Developmental initiation of elastin gene expression by human fetal skin fibroblasts

Elastic Fibre Proteins in Elastogenesis and Wound Healing

As essential components of our connective tissues, elastic fibres give tissues such as major blood vessels, skin and the lungs their elasticity. Their formation is complex and co-ordinately regulated by multiple factors. In this review, we describe key players in elastogenesis: fibrillin-1, tropoelastin, latent TGFβ binding protein-4, and fibulin-4 and -5. We summarise their roles in elastogenesis, discuss the effect of their mutations on relevant diseases, and describe their interactions involved in forming the elastic fibre network. Moreover, we look into their roles in wound repair for a better understanding of their potential application in tissue regeneration.

Cells, Materials, and Fabrication Processes for Cardiac Tissue Engineering

Cardiovascular disease is the number one killer worldwide, with myocardial infarction (MI) responsible for approximately 1 in 6 deaths. The lack of endogenous regenerative capacity, added to the deleterious remodelling programme set into motion by myocardial necrosis, turns MI into a progressively debilitating disease, which current pharmacological therapy cannot halt. The advent of Regenerative Therapies over 2 decades ago kick-started a whole new scientific field whose aim was to prevent or even reverse the pathological processes of MI. As a highly dynamic organ, the heart displays a tight association between 3D structure and function, with the non-cellular components, mainly the cardiac extracellular matrix (ECM), playing both fundamental active and passive roles. Tissue engineering aims to reproduce this tissue architecture and function in order to fabricate replicas able to mimic or even substitute damaged organs. Recent advances in cell reprogramming and refinement of methods for additive manufacturing have played a critical role in the development of clinically relevant engineered cardiovascular tissues. This review focuses on the generation of human cardiac tissues for therapy, paying special attention to human pluripotent stem cells and their derivatives. We provide a perspective on progress in regenerative medicine from the early stages of cell therapy to the present day, as well as an overview of cellular processes, materials and fabrication strategies currently under investigation. Finally, we summarise current clinical applications and reflect on the most urgent needs and gaps to be filled for efficient translation to the clinical arena.

A blackberry-dill extract combination synergistically increases skin elasticity

BACKGROUND

The loss of structural elastin due to intrinsic and extrinsic ageing results in the skin's inability to stretch and recoil (decrease in elasticity) and manifests as loss of skin firmness and sagging. While other extracellular matrix (ECM) components such as collagen and hyaluronic acid are continually synthesized and assembled through life, elastic fibres are not. Elastic fibre assembly and functionality require fibre cross-linking, induced by the lysyl oxidase-like (LOXL) enzymes, which sharply decrease during ageing.

OBJECTIVE

To evaluate the enhanced elastogenic effect of a blackberry-dill extract combination, which was hypothesized to induce elastin fibre component synthesis, fibre cross-linking and reduce elastin fibre degradation.

METHODS

The blackberry and the dill extracts were tested separately and in combination to confirm single ingredient bioactivity and synergistic benefits. Human skin explants, dermal fibroblasts, elastase assays, ELISAs, quantitative real-time PCRs and spectrofluorometer measurements were used. Moreover, a double-blinded, placebo-controlled clinical study was carried out to assess skin elasticity using Cutometer and histologically from biopsies.

RESULTS

The blackberry extract induced elastin gene expression, elastin promoter activity and inhibited elastic fibre degradation by matrix metalloproteinases (MMPs) 9 and 12. The dill extract induced elastin, collagen and LOXL1 gene expression, resulting in enhanced fibre cross-linking in human skin explants. Clinically, the blackberry and dill combination treatment displayed synergistic pro-elasticity activity as compared to each ingredient alone and placebo.

CONCLUSION

Taken together, these results demonstrated the two multimodal plant-based extracts complemented each other in terms of bioactivity and resulted in a synergistic elastogenesis induction.

Photoaging Skin Therapy with PRP and ADSC: A Comparative Study

BACKGROUND

Stem cells from adipose tissue (ADSCs) and platelet-rich plasma (PRP) are innovative modalities that arise due to their regenerative potential.

OBJECTIVE

The aim of this study was to characterize possible histological changes induced by PRP and ADSC therapies in photoaged skin.

METHODS

A prospective randomized study involving 20 healthy individuals, showing skin aging. They underwent two therapeutic protocols (protocol 1: PRP; protocol 2: ADSCs). Biopsies were obtained before and after treatment (4 months).

RESULTS

PRP protocol showed unwanted changes in the reticular dermis, mainly due to the deposition of a horizontal layer of collagen (fibrosis) and elastic fibers tightly linked. Structural analyses revealed infiltration of mononuclear cells and depot of fibrotic material in the reticular dermis. The ADSC protocol leads to neoelastogenesis with increase of tropoelastin and fibrillin. There was an improvement of solar elastosis inducing an increment of macrophage polarization and matrix proteinases. These last effects are probably related to the increase of elastinolysis and the remodeling of the dermis.

CONCLUSIONS

The PRP promoted an inflammatory process with an increase of reticular dermis thickness with a fibrotic aspect. On the other hand, ADSC therapy is a promising modality with an important antiaging effect on photoaged human skin.

Elastin, arterial mechanics, and cardiovascular disease

Large, elastic arteries are composed of cells and a specialized extracellular matrix that provides reversible elasticity and strength. Elastin is the matrix protein responsible for this reversible elasticity that reduces the workload on the heart and dampens pulsatile flow in distal arteries. Here, we summarize the elastin protein biochemistry, self-association behavior, cross-linking process, and multistep elastic fiber assembly that provide large arteries with their unique mechanical properties. We present measures of passive arterial mechanics that depend on elastic fiber amounts and integrity such as the Windkessel effect, structural and material stiffness, and energy storage. We discuss supravalvular aortic stenosis and autosomal dominant cutis laxa-1, which are genetic disorders caused by mutations in the elastin gene. We present mouse models of supravalvular aortic stenosis, autosomal dominant cutis laxa-1, and graded elastin amounts that have been invaluable for understanding the role of elastin in arterial mechanics and cardiovascular disease. We summarize acquired diseases associated with elastic fiber defects, including hypertension and arterial stiffness, diabetes, obesity, atherosclerosis, calcification, and aneurysms and dissections. We mention animal models that have helped delineate the role of elastic fiber defects in these acquired diseases. We briefly summarize challenges and recent advances in generating functional elastic fibers in tissue-engineered arteries. We conclude with suggestions for future research and opportunities for therapeutic intervention in genetic and acquired elastinopathies.

Tropoelastin Expression by Periodontal Fibroblasts

Elastic system fibers are load-bearing proteins found in periodontal tissue. There are three types—oxytalan, elaunin, and elastic fibers—which differ in their relative microfibril and elastin contents. Oxytalan fibers are known to be distributed in the periodontal ligaments and gingiva, whereas elaunin and elastic fibers are present only in the gingiva. We examined gene expression and accumulation of tropoelastin in the cell-matrix layers of human gingival fibroblasts (HGF) and periodontal ligament fibroblasts (HPLF) in vitro. HGF and HPLF were cultured in MEM containing 10% newborn calf serum for 8 wks. Northern blotting and RT-PCR analyses showed that only HGF expressed mRNA encoding tropoelastin. Western blotting analysis demonstrated 77-kDa protropoelastin and 68-kDa tropoelastin only in the cell-matrix layer of HGF cultured for 8 wks. These results suggest that the different tropoelastin expression patterns reflect the difference between HGF and HPLF phenotypes.

Synthetic ligands of the elastin receptor induce elastogenesis in human dermal fibroblasts via activation of their IGF-1 receptors

BACKGROUND

We have previously reported that a mixture of peptides obtained after chemical or enzymatic degradation of bovine elastin, induced new elastogenesis in human skin.

OBJECTIVE

Now, we investigated the elastogenic potential of synthetic peptides mimicking the elastin-derived, VGVAPG sequence, IGVAPG sequence that we found in the rice bran, and a similar peptide, VGVTAG that we identified in the IGF-1-binding protein-1 (IGFBP-1).

RESULTS

We now demonstrate that treatment with each of these xGVxxG peptides (recognizable by the anti-elastin antibody), up-regulated the levels of elastin-encoding mRNA, tropoelastin protein, and the deposition of new elastic fibers in cultures of human dermal fibroblasts and in cultured explants of human skin. Importantly, we found that such induction of new elastogenesis may involve two parallel signaling pathways triggered after activation of IGF-1 receptor. In the first one, the xGVxxG peptides interact with the cell surface elastin receptor, thereby causing the downstream activation of the c-Src kinase and a consequent cross-activation of the adjacent IGF-1R, even in the absence of its principal ligand. In the second pathway their hydrophobic association with the N-terminal domain (VGVTAG) of the serum-derived IGFBP-1 induces conformational changes of this IGF-1 chaperone allowing for the release of its cargo and a consequent ligand-specific phosphorylation of IGF-1R.

CONCLUSION

We present a novel, clinically relevant mechanism in which products of partial degradation of dermal elastin may stimulate production of new elastic fibers by dermal fibroblasts. Our findings particularly encourage the use of biologically safe synthetic xGVxxG peptides for regeneration of the injured or aged human skin.

Longitudinal epigenetic and gene expression profiles analyzed by three-component analysis reveal down-regulation of genes involved in protein translation in human aging

Data on biological mechanisms of aging are mostly obtained from cross-sectional study designs. An inherent disadvantage of this design is that inter-individual differences can mask small but biologically significant age-dependent changes. A serially sampled design (same individual at different time points) would overcome this problem but is often limited by the relatively small numbers of available paired samples and the statistics being used. To overcome these limitations, we have developed a new vector-based approach, termed three-component analysis, which incorporates temporal distance, signal intensity and variance into one single score for gene ranking and is combined with gene set enrichment analysis. We tested our method on a unique age-based sample set of human skin fibroblasts and combined genome-wide transcription, DNA methylation and histone methylation (H3K4me3 and H3K27me3) data. Importantly, our method can now for the first time demonstrate a clear age-dependent decrease in expression of genes coding for proteins involved in translation and ribosome function. Using analogies with data from lower organisms, we propose a model where age-dependent down-regulation of protein translation-related components contributes to extend human lifespan.

Fetal wound healing biomarkers

Fetal skin has the intrinsic capacity for wound healing, which is not correlated with the intrauterine environment. This intrinsic ability requires biochemical signals, which start at the cellular level and lead to secretion of transforming factors and expression of receptors, and specific markers that promote wound healing without scar formation. The mechanisms and molecular pathways of wound healing still need to be elucidated to achieve a complete understanding of this remodeling system. The aim of this paper is to discuss the main biomarkers involved in fetal skin wound healing as well as their respective mechanisms of action.

Age-related dermal collagen changes during development, maturation and ageing - a morphometric and comparative study

The tissue organisation of dermal collagen is gaining importance as a contributing factor both in development and ageing, as well as in skin maturation processes. In this work we aim to study different representative parameters of this structural organisation in 45 human skin samples of assorted ages, by means of image analysis. The variation of these parameters on the basis of age was assessed using several regression models (linear, quadratic and cubic). The area occupied by collagen was significantly reduced as a function of age in the papillary dermis (R(2) = 0.437, P < 0.0001), as well as the thickness of the collagen bundles (R(2) = 0.461, P < 0.0001), following statistical models of cubic and quadratic regression, respectively. The width of the papillary dermis increased in a significant manner over a linear regression model (R(2) = 0.26, P < 0.0001). In the reticular dermis, the cubic regression indicated a significant decline (R(2) = 0.392, P = 0.002) of the area filled with collagen according to the age. Both collagen thickness and bundle orientation parameters fit a quadratic regression over the age in a significant way (R(2) = 0.433 and R(2) = 0.334, respectively, both P < 0.0001). The width of the reticular dermis followed also a significant quadratic distribution according to age (R(2) = 0.193, P = 0.011). These parameters could partially explain the lifelong functional changes taking place in the skin and propose a baseline providing a useful entry point for future investigation.

Rejuvenation of chondrogenic potential in a young stem cell microenvironment

Autologous cells suffer from limited cell number and senescence during ex vivo expansion for cartilage repair. Here we found that expansion on extracellular matrix (ECM) deposited by fetal synovium-derived stem cells (SDSCs) (FE) was superior to ECM deposited by adult SDSCs (AE) in promoting cell proliferation and chondrogenic potential. Unique proteins in FE might be responsible for the rejuvenation effect of FE while advantageous proteins in AE might contribute to differentiation more than to proliferation. Compared to AE, the lower elasticity of FE yielded expanded adult SDSCs with lower elasticity which could be responsible for the enhancement of chondrogenic and adipogenic differentiation. MAPK and noncanonical Wnt signals were actively involved in ECM-mediated adult SDSC rejuvenation.

Elastin signaling in wound repair

Skin is an important organ to the human body as it functions as an interface between the body and environment. Cutaneous injury elicits a complex wound healing process, which is an orchestration of cells, matrix components, and signaling factors that re-establishes the barrier function of skin. In adults, an unavoidable consequence of wound healing is scar formation. However, in early fetal development, wound healing is scarless. This phenomenon is characterized by an attenuated inflammatory response, differential expression of signaling factors, and regeneration of normal skin architecture. Elastin endows a range of mechanical and cell interactive properties to skin. In adult wound healing, elastin is severely lacking and only a disorganized elastic fiber network is present after scar formation. The inherent properties of elastin make it a desirable inclusion to adult wound healing. Elastin imparts recoil and resistance and induces a range of cell activities, including cell migration and proliferation, matrix synthesis, and protease production. The effects of elastin align with the hallmarks of fetal scarless wound healing. Elastin synthesis is substantial in late stage in utero and drops to a trickle in adults. The physical and cell signaling advantages of elastin in a wound healing context creates a parallel with the innate features of fetal skin that can allow for scarless healing.

Comparison between human fetal and adult skin

Healing of early-gestation fetal wounds results in scarless healing. Since the capacity for regeneration is probably inherent to the fetal skin itself, knowledge of the fetal skin composition may contribute to the understanding of fetal wound healing. The aim of this study was to analyze the expression profiles of different epidermal and dermal components in the human fetal and adult skin. In the human fetal skin (ranging from 13 to 22 weeks' gestation) and adult skin biopsies, the expression patterns of several epidermal proteins (K10, K14, K16, K17, SKALP, involucrin), basement membrane proteins, Ki-67, blood vessels and extracellular matrix proteins (fibronectin, chondroitin sulfate, elastin) were determined using immunohistochemistry. The expression profiles of K17, involucrin, dermal Ki-67, fibronectin and chondroitin sulfate were higher in the fetal skin than in adult skin. In the fetal skin, elastin was not present in the dermis, but it was found in the adult skin. The expression patterns of basement membrane proteins, blood vessels, K10, K14, K16 and epidermal Ki-67 were similar in human fetal skin and adult skin. In this systematic overview, most of the differences between fetal and adult skin were found at the level of dermal extracellular matrix molecules expression. This study suggests that, especially, dermal components are important in fetal scarless healing.

Regulation of elastin synthesis in pathological states

Elastin is rapidly deposited during late gestation in resilient tissues such as the arteries, lungs and skin owing to increased concentration of its mRNA. Pathological states can arise from congenital insufficiency or disorganization of elastin (cutis laxa). Other elastin deficiencies may be due to excess elastolysis or gene dosage effects. In the former, high turnover rates can be assessed by measurements of elastin degradation products in urine. Excess elastin accumulation by skin fibroblasts is characteristic of genetic diseases such as Buschke-Ollendorff syndrome, Hutchinson-Gilford progeria and keloid. Elastin expression is modulated by peptide growth factors, steroid hormones and phorbol esters, among which transforming growth factor beta (TGF-beta) is an especially potent up-regulator, acting largely through stabilization of mRNA. Recent evidence indicates cutis laxa fibroblasts that express little or no elastin have normal transcriptional activity but abnormal rates of elastin mRNA degradation. This defect is substantially reversed by TGF-beta through mRNA stabilization. Current studies explore the hypothesis that stability determinants lie within the 3' untranslated region of elastin mRNA. Post-transcriptional control of elastin expression appears to be a major regulatory mechanism.

Elastin Expression in a Newly Developed Full-Thickness Skin Equivalent

The resilience of the human skin is mediated by elastic fibres mainly consisting of fibrillins and elastin. In order to establish a model system to study the impact of cosmetic and pharmaceutical compounds on the elastic system in vitro, we analyzed the expression of elastin in a newly developed full-thickness skin model. After a 5-week cultivation period the skin model developed a fully differentiated epidermis including a stratum corneum. The dermis contains fibroblasts embedded in extracellular matrix proteins. The models were viable until at least 51 days at the air-liquid interface (ALI) culture. Using immunohistochemistry we detected elastin first on day 7 of ALI. With proceeding culture time, elastin-positive fibres of different lengths and distribution patterns accumulated in the dermal compartment. Elastin mRNA expression started on day 7 of ALI, increased until day 10 and then dropped to a level comparable to that of day 7. Our results demonstrate that in our full-thickness skin model an in vivo-like elastic system, which clearly mimics at least two subsets of dermal elastic fibres, is generated. This physiological property favours the model as a promising animal-free approach to study those processes leading to an environment- and age-dependent decrease in skin elasticity.

LOXL as a target to increase the elastin content in adult skin: a dill extract induces the LOXL gene expression

The lysyl oxidases lysyl oxidase (LOX) and lysyl oxidase-like (LOXL) are responsible for elastin cross-linking. It was shown recently that LOXL is essential for the elastic fibres homeostasis and for their maintenance at adult age. We first determined whether or not elastin, LOX and LOXL are less expressed during adulthood. The LOX and LOXL mRNA level, quantified by real-time reverse transcriptase-polymerase chain reaction decreased in adult skin fibroblasts compared with fibroblasts from children. In contrast, the elastin mRNA level remains stable at all ages. The goal of this study was to induce elastogenesis at the adult age. Therefore, both enzymes, and in particular LOXL, of which expression is the most affected by age, could be targeted to induce elastogenesis in adult skin. We screened a library of about 1000 active ingredients to find activators capable to stimulate specifically the LOXL gene expression in adult dermal fibroblasts. The positive effect of selected active ingredients was confirmed on fibroblasts grown on monolayers and on dermal and skin equivalent cultures. One extract, obtained from dill (LYS'LASTINE V, Engelhard, Lyon, France), stimulates the LOXL gene expression in dermal equivalents (+64% increase in the LOXL mRNA level when compared with control). At the same time, the elastin detection is increased in dermal equivalents and under the dermal-epidermal junction of skin equivalents, without increase of the elastin mRNA. In conclusion, LOXL can be considered as a new target to reinduce elastogenesis. Its stimulation by a dill extract is correlated with increased elastin detection, suggesting an increase in elastogenesis efficiency.

Keratinocytes influence the maturation and organization of the elastin network in a skin equivalent

Elastic fibers form a complex network that contributes to the elasticity of connective tissues. Alterations in the elastic fiber network are involved in several disease affecting organs in which compliance of the connective tissue is essential: skin, main vasculature, lung, joints, muscle, and ligament. The aim of our work was to study the deposition, maturation, and organization of elastic fiber components in a dermal equivalent model consisting of collagen-GAG-chitosan seeded with fibroblasts. The influence of keratinocytes was studied in parallel, thus constituting a skin equivalent model. These models were examined by transmission electron microscopy (TEM) and by immunohistochemistry to determine the staining patterns of fibrillin-1 and elastin proteins representative of the microfibrillar framework and of the elastic fibers, respectively. After 2 mo of fibroblast culture in the dermal equivalent, elastin was undetectable, whereas fibrillin-1 staining was weak and microfibrils were infrequently observed by TEM. In the skin equivalent, fibrillin-1 and elastin were detected by immunostaining 15 d after epidermization and TEM revealed the typical structure and organization of the elastic network in the dermis, with elastin deposition on the microfibrillar scaffold. This in vitro skin equivalent model is to our knowledge the first in which elastic fibers have been detected, thus demonstrating the influence of keratinocytes on the maturation and organization of the elastic network.

Collagen and elastin synthesis by desmoid tumor in vitro

In order to characterize human desmoid tumors in vitro, the production of collagen and elastin and the expression of collagen types alpha1(I), alpha1(III) and transforming growth factor (TGF)-beta1 mRNA were investigated in six desmoid tumors; five derived from familial adenomatous polyposis patients and one from a sporadic case. The proportion of collagen production to total protein production was determined by 3H-imino acid incorporation, an indicator of collagen synthesis, using high-performance liquid chromatography (HPLC). The proportion of collagen production to total protein production was much higher in all six desmoid tumors compared with human skin fibroblasts (HSF). Quantitatively, the rate of elastin synthesis in desmoid tumor cells monitored by valine-proline peptide was also significantly higher than in HSF. Pro-alpha1(I) collagen mRNA was highly expressed in both desmoid tumors and HSF at approximately the same level, whereas pro-alpha1(III) collagen mRNA was more abundant in some of the desmoid tumors than the normal skin fibroblastic cell lines. Tumor growth factor-beta1 mRNA, which is believed to stimulate collagen synthesis, was expressed in both desmoid tumors and HSF to the same extent. These results demonstrate the increased formation of collagen and elastin in desmoid tumors in vitro and suggest that the increased synthesis of elastin rather than of collagen and TGF-beta1 may be involved in increased fibrogenesis by desmoid tumors.

Elastic fiber during development and aging

Elastin molecules aggregate in the extracellular space where they are crosslinked by stable desmosine bridges. The resulting polymer is structurally organized as branched fibers and lamellae, which, in skin, are wider (a few microns) in the deep dermis and become progressively thinner (fraction of a micron) towards the papillary dermis. Several general and local factors seem to regulate elastin gene expression, deposition and degradation. In skin, the volume density of the elastin network increases from birth up to maturity, when it accounts for about 3-4% of the tissue. However, its amount and distribution depend on dermis areas, which are different among subjects and change with age. Several matrix molecules (glycosaminoglycans, decorin, biglycan, osteopontin) have been found to be associated with elastin into the normal fiber, and several others have been recognized within pathologic elastic fiber (osteonectin, vitronectin, alkaline phosphatase in PXE). With age, and in some pathologic conditions, skin elastin may undergo irreversible structural and compositional changes, which seem to progress from localized deposition of osmiophilic materials to the substitution of the great majority of the amorphous elastin with interwoven filaments negative for elastin specific antibodies.

Ultraviolet radiation increases tropoelastin accumulation by a post-transcriptional mechanism in dermal fibroblasts

Chronically sun-damaged human skin is characterized by dermal connective tissue damage that includes the massive accumulation of abnormal elastic fibers. The content of elastin, the major protein component of elastic fibers, is increased two- to sixfold in sun-damaged skin. The aim of this study was to determine the mechanism responsible for the increase in elastin levels after ultraviolet (UV) irradiation. Confluent cultures of normal dermal fibroblasts were irradiated with 4.5 mJ/cm2 of UVB; sham-treated cells served as the control group. The accumulation of tropoelastin was determined at 5 d after treatment by measuring the incorporation of 14C-proline into radiolabeled tropoelastin isolated from cell layers and media. UV irradiation increased radiolabeled tropoelastin accumulation approximately twofold without affecting DNA content, the total amount of radiolabeled protein, or tropoelastin secretion. Moreover, the steady-state levels of tropoelastin mRNA, as determined by slot blot hybridizations, were unaffected by UV treatment. However, the translation of tropoelastin mRNA was increased when total RNA from irradiated cells was used in cell-free translation experiments. These results suggest that altered translational efficiency may account for the increase in tropoelastin accumulation after UV irradiation. In support of this hypothesis, nucleotide sequences were derived from tropoelastin mRNA isolated from UV-irradiated and nonirradiated dermal fibroblasts. Almost a 12% substitution rate was observed in nucleotide sequences derived from the 3' untranslated region of tropoelastin mRNA from the UV-treated cells. In contrast, a coding domain of tropoelastin did not contain base-substitution mutations. These multiple base substitutions in a noncoding domain of tropoelastin mRNA may be responsible for the post-transcriptional increase in tropoelastin accumulation after UV irradiation.

Developmental regulation of elastin production. Expression of tropoelastin pre-mRNA persists after down-regulation of steady-state mRNA levels

To assess the mechanisms controlling the developmental regulation of tropoelastin expression in vivo, we developed a reverse-transcription-polymerase chain reaction (RT-PCR) assay to detect tropoelastin pre-mRNA as an indicator of ongoing transcription in intact tissue. RNA was isolated from mid-fetal (early-elastogenic), neonatal (peak tropoelastin expression), and adult (very low tropoelastin expression) rat lungs and reverse transcribed, and the cDNA was amplified with intron specific primers. A weak hybridization signal for tropoelastin pre-mRNA was seen in mid-fetal samples, and paralleling the increase in steady-state mRNA levels, a strong signal for pre-mRNA was detected in neonatal samples, indicating transcriptional regulation. Stimulation of fetal lung tropoelastin expression by maternal administration of dexamethasone also led to an increase in pre-mRNA levels. However, signal for tropoelastin pre-mRNA in adult samples was equal to that detected in neonatal samples, even though mRNA levels had dropped about 80-fold. Persistence of tropoelastin transcription in adult tissue was also seen in cell culture models and was verified by nuclear runoff assay. In addition, an RT-PCR assay for alpha 1 (I) procollagen pre-mRNA accurately revealed the known transcriptional regulation of this gene. Our results demonstrate that the induction and maintenance of elastogenesis is controlled by a transcriptional mechanism, whereas, the cessation of tropoelastin expression is controlled by a post-transcriptional mechanism.

Prenatal development of the integument in Delphinidae (Cetacea: Odontoceti)

The prenatal development of epidermis, dermis, and hypodermis was studied in embryos of different age of two delphinid species (Stenella attenuata, Delphinus delphis), using light and transmission electron microscopical methods. The delphinid embryo is covered by a multilayered tissue formed by four different epidermal generations (periderm, stratum intermedium-I, str. intermedium-II, str. spinosum) produced by the str. basale. The first layer appears at about 40-50 mm of body length, the second type (s.i.-I) about 60-160 mm, and the third type (s.i.-II) is present at 160-500 mm. The first spinosal cells are produced at 225-260 mm body length; thenceforth, the epidermis increases continuously in thickness. Epidermal ridge formation begins about 400-mm body length. The development of the dermis is characterized by the early production of thin connective tissue fibers (40-70-mm body length) and simultaneously the cutaneous muscle matures in structure. Vascular development intensifies between embryos of 150-225 mm, and collagen production increases markedly in fetuses of 225-260-mm length. These events are paralleled by an increase in dermal thickness. The first elastic fibers can be recognized in the skin from the abdomen at about 600-mm body length. The development of the hypodermis is marked by very rapid and constantly progressing growth, beginning about 60-mm body length. The first typical fat cells appear in animals of 360-400 mm. Regional differences are obvious for all skin layers with regard to the flippers, where structural maturation proceeds more rapidly than in dorsal or abdominal regions.

Glucocorticoid regulation of elastin synthesis in human fibroblasts: down-regulation in fibroblasts from normal dermis but not from keloids

Keloids arise as benign connective tissue masses at sites of injury in genetically predisposed individuals. In addition to excessive collagen accumulation, there is biochemical and histologic evidence of elastic tissue. Previous studies showed that glucocorticoid regulation of collagen synthesis differs in fibroblasts from normal adult dermis and keloids. To define further the abnormal regulation of matrix synthesis in keloid fibroblasts, we examined glucocorticoid regulation of elastin synthesis. The basal level of elastin synthesis was significantly higher in keloid than in normal cells, and hydrocortisone reduced synthesis of elastin and elastin mRNA in normal but not in keloid fibroblasts. We had shown previously that fibroblasts from fetal dermis resembled keloid fibroblasts in glucocorticoid regulation of growth and collagen synthesis. In this study, glucocorticoids failed to down-regulate elastin synthesis in fetal cells that had not differentiated to produce normal levels of elastin, whereas fetal cells with normal elastin production exhibited glucocorticoid down-regulation. Abnormal regulation in keloid cells was independent of cell density and was confined to fibroblasts cultured from the keloid nodule. These findings reinforce the conclusion that a matrix-regulatory pathway is deranged in these focal lesions. Coordinate down-regulation of collagen and elastin by hydrocortisone in normal adult dermal fibroblasts and the failure of hydrocortisone to down-regulate synthesis of either protein in keloid cells support the existence of common elements in the regulatory pathways of these two matrix proteins.

Abnormal accumulation of elastin-associated microfibrils during elastolysis in the arterial wall

We examined the correlation between elastolysis and abnormal accumulation of microfibrils in the arteries of rabbits using light and electron microscopic and tissue culture techniques. Partial constriction of the common carotid arteries of rabbits gave rise to gradual atrophy of the media with elastolysis and an unusual accumulation of microfibrils. With advancing experimental atherosclerosis in cholesterol-fed rabbits, the elastofibrotic intima generally became thick and hyalinized and was replaced by bundles of microfibrils lacking elastin or associated with only tiny elastin aggregates and disrupted elastic fibers. Organ cultures of aortic explants from rabbits with or without pancreatic elastase supplementation for 5 days disclosed that there was complete loss of medial elastic fibers and increasing deposition of microfibrils, morphologically identical to elastin-associated microfibrils, around viable smooth muscle cells only in the elastase supplemented group. These observations suggest that abnormal accumulation of microfibrils in the elastic tissue is closely associated with excessive elastolysis of preformed or newly formed elastic fibers during elastic tissue remodeling. Enhanced synthesis of microfibrils may occur in response to elastolysis as a reparative phenomenon.

Skin is a window on heritable disorders of connective tissue

A skin biopsy contains the macromolecules present in most connective tissues: collagens, elastin, glycoproteins, and proteoglycans. The specific combination and assembly of these matrix components and their interactions with other structures (e.g., epidermal appendages, nerve and vascular networks) and cells are responsible for the distinction among specific regions of the dermis. The matrix components are interactive and interdependent and modification of one of them, by extrinsic (environmental) and/or intrinsic (systemic, genetic, age-related) factors, may have consequences on the tissue as a whole. The skin, therefore, provides a window through which it is possible to examine how mutations in one connective tissue macromolecule can change the interactions among matrix components and affect tissue structure and organization. Light and electron microscopic studies of skin from patients with inherited connective tissue disorders (e.g., Ehlers-Danlos syndrome, osteogenesis imperfecta, Marfan syndrome, cutis laxa) have led us to the following generalizations about what components change, how individual collagen or elastic fibers are altered and how individual alterations affect overall dermal organization: 1) There is a limited change in the repertoire of collagen fibrils in the skin; 2) there appears to be a greater range of abnormal structure in dermal elastic fibers than in the collagen fibrils; 3) the morphology of the fibroblastic cells may provide clues to the defect in matrix components; 4) similar structural abnormalities result from different molecular defect; 5) a molecular defect in one connective tissue molecule has consequences for the structural properties of other connective tissue components; and 6) although structural alterations in connective tissue fibers are rarely specific for a given disease, there are characteristic patterns of structural change in the matrix that may be used to confirm a diagnosis. These generalizations show that mutations rarely affect only a single aspect of macromolecular function and because of the interactions of matrix components in this complex organ (skin) often disturb the organization of the entire dermis. Genotype-phenotype relationships are important to understand if effective therapies are to be designed. The structure of skin should provide the next level of integration in our efforts to determine how mutations produce disease.

Heterogeneity of elastin expression in cutis laxa fibroblast strains

Cutis laxa is a genetically heterogeneous connective tissue disease that occurs in both inherited and acquired forms. The most apparent defect is loose, redundant, nonresilient skin, but systemic connective tissue abnormalities exist, especially in conjunction with the early onset or autosomal recessive variety. The elastic fiber shows morphologic alterations. We studied dermal skin biopsies and cultured skin fibroblasts from 6 patients with congenital forms of cutis laxa in an effort to correlate alterations in elastin morphology and metabolism. In general, ultrastructural analysis revealed occasional variance in collagen fiber diameter, whereas elastic tissue varied in content, appearance, and the proportion and manner by which elastin and microfibrillar component associated. Fibroblast cell lines comprised of normal donors from a similar age group produced an average of 35 +/- 10 X 10(3) tropoelastin molecular equivalents per cell per hour, as measured by an ELISA. Three of six cutis laxa cell strains were markedly (5-20-fold) reduced in tropoelastin production. Two of these cell strains had specifically reduced levels of tropoelastin production relative to total protein synthesis. Analysis of elastin specific messenger RNA levels indicated this reduced expression of tropoelastin was regulated at a pretranslational level. In other strains, diminished production of elastin did not appear to be the primary defect, underscoring the heterogeneous nature of cutis laxa at both the biochemical and ultrastructural levels.

Cloning of full-length elastin cDNAs from a human skin fibroblast recombinant cDNA library: further elucidation of alternative splicing utilizing exon-specific oligonucleotides

A human cDNA library was constructed utilizing RNA isolated from cultured skin fibroblasts. Recombinant clones containing elastin sequences were identified by plaque hybridizations with previously characterized human placental elastin cDNAs. Seven positive recombinant clones with inserts of approximately 3.2-2.2 kb were isolated. Characterization of the clones by restriction endonuclease analysis and dot-blot hybridizations with exon-specific synthetic oligonucleotides demonstrated considerable variability in the primary nucleotide sequence. Dideoxy nucleotide sequencing confirmed this finding. The variability is most likely a result of alternative splicing of exons from the primary elastin transcripts. The two largest clones contained approximately 1 kb of 3' untranslated sequence and approximately 2.2 kb of translated sequence encoding 730 amino acids. Six amino acids, encoded by exon 12A, have not been previously noted in human elastin cDNAs. In addition, these human skin fibroblast clones contained a 49 bp 5' untranslated sequence. These results demonstrate that there is considerable variability in the processed nucleotide sequence of the elastin mRNAs. These transcripts may code for isoforms of tropoelastin with different biologic properties.