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Brain Structure & Function Mar 2020Evidence suggests that extracellular matrix molecules of perivascular basal laminae help orchestrate the molecular assemblies at the gliovascular interface....
Evidence suggests that extracellular matrix molecules of perivascular basal laminae help orchestrate the molecular assemblies at the gliovascular interface. Specifically, laminin and agrin are thought to tether the dystrophin-associated protein (DAP) complex to the astrocytic basal lamina. This complex includes α-syntrophin (α-Syn), which is believed to anchor aquaporin-4 (AQP4) to astrocytic endfoot membrane domains. We have previously shown that the size of the perivascular AQP4 pool differs considerably between brain regions in an α-Syn-dependent manner. Also, both AQP4 and α-Syn occur at higher densities in endfoot membrane domains facing pericytes than in endfoot membrane domains facing endothelial cells. The heterogeneous distribution of AQP4 at the regional and capillary level has been attributed to a direct interaction between AQP4 and α-Syn. This would be challenged (1) if the microdistributions of laminin and agrin fail to align with those of DAP and AQP4 and (2) if targeted deletion of α-Syn leads to a loss of laminin and/or agrin. Here, we provide the first detailed and quantitative analysis of laminin and agrin in brain basal laminae of mice. We show that the microdistributions of these molecules vary in a fashion that is well aligned with the previously reported microdistribution of AQP4. We also demonstrate that the expression patterns of laminin and agrin are insensitive to targeted deletion of α-Syn, suggesting that α-Syn deletion affects AQP4 directly and not indirectly via laminin or agrin. These data fill remaining voids in the current model of how key molecules are assembled and tethered at the gliovascular interface.
Topics: Agrin; Animals; Brain; Calcium-Binding Proteins; Capillaries; Extracellular Matrix; Extracellular Matrix Proteins; Laminin; Male; Membrane Proteins; Mice, Inbred C57BL; Muscle Proteins; RNA, Messenger
PubMed: 32072250
DOI: 10.1007/s00429-020-02036-3 -
Molecular Neurobiology Feb 2002Fast and accurate synaptic transmission requires high-density accumulation of neurotransmitter receptors in the postsynaptic membrane. During development of the... (Review)
Review
Fast and accurate synaptic transmission requires high-density accumulation of neurotransmitter receptors in the postsynaptic membrane. During development of the neuromuscular junction, clustering of acetylcholine receptors (AChR) is one of the first signs of postsynaptic specialization and is induced by nerve-released agrin. Recent studies have revealed that different mechanisms regulate assembly vs stabilization of AChR clusters and of the postsynaptic apparatus. MuSK, a receptor tyrosine kinase and component of the agrin receptor, and rapsyn, an AChR-associated anchoring protein, play crucial roles in the postsynaptic assembly. Once formed, AChR clusters and the postsynaptic membrane are stabilized by components of the dystrophin/utrophin glycoprotein complex, some of which also direct aspects of synaptic maturation such as formation of postjunctional folds. Nicotinic receptors are also expressed across the peripheral and central nervous system (PNS/CNS). These receptors are localized not only at the pre- but also at the postsynaptic sites where they carry out major synaptic transmission. In neurons, they are found as clusters at synaptic or extrasynaptic sites, suggesting that different mechanisms might underlie this specific localization of nicotinic receptors. This review summarizes the current knowledge about formation and stabilization of the postsynaptic apparatus at the neuromuscular junction and extends this to explore the synaptic structures of interneuronal cholinergic synapses.
Topics: Agrin; Animals; Cholinergic Fibers; Cytoskeletal Proteins; Dystrophin; Humans; Interneurons; Laminin; Macromolecular Substances; Membrane Proteins; Mice; Mice, Neurologic Mutants; Models, Neurological; Muscle Proteins; Nerve Tissue Proteins; Neuromuscular Junction; Neurons; Oligosaccharides; Receptor Protein-Tyrosine Kinases; Receptors, Cholinergic; Receptors, Growth Factor; Receptors, Nicotinic; Signal Transduction; Synapses; Synaptic Transmission; Utrophin; src-Family Kinases
PubMed: 11890459
DOI: 10.1385/MN:25:1:079 -
Development (Cambridge, England) Nov 2021The receptor tyrosine kinase MuSK, its co-receptor Lrp4 and the Agrin ligand constitute a signaling pathway that is crucial in axial muscle for neuromuscular synapse...
The receptor tyrosine kinase MuSK, its co-receptor Lrp4 and the Agrin ligand constitute a signaling pathway that is crucial in axial muscle for neuromuscular synapse development, yet whether this pathway functions similarly in appendicular muscle is unclear. Here, using the larval zebrafish pectoral fin, equivalent to tetrapod forelimbs, we show that, similar to axial muscle, developing appendicular muscles form aneural acetylcholine receptor (AChR) clusters prior to innervation. As motor axons arrive, neural AChR clusters form, eventually leading to functional synapses in a MuSK-dependent manner. We find that loss of Agrin or Lrp4 function, which abolishes synaptic AChR clusters in axial muscle, results in enlarged presynaptic nerve regions and progressively expanding appendicular AChR clusters, mimicking the consequences of motoneuron ablation. Moreover, musk depletion in lrp4 mutants partially restores synaptic AChR patterning. Combined, our results provide compelling evidence that, in addition to the canonical pathway in which Agrin/Lrp4 stimulates MuSK activity, Agrin/Lrp4 signaling in appendicular muscle constrains MuSK-dependent neuromuscular synapse organization. Thus, we reveal a previously unappreciated role for Agrin/Lrp4 signaling, thereby highlighting distinct differences between axial and appendicular synapse development.
Topics: Agrin; Animal Fins; Animals; Axons; Homeodomain Proteins; LDL-Receptor Related Proteins; Muscle, Skeletal; Mutation; Neuromuscular Junction; Receptors, Cholinergic; Signal Transduction; Zebrafish; Zebrafish Proteins
PubMed: 34714331
DOI: 10.1242/dev.199790 -
Trends in Cancer Feb 2020Angiogenesis represents a hallmark of cancer. Several proteoglycans associate with cell surface receptors and regulate angiogenesis within the tumor microenvironment...
Angiogenesis represents a hallmark of cancer. Several proteoglycans associate with cell surface receptors and regulate angiogenesis within the tumor microenvironment (TME). We highlight the recent discovery that the proteoglycan Agrin cross talks between the tumor and the endothelium to promote an angiogenesis privileged niche during cancer progression.
Topics: Agrin; Alternative Splicing; Angiogenesis Inhibitors; Carcinogenesis; Carcinoma, Hepatocellular; Cell Line, Tumor; Disease Progression; Endothelium, Vascular; Extracellular Matrix; Humans; Liver; Liver Neoplasms; Neovascularization, Pathologic; Protein Isoforms; Tumor Microenvironment
PubMed: 32061308
DOI: 10.1016/j.trecan.2019.12.002 -
Molecules and Cells May 2009Proteoglycans located in basement membranes, the nanostructures underling epithelial and endothelial layers, are unique in several respects. They are usually large,... (Review)
Review
Proteoglycans located in basement membranes, the nanostructures underling epithelial and endothelial layers, are unique in several respects. They are usually large, elongated molecules with a collage of domains that share structural and functional homology with numerous extracellular matrix proteins, growth factors and surface receptors. They mainly carry heparan sulfate side chains and these contribute not only to storing and preserving the biological activity of various heparan sulfate-binding cytokines and growth factors, but also in presenting them in a more "active configuration" to their cognate receptors. Abnormal expression or deregulated function of these proteoglycans affect cancer and angiogenesis, and are critical for the evolution of the tumor microenvironment. This review will focus on the functional roles of the major heparan sulfate proteoglycans from basement membrane zones: perlecan, agrin and collagen XVIII, and on their roles in modulating cancer growth and angiogenesis.
Topics: Agrin; Allosteric Regulation; Animals; Basement Membrane; Cell Growth Processes; Collagen Type XVIII; Feedback, Physiological; Fibroblast Growth Factors; Gene Expression Regulation, Neoplastic; Heparan Sulfate Proteoglycans; Humans; Neoplasms; Neovascularization, Pathologic; Signal Transduction; Vascular Endothelial Growth Factor A
PubMed: 19466598
DOI: 10.1007/s10059-009-0069-0 -
Muscle & Nerve Sep 2020Our aim in this study was to identify the prevalence and clinical characteristics of LRP4/agrin-antibody-positive double-seronegative myasthenia gravis (DNMG).
INTRODUCTION
Our aim in this study was to identify the prevalence and clinical characteristics of LRP4/agrin-antibody-positive double-seronegative myasthenia gravis (DNMG).
METHODS
DNMG patients at 16 sites in the United States were tested for LRP4 and agrin antibodies, and the clinical data were collected.
RESULTS
Of 181 DNMG patients, 27 (14.9%) were positive for either low-density lipoprotein receptor-related protein 4 (LRP4) or agrin antibodies. Twenty-three DNMG patients (12.7%) were positive for both antibodies. More antibody-positive patients presented with generalized symptoms (69%) compared with antibody-negative patients (43%) (P ≤ .02). Antibody-positive patients' maximum classification on the Myasthenia Gravis Foundation of America (MGFA) scale was significantly higher than that for antibody-negative patients (P ≤ .005). Seventy percent of antibody-positive patients were classified as MGFA class III, IV, or V compared with 39% of antibody-negative patients. Most LRP4- and agrin-antibody-positive patients (24 of 27, 89%) developed generalized myathenia gravis (MG), but with standard MG treatment 81.5% (22 of 27) improved to MGFA class I or II during a mean follow-up of 11 years.
DISCUSSION
Antibody-positive patients had more severe clinical disease than antibody-negative patients. Most DNMG patients responded to standard therapy regardless of antibody status.
Topics: Adult; Agrin; Autoantibodies; Female; Humans; LDL-Receptor Related Proteins; Male; Middle Aged; Myasthenia Gravis; Prevalence; Symptom Assessment; United States
PubMed: 32483837
DOI: 10.1002/mus.26985 -
Annals of the Rheumatic Diseases Jun 2016Osteoarthritis (OA) is a leading cause of disability for which there is no cure. The identification of molecules supporting cartilage homeostasis and regeneration is...
OBJECTIVES
Osteoarthritis (OA) is a leading cause of disability for which there is no cure. The identification of molecules supporting cartilage homeostasis and regeneration is therefore a major pursuit in musculoskeletal medicine. Agrin is a heparan sulfate proteoglycan which, through binding to low-density lipoprotein receptor-related protein 4 (LRP4), is required for neuromuscular synapse formation. In other tissues, it connects the cytoskeleton to the basement membrane through binding to α-dystroglycan. Prompted by an unexpected expression pattern, we investigated the role and receptor usage of agrin in cartilage.
METHODS
Agrin expression pattern was investigated in human osteoarthritic cartilage and following destabilisation of the medial meniscus in mice. Extracellular matrix (ECM) formation and chondrocyte differentiation was studied in gain and loss of function experiments in vitro in three-dimensional cultures and gain of function in vivo, using an ectopic cartilage formation assay in nude mice. Receptor usage was investigated by disrupting LRP4 and α-dystroglycan by siRNA and blocking antibodies respectively.
RESULTS
Agrin was detected in normal cartilage but was progressively lost in OA. In vitro, agrin knockdown resulted in reduced glycosaminoglycan content, downregulation of the cartilage transcription factor SOX9 and other cartilage-specific ECM molecules. Conversely, exogenous agrin supported cartilage differentiation in vitro and ectopic cartilage formation in vivo. In the context of cartilage differentiation, agrin used an unusual receptor repertoire requiring both LRP4 and α-dystroglycan.
CONCLUSIONS
We have discovered that agrin strongly promotes chondrocyte differentiation and cartilage formation in vivo. Our results identify agrin as a novel potent anabolic growth factor with strong therapeutic potential in cartilage regeneration.
Topics: Agrin; Animals; Arthritis, Experimental; Cartilage, Articular; Cells, Cultured; Chondrocytes; Chondrogenesis; Down-Regulation; Dystroglycans; Gene Knockdown Techniques; Homeostasis; Humans; LDL-Receptor Related Proteins; Male; Mice, Inbred DBA; Mice, Knockout; Osteoarthritis; Osteogenesis; RNA, Messenger; RNA, Small Interfering; Receptors, LDL; SOX9 Transcription Factor; Up-Regulation
PubMed: 26290588
DOI: 10.1136/annrheumdis-2015-207316 -
The FEBS Journal Oct 2010The expression of proteoglycans (PGs), essential macromolecules of the tumor microenvironment, is markedly altered during malignant transformation and tumor progression.... (Review)
Review
The expression of proteoglycans (PGs), essential macromolecules of the tumor microenvironment, is markedly altered during malignant transformation and tumor progression. Synthesis of stromal PGs is affected by factors secreted by cancer cells and the unique tumor-modified extracellular matrix may either facilitate or counteract the growth of solid tumors. The emerging theme is that this dual activity has intrinsic tissue specificity. Matrix-accumulated PGs, such as versican, perlecan and small leucine-rich PGs, affect cancer cell signaling, growth and survival, cell adhesion, migration and angiogenesis. Furthermore, expression of cell-surface-associated PGs, such as syndecans and glypicans, is also modulated in both tumor and stromal cells. Cell-surface-associated PGs bind various factors that are involved in cell signaling, thereby affecting cell proliferation, adhesion and motility. An important mechanism of action is offered by a proteolytic processing of cell-surface PGs known as ectodomain shedding of syndecans; this facilitates cancer and endothelial cell motility, protects matrix proteases and provides a chemotactic gradient of mitogens. However, syndecans on stromal cells may be important for stromal cell/cancer cell interplay and may promote stromal cell proliferation, migration and angiogenesis. Finally, abnormal PG expression in cancer and stromal cells may serve as a biomarker for tumor progression and patient survival. Enhanced understanding of the regulation of PG metabolism and the involvement of PGs in cancer may offer a novel approach to cancer therapy by targeting the tumor microenvironment. In this minireview, the implication of PGs in cancer development and progression, as well as their pharmacological targeting in malignancy, are presented and discussed.
Topics: Aggrecans; Agrin; Biomarkers; Brevican; Cartilage; Cell Division; Chondroitin Sulfate Proteoglycans; Decorin; Disease Progression; Extracellular Matrix Proteins; Glioma; Humans; Hyaluronic Acid; Inflammation; Lectins, C-Type; Neoplasms; Neovascularization, Pathologic; Nerve Tissue Proteins; Prognosis; Proteoglycans; Versicans
PubMed: 20840587
DOI: 10.1111/j.1742-4658.2010.07800.x -
BioMed Research International 2018White matter lesion (WML) is popular in the patients aged over 65. Brain edema and blood-brain barrier (BBB) dysfunction due to cerebral chronic hypoperfusion (CCH)...
White matter lesion (WML) is popular in the patients aged over 65. Brain edema and blood-brain barrier (BBB) dysfunction due to cerebral chronic hypoperfusion (CCH) contributed to WML. Preserving astrocyte polarity is vital for BBB integrity. In our experiment, CCH model is established by bilateral carotid arteries occlusion (2VO). Leukoaraiosis was verified by fiber density stain, and brain edema was evaluated using brain water content measuring. The expressions of agrin and aquaporin-4 (AQP4) were evaluated, as well as the integrity of BBB. Astrocyte polarity was assessed by visualizing the distribution of AQP4 on astrocyte end-feet membranes. The results showed that expression of AQP4 firstly increased and then decreased, as agrin expression decreased gradually. At 3 days after 2VO, AQP4 and agrin displayed the most opposite expression with the former increasing and the latter decreasing; at the same time, brain edema reached high point as well as BBB permeability, and astrocyte polarity was degeneration. In the later phase, brain edema and BBB permeability were getting recovered, but WML was getting more evident. In accordance with that, agrin and AQP4 expression decreased significantly with astrocyte polarity reducing. We speculated that agrin and AQP4 played key roles in development of WML by mediating BBB damage in CCH, and BBB dysfunction due to reduced astrocyte polarity is the starting point of WMH.
Topics: Agrin; Animals; Aquaporin 4; Astrocytes; Biological Transport; Blood-Brain Barrier; Brain; Brain Edema; Brain Ischemia; Cell Polarity; Leukoaraiosis; Male; Permeability; Rats; Rats, Wistar
PubMed: 29682525
DOI: 10.1155/2018/2321797 -
Laboratory Investigation; a Journal of... Nov 2010In this study, we investigated the involvement of dystrophin-associated proteins (DAPs) and their relationship with the perivascular basement membrane in the brains of...
In this study, we investigated the involvement of dystrophin-associated proteins (DAPs) and their relationship with the perivascular basement membrane in the brains of mdx mice and controls at the age of 2 months. We analyzed (1) the expression of glial DAPs α-β-dystroglycan (DG), α-syntrophin, aquaporin-4 (AQP4) water channel, Kir 4.1 and dystrophin isoform (Dp71) by immunocytochemistry, laser confocal microscopy, immunogold electron microscopy, immunoblotting and RT-PCR; (2) the ultrastructure of the basement membrane and expression of laminin and agrin; and (3) the dual immunofluorescence colocalization of AQP4/α-β-DG, and of Kir 4.1/agrin. The following results were observed in mdx brain as compared with controls: (1) a significant reduction in protein content and mRNA expression of DAPs; (2) ultrastructurally, a thickened and discontinuous appearance of the basement membrane and a significant reduction in laminin and agrin; and (3) a molecular rearrangment of α-β-DG, coupled with a parallel loss of agrin and Kir 4.1 on basement membrane and glial endfeet. These data indicate that in mdx brain the deficiency in dystrophin and dystrophin isoform (Dp71) is coupled with a reduction of DAP components, coupled with an altered anchoring to the basement membrane.
Topics: Agrin; Animals; Aquaporin 4; Blotting, Western; Brain; Calcium-Binding Proteins; Disease Models, Animal; Down-Regulation; Dystroglycans; Dystrophin-Associated Proteins; Fluorescent Antibody Technique; Laminin; Membrane Proteins; Mice; Mice, Inbred C57BL; Mice, Inbred mdx; Microscopy, Confocal; Microscopy, Electron; Muscle Proteins; Muscular Dystrophy, Duchenne; Potassium Channels, Inwardly Rectifying
PubMed: 20714324
DOI: 10.1038/labinvest.2010.149