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

The Matrix Protein Tropoelastin Prolongs Mesenchymal Stromal Cell Vitality and Delays Senescence During Replicative Aging

Cellular senescence leads to the functional decline of regenerative cells such as mesenchymal stromal/stem cells (MSCs), which gives rise to chronic conditions and contributes to poor cell therapy outcomes. Aging tissues are associated with extracellular matrix (ECM) dysregulation, including loss of elastin. However, the role of the ECM in modulating senescence is underexplored. In this work, it is shown that tropoelastin, the soluble elastin precursor, is not only a marker of young MSCs but also actively preserves cell fitness and delays senescence during replicative aging. MSCs briefly exposed to tropoelastin exhibit upregulation of proliferative genes and concurrent downregulation of senescence genes. The seno-protective benefits of tropoelastin persist during continuous, long-term MSC culture, and significantly extend the MSC replicative lifespan. Tropoelastin-expanded MSCs further maintain youth-associated phenotype and function compared to age-matched controls, including preserved clonogenic potential, minimal senescence-associated beta-galactosidase activity, maintained cell sizes, reduced expression of senescence markers, suppressed secretion of senescence-associated factors, and increased production of youth-associated proteins. This work points to the utility of exogenously-supplemented tropoelastin for manufacturing MSCs that robustly maintain regenerative potential with age. It further reveals the active role of classical structural ECM proteins in driving cellular age-associated fitness, potentially leading to future interventions for aging-related pathologies.

Elastogenesis in Focus: Navigating Elastic Fibers Synthesis for Advanced Dermal Biomaterial Formulation

Elastin, a fibrous extracellular matrix (ECM) protein, is the main component of elastic fibers that are involved in tissues' elasticity and resilience, enabling them to undergo reversible extensibility and to endure repetitive mechanical stress. After wounding, it is challenging to regenerate elastic fibers and biomaterials developed thus far have struggled to induce its biosynthesis. This review provides a comprehensive summary of elastic fibers synthesis at the cellular level and its implications for biomaterial formulation, with a particular focus on dermal substitutes. The review delves into the intricate process of elastogenesis by cells and investigates potential triggers for elastogenesis encompassing elastin-related compounds, ECM components, and other molecules for their potential role in inducing elastin formation. Understanding of the elastogenic processes is essential for developing biomaterials that trigger not only the synthesis of the elastin protein, but also the formation of a functional and branched elastic fiber network.

The role of human extracellular matrix proteins in defining Staphylococcus aureus biofilm infections

Twenty to forty one percent of the world's population is either transiently or permanently colonized by the Gram-positive bacterium, Staphylococcus aureus. In 2017, the CDC designated methicillin-resistant S. aureus (MRSA) as a serious threat, reporting ∼300 000 cases of MRSA-associated hospitalizations annually, resulting in over 19 000 deaths, surpassing that of HIV in the USA. S. aureus is a proficient biofilm-forming organism that rapidly acquires resistance to antibiotics, most commonly methicillin (MRSA). This review focuses on a large group of (>30) S. aureus adhesins, either surface-associated or secreted that are designed to specifically bind to 15 or more of the proteins that form key components of the human extracellular matrix (hECM). Importantly, this includes hECM proteins that are pivotal to the homeostasis of almost every tissue environment [collagen (skin), proteoglycans (lung), hemoglobin (blood), elastin, laminin, fibrinogen, fibronectin, and fibrin (multiple organs)]. These adhesins offer S. aureus the potential to establish an infection in every sterile tissue niche. These infections often endure repeated immune onslaught, developing into chronic, biofilm-associated conditions that are tolerant to ∼1000 times the clinically prescribed dose of antibiotics. Depending on the infection and the immune response, this allows S. aureus to seamlessly transition from colonizer to pathogen by subtly manipulating the host against itself while providing the time and stealth that it requires to establish and persist as a biofilm. This is a comprehensive discussion of the interaction between S. aureus biofilms and the hECM. We provide particular focus on the role of these interactions in pathogenesis and, consequently, the clinical implications for the prevention and treatment of S. aureus biofilm infections.

Improving solubility of poorly water-soluble drugs by protein-based strategy: A review

Poorly water-soluble drugs are frequently encountered and present a most challengeable difficulty in pharmaceutical development. Poor solubility of drugs can lead to suboptimal bioavailability and therapeutic efficiency. Increasing efforts have been contributed to improve the solubility of poorly water-soluble drugs for better pharmacokinetics and pharmacodynamics. Among various solubility enhancement technologies, protein-based strategy to address poorly water-soluble drugs issues has special interests for natural advantages including versatile interactions between proteins and hydrophobic drugs, biocompatibility, biodegradation, and metabolization of proteins. The protein-drug formulations could be formed by covalent conjugations or noncovalent interactions to facilitate solubility of poorly water-soluble drugs. This review is to summarize the advances using proteins including plant proteins, mammalian proteins, and recombinant proteins, to enhance water solubility of poorly water-soluble drugs.

Role of elastic fiber degradation in disease pathogenesis

Elastin is a crucial extracellular matrix protein that provides structural integrity to tissues. Crosslinked elastin and associated microfibrils, named elastic fiber, contribute to biomechanics by providing the elasticity required for proper function. During aging and disease, elastic fiber can be progressively degraded and since there is little elastin synthesis in adults, degraded elastic fiber is not regenerated. There is substantial evidence linking loss or damage of elastic fibers to the clinical manifestation and pathogenesis of a variety of diseases. Disruption of elastic fiber networks by hereditary mutations, aging, or pathogenic stimuli results in systemic ailments associated with the production of elastin degradation products, inflammatory responses, and abnormal physiology. Due to its longevity, unique mechanical properties, and widespread distribution in the body, elastic fiber plays a central role in homeostasis of various physiological systems. While pathogenesis related to elastic fiber degradation has been more thoroughly studied in elastic fiber rich tissues such as the vasculature and the lungs, even tissues containing relatively small quantities of elastic fibers such as the eyes or joints may be severely impacted by elastin degradation. Elastic fiber degradation is a common observation in certain hereditary, age, and specific risk factor exposure induced diseases representing a converging point of pathological clinical phenotypes which may also help explain the appearance of co-morbidities. In this review, we will first cover the role of elastic fiber degradation in the manifestation of hereditary diseases then individually explore the structural role and degradation effects of elastic fibers in various tissues and organ systems. Overall, stabilizing elastic fiber structures and repairing lost elastin may be effective strategies to reverse the effects of these diseases.

The role of antenatal corticosteroids in twin pregnancy

Twin pregnancy was associated with significantly higher rates of adverse neonatal and perinatal outcomes. One of the underlying causes is that twins are prone to preterm birth. Antenatal corticosteroids are widely used for reducing the incidence of neonatal respiratory distress syndrome initially and other neonatal mortality and morbidities subsequently. As it is widely used as a prophylactic treatment for potential premature births, there remain controversies of issues relating to twin gestations, including window for opportunity, timing of use, repeat course, optimal administration-to-delivery intervals, dosage, and type of corticosteroid. Thus, we present a thorough review of antenatal corticosteroids usage in twin gestation, emphasizing the aforementioned issues and attempting to offer direction for future investigation and clinical practice.

Emerging mechanisms of elastin transcriptional regulation

Elastin provides recoil to tissues that stretch such as the lung, blood vessels, and skin. It is deposited in a brief window starting in the prenatal period and extending to adolescence in vertebrates, and then slowly turns over. Elastin insufficiency is seen in conditions such as Williams-Beuren syndrome and elastin-related supravalvar aortic stenosis, which are associated with a range of vascular and connective tissue manifestations. Regulation of the elastin (ELN) gene occurs at multiple levels including promoter activation/inhibition, mRNA stability, interaction with microRNAs, and alternative splicing. However, these mechanisms are incompletely understood. Better understanding of the processes controlling ELN gene expression may improve medicine's ability to intervene in these rare conditions, as well as to replace age-associated losses by re-initiating elastin production. This review describes what is known about the ELN gene promoter structure, transcriptional regulation by cytokines and transcription factors, and posttranscriptional regulation via mRNA stability and micro-RNA and highlights new approaches that may influence regenerative medicine.

Real and Simulated Microgravity: Focus on Mammalian Extracellular Matrix

The lack of gravitational loading is a pivotal risk factor during space flights. Biomedical studies indicate that because of the prolonged effect of microgravity, humans experience bone mass loss, muscle atrophy, cardiovascular insufficiency, and sensory motor coordination disorders. These findings demonstrate the essential role of gravity in human health quality. The physiological and pathophysiological mechanisms of an acute response to microgravity at various levels (molecular, cellular, tissue, and physiological) and subsequent adaptation are intensively studied. Under the permanent gravity of the Earth, multicellular organisms have developed a multi-component tissue mechanosensitive system which includes cellular (nucleo- and cytoskeleton) and extracellular (extracellular matrix, ECM) “mechanosensory” elements. These compartments are coordinated due to specialized integrin-based protein complexes, forming a distinctive mechanosensitive unit. Under the lack of continuous gravitational loading, this unit becomes a substrate for adaptation processes, acting as a gravisensitive unit. Since the space flight conditions limit large-scale research in space, simulation models on Earth are of particular importance for elucidating the mechanisms that provide a response to microgravity. This review describes current state of art concerning mammalian ECM as a gravisensitive unit component under real and simulated microgravity and discusses the directions of further research in this field.

The Role of the Extracellular Matrix (ECM) in Wound Healing: A Review

The extracellular matrix (ECM) is a 3-dimensional structure and an essential component in all human tissues. It is comprised of varying proteins, including collagens, elastin, and smaller quantities of structural proteins. Studies have demonstrated the ECM aids in cellular adherence, tissue anchoring, cellular signaling, and recruitment of cells. During times of integumentary injury or damage, either acute or chronic, the ECM is damaged. Through a series of overlapping events called the wound healing phases—hemostasis, inflammation, proliferation, and remodeling—the ECM is synthesized and ideally returned to its native state. This article synthesizes current and historical literature to demonstrate the involvement of the ECM in the varying phases of the wound healing cascade.

Long-Term Controlled Growth Factor Release Using Layer-by-Layer Assembly for the Development of In Vivo Tissue-Engineered Blood Vessels

The development of a well-designed tissue-engineered blood vessel (TEBV) still remains a challenge. In recent years, approaches in which the host response to implanted biomaterials is used to generate vascular constructs within the patient's body have gained increasing interest. The delivery of growth factors to these in situ-engineered vascular grafts might enhance myofibroblast recruitment and the secretion of essential extracellular matrix proteins, thereby optimizing their functional properties. Layer-by-layer (LbL) coating has emerged as an innovative technology for the controlled delivery of growth factors in tissue engineering applications. In this study, we combined the use of surface-etched polymeric rods with LbL coatings to control the delivery of TGF-β1, PDGF-BB, and IGF-1 and steer the foreign body response toward the formation of a functional vascular graft. Results showed that the regenerated tissue is composed of elastin, glycosaminoglycans, and circumferentially oriented collagen fibers, without calcification or systemic spill of the released growth factors. Functional controlled delivery was observed, whereas myofibroblast-rich tissue capsules were formed with enhanced collagen and elastin syntheses using TGF-β1 and TGF-β1/PDGF-BB releasing rods, when compared to control rods that were solely surface-engineered by chloroform etching. By combining our optimized LbL method and surface-engineered rods in an in vivo bioreactor approach, we could regulate the fate and ECM composition of in situ-engineered vascular grafts to create a successful in vivo vascular tissue-engineered replacement.

Newborn and elderly skin: two fragile skins at higher risk of pressure injury

Skin is a key organ maintaining internal homeostasis by performing many functions such as water loss prevention, body temperature regulation and protection from noxious substance absorption, microorganism intrusion and physical trauma. Skin ageing has been well studied and it is well known that physiological changes in the elderly result in higher skin fragility favouring the onset of skin diseases. For example, prolonged and/or high-intensity pressure may suppress local blood flow more easily, disturbing cell metabolism and inducing pressure injury (PI) formation. Pressure injuries (PIs) represent a significant problem worldwide and their prevalence remains too high. A higher PI prevalence is correlated with an elderly population. Newborn skin evolution has been less studied, but some data also report a higher PI prevalence in this population compared to older children, and several authors also consider this skin as physiologically fragile. In this review, we compare the characteristics of newborn and elderly skin in order to determine common features that may explain their fragility, especially regarding PI risk. We show that, despite differences in appearance, they share many common features leading to higher fragility to shear and pressure forces, not only at the structural level but also at the cellular and molecular level and in terms of physiology. Both newborn and elderly skin have: (i) a thinner epidermis; (ii) a thinner dermis containing a less-resistant collagen network, a higher collagen III:collagen I ratio and less elastin; (iii) a flatter dermal-epidermal junction (DEJ) with lower anchoring systems; and (iv) a thinner hypodermis, resulting in lower mechanical resistance to skin damage when pressure or shear forces are applied. At the molecular level, reduced expression of transforming growth factor β (TGFβ) and its receptor TGFβ receptor II (TβRII) is involved in the decreased production and/or increased degradation of various dermal extracellular matrix (ECM) components. Epidermal fragility also involves a higher skin pH which decreases the activity of key enzymes inducing ceramide deficiency and reduced barrier protection. This seems to be correlated with higher PI prevalence in some situations. Some data also suggest that stratum corneum (SC) dryness, which may disturb cell metabolism, also increases the risk of PI formation. Besides this structural fragility, several skin functions are also less efficient. Low applied pressures induce skin vessel vasodilation via a mechanism called pressure-induced vasodilation (PIV). Individuals lacking a normal PIV response show an early decrease in cutaneous blood flow in response to the application of very low pressures, reflecting vascular fragility of the skin that increases the risk of ulceration. Due to changes in endothelial function, skin PIV ability decreases during skin ageing, putting it at higher risk of PI formation. In newborns, some data lead us to hypothesize that the nitric oxide (NO) pathway is not fully functional at birth, which may partly explain the higher risk of PI formation in newborns. In the elderly, a lower PIV ability results from impaired functionality of skin innervation, in particular that of C-fibres which are involved in both touch and pain sensation and the PIV mechanism. In newborns, skin sensitivity differs from adults due to nerve system immaturity, but the role of this in PIV remains to be determined.

Elastin Structure, Synthesis, Regulatory Mechanism and Relationship With Cardiovascular Diseases

As the primary component of elastic fibers, elastin plays an important role in maintaining the elasticity and tensile ability of cardiovascular, pulmonary and many other tissues and organs. Studies have shown that elastin expression is regulated by a variety of molecules that have positive and negative regulatory effects. However, the specific mechanism is unclear. Moreover, elastin is reportedly involved in the development and progression of many cardiovascular diseases through changes in its expression and structural modifications once deposited in the extracellular matrix. This review article summarizes the role of elastin in myocardial ischemia-reperfusion, atherosclerosis, and atrial fibrillation, with emphasis on the potential molecular regulatory mechanisms.

Structural studies of elastic fibre and microfibrillar proteins

Elastic tissues owe their functional properties to the composition of their extracellular matrices, particularly the range of extracellular, multidomain extensible elastic fibre and microfibrillar proteins. These proteins include elastin, fibrillin, latent TGFβ binding proteins (LTBPs) and collagens, where their biophysical and biochemical properties not only give the matrix structural integrity, but also play a vital role in the mechanisms that underlie tissue homeostasis. Thus far structural information regarding the structure and hierarchical assembly of these molecules has been challenging and the resolution has been limited due to post-translational modification and their multidomain nature leading to flexibility, which together result in conformational and structural heterogeneity. In this review, we describe some of the matrix proteins found in elastic fibres and the new emerging techniques that can shed light on their structure and dynamic properties.

Clinical Relevance of Elastin in the Structure and Function of Skin

Elastin is the main component of elastic fibers, which provide stretch, recoil, and elasticity to the skin. Normal levels of elastic fiber production, organization, and integration with other cutaneous extracellular matrix proteins, proteoglycans, and glycosaminoglycans are integral to maintaining healthy skin structure, function, and youthful appearance. Although elastin has very low turnover, its production decreases after individuals reach maturity and it is susceptible to damage from many factors. With advancing age and exposure to environmental insults, elastic fibers degrade. This degradation contributes to the loss of the skin's structural integrity; combined with subcutaneous fat loss, this results in looser, sagging skin, causing undesirable changes in appearance. The most dramatic changes occur in chronically sun-exposed skin, which displays sharply altered amounts and arrangements of cutaneous elastic fibers, decreased fine elastic fibers in the superficial dermis connecting to the epidermis, and replacement of the normal collagen-rich superficial dermis with abnormal clumps of solar elastosis material. Disruption of elastic fiber networks also leads to undesirable characteristics in wound healing, and the worsening structure and appearance of scars and stretch marks. Identifying ways to replenish elastin and elastic fibers should improve the skin's appearance, texture, resiliency, and wound-healing capabilities. However, few therapies are capable of repairing elastic fibers or substantially reorganizing the elastin/microfibril network. This review describes the clinical relevance of elastin in the context of the structure and function of healthy and aging skin, wound healing, and scars and introduces new approaches being developed to target elastin production and elastic fiber formation.

An evolutionary perspective on the interplays between hydrogen sulfide and oxygen in cellular functions

The physiological effects of the endogenously generated hydrogen sulfide (H2S) have been extensively studied in recent years. This review summarized the role of H2S in the origin of life and H2S metabolism in organisms from bacteria to vertebrates, examined the relationship between H2S and oxygen from an evolutionary perspective and emphasized the oxygen-dependent manner of H2S signaling in various physiological and pathological processes. H2S and oxygen are inextricably linked in various cellular functions. H2S is involved in aerobic respiration and stimulates oxidative phosphorylation and ATP production within the cell. Besides, H2S has protective effects on ischemia and reperfusion injury in several organs by acting as an oxygen sensor. Also, emerging evidence suggests the role of H2S is in an oxygen-dependent manner. All these findings indicate the subtle relationship between H2S and oxygen and further explain why H2S, a toxic molecule thriving in an anoxia environment several billion years ago, still affects homeostasis today despite the very low content in the body.

Spatiotemporal changes in mechanical matrisome components of the human ovary from prepuberty to menopause

STUDY QUESTION

How do elastic matrisome components change during the lifetime of the human ovary?

SUMMARY ANSWER

The deposition and remodeling of mechanical matrisome components (collagen, elastin, elastin microfibril interface-located protein 1 (EMILIN-1), fibrillin-1 and glycosaminoglycans (GAGs)) that play key roles in signaling pathways related to follicle activation and development evolve in an age- and follicle stage-related manner.

WHAT IS KNOWN ALREADY

The mechanobiology of the human ovary and dynamic reciprocity that exists between ovarian cells and their microenvironment is of high importance. Indeed, while the localization of primordial follicles in the collagen-rich ovarian cortex offers a rigid physical environment that supports follicle architecture and probably plays a role in their survival, ovarian extracellular matrix (ECM) stiffness limits follicle expansion and hence oocyte maturation, maintaining follicles in their quiescent state. As growing follicles migrate to the medulla of the ovary, they encounter a softer, more pliant ECM, allowing expansion and development. Thus, changes in the rigidity of the ovarian ECM have a direct effect on follicle behavior. Evidence supporting a role for the physical environment in follicle activation was provided in clinical practice by ovarian tissue fragmentation, which promoted actin polymerization and disrupted ovarian Hippo signaling, leading to increased expression of downstream growth factors, promotion of follicle growth and generation of mature oocytes.

STUDY DESIGN, SIZE, DURATION

We investigated quantitative spatiotemporal changes in collagen, elastin, EMILIN-1, fibrillin-1 and GAGs from prepuberty to menopause, before conducting a closer analysis of the ECM surrounding follicles, from primordial to secondary stages, in both prepubertal and tissue from women of reproductive age. The study included ovarian tissue (cortex) from 68 patients of different ages: prepubertal (n = 16; mean age [±SD]=8 ± 2 years); reproductive (n = 21; mean age [±SD]=27 ± 4 years); menopausal with estrogen-based HRT (n = 7; mean age [±SD]=58 ± 4 years); and menopausal without HRT (n = 24; mean age [±SD]=61 ± 5 years).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Quantitative investigations of collagen and GAG deposition in ovarian tissue throughout a woman's lifetime were conducted by analyzing brightfield images. Characteristic features of collagen fiber content were based on polarized light microscopy, since polarized light changes with fiber thickness. To evaluate the deposition and distribution of elastin, fibrillin-1 and EMILIN-1, multiplex immunofluorescence was used on at least three sections from each patient. Image processing and tailored bioinformatic analysis were applied to enable spatiotemporal quantitative evaluation of elastic system component deposition in the human ovary over its lifetime.

MAIN RESULTS AND THE ROLE OF CHANCE

While collagen levels increased with age, fibrillin-1 and EMILIN-1 declined. Interestingly, collagen and elastin reached their peak in reproductive-age women compared to prepubertal (P < 0.01; P = 0.262) and menopausal subjects with (P = 0.706; P < 0.01) and without (P = 0.987; P = 0.610) HRT, indicating a positive impact of secreted estrogen and hormone treatment on collagen and elastin preservation. Interestingly, HRT appears to affect elastin presence in ovarian tissue, since a significantly higher (P < 0.05) proportion of elastin was detected in biopsies from menopausal women taking HRT compared to those not. Higher GAG levels were found in adult ovaries compared to prepubertal ovaries (P < 0.05), suggesting changes in tissue ultrastructure and elasticity with age. In this context, elevated GAG values are suspected to participate in hampering formation of the fibrillin-1 network (r = -0.2475; P = 0.04687), which explains its decline over time. This decline partially accounts for the decrease in EMILIN-1 (r = 0.4149; P = 0.00059). Closer examination of the ECM surrounding follicles from the primordial to the secondary stage, both before and after puberty, points to high levels of mechanical stress placed on prepubertal follicles compared to the more compliant ECM around reproductive-age follicles, as suggested by the higher collagen levels and lower elastin content detected mainly around primordial (P < 0.0001; P < 0.0001, respectively) and primary (P < 0.0001; P < 0.001, respectively) follicles. Such a stiff niche is nonpermissive to prepubertal follicle activation and growth, and is more inclined to quiescence.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

The duration and form of administered HRT were not considered when studying the menopausal patient group undergoing treatment. Moreover, we cannot exclude interference from other nongynecological medications taken by the study patients on ovarian ECM properties since there is no information in the literature describing the impact of each medication on the ECM. Finally, since the ECM is by definition a very heterogeneous meshwork of proteins, the use of two-dimensional histology could be a limitation. Single time points on fixed tissues could also present limitations, since following ovary dynamics from prepuberty to menopause in the same patient is not feasible.

WIDER IMPLICATIONS OF THE FINDINGS

From a biomechanical perspective, our study revealed important changes to ECM properties dictating the mechanical features of ovarian tissue, in line with the existing literature. Our findings pave the way for possible therapeutic targets at the ECM level in the context of female fertility and ovarian rejuvenation, such as mechanical stimulation, antifibrotic treatments, and prevention or reversion of elastic ECM degradation. Our study also sheds light on the follicle-specific ECM composition that is dependent on follicle stage and age. These data will prove very useful in designing biomimetic scaffolds and tissue-engineered models like the artificial ovary. Indeed, they emphasize the importance of encapsulating each type of isolated follicle in an appropriate biomaterial that must replicate the corresponding functional perifollicular ECM and respect ovarian tissue heterogeneity in order to guarantee its biomimicry.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS) (C.A.A. is an FRS-FNRS research associate; grant 5/4/150/5 awarded to M.M.D.) and the Université Catholique de Louvain (PhD grant 'Coopération au développement' awarded to E.O.). None of the authors have any competing interests to declare.

Elastic fibers: formation, function, and fate during aging and disease

Elastic fibers are extracellular components of higher vertebrates and confer elasticity and resilience to numerous tissues and organs such as large blood vessels, lungs, and skin. Their formation and maturation take place in a complex multistage process called elastogenesis. It requires interactions between very different proteins but also other molecules and leads to the deposition and crosslinking of elastin's precursor on a scaffold of fibrillin-rich microfibrils. Mature fibers are exceptionally resistant to most influences and, under healthy conditions, retain their biomechanical function over the life of the organism. However, due to their longevity, they accumulate damages during aging. These are caused by proteolytic degradation, formation of advanced glycation end products, calcification, oxidative damage, aspartic acid racemization, lipid accumulation, carbamylation, and mechanical fatigue. The resulting changes can lead to diminution or complete loss of elastic fiber function and ultimately affect morbidity and mortality. Particularly, the production of elastokines has been clearly shown to influence several life-threatening diseases. Moreover, the structure, distribution, and abundance of elastic fibers are directly or indirectly influenced by a variety of inherited pathological conditions, which mainly affect organs and tissues such as skin, lungs, or the cardiovascular system. A distinction can be made between microfibril-related inherited diseases that are the result of mutations in diverse microfibril genes and indirectly affect elastogenesis, and elastinopathies that are linked to changes in the elastin gene. This review gives an overview on the formation, structure, and function of elastic fibers and their fate over the human lifespan in health and disease.

Elastic fibers in orthopedics: Form and function in tendons and ligaments, clinical implications, and future directions

Elastic fibers are an essential component of the extracellular matrix of connective tissues. The focus of both clinical management and scientific investigation of elastic fiber disorders has centered on the cardiovascular manifestations due to their significant impact on morbidity and mortality. As such, the current understanding of the orthopedic conditions experienced by these patients is limited. The musculoskeletal implications of more subtle elastic fiber abnormalities, whether due to allelic variants or age-related tissue degeneration, are also not well understood. Recent advances have begun to uncover the effects of elastic fiber deficiency on tendon and ligament biomechanics; future research must further elucidate mechanisms governing the role of elastic fibers in these tissues. The identification of population-based genetic variations in elastic fibers will also be essential. Minoxidil administration, modulation of protein expression with micro-RNA molecules, and direct injection of recombinant elastic fiber precursors have demonstrated promise for therapeutic intervention, but further work is required prior to consideration for orthopedic clinical application. This review provides an overview of the role of elastic fibers in musculoskeletal tissue, summarizes current knowledge of the orthopedic manifestations of elastic fiber abnormalities, and identifies opportunities for future investigation and clinical application.

The anti-ageing effects of a natural peptide discovered by artificial intelligence

OBJECTIVE

As skin ages, impaired extracellular matrix (ECM) protein synthesis and increased action of degradative enzymes manifest as atrophy, wrinkling and laxity. There is mounting evidence for the functional role of exogenous peptides across many areas, including in offsetting the effects of cutaneous ageing. Here, using an artificial intelligence (AI) approach, we identified peptide RTE62G (pep_RTE62G), a naturally occurring, unmodified peptide with ECM stimulatory properties. The AI-predicted anti-ageing properties of pep_RTE62G were then validated through in vitro, ex vivo and proof of concept clinical testing.

METHODS

A deep learning approach was applied to unlock pep_RTE62G from a plant source, Pisum sativum (pea). Cell culture assays of human dermal fibroblasts (HDFs) and keratinocytes (HaCaTs) were subsequently used to evaluate the in vitro effect of pep_RTE62G. Distinct activities such as cell proliferation and ECM protein production properties were determined by ELISA assays. Cell migration was assessed using a wound healing assay, while ECM protein synthesis and gene expression were analysed, respectively, by immunofluorescence microscopy and PCR. Immunohistochemistry of human skin explants was employed to further investigate the induction of ECM proteins by pep_RTE62G ex vivo. Finally, the clinical effect of pep_RTE626 was evaluated in a proof of concept 28-day pilot study.

RESULTS

In vitro testing confirmed that pep_RTE62G is an effective multi-functional anti-ageing ingredient. In HaCaTs, pep_RTE62G treatment significantly increases both cellular proliferation and migration. Similarly, in HDFs, pep_RTE62G consistently induced the neosynthesis of ECM protein elastin and collagen, effects that are upheld in human skin explants. Lastly, in our proof of concept clinical study, application of pep_RTE626 over 28 days demonstrated anti-wrinkle and collagen stimulatory potential.

CONCLUSION

pep_RTE62G represents a natural, unmodified peptide with AI-predicted and experimentally validated anti-ageing properties. Our results affirm the utility of AI in the discovery of novel, functional topical ingredients.

Expression of elastolytic cathepsins in human skin and their involvement in age-dependent elastin degradation

BACKGROUND

Skin ageing is associated with structure-functional changes in the extracellular matrix, which is in part caused by proteolytic degradation. Since cysteine cathepsins are major matrix protein-degrading proteases, we investigated the age-dependent expression of elastolytic cathepsins K, S, and V in human skin, their in vitro impact on the integrity of the elastic fibre network, their cleavage specificities, and the release of bioactive peptides.

METHODS

Cathepsin-mediated degradation of human skin elastin samples was assessed from young to very old human donors using immunohistochemical and biochemical assays, scanning electron microscopy, and mass spectrometry.

RESULTS

Elastin samples derived from patients between 10 and 86 years of age were analysed and showed an age-dependent deterioration of the fibre structure from a dense network of thinner fibrils into a beaded and porous mesh. Reduced levels of cathepsins K, S, and V were observed in aged skin with a predominant epidermal expression. Cathepsin V was the most potent elastase followed by cathepsin K and S. Biomechanical analysis of degraded elastin fibres corroborated the destructive activity of cathepsins. Mass spectrometric determination of the cleavage sites in elastin revealed that all three cathepsins predominantly cleaved in hydrophobic domains. The degradation of elastin was efficiently inhibited by an ectosteric inhibitor. Furthermore, the degradation of elastin fibres resulted in the release of bioactive peptides, which have previously been associated with various pathologies.

CONCLUSION

Cathepsins are powerful elastin-degrading enzymes and capable of generating a multitude of elastokines. They may represent a viable target for intervention strategies to reduce skin ageing.

The role of fibrillin and microfibril binding proteins in elastin and elastic fibre assembly

Fibrillin is a large evolutionarily ancient extracellular glycoprotein that assembles to form beaded microfibrils which are essential components of most extracellular matrices. Fibrillin microfibrils have specific biomechanical properties to endow animal tissues with limited elasticity, a fundamental feature of the durable function of large blood vessels, skin and lungs. They also form a template for elastin deposition and provide a platform for microfibril-elastin binding proteins to interact in elastic fibre assembly. In addition to their structural role, fibrillin microfibrils mediate cell signalling via integrin and syndecan receptors, and microfibrils sequester transforming growth factor (TGF)β family growth factors within the matrix to provide a tissue store which is critical for homeostasis and remodelling.

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.

Role of elastin peptides and elastin receptor complex in metabolic and cardiovascular diseases

The Cardiovascular Continuum describes a sequence of events from cardiovascular risk factors to end-stage heart disease. It includes conventional pathologies affecting cardiovascular functions such as hypertension, atherosclerosis or thrombosis and was traditionally considered from the metabolic point of view. This Cardiovascular Continuum, originally described by Dzau and Braunwald, was extended by O'Rourke to consider also the crucial role played by degradation of elastic fibers, occurring during aging, in the appearance of vascular stiffness, another deleterious risk factor of the continuum. However, the involvement of the elastin degradation products, named elastin-derived peptides, to the Cardiovascular Continuum progression has not been considered before. Data from our laboratory and others clearly showed that these bioactive peptides are central regulators of this continuum, thereby amplifying appearance and evolution of cardiovascular risk factors such as diabetes or hypertension, of vascular alterations such as atherothrombosis and calcification, but also nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. The Elastin Receptor Complex has been shown to be a crucial actor in these processes. We propose here the participation of these elastin-derived peptides and of the Elastin Receptor Complex in these events, and introduce a revisited Cardiovascular Continuum based on their involvement, for which elastin-based pharmacological strategies could have a strong impact in the future.

Modeling elastin-associated vasculopathy with patient induced pluripotent stem cells and tissue engineering

Elastin-associated vasculopathies are life-threatening conditions of blood vessel dysfunction. The extracellular matrix protein elastin endows the recoil and compliance required for physiologic arterial function, while disruption of function can lead to aberrant vascular smooth muscle cell proliferation manifesting through stenosis, aneurysm, or vessel dissection. Although research efforts have been informative, they remain incomplete as no viable therapies exist outside of a heart transplant. Induced pluripotent stem cell technology may be uniquely suited to address current obstacles as these present a replenishable supply of patient-specific material with which to study disease. The following review will cover the cutting edge in vascular smooth muscle cell modeling of elastin-associated vasculopathy, and aid in the development of human disease modeling and drug screening approaches to identify potential treatments. Vascular proliferative disease can affect up to 50% of the population throughout the world, making this a relevant and critical area of research for therapeutic development.

Soluble matrix protein is a potent modulator of mesenchymal stem cell performance

We challenge the conventional designation of structural matrix proteins primarily as supporting scaffolds for resident cells. The extracellular matrix protein tropoelastin is classically regarded as a structural component that confers mechanical strength and resilience to tissues subject to repetitive elastic deformation. Here we describe how tropoelastin inherently induces a range of biological responses, even in cells not typically associated with elastic tissues and in a manner unexpected of typical substrate-dependent matrix proteins. We show that tropoelastin alone drives mesenchymal stem cell (MSC) proliferation and phenotypic maintenance, akin to the synergistic effects of potent growth factors such as insulin-like growth factor 1 and basic fibroblast growth factor. In addition, tropoelastin functionally surpasses these growth factors, as well as fibronectin, in allowing substantial media serum reduction without loss of proliferative potential. We further demonstrate that tropoelastin elicits strong mitogenic and cell-attractive responses, both as an immobilized substrate and as a soluble additive, via direct interactions with cell surface integrins αvβ3 and αvβ5. This duality of action converges the long-held mechanistic dichotomy between adhesive matrix proteins and soluble growth factors and uncovers the powerful, untapped potential of tropoelastin for clinical MSC expansion and therapeutic MSC recruitment. We propose that the potent, growth factor-like mitogenic and motogenic abilities of tropoelastin are biologically rooted in the need for rapid stem cell homing and proliferation during early development and/or wound repair.

A Review of Integrin-Mediated Endothelial Cell Phenotype in the Design of Cardiovascular Devices

Sustained biomaterial thromboresistance has long been a goal and challenge in blood-contacting device design. Endothelialization is one of the most successful strategies to achieve long-term thromboresistance of blood-contacting devices, with the endothelial cell layer providing dynamic hemostatic regulation. It is well established that endothelial cell behavior is influenced by interactions with the underlying extracellular matrix (ECM). Numerous researchers have sought to exploit these interactions to generate improved blood-contacting devices by investigating the expression of hemostatic regulators in endothelial cells on various ECM coatings. The ability to select substrates that promote endothelial cell-mediated thromboresistance is crucial to advancing material design strategies to improve cardiovascular device outcomes. This review provides an overview of endothelial cell regulation of hemostasis, the major components found within the cardiovascular basal lamina, and the interactions of endothelial cells with prominent ECM components of the basement membrane. A summary of ECM-mimetic strategies used in cardiovascular devices is provided with a focus on the effects of key adhesion modalities on endothelial cell regulators of hemostasis.

Lung tissue destruction by proteinase 3 and cathepsin G mediated elastin degradation is elevated in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by high levels of protease activity leading to degradation of elastin followed by loss of elasticity of the lung and the development of emphysema. Elastin is an essential structural component of the lung parenchyma to support the expansion and recoil of the alveoli during breathing. The lung extracellular matrix is vulnerable to pathological structural changes upon upregulation of serine proteases, including cathepsin G (CG) and proteinase 3 (PR3). In this study, we explored the diagnostic features of elastin neo-epitopes generated by CG and PR3. Two novel competitive enzyme-linked immunosorbent assays (ELISA) measuring CG and PR3 generated elastin fragments (EL-CG and ELP-3 respectively) were developed for assessment in serum. Both assays were technically robust and biologically validated in serum from patients with COPD. Serological levels of both elastin fragments were significantly elevated in patients with COPD compared to healthy controls. These data suggest that EL-CG and ELP-3 may serve as plausible biologic markers of destructive changes in COPD.

De Novo Synthesis of Elastin by Exogenous Delivery of Synthetic Modified mRNA into Skin and Elastin-Deficient Cells

Elastin is one of the most important and abundant extracellular matrix (ECM) proteins that provide elasticity and resilience to tissues and organs, including vascular walls, ligaments, skin, and lung. Besides hereditary diseases, such as Williams-Beuren syndrome (WBS), which results in reduced elastin synthesis, injuries, aging, or acquired diseases can lead to the degradation of existing elastin fibers. Thus, the de novo synthesis of elastin is required in several medical conditions to restore the elasticity of affected tissues. Here, we applied synthetic modified mRNA encoding tropoelastin (TE) for the de novo synthesis of elastin and determined the mRNA-mediated elastin synthesis in cells, as well as ex vivo in porcine skin. EA.hy926 cells, human fibroblasts, and mesenchymal stem cells (MSCs) isolated from a patient with WBS were transfected with 2.5 μg TE mRNA. After 24 hr, the production of elastin was analyzed by Fastin assay and dot blot analyses. Compared with untreated cells, significantly enhanced elastin amounts were detected in TE mRNA transfected cells. The delivered synthetic TE mRNA was even able to significantly increase the elastin production in elastin-deficient MSCs. In porcine skin, approximately 20% higher elastin amount was detected after the intradermal delivery of synthetic mRNA by microinjection. In this study, we demonstrated the successful applicability of synthetic TE encoding mRNA to produce elastin in elastin-deficient cells as well as in skin. Thus, this auspicious mRNA-based integration-free method has a huge potential in the field of regenerative medicine to induce de novo elastin synthesis, e.g., in skin, blood vessels, or alveoli.

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.

Understanding the developmental pathways pulmonary fibroblasts may follow during alveolar regeneration

Although pulmonary alveolar interstitial fibroblasts are less specialized than their epithelial and endothelial neighbors, they play essential roles during development and in response to lung injury. At birth, they must adapt to the sudden mechanical changes imposed by the onset of respiration and to a higher ambient oxygen concentration. In diseases such as bronchopulmonary dysplasia and interstitial fibrosis, their adaptive responses are overwhelmed leading to compromised gas-exchange function. Thus, although fibroblasts do not directly participate in gas-exchange, they are essential for creating and maintaining an optimal environment at the alveolar epithelial-endothelial interface. This review summarizes new information and concepts about the ontogeny differentiation, and function of alveolar fibroblasts. Alveolar development will be emphasized, because the development of strategies to evoke alveolar repair and regeneration hinges on thoroughly understanding the way that resident fibroblasts populate specific locations in which extracellular matrix must be produced and remodeled. Other recent reviews have described the disruption that diseases cause to the fibroblast niche and so my objective is to illustrate how the unique developmental origins and differentiation pathways could be harnessed favorably to augment certain fibroblast subpopulations and to optimize the conditions for alveolar regeneration.

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.

Visualizing tropoelastin in a long-term human elastic fibre cell culture model

Elastin is an essential protein found in a variety of tissues where resilience and flexibility are needed, such as the skin and the heart. When aiming to engineer suitable implants, elastic fibres are needed to allow adequate tissue renewal. However, the visualization of human elastogenesis remains in the dark. To date, the visualization of human tropoelastin (TE) production in a human cell context and its fibre assembly under live cell conditions has not been achieved. Here, we present a long-term cell culture model of human dermal fibroblasts expressing fluorescence-labelled human TE. We employed a lentiviral system to stably overexpress Citrine-labelled TE to build a fluorescent fibre network. Using immunofluorescence, we confirmed the functionality of the Citrine-tagged TE. Furthermore, we visualized the fibre assembly over the course of several days using confocal microscopy. Applying super resolution microscopy, we were able to investigate the inner structure of the elastin–fibrillin-1 fibre network. Future investigations will allow the tracking of TE produced under various conditions. In tissue engineering applications the fluorescent fibre network can be visualized under various conditions or it serves as a tool for investigating fibre degradation processes in disease-in-a-dish-models.

Transcriptional and posttranscriptional mechanisms contribute to the dysregulation of elastogenesis in Schimke immuno-osseous dysplasia

BACKGROUND

Schimke immuno-osseous dysplasia (SIOD) is an autosomal recessive disorder caused by mutations in SMARCAL1. A frequent complication is arteriosclerosis associated with reduced elastin expression; however, the mechanism underlying the reduced elastin expression remains unknown.

METHODS

Expression of transcriptional regulators of elastin (ELN) and microRNA (miRNA) regulators of ELN messenger RNA (mRNA), ELN promoter methylation, and ELN mRNA poly(A) tail length were assessed by quantitative RT-PCR, bisulfite Sanger sequencing, and the Poly(A) Tail Length Assay Kit, respectively, in unaffected developing human aortae and in an SIOD aorta.

RESULTS

Comparing unaffected fetal and adult aortae, ELN precursor mRNA (pre-mRNA) levels remained nearly constant, whereas mRNA levels declined by ~10(2)-fold. This corresponded with a reduction in poly(A) tail length but not with changes in the other parameters. In contrast, compared to the unaffected fetal aortae, the SIOD aorta had 18-fold less ELN pre-mRNA and 10(4)-fold less mRNA. This corresponded with increased expression of miRNA regulators and shorter ELN mRNA poly(A) tail lengths but not with altered expression of ELN transcriptional regulators or ELN promoter methylation.

CONCLUSION

Posttranscriptional mechanisms account for the reduction in ELN mRNA levels in unaffected aortae, whereas transcriptional and posttranscriptional mechanisms reduce elastin expression in SIOD aorta and predispose to arteriosclerosis.

Recombinant Technology in the Development of Materials and Systems for Soft-Tissue Repair

The field of biomedicine is constantly investing significant research efforts in order to gain a more in-depth understanding of the mechanisms that govern the function of body compartments and to develop creative solutions for the repair and regeneration of damaged tissues. The main overall goal is to develop relatively simple systems that are able to mimic naturally occurring constructs and can therefore be used in regenerative medicine. Recombinant technology, which is widely used to obtain new tailored synthetic genes that express polymeric protein-based structures, now offers a broad range of advantages for that purpose by permitting the tuning of biological and mechanical properties depending on the intended application while simultaneously ensuring adequate biocompatibility and biodegradability of the scaffold formed by the polymers. This Progress Report is focused on recombinant protein-based materials that resemble naturally occurring proteins of interest for use in soft tissue repair. An overview of recombinant biomaterials derived from elastin, silk, collagen and resilin is given, along with a description of their characteristics and suggested applications. Current endeavors in this field are continuously providing more-improved materials in comparison with conventional ones. As such, a great effort is being made to put these materials through clinical trials in order to favor their future use.

Androgen Receptor-Mediated Growth Suppression of HPr-1AR and PC3-Lenti-AR Prostate Epithelial Cells

The androgen receptor (AR) mediates the developmental, physiologic, and pathologic effects of androgens including 5α-dihydrotestosterone (DHT). However, the mechanisms whereby AR regulates growth suppression and differentiation of luminal epithelial cells in the prostate gland and proliferation of malignant versions of these cells are not well understood, though they are central to prostate development, homeostasis, and neoplasia. Here, we identify androgen-responsive genes that restrain cell cycle progression and proliferation of human prostate epithelial cell lines (HPr-1AR and PC3-Lenti-AR), and we investigate the mechanisms through which AR regulates their expression. DHT inhibited proliferation of HPr-1AR and PC3-Lenti-AR, and cell cycle analysis revealed a prolonged G₁ interval. In the cell cycle, the G₁/S-phase transition is initiated by the activity of cyclin D and cyclin-dependent kinase (CDK) complexes, which relieve growth suppression. In HPr-1AR, cyclin D1/2 and CDK4/6 mRNAs were androgen-repressed, whereas CDK inhibitor, CDKN1A, mRNA was androgen-induced. The regulation of these transcripts was AR-dependent, and involved multiple mechanisms. Similar AR-mediated down-regulation of CDK4/6 mRNAs and up-regulation of CDKN1A mRNA occurred in PC3-Lenti-AR. Further, CDK4/6 overexpression suppressed DHT-inhibited cell cycle progression and proliferation of HPr-1AR and PC3-Lenti-AR, whereas CDKN1A overexpression induced cell cycle arrest. We therefore propose that AR-mediated growth suppression of HPr-1AR involves cyclin D1 mRNA decay, transcriptional repression of cyclin D2 and CDK4/6, and transcriptional activation of CDKN1A, which serve to decrease CDK4/6 activity. AR-mediated inhibition of PC3-Lenti-AR proliferation occurs through a similar mechanism, albeit without down-regulation of cyclin D. Our findings provide insight into AR-mediated regulation of prostate epithelial cell proliferation.

Collagen and elastin cross-linking is altered during aberrant late lung development associated with hyperoxia

Maturation of the lung extracellular matrix (ECM) plays an important role in the formation of alveolar gas exchange units. A key step in ECM maturation is cross-linking of collagen and elastin, which imparts stability and functionality to the ECM. During aberrant late lung development in bronchopulmonary dysplasia (BPD) patients and animal models of BPD, alveolarization is blocked, and the function of ECM cross-linking enzymes is deregulated, suggesting that perturbed ECM cross-linking may impact alveolarization. In a hyperoxia (85% O2)-based mouse model of BPD, blunted alveolarization was accompanied by alterations to lung collagen and elastin levels and cross-linking. Total collagen levels were increased (by 63%). The abundance of dihydroxylysinonorleucine collagen cross-links and the dihydroxylysinonorleucine-to-hydroxylysinonorleucine ratio were increased by 11 and 18%, respectively, suggestive of a profibrotic state. In contrast, insoluble elastin levels and the abundance of the elastin cross-links desmosine and isodesmosine in insoluble elastin were decreased by 35, 30, and 21%, respectively. The lung collagen-to-elastin ratio was threefold increased. Treatment of hyperoxia-exposed newborn mice with the lysyl oxidase inhibitor β-aminopropionitrile partially restored normal collagen levels, normalized the dihydroxylysinonorleucine-to-hydroxylysinonorleucine ratio, partially normalized desmosine and isodesmosine cross-links in insoluble elastin, and partially restored elastin foci structure in the developing septa. However, β-aminopropionitrile administration concomitant with hyperoxia exposure did not improve alveolarization, evident from unchanged alveolar surface area and alveoli number, and worsened septal thickening (increased by 12%). These data demonstrate that collagen and elastin cross-linking are perturbed during the arrested alveolarization of developing mouse lungs exposed to hyperoxia.

Mesenchymal glucocorticoid receptor regulates the development of multiple cell layers of the mouse lung

Endogenous glucocorticoid (GC) hormones, signaling via the GC receptor (GR), are essential for normal lung development, and synthetic GCs are routinely used to treat respiratory disorders of very preterm babies. Germline GR knockout (GR(-/-)) mice show immature lung morphology and severe lung cellular hyperplasia during embryogenesis and die at birth due to respiratory failure. Two recent studies have reported contradictory results regarding the necessity for GR expression in specific lung germ layers during respiratory maturation. We further investigate in detail the lung phenotype in mice with a conditional deletion of GR in the endothelium, mesenchyme, and lung epithelium. We show that loss of GR in the mesenchyme alone produces a retarded lung phenotype almost identical to that of germline GR(-/-) mice, including severe postnatal lethality and lung cell hyperplasia. Loss of GR in lung epithelial cells and the endothelium had no gross effect on survival or lung morphology, but loss of epithelial GR caused increased cell proliferation in multiple compartments. Mesenchymal GR loss also produced increased epithelial cell proliferation, implying the existence of GC-regulated germ layer cross-talk. Protein levels of GR-mediated cell cycle regulators, including the cyclin-dependent kinase inhibitor p21(CIP1) and the growth factor midkine, were unaffected by mesenchymal GR deletion, yet expression of the extracellular matrix proteoglycan versican was up-regulated in the distal lung on loss of mesenchymal GR. These results show that GR-mediated signaling from the mesenchyme regulates respiratory maturation and ultimately survival at birth and that a key GR-repressed transcriptional target in lung mesenchymal cells is versican.

Repeat antenatal steroid exposure and later blood pressure, arterial stiffness, and metabolic profile

OBJECTIVE

To determine the relationship between repeat courses of antenatal corticosteroids (ACS) and risk factors for cardiovascular disease in adolescents and young adults.

STUDY DESIGN

We assessed body mass index, blood pressure, arterial stiffness, blood lipids, and insulin resistance (IR) in a Swedish population-based cohort (n = 100) at a median age of 18 (range 14-26) years. Fifty-eight subjects (36 males) had been exposed to 2-9 weekly courses of antenatal betamethasone and 42 (23 males) were unexposed subjects matched for age, sex, and gestational age (GA).

RESULTS

There were no significant differences between the groups regarding body mass index, systolic or diastolic blood pressures, arterial stiffness measured by augmentation index, blood lipids, IR, or morning cortisol levels either in simple regression or in multivariable models. However, more subjects with elevated augmentation index had been exposed to repeat courses of ACS (n = 7) compared with unexposed subjects (n =1, P = .06), and glucose, insulin, and IR correlated inversely to GA at start of ACS (P < .01).

CONCLUSIONS

Repeat courses of ACS did not correlate to adverse cardiovascular risk profile in adolescence and young adulthood, but long-standing effects on the arterial tree and glucose metabolism, the latter dependent on GA at ACS exposure, cannot be excluded. These observations have clinical implications for the ongoing discussion on short-term benefits and long-term safety of repeat ACS treatment.

Potassium channel openers increase aortic elastic fiber formation and reverse the genetically determined elastin deficit in the BN rat

Hypertension is a cardiovascular disorder that appears in more than half of the patients with Williams-Beuren syndrome, hemizygous for the elastin gene among 26 to 28 other genes. It was shown that the antihypertensive drug minoxidil, an ATP-dependent potassium channel opener, enhances elastic fiber formation; however, no wide clinical application was developed because of its adverse side effects. The Brown Norway rat was used here as an arterial elastin-deficient model. We tested 3 different potassium channel openers, minoxidil, diazoxide, and pinacidil, and 1 potassium channel blocker, glibenclamide, on cultured smooth muscle cells from Brown Norway rat aorta. All tested potassium channel openers increased mRNAs encoding proteins and enzymes involved in elastic fiber formation, whereas glibenclamide had the opposite effect. The higher steady-state level of tropoelastin mRNA in minoxidil-treated cells was attributable to an increase in both transcription and mRNA stability. Treatment of Brown Norway rats for 10 weeks with minoxidil or diazoxide increased elastic fiber content and decreased cell number in the aortic media, without changing collagen content. The minoxidil-induced cardiac hypertrophy was reduced when animals simultaneously received irbesartan, an angiotensin II-receptor antagonist. This side effect of minoxidil was not observed in diazoxide-treated animals. In conclusion, diazoxide, causing less undesirable side effects than minoxidil, or coadministration of minoxidil and irbesartan, increases elastic fiber content, decreases cell number in the aorta and, thus, could be suitable for treating vascular pathologies characterized by diminished arterial elastin content and simultaneous hypertension.

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.

Deletion of mesenchymal glucocorticoid receptor attenuates embryonic lung development and abdominal wall closure

As a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors, the glucocorticoid receptor (GR) is essential for normal embryonic development. To date, the role of mesenchymal glucocorticoid signaling during development has not been fully elucidated. In the present study, we investigated the role of the GR during embryogenesis specifically in mesenchymal tissues. To this aim, we crossed GRflox mice with Dermo1-Cre mice to generate GR(Dermo1) mice, where the GR gene was deleted within mesenchymal cells. Compared to their wild type littermates, GR(Dermo1) mice displayed severe pulmonary atelectasis, defects in abdominal wall formation resulting in intestinal herniation, abnormal extracellular matrix synthesis in connective tissues and high postnatal lethality. Lungs of GR(Dermo1) mice failed to progress from the canalicular to saccular stage, as evidenced by the presence of immature air sacs, thickened interstitial mesenchyme and an underdeveloped vascular network between E17.5 and E18.5. Furthermore, myofibroblasts and vascular smooth muscle cells, although present in normal numbers in GR(Dermo1) animals, were characterized by significantly reduced elastin synthesis, whilst epithelial lining cells of the immature saccules were poorly differentiated. A marked reduction in normal elastin and collagen deposits were also observed in connective tissues adjacent to the umbilical hernia. This study demonstrates that eliminating the GR in cells of the mesenchymal lineage results in marked effects on interstitial fibroblast function, including a significant decrease in elastin synthesis. This results in lung atelectasis and postnatal lethality, as well as additional and hitherto unrecognized developmental defects in abdominal wall formation. In addition, altered glucocorticoid signaling in the mesenchyme attenuates normal lung epithelial differentiation.

Perspectives on stem cell-based elastic matrix regenerative therapies for abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are potentially fatal conditions that are characterized by decreased flexibility of the aortic wall due to proteolytic loss of the structural matrix. This leads to their gradual weakening and ultimate rupture. Drug-based inhibition of proteolytic enzymes may provide a nonsurgical treatment alternative for growing AAAs, although it might at best be sufficient to slow their growth. Regenerative repair of disrupted elastic matrix is required if regression of AAAs to a healthy state is to be achieved. Terminally differentiated adult and diseased vascular cells are poorly capable of affecting such regenerative repair. In this context, stem cells and their smooth muscle cell-like derivatives may represent alternate cell sources for regenerative AAA cell therapies. This article examines the pros and cons of using different autologous stem cell sources for AAA therapy, the requirements they must fulfill to provide therapeutic benefit, and the current progress toward characterizing the cells' ability to synthesize elastin, assemble elastic matrix structures, and influence the regenerative potential of diseased vascular cell types. The article also provides a detailed perspective on the limitations, uncertainties, and challenges that will need to be overcome or circumvented to translate current strategies for stem cell use into clinically viable AAA therapies. These therapies will provide a much needed nonsurgical treatment option for the rapidly growing, high-risk, and vulnerable elderly demographic.