Monoclonal antibodies specific to the integral membrane protein P0 of bovine peripheral nerve myelin

Myelin Protein Zero Immunohistochemistry Is Not a Reliable Marker of Extrinsic Mucosal Innervation in Patients With Hirschsprung Disease

BACKGROUND

Innervation of aganglionic rectum in Hirschsprung disease derives from extrinsic nerves which project from cell bodies located outside the bowel wall and markers that distinguish extrinsic from intrinsic innervation are diagnostically useful. Myelin protein zero (MPZ) is a putative marker of extrinsic glial cells which could distinguish mucosal innervation in aganglionic vs ganglionic colon.

METHODS

Sections and protein blots from ganglionic and aganglionic colon were immunolabeled with MPZ-specific antibodies.

RESULTS

Immunolabeling of MPZ with a chicken polyclonal or mouse monoclonal antibody confirmed glial specificity and reliably labeled hypertrophic submucosal nerves in Hirschsprung disease. In contrast, a rabbit polyclonal antibody strongly labeled extrinsic and intrinsic nerves, including most mucosal branches. Immunoblots showed MPZ is expressed in mucosal glial cells, albeit at lower levels than in extrinsic nerves, and that the rabbit antibody is more sensitive that the other two probes. Unfortunately, none of these antibodies consistently distinguished mucosal innervation in aganglionic vs ganglionic rectum.

CONCLUSIONS

The results suggest that (a) glial cell myelin protein zero expression is influenced more by location (mucosa vs submucosa) than the extrinsic vs intrinsic origin of the accompanied nerves and (b) myelin protein zero immunohistochemistry has limited value as a diagnostic adjunct for Hirschsprung disease.

Bmal1 is an essential regulator for circadian cytosolic Ca²⁺ rhythms in suprachiasmatic nucleus neurons

The hypothalamic suprachiasmatic nucleus (SCN) plays a pivotal role in the mammalian circadian clock system. Bmal1 is a clock gene that drives transcriptional-translational feedback loops (TTFLs) for itself and other genes, and is expressed in nearly all SCN neurons. Despite strong evidence that Bmal1-null mutant mice display arrhythmic behavior under constant darkness, the function of Bmal1 in neuronal activity is unknown. Recently, periodic changes in the levels of intracellular signaling messengers, such as cytosolic Ca(2+) and cAMP, were suggested to regulate TTFLs. However, the opposite aspect of how clock gene TTFLs regulate cytosolic signaling remains unclear. To investigate intracellular Ca(2+) dynamics under Bmal1 perturbations, we cotransfected some SCN neurons with yellow cameleon together with wild-type or dominant-negative Bmal1 using a gene-gun applied for mouse organotypic cultures. Immunofluorescence staining for a tag protein linked to BMAL1 showed nuclear expression of wild-type BMAL1 and its degradation within 1 week after transfection in SCN neurons. However, dominant-negative BMAL1 did not translocate into the nucleus and the cytosolic signals persisted beyond 1 week. Consistently, circadian Ca(2+) rhythms in SCN neurons were inhibited for longer periods by dominant-negative Bmal1 overexpression. Furthermore, SCN neurons transfected with a Bmal1 shRNA lengthened, whereas those overexpressing wild-type Bmal1 shortened, the periods of Ca(2+) rhythms, with a significant reduction in their amplitude. BMAL1 expression was intact in the majority of neighboring neurons in organotypic cultures. Therefore, we conclude that proper intrinsic Bmal1 expression, but not passive signaling via cell-to-cell interactions, is the determinant of circadian Ca(2+) rhythms in SCN neurons.

Role of endogenous Schwann cells in tissue repair after spinal cord injury

Schwann cells are glial cells of peripheral nervous system, responsible for axonal myelination and ensheathing, as well as tissue repair following a peripheral nervous system injury. They are one of several cell types that are widely studied and most commonly used for cell transplantation to treat spinal cord injury, due to their intrinsic characteristics including the ability to secrete a variety of neurotrophic factors. This mini review summarizes the recent findings of endogenous Schwann cells after spinal cord injury and discusses their role in tissue repair and axonal regeneration. After spinal cord injury, numerous endogenous Schwann cells migrate into the lesion site from the nerve roots, involving in the construction of newly formed repaired tissue and axonal myelination. These invading Schwann cells also can move a long distance away from the injury site both rostrally and caudally. In addition, Schwann cells can be induced to migrate by minimal insults (such as scar ablation) within the spinal cord and integrate with astrocytes under certain circumstances. More importantly, the host Schwann cells can be induced to migrate into spinal cord by transplantation of different cell types, such as exogenous Schwann cells, olfactory ensheathing cells, and bone marrow-derived stromal stem cells. Migration of endogenous Schwann cells following spinal cord injury is a common natural phenomenon found both in animal and human, and the myelination by Schwann cells has been examined effective in signal conduction electrophysiologically. Therefore, if the inherent properties of endogenous Schwann cells could be developed and utilized, it would offer a new avenue for the restoration of injured spinal cord.

Protein 4.1B contributes to the organization of peripheral myelinated axons

Neurons are characterized by extremely long axons. This exceptional cell shape is likely to depend on multiple factors including interactions between the cytoskeleton and membrane proteins. In many cell types, members of the protein 4.1 family play an important role in tethering the cortical actin-spectrin cytoskeleton to the plasma membrane. Protein 4.1B is localized in myelinated axons, enriched in paranodal and juxtaparanodal regions, and also all along the internodes, but not at nodes of Ranvier where are localized the voltage-dependent sodium channels responsible for action potential propagation. To shed light on the role of protein 4.1B in the general organization of myelinated peripheral axons, we studied 4.1B knockout mice. These mice displayed a mildly impaired gait and motility. Whereas nodes were unaffected, the distribution of Caspr/paranodin, which anchors 4.1B to the membrane, was disorganized in paranodal regions and its levels were decreased. In juxtaparanodes, the enrichment of Caspr2, which also interacts with 4.1B, and of the associated TAG-1 and Kv1.1, was absent in mutant mice, whereas their levels were unaltered. Ultrastructural abnormalities were observed both at paranodes and juxtaparanodes. Axon calibers were slightly diminished in phrenic nerves and preterminal motor axons were dysmorphic in skeletal muscle. βII spectrin enrichment was decreased along the axolemma. Electrophysiological recordings at 3 post-natal weeks showed the occurrence of spontaneous and evoked repetitive activity indicating neuronal hyperexcitability, without change in conduction velocity. Thus, our results show that in myelinated axons 4.1B contributes to the stabilization of membrane proteins at paranodes, to the clustering of juxtaparanodal proteins, and to the regulation of the internodal axon caliber.

A new monoclonal antibody, 4F2, specific for the oligodendroglial cell lineage, recognizes ATP-dependent RNA helicase Ddx54: possible association with myelin basic protein

Recent research in neural development has highlighted the importance of markers to discriminate phenotypic alterations of neural cells at various developmental stages. We isolated a new monoclonal antibody, 4F2, which was shown to be specific for an oligodendrocyte lineage. In primary cultures of oligodendroglial and mixed neural cells, the 4F2 antibody labeled a large proportion of Sox2(+) , Sox10(+) , A2B5(+) , NG2(+) , Olig2(+) , O4(+) , and myelin basic protein (MBP)(+) cells but did not label any GFAP(+) or NeuN(+) cells. In immunohistochemisty of rat embryos, the 4F2 antibody labeled a portion of neuroepithelial cells of the neural tube at embryonic day 9. The 4F2-positive cells were located initially in the ventricular zone as Musashi1(+) Tuj1(-) populations and distributed throughout the striatum; thereafter, they populated the whole brain and spinal cord. These cells showed ramified processes during embryonal development. The 4F2 antigen was associated with all four isoforms of MBP in coimmunoprecipitation experiments using brain homogenates or cell lysates of cultured oligodendrocytes. Immunoscreening of a brain cDNA library identified the antigen as DEAD (Asp-Glu-Ala-Asp) box polypeptide 54 (Ddx54), a member of the DEAD box family of RNA helicases involved in RNA metabolism, transcription, and translation. Cotransfection of the Ddx54 gene with MBP isoform genes increased the nuclear localization of the 21.5-kDa MBP isoform, which has been reported to function as a nuclear signal transduction molecule. These data indicate that Ddx54 might be not only a useful marker for investigating the ontogeny of oligodendrocytes but also an important factor in oligodendrocyte differentiation and myelination.

Ectopic expression of polysialylated neural cell adhesion molecule in adult macaque Schwann cells promotes their migration and remyelination potential in the central nervous system

Recent findings suggested that inducing neural cell adhesion molecule polysialylation in rodents is a promising strategy for promoting tissue repair in the injured central nervous system. Since autologous grafting of Schwann cells is one potential strategy to promote central nervous system remyelination, it is essential to show that such a strategy can be translated to adult primate Schwann cells and is of interest for myelin diseases. Adult macaque Schwann cells were transduced with a lentiviral vector encoding sialyltransferase, an enzyme responsible for neural cell adhesion molecule polysialylation. In vitro, we found that ectopic expression of polysialylate promoted adult macaque Schwann cell migration and improved their integration among astrocytes in vitro without modifying their antigenic properties as either non-myelinating or pro-myelinating. In addition, forced expression of polysialylate in adult macaque Schwann cells decreased their adhesion with sister cells. To investigate the ability of adult macaque Schwann cells to integrate and migrate in vivo, focally induced demyelination was targeted to the spinal cord dorsal funiculus of nude mice, and both control and sialyltransferase expressing Schwann cells overexpressing green fluorescein protein were grafted remotely from the lesion site. Analysis of the spatio-temporal distribution of the grafted Schwann cells performed in toto and in situ, showed that in both groups, Schwann cells migrated towards the lesion site. However, migration of sialyltransferase expressing Schwann cells was more efficient than that of control Schwann cells, leading to their accelerated recruitment by the lesion. Moreover, ectopic expression of polysialylated neural cell adhesion molecule promoted adult macaque Schwann cell interaction with reactive astrocytes when exiting the graft, and their ‘chain-like’ migration along the dorsal midline. The accelerated migration of sialyltransferase expressing Schwann cells to the lesion site enhanced their ability to compete for myelin repair with endogenous cells, while control Schwann cells were unable to do so. Finally, remyelination by the exogenous sialyltransferase expressing Schwann cells restored the normal distribution of paranodal and nodal elements on the host axons. These greater performances of sialyltransferase expressing Schwann cell correlated with their sustained expression of polysialylated neural cell adhesion molecule at early times when migrating from the graft to the lesion, and its progressive downregulation at later times during remyelination. These results underline the potential therapeutic benefit to genetically modify Schwann cells to overcome their poor migration capacity and promote their repair potential in demyelinating disorders of the central nervous system.

Disruption of Krox20-Nab interaction in the mouse leads to peripheral neuropathy with biphasic evolution

Krox20/Egr2 is a zinc finger transcription factor that plays essential roles in several developmental processes, including peripheral nervous system myelination by Schwann cells, where it acts as a master gene regulator. Krox20 is known to interact with cofactors of the Nab family and a mutation affecting isoleucine 268, which prevents this interaction, has been shown to result in congenital hypomyelinating neuropathy in humans. To further investigate the role of this interaction, we have introduced such a mutation, Krox20(I268F), in the mouse germ line. Clinical, immunohistochemical, and ultrastructural analyses of the homozygous mutants reveal that they develop a severe hypomyelination phenotype that mimics the human syndrome. Furthermore, a time-course analysis of the disease indicates that it follows a biphasic evolution, the hypomyelination phase being followed by a dramatic demyelination. Although for the regulation of most analyzed Krox20 target genes the mutation behaves as a loss of function, this is not the case for a few of them. This differential effect indicates that the molecular function of the Krox20-Nab interaction is target dependent and might explain the degradation of the residual myelin, because of imbalances in its composition. In conclusion, this work provides a novel and useful model for severe human peripheral neuropathies.

Alterations in mRNA expression of myelin proteins in the sciatic nerves and brains of streptozotocin-induced diabetic rats

Diabetic neuropathy is the most common complication of diabetes. We examined the levels and the mRNA expression of myelin proteins in the sciatic nerves and the brains of streptozotocin-induced diabetic rats. The diabetic rats exhibited a decrease in body weight, elevation of the blood glucose level and a decrease in motor nerve conduction velocity at 2 weeks after streptozotocin injection. In the sciatic nerves of diabetic rats, the level of P0 protein and its mRNA expression were markedly reduced at 20 weeks after the injection. In the brains, the levels of proteolipid protein and myelin-associated glycoprotein and their mRNA expression were selectively decreased at 20 weeks after the injection. This affected expression of myelin proteins was found even when no histological abnormalities were detectable. Considering the functional significance of myelin proteins, this impairment of protein expression is possibly involved in the pathogenesis of diabetic neuropathy, including that in brain disorders.

Grafts of brain-derived neurotrophic factor and neurotrophin 3-transduced primate Schwann cells lead to functional recovery of the demyelinated mouse spinal cord

Experimental studies provided overwhelming proof that transplants of myelin-forming cells achieve efficient remyelination in the CNS. Among cellular candidates, Schwann cells can be used for autologous transplantation to ensure robust remyelination of lesions and to deliver therapeutic factors in the CNS. In the present study, macaque Schwann cells expressing green fluorescent protein (GFP) were infected with human immunodeficiency virus-derived vectors overexpressing brain-derived neurotrophic factor (BDNF) or Neurotrophin 3 (NT-3), two neurotrophins that also modulate glial cell biology. The ability of transgenic Schwann cells to secrete growth factors was assessed by ELISA and showed 35- and 62-fold increases in BDNF and NT-3, respectively, in transduced macaque Schwann cell supernatants. Conditioned media of BDNF- and NT-3-transduced Schwann cells reduced Schwann cell proliferation and favored their differentiation in vitro. Transgenic cells were grafted in demyelinated spinal cords of adult nude mice. Two behavioral assays showed that NT-3- and BDNF-transduced Schwann cells promoted faster and stronger functional recovery than GFP-transduced Schwann cells. Morphological analysis indicated that functional recovery correlated with enhanced proliferation and differentiation of resident oligodendrocyte progenitors and enhanced oligodendrocyte and Schwann cell differentiation. Moreover, NT-3-transduced Schwann cells provided neuroprotection and reduced astrogliosis. These results underline the potential therapeutic benefit of combining neuroprotection and activation of myelin-forming cells to restore altered functions in demyelinating diseases of the CNS.

A possible novel isoform of peripheral myelin P0 protein: a target antigen recognized by an autoantibody in a patient with malignant lymphoma and peripheral neuropathy

We tried to characterize a 35-kD antigen recognized by the serum IgG of a patient with malignant lymphoma and peripheral neuropathy. By Western blotting, the serum IgG reacted with the 35-kD antigen in the human, bovine and mouse peripheral nerve (PN) but not with other neural and non-neural tissues. Immunohistochemical analysis showed immunoreactivity of the IgG in the compact myelin of PN. We constructed a human sciatic nerve cDNA library and screened it using IgG of the patient. Three independent clones were obtained. Sequence alignment indicated that the inserts of these clones were homologous to the P0 cDNA, but that all three corresponded to the 3'-untranslational region of the P0 cDNA. To biochemically analyze the 35-kD antigen, myelin fractions of the human and bovine PN were prepared. The 35-kD antigen was purified from the crude myelin fraction by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. When the immunoreactivities of the 35-kD antigen for the IgG of the patient and a monoclonal anti-P0 antibody were compared with those of P0 protein for these antibodies, the 35-kD antigen reacted with both antibodies, but the P0 protein reacted with only the monoclonal anti-P0 antibody. These results suggest that the 35-kD antigen is an isoform of P0 protein. Although it is unlikely that the autoantibody may be the primary cause of neuropathy, because they were also detected in patients with lymphoma without overt neuropathy, they appear to be a modifying factor in the progression of neuropathy.

Stimulation of myelin gene expression in vitro and of sciatic nerve remyelination by interleukin-6 receptor-interleukin-6 chimera

Induction of myelin gene expression denotes the last stage of differentiation of myelinating glial cells. Following peripheral nerve transection, Schwann cells (SC) lose myelin gene expression and proliferate, resembling premyelinating embryonic SC (eSC). We show that a fusion protein of the soluble interleukin-6 receptor to interleukin-6 (IL6RIL6), a potent activator of the gp130 signaling receptor, is an inducer of MBP and Po gene products in rat E18 embryonic dorsal root ganglia (DRG) 3 day cultures. Cells whose growth is dependent on the IL6RIL6 chimera were isolated from DRG. These cells (designated CH cells) express Krox-20, as do promyelinating and myelinating SC (mSC). IL6RIL6 induces Po and MBP in CH cells and their cocultures with neurons. In addition, IL6RIL6 leads to a disappearance of Pax-3, a marker of eSC and nonmyelinating Schwann cells (nmSC). Glial fibrillary acidic protein, present in nmSC, is not significantly induced by IL6RIL6. The CH cells acquire glial morphology when exposed to IL6RIL6 and cover axons in cocultures. In a sciatic nerve-derived SC line, IL6RIL6 also induces Po and triggers a rapid attachment along axons. In vivo administration of IL6RIL6 intraperitoneally to rats after sciatic nerve transection and resuture increases 4-fold the number of myelinated nerve fibers (MF) measured on day 12, 2.5-5 mm distal to the suture. The stimulation by IL6RIL6 treatment is highest (7.1-fold) at the more distant 5 mm site, and the thickness of myelin sheaths is increased. Compared to known SC growth factors, the gp130 activator IL6RIL6 appears to combine both in vitro mitogenic effects and promotion of myelin gene expression.

Antigens of monoclonal antibody NB3C4 are novel markers for oligodendrocytes

We produced NB3C4, a novel monoclonal antibody specific for oligodendrocytes, using human neuroblastoma IMR-32 cells. NB3C4 specifically recognized oligodendrocytes in the CNS, although it bound to neuroblastoma IMR-32 cells and oligodendrocytes in vitro. Double immunofluorescence staining of rat brain using NB3C4 and anti-GST-pi, anti-glial fibrillary acidic protein (GFAP), or anti-neurofilament 200 (NF) antibody revealed that anti-GST-pi antibody identified an oligodendrocyte marker recognizing NB3C4-positive cells, while both anti-GFAP and anti-NF antibody did not. Western blotting of rat brain homogenates showed that NB3C4 bound three proteins of 22-28 kDa, while the anti-GST-pi recognized a 27 kDa protein. Therefore, antigens recognized by NB3C4 could be novel markers for oligodendrocytes.

Induction of myelin gene expression in Schwann cell cultures by an interleukin-6 receptor-interleukin-6 chimera

Expression of myelin basic protein (MBP) and Po gene products is induced during the final postnatal maturation of Schwann cells and reinduced during nerve regeneration. We show that a chimeric protein containing interleukin-6 fused to its soluble receptor (IL6RIL6 chimera) induces MBP and Po RNAs and proteins in cultures of dorsal root ganglia (DRG) from 14 day old mouse embryos. Activation of gp130 signaling by IL6RIL6 appears comparable to cyclic AMP elevating agents to induce the myelin gene products in DRG and in pure Schwann cell cultures.

Monoclonal antibody 14F7, which recognizes a stage-specific immature oligodendrocyte surface molecule, inhibits oligodendrocyte differentiation mediated in co-culture with astrocytes

Cells at an intermediate stage of oligodendrocyte lineage are not only well characterized by biochemical studies but also are likely to relate to the outcome of physiological events. To elucidate the molecular events leading to the development of oligodendrocyte lineage cells, we have raised monoclonal antibodies against stage-specific immature oligodendrocytes, which have previously been isolated by a novel oligodendrocyte-lineage cell culture technique (Sakurai et al.: J Neurosci Res 52:17-26, 1998). We have isolated a mouse monoclonal antibody termed 14F7 which predominantly labels stage-specific immature oligodendrocytes and have found that the expression of 14F7 immunoreactivity in the developing neonatal rat forebrain is closely associated with cells expressing the oligodendrocyte progenitor marker A2B5 and to immature oligodendrocyte expressing O4 antigen. 14F7+ cells were distributed in the ventricular and subventricular zone and the nearby forming corpus callosum as non-myelinating cells. In contrast to cell culture observations, 14F7+ cells were seen only in oligodendrocyte lineage cells. For instance, dissociated cell culture studies indicated that 14F7 labels a cell surface molecule, and its cellular distribution is coincident with all of O4+ cells and A2B5+ cells, and even A2B5- cells. By contrast, 14F7-positive cells did not label astrocytes and, furthermore, did not label myelin basic protein (MBP)-positive oligodendrocytes. 14F7 recognized a 48-kDa protein on sodium dodecyl sulfate polyacrylamide gel electrophoresis. 14F7 immunoreactivity was detectable in rat brain as early as embryonic day 18. Furthermore, in these cells, the total time for differentiation was extended, and on maturation, these cells subsequently expressed an array of myelin-specific proteins, which normally occurs by direct contact with type-1 astrocytes. However, in the presence of 14F7, stage-specific oligodendrocytes co-cultured with astrocytes completely failed to express MBP. These data suggest that the 14F7 antigen is a novel cell surface molecule that is expressed in the intermediate stage of oligodendrocyte-lineage cells, and it is expected that it regulates the differentiation of oligodendrocyte throughout development.