Elastic fiber-associated proteins of skin in development and photoaging

Examination of age-related changes of viscoelasticity in the dermis and subcutaneous fat layer using ultrasound elastography

BACKGROUND

Using ultrasound elastography, the present study aimed to measure the viscoelasticity in each skin layer and to determine the relationship between the measured value, age, and body mass index (BMI).

MATERIALS AND METHODS

The present study included 77 Japanese women. We calculated the BMI and measured the facial cheek via elastography. With the use of the elastographic image, the dermis was divided into two layers, and the subcutaneous fat layer was divided into five equal sections according to the depth, ultimately obtaining seven layers. Furthermore, the thickness and viscoelasticity of each divided layer were measured.

RESULTS

The analysis of echo images revealed that the thickness of the upper dermis layer decreased with age, whereas that of the subcutaneous fat layer tended to increase with age and BMI. As measured by elastography, the viscoelasticity of both the lower dermis and the upper subcutaneous fat layer decreased with age. As the BMI increased, the viscoelasticity of the lower subcutaneous layer also increased, but that of the upper subcutaneous layer decreased.

CONCLUSIONS

The present study revealed the relationship between aging and viscoelasticity in the lower dermis and the relationship between aging, BMI, and viscoelasticity in the upper subcutaneous fat layer.

Tissue elasticity and the ageing elastic fibre

The ability of elastic tissues to deform under physiological forces and to subsequently release stored energy to drive passive recoil is vital to the function of many dynamic tissues. Within vertebrates, elastic fibres allow arteries and lungs to expand and contract, thus controlling variations in blood pressure and returning the pulmonary system to a resting state. Elastic fibres are composite structures composed of a cross-linked elastin core and an outer layer of fibrillin microfibrils. These two components perform distinct roles; elastin stores energy and drives passive recoil, whilst fibrillin microfibrils direct elastogenesis, mediate cell signalling, maintain tissue homeostasis via TGFβ sequestration and potentially act to reinforce the elastic fibre. In many tissues reduced elasticity, as a result of compromised elastic fibre function, becomes increasingly prevalent with age and contributes significantly to the burden of human morbidity and mortality. This review considers how the unique molecular structure, tissue distribution and longevity of elastic fibres pre-disposes these abundant extracellular matrix structures to the accumulation of damage in ageing dermal, pulmonary and vascular tissues. As compromised elasticity is a common feature of ageing dynamic tissues, the development of strategies to prevent, limit or reverse this loss of function will play a key role in reducing age-related morbidity and mortality.

Photoschadigung und Photoalterung - Pravention und Behandlung. Photodamage and photoaging - prevention and treatment

The exposure of human skin to environmental and artificial ultraviolet irradiation has increased significantly. This is not only due to an increased solar UV irradiation as a consequence of the stratospheric ozone depletion, but also the result of an inappropriate social behaviour with the use of tanning parlors being very popular. Besides this, leisure activities and living style with travelling to equatorial regions also add to the individual annual UV load. Since the population in industrialised countries shows an increasing total life span, in parallel the cumulative life time dose of solar and artificial UV-irradiation is dramatically augmented. In addition to the common longterm detrimental effects like immunosuppression and skin cancer, the photooxidative damage due to energy absorption of UV photons in an oxygenized environment leads to alterations of cells, subcellular compartments and macromolecules. The clinical manifestations of UV/ROS induced disturbances result in photoaged skin with wrinkle formation, laxity, leathery appearance as well as fragility, impaired wound healing and higher vulnerability. Strategies to prevent or to minimize photoaging and intrinsic aging of the skin necessarily include protection against UV irradiation and antioxidant homoeostasis. New developments of therapeutic interventions including DNA repair enzymes will be discussed.

Photoaging in Asians

The aging process of the skin can be divided into intrinsic and photoaging. Clinically, naturally aged skin is smooth, pale and finely wrinkled. In contrast, photoaged skin is coarsely wrinkled and associated with dyspigmentation and telangiectasia. Although the population of Asia is more than half the population of the Earth, no well-designed study has been undertaken to investigate the characteristics of cutaneous photodamage in Asian skin. As Asian skin is more pigmented, the acute and chronic cutaneous responses to UV irradiation seen in brown skin differ from those in white skin. The clinical characteristics of photoaging in Asian skin, such as pigmentary changes and wrinkle patterns, differ from those of Caucasian skin. This review provides an outline of the characteristic features of photoaging on the brown skin of Asians.

Solar UV irradiation and dermal photoaging

The skin is increasingly exposed to ambient UV-irradiation thus increasing risks for photooxidative damage with long-term detrimental effects like photoaging, characterized by wrinkles, loss of skin tone and resilience. Photoaged skin displays alterations in the cellular component and extracellular matrix with accumulation of disorganized elastin and its microfibrillar component fibrillin in the deep dermis and a severe loss of interstitial collagens, the major structural proteins of the dermal connective tissue. The unifying pathogenic agents for these changes are UV-generated reactive oxygen species (ROS) which deplete and damage non-enzymatic and enzymatic antioxidant defense systems of the skin. As well as causing permanent genetic changes, ROS activate cytoplasmic signal transduction pathways in resident fibroblasts that are related to growth, differentiation, senescence and connective tissue degradation. This review focuses on the role of UV-induced ROS in the photodamage of the skin resulting in clinical and biochemical characteristics of photoaging. In addition, the relationship of photoaging to intrinsic aging of the skin will be briefly discussed. A decrease in the overall ROS load by efficient sunscreens or other protective agents may represent promising strategies to prevent or at least minimize ROS-induced photoaging.

Chronological ageing and photoageing of the fibroblasts and the dermal connective tissue

In recent years, the exposure of human skin to environmental and artificial UV irradiation has increased dramatically. This is due not only to increased solar UV irradiation as a consequence of stratospheric ozone depletion, but also to inappropriate social behaviour with the use of tanning salons still being very popular in the public view. Besides this, leisure activities and a lifestyle that often includes travel to equatorial regions add to the individual annual UV load. In addition to the common long-term detrimental effects such as immunosuppression and skin cancer, the photo-oxidative damage due to energy absorption of UV photons in an oxygenized environment leads to quantitative and qualitative alterations of cells and structural macromolecules of the dermal connective tissue responsible for tensile strength, resilience and stability of the skin. The clinical manifestations of UV/reactive oxygen species (ROS)-induced disturbances result in photoaged skin with wrinkle formation, laxity, leathery appearance as well as fragility, impaired wound healing capacities and higher vulnerability. Strategies to prevent or at least minimize ROS-induced photo-ageing and intrinsic ageing of the skin necessarily include protection against UV irradiation and antioxidant homeostasis.

Ultraviolet radiation increases tropoelastin mRNA expression in the epidermis of human skin in vivo

Photoaged skin contains elastotic materials in the upper reticular dermis. This phenomenon is commonly known as solar elastosis. Little is known about the mechanisms leading to the accumulation of elastotic materials in photoaged skin, however. In this study, it was demonstrated that ultraviolet irradiation induced tropoelastin mRNA expression in the keratinocytes of human skin in vivo and also in cultured human keratinocytes by in situ hybridization and reverse transcriptase polymerase chain reaction. It was also shown by northern blot analysis (n = 5) that there were increased tropoelastin mRNA levels in the forearm (sun-exposed) skin of elderly persons, compared with upper-inner arm (sun-protected) skin of the same individuals. As demonstrated by in situ hybridization compared to sun-protected skin (upper-inner arm) (n = 5), tropoelastin mRNA expression in photoaged skin was higher in keratinocytes as well as in fibroblasts. Therefore, our results suggest that keratinocytes are another source of tropoelastin production after acute and chronic ultraviolet irradiation in human skin in vivo.

A Short-Term Screening Protocol, Using Fibrillin-1 as a Reporter Molecule, for Photoaging Repair Agents

Photoaged skin is characterized by coarse and fine wrinkles. The mechanisms of wrinkle formation are undetermined, but appear to be due to changes within the matrix of the dermis and at the dermal-epidermal junction. Previous studies have identified marked reductions in procollagens I and III, collagen VII, and the fibrillin-rich microfibrillar apparatus in this area. Topically applied all-trans retinoic acid can repair photoaged dermal matrix, but this takes at least 6 mo of treatment. In this study, we have examined the abundance and distribution of fibrillin-1 prior to, and following, 192 wk of all-trans retinoic acid treatment. We have further developed a short-term protocol to determine the utility of potential repair agents, using fibrillin-1 as the marker for outcome. Individuals with clinically assessed severe photoaging were recruited to the study (n = 8). 0.025% all-trans retinoic acid, 5% sodium lauryl sulfate (irritant control), or vehicle were applied under occlusion to photoaged extensor forearm. A fourth control area was also occluded. After 96 h, punch biopsies were taken under local anesthesia and processed for either transmission electron microscopy or snap frozen. Frozen sections were prepared for immunohistochemistry and in situ hybridization immunohistochemistry. Electron microscopy revealed aberrant elastic fibers in the papillary dermis of photoaged forearm skin, with sparse microfibrillar apparatus and interstitial collagen. After application of 0.025% all-trans retinoic acid, there was increased deposition of both these dermal matrix components, with the aberrant elastic fibers no longer apparent. Significant increases (p < 0.05) were observed at the protein and mRNA levels for fibrillin-1 following all-trans retinoic acid and sodium lauryl sulfate treatments, with all-trans retinoic acid having a significantly greater effect than irritant control (p < 0.001); however, neither application had significant effect on the abundance of collagen VII or its mRNA. Investigation of collagen I synthesis revealed no difference following treatments. To ascertain the clinical relevance of using fibrillin-1 as a marker for photoaging, facial skin was biopsied at baseline and after long-term (192 wk) topical all-trans retinoic acid treatment (n = 5). Biopsies were wax-embedded and sections prepared for immunohistochemistry for fibrillin-1. Significant increases in the abundance of the microfibrillar apparatus was observed proximal to the dermal- epidermal junction (p < 0.001) following long-term all-trans retinoic acid application. This study indicates that all-trans retinoic acid can significantly affect fibrillin-1 content in photoaged skin. Furthermore, fibrillin-1 can be used as a "reporter" molecule in short-term protocols for testing the utility of topical agents in the repair of photoaged skin.

Synthesis of elastic microfibrillar components fibrillin-1 and fibrillin-2 by human optic nerve head astrocytes in situ and in vitro

The purpose of this study was to identify elastic microfibrillar components fibrillin-1 and fibrillin-2 in optic nerve heads of adult normal and glaucomatous subjects, in cultured optic nerve head astrocytes (type 1B astrocytes), as well as fibrillin-1 in fetal optic nerve heads. To characterize synthesis and gene expression of microfibrillar proteins in human optic nerve heads and cultured type 1B astrocytes, light microscopy immunohistochemistry, in situ hybridization, and RT-PCR or Northern blots were performed. Our results demonstrated that fibrillin-1 was associated with blood vessels, astrocytes in the glial columns and cribriform plates, and with astrocyte processes in the nerve bundles in all samples. In glaucomatous optic nerves there was enhanced fibrillin-1 immunoreactivity, especially surrounding blood vessels. Fibrillin-2 was localized primarily to blood vessels in all samples, without qualitative differences between normal and glaucomatous samples. In fetal optic nerve heads fibrillin-1 mRNA was localized to glial cells and to the blood vessel walls. In adult optic nerve heads, there was little fibrillin-1 mRNA as detectable by in situ hybridization and RT-PCR. There was no detectable upregulation of fibrillin-1 mRNA in glaucoma. In cultured type 1B astrocytes, fibrillin-1 staining was mostly pericellular. There was little fibrillin-2 immunoreactivity. In conclusion, astrocytes from the optic nerve head deposit elastic microfibrillar components in situ and in vitro, with a predominance of fibrillin-1. Upregulation of fibrillin-1 mRNA was not observed in glaucoma, suggesting that increased transcription may occur early in the disease process. Cultures of type 1B astrocytes from the optic nerve head provides a useful model to study mechanisms regulating the interactions of elastin and the microfibrils in optic nerve head astrocytes.

Photoaging of the skin from phenotype to mechanisms

The skin is increasingly exposed to ambient UV-irradiation thus increasing its risk for photooxidative damage with longterm detrimental effects like photoaging, which is characterized by wrinkles, loss of skin tone, and resilience. Photoaged skin displays prominent alterations in the cellular component and the extracellular matrix of the connective tissue with an accumulation of disorganized elastin and its microfibrillar component fibrillin in the deep dermis and a severe loss of interstitial collagens, the major structural proteins of the dermal connective tissue. The unifying pathogenic agents for these changes are UV-generated reactive oxygen species (ROS) that deplete and damage non-enzymatic and enzymatic antioxidant defense systems of the skin. As well as causing permanent genetic changes, ROS activate cytoplasmic signal transduction pathways in resident fibroblasts that are related to growth, differentiation, senescence, and connective tissue degradation. This review focuses on the role of UV-induced ROS in the photodamage of the skin resulting in biochemical and clinical characteristics of photoaging. In addition, the relationship of photoaging to intrinsic aging of the skin will be discussed. A decrease in the overall ROS load by efficient sunscreens or other protective agents may represent promising strategies to prevent or at least minimize ROS induced photoaging.

Wavelength-specific synergy between ultraviolet radiation and interleukin-1 alpha in the regulation of matrix-related genes: mechanistic role for tumor necrosis factor-alpha

Ultraviolet light causes both acute and chronic changes in extracellular matrix. We sought to examine the effects of different ultraviolet wavelengths on expression of matrix-related genes in fibroblasts. We previously reported that tropoelastin gene expression in vivo decreases with acute ultraviolet B exposure, and interleukin-1 alpha-mediated upregulation of tropoelastin is blocked in vitro after ultraviolet B radiation. In this study, we found that only ultraviolet B, but not ultraviolet A or ultraviolet A1, blocked the ability of interleukin-1 alpha to stimulate tropoelastin expression in vitro. Ultraviolet B and interleukin-1 alpha synergistically increased tumor necrosis factor-alpha secretion by fibroblasts, a finding not seen with ultraviolet B alone nor with ultraviolet A or ultraviolet A1 combined with interleukin-1 alpha. Keratinocytes showed a similar ultraviolet B-specific induction of tumor necrosis factor-alpha production. Addition of tumor necrosis factor-alpha to cultured fibroblasts blocked interleukin-1 alpha-induced stimulation of tropoelastin message, and addition of anti-tumor necrosis factor-alpha antibodies restored the responsiveness of tropoelastin and collagen messages to exogenous interleukin-1 alpha after ultraviolet B exposure. We conclude that interleukin-1 alpha in combination specifically with ultraviolet B induces fibroblasts to secrete tumor necrosis factor-alpha, and that this ultraviolet B-specific induction of tumor necrosis factor-alpha secretion is responsible for effects of ultraviolet B on the expression of matrix-related genes in the skin.

Degenerative processes of elastic fibers in sun-protected and sun-exposed skin: immunoelectron microscopic observation of elastin, fibrillin-1, amyloid P component, lysozyme and alpha1-antitrypsin

Degenerative processes of elastic fibers in sun-protected and sun-exposed skin were analyzed by light and electron microscopic (post-embedding) immunocytochemistry using antisera to elastin, fibrillin-1, amyloid P component, lysozyme and alpha1-antitrypsin. To assess the effect of aging and sun exposure, biopsy specimens of sun-protected skin (back) and severely and moderately sun-exposed skin (face and forearms) were obtained from a young age group (1-27 years), an adult group (31-56 years) and an old aged group (61-100 years). Elastin and fibrillin-1 were the essential components of elastic fibers; elastin being localized in the electron-lucent matrix and fibrillin-1 in the dense microfibrillar strands. Aging and sun exposure provoked degenerative condensed spots, which represented widened dense microfibrillar strands, in the matrix of altered elastic fibers in the reticular dermis. Amyloid P component was first deposited on the peripheral microfibrils, and then in the intermediate density zone of the spots. Lysozyme was observed in both the electron-dense core and in the intermediate density zone of the spots. Deposition of lysozyme correlated with basophilic degeneration of the elastic fibers. In the severely photodamaged facial skin of the aged, which showed solar elastosis in the upper reticular dermis, fibrillin-1 immunoreactivity was lost from the thickened and vacuolated elastic fibers that lacked condensed spots, and amyloid P component, lysozyme and alpha1-antitrypsin were diffusely deposited in the elastin-positive matrix. It seemed that amyloid P component deposition on the elastic fibers was closely associated with aging, while immunoreactive lysozyme was related to sun exposure. Vertically oriented, thin, elastic (oxytalan) fibers in the papillary dermis tended to decrease with age, with frequent deposition of amyloid P component but no lysozyme. In the facial skin of the aged, dermal papillae disappeared, with the formation of degenerative elastic globules beneath the dermal-epidermal junction. The present study demonstrated an intimate relationship between ultrastructural alterations and deposition of exogenous substances on the degenerative elastic fibers in sun-exposed and/or aged skin.

Fibrillin-rich microfibrils are reduced in photoaged skin. Distribution at the dermal-epidermal junction

Chronic sun exposure results in photoaged skin with deep coarse wrinkles and loss of elasticity. We have examined the distribution and abundance of fibrillin-rich microfibrils, key structural components of the elastic fiber network, in photoaged and photoprotected skin. Punch biopsies taken from photoaged forearm and from photoprotected hip and upper inner arm of 16 subjects with a clinical range of photoaging were examined for fibrillin-1 and fibrillin-2 expression and microfibril distribution. In situ hybridization revealed decreased fibrillin-1 mRNA but unchanged fibrillin-2 mRNA levels in severely photoaged forearm biopsies relative to photoprotected dermal sites. An immunohistochemical approach demonstrated that microfibrils at the dermal-epidermal junction were significantly reduced in moderate to severely photoaged forearm skin. Confocal microscopy revealed that the papillary dermal microfibrillar network was truncated and depleted in photoaged skin. These studies highlight that the fibrillin-rich microfibrillar network associated with the upper dermis undergoes extensive remodeling following solar irradiation. These changes may contribute to the clinical features of photoaging, such as wrinkle formation and loss of elasticity.

Elastosis of the lamina cribrosa in glaucomatous optic neuropathy

The purpose of this study was to determine whether elastotic degeneration of the elastin component of the lamina cribrosa occurs in optic neuropathy associated with different types of glaucoma. Human optic nerve heads with primary open-angle, neovascular, chronic angle closure and pseudoexfoliation glaucoma, and with varying duration of disease were compared with age-matched normal eyes, using electron microscopy and immunogold labeling of elastin. The percent area occupied by immunogold-labeled elastin material was determined using a digital image analysis system. In all eyes with a history of glaucoma, elastosis was found in the lamina cribrosa and there was a significantly greater percentage of area occupied by elastin compared with age-matched control eyes (P<0.0001). Among the glaucomatous eyes, pseudoexfoliation glaucoma had the largest area of elastosis, followed by primary open-angle and secondary glaucoma (neovascular and chronic angle closure). In all glaucoma samples, large, confluent elastin aggregates of irregular and varied shapes (elastosis) were observed in the lamina cribrosa and insertion region. These results demonstrate that glaucomatous optic neuropathy is associated with elastosis of the lamina cribrosa, which may contribute to the changes in compliance of the optic nerve heads of glaucomatous eyes.

Differential distribution of Fc gamma RIIIa in normal human tissues and co-localization with DAF and fibrillin-1: implications for immunological microenvironments

Fc gamma RIIIa is a cytokine-inducible IgG Fc receptor implicated in the activation of macrophages by immune complexes. Differential expression of Fc gamma RIIIa by macrophages in different tissues may therefore modulate local immune responsiveness. Fc gamma RIIIa expression in normal human tissues was assessed semiquantitatively using microdensitometry. Synovial intimal, serosal, alveolar, salivary gland and placental macrophages, Kupffer cells, and macrophages in mechanically stressed dermis expressed high levels of Fc gamma RIIIa. Less consistent expression was seen in skeletal muscle and lymphoid organs. No significant expression was observed in brain, thyroid, spine, intestine, myocardium, prostate, uterus, flexor forearm dermis, uterus, or kidney. Staining for Fc gamma RIII was also observed on extracellular matrix, and co-localized with both complement decay-accelerating factor and fibrillin-1. It is proposed that differential levels of both cellular and extracellular Fc gamma RIIIa, by modulating the response to immune complexes, may contribute to relative tissue susceptibility to infection and autoimmune disease.

Physiologic and structural changes associated with aging skin

The spectrum of photoaging in human skin shows a recognizable progression from subtle to profound, reflecting the various anatomic and structural changes that appear with aging skin. Qualification and quantification of these changes on both the macroscopic and microscopic levels enable the physician to select and evaluate appropriate therapeutic approaches to the problem of chronic solar damage. Comparative studies remain to be done that will further refine our abilities to match the right solutions to the recognized problems.

UVB irradiation alters cellular responses to cytokines: role in extracellular matrix gene expression

Solar radiation causes cutaneous photodamage characterized by alterations in the quantity and structure of the extracellular matrix. We determined the direct and cytokine-mediated effects of UV irradiation on mRNA levels for two matrix elements, tropoelastin and fibrillin 1. (i) Comparison of normal versus end-stage photodamaged skin failed to reveal differences in these message levels. (ii) Acutely irradiated skin showed suppression of both tropoelastin and fibrillin mRNAs. (iii) UVB irradiation (50 mJ) of cultured skin fibroblasts suppressed fibrillin mRNA by 50%, consistent with a direct effect of radiation. Addition to the cultured fibroblasts of several cytokines upregulated by UVB showed that IL-1alpha had no effect on fibrillin mRNA in unirradiated cells, but in irradiated cells, this cytokine enhanced the suppression of fibrillin mRNA. There were no changes in the message stability, suggesting altered gene transcription. In contrast, UVB had no effect on tropoelastin mRNA levels in cultured fibroblasts, indicating the absence of a direct effect of radiation. IL-1alpha stimulated tropoelastin mRNA 2.8-fold in unirradiated cells, and this stimulation was entirely blocked by UVB. Overall, our results indicate acute suppression of matrix genes by UVB in vivo. The suppression of fibrillin message was a direct effect of UVB on fibroblasts and was augmented by IL-1alpha. Suppression of tropoelastin message by UVB occurred in vitro only in IL-1alpha-stimulated cells. We conclude that UVB substantially alters the pattern of cellular response to cytokines. The interplay between UVB and cytokines is essential to explain the acute responses of matrix genes to UVB in vivo.