Vitamin A antagonizes decreased cell growth and elevated collagen-degrading matrix metalloproteinases and stimulates collagen accumulation in naturally aged human skin

Damage to human skin due to ultraviolet light from the sun (photoaging) and damage occurring as a consequence of the passage of time (chronologic or natural aging) are considered to be distinct entities. Photoaging is caused in part by damage to skin connective tissue by increased elaboration of collagen-degrading matrix metalloproteinases, and by reduced collagen synthesis. As matrix metalloproteinase levels are known to rise in fibroblasts as a function of age, and as oxidant stress is believed to underlie changes associated with both photoaging and natural aging, we determined whether natural skin aging, like photoaging, gives rise to increased matrix metalloproteinases and reduced collagen synthesis. In addition, we determined whether topical vitamin A (retinol) could stimulate new collagen deposition in sun-protected aged skin, as it does in photoaged skin. Sun-protected skin samples were obtained from 72 individuals in four age groups: 18-29 y, 30-59 y, 60-79 y, and 80+ y. Histologic and cellular markers of connective tissue abnormalities were significantly elevated in the 60-79 y and 80+ y groups, compared with the two younger age groups. Increased matrix metalloproteinase levels and decreased collagen synthesis/expression were associated with this connective tissue damage. In a separate group of 53 individuals (80+ y of age), topical application of 1% vitamin A for 7 d increased fibroblast growth and collagen synthesis, and concomitantly reduced the levels of matrix-degrading matrix metalloproteinases. Our findings indicate that naturally aged, sun-protected skin and photoaged skin share important molecular features including connective tissue damage, elevated matrix metalloproteinase levels, and reduced collagen production. In addition, vitamin A treatment reduces matrix metalloproteinase expression and stimulates collagen synthesis in naturally aged, sun-protected skin, as it does in photoaged skin.     

Collagen degradation in aged/photodamaged skin in vivo and after exposure to matrix metalloproteinase-1 in vitro

Biochemical and ultrastructural approaches were used to assess collagen changes in photodamaged skin. Extensive collagen fragmentation, clumping of the fragmented collagen, and interaction of fibroblasts with the damaged matrix were observed. Similar, though less extensive, collagen damage was also observed in sun-protected skin-individuals aged 80 y or older (naturally aged skin). In comparison, sun-protected skin from young individuals (18-29 y of age) demonstrated little damage. A uniform distribution of collagen fibrils was seen. Interstitial fibroblasts were embedded in the collagen matrix and in close apposition with intact collagen fibrils. In additional studies, three-dimensional lattices of type I collagen were exposed in vitro to matrix metalloproteinase-1 (interstitial collagenase), and examined for biochemical and ultrastructural alterations. Under conditions in which enzyme treatment produced fragmentation in 30-40% of the collagen molecules, the lattices demonstrated collagen fragmentation and clumping of the damaged matrix. Recent studies have demonstrated a loss of procollagen production by fibroblasts in contact with collagen fragments in vitro. This study demonstrates similar changes in collagen structure in vivo in aged and photodamaged skin. We suggest that collagen fragmentation in vivo could underlie the loss of collagen synthesis in photodamaged skin and, to a lesser extent perhaps, in aged skin.     

Retinoids suppress cysteine-rich protein 61 (CCN1), a negative regulator of collagen homeostasis, in skin equivalent cultures and aged human skin in vivo

Alterations in connective tissue collagen are prominent features of both chronologically aged and photoaged (ageing because of sun exposure) human skin. These age-related abnormalities are mediated in part by cysteine-rich protein 61 (CCN1). CCN1 is elevated in the dermis of both chronologically aged and photoaged human skin in vivo and promotes aberrant collagen homeostasis by down-regulating type I collagen, the major structural protein in skin, and promoting collagen degradation. Vitamin A and its metabolites have been shown to improve chronologically aged and photoaged skin by promoting deposition of new collagen and preventing its degradation. Here, we investigated regulation of CCN1 expression by retinoids in skin equivalent cultures and chronologically aged and photoaged human skin in vivo. In skin equivalent cultures, all-trans retinoic acid (RA), the major bioactive form of vitamin A in skin, significantly increased type I procollagen and reduced collagenase (matrix metalloproteinases-1, MMP-1). Addition of recombinant human CCN1 to skin equivalent cultures significantly reduced type I procollagen and increased MMP-1. Importantly, RA significantly reduced CCN1 expression in skin equivalent cultures. Topical treatment with retinol (vitamin A, 0.4%) for 7days significantly reduced CCN1 mRNA and protein expression in both chronologically aged (80+years) and photoaged human skin in vivo, compared to vehicle-treated skin. These data indicate that the mechanism by which retinoids improve aged skin, through increased collagen production, involves down-regulation of CCN1.     

Modulation of collagen metabolism by the topical application of dehydroepiandrosterone to human skin

Dehydroepiandrosterone (DHEA) and its sulfate conjugate (DHEA-S) are the most abundantly produced human adrenal steroids to be reduced with age. DHEA may be related to the process of skin aging through the regulation and degradation of extracelluar matrix protein. In this study, we demonstrate that DHEA can increase procollagen synthesis and inhibit collagen degradation by decreasing matrix metalloproteinases (MMP)-1 synthesis and increasing tisuue inhibitor of matrix metalloprotease (TIMP-1) production in cultured dermal fibroblasts. DHEA was found to inhibit ultraviolet (UV)-induced MMP-1 production and the UV-induced decrease of procollagen synthesis, probably due to the inhibition of UV-induced AP-1 activity. DHEA (5%) in ethanol:olive oil (1:2) was topically applied to buttock skin of volunteers 12 times over 4 weeks, and was found to significantly increase the expression of procollagen alpha1(I) mRNA and protein in both aged and young skin. On the other hand, topical DHEA significantly decreased the basal expression of MMP-1 mRNA and protein, but increased the expression of TIMP-1 protein in aged skin. We also found that DHEA induced the expressions of transforming growth factor-beta1 and connective tissue growth factor mRNA in cultured fibroblasts and aged skin, which may play a role in the DHEA-induced changes of procollagen and MMP-1 expression. Our results suggest the possibility of using DHEA as an anti-skin aging agent.     

Inhibition of type I procollagen production in photodamage: correlation between presence of high molecular weight collagen fragments and reduced procollagen synthesis

Three-dimensional lattices of reconstituted, polymerized type I collagen were subjected to partial hydrolysis by organ culture fluid from human skin or by various matrix metalloproteinases, including matrix metalloproteinase-1 (interstitial collagenase), -2 (72 kDa gelatinase A), -8 (neutrophil collagenase), -9 (92 kDa gelatinase B), or -13 (collagenase 3). Following partial digestion, human dermal fibroblasts were incubated on the enzyme-treated or control lattices and examined for ability to contract the collagen lattice and synthesize type I procollagen. Collagen lattices partially degraded by organ culture fluid were contracted by fibroblasts under conditions in which control collagen lattices were not. On the partially degraded collagen, fibroblasts synthesized reduced amounts of type I procollagen (approximately 70% reduction). Purified matrix metalloproteinases with collagenolytic activity duplicated the effects of the human skin organ culture fluid, although matrix metalloproteinases 8 and 13 were less efficient than matrix metalloproteinase-1 (65% vs 40% and 18% reduction in type I procollagen production for matrix metalloproteinases 1, 8, and 13, respectively). Matrix metalloproteinases 2 and 9 were without effect on intact collagen; however, when collagen lattices were subjected to digestion by a combination of matrix metalloproteinases 1 and 9, fragments produced by matrix metalloproteinase-1 were further degraded by the gelatinase. Collagen contraction and inhibition of procollagen synthesis were both reduced. Matrix metalloproteinase-2 was less effective than matrix metalloproteinase-9 in clearing matrix metalloproteinase-1-generated fragments. Matrix metalloproteinase-2 was also less effective in preventing contraction and inhibiting the downregulation of type I procollagen synthesis. These observations suggest that in the presence of high molecular weight fragments of type I collagen, type I procollagen synthesis is inhibited. As these fragments are processed further, there is less inhibition of type I procollagen production.     

Changes in S100A8 expression in UV-irradiated and aged human skin in vivo

S100A8, a calcium-binding protein, is associated with keratinocyte differentiation, inflammation and wound healing. S100A8 is induced by various skin stresses and diseases, which suggests that S100A8 plays a role in those processes. However, it has not been reported how the expression of S100A8 is affected during skin aging or whether S100A8 plays a role in the skin aging process. In this study, we investigated the changes in S100A8 mRNA and protein following acute UV irradiation to human buttock skin and by intrinsic aging and photoaging in human sun-protected (upper-inner arm) and sun-exposed (forearm) skin of elderly subjects. Real-time PCR, western blot and immunohistochemical staining analyses of UV-irradiated young buttock skin revealed that S100A8 protein expression was increased at 24 h (3.0-fold) and 48 h (4.4-fold) after UV irradiation. S100A8 mRNA and protein were more highly expressed by 2.3- and 4.0-fold, respectively, in the sun-protected skin of elderly people than in that of young people. In addition, the sun-exposed skin of elderly expressed more S100A8 mRNA and protein than the sun-protected skin of the same individuals. In immunohistochemical staining, facial (photoaged) skin ≥72 years showed higher epidermal expression of S100A8 than that of the other age groups. Based on the above results, our data suggest that the expression of S100A8 is affected by acute UV irradiation, intrinsic aging and photoaging processes.     

Increased expression of TRPV1 channel in intrinsically aged and photoaged human skin in vivo

Abstract:  Transient receptor potential vanilloid type 1 (TRPV1) is activated by various stimuli including capsaicin, heat and acid. While TRPV1 has been localized in the epidermis, little is known about the physiological role of TRPV1 in the skin, especially in skin ageing. In this study, we investigated the effect of acute UV irradiation on TRPV1 expression in human skin and the changes in TRPV1 mRNA and protein in intrinsic ageing and photoageing using human sun-protected (upper inner arm) and sun-exposed (forearm) skin of young and elderly subjects.
Western blot analysis of UV-irradiated young buttock skin revealed that the expression of TRPV1 protein was increased at 24 h (2.3-fold) and 48 h (2.4-fold) after UV irradiation. Real-time PCR analysis also showed that the mRNA level of TRPV1 was augmented by 2.4-fold at 4 h after UV irradiation. TRPV1 protein was expressed at higher levels by 2.6-fold in the sun-protected skin of the elderly subjects than in that of young people according to western blotting, real-time PCR analysis and immunohistochemical staining. In addition, the photoaged skin of elderly showed increased expression of TRPV1 mRNA and protein compared with that of the sun-protected skin of the same individuals. Also, we found increased expression of TRPV1 in nerve fibres of elderly persons using double staining of TRPV1 and nerve fibres.
Based on the above results, our data suggest that the expression of TRPV1 is affected by both the intrinsic ageing and photoageing processes.     

Increase of collagen synthesis by obovatol through stimulation of the TGF-beta signaling and inhibition of matrix metalloproteinase in UVB-irradiated human fibroblast

BACKGROUND: Alterations of the extracellular matrix (ECM) is critical in the photo and age-damaged skin. Thus any compounds keep ECM can protected from photo and aged-damaged skin. ECM is predominantly composed of type I and type III collagens in the dermis. Transforming growth factor (TGF-beta)s play important roles in cellular biosynthesis of extracellular matrix. Activator protein 1 (AP-1) and Smad are significant factors that mediate TGF-beta. OBJECTIVE: We have investigated increasing effects of obovatol, a biphenolic compound isolated from leaves of Magnolia obovata on the collagen synthesis through stimulation of the TGF-beta signaling and inhibition of matrix metalloproteinase, thereby protect against from UV damages via maintain of collagen in the UVB irradiated human fibroblast cells. METHODS: The fibroblasts were pretreated with obovatol for 24h and then the cells were irradiated with UVB. UVB-exposed cells were further cultured for 24h. Type I procollagen, MMP-3, TGF-beta and Smad as well as phosphorylation of MAPK family expression were determined by Western blot. The activation of AP-1 was investigated using EMSA. The released type I procollagen and TGF-beta into cell culture medium were determined by Western blot after concentration of these proteins. RESULTS: The results showed that obovatol stimulated type I procollagen, TGF-beta, and Smad expression and inhibited matrix metalloproteinase-3 (MMP-3) in dose-dependent manner (1-5muM) in UVB-irradiated human fibroblast cells. Obovatol also inhibited UVB-induced activation of AP-1 and MAP kinases. CONCLUSION: These results suggest that obovatol increases collagen synthesis through stimulation of the TGF-beta signaling and inhibition of matrix metalloproteinase in UVB-irradiated human fibroblast, thus obovatol could be effective against photo-damaged skin.     

Collagen loss in photoaged human skin is overestimated by histochemistry

It is well known that photoaged skin is characterized by increases in dermal matrix components that include glycosaminoglycans, proteoglycans and masses of abnormal elastic fibers accompanied by substantial collagen loss. Histochemical staining of such tissue gives the impression of "massive" loss of collagen and its replacement by these other matrix components. Early biochemical studies have lent support to this notion with a reported decrease in total collagen of approximately 45% compared to protected skin. More recent studies report considerably less, but varying, amounts of collagen loss. Rarely have the two approaches, histochemistry and biochemical analysis, been used in the same study to examine the same tissue. In this study, collagen loss was quantified biochemically in paired biopsies from sun-protected and sun-exposed arm skin of moderately photoaged female subjects (age 51-77 years). The values obtained were compared with histochemical and immunochemical findings. Quantitatively, collagen loss on a per mg protein basis was small compared to the histochemical appearance.     

Partial depletion of mitochondrial DNA from human skin fibroblasts induces a gene expression profile reminiscent of photoaged skin

In photoaged skin, wrinkles result from an increased degradation and a decreased de novo synthesis of collagen fibers. At the molecular level, photoaged skin is characterized by increased amounts of large-scale deletions of the mitochondrial (mt) genome such as the 4,977 bp common deletion. The common deletion can be generated in dermal fibroblasts through repetitive ultraviolet (UV) A irradiation, and this was found to be associated with an increased expression of the collagen-degrading enzyme matrix metalloproteinase-1 (MMP-1). These studies did not clarify whether increased MMP-1 expression was caused by a disturbance of mtDNA integrity or whether it occurred independently. We have therefore generated a phenocopy of cells bearing large-scale deletions of mtDNA by gradually depleting the mtDNA from unirradiated human skin fibroblasts. Gradual depletion of mtDNA caused a gene expression profile, which was reminiscent of that observed in photoaged skin. Accordingly, in these cells an increased expression of MMP-1 without a concomitant change in tissue inhibitor metalloproteinase-1 as well as a decreased expression of collagen type 1 alpha-1, that is, a gene involved in collagen de novo synthesis, was observed. This altered gene expression resulted from intracellular, mitochondria-derived oxidative stress. Our results support the concept that disruption of mt integrity, for example, by UV-induced mtDNA mutagenesis, is of pathogenetic relevance for photoaging of human skin.     

Collagen mRNA expression detected by in situ hybridization in keloid tissue

The keloid fibroblasts exhibited increased extracellular matrix gene expression, and prominent elevated type I procollagen mRNA when compared to control fibroblasts cultured from the uninvolved skin of normal people. It also showed markedly elevated type I/III procollagen mRNA ratios, but no synthesis of type IV procollagen mRNA by keloid fibroblasts was observed. By in situ hybridization in keloid tissue, high levels of type I and type III procollagen mRNAs were detected in most of the fibroblasts, suggesting the presence of a subpopulation responsible for the increased collagen production. The levels of type I and type III procollagen mRNAs in these fibroblasts were clearly elevated compared to control skin specimens. And concentration of type I procollagen mRNA was found more predominantly than was type III. These results suggest that deposition of collagen in keloid could result from activation of certain fibroblasts responsible for type I procollagen production.     

Exogenous nitric oxide enhances the synthesis of type I collagen and heat shock protein 47 by normal human dermal fibroblasts

BACKGROUND: It is well established that the alterations of dermal matrix contributes to skin aging characterized by wrinkles. On the other hand, physiological NO is useful to maintain skin homeostasis such as a vasodilatation. However, a role of NO on production of dermal matrix has been clarified. OBJECTIVE: In this study, we have attempted to analyze the role of NO on type I collagen synthesis of normal human dermal fibroblasts including expression of procollagen alphaI S(1) mRNA/protein and heat shock protein 47 (HSP47). METHODS: The effects of NO which was generated by two types of NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP), on type I collagen and HSP47 and their related mRNA expression were examined with ELISA and RT-PCR. RESULTS: NO was significantly accelerated the production of type I collagen by fibroblasts corresponding with up-regulation of procollagen alphaI (1) mRNA. Furthermore, NO increased both levels of HSP47 protein and mRNA in fibroblasts in a dose-dependent manner. CONCLUSIONS: These results suggest that NO has dual effects on collagen synthesis by fibroblasts as follows; one is the direct stimulation of collagen synthesis due to the up-regulation of procollagen alphaI(1) mRNA, and the other is an indirect effect through the increase of HSP47 mRNA expression. This is the first report that exogenous NO stimulates HSP47 production by dermal fibroblasts.     

Photoaging-associated changes in epidermal proliferative cell fractions in vivo

The epidermis is a dynamic epithelium with constant renewal throughout life. Epidermal homeostasis depends on two types of proliferative cells, keratinocyte stem cells (KSCs), and transit amplifying (TA) cells. In the case of chronologic aging, levels of KSCs tend to decrease and change functionally. However, little is known about the effect of photoaging on epidermal proliferative subtype populations. The aim of this study was to validate involucrin/β1-integrin ratio as a molecular marker of epidermal photoaging, and to investigate the effects of photoaging caused by chronic UV exposure on the proliferative subtype populations. A total of 15 male volunteers (age range 20–24 and 77–85 years, Fitzpatrick skin phototype III–IV) provided sun-exposed and sun-protected skin samples for real-time RT-PCR, Western blot analysis and immunostaining. Fractional changes in proliferative subtype populations in photoaged and chronologically aged skins were analyzed by flow cytometry. The expression of β1-integrin was found to be significantly reduced in photoaged skin and ratios of the expressions of involucrin to β1-integrin were increased 2.6-fold only in elderly subjects. Interestingly, immunostaining of the sun-exposed skins of elderly subjects showed aberrant β1-integrin expression over the basal layer and greater numbers of Ki-67-positive cells than in sun-protected buttock skin. Flow cytometric analysis revealed that the proportion of KSCs to TA cells was reversed in sun-exposed and sun-protected skins of elderly subjects. Our results suggest that KSC numbers may be lower in photoaged skin than in chronologically aged skin and could be applied to hyperplastic pattern of photoaging. These findings suggest that the epidermis of photoaged skin is impaired in terms of its proliferative potential by attempting to repair chronic UV exposure and that photoaging may be associated with alteration in the two proliferative cell fractions.     

Fermentable metabolite of Zymomonas mobilis controls collagen reduction in photoaging skin by improving TGF-beta/Smad signaling suppression

Solar ultraviolet (UV) irradiation causes damages on human skin and premature skin aging (photoaging). UV-induced reduction of type I collagen in dermis is widely considered primarily induction of wrinkled appearance of photoaging skin. Type I procollagen synthesis is reduced under UV irradiation by blocking transforming growth factor-beta (TGF-beta)/Smad signaling; more specifically, it is down-regulation of TGF-beta type II receptor (T beta RII). Therefore, preventing UV-induced loss of T beta RII results decreased type I collagen reduction in photoaging skin. Zymomonas mobilis is an alcohol fermentable, gram-negative facultative anaerobic bacterium whose effect on skin tissue is scarcely studied. We investigated the protective effects of fermentable metabolite of Z. mobilis (FM of Z. mobilis) against reduction of type I procollagen synthesis of UV-induced down-regulation of T beta RII in human dermal fibroblasts FM of Z. mobilis was obtained from lyophilization of bacterium culture supernatant. The levels of T beta RII and type I procollagen mRNA in human dermal fibroblasts were measured by quantitative real-time RT-PCR, and T beta RII protein levels were assayed by western blotting. T beta RII, type I procollagen, and type I collagen proteins in human dermal fibroblasts or hairless mouse skin were detected by immunostaining. FM of Z. mobilis inhibited down regulation of T beta RII mRNA, and protein levels in UVB irradiated human dermal fibroblasts consequently recover reduced type I procollagen synthesis. These results indicate UVB irradiation inhibits type I procollagen synthesis by suppression of TGF-beta/Smad signaling pathway, and FM of Z. mobilis has inhibitory effect on UVB-induced reduction of type I procollagen synthesis. While short period UVB irradiation decreased both T beta RII and type I procollagen protein levels in hairless mouse skin, topical application of FM of Z. mobilis prevented this decrease. Wrinkle formation in hairless mouse skin surface was accelerated by continuous 5 month UVB irradiation along with a reduction of type I collagen in the dermis, but this change was prevented by topical application of FM of Z. mobilis. From this experimental data, it is suggested that FM of Z. mobilis is effective for suppression of wrinkle formation in photoaging skin by inhibition of type I procollagen synthesis reduction.     

Increased deposition of fibulin-2 in solar elastosis and its colocalization with elastic fibres

BACKGROUND: Fibulin-2 is a 195-kDa protein belonging to a novel family of extracellular matrix proteins that might be involved in microfibril and elastic fibre organization. OBJECTIVES: To determine the localization of fibulin-2 in relation to elastic fibres in normal skin and in solar elastosis characterized by increased elastotic material in the papillary dermis. METHODS: The expression and synthesis of fibulin-2 was investigated by means of in situ hybridization, immunohistochemistry and Western blot analysis in normal and photoaged skin. RESULTS: Immunohistochemistry and elastic tissue staining revealed that fibulin-2 deposition mainly colocalized with microfibrils and elastin fibres, with a marked staining of elastotic material in solar elastosis. Western blot analysis demonstrated that in photoaged skin fibulin-2 showed the same electrophoretic mobility as in sun-protected skin. However, in actinic elastosis the amount of fibulin-2 was significantly higher. In addition, smaller degradation products were detectable, presumably reflecting increased proteinase activity in photodamaged skin. CONCLUSIONS: This study shows that deposition of fibulin-2 and elastin is highly co-ordinated, indicating that this protein plays an important role in elastic fibre and microfibril formation in normal and actinically damaged skin.     

The role of TRPV1 channel in aged human skin

Transient receptor potential vanilloid 1 (TRPV1) is a member of the nonselective cationic channel family. Activation of TRPV1 induces an influx of divalent and monovalent cations (i.e., Ca²⁺, Na⁺, and Mg²⁺) which are activated by capsaicin, heat, and acid. TRPV1 is known to be expressed in the epidermis, but little is known about the physiological significance and functional role of TRPV1 in skin.Recent studies suggested that heat- and ultraviolet (UV)-induced matrix metalloproteinases-1 (MMP-1) expression may be partly mediated by TRPV1 activation in human keratinocytes. Also, heat and UV increased expression of TRPV1 proteins in human skin in vivo. TRPV1 protein was expressed more in the sun-protected (upper-inner arm) skin of the elderly than in young subjects. In addition, the photoaged (forearm) skin of the elderly showed increased TRPV1 expression compared to sun-protected skin of the same individuals. The increased TRPV1 expression in the old skin implies that TRPV1 may be related to senile skin symptoms, such as senile pruritus and neurogenic inflammation. This review provides a summary of current researches on the role of TRPV1 channel in human skin, especially in aged skin.     

Photoageing shows histological features of chronic skin inflammation without clinical and molecular abnormalities

BACKGROUND: Photodamage is characterized by degradation of collagen and accumulation of abnormal elastin in the superficial dermis. Mast cells and macrophages, which are found in higher numbers in photoaged skin, have been implicated in this process. OBJECTIVES: To analyse the phenotype of haematopoietic-derived infiltrating cells in photodamaged skin. METHODS: Chronically sun-exposed (preauricular) and control sun-protected (postauricular) skin was recovered from eight healthy subjects undergoing cosmetic surgery (facial lifting). RESULTS: Histological analysis showed that sun-exposed skin harboured more infiltrating mononuclear cells than sun-protected skin. Cellular infiltrates were found at the periphery of areas of elastolysis around hair follicles in sun-exposed sites, whereas they were found in the interfollicular dermis around blood vessels and around hair follicles in sun-protected samples. Immunohistochemical analysis revealed an increased number of mast cells, macrophages and CD4+ CD45RO+ T cells in sun-exposed dermis as well as a higher number of CD1a+ dendritic cells in sun-exposed epidermis, compared with the sun-protected samples. Thus photoageing displays histological features of chronic skin inflammation. However, no molecular sign of inflammation was observed and we even found a decreased expression of interleukin-1beta mRNA in sun-exposed compared with sun-protected sites. Furthermore, the patients' skin looked normal and did not display any clinical inflammation. CONCLUSIONS: Collectively, these data show that chronic ultraviolet irradiation induces alterations of innate immune cells which are recruited in sun-exposed skin without being activated.     

The matricellular protein periostin contributes to proper collagen function and is downregulated during skin aging

Background Periostin is a secreted 90 kDa matricellular protein, which is predominantly expressed in collagen-rich tissues. Collagen is the most abundant protein in mammals and has great tensile strength. Recent investigations have shown that periostin influences collagen fibrillogenesis and biomechanical properties of murine connective tissues.ObjectiveWe investigated the function of periostin concerning collagen homeostasis during intrinsic and extrinsic skin aging. For this purpose, human skin samples of young and old donors as well as samples of photoaged and sun-protected skin areas were analyzed for periostin expression. Using in vitro models, we determined the cell types responsible for periostin expression and performed functional analyses with periostin knockdown cells.MethodsTaqMan Real-Time PCR, UV irradiation, knockdown experiments, immunostaining, electron microscopy, collagen degradation assay, collagen crosslink analysis.ResultsPeriostin expression is highest in the papillary dermis and downregulated during skin aging. Fibroblasts and non-follicular skin derived precursors were identified as main source for periostin expression in human skin. Periostin knockdown in fibroblasts has no effect on collagen expression, but results in an increased fibril diameter and aberrant collagen structure. This leads to an increased susceptibility of collagen toward proteases, whereas recombinant periostin protects collagen fibrils from degradation.ConclusionOur data show that periostin plays an important role for proper collagen assembly and homeostasis. During skin aging periostin expression decreases and contributes to the phenotype of aged skin.     

Repair of photoaged dermal matrix by topical application of a cosmetic 'antiageing' product

BACKGROUND: Photoaged skin is characterized by coarse and fine wrinkles. The mechanism of wrinkle formation appears to involve changes to components of the dermal extracellular matrix. Topical treatment with all-trans retinoic acid (RA) can repair photoaged dermal matrix; this is regarded as the 'gold standard' against which repair agents are judged. To date, little is known regarding the ability of over-the-counter 'antiageing' products to repair photoaged skin. OBJECTIVES: We used a modified occluded patch test to ascertain whether topical applications of cosmetic 'antiageing' products are able to repair photoaged human skin. METHODS: Commercially available test products [basic moisturizer, 'antiageing' cream containing different active complex levels (6% active: lipopentapeptide, white lupin peptides, antioxidants, retinyl palmitate; 2% active: lipopentapeptide, white lupin peptides, antioxidants)] were applied under occlusion for 12 days prior to biopsy and histological assessment in photoaged volunteers (n=9). RA was used as a positive control. RESULTS: In agreement with previous studies, the patch-test study revealed that RA produced significant fibrillin-1 deposition in the papillary dermis (P<0.01) but had little effect on procollagen I or matrix metalloproteinase-1 expression. The 6% total active complex formulation, however, increased the deposition of fibrillin-1 and procollagen I (P<0.01, P<0.05, respectively). CONCLUSIONS: This study indicates that in an in vivo 12-day patch test an over-the-counter cosmetic product can induce changes in photoaged dermal extracellular matrix, which are indicative of repair.