Glypican-6 stimulates intestinal elongation by simultaneously regulating Hedgehog and non-canonical Wnt signaling

Combined genetic-pharmacologic inactivation of tightly linked ADAMTS proteases in temporally specific windows uncovers distinct roles for versican proteolysis and glypican-6 in cardiac development

Extracellular matrix remodeling mechanisms are understudied in cardiac development and congenital heart defects. We show that matrix-degrading metalloproteases ADAMTS1 and ADAMTS5, are extensively co-expressed during mouse cardiac development. The mouse mutants of each gene have mild cardiac anomalies, however, their combined genetic inactivation to elicit cooperative roles is precluded by tight gene linkage. Therefore, we coupled Adamts1 inactivation with pharmacologic ADAMTS5 blockade to uncover stage-specific cooperative roles and investigated their potential substrates in mouse cardiac development. ADAMTS5 blockade was achieved in Adamts1 null mouse embryos using an activity-blocking monoclonal antibody during distinct developmental windows spanning myocardial compaction or cardiac septation and outflow tract rotation. Synchrotron imaging, RNA in situ hybridization, immunofluorescence microscopy and electron microscopy were used to determine the impact on cardiac development and compared to Gpc6 and ADAMTS-cleavage resistant versican mutants. Mass spectrometry-based N-terminomics was used to seek relevant substrates. Combined inactivation of ADAMTS1 and ADAMTS5 prior to 12.5 days of gestation led to dramatic accumulation of versican-rich cardiac jelly and inhibited formation of compact and trabecular myocardium, which was also observed in mice with ADAMTS cleavage-resistant versican. Combined inactivation after 12.5 days impaired outflow tract development and ventricular septal closure, generating a tetralogy of Fallot-like defect. N-terminomics of combined ADAMTS knockout and control hearts identified a cleaved glypican-6 peptide only in the controls. ADAMTS1 and ADAMTS5 expression in cells was associated with specific glypican-6 cleavages. Paradoxically, combined ADAMTS1 and ADAMTS5 inactivation reduced cardiac glypican-6 and outflow tract Gpc6 transcription. Notably, Gpc6-/- hearts demonstrated similar rotational defects as combined ADAMTS inactivated hearts and both had reduced hedgehog signaling. Thus, versican proteolysis in cardiac jelly at the canonical Glu441-Ala442 site is cooperatively mediated by ADAMTS1 and ADAMTS5 and required for proper ventricular cardiomyogenesis, whereas, reduced glypican-6 after combined ADAMTS inactivation impairs hedgehog signaling, leading to outflow tract malrotation.

Hippo cell signaling and HS-proteoglycans regulate tissue form and function, age-dependent maturation, extracellular matrix remodeling, and repair

This review examined how Hippo cell signaling and heparan sulfate (HS)-proteoglycans (HSPGs) regulate tissue form and function. Despite being a nonweight-bearing tissue, the brain is regulated by Hippo mechanoresponsive cell signaling pathways during embryonic development. HS-proteoglycans interact with growth factors, morphogens, and extracellular matrix components to regulate development and pathology. Pikachurin and Eyes shut (Eys) interact with dystroglycan to stabilize the photoreceptor axoneme primary cilium and ribbon synapse facilitating phototransduction and neurotransduction with bipolar retinal neuronal networks in ocular vision, the primary human sense. Another HSPG, Neurexin interacts with structural and adaptor proteins to stabilize synapses and ensure specificity of neural interactions, and aids in synaptic potentiation and plasticity in neurotransduction. HSPGs also stabilize the blood-brain barrier and motor neuron basal structures in the neuromuscular junction. Agrin and perlecan localize acetylcholinesterase and its receptors in the neuromuscular junction essential for neuromuscular control. The primary cilium is a mechanosensory hub on neurons, utilized by YES associated protein (YAP)-transcriptional coactivator with PDZ-binding motif (TAZ) Hippo, Hh, Wnt, transforming growth factor (TGF)-β/bone matrix protein (BMP) receptor tyrosine kinase cell signaling. Members of the glypican HSPG proteoglycan family interact with Smoothened and Patched G-protein coupled receptors on the cilium to regulate Hh and Wnt signaling during neuronal development. Control of glycosyl sulfotransferases and endogenous protease expression by Hippo TAZ YAP represents a mechanism whereby the fine structure of HS-proteoglycans can be potentially modulated spatiotemporally to regulate tissue morphogenesis in a similar manner to how Hippo signaling controls sialyltransferase expression and mediation of cell-cell recognition, dysfunctional sialic acid expression is a feature of many tumors.

Extracellular matrix-induced signaling pathways in mesenchymal stem/stromal cells

The extracellular matrix (ECM) is a crucial component of the stem cell microenvironment, or stem-cell niches, and contributes to the regulation of cell behavior and fate. Accumulating evidence indicates that different types of stem cells possess a large variety of molecules responsible for interactions with the ECM, mediating specific epigenetic rearrangements and corresponding changes in transcriptome profile. Signals from the ECM are crucial at all stages of ontogenesis, including embryonic and postnatal development, as well as tissue renewal and repair. The ECM could regulate stem cell transition from a quiescent state to readiness to perceive the signals of differentiation induction (competence) and the transition between different stages of differentiation (commitment). Currently, to unveil the complex networks of cellular signaling from the ECM, multiple approaches including screening methods, the analysis of the cell matrixome, and the creation of predictive networks of protein-protein interactions based on experimental data are used. In this review, we consider the existing evidence regarded the contribution of ECM-induced intracellular signaling pathways into the regulation of stem cell differentiation focusing on mesenchymal stem/stromal cells (MSCs) as well-studied type of postnatal stem cells totally depended on signals from ECM. Furthermore, we propose a system biology-based approach for the prediction of ECM-mediated signal transduction pathways in target cells. Video Abstract.

Heparan sulfate proteoglycans (HSPGs) of the ocular lens

Heparan sulfate proteoglycans (HSPGs) reside in most cells; on their surface, in the pericellular milieu and/or extracellular matrix. In the eye, HSPGs can orchestrate the activity of key signalling molecules found in the ocular environment that promote its development and homeostasis. To date, our understanding of the specific roles played by individual HSPG family members, and the heterogeneity of their associated sulfated HS chains, is in its infancy. The crystalline lens is a relatively simple and well characterised ocular tissue that provides an ideal stage to showcase and model the expression and unique roles of individual HSPGs. Individual HSPG core proteins are differentially localised to eye tissues in a temporal and spatial developmental- and cell-type specific manner, and their loss or functional disruption results in unique phenotypic outcomes for the lens, and other ocular tissues. More recent work has found that different HS sulfation enzymes are also presented in a cell- and tissue-specific manner, and that disruption of these different sulfation patterns affects specific HS-protein interactions. Not surprisingly, these sulfated HS chains have also been reported to be required for lens and eye development, with dysregulation of HS chain structure and function leading to pathogenesis and eye-related phenotypes. In the lens, HSPGs undergo significant and specific changes in expression and function that can drive pathology, or in some cases, promote tissue repair. As master signalling regulators, HSPGs may one day serve as valuable biomarkers, and even as putative targets for the development of novel therapeutics, not only for the eye but for many other systemic pathologies.

Role of Wnt signaling in the maintenance and regeneration of the intestinal epithelium

The intestinal epithelium plays a key role in digestion and protection against external pathogens. This tissue presents a high cellular turnover with the epithelium being completely renewed every 5days, driven by intestinal stem cells (ISCs) residing in the crypt bases. To sustain this dynamic renewal of the intestinal epithelium, the maintenance, proliferation, and differentiation of ISCs must be precisely controlled. One of the central pathways supporting ISC maintenance and dynamics is the Wnt pathway. In this chapter, we examine the role of Wnt signaling in intestinal epithelial homeostasis and tissue regeneration, including mechanisms regulating ISC identity and fine-tuning of Wnt pathway activation. We extensively discuss the contribution of the stem cell niche in maintaining Wnt signaling in the intestinal crypts that support ISC functions. The integration of these findings highlights the complex interplay of multiple niche signals and cellular components sustaining ISC behavior and maintenance, which together supports the immense plasticity of the intestinal epithelium.

Glypican-6 and Glypican-4 stimulate embryonic stomach growth by regulating Hedgehog and noncanonical Wnt signaling

BACKGROUND

Glypicans are a family of proteoglycans that play important roles in embryonic morphogenesis. The mammalian genome contains six glypicans (GPC1 to GPC6). GPC6 and GPC4 are the pair of glypicans that show the highest degree of homology within the family. GPC6-null embryos display bone abnormalities and severely shortened intestines.

RESULTS

We show that GPC6-null embryos display significantly smaller stomachs, and that Hedgehog and noncanonical Wnt signaling are dysregulated in GPC6-null stomachs. Like GPC6, GPC4 is expressed by the developing stomach. However, GPC4-null embryos have normal stomachs. To investigate whether GPC6 and GPC4 display functional overlap in the developing stomach, we crossed GPC4-null mice with GPC6 conditional mutants in which the expression of this glypican is severely reduced in the stomach. Notably, we found that the compound mutants display stomachs that are smaller than those of the GPC6 conditional mutants. We also found that this functional overlap between GPC6 and GPC4 is mediated by the noncanonical Wnt pathway.

CONCLUSION

This study demonstrates that GPC6 stimulates the growth of the embryonic stomach via Wnt and Hh signaling. In addition, we uncovered a Wnt-mediated functional overlap between GPC6 and GPC4 in the developing stomach.

Coreceptor Functions of Cell Surface Heparan Sulfate Proteoglycans

Receptor-ligand interactions play an important role in many biological processes by triggering specific cellular responses. These interactions are frequently regulated by coreceptors that facilitate, alter, or inhibit signaling. Coreceptors work in parallel with other specific and accessory molecules to coordinate receptor-ligand interactions. Cell surface heparan sulfate proteoglycans (HSPGs) function as unique coreceptors because they can bind to many ligands and receptors through their HS and core protein motifs. Cell surface HSPGs are typically expressed in abundance of the signaling receptors and, thus, are capable of mediating the initial binding of ligands to the cell surface. HSPG coreceptors do not possess kinase domains or intrinsic enzyme activities and, for the most part, binding to cell surface HSPGs does not directly stimulate intracellular signaling. Because of these features, cell surface HSPGs primarily function as coreceptors for many receptor-ligand interactions. Given that cell surface HSPGs are widely conserved, they likely serve fundamental functions to preserve basic physiological processes. Indeed, cell surface HSPGs can support specific cellular interactions with growth factors, morphogens, chemokines, extracellular matrix (ECM) components, and microbial pathogens and their secreted virulence factors. Through these interactions, HSPG coreceptors regulate cell adhesion, proliferation, migration and differentiation, and impact the onset, progression, and outcome of pathophysiological processes, such as development, tissue repair, inflammation, infection, and tumorigenesis. This review seeks to provide an overview of the various mechanisms of how cell surface HSPGs function as coreceptors.

The function of Glypicans in the mammalian embryo

Glypicans are proteoglycans that are bound to the outer surface of the plasma membrane by a glycosylphosphatidylinositol anchor. The mammalian genome contains six members of the glypican family (GPC1 to GPC6). Although the degree of sequence homology within the family is rather low, the three-dimensional structure of these proteoglycans is highly conserved. Glypicans are predominantly expressed during embryonic development. Genetic and biochemical studies have shown that glypicans can stimulate or inhibit the signaling pathways triggered by Wnts, Hedgehogs, Fibroblast Growth Factors, and Bone Morphogenetic Proteins. The study of mutant mouse strains demonstrated that glypicans have important functions in the developmental morphogenesis of various organs. In addition, a role of glypicans in synapsis formation has been established. Notably, glypican loss-of-function mutations are the cause of three human inherited syndromes. Recent analysis of glypican compound mutant mice have demonstrated that members of this protein family display redundant functions during embryonic development.

The Glypican-1/HGF/C-Met and Glypican-1/VEGF/VEGFR2 Ternary Complexes Regulate Hair Follicle Angiogenesis

The hair renewal involves changes in the morphology of the hair follicle and its micro-vascularization. In alopecia, the hair cycle is accelerated, resulting in the formation of thinner and shorter hair. In addition, alopecia is associated with a decrease in the micro-vascularization of the hair follicles. In this study, the role of glypicans (GPCs) was analyzed in the regulation of the angiogenesis of human dermal microvascular endothelial cells (HDMEC). The analysis of glypican gene expression showed that GPC1 is the major glypican expressed by human keratinocytes of outer root sheath (KORS), human hair follicle dermal papilla cells (HHFDPC) and HDMEC. KORS were demonstrated to secrete VEGF and HGF. The HDMEC pseudotube formation was induced by KORS conditioned media (KORS_CM). It was totally abrogated after GPC1 siRNA transfection of HDMEC. Moreover, when cleaved by phospholipase C (PLC), GPC1 promotes the proliferation of HDMEC. Finally, GPC1 was shown to interact directly with VEGFR2 or c-Met to regulate angiogenesis induced by the activation of these receptors. Altogether, these results showed that GPC1 is a key regulator of microvascular endothelial cell angiogenesis induced by VEGF and HGF secreted by KORS. Thus, GPC1 might constitute an interesting target to tackle alopecia in dermatology research.

Stem Cells from Human Exfoliated Deciduous teeth Promote Hair Regeneration in Mouse

Stem cells in different types may interact with each other to maintain homeostasis or growth and the interactions are complicated and extensive. There is increasing evidence that mesenchymal-epithelial interactions in early morphogenesis stages of both tooth and hair follicles show many similarities. In order to explore whether stem cells from one tissue could interact with cells from another tissue, a series of experiments were carried out. Here we successfully extracted and identified stem cells from human exfoliated deciduous teeth (SHED) of 8–12 years old kids, and then found that SHED could promote hair regeneration in a mouse model. In vitro, SHED shortened the hair regeneration cycle and promoted the proliferation and aggregation of dermal cells. In vivo, when SHED and skin cells of C57 mice were subcutaneously co-transplanted to nude mice, more hair was formed than skin cells without SHED. To further explore the molecular mechanism, epidermal and dermal cells were freshly extracted and co-cultured with SHED. Then several signaling molecules in hair follicle regeneration were detected and we found that the expression of Sonic Hedgehog (Shh) and Glioma-associated oncogene 1 (Gli1) was up-regulated. It seems that SHED may boost the prosperity of hairs by increase Shh/Gli1 pathway, which brings new perspectives in tissue engineering and damaged tissue repairing.

Heparan sulfate proteoglycan expression in the regenerating zebrafish fin

BACKGROUND

Heparan sulfate proteoglycan (HSPG) expression is found in many animal tissues and regulates growth factor signaling such as of Fibroblast growth factors (Fgf), Wingless/Int (Wnt) and Hedgehog (HH). Glypicans, which are GPI (glycosylphosphatidylinositol)-anchored proteins, and transmembrane-anchored syndecans represent two major HSPG protein families whose involvement in development and disease has been demonstrated. Their participation in regenerative processes both of the central nervous system and of regenerating limbs is well documented. However, whether HSPG are expressed in regenerating zebrafish fins, is currently unknown.

RESULTS

Here, we carried out a systematic screen of glypican and syndecan mRNA expression in regenerating zebrafish fins during the outgrowth phase. We find that 8 of the 10 zebrafish glypicans and the three known zebrafish syndecans show specific expression at 3 days post amputation. Expression is found in different domains of the regenerate, including the distal and lateral basal layers of the wound epidermis, the distal most blastema and more proximal blastema regions.

CONCLUSIONS

HSPG expression is prevalent in regenerating zebrafish fins. Further research is needed to delineate the function of glypican and syndecan action during zebrafish fin regeneration.

FoxL1+ mesenchymal cells are a critical source of Wnt5a for midgut elongation during mouse embryonic intestinal development

Wnt5a is a non-canonical Wnt ligand that is essential for normal embryonic development in mammals. The role of Wnt5a in early intestinal development has been examined in gene ablation models, where Wnt5a-/- mice exhibit strikingly shortened intestines. However, the exact cellular source of Wnt5a has remained elusive, until a recent study found that FoxL1-expressing mesenchymal cells (FoxL1+ cells), which are localized directly beneath the intestinal epithelium, express Wnt5a. To determine whether FoxL1+ cells are a required source of Wnt5a during intestinal development, we derived FoxL1-Cre; Wnt5af/f mice, which is the first mouse model to ablate Wnt5a in a cell type-specific manner in the intestine in vivo. Our results show that Wnt5a deletion in FoxL1+ cells during fetal life causes a shortened gut phenotype in neonatal mice, and that our model is sufficient to increase rate of apoptosis in the elongating epithelium, thus explaining the shortened gut phenotype. However, in contrast to previous studies using Wnt5a null mice, we did not observe dysregulation of epithelial structure or apical-basal protein localization. Altogether, our findings establish a developmental role for FoxL1+ mesenchymal cells in controlling non-canonical Wnt signaling during midgut elongation.

A guide to the composition and functions of the extracellular matrix

Extracellular matrix (ECM) is a dynamic 3-dimensional network of macromolecules that provides structural support for the cells and tissues. Accumulated knowledge clearly demonstrated over the last decade that ECM plays key regulatory roles since it orchestrates cell signaling, functions, properties and morphology. Extracellularly secreted as well as cell-bound factors are among the major members of the ECM family. Proteins/glycoproteins, such as collagens, elastin, laminins and tenascins, proteoglycans and glycosaminoglycans, hyaluronan, and their cell receptors such as CD44 and integrins, responsible for cell adhesion, comprise a well-organized functional network with significant roles in health and disease. On the other hand, enzymes such as matrix metalloproteinases and specific glycosidases including heparanase and hyaluronidases contribute to matrix remodeling and affect human health. Several cell processes and functions, among them cell proliferation and survival, migration, differentiation, autophagy, angiogenesis, and immunity regulation are affected by certain matrix components. Structural alterations have been also well associated with disease progression. This guide on the composition and functions of the ECM gives a broad overview of the matrisome, the major ECM macromolecules, and their interaction networks within the ECM and with the cell surface, summarizes their main structural features and their roles in tissue organization and cell functions, and emphasizes the importance of specific ECM constituents in disease development and progression as well as the advances in molecular targeting of ECM to design new therapeutic strategies.

Syndecan receptors: pericellular regulators in development and inflammatory disease

The syndecans are the major family of transmembrane proteoglycans, usually bearing multiple heparan sulfate chains. They are present on virtually all nucleated cells of vertebrates and are also present in invertebrates, indicative of a long evolutionary history. Genetic models in both vertebrates and invertebrates have shown that syndecans link to the actin cytoskeleton and can fine-tune cell adhesion, migration, junction formation, polarity and differentiation. Although often associated as co-receptors with other classes of receptors (e.g. integrins, growth factor and morphogen receptors), syndecans can nonetheless signal to the cytoplasm in discrete ways. Syndecan expression levels are upregulated in development, tissue repair and an array of human diseases, which has led to the increased appreciation that they may be important in pathogenesis not only as diagnostic or prognostic agents, but also as potential targets. Here, their functions in development and inflammatory diseases are summarized, including their potential roles as conduits for viral pathogen entry into cells.