rat epidermal keratinocytes. More than 80% of the intracellular hyaluronan was small (<90 kDa). Approximately 25% of newly synthesized hyaluronan was endocytosed by the keratinocytes and had a half-life of 2-3 h. A biotinylated aggrecan G 1 domain/link protein probe demonstrated hyaluronan in small vesicles of ϳ100 nm diameter close to the plasma membrane, and in large vesicles and multivesicular bodies up to 1300 nm diameter around the nucleus. Hyaluronan did not co-localize with markers of lysosomes. However, inhibition of lysosomal acidification with NH 4 Cl or chloroquine, or treating the cells with the hyaluronidase inhibitor apigenin increased intracellular hyaluronan staining, suggesting that it resided in prelysosomal endosomes. Competitive displacement of hyaluronan from surface receptors using hyaluronan decasaccharides, resulted in a rapid disappearance of this endosomal hyaluronan (t1 ⁄2 ϳ5 min), indicating its transitory nature. The ultrastructure of the hyaluronancontaining vesicles, co-localization with marker proteins for different vesicle types, and application of specific uptake inhibitors demonstrated that the formation of hyaluronan-containing vesicles did not involve clathrincoated pits or caveolae. Treatment of rat epidermal keratinocytes with the OX50 monoclonal antibody against the hyaluronan receptor CD44 increased endosomal hyaluronan. However, no CD44-hyaluronan co-localization was observed intracellularly unless endosomal trafficking was retarded by monensin, or cultivation at 20°C, suggesting CD44 recycling. Rat epidermal keratinocytes thus internalize a large proportion of their newly synthesized hyaluronan into non-clathrin-coated endosomes in a receptor mediated way, and rapidly transport it to slower degradation in the endosomal/lysosomal system.

Hyaluronan is an abundant and rapidly turned over matrix molecule between the vital cell layers of the epidermis. In this study, epidermal growth factor (EGF) induced a coat of hyaluronan and a 3-5-fold increase in its rate of synthesis in a rat epidermal keratinocyte cell line that has retained its ability for differentiation. EGF also increased hyaluronan in perinuclear vesicles, suggesting concurrent enhancement in its endocytosis. Cell-associated hyaluronan was most abundant in elongated cells that were stimulated to migrate by EGF, as determined in vitro in a wound healing assay. Large fluctuations in the pool size of UDP-N-acetylglucosamine, the metabolic precursor of hyaluronan, correlated with medium glucose concentrations but not with EGF. Reverse transcriptase-polymerase chain reaction (RT-PCR) showed no increase in hyaluronan synthases 1 and 3 (Has1 and Has3), whereas Has2 mRNA increased 2-3-fold in less than 2 h following the introduction of EGF, as estimated by quantitative RT-PCR with a truncated Has2 mRNA internal standard. The average level of Has2 mRNA increased from ϳ6 copies/ cell in cultures before change of fresh medium, up to ϳ54 copies/cell after 6 h in EGF-containing medium. A control medium with 10% serum caused a maximum level of ϳ21 copies/cell at 6 h. The change in the Has2 mRNA levels and the stimulation of hyaluronan synthesis followed a similar temporal pattern, reaching a maximum level at 6 h and declining toward 24 h, a finding in line with a predominantly Has2-dependent hyaluronan synthesis and its transcriptional regulation.Hyaluronan is a large glycosaminoglycan found in the extracellular space of most animal tissues. It forms a loose, highly hydrated, gel-like matrix that contributes to the maintenance of the extracellular space and facilitates nutrient diffusion. Furthermore, hyaluronan is involved in cell proliferation and differentiation, produces an environment favorable for migration (1), and stimulates cell locomotion (2, 3). Elevated tissue levels of hyaluronan occur during embryonic growth of tissues and organs (1), wound healing (4, 5), inflammation (6), and invasion of certain cancers (7-10).In skin epidermis, the narrow extracellular space surrounding keratinocytes contains a high concentration of hyaluronan (11, 12), as do other stratifying squamous epithelia (13, 14). The half-life of labeled epidermal hyaluronan in human skin organ culture is ϳ1 day (15), indicating fast local turnover by keratinocytes. The importance of the strikingly high concentration and turnover of hyaluronan in the multilayered squamous epithelia is not completely understood, but we have hypothesized that the former is necessary to maintain an extracellular space for the nutritional needs of the more superficial cell layers, whereas the latter allows the dramatic modulation of cell shape that occurs during differentiation and for the high migratory potential of keratinocytes that is activated, e.g. in wound healing (16).Unlike other glycosaminoglycans, hyaluronan is synthesized at the inne...

Keratinocyte growth factor (KGF) activates keratinocyte migration and stimulates wound healing. Hyaluronan, an extracellular matrix glycosaminoglycan that accumulates in wounded epidermis, is known to promote cell migration, suggesting that increased synthesis of hyaluronan might be associated with the KGF response in keratinocytes. Treatment of monolayer cultures of rat epidermal keratinocytes led to an elongated and lifted cell shape, increased filopodial protrusions, enhanced cell migration, accumulation of intermediate size hyaluronan in the culture medium and within keratinocytes, and a rapid increase of hyaluronan synthase 2 (Has2) mRNA, suggesting a direct influence on this gene. In stratified, organotypic cultures of the same cell line, both Has2 and Has3 with the hyaluronan receptor CD44 were up-regulated and hyaluronan accumulated in the epidermis, the spinous cell layer in particular. At the same time the expression of the early differentiation marker keratin 10 was inhibited, whereas filaggrin expression and epidermal permeability were less affected. The data indicate that Has2 and Has3 belong to the targets of KGF in keratinocytes, and support the idea that enhanced hyaluronan synthesis acts an effector for the migratory response of keratinocytes in wound healing, whereas it may delay keratinocyte terminal differentiation.

An ideal application of CD spectroscopy is the study of hyaluronan (HA) interaction with HA binding proteinlreceptor, chiral and non-chiral ligandsldrugs. For a non-chiral ligand, an induced CD (ICD) will be observed only for the bound ligand species whilst no CD will be detected for the free ligand species. For chiral ligands, changes in the CD of the ligand upon binding can still be used to discriminate binding interactions though this is less direct than ICD for non-chiral ligands. The ability to discriminate binding interactions in vdm is important to ascertain the drug-carrier properties of any polymer. For the non-chiral diclofenac anti inflammatory drug, the lack of ICD was indicative of no interaction with HA. However, the binding of diclofenac to human serum albumin (HSA) was found to be affected by HA in a concentration dependent manner. To elucidate this, the effect of pH, temperature and n-octanoate on the diclofenadHSA binding were investigated by CD spectroscopy. Hyaluronan bound to CD44 on keratinocytes is displaced by hyaluronan decasaccharides and not hexasaccharides 34 AN N-TERMINAL LINK PROTEIN PEPTIDE 36 Epidermal growth factor regulates keratinocyte hyaluronan STIMULATES BIOSYNTHESIS OF COLLAGEN AND PROTEOGLYCANS BY EXPLANTS OF HUMAN ARTICULAR CARTILAGE. metabolism We measured the effects of a 16 amino acid peptide, identical in sequence to the N-terminal of link protein, on the synthesis of collagen and proteoglycan by explants of human articular cartilage. Explants !?om normal adult knee cartilage were maintained for periods between 2 to 10 days in Dulbecco's modified Eagle's medium with or without 2% foetal calf serum. Peptides were added during each day of culture. Synthesis of collagen was determined by measuring the incorporation of ['Hlproline into hydroxyproline and proteoglycms by incorporation of [)'S]sulphate. The sizes and types of newly synthesised proteoglycan molecules were measured by gel chromatography and collagen by SDS PAGE. The LN peptide stimulated synthesis of type I1 collagen and aggrecan in cartilage !?om a number of different subjects. Maximum upregulation of both collagen and proteoglycam was attained at an identical concentration of 10 ng/d of peptide. Synthesis was upregulated both m the presence and absence of serum, although stimulation was greater when serum was added. It was concluded that the peptide may act as a growth factor and have an important role in the feed-back control of cartilage matrix synthesis. We wish to thank Action Research and The Home of Rest for Horses for their financial support and The Bone Tumor Service, Royal Orthopaedic Hospital, Birmingham, for human cartilage.

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