Perlecan maintains the integrity of cartilage and some basement membranes

Extracellular matrix: The driving force of mammalian diseases

Like the major theme of a Mozart concerto, the immense and pervasive extracellular matrix drives each movement and ultimately closes the symphony, embracing a unique role as the fundamental mediator for most, if not all, ensuing intracellular events. As such, it comes as no surprise that the mechanism of just about every known disease can be traced back to some part of the matrix, typically in the form of an abnormal amount or activity level of a particular matrix component. These defects considerably affect downstream signaling axes leading to overt cellular dysfunction, organ failure, and death. From skin to bone, from vessels to brain, from eyes to all the internal organs, the matrix plays an incredible role as both a cause and potential means to reverse diseases. Human malaises including connective tissue disorders, muscular dystrophy, fibrosis, and cancer are all extracellular matrix-driven diseases. The ability to understand and modulate these matrix-related mechanisms may lead to the future discovery of novel therapeutic options for these patients.

Chimeric protein identification of dystrophic, Pierson and other laminin polymerization residues

Laminin polymerization is a key step of basement membrane self-assembly that depends on the binding of the three different N-terminal globular LN domains. Several mutations in the LN domains cause LAMA2-deficient muscular dystrophy and LAMB2-deficient Pierson syndrome. These mutations may affect polymerization. A novel approach to identify the amino acid residues required for polymerization has been applied to an analysis of these and other laminin LN mutations. The approach utilizes laminin-nidogen chimeric fusion proteins that bind to recombinant non-polymerizing laminins to provide a missing functional LN domain. Single amino acid substitutions introduced into these chimeras were tested to determine if polymerization activity and the ability to assemble on cell surfaces were lost. Several laminin-deficient muscular dystrophy mutations, renal Pierson syndrome mutations, and Drosophila mutations causing defects of heart development were identified as ones causing loss of laminin polymerization. In addition, two novel residues required for polymerization were identified in the laminin γ1 LN domain.

Basement Membranes in Development and Disease

The basement membrane is a thin but dense, sheet-like specialized type of extracellular matrix that has remarkably diverse functions tailored to individual tissues and organs. Tightly controlled spatial and temporal changes in its composition and structure contribute to the diversity of basement membrane functions. These different basement membranes undergo dynamic transformations throughout animal life, most notably during development. Numerous developmental mechanisms are regulated or mediated by basement membranes, often by a combination of molecular and mechanical processes. A particularly important process involves cell transmigration through a basement membrane because of its link to cell invasion in disease. While developmental and disease processes share some similarities, what clearly distinguishes the two is dysregulation of cells and extracellular matrices in disease. With its relevance to many developmental and disease processes, the basement membrane is a vitally important area of research that may provide novel insights into biological mechanisms and development of innovative therapeutic approaches. Here we present a review of developmental and disease dynamics of basement membranes in Caenorhabditis elegans, Drosophila, and vertebrates.

The multifaceted roles of perlecan in fibrosis

Perlecan, or heparan sulfate proteoglycan 2 (HSPG2), is a ubiquitous heparan sulfate proteoglycan that has major roles in tissue and organ development and wound healing by orchestrating the binding and signaling of mitogens and morphogens to cells in a temporal and dynamic fashion. In this review, its roles in fibrosis are reviewed by drawing upon evidence from tissue and organ systems that undergo fibrosis as a result of an uncontrolled response to either inflammation or traumatic cellular injury leading to an over production of a collagen-rich extracellular matrix. This review focuses on examples of fibrosis that occurs in lung, liver, kidney, skin, kidney, neural tissues and blood vessels and its link to the expression of perlecan in that particular organ system.

Engineered basement membranes: from in vivo considerations to cell-based assays

Engineered basement membranes are required to mimic in vivo properties within cell-based assays.

Diabetes-related changes in the protein composition and the biomechanical properties of human retinal vascular basement membranes

Basement membranes (BMs) are specialized sheets of extracellular matrix that outline epithelial cell layers, muscle fibers, blood vessels, and peripheral nerves. A well-documented histological hallmark of progressing diabetes is a major increase in vascular BM thickness. In order to investigate whether this structural change is accompanied by a change in the protein composition, we compared the proteomes of retinal vascular BMs from diabetic and non-diabetic donors by using LC-MS/MS. Data analysis showed that seventeen extracellular matrix (ECM)-associated proteins were more abundant in diabetic than non-diabetic vascular BMs. Four ECM proteins were more abundant in non-diabetic than in diabetic BMs. Most of the over-expressed proteins implicate a complement-mediated chronic inflammatory process in the diabetic retinal vasculature. We also found an up-regulation of norrin, a protein that is known to promote vascular proliferation, possibly contributing to the vascular remodeling during diabetes. Many of the over-expressed proteins were localized to microvascular aneurisms. Further, the overall stoichiometry of proteins was changed, such that the relative abundance of collagens in BMs from diabetic patients was higher than normal. Biomechanical measurements of vascular BM flat mounts using AFM showed that their outer surface was softer than normal.

Retinal Proteoglycans Act as Cellular Receptors for Basement Membrane Assembly to Control Astrocyte Migration and Angiogenesis

The basement membrane is crucial for cell polarity, adhesion, and motility, but how it is assembled on the cell surface remains unclear. Here, we find that ablation of glycosaminoglycan (GAG) side chains of proteoglycans in the neuroretina disrupts the retinal basement membrane, leading to arrested astrocyte migration and reduced angiogenesis. Using genetic deletion and time-lapse imaging, we show that retinal astrocytes require neuronal-derived PDGF as a chemoattractive cue and the retinal basement membrane as a migratory substrate. Genetic ablation of heparan sulfates does not produce the same defects as GAG null mutants. In contrast, enzymatic removal of heparan sulfates and chondroitin sulfates together inhibits de novo laminin network assembly. These results indicate that both heparan and chondroitin sulfate proteoglycans participate in retinal basement membrane assembly, thus promoting astrocyte migration and angiogenesis.

The vascular basement membrane in the healthy and pathological brain

The vascular basement membrane contributes to the integrity of the blood-brain barrier (BBB), which is formed by brain capillary endothelial cells (BCECs). The BCECs receive support from pericytes embedded in the vascular basement membrane and from astrocyte endfeet. The vascular basement membrane forms a three-dimensional protein network predominantly composed of laminin, collagen IV, nidogen, and heparan sulfate proteoglycans that mutually support interactions between BCECs, pericytes, and astrocytes. Major changes in the molecular composition of the vascular basement membrane are observed in acute and chronic neuropathological settings. In the present review, we cover the significance of the vascular basement membrane in the healthy and pathological brain. In stroke, loss of BBB integrity is accompanied by upregulation of proteolytic enzymes and degradation of vascular basement membrane proteins. There is yet no causal relationship between expression or activity of matrix proteases and the degradation of vascular matrix proteins in vivo. In Alzheimer's disease, changes in the vascular basement membrane include accumulation of Aβ, composite changes, and thickening. The physical properties of the vascular basement membrane carry the potential of obstructing drug delivery to the brain, e.g. thickening of the basement membrane can affect drug delivery to the brain, especially the delivery of nanoparticles.

Neural tube closure: cellular, molecular and biomechanical mechanisms

Neural tube closure has been studied for many decades, across a range of vertebrates, as a paradigm of embryonic morphogenesis. Neurulation is of particular interest in view of the severe congenital malformations - 'neural tube defects' - that result when closure fails. The process of neural tube closure is complex and involves cellular events such as convergent extension, apical constriction and interkinetic nuclear migration, as well as precise molecular control via the non-canonical Wnt/planar cell polarity pathway, Shh/BMP signalling, and the transcription factors Grhl2/3, Pax3, Cdx2 and Zic2. More recently, biomechanical inputs into neural tube morphogenesis have also been identified. Here, we review these cellular, molecular and biomechanical mechanisms involved in neural tube closure, based on studies of various vertebrate species, focusing on the most recent advances in the field.

Real-time acquisition of transendothelial electrical resistance in an all-human, in vitro, 3-dimensional, blood-brain barrier model exemplifies tight-junction integrity

The blood–brain barrier (BBB) consists of endothelial cells, astrocytes, and pericytes embedded in basal lamina (BL). Most in vitro models use nonhuman, monolayer cultures for therapeutic-delivery studies, relying on transendothelial electrical resistance (TEER) measurements without other tight-junction (TJ) formation parameters. We aimed to develop reliable, reproducible, in vitro 3-dimensional (3D) models incorporating relevant human, in vivo cell types and BL proteins. The 3D BBB models were constructed with human brain endothelial cells, human astrocytes, and human brain pericytes in mono-, co-, and tricultures. TEER was measured in 3D models using a volt/ohmmeter and cellZscope. Influence of BL proteins—laminin, fibronectin, collagen type IV, agrin, and perlecan—on adhesion and TEER was assessed using an electric cell-substrate impedance–sensing system. TJ protein expression was assessed by Western blotting (WB) and immunocytochemistry (ICC). Perlecan (10 µg/ml) evoked unreportedly high, in vitro TEER values (1200 Ω) and the strongest adhesion. Coculturing endothelial cells with astrocytes yielded the greatest resistance over time. ICC and WB results correlated with resistance levels, with evidence of prominent occludin expression in cocultures. BL proteins exerted differential effects on TEER, whereas astrocytes in contact yielded higher TEER values and TJ expression.—Maherally, Z., Fillmore, H. L., Tan, S. L., Tan, S. F., Jassam, S. A., Quack, F. I., Hatherell, K. E., Pilkington, G. J. Real-time acquisition of transendothelial electrical resistance in an all-human, in vitro, 3-dimensional, blood–brain barrier model exemplifies tight-junction integrity.

Heparanase: Potential roles in multiple sclerosis

Heparanase is a heparan sulfate degrading enzyme that cleaves heparan sulfate (HS) chains present on HS proteoglycans (HSPGs), and has been well characterized for its roles in tumor metastasis and inflammation. However, heparanase is emerging as a contributing factor in the genesis and severity of a variety of neurodegenerative diseases and conditions. This is in part due to the wide variety of HSPGs on which the presence or absence of HS moieties dictates protein function. This includes growth factors, chemokines, cytokines, as well as components of the extracellular matrix (ECM) which in turn regulate leukocyte infiltration into the CNS. Roles for heparanase in stroke, Alzheimer's disease, and glioma growth have been described; roles for heparanase in other disease such as multiple sclerosis (MS) are less well established. However, given its known roles in inflammation and leukocyte infiltration, it is likely that heparanase also contributes to MS pathology. In this review, we will briefly summarize what is known about heparanase roles in the CNS, and speculate as to its potential role in regulating disease progression in MS and its animal model EAE (experimental autoimmune encephalitis), which may justify testing of heparanase inhibitors for MS treatment.

Perlecan is required for the chondrogenic differentiation of synovial mesenchymal cells through regulation of Sox9 gene expression

We previously reported that perlecan, a heparan-sulfate proteoglycan (Hspg2), expressed in the synovium at the cartilage-synovial junction, is required for osteophyte formation in knee osteoarthritis. To examine the mechanism underlying this process, we examined the role of perlecan in the proliferation and differentiation of synovial mesenchymal cells (SMCs), using a recently established mouse synovial cell culture method. Primary SMCs isolated from Hspg2^-/- -Tg (Hspg2^-/- ;Col2a1-Hspg2^Tg/- ) mice, in which the perlecan-knockout was rescued from perinatal lethality, lack perlecan. The chondrogenic-, osteogenic-, and adipogenic-potentials were examined in the Hspg2^-/- -Tg SMCs compared to the control SMCs prepared from wild-type Hspg2^+/+ -Tg (Hspg2^+/+ ;Col2a1-Hspg2^Tg/- ) littermates. In a culture condition permitting proliferation, both control and Hspg2^-/- -Tg SMCs showed similar rates of proliferation and expression of cell surface markers. However, in micromass cultures, the cartilage matrix production and Sox9 and Col2a1 mRNA levels were significantly reduced in Hspg2^-/- -Tg SMCs, compared with control SMCs. The reduced level of Sox9 mRNA was restored by the supplementation with exogenous perlecan protein. There was no difference in osteogenic differentiation between the control and Hspg2^-/- -Tg SMCs, as measured by the levels of Runx2 and Col1a1 mRNA. The adipogenic induction and PPARγ mRNA levels were significantly reduced in Hspg2^-/- -Tg SMCs compared to control SMCs. The reduction of PPARγ mRNA levels in Hspg2^-/- -Tg SMCs was restored by supplementation of perlecan. Perlecan is required for the chondrogenic and adipogenic differentiation from SMCs via its regulation of the Sox9 and PPARγ gene expression, but not for osteogenic differentiation via Runx2. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:837-846, 2017.

The binding capacity of α1β1-, α2β1- and α10β1-integrins depends on non-collagenous surface macromolecules rather than the collagens in cartilage fibrils

Interactions of cells with supramolecular aggregates of the extracellular matrix (ECM) are mediated, in part, by cell surface receptors of the integrin family. These are important molecular components of cell surface-suprastructures regulating cellular activities in general. A subfamily of β1-integrins with von Willebrand-factor A-like domains (I-domains) in their α-chains can bind to collagen molecules and, therefore, are considered as important cellular mechano-receptors. Here we show that chondrocytes strongly bind to cartilage collagens in the form of individual triple helical molecules but very weakly to fibrils formed by the same molecules. We also find that chondrocyte integrins α1β1-, α2β1- and α10β1-integrins and their I-domains have the same characteristics. Nevertheless we find integrin binding to mechanically generated cartilage fibril fragments, which also comprise peripheral non-collagenous material. We conclude that cell adhesion results from binding of integrin-containing adhesion suprastructures to the non-collagenous fibril periphery but not to the collagenous fibril cores. The biological importance of the well-investigated recognition of collagen molecules by integrins is unknown. Possible scenarios may include fibrillogenesis, fibril degradation and/or phagocytosis, recruitment of cells to remodeling sites, or molecular signaling across cytoplasmic membranes. In these circumstances, collagen molecules may lack a fibrillar organization. However, other processes requiring robust biomechanical functions, such as fibril organization in tissues, cell division, adhesion, or migration, do not involve direct integrin-collagen interactions.

Structure and Function of Basement Membranes

Basement membranes (BMs) are present in every tissue of the human body. All epithelium and endothelium is in direct association with BMs. BMs are a composite of several large glycoproteins and form an organized scaffold to provide structural support to the tissue and also offer functional input to modulate cellular function. While collagen I is the most abundant protein in the human body, type IV collagen is the most abundant protein in BMs. Matrigel is commonly used as surrogate for BMs in many experiments, but this is a tumor-derived BM–like material and does not contain all of the components that natural BMs possess. The structure of BMs and their functional role in tissues are unique and unlike any other class of proteins in the human body. Increasing evidence suggests that BMs are unique signal input devices that likely fine tune cellular function. Additionally, the resulting endothelial and epithelial heterogeneity in human body is a direct contribution of cell-matrix interaction facilitated by the diverse compositions of BMs.

A Comprehensive View of the Structural and Functional Alterations of Extracellular Matrix by Snake Venom Metalloproteinases (SVMPs): Novel Perspectives on the Pathophysiology of Envenoming

Snake venom metalloproteinases (SVMPs) affect the extracellular matrix (ECM) in multiple and complex ways. Previously, the combination of various methodological platforms, including electron microscopy, histochemistry, immunohistochemistry, and Western blot, has allowed a partial understanding of such complex pathology. In recent years, the proteomics analysis of exudates collected in the vicinity of tissues affected by SVMPs has provided novel and exciting information on SVMP-induced ECM alterations. The presence of fragments of an array of ECM proteins, including those of the basement membrane, has revealed a complex pathological scenario caused by the direct action of SVMPs. In addition, the time-course analysis of these changes has underscored that degradation of some fibrillar collagens is likely to depend on the action of endogenous proteinases, such as matrix metalloproteinases (MMPs), synthesized as a consequence of the inflammatory process. The action of SVMPs on the ECM also results in the release of ECM-derived biologically-active peptides that exert diverse actions in the tissue, some of which might be associated with reparative events or with further tissue damage. The study of the effects of SVMP on the ECM is an open field of research which may bring a renewed understanding of snake venom-induced pathology.

A current view of perlecan in physiology and pathology: A mosaic of functions

Perlecan, a large basement membrane heparan sulfate proteoglycan, is expressed in a wide array of tissues where it regulates diverse cellular processes including bone formation, inflammation, cardiac development, and angiogenesis. Here we provide a contemporary review germane to the biology of perlecan encompassing its genetic regulation as well as an analysis of its modular protein structure as it pertains to function. As perlecan signaling from the extracellular matrix converges on master regulators of autophagy, including AMPK and mTOR, via a specific interaction with vascular endothelial growth factor receptor 2, we specifically focus on the mechanism of action of perlecan in autophagy and angiogenesis and contrast the role of endorepellin, the C-terminal fragment of perlecan, in these cellular and morphogenic events.

Knockdown of the pericellular matrix molecule perlecan lowers in situ cell and matrix stiffness in developing cartilage

The pericellular matrix (PCM) is a component of the extracellular matrix that is found immediately surrounding individual chondrocytes in developing and adult cartilage, and is rich in the proteoglycan perlecan. Mutations in perlecan are the basis of several developmental disorders, which are thought to arise from disruptions in the mechanical stability of the PCM. We tested the hypothesis that defects in PCM organization will reduce the stiffness of chondrocytes in developing cartilage by combining a murine model of Schwartz-Jampel syndrome, in which perlecan is knocked down, with our novel atomic force microscopy technique that can measure the stiffness of living cells and surrounding matrix in embryonic and postnatal tissues in situ. Perlecan knockdown altered matrix organization and significantly decreased the stiffness of both chondrocytes and interstitial matrix as a function of age and genotype. Our results demonstrate that the knockdown of a spatially restricted matrix molecule can have a profound influence on cell and tissue stiffness, implicating a role for outside-in mechanical signals from the PCM in regulating the intracellular mechanisms required for the overall development of cartilage.

Integrin and dystroglycan compensate each other to mediate laminin-dependent basement membrane assembly and epiblast polarization

During early embryogenesis, endodermal γ1-laminin expression is required for basement membrane (BM) assembly, promoting conversion of non-polar pluripotent cells into polarized epiblast. The influence of laminin-111 (Lm111) and its integrin and dystroglycan (DG) receptors on epiblast in embryoid bodies (EBs), a model for differentiation of the embryonic plate, was further investigated. Lm111 added to the medium of EBs initiated conversion of inner nonpolar cell to the polarized epiblast epithelium with an exterior-to-central basal-to-apical orientation. Microinjection of Lm111 into EB interiors resulted in an interior BM with complete inversion of cell polarity. Lm111 assembled a BM on integrin-β1 null EBs with induction of polarization at reduced efficiency. β-Integrin compensation was not detected in these nulls with integrin adaptor proteins failing to assemble. A dimer of laminin LG domains 4-5 (LZE3) engineered to strongly bind to α-dystroglycan almost completely inhibited laminin accumulation on integrin β1-null EBs, reducing BM and ablating cell polarization. When Lm111 was incubated with integrin-β1/dystroglycan double-knockout EBs, laminin failed to accumulate on the EBs, the EBs did not differentiate, and the EBs underwent apoptosis. Collectively the findings support the hypotheses that the locus of laminin cell surface assembly can determine the axis of epithelial polarity. This requires integrin- and/or dystroglycan-dependent binding to laminin LG domains with the highest efficiency achieved when both receptors are present. Finally, EBs that cannot assemble a matrix undergo apoptosis.

The role of heparan sulphate in development: the ectodermal story

Heparan sulphate (HS) is ubiquitously expressed and is formed of repeating glucosamine and glucuronic/iduronic acid units which are generally highly sulphated. HS is found in tissues bound to proteins forming HS proteoglycans (HSPGs) which are present on the cell membrane or in the extracellular matrix. HSPGs influence a variety of biological processes by interacting with physiologically important proteins, such as morphogens, creating storage pools, generating morphogen gradients and directly mediating signalling pathways, thereby playing vital roles during development. This review discusses the vital role HS plays in the development of tissues from the ectodermal lineage. The ectodermal layer differentiates to form the nervous system (including the spine, peripheral nerves and brain), eye, epidermis, skin appendages and tooth enamel.

Perlecan, a Basement Membrane-type Heparan Sulfate Proteoglycan, in the Enamel Organ: Its Intraepithelial Localization in the Stellate Reticulum

The localization and biosynthesis of perlecan, a basement membrane-type heparan sulfate proteoglycan, were studied in developing tooth germs by using murine molars in neonatal and postnatal stages and primary cultured cells of the enamel organ and dental papilla to demonstrate the role of perlecan in normal odontogenesis. Perlecan was immunolocalized mainly in the intercellular spaces of the enamel organ as well as in the dental papilla/pulp or in the dental follicle. By in situ hybridization, mRNA signals for perlecan core protein were intensely demonstrated in the cytoplasm of stellate reticulum cells and in dental papilla/pulp cells, including odontoblasts and fibroblastic cells in the dental follicle. Furthermore, the in vitro biosyntheses of perlecan core protein by the enamel organ and dental papilla/pulp cells were confirmed by immunofluorescence, immunoprecipitation, and reverse transcriptase-polymerase chain reaction. The results indicate that perlecan is synthesized by the dental epithelial cells and is accumulated in their intercellular spaces to form the characteristic stellate reticulum, whose function is still unknown.

The extracellular matrix niche microenvironment of neural and cancer stem cells in the brain

Numerous studies demonstrated that neural stem cells and cancer stem cells (NSCs/CSCs) share several overlapping characteristics such as self-renewal, multipotency and a comparable molecular repertoire. In addition to the intrinsic cellular properties, NSCs/CSCs favor a similar environment to acquire and maintain their characteristics. In the present review, we highlight the shared properties of NSCs and CSCs in regard to their extracellular microenvironment called the NSC/CSC niche. Moreover, we point out that extracellular matrix (ECM) molecules and their complementary receptors influence the behavior of NSCs/CSCs as well as brain tumor progression. Here, we focus on the expression profile and functional importance of the ECM glycoprotein tenascin-C, the chondroitin sulfate proteoglycan DSD-1-PG/phosphacan but also on other important glycoprotein/proteoglycan constituents. Within this review, we specifically concentrate on glioblastoma multiforme (GBM). GBM is the most common malignant brain tumor in adults and is associated with poor prognosis despite intense and aggressive surgical and therapeutic treatment. Recent studies indicate that GBM onset is driven by a subpopulation of CSCs that display self-renewal and recapitulate tumor heterogeneity. Based on the CSC hypothesis the cancer arises just from a small subpopulation of self-sustaining cancer cells with the exclusive ability to self-renew and maintain the tumor. Besides the fundamental stem cell properties of self-renewal and multipotency, GBM stem cells share further molecular characteristics with NSCs, which we would like to review in this article.

Muscle Tissue Damage Induced by the Venom of Bothrops asper: Identification of Early and Late Pathological Events through Proteomic Analysis

The time-course of the pathological effects induced by the venom of the snake Bothrops asper in muscle tissue was investigated by a combination of histology, proteomic analysis of exudates collected in the vicinity of damaged muscle, and immunodetection of extracellular matrix proteins in exudates. Proteomic assay of exudates has become an excellent new methodological tool to detect key biomarkers of tissue alterations for a more integrative perspective of snake venom-induced pathology. The time-course analysis of the intracellular proteins showed an early presence of cytosolic and mitochondrial proteins in exudates, while cytoskeletal proteins increased later on. This underscores the rapid cytotoxic effect of venom, especially in muscle fibers, due to the action of myotoxic phospholipases A2, followed by the action of proteinases in the cytoskeleton of damaged muscle fibers. Similarly, the early presence of basement membrane (BM) and other extracellular matrix (ECM) proteins in exudates reflects the rapid microvascular damage and hemorrhage induced by snake venom metalloproteinases. The presence of fragments of type IV collagen and perlecan one hour after envenoming suggests that hydrolysis of these mechanically/structurally-relevant BM components plays a key role in the genesis of hemorrhage. On the other hand, the increment of some ECM proteins in the exudate at later time intervals is likely a consequence of the action of endogenous matrix metalloproteinases (MMPs) or of de novo synthesis of ECM proteins during tissue remodeling as part of the inflammatory reaction. Our results offer relevant insights for a more integrative and systematic understanding of the time-course dynamics of muscle tissue damage induced by B. asper venom and possibly other viperid venoms.

Endostatin and endorepellin: A common route of action for similar angiostatic cancer avengers

Traditional cancer therapy typically targets the tumor proper. However, newly-formed vasculature exerts a major role in cancer development and progression. Autophagy, as a biological mechanism for clearing damaged proteins and oxidative stress products released in the tumor milieu, could help in tumor resolution by rescuing cells undergoing modifications or inducing autophagic-cell death of tumor blood vessels. Cleaved fragments of extracellular matrix proteoglycans are emerging as key players in the modulation of angiogenesis and endothelial cell autophagy. An essential characteristic of cancer progression is the remodeling of the basement membrane and the release of processed forms of its constituents. Endostatin, generated from collagen XVIII, and endorepellin, the C-terminal segment of the large proteoglycan perlecan, possess a dual activity as modifiers of both angiogenesis and endothelial cell autophagy. Manipulation of these endogenously-processed forms, located in the basement membrane within tumors, could represent new therapeutic approaches for cancer eradication.

The cartilage extracellular matrix as a transient developmental scaffold for growth plate maturation

The cartilage growth plate is a specialized developmental tissue containing characteristic zonal arrangements of chondrocytes. The proliferative and differentiative states of chondrocytes are tightly regulated at all stages including the initial limb bud and rudiment cartilage stages of development, the establishment of the primary and secondary ossification centers, development of the growth plates and laying down of bone. A multitude of spatio-temporal signals, including transcription factors, growth factors, morphogens and hormones, control chondrocyte maturation and terminal chondrocyte differentiation/hypertrophy, cell death/differentiation, calcification and vascular invasion of the growth plate and bone formation during morphogenetic transition of the growth plate. This involves hierarchical, integrated signaling from growth and factors, transcription factors, mechanosensory cues and proteases in the extracellular matrix to regulate these developmental processes to facilitate progressive changes in the growth plate culminating in bone formation and endochondral ossification. This review provides an overview of selected components which have particularly important roles in growth plate biology including collagens, proteoglycans, glycosaminoglycans, growth factors, proteases and enzymes.

Pannexin 3 and connexin 43 modulate skeletal development through their distinct functions and expression patterns

Pannexin 3 (Panx3) and connexin 43 (Cx43; also known as GJA1) are two major gap junction proteins expressed in osteoblasts. Here, we studied their functional relationships in skeletal formation by generating Panx3(-/-) and Panx3(-/-);Cx43(-/-) mice and comparing their skeletal phenotypes with Cx43(-/-) mice. Panx3(-/-) mice displayed defects in endochondral and intramembranous ossification, resulting in severe dwarfism and reduced bone density. The skeletal abnormalities of Panx3(-/-);Cx43(-/-) mice were similar to those in Panx3(-/-) mice. The gross appearance of newborn Cx43(-/-) skeletons showed no obvious abnormalities, except for less mineralization of the skull. In Panx3(-/-) mice, proliferation of chondrocytes and osteoblasts increased and differentiation of these cells was inhibited. Panx3 promoted expression of osteogenic proteins such as ALP and Ocn (also known as ALPL and BGLAP, respectively), as well as Cx43, by regulating Osx (also known as SP7) expression. Panx3 was induced in the early differentiation stage and reduced during the maturation stage of osteoblasts, when Cx43 expression increased in order to promote mineralization. Furthermore, only Panx3 functioned as an endoplasmic reticulum (ER) Ca(2+) channel to promote differentiation, and it could rescue mineralization defects in Cx43(-/-) calvarial cells. Our findings reveal that Panx3 and Cx43 have distinct functions in skeletal formation.

Perturbations of the cerebrovascular matrisome: A convergent mechanism in small vessel disease of the brain?

The term matrisome refers to the ensemble of proteins constituting the extracellular matrix (ECM) (core matrisome) as well as the proteins associated with the ECM. Every organ has an ECM with a unique composition that not only provides the support and anchorage for cells, but also controls fundamental cellular processes as diverse as differentiation, survival, proliferation, and polarity. The current knowledge of the matrisome of small brain vessels is reviewed with a focus on the basement membrane (BM), a specialized form of ECM located at the interface between endothelial cells, contractile cells (smooth muscle cells and pericytes), and astrocyte endfeet—a very strategic location in the communication pathway between the cerebral microcirculation and astrocytes. We discuss some of the most recent genetic data and relevant findings from experimental models of nonamyloid cerebral small vessel disease (SVD). We propose the concept that perturbations of the cerebrovascular matrisome is a convergent pathologic pathway in monogenic forms of SVD, and is likely relevant to the sporadic disease.

Tangential migration of glutamatergic neurons and cortical patterning during development: Lessons from Cajal-Retzius cells

Tangential migration is a mode of cell movement, which in the developing cerebral cortex, is defined by displacement parallel to the ventricular surface and orthogonal to the radial glial fibers. This mode of long-range migration is a strategy by which distinct neuronal classes generated from spatially and molecularly distinct origins can integrate to form appropriate neural circuits within the cortical plate. While it was previously believed that only GABAergic cortical interneurons migrate tangentially from their origins in the subpallial ganglionic eminences to integrate in the cortical plate, it is now known that transient populations of glutamatergic neurons also adopt this mode of migration. These include Cajal-Retzius cells (CRs), subplate neurons (SPs), and cortical plate transient neurons (CPTs), which have crucial roles in orchestrating the radial and tangential development of the embryonic cerebral cortex in a noncell-autonomous manner. While CRs have been extensively studied, it is only in the last decade that the molecular mechanisms governing their tangential migration have begun to be elucidated. To date, the mechanisms of SPs and CPTs tangential migration remain unknown. We therefore review the known signaling pathways, which regulate parameters of CRs migration including their motility, contact-redistribution and adhesion to the pial surface, and discuss this in the context of how CR migration may regulate their signaling activity in a spatial and temporal manner. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 847-881, 2016.

Perlecan Diversely Regulates the Migration and Proliferation of Distinct Cell Types in vitro

Perlecan is a multifunctional component of the extracellular matrix. It shows different effects on distinct cell types, and therefore it is thought to show potential for therapies targeting multiple cell types. However, the full range of multifunctionality of perlecan remains to be elucidated. We cultured various cell types, which were derived from epithelial/endothelial, connective and muscle tissues, in the presence of either antiserum against perlecan or exogenous perlecan, and examined the effects of perlecan on cell migration and proliferation. Cell migration was determined using a scratch assay. Blocking of perlecan by anti-perlecan antiserum inhibited the migration of vascular endothelial cells (VECs) and bone marrow-derived mesenchymal stem cells, and exogenous perlecan added to the culture medium promoted the migration of these cell types. The migration of other cell types was inhibited or was not promoted by exogenous perlecan. Cell proliferation was measured using a water-soluble tetrazolium dye. When cells were cultured at low densities, perlecan blocking inhibited the proliferation of VECs, and exogenous perlecan promoted the proliferation of keratinocytes. In contrast, the proliferation of fibroblasts, pre-adipocytes and vascular smooth muscle cells cultured at low densities was inhibited by exogenous perlecan. When cells were cultured at high densities, perlecan blocking promoted the proliferation of most cell types, with the exception of skeletal system-derived cells (chondrocytes and osteoblasts), which were inhibited by exogenous perlecan. Our results provide an overview of the multiple functions of perlecan in various cell types, and implicate a potential role of perlecan to inhibit undesirable activities, such as fibrosis, obesity and intimal hyperplasia.

Single molecule force measurements of perlecan/HSPG2: A key component of the osteocyte pericellular matrix

Perlecan/HSPG2, a large, monomeric heparan sulfate proteoglycan (HSPG), is a key component of the lacunar canalicular system (LCS) of cortical bone, where it is part of the mechanosensing pericellular matrix (PCM) surrounding the osteocytic processes and serves as a tethering element that connects the osteocyte cell body to the bone matrix. Within the pericellular space surrounding the osteocyte cell body, perlecan can experience physiological fluid flow drag force and in that capacity function as a sensor to relay external stimuli to the osteocyte cell membrane. We previously showed that a reduction in perlecan secretion alters the PCM fiber composition and interferes with bone's response to a mechanical loading in vivo. To test our hypothesis that perlecan core protein can sustain tensile forces without unfolding under physiological loading conditions, atomic force microscopy (AFM) was used to capture images of perlecan monomers at nanoscale resolution and to perform single molecule force measurement (SMFMs). We found that the core protein of purified full-length human perlecan is of suitable size to span the pericellular space of the LCS, with a measured end-to-end length of 170±20 nm and a diameter of 2-4 nm. Force pulling revealed a strong protein core that can withstand over 100 pN of tension well over the drag forces that are estimated to be exerted on the individual osteocyte tethers. Data fitting with an extensible worm-like chain model showed that the perlecan protein core has a mean elastic constant of 890 pN and a corresponding Young's modulus of 71 MPa. We conclude that perlecan has physical properties that would allow it to act as a strong but elastic tether in the LCS.

The Basement Membrane Proteoglycans Perlecan and Agrin: Something Old, Something New

Several members of the proteoglycan family are integral components of basement membranes; other proteoglycan family members interact with or bind to molecular residents of the basement membrane. Proteoglycans are polyfunctional molecules, for they derive their inherent bioactivity from the amino acid motifs embedded in the core protein structure as well as the glycosaminoglycan (GAG) chains that are covalently attached to the core protein. The presence of the covalently attached GAG chains significantly expands the "partnering" potential of proteoglycans, permitting them to interact with a broad spectrum of targets, including growth factors, cytokines, chemokines, and morphogens. Thus proteoglycans in the basement membrane are poised to exert diverse effects on the cells intimately associated with basement membranes.

An in situ hybridization study of perlecan, DMP1, and MEPE in developing condylar cartilage of the fetal mouse mandible and limb bud cartilage

The main purpose of this in situ hybridization study was to investigate mRNA expression of three bone/cartilage matrix components (perlecan, DMP1, and MEPE) in developing primary (tibial) and secondary (condylar) cartilage. Perlecan mRNA expression was first detected in newly formed chondrocytes in tibial cartilage at E13.0, but this expression decreased in hypertrophic chondrocytes at E14.0. In contrast, at E15.0, perlecan mRNA was first detected in the newly formed chondrocytes of condylar cartilage; these chondrocytes had characteristics of hypertrophic chondrocytes, which confirmed the previous observation that progenitor cells of developing secondary cartilage rapidly differentiate into hypertrophic chondrocytes. DMP1 mRNA was detected in many chondrocytes within the lower hypertrophic cell zone in tibial cartilage at E14.0. In contrast, DMP1 mRNA expression was only transiently detected in a few chondrocytes of condylar cartilage at E15.0. Thus, DMP1 may be less important in the developing condylar cartilage than in the tibial cartilage. Another purpose of this study was to test the hypothesis that MEPE may be a useful marker molecule for cartilage. MEPE mRNA was not detected in any chondrocytes in either tibial or condylar cartilage; however, MEPE immunoreactivity was detected throughout the cartilage matrix. Western immunoblot analysis demonstrated that MEPE antibody recognized two bands, one of 67 kDa and another of 59 kDa, in cartilage-derived samples. Thus MEPE protein may gradually accumulate in the cartilage, even though mRNA expression levels were below the limits of detection of in situ hybridization. Ultimately, we could not designate MEPE as a marker molecule for cartilage, and would modify our original hypothesis.

Breeding Strategy Determines Rupture Incidence in Post-Infarct Healing WARPing Cardiovascular Research

Background

Von Willebrand A domain Related Protein (WARP), is a recently identified extracellular matrix protein. Based upon its involvement in matrix biology and its expression in the heart, we hypothesized that WARP regulates cardiac remodeling processes in the post-infarct healing process.

Methods and results

In the mouse model of myocardial infarction (MI), WARP expression increased in the infarcted area 3-days post-MI. In the healthy myocardium WARP localized with perlecan in the basement membrane, which was disrupted upon injury. In vitro studies showed high expression of WARP by cardiac fibroblasts, which further increases upon TGFβ stimulation. Furthermore, WARP expression correlated with aSMA and COL1 expression, markers of fibroblast to myofibroblast transition, in vivo and in vitro. Finally, WARP knockdown in vitro affected extra- and intracellular basic fibroblast growth factor production in myofibroblasts. To investigate the function for WARP in infarction healing, we performed an MI study in WARP knockout (KO) mice backcrossed more than 10 times on an Australian C57Bl/6-J background and bred in-house, and compared to wild type (WT) mice of the same C57Bl/6-J strain but of commercial European origin. WARP KO mice showed no mortality after MI, whereas 40% of the WT mice died due to cardiac rupture. However, when WARP KO mice were backcrossed on the European C57Bl/6-J background and bred heterozygous in-house, the previously seen protective effect in the WARP KO mice after MI was lost. Importantly, comparison of the cardiac response post-MI in WT mice bred heterozygous in-house versus commercially purchased WT mice revealed differences in cardiac rupture.

Conclusion

These data demonstrate a redundant role for WARP in the wound healing process after MI but demonstrate that the continental/breeding/housing origin of mice of the same C57Bl6-J strain is critical in determining the susceptibility to cardiac rupture and stress the importance of using the correct littermate controls.

New concepts in basement membrane biology

Basement membranes (BMs) are thin sheets of extracellular matrix that outline epithelia, muscle fibers, blood vessels and peripheral nerves. The current view of BM structure and functions is based mainly on transmission electron microscopy imaging, in vitro protein binding assays, and phenotype analysis of human patients, mutant mice and invertebrata. Recently, MS-based protein analysis, biomechanical testing and cell adhesion assays with in vivo derived BMs have led to new and unexpected insights. Proteomic analysis combined with ultrastructural studies showed that many BMs undergo compositional and structural changes with advancing age. Atomic force microscopy measurements in combination with phenotype analysis have revealed an altered mechanical stiffness that correlates with specific BM pathologies in mutant mice and human patients. Atomic force microscopy-based height measurements strongly suggest that BMs are more than two-fold thicker than previously estimated, providing greater freedom for modelling the large protein polymers within BMs. In addition, data gathered using BMs extracted from mutant mice showed that laminin has a crucial role in BM stability. Finally, recent evidence demonstrate that BMs are bi-functionally organized, leading to the proposition that BM-sidedness contributes to the alternating epithelial and stromal tissue arrangements that are found in all metazoan species. We propose that BMs are ancient structures with tissue-organizing functions and were essential in the evolution of metazoan species.

Perlecan inhibits autophagy to maintain muscle homeostasis in mouse soleus muscle

The autophagy-lysosome system is essential for muscle protein synthesis and degradation equilibrium, and its dysfunction has been linked to various muscle disorders. It has been reported that a diverse collection of extracellular matrix constituents, including decorin, collagen VI, laminin α2, endorepellin, and endostatin, can modulate autophagic signaling pathways. However, the association between autophagy and perlecan in muscle homeostasis remains unclear. The mechanical unloading of perlecan-deficient soleus muscles resulted in significantly decreased wet weights and cross-section fiber area compared with those of control mice. We found that perlecan deficiency in slow-twitch soleus muscles enhanced autophagic activity. This was accompanied by a decrease in autophagic substrates, such as p62, and an increase in LC3II levels. Furthermore, perlecan deficiency caused a reduction in the phosphorylation levels of p70S6k and Akt and increased the phosphorylation of AMPKα. Our findings suggested that perlecan inhibits the autophagic process through the activation of the mTORC1 pathway. This autophagic response may be a novel target for enhancing the efficacy of skeletal muscle atrophy treatment.

1p36 deletion syndrome: an update

Deletions of chromosome 1p36 affect approximately 1 in 5,000 newborns and are the most common terminal deletions in humans. Medical problems commonly caused by terminal deletions of 1p36 include developmental delay, intellectual disability, seizures, vision problems, hearing loss, short stature, distinctive facial features, brain anomalies, orofacial clefting, congenital heart defects, cardiomyopathy, and renal anomalies. Although 1p36 deletion syndrome is considered clinically recognizable, there is significant phenotypic variation among affected individuals. This variation is due, at least in part, to the genetic heterogeneity seen in 1p36 deletions which include terminal and interstitial deletions of varying lengths located throughout the 30 Mb of DNA that comprise chromosome 1p36. Array-based copy number variant analysis can easily identify genomic regions of 1p36 that are deleted in an affected individual. However, predicting the phenotype of an individual based solely on the location and extent of their 1p36 deletion remains a challenge since most of the genes that contribute to 1p36-related phenotypes have yet to be identified. In addition, haploinsufficiency of more than one gene may contribute to some phenotypes. In this article, we review recent successes in the effort to map and identify the genes and genomic regions that contribute to specific 1p36-related phenotypes. In particular, we highlight evidence implicating MMP23B, GABRD, SKI, PRDM16, KCNAB2, RERE, UBE4B, CASZ1, PDPN, SPEN, ECE1, HSPG2, and LUZP1 in various 1p36 deletion phenotypes.

Decoding the Matrix: Instructive Roles of Proteoglycan Receptors

The extracellular matrix is a dynamic repository harboring instructive cues that embody substantial regulatory dominance over many evolutionarily conserved intracellular activities, including proliferation, apoptosis, migration, motility, and autophagy. The matrix also coordinates and parses hierarchical information, such as angiogenesis, tumorigenesis, and immunological responses, typically providing the critical determinants driving each outcome. We provide the first comprehensive review focused on proteoglycan receptors, that is, signaling transmembrane proteins that use secreted proteoglycans as ligands, in addition to their natural ligands. The majority of these receptors belong to an exclusive subset of receptor tyrosine kinases and assorted cell surface receptors that specifically bind, transduce, and modulate fundamental cellular processes following interactions with proteoglycans. The class of small leucine-rich proteoglycans is the most studied so far and constitutes the best understood example of proteoglycan-receptor interactions. Decorin and biglycan evoke autophagy and immunological responses that deter, suppress, or exacerbate pathological conditions such as tumorigenesis, angiogenesis, and chronic inflammatory disease. Basement membrane-associated heparan sulfate proteoglycans (perlecan, agrin, and collagen XVIII) represent a unique cohort and provide proteolytically cleaved bioactive fragments for modulating cellular behavior. The receptors that bind the genuinely multifactorial and multivalent proteoglycans represent a nexus in understanding basic biological pathways and open new avenues for therapeutic and pharmacological intervention.

Epidermal Basement Membrane in Health and Disease

Skin, as the organ protecting the individual from environmental aggressions, constantly meets external insults and is dependent on mechanical toughness for its preserved function. Accordingly, the epidermal basement membrane (BM) zone has adapted to enforce tissue integrity. It harbors anchoring structures created through unique organization of common BM components and expression of proteins exclusive to the epidermal BM zone. Evidence for the importance of its correct assembly and the nonredundancy of its components for skin integrity is apparent from the multiple skin blistering disorders caused by mutations in genes coding for proteins associated with the epidermal BM and from autoimmune disorders in which autoantibodies target these molecules. However, it has become clear that these proteins not only provide mechanical support but are also critically involved in tissue homeostasis, repair, and regeneration. In this chapter, we provide an overview of the unique organization and components of the epidermal BM. A special focus will be given to its function during regeneration, and in inherited and acquired diseases.

A missense mutation in domain III in HSPG2 in Schwartz-Jampel syndrome compromises secretion of perlecan into the extracellular space

Schwartz-Jampel syndrome (SJS) type 1 is characterized by short stature, myotonia, and chondrodysplasia, and is caused by partial loss-of-function mutations in HSPG2 encoding perlecan. Six missense mutations have been reported in SJS to date and only one has been characterized using a recombinant protein. We report an 11-year-old Japanese boy with SJS, who shows "rigid" walking with less flexion of knees/ankles and protruded mouth. His intelligence is normal. We identified by whole genome resequencing a heterozygous missense p.Leu1088Pro in domain III-2 and a heterozygous nonsense p.Gln3061Ter in domain IV of perlecan. Expression studies revealed that p.Leu1088Pro markedly reduces the cellular expression of domain III-2 and almost nullifies its secretion into the culture medium. As five of the seven missense mutations in SJS affect domain III of perlecan, domain III is likely to be essential for secretion of perlecan into the extracellular space.

An active role for basement membrane assembly and modification in tissue sculpting

Basement membranes are a dense, sheet-like form of extracellular matrix (ECM) that underlie epithelia and endothelia, and surround muscle, fat and Schwann cells. Basement membranes separate tissues and protect them from mechanical stress. Although traditionally thought of as a static support structure, a growing body of evidence suggests that dynamic basement membrane deposition and modification instructs coordinated cellular behaviors and acts mechanically to sculpt tissues. In this Commentary, we highlight recent studies that support the idea that far from being a passive matrix, basement membranes play formative roles in shaping tissues.

The potential role of perlecan domain V as novel therapy in vascular dementia

Vascular dementia (VaD) is the second most common cause of dementia and leads to a decline in cognitive thinking via conditions that lead to blockage or reduced blood flow to the brain. It is a poorly understood disease, and the changes that occur are often linked to other types of dementia such as Alzheimer's disease. To date, there are no approved therapies or drugs to treat the symptoms of VaD, even though there is some evidence of drugs approved for Alzheimer's that might have some benefit in patients diagnosed with VaD. The altered blood flow that precedes VaD may result in compensatory mechanisms, such as angiogenesis, to increase blood flow in the brain. Angiogenesis, the process of new blood vessel formations from pre-existing ones, involves several pro-angiogenic factors such as vascular endothelial growth factor (VEGF) and is regulated by a variety of growth factors from neurons, astrocytes, and pericytes in the brain as well the extracellular matrix (ECM). The ECM highly regulates angiogenesis and other processes in the brain. One such ECM component is the heparan sulfate proteoglycan perlecan and its bioactive region, Domain V (DV). Here we discuss the potential role of DV as a novel therapy to treat VaD.

Perlecan deficiency causes endothelial dysfunction by reducing the expression of endothelial nitric oxide synthase

Perlecan is a major heparan sulfate proteoglycan found in the subendothelial extracellular matrix of the vascular wall. The aim of this study was to investigate the role of perlecan in the regulation of vascular tone. A previously developed conditional perlecan‐deficient mouse model was used to measure changes in the isometric force of isolated aortic rings. The vessels were first precontracted with phenylephrine, and then treated with increasing concentrations of vasorelaxants. Endothelium‐dependent relaxation, elicited by acetylcholine, was significantly reduced in the perlecan‐deficient aortas, whereas endothelium‐independent relaxation caused by the exogenous nitric oxide donor sodium nitroprusside remained well preserved. The expression of the endothelial nitric oxide synthase (eNOS) gene, detected by real‐time polymerase chain reaction, was significantly decreased in the perlecan‐deficient aortas. The expression of eNOS protein detected using Western blotting was also significantly decreased in the perlecan‐deficient aortas. We examined the role of perlecan in eNOS gene expression by creating perlecan knockdown human aortic endothelial cells using small interfering RNA (siRNA) for perlecan. Perlecan gene expression was significantly reduced in the perlecan siRNA‐treated cells, resulting in a significant decrease in eNOS gene expression. Perlecan deficiency induced endothelial dysfunction, as indicated by a reduction in endothelium‐dependent relaxation due, at least partly, to a reduction in eNOS expression. These findings suggest that perlecan plays a role in the activation of eNOS gene expression during normal growth processes.

Perlecan deficiency induced endothelial dysfunction at least partly, to a reduction in eNOS expression. These findings suggest that perlecan plays a role in the activation of the eNOS expression during normal growth processes.

The role of perlecan and endorepellin in the control of tumor angiogenesis and endothelial cell autophagy

During tumor growth and angiogenesis there is a dynamic remodeling of tissue architecture often accompanied by the release of extracellular matrix constituents full of biological activity. One of the key constituents of the tumor microenvironment is the large heparan sulfate proteoglycan perlecan. This proteoglycan, strategically located at cell surfaces and within basement membranes, is a well-defined pro-angiogenic molecule when intact. However, when partially processed by proteases released during cancer remodeling and invasion, the C-terminal fragment of perlecan, known as endorepellin, has opposite effects than its parent molecule. Endorepellin is a potent inhibitor of angiogenesis by exerting a dual receptor antagonism by simultaneously engaging VEGFR2 and α2β1 integrin. Signaling through the α2β1 integrin leads to actin disassembly and block of endothelial cell migration, necessary for capillary morphogenesis. Signaling through the VEGFR2 induces dephosphorylation of the receptor via activation of SHP-1 and suppression of downstream proangiogenic effectors, especially attenuating VEGFA expression. A novel and emerging role of endorepellin is its ability to evoke autophagy by activating Peg3 and various canonical autophagic markers. This effect is specific for endothelial cells as these are the primary cells expressing both VEGFR2 and α2β1 integrin. Thus, an endogenous fragment of a ubiquitous proteoglycan can regulate both angiogenesis and autophagy through a dual receptor antagonism. The biological properties of this natural endogenous protein place endorepellin as a potential therapeutic agent against cancer or diseases where angiogenesis is prominent.

Exome sequencing identifies a rare HSPG2 variant associated with familial idiopathic scoliosis

Idiopathic scoliosis occurs in 3% of individuals and has an unknown etiology. The objective of this study was to identify rare variants that contribute to the etiology of idiopathic scoliosis by using exome sequencing in a multigenerational family with idiopathic scoliosis. Exome sequencing was completed for three members of this multigenerational family with idiopathic scoliosis, resulting in the identification of a variant in the HSPG2 gene as a potential contributor to the phenotype. The HSPG2 gene was sequenced in a separate cohort of 100 unrelated individuals affected with idiopathic scoliosis and also was examined in an independent idiopathic scoliosis population. The exome sequencing and subsequent bioinformatics filtering resulted in 16 potentially damaging and rare coding variants. One of these variants, p.Asn786Ser, is located in the HSPG2 gene. The variant p.Asn786Ser also is overrepresented in a larger cohort of idiopathic scoliosis cases compared with a control population (P = 0.024). Furthermore, we identified additional rare HSPG2 variants that are predicted to be damaging in two independent cohorts of individuals with idiopathic scoliosis. The HSPG2 gene encodes for a ubiquitous multifunctional protein within the extracellular matrix in which loss of function mutation are known to result in a musculoskeletal phenotype in both mouse and humans. Based on these results, we conclude that rare variants in the HSPG2 gene potentially contribute to the idiopathic scoliosis phenotype in a subset of patients with idiopathic scoliosis. Further studies must be completed to confirm the effect of the HSPG2 gene on the idiopathic scoliosis phenotype.

Vitamin C Depletion in Prenatal Guinea Pigs as a Model of Lissencephaly Type II

Humans and guinea pigs are unable to produce vitamin C, with deficiency resulting in a well-known disorder of collagen synthesis. Pial basement membrane structure preservation is essential in the proper migration of neurons. In our study, intrauterine deprivation of vitamin C in guinea pig fetuses led to a collagen synthesis disorder, weakness, and finally a breach of pial basement membrane. We found excessive migration of the external germinal layer cells into the subarachnoid space of the cerebellum through defects in the pial basement membrane. The changes ranged from focal rupture of pial basement membranes to their complete disintegration. The loss of proper folia formation resulted in macroscopically visible flattening of the cerebellar surface. Different grades of dysplastic changes in the folia of the cerebellar cortex were observed in 2 experimental groups assigned different limits to mark the time of commencement and duration of vitamin C deprivation. The most severe form of dysplastic changes was characterized by marked irregularity of the cerebellar cortex similar to that in lissencephaly type II. Thus, prenatal vitamin C deficiency represents a novel animal model to study the effects of collagen synthesis on development of breaches in the pial basement membrane, disordered migration of neurons, dysplasia of cerebellar cortex, and the pathogenesis of lissencephaly.

Extracellular matrix and developing growth plate

Growth plate is a specialized cartilaginous structure that mediates the longitudinal growth of skeletal bones. It consists of ordered zones of chondrocytes that secrete an extracellular matrix (ECM) composed of specific types of collagens and proteoglycans. Several heritable human skeletal dysplasias are caused by mutations in these ECM components and this review focuses on the roles of type II, IX, X, and XI collagens, aggrecan, matrilins, perlecan, and cartilage oligomeric matrix protein in the growth plate as deduced from human disease phenotypes and mouse models. Substantial advances have been achieved in deciphering the interaction networks and individual roles of these components in the construction of the growth plate ECM. Furthermore, ER stress and other cellular responses have been identified as key downstream effects of the ECM mutations contributing to abnormal growth plate development. The next challenge is to utilize the molecular level knowledge for the development of potential therapeutics.