Structural characterization of human elastin derived peptides containing the GXXP sequence

Matrikines in the skin: Origin, effects, and therapeutic potential

The extracellular matrix (ECM) represents a complex multi-component environment that has a decisive influence on the biomechanical properties of tissues and organs. Depending on the tissue, ECM components are subject to a homeostasis of synthesis and degradation, a subtle interplay that is influenced by external factors and the intrinsic aging process and is often disturbed in pathologies. Upon proteolytic cleavage of ECM proteins, small bioactive peptides termed matrikines can be formed. These bioactive peptides play a crucial role in cell signaling and contribute to the dynamic regulation of both physiological and pathological processes such as tissue remodeling and repair as well as inflammatory responses. In the skin, matrikines exert an influence for instance on cell adhesion, migration, and proliferation as well as vasodilation, angiogenesis and protein expression. Due to their manifold functions, matrikines represent promising leads for developing new therapeutic options for the treatment of skin diseases. This review article gives a comprehensive overview on matrikines in the skin, including their origin in the dermal ECM, their biological effects and therapeutic potential for the treatment of skin pathologies such as melanoma, chronic wounds and inflammatory skin diseases or for their use in anti-aging cosmeceuticals.

Structural and physical basis for the elasticity of elastin

Elastin function is to endow vertebrate tissues with elasticity so that they can adapt to local mechanical constraints. The hydrophobicity and insolubility of the mature elastin polymer have hampered studies of its molecular organisation and structure-elasticity relationships. Nevertheless, a growing number of studies from a broad range of disciplines have provided invaluable insights, and several structural models of elastin have been proposed. However, many questions remain regarding how the primary sequence of elastin (and the soluble precursor tropoelastin) governs the molecular structure, its organisation into a polymeric network, and the mechanical properties of the resulting material. The elasticity of elastin is known to be largely entropic in origin, a property that is understood to arise from both its disordered molecular structure and its hydrophobic character. Despite a high degree of hydrophobicity, elastin does not form compact, water-excluding domains and remains highly disordered. However, elastin contains both stable and labile secondary structure elements. Current models of elastin structure and function are drawn from data collected on tropoelastin and on elastin-like peptides (ELPs) but at the tissue level, elasticity is only achieved after polymerisation of the mature elastin. In tissues, the reticulation of tropoelastin chains in water defines the polymer elastin that bears elasticity. Similarly, ELPs require polymerisation to become elastic. There is considerable interest in elastin especially in the biomaterials and cosmetic fields where ELPs are widely used. This review aims to provide an up-to-date survey of/perspective on current knowledge about the interplay between elastin structure, solvation, and entropic elasticity.

Bioactive extracellular matrix fragments in tendon repair

Tendinopathy is a common tendon disorder that causes pain, loss of strength and function, and local inflammation mainly characterized by hypoxia, collagen degradation, and extracellular matrix (ECM) disorganization. Generally, ECM degradation and remodeling is tightly regulated; however, hyperactivation of matrix metalloproteases (MMPs) contributes to excessive collagenolysis under pathologic conditions resulting in tendon ECM degradation. This review article focuses on the production, function, and signaling of matrikines for tendon regeneration following injury with insights into the expression, tissue compliance, and cell proliferation exhibited by various matrikines. Furthermore, the regenerative properties suggest translational significance of matrikines to improve the outcomes post-injury by assisting with tendon healing.

Elastases and elastokines: elastin degradation and its significance in health and disease

Elastin is an important protein of the extracellular matrix of higher vertebrates, which confers elasticity and resilience to various tissues and organs including lungs, skin, large blood vessels and ligaments. Owing to its unique structure, extensive cross-linking and durability, it does not undergo significant turnover in healthy tissues and has a half-life of more than 70 years. Elastin is not only a structural protein, influencing the architecture and biomechanical properties of the extracellular matrix, but also plays a vital role in various physiological processes. Bioactive elastin peptides termed elastokines - in particular those of the GXXPG motif - occur as a result of proteolytic degradation of elastin and its non-cross-linked precursor tropoelastin and display several biological activities. For instance, they promote angiogenesis or stimulate cell adhesion, chemotaxis, proliferation, protease activation and apoptosis. Elastin-degrading enzymes such as matrix metalloproteinases, serine proteases and cysteine proteases slowly damage elastin over the lifetime of an organism. The destruction of elastin and the biological processes triggered by elastokines favor the development and progression of various pathological conditions including emphysema, chronic obstructive pulmonary disease, atherosclerosis, metabolic syndrome and cancer. This review gives an overview on types of human elastases and their action on human elastin, including the formation, structure and biological activities of elastokines and their role in common biological processes and severe pathological conditions.

Construction and evaluation of an antibody phage display library targeting heparan sulfate

Heparan sulfate (HS) is a linear polysaccharide with high structural diversity. Different HS epitopes have been detected and localized using single chain variable fragment (scFv) antibodies from a ‘single pot’ phage display library containing a randomized complementarity determining region of the heavy chain (CDR3). In this study, we created a new library containing anti-HS scFvs that all harbor a dp-38 heavy chain segment where the CDR3 region was engineered to contain the XBBXBX heparin binding consensus site (X = any amino acid, B = R, K or H). The library contained ~1.73 × 10⁶ unique antibodies and was biopanned against HS from several sources. The selected antibodies were sequenced and chemically/immunohistologically characterized. A number of 67 anti-HS scFv antibodies were selected, of which 31 contained a XBBXBX CDR3 sequence. There was a clear preference for glycine at the first and proline at the fourth position of the CDR3. The sequence GZZP(R/K)X (Z = R, K or H, but may also contain N, S, or Q) was unusually overrepresented. Selected antibodies reacted with HS/heparin, but not with other glycosaminoglycans. Antibodies reacted differentially with respect to N-, 2-O, or 6-O-desulfated heparin preparations, and showed distinct topologies of HS epitopes in rat kidney sections. The library may be instrumental in the selection of a large pool of HS epitope-specific antibodies, and - since all antibodies differ only in their 6 amino acid CDR region - may be a tool for a rational design of antibodies recognizing specific HS sulfation patterns.

Elastin in the Tumor Microenvironment

Elastic fibers are found in the extracellular matrix (ECM) of tissues requiring resilience and depend on elasticity. Elastin and its degradation products have multiple roles in the oncologic process. In many malignancies, the remodeled ECM expresses high levels of the elastin protein which may have either positive or negative effects on tumor growth. Elastin cross-linking with other ECM components and the enzymes governing this process all have effects on tumorigenesis. Elastases, and specifically neutrophil elastase, are key drivers of invasion and metastasis and therefore are important targets for inhibition. Elastin degradation leads to the generation of bioactive fragments and elastin-derived peptides that further modulate tumor growth and spread. Interestingly, elastin-like peptides (ELP) and elastin-derived peptides (EDP) may also be utilized as nano-carriers to combat tumor growth. EDPs drive tumor development in a variety of ways, and specifically targeting EDPs and their binding proteins are major objectives for ongoing and future anti-cancer therapies. Research on both the direct anti-cancer activity and the drug delivery capabilities of ELPs is another area likely to result in novel therapeutic agents in the near future.

Elastic fibers and elastin receptor complex: Neuraminidase-1 takes the center stage

Extracellular matrix (ECM) has for a long time being considered as a simple architectural support for cells. It is now clear that ECM presents a fundamental influence on cells driving their phenotype and fate. This complex network is highly specialized and the different classes of macromolecules that comprise the ECM determine its biological functions. For instance, collagens are responsible for the tensile strength of tissues, proteoglycans and glycosaminoglycans are essential for hydration and resistance to compression, and glycoproteins such as laminins facilitate cell attachment. The largest structures of the ECM are the elastic fibers found in abundance in tissues suffering high mechanical constraints such as skin, lungs or arteries. These structures present a very complex composition whose core is composed of elastin surrounded by a microfibrils mantle. Elastogenesis is a tightly regulated process involving the sialidase activity of the Neuraminidase-1 (Neu-1) sub-unit of the Elastin Receptor Complex. Interestingly, Neu-1 subunit also serves as a sensor of elastin degradation via its ability to transmit elastin-derived peptides signaling. Finally, reports showing that neuraminidase activity is able to regulate TGF-β activation raises questions about a possible role for Neu-1 in elastic fibers remodeling. In this mini review, we develop the concept of the regulation of the whole life of elastic fibers through an original scope, the key role of Neu-1 sialidase enzymatic activity.

Induction and regulation of murine emphysema by elastin peptides

Emphysema is the major component of chronic obstructive pulmonary disease (COPD). During emphysema, elastin breakdown in the lung tissue originates from the release of large amounts of elastase by inflammatory cells. Elevated levels of elastin-derived peptides (EP) reflect massive pulmonary elastin breakdown in COPD patients. Only the EP containing the GXXPG conformational motif with a type VIII β-turn are elastin receptor ligands inducing biological activities. In addition, the COOH-terminal glycine residue of the GXXPG motif seems a prerequisite to the biological activity. In this study, we endotracheally instilled C57BL/6J mice with GXXPG EP and/or COOH-terminal glycine deleted-EP whose sequences were designed by molecular dynamics and docking simulations. We investigated their effect on all criteria associated with the progression of murine emphysema. Bronchoalveolar lavages were recovered to analyze cell profiles by flow cytometry and lungs were prepared to allow morphological and histological analysis by immunostaining and confocal microscopy. We observed that exposure of mice to EP elicited hallmark features of emphysema with inflammatory cell accumulation associated with increased matrix metalloproteinases and desmosine expression and of remodeling of parenchymal tissue. We also identified an inactive COOH-terminal glycine deleted-EP that retains its binding-activity to EBP and that is able to inhibit the in vitro and in vivo activities of emphysema-inducing EP. This study demonstrates that EP are key actors in the development of emphysema and that they represent pharmacological targets for an alternative treatment of emphysema based on the identification of EP analogous antagonists by molecular modeling studies.

Uncoupling of Elastin Complex Receptor during In Vitro Aging Is Related to Modifications in Its Intrinsic Sialidase Activity and the Subsequent Lactosylceramide Production

Degradation of elastin leads to the production of elastin-derived peptides (EDP), which exhibit several biological effects, such as cell proliferation or protease secretion. Binding of EDP on the elastin receptor complex (ERC) triggers lactosylceramide (LacCer) production and ERK1/2 activation following ERC Neu-1 subunit activation. The ability for ERC to transduce signals is lost during aging, but the mechanism involved is still unknown. In this study, we characterized an in vitro model of aging by subculturing human dermal fibroblasts. This model was used to understand the loss of EDP biological activities during aging. Our results show that ERC uncoupling does not rely on Neu-1 or PPCA mRNA or protein level changes. Furthermore, we observe that the membrane targeting of these subunits is not affected with aging. However, we evidence that Neu-1 activity and LacCer production are altered. Basal Neu-1 catalytic activity is strongly increased in aged cells. Consequently, EDP fail to promote Neu-1 catalytic activity and LacCer production in these cells. In conclusion, we propose, for the first time, an explanation for ERC uncoupling based on the age-related alterations of Neu-1 activity and LacCer production that may explain the loss of EDP-mediated effects occurring during aging.

Soluble elastin peptides in cardiovascular homeostasis: Foe or ally

Elastin peptides, also known as elastin-derived peptides or elastokines, are soluble polypeptides in blood and tissue. The blood levels of elastin peptides are usually low but can increase during cardiovascular diseases, such as atherosclerosis, aortic aneurysm and diabetes with vascular complications. Generally, elastin peptides are derived from the degradation of insoluble elastic polymers. The biological activities of elastin peptides are bidirectional, e.g., a pro-inflammatory effect on monocyte migration induction vs. a protective effect on vasodilation promotion. However, recent in vivo studies have demonstrated that elastin peptides promote the formation of atherosclerotic plaques in hypercholesterolemic mice and induce hyperglycemia and elevations in plasma lipid levels in fasted mice. More important, the detrimental effects induced by elastin peptides can be largely inhibited by genetic or pharmacological blockade of the elastin receptor complex or by neutralization of an antibody against elastin peptides. These studies indicate new therapeutic strategies for the treatment of cardiovascular diseases by targeting elastin peptide metabolism. Therefore, the goal of this review is to summarize current knowledge about elastin peptides relevant to cardiovascular pathologies to further delineate their potential application in cardiovascular disease.

Elastin-derived peptides increase invasive capacities of lung cancer cells by post-transcriptional regulation of MMP-2 and uPA

Elastin-rich lung extracellular matrix is largely remodeled during tumor invasion. Elastin degradation produces peptides displaying a wide range of biological activities. These elastin derived peptides (EP) interact with the elastin receptor complex (ERC) but also bind to α(V)β(3) integrin and galectin-3. In this study, we explored the role of EP and their receptors in tumor progression of lung carcinomas. Non-invasive and invasive lung tumor cell lines were incubated in presence of kappa-elastin (κE) or with synthetic peptides displaying receptor-specific sequences (VGVAPG, GRKRK, AGVPGLGVG and AGVPGFGAG). Modified Boyden chamber assays revealed an increased invasive capacity of invasive cells induced by κE. EP treatment had no effect on cell proliferation but zymography analysis revealed an increase of pro-MMP-2 and uPA levels in the conditioned media of treated cells. Moreover, the active form of MMP-2 was increased in invasive cells. Interestingly, this regulation was not observed at the mRNA level and actinomycin D was unable to inhibit κE effects. We also observed that the regulation of proteases protein level following κE treatment was an early process detectable after 1 h. All these effects could not be inhibited by lactose and V14, two ERC antagonists, or by blocking antibodies against α(V)β(3) integrin and galectin-3. Finally, VGVAPG and GRKRK failed to reproduce κE effects whereas nonapeptides partially mimicked them. These results demonstrate that treatment with EP up-regulates invasiveness of lung tumor cells via the release of proteolytic enzymes. This modulation involves post-transcriptional mechanisms and a nonapeptide-receptor different from the ERC, α(V)β(3) integrin and galectin-3.

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.

Degradation of tropoelastin by matrix metalloproteinases--cleavage site specificities and release of matrikines

To provide a basis for the development of approaches to treat elastin-degrading diseases, the aim of this study was to investigate the degradation of the natural substrate tropoelastin by the elastinolytic matrix metalloproteinases MMP-7, MMP-9, and MMP-12 and to compare the cleavage site specificities of the enzymes using complementary MS techniques and molecular modeling. Furthermore, the ability of the three proteases to release bioactive peptides was studied. Tropoelastin was readily degraded by all three MMPs. Eighty-nine cleavage sites in tropoelastin were identified for MMP-12, whereas MMP-7 and MMP-9 were found to cleave at only 58 and 63 sites, respectively. Cleavages occurred predominantly in the N-terminal and C-terminal regions of tropoelastin. With respect to the cleavage site specificities, the study revealed that all three MMPs similarly tolerate hydrophobic and/or aliphatic amino acids, including Pro, Gly, Ile, and Val, at P(1)'. MMP-7 shows a strong preference for Leu at P(1)', which is also well accepted by MMP-9 and MMP-12. Of all three MMPs, MMP-12 best tolerates bulky charged and aromatic amino acids at P(1)'. All three MMPs showed a clear preference for Pro at P(3) that could be structurally explained by molecular modeling. Analysis of the generated peptides revealed that all three MMPs show a similar ability to release bioactive sequences, with MMP-12 producing the highest number of these peptides. Furthermore, the generated peptides YTTGKLPYGYGPGG, YGARPGVGVGGIP, and PGFGAVPGA, containing GxxPG motifs that have not yet been proven to be bioactive, were identified as new matrikines upon biological activity testing.

A proposed interaction mechanism between elastin-derived peptides and the elastin/laminin receptor-binding domain

Elastin-derived peptides (EDPs) have been intensively studied in view of their widely diverse biological activities. These are triggered both in normal and tumor cells, through peptide anchoring at the surface of the elastin-binding protein (EBP), a subunit of the elastin/laminin receptor. In this study, we investigated both the structure of the Sgal peptide, representing the elastin-binding domain of EBP, and its interaction with EDPs, through a combination of experimental and theoretical methods. Although the conformation of the Sgal peptide is highly flexible, we detected a type I beta-turn at the QDEA sequence. This represents the best structured motif in the entire Sgal peptide, which might therefore contribute to its binding activity. We further propose a novel three-dimensional model for the interaction between the Sgal peptide and EDPs; folding of the EDPs at the GXXP motif, in a conformation close to a type VIII beta-turn, provides the efficient contact of the protein with the Q residue of the Sgal peptide. This residue is exposed to the peptide surface, because of the beta-turn structure of the QDEA residues in the peptide sequence. We further show that this complex is stabilized by three hydrogen bonds involving EDPs backbone atoms.

High-sensitivity nanoLC-MS/MS analysis of urinary desmosine and isodesmosine

Chronic obstructive pulmonary disease (COPD) is characterized by the degradation of elastin, the major insoluble protein of lung tissues. The degradation of elastin gives rise to desmosine (DES) and isodesmosine (IDES), two major urinary products typified by a hydrophilic pyridinium-based cross-linker structure. A high sensitivity method based on nanoflow liquid chromatography tandem mass spectrometry with multiple reaction monitoring was developed for the analysis of urinary DES and IDES. The analytes were derivatized with propionic anhydride and deuterated DES (D(4)-DES) was used as an internal standard. This method enables the quantification of DES and IDES in as little as 50 microL of urine and provides a detection limit of 0.10 ng/mL (0.95 fmol on-column). We report the analysis of DES and IDES in a cohort of 40 urine specimens from four groups of individuals: (a) COPD rapid decliners (11.8 +/- 3.7 ng/mg creatine (crea)), (b) COPD slow decliners (16.0 +/- 3.1 ng/mg crea), (c) healthy smokers (13.2 +/- 1.9 ng/mg crea), and (d) healthy nonsmokers (14.9 +/- 2.9 ng/mg crea). Our analysis reveals a statistically significant decrease in the level of urinary DES and IDES in COPD rapid decliner patients compared to healthy nonsmoker controls and COPD slow decliner patients. This methodology may be useful for monitoring DES and IDES levels in well controlled animal models for COPD or for longitudinal studies in COPD patients.

In vitro degradation of human tropoelastin by MMP-12 and the generation of matrikines from domain 24

Degradation of elastic fibers in tissues can result in the development of disorders that include aneurysms, atherosclerosis, and loss of skin elasticity. Tropoelastin is the precursor of the cross-linked elastin and its expression is triggered by elastin-degrading factors as a response to damage. Factors like UV radiation not only increase the expression of tropoelastin but also potent metalloelastases such as macrophage elastase (MMP-12). The development of elastin-degrading diseases, moreover, is a chronic process during which elastin and tropoelastin are repeatedly exposed to attacks by MMP-12. Hence, in this work we report the in vitro susceptibility of tropoelastin and the potential of MMP-12 to generate matrikines. This work provides evidence that tropoelastin is substantially and rapidly degraded by MMP-12 even at very dilute enzyme concentrations. MMP-12 cleaves at least 86 sites in tropoelastin. Analysis of the generated peptides revealed that some small peptides contained the motif GXXPG that may enable them to bind with the elastin binding protein (EBP). Furthermore, using synthesized peptides it was confirmed that several sites in the sequence encoded by exon 24 which contains repetitive units of biologically active VGVAPG domains are susceptible to attack by MMP-12, provided that the active subsites in MMP-12 (S(4) to S(4)') are occupied. Such cleavage events have lead to the generation of ligands that may bind to EBP.

Kinetics and thermodynamics of type VIII beta-turn formation: a CD, NMR, and microsecond explicit molecular dynamics study of the GDNP tetrapeptide

We report an experimental and theoretical study on type VIII beta-turn using a designed peptide of sequence GDNP. CD and NMR studies reveal that this peptide exists in equilibrium between type VIII beta-turn and extended conformations. Extensive MD simulations give a description of the free energy landscape of the peptide in which we retrieve the same two main conformations suggested by the experiments. The free energy difference between the two conformational states is very small and the transition between them occurs within a few kT at 300 K on a nanosecond timescale. The equilibrium is mainly driven by entropic contribution, which favors extended conformations over beta-turns. This confirms other theoretical studies showing that beta-turns are marginally stable in water solution because of the larger entropy of the extended state unless some stabilizing interactions exist. Our observations may be extended to any type of beta-turn and have important consequences for protein folding. A comparison of our MD and CD results also suggests a possible type VIII beta-turn CD signature indicated by one main band at 200 nm, close to that of random coil, and a fairly large shoulder at 220 nm. Last, our results clearly show that the XXXP motif can only fold into a type VIII beta-turn, which is consistent with its fairly strong propensity for this type of turn. This important finding may help for peptide design and is in line with recent studies on bioactive elastin peptides.