Tacrolimus induces fibroblast-to-myofibroblast transition via a TGF-β-dependent mechanism to contribute to renal fibrosis

Use of immunosuppressant calcineurin inhibitors (CNIs) is limited by irreversible kidney damage, hallmarked by renal fibrosis. CNIs directly damage many renal cell types. Given the diverse renal cell populations, additional targeted cell types and signaling mechanisms warrant further investigation. We hypothesized that fibroblasts contribute to CNI-induced renal fibrosis and propagate profibrotic effects via the transforming growth factor-β (TGF-β)/Smad signaling axis. To test this, kidney damage-resistant mice (C57BL/6) received tacrolimus (10 mg/kg) or vehicle for 21 days. Renal damage markers and signaling mediators were assessed. To investigate their role in renal damage, mouse renal fibroblasts were exposed to tacrolimus (1 nM) or vehicle for 24 h. Morphological and functional changes in addition to downstream signaling events were assessed. Tacrolimus-treated kidneys displayed evidence of renal fibrosis. Moreover, α-smooth muscle actin expression was significantly increased, suggesting the presence of fibroblast activation. TGF-β receptor activation and downstream Smad2/3 signaling were also upregulated. Consistent with in vivo findings, tacrolimus-treated renal fibroblasts displayed a phenotypic switch known as fibroblast-to-myofibroblast transition (FMT), as α-smooth muscle actin, actin stress fibers, cell motility, and collagen type IV expression were significantly increased. These findings were accompanied by concomitant induction of TGF-β signaling. Pharmacological inhibition of the downstream TGF-β effector Smad3 attenuated tacrolimus-induced phenotypic changes. Collectively, these findings suggest that 1) tacrolimus inhibits the calcineurin/nuclear factor of activated T cells axis while inducing TGF-β1 ligand secretion and receptor activation in renal fibroblasts; 2) aberrant TGF-β receptor activation stimulates Smad-mediated production of myofibroblast markers, notable features of FMT; and 3) FMT contributes to extracellular matrix expansion in tacrolimus-induced renal fibrosis. These results incorporate renal fibroblasts into the growing list of CNI-targeted cell types and identify renal FMT as a process mediated via a TGF-β-dependent mechanism.NEW & NOTEWORTHY Renal fibrosis, a detrimental feature of irreversible kidney damage, remains a sinister consequence of long-term calcineurin inhibitor (CNI) immunosuppressive therapy. Our study not only incorporates renal fibroblasts into the growing list of cell types negatively impacted by CNIs but also identifies renal fibroblast-to-myofibroblast transition as a process mediated via a TGF-β-dependent mechanism. This insight will direct future studies investigating the feasibility of inhibiting TGF-β signaling to maintain CNI-mediated immunosuppression while ultimately preserving kidney health.

Distinct Changes in Calpain and Calpastatin during PNS Myelination and Demyelination in Rodent Models

Myelin forming around axons provides electrical insulation and ensures rapid and efficient transmission of electrical impulses. Disruptions to myelinated nerves often result in nerve conduction failure along with neurological symptoms and long-term disability. In the central nervous system, calpains, a family of calcium dependent cysteine proteases, have been shown to have a role in developmental myelination and in demyelinating diseases. The roles of calpains in myelination and demyelination in the peripheral nervous system remain unclear. Here, we show a transient increase of activated CAPN1, a major calpain isoform, in postnatal rat sciatic nerves when myelin is actively formed. Expression of the endogenous calpain inhibitor, calpastatin, showed a steady decrease throughout the period of peripheral nerve development. In the sciatic nerves of Trembler-J mice characterized by dysmyelination, expression levels of CAPN1 and calpastatin and calpain activity were significantly increased. In lysolecithin-induced acute demyelination in adult rat sciatic nerves, we show an increase of CAPN1 and decrease of calpastatin expression. These changes in the calpain-calpastatin system are distinct from those during central nervous system development or in acute axonal degeneration in peripheral nerves. Our results suggest that the calpain-calpastatin system has putative roles in myelination and demyelinating diseases of peripheral nerves.

TDP-43 maximizes nerve conduction velocity by repressing a cryptic exon for paranodal junction assembly in Schwann cells

TDP-43 is extensively studied in neurons in physiological and pathological contexts. However, emerging evidence indicates that glial cells are also reliant on TDP-43 function. We demonstrate that deletion of TDP-43 in Schwann cells results in a dramatic delay in peripheral nerve conduction causing significant motor deficits in mice, which is directly attributed to the absence of paranodal axoglial junctions. By contrast, paranodes in the central nervous system are unaltered in oligodendrocytes lacking TDP-43. Mechanistically, TDP-43 binds directly to Neurofascin mRNA, encoding the cell adhesion molecule essential for paranode assembly and maintenance. Loss of TDP-43 triggers the retention of a previously unidentified cryptic exon, which targets Neurofascin mRNA for nonsense-mediated decay. Thus, TDP-43 is required for neurofascin expression, proper assembly and maintenance of paranodes, and rapid saltatory conduction. Our findings provide a framework and mechanism for how Schwann cell-autonomous dysfunction in nerve conduction is directly caused by TDP-43 loss-of-function.

Precise Spatiotemporal Control of Nodal Na+ Channel Clustering by Bone Morphogenetic Protein-1/Tolloid-like Proteinases

During development of the peripheral nervous system (PNS), Schwann-cell-secreted gliomedin induces the clustering of Na⁺ channels at the edges of each myelin segment to form nodes of Ranvier. Here we show that bone morphogenetic protein-1 (BMP1)/Tolloid (TLD)-like proteinases confine Na⁺ channel clustering to these sites by negatively regulating the activity of gliomedin. Eliminating the Bmp1/TLD cleavage site in gliomedin or treating myelinating cultures with a Bmp1/TLD inhibitor results in the formation of numerous ectopic Na⁺ channel clusters along axons that are devoid of myelin segments. Furthermore, genetic deletion of Bmp1 and Tll1 genes in mice using a Schwann-cell-specific Cre causes ectopic clustering of nodal proteins, premature formation of heminodes around early ensheathing Schwann cells, and altered nerve conduction during development. Our results demonstrate that by inactivating gliomedin, Bmp1/TLD functions as an additional regulatory mechanism to ensure the correct spatial and temporal assembly of PNS nodes of Ranvier.

Impairment of cognitive flexibility in type 2 diabetic db/db mice

Impaired executive function is a major peril for patients with type 2 diabetes, reducing quality of life and ability for diabetes management. Despite the significance of this impairment, few animal models of type 2 diabetes examine domains of executive function such as cognitive flexibility or working memory. Here, we evaluated these executive function domains in db/db mice, an established model of type 2 diabetes, at 10 and 24 weeks of age. The db/db mice showed impaired cognitive flexibility in the Morris water maze reversal phase. However, the db/db mice did not show apparent working memory disturbance in the spatial working memory version of the Morris water maze or in the radial water maze. We also examined axon initial segments (AIS) and nodes of Ranvier, key axonal domains for action potential initiation and propagation. AIS were significantly shortened in medial prefrontal cortex and hippocampus of 26-week-old db/db mice compared with controls, similar to our previous findings in 10-week-old mice. Nodes of Ranvier in corpus callosum, previously shown to be unchanged at 10 weeks, were elongated at 26 weeks, suggesting an important role for this domain in disease progression. Together, the findings help establish db/db mice as a model of impaired cognitive flexibility in type 2 diabetes and advance our understanding of its pathophysiology.

Methylglyoxal Disrupts Paranodal Axoglial Junctions via Calpain Activation

Nodes of Ranvier and associated paranodal and juxtaparanodal domains along myelinated axons are essential for normal function of the peripheral and central nervous systems. Disruption of these domains as well as increases in the reactive carbonyl species methylglyoxal are implicated as a pathophysiology common to a wide variety of neurological diseases. Here, using an ex vivo nerve exposure model, we show that increasing methylglyoxal produces paranodal disruption, evidenced by disorganized immunostaining of axoglial cell-adhesion proteins, in both sciatic and optic nerves from wild-type mice. Consistent with previous studies showing that increase of methylglyoxal can alter intracellular calcium homeostasis, we found upregulated activity of the calcium-activated protease calpain in sciatic nerves after methylglyoxal exposure. Methylglyoxal exposure altered clusters of proteins that are known as calpain substrates: ezrin in Schwann cell microvilli at the perinodal area and zonula occludens 1 in Schwann cell autotypic junctions at paranodes. Finally, treatment with the calpain inhibitor calpeptin ameliorated methylglyoxal-evoked ezrin loss and paranodal disruption in both sciatic and optic nerves. Our findings strongly suggest that elevated methylglyoxal levels and subsequent calpain activation contribute to the disruption of specialized axoglial domains along myelinated nerve fibers in neurological diseases.

Methylglyoxal and a spinal TRPA1-AC1-Epac cascade facilitate pain in the db/db mouse model of type 2 diabetes

Painful diabetic neuropathy (PDN) is a devastating neurological complication of diabetes. Methylglyoxal (MG) is a reactive metabolite whose elevation in the plasma corresponds to PDN in patients and pain-like behavior in rodent models of type 1 and type 2 diabetes. Here, we addressed the MG-related spinal mechanisms of PDN in type 2 diabetes using db/db mice, an established model of type 2 diabetes, and intrathecal injection of MG in conventional C57BL/6J mice. Administration of either a MG scavenger (GERP10) or a vector overexpressing glyoxalase 1, the catabolic enzyme for MG, attenuated heat hypersensitivity in db/db mice. In C57BL/6J mice, intrathecal administration of MG produced signs of both evoked (heat and mechanical hypersensitivity) and affective (conditioned place avoidance) pain. MG-induced Ca²⁺ mobilization in lamina II dorsal horn neurons of C57BL/6J mice was exacerbated in db/db, suggestive of MG-evoked central sensitization. Pharmacological and/or genetic inhibition of transient receptor potential ankyrin subtype 1 (TRPA1), adenylyl cyclase type 1 (AC1), protein kinase A (PKA), or exchange protein directly activated by cyclic adenosine monophosphate (Epac) blocked MG-evoked hypersensitivity in C57BL/6J mice. Similarly, intrathecal administration of GERP10, or inhibitors of TRPA1 (HC030031), AC1 (NB001), or Epac (HJC-0197) attenuated hypersensitivity in db/db mice. We conclude that MG and sensitization of a spinal TRPA1-AC1-Epac signaling cascade facilitate PDN in db/db mice. Our results warrant clinical investigation of MG scavengers, glyoxalase inducers, and spinally-directed pharmacological inhibitors of a MG-TRPA1-AC1-Epac pathway for the treatment of PDN in type 2 diabetes.

Functional Domains in Myelinated Axons

Propagation of action potentials along axons is optimized through interactions between neurons and myelinating glial cells. Myelination drives division of the axons into distinct molecular domains including nodes of Ranvier. The high density of voltage-gated sodium channels at nodes generates action potentials allowing for rapid and efficient saltatory nerve conduction. At paranodes flanking both sides of the nodes, myelinating glial cells interact with axons, forming junctions that are essential for node formation and maintenance. Recent studies indicate that the disruption of these specialized axonal domains is involved in the pathophysiology of various neurological diseases. Loss of paranodal axoglial junctions due to genetic mutations or autoimmune attack against the paranodal proteins leads to nerve conduction failure and neurological symptoms. Breakdown of nodal and paranodal proteins by calpains, the calcium-dependent cysteine proteases, may be a common mechanism involved in various nervous system diseases and injuries. This chapter reviews recent progress in neurobiology and pathophysiology of specialized axonal domains along myelinated nerve fibers.

Type 2 Diabetes Leads to Axon Initial Segment Shortening in db/db Mice

Cognitive and mood impairments are common central nervous system complications of type 2 diabetes, although the neuronal mechanism(s) remains elusive. Previous studies focused mainly on neuronal inputs such as altered synaptic plasticity. Axon initial segment (AIS) is a specialized functional domain within neurons that regulates neuronal outputs. Structural changes of AIS have been implicated as a key pathophysiological event in various psychiatric and neurological disorders. Here we evaluated the structural integrity of the AIS in brains of db/db mice, an established animal model of type 2 diabetes associated with cognitive and mood impairments. We assessed the AIS before (5 weeks of age) and after (10 weeks) the development of type 2 diabetes, and after daily exercise treatment of diabetic condition. We found that the development of type 2 diabetes is associated with significant AIS shortening in both medial prefrontal cortex and hippocampus, as evident by immunostaining of the AIS structural protein βIV spectrin. AIS shortening occurs in the absence of altered neuronal and AIS protein levels. We found no change in nodes of Ranvier, another neuronal functional domain sharing a molecular organization similar to the AIS. This is the first study to identify AIS alteration in type 2 diabetes condition. Since AIS shortening is known to lower neuronal excitability, our results may provide a new avenue for understanding and treating cognitive and mood impairments in type 2 diabetes.

Chronic peripheral nerve compression disrupts paranodal axoglial junctions

INTRODUCTION

Peripheral nerves are often exposed to mechanical stress leading to compression neuropathies. The pathophysiology underlying nerve dysfunction by chronic compression is largely unknown.

METHODS

We analyzed molecular organization and fine structures at and near nodes of Ranvier in a compression neuropathy model in which a silastic tube was placed around the mouse sciatic nerve.

RESULTS

Immunofluorescence study showed that clusters of cell adhesion complex forming paranodal axoglial junctions were dispersed and overlapped frequently with juxtaparanodal components. These paranodal changes occurred without internodal myelin damage. The distribution and pattern of paranodal disruption suggests that these changes are the direct result of mechanical stress. Electron microscopy confirmed loss of paranodal axoglial junctions.

CONCLUSIONS

Our data show that chronic nerve compression disrupts paranodal junctions and axonal domains required for proper peripheral nerve function. These results provide important clues toward better understanding of the pathophysiology underlying nerve dysfunction in compression neuropathies. Muscle Nerve 55: 544-554, 2017.

Formation and disruption of functional domains in myelinated CNS axons

Communication in the central nervous system (CNS) occurs through initiation and propagation of action potentials at excitable domains along axons. Action potentials generated at the axon initial segment (AIS) are regenerated at nodes of Ranvier through the process of saltatory conduction. Proper formation and maintenance of the molecular structure at the AIS and nodes are required for sustaining conduction fidelity. In myelinated CNS axons, paranodal junctions between the axolemma and myelinating oligodendrocytes delineate nodes of Ranvier and regulate the distribution and localization of specialized functional elements, such as voltage-gated sodium channels and mitochondria. Disruption of excitable domains and altered distribution of functional elements in CNS axons is associated with demyelinating diseases such as multiple sclerosis, and is likely a mechanism common to other neurological disorders. This review will provide a brief overview of the molecular structure of the AIS and nodes of Ranvier, as well as the distribution of mitochondria in myelinated axons. In addition, this review highlights important structural and functional changes within myelinated CNS axons that are associated with neurological dysfunction.

Activity-dependent regulation of excitable axonal domains

Rapid action potential propagation along myelinated axons requires voltage-gated Na(+) channel clustering at the axon initial segments (AISs) and nodes of Ranvier. The AIS is intrinsically defined by cytoskeletal proteins expressed in axons, whereas nodes of Ranvier are formed by interaction between neurons and myelinating glia. These axonal domains have long been considered stable structures, but recent studies revealed that they are plastic and contribute to fine adjustment of neuronal activities and circuit function. The AIS changes its distribution and maintains neural circuit activity at a constant level. Morphological changes in myelinated nerve structures presumably modulate the excitability of nodal regions and regulate the timing of activity, thereby optimizing signal processing in a neural circuit. This review highlights recent findings on the structural plasticity of these excitable axonal domains.

Submembranous cytoskeletons stabilize nodes of Ranvier

Rapid action potential propagation along myelinated axons requires voltage-gated Na(+) (Nav) channel clustering at nodes of Ranvier. At paranodes flanking nodes, myelinating glial cells interact with axons to form junctions. The regions next to the paranodes called juxtaparanodes are characterized by high concentrations of voltage-gated K(+) channels. Paranodal axoglial junctions function as barriers to restrict the position of these ion channels. These specialized domains along the myelinated nerve fiber are formed by multiple molecular mechanisms including interactions between extracellular matrix, cell adhesion molecules, and cytoskeletal scaffolds. This review highlights recent findings into the roles of submembranous cytoskeletal proteins in the stabilization of molecular complexes at and near nodes. Axonal ankyrin-spectrin complexes stabilize Nav channels at nodes. Axonal protein 4.1B-spectrin complexes contribute to paranode and juxtaparanode organization. Glial ankyrins enriched at paranodes facilitate node formation. Finally, disruption of spectrins or ankyrins by genetic mutations or proteolysis is involved in the pathophysiology of various neurological or psychiatric disorders.

Sialylation regulates brain structure and function

Every cell expresses a molecularly diverse surface glycan coat (glycocalyx) comprising its interface with its cellular environment. In vertebrates, the terminal sugars of the glycocalyx are often sialic acids, 9-carbon backbone anionic sugars implicated in intermolecular and intercellular interactions. The vertebrate brain is particularly enriched in sialic acid-containing glycolipids termed gangliosides. Human congenital disorders of ganglioside biosynthesis result in paraplegia, epilepsy, and intellectual disability. To better understand sialoglycan functions in the nervous system, we studied brain anatomy, histology, biochemistry, and behavior in mice with engineered mutations in St3gal2 and St3gal3, sialyltransferase genes responsible for terminal sialylation of gangliosides and some glycoproteins. St3gal2/3 double-null mice displayed dysmyelination marked by a 40% reduction in major myelin proteins, 30% fewer myelinated axons, a 33% decrease in myelin thickness, and molecular disruptions at nodes of Ranvier. In part, these changes may be due to dysregulation of ganglioside-mediated oligodendroglial precursor cell proliferation. Neuronal markers were also reduced up to 40%, and hippocampal neurons had smaller dendritic arbors. Young adult St3gal2/3 double-null mice displayed impaired motor coordination, disturbed gait, and profound cognitive disability. Comparisons among sialyltransferase mutant mice provide insights into the functional roles of brain gangliosides and sialoglycoproteins consistent with related human congenital disorders.

Membrane domain organization of myelinated axons requires βII spectrin

The spectrin-based cytoskeleton functions as a barrier to restrict axonal proteins, such as juxtaparanodal K⁺ channels, to specific membrane domains.

The precise and remarkable subdivision of myelinated axons into molecularly and functionally distinct membrane domains depends on axoglial junctions that function as barriers. However, the molecular basis of these barriers remains poorly understood. Here, we report that genetic ablation and loss of axonal βII spectrin eradicated the paranodal barrier that normally separates juxtaparanodal K⁺ channel protein complexes located beneath the myelin sheath from Na⁺ channels located at nodes of Ranvier. Surprisingly, the K⁺ channels and their associated proteins redistributed into paranodes where they colocalized with intact Caspr-labeled axoglial junctions. Furthermore, electron microscopic analysis of the junctions showed intact paranodal septate-like junctions. Thus, the paranodal spectrin-based submembranous cytoskeleton comprises the paranodal barriers required for myelinated axon domain organization.

Three mechanisms assemble central nervous system nodes of Ranvier

Rapid action potential propagation in myelinated axons requires Na⁺ channel clustering at nodes of Ranvier. However, the mechanism of clustering at CNS nodes remains poorly understood. Here, we show that the assembly of nodes of Ranvier in the CNS involves three mechanisms: a glia-derived extracellular matrix (ECM) complex containing proteoglycans and adhesion molecules that cluster NF186, paranodal axoglial junctions that function as barriers to restrict the position of nodal proteins, and axonal cytoskeletal scaffolds (CSs) that stabilize nodal Na⁺ channels. We show that while mice with a single disrupted mechanism had mostly normal nodes, disruptions of the ECM and paranodal barrier, the ECM and CS, or the paranodal barrier and CS all lead to juvenile lethality, profound motor dysfunction, and significantly reduced Na⁺ channel clustering. Our results demonstrate that ECM, paranodal, and axonal cytoskeletal mechanisms ensure robust CNS nodal Na⁺ channel clustering.

Dysfunction of nodes of Ranvier: a mechanism for anti-ganglioside antibody-mediated neuropathies

Autoantibodies against gangliosides GM1 or GD1a are associated with acute motor axonal neuropathy (AMAN) and acute motor-sensory axonal neuropathy (AMSAN), whereas antibodies to GD1b ganglioside are detected in acute sensory ataxic neuropathy (ASAN). These neuropathies have been proposed to be closely related and comprise a continuous spectrum, although the underlying mechanisms, especially for sensory nerve involvement, are still unclear. Antibodies to GM1 and GD1a have been proposed to disrupt the nodes of Ranvier in motor nerves via complement pathway. We hypothesized that the disruption of nodes of Ranvier is a common mechanism whereby various anti-ganglioside antibodies found in these neuropathies lead to nervous system dysfunction. Here, we show that the IgG monoclonal anti-GD1a/GT1b antibody injected into rat sciatic nerves caused deposition of IgG and complement products on the nodal axolemma and disrupted clusters of nodal and paranodal molecules predominantly in motor nerves, and induced early reversible motor nerve conduction block. Injection of IgG monoclonal anti-GD1b antibody induced nodal disruption predominantly in sensory nerves. In an ASAN rabbit model associated with IgG anti-GD1b antibodies, complement-mediated nodal disruption was observed predominantly in sensory nerves. In an AMAN rabbit model associated with IgG anti-GM1 antibodies, complement attack of nodes was found primarily in motor nerves, but occasionally in sensory nerves as well. Periaxonal macrophages and axonal degeneration were observed in dorsal roots from ASAN rabbits and AMAN rabbits. Thus, nodal disruption may be a common mechanism in immune-mediated neuropathies associated with autoantibodies to gangliosides GM1, GD1a, or GD1b, providing an explanation for the continuous spectrum of AMAN, AMSAN, and ASAN.

187 EFFICIENCY OF DIAGNOSIS OF CLINICAL AND SUBCLINICAL ENDOMETRITIS IN CATTLE EVALUATED BY HYSTEROSCOPY

The objective of this study was to evaluate the efficiency of vaginoscopy and rectal palpation (palpable liquid in uterine horns) compared with hysteroscopy (presence of pus in the uterine lumen) for the diagnosis of clinical endometritis (CE), and hysteroscopy compared with endometrial cytology for the diagnosis of subclinical endometritis (SE) in postpartum dairy cows. Thirty Holstein cows between 20 and 35 days postpartum were examined for diagnosis of CE with a vaginal speculum, by rectal palpation, and by hysteroscopy; and examined for diagnosis of SE with hysteroscopy and endometrial cytology. Categorical data were analyzed with PROC CATMOD (SAS®, SAS Institute, Cary, NC, USA) and continuous data were analyzed with PROC GLM (SAS®, SAS Institute, Cary, NC, USA). Sensitivity, specificity, predicted value of a positive and negative result, and efficiency were calculated using Win Episcope® 2.0 software (Clive, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, UK). Prevalence of CE diagnosed by vaginoscopy was 27%, by rectal palpation was 23%, and by hysteroscopy was 13%. When hysteroscopy, the only tool for direct examination of the endometrium, was used as the gold standard for diagnosis of CE, vaginoscopy had 100% sensitivity, 85% specificity, and 87% efficiency, and rectal palpation had 75% sensitivity, 85% specificity, and 83% efficiency. Prevalence of SE diagnosed by endometrial cytology was 35.3%. When endometrial cytology was used as the gold standard for diagnosis of SE, hysteroscopy had 11% sensitivity, 92% specificity, and 59% efficiency. In conclusion, vaginoscopy had higher sensitivity than, and similar specificity and efficiency to, rectal palpation for diagnosis of CE. Conversely, hysteroscopy, although having high specificity, had low sensitivity and efficiency for diagnosis of SE. Hysteroscopy proved to be efficient for diagnosis of CE but inefficient for diagnosis of SE. The authors gratefully acknowledge the support of the study by World of Medicine (WOM), Berlin, Germany, for providing all endoscopic equipment and the cooperation with the dairy farm in Brandenburg, Germany. Vanina Madoz visit to the Freie Universität Berlin was supported by a fellowship from the Deutscher Akademischer Austauschdienst, DAAD.

Molecular mechanisms of node of Ranvier formation

Action potential propagation along myelinated nerve fibers requires high-density protein complexes that include voltage-gated Na(+) channels at the nodes of Ranvier. Several complementary mechanisms may be involved in node assembly including: (1) interaction of nodal cell adhesion molecules with the extracellular matrix; (2) restriction of membrane protein mobility by paranodal junctions; and (3) stabilization of ion channel clusters by axonal cytoskeletal scaffolds. In the peripheral nervous system, a secreted glial protein at the nodal extracellular matrix interacts with axonal cell adhesion molecules to initiate node formation. In the central nervous system, both glial soluble factors and paranodal axoglial junctions may function in a complementary manner to contribute to node formation.

Complement inhibitor prevents disruption of sodium channel clusters in a rabbit model of Guillain-Barré syndrome

Complement-mediated disruption of voltage-gated sodium channels at the nodes of Ranvier acts in the development of acute motor axonal neuropathy. Nafamostat mesilate, a synthetic serine protease inhibitor, used in clinical practice for more than 20 years, has anti-complement activity. Acute motor axonal neuropathy rabbits obtained by GM1 ganglioside sensitization were or were not given nafamostat mesilate intravenously. Complement deposition and sodium channel disruption in the spinal anterior roots were significantly less frequent in the treated rabbits than in the controls. Nafamostat mesilate inhibited complement deposition and prevented sodium channel disruption. This provided the rationale for a clinical trial.

Spectrin and ankyrin-based cytoskeletons at polarized domains in myelinated axons

In myelinated nerve fibers, action potential initiation and propagation requires that voltage-gated ion channels be clustered at high density in the axon initial segments and nodes of Ranvier. The molecular organization of these subdomains depends on specialized cytoskeletal and scaffolding proteins such as spectrins, ankyrins, and 4.1 proteins. These cytoskeletal proteins are considered to be important for 1) formation, localization, and maintenance of specific integral membrane protein complexes, 2) a barrier restricting the diffusion of both cytoplasmic and membrane proteins to distinct regions or compartments of the cell, and 3) stabilization of axonal membrane integrity. Increased insights into the role of the cytoskeleton could provide important clues about the pathophysiology of various neurological disorders.

Anti-GM1 antibodies cause complement-mediated disruption of sodium channel clusters in peripheral motor nerve fibers

Voltage-gated Na+ (Na(v)) channels are highly concentrated at nodes of Ranvier in myelinated axons and facilitate rapid action potential conduction. Autoantibodies to gangliosides such as GM1 have been proposed to disrupt nodal Nav channels and lead to Guillain-Barré syndrome, an autoimmune neuropathy characterized by acute limb weakness. To test this hypothesis, we examined the molecular organization of nodes in a disease model caused by immunization with gangliosides. At the acute phase with progressing limb weakness, Na(v) channel clusters were disrupted or disappeared at abnormally lengthened nodes concomitant with deposition of IgG and complement products. Paranodal axoglial junctions, the nodal cytoskeleton, and Schwann cell microvilli, all of which stabilize Na(v) channel clusters, were also disrupted. The nodal molecules disappeared in lesions with complement deposition but no localization of macrophages. During recovery, complement deposition at nodes decreased, and Na(v) channels redistributed on both sides of affected nodes. These results suggest that Na(v) channel alterations occur as a consequence of complement-mediated disruption of interactions between axons and Schwann cells. Our findings support the idea that acute motor axonal neuropathy is a disease that specifically disrupts the nodes of Ranvier.

Leukocyte and complement activation by GM1-specific antibodies is associated with acute motor axonal neuropathy in rabbits

Acute motor axonal neuropathy (AMAN) in humans is associated with the presence of GM1-specific antibodies. Immunization of rabbits with GM1-containing ganglioside mixtures, purified GM1, or Campylobacter jejuni lipo-oligosaccharide exhibiting a GM1-like structure elicits GM1-specific antibodies, but axonal polyneuropathy only occurs in a subset of animals. This study aimed to dissect the molecular basis for the variable induction of AMAN in rabbits. Therefore, we analyzed the pro-inflammatory characteristics of GM1-specific antibodies in plasma samples from ganglioside-immunized rabbits with and without neurological deficits. GM1-specific plasma samples from all rabbits with AMAN were capable of activating both complement and leukocytes, in contrast to none of the plasma samples from rabbits without paralysis. Furthermore, GM1-specific IgG-mediated activation of leukocytes was detected before the onset of clinical signs. These data suggest that AMAN only occurs in rabbits that develop GM1-specific antibodies with pro-inflammatory properties.

Gangliosides contribute to stability of paranodal junctions and ion channel clusters in myelinated nerve fibers

Paranodal axo-glial junctions are important for ion channel clustering and rapid action potential propagation in myelinated nerve fibers. Paranode formation depends on the cell adhesion molecules neurofascin (NF) 155 in glia, and a Caspr and contactin heterodimer in axons. We found that antibody to ganglioside GM1 labels paranodal regions. Autoantibodies to the gangliosides GM1 and GD1a are thought to disrupt nodes of Ranvier in peripheral motor nerves and cause Guillain-Barré syndrome, an autoimmune neuropathy characterized by acute limb weakness. To elucidate ganglioside function at and near nodes of Ranvier, we examined nodes in mice lacking gangliosides including GM1 and GD1a. In both peripheral and central nervous systems, some paranodal loops failed to attach to the axolemma, and immunostaining of Caspr and NF155 was attenuated. K(+) channels at juxtaparanodes were mislocalized to paranodes, and nodal Na(+) channel clusters were broadened. Abnormal immunostaining at paranodes became more prominent with age. Moreover, the defects were more prevalent in ventral than dorsal roots, and less frequent in mutant mice lacking the b-series gangliosides but with excess GM1 and GD1a. Electrophysiological studies revealed nerve conduction slowing and reduced nodal Na(+) current in mutant peripheral motor nerves. The amounts of Caspr and NF155 in low density, detergent insoluble membrane fractions were reduced in mutant brains. These results indicate that gangliosides are lipid raft components that contribute to stability and maintenance of neuron-glia interactions at paranodes.

Ganglioside-specific IgG and IgA recruit leukocyte effector functions in Guillain-Barré syndrome

The capacity of ganglioside-specific autoantibodies to recruit leukocyte effector functions was studied. Serum samples from 87 patients with Guillain-Barré (GBS) or Miller Fisher syndrome (MFS), containing GM1-, GQ1b-, or GD1b-specific IgG or IgA, were tested for leukocyte activating capacity. Ganglioside-specific IgG antibodies generally induced leukocyte activation, irrespective of specificity. The magnitude of leukocyte degranulation correlated with GM1- and GQ1b-specific IgG titers, but not with disease severity. Finally, GM1-specific IgA activated leukocytes through the IgA receptor, FcalphaRI (CD89). Therefore, both ganglioside-specific IgG and IgA can recruit leukocyte effector functions, which may be relevant in the pathogenesis of GBS and MFS.

Anti-GT1a IgG antibodies in a child with severe Guillain-Barré syndrome

This report describes a male, age 8 years 10 months, with severe Guillain-Barré syndrome after Campylobacter jejuni infection. The patient developed fulminant muscle weakness, external ophthalmoplegia, bulbar palsy, and respiratory distress. A high level of serum monospecific anti-GT1a immunoglobulin G antibody was detected. He was treated with intravenous immunoglobulins and artificial ventilation. Two years after the onset, the patient still suffered from residual leg weakness and foot drop. After 3 years and clinical recovery, the antibody was no longer detectable. This report presents the first case in childhood suggesting an association between a severe Guillain-Barré syndrome after C. jejuni enteritis with monospecific anti-GT1a immunoglobulin G antibody.

Rituximab therapy in chronic inflammatory demyelinating polyradiculoneuropathy with anti-SGPG IgM antibody

We report a patient with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) who showed high titers of anti-sulfated glucuronyl paragloboside (SGPG) IgM antibody without M-protein in serum. The patient was resistant to corticosteroids and immunosuppressants, but after administration of rituximab, clinical symptoms improved and the patient remained in a stable state for approximately 10 months. Rituximab may be a potent therapeutic option for refractory cases of CIDP irrespective of detectable M-protein in either serum or urine.

Spectrins and ankyrinB constitute a specialized paranodal cytoskeleton

Paranodal junctions of myelinated nerve fibers are important for saltatory conduction and function as paracellular and membrane protein diffusion barriers flanking nodes of Ranvier. The formation of these specialized axoglial contacts depends on the presence of three cell adhesion molecules: neurofascin 155 on the glial membrane and a complex of Caspr and contactin on the axon. We isolated axonal and glial membranes highly enriched in these paranodal proteins and then used mass spectrometry to identify additional proteins associated with the paranodal axoglial junction. This strategy led to the identification of three novel components of the paranodal cytoskeleton: ankyrinB, alphaII spectrin, and betaII spectrin. Biochemical and immunohistochemical analyses revealed that these proteins associate with protein 4.1B in a macromolecular complex that is concentrated at central and peripheral paranodal junctions in the adult and during early myelination. Furthermore, we show that the paranodal localization of ankyrinB is disrupted in Caspr-null mice with aberrant paranodal junctions, demonstrating that paranodal neuron-glia interactions regulate the organization of the underlying cytoskeleton. In contrast, genetic disruption of the juxtaparanodal protein Caspr2 or the nodal cytoskeletal protein betaIV spectrin did not alter the paranodal cytoskeleton. Our results demonstrate that the paranodal junction contains specialized cytoskeletal components that may be important to stabilize axon-glia interactions and contribute to the membrane protein diffusion barrier found at paranodes.

[A case of acute oropharyngeal palsy with nasal voice as main symptom]

We report a patient with acute oropharyngeal palsy following enteritis. A 19-year-old woman developed increasing nasal voice over a few days. Neurological examination on day 7 of her course showed paretic dysarthria and mild weakness of neck flexion and quadriceps femoris muscle (Medical Research Council grade, 4+). Her palatal movement was diminished, whereas both palatal and pharyngeal reflex was normal. She could swallow water, although she had a slight amount of liquid reflux to her nose on swallowing. High titers of serum anti-Campylobacter jejuni, anti-GQ1b and anti-GT1a IgG antibodies were detected. Her symptoms improved gradually without any treatment, and disappeared by 40 days from neurological onset. Nasal voice with slight swallowing impairment as initial symptom has been rarely reported, but can occur in acute oropharyngeal palsy. Therefore, neurologists should take into account the possibility of Guillain-Barré syndrome and the regional variants in patients who show nasal voice during the initial stage.

Difference in neuropathogenetic mechanisms in human furious and paralytic rabies

Whereas paralysis is the hallmark for paralytic rabies, the precise pathological basis of paralysis is not known. It is unclear whether weakness results from involvement of anterior horn cells or of motor nerve fibers. There is also no conclusive data on the cause of the neuropathic pain which occurs at the bitten region, although it has been presumed to be related to sensory ganglionopathy. In this study, six laboratory-proven rabies patients (three paralytic and three furious) were assessed clinically and electrophysiologically. Our data suggests that peripheral nerve dysfunction, most likely demyelination, contributes to the weakness in paralytic rabies. In furious rabies, progressive focal denervation, starting at the bitten segment, was evident even in the absence of demonstrable weakness and the electrophysiologic study suggested anterior horn cell dysfunction. In two paralytic and one furious rabies patients who had severe paresthesias as a prodrome, electrophysiologic studies suggested dorsal root ganglionopathy. Postmortem studies in two paralytic and one furious rabies patients, who had local neuropathic pain, showed severe dorsal root ganglionitis. Intense inflammation of the spinal nerve roots was observed more in paralytic rabies patients. Inflammation was mainly noted in the spinal cord segment corresponding to the bite in all cases; however, central chromatolysis of the anterior horn cells could be demonstrated only in furious rabies patient. We conclude that differential sites of neural involvement and possibly different neuropathogenetic mechanisms may explain the clinical diversity in human rabies.

Intractable chronic inflammatory demyelinating polyneuropathy treated successfully with ciclosporin

BACKGROUND

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a heterogeneous disorder and both clinical course and response to treatment vary widely. Because of the propensity for relapse, CIDP requires maintenance therapy after the initial response to treatment. There is no consensus regarding this in the published literature.

PRESENT REPORT

A patient with CIDP was treated with oral prednisolone and cyclophosphamide pulse therapy but required repeated plasma exchange and intravenous immunoglobulin (IVIg). Treatment with ciclosporin freed the patient from repeated IVIg administration. Therapeutic responses in 14 subsequent cases including three patients who showed improvement with ciclosporin are also presented along with an algorithm of the authors' suggested protocol for treatment.

CONCLUSION

Ciclosporin should be considered for patients with intractable CIDP who require repeated IVIg.

Guillain-Barre syndrome with meningoencephalitis after Campylobacter jejuni infection

A 14-year-old boy presented with progressive ascending muscle weakness, urinary retention and disturbed consciousness. Initially his cerebrospinal fluid showed pleocytosis, and protein-cellular dissociation developed later. Campylobacter jejuni was isolated from his stool and serum anti-ganglioside antibodies were positive. Our case suggests that coexistence of meningoencephalitis at an early stage of illness does not necessarily exclude the diagnosis of Guillain-Barre syndrome.

Various immunization protocols for an acute motor axonal neuropathy rabbit model compared

Various ganglioside immunization protocols were examined to refine the procedure for establishing an animal model of acute motor axonal neuropathy. The most effective was subcutaneous injection of an emulsion of 2.5mg of bovine brain ganglioside mixtures, keyhole lympet hemocyanin, and complete Freund's adjuvant to Japanese white rabbits, repeated at 3-week intervals. Under that protocol, all the rabbits developed marked flaccid paralysis associated with plasma anti-GM1 IgG antibody. This acute motor axonal neuropathy rabbit model also could be reproduced by the use of incomplete Freund's adjuvant, methylated bovine serum albumin, and New Zealand white rabbits. These results provide useful information for the confirmation of and further research on the model.

[A variant of Guillain-Barré syndrome with prominent bilateral peripheral facial nerve palsy--facial diplegia and paresthesias]

A patient with Facial diplegia and paresthesias, a rare regional variant of Guillain-Barré syndrome (GBS), is described. A 37-year-old woman developed paresthesias in the distal limbs and subsequently bifacial weakness. She had had a preceding episode of laryngitis. Neurological examination showed severe facial diplegia with loss of taste sensation on the tip of the tongue. Limb muscle power was preserved. Deep tendon reflexes were generally absent. She complained of paresthesias in the distal limbs, but sensory examination was normal. Cerebrospinal fluid showed albuminocytological dissociation. Electrophysiological studies revealed severe facial nerve involvements and demyelinative findings in her limbs. Intravenous immunoglobulin rapidly improved the abnormal sensation in her limbs. Although facial diplegia gradually lessened after the therapy, mild residual weakness was noted 6 months after the neurological onset. To diagnose facial diplegia and paresthesias, it is important to clarify the findings common to typical GBS such as the antecedent illness, acute and monophasic course, distal paresthesias, areflexia, cerebrospinal fluid albuminocytological dissociation, and demyelinative conduction abnormalities in the limbs.

Carbohydrate mimicry between human ganglioside GM1 and Campylobacter jejuni lipooligosaccharide causes Guillain-Barre syndrome

Molecular mimicry between microbial and self-components is postulated as the mechanism that accounts for the antigen and tissue specificity of immune responses in postinfectious autoimmune diseases. Little direct evidence exists, and research in this area has focused principally on T cell-mediated, antipeptide responses, rather than on humoral responses to carbohydrate structures. Guillain-Barré syndrome, the most frequent cause of acute neuromuscular paralysis, occurs 1-2 wk after various infections, in particular, Campylobacter jejuni enteritis. Carbohydrate mimicry [Galbeta1-3GalNAcbeta1-4(NeuAcalpha2-3)Galbeta1-] between the bacterial lipooligosaccharide and human GM1 ganglioside is seen as having relevance to the pathogenesis of Guillain-Barré syndrome, and conclusive evidence is reported here. On sensitization with C. jejuni lipooligosaccharide, rabbits developed anti-GM1 IgG antibody and flaccid limb weakness. Paralyzed rabbits had pathological changes in their peripheral nerves identical with those present in Guillain-Barré syndrome. Immunization of mice with the lipooligosaccharide generated a mAb that reacted with GM1 and bound to human peripheral nerves. The mAb and anti-GM1 IgG from patients with Guillain-Barré syndrome did not induce paralysis but blocked muscle action potentials in a muscle-spinal cord coculture, indicating that anti-GM1 antibody can cause muscle weakness. These findings show that carbohydrate mimicry is an important cause of autoimmune neuropathy.

Acute motor axonal neuropathy after Mycoplasma infection: Evidence of molecular mimicry

BACKGROUND

Patients with Guillain-Barré syndrome (GBS) after Mycoplasma pneumoniae infection often have antibodies to galactocerebroside (GalC). Electrodiagnosis may show acute inflammatory demyelinating polyneuropathy (AIDP).

METHODS

The authors report a patient with acute motor axonal neuropathy (AMAN) after Mycoplasma infection and review seven cases of Mycoplasma-associated GBS. They investigated anti-GalC serology under various conditions associated with Mycoplasma infection.

RESULTS

The patient had immunoglobulin (Ig)G and IgM antibodies against GM1 and GalC, which cross-reacted. During the acute phase, IgM selectively immunostained axons. The cholera toxin B-subunit and rabbit anti-GM1 IgG stained a band in the lipid extract from M pneumoniae, indicative of the presence of a GM1 epitope. Six Mycoplasma-associated GBS patients with anti-GalC antibodies had non-AIDP electrodiagnoses, whereas one with Mycoplasma-associated AIDP had no anti-GalC antibodies. Anti-GalC antibodies were positive in two of five patients who had neurologic diseases other than GBS after Mycoplasma infection and in one of 12 who had acute respiratory disease caused by M pneumoniae not followed by a neurologic disease.

CONCLUSIONS

Anti-GalC antibodies in Mycoplasma-associated GBS may be an epiphenomenon. In certain cases, anti-GM1 antibodies induced by molecular mimicry with M pneumoniae may cause acute motor axonal neuropathy.

Acute facial diplegia and hyperreflexia: A Guillain-Barre syndrome variant

Two patients with acute facial diplegia and hyperreflexia are described. Both patients had serologic evidence of preceding Campylobacter jejuni infection and antiganglioside IgG antibodies as well as other laboratory and electrophysiologic findings suggesting Guillain-Barré syndrome (GBS). IV immunoglobulin produced recovery. Hyperreflexia does not necessarily exclude the diagnosis of a GBS variant. Antiganglioside antibodies can help with diagnosis in difficult cases.

Acute motor axonal neuropathy rabbit model: immune attack on nerve root axons

Macrophages in the periaxonal space and surrounding intact myelin sheath are the most prominent pathological feature of acute motor axonal neuropathy (AMAN). We describe this characteristic in nerve roots from paralyzed rabbits immunized with bovine brain ganglioside or GM1. IgG was deposited on nerve root axons. Distal nerve conduction was preserved, and late F wave components were absent during the acute phase. Initial lesions were located mainly on nerve root axons, as in human AMAN. This study thus provides supportive evidence that the rabbits constitute a model of AMAN.

[Ataxic Guillain-Barré syndrome with delayed facial diplegia]

We described a patient with ataxic Guillain-Barré syndrome who subsequently developed facial diplegia. A 38-year-old man developed ataxia, distal limb paresthesias, mild dysphagia, urinary retention and orthostatic hypotension a week after an episode of laryngitis. He had high titers of serum anti-GQ1b, anti-GD1b, anti-GM1b, anti-GT1a, and anti-GD1a IgG antibodies during the acute phase. Although the initial symptoms markedly improved by intravenous immunoglobulin therapy, asymmetric facial diplegia subsequently occurred and remained longer than ataxia. Similar course of facial nerve palsy has been reported in patients with Fisher syndrome. Common pathophysiological mechanism may function in the development of delayed facial diplegia in Fisher syndrome and ataxic Guillain-Barre syndrome.

Axonal pharyngeal-cervical-brachial variant of Guillain-Barré syndrome without Anti-GT1a IgG antibody

We report two cases of pharyngeal-cervical-brachial (PCB) variant of Guillain-Barré syndrome (GBS). The patients developed dysphagia and weakness of the neck and arms subsequent to Campylobacter jejuni infection. Oropharyngeal palsy recovered poorly. Electrophysiological findings demonstrated axonal conduction failure. Anti-GD1a immunoglobulin G (IgG) antibody was detected in one case, and anti-GM1b IgG antibody in another. Anti-GT1a IgG and immunoglobulin M (IgM) antibodies were negative in both cases. The current cases suggest that the PCB and axonal variants of GBS form a continuous spectrum from the viewpoint of electrophysiological studies as well as antiganglioside serology.