Recent updates on the molecular network of elastic fiber formation

An Update on Molecular Mechanisms of Scarring-A Narrative Review

Fibroblasts, the principal cellular mediators of connective tissue remodeling, play a crucial role in the formation of physiological and pathological scars. Understanding the intricate interplay between fibroblasts and other cellular and molecular components is essential for elucidating the underlying mechanisms driving scar formation. Hypertrophic scars, keloids and atrophic scars arise from dysregulated wound healing processes characterized by persistent inflammation, aberrant collagen deposition, and impaired extracellular matrix remodeling. Fibroblasts play a central role in the pathogenesis of such pathological scars, driving aberrant extracellular matrix remodeling, subsequently contributing to the formation of raised or depressed fibrotic lesions. The investigation of complex interactions between fibroblasts and the microenvironment is crucial for developing targeted therapeutic interventions aimed at modulating fibroblast activity and improving clinical outcomes in patients with pathological scars. Further research into the molecular pathways governing fibroblast behavior and their heterogeneity holds promise for advancing scar management strategies. This narrative review was performed to shed light on the mechanisms behind scar formation, with a special focus on the role of fibroblasts in the formation of different types of scars, providing insights into the pathophysiology of these conditions. Through the analysis of current knowledge, this review seeks to identify the key cellular and molecular mechanisms involved in fibroblast activation, collagen synthesis, and extracellular matrix remodeling in hypertrophic scar, keloid, or atrophic scar formation.

Label-Free Assessment of Key Biological Autofluorophores: Material Characteristics and Opportunities for Clinical Applications

Autofluorophores are endogenous fluorescent compounds that naturally occur in the intra and extracellular spaces of all tissues and organs. Most have vital biological functions - like the metabolic cofactors NAD(P)H and FAD+, as well as the structural protein collagen. Others are considered to be waste products - like lipofuscin and advanced glycation end products - which accumulate with age and are associated with cellular dysfunction. Due to their natural fluorescence, these materials have great utility for enabling non-invasive, label-free assays with direct ties to biological function. Numerous technologies, with different advantages and drawbacks, are applied to their assessment, including fluorescence lifetime imaging microscopy, hyperspectral microscopy, and flow cytometry. Here, the applications of label-free autofluorophore assessment are reviewed for clinical and health-research applications, with specific attention to biomaterials, disease detection, surgical guidance, treatment monitoring, and tissue assessment - fields that greatly benefit from non-invasive methodologies capable of continuous, in vivo characterization.

Mechanisms of mechanical force in periodontal homeostasis: a review

Mechanical forces affect periodontal health through multiple mechanisms. Normally, mechanical forces can boost soft and hard tissue metabolism. However, excessive forces may damage the periodontium or result in irreversible inflammation, whereas absence of occlusion forces also leads to tissue atrophy and bone resorption. We systemically searched the PubMed and Web of Science databases and found certain mechanisms of mechanical forces on immune defence, extracellular matrix (ECM) metabolism, specific proteins, bone metabolism, characteristic periodontal ligament stem cells (PDLSCs) and non-coding RNAs (ncRNAs) as these factors contribute to periodontal homeostasis. The immune defence functions change under forces; genes, signalling pathways and proteinases are altered under forces to regulate ECM metabolism; several specific proteins are separately discussed due to their important functions in mechanotransduction and tissue metabolism. Functions of osteocytes, osteoblasts, and osteoclasts are activated to maintain bone homeostasis. Additionally, ncRNAs have the potential to influence gene expression and thereby, modify tissue metabolism. This review summarizes all these mechanisms of mechanical forces on periodontal homeostasis. Identifying the underlying causes, this review provides a new perspective of the mechanisms of force on periodontal health and guides for some new research directions of periodontal homeostasis.

Directed Assembly of Elastic Fibers via Coacervate Droplet Deposition on Electrospun Templates

Elastic fibers provide critical elasticity to the arteries, lungs, and other organs. Elastic fiber assembly is a process where soluble tropoelastin is coacervated into liquid droplets, cross-linked, and deposited onto and into microfibrils. While much progress has been made in understanding the biology of this process, questions remain regarding the timing of interactions during assembly. Furthermore, it is unclear to what extent fibrous templates are needed to guide coacervate droplets into the correct architecture. The organization and shaping of coacervate droplets onto a fiber template have never been previously modeled or employed as a strategy for shaping elastin fiber materials. Using an in vitro system consisting of elastin-like polypeptides (ELPs), genipin cross-linker, electrospun polylactic-co-glycolic acid (PLGA) fibers, and tannic acid surface coatings for fibers, we explored ELP coacervation, cross-linking, and deposition onto fiber templates. We demonstrate that integration of coacervate droplets into a fibrous template is primarily influenced by two factors: (1) the balance of coacervation and cross-linking and (2) the surface energy of the fiber templates. The success of this integration affects the mechanical properties of the final fiber network. Our resulting membrane materials exhibit highly tunable morphologies and a range of elastic moduli (0.8-1.6 MPa) comparable to native elastic fibers.

The rs2018736 fibulin-5 polymorphism as a determinant for pelvic organ prolapse: a case-control study

OBJECTIVE

Fibulin-5 is a connective tissue component and may play a role in pelvic organ prolapse (POP) pathogenesis. This study aimed to verify the association of the rs2018736 polymorphism of the fibulin-5 gene with POP in postmenopausal Brazilian women, and to determine the risk factors for POP.

METHOD

This observational, cross-sectional, case-control study assessed postmenopausal women with advanced POP (stages III and IV) and control women (stages 0 and I) by examination and peripheral blood sample collection. DNA sequences were analyzed by real-time reverse-transcriptase polymerase chain reaction. A logistic regression model was used with p < 0.05 for significance.

RESULTS

A total of 565 participants were evaluated (325 POP and 240 control). The homozygous C allele of rs2018736 (CC) was protective against POP (odds ratio [OR] 0.49, 95% confidence interval [CI] 0.26-0.91). Age (OR 1.09, 95% CI 1.05-1.13), number of pregnancies (OR 1.14, 95% CI 1.01-1.28), vaginal delivery (OR 5.32, 95% CI 2.58-11.01), forceps delivery (OR 3.34, 95% CI 1.72-6.47), weight of newborn (OR 1.0007, 95% CI 1.0002-1.0011), family history of POP (OR 2.35, 95% CI 1.24-4.44), hypertension (OR 1.74, 95% CI 1.01-3.00) and diabetes (OR 2.19, 95% CI 1.07-4.48)] were independent predictors for POP; cesarean (OR 0.02, 95% CI 0.005-0.09) was protective.

CONCLUSION

The rs2018736-CC genotype of the fibulin-5 gene has a protective role against POP.

Genetic background determines severity of Loxl1-mediated systemic and ocular elastosis in mice

Pseudoexfoliation syndrome (PEX) is a systemic, age-related disorder characterized by elastosis and extracellular matrix deposits. Its most significant ocular manifestation is an aggressive form of glaucoma associated with variants in the gene encoding lysyl oxidase-like 1 (LOXL1). Depending upon the population, variants in LOXL1 can impart risk or protection for PEX, suggesting the importance of genetic context. As LOXL1 protein levels are lower and the degree of elastosis is higher in people with PEX, we studied Loxl1-deficient mice on three different genetic backgrounds: C57BL/6 (BL/6), 129S×C57BL/6 (50/50) and 129S. Early onset and high prevalence of spontaneous pelvic organ prolapse in BL/6 Loxl1-/- mice necessitated the study of mice that were <2 months old. Similar to pelvic organ prolapse, most elastosis endpoints were the most severe in BL/6 Loxl1-/- mice, including skin laxity, pulmonary tropoelastin accumulation, expansion of Schlemm's canal and dilation of intrascleral veins. Interestingly, intraocular pressure was elevated in 50/50 Loxl1-/- mice, depressed in BL/6 Loxl1-/- mice and unchanged in 129S Loxl1-/- mice compared to that of control littermates. Overall, the 129S background was protective against most elastosis phenotypes studied. Thus, repair of elastin-containing tissues is impacted by the abundance of LOXL1 and genetic context in young animals.

N-Acetylglucosamine mitigates lung injury and pulmonary fibrosis induced by bleomycin

Lung injury and pulmonary fibrosis contribute to morbidity and mortality, and, in particular, are characterized as leading cause on confirmed COVID-19 death. To date, efficient therapeutic approach for such lung diseases is lacking. N-Acetylglucosamine (NAG), an acetylated derivative of glucosamine, has been proposed as a potential protector of lung function in several types of lung diseases. The mechanism by which NAG protects against lung injury, however, remains unclear. Here, we show that NAG treatment improves pulmonary function in bleomycin (BLM)-induced lung injury model measured by flexiVent system. At early phase of lung injury, NAG treatment results in silenced immune response by targeting ARG1+ macrophages activation, and, consequently, blocks KRT8+ transitional stem cell in the alveolar region to stimulate PDGF Rβ+ fibroblasts hyperproliferation, thereby attenuating the pulmonary fibrosis. This combinational depression of immune response and extracellular matrix deposition within the lung mitigates lung injury and pulmonary fibrosis induced by BLM. Our findings provide novel insight into the protective role of NAG in lung injury.

Potential molecular targets for intervention in pelvic organ prolapse

Pelvic organ prolapse (POP) is a concerning gynecological benign illness in middle-aged and senior women. Its etiology is complex, the incidence rate is high, symptoms are clinically subjective, and its influence tends to be polarized. At present, for those who need medical treatment, whether surgical or non-surgical, complications cannot be ignored, and treatment effect needs to be optimized. However, there is a lack of accurate molecular biological interventions for the prevention, diagnosis, progression delay, and treatment of POP. Here, we reviewed the current state of understanding of the molecular mechanisms and factors associated with POP etiology. These factors include cyclins, matrix metal peptidases/tissue inhibitors of metalloproteinases, microRNAs, homeobox A11, transforming growth factor β1, insulin-like growth factor 1, fibulin 5, lysyl oxidase-like 1, oxidative stress, inflammatory response, estrogen, and other potential biomarkers associated with POP. In addition, relevant molecular targets that may be used to intervene in POP are summarized. The aim of this review was to provide more information to identify accurate potential biomarkers and/or molecular targets for the prevention, diagnosis, progression delay, and treatment of POP, with the goal of improving medical treatment for patients at-risk for POP or having POP. Continued research is needed to identify additional details of currently accepted molecular mechanisms and to identify additional mechanisms that contribute to POP.

Role of fibrilins in human cancer: A narrative review

Background

Fibrillin is one of the extracellular matrix glycoproteins and participates in forming microfibrils found in many connective tissues. The microfibrils enable the elasticity and stretching properties of the ligaments and support connective tissues. There are three isoforms of fibrillin molecules identified in mammals: fibrillin 1 (FBN1), fibrillin 2 (FBN2), and fibrillin 3.

Objective

Multiple studies have shown that mutations in these genes or changes in their expression levels can be related to various diseases, including cancers. In this study, we focus on reviewing the role of the fibrillin family in multiple cancers.

Methods and Results

We performed a comprehensive literature review to search PubMed and Google Scholar for studies published so far on fibrillin gene expression and its role in cancers. In this review, we have focused on the expression of FBN1 and FBN2 genes in cancers such as the lung, intestine, ovary, pancreatic ductal, esophagus, and thyroid.

Conclusion

Altogether various studies showed higher expression of fibrillins in different tumor tissues correlated with the patient's survival. However, there are controversial findings, as some other cancers showed hypermethylated FBN promoters with lower gene expression levels.

Mechanical Properties and Functions of Elastin: An Overview

Human tissues must be elastic, much like other materials that work under continuous loads without losing functionality. The elasticity of tissues is provided by elastin, a unique protein of the extracellular matrix (ECM) of mammals. Its function is to endow soft tissues with low stiffness, high and fully reversible extensibility, and efficient elastic-energy storage. Depending on the mechanical functions, the amount and distribution of elastin-rich elastic fibers vary between and within tissues and organs. The article presents a concise overview of the mechanical properties of elastin and its role in the elasticity of soft tissues. Both the occurrence of elastin and the relationship between its spatial arrangement and mechanical functions in a given tissue or organ are overviewed. As elastin in tissues occurs only in the form of elastic fibers, the current state of knowledge about their mechanical characteristics, as well as certain aspects of degradation of these fibers and their mechanical performance, is presented. The overview also outlines the latest understanding of the molecular basis of unique physical characteristics of elastin and, in particular, the origin of the driving force of elastic recoil after stretching.

Fibrillin-1 and asprosin, novel players in metabolic syndrome

Fibrillin-1 is a major component of the extracellular microfibrils, where it interacts with other extracellular matrix proteins to provide elasticity to connective tissues, and regulates the bioavailability of TGFβ family members. A peptide consisting of the C-terminal 140 amino acids of fibrillin-1 has recently been identified as a glucogenic hormone, secreted from adipose tissue during fasting and targeting the liver to release glucose. This fragment, called asprosin, also signals in the hypothalamus to stimulate appetite. Asprosin levels are correlated with many of the pathologies indicative of metabolic syndrome, including insulin resistance and obesity. Previous studies and reviews have addressed the therapeutic potential of asprosin as a target in obesity, diabetes and related conditions without considering mechanisms underlying the relationship between generation of asprosin and expression of the much larger fibrillin-1 protein. Profibrillin-1 undergoes obligatory cleavage at the cell surface as part of its assembly into microfibrils, producing the asprosin peptide as well as mature fibrillin-1. Patterns of FBN1 mRNA expression are inconsistent with the necessity for regulated release of asprosin. The asprosin peptide may be protected from degradation in adipose tissue. We present evidence for an alternative possibility, that asprosin mRNA is generated independently from an internal promoter within the 3' end of the FBN1 gene, which would allow for regulation independent of fibrillin-synthesis and is more economical of cellular resources. The discovery of asprosin opened exciting possibilities for treatment of metabolic syndrome related conditions, but there is much to be understood before such therapies could be introduced into the clinic.

STEAP2 promotes osteosarcoma progression by inducing epithelial-mesenchymal transition via the PI3K/AKT/mTOR signaling pathway and is regulated by EFEMP2

This study was designed to explore the prognostic significance and functionality of STEAP2 (six-transmembrane epithelial antigen of prostate 2) in osteosarcomas and determine whether EFEMP2 (Epidermal growth factor-containing fibulin-like extracellular matrix protein 2) targets STEAP2 to facilitate osteosarcoma cell infiltration and migration. STEAP2 expression in peritumoral tissues, osteosarcoma, benign fibrous dysplasia, osteosarcoma cells, normal osteoblastic hFOB cells, and various invasive subclones was evaluated using IHC, ICC, and qRT-PCR. We also evaluated the association between STEAP2 expression and disease outcome using Kaplan-Meier analyses and then investigated STEAP2 regulation and its functional effects using both in vitro and in vivo assays. The results revealed that the upregulation of STEAP2 in osteosarcoma tissues positively correlated with both the malignant osteosarcoma phenotype and poor patient outcomes. In addition, STEAP2 expression induced epithelial-mesenchymal transition (EMT) via the PI3K/AKT/mTOR axis and facilitated osteosarcoma cell infiltration and migration. Changes in EFEMP2 expression resulted in correlating changes in STEAP2 expression, with EFEMP2-overexpressing osteosarcoma cells exhibiting a less invasive phenotype and reduced EMT following STEAP2 inhibition. It is also worth noting that although EFEMP2 overexpression activated the PI3K/AKT/mTOR pathway promoting EMT, it did not affect osteosarcoma cells in which STEAP2 or Akt was knocked down. Thus, we can conclude that STEAP2 acts as an oncogene in osteosarcoma progression, while EFEMP2 enables PI3K/AKT/mTOR axis initiation and EMT by partly targeting STEAP2, thereby facilitating osteosarcoma cell infiltration and migration.

Elastic Fibers and F-Box and WD-40 Domain-Containing Protein 2 in Bovine Periosteum and Blood Vessels

Elastic fibers form vessel walls, and elastic fiber calcification causes serious vascular diseases. Elastin is a well-known elastic fiber component; however, the insoluble nature of elastic fibers renders elastic fiber component analysis difficult. A previous study investigated F-box and WD-40 domain-containing protein 2 (FBXW2) in the cambium layer of bovine periosteum and hypothesized that fiber structures of FBXW2 are coated with osteocalcin during explant culture. Here, FBXW2 was expressed around some endothelial cells but not in all microvessels of the bovine periosteum. The author hypothesized that FBXW2 is expressed only in blood vessels with elastic fibers. Immunostaining and Elastica van Gieson staining indicated that FBXW2 was expressed in the same regions as elastic fibers and elastin in the cambium layer of the periosteum. Alpha-smooth muscle actin (αSMA) was expressed in microvessels and periosteum-derived cells. Immunostaining and observation of microvessels with serial sections revealed that osteocalcin was not expressed around blood vessels at 6 and 7 weeks. However, blood vessels and periosteum connoted elastic fibers, FBXW2, and αSMA. These findings are expected to clarify the processes involved in the calcification of elastic fibers in blood vessels.

Genotype-phenotype correlations of marfan syndrome and related fibrillinopathies: Phenomenon and molecular relevance

Marfan syndrome (MFS, OMIM: 154700) is a heritable multisystemic disease characterized by a wide range of clinical manifestations. The underlying molecular defect is caused by variants in the FBN1. Meanwhile, FBN1 variants are also detected in a spectrum of connective tissue disorders collectively termed as ‘type I fibrillinopathies’. A multitude of FBN1 variants is reported and most of them are unique in each pedigree. Although MFS is being considered a monogenic disorder, it is speculated that the allelic heterogeneity of FBN1 variants contributes to various manifestations, distinct prognoses, and differential responses to the therapies in affected patients. Significant progress in the genotype–phenotype correlations of MFS have emerged in the last 20 years, though, some of the associations were still in debate. This review aims to update the recent advances in the genotype-phenotype correlations of MFS and related fibrillinopathies. The molecular bases and pathological mechanisms are summarized for better support of the observed correlations. Other factors contributing to the phenotype heterogeneity and future research directions were also discussed. Dissecting the genotype-phenotype correlation of FBN1 variants and related disorders will provide valuable information in risk stratification, prognosis, and choice of therapy.

The synergistic mechanism of fibroblast growth factor 18 and integrin β1 in rat abdominal aortic aneurysm repair

Background

Abdominal aortic aneurysms have a high mortality rate. While surgery is the preferred treatment method, the biological repair of abdominal aortic aneurysms is being increasingly studied. We performed cellular and animal experiments to investigate the simultaneous function and mechanism of fibroblast growth factor 18 and integrin β1 in the biological repair of abdominal aortic aneurysms.

Methods

Endothelial and smooth muscle cells of rat arteries were used for the cellular experiments. Intracellular integrin β1 expression was regulated through lentiviral transfection. Interventions with fibroblast growth factor 18 were determined according to the experimental protocol. Several methods were used to detect the expression of elastic fiber component proteins, cell proliferation, and migratory activity of endothelial and smooth muscle cells after different treatments. For animal experiments, abdominal aortic aneurysms were induced in rats by wrapping the abdominal aortae in sterile cotton balls soaked with CaCl₂ solution. Fibroblast growth factor 18 was administered through tail vein injections. The local expression of integrin β1 was regulated through lentiviral injections into the adventitia of the abdominal aortic aneurysms. The abdominal aortae were harvested for pathological examinations and tensile mechanical tests.

Results

The expression of integrin β1 in endothelial and smooth muscle cells could be regulated effectively through lentiviral transfection. Animal and cellular experiments showed that fibroblast growth factor 18 + integrin β1 could improve the expression of elastic fiber component proteins and enhance the migratory and proliferative activities of smooth muscle and endothelial cells. Moreover, animal experiments showed that fibroblast growth factor 18 + integrin β1 could enhance the aortic integrity to withstand stretch of aortic aneurysm tissue.

Conclusion

Fibroblast growth factor 18 + integrin β1 improved the biological repair of abdominal aortic aneurysms in rats by increasing the expression of elastic proteins, improving the migratory and proliferative abilities of endothelial and smooth muscle cells, and improving aortic remodeling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02851-y.

Proteolysis of fibrillin-2 microfibrils is essential for normal skeletal development

The embryonic extracellular matrix (ECM) undergoes transition to mature ECM as development progresses, yet few mechanisms ensuring ECM proteostasis during this period are known. Fibrillin microfibrils are macromolecular ECM complexes serving structural and regulatory roles. In mice, Fbn1 and Fbn2, encoding the major microfibrillar components, are strongly expressed during embryogenesis, but fibrillin-1 is the major component observed in adult tissue microfibrils. Here, analysis of Adamts6 and Adamts10 mutant mouse embryos, lacking these homologous secreted metalloproteases individually and in combination, along with in vitro analysis of microfibrils, measurement of ADAMTS6-fibrillin affinities and N-terminomics discovery of ADAMTS6-cleaved sites, identifies a proteostatic mechanism contributing to postnatal fibrillin-2 reduction and fibrillin-1 dominance. The lack of ADAMTS6, alone and in combination with ADAMTS10 led to excess fibrillin-2 in perichondrium, with impaired skeletal development defined by a drastic reduction of aggrecan and cartilage link protein, impaired BMP signaling in cartilage, and increased GDF5 sequestration in fibrillin-2-rich tissue. Although ADAMTS6 cleaves fibrillin-1 and fibrillin-2 as well as fibronectin, which provides the initial scaffold for microfibril assembly, primacy of the protease-substrate relationship between ADAMTS6 and fibrillin-2 was unequivocally established by reversal of the defects in Adamts6^-/- embryos by genetic reduction of Fbn2, but not Fbn1.

LTBP1 promotes fibrillin incorporation into the extracellular matrix

LTBP1 is a large extracellular matrix protein and an associated ligand of fibrillin-microfibrils. Knowledge of LTBP1 functions is largely limited to its role in targeting and sequestering TGFβ growth factors within the extracellular matrix, thereby regulating their bioavailability. However, the recent description of a wide spectrum of phenotypes in multiple tissues in patients harboring LTBP1 pathogenic variants suggests a multifaceted role of the protein in the homeostasis of connective tissues. To better understand the human pathology caused by LTBP1 deficiency it is important to investigate its functional role in extracellular matrix formation. In this study, we show that LTBP1 coordinates the incorporation of fibrillin-1 and -2 into the extracellular matrix in vitro. We also demonstrate that this function is differentially exerted by the two isoforms, the short and long forms of LTBP1. Thereby our findings uncover a novel TGFβ-independent LTBP1 function potentially contributing to the development of connective tissue disorders.

Elastic Fibre Proteins in Elastogenesis and Wound Healing

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

The Multiple Functions of Fibrillin-1 Microfibrils in Organismal Physiology

Fibrillin-1 is the major structural component of the 10 nm-diameter microfibrils that confer key physical and mechanical properties to virtually every tissue, alone and together with elastin in the elastic fibers. Mutations in fibrillin-1 cause pleiotropic manifestations in Marfan syndrome (MFS), including dissecting thoracic aortic aneurysms, myocardial dysfunction, progressive bone loss, disproportionate skeletal growth, and the dislocation of the crystalline lens. The characterization of these MFS manifestations in mice, that replicate the human phenotype, have revealed that the underlying mechanisms are distinct and organ-specific. This brief review summarizes relevant findings supporting this conclusion.

Mouse Knockout Models for Pelvic Organ Prolapse: a Systematic Review

INTRODUCTION AND HYPOTHESIS

Mouse knockout (KO) models of pelvic organ prolapse (POP) have contributed mechanistic evidence for the role of connective tissue defects, specifically impaired elastic matrix remodeling. Our objective was to summarize what mouse KO models for POP are available and what have we learned from these mouse models about the pathophysiological mechanisms of POP development.

METHODS

We conducted a systematic review and reported narrative findings according to PRISMA guidelines. Two independent reviewers searched PubMed, Scopus and Embase for relevant manuscripts and conference abstracts for the time frame of January 1, 2000, to March 31, 2021. Conference abstracts were limited to the past 5 years.

RESULTS

The search strategy resulted in 294 total titles. We ultimately included 25 articles and an additional 11 conference abstracts. Five KO models have been studied: Loxl1, Fbln5, Fbln3, Hoxa11 and Upii-sv40t. Loxl1 and Fbln5 KO models have provided the most reliable and predictable POP phenotype. Loxl1 KO mice develop POP primarily from failure to heal after giving birth, whereas Fbln5 KO mice develop POP with aging. These mouse KO models have been used for a wide variety of investigations including genetic pathways involved in development of POP, biomechanical properties of the pelvic floor, elastic fiber deposition, POP therapies and the pathophysiology associated with mesh complications.

CONCLUSIONS

Mouse KO models have proved to be a valuable tool in the study of specific genes and their role in the development and progression of POP. They may be useful to study POP treatments and POP complications.

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.

Cadherin-11 promotes the mechanical strength of engineered elastic cartilage by enhancing extracellular matrix synthesis and microstructure

Limitations of current treatments for auricular cartilage defects have prompted the field of auricular cartilage tissue engineering. To date, inducing the formation of cartilaginous constructs with biochemical and biomechanical properties of native tissue is the final aim. Through hematoxylin-eosin and immunohistochemistry staining, Cadherin-11(CDH11) was confirmed highly expressed in the auricular cartilage tissue and chondrocytes. In vitro, by knockdown and overexpression of CDH11 in chondrocytes, CDH11 was demonstrated to promote the expression of collagen type II (COL2A), elastin (ELN), aggrecan (ACAN), and cartilage oligomeric matrix protein (COMP). In addition, the CDH11 overexpressed chondrocytes promoted neo-cartilage formation and its biomechanical property by increasing the key transcription factor of chondrogenesis SOX9 expression and cartilage extracellular matrix (ECM) production. The young's modulus and yield stress of the neo-cartilage in CDH11 overexpression group were about 1.7 times (p = 0.0152) and 2 times (p = 0.0428) higher than those in control group, respectively. Then, the immunohistochemistry staining, qRT-PCR and western blot examination results showed that the expression of COL2A and ELN were significantly increased. Notably, the electron microscopy results showed that the collagen and elastic fibers of the neo-cartilage in CDH11-OV group arranged in bunches and were more uniform and compact compared to the control group. Furthermore, CDH11 promoted elastic fiber assembly by increasing lysyl oxidase (LOX), fibrillin-1 (FBN1) expression. Taken together, our results demonstrated that CDH11 improves the mechanical strength of tissue-engineered elastic cartilage by promoting ECM synthesis and elastic fiber assembly.

Clinical and Molecular Delineation of Cutis Laxa Syndromes: Paradigms for Homeostasis

Cutis laxa (CL) syndromes are a large and heterogeneous group of rare connective tissue disorders that share loose redundant skin as a hallmark clinical feature, which reflects dermal elastic fiber fragmentation. Both acquired and congenital-Mendelian- forms exist. Acquired forms are progressive and often preceded by inflammatory triggers in the skin, but may show systemic elastolysis. Mendelian forms are often pleiotropic in nature and classified upon systemic manifestations and mode of inheritance. Though impaired elastogenesis is a common denominator in all Mendelian forms of CL, the underlying gene defects are diverse and affect structural components of the elastic fiber or impair metabolic pathways interfering with cellular trafficking, proline synthesis, or mitochondrial functioning. In this chapter we provide a detailed overview of the clinical and molecular characteristics of the different cutis laxa types and review the latest insights on elastic fiber assembly and homeostasis from both human and animal studies.

Elastin in healthy and diseased lung

Elastic fibers are an essential part of the pulmonary extracellular matrix (ECM). Intact elastin is required for normal function and its damage contributes profoundly to the etiology and pathology of lung disease. This highlights the need for novel lung-specific imaging methodology that enables high-resolution 3D visualization of the ECM. We consider elastin's involvement in chronic respiratory disease and examine recent methods for imaging and modeling of the lung in the context of advances in lung tissue engineering for research and clinical application.

Alveologenesis: What Governs Secondary Septa Formation

The simplification of alveoli leads to various lung pathologies such as bronchopulmonary dysplasia and emphysema. Deep insight into the process of emergence of the secondary septa during development and regeneration after pneumonectomy, and into the contribution of the drivers of alveologenesis and neo-alveolarization is required in an efficient search for therapeutic approaches. In this review, we describe the formation of the gas exchange units of the lung as a multifactorial process, which includes changes in the actomyosin cytoskeleton of alveocytes and myofibroblasts, elastogenesis, retinoic acid signaling, and the contribution of alveolar mesenchymal cells in secondary septation. Knowledge of the mechanistic context of alveologenesis remains incomplete. The characterization of the mechanisms that govern the emergence and depletion of αSMA will allow for an understanding of how the niche of fibroblasts is changing. Taking into account the intense studies that have been performed on the pool of lung mesenchymal cells, we present data on the typing of interstitial fibroblasts and their role in the formation and maintenance of alveoli. On the whole, when identifying cell subpopulations in lung mesenchyme, one has to consider the developmental context, the changing cellular functions, and the lability of gene signatures.

Extracellular matrix-mediated remodeling and mechanotransduction in large vessels during development and disease

The vascular extracellular matrix (ECM) is synthesized and secreted during embryogenesis and facilitates the growth and remodeling of large vessels. Proper interactions between the ECM and vascular cells are pivotal for building the vasculature required for postnatal dynamic circulation. The ECM serves as a structural component by maintaining the integrity of the vessel wall while also regulating intercellular signaling, which involves cytokines and growth factors. The major ECM component in large vessels is elastic fibers, which include elastin and microfibrils. Elastin is predominantly synthesized by vascular smooth muscle cells (SMCs) and uses microfibrils as a scaffold to lay down and assemble cross-linked elastin. The absence of elastin causes developmental defects that result in the subendothelial proliferation of SMCs and inward remodeling of the vessel wall. Notably, elastic fiber formation is attenuated in the ductus arteriosus and umbilical arteries. These two vessels function during embryogenesis and close after birth via cellular proliferation, migration, and matrix accumulation. In dynamic postnatal mechano-environments, the elastic fibers in large vessels also serve an essential role in proper signal transduction as a component of elastin-contractile units. Disrupted mechanotransduction in SMCs leads to pathological conditions such as aortic aneurysms that exhibit outward remodeling. This review discusses the importance of the ECM-mainly the elastic fiber matrix-in large vessels during developmental remodeling and under pathological conditions. By dissecting the role of the ECM in large vessels, we aim to provide insights into the role of ECM-mediated signal transduction that can provide a basis for seeking new targets for intervention in vascular diseases.

Bi-allelic premature truncating variants in LTBP1 cause cutis laxa syndrome

Latent transforming growth factor β (TGFβ)-binding proteins (LTBPs) are microfibril-associated proteins essential for anchoring TGFβ in the extracellular matrix (ECM) as well as for correct assembly of ECM components. Variants in LTBP2, LTBP3, and LTBP4 have been identified in several autosomal recessive Mendelian disorders with skeletal abnormalities with or without impaired development of elastin-rich tissues. Thus far, the human phenotype associated with LTBP1 deficiency has remained enigmatic. In this study, we report homozygous premature truncating LTBP1 variants in eight affected individuals from four unrelated consanguineous families. Affected individuals present with connective tissue features (cutis laxa and inguinal hernia), craniofacial dysmorphology, variable heart defects, and prominent skeletal features (craniosynostosis, short stature, brachydactyly, and syndactyly). In vitro studies on proband-derived dermal fibroblasts indicate distinct molecular mechanisms depending on the position of the variant in LTBP1. C-terminal variants lead to an altered LTBP1 loosely anchored in the microfibrillar network and cause increased ECM deposition in cultured fibroblasts associated with excessive TGFβ growth factor activation and signaling. In contrast, N-terminal truncation results in a loss of LTBP1 that does not alter TGFβ levels or ECM assembly. In vivo validation with two independent zebrafish lines carrying mutations in ltbp1 induce abnormal collagen fibrillogenesis in skin and intervertebral ligaments and ectopic bone formation on the vertebrae. In addition, one of the mutant zebrafish lines shows voluminous and hypo-mineralized vertebrae. Overall, our findings in humans and zebrafish show that LTBP1 function is crucial for skin and bone ECM assembly and homeostasis.

The molecular mechanism of mechanotransduction in vascular homeostasis and disease

Blood vessels are constantly exposed to mechanical stimuli such as shear stress due to flow and pulsatile stretch. The extracellular matrix maintains the structural integrity of the vessel wall and coordinates with a dynamic mechanical environment to provide cues to initiate intracellular signaling pathway(s), thereby changing cellular behaviors and functions. However, the precise role of matrix-cell interactions involved in mechanotransduction during vascular homeostasis and disease development remains to be fully determined. In this review, we introduce hemodynamics forces in blood vessels and the initial sensors of mechanical stimuli, including cell-cell junctional molecules, G-protein-coupled receptors (GPCRs), multiple ion channels, and a variety of small GTPases. We then highlight the molecular mechanotransduction events in the vessel wall triggered by laminar shear stress (LSS) and disturbed shear stress (DSS) on vascular endothelial cells (ECs), and cyclic stretch in ECs and vascular smooth muscle cells (SMCs)-both of which activate several key transcription factors. Finally, we provide a recent overview of matrix-cell interactions and mechanotransduction centered on fibronectin in ECs and thrombospondin-1 in SMCs. The results of this review suggest that abnormal mechanical cues or altered responses to mechanical stimuli in EC and SMCs serve as the molecular basis of vascular diseases such as atherosclerosis, hypertension and aortic aneurysms. Collecting evidence and advancing knowledge on the mechanotransduction in the vessel wall can lead to a new direction of therapeutic interventions for vascular diseases.

Perlecan in Pericellular Mechanosensory Cell-Matrix Communication, Extracellular Matrix Stabilisation and Mechanoregulation of Load-Bearing Connective Tissues

In this study, we review mechanoregulatory roles for perlecan in load-bearing connective tissues. Perlecan facilitates the co-acervation of tropoelastin and assembly of elastic microfibrils in translamellar cross-bridges which, together with fibrillin and elastin stabilise the extracellular matrix of the intervertebral disc annulus fibrosus. Pericellular perlecan interacts with collagen VI and XI to define and stabilize this matrix compartment which has a strategic position facilitating two-way cell-matrix communication between the cell and its wider extracellular matrix. Cues from the extracellular matrix are fed through this pericellular matrix back to the chondrocyte, allowing it to perceive and respond to subtle microenvironmental changes to regulate tissue homeostasis. Thus perlecan plays a key regulatory role in chondrocyte metabolism, and in chondrocyte differentiation. Perlecan acts as a transport proteoglycan carrying poorly soluble, lipid-modified proteins such as the Wnt or Hedgehog families facilitating the establishment of morphogen gradients that drive tissue morphogenesis. Cell surface perlecan on endothelial cells or osteocytes acts as a flow sensor in blood and the lacunar canalicular fluid providing feedback cues to smooth muscle cells regulating vascular tone and blood pressure, and the regulation of bone metabolism by osteocytes highlighting perlecan's multifaceted roles in load-bearing connective tissues.

Elastic fibers during aging and disease

Elastic fibers are essential constituents of the extracellular matrix of higher vertebrates and endow several tissues and organs including lungs, skin and blood vessels with elasticity and resilience. During the human lifespan, elastic fibers are exposed to a variety of enzymatic, chemical and biophysical influences, and accumulate damage due to their low turnover. Aging of elastin and elastic fibers involves enzymatic degradation, oxidative damage, glycation, calcification, aspartic acid racemization, binding of lipids and lipid peroxidation products, carbamylation and mechanical fatigue. These processes can trigger an impairment or loss of elastic fiber function and are associated with severe pathologies. There are different inherited or acquired pathological conditions, which influence the structure and function of elastic fibers and microfibrils predominantly in the cardiorespiratory system and skin. Inherited elastic-fiber pathologies have a direct or indirect impact on elastic-fiber formation due to mutations in the fibrillin genes (fibrillinopathies), in the elastin gene (elastinopathies) or in genes encoding proteins that are associated with microfibrils or elastic fibers. Acquired elastic-fiber pathologies appear age-related or as a result of multiple factors impairing tissue homeostasis. This review gives an overview on the fate of elastic fibers over the human lifespan in health and disease.

Weighted gene co-expression network analysis identifies molecular pathways and hub genes involved in broiler White Striping and Wooden Breast myopathies

In recent years, the poultry industry has experienced an increased incidence of myopathies affecting breasts of fast-growing broilers, such as White Striping (WS) and Wooden Breast (WB) defects. To explore the molecular mechanisms and genes involved in WS and WB onset, we decided to perform a Weighted Gene Co-expression Network Analysis (WGCNA) using the gene expression profile and meat quality parameters of Pectoralis major muscles analysed in our previous study. Among the 212 modules identified by WGCNA, the red, darkred, midnightblue and paleturquoise4 modules were chosen for subsequent analysis. Functional analysis evidenced pathways involved in extracellular matrix (ECM) organization, collagen metabolism, cellular signaling and unfolded protein response. The hub gene analysis showed several genes coding for ECM components as the most interconnected nodes in the gene network (e.g. COL4A1, COL4A2, LAMA2, LAMA4, FBLN5 and FBN1). In this regard, this study suggests that alterations in ECM composition could somehow activate the cascade of biological reactions that result in the growth-related myopathies onset, and the involvement of Collagen IV alterations in activating the endoplasmic reticulum (ER) stress response may be hypothesized. Therefore, our findings provide further and innovative knowledge concerning the molecular mechanisms related to the breast abnormalities occurrence in modern broilers.

Identification of key genes in ruptured atherosclerotic plaques by weighted gene correlation network analysis

The rupture of atherosclerotic plaques is essential for cardiovascular and cerebrovascular events. Identification of the key genes related to plaque rupture is an important approach to predict the status of plaque and to prevent the clinical events. In the present study, we downloaded two expression profiles related to the rupture of atherosclerotic plaques (GSE41571 and GSE120521) from GEO database. 11 samples in GSE41571 were used to identify the differentially expressed genes (DEGs) and to construct the weighted gene correlation network analysis (WGCNA) by R software. The gene oncology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment tool in DAVID website, and the Protein-protein interactions in STRING website were used to predict the functions and mechanisms of genes. Furthermore, we mapped the hub genes extracted from WGCNA to DEGs, and constructed a sub-network using Cytoscape 3.7.2. The key genes were identified by the molecular complex detection (MCODE) in Cytoscape. Further validation was conducted using dataset GSE120521 and human carotid endarterectomy (CEA) plaques. Results: In our study, 868 DEGs were identified in GSE41571. Six modules with 236 hub genes were identified through WGCNA analysis. Among these six modules, blue and brown modules were of the highest correlations with ruptured plaques (with a correlation of 0.82 and −0.9 respectively). 72 hub genes were identified from blue and brown modules. These 72 genes were the most likely ones being related to cell adhesion, extracellular matrix organization, cell growth, cell migration, leukocyte migration, PI₃K-Akt signaling, focal adhesion, and ECM-receptor interaction. Among the 72 hub genes, 45 were mapped to the DEGs (logFC > 1.0, p-value < 0.05). The sub-network of these 45 hub genes and MCODE analysis indicated 3 clusters (13 genes) as key genes. They were LOXL1, FBLN5, FMOD, ELN, EFEMP1 in cluster 1, RILP, HLA-DRA, HLA-DMB, HLA-DMA in cluster 2, and SFRP4, FZD6, DKK3 in cluster 3. Further expression detection indicated EFEMP1, BGN, ELN, FMOD, DKK3, FBLN5, FZD6, HLA-DRA, HLA-DMB, HLA-DMA, and RILP might have potential diagnostic value.

The role of lysyl oxidase-like 1 (LOXL1) in exfoliation syndrome and glaucoma

Exfoliation syndrome (XFS) is an age-related systemic disease that affects the extracellular matrix. It increases the risk of glaucoma (exfoliation glaucoma, XFG) and susceptibility to diseases of elastin-rich connective tissues. LOXL1 (lysyl oxidase-like 1) is still recognized as the major genetic effect locus in XFS and XFG in all populations worldwide, although its genetic architecture is incompletely understood. LOXL1 is a key cross-linking enzyme in elastic fiber formation and remodeling, which is compatible with the pathogenetic concept of XFS as a specific type of elastosis. This review provides an overview on the current knowledge about the role of LOXL1 in the etiology and pathophysiology of XFS and XFG. It covers the known genetic associations at the LOXL1 locus, potential mechanisms of gene regulation, implications of LOXL1 in XFS-associated fibrosis and connective tissue homeostasis, its role in the development of glaucoma and associated systemic diseases, and the currently available LOXL1-based in vivo and in vitro models. Finally, it also identifies gaps in knowledge and suggests potential areas for future research.