UVA- and UVB-induced changes in collagen and fibronectin biosynthesis in the skin of hairless mice

Effects of topical application of different molecular weight marine fish skin collagen oligopeptides on UVB-induced photoaging rat skin

OBJECTIVE

The objective of this work was to develop a peptide production process of the exact molecular weight propitious to topical application for cosmetics and to investigate the effects of enzymolysis-derived peptide on UVB-induced photoaging rat skin.

METHODS

The chum salmon fish skins were hydrolyzed by alkaline protease and neutral protease and spray-dried at different conditions, and three kinds of molecular weight peptide (MFSOP) were obtained. A total of 66 ICR rats (female, 20 ± 1 g) were randomly divided into eleven groups, including the normal, model, and experimental groups. The three kinds of MFSOP were dissolved at different dosages (5‰, 2.5%, and 5%) and then applied on the ICR hairless back skins prior to exposing UVB irradiation of 3000mJ/cm² to them 4 h later. After 8 weeks, the rats were killed and the hair-shaved skins were tested for skin moisture, hyaluronic acid, hydroxyproline, antioxidant activity, and RNA expression.

RESULTS

Three kinds of MFSOP were obtained, with the average molecular weights of 495.16, 1194.00, and 2032.46 Dalton, respectively. The MFSOPs, especially the MFSOP of average molecular weight of 1194.00 Dalton, played an important role in the recovery of the UVB-injured skin tissue in lock in moisture, in antioxidant activity and in promotion in collagen and elastin protein to some extent.

CONCLUSION

MFSOPs, especially MFSOP of average molecular weight of 1194.00 Dalton, derived from enzymolysis are potential materials to apply in cosmetics for the UVB9-induced anti-photoaging activity (lock in moisture, antioxidant activity, and promotion in collagen and elastin protein).

Investigation of psoriasis skin tissue by label-free multi-modal imaging: a case study on a phototherapy-treated patient

Background: Psoriasis is a systemic inflammatory disease characterized by epidermal proliferation in the skin. Altered lipid metabolism is considered to be a central factor in the psoriatic etiopathogenesis. Thus, it is necessary to visualize chemical specificity of the samples for better medical diagnosis and treatment. Here, we investigate its role in the development of psoriatic lesions, before and after ultraviolet phototherapy, in a case study.

Methods: The distribution and morphology of different lipids and fibrous proteins in psoriatic (lesional) tissues were visualized by two complementary label-free imaging techniques: 1) non-linear microscopy (NLM), providing images of lipids/proteins throughout the skin layers at submicrometer resolution; and 2) mass spectrometry imaging (MSI), offering high chemical specificity and hence the detection of different lipid species in the epidermal and dermal regions. A conventional method of histological evaluation was performed on the tissues, with no direct comparison with NLM and MSI.

Results: Psoriatic tissues had a higher lipid content, mainly in cholesterol, in both the epidermal and dermal regions, compared to healthy tissues. Moreover, the collagen and elastin fibers in the psoriatic tissues had a tendency to assemble as larger bundles, while healthy tissues showed smaller fibers more homogeneously spread. Although phototherapy significantly reduced the cholesterol content, it also increased the amounts of collagen in both lesional and non-lesional tissues.

Conclusion: This study introduces NLM and MSI as two complementary techniques which are chemical specific and can be used to assess and visualize the distribution of lipids, collagen, and elastin in a non-invasive and label-free manner.

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Evaluation of the UVB-screening capacity and restorative effects exerted by farnesol gel on UVB-caused sunburn

Farnesol, a natural 15-carbon organic compound, has various microbiological and cellular activities. It has been found to exert apoptosis-inducing effects against carcinoma cells as well as antiallergic and anti-inflammatory effects in vivo. In the current study, a series of formulations composed of various concentrations of hydroxypropyl methylcellulose (HPMC) with the addition of hyaluronan (HA) and xanthan gum (XG) was designed to evaluate the UVB-screening and H₂ O₂ -eliminating effects of farnesol in normal fibroblasts. Farnesol at 0.005, 0.0075, and 0.01% exhibited significant capacity for H₂ O₂ scavenging; at 0.0025%, it showed insignificant effects. Under 120-min UVB exposure, screening with plural gel composed of 0.0025% farnesol, 0.5% HA, and 0.5% XG containing 1.5% or 2% HPMC retained normal fibroblast viability. After 60-min exposure to UVB, screening with plural gel composed of farnesol, HA, XG, and 0.5%, 1.0%, 1.5%, or 2% HPMC decreased the ratio of the G1 phase and increased ratio of the S phase in comparison with the accumulated cell cycle of the normal fibroblasts without screening. The gel with 2% HPMC displayed the strongest cell cycle-reversal ability. In vivo histopathological results showed that the prepared plural gels with 0.5% or 2% HPMC and farnesol, HA, and XG had greater antiphotoaging and reparative effects against UVB-induced changes and damage in the skin. In conclusion, the current in vitro and in vivo results demonstrated that the prepared plural composed of 0.0025% farnesol, 0.5% HA, 0.5% XG, and 2% HPMC possessed the greatest UVB-screening capacity and the strongest restorative effects on UVB-induced sunburned skin.

A genetic anomaly of oriented collagen biosynthesis and cross-linking: Keratoconus

Oriented collagen biosynthesis is one of the major mechanisms involved in tissue and organ formation during development. Corneal biogenesis is one example. Defects in this process lead to anomalies in tissue structure and function. The transparency of cornea and its achievement are a good example as well as its pathological modifications. Keratoconus is one example of this type of pathologies, involving also inappropriate cross-linking of collagen fibers. Among the tentatives to correct this anomaly, the riboflavin-potentiated UV-cross-linking (CXL) of keratoconus corneas appears clinically satisfactory, although none of the experiments and clinical results published prove effective cross-linking. The published results are reviewed in this article.

Importance of amino acid composition to improve skin collagen protein synthesis rates in UV-irradiated mice

Skin collagen metabolism abnormalities induced by ultraviolet (UV) radiation are the major causes of skin photoaging. It has been shown that the one-time exposure of UV irradiation decreases procollagen mRNA expression in dermis and that chronic UV irradiation decreases collagen amounts and induces wrinkle formation. Amino acids are generally known to regulate protein metabolism. Therefore, we investigated the effects of UV irradiation and various orally administered amino acids on skin collagen synthesis rates. Groups of 4–5 male, 8-week-old HR-1 hairless mice were irradiated with UVB (66 mJ/cm²) twice every other day, then fasted for 16 h. The fractional synthesis rate (FSR; %/h) of skin tropocollagen was evaluated by incorporating l-[ring-²H₅]-phenylalanine. We confirmed that the FSR of dermal tropocollagen decreased after UVB irradiation. The FSR of dermal tropocollagen was measured 30 min after a single oral administration of amino acids (1 g/kg) to groups of 5–16 UVB-irradiated mice. Branched-chain amino acids (BCAA, 1.34 ± 0.32), arginine (Arg, 1.66 ± 0.39), glutamine (Gln, 1.75 ± 0.60), and proline (Pro, 1.48 ± 0.26) did not increase the FSR of skin tropocollagen compared with distilled water, which was used as a control (1.56 ± 0.30). However, essential amino acids mixtures (BCAA + Arg + Gln, BCAA + Gln, and BCAA + Pro) significantly increased the FSR (2.07 ± 0.58, 2.04 ± 0.54, 2.01 ± 0.50 and 2.07 ± 0.59, respectively). This result suggests that combinations of BCAA and glutamine or proline are important for restoring dermal collagen protein synthesis impaired by UV irradiation.

Influence of stress on extracellular matrix and integrin biology

Dynamic interactions between cells and extracellular matrix (ECM) through integrins influence most cellular functions. Normal cells, but even more, tumor cells are subjected to different forms of stress, including ischemia, radical oxygen species production, starvation, mechanical stress or genotoxic insults due to anti-cancer drugs or irradiation. In these situations, an adaptative cellular response occurs, integrating a complex network of intracellular signaling modules, which, depending on stress intensity, may result to either damage repair followed by complete restitution of cellular functions, or programmed cell death. Because of its implication in oncogenesis and anti-cancer therapy, cellular stress response has been thoroughly investigated. However, most of these studies have been performed in the context of isolated cells without taking into consideration that most cells are part of the tissue within which they interact with ECM through integrin. Few studies have described the influence of stress on cell-to-ECM interaction. However, one can speculate that, in these conditions, cells could functionally interact with protein microenvironment either to create positive interactions to survive (for example by facilitating protective pathways) or negative interaction to die (for example by facilitating detachment). In this review, we summarize the knowledge relative to the influence of different stress modalities on ECM remodeling, integrin expression and/or function modifications, and possible functional consequences, independently from the cellular model as these findings came from a large variety of cells (mesenchymal, endothelial, muscular, epithelial and glandular) and fields of application (cancer, vascular biology and tissue engineering). Most studies support the general notion that non-lethal stress favors ECM stiffness, integrin activation and enhanced survival. This field opens large perspectives not only in tumor biology but also in anti-cancer therapy by targeting one or several steps of the integrin-mediated signaling pathway, including integrin ligation, or activation of integrin-linked enzymes or integrin adaptors.

UVA induces granzyme B in human keratinocytes through MIF: implication in extracellular matrix remodeling

In a previous study, we have described that UVB induces granzyme B (GrB) in human keratinocyte cells, and that confers potent cellular cytotoxicity against various cellular models, including immune cells (Hernandez-Pigeon, H., Jean, C., Charruyer, A., Haure, M. J., Titeux, M., Tonasso, L., Quillet-Mary, A., Baudouin, C., Charveron, M., and Laurent, G. (2006) J. Biol. Chem. 281, 13525-13532). Herein, we have found that, in contrast to UVB, UVA failed to enhance keratinocyte cellular cytotoxicity but was still able to trigger GrB production. We show that GrB is accumulated through a p38 MAPK-dependent transcriptional mechanism stimulated by redox-dependent migration inhibitory factor release. Moreover, GrB purified from UVA-treated cellular extracts was found to degrade fibronectin in vitro. Treatment with antisense oligonucleotide directed against GrB resulted in the inhibition of UVA-induced cell detachment and cell death and facilitated cell migration through fibronectin and vitronectin matrix upon UVA exposure. Altogether, these results suggest another function for GrB in the context of the UV response. Indeed, combined with our previous study, it appears that, whereas this enzyme mediates keratinocyte cellular cytotoxicity following UVB irradiation, GrB supports the capacity of keratinocyte to degrade extracellular matrix components following UVA irradiation. UV-mediated GrB production may thus have important consequences in photoaging and photocarcinogenesis.

Age-dependent remodeling of connective tissue: role of fibronectin and laminin

Connective tissues differ from other tissues in their more abundant extracellular matrix (ECM). This matrix is composed of a relatively large number of macromolecules interacting with each other as well as with the cells they are surrounding. Such cells, fibroblasts, chondrocytes and others, secrete the macromolecules of ECM according to a genetically and environmentally regulated "program". It appeared recently that one type of macromolecular interactions is characterized by the selective cleavage of some of the ECM components. Some of these proteolytic cleavage products were shown to possess remarkable biological activities absent from the parent molecules. Such mechanisms were shown to play an important role in aging processes. Also called matricryptins such peptides and their activities are produced from several matrix components. Of special interest are these matricryptins which are derived from fibronectin, laminin and elastin. Their production by proteolytic attack of the original ECM components, followed by their novel biological activities, form in some instances autoamplifying vicious circles. Such "epigenetic", post-translational mechanisms are not coded in the genome, they are neither "accidental", nor "chaotic" but remarkably predictable, the result of the presence in several ECM components of "matricryptic" sites and coregulated synthesis of matrix components carrying such sites and of proteolytic enzymes producing the matricryptins. Some examples will be discussed, derived from the experiments carried out in our laboratory and others over the years, involved in aging and in some of the age-dependent pathologies.

Oxidative and premature skin ageing

To elucidate the scientific state of the art with respect to the role of nutrition in skin ageing, nine experts from different disciplines discussed the role of micronutrients on 'oxidative and premature skin ageing'. In this 25th Hohenheim Consensus Meeting, 13 questions were discussed and, based on published valid data, answered by mutual agreement. The consensus answers achieved during the meeting are justified by a scientific background text. The importance of in vitro and in vivo models regarding oxidative and premature skin ageing was critically evaluated. There was a special focus on prevention and intervention of skin ageing with nutrition. Finally, the paper summarizes the scientific background from different areas related to oxidative and premature skin ageing.

Age dependent increase of elastase type protease activity in mouse skin. Effect of UV-irradiation

The effect of chronological aging and photoaging (UV-radiation) on elastase-type enzyme activity of hairless mouse skin was studied. Aging resulted in the increase of elastase type endopeptidase activity extractable from mouse skins. Both chronic UVA and UVB radiation resulted in a significant increase of elastase type activity. PBS extracted only small part of the elastase activity, UV-A produced an increase of about 90-120% according to the type of irradiation (xenon or UV-A SUN) and UV-B produced a 72% increase. Extraction by Triton X-100 suggested that most of the activity is bound to cells and fibrous structures. EDTA inhibited 80-90% of the elastase activity in chronologically aged skin extracts and also the activity induced by UVA radiation suggesting that metallo-elastase(s) are involved. About 30% of the UVB induced activity could only be inhibited by EDTA and about 50% by PMSF suggesting that irradiation by UVB increased more serine endopeptidase activity but also MMP-activity. Chronic UVA radiation produced an increase of skin elastase activity equivalent to that observed after 24 months of aging in non-irradiated animals (approximately 100 weeks) corresponding to approximately 90% of total life span of these mice. The total increase produced by UVB was less, but the strong increase of a serine elastase, presumably from PMN-s, appear to produce a much more pronounced biological activity as shown by the presence of fibronectin degradation products in skin extracts. Such degradation products were shown to exert harmful effects on tissues. These results may well have biological significance and distinguish chronological aging and photoaging.

Cellular fibronectin is induced in ultraviolet-exposed human skin and induces IL-10 production by monocytes/macrophages

CD11b+ monocytic/macrophagic cells that infiltrate human skin after in vivo ultraviolet exposure potently produce interleukin-10. We hypothesized that binding of monocyte beta1 integrins to ultraviolet-induced extracellular matrix ligands, such as fibronectin, after entry of blood monocytes into the dermis, is involved in the modulation of immunoregulatory monocytic cytokines. Immunostaining of human skin and reverse transcriptase-polymerase chain reaction studies revealed that the embryonic isoform of cellular fibronectin, in which the extra domain A (EDA) segment is spliced in (EDA+ cellular fibronectin), and confers enhanced binding to beta1 integrins, is newly induced and is associated with infiltrating CD11b+ cells post in vivo ultraviolet exposure. We then tested the effect of fibronectin on resting purified peripheral monocytes in vitro. We found that monocyte interleukin-10, but not interleukin-12, was significantly induced in a concentration-dependent manner by in vitro binding to cellular fibronectin (n = 6), but not plasma fibronectin. Tumor necrosis factor-alpha was also induced in a concentration-dependent manner, but to a lesser extent. Monoclonal antibodies to beta1 integrins beta-subunit (CD29) also strongly induced tumor necrosis factor-alpha and interleukin-10 production, but not interleukin-12. Neutralization of tumor necrosis factor-alpha reduced by 54% the interleukin-10 production that was induced by monocytes binding to cellular fibronectin, indicating that interleukin-10 induction is at least in part dependent upon concomitant autocrine tumor necrosis factor-alpha release. In conclusion, ultraviolet skin injury results in increased production and deposition of EDA+ cellular fibronectin in the papillary dermis, which may be one of the key signals capable of inducing interleukin-10 but not interleukin-12 in monocytes that infiltrate micromilieu of human skin after ultraviolet exposure.

Low doses of ultraviolet A radiation stimulate adhesion of human dermal fibroblasts by integrins in a protein kinase C-dependent pathway

In this work, we have studied the modulation of fibroblast-extracellular matrix interactions by physiological doses of ultraviolet A (UV-A) radiation using an adhesion assay on collagen. We have shown that low doses of UV-A (20 kJ/m2) stimulate fibroblast adhesion while higher doses (100 and 200 kJ/m2) inhibit it. By measurement of the thiobarbituric acid reactive substances (TBARS) and use of the chain-breaking antioxidant vitamin E, no role of lipid peroxidation can be detected in these effects. By incubating fibroblasts with a specific protein kinase C (PKC) inhibitor, GF109203X, we have demonstrated that the stimulation of the adhesion by low doses of UV-A involves, at least in part, a PKC-dependent mechanism. In addition, using function-blocking antibodies of alpha 1, alpha 2 or alpha 5 integrin chains involved in extracellular matrix anchorage, we have shown that they decrease the stimulation of adhesion following low doses of UV-A radiation, demonstrating the involvement of these three integrin chains in this UV-A effect. In parallel, 20 kJ/M2 of UV-A are found to rapidly stimulate membrane expression of alpha 1, alpha 2 and alpha 5 integrin chains. This work, which underlines the involvement of integrins in UV-A effects, contributes to the evaluation of the mechanisms by which cell-matrix interactions modulate cell behaviour.

Effects of simulated solar radiation on type I and type III collagens, collagenase (MMP-1) and stromelysin (MMP-3) gene expression in human dermal fibroblasts cultured in collagen gels

Understanding the mechanisms responsible for photodamage to the skin is most important for dermatology. 3-D cultures have been used as tools to mimic the in vivo situation for several years. We irradiated such a system containing human dermal fibroblasts cultured in collagen gels, a well-known model considered to be a dermal equivalent, which reproduces the interaction between cells and the surrounding extracellular matrix. The effects of solar irradiation (315-800 nm) on the steady-state levels of the mRNAs of extracellular matrix components (type I and III collagens) and their degrading enzymes (interstitial collagenase, MMP-1 and stromelysin 1, MMP-3) were measured. Exposure to low levels of solar radiation (0-10 J cm-2 in the UVA, i.e. suberythemal UVA doses) caused a transient decrease in type I procollagen mRNA, an increase in MMP-mRNA, and no change in type III procollagen mRNA steady-state levels. These results describe the early changes in the connective tissue of the skin following exposure to low-level solar stimulation, and may help explain the long-term changes in photodamaged skin.

UVR modulates the steady-state levels of skin collagen transcripts in hairless mice

Exposure to solar UV radiation (UVR) leads to changes in the extracellular matrix of the dermis, which is largely composed of collagen and elastin. Collagen and elastin proteins and their corresponding mRNA were assessed in dorsal skins of hairless mice exposed to 0.64 J/cm2 UVR (295-400 nm), 5 days per week, over a 12 week period. A 48% increase in skin-fold thickness was accompanied by increased elastic tissue deposition and more compressed collagen bundles as assessed histologically. Collagen I mRNA levels were similar to those in control skins at 1, 2, 3 and 6 weeks of UVR and less than control levels at 9 and 12 weeks. Collagen III mRNA levels were elevated after 1 week of UVR, remained elevated for a further 2 weeks and then returned to control levels at weeks 6, 9 and 12 when changes are occurring in collagen I transcripts. There was no evidence of corresponding changes in collagen I and III protein levels assessed using electrophoretic techniques. These results suggest that damage to the extracellular matrix, consequent on UVR, is associated with some pretranslational events. Elastin mRNA levels were unaffected by UVR, suggesting that elastic tissue hyperplasia is a posttranscriptional phenomenon.

The relationship between quantitative changes in collagen and formation of wrinkles on hairless mouse skin after chronic UV irradiation

Female albino hairless mice were irradiated chronically with sub-erythemal doses of UVB radiation. Collagen extracted from the irradiated or non-irradiated dorsal skin of mice was fractionated into neutral salt-soluble (NSC), acid-soluble (ASC) and insoluble fractions (ISC). An age-related exponential decrease in the content and proportion of acid-soluble collagen was found in each group. The contents and the proportions of ASC from irradiated mice were always significantly lower than those from age-matched control animals. Age-related slight decreases were observed in the contents (per fresh weight of tissues) of NSC, ISC and total collagen in the control group but decreases in these collagen contents after UVB irradiation were marked. A dramatic decrease in ASC occurred nearly concomitantly with wrinkle formation in the irradiated mice. The decrease of acid-soluble skin collagen in irradiated mice may play a role in the formation of wrinkles on hairless mouse dorsal skin.

The effect of chronic low-dose UVB radiation on Langerhans cells, sunburn cells, urocanic acid isomers, contact hypersensitivity and serum immunoglobulins in mice

C3H mice were irradiated three times a week for up to 6 weeks with either 500 J/m2 or 1000 J/m2 broadband UVB (270-350 nm) or 3000 J/m2 narrowband UVB (311-312 nm; TL01 source). Each dose was suberythemal to the mouse strain used. The number of Langerhans cells (LC) in the epidermis was reduced by over 50% after 2 weeks of irradiation with the UVB source and by 20% following TL01 irradiation. Continued irradiation for up to 6 weeks resulted in no further decrease in LC numbers in the case of the UVB source but a steady decline to 40% in the case of the TL01 source. Sunburn cells were detected following irradiation with both sources but the numbers were very low in comparison with acute exposure. Ultraviolet-B exposure resulted in doubling of the thickness of the epidermis throughout the 6 weeks of irradiation while TL01 exposure did not alter epidermal thickness. Conversion of trans- to cis-urocanic acid (UCA) was observed with both UVB and TL01 sources. The percentage of cis-UCA started to return to normal after 4 weeks of TL01 exposure despite continued irradiation. As observed following a single exposure, the contact hypersensitivity (CH) response was significantly reduced following 6 weeks of UVB irradiation but was unaffected by TL01 exposure, indicating no correlation between cis-UCA levels and CH response. Total serum immunoglobulin levels remained unchanged throughout the 6 weeks of UVB or TL01 irradiation but IgE titers significantly increased in all cases in the first 2 weeks of irradiation, indicating a possible shift to a TH2 cytokine profile.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic UVB- and all-trans retinoic-acid-induced qualitative and quantitative changes in hairless mouse skin

Histochemical and ultrastructural studies have already demonstrated that chronic exposure to UV radiation induces profound alterations in all structural elements of the skin and that topical all-trans retinoic acid (tRA) can substantially correct much of the tissue damage. However, previous biochemical studies on dermal components of the extracellular matrix have led to contradictory results, particularly with regard to the effect of chronic UV exposure. The aim of our study was to investigate changes in collagen content and other dermal modifications induced by tRA in irradiated and non-irradiated hairless mouse skin. Hairless mice were exposed to increasing doses of UVB for 10 weeks (the cumulative total dose was 4.6 J cm-2). After the UV irradiation period the animals were treated with 0.05% tRA or with ethanol-polyethylene glycol vehicle alone three times a week for up to 10 weeks. Non-irradiated animals underwent the same treatments. The main clinical and histological changes induced by UVB exposure were erythema, wrinkling, keratosis and epidermal thickening. Following UVB exposure, tRA treatment did not improve the clinical aspect but increased the width of the dermal repair zone. Fibronectin, laminin and type I and VI collagens were detected by indirect immunofluorescence techniques in this zone. Type I and III collagens were quantitated in skin fragments after cyanogen bromide digestion and polyacrylamide gel electrophoresis. Under our experimental conditions, UVB irradiation alone induced neither changes in total collagen nor in type I and III collagen levels. tRA treatment of irradiated skin significantly increased both type I and III collagen levels by factors of 1.33 and 1.88 respectively. The ratio of type III to types I + III increased significantly. Topical tRA also increased collagen type levels in non-irradiated hairless mouse skin. Type I collagen increased proportionally to type III. This study leads to the conclusion that topical tRA exerts direct or indirect effects on collagen metabolism in irradiated as well as non-irradiated hairless mouse skin.

Keratinocyte extracellular matrix-mediated regulation of normal human melanocyte functions

Active roles of cell-cell interaction between melanocytes and neighboring keratinocytes for the regulation of melanocyte functions in the skin have been suggested. We examined substantial regulatory mechanisms of keratinocyte extracellular matrix (kECMs) for normal human melanocyte functions without direct cell-cell contact. We specially devised kECMs from proliferating or differentiating keratinocytes and further treated them with environmental stimulus ultraviolet B (UVB) for skin pigmentary system. Normal human melanocytes (NHM) were cultured on the various keratinocyte ECMs and initially the effects of the kECMs upon melanocyte morphology (dendrite formation and extension), growth, melanin production and expressions of pigmentation-associated protein (MEL-5) and proliferation-associated protein (proliferating cell nuclear antigen; PCNA/cyclin) were studied. Then we compared the effects of these cell-matrix interactions with those of direct melanocyte-keratinocyte, cell-cell contact in co-culture on melanocyte functions. Melanocytes cultured on any types of the kECMs that were tested significantly extended dendrites more than that on plastic cell culture dish without kECM (control). Melanocytes cultured on any types of the kECMs that were tested significantly extended dendrites more than that on plastic cell culture dish without kECM (control). Melanocytes cultured on the kECM prepared from UVB irradiated differentiating keratinocytes resulted in 219% increase in the number of dendrites. The growth of melanocytes on kECMs was also stimulated up to 280% of control. The kECM produced by proliferating keratinocytes had a more significant effect on the growth than kECM from differentiating keratinocytes. This melanocyte growth stimulating effect was decreased with kECM from UVB treated differentiating keratinocytes. The melanin content per melanocyte was constant on any of the kECMs.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen synthesis in (sun-) aged human skin and in fibroblasts derived from sun-exposed and sun-protected body sites

Endogenous and sun-induced aging of the skin cause distinct morphological alterations. In this study, we have analysed the ratio of collagen III to collagen III plus I in extracts of sun-exposed (face) and sun-protected (abdomen) aged skin, as well as in collagens synthesized by fibroblasts during in vitro culture derived from actinically damaged and sun-protected skin of other subjects (face, medial aspect of the upper arm vs. abdomen, lateral aspect of the forearm). Furthermore, the amount and extent of post-translational modifications of newly synthesized collagens were determined. Chronic sun exposure of the skin does not have an impact on the quantity of collagenous proteins newly synthesized in cell culture. The proportion of collagen III in pepsin extracts of sun-damaged skin is increased relative to sun-protected skin. However, fibroblasts derived from sun-exposed skin synthesize a lower proportion of collagen III than cells from sun-protected skin. The hydroxylation of lysyl residues in newly synthesized alpha 2(I) and alpha 1(III) collagen chains is reduced by UV irradiation, whereas hydroxylation of lysyl residues in alpha 1(I) chains and of prolyl residues in alpha 1(I), alpha 2(I) and alpha 1(III) chains is unaffected by UV irradiation. These data provide circumstantial evidence to indicate that collagen synthesis is influenced independently by endogenous and sun-induced aging.

UVA- and UVB-induced changes in hairless mouse skin collagen

UVA- and UVB-induced alterations in dermal collagen were investigated in a murine animal model. Groups of hairless mice were exposed to UVA and UVB for 28 weeks at a dose of 60 J/cm2 three times weekly and 0.06 J/cm2 three times weekly, respectively. Untreated animals were used as controls. Every 4 weeks dorsal skin was examined for quantitative and qualitative changes in dermal collagen. Neither UVA nor UVB caused a significant alteration in total skin collagen content. However, after UVA treatment the ability of skin collagen to be digested by pepsin decreased dramatically (up to 65% of skin collagen remained insoluble after 4 months), whereas exposure to UVB had no significant effect. Furthermore a shift in the ratio of alpha 1(I,III) chains to alpha 2(I) chains was detected after UVA exposure. The amount of type V collagen in mouse skin, as determined by a sensitive ELISA method, was markedly decreased after UVA treatment, but not after UVB treatment.

Alterations of proteoglycans in ultraviolet-irradiated skin

The effect of UVB exposure on the distribution and synthesis of dermal proteoglycans was measured in the skin of hairless mice. Two groups of mice were included: one was irradiated for 10 weeks; the other was kept as control. After intraperitoneal injection of sodium 35-S-sulfate, punch biopsies were taken for histology and proteoglycans were extracted from the remaining skin with 4 M guanidinium chloride, containing 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (0.5%, weight per volume). Following proteolytic digestion, the glycosaminoglycan constituents were isolated and analyzed by quantitative cellulose acetate electrophoresis and enzymatic digestibility. Under the influence of UVB radiation, newly synthesized proteoglycans measured by 35SO4 uptake increased as much as 60%. In addition, the irradiated skin had a higher average content of proteoglycan than had control skin (4981 micrograms vs 4134 micrograms/g dry weight). This could be ascribed to an increase in heparin (1400 vs 533 micrograms/g dry weight) and heparan sulfate (472 vs 367 micrograms/g dry weight), whereas no change in the concentration of hyaluronic acid (1243 vs 1372 micrograms/g dry weight) and dermatan sulfate (1866 vs 1863 micrograms/g dry weight) was observed. The irradiated animals also exhibited a marked increase in the synthesis of heparan sulfate and heparin (62% and 71%, respectively). These results demonstrate that chronic doses of UVB altered proteoglycan metabolism through both quantitative and qualitative changes.