Small leucine-rich proteoglycans exhibit unique spatiotemporal expression profiles during cardiac valve development

Fibromodulin facilitates the osteogenic effect of Masquelet's induced membrane by inhibiting the TGF-β/SMAD signaling pathway

Masquelet's induced membrane (IM) technique is a promising treatment strategy for the repair of substantial bone defects. The formation of an IM around polymethylmethacrylate bone cement plays a crucial role in this technique. Several studies have indicated that IMs have bioactivity because they contain abundant blood vessels, a variety of cells, and biological factors. The bioactivity of an IM increases during the initial stages of formation, thereby facilitating bone regeneration and remodeling. Nevertheless, the precise mechanisms underlying the enhancement of IM bioactivity and the promotion of bone regeneration necessitate further investigation. In this study, we successfully developed a Masquelet IM model of critical femur defects in rats. By employing proteomics analysis and biological detection techniques, we identified fibromodulin (FMOD) as a pivotal factor contributing to angiogenesis and the enhanced bioactivity of the IM. A significant increase in angiogenesis and the expression of bioactive factors in the IM was also observed with the upregulation of FMOD expression. Furthermore, this effect is mediated through the inhibition of the transforming growth factor beta (TGF-β)/SMAD signaling pathway. We also demonstrated that administering recombinant human FMOD enhanced osteogenesis in rat bone marrow mesenchymal stem cells and angiogenesis in human umbilical vein endothelial cells in vitro. Furthermore, the negative regulatory effect of the TGF-β signaling pathway was verified. In conclusion, this study provides a novel theoretical basis for the application of IMs in bone-defect reconstruction and explores possible new mechanisms that may play an important role in promoting the bioactivity and osteogenic potential of IMs.

Targeting CD301+ macrophages inhibits endometrial fibrosis and improves pregnancy outcome

Macrophages are a key and heterogeneous cell population involved in endometrial repair and regeneration during the menstrual cycle, but their role in the development of intrauterine adhesion (IUA) and sequential endometrial fibrosis remains unclear. Here, we reported that CD301+ macrophages were significantly increased and showed their most active interaction with profibrotic cells in the endometria of IUA patients compared with the normal endometria by single-cell RNA sequencing, bulk RNA sequencing, and experimental verification. Increasing CD301+ macrophages promoted the differentiation of endometrial stromal cells into myofibroblasts and resulted in extracellular matrix accumulation, which destroyed the physiological architecture of endometrial tissue, drove endometrial fibrosis, and ultimately led to female infertility or adverse pregnancy outcomes. Mechanistically, CD301+ macrophages secreted GAS6 to activate the AXL/NF-κB pathway, upregulating the profibrotic protein synthesis. Targeted deletion of CD301+ macrophages or inhibition of AXL by Bemcentinib blunted the pathology and improved the outcomes of pregnancy in mice, supporting the therapeutic potential of targeting CD301+ macrophages for treating endometrial fibrosis.

Fibromodulin, a Multifunctional Matricellular Modulator

Fibromodulin (FMOD) is an archetypal member of the class II small leucine-rich proteoglycan family. By directly binding to extracellular matrix structural components, such as collagen and lysyl oxidase, FMOD regulates collagen cross-linking, packing, assembly, and fibril architecture via a multivalent interaction. Meanwhile, as a pluripotent molecule, FMOD acts as a ligand of various cytokines and growth factors, especially those belonging to the transforming growth factor (TGF) β superfamily, by interacting with the corresponding signaling molecules involved in cell adhesion, spreading, proliferation, migration, invasion, differentiation, and metastasis. Consequently, FMOD exhibits promigratory, proangiogenic, anti-inflammatory, and antifibrogenic properties and plays essential roles in cell fate determination and maturation, progenitor cell recruitment, and tissue regeneration. The multifunctional nature of FMOD thus enables it to be a promising therapeutic agent for a broad repertoire of diseases, including but not limited to arthritis, temporomandibular joint disorders, caries, and fibrotic diseases among different organs, as well as to be a regenerative medicine candidate for skin, muscle, and tendon injuries. Moreover, FMOD is also considered a marker for tumor diagnosis and prognosis prediction and a potential target for cancer treatment. Furthermore, FMOD itself is sufficient to reprogram somatic cells into a multipotent state, creating a safe and efficient cell source for various tissue reconstructions and thus opening a new avenue for regenerative medicine. This review focuses on the recent preclinical efforts bringing FMOD research and therapies to the forefront. In addition, a contemporary understanding of the mechanism underlying FMOD's function, particularly its interaction with TGFβ superfamily members, is also discussed at the molecular level to aid the discovery of novel FMOD-based treatments.

Excess Provisional Extracellular Matrix: A Common Factor in Bicuspid Aortic Valve Formation

A bicuspid aortic valve (BAV) is the most common cardiac malformation, found in 0.5% to 2% of the population. BAVs are present in approximately 50% of patients with severe aortic stenosis and are an independent risk factor for aortic aneurysms. Currently, there are no therapeutics to treat BAV, and the human mutations identified to date represent a relatively small number of BAV patients. However, the discovery of BAV in an increasing number of genetically modified mice is advancing our understanding of molecular pathways that contribute to BAV formation. In this study, we utilized the comparison of BAV phenotypic characteristics between murine models as a tool to advance our understanding of BAV formation. The collation of murine BAV data indicated that excess versican within the provisional extracellular matrix (P-ECM) is a common factor in BAV development. While the percentage of BAVs is low in many of the murine BAV models, the remaining mutant mice exhibit larger and more amorphous tricuspid AoVs, also with excess P-ECM compared to littermates. The identification of common molecular characteristics among murine BAV models may lead to BAV therapeutic targets and biomarkers of disease progression for this highly prevalent and heterogeneous cardiovascular malformation.

Spatiotemporal single-cell RNA sequencing of developing chicken hearts identifies interplay between cellular differentiation and morphogenesis

Single-cell RNA sequencing is a powerful tool to study developmental biology but does not preserve spatial information about tissue morphology and cellular interactions. Here, we combine single-cell and spatial transcriptomics with algorithms for data integration to study the development of the chicken heart from the early to late four-chambered heart stage. We create a census of the diverse cellular lineages in developing hearts, their spatial organization, and their interactions during development. Spatial mapping of differentiation transitions in cardiac lineages defines transcriptional differences between epithelial and mesenchymal cells within the epicardial lineage. Using spatially resolved expression analysis, we identify anatomically restricted expression programs, including expression of genes implicated in congenital heart disease. Last, we discover a persistent enrichment of the small, secreted peptide, thymosin beta-4, throughout coronary vascular development. Overall, our study identifies an intricate interplay between cellular differentiation and morphogenesis.

The Non-Fibrillar Side of Fibrosis: Contribution of the Basement Membrane, Proteoglycans, and Glycoproteins to Myocardial Fibrosis

The extracellular matrix (ECM) provides structural support and a microenvironmentfor soluble extracellular molecules. ECM is comprised of numerous proteins which can be broadly classified as fibrillar (collagen types I and III) and non-fibrillar (basement membrane, proteoglycans, and glycoproteins). The basement membrane provides an interface between the cardiomyocytes and the fibrillar ECM, while proteoglycans sequester soluble growth factors and cytokines. Myocardial fibrosis was originally only linked to accumulation of fibrillar collagens, but is now recognized as the expansion of the ECM including the non-fibrillar ECM proteins. Myocardial fibrosis can be reparative to replace the lost myocardium (e.g., ischemic injury or myocardial infarction), or can be reactive resulting from pathological activity of fibroblasts (e.g., dilated or hypertrophic cardiomyopathy). Contribution of fibrillar collagens to fibrosis is well studied, but the role of the non-fibrillar ECM proteins has remained less explored. In this article, we provide an overview of the contribution of the non-fibrillar components of the extracellular space of the heart to highlight the potential significance of these molecules in fibrosis, with direct evidence for some, although not all of these molecules in their direct contribution to fibrosis.

Degenerative aortic valve disease and diabetes: Implications for a link between proteoglycans and diabetic disorders in the aortic valve

Degenerative aortic valve disease in combination with diabetes is an increasing burden worldwide. There is growing evidence that particularly small leucine-rich proteoglycans are involved in the development of degenerative aortic valve disease. Nevertheless, the role of these molecules in this disease in the course of diabetes has not been elucidated in detail and previous studies remain controversial. Therefore, the aim of this study is to broaden the knowledge about small leucine-rich proteoglycans in degenerative aortic valve disease and the influence of diabetes and hyperglycaemia on aortic valves and valvular interstitial cells is examined. Analyses were performed using reverse-transcription polymerase chain reaction, Western blot, enzyme-linked immunosorbent assay, (immuno)histology and colorimetric assays. We could show that biglycan, but not decorin and lumican, is upregulated in degenerated human aortic valve cusps. Subgroup analysis reveals that upregulation of biglycan is stage-dependent. In vivo, loss of biglycan leads to stage-dependent calcification and also to migratory effects on interstitial cells within the extracellular matrix. In late stages of degenerative aortic valve disease, diabetes increases the expression of biglycan in aortic valves. In vitro, the combinations of hyperglycaemic with pro-degenerative conditions lead to an upregulation of biglycan. In conclusion, biglycan represents a potential link between degenerative aortic valve disease and diabetes.

Surface functionalization of electrospun scaffolds using recombinant human decorin attracts circulating endothelial progenitor cells

Decorin (DCN) is an important small leucine-rich proteoglycan present in the extracellular matrix (ECM) of many organs and tissues. Endothelial progenitor cells (EPCs) are able to interact with the surrounding ECM and bind to molecules such as DCN. Here, we recombinantly produced full-length human DCN under good laboratory practice (GLP) conditions, and after detailed immunological characterization, we investigated its potential to attract murine and human EPCs (mEPCs and hECFCs). Electrospun polymeric scaffolds were coated with DCN or stromal cell-derived factor-1 (SDF-1α) and were then dynamically cultured with both cell types. Cell viability was assessed via imaging flow cytometry. The number of captured cells was counted and compared with the non-coated controls. To characterize cell-scaffold interactions, immunofluorescence staining and scanning electron microscopy analyses were performed. We identified that DCN reduced T cell responses and attracted innate immune cells, which are responsible for ECM remodeling. A significantly higher number of EPCs attached on DCN- and SDF-1α-coated scaffolds, when compared with the uncoated controls. Interestingly, DCN showed a higher attractant effect on hECFCs than SDF-1α. Here, we successfully demonstrated DCN as promising EPC-attracting coating, which is particularily interesting when aiming to generate off-the-shelf biomaterials with the potential of in vivo cell seeding.

Development of myotendinous-like junctions that anchor cardiac valves requires fibromodulin and lumican

BACKGROUND

There are many patients that exhibit connective tissue related cardiac malformations but do not have mutations in collagen genes. The Small Leucine Rich Proteoglycans (SLRP) fibromodulin (FMOD) and lumican (LUM) bind collagen and regulate fibril assembly in other biological contexts.

RESULTS

FMOD deficient mice and double deficient FMOD; LUM mice exhibited anomalies in regions where cardiac valve tissue interdigitates with adjacent muscle for support. Ectopic connective and/or myocardial tissue(s) was associated with the more severe cardiac valve anomalies in FMOD; LUM deficient mice. At postnatal day 0 (P0) there was an increase in the mesenchymal cell number in the regions where valve cusps anchor in FMOD; LUM deficient mice compared to WT. The cardiac valve anomalies correlated with the highest levels of FMOD expression in the heart and also where myotendinous junctions (MTJ) components biglycan, collagen type I alpha 1, and collagen type VI, are also localized.

CONCLUSIONS

The postnatal assembly of the collagen-rich ECM in regions where cardiac valves anchor, that we have designated 'myotendinous-like junctions' (MTLJ) requires the SLRPs FMOD and LUM. Moreover, FMOD and LUM may facilitate mesenchymal cell differentiation in late stages of cardiac valve development. Developmental Dynamics 245:1029-1042, 2016. © 2016 Wiley Periodicals, Inc.

Molecular Functions of Glycoconjugates in Autophagy

Glycoconjugates, glycans, carbohydrates, and sugars: these terms encompass a class of biomolecules that are diverse in both form and function ranging from free oligosaccharides, glycoproteins, and proteoglycans, to glycolipids that make up a complex glycan code that impacts normal physiology and disease. Recent data suggest that one mechanism by which glycoconjugates impact physiology is through the regulation of the process of autophagy. Autophagy is a degradative pathway necessary for differentiation, organism development, and the maintenance of cell and tissue homeostasis. In this review, we will highlight what is known about the regulation of autophagy by glycoconjugates focusing on signaling mechanisms from the extracellular surface and the regulatory roles of intracellular glycans. Glycan signaling from the extracellular matrix converges on "master" regulators of autophagy including AMPK and mTORC1, thus impacting their localization, activity, and/or expression. Within the intracellular milieu, gangliosides are constituents of the autophagosome membrane, a subset of proteins composing the autophagic machinery are regulated by glycosylation, and oligosaccharide exposure in the cytosol triggers an autophagic response. The examples discussed provide some mechanistic insights into glycan regulation of autophagy and reveal areas for future investigation.

The small leucine-rich repeat secreted protein Asporin induces eyes in Xenopus embryos through the IGF signalling pathway

Small leucine-rich repeat proteoglycan (SLRP) family proteins play important roles in a number of biological events. Here, we demonstrate that the SLRP family member Asporin (ASPN) plays a crucial role in the early stages of eye development in Xenopus embryos. During embryogenesis, ASPN is broadly expressed in the neuroectoderm of the embryo. Overexpression of ASPN causes the induction of ectopic eyes. By contrast, blocking ASPN function with a morpholino oligonucleotide (ASPN-MO) inhibits eye formation, indicating that ASPN is an essential factor for eye development. Detailed molecular analyses revealed that ASPN interacts with insulin growth factor receptor (IGFR) and is essential for activating the IGF receptor-mediated intracellular signalling pathway. Moreover, ASPN perturbed the Wnt, BMP and Activin signalling pathways, suggesting that ASPN thereby creates a favourable environment in which the IGF signal can dominate. ASPN is thus a novel secreted molecule essential for eye induction through the coordination of multiple signalling pathways.

Histone Deacetylase 3 Coordinates Deacetylase-independent Epigenetic Silencing of Transforming Growth Factor-β1 (TGF-β1) to Orchestrate Second Heart Field Development

About two-thirds of human congenital heart disease involves second heart field-derived structures. Histone-modifying enzymes, histone deacetylases (HDACs), regulate the epigenome; however, their functions within the second heart field remain elusive. Here we demonstrate that histone deacetylase 3 (HDAC3) orchestrates epigenetic silencing of Tgf-β1, a causative factor in congenital heart disease pathogenesis, in a deacetylase-independent manner to regulate development of second heart field-derived structures. In murine embryos lacking HDAC3 in the second heart field, increased TGF-β1 bioavailability is associated with ascending aortic dilatation, outflow tract malrotation, overriding aorta, double outlet right ventricle, aberrant semilunar valve development, bicuspid aortic valve, ventricular septal defects, and embryonic lethality. Activation of TGF-β signaling causes aberrant endothelial-to-mesenchymal transition and altered extracellular matrix homeostasis in HDAC3-null outflow tracts and semilunar valves, and pharmacological inhibition of TGF-β rescues these defects. HDAC3 recruits components of the PRC2 complex, methyltransferase EZH2, EED, and SUZ12, to the NCOR complex to enrich trimethylation of Lys-27 on histone H3 at the Tgf-β1 regulatory region and thereby maintains epigenetic silencing of Tgf-β1 specifically within the second heart field-derived mesenchyme. Wild-type HDAC3 or catalytically inactive HDAC3 expression rescues aberrant endothelial-to-mesenchymal transition and epigenetic silencing of Tgf-β1 in HDAC3-null outflow tracts and semilunar valves. These findings reveal that epigenetic dysregulation within the second heart field is a predisposing factor for congenital heart disease.

Cross Talk between NOTCH Signaling and Biomechanics in Human Aortic Valve Disease Pathogenesis

Aortic valve disease is a burgeoning public health problem associated with significant mortality. Loss of function mutations in NOTCH1 cause bicuspid aortic valve (BAV) and calcific aortic valve disease. Because calcific nodules manifest on the fibrosa side of the cusp in low fluidic oscillatory shear stress (OSS), elucidating pathogenesis requires approaches that consider both molecular and mechanical factors. Therefore, we examined the relationship between NOTCH loss of function (LOF) and biomechanical indices in healthy and diseased human aortic valve interstitial cells (AVICs). An orbital shaker system was used to apply cyclic OSS, which mimics the cardiac cycle and hemodynamics experienced by AVICs in vivo. NOTCH LOF blocked OSS-induced cell alignment in human umbilical vein endothelial cells (HUVECs), whereas AVICs did not align when subjected to OSS under any conditions. In healthy AVICs, OSS resulted in decreased elastin (ELN) and α-SMA (ACTA2). NOTCH LOF was associated with similar changes, but in diseased AVICs, NOTCH LOF combined with OSS was associated with increased α-SMA expression. Interestingly, AVICs showed relatively higher expression of NOTCH2 compared to NOTCH1. Biomechanical interactions between endothelial and interstitial cells involve complex NOTCH signaling that contributes to matrix homeostasis in health and disorganization in disease.

Advances in the treatment of aortic valve disease: is it time for companion diagnostics?

PURPOSE OF REVIEW

Aortic valve disease (AVD) is a growing public health problem, and the pathogenesis underlying AVD is complex. The lack of durable bioprostheses and pharmacologic therapies remain central needs in care. The purpose of this review is to highlight recent clinical studies that impact the care of children with AVD and is to explore ongoing translational research efforts.

RECENT FINDINGS

Clinical studies have evaluated the durability of bioprosthetics and surgical strategies, tested statins during early disease, and identified new predictive biomarkers. Large animal models have demonstrated the effectiveness of a novel bioprosthetic scaffold. Mouse models of latent AVD have advanced our ability to elucidate natural history and perform preclinical studies that test new treatments in the context of early disease.

SUMMARY

Current priorities for AVD patients include identifying new pharmacologic treatments and developing durable bioprostheses. Multidisciplinary efforts are needed that bridge pediatric and adult programs, and bring together different types of expertise and leverage network and consortium resources. As our understanding of the underlying complex genetics is better defined, companion diagnostics may transform future clinical trials and ultimately improve the care of patients with AVD by promoting personalized medicine and early intervention.