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Cell and Tissue Research Aug 2009Accumulating evidence indicates that agrin, a heparan sulphate proteoglycan of the extracellular matrix, plays a role in the organization and maintenance of the...
Accumulating evidence indicates that agrin, a heparan sulphate proteoglycan of the extracellular matrix, plays a role in the organization and maintenance of the blood-brain barrier. This evidence is based on the differential effects of agrin isoforms on the expression and distribution of the water channel protein, aquaporin-4 (AQP4), on the swelling capacity of cultured astrocytes of neonatal mice and on freeze-fracture data revealing an agrin-dependent clustering of orthogonal arrays of particles (OAPs), the structural equivalent of AQP4. Here, we show that the OAP density in agrin-null mice is dramatically decreased in comparison with wild-types, by using quantitative freeze-fracture analysis of astrocytic membranes. In contrast, anti-AQP4 immunohistochemistry has revealed that the immunoreactivity of the superficial astrocytic endfeet of the agrin-null mouse is comparable with that in wild-type mice. Moreover, in vitro, wild-type and agrin-null astrocytes cultured from mouse embryos at embryonic day 19.5 differ neither in AQP4 immunoreactivity, nor in OAP density in freeze-fracture replicas. Analyses of brain tissue samples and cultured astrocytes by reverse transcription with the polymerase chain reaction have not demonstrated any difference in the level of AQP4 mRNA between wild-type astrocytes and astrocytes from agrin-null mice. Furthermore, we have been unable to detect any difference in the swelling capacity between wild-type and agrin-null astrocytes. These results clearly demonstrate, for the first time, that agrin plays a pivotal role for the clustering of OAPs in the endfoot membranes of astrocytes, whereas the mere presence of AQP4 is not sufficient for OAP clustering.
Topics: Agrin; Animals; Aquaporin 4; Astrocytes; Cell-Derived Microparticles; Cells, Cultured; Freeze Fracturing; Mice; Mice, Inbred C57BL; Mice, Knockout; Microscopy, Electron, Scanning
PubMed: 19449033
DOI: 10.1007/s00441-009-0812-z -
The Journal of Biological Chemistry Jun 2009Drugs that inhibit Na,K-ATPases, such as digoxin and ouabain, alter cardiac myocyte contractility. We recently demonstrated that agrin, a protein first identified at the...
Drugs that inhibit Na,K-ATPases, such as digoxin and ouabain, alter cardiac myocyte contractility. We recently demonstrated that agrin, a protein first identified at the vertebrate neuromuscular junction, binds to and regulates the activity of alpha3 subunit-containing isoforms of the Na,K-ATPase in the mammalian brain. Both agrin and the alpha3 Na,K-ATPase are expressed in heart, but their potential for interaction and effect on cardiac myocyte function was unknown. Here we show that agrin binds to the alpha3 subunit of the Na,K-ATPase in cardiac myocyte membranes, inducing tyrosine phosphorylation and inhibiting activity of the pump. Agrin also triggers a rapid increase in cytoplasmic Na(+) in cardiac myocytes, suggesting a role in cardiac myocyte function. Consistent with this hypothesis, spontaneous contraction frequencies of cultured cardiac myocytes prepared from mice in which agrin expression is blocked by mutation of the Agrn gene are significantly higher than in the wild type. The Agrn mutant phenotype is rescued by acute treatment with recombinant agrin. Furthermore, exposure of wild type myocytes to an agrin antagonist phenocopies the Agrn mutation. These data demonstrate that the basal frequency of myocyte contraction depends on endogenous agrin-alpha3 Na,K-ATPase interaction and suggest that agrin modulation of the alpha3 Na,K-ATPase is important in regulating heart function.
Topics: Agrin; Animals; Binding Sites; Cells, Cultured; Cross-Linking Reagents; Fetal Heart; In Vitro Techniques; Mice; Mice, Knockout; Multiprotein Complexes; Mutation; Myocardial Contraction; Myocytes, Cardiac; Peptide Fragments; Phosphorylation; Protein Binding; Sodium-Potassium-Exchanging ATPase; Tyrosine
PubMed: 19376779
DOI: 10.1074/jbc.M806855200 -
Mathematical Biosciences and... Aug 2019The heparan sulfate proteoglycan agrin is known to accumulate in the context of hepatocellular carcinoma (HCC). Agrin is important for neoangiogenesis in HCC tissues,...
The heparan sulfate proteoglycan agrin is known to accumulate in the context of hepatocellular carcinoma (HCC). Agrin is important for neoangiogenesis in HCC tissues, and is incorporated into newly formed vasculature, but exactly how agrin contributes to the pathology of HCC remains to be fully defined. We therefore examined the clinical relevance of agrin as it pertains to HCC progression and prognosis using tissue sections from a total of 313 HCC patients. We found that agrin expression was detectable in more HCC samples (25.4% vs. 77.1%; P < 0.05) compared to normal tissue controls. Agrin expression was notably linked to tumor size (P = 0.041) and metastasis (P = 0.034). The recurrence free survival rate of agrin-positive HCC patients was considerably lower than that of agrin-negative patients (P = 0.001). We further confirmed HCC survival to be independently correlated with tumor size, metastasis, microvascular invasion and edmondson Grade via a Cox regression analysis. Upregulation of Agrin may play a crucial role in HCC progression. Together our results suggest that Agrin has the potential to be used as a prognostic indicator in predicting HCC patient outcomes.
Topics: Adult; Aged; Aged, 80 and over; Agrin; Carcinoma, Hepatocellular; Disease Progression; Female; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Humans; Liver Neoplasms; Male; Middle Aged; Neovascularization, Pathologic; Prognosis; Tissue Array Analysis
PubMed: 31698617
DOI: 10.3934/mbe.2019368 -
EMBO Molecular Medicine Aug 2011Mutations in LAMA2 cause a severe form of congenital muscular dystrophy, called MDC1A. Studies in mouse models have shown that transgenic expression of a designed,...
Mutations in LAMA2 cause a severe form of congenital muscular dystrophy, called MDC1A. Studies in mouse models have shown that transgenic expression of a designed, miniaturized form of the extracellular matrix molecule agrin ('mini-agrin') or apoptosis inhibition by either overexpression of Bcl2 or application of the pharmacological substance omigapil can ameliorate the disease. Here, we tested whether mini-agrin and anti-apoptotic agents act on different pathways and thus exert additive benefits in MDC1A mouse models. By combining mini-agrin with either transgenic Bcl2 expression or oral omigapil application, we show that the ameliorating effect of mini-agrin, which acts by restoring the mechanical stability of muscle fibres and, thereby, reduces muscle fibre breakdown and concomitant fibrosis, is complemented by apoptosis inhibitors, which prevent the loss of muscle fibres. Treatment of mice with both agents results in improved muscle regeneration and increased force. Our results show that the combination of mini-agrin and anti-apoptosis treatment has beneficial effects that are significantly bigger than the individual treatments and suggest that such a strategy might also be applicable to MDC1A patients.
Topics: Agrin; Animals; Disease Models, Animal; Histocytochemistry; Immunohistochemistry; Laminin; Mice; Mice, Transgenic; Muscles; Muscular Dystrophies; Neuromuscular Agents; Oxepins; Proto-Oncogene Proteins c-bcl-2; Rodent Diseases; Survival Analysis
PubMed: 21674808
DOI: 10.1002/emmm.201100151 -
The Journal of Neuroscience : the... Sep 2001In the present study, we examined the role of agrin in axonal and dendritic elongation in central neurons. Dissociated hippocampal neurons were grown in the presence of...
In the present study, we examined the role of agrin in axonal and dendritic elongation in central neurons. Dissociated hippocampal neurons were grown in the presence of either recombinant agrin or antisense oligonucleotides designed to block agrin expression. Our results indicate that agrin differentially regulates axonal and dendritic growth. Recombinant agrin decreased the rate of elongation of main axons but induced the formation of axonal branches. On the other hand, agrin induced both dendritic elongation and dendritic branching. Conversely, cultured hippocampal neurons depleted of agrin extended longer, nonbranched axons and shorter dendrites when compared with controls. These changes in the rates of neurite elongation and branching were paralleled by changes in the composition of the cytoskeleton. In the presence of agrin, there was an upregulation of the expression of microtubule-associated proteins MAP1B, MAP2, and tau. In contrast, a downregulation of the expression of these MAPs was detected in agrin-depleted cells. Taken collectively, these results suggest an important role for agrin as a trigger of the transcription of neuro-specific genes involved in neurite elongation and branching in central neurons.
Topics: Agrin; Animals; Axons; Cells, Cultured; Cytoskeleton; Dendrites; Dose-Response Relationship, Drug; Gene Expression Regulation; Hippocampus; Microtubule-Associated Proteins; Neurites; Neurons; Oligonucleotides, Antisense; Phenotype; RNA, Messenger; Rats; Recombinant Proteins; Time Factors
PubMed: 11517268
DOI: 10.1523/JNEUROSCI.21-17-06802.2001 -
The Journal of Cell Biology Apr 2001At the developing neuromuscular junction, a motoneuron-derived factor called agrin signals through the muscle-specific kinase receptor to induce postsynaptic aggregation...
At the developing neuromuscular junction, a motoneuron-derived factor called agrin signals through the muscle-specific kinase receptor to induce postsynaptic aggregation of the acetylcholine receptor (AChR). The agrin signaling pathway involves tyrosine phosphorylation of the AChR beta subunit, and we have tested its role in receptor localization by expressing tagged, tyrosine-minus forms of the beta subunit in mouse Sol8 myotubes. We find that agrin-induced phosphorylation of the beta subunit occurs only on cell surface AChR, and that AChR-containing tyrosine-minus beta subunit is targeted normally to the plasma membrane. Surface AChR that is tyrosine phosphorylated is less detergent extractable than nonphosphorylated AChR, indicating that it is preferentially linked to the cytoskeleton. Consistent with this, we find that agrin treatment reduces the detergent extractability of AChR that contains tagged wild-type beta subunit but not tyrosine-minus beta subunit. In addition, agrin-induced clustering of AChR containing tyrosine-minus beta subunit is reduced in comparison to wild-type receptor. Thus, we find that agrin-induced phosphorylation of AChR beta subunit regulates cytoskeletal anchoring and contributes to the clustering of the AChR, and this is likely to play an important role in the postsynaptic localization of the receptor at the developing synapse.
Topics: Agrin; Animals; Cell Line; Cytoskeleton; Mice; Phosphorylation; Receptors, Cholinergic; Time Factors; Tyrosine
PubMed: 11285269
DOI: 10.1083/jcb.153.1.1 -
Journal of Molecular Neuroscience : MN Jul 2014Proteins in living organisms have names that are usually derived from their function in the biochemical system their discoverer was investigating. Typical examples are...
Proteins in living organisms have names that are usually derived from their function in the biochemical system their discoverer was investigating. Typical examples are acetylcholinesterase and agrin; however, for both of these, various other functions that are not related to the cholinergic system have been revealed. Our investigations have been focused on the alternative roles of acetylcholinesterase and agrin in the processes of muscle development and regeneration. Previously, we described a role for agrin in the development of excitability in muscle contraction. In this study, we report the effects of agrin on secretion of interleukin 6 in developing human muscle. At the myoblast stage, agrin increases interleukin 6 secretion. This effect seems to be general as it was observed in all of the cell models analysed (human, mouse, cell lines). After fusion of myoblasts into myotubes, the effects of agrin are no longer evident, although agrin has further effects at the innervation stage, at least in in vitro innervated human muscle. These effects of agrin are another demonstration of its non-synaptic roles that are apparently developmental-stage specific. Our data support the view that acetylcholinesterase and agrin participate in various processes during development of skeletal muscle.
Topics: Acetylcholinesterase; Agrin; Animals; Cell Differentiation; Cells, Cultured; Culture Media, Conditioned; HEK293 Cells; Humans; Interleukin-6; Mice; Muscle Fibers, Skeletal; Myoblasts
PubMed: 24326956
DOI: 10.1007/s12031-013-0188-0 -
The Journal of Neuroscience : the... Mar 2012In the adult forebrain, new interneurons are continuously generated and integrated into the existing circuitry of the olfactory bulb (OB). In an attempt to identify... (Comparative Study)
Comparative Study
In the adult forebrain, new interneurons are continuously generated and integrated into the existing circuitry of the olfactory bulb (OB). In an attempt to identify signals that regulate this synaptic integration process, we found strong expression of agrin in adult generated neuronal precursors that arrive in the olfactory bulb after their generation in the subventricular zone. While the agrin receptor components MuSK and Lrp4 were below detection level in neuron populations that represent synaptic targets for the new interneurons, the alternative receptor α3-Na(+)K(+)-ATPase was strongly expressed in mitral cells. Using a transplantation approach, we demonstrate that agrin-deficient interneuron precursors migrate correctly into the OB. However, in contrast to wild-type neurons, which form synapses and survive for prolonged periods, mutant neurons do not mature and are rapidly eliminated. Using in vivo brain electroporation of the olfactory system, we show that the transmembrane form of agrin alone is sufficient to mediate integration and demonstrate that excess transmembrane agrin increases the number of dendritic spines. Last, we provide in vivo evidence that an interaction between agrin and α3-Na(+)K(+)-ATPase is of functional importance in this system.
Topics: Age Factors; Agrin; Animals; Cells, Cultured; Female; Gene Expression Regulation, Enzymologic; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Neurogenesis; Neurons; Olfactory Bulb; Signal Transduction; Sodium-Potassium-Exchanging ATPase; Synapses
PubMed: 22423096
DOI: 10.1523/JNEUROSCI.4906-11.2012 -
Cold Spring Harbor Symposia on... 1996
Review
Topics: Agrin; Animals; Humans; Mice; Neuromuscular Junction; Receptor Protein-Tyrosine Kinases; Receptors, Cell Surface; Signal Transduction
PubMed: 9246472
DOI: No ID Found -
Steroids 1997Androgen-binding protein/sex hormone-binding globulin (ABP/SHBG) is an extracellular binding protein that regulates the bioavailability of sex steroids. ABP/SHBG is... (Comparative Study)
Comparative Study Review
Androgen-binding protein/sex hormone-binding globulin (ABP/SHBG) is an extracellular binding protein that regulates the bioavailability of sex steroids. ABP/SHBG is closely related to the globular (G) domain of vitamin K-dependent protein S family of proteins and more distantly related to the G domains of several extracellular matrix proteins. ABP/SHBG appears to have evolved from the fusion of two ancestral G domains. Expanding evidence suggests that ABP/SHBG has other functions that are mediated through membrane binding, including signal transduction; however, the types of binding proteins (receptors) have not been identified. Sequence comparisons of ABP/SHBG with G domains of its homologs protein S, Gas6, laminin, and agrin have identified regions of ABP/SHBG that may bind receptors related to homolog receptors. These membrane receptors include beta-integrins, alpha-dystroglycan, and receptor tyrosine kinases. The G domains of laminin and related proteins have clearly evolved from a common ancestor to interact with specific receptors and binding proteins. It remains to be determined if ABP/SHBG followed this evolutionary pathway.
Topics: Agrin; Alternative Splicing; Amino Acid Sequence; Androgen-Binding Protein; Animals; Binding Sites; Cytoskeletal Proteins; Dystroglycans; Heparan Sulfate Proteoglycans; Humans; Intercellular Signaling Peptides and Proteins; Laminin; Membrane Glycoproteins; Molecular Sequence Data; Protein S; Proteins; Receptor Protein-Tyrosine Kinases; Sequence Homology; Sex Hormone-Binding Globulin; Signal Transduction
PubMed: 9292933
DOI: 10.1016/s0039-128x(97)00045-7