Rachel E.B. Watson

Molecular aspects of skin ageing

Ageing of human skin may result from both the passage of time (intrinsic ageing) and from cumulative exposure to external influences (extrinsic ageing) such as ultraviolet radiation (UVR) which promote wrinkle formation and loss of tissue elasticity. Whilst both ageing processes are associated with phenotypic changes in cutaneous cells, the major functional manifestations of ageing occur as a consequence of structural and compositional remodeling of normally long-lived dermal extracellular matrix proteins. This review briefly considers the effects of ageing on dermal collagens and proteoglycans before focusing on the mechanisms, functional consequences and treatment of elastic fibre remodeling in ageing skin. The early stages of photoageing are characterised by the differential degradation of elastic fibre proteins and whilst the activity of extracellular matrix proteases is increased in photoexposed skin, the substrate specificity of these enzymes is low. We have recently shown however, that isolated fibrillin microfibrils are susceptible to direct degradation by physiologically attainable doses of UV-B radiation and that elastic fibre proteins as a group are highly enriched in UV-absorbing amino acid residues. Functionally, elastic fibre remodeling events may adversely impact on: the mechanical properties of tissues, the recruitment and activation of immune cells, the expression of matrix metalloproteinases and cytokine signaling (by perturbing fibrillin microfibril sequestration of TGFβ). Finally, newly developed topical interventions appear to be capable of regenerating elements of the elastic fibre system in ageing skin, whilst systemic treatments may potentially prevent the pathological tissue remodeling events which occur in response to elastic fibre degradation.

Fibrillin microfibrils are reduced in skin exhibiting striae distensae

Striae distensae (striae: stretch marks) are a common disfiguring condition associated with continuous and progressive stretching of the skin—as occurs during pregnancy. The pathogenesis of striae is unknown but probably relates to changes in those structures that provide skin with its tensile strength and elasticity. Such structures are components of the extracellular matrix, including fibrillin, elastin and collagens. Using a variety of histological techniques, we assessed the distribution of these extracellular matrix components in skin affected by striae. Pregnant women were assessed for the presence of striae, and punch biopsies were obtained from lesional striae and adjacent normal skin. Biopsies were processed for electron microscopy, light microscopy and immunohistochemistry. For histological examination, 7 μm frozen sections were stained so as to identify the elastic fibre network and glycosaminoglycans. Biopsies were also examined with a panel of polyclonal antibodies against collagens I and III, and fibrillin and elastin. Ultrastructural analysis revealed alterations in the appearance of skin affected by striae compared with that of normal skin in that the dermal matrix of striae was looser and more floccular. Light microscopy revealed an increase in glycosaminoglycan content in striae. Furthermore, the number of vertical fibrillin fibres subjacent to the dermal–epidermal junction (DEJ) and elastin fibres in the papillary dermis was significantly reduced in striae compared with normal skin. The orientation of elastin and fibrillin fibres in the deep dermis showed realignment in that the fibres ran parallel to the DEJ. However, no significant alterations were observed in any other extracellular matrix components. This study identifies a reorganization and diminution of the elastic fibre network of skin affected by striae. Continuous strain on the dermal extracellular matrix, as occurs during pregnancy, may remodel the elastic fibre network in susceptible individuals and manifest clinically as striae distensae.

Tomato paste rich in lycopene protects against cutaneous photodamage in humans in vivo: A randomized controlled trial

Background  Previous epidemiological, animal and human data report that lycopene has a protective effect against ultraviolet radiation (UVR)‐induced erythema.

Tissue section AFM: In situ ultrastructural imaging of native biomolecules.

Conventional approaches for ultrastructural high-resolution imaging of biological specimens induce profound changes in bio-molecular structures. By combining tissue cryo-sectioning with non-destructive atomic force microscopy (AFM) imaging we have developed a methodology that may be applied by the non-specialist to both preserve and visualize bio-molecular structures (in particular extracellular matrix assemblies) in situ. This tissue section AFM technique is capable of: i) resolving nm–µm scale features of intra- and extracellular structures in tissue cryo-sections; ii) imaging the same tissue region before and after experimental interventions; iii) combining ultrastructural imaging with complimentary microscopical and micromechanical methods. Here, we employ this technique to: i) visualize the macro-molecular structures of unstained and unfixed fibrillar collagens (in skin, cartilage and intervertebral disc), elastic fibres (in aorta and lung), desmosomes (in nasal epithelium) and mitochondria (in heart); ii) quantify the ultrastructural effects of sequential collagenase digestion on a single elastic fibre; iii) correlate optical (auto fluorescent) with ultrastructural (AFM) images of aortic elastic lamellae.

Clinical features of photodamaged human skin are associated with a reduction in collagen VII

Chronically sun‐exposed or photodamaged human skin is characterized by a number of clinical features, including wrinkles. However, little is known about the molecular mechanisms that underlie these features. We investigated the hypothesis that the mechanism of wrinkle formation may involve loss of anchoring fibrils, composed mainly of collagen VII, which are important in maintaining dermal‐epidermal junction integrity. Ten volunteers with moderate to severe photodamage of dorsal forearm skin were recruited to the study. Using immunohistochemistry, transmission electron microscopy and in situ hybridization, we compared collagen VII protein and mRNA content of photodamaged forearm skin with that of sun‐protected hip and upper inner arm skin from the same subjects. Numbers of anchoring fibrils per linear μm of basement membrane (mean ± SEM) were significantly lower in photodamaged skin (1·79±0·10) as compared with sun‐protected hip (2·28±0·11) and upper inner arm skin (2·21±0·10) (P<0·01), and similarly keratinocyte expression of collagen VII mRNA, quantitated as number of positively stained keratinocytes per high power field, was significantly reduced in photodamaged skin (6·3±2·5) as compared with sunprotected hip (20·0±5·6) and upper inner arm skin (17·7±4·9) (P<0·001). Semiquantitative assessment of immunohistochemical staining for collagen VII showed a non‐significant reduction in photodamaged skin as compared with sun‐protected skin. We propose that reduced content of collagen VII in photodamaged skin contributes to wrinkle formation by weakening the bond between the dermis and epidermis.

Altered claudin expression is a feature of chronic plaque psoriasis.

Epithelial tight junctions play a central role in cell–cell adhesion and are necessary for the selective paracellular movement of ions. Claudins are key components of tight junctions and their expression is altered in gut epithelia in a variety of inflammatory enteropathies, including ulcerative colitis and Crohns disease. Psoriasis is a chronic inflammatory skin disease affecting approximately 2% of the western population, with significantly increased occurrence in individuals with Crohns disease. Initial studies investigated the expression of claudins in skin of healthy volunteers and patients with chronic plaque psoriasis. We report here that claudins‐1 and ‐3 are the major protein species present in the epidermis of healthy skin; they are expressed on the surface of epidermal keratinocytes, consistent with their localization to tight junctions. In plaques of psoriasis, claudin‐1 was not identifiable in the epidermis, although typical staining patterns were observed in clinically normal, uninvolved skin of patients with psoriasis. Claudin‐3 was present in the epidermal granular cell layer in normal skin, but was only identified within the cytosol of epidermal keratinocytes in both involved and uninvolved skin of psoriasis patients. We examined further whether exposure of keratinocytes in vitro to pro‐inflammatory cytokines mimicked the observed changes in claudin expression seen in chronic plaque psoriasis; lipopolysaccharide, interferon‐γ and tumour necrosis factor‐α had no effect on claudin protein expression or distribution. Addition of interleukin‐1β, however, resulted in down‐regulation of claudins‐1 and ‐3. Tumour necrosis factor‐α and interleukin‐1β were further used in an in vivo model of skin inflammation; interleukin‐1β alone modulated claudin protein expression in this system. These data demonstrate that epidermal claudin expression is altered in chronic plaque psoriasis and that expression is in part modulated by interleukin‐1β. Copyright

Influence of Eicosapentaenoic Acid, an Omega-3 Fatty Acid, on Ultraviolet-B Generation of Prostaglandin-E2 and Proinflammatory Cytokines Interleukin-1β, Tumor Necrosis Factor-α, Interleukin-6 and Interleukin-8 in Human Skin In Vivo¶

Abstract Dietary omega-3 polyunsaturated fatty acids (ω-3 PUFA) reduce sunburn, an acute inflammatory response, in humans. We assessed whether this may be mediated by reduced ultraviolet-B (UV-B) induction of proinflammatory mediators tumor necrosis factor–α (TNF-α), interleukin (IL)-1β, IL-6, IL-8 and prostaglandin (PG)E2 in healthy skin. In a double-blind, randomized study, 28 humans received 4 g daily of 95% ethyl esters of eicosapentaenoic acid (EPA) or oleic acid (OA) orally for 3 months. Skin biopsies and suction blister fluid were taken from unexposed and UV-B–exposed skin and examined for mediator expression immunohistochemically and quantitatively by immunoassay; plasma levels were also assayed. The subjects taking EPA, but not OA, showed a significant rise in their minimal erythemal dose (MED) (data reported elsewhere). Before supplementation, irradiation with 3× MED UV-B increased blister fluid TNF-α, IL-6, IL-8 and PGE2 at 16 h (all P < 0.001). No significant change occurred in baseline or UV-B–induced skin levels of cytokines after either supplement, whereas UV-B induction of PGE2 was abolished after EPA but not OA. Immunohistochemical expression of the cytokines at baseline and after UV-B was unaltered by EPA and OA; circulating cytokine and PGE2 levels were also unchanged. Hence, in healthy skin in vivo, there was no evidence that reduction of the sunburn response by EPA is mediated by the proinflammatory cytokines examined; abrogation of UV-B–generated PGE2 may play a role.

A new wrinkle on old skin: the role of elastic fibres in skin ageing.

Cutaneous ageing is the result of two distinct, biological processes which may occur concurrently: (i) the passage of time, termed intrinsic ageing and (ii) environmental influences, termed extrinsic ageing. Intrinsic ageing of the skin is a slow process which causes changes in tissue structure and impairs function in the absence of additional biological, chemical and physical factors. The clinical features of intrinsically aged skin are not usually evident until old age when, although smooth and unblemished, the skin surface appears pale and is characterized by fine wrinkles with occasional exaggerated expression lines. Functionally, intrinsically aged skin is dry and less elastic than more youthful skin. In contrast, extrinsically aged skin is exemplified by deep, coarse wrinkles, mottled hyperpigmentation and a marked loss of elasticity and recoil. The two major environmental influences which induce extrinsic ageing are: (i) chronic exposure to solar ultraviolet (UV) irradiation (termed photoageing) and (ii) smoking. This review discusses the changes associated with the ageing process in the skin, with particular emphasis on the role played by the elastic fibre network in maintaining dermal function. The review concludes with a discussion of a short‐term assay for independent assessment of the efficacy of anti‐ageing cosmetic products using the elastic fibre component fibrillin‐1 as a biomarker of extracellular matrix repair.

Nanoindentation of histological specimens: Mapping the elastic properties of soft tissues

Although alterations in the gross mechanical properties of dynamic and compliant tissues have a major impact on human health and morbidity, there are no well-established techniques to characterize the micromechanical properties of tissues such as blood vessels and lungs. We have used nanoindentation to spatially map the micromechanical properties of 5-mum-thick sections of ferret aorta and vena cava and to relate these mechanical properties to the histological distribution of fluorescent elastic fibers. To decouple the effect of the glass substrate on our analysis of the nanoindentation data, we have used the extended Oliver and Pharr method. The elastic modulus of the aorta decreased progressively from 35 MPa in the adventitial (outermost) layer to 8 MPa at the intimal (innermost) layer. In contrast, the vena cava was relatively stiff, with an elastic modulus >30 MPa in both the extracellular matrix-rich adventitial and intimal regions of the vessel. The central, highly cellularized, medial layer of the vena cava, however, had an invariant elastic modulus of ~20 MPa. In extracellular matrix-rich regions of the tissue, the elastic modulus, as determined by nanoindentation, was inversely correlated with elastic fiber density. Thus, we show it is possible to distinguish and spatially resolve differences in the micromechanical properties of large arteries and veins, which are related to the tissue microstructure.

The cycling hair follicle as an ideal systems biology research model

Please cite this paper as: The cycling hair follicle as an ideal systems biology research model. Experimental Dermatology 2010; 19: 707–713.