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Frontiers in Cardiovascular Medicine 2021Recently, the extracellular matrix protein agrin has been reported to promote tumor angiogenesis that supports tumorigenesis and metastasis; however, there is a lack of...
Recently, the extracellular matrix protein agrin has been reported to promote tumor angiogenesis that supports tumorigenesis and metastasis; however, there is a lack of genetic evidence to prove whether agrin derived from the tumors or endothelial cells (ECs) systemically should be the therapeutic target. To date, the physiological role of endothelial agrin has also not been investigated. In the EC-specific agrin knockout mice, we observed normal endothelial and haematopoietic cell development during embryogenesis. Moreover, these mice develop normal vascular barrier integrity and vasoreactivity at the adult stage. Importantly, the growth of localized or metastatic cancer cells was not affected after implantation into endothelial agrin depleted mice. Mechanistically, agrin did not regulate endothelial ERK1/2, YAP or p53 activation that is central to support endothelial proliferation, survival and invasion. Cumulatively, our findings may suggest that agrin could play a redundant role in endothelial development during physiological and tumor angiogenesis. Targeting the endothelial derived agrin might not be effective in inhibiting tumor angiogenesis.
PubMed: 35174224
DOI: 10.3389/fcvm.2021.810477 -
Frontiers in Molecular Biosciences 2019Synapse formation is a very elaborate process dependent upon accurate coordination of pre and post-synaptic specialization, requiring multiple steps and a variety of... (Review)
Review
Synapse formation is a very elaborate process dependent upon accurate coordination of pre and post-synaptic specialization, requiring multiple steps and a variety of receptors and signaling molecules. Due to its relative structural simplicity and the ease in manipulation and observation, the neuromuscular synapse or neuromuscular junction (NMJ)-the connection between motor neurons and skeletal muscle-represents the archetype junction system for studying synapse formation and conservation. This junction is essential for survival, as it controls our ability to move and breath. NMJ formation requires coordinated interactions between motor neurons and muscle fibers, which ultimately result in the formation of a highly specialized post-synaptic architecture and a highly differentiated nerve terminal. Furthermore, to ensure a fast and reliable synaptic transmission following neurotransmitter release, ligand-gated channels (acetylcholine receptors, AChRs) are clustered on the post-synaptic muscle cell at high concentrations in sites opposite the presynaptic active zone, supporting a direct role for nerves in the organization of the post-synaptic membrane architecture. This organized clustering process, essential for NMJ formation and for life, relies on key signaling molecules and receptors and is regulated by soluble extracellular molecules localized within the synaptic cleft. Notably, several mutations as well as auto-antibodies against components of these signaling complexes have been related to neuromuscular disorders. The recent years have witnessed strong progress in the understanding of molecular identities, architectures, and functions of NMJ macromolecules. Among these, prominent roles have been proposed for neural variants of the proteoglycan agrin, its receptor at NMJs composed of the lipoprotein receptor-related protein 4 (LRP4) and the muscle-specific kinase (MuSK), as well as the regulatory soluble synapse-specific protease Neurotrypsin. In this review we summarize the current state of the art regarding molecular structures and (agrin-dependent) canonical, as well as (agrin-independent) non-canonical, MuSK signaling mechanisms that underscore the formation of neuromuscular junctions, with the aim of providing a broad perspective to further stimulate molecular, cellular and tissue biology investigations on this fundamental intercellular contact.
PubMed: 31998752
DOI: 10.3389/fmolb.2019.00156 -
Neuroscience Letters Jul 2020The neuromuscular junction (NMJ) is the vehicle for fast, reliable and robust communication between motor neuron and muscle. The unparalleled accessibility of this... (Review)
Review
The neuromuscular junction (NMJ) is the vehicle for fast, reliable and robust communication between motor neuron and muscle. The unparalleled accessibility of this synapse to morphological, electrophysiological and genetic analysis has yielded an in depth understanding of many molecular components mediating its formation, maturation and stability. However, key questions surrounding the signaling pathways mediating these events and how they play out across the lifetime of the synapse remain unanswered. Such information is critical since the NMJ is necessary for normal movement and is compromised in several settings including myasthenia gravis, amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), muscular dystrophy, sarcopenia and aging. Muscle specific kinase (MuSK) is a central player in most if not all contexts of NMJ formation and stability. However, elucidating the function of this receptor in this range of settings is challenging since MuSK participates in at least three signaling pathways: as a tyrosine kinase-dependent receptor for agrin-LRP4 and Wnts; and, as a kinase-independent BMP co-receptor. Here we focus on NMJ stability during aging and discuss open questions regarding the molecular mechanisms that govern active maintenance of the NMJ, with emphasis on MuSK and the potential role of its multiple signaling contexts.
Topics: Aging; Agrin; Animals; Humans; Motor Neurons; Neuromuscular Junction; Receptor Protein-Tyrosine Kinases; Receptors, Cholinergic
PubMed: 32353380
DOI: 10.1016/j.neulet.2020.135014 -
Clinical Cancer Research : An Official... Mar 2022There is an unmet need for identifying novel biomarkers in Barrett's esophagus that could stratify patients with regards to neoplastic progression. We investigate the...
PURPOSE
There is an unmet need for identifying novel biomarkers in Barrett's esophagus that could stratify patients with regards to neoplastic progression. We investigate the expression patterns of extracellular matrix (ECM) molecules in Barrett's esophagus and Barrett's esophagus-related neoplasia, and assess their value as biomarkers for the diagnosis of Barrett's esophagus-related neoplasia and to predict neoplastic progression.
EXPERIMENTAL DESIGN
Gene-expression analyses of ECM matrisome gene sets were performed using publicly available data on human Barrett's esophagus, Barrett's esophagus-related dysplasia, esophageal adenocarcinoma (ADCA) and normal esophagus. Immunohistochemical expression of basement membrane (BM) marker agrin (AGRN) and p53 was analyzed in biopsies of Barrett's esophagus-related neoplasia from 321 patients in three independent cohorts.
RESULTS
Differential gene-expression analysis revealed significant enrichment of ECM matrisome gene sets in dysplastic Barrett's esophagus and ADCA compared with controls. Loss of BM AGRN expression was observed in both Barrett's esophagus-related dysplasia and ADCA. The mean AGRN loss in Barrett's esophagus glands was significantly higher in Barrett's esophagus-related dysplasia and ADCA compared with non-dysplastic Barrett's esophagus (NDBE; P < 0.001; specificity = 82.2% and sensitivity = 96.4%). Loss of AGRN was significantly higher in NDBE samples from progressors compared with non-progressors (P < 0.001) and identified patients who progressed to advanced neoplasia with a specificity of 80.2% and sensitivity of 54.8%. Moreover, the combination of AGRN loss and abnormal p53 staining identified progression to Barrett's esophagus-related advanced neoplasia with a specificity and sensitivity of 86.5% and 58.7%.
CONCLUSIONS
We highlight ECM changes during Barrett's esophagus progression to neoplasia. BM AGRN loss is a novel diagnostic biomarker that can identify patients with NDBE at increased risk of developing advanced neoplasia.
Topics: Agrin; Barrett Esophagus; Biomarkers; Esophageal Neoplasms; Humans; Tumor Suppressor Protein p53
PubMed: 34785582
DOI: 10.1158/1078-0432.CCR-21-2822 -
Severe congenital myasthenic syndromes caused by agrin mutations affecting secretion by motoneurons.Acta Neuropathologica Oct 2022Congenital myasthenic syndromes (CMS) are predominantly characterized by muscle weakness and fatigability and can be caused by a variety of mutations in genes required...
Congenital myasthenic syndromes (CMS) are predominantly characterized by muscle weakness and fatigability and can be caused by a variety of mutations in genes required for neuromuscular junction formation and maintenance. Among them, AGRN encodes agrin, an essential synaptic protein secreted by motoneurons. We have identified severe CMS patients with uncharacterized p.R1671Q, p.R1698P and p.L1664P mutations in the LG2 domain of agrin. Overexpression in primary motoneurons cultures in vitro and in chick spinal motoneurons in vivo revealed that the mutations modified agrin trafficking, leading to its accumulation in the soma and/or in the axon. Expression of mutant agrins in cultured cells demonstrated accumulation of agrin in the endoplasmic reticulum associated with induction of unfolded protein response (UPR) and impaired secretion in the culture medium. Interestingly, evaluation of the specific activity of individual agrins on AChR cluster formation indicated that when secreted, mutant agrins retained a normal capacity to trigger the formation of AChR clusters. To confirm agrin accumulation and secretion defect, iPS cells were derived from a patient and differentiated into motoneurons. Patient iPS-derived motoneurons accumulated mutant agrin in the soma and increased XBP1 mRNA splicing, suggesting UPR activation. Moreover, co-cultures of patient iPS-derived motoneurons with myotubes confirmed the deficit in agrin secretion and revealed a reduction in motoneuron survival. Altogether, we report the first mutations in AGRN gene that specifically affect agrin secretion by motoneurons. Interestingly, the three patients carrying these mutations were initially suspected of spinal muscular atrophy (SMA). Therefore, in the presence of patients with a clinical presentation of SMA but without mutation in the SMN1 gene, it can be worth to look for mutations in AGRN.
Topics: Agrin; Humans; Motor Neurons; Mutation; Myasthenic Syndromes, Congenital; Neuromuscular Junction
PubMed: 35948834
DOI: 10.1007/s00401-022-02475-8 -
Cells Jul 2019Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction (NMJ). Autoantibodies target key molecules at the NMJ, such as the nicotinic acetylcholine... (Review)
Review
Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction (NMJ). Autoantibodies target key molecules at the NMJ, such as the nicotinic acetylcholine receptor (AChR), muscle-specific kinase (MuSK), and low-density lipoprotein receptor-related protein 4 (Lrp4), that lead by a range of different pathogenic mechanisms to altered tissue architecture and reduced densities or functionality of AChRs, reduced neuromuscular transmission, and therefore a severe fatigable skeletal muscle weakness. In this review, we give an overview of the history and clinical aspects of MG, with a focus on the structure and function of myasthenic autoantigens at the NMJ and how they are affected by the autoantibodies' pathogenic mechanisms. Furthermore, we give a short overview of the cells that are implicated in the production of the autoantibodies and briefly discuss diagnostic challenges and treatment strategies.
Topics: Agrin; Animals; Autoantibodies; Autoantigens; Humans; LDL-Receptor Related Proteins; Muscle, Skeletal; Myasthenia Gravis; Neuromuscular Junction; Receptor Protein-Tyrosine Kinases; Receptors, Cholinergic; Receptors, Nicotinic
PubMed: 31269763
DOI: 10.3390/cells8070671 -
Neurochemistry International Nov 2012Development of the neuromuscular junction (NMJ) requires secretion of specific isoforms of the proteoglycan agrin by motor neurons. Secreted agrin is widely expressed in... (Review)
Review
Development of the neuromuscular junction (NMJ) requires secretion of specific isoforms of the proteoglycan agrin by motor neurons. Secreted agrin is widely expressed in the basal lamina of various tissues, whereas a transmembrane form is highly expressed in the brain. Expression in the brain is greatest during the period of synaptogenesis, but remains high in regions of the adult brain that show extensive synaptic plasticity. The well-established role of agrin in NMJ development and its presence in the brain elicited investigations of its possible role in synaptogenesis in the brain. Initial studies on the embryonic brain and neuronal cultures of agrin-null mice did not reveal any defects in synaptogenesis. However, subsequent studies in culture demonstrated inhibition of synaptogenesis by agrin antisense oligonucleotides or agrin siRNA. More recently, a substantial loss of excitatory synapses was found in the brains of transgenic adult mice that lacked agrin expression everywhere but in motor neurons. The mechanisms by which agrin influences synapse formation, maintenance and plasticity may include enhancement of excitatory synaptic signaling, activation of the "muscle-specific" receptor tyrosine kinase (MuSK) and positive regulation of dendritic filopodia. In this article I will review the evidence that agrin regulates synapse development, plasticity and signaling in the brain and discuss the evidence for the proposed mechanisms.
Topics: Agrin; Animals; Central Nervous System; Mice; Mice, Knockout; Neuronal Plasticity; Signal Transduction; Synapses
PubMed: 22414531
DOI: 10.1016/j.neuint.2012.02.028 -
Scientific Reports Nov 2022SMN protein deficiency causes motoneuron disease spinal muscular atrophy (SMA). SMN-based therapies improve patient motor symptoms to variable degrees. An early hallmark...
SMN protein deficiency causes motoneuron disease spinal muscular atrophy (SMA). SMN-based therapies improve patient motor symptoms to variable degrees. An early hallmark of SMA is the perturbation of the neuromuscular junction (NMJ), a synapse between a motoneuron and muscle cell. NMJ formation depends on acetylcholine receptor (AChR) clustering triggered by agrin and its co-receptors lipoprotein receptor-related protein 4 (LRP4) and transmembrane muscle-specific kinase (MuSK) signalling pathway. We have previously shown that flunarizine improves NMJs in SMA model mice, but the mechanisms remain elusive. We show here that flunarizine promotes AChR clustering in cell-autonomous, dose- and agrin-dependent manners in C2C12 myotubes. This is associated with an increase in protein levels of LRP4, integrin-beta-1 and alpha-dystroglycan, three agrin co-receptors. Furthermore, flunarizine enhances MuSK interaction with integrin-beta-1 and phosphotyrosines. Moreover, the drug acts on the expression and splicing of Agrn and Cacna1h genes in a muscle-specific manner. We reveal that the Cacna1h encoded protein Cav3.2 closely associates in vitro with the agrin co-receptor LRP4. In vivo, it is enriched nearby NMJs during neonatal development and the drug increases this immunolabelling in SMA muscles. Thus, flunarizine modulates key players of the NMJ and identifies Ca3.2 as a new protein involved in the NMJ biology.
Topics: Animals; Mice; Agrin; Flunarizine; Integrins; Muscular Atrophy, Spinal; Neuromuscular Junction; Receptor Protein-Tyrosine Kinases; Receptors, Cholinergic
PubMed: 36347955
DOI: 10.1038/s41598-022-23703-x -
Developmental Biology Jan 2019The role of agrin, Lrp4 and MuSK, key organizers of neuromuscular synaptogenesis, in the developing CNS is only poorly understood. We investigated the role of these...
The role of agrin, Lrp4 and MuSK, key organizers of neuromuscular synaptogenesis, in the developing CNS is only poorly understood. We investigated the role of these proteins in cultured mouse embryonic cortical neurons from wildtype and from Lrp4- and MuSK-deficient mice. Neurons from Lrp4-deficient mice had fewer but longer primary dendrites and a decreased density of puncta containing excitatory and inhibitory synapse-associated proteins. Neurons from MuSK-deficient mice had an altered dendritic branching pattern but no change in the density of puncta stained by antibodies against synapse-associated proteins. Transfection of TM-agrin compensated the dendritic branching deficits in Lrp4-deficient but not in MuSK-deficient neurons. TM-agrin transfection increased the density of excitatory synaptic puncta in MuSK-deficient but not in Lrp4-deficient mice and reduced the number of inhibitory synaptic puncta irrespective of MuSK and Lrp4 expression. Addition of purified soluble agrin to microisland cultures of cortical neurons revealed an Lrp4-dependent increase in the size and density of glutamatergic synaptic puncta and in mEPSC but not in mIPSC frequency and amplitude. Thus, agrin induced an Lrp4-independent increase in dendritic branch complexity, an Lrp4-dependent increase of excitatory synaptic puncta and an Lrp4- and MuSK-independent decrease in the density of puncta containing inhibitory synapse-associated proteins. These results establish selective roles for agrin, Lrp4 and MuSK during dendritogenesis and synaptogenesis in cultured CNS neurons.
Topics: Agrin; Animals; Cell Line; Cells, Cultured; Central Nervous System; Dendrites; Female; LDL-Receptor Related Proteins; Male; Mice; Mice, Inbred C57BL; Neurogenesis; Neuromuscular Junction; Neuronal Plasticity; Neurons; Receptor Protein-Tyrosine Kinases; Receptors, LDL; Synapses
PubMed: 30385274
DOI: 10.1016/j.ydbio.2018.10.017 -
Investigative Ophthalmology & Visual... May 2020To investigate the effect and mechanism of Agrin on limbal stem cell proliferation and corneal wound healing.
PURPOSE
To investigate the effect and mechanism of Agrin on limbal stem cell proliferation and corneal wound healing.
METHODS
Limbal stem cells were isolated and treated with different concentrations of Agrin. CCK-8 and cell proliferation markers (Ki67 and pH3) were detected to evaluate cell numbers or proliferative potential of limbal stem cells. The corneal epithelium wound model was induced by debridement of central corneal epithelial, and the effects of Agrin on limbal stem cell proliferation and corneal epithelial wound healing rate were determined.
RESULTS
Agrin promoted the proliferation of cultured limbal stem cells in vitro and increased the expression level of p63α rather than keratin 12. Furthermore, Agrin accelerated the wound healing rate of corneal epithelium through activating limbal stem cell proliferation in vivo. In terms of mechanism, Agrin could facilitate the dephosphorylation of Yap1, which contributed to the nuclear translocation of Yap1 and expression of Cyclin D1, and subsequently promoted proliferation of limbal stem cells.
CONCLUSIONS
Agrin promotes the proliferation of limbal stem cells and accelerates the healing rate of corneal wound through Hippo-Yap signaling pathway.
Topics: Adaptor Proteins, Signal Transducing; Agrin; Animals; Cell Cycle Proteins; Cell Proliferation; Cells, Cultured; Corneal Injuries; Epithelium, Corneal; Hippo Signaling Pathway; Limbus Corneae; Mice, Inbred C57BL; Models, Animal; Protein Serine-Threonine Kinases; Signal Transduction; Stem Cells; Wound Healing; YAP-Signaling Proteins
PubMed: 32392315
DOI: 10.1167/iovs.61.5.7