Modulation of elastin exon 26A mRNA and protein expression in human skinin vivo

The Role of Extracellular Matrix in Wound Healing

BACKGROUND

Extracellular matrix communicates with surrounding cells to maintain skin homeostasis and modulate multiple cellular processes including wound healing.

OBJECTIVE

To elucidate the dynamic composition and potential roles of extracellular matrix in normal skin, wound healing process, and abnormal skin scarring.

MATERIALS AND METHODS

Literature review was performed to identify relevant publications pertaining to the extracellular matrix deposition in normal skin and wound healing process, as well as in abnormal scars.

RESULTS

A summary of the matrix components in normal skin is presented. Their primary roles in hemostasis, inflammation, proliferation, and remodeling phases of wound healing are briefly discussed. Identification of novel extracellular matrix in keloids is also provided.

CONCLUSION

Abnormal scarring remains a challenging condition with unmet satisfactory treatments. Illumination of extracellular matrix composition and functions in wound healing process will allow for the development of targeted therapies in the future.

Modulation of Photoaging-Induced Cutaneous Elastin: Evaluation of Gene and Protein Expression of Markers Related to Elastogenesis Under Different Photoexposure Conditions

INTRODUCTION

Photoaging is the process by which ultraviolet rays gradually induce clinical and histological changes in the skin through the production and organization of biological molecules, such as elastin, which is critical to skin strength and elasticity. After exposure to radiation, elastin may undergo alternative mRNA splicing, resulting in modified proteins that contribute to the formation of aging characteristics, such as solar elastosis. The present work aimed to study two different forms of elastin under these conditions: normal elastin and elastin that had been altered in exon 26A.

METHODS

These different forms of elastin were characterized for gene expression by quantitative real-time polymerase chain reaction (qPCR) and for protein expression by immunohistochemistry of ex vivo skins (from photoexposed and non-photoexposed areas) and in vitro reconstituted skin. In addition, up- and downstream molecules in the elastin signaling cascade were evaluated.

RESULTS

As a result, a significant increase in the gene expression of elastin 26A was observed in both ex vivo photoexposed skin tissues and the in vitro photoexposed reconstituted skins. Additionally, significant increases in the gene expression levels of matrix metalloproteinase-12 (MMP12) and lysyl oxidase (LOX) were observed in the ex vivo skin model. The evaluation of protein expression levels of some photoaging markers on the reconstituted skin revealed increased tropoelastin and fibrillin-1 expression after photoexposure.

CONCLUSION

This work contributes to a better understanding of the biological mechanisms involved in photoaging, making it possible to obtain new strategies for the development of dermocosmetic active ingredients to prevent and treat skin aging.

New approaches to skin photodamage histology-Differentiating 'good' versus 'bad' Elastin

Background

Photodamage creates changes within the skin layers known as solar elastosis. This presents as fragmentation of collagen and elastin fibers, decreases in the extracellular matrix (ECM) ground substance, as well as hyaluronic acid decrease in the thinning epidermis. Traditional immunohistochemistry (IHC) staining has failed to differentiate degenerated elastin from new elastin fibers generated with various topical strategies.

Aims

A combination of stains that can offer a regenerative narrative distinguishing newly formed collagen and elastin from that of degenerated protein, thus distinguishing “good” vs “bad” elastin.

Methods

A series of stains were explored based on their ability to identify early regenerative changes within epidermal, dermal, and ECM areas to examine consistency of outcomes and reliability.

Results

A combination of Movat, fibrillin, elafin, and versican for elastogenesis and reversal of solar elastosis. CD44 for HA status (mainly epidermal) and Herovici stain for identifying early collagenesis in the ECM provides a comprehensive range of stains for identifying new elastin and collagen

Conclusion

This suggested stain combination appears to offer an ideal collection of stains for identifying regenerative events within the skin layers.

Alterations in extracellular matrix composition during aging and photoaging of the skin

Human skin is composed of the cell-rich epidermis, the extracellular matrix (ECM) rich dermis, and the hypodermis. Within the dermis, a dense network of ECM proteins provides structural support to the skin and regulates a wide variety of signaling pathways which govern cell proliferation and other critical processes. Both intrinsic aging, which occurs steadily over time, and extrinsic aging (photoaging), which occurs as a result of external insults such as solar radiation, cause alterations to the dermal ECM. In this study, we utilized both quantitative and global proteomics, alongside single harmonic generation (SHG) and two-photon autofluorescence (TPAF) imaging, to assess changes in dermal composition during intrinsic and extrinsic aging. We find that both intrinsic and extrinsic aging result in significant decreases in ECM-supporting proteoglycans and structural ECM integrity, evidenced by decreasing collagen abundance and increasing fibril fragmentation. Intrinsic aging also produces changes distinct from those produced by photoaging, including reductions in elastic fiber and crosslinking enzyme abundance. In contrast, photoaging is primarily defined by increases in elastic fiber-associated protein and pro-inflammatory proteases. Changes associated with photoaging are evident even in young (mid 20s) sun-exposed forearm skin, indicating that proteomic evidence of photoaging is present decades prior to clinical signs of photoaging. GO term enrichment revealed that both intrinsic aging and photoaging share common features of chronic inflammation. The proteomic data has been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier PXD015982.

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Intrinsic aging and photoaging both decrease ECM-supporting proteoglycans and structural ECM.

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Intrinsic aging produces reductions in elastic fiber and crosslinking enzyme abundance.

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Photoaging results in increases in pro-inflammatory proteases and elastic fiber abundance.

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Intrinsic aging and photoaging share common features associated with chronic inflammation.

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Proteomic changes associated with photoaging are evident decades prior to clinical aging signs.

A comprehensive map of human elastin cross-linking during elastogenesis

Elastin is an essential structural protein in the extracellular matrix of vertebrates. It is the core component of elastic fibers, which enable connective tissues such as those of the skin, lungs or blood vessels to stretch and recoil. This function is provided by elastin's exceptional properties, which mainly derive from a unique covalent cross-linking between hydrophilic lysine-rich motifs of units of the monomeric precursor tropoelastin. To date, elastin's cross-linking is poorly investigated. Here, we purified elastin from human tissue and cleaved it into soluble peptides using proteases with different specificities. We then analyzed elastin's molecular structure by identifying unmodified residues, post-translational modifications and cross-linked peptides by high-resolution mass spectrometry and amino acid analysis. The data revealed the presence of multiple isoforms in parallel and a complex and heterogeneous molecular interconnection. We discovered that the same lysine residues in different monomers were simultaneously involved in various cross-link types or remained unmodified. Furthermore, both types of cross-linking domains, Lys-Pro and Lys-Ala domains, participate not only in bifunctional inter- but also in intra-domain cross-links. We elucidated the sequences of several desmosine-containing peptides and the contribution of distinct domains such as 6, 14 and 25. In contrast to earlier assumptions proposing that desmosine cross-links are formed solely between two domains, we elucidated the structure of a peptide that proves a desmosine formation with participation of three Lys-Ala domains. In summary, these results provide new and detailed insights into the cross-linking process, which takes place within and between human tropoelastin units in a stochastic manner.

Enhancement of synthesis of extracellular matrix proteins on retinoic acid loaded electrospun scaffolds

Electrospinning is a renowned technique for the generation of ultrafine, micro- and nanoscale fibres due to its simplicity, versatility and tunability. Owing to its adaptability to a wide selection of materials and scaffold architectures, electrospun meshes have been developed as biocompatible scaffolds and drug delivery systems for tissue engineering. Here, we developed a drug delivery scaffold by electrospinning poly(ε-caprolactone) (PCL) directly blended with a therapeutic agent, retinoic acid (RA), at different concentrations. The release profile, DNA, and elastin analysis of direct and transwell seeded RA-loaded PCL electrospun scaffolds showed desirable controlled release at 15 kV fabrication, with 0.01% RA as the optimum concentration. The selected 0.01% (w/v) RA-loaded PCL meshes were further analysed using five different seeding cultures to investigate and extensively distinguish the effects of RA release with or without cell contact to the PCL electrospun meshes for cell morphology, proliferation and extracellular matrix (ECM) protein secretion of collagen and elastin. Upon exposure to RA-loaded PCL scaffolds, an increase of human dermal fibroblast (HDF) proliferation was observed. In contrast, human mesenchymal stromal cell (hMSC) cultures showed a decrease in cell proliferation. For both hMSC and HDF cultures, exposure to RA-loaded PCL scaffolds provided a significant increase in elastin production per cell. For collagen expression, a slight increase was measured and was outperformed by the 3D geometry stimulation from PCL scaffolds. In contrast to hMSCs, HDFs showed enhanced stress actin fibres in cultures with RA-loaded PCL scaffolds. Both cell types exhibited more vinculin expression when seeded to RA-loaded PCL scaffolds. Hence, electrospun scaffolds releasing RA in a controlled manner were able to regulate cell proliferation, morphology and ECM secretion, and present an attractive approach for optimizing tissue regeneration.

Elastin structure and its involvement in skin photoageing

Skin aging is a complex process that may be caused by factors that are intrinsic and extrinsic to the body. Ultraviolet (UV) radiation represents one of the main sources of skin damage over the years and characterizes a process known as photoaging. Among the changes that affect cutaneous tissue with age, the loss of elastic properties caused by changes in elastin production, increased degradation and/or processing produces a substantial impact on tissue esthetics and health. The occurrence of solar elastosis is one of the main markers of cutaneous photoaging and is characterized by disorganized and non-functional deposition of elastic fibers. The occurrence of UV radiation-induced alternative splicing of the elastin gene, which leads to inadequate synthesis of the proteins required for the correct assembly of elastic fibers, is a potential explanation for this phenomenon. Innovative studies have been fundamental for the elucidation of rarely explored photoaging mechanisms and have enabled the identification of effective therapeutic alternatives such as cosmetic products. This review addresses cutaneous photoaging and the changes that affect elastin in this process.

The RNA Response to DNA Damage

Multicellular organisms must ensure genome integrity to prevent accumulation of mutations, cell death, and cancer. The DNA damage response (DDR) is a complex network that senses, signals, and executes multiple programs including DNA repair, cell cycle arrest, senescence, and apoptosis. This entails regulation of a variety of cellular processes: DNA replication and transcription, RNA processing, mRNA translation and turnover, and post-translational modification, degradation, and relocalization of proteins. Accumulated evidence over the past decades has shown that RNAs and RNA metabolism are both regulators and regulated actors of the DDR. This review aims to present a comprehensive overview of the current knowledge on the many interactions between the DNA damage and RNA fields.

Subtle balance of tropoelastin molecular shape and flexibility regulates dynamics and hierarchical assembly

The assembly of the tropoelastin monomer into elastin is vital for conferring elasticity on blood vessels, skin, and lungs. Tropoelastin has dual needs for flexibility and structure in self-assembly. We explore the structure-dynamics-function interplay, consider the duality of molecular order and disorder, and identify equally significant functional contributions by local and global structures. To study these organizational stratifications, we perturb a key hinge region by expressing an exon that is universally spliced out in human tropoelastins. We find a herniated nanostructure with a displaced C terminus and explain by molecular modeling that flexible helices are replaced with substantial β sheets. We see atypical higher-order cross-linking and inefficient assembly into discontinuous, thick elastic fibers. We explain this dysfunction by correlating local and global structural effects with changes in the molecule's assembly dynamics. This work has general implications for our understanding of elastomeric proteins, which balance disordered regions with defined structural modules at multiple scales for functional assembly.

Supravalvular aortic stenosis: elastin arteriopathy

Supravalvular aortic stenosis is a systemic elastin (ELN) arteriopathy that disproportionately affects the supravalvular aorta. ELN arteriopathy may be present in a nonsyndromic condition or in syndromic conditions such as Williams-Beuren syndrome. The anatomic findings include congenital narrowing of the lumen of the aorta and other arteries, such as branches of pulmonary or coronary arteries. Given the systemic nature of the disease, accurate evaluation is recommended to establish the degree and extent of vascular involvement and to plan appropriate interventions, which are indicated whenever hemodynamically significant stenoses occur. ELN arteriopathy is genetically heterogeneous and occurs as a consequence of haploinsufficiency of the ELN gene on chromosome 7q11.23, owing to either microdeletion of the entire chromosomal region or ELN point mutations. Interestingly, there is a prevalence of premature termination mutations resulting in null alleles among ELN point mutations. The identification of the genetic defect in patients with supravalvular aortic stenosis is essential for a definitive diagnosis, prognosis, and genetic counseling.

The complexity of elastic fibre biogenesis in the skin--a perspective to the clinical heterogeneity of cutis laxa

Elastic fibres are critical connective tissue components providing elasticity and resilience to skin and other tissues. These fibres are composed of elastin and a number of elastin-associated microfibrillar proteins that assemble in a complex fibre network in a multi-step process. Multiple cellular processes, including mitochondrial function, specific molecules in the secretory pathways and temporally and spatially ordered production of elastic fibre components, are required for the biogenesis of functional elastic fibres. Abnormalities in these processes can lead to loss of functional elastic fibres manifesting phenotypically as a skin disease. The paradigm of elastic fibre diseases affecting the skin is cutis laxa, a clinically and genetically heterogeneous group of disorders characterized by loose and sagging skin, frequently associated with extracutaneous manifestations in the lungs and the arterial blood vessels. The complexity of cutis laxa is emphasized by the fact that as many as 10 distinct genes can harbour mutations in this and related disorders. Understanding of the pathomechanistic pathways involved in perturbed elastic fibre assembly in cutis laxa provides information potentially helpful for the development of molecular strategies towards treatment of these, currently intractable, diseases.

Elastolytic mechanism of a novel M23 metalloprotease pseudoalterin from deep-sea Pseudoalteromonas sp. CF6-2: cleaving not only glycyl bonds in the hydrophobic regions but also peptide bonds in the hydrophilic regions involved in cross-linking

Elastin is a common insoluble protein that is abundant in marine vertebrates, and for this reason its degradation is important for the recycling of marine nitrogen. It is still unclear how marine elastin is degraded because of the limited study of marine elastases. Here, a novel protease belonging to the M23A subfamily, secreted by Pseudoalteromonas sp. CF6-2 from deep-sea sediment, was purified and characterized, and its elastolytic mechanism was studied. This protease, named pseudoalterin, has low identities (<40%) to the known M23 proteases. Pseudoalterin has a narrow specificity but high activity toward elastin. Analysis of the cleavage sites of pseudoalterin on elastin showed that pseudoalterin cleaves the glycyl bonds in hydrophobic regions and the peptide bonds Ala-Ala, Ala-Lys, and Lys-Ala involved in cross-linking. Two peptic derivatives of desmosine, desmosine-Ala-Ala and desmosine-Ala-Ala-Ala, were detected in the elastin hydrolysate, indicating that pseudoalterin can dissociate cross-linked elastin. These results reveal a new elastolytic mechanism of the M23 protease pseudoalterin, which is different from the reported mechanism where the M23 proteases only cleave glycyl bonds in elastin. Genome analysis suggests that M23 proteases may be popular in deep-sea sediments, implying their important role in elastin degradation. An elastin degradation model of pseudoalterin was proposed, based on these results and scanning electron microscopic analysis of the degradation by pseudoalterin of bovine elastin and cross-linked recombinant tropoelastin. Our results shed light on the mechanism of elastin degradation in deep-sea sediment.

Chronic heat treatment causes skin wrinkle formation and oxidative damage in hairless mice

We have previously demonstrated that heat shock could induce expression of matrix metalloproteinases (MMPs) in skin cells. These results implicated that chronic heat treatment may cause skin wrinkles. Therefore, in the present study, we investigated the effects of chronic heat treatment (43 °C, 30 min, 3 times/week, 6 weeks) on wrinkle formation in skin of hairless mice. We found that repetitive heat treatment induced skin wrinkles after a period of 6 weeks in skin of hairless mice. Histologically, heat treatment resulted in increased thickness of the epidermis and dermis. And repetitive heat treatment resulted in significantly increased expression of MMP-13 protein and mRNA, but not MMP-2 and -9, in skin of hairless mice. We also demonstrated that activities of antioxidant enzymes, catalase, and superoxide dismutase (SOD), were reduced by chronic heat treatment. In addition, oxidative damage was increased in skin of mice after chronic exposure to heat shock. Taken together, our results suggested that chronic exposure of the skin to heat can cause skin wrinkling. And, increase of MMP-13, decrease of antioxidant enzymes activity, and consequent oxidative damage by chronic heat treatment may play an important role in development of skin aging in hairless mice.

Elastomeric polypeptides

Elastomeric polypeptides are very interesting biopolymers and are characterized by rubber-like elasticity, large extensibility before rupture, reversible deformation without loss of energy, and high resilience upon stretching. Their useful properties have motivated their use in a wide variety of materials and biological applications. This chapter focuses on elastin and resilin - two elastomeric biopolymers - and the recombinant polypeptides derived from them (elastin-like polypeptides and resilin-like polypeptides). This chapter also discusses the applications of these recombinant polypeptides in the fields of purification, drug delivery, and tissue engineering.

The action of neutrophil serine proteases on elastin and its precursor

This study aimed to investigate the degradation of the natural substrates tropoelastin and elastin by the neutrophil-derived serine proteases human leukocyte elastase (HLE), proteinase 3 (PR3) and cathepsin G (CG). Focus was placed on determining their cleavage site specificities using mass spectrometric techniques. Moreover, the release of bioactive peptides from elastin by the three proteases was studied. Tropoelastin was comprehensively degraded by all three proteases, whereas less cleavage occurred in mature cross-linked elastin. An analysis of the cleavage site specificities of the three proteases in tropoelastin and elastin revealed that HLE and PR3 similarly tolerate hydrophobic and/or aliphatic amino acids such as Ala, Gly and Val at P(1), which are also preferred by CG. In addition, CG prefers the bulky hydrophobic amino acid Leu and accepts the bulky aromatic amino acids Phe and Tyr. CG shows a strong preference for the charged amino acid Lys at P(1) in tropoelastin, whereas Lys was not identified at P(1) in CG digests of elastin due to extensive cross-linking at Lys residues in mature elastin. All three serine proteases showed a clear preference for Pro at P(2) and P(4)'. With respect to the liberation of potentially bioactive peptides from elastin, the study revealed that all three serine proteases have a similar ability to release bioactive sequences, with CG producing the highest number of these peptides. In bioactivity studies, potentially bioactive peptides that have not been investigated on their bioactivity to date, were tested. Three new bioactive GxxPG motifs were identified; GVYPG, GFGPG and GVLPG.

A novel anti-ageing mechanism for retinol: induction of dermal elastin synthesis and elastin fibre formation

Dermal elastic fibres are extracellular matrix protein complexes produced by fibroblasts and involved in skin elasticity. Elastin fibres decrease with age as a result of reduced synthesis and increased degradation, resulting in skin sagging and reduced skin elasticity. In this study, we show that retinol (ROL), known to enhance dermal collagen production, is also enhancing elastin fibre formation. ROL induced elastin gene expression and elastin fibre formation in cultured human dermal fibroblasts. Topical treatment of cultured human skin explants with a low dose (0.04%) of ROL increased mRNA and protein levels of tropoelastin and of fibrillin-1, an elastin accessory protein, as documented by QPCR and immunohistochemistry staining. Luna staining confirmed the increased elastin fibre network in the ROL-treated skin explants, as compared with untreated controls. These data demonstrate that ROL exerts its anti-ageing benefits not only via enhanced epidermal proliferation and increased collagen production, but also through an increase in elastin production and assembly.

Structural disorder and dynamics of elastin

Elastin is a self-assembling, extracellular-matrix protein that is the major provider of tissue elasticity. Here we review structural studies of elastin from over four decades, and draw together evidence for solution flexibility and conformational disorder that is inherent in all levels of structural organization. The characterization of disorder is consistent with an entropy-driven mechanism of elastic recoil. We conclude that conformational disorder is a constitutive feature of elastin structure and function.