Fibulin-4 exerts a dual role in LTBP-4L-mediated matrix assembly and function.

Elastogenesis is a hierarchical process by which cells form functional elastic fibers, providing elasticity and the ability to regulate growth factor bioavailability in tissues, including blood vessels, lung, and skin. This process requires accessory proteins, including fibulin-4 and -5, and latent TGF binding protein (LTBP)-4. Our data demonstrate mechanisms in elastogenesis, focusing on the interaction and functional interdependence between fibulin-4 and LTBP-4L and its impact on matrix deposition and function. We show that LTBP-4L is not secreted in the expected extended structure based on its domain composition, but instead adopts a compact conformation. Interaction with fibulin-4 surprisingly induced a conformational switch from the compact to an elongated LTBP-4L structure. This conversion was only induced by fibulin-4 multimers associated with increased avidity for LTBP-4L; fibulin-4 monomers were inactive. The fibulin-4-induced conformational change caused functional consequences in LTBP-4L in terms of binding to other elastogenic proteins, including fibronectin and fibrillin-1, and of LTBP-4L assembly. A transient exposure of LTBP-4L with fibulin-4 was sufficient to stably induce conformational and functional changes; a stable complex was not required. These data define fibulin-4 as a molecular extracellular chaperone for LTBP-4L. The altered LTBP-4L conformation also promoted elastogenesis, but only in the presence of fibulin-4, which is required to escort tropoelastin onto the extended LTBP-4L molecule. Altogether, this study provides a dual mechanism for fibulin-4 in 1) inducing a stable conformational and functional change in LTBP-4L, and 2) promoting deposition of tropoelastin onto the elongated LTBP-4L.

Roles of fibronectin isoforms in neonatal vascular development and matrix integrity.

Fibronectin (FN) exists in two forms-plasma FN (pFN) and cellular FN (cFN). Although the role of FN in embryonic blood vessel development is well established, its function and the contribution of individual isoforms in early postnatal vascular development are poorly understood. Here, we employed a tamoxifen-dependent cFN inducible knockout (cFN iKO) mouse model to study the consequences of postnatal cFN deletion in smooth muscle cells (SMCs), the major cell type in the vascular wall. Deletion of cFN influences collagen deposition but does not affect life span. Unexpectedly, pFN translocated to the aortic wall in the cFN iKO and in control mice, possibly rescuing the loss of cFN. Postnatal pFN deletion did not show a histological aortic phenotype. Double knockout (dKO) mice lacking both, cFN in SMCs and pFN, resulted in postnatal lethality. These data demonstrate a safeguard role of pFN in vascular stability and the dispensability of the individual FN isoforms in postnatal vascular development. Complete absence of FNs in the dKOs resulted in a disorganized tunica media of the aortic wall. Matrix analysis revealed common and differential roles of the FN isoforms in guiding the assembly/deposition of elastogenic extracellular matrix (ECM) proteins in the aortic wall. In addition, we determined with two cell culture models that that the two FN isoforms acted similarly in supporting matrix formation with a greater contribution from cFN. Together, these data show that pFN exerts a critical role in safeguarding vascular organization and health, and that the two FN isoforms function in an overlapping as well as distinct manner to maintain postnatal vascular matrix integrity.

Mutations in Fibronectin Cause a Subtype of Spondylometaphyseal Dysplasia with "Corner Fractures".

Fibronectin is a master organizer of extracellular matrices (ECMs) and promotes the assembly of collagens, fibrillin-1, and other proteins. It is also known to play roles in skeletal tissues through its secretion by osteoblasts, chondrocytes, and mesenchymal cells. Spondylometaphyseal dysplasias (SMDs) comprise a diverse group of skeletal dysplasias and often manifest as short stature, growth-plate irregularities, and vertebral anomalies, such as scoliosis. By comparing the exomes of individuals with SMD with the radiographic appearance of "corner fractures" at metaphyses, we identified three individuals with fibronectin (FN1) variants affecting highly conserved residues. Furthermore, using matching tools and the SkelDys emailing list, we identified other individuals with de novo FN1 variants and a similar phenotype. The severe scoliosis in most individuals and rare developmental coxa vara distinguish individuals with FN1 mutations from those with classical Sutcliffe-type SMD. To study functional consequences of these FN1 mutations on the protein level, we introduced three disease-associated missense variants (p.Cys87Phe [c.260G>T], p.Tyr240Asp [c.718T>G], and p.Cys260Gly [c.778T>G]) into a recombinant secreted N-terminal 70 kDa fragment (rF70K) and the full-length fibronectin (rFN). The wild-type rF70K and rFN were secreted into the culture medium, whereas all mutant proteins were either not secreted or secreted at significantly lower amounts. Immunofluorescence analysis demonstrated increased intracellular retention of the mutant proteins. In summary, FN1 mutations that cause defective fibronectin secretion are found in SMD, and we thus provide additional evidence for a critical function of fibronectin in cartilage and bone.

Mutant p53 Exploits Enhancers to Elevate Immunosuppressive Chemokine Expression and Impair Immune Checkpoint Inhibitors in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer without effective treatments. It is characterized by activating KRAS mutations and p53 alterations. However, how these mutations dysregulate cancer-cell-intrinsic gene programs to influence the immune landscape of the tumor microenvironment (TME) remains poorly understood. Here, we show that p53R172H establishes an immunosuppressive TME, diminishes the efficacy of immune checkpoint inhibitors (ICIs), and enhances tumor growth. Our findings reveal that the upregulation of the immunosuppressive chemokine Cxcl1 mediates these pro-tumorigenic functions of p53R172H. Mechanistically, we show that p53R172H associates with the distal enhancers of the Cxcl1 gene, increasing enhancer activity and Cxcl1 expression. p53R172H occupies these enhancers in an NF-κB-pathway-dependent manner, suggesting NF-κB's role in recruiting p53R172H to the Cxcl1 enhancers. Our work uncovers how a common mutation in a tumor-suppressor transcription factor appropriates enhancers, stimulating chemokine expression and establishing an immunosuppressive TME that diminishes ICI efficacy in PDAC.

Lymphatic muscle cells are unique cells that undergo aging induced changes.

Lymphatic muscle cells (LMCs) within the wall of collecting lymphatic vessels exhibit tonic and autonomous phasic contractions, which drive active lymph transport to maintain tissue-fluid homeostasis and support immune surveillance. Damage to LMCs disrupts lymphatic function and is related to various diseases. Despite their importance, knowledge of the transcriptional signatures in LMCs and how they relate to lymphatic function in normal and disease contexts is largely missing. We have generated a comprehensive transcriptional single-cell atlas-including LMCs-of collecting lymphatic vessels in mouse dermis at various ages. We identified genes that distinguish LMCs from other types of muscle cells, characterized the phenotypical and transcriptomic changes in LMCs in aged vessels, and uncovered a pro-inflammatory microenvironment that suppresses the contractile apparatus in advanced-aged LMCs. Our findings provide a valuable resource to accelerate future research for the identification of potential drug targets on LMCs to preserve lymphatic vessel function as well as supporting studies to identify genetic causes of primary lymphedema currently with unknown molecular explanation.

Addition of Losartan to FOLFIRINOX and Chemoradiation Reduces Immunosuppression-Associated Genes, Tregs, and FOXP3+ Cancer Cells in Locally Advanced Pancreatic Cancer.

PURPOSE: Adding losartan (LOS) to FOLFIRINOX (FFX) chemotherapy followed by chemoradiation (CRT) resulted in 61% R0 surgical resection in our phase II trial in patients with locally advanced pancreatic cancer (LAPC). Here we identify potential mechanisms of benefit by assessing the effects of neoadjuvant LOS on the tumor microenvironment. EXPERIMENTAL DESIGN: We performed a gene expression and immunofluorescence (IF) analysis using archived surgical samples from patients treated with LOS+FFX+CRT (NCT01821729), FFX+CRT (NCT01591733), or surgery upfront, without any neoadjuvant therapy. We also conducted a longitudinal analysis of multiple biomarkers in the plasma of treated patients. RESULTS: In comparison with FFX+CRT, LOS+FFX+CRT downregulated immunosuppression and pro-invasion genes. Overall survival (OS) was associated with dendritic cell (DC) and antigen presentation genes for patients treated with FFX+CRT, and with immunosuppression and invasion genes or DC- and blood vessel-related genes for those treated with LOS+FFX+CRT. Furthermore, LOS induced specific changes in circulating levels of IL-8, sTie2, and TGF-ß. IF revealed significantly less residual disease in lesions treated with LOS+FFX+CRT. Finally, patients with a complete/near complete pathologic response in the LOS+FFX+CRT-treated group had reduced CD4+FOXP3+ regulatory T cells (Tregs), fewer immunosuppressive FOXP3+ cancer cells (C-FOXP3), and increased CD8+ T cells in pancreatic ductal adenocarcinoma lesions. CONCLUSIONS: Adding LOS to FFX+CRT reduced pro-invasion and immunosuppression-related genes, which were associated with improved OS in patients with LAPC. Lesions from responders in the LOS+FFX+CRT-treated group had reduced Tregs, decreased C-FOXP3 and increased CD8+ T cells. These findings suggest that LOS may potentiate the benefit of FFX+CRT by reducing immunosuppression.

Quantification of Extracellular Matrix Fiber Systems Related to ADAMTS Proteins.

ADAMTS (a disintegrin-like and metalloprotease domain with thrombospondin type 1 motifs) proteins regulate tissue homeostasis and extracellular matrix (ECM)-related pathogenesis. Some ADAMTS proteins interact with or process multiple ECM proteins, including fibrillins, fibronectin, and collagens. Therefore, characterization and quantification of these ECM fiber systems is essential to understand their functional relationship with ADAMTS proteins. Here we describe unbiased methods to quantify various aspects of ADAMTS-related ECM fiber systems in cell culture and in tissues. We focus on cell counting, overall fiber intensity, fiber length, and focal adhesion analysis in cell culture, and on the quantification of immunohistochemical and immunofluorescent tissue sections. We use ImageJ/Fiji, a widely used Java-based open source software which provides efficient and customizable quantification methods for microscopy images.

The Fibrillin-1 RGD Integrin Binding Site Regulates Gene Expression and Cell Function through microRNAs.

Fibrillins are the major components of microfibrils in the extracellular matrix of elastic and non-elastic tissues. Fibrillin-1 contains one evolutionarily conserved RGD sequence that mediates cell-matrix interactions through cell-surface integrins. Here, we present a novel paradigm how extracellular fibrillin-1 controls cellular function through integrin-mediated microRNA regulation. Comparative mRNA studies by global microarray analysis identified growth factor activity, actin binding and integrin binding as the most important functional groups that are regulated upon fibrillin-1 binding to dermal fibroblasts. Many of these mRNAs are targets of miRNAs that were identified when RNA from the fibrillin-1-ligated fibroblasts was analyzed by a miRNA microarray. The expression profile was specific to fibrillin-1 since interaction with fibronectin displayed a partially distinct profile. The importance of selected miRNAs for the regulation of the identified mRNAs was suggested by bioinformatics prediction and the interactions between miRNAs and mRNAs were experimentally validated. Functionally, we show that miR-503 controls p-Smad2-dependent TGF-ß signaling, and that miR-612 and miR-3185 are involved in the focal adhesion formation regulated by fibrillin-1. In conclusion, we demonstrate that fibrillin-1 interaction with fibroblasts regulates miRNA expression profiles which in turn control critical cell functions.

Increasing Cell Seeding Density Improves Elastin Expression and Mechanical Properties in Collagen Gel-Based Scaffolds Cellularized with Smooth Muscle Cells.

Vascular tissue engineering combines cells with scaffold materials in vitro aiming the development of physiologically relevant vascular models. For natural scaffolds such as collagen gels, where cells can be mixed with the material solution before gelation, cell seeding density is a key parameter that can affect extracellular matrix deposition and remodeling. Nonetheless, this parameter is often overlooked and densities sensitively lower than those of native tissues, are usually employed. Herein, the effect of seeding density on the maturation of tubular collagen gel-based scaffolds cellularized with smooth muscle cells is investigated. The compaction, the expression, and deposition of key vascular proteins and the resulting mechanical properties of the constructs are evaluated up to 1 week of maturation. Results show that increasing cell seeding density accelerates cell-mediated gel compaction, enhances elastin expression (more than sevenfold increase at the highest density, Day 7) and finally improves the overall mechanical properties of constructs. Of note, the tensile equilibrium elastic modulus, evaluated by stress-relaxation tests, reach values comparable to native arteries for the highest cell density, after a 7-day maturation. Altogether, these results show that higher cell seeding densities promote the rapid maturation of collagen gel-based vascular constructs toward structural and mechanical properties better mimicking native arteries.

Fibulin-4 deficiency differentially affects cytoskeleton structure and dynamics as well as TGFß signaling.

Fibulin-4 is an extracellular matrix (ECM) protein essential for elastogenesis and mutations in this protein lead to aneurysm formation. In this study, we isolated vascular smooth muscle cells (VSMCs) from mice with reduced fibulin-4 protein expression (Fibulin-4R/R) and from mice with a smooth muscle cell specific deletion of the Fibulin-4 gene (Fibulin-4f/-/SM22Cre+). We subsequently analyzed and compared the molecular consequences of reduced Fibulin-4 expression versus total ablation of Fibulin-4 expression with regard to effects on the SMC specific contractile machinery, cellular migration and TGFß signaling. Analysis of the cytoskeleton showed that while Fibulin-4f/-/SM22Cre+ VSMCs lack smooth muscle actin (SMA) fibers, Fibulin-4R/R VSMCs were able to form SMA fibers. Furthermore, Fibulin-4f/-/SM22Cre+ VSMCs showed a decreased pCofilin to Cofilin ratio, suggesting increased actin depolymerization, while Fibulin-4R/R VSMCs did not display this decrease. Yet, both Fibulin-4 mutant VSMCs showed decreased migration. We found increased activation of TGFß signaling in Fibulin-4R/R VSMCs. However, TGFß signaling was not increased in Fibulin-4f/-/SM22Cre+ VSMCs. From these results we conclude that both reduction and absence of Fibulin-4 leads to structural and functional impairment of the SMA cytoskeleton. However, while reduced levels of Fibulin-4 result in increased TGFß activation, complete absence of Fibulin-4 does not result in increased TGFß activation. Since both mouse models show thoracic aortic aneurysm formation, we conclude that not only hampered TGFß signaling, but also SMA cytoskeleton dynamics play an important role in aortic aneurysmal disease.

Fibrillins.

Fibrillins are one of the major components of supramolecular fibrous structures in the extracellular matrix of elastic and nonelastic tissues, termed microfibrils. Microfibrils provide tensile strength in nonelastic tissues and scaffolds for the assembly of tropoelastin in elastic tissues, and act a regulator of growth factor bioavailability and activity in connective tissues. Mutations in fibrillins lead to a variety of connective tissue disorders including Marfan syndrome, stiff skin syndrome, dominant Weill-Marchesani syndrome, and others. Therefore, fibrillins are frequently studied to understand the pathophysiology of these diseases and to identify effective treatment strategies. Extraction of endogenous microfibrils from cells and tissues can aid in obtaining structural insights of microfibrils. Recombinant production of fibrillins is an important tool which can be utilized to study the properties of normal fibrillins and the consequences of disease causing mutations. Other means of studying the role of fibrillins in the context of various physiological settings is by knocking down the mRNA expression and analyzing its downstream consequences. It is also important to study the interactome of fibrillins by protein-protein interactions, which can be derailed in pathological situations. Interacting proteins can affect the assembly of fibrillins in cells and tissues or can affect the levels of growth factors in the matrix. This chapter describes important techniques in the field that facilitate answering relevant questions of fibrillin biology and pathophysiology.

Fibronectin promotes elastin deposition, elasticity and mechanical strength in cellularised collagen-based scaffolds.

One of the tightest bottlenecks in vascular tissue engineering (vTE) is the lack of strength and elasticity of engineered vascular wall models caused by limited elastic fiber deposition. In this study, flat and tubular collagen gel-based scaffolds were cellularised with vascular smooth muscle cells (SMCs) and supplemented with human plasma fibronectin (FN), a known master organizer of several extracellular matrix (ECM) fiber systems. The consequences of FN on construct maturation was investigated in terms of geometrical contraction, viscoelastic mechanical properties and deposition of core elastic fiber proteins. FN was retained in the constructs and promoted deposition of elastin by SMCs as well as of several proteins required for elastogenesis such as fibrillin-1, lysyl oxidase, fibulin-4 and latent TGF-ß binding protein-4. Notably, gel contraction, tensile equilibrium elastic modulus and elasticity were strongly improved in tubular engineered tissues, approaching the behaviour of native arteries. In conclusion, this study demonstrates that FN exerts pivotal roles in directing SMC-mediated remodeling of scaffolds toward the production of a physiological-like, elastin-containing ECM with excellent mechanical properties. The developed FN-supplemented systems are promising for tissue engineering applications where the generation of mature elastic tissue is desired and represent valuable advanced in vitro models to investigate elastogenesis.

Fibronectin-targeted drug delivery in cancer.

Fibronectin is an extracellular matrix protein with pivotal physiological and pathological functions in development and adulthood. Alternative splicing of the precursor mRNA, produced from the single copy fibronectin gene, occurs at three sites coding for the EDA, EDB and IIICS domains. Fibronectin isoforms comprising the EDA or EDB domains are known as oncofetal forms due to their developmental importance and their re-expression in tumors, contrasting with restricted presence in normal adult tissues. These isoforms are also recognized as important markers of angiogenesis, a crucial physiological process in development and required by tumor cells in cancer progression. Attributed to this feature, EDA and EDB domains have been extensively used for the targeted delivery of cytokines, cytotoxic agents, chemotherapy drugs and radioisotopes to fibronectin-expressing tumors to exert therapeutic effects on primary cancers and metastatic lesions. In addition to drug delivery, the EDA and EDB domains of fibronectin have also been utilized to develop imaging strategies for tumor tissues. Furthermore, EDA and EDB based vaccines seem to be promising for the treatment and prevention of certain cancer types. In this review, we will summarize recent advances in fibronectin EDA and EDB-based therapeutic strategies developed to treat cancer.

A planar model of the vessel wall from cellularized-collagen scaffolds: focus on cell-matrix interactions in mono-, bi- and tri-culture models.

The acquisition of new thorough knowledge on the interactions existing between vascular cells would represent a step forward in the engineering of vascular tissues. In this light, herein we designed a physiological-like tri-culture in vitro vascular wall model using a planar cellularized collagen gel as the scaffold. The model can be obtained in 24 h and features multi-layered hierarchical organization composed of a fibroblast-containing adventitia-like layer, a media-like layer populated by smooth muscle cells and an intima-like endothelial cell monolayer. After 7 days of static culture, the compaction of the collagen matrix by the vascular cells was achieved, and the deposition of the vascular extracellular matrix components fibronectin, fibrillin-1 and tropoelastin was observed. The blood-compatible functionality of the endothelial cell monolayer was demonstrated by a blood clotting assay: after 7 days of maturation, clotting was prevented on the endothelialized constructs (more than 80% free hemoglobin maintained after 60 min of blood contact) but not at all on non-endothelialized ones (less than 20% free hemoglobin). In addition, western blotting results suggested that in the tri-culture model the loss of smooth muscle cell phenotype was delayed compared to what was observed in the mono-culture model, finally resulting in a behaviour more similar to the in vivo conditions. Overall, our findings indicate that this in vitro model has the potential to be used as an advanced system to examine vascular cell behavioural interactions, as well as for drug testing and the investigation of physiological and pathological processes.

Utility of saliva and hair follicles in donor selection for hematopoietic stem cell transplantation and chimerism monitoring.

Selection of an HLA identical donor is a critical pre-requisite for successful hematopoietic stem cell transplantation (HSCT). Most transplant centers utilize blood as the most common source of DNA for HLA testing. However, obtaining blood through phlebotomy is often challenging in patients with conditions like severe leucopenia or hemophilia, pediatric and elderly patients. We have used a simple in-house protocol and shown that HLA genotypes obtained on DNA extracted from saliva or hair are concordant with blood and hence can be used for selection of donors for HSCT or organ transplantation. Similarly, for post-HSCT chimerism monitoring, non-availability of pre-transplant DNA samples poses a major limitation of reference STR fingerprints. This study shows that DNA obtained post-HSCT from hair follicles can be used to generate pre-transplant patient specific fingerprints while the STR profiles obtained in saliva samples cannot as these display a mixed state of chimerism.