Detection of an Integrin-Binding Mechanoswitch within Fibronectin during Tissue Formation and Fibrosis

Reproductive toxicity and molecular mechanisms of benzo[a]pyrene exposure on ovary, testis, and brood pouch of sex-role-reversed seahorses (Hippocampus erectus)

As a flagship taxa for marine ecosystems, seahorses possess a unique reproductive strategy of "male pregnancy". They are severely threatened by marine petroleum-based pollution but the molecular mechanism involved remains unclear. We evaluated the toxic effects and mechanisms of sub-acute exposure to benzo[a]pyrene (BaP), a representative polycyclic aromatic hydrocarbon (PAH), at three environmental related dosages (0.5, 5, and 50 μg/L) on the reproductive organs of sex-role-reversed lined seahorses (Hippocampus erectus). BaP induced ovary, testis and brood pouch tissue damage in a concentration-dependent manner. Transcriptomic results suggested that reproductive organs of the seahorse could undergo biotransformation and detoxification of BaP via the P450 enzyme system; the differential expression of key genes related to these pathways determined the differences in the accumulation of toxic substances in the reproductive organs. Moreover, toxic substances directly induced differential tissue damage in situ by activating tissue-specific signaling pathways: BaP-induced ovarian apoptosis and failure by upregulation of the pro-apoptotic genes, vadc1, traf2b, tnfsf10, and pycard (P < 0.05); inhibition of testicular function through disruption of genes associated with "ECM-receptor interaction", "Tight junction", and "Spermatogenesis" pathways; and interference with brood pouch immune responses, significantly suppressing the expression of ripk1, il-1b, casp3a, apaf1, calr, and canx (P < 0.05), thereby impairing "Apoptosis", "Phagosome", and "Necroptosis" processes, ultimately compromising brood pouch maintenance. Toxic substances exacerbate damage to the reproductive organs in seahorses by disrupting Ca2+ homeostasis. At environmentally-relevant concentrations of BaP, the reproductive efficiency of seahorses may be severely affected, increasing the risk of a decline in the abundance and diversity of wild populations.

Relaxation of mucosal fibronectin fibers in late gut inflammation following neutrophil infiltration in mice

The continuously remodeled extracellular matrix (ECM) plays a pivotal role in gastrointestinal health and disease, yet its precise functions remain elusive. In this study, we employed laser capture microdissection combined with low-input proteomics to investigate ECM remodeling during Salmonella-driven inflammation. To complement this, we probed how fibronectin fiber tension is altered using a mechanosensitive peptide probe. While fibronectin fibers in healthy intestinal tissue are typically stretched, many lose their tension in intestinal smooth muscles only hours after infection, despite the absence of bacteria in that area. In contrast, within the mucosa, where Salmonella is present starting 12 h post infection, fibronectin fiber relaxation occurred exclusively during late-stage infection at 72 h and was localized to already existing clusters of infiltrated neutrophils. Using N-terminomics, we identified three new cleavage sites in fibronectin in the inflamed cecum. The unique, tissue layer-specific changes in the molecular compositions and ECM fiber tension revealed herein might trigger new therapeutic strategies to fight acute intestinal inflammation.

APOE- ε4-induced Fibronectin at the blood-brain barrier is a conserved pathological mediator of disrupted astrocyte-endothelia interaction in Alzheimer's disease

Blood-brain barrier (BBB) dysfunction is a key feature of Alzheimer's disease (AD), particularly in individuals carrying the APOE-ε4 allele. This dysfunction worsens neuroinflammation and hinders the removal of toxic proteins, such as amyloid-beta (Aβ42), from the brain. In post-mortem brain tissues and in animal models, we previously reported that fibronectin accumulates at the BBB predominantly in APOE-ε4 carriers. Furthermore, we found a loss-of-function variant in the fibronectin 1 ( FN1 ) gene significantly reduces aggregated fibronectin levels and decreases AD risk among APOE-ε4 carriers. Yet, the molecular mechanisms downstream of fibronectin at the BBB remain unclear. The extracellular matrix (ECM) plays a crucial role in maintaining BBB homeostasis and orchestrating the interactions between BBB cell types, including endothelia and astrocytes. Understanding the mechanisms affecting the ECM and BBB cell types will be critical for developing effective therapies against AD, especially among APOE-ε4 carriers. Here, we demonstrate that APOE-ε4 , Aβ42, and inflammation drive the induction of FN1 expression in several models including zebrafish, mice, iPSC-derived human 3D astrocyte and 3D cerebrovascular cell cultures, and in human brains. Fibronectin accumulation disrupts astroglial-endothelial interactions and the signalling cascade between vascular endothelial growth factor (VEGF), heparin-binding epidermal growth factor (HBEGF) and Insulin-like growth factor 1 (IGF1). This accumulation of fibronectin in APOE-ε4- associated AD potentiates BBB dysfunction, which strongly implicates reducing fibronectin deposition as a potential therapeutic target for AD.

Graphical abstract

Accessibility text

This image illustrates the effects of different APOE isoforms (ApoE-ε3 and ApoE-ε4) on blood-brain barrier (BBB) integrity, focusing on the molecular interactions between astrocytes and endothelial cells. This figure emphasizes the detrimental effects of ApoE-ε4 on BBB integrity via fibronectin accumulation and altered signaling pathways. The top section provides a schematic overview of the blood-brain barrier, highlighting astrocytes, endothelial cells, and their interface. The left panel represents the ApoE-ε3 condition: Normal fibronectin (FN1) levels support healthy interactions between astrocytes and endothelial cells. Growth factors, including VEGFA, HBEGF, and IGF1, maintain BBB integrity through their respective receptors (VEGFR and EGFR). Green arrows indicate activation of these signaling pathways. The right panel depicts the ApoE-ε4 condition: Elevated fibronectin (FN1) disrupts astrocyte-endothelium interactions. FN1 binds integrins and activates focal adhesion kinase (FAK), inhibiting VEGFA, which is required for endothelial HBEGF that in turn activates IGF1 signaling. Red symbols indicate inhibition of HBEGF, VEGFA, and IGF1 pathways, leading to BBB dysfunction.

Highlights

APOE-ε4 drives fibronectin deposition in Alzheimer's, disrupting astrocyte-endothelia interactions. APOE-ε4 and fibronectin co-localize, forming aggregates at blood-brain barrier (BBB). Fibronectin alters the signaling between VEGF, IGF1, and HBEGF impairing BBB function. Reducing fibronectin restores BBB integrity and offsets APOE-ε4 pathology.

Exploring the Structural and Functional Consequences of Deleterious Missense Nonsynonymous SNPs in the EPOR Gene: A Computational Approach

BACKGROUND

Mutations in the EPOR gene can disrupt its normal signaling pathways, leading to hematological disorders such as polycythemia vera and other myeloproliferative diseases.

METHODOLOGY

In this study, a range of bioinformatics tools, including SIFT, PolyPhen-2, SNAP2, SNPs & Go, PhD-SNP, I-Mutant2.0, MuPro, MutPred, ConSurf, HOPE, and Interpro were used to assess the deleterious effects of missense nonsynonymous single nucleotide polymorphisms (nsSNPs) on protein structure and function. Furthermore, molecular dynamics simulations (MDS) were conducted to assess the structural deviations of the identified mutant variants in comparison to the wild type.

RESULTS

The results identified two nsSNPs, R223P and G302S, as deleterious, significantly affecting protein structure and function. Both substitutions occur in functionally conserved regions and are predicted to be pathogenic, associated with altered molecular mechanisms. The MDSs indicated that while the wild-type EPOR maintained optimal stability, the G302S and R223P variants exhibited substantial deviations, adversely affecting overall protein stability and compactness.

CONCLUSIONS

The computational analysis of missense nsSNPs in the EPOR gene identified two missense SNPs, R223P and G302S, as deleterious, occurring at highly conserved regions, and having substantial effects on erythropoietin receptor (EPO-R) protein structure and function, suggesting their potential pathogenic consequences.

Strain-dependent glutathionylation of fibronectin fibers impacts mechano-chemical behavior and primes an integrin switch

The extracellular matrix (ECM) is a protein polymer network that physically supports cells within a tissue. It acts as an important physical and biochemical stimulus directing cell behaviors. For fibronectin (Fn), a predominant component of the ECM, these physical and biochemical activities are inextricably linked as physical forces trigger conformational changes that impact its biochemical activity. Here, we analyze whether oxidative post-translational modifications, specifically glutathionylation, alter Fn's mechano-chemical characteristics through stretch-dependent protein modification. ECM post-translational modifications represent a potential for time- or stimulus-dependent changes in ECM structure-function relationships that could persist over time with potentially significant impacts on cell and tissue behaviors. In this study, we show evidence that glutathionylation of Fn ECM fibers is stretch-dependent and alters Fn fiber mechanical properties with implications on the selectivity of engaging integrin receptors. These data demonstrate the existence of multimodal post-translational modification mechanisms within the ECM with high relevance to the microenvironmental regulation of downstream cell behaviors.

Integrin mechanosensing relies on a pivot-clip mechanism to reinforce cell adhesion

Cells intricately sense mechanical forces from their surroundings, driving biophysical and biochemical activities. This mechanosensing phenomenon occurs at the cell-matrix interface, where mechanical forces resulting from cellular motion, such as migration or matrix stretching, are exchanged through surface receptors, primarily integrins, and their corresponding matrix ligands. A pivotal player in this interaction is the α5β1 integrin and fibronectin (FN) bond, known for its role in establishing cell adhesion sites for migration. However, upregulation of the α5β1-FN bond is associated with uncontrolled cell metastasis. This bond operates through catch bond dynamics, wherein the bond lifetime paradoxically increases with greater force. The mechanism sustaining the characteristic catch bond dynamics of α5β1-FN remains unclear. Leveraging molecular dynamics simulations, our approach unveils a pivot-clip mechanism. Two key binding sites on FN, namely the synergy site and the RGD (Arg-Gly-Asp) motif, act as active points for structural changes in α5β1 integrin. Conformational adaptations at these sites are induced by a series of hydrogen bond formations and breaks at the synergy site. We disrupt these adaptations through a double mutation on FN, known to reduce cell adhesion. A whole-cell finite-element model is employed to elucidate how the synergy site may promote dynamic α5β1-FN binding, resisting cell contraction. In summary, our study integrates molecular- and cellular-level modeling to propose that FN's synergy site reinforces cell adhesion through enhanced binding dynamics and a mechanosensitive pivot-clip mechanism. This work sheds light on the interplay between mechanical forces and cell-matrix interactions, contributing to our understanding of cellular behaviors in physiological and pathological contexts.

Rare genetic variation in fibronectin 1 (FN1) protects against APOEε4 in Alzheimer's disease

The risk of developing Alzheimer's disease (AD) significantly increases in individuals carrying the APOEε4 allele. Elderly cognitively healthy individuals with APOEε4 also exist, suggesting the presence of cellular mechanisms that counteract the pathological effects of APOEε4; however, these mechanisms are unknown. We hypothesized that APOEε4 carriers without dementia might carry genetic variations that could protect them from developing APOEε4-mediated AD pathology. To test this, we leveraged whole-genome sequencing (WGS) data in the National Institute on Aging Alzheimer's Disease Family Based Study (NIA-AD FBS), Washington Heights/Inwood Columbia Aging Project (WHICAP), and Estudio Familiar de Influencia Genetica en Alzheimer (EFIGA) cohorts and identified potentially protective variants segregating exclusively among unaffected APOEε4 carriers. In homozygous unaffected carriers above 70 years old, we identified 510 rare coding variants. Pathway analysis of the genes harboring these variants showed significant enrichment in extracellular matrix (ECM)-related processes, suggesting protective effects of functional modifications in ECM proteins. We prioritized two genes that were highly represented in the ECM-related gene ontology terms, (FN1) and collagen type VI alpha 2 chain (COL6A2) and are known to be expressed at the blood-brain barrier (BBB), for postmortem validation and in vivo functional studies. An independent analysis in a large cohort of 7185 APOEε4 homozygous carriers found that rs140926439 variant in FN1 was protective of AD (OR = 0.29; 95% CI [0.11, 0.78], P = 0.014) and delayed age at onset of disease by 3.37 years (95% CI [0.42, 6.32], P = 0.025). The FN1 and COL6A2 protein levels were increased at the BBB in APOEε4 carriers with AD. Brain expression of cognitively unaffected homozygous APOEε4 carriers had significantly lower FN1 deposition and less reactive gliosis compared to homozygous APOEε4 carriers with AD, suggesting that FN1 might be a downstream driver of APOEε4-mediated AD-related pathology and cognitive decline. To validate our findings, we used zebrafish models with loss-of-function (LOF) mutations in fn1b-the ortholog for human FN1. We found that fibronectin LOF reduced gliosis, enhanced gliovascular remodeling, and potentiated the microglial response, suggesting that pathological accumulation of FN1 could impair toxic protein clearance, which is ameliorated with FN1 LOF. Our study suggests that vascular deposition of FN1 is related to the pathogenicity of APOEε4, and LOF variants in FN1 may reduce APOEε4-related AD risk, providing novel clues to potential therapeutic interventions targeting the ECM to mitigate AD risk.

Relaxed fibronectin: a potential novel target for imaging endometriotic lesions

BACKGROUND

Endometriosis is characterized by the ectopic occurrence of endometrial tissue. Though considered benign, endometriotic lesions possess tumor-like properties such as tissue invasion and remodeling of the extracellular matrix. One major clinical hurdle concerning endometriosis is its diagnosis. The diagnostic modalities ultrasound and MRI are often unable to detect all lesions, and a clear correlation between imaging and clinical symptoms is still controversial. Therefore, it was our aim to identify a potential target to image active endometriotic lesions.

RESULTS

For our studies, we employed the preclinical radiotracer [111In]In-FnBPA5, which specifically binds to relaxed fibronectin-an extracellular matrix protein with key functions in homeostasis that has been implicated in the pathogenesis of diseases such as cancer and fibrosis. We employed this tracer in biodistribution as well as SPECT/CT studies in mice and conducted immunohistochemical stainings on mouse uterine tissue as well as on patient-derived endometriosis tissue. In biodistribution and SPECT/CT studies using the radiotracer [111In]In-FnBPA5, we found that radiotracer uptake in the myometrium varies with the estrous cycle of the mouse, leading to higher uptake of [111In]In-FnBPA5 during estrogen-dependent phases, which indicates an increased abundance of relaxed fibronectin when estrogen levels are high. Finally, immunohistochemical analysis of patient samples demonstrated that there is preferential relaxation of fibronectin in the proximity of the endometriotic stroma.

CONCLUSION

Estrous cycle stages characterized by high estrogen levels result in a higher abundance of relaxed fibronectin in the murine myometrium. This finding together with a first proof-of-concept study employing human endometriosis tissues suggests that relaxed fibronectin could be a potential target for the development of a diagnostic radiotracer targeting endometriotic lesions. With [111In]In-FnBPA5, the matching targeting molecule is in preclinical development.

The Role of Mechanotransduction in Contact Inhibition of Locomotion and Proliferation

Contact inhibition (CI) represents a crucial tumor-suppressive mechanism responsible for controlling the unbridled growth of cells, thus preventing the formation of cancerous tissues. CI can be further categorized into two distinct yet interrelated components: CI of locomotion (CIL) and CI of proliferation (CIP). These two components of CI have historically been viewed as separate processes, but emerging research suggests that they may be regulated by both distinct and shared pathways. Specifically, recent studies have indicated that both CIP and CIL utilize mechanotransduction pathways, a process that involves cells sensing and responding to mechanical forces. This review article describes the role of mechanotransduction in CI, shedding light on how mechanical forces regulate CIL and CIP. Emphasis is placed on filamin A (FLNA)-mediated mechanotransduction, elucidating how FLNA senses mechanical forces and translates them into crucial biochemical signals that regulate cell locomotion and proliferation. In addition to FLNA, trans-acting factors (TAFs), which are proteins or regulatory RNAs capable of directly or indirectly binding to specific DNA sequences in distant genes to regulate gene expression, emerge as sensitive players in both the mechanotransduction and signaling pathways of CI. This article presents methods for identifying these TAF proteins and profiling the associated changes in chromatin structure, offering valuable insights into CI and other biological functions mediated by mechanotransduction. Finally, it addresses unanswered research questions in these fields and delineates their possible future directions.

Rare genetic variation in Fibronectin 1 ( FN1 ) protects against APOEe4 in Alzheimer's disease

The risk of developing Alzheimer's disease (AD) significantly increases in individuals carrying the APOEε4 allele. Elderly cognitively healthy individuals with APOEε4 also exist, suggesting the presence of cellular mechanisms that counteract the pathological effects of APOEε4 ; however, these mechanisms are unknown. We hypothesized that APOEε4 carriers without dementia might carry genetic variations that could protect them from developing APOEε4- mediated AD pathology. To test this, we leveraged whole genome sequencing (WGS) data in National Institute on Aging Alzheimer's Disease Family Based Study (NIA-AD FBS), Washington Heights/Inwood Columbia Aging Project (WHICAP), and Estudio Familiar de Influencia Genetica en Alzheimer (EFIGA) cohorts and identified potentially protective variants segregating exclusively among unaffected APOEε4 carriers. In homozygous unaffected carriers above 70 years old, we identified 510 rare coding variants. Pathway analysis of the genes harboring these variants showed significant enrichment in extracellular matrix (ECM)-related processes, suggesting protective effects of functional modifications in ECM proteins. We prioritized two genes that were highly represented in the ECM-related gene ontology terms, (FN1) and collagen type VI alpha 2 chain ( COL6A2 ) and are known to be expressed at the blood-brain barrier (BBB), for postmortem validation and in vivo functional studies. The FN1 and COL6A2 protein levels were increased at the BBB in APOEε4 carriers with AD. Brain expression of cognitively unaffected homozygous APOEε4 carriers had significantly lower FN1 deposition and less reactive gliosis compared to homozygous APOEε4 carriers with AD, suggesting that FN1 might be a downstream driver of APOEε4 -mediated AD-related pathology and cognitive decline. To validate our findings, we used zebrafish models with loss-of-function (LOF) mutations in fn1b - the ortholog for human FN1 . We found that fibronectin LOF reduced gliosis, enhanced gliovascular remodeling and potentiated the microglial response, suggesting that pathological accumulation of FN1 could impair toxic protein clearance, which is ameliorated with FN1 LOF. Our study suggests vascular deposition of FN1 is related to the pathogenicity of APOEε4 , LOF variants in FN1 may reduce APOEε4 -related AD risk, providing novel clues to potential therapeutic interventions targeting the ECM to mitigate AD risk.

Wogonin Attenuates Bleomycin-Induced Pulmonary Fibrosis and Oxidative Stress Injury via the MAPK Signaling Pathway

Idiopathic pulmonary fibrosis (PF) is an irreversible and chronic inflammatory condition with limited therapeutic options and a high mortality rate. We aimed to determine the possible role and mechanisms of wogonin (WGN) on PF. A rat model of PF was established with intratracheally administrated with bleomycin (BLM), followed by intravenously injecting with WGN and weekly body weight measurements for four weeks. Hematoxylin-eosin (H&E) and Masson's trichrome staining were implemented for histopathological analysis. In addition, the levels of fibrotic proteins and indicators of the mitogen-activated protein kinase (MAPK) pathway were assessed with Western blot. RT-quantitative (q)PCR experiment was conducted to investigate the fibrotic proteins' mRNA expression. Ultimately, the concentrations of glutathione peroxidase (GSH-PX), malonaldehyde (MDA), and superoxide dismutase (SOD) were ascertained with appropriate kits. The results showed that WGN administration significantly reversed BLM-induced body weight reduction, alleviated pathological fibrosis, and reduced the Ashcroft score and the lung wet-to-dry weight ratio. Additionally, WGN suppressed the rise of fibrotic protein levels in BLM-treated rat's lung tissues. Furthermore, WGN attenuated BLM-stimulated oxidative stress, as evidenced by the increased GSH-PX and SOD levels and decreased MDA levels in vivo. Finally, wogonin supplements significantly lowered the extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK phosphorylation levels in the BLM-treated rat's lung tissues. In conclusion, our study proved that PF induced by BLM administration can be mitigated by WGN treatment via suppressing the MAPK pathway, indicating that WGN is a candidate therapeutic agent for managing PF.

Design matters: A comparison of natural versus synthetic skin substitutes across benchtop and porcine wound healing metrics: An experimental study

Background and Aims

Skin substitutes, essential tools for helping close full thickness wounds with minimal scarring, are available in both collagen-based and synthetic polyurethane constructions. Here we explore fundamental differences between two frequently used skin substitutes and discuss how these differences may impact in vivo performance.

Methods

Polyurethane- and collagen-based matrices were characterized in vitro for pore size via scanning electron microscopy, hydrophobicity via liquid contact angle, conformability via bending angle, and biocompatibility via fibroblast and keratinocyte adhesion and proliferation. These matrices were then evaluated in a full-thickness excisional pig wound study followed by histological analysis. Statistical analysis was performed using t-tests or one-way analysis of variances with Tukey's multiple post hoc comparisons, where appropriate.

Results

Average pore diameter in the tested polyurethane matrix was over four times larger than that of the collagen matrix (589 ± 297 µm vs. 132 ± 91 µm). Through liquid contact angle measurement, the collagen matrix (not measurable) was found to be hydrophilic compared to the hydrophobic polyurethane matrix (>90°). The collagen matrix was significantly more conformable than the polyurethane matrix (9 ± 2° vs. 84 ± 5° bending angle, respectively). Fibroblast and keratinocyte adhesion and proliferation assays elucidated a significantly greater ability of both cell types to attach and proliferate on collagen versus polyurethane. While the porcine study showed minimal contraction of either matrix material, histological findings between the two treatments were markedly different. Collagen matrices were associated with early fibroblast infiltration and fibroplasia, whereas polyurethane matrices elicited a strong multinucleated giant cell response and produced a network of comparatively aligned collagen fibrils.

Conclusions

The more favorable in vitro properties of the collagen matrix led to less inflammation and better overall tissue response in vivo. Overall, our findings demonstrate how the choice of biomaterial and its design directly translate to differing in vivo mechanisms of action and overall tissue quality.

Initiation of fibronectin fibrillogenesis is an enzyme-dependent process

Fibronectin fibrillogenesis and mechanosensing both depend on integrin-mediated force transmission to the extracellular matrix. However, force transmission is in itself dependent on fibrillogenesis, and fibronectin fibrils are found in soft embryos where high forces cannot be applied, suggesting that force cannot be the sole initiator of fibrillogenesis. Here, we identify a nucleation step prior to force transmission, driven by fibronectin oxidation mediated by lysyl oxidase enzyme family members. This oxidation induces fibronectin clustering, which promotes early adhesion, alters cellular response to soft matrices, and enhances force transmission to the matrix. In contrast, absence of fibronectin oxidation abrogates fibrillogenesis, perturbs cell-matrix adhesion, and compromises mechanosensation. Moreover, fibronectin oxidation promotes cancer cell colony formation in soft agar as well as collective and single-cell migration. These results reveal a force-independent enzyme-dependent mechanism that initiates fibronectin fibrillogenesis, establishing a critical step in cell adhesion and mechanosensing.

Inhibition of long noncoding RNA Gm41724 alleviates pressure overload-induced cardiac fibrosis by regulating lamina-associated polypeptide 2α

Cardiac fibrosis is a pathological process underlying myocardial remodeling and is characterized by excessive deposition of the myocardial extracellular matrix. Long noncoding RNAs (lncRNAs) have emerged as critical regulators of various biological processes. In this study, we investigated the role of a novel lncRNA, Gm41724, in cardiac fibrosis induced by pressure overload. High-throughput whole transcriptome sequencing analysis was performed to detect differentially expressed lncRNAs in cardiac fibroblasts (CFs) with or without TGF-β1 treatment. Differential expression analysis and gene set enrichment analysis identified Gm41724 as a potential molecule targeting fibrosis. Gm41724 positively regulated the activation of CFs induced by TGF-β1 and pressure overload. Knocking down Gm41724 could inhibit the differentiation of CFs into myofibroblasts and alleviate cardiac fibrosis induced by pressure overload. Mechanistically, comprehensive identification of RNA-binding proteins by mass spectrometry (CHIRP-MS) and RNA immunoprecipitation (RIP) assay combined with other methods of molecular biological revealed the important role of Gm41724 binding to lamina-associated polypeptide 2α (lap2α) for the activation of CFs. Further mechanistic studies indicated that the regulator of G protein signaling 4 (Rgs4), as the downstream effector of Gm41724/lap2α, regulated CFs activation. Our results implicated the involvement of Gm41724 in cardiac fibrosis induced by pressure overload and it is expected to be a promising target for anti-fibrotic therapy.

Fibronectin anchoring to viscoelastic poly(dimethylsiloxane) elastomers controls fibroblast mechanosensing and directional motility

The established link between deregulated tissue mechanics and various pathological states calls for the elucidation of the processes through which cells interrogate and interpret the mechanical properties of their microenvironment. In this work, we demonstrate that changes in the presentation of the extracellular matrix protein fibronectin on the surface of viscoelastic silicone elastomers have an overarching effect on cell mechanosensing, that is independent of bulk mechanics. Reduction of surface hydrophilicity resulted in altered fibronectin adsorption strength as monitored using atomic force microscopy imaging and pulling experiments. Consequently, primary human fibroblasts were able to remodel the fibronectin coating, adopt a polarized phenotype and migrate directionally even on soft elastomers, that otherwise were not able to resist the applied traction forces. The findings presented here provide valuable insight on how cellular forces are regulated by ligand presentation and used by cells to probe their mechanical environment, and have implications on biomaterial design for cell guidance.

Fibronectin Functions as a Selective Agonist for Distinct Toll-like Receptors in Triple-Negative Breast Cancer

The microenvironment of tumors is characterized by structural changes in the fibronectin matrix, which include increased deposition of the EDA isoform of fibronectin and the unfolding of the fibronectin Type III domains. The impact of these structural changes on tumor progression is not well understood. The fibronectin EDA (FnEDA) domain and the partially unfolded first Type III domain of fibronectin (FnIII-1c) have been identified as endogenous damage-associated molecular pattern molecules (DAMPs), which induce innate immune responses by serving as agonists for Toll-Like Receptors (TLRs). Using two triple-negative breast cancer (TNBC) cell lines MDA-MB-468 and MDA-MB-231, we show that FnEDA and FnIII-1c induce the pro-tumorigenic cytokine, IL-8, by serving as agonists for TLR5 and TLR2, the canonical receptors for bacterial flagellin and lipoprotein, respectively. We also find that FnIII-1c is not recognized by MDA-MB-468 cells but is recognized by MDA-MB-231 cells, suggesting a cell type rather than ligand specific utilization of TLRs. As IL-8 plays a major role in the progression of TNBC, these studies suggest that tumor-induced structural changes in the fibronectin matrix promote an inflammatory microenvironment conducive to metastatic progression.

Pathogenesis of glaucoma: Extracellular matrix dysfunction in the trabecular meshwork-A review

The trabecular meshwork regulates aqueous humour outflow from the anterior chamber of the eye. It does this by establishing a tunable outflow resistance, defined by the interplay between cells and their extracellular matrix (ECM) milieu, and the molecular interactions between ECM proteins. During normal tissue homeostasis, the ECM is remodelled and trabecular cell behaviour is modified, permitting increased aqueous fluid outflow to maintain intraocular pressure (IOP) within a relatively narrow physiological pressure. Dysfunction in the normal homeostatic process leads to increased outflow resistance and elevated IOP, which is a primary risk factor for glaucoma. This review delineates some of the changes in the ECM that lead to gross as well as some more subtle changes in the structure and function of the ECM, and their impact on trabecular cell behaviour. These changes are discussed in the context of outflow resistance and glaucoma.

The Combined Influence of Viscoelastic and Adhesive Cues on Fibroblast Spreading and Focal Adhesion Organization

Introduction

Tissue fibrosis is characterized by progressive extracellular matrix (ECM) stiffening and loss of viscoelasticity that ultimately impairs organ functionality. Cells bind to the ECM through integrins, where αv integrin engagement in particular has been correlated with fibroblast activation into contractile myofibroblasts that drive fibrosis progression. There is a significant unmet need for in vitro hydrogel systems that deconstruct the complexity of native tissues to better understand the individual and combined effects of stiffness, viscoelasticity, and integrin engagement on fibroblast behavior.

Methods

We developed hyaluronic acid hydrogels with independently tunable cell-instructive properties (stiffness, viscoelasticity, ligand presentation) to address this challenge. Hydrogels with mechanics matching normal or fibrotic lung tissue were synthesized using a combination of covalent crosslinks and supramolecular interactions to tune viscoelasticity. Cell adhesion was mediated through incorporation of either RGD peptide or engineered fibronectin fragments promoting preferential integrin engagement via αvβ3 or α5β1.

Results

On fibrosis-mimicking stiff elastic hydrogels, preferential αvβ3 engagement promoted increased spreading, actin stress fiber organization, and focal adhesion maturation as indicated by paxillin organization in human lung fibroblasts. In contrast, preferential α5β1 binding suppressed these metrics. Viscoelasticity, mimicking the mechanics of healthy tissue, largely curtailed fibroblast spreading and focal adhesion organization independent of adhesive ligand type, highlighting its role in reducing fibroblast-activating behaviors.

Conclusions

Together, these results provide new insights into how mechanical and adhesive cues collectively guide disease-relevant cell behaviors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-021-00672-1.

Biomaterials patterning regulates neural stem cells fate and behavior: The interface of biology and material science

The combination of nanotechnology and stem cell biology is one of the most promising advances in the field of regenerative medicine. This novel combination has widely been utilized in vitro settings in an attempt to develop efficient therapeutic strategies to overcome the limited capacity of the central nervous system (CNS) in replacing degenerating neural cells with functionally normal cells after the onset of acute and chronic neurological disorders. Importantly, biomaterials, not only, enhance the endogenous CNS neurogenesis and plasticity, but also, could provide a desirable supportive microenvironment to harness the full potential of the in vitro expanded neural stem cells (NSCs) for regenerative purposes. Here, first, we discuss how the physical and biochemical properties of biomaterials, such as their stiffness and elasticity, could influence the behavior of NSCs. Then, since the NSCs niche or microenvironment is of fundamental importance in controlling the dynamic destiny of NSCs such as their quiescent and proliferative states, topographical effects of surface diversity in biomaterials, that is, the micro-and nano-patterned surfaces will be discussed in detail. Finally, the influence of biomaterials as artificial microenvironments on the behavior of NSCs through the specific mechanotransduction signaling pathway mediated by focal adhesion formation will be reviewed.

The Amot/integrin protein complex transmits mechanical forces required for vascular expansion

Vascular development is a complex multistep process involving the coordination of cellular functions such as migration, proliferation, and differentiation. How mechanical forces generated by cells and transmission of these physical forces control vascular development is poorly understood. Using an endothelial-specific genetic model in mice, we show that deletion of the scaffold protein Angiomotin (Amot) inhibits migration and expansion of the physiological and pathological vascular network. We further show that Amot is required for tip cell migration and the extension of cellular filopodia. Exploiting in vivo and in vitro molecular approaches, we show that Amot binds Talin and is essential for relaying forces between fibronectin and the cytoskeleton. Finally, we provide evidence that Amot is an important component of the endothelial integrin adhesome and propose that Amot integrates spatial cues from the extracellular matrix to form a functional vascular network.

Engineering of Bio-Adhesive Ligand Containing Recombinant RGD and PHSRN Fibronectin Cell-Binding Domains in Fusion with a Colored Multi Affinity Tag: Simple Approach for Fragment Study from Expression to Adsorption

Engineering of biomimetic motives have emerged as promising approaches to improving cells’ binding properties of biomaterials for tissue engineering and regenerative medicine. In this study, a bio-adhesive ligand including cell-binding domains of human fibronectin (FN) was engineered using recombinant protein technology, a major extracellular matrix (ECM) protein that interacts with a variety of integrins cell-surface’s receptors and other ECM proteins through specific binding domains. 9th and 10th fibronectin type III repeat containing Arginine-Glycine-Aspartic acid (RGD) and Pro-His-Ser-Arg-Asn (PHSRN) synergic site (FNIII9-10) were expressed in fusion with a Colored Multi Affinity Tag (CMAT) to develop a simplified production and characterization process. A recombinant fragment was produced in the bacterial system using E. coli with high yield purified protein by double affinity chromatography. Bio-adhesive surfaces were developed by passive coating of produced fragment onto non adhesive surfaces model. The recombinant fusion protein (CMAT-FNIII9/10) demonstrated an accurate monitoring capability during expression purification and adsorption assay. Finally, biological activity of recombinant FNIII9/10 was validated by cellular adhesion assay. Binding to α5β1 integrins were successfully validated using a produced fragment as a ligand. These results are robust supports to the rational development of bioactivation strategies for biomedical and biotechnological applications.

Extracellular matrix remodeling associated with bleomycin-induced lung injury supports pericyte-to-myofibroblast transition

Of the many origins of pulmonary myofibroblasts, microvascular pericytes are a known source. Prior literature has established the ability of pericytes to transition into myofibroblasts, but provide limited insight into molecular cues that drive this process during lung injury repair and fibrosis. Fibronectin and RGD-binding integrins have long been considered pro-fibrotic factors in myofibroblast biology, and here we test the hypothesis that these known myofibroblast cues coordinate pericyte-to-myofibroblast transitions. Specifically, we hypothesized that αvβ3 integrin engagement on fibronectin induces pericyte transition into myofibroblastic phenotypes in the murine bleomycin lung injury model. Myosin Heavy Chain 11 (Myh11)-CreERT2 lineage tracing in transgenic mice allows identification of cells of pericyte origin and provides a robust tool for isolating pericytes from tissues for further evaluation. We used this murine model to track and characterize pericyte behaviors during tissue repair. The majority of Myh11 lineage-positive cells are positive for the pericyte surface markers, PDGFRβ (55%) and CD146 (69%), and display typical pericyte morphology with spatial apposition to microvascular networks. After intratracheal bleomycin treatment of mice, Myh11 lineage-positive cells showed significantly increased contractile and secretory markers, as well as αv integrin expression. According to RNASeq measurements, many disease and tissue-remodeling genesets were upregulated in Myh11 lineage-positive cells in response to bleomycin-induced lung injury. In vitro, blocking αvβ3 binding through cycloRGDfK prevented expression of the myofibroblastic marker αSMA relative to controls. In response to RGD-containing provisional matrix proteins present in lung injury, pericytes may alter their integrin profile.

Effects of tributyltin on gonad and brood pouch development of male pregnant lined seahorse (Hippocampus erectus) at environmentally relevant concentrations

The male pregnancy of seahorses is unique, but their reproductive response to environmental disturbances has not yet been clarified. Tributyltin (TBT) is known to have an endocrine disrupting effect on the reproductive system of coastal marine organisms. This study evaluated the potential effects of exposure to environmentally relevant concentrations of TBT on the development of gonads and brood pouch of the lined seahorse (Hippocampus erectus). Physiological, histological, and transcriptional analyses were conducted, and results showed that high levels of TBT bioaccumulation occurred in male and female seahorses. TBT led to ovarian follicular atresia and apoptosis with the elevation of androgen levels, accompanied by the induction of genes associated with lysosomes and autophagosomes. Comparative transcriptional analyses revealed the likely inhibition of spermatogenesis via the suppression of cyclic AMP and androgen synthesis. Notably, the transcriptional profiles showed that TBT potentially affects the immune system, angiogenesis, and embryo nourishment of the brood pouch, which indicates that it has negative effects on the male reproductive system of seahorses. In summary, this study reveals that environmental levels of TBT potentially affect the reproductive efficiency of seahorses, and may ultimately lead to a reduction in their populations in coastal environments.

Regulatory long non-coding RNAs of hepatic stellate cells in liver fibrosis (Review)

Liver fibrosis (LF) is a continuous wound healing process caused by numerous chronic hepatic diseases and poses a major threat to human health. Activation of hepatic stellate cells (HSCs) is a critical event in the development of hepatic fibrosis. Long non-coding RNAs (lncRNAs) that are involved in HSC activation, participate in the development of LF and are likely to be therapeutic targets for LF. In the present review, the cellular signaling pathways of LF with respect to HSCs were discussed. In particular, this present review highlighted the current knowledge on the role of lncRNAs in activating or inhibiting LF, revealing lncRNAs that are likely to be biomarkers or therapeutic targets for LF. Additional studies should be performed to elucidate the potential of lncRNAs in the diagnosis and prognosis of LF and to provide novel therapeutic approaches for the reversion of LF.

The anti-tumor effect of ursolic acid on papillary thyroid carcinoma via suppressing Fibronectin-1

This study aims to discover the effects of ursolic acid (UA) on papillary thyroid carcinoma (PTC). Human PTC cells were under UA treatment, and cell viability, clone formation, and apoptosis were measured by MTT assay, clone formation assay, and flow cytometry, respectively. Expressions of apoptosis- and epithelial-mesenchymal transition (EMT)-related markers were determined via qRT-PCR and western blot. Fibronectin-1 (FN1) expression in thyroid carcinoma was analyzed by GEPIA2 and qRT-PCR. The effects of overexpressed FN1 on UA-treated cells were detected following the previous procedures. Cell viability, proliferation, and EMT-related marker expressions were inhibited, while cell apoptosis and apoptosis-related marker expressions were promoted by UA. FN1 was higher expressed in thyroid carcinoma and downregulated by UA. Effects of FN1 on cell viability, proliferation, and apoptosis- and EMT-related marker expressions were partially reversed by UA. UA inhibited human PTC cell viability, proliferation, and EMT but promoted apoptosis via suppressing FN1.

Interactions at engineered graft-tissue interfaces: A review

The interactions at the graft-tissue interfaces are critical for the results of engraftments post-implantation. To improve the success rate of the implantations, as well as the quality of the patients' life, understanding the possible reactions between artificial materials and the host tissues is helpful in designing new generations of material-based grafts aiming at inducing specific responses from surrounding tissues for their own reparation and regeneration. To help researchers understand the complicated interactions that occur after implantations and to promote the development of better-designed grafts with improved biocompatibility and patient responses, in this review, the topics will be discussed from the basic reactions that occur chronologically at the graft-tissue interfaces after implantations to the existing and potential applications of the mechanisms of such reactions in designing of grafts. It offers a chance to bring up-to-date advances in the field and new strategies of controlling the graft-tissue interfaces.

Particulate matters increase epithelial-mesenchymal transition and lung fibrosis through the ETS-1/NF-κB-dependent pathway in lung epithelial cells

Background

Particulate matters (PMs) in ambient air pollution are closely related to the incidence of respiratory diseases and decreased lung function. Our previous report demonstrated that PMs-induced oxidative stress increased the expression of proinflammatory intracellular adhesion molecule-1 (ICAM-1) through the IL-6/AKT/STAT3/NF-κB pathway in A549 cells. However, the role of O-PMs in epithelial-mesenchymal transition (EMT) development and pulmonary fibrosis and the related mechanisms have not been determined. The aim of this study was to investigate the effects of O-PMs on the pathogenesis of EMT and pulmonary fibrosis as well as the expression of ETS-1 and NF-κB p65, in vitro and in vivo.

Results

O-PMs treatment induced EMT development, fibronectin expression, and cell migration. O-PMs affected the expression of the EMT-related transcription factors NF-κB p65 and ETS-1. Interference with NF-κB p65 significantly decreased O-PMs-induced fibronectin expression. In addition, O-PMs affected the expression of fibronectin, E-cadherin, and vimentin through modulating ETS-1 expression. ATN-161, an antagonist of integrin α5β1, decreased the expression of fibronectin and ETS-1 and EMT development. EMT development and the expression of fibronectin and ETS-1 were increased in the lung tissue of mice after exposure to PMs for 7 and 14 days. There was a significant correlation between fibronectin and ETS-1 expression in human pulmonary fibrosis tissue.

Conclusion

O-PMs can induce EMT and fibronectin expression through the activation of transcription factors ETS-1 and NF-κB in A549 cells. PMs can induce EMT development and the expression of fibronectin and ETS-1 in mouse lung tissues. These findings suggest that the ETS-1 pathway could be a novel and alternative mechanism for EMT development and pulmonary fibrosis.

Fibronectin fibers are highly tensed in healthy organs in contrast to tumors and virus-infected lymph nodes

The extracellular matrix (ECM) acts as reservoir for a plethora of growth factors and cytokines some of which are hypothesized to be regulated by ECM fiber tension. Yet, ECM fiber tension has never been mapped in healthy versus diseased organs. Using our recently developed tension nanoprobe derived from the bacterial adhesin FnBPA5, which preferentially binds to structurally relaxed fibronectin fibers, we discovered here that fibronectin fibers are kept under high tension in selected healthy mouse organs. In contrast, tumor tissues and virus-infected lymph nodes exhibited a significantly higher content of relaxed or proteolytically cleaved fibronectin fibers. This demonstrates for the first time that the tension of ECM fibers is significantly reduced upon pathological tissue transformations. This has wide implications, as the active stretching of fibronectin fibers adjusts critical cellular niche parameters and thereby tunes the reciprocal cell-ECM crosstalk. Mapping the tensional state of fibronectin fibers opens novel and unexpected diagnostic opportunities.

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Mechanobiology of extracellular matrix changes upon pathological transformations.

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Fibronectin is significantly more relaxed in tumors than in healthy organs.

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Relaxed fibronectin is found close to myofibroblasts and dense collagen fibers.

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Viral infection reduces fibronectin fiber tension in lymph nodes.

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Use of a tension-sensitive adhesin to probe fibronectin fiber tension in tissues

Feeling Things Out: Bidirectional Signaling of the Cell-ECM Interface, Implications in the Mechanobiology of Cell Spreading, Migration, Proliferation, and Differentiation

Biophysical cues stemming from the extracellular environment are rapidly transduced into discernible chemical messages (mechanotransduction) that direct cellular activities-placing the extracellular matrix (ECM) as a potent regulator of cell behavior. Dynamic reciprocity between the cell and its associated matrix is essential to the maintenance of tissue homeostasis and dysregulation of both ECM mechanical signaling, via pathological ECM turnover, and internal mechanotransduction pathways contribute to disease progression. This review covers the current understandings of the key modes of signaling used by both the cell and ECM to coregulate one another. By taking an outside-in approach, the inherent complexities and regulatory processes at each level of signaling (ECM, plasma membrane, focal adhesion, and cytoplasm) are captured to give a comprehensive picture of the internal and external mechanoregulatory environment. Specific emphasis is placed on the focal adhesion complex which acts as a central hub of mechanical signaling, regulating cell spreading, migration, proliferation, and differentiation. In addition, a wealth of available knowledge on mechanotransduction is curated to generate an integrated signaling network encompassing the central components of the focal adhesion, cytoplasm and nucleus that act in concert to promote durotaxis, proliferation, and differentiation in a stiffness-dependent manner.

Fibronectin is a smart adhesive that both influences and responds to the mechanics of early spinal column development

An extracellular matrix of Fibronectin adheres the neural tube to the two flanking columns of paraxial mesoderm and is required for normal vertebrate development. Here, we find that the bilaterally symmetric interfaces between the zebrafish neural tube and paraxial mesoderm function as optimally engineered adhesive lap joints with rounded edges, graded Fibronectin ‘adhesive’ and an arced adhesive spew filet. Fibronectin is a ‘smart adhesive’ that remodels to the lateral edges of the neural tube-paraxial mesoderm interfaces where shear stress is highest. Fibronectin remodeling is mechanically responsive to contralateral variation morphogenesis, and Fibronectin-mediated inter-tissue adhesion is required for bilaterally symmetric morphogenesis of the paraxial mesoderm. Strikingly, however, perturbation of the Fibronectin matrix rescues the neural tube convergence defect of cadherin 2 mutants. Therefore, Fibronectin-mediated inter-tissue adhesion dynamically coordinates bilaterally symmetric morphogenesis of the vertebrate trunk but predisposes the neural tube to convergence defects that lead to spina bifida.

In embryos, the spinal cord starts out as a flat sheet of cells that curls up to form a closed cylinder called the neural tube. The folding tube is attached to the surrounding tissues through an extracellular matrix of proteins and sugars. Overlapping strands of a protein from the extracellular matrix called Fibronectin connect the neural tube to adjacent tissues, like a kind of biological glue. However, it remained unclear what effect this attachment had on the embryonic development of the spinal cord.

Connecting two overlapping objects with glue to form what is known as an ‘adhesive lap joint’ is common in fields such as woodworking and aeronautical engineering. The glue in these joints comes under shearing stress whenever the two objects it connects try to pull apart. But, thanks to work in engineering, it is possible to predict how different joints will perform under tension. Now, Guillon et al. have deployed these engineering principles to shed light on neural tube development.

Using zebrafish embryos and computational models, Guillon et al. investigated what happens when the strength of the adhesive lap joints in the developing spine changes. This revealed that Fibronectin works like a smart adhesive: rather than staying in one place like a conventional glue, it moves around. As the neural tube closes, cells remodel the Fibronectin, concentrating it on the areas under the highest stress. This seemed to both help and hinder neural tube development. On the one hand, by anchoring the tube equally to the left and right sides of the embryo, the Fibronectin glue helped the spine to develop symmetrically. On the other hand, the strength of the adhesive lap joints made it harder for the neural tube to curl up and close.

If the neural tube fails to close properly, it can lead to birth defects like spina bifida. One of the best-known causes of these birth defects in humans is a lack of a vitamin known as folic acid. Cell culture experiments suggest that this might have something to do with the mechanics of the cells during development. It may be that faulty neural tubes could close more easily if they were able to unglue themselves from the surrounding tissues. Further use of engineering principles could shed more light on this idea in the future.

McKeown-Longo P. Role of TLR4 Receptor Complex in the Regulation of the Innate Immune Response by Fibronectin

Chronic inflammation and subsequent tissue fibrosis are associated with a biochemical and mechanical remodeling of the fibronectin matrix. Due to its conformational lability, fibronectin is considerably stretched by the contractile forces of the fibrotic microenvironment, resulting in the unfolding of its Type III domains. In earlier studies, we have shown that a peptide mimetic of a partially unfolded fibronectin Type III domain, FnIII-1c, functions as a Damage Associated Molecular Pattern (DAMP) molecule to induce activation of a toll-like receptor 4 (TLR4)/NF-B pathway and the subsequent release of fibro-inflammatory cytokines from human dermal fibroblasts. In the current study, we evaluated the requirement of the canonical TLR4/MD2/CD14 receptor complex in the regulation of FnIII-1c induced cytokine release. Using dermal fibroblasts and human embryonic kidney (HEK) cells, we found that all the components of the TLR4/MD2/CD14 complex were required for the release of the fibro-inflammatory cytokine, interleukin 8 (IL-8) in response to both FnIII-1c and the canonical TLR4 ligand, lipopolysaccharide (LPS). However, FnIII-1c mediated IL-8 release was strictly dependent on membrane-associated CD14, while LPS could use soluble CD14. These findings demonstrate that LPS and FnIII-1c share a similar but not identical mechanism of TLR4 activation in human dermal fibroblasts.

Laminin-driven Epac/Rap1 regulation of epithelial barriers on decellularized matrix

Decellularized tissues offer a unique tool for developing regenerative biomaterials or in vitro platforms for the study of cell-extracellular matrix (ECM) interactions. One main challenge associated with decellularized lung tissue is that ECM components can be stripped away or altered by the detergents used to remove cellular debris. Without characterizing the composition of lung decellularized ECM (dECM) and the cellular response caused by the altered composition, it is difficult to utilize dECM for regeneration and specifically, engineering the complexities of the alveolar-capillary barrier. This study takes steps towards uncovering if dECM must be enhanced with lost ECM proteins to achieve proper epithelial barrier formation. To achieve this, the epithelial barrier function was assessed on dECM coatings with and without the systematic addition of several key basement membrane proteins. After comparing barrier function on collagen I, fibronectin, laminin, and dECM in varying combinations as an in vitro coating, the alveolar epithelium exhibited superior barrier function when dECM was supplemented with laminin as evidenced by trans-epithelial electrical resistance (TEER) and permeability assays. Increased barrier resistance with laminin addition was associated with upregulation of Claudin-18, E-cadherin, and junction adhesion molecule (JAM)-A, and stabilization of zonula occludens (ZO)-1 at junction complexes. The Epac/Rap1 pathway was observed to play a role in the ECM-mediated barrier function determined by protein expression and Epac inhibition. These findings revealed potential ECM coatings and molecular therapeutic targets for improved regeneration with decellularized scaffolds. STATEMENT OF SIGNIFICANCE: Efforts to produce a transplantable organ-scale biomaterial for lung regeneration has not been entirely successful to date, due to incomplete cell-cell junction formation, ultimately leading to severe edema in vivo. To fully understand the process of alveolar junction formation on ECM-derived biomaterials, this research has characterized and tailored decellularized ECM (dECM) to mitigate reductions in barrier strength or cell attachment caused by abnormal ECM compositions or detergent damage to dECM. These results indicate that laminin-driven Epac signaling plays a vital role in the stabilization of the alveolar barrier. Addition of laminin or Epac agonists during alveolar regeneration can reduce epithelial permeability within bioengineered lungs.

Role of Fibronectin in Primary Open Angle Glaucoma

Primary open angle glaucoma (POAG) is the most common form of glaucoma and the 2nd most common cause of irreversible vision loss in the United States. Nearly 67 million people have the disease worldwide including >3 million in the United States. A major risk factor for POAG is an elevation in intraocular pressure (IOP). The increase in IOP is believed to be caused by an increase in the deposition of extracellular matrix proteins, in particular fibronectin, in a region of the eye known as the trabecular meshwork (TM). How fibronectin contributes to the increase in IOP is not well understood. The increased density of fibronectin fibrils is thought to increase IOP by altering the compliance of the trabecular meshwork. Recent studies, however, also suggest that the composition and organization of fibronectin fibrils would affect IOP by changing the cell-matrix signaling events that control the functional properties of the cells in the trabecular meshwork. In this article, we will discuss how changes in the properties of fibronectin and fibronectin fibrils could contribute to the regulation of IOP.

A Matricryptic Conformation of the Integrin-Binding Domain of Fibronectin Regulates Platelet-Derived Growth Factor-Induced Intracellular Calcium Release

Platelet-derived growth factor (PDGF) signaling is dysregulated in a wide variety of diseases, making PDGF an attractive therapeutic target. However, PDGF also affects numerous signaling cascades essential for tissue homeostasis, limiting the development of PDGF-based therapies that lack adverse side-effects. Recent studies showed that fibroblast-mediated assembly of extracellular matrix (ECM) fibronectin fibrils attenuates PDGF-induced intracellular calcium release by selectively inhibiting phosphoinositol 3-kinase (PI3K) activation while leaving other PDGF-mediated signaling cascades intact. In the present study, a series of recombinant fibronectin-derived fusion proteins were used to localize the sequences in fibronectin that are responsible for this inhibition. Results demonstrate that attenuation of PDGF-induced intracellular calcium release by the fibronectin matrix mimetic, FNIII1H,8-10 requires α5β1 integrin ligation, but is not dependent upon the matricryptic, heparin-binding site of FNIII1. Intact cell-binding fibronectin fragments were also unable to attenuate PDGF-induced intracellular calcium release. In contrast, a novel integrin-binding fragment that adopts an extended and aligned conformational state, inhibited both PI3K activation and intracellular calcium release in response to PDGF. Taken together, these studies provide evidence that attenuation of PDGF-induced intracellular calcium release by fibronectin is mediated by a novel conformation of the α5β1 integrin-binding, FNIII9-10 modules, that is expressed by fibrillar fibronectin.

Cell Adhesion by Integrins

Integrins are heterodimeric cell surface receptors ensuring the mechanical connection between cells and the extracellular matrix. In addition to the anchorage of cells to the extracellular matrix, these receptors have critical functions in intracellular signaling, but are also taking center stage in many physiological and pathological conditions. In this review, we provide some historical, structural, and physiological notes so that the diverse functions of these receptors can be appreciated and put into the context of the emerging field of mechanobiology. We propose that the exciting journey of the exploration of these receptors will continue for at least another new generation of researchers.

Mechanosensitivity Occurs along the Adhesome's Force Train and Affects Traction Stress

Herein, we consider the process of force development along the adhesome within cell focal adhesions. Our model adhesome consists of the actin cytoskeleton-vinculin-talin-integrin-ligand-extracellular matrix-substrate force train. We specifically consider the effects of substrate stiffness on the force levels expected along the train and on the traction stresses they create at the substrate. We find that significant effects of substrate stiffness are manifest within each constitutive component of the force train and on the density and distribution of integrin/ligand anchorage points with the substrate. By following each component of the force train, we are able to delineate specific gaps in the quantitative descriptions of bond survival that must be addressed so that improved quantitative forecasts become possible. Our analysis provides, however, a rational description for the various levels of traction stresses that have been reported and of the effect of substrate stiffness. Our approach has the advantage of being quite clear as to how each constituent contributes to the net development of force and traction stress. We demonstrate that to provide truly quantitative forecasts for traction stress, a far more detailed description of integrin/ligand density and distribution is required. Although integrin density is already a well-recognized important feature of adhesion, our analysis places a finer point on it in the manner of how we evaluate the magnitude of traction stress. We provide mechanistic insight into how understanding of this vital element of the adhesion process may proceed by addressing mechanistic causes of integrin clustering that may lead to patterning.

Citrullination of fibronectin alters integrin clustering and focal adhesion stability promoting stromal cell invasion

The extracellular matrix (ECM) microenvironment is increasingly implicated in the instruction of pathologically relevant cell behaviors, from aberrant transdifferentation to invasion and beyond. Indeed, pathologic ECMs possess a panoply of alterations that provide deleterious instructions to resident cells. Here we demonstrate the precise manner in which the ECM protein fibronectin (FN) undergoes the posttranslational modification citrullination in response to peptidyl-arginine deiminase (PAD), an enzyme associated with innate immune cell activity and implicated in systemic ECM-centric diseases, like cancer, fibrosis and rheumatoid arthritis. FN can be citrullinated in at least 24 locations, 5 of which reside in FN's primary cell-binding domain. Citrullination of FN alters integrin clustering and focal adhesion stability with a concomitant enhancement in force-triggered integrin signaling along the FAK-Src and ILK-Parvin pathways within fibroblasts. In vitro migration and in vivo wound healing studies demonstrate the ability of citrullinated FN to support a more migratory/invasive phenotype that enables more rapid wound closure. These findings highlight the potential of ECM, particularly FN, to "record" inflammatory insults via post-translational modification by inflammation-associated enzymes that are subsequently "read" by resident tissue fibroblasts, establishing a direct link between inflammation and tissue homeostasis and pathogenesis through the matrix.

Matrisome Properties of Scaffolds Direct Fibroblasts in Idiopathic Pulmonary Fibrosis

In idiopathic pulmonary fibrosis (IPF) structural properties of the extracellular matrix (ECM) are altered and influence cellular responses through cell-matrix interactions. Scaffolds (decellularized tissue) derived from subpleural healthy and IPF lungs were examined regarding biomechanical properties and ECM composition of proteins (the matrisome). Scaffolds were repopulated with healthy fibroblasts cultured under static stretch with heavy isotope amino acids (SILAC), to examine newly synthesized proteins over time. IPF scaffolds were characterized by increased tissue density, stiffness, ultimate force, and differential expressions of matrisome proteins compared to healthy scaffolds. Collagens, proteoglycans, and ECM glycoproteins were increased in IPF scaffolds, however while specific basement membrane (BM) proteins such as laminins and collagen IV were decreased, nidogen-2 was also increased. Findings were confirmed with histology, clearly showing a disorganized BM. Fibroblasts produced scaffold-specific proteins mimicking preexisting scaffold composition, where 11 out of 20 BM proteins were differentially expressed, along with increased periostin and proteoglycans production. We demonstrate how matrisome changes affect fibroblast activity using novel approaches to study temporal differences, where IPF scaffolds support a disorganized BM and upregulation of disease-associated proteins. These matrix-directed cellular responses emphasize the IPF matrisome and specifically the BM components as important factors for disease progression.

Switchable and Obedient Interfacial Properties That Grant New Biomedical Applications

Toward imitating the natural smartness and responsivity of biological systems, surface interfacial properties are considered to be responsive and tunable if they show a reactive behavior to an environmental stimulus. This is still quite different from many contemporary biomaterials that lack responsiveness to interact with blood and different body tissues in a physiological manner. Meanwhile it is possible to even go one step further from responsiveness to dual-mode switchability and explore "switchable" or "reversible" responses of synthetic materials. We understand "switchable biomaterials" as materials undergoing a stepwise, structural transformation coupled with considerable changes of interfacial and other surface properties as a response to a stimulus. Therewith, a survey on stimuli-induced dynamic changes of charge, wettability, stiffness, topography, porosity, and thickness/swelling is presented here, as potentially powerful new technologies especially for future biomaterial development. Since living cells constantly sense their environment through a variety of surface receptors and other mechanisms, these obedient interfacial properties were particularly discussed regarding their advantageous multifunctionality for protein adsorption and cell adhesion signaling, which may alter in time and with environmental conditions.

Unraveling the Mechanobiology of Extracellular Matrix

Cells need to be anchored to extracellular matrix (ECM) to survive, yet the role of ECM in guiding developmental processes, tissue homeostasis, and aging has long been underestimated. How ECM orchestrates the deterioration of healthy to pathological tissues, including fibrosis and cancer, also remains poorly understood. Inquiring how alterations in ECM fiber tension might drive these processes is timely, as mechanobiology is a rapidly growing field, and many novel mechanisms behind the mechanical forces that can regulate protein, cell, and tissue functions have recently been deciphered. The goal of this article is to review how forces can switch protein functions, and thus cell signaling, and thereby inspire new approaches to exploit the mechanobiology of ECM in regenerative medicine as well as for diagnostic and therapeutic applications. Some of the mechanochemical switching concepts described here for ECM proteins are more general and apply to intracellular proteins as well.

LncRNA: Shedding light on mechanisms and opportunities in fibrosis and aging

Fibrosis is universally observed in multiple aging-related diseases and progressions and is characterized by excess accumulation of the extracellular matrix. Fibrosis occurs in various human organs and eventually results in organ failure. Noncoding RNAs (ncRNAs) have emerged as essential regulators of cellular signaling and relevant human diseases. In particular, the enigmatic class of long noncoding RNAs (lncRNAs) is a kind of noncoding RNA that is longer than 200 nucleotides and does not possess protein coding ability. LncRNAs have been identified to exert both promotive and inhibitory effects on the multifaceted processes of fibrosis. A growing body of studies has revealed that lncRNAs are involved in fibrosis in various organs, including the liver, heart, lung, and kidney. As lncRNAs have been increasingly identified, they have become promising targets for anti-fibrosis therapies. This review systematically highlights the recent advances regarding the roles of lncRNAs in fibrosis and sheds light on the use of lncRNAs as a potential treatment for fibrosis.

On Force and Form: Mechano-Biochemical Regulation of Extracellular Matrix

The extracellular matrix is well-known for its structural role in supporting cells and tissues, and its important biochemical role in providing signals to cells has increasingly become apparent. These structural and biochemical roles are closely coupled through mechanical forces: the biochemistry of the extracellular matrix determines its mechanical properties, mechanical forces control release or display of biochemical signals from the extracellular matrix, and the mechanical properties of the matrix in turn influence the mechanical set point at which signals are sent. In this Perspective, we explain how the extracellular matrix is regulated by strain and mechanical forces. We show the impact of biochemistry and mechanical forces on in vivo assembly of extracellular matrix and illustrate how matrix can be generated in vitro using a variety of methods. We cover how the matrix can be characterized in terms of mechanics, composition, and conformation to determine its properties and to predict interactions. Finally, we explore how extracellular matrix remodeling, ligand binding, and hemostasis are regulated by mechanical forces. These recently discovered mechano-biochemical interactions have important functions in wound healing and disease progression. It is likely that mechanically altered extracellular matrix interactions are a commonly recurring theme, but due to limited tools to generate extracellular matrix fibers in vitro and lack of high-throughput methods to detect these interactions, it is hypothesized that many of these interactions have yet to be discovered.

Fibronectin fiber creep under constant force loading

Viscoelasticity is a fundamental property of virtually all biological materials, and proteinaceous, fibrous materials that constitute the extracellular matrix (ECM) are no exception. Viscoelasticity may be particularly important in the ECM since cells can apply mechanical stress resulting from cell contractility over very long periods of time. However, measurements of ECM fiber response to long-term constant force loading are scarce, despite the increasing recognition that mechanical strain regulates the biological function of some ECM fibers. We developed a dual micropipette system that applies constant force to single fibers for up to 8 h. We utilized this system to study the time dependent response of fibronectin (Fn) fibers to constant force, as Fn fibers exhibit tremendous extensibility before mechanical failure as well as strain dependent alterations in biological properties. These data demonstrate the Fn fibers continue to stretch under constant force loading for at least 8 h and that this long-term creep results in plastic deformation of Fn fibers, in contrast to elastic deformation of Fn fibers under short-term, but fast loading rate extension. These data demonstrate that physiologically-relevant loading may impart mechanical features to Fn fibers by switching them into an extended state that may have altered biological functions. STATEMENT OF SIGNIFICANCE: Measurements of extracellular matrix (ECM) fiber response to constant force loading are scarce, so we developed a novel technique for applying constant force to single ECM fibers. We used this technique to measure constant force creep of fibronectin fibers since these fibers have been shown to be mechanotransducers whose functions can be altered by mechanical strain. We found that fibronectin fibers creep under constant force loading for the duration of the experiment and that this creep behavior resembles a power law. Furthermore, we found that constant force creep results in plastic deformation of the fibers, which suggests that the mechanobiological switching of fibronectin can only occur once after long-term loading.

Recruitment of integrin ανβ3 to integrin α5β1-induced clusters enables focal adhesion maturation and cell spreading

The major fibronectin (FN) binding integrins α5β1 and αvβ3 exhibit cooperativity during cell adhesion, migration and mechanosensing, through mechanisms that are not yet fully resolved. Exploiting mechanically-tunable, nano-patterned substrates, and peptidomimetic ligands designed to selectively bind corresponding integrins, we report that focal adhesions (FAs) of endothelial cells assembled on integrin α5β1-selective substrates, rapidly recruit αvβ3 integrins, but not vice versa. Blocking of integrin αvβ3 hindered FA maturation and cell spreading on α5β1-selective substrates, indicating a mechanism dependent on extracellular ligand binding and highlighting the requirement of αvβ3 engagement for efficient adhesion. Recruitment of αvβ3 integrins additionally occurred on hydrogel substrates of varying mechanical properties, above a threshold stiffness supporting FA formation. Mechanistic studies revealed the need for soluble factors present in serum to allow recruitment, and excluded exogenous, or endogenous, FN as the responsible ligand for integrin αvβ3 accumulation to adhesion clusters. Our findings highlight a novel mechanism of integrin co-operation and the critical role for αvβ3 integrins in promoting cell adhesion on α5β1-selective substrates.

Surface potential-governed cellular osteogenic differentiation on ferroelectric polyvinylidene fluoride trifluoroethylene films

Surface potential of biomaterials can dramatically influence cellular osteogenic differentiation. In this work, a wide range of surface potential on ferroelectric polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) films was designed to get insight into the interfacial interaction of cell-charged surface. The P(VDF-TrFE) films poled by contact electric poling at various electric fields obtained well stabilized surface potential, with wide range from -3 to 915 mV. The osteogenic differentiation level of cells cultured on the films was strongly dependent on surface potential and reached the optimum at 391 mV in this system. Binding specificity assay indicated that surface potential could effectively govern the binding state of the adsorbed fibronectin (FN) with integrin. Molecular dynamic (MD) simulation further revealed that surface potential brought a significant difference in the relative distance between RGD and synergy PHSRN sites of adsorbed FN, resulting in a distinct integrin-FN binding state. These results suggest that the full binding of integrin α5β1 with both RGD and PHSRN sites of FN possesses a strong ability to activate osteogenic signaling pathway. This work sheds light on the underlying mechanism of osteogenic differentiation behavior on charged material surfaces, and also provides a guidance for designing a reasonable charged surface to enhance osteogenic differentiation.

STATEMENT OF SIGNIFICANCE

The ferroelectric P(VDF-TrFE) films with steady and a wide range of surface potential were designed to understand underlying mechanism of cell-charged surface interaction. The results showed that the charged surface well favored upregulation of osteogenic differentiation of MC3T3-E1 cells, and more importantly, a highest level occurred on the film with a moderate surface potential. Experiments and molecular dynamics simulation demonstrated that the surface potential could govern fibronectin conformation and then the integrin-fibronectin binding. We propose that a full binding state of integrin α5β1 with fibronectin induces effective activation of integrin-mediated FAK/ERK signaling pathway to upregulate cellular osteogenic differentiation. This work provides a guidance for designing a reasonable charged surface to enhance osteogenic differentiation.

The fibrotic tumor stroma

Intratumoral fibrosis results from the deposition of a cross-linked collagen matrix by cancer-associated fibroblasts (CAFs). This type of fibrosis has been shown to exert mechanical forces and create a biochemical milieu that, together, shape intratumoral immunity and influence tumor cell metastatic behavior. In this Review, we present recent evidence that CAFs and tumor cells are regulated by provisional matrix molecules, that metastasis results from a change in the type of stromal collagen cross-link, and that fibrosis and inflammation perpetuate each other through proteolytic and chemotactic mediators released into the tumor stroma. We also discuss aspects of the emerging biology that have potential therapeutic value.

Hydrogels with precisely controlled integrin activation dictate vascular patterning and permeability

Integrin binding to bioengineered hydrogel scaffolds is essential for tissue regrowth and regeneration, yet not all integrin binding can lead to tissue repair. Here, we show that through engineering hydrogel materials to promote α3/α5β1 integrin binding, we can promote the formation of a space-filling and mature vasculature compared with hydrogel materials that promote αvβ3 integrin binding. In vitro, α3/α5β1 scaffolds promoted endothelial cells to sprout and branch, forming organized extensive networks that eventually reached and anastomosed with neighbouring branches. In vivo, α3/α5β1 scaffolds delivering vascular endothelial growth factor (VEGF) promoted non-tortuous blood vessel formation and non-leaky blood vessels by 10 days post-stroke. In contrast, materials that promote αvβ3 integrin binding promoted endothelial sprout clumping in vitro and leaky vessels in vivo. This work shows that precisely controlled integrin activation from a biomaterial can be harnessed to direct therapeutic vessel regeneration and reduce VEGF-induced vascular permeability in vivo.