Elastin peptides antagonize ceramide-induced apoptosis

The Role of PGC-1α in Aging Skin Barrier Function

Skin provides a physical and immune barrier to protect the body from foreign substances, microbial invasion, and desiccation. Aging reduces the barrier function of skin and its rate of repair. Aged skin exhibits decreased mitochondrial function and prolonged low-level inflammation that can be seen in other organs with aging. Peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α (PGC-1α), an important transcriptional coactivator, plays a central role in modulating mitochondrial function and antioxidant production. Mitochondrial function and inflammation have been linked to epidermal function, but the mechanisms are unclear. The aim of this review is to discuss the mechanisms by which PGC-1α might exert a positive effect on aged skin barrier function. Initially, we provide an overview of the function of skin under physiological and aging conditions, focusing on the epidermis. We then discuss mitochondrial function, oxidative stress, cellular senescence, and inflamm-aging, the chronic low-level inflammation observed in aging individuals. Finally, we discuss the effects of PGC-1α on mitochondrial function, as well as the regulation and role of PGC-1α in the aging epidermis.

Understanding Acquired Brain Injury: A Review

Any type of brain injury that transpires post-birth is referred to as Acquired Brain Injury (ABI). In general, ABI does not result from congenital disorders, degenerative diseases, or by brain trauma at birth. Although the human brain is protected from the external world by layers of tissues and bone, floating in nutrient-rich cerebrospinal fluid (CSF); it remains susceptible to harm and impairment. Brain damage resulting from ABI leads to changes in the normal neuronal tissue activity and/or structure in one or multiple areas of the brain, which can often affect normal brain functions. Impairment sustained from an ABI can last anywhere from days to a lifetime depending on the severity of the injury; however, many patients face trouble integrating themselves back into the community due to possible psychological and physiological outcomes. In this review, we discuss ABI pathologies, their types, and cellular mechanisms and summarize the therapeutic approaches for a better understanding of the subject and to create awareness among the public.

Matrikines as mediators of tissue remodelling

Extracellular matrix (ECM) proteins confer biomechanical properties, maintain cell phenotype and mediate tissue repair (via release of sequestered cytokines and proteases). In contrast to intracellular proteomes, where proteins are monitored and replaced over short time periods, many ECM proteins function for years (decades in humans) without replacement. The longevity of abundant ECM proteins, such as collagen I and elastin, leaves them vulnerable to damage accumulation and their host organs prone to chronic, age-related diseases. However, ECM protein fragmentation can potentially produce peptide cytokines (matrikines) which may exacerbate and/or ameliorate age- and disease-related ECM remodelling. In this review, we discuss ECM composition, function and degradation and highlight examples of endogenous matrikines. We then critically and comprehensively analyse published studies of matrix-derived peptides used as topical skin treatments, before considering the potential for improvements in the discovery and delivery of novel matrix-derived peptides to skin and internal organs. From this, we conclude that while the translational impact of matrix-derived peptide therapeutics is evident, the mechanisms of action of these peptides are poorly defined. Further, well-designed, multimodal studies are required.

Elastin-Derived Peptides in the Central Nervous System: Friend or Foe

Elastin is one of the main structural matrix proteins of the arteries, lung, cartilage, elastic ligaments, brain vessels, and skin. These elastin fibers display incredible resilience and structural stability with long half-life. However, during some physiological and pathophysiological conditions, elastin is prone to proteolytic degradation and, due to the extremely low turnover rate, its degradation is practically an irreversible and irreparable phenomenon. As a result of elastin degradation, new peptides called elastin-derived peptides (EDPs) are formed. A growing body of evidence suggests that these peptides play an important role in the development of age-related vascular disease. They are also detected in the cerebrospinal fluid of healthy people, and their amount increases in patients after ischemic stroke. Recently, elastin-like polypeptides have been reported to induce overproduction of beta-amyloid in a model of Alzheimer's disease. Nevertheless, the role and mechanism of action of EDPs in the nervous system is largely unknown and limited to only a few studies. The article summarizes the current state of knowledge on the role of EDPs in the nervous system.

Elastin-derived peptide VGVAPG decreases differentiation of mouse embryo fibroblast (3T3-L1) cells into adipocytes

Elastin is a highly elastic protein present in connective tissue. As a result of protease activity, elastin hydrolysis occurs, and during this process, elastin-derived peptides (EDPs) are released. One of the constitutively repeating elastin and EDP building sequences is the hexapeptide VGVAPG. Therefore, the aim of our research was to define the effect of VGVAPG peptide on adipogenesis in a mouse 3T3-L1 cell line. 3T3-L1 cells were differentiated according to a previously described protocol and exposed to increasing concentrations of VGVAPG or VVGPGA peptide. The obtained results showed that VGVAPG peptide does not stimulate reactive oxygen species (ROS) production, caspase-1 activation, and 3T3-L1 cell proliferation. In the second part of the experiments, it was proved that VGVAPG peptide decreased lipid accumulation as measured by oil red O staining, which was confirmed by the profile of increased expression markers of undifferentiated preadipocytes. In our experiments, 10 nM VGVAPG added for differentiating to adipocytes increased the expression of Pref-1, serpin E1, and adiponectin as compared to rosiglitazone (PPARγ agonist)-treated group and simultaneously decreased the expression of VEGF and resistin as compared to the rosiglitazone-treated group. The obtained results show that VGVAPG peptide sustains 3T3 cells in undifferentiated state.

ABBREVIATIONS

DMSO: dimethyl sulphoxide; EBP: elastin-binding protein; EDPs: elastin-derived peptides; FBS: foetal bovine serum; Glb1: gene for beta-galactosidase; LDL: low-density-lipoprotein; PAI-1 (Serpin E1): plasminogen activator inhibitor-1; PBS: phosphate-buffered saline; PPARγ: peroxisome proliferator-activated receptor gamma; Pref-1: preadipocyte factor 1; ROS: reactive oxygen species; VEGF-A: vascular endothelial growth factor-A; VGVAPG: Val-Gly-Val-Ala-Pro-Gly; β-Gal: beta-galactosidase; ORO: oil red O; IBMX: 3-isobutyl-1-methylxanthine; H2DCFDA: 2',7'-dichlorodihydrofluorescein diacetate; DMEM: Dulbecco's Modified Eagle's Medium; VVGPGA: Val-Val-Gly-Pro-Gly-Ala.

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.

Elastin-derived peptide VGVAPG affects the proliferation of mouse cortical astrocytes with the involvement of aryl hydrocarbon receptor (Ahr), peroxisome proliferator-activated receptor gamma (Pparγ), and elastin-binding protein (EBP)

During aging and ischemic and hemorrhagic stroke, elastin molecules are degraded and elastin-derived peptides are released into the brain microenvironment. Val-Gly-Val-Ala-Pro-Gly (VGVAPG) is a repeating hexapeptide in the elastin molecule. It is well documented that the peptide sequence binds with high affinity to elastin-binding protein (EBP) located on the cell surface, thereby transducing a molecular signal into the cell. The aim of our study was to investigate whether EBP, aryl hydrocarbon receptor (Ahr), and peroxisome proliferator-activated receptor gamma (Pparγ) are involved in VGVAPG-stimulated proliferation. Primary astrocytes were maintained in DMEM/F12 medium without phenol red, supplemented with 10 or 1% charcoal/dextran-treated fetal bovine serum (FBS). The cells were exposed to increasing concentrations of VGVAPG peptide, and resazurin reduction was measured. In addition, Glb1, Pparγ, and Ahr genes were silenced. After 48 h of exposure to 10 nM and 1 µM of VGVAPG peptide, the level of estradiol (E₂) and the expression of Ki67 and S100B proteins were measured. The results showed that at a wide range of concentrations, VGVAPG peptide increased the metabolism of astrocytes depending on the concentration of FBS. After silencing of Glb1, Pparγ, and Ahr genes, VGVAPG peptide did not affect the cell metabolism which suggests the involvement of all the mentioned receptors in its mechanism of action. Interestingly, in the low-FBS medium, the silencing of Glb1 gene did not result in complete inhibition of VGVAPG-stimulated proliferation. On the other hand, in the medium with 10% FBS VGVAPG increased Ki67 expression after Pparγ silencing, whereas in the medium with 1% FBS VGVAPG decreased Ki67 expression. Following the application of Ahr siRNA, VGVAPG peptide decreased the production of E₂ and increased the expression of Ki67 and S100B proteins.

The role of elastin-derived peptides in human physiology and diseases

Once considered as inert, the extracellular matrix recently revealed to be biologically active. Elastin is one of the most important components of the extracellular matrix. Many vital organs including arteries, lungs and skin contain high amounts of elastin to assure their correct function. Physiologically, the organism contains a determined quantity of elastin from the early development which may remain physiologically constant due to its very long half-life and very low turnover. Taking into consideration the continuously ongoing challenges during life, there is a physiological degradation of elastin into elastin-derived peptides which is accentuated in several disease states such as obstructive pulmonary diseases, atherosclerosis and aortic aneurysm. These elastin-derived peptides have been shown to have various biological effects mediated through their interaction with their cognate receptor called elastin receptor complex eliciting several signal transduction pathways. In this review, we will describe the production and the biological effects of elastin-derived peptides in physiology and pathology.

Antiproliferative Effect of Elastin-Derived Peptide VGVAPG on SH-SY5Y Neuroblastoma Cells

Throughout the lifetime of humans, the amount of stem cells and the rate of cell proliferation continue to decrease. Reactive oxygen species (ROS) are one among the many factors that promote stem cell aging. Both a decrease in the level of stem cells and increase in ROS production can lead to the development of different neurodegenerative diseases. This study was conducted to determine how the VGVAPG peptide, liberated from elastin during the aging process and under pathological conditions, affects ROS production and activities of antioxidant enzymes in undifferentiated, proliferating SH-SY5Y cells. SH-SY5Y cells were maintained in Dulbecco's modified Eagle's medium/nutrient mixture F-12 supplemented with 10% heat-inactivated fetal bovine serum (FBS). After treating the SH-SY5Y cells with VGVAPG peptide, we measured ROS production; cell metabolism, proliferation, and expression; and activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT). We demonstrated that the VGVAPG peptide increases GPx expression and activity, whereas it decreases CAT expression in SH-SY5Y cells. Silencing of the GLB1 gene prevents changes in GPx activity. Despite the fact that the VGVAPG peptide increases GPx expression, it increases the ROS level. Moreover, the VGVAPG peptide decreases SH-SY5Y proliferation, which is prevented by the ROS scavenger N-acetyl-L-cysteine. Our data suggest that ROS production and decreased proliferation of SH-SY5Y cells are the results of excitotoxicity meditated through close unrecognized molecular pathways. More research is needed to elucidate the unknown mechanism of action of VGVAPG peptide in the nervous system.

Elastin molecular aging promotes MDA-MB-231 breast cancer cell invasiveness

Elastin is a long-lived extracellular matrix protein responsible for the structural integrity and function of tissues. Breast cancer elastosis is a complex phenomenon resulting in both the deposition of elastotic masses and the local production of elastin fragments. In invasive human breast cancers, an increase in elastosis is correlated with severity of the disease and age of the patient. Elastin-derived peptides (EDPs) are a hallmark of aging and are matrikines - matrix fragments having the ability to regulate cell physiology. They are known to promote processes linked to tumor progression, but their effects on breast cancer cells remain unexplored. Our data show that EDPs enhance the invasiveness of MDA-MB-231 breast cancer cells through the engagement of matrix metalloproteases 14 and 2. We therefore suggest that elastosis and/or an aged stroma could promote breast cancer cell invasiveness.

The Elastin Receptor Complex: A Unique Matricellular Receptor with High Anti-tumoral Potential

Elastin, one of the longest-lived proteins, confers elasticity to tissues with high mechanical constraints. During aging or pathophysiological conditions such as cancer progression, this insoluble polymer of tropoelastin undergoes an important degradation leading to the release of bioactive elastin-derived peptides (EDPs), named elastokines. EDP exhibit several biological functions able to drive tumor development by regulating cell proliferation, invasion, survival, angiogenesis, and matrix metalloproteinase expression in various tumor and stromal cells. Although, several receptors have been suggested to bind elastokines (α_vβ₃ and α_vβ₅ integrins, galectin-3), their main receptor remains the elastin receptor complex (ERC). This heterotrimer comprises a peripheral subunit, named elastin binding protein (EBP), associated to the protective protein/cathepsin A (PPCA). The latter is bound to a membrane-associated protein called Neuraminidase-1 (Neu-1). The pro-tumoral effects of elastokines have been linked to their binding onto EBP. Additionally, Neu-1 sialidase activity is essential for their signal transduction. Consistently, EDP-EBP interaction and Neu-1 activity emerge as original anti-tumoral targets. Interestingly, besides its direct involvement in cancer progression, the ERC also regulates diabetes outcome and thrombosis, an important risk factor for cancer development and a vascular process highly increased in patients suffering from cancer. In this review, we will describe ERC and elastokines involvement in cancer development suggesting that this unique receptor would be a promising therapeutic target. We will also discuss the pharmacological concepts aiming at blocking its pro-tumoral activities. Finally, its emerging role in cancer-associated complications and pathologies such as diabetes and thrombotic events will be also considered.

Design, synthesis and evaluation of novel indole derivatives as AKT inhibitors

Herein, we describe the discovery and synthesis of a new series of 1,2,4,7-tetra-substituted indole derivatives as novel AKT inhibitors by optimization of a weak hit methyl 4-(2-aminoethoxy)-1H-indole-2-carboxylate (1). Both representative compounds 6a and 6o exhibited the most potent inhibitory activities against AKT1, with inhibition rates of 72.5% and 78.6%, respectively, at concentrations of 10nM. In addition, compounds 6a and 6o also potently inhibited the phosphorylation of the downstream GSK3 protein and displayed slightly better anti-proliferative activities in a prostate cancer cell line.

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.

Elastin sequences trigger transient proinflammatory responses by human dermal fibroblasts

Following penetrating injury of the skin, a highly orchestrated and overlapping sequence of events helps to facilitate wound resolution. Inflammation is a hallmark that is initiated early, but the reciprocal relationship between cells and matrix molecules that triggers and maintains inflammation is poorly appreciated. Elastin is enriched in the deep dermis of skin. We propose that deep tissue injury encompasses elastin damage, yielding solubilized elastin that triggers inflammation. As dermal fibroblasts dominate the deep dermis, this means that a direct interaction between elastin sequences and fibroblasts would reveal a proinflammatory signature. Tropoelastin was used as a surrogate for elastin sequences. Tropoelastin triggered fibroblast expression of the metalloelastase MMP-12, which is normally expressed by macrophages. MMP-12 expression increased 1056 ± 286-fold by 6 h and persisted for 24 h. Chemokine expression was more transient, as chemokine C-X-C motif ligand 8 (CXCL8), CXCL1, and CXCL5 transcripts increased 11.8 ± 2.6-, 10.2 ± 0.4-, and 8593 ± 996-fold, respectively, by 6-12 h and then decreased. Through the use of specific inhibitors and protein truncation, we found that transduction of the tropoelastin signal was mediated by the fibroblast elastin binding protein (EBP). In silico modeling using a predictive computational fibroblast model confirmed the up-regulation, and simulations revealed PKA as a key part of the signaling circuit. We tested this prediction with 1 μM PKA inhibitor H-89 and found that 2 h of exposure correspondingly reduced expression of MMP-12 (63.9±12.3%) and all chemokine markers, consistent with the levels seen with EBP inhibition, and validated PKA as a novel node and druggable target to ameliorate the proinflammatory state. A separate trigger that utilized C-terminal RKRK of tropoelastin reduced marker expression to 65.0-76.5% and suggests the parallel involvement of integrin αVβ3. We propose that the solubilization of elastin as a result of dermal damage leads to rapid chemokine up-regulation by fibroblasts that is quenched when exposed elastin is removed by MMP-12.

Engineered tropoelastin and elastin-based biomaterials

Elastin is a key mammalian extracellular matrix protein that is critical to the elasticity, compliance, and resilience of a range of tissues including the vasculature, skin, and lung. In addition to providing mechanical integrity to tissues, elastin also has critical functions in the regulation of cell behavior and may help to modulate the coagulation cascade. The high insolubility of elastin has limited its use to researchers, while soluble derivatives of elastin including elastin peptides, digested elastins, and tropoelastin have much broader applications. Recombinantly produced tropoelastin, the soluble monomer of elastin, has been shown to exhibit many of the properties intrinsic to the mature biopolymer. As such, recombinant human tropoelastin provides a versatile building block for the manufacture of biomaterials with potential for diverse applications in elastic tissues. One of the major benefits of soluble elastins is that they can be engineered into a range of physical forms. As a dominant example, soluble elastins including tropoelastin can form hydrogels when they are chemically cross-linked. These self-organized constructs swell when transferred from a saline to aqueous environment and are highly elastic; these tunable responses are dependent on the types of cross-linker and elastin used. Soluble elastins can also be drawn into fine fibers using electrospinning. The morphology of these fibers can be altered by modifying spinning parameters that include delivery flow rate and the starting protein concentration. The resulting fibers then accumulate to form porous scaffolds, and can be wound around mandrils to create conduits for vascular applications. Electrospun scaffolds retain the elasticity and cell-interactive properties inherent in the tropoelastin precursor. Additionally, soluble elastins serve as versatile biomaterial coatings, enhancing cellular interactions and modulating the blood compatibility of polymer- and metal-based prostheses. Soluble elastins, and in particular tropoelastin, have highly favorable intrinsic physical and cell-interactive properties, warranting their adaption through incorporation into biomaterials and modification of implantable devices. The multiple choices of ways to produce elastin-based biomaterials mean that they are well suited to the tailoring of elastic biomaterials and hybrid constructs.