Loss of Col3a1, the gene for Ehlers-Danlos syndrome type IV, results in neocortical dyslamination

Human Cell-Derived Matrix Composite Hydrogels with Diverse Composition for Use in Vasculature-on-chip Models

Microphysiological and organ-on-chip platforms seek to address critical gaps in human disease models and drug development that underlie poor rates of clinical success for novel interventions. While the fabrication technology and model cells used to synthesize organs-on-chip have advanced considerably, most platforms rely on animal-derived or synthetic extracellular matrix as a cell substrate, limiting mimicry of human physiology and precluding use in modeling diseases in which matrix dynamics play a role in pathogenesis. Here, the development of human cell-derived matrix (hCDM) composite hydrogels for use in 3D microphysiologic models of the vasculature is reported. hCDM composite hydrogels are derived from human donor fibroblasts and maintain a complex milieu of basement membrane, proteoglycans, and nonfibrillar matrix components. The use of hCDM composite hydrogels as 2D and 3D cell culture substrates is demonstrated, and hCDM composite hydrogels are patterned to form engineered human microvessels. Interestingly, hCDM composite hydrogels are enriched in proteins associated with vascular morphogenesis as determined by mass spectrometry, and functional analysis demonstrates proangiogenic signatures in human endothelial cells cultured in these hydrogels. In conclusion, this study suggests that human donor-derived hCDM composite hydrogels could address technical gaps in human organs-on-chip development and serve as substrates to promote vascularization.

Genomic Analysis of Multiplex Consanguineous Families Reveals Causes of Neurodevelopmental Disorders with Epilepsy

INTRODUCTION

Neurodevelopmental disorders (NDD) are a diverse group of disorders that affect the development of the nervous system. Epilepsy is a common phenotypic aspect of NDD.

METHODS

We recruited eight consanguineous families from Pakistan which segregated recessively inherited NDD with epilepsy. Magnetic Resonance imaging (MRI) and Electroencephalogram (EEG) were completed. Exome sequencing was carried out for selected participants from each family. The exome data were analyzed for exonic and splice-site variants that had allele frequencies of less than 0.01 in public databases.

RESULTS

Clinical investigations determined that developmental delay, intellectual disability and seizures were manifested by most patients in early childhood. EEG findings were abnormal in the participants of four families. MRI revealed demyelination orcerebral atrophic changes in multiple participants. We identified four novel homozygous variants including nonsense andmissense variants in OCLN, ALDH7A1, IQSEC2 and COL3A1, segregating with the phenotypes in the participants of four families. Previously reported homozygous variants of CNTNAP2, TRIT1 and NARS1 were found in individuals from three families. Clinical utility was observed in directing treatment in case of patients with an ALDH7A1 variant which included pyridoxine administration and enabling accurate counseling about the natural history and recurrence risk.

CONCLUSION

Our results add to the clinical and molecular delineation of very rare NDD with epilepsy. The high success rate of exome sequencing is likely attributable to the expectation of homozygous variants in patients of consanguineous families, and in one case, the availability of positional mapping data that greatly aided the variant prioritization.

Adhesion G protein-coupled receptors: structure, signaling, physiology, and pathophysiology

Adhesion G protein-coupled receptors (AGPCRs) are a family of 33 receptors in humans exhibiting a conserved general structure but diverse expression patterns and physiological functions. The large NH2 termini characteristic of AGPCRs confer unique properties to each receptor and possess a variety of distinct domains that can bind to a diverse array of extracellular proteins and components of the extracellular matrix. The traditional view of AGPCRs, as implied by their name, is that their core function is the mediation of adhesion. In recent years, though, many surprising advances have been made regarding AGPCR signaling mechanisms, activation by mechanosensory forces, and stimulation by small-molecule ligands such as steroid hormones and bioactive lipids. Thus, a new view of AGPCRs has begun to emerge in which these receptors are seen as massive signaling platforms that are crucial for the integration of adhesive, mechanosensory, and chemical stimuli. This review article describes the recent advances that have led to this new understanding of AGPCR function and also discusses new insights into the physiological actions of these receptors as well as their roles in human disease.

Functions of G protein-coupled receptor 56 in health and disease

Human G protein-coupled receptor 56 (GPR56) is encoded by gene ADGRG1 from chromosome 16q21 and is homologously encoded in mice, at chromosome 8. Both 687 and 693 splice forms are present in humans and mice. GPR56 has a 381 amino acid-long N-terminal extracellular segment and a GPCR proteolysis site upstream from the first transmembrane domain. GPR56 is mainly expressed in the heart, brain, thyroid, platelets, and peripheral blood mononuclear cells. Accumulating evidence indicates that GPR56 promotes the formation of myelin sheaths and the development of oligodendrocytes in the cerebral cortex of the central nervous system. Moreover, GPR56 contributes to the development and differentiation of hematopoietic stem cells, induces adipogenesis, and regulates the function of immune cells. The lack of GPR56 leads to nervous system dysfunction, platelet disorders, and infertility. Abnormal expression of GPR56 is related to the malignant transformation and tumor metastasis of several cancers including melanoma, neuroglioma, and gastrointestinal cancer. Metabolic disorders and cardiovascular diseases are also associated with dysregulation of GPR56 expression, and GPR56 is involved in the pharmacological resistance to some antidepressant and cancer drug treatments. In this review, the molecular structure, expression profile, and signal transduction of GPR56 are introduced, and physiological and pathological functions of GRP56 are comprehensively summarized. Attributing to its significant biological functions and its long N-terminal extracellular region that interacts with multiple ligands, GPR56 is becoming an attractive therapeutic target in treating neurological and hematopoietic diseases.

Animal Models of Ehlers-Danlos Syndromes: Phenotype, Pathogenesis, and Translational Potential

The Ehlers–Danlos syndromes (EDS) are a group of heritable connective tissues disorders mainly characterized by skin hyperextensibility, joint hypermobility and generalized tissue fragility. Currently, 14 EDS subtypes each with particular phenotypic features are recognized and are caused by genetic defects in 20 different genes. All of these genes are involved in the biosynthesis and/or fibrillogenesis of collagens at some level. Although great progress has been made in elucidating the molecular basis of different EDS subtypes, the pathogenic mechanisms underlying the observed phenotypes remain poorly understood, and consequentially, adequate treatment and management options for these conditions remain scarce. To date, several animal models, mainly mice and zebrafish, have been described with defects in 14 of the 20 hitherto known EDS-associated genes. These models have been instrumental in discerning the functions and roles of the corresponding proteins during development, maturation and repair and in portraying their roles during collagen biosynthesis and/or fibrillogenesis, for some even before their contribution to an EDS phenotype was elucidated. Additionally, extensive phenotypical characterization of these models has shown that they largely phenocopy their human counterparts, with recapitulation of several clinical hallmarks of the corresponding EDS subtype, including dermatological, cardiovascular, musculoskeletal and ocular features, as well as biomechanical and ultrastructural similarities in tissues. In this narrative review, we provide a comprehensive overview of animal models manifesting phenotypes that mimic EDS with a focus on engineered mouse and zebrafish models, and their relevance in past and future EDS research. Additionally, we briefly discuss domestic animals with naturally occurring EDS phenotypes. Collectively, these animal models have only started to reveal glimpses into the pathophysiological aspects associated with EDS and will undoubtably continue to play critical roles in EDS research due to their tremendous potential for pinpointing (common) signaling pathways, unveiling possible therapeutic targets and providing opportunities for preclinical therapeutic interventions.

Primate-specific stress-induced transcription factor POU2F1Z protects human neuronal cells from stress

The emergence of new primate-specific genes is an essential factor in human and primate brain development and functioning. POU2F1/Oct-1 is a transcription regulator in higher eukaryotes which is involved in the regulation of development, differentiation, stress response, and other processes. We have demonstrated that the Tigger2 transposon insertion into the POU2F1 gene which occurred in the primate lineage led to the formation of an additional exon (designated the Z-exon). Z-exon-containing primate-specific Oct-1Z transcript includes a short upstream ORF (uORF) located at its 5’-end and the main ORF encoding the Oct-1Z protein isoform (Pou2F1 isoform 3, P14859-3), which differs from other Oct-1 isoforms by its N-terminal peptide. The Oct-1Z-encoding transcript is expressed mainly in human brain cortex. Under normal conditions, the translation of the ORF coding for the Oct-1Z isoform is repressed by uORF. Under various stress conditions, uORF enables a strong increase in the translation of the Oct-1Z-encoding ORF. Increased Oct-1Z expression levels in differentiating human neuroblasts activate genes controlling stress response, neural cell differentiation, brain formation, and organogenesis. We have shown that the Oct-1Z isoform of the POU2F1/Oct-1 transcription factor is an example of a primate-specific genomic element contributing to brain development and cellular stress defense.

Identification of Novel Choroidal Neovascularization-Related Genes Using Laplacian Heat Diffusion Algorithm

Choroidal neovascularization (CNV) is a type of eye disease that can cause vision loss. In recent years, many studies have attempted to investigate the major pathological processes and molecular pathogenic mechanisms of CNV. Because many diseases are related to genes, the genes associated with CNV need to be identified. In this study, we proposed a network-based approach for identifying novel CNV-associated genes. To execute such method, we first employed a protein-protein interaction network reported in STRING. Then, we applied a network diffusion algorithm, Laplacian heat diffusion, on this network by selecting validated CNV-related genes as the seed nodes. As a result, some novel genes that had unknown but strong relationships with validated genes were identified. Furthermore, we used a screening procedure to extract the most essential genes. Eleven latent CNV-related genes were finally obtained. Extensive analyses were performed to confirm that these genes are novel CNV-related genes.

Type III Collagen is Required for Adipogenesis and Actin Stress Fibre Formation in 3T3-L1 Preadipocytes

GPR56 is required for the adipogenesis of preadipocytes, and the role of one of its ligands, type III collagen (ColIII), was investigated here. ColIII expression was examined by reverse transcription quantitative polymerase chain reaction, immunoblotting and immunostaining, and its function investigated by knockdown and genome editing in 3T3-L1 cells. Adipogenesis was assessed by oil red O staining of neutral cell lipids and production of established marker and regulator proteins. siRNA-mediated knockdown significantly reduced Col3a1 transcripts, ColIII protein and lipid accumulation in 3T3-L1 differentiating cells. Col3a1^−/− 3T3-L1 genome-edited cell lines abolished adipogenesis, demonstrated by a dramatic reduction in adipogenic moderators: Pparγ₂ (88%) and C/ebpα (96%) as well as markers aP2 (93%) and oil red O staining (80%). Col3a1^−/− 3T3-L1 cells displayed reduced cell adhesion, sustained active β-catenin and deregulation of fibronectin (Fn) and collagen (Col4a1, Col6a1) extracellular matrix gene transcripts. Col3a1^−/− 3T3-L1 cells also had dramatically reduced actin stress fibres. We conclude that ColIII is required for 3T3-L1 preadipocyte adipogenesis as well as the formation of actin stress fibres. The phenotype of Col3a1^−/− 3T3-L1 cells is very similar to that of Gpr56^−/− 3T3-L1 cells, suggesting a functional relationship between ColIII and Gpr56 in preadipocytes.

Insight into developmental mechanisms of global and focal migration disorders of cortical development

Cortical development involves neurogenesis followed by migration, maturation, and myelination of immature neurons. Disruptions in these processes can cause malformations of cortical development (MCD). Radial glia (RG) are the stem cells of the brain, both generating neurons and providing the scaffold upon which immature neurons radially migrate. Germline mutations in genes required for cell migration, or cell-cell contact, often lead to global MCDs. Somatic mutations in RG in genes involved in homeostatic function, like mTOR signaling, often lead to focal MCDs. Two different mutations occurring in the same patient can combine in ways we are just beginning to understand. Our growing knowledge about MCD suggests mTOR inhibitors may have expanded utility in treatment-resistant epilepsy, while imaging techniques can better delineate the type and extent of these lesions.

Extracellular Control of Radial Glia Proliferation and Scaffolding During Cortical Development and Pathology

During the development of the cortex, newly generated neurons migrate long-distances in the expanding tissue to reach their final positions. Pyramidal neurons are produced from dorsal progenitors, e.g., radial glia (RGs) in the ventricular zone, and then migrate along RG processes basally toward the cortex. These neurons are hence dependent upon RG extensions to support their migration from apical to basal regions. Several studies have investigated how intracellular determinants are required for RG polarity and subsequent formation and maintenance of their processes. Fewer studies have identified the influence of the extracellular environment on this architecture. This review will focus on extracellular factors which influence RG morphology and pyramidal neuronal migration during normal development and their perturbations in pathology. During cortical development, RGs are present in different strategic positions: apical RGs (aRGs) have their cell bodies located in the ventricular zone with an apical process contacting the ventricle, while they also have a basal process extending radially to reach the pial surface of the cortex. This particular conformation allows aRGs to be exposed to long range and short range signaling cues, whereas basal RGs (bRGs, also known as outer RGs, oRGs) have their cell bodies located throughout the cortical wall, limiting their access to ventricular factors. Long range signals impacting aRGs include secreted molecules present in the embryonic cerebrospinal fluid (e.g., Neuregulin, EGF, FGF, Wnt, BMP). Secreted molecules also contribute to the extracellular matrix (fibronectin, laminin, reelin). Classical short range factors include cell to cell signaling, adhesion molecules and mechano-transduction mechanisms (e.g., TAG1, Notch, cadherins, mechanical tension). Changes in one or several of these components influencing the RG extracellular environment can disrupt the development or maintenance of RG architecture on which neuronal migration relies, leading to a range of cortical malformations. First, we will detail the known long range signaling cues impacting RG. Then, we will review how short range cell contacts are also important to instruct the RG framework. Understanding how RG processes are structured by their environment to maintain and support radial migration is a critical part of the investigation of neurodevelopmental disorders.

A splicing isoform of GPR56 mediates microglial synaptic refinement via phosphatidylserine binding

Developmental synaptic remodeling is important for the formation of precise neural circuitry, and its disruption has been linked to neurodevelopmental disorders such as autism and schizophrenia. Microglia prune synapses, but integration of this synapse pruning with overlapping and concurrent neurodevelopmental processes, remains elusive. Adhesion G protein-coupled receptor ADGRG1/GPR56 controls multiple aspects of brain development in a cell type-specific manner: In neural progenitor cells, GPR56 regulates cortical lamination, whereas in oligodendrocyte progenitor cells, GPR56 controls developmental myelination and myelin repair. Here, we show that microglial GPR56 maintains appropriate synaptic numbers in several brain regions in a time- and circuit-dependent fashion. Phosphatidylserine (PS) on presynaptic elements binds GPR56 in a domain-specific manner, and microglia-specific deletion of Gpr56 leads to increased synapses as a result of reduced microglial engulfment of PS+ presynaptic inputs. Remarkably, a particular alternatively spliced isoform of GPR56 is selectively required for microglia-mediated synaptic pruning. Our present data provide a ligand- and isoform-specific mechanism underlying microglial GPR56-mediated synapse pruning in the context of complex neurodevelopmental processes.

Type III collagen is a key regulator of the collagen fibrillar structure and biomechanics of articular cartilage and meniscus

Despite the fact that type III collagen is the second most abundant collagen type in the body, its contribution to the physiologic maintenance and repair of skeletal tissues remains poorly understood. This study queried the role of type III collagen in the structure and biomechanical functions of two structurally distinctive tissues in the knee joint, type II collagen-rich articular cartilage and type I collagen-dominated meniscus. Integrating outcomes from atomic force microscopy-based nanomechanical tests, collagen fibril nanostructural analysis, collagen cross-link analysis and histology, we elucidated the impact of type III collagen haplodeficiency on the morphology, nanostructure and biomechanical properties of articular cartilage and meniscus in Col3a1^+/- mice. Reduction of type III collagen leads to increased heterogeneity and mean thickness of collagen fibril diameter, as well as reduced modulus in both tissues, and these effects became more pronounced with skeletal maturation. These data suggest a crucial role of type III collagen in mediating fibril assembly and biomechanical functions of both articular cartilage and meniscus during post-natal growth. In articular cartilage, type III collagen has a marked contribution to the micromechanics of the pericellular matrix, indicating a potential role in mediating the early stage of type II collagen fibrillogenesis and chondrocyte mechanotransduction. In both tissues, reduction of type III collagen leads to decrease in tissue modulus despite the increase in collagen cross-linking. This suggests that the disruption of matrix structure due to type III collagen deficiency outweighs the stiffening of collagen fibrils by increased cross-linking, leading to a net negative impact on tissue modulus. Collectively, this study is the first to highlight the crucial structural role of type III collagen in both articular cartilage and meniscus extracellular matrices. We expect these results to expand our understanding of type III collagen across various tissue types, and to uncover critical molecular components of the microniche for regenerative strategies targeting articular cartilage and meniscus repair.

GAIN domain-mediated cleavage is required for activation of G protein-coupled receptor 56 (GPR56) by its natural ligands and a small-molecule agonist

Adhesion G protein-coupled receptors (aGPCRs) represent a distinct family of GPCRs that regulate several developmental and physiological processes. Most aGPCRs undergo GPCR autoproteolysis-inducing domain-mediated protein cleavage, which produces a cryptic tethered agonist (termed Stachel (stinger)), and cleavage-dependent and -independent aGPCR signaling mechanisms have been described. aGPCR G1 (ADGRG1 or G protein-coupled receptor 56 (GPR56)) has pleiotropic functions in the development of multiple organ systems, which has broad implications for human diseases. To date, two natural GPR56 ligands, collagen III and tissue transglutaminase (TG2), and one small-molecule agonist, 3-α-acetoxydihydrodeoxygedunin (3-α-DOG), have been identified, in addition to a synthetic peptide, P19, that contains seven amino acids of the native Stachel sequence. However, the mechanisms by which these natural and small-molecule agonists signal through GPR56 remain unknown. Here we engineered a noncleavable receptor variant that retains signaling competence via the P19 peptide. We demonstrate that both natural and small-molecule agonists can activate only cleaved GPR56. Interestingly, TG2 required both receptor cleavage and the presence of a matrix protein, laminin, to activate GPR56, whereas collagen III and 3-α-DOG signaled without any cofactors. On the other hand, both TG2/laminin and collagen III activate the receptor by dissociating the N-terminal fragment from its C-terminal fragment, enabling activation by the Stachel sequence, whereas P19 and 3-α-DOG initiate downstream signaling without disengaging the N-terminal fragment from its C-terminal fragment. These findings deepen our understanding of how GPR56 signals via natural ligands, and a small-molecule agonist may be broadly applicable to other aGPCR family members.

Type III collagen (COL3A1): Gene and protein structure, tissue distribution, and associated diseases

Collagen alpha-1(III) chain, also known as the alpha 1 chain of type III collagen, is a protein that in humans is encoded by the COL3A1 gene. Three alpha 1 chains are required to form the type III collagen molecule which has a long triple-helical domain. Type III collagen, an extracellular matrix protein, is synthesized by cells as a pre-procollagen. It is found as a major structural component in hollow organs such as large blood vessels, uterus and bowel. Other functions of type III collagen include interaction with platelets in the blood clotting cascade and it is also an important signaling molecule in wound healing. Mutations in the COL3A1 gene cause the vascular type of Ehlers-Danlos syndrome (vEDS; OMIM 130050). It is the most serious form of EDS, since patients often die suddenly due to a rupture of large arteries. Inactivation of the murine Col3a1 gene leads to a shorter life span in homozygous mutant mice. The mice die prematurely from a rupture of major arteries mimicking the human vEDS phenotype. The biochemical and cellular effects of COL3A1 mutations have been studied extensively. Most of the glycine mutations lead to the synthesis of type III collagen with reduced thermal stability, which is more susceptible for proteinases. Intracellular accumulation of this normally secreted protein is also found. Ultrastructural analyses have demonstrated dilated rough endoplasmic reticulum and changes in the diameter of collagen fibers. Other clinical conditions associated with type III collagen are several types of fibroses in which increased amounts of type III collagen accumulate in the target organs.

Overlap of polymicrogyria, hydrocephalus, and Joubert syndrome in a family with novel truncating mutations in ADGRG1/GPR56 and KIAA0556

Genetic mutations associated with brain malformations can lead to a spectrum of severity and it is often difficult to determine whether there are additional pathogenic variants contributing to the phenotype. Here, we present a family affected by a severe brain malformation including bilateral polymicrogyria, hydrocephalus, patchy white matter signal changes, and cerebellar and pontine hypoplasia with elongated cerebellar peduncles leading to the molar tooth sign. While the malformation is reminiscent of bilateral frontoparietal polymicrogyria (BFPP), the phenotype is more severe than previously reported and also includes features of Joubert syndrome (JBTS). Via exome sequencing, we identified homozygous truncating mutations in both ADGRG1/GPR56 and KIAA0556, which are known to cause BFPP and mild brain-specific JBTS, respectively. This study shows how two independent mutations can interact leading to complex brain malformations.

RNA localization is a key determinant of neurite-enriched proteome

Protein subcellular localization is fundamental to the establishment of the body axis, cell migration, synaptic plasticity, and a vast range of other biological processes. Protein localization occurs through three mechanisms: protein transport, mRNA localization, and local translation. However, the relative contribution of each process to neuronal polarity remains unknown. Using neurons differentiated from mouse embryonic stem cells, we analyze protein and RNA expression and translation rates in isolated cell bodies and neurites genome-wide. We quantify 7323 proteins and the entire transcriptome, and identify hundreds of neurite-localized proteins and locally translated mRNAs. Our results demonstrate that mRNA localization is the primary mechanism for protein localization in neurites that may account for half of the neurite-localized proteome. Moreover, we identify multiple neurite-targeted non-coding RNAs and RNA-binding proteins with potential regulatory roles. These results provide further insight into the mechanisms underlying the establishment of neuronal polarity.

Subcellular localization of RNAs and proteins is important for polarized cells such as neurons. Here the authors differentiate mouse embryonic stem cells into neurons, and analyze the local transcriptome, proteome, and translated transcriptome in their cell bodies and neurites, providing a unique resource for future studies on neuronal polarity.

Biallelic COL3A1 mutations result in a clinical spectrum of specific structural brain anomalies and connective tissue abnormalities

Vascular Ehlers-Danlos syndrome (type IV) is an autosomal dominant disorder caused by heterozygous variants of COL3A1. We identified biallelic COL3A1 variants in two unrelated families. In a 3-year-old female with developmental delay the nonsense variant c.1282C>T, p.(Arg428*) was detected in combination the c.2057delC, p.(Pro686Leufs*105) frame shift variant. Both compound heterozygous variants were novel. This patient was born with bilateral clubfoot, joint laxity, and dysmorphic facial features. At the age of 2 years she developed an aneurysmal brain hemorrhage. Cerebral MRI showed a peculiar pattern of profound cerebral abnormalities including bilateral frontoparietal polymicrogyria of the cobblestone variant. In the second family, the two affected siblings were homozygous for the missense variant c.145C<G, p.(Pro49Ala) of COL3A1 and showed cobblestone-like cortical malformation, cerebellar cysts, and white matter abnormalities, developmental delay, and seizures. To date, three further families have been reported with biallelic variants of this gene and specific structural brain anomalies in all, and a severe Ehlers-Danlos syndrome phenotype in some. Bilateral frontoparietal polymicrogyria of the cobblestone variant, cerebellar microcysts, and abnormalities of the white matter characterize this brain phenotype and resemble neurological manifestations in individuals with autosomal recessive mutations in GPR56, which serves as a ligand of COL3A1. In concordance with the findings in knock out mice, the collagen III protein plays a role in the regulation of cortical development in addition to its well-known function in connective tissue formation.

Altered expression of circadian rhythm and extracellular matrix genes in the medial prefrontal cortex of a valproic acid rat model of autism

Autism spectrum disorders (ASD) are a highly heterogeneous group of neurodevelopmental disorders caused by complex interplay between various genes and environmental factors during embryonic development. Changes at the molecular, cellular and neuroanatomical levels are especially evident in the medial prefrontal cortex (mPFC) of ASD patients and are particularly contributing to social impairments. In the present study we tested the hypothesis that altered neuronal development and plasticity, as seen in the mPFC of ASD individuals, may result from aberrant expression of functionally connected genes. Towards this end, we combined transcriptome sequencing and computational gene ontology analysis to identify the molecular networks impaired in the mPFC of a valproic acid (VPA) rat model of autism. This investigation identified two subsets of genes differentially expressed in the mPFC of VPA rats: one group of genes being functionally involved in the regulation of the circadian rhythm, while the second group encompasses a set of differentially expressed collagen genes acting within the extracellular matrix. Ultimately, our integrated transcriptome analysis identified a distinct subset of altered gene networks in the mPFC of VPA rats, contributing to our understanding of autism at the molecular level, thus providing novel insight into the genetic alterations associated with this neurodevelopmental disorder.

Bi-allelic variants in COL3A1 encoding the ligand to GPR56 are associated with cobblestone-like cortical malformation, white matter changes and cerebellar cysts

BACKGROUND

Collagens are one of the major constituents of the pial membrane, which plays a crucial role in neuronal migration and cortical lamination during brain development. Type III procollagen, the chains of which are encoded by COL3A1, is the ligand of the G protein-coupled receptor 56 (GPR56), also known as adhesion G protein-coupled receptor G1. Bi-allelic mutations in GPR56 give rise to cobblestone-like malformation, white matter changes and cerebellar dysplasia. This report shows that bi-allelic mutations in COL3A1 are associated with a similar phenotype.

METHODS

Exome analysis was performed in a family consisting of two affected and two non-affected siblings. Brain imaging studies of this family and of two previously reported individuals with bi-allelic mutations in COL3A1 were reviewed. Functional assays were performed on dermal fibroblasts.

RESULTS

Exome analysis revealed a novel homozygous variant c.145C>G (p.Pro49Ala) in exon 2 of COL3A1. Brain MRI in the affected siblings as well as in the two previously reported individuals with bi-allelic COL3A1 mutations showed a brain phenotype similar to that associated with mutations in GPR56.

CONCLUSION

Homozygous or compound heterozygous mutations in COL3A1 are associated with cobblestone-like malformation in all three families reported to date. The variability of the phenotype across patients suggests that genetic alterations in distinct domains of type III procollagen can lead to different outcomes. The presence of cobblestone-like malformation in patients with bi-allelic COL3A1 mutations emphasises the critical role of the type III collagen-GPR56 axis and the pial membrane in the regulation of brain development and cortical lamination.

Tethered agonists: a new mechanism underlying adhesion G protein-coupled receptor activation

The family of adhesion G protein-coupled receptors (aGPCRs) comprises 33 members in the human genome, which are subdivided into nine subclasses. Many aGPCRs undergo an autoproteolytic process via their GPCR Autoproteolysis-INducing (GAIN) domain during protein maturation to generate an N- and a C-terminal fragments, NTF and CTF, respectively. The NTF and CTF are non-covalently reassociated on the plasma membrane to form a single receptor unit. How aGPCRs are activated upon ligand binding remains one of the leading questions in the field of aGPCR research. Recent work from our labs and others shows that ligand binding can remove the NTF from the plasma membrane-bound CTF, exposing a tethered agonist which potently activates downstream signaling.

Neuronal migration disorders: Focus on the cytoskeleton and epilepsy

A wide spectrum of focal, regional, or diffuse structural brain abnormalities, collectively known as malformations of cortical development (MCDs), frequently manifest with intellectual disability (ID), epilepsy, and/or autistic spectrum disorder (ASD). As the acronym suggests, MCDs are perturbations of the normal architecture of the cerebral cortex and hippocampus. The pathogenesis of these disorders remains incompletely understood; however, one area that has provided important insights has been the study of neuronal migration. The amalgamation of human genetics and experimental studies in animal models has led to the recognition that common genetic causes of neurodevelopmental disorders, including many severe epilepsy syndromes, are due to mutations in genes regulating the migration of newly born post-mitotic neurons. Neuronal migration genes often, though not exclusively, code for proteins involved in the function of the cytoskeleton. Other cellular processes, such as cell division and axon/dendrite formation, which similarly depend on cytoskeletal functions, may also be affected. We focus here on how the susceptibility of the highly organized neocortex and hippocampus may be due to their laminar organization, which involves the tight regulation, both temporally and spatially, of gene expression, specialized progenitor cells, the migration of neurons over large distances and a birthdate-specific layering of neurons. Perturbations in neuronal migration result in abnormal lamination, neuronal differentiation defects, abnormal cellular morphology and circuit formation. Ultimately this results in disorganized excitatory and inhibitory activity leading to the symptoms observed in individuals with these disorders.

Overrepresentation of the COL3A1 AA genotype in Polish skiers with anterior cruciate ligament injury

Although various intrinsic and extrinsic risk factors for anterior cruciate ligament (ACL) rupture have been identified, the exact aetiology of the injury is not yet fully understood. Type III collagen is an important factor in the repair of connective tissue, and certain gene polymorphisms may impair the tensile strength. The aim of this study was to examine the association of the COL3A1 rs1800255 polymorphism with ACL rupture in Polish male recreational skiers. A total of 321 male Polish recreational skiers were recruited for this study; 138 had surgically diagnosed primary ACL ruptures (ACL-injured group) and 183 were apparently healthy male skiers (control group – CON) who had no self-reported history of ligament or tendon injury. Both groups had a comparable level of exposure to ACL injury. Genomic DNA was extracted from the oral epithelial cells. All samples were genotyped on a real-time polymerase chain reaction instrument. The genotype distribution in the ACL-injured group was significantly different than in CON (respectively: AA=10.1 vs 2.2%, AG=22.5 vs 36.1, GG=67.4 vs 61.8%; p=0.0087). The AA vs AG+GG genotype of COL3A1 (odds ratio (OR)=5.05; 95% confidence interval (CI), 1.62-15.71, p=0.003) was significantly overrepresented in the ACL-injured group compared with CON. The frequency of the A allele was higher in the ACL-injured group (21.4%) compared with CON (20.2%), but the difference was not statistically significant (p=0.72). This study revealed an association between the COL3A1 rs1800255 polymorphism and ACL ruptures in Polish skiers.

The adhesion G protein-coupled receptor GPR56 is a cell-autonomous regulator of oligodendrocyte development

Mutations in GPR56, a member of the adhesion G protein-coupled receptor family, cause a human brain malformation called bilateral frontoparietal polymicrogyria (BFPP). Magnetic resonance imaging (MRI) of BFPP brains reveals myelination defects in addition to brain malformation. However, the cellular role of GPR56 in oligodendrocyte development remains unknown. Here, we demonstrate that loss of Gpr56 leads to hypomyelination of the central nervous system in mice. GPR56 levels are abundant throughout early stages of oligodendrocyte development, but are downregulated in myelinating oligodendrocytes. Gpr56-knockout mice manifest with decreased oligodendrocyte precursor cell (OPC) proliferation and diminished levels of active RhoA, leading to fewer mature oligodendrocytes and a reduced number of myelinated axons in the corpus callosum and optic nerves. Conditional ablation of Gpr56 in OPCs leads to a reduced number of mature oligodendrocytes as seen in constitutive knockout of Gpr56. Together, our data define GPR56 as a cell-autonomous regulator of oligodendrocyte development.

Vascular Ehlers-Danlos Syndrome in siblings with biallelic COL3A1 sequence variants and marked clinical variability in the extended family

Vascular Ehlers-Danlos Syndrome (vEDS), also known as EDS type IV, is considered to be an autosomal dominant disorder caused by sequence variants in COL3A1, which encodes the chains of type III procollagen. We identified a family in which there was marked clinical variation with the earliest death due to extensive aortic dissection at age 15 years and other family members in their eighties with no complications. The proband was born with right-sided clubfoot but was otherwise healthy until he died unexpectedly at 15 years. His sister, in addition to signs consistent with vascular EDS, had bilateral frontal and parietal polymicrogyria. The proband and his sister each had two COL3A1 sequence variants, c.1786C>T, p.(Arg596*) in exon 26 and c.3851G>A, p.(Gly1284Glu) in exon 50 on different alleles. Cells from the compound heterozygote produced a reduced amount of type III procollagen, all the chains of which had abnormal electrophoretic mobility. Biallelic sequence variants have a significantly worse outcome than heterozygous variants for either null mutations or missense mutations, and frontoparietal polymicrogyria may be an added phenotype feature. This genetic constellation provides a very rare explanation for marked intrafamilial clinical variation due to sequence variants in COL3A1.

Type IV collagen is an activating ligand for the adhesion G protein-coupled receptor GPR126

GPR126 is an orphan heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptor (GPCR) that is essential for the development of diverse organs. We found that type IV collagen, a major constituent of the basement membrane, binds to Gpr126 and activates its signaling function. Type IV collagen stimulated the production of cyclic adenosine monophosphate in rodent Schwann cells, which require Gpr126 activity to differentiate, and in human embryonic kidney (HEK) 293 cells expressing exogenous Gpr126. Type IV collagen specifically bound to the extracellular amino-terminal region of Gpr126 containing the CUB (complement, Uegf, Bmp1) and pentraxin domains. Gpr126 derivatives lacking the entire amino-terminal region were constitutively active, suggesting that this region inhibits signaling and that ligand binding relieves this inhibition to stimulate receptor activity. A new zebrafish mutation that truncates Gpr126 after the CUB and pentraxin domains disrupted development of peripheral nerves and the inner ear. Thus, our findings identify type IV collagen as an activating ligand for GPR126, define its mechanism of activation, and highlight a previously unrecognized signaling function of type IV collagen in basement membranes.

Mechanism for adhesion G protein-coupled receptor GPR56-mediated RhoA activation induced by collagen III stimulation

GPR56 is a member of the adhesion G protein-coupled receptor (GPCR) family. Despite the importance of GPR56 in brain development, where mutations cause a devastating human brain malformation called bilateral frontoparietal polymicrogyria (BFPP), the signaling mechanism(s) remain largely unknown. Like many other adhesion GPCRs, GPR56 is cleaved via a GPCR autoproteolysis-inducing (GAIN) domain into N- and C-terminal fragments (GPR56N and GPR56C); however, the biological significance of this cleavage is elusive. Taking advantage of the recent identification of a GPR56 ligand and the presence of BFPP-associated mutations, we investigated the molecular mechanism of GPR56 signaling. We demonstrate that ligand binding releases GPR56N from the membrane-bound GPR56C and triggers the association of GPR56C with lipid rafts and RhoA activation. Furthermore, one of the BFPP-associated mutations, L640R, does not affect collagen III-induced lipid raft association of GPR56. Instead, it specifically abolishes collagen III-mediated RhoA activation. Together, these findings reveal a novel signaling mechanism that may apply to other members of the adhesion GPCR family.

Identification of COL3A1 and RAB2A as novel translocation partner genes of PLAG1 in lipoblastoma

Lipoblastoma is a rapidly growing, benign neoplasm in children. Surgical excision is usually curative, with a recurrence rate of about 20%. Because the histology of lipoblastoma is heterogeneous and overlaps with other lipomatous tumors, some lipoblastoma cases have been difficult to diagnose. The detection of PLAG1 gene rearrangement is useful for the diagnosis of lipoblastoma. Three fusion partner genes are known in relation to PLAG1 in lipoblastoma HAS2 at 8q24.1, COL1A2 at 7q22, and RAD51L1 at 14q24. Herein, we describe another two novel fusion genes in lipoblastoma tumor specimens. We checked six tumors for the presence of two known fusion genes, HAS2-PLAG1 and COL1A2-PLAG1. Only HAS2-PLAG1 was found in one of the cases. Next, we attempted to identify potential PLAG1 fusion partners using 5'RACE. Sequence analysis revealed two novel fusion genes, COL3A1-PLAG1 in three cases and RAB2A-PLAG1 in one case, respectively. As a result of the translocations, the constitutively active promoter of the partner gene drives the ectopic expression of PLAG1. We also evaluated whether a high level of PLAG1 expression can be used to help differentiate lipomatous tumors. PLAG1 expression was evaluated by real-time PCR in five lipoblastoma tumor specimens. The expressions were 70-150 times higher in lipoblastomas than in human adipocytes. However, PLAG1 expression was low in one case of lipoma. These results demonstrate that PLAG1 overexpression is a potential marker of lipoblastoma. Our findings, in agreement with previous studies, show that lipoblastoma is a group of lipomatous tumors with PLAG1 rearrangement and overexpression. © 2014 Wiley Periodicals, Inc.

Mutations in LAMB1 cause cobblestone brain malformation without muscular or ocular abnormalities

Cobblestone brain malformation (COB) is a neuronal migration disorder characterized by protrusions of neurons beyond the first cortical layer at the pial surface of the brain. It is usually seen in association with dystroglycanopathy types of congenital muscular dystrophies (CMDs) and ocular abnormalities termed muscle-eye-brain disease. Here we report homozygous deleterious mutations in LAMB1, encoding laminin subunit beta-1, in two families with autosomal-recessive COB. Affected individuals displayed a constellation of brain malformations including cortical gyral and white-matter signal abnormalities, severe cerebellar dysplasia, brainstem hypoplasia, and occipital encephalocele, but they had less apparent ocular or muscular abnormalities than are typically observed in COB. LAMB1 is localized to the pial basement membrane, suggesting that defective connection between radial glial cells and the pial surface mediated by LAMB1 leads to this malformation.

Dissecting signaling and functions of adhesion G protein-coupled receptors

G protein-coupled receptors (GPCRs) comprise an expanded superfamily of receptors in the human genome. Adhesion class G protein-coupled receptors (adhesion-GPCRs) form the second largest class of GPCRs. Despite the abundance, size, molecular structure, and functions in facilitating cell and matrix contacts in a variety of organ systems, adhesion-GPCRs are by far the most poorly understood GPCR class. Adhesion-GPCRs possess a unique molecular structure, with extended N-termini containing various adhesion domains. In addition, many adhesion-GPCRs are autoproteolytically cleaved into an N-terminal fragment (NTF, NT, α-subunit) and C-terminal fragment (CTF, CT, β-subunit) at a conserved GPCR autoproteolysis-inducing (GAIN) domain that contains a GPCR proteolysis site (GPS). These two features distinguish adhesion-GPCRs from other GPCR classes. Though active research on adhesion-GPCRs in diverse areas, such as immunity, neuroscience, and development and tumor biology has been intensified in the recent years, the general biological and pharmacological properties of adhesion-GPCRs are not well known, and they have not yet been used for biomedical purposes. The "6th International Adhesion-GPCR Workshop," held at the Institute of Physiology of the University of Würzburg on September 6-8, 2012, assembled a majority of the investigators currently actively pursuing research on adhesion-GPCRs, including scientists from laboratories in Europe, the United States, and Asia. The meeting featured the nascent mechanistic understanding of the molecular events driving the signal transduction of adhesion-GPCRs, novel models to evaluate their functions, and evidence for their involvement in human disease.

GPR56 and the developing cerebral cortex: cells, matrix, and neuronal migration

GPR56, a member of the adhesion G protein-coupled receptor (GPCR) family, is integral to the development of the cortex, as mutations in GPR56 cause bilateral frontoparietal polymicrogyria (BFPP). BFPP is a cobblestone-like cortical malformation, characterized by overmigrating neurons and the formation of neuronal ectopias on the surface of the brain. Since its original cloning a decade ago, GPR56 has emerged from an orphaned and uncharacterized protein to an increasingly well-understood receptor, both in terms of its signaling and function. Collagen III is the ligand of GPR56 in the developing brain. Upon binding to collagen III, GPR56 activates RhoA via coupling to Gα(12/13). This pathway appears to be particularly critical in the preplate neurons, which are the earliest born neurons in the cortex, as the expression pattern of GPR56 in these neurons mimics the anterior to posterior gradient of malformation associated with loss of GPR56 in both humans and mice. Further characterizing the role of GPR56 in the preplate will shed light on the mechanism of cortical development and patterning.

Adhesion G protein-coupled receptors: signaling, pharmacology, and mechanisms of activation

The adhesion G protein-coupled receptors (GPCRs) are a distinct family of more than 30 receptors in vertebrate genomes. These receptors have been shown to play pivotal roles in a diverse range of biological functions and are characterized by extremely large N termini featuring various adhesion domains capable of mediating cell-cell and cell-matrix interactions. The adhesion GPCR N termini also contain GPCR proteolytic site motifs that undergo autocatalytic cleavage during receptor processing to create mature GPCRs existing as noncovalently attached complexes between the N terminus and transmembrane regions. There is mounting evidence that adhesion GPCRs can couple to G proteins to activate a variety of different downstream signaling pathways. Furthermore, recent studies have demonstrated that adhesion GPCR N termini can bind to multiple ligands, which may differentially activate receptor signaling and/or mediate cell adhesion. In addition, studies on several distinct adhesion GPCRs have revealed that truncations of the N termini result in constitutively active receptors, suggesting a model of receptor activation in which removal of the N terminus may be a key event in stimulating receptor signaling. Because mutations to certain adhesion GPCRs cause human disease and because many members of this receptor family exhibit highly discrete distribution patterns in different tissues, the adhesion GPCRs represent a class of potentially important drug targets that have not yet been exploited. For this reason, understanding the mechanisms of activation for these receptors and elucidating their downstream signaling pathways can provide insights with the potential to lead to novel therapeutic agents.