Myelin basic protein-related proteins in mouse brain and immune tissues

Molecular characterization of myelin basic protein a (mbpa) gene from red-bellied pacu (Piaractus brachypomus)

Background

Myelin basic protein (MBP) is one of the most important structural components of the myelin sheaths in both central and peripheral nervous systems. MBP has several functions including organization of the myelin membranes, reorganization of the cytoskeleton during the myelination process, and interaction with the SH3 domain in signaling pathways. Likewise, MBP has been proposed as a marker of demyelination in traumatic brain injury and chemical exposure.

Methods

The aim of this study was to molecularly characterize the myelin basic protein a (mbpa) gene from the Colombian native fish, red-bellied pacu, Piaractus brachypomus. Bioinformatic tools were used to identify the phylogenetic relationships, physicochemical characteristics, exons, intrinsically disordered regions, and conserved domains of the protein. Gene expression was assessed by qPCR in three models corresponding to sublethal chlorpyrifos exposure, acute brain injury, and anesthesia experiments.

Results

mbpa complete open reading frame was identified with 414 nucleotides distributed in 7 exons that encode 137 amino acids. MBPa was recognized as belonging to the myelin basic protein family, closely related with orthologous proteins, and two intrinsically disordered regions were established within the sequence. Gene expression of mbpa was upregulated in the optic chiasm of the chlorpyrifos exposed fish in contrast to the control group.

Conclusions

The physicochemical computed features agree with the biological functions of MBP, and basal gene expression was according to the anatomical distribution in the tissues analyzed. This study is the first molecular characterization of mbpa from the native species Piaractus brachypomus.

Increased expression of NDEL1 and MBP genes in the peripheral blood of antipsychotic-naïve patients with first-episode psychosis

Schizophrenia is a multifactorial neurodevelopmental disorder with high heritability. First-episode psychosis (FEP) is a critical period for determining the disease prognosis and is especially helpful for identifying potential biomarkers associated with the onset and progression of the disorder. We investigated the mRNA expression of 12 schizophrenia-related genes in the blood of antipsychotic-naïve FEP patients (N=73) and healthy controls (N=73). To evaluate the influences of antipsychotic treatment and progression of the disorder, we compared the gene expression within patients before and after two months of treatment with risperidone (N=64). We observed a significantly increased myelin basic protein (MBP) and nuclear distribution protein nudE-like 1 (NDEL1) mRNA levels in FEP patients compared with controls. Comparing FEP before and after risperidone treatment, no significant differences were identified; however; a trend of relatively low NDEL1 expression was observed after risperidone treatment. Animals chronically treated with saline or risperidone exhibited no significant change in Ndel1 expression levels in the blood or the prefrontal cortex (PFC), suggesting that the trend of low NDEL1 expression observed in FEP patients after treatment is likely due to factors other than risperidone treatment (i.e., disease progression). In addition to the recognized association with schizophrenia, MBP and NDEL1 gene products also play an essential role in the functions that are deregulated in schizophrenia, such as neurodevelopment. Our data strengthen the importance of these biological processes in psychotic disorders, indicating that these changes can be detected peripherally and potentially represent putative novel blood biomarkers of susceptibility and disorder progression.

Myelin management by the 18.5-kDa and 21.5-kDa classic myelin basic protein isoforms

The classic myelin basic protein (MBP) splice isoforms range in nominal molecular mass from 14 to 21.5 kDa, and arise from the gene in the oligodendrocyte lineage (Golli) in maturing oligodendrocytes. The 18.5-kDa isoform that predominates in adult myelin adheres the cytosolic surfaces of oligodendrocyte membranes together, and forms a two-dimensional molecular sieve restricting protein diffusion into compact myelin. However, this protein has additional roles including cytoskeletal assembly and membrane extension, binding to SH3-domains, participation in Fyn-mediated signaling pathways, sequestration of phosphoinositides, and maintenance of calcium homeostasis. Of the diverse post-translational modifications of this isoform, phosphorylation is the most dynamic, and modulates 18.5-kDa MBP's protein-membrane and protein-protein interactions, indicative of a rich repertoire of functions. In developing and mature myelin, phosphorylation can result in microdomain or even nuclear targeting of the protein, supporting the conclusion that 18.5-kDa MBP has significant roles beyond membrane adhesion. The full-length, early-developmental 21.5-kDa splice isoform is predominantly karyophilic due to a non-traditional P-Y nuclear localization signal, with effects such as promotion of oligodendrocyte proliferation. We discuss in vitro and recent in vivo evidence for multifunctionality of these classic basic proteins of myelin, and argue for a systematic evaluation of the temporal and spatial distributions of these protein isoforms, and their modified variants, during oligodendrocyte differentiation.

Adult hematopoietic progenitors are multipotent in chimeric mice

Embryonic stem cells (ESCs) and adult somatic cells, induced to pluripotency (iPSCs), can differentiate into multiple cell lineages. We previously reported that adult mammalian bone marrow contains a sub-population of CD34+ cells that express genes of ESCs and genes required to generate iPSCs. They also express lineage genes of the three embryonic germ layers. Are these CD34+ cells multipotent? Here, CD34+ bone marrow stem cells from adult male ROSA mice, which carry two markers: the β-galactosidase gene and the male Y chromosome, were transplanted into blastocysts of wildtype mice. Each female ROSA chimera generated had a distinct pattern of male-derived organs expressing β-galactosidase; e.g., ectodermal brain, dorsal root ganglia and skin; mesodermal heart, bone and bone marrow; and endodermal pancreas, intestine, and liver. Thus, adult mammals carry cells that appear to exhibit a developmental potential reminiscent of ESCs and iPSCs suggesting they could be used for cell replacement therapy.

The activation status of neuroantigen-specific T cells in the target organ determines the clinical outcome of autoimmune encephalomyelitis

The clinical picture of experimental autoimmune encephalomyelitis (EAE) is critically dependent on the nature of the target autoantigen and the genetic background of the experimental animals. Potentially lethal EAE is mediated by myelin basic protein (MBP)–specific T cells in Lewis rats, whereas transfer of S100β- or myelin oligodendrocyte glycoprotein (MOG)–specific T cells causes intense inflammatory response in the central nervous system (CNS) with minimal disease. However, in Dark Agouti rats, the pathogenicity of MOG-specific T cells resembles the one of MBP-specific T cells in the Lewis rat. Using retrovirally transduced green fluorescent T cells, we now report that differential disease activity reflects different levels of autoreactive effector T cell activation in their target tissue. Irrespective of their pathogenicity, the migratory activity, gene expression patterns, and immigration of green fluorescent protein⁺ T cells into the CNS were similar. However, exclusively highly pathogenic T cells were significantly reactivated within the CNS. Without local effector T cell activation, production of monocyte chemoattractants was insufficient to initiate and propagate a full inflammatory response. Low-level reactivation of weakly pathogenic T cells was not due to anergy because these cells could be activated by specific antigen in situ as well as after isolation ex vivo.

The magnitude and encephalogenic potential of autoimmune response to MOG is enhanced in MOG deficient mice

Myelin oligodendrocyte glycoprotein (MOG) is a minor component of central nervous system myelin presumably implicated in the pathogenesis of Multiple Sclerosis (MS). Immunization with MOG leads to the development of Experimental Autoimmune Encephalomyelitis (EAE), the experimental model of MS. It has been suggested that its encephalitogenic potential may be due to the lack of MOG self-immune tolerance. To clarify this, we have generated a MOG deficient mouse (MOG(-/-)) strain. Surprisingly, MOG(35-55)specific proliferation and Th1-type cytokine production were markedly enhanced in MOG(-/-)mice compared to wild type control. Furthermore, adoptive transfer of MOG(35-55)specific T cells, isolated from MOG deficient mice, into wild-type recipients resulted in the development of a more severe disease, indicating a high capacity of MOG(-/-)T cells to initiate effector responses. Interestingly, T cell reactivity to overlapping MOG peptides in MOG(-/-)mice did not reveal new potential immunodominant epitopes in H-2(b)mice. Taken together, our data suggests that MOG self-tolerance modulates the encephalitogenic potential of autoreactive MOG T cells in the periphery.

Experimental autoimmune encephalomyelitis relapses are reduced in heterozygous golli MBP knockout mice

Increased golli MBP (golli) expression has been observed in the peripheral immune system of mice in the relapsing phase of EAE, raising the possibility that golli MBP expression in the periphery may contribute to relapses. Here we describe the generation of golli MBP-deficient mice and a comparison of the clinical course of EAE between heterozygous (golli(+/-)) and wild-type (golli(+/+)) mice. There was no difference between the two groups in incidence of disease, severity of the first episode of disease, or remission after the first episode. However, there was a significant reduction in relapses in golli(+/-) mice vs. controls, suggesting a role for golli proteins in the relapses in EAE.

The myelin basic protein gene is expressed in differentiated blood cell lineages and in hemopoietic progenitors

Myelin basic proteins (MBP) are major constituents of the myelin sheath of oligodendrocytes and Schwann cells in the central nervous system and the peripheral nervous system, respectively. We previously showed that MBP-related transcripts are present in the bone marrow and the immune system. These mRNAs are transcribed from a region called 0', consisting of three exons, located upstream of the classical MBP exons; these three exons belong to the long MBP gene otherwise called "Golli-MBP." The most abundant of these mRNAs, now called HMBP (hemopoietic MBP), encompasses the sequence encoded by the region 0' plus exon 1 and part of intron 1 of the classic MBP gene. Antisera to recombinant HMBP proteins are immunoreactive with proteins of about 26-28 kDa in brain, thymus, and spleen. This report demonstrates that HMBP proteins are present in the vast majority (>95%) of thymic T cells, which express the corresponding transcripts, as do mature T cells from lymph nodes and spleen. HMBP mRNAs and proteins are also manifest in the majority of spleen B lymphocytes and in B cell lines. In addition to lymphoid cells, HMBP proteins are in all types of myeloid lineage cells, i.e., macrophages, dendritic cells, and granulocytes, as well as in megakaryocytes and erythroblasts. Finally, HMBP proteins are present in CD34+ bone marrow cells, and, furthermore, in highly proliferative cultures, these CD34+ cells express HMBP RNAs and proteins. Thus, MBP gene products are present both in the nervous system and in the entire hemopoietic system.

Effect of cyclic AMP on the expression of myelin basic protein species and myelin proteolipid protein in committed oligodendrocytes: differential involvement of the transcription factor CREB

Our previous results support the idea that CREB (cyclic AMP-response element binding protein) may be a mediator of neuroligand and growth factor signals that, coupled to different signal transduction pathways, play different roles at specific stages of oligodendrocyte development. In the early stages, when cells are immature precursors, CREB may play a role as a mediator of protein kinase C (PKC)/mitogen-activated protein kinase (MAPK) pathways regulating cell proliferation. In contrast, at a later stage, when cells are already committed oligodendrocytes, CREB seems to play an important role as a mediator in the stimulation of myelin basic protein (MBP) expression by cyclic AMP (cAMP). In this study, we have investigated whether cAMP and CREB play a role in regulating the expression of all or on the other hand particular MBP isoforms. The results indicated that treatment of committed oligodendrocytes with the cAMP analogue db-cAMP results in a pattern of expression of MBP-related polypeptides that most closely resembles the pattern of MBPs observed in cerebra from adult animals. Experiments in which CREB expression was inhibited using a CREB antisense oligonucleotide, suggested that CREB is involved in the cAMP-dependent stimulation of all the MBP isoforms. In contrast, we have found that db-cAMP stimulates the expression of myelin proteolipid protein (PLP) in a process that occurs despite inhibition of CREB expression. These results support the idea that cAMP stimulates the maturation of oligodendrocytes and stress the fact multiple mechanisms may convey the action of this second messenger modulating oligodendrocyte differentiation and myelination.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

Expression of myelin basic protein (MBP) epitopes in human non-neural cells revealed by two anti-MBP IgM monoclonal antibodies

Two monoclonal antibodies (1H6.2 and 45.30) were raised against MBP purified from human brain under experimental conditions that allowed MBP to retain binding to surrounding myelin lipids (human lipid-bound MBP (hLB-MBP)). 1H6.2 and 45.30 MoAbs were selected on the basis of their different binding properties to: hLB-MBP, human lipid-free-MBP (hLF-MBP) and bovine lipid-free-MBP (bLF-MBP). Although the isotype of both MoAbs was IgM, their specificity, as tested in ELISA assays against chemical haptens and unrelated protein antigens, was restricted to MBP. 1H6.2 and 45.30 MoAbs stained MBP from human brain white matter tissue extracts, as well as bLF-MBP, in Western blot assays. Both MoAbs stained oligodendrocytes and myelin in immunohistochemical analysis of white matter from human brain. Tissue sections from human peripheral nerves were labelled by 1H6.2 only, however, demonstrating that the MoAbs recognize two different epitopes. Epitopes recognized by 1H6.2 and 45.30 MoAbs were also expressed by a wide array of human non-neural cells of either normal or pathological origin, as evidenced by cytofluorimetric assays. In particular, MBP epitopes (MEs) were expressed by lymphoid cells as well as by cells which play a pivotal role in immune homeostasis and in the immune response, such as thymic epithelial cells and professional antigen-presenting cells. Both MoAbs were efficiently internalized by cells from a human B cell line, suggesting trafficking of MEs along the endocytic pathways. These findings support hypotheses regarding the role of MEs expressed by non-neural cells in establishing self-tolerance and/or in triggering the immune response against MBP antigen.

The fate of adoptively transferred quiescent encephalitogenic T cells in normal and antigen-tolerized mice

Adoptive transfer of quiescent encephalitogenic T cells to normal syngeneic recipients was without clinical effect. RT-PCR was used to assess localization of an adoptively transferred quiescent encephalitogenic T cell clone in normal and antigen-unresponsive mice prior to or after challenge with neuroantigen/CFA. The T cell clone was not detectable in lymphoid tissues prior to challenge with neuroantigen; however, following challenge, the clone was found in the spleen, lymph nodes and spinal cord of both normal and antigen-tolerized mice. The latter animals remained clinically normal. Non-activated encephalitogenic T cells transferred to wild-type recipients pretreated i.p. with neuroantigen/IFA were rendered unresponsive. Transfer of the same T cells to alpha/beta T cell-deficient mice pretreated with neuroantigen/IFA resulted in spontaneous disease indicating that an intact alpha/beta T cell system was required for development of the unresponsive state.

Immunological self/nonself discrimination: integration of self vs nonself during cognate T cell interactions with antigen-presenting cells

The hypothesis is presented that immunological integration of nonefficacious vs efficacious T cell antigen receptor (TCR) signals are foundational for self/nonself discrimination and that multiple integrative mechanisms are intrinsic to the molecular to molar organization of an adaptive immune response. These integrative mechanisms are proposed to adaptively regulate expression of costimulatory signals, such that foreign proteins are associated with the expression of costimulatory signals, whereas self-proteins are associated with the lack of costimulatory signaling. Overall, this model offers several unique contributions to the study of immunology. First, this model postulates that cognate TCR/major histocompatibility complex (MHC) interactions are sufficient to adaptively mediate immunological self/nonself discrimination. This model thereby offers a unique alternative to models that largely rely on innate immunity to prime immune discrimination. Second, the integrative model argues that the immune system can simultaneously reinforce self-tolerance and promote immunity to foreign organisms at the same time and in the same location. Many alternative models presume that pathogenic self-reactive T cells do not exist at the outset of an immune response against foreign agents. Third, the integrative model uniquely predicts relationships between immunodeficiency and autoimmune pathogenesis. Fourth, this model illustrates the regulatory advantages of cognate antigen presenting cell (APC) systems (i.e., T cell or B cell APC) compared to nonspecific APC. Cognate APC systems together with the respective clonotypic responders may comprise a fundamental "network" of lymphoid cells. Such networks would have clone-specific regulatory capabilities and may be central for immunological self/nonself discrimination. Fifth, this model provides an explanation for "infectious" tolerance without creating specialized subsets of "suppressor" or "regulatory" T cells. Each mature T cell retains the potential to reinforce tolerance or mediate immunity, depending on the specific antigenic cues present in the immediate environment.

Identification and characterization of early glial progenitors using a transgenic selection strategy

To define the spatiotemporal development of and simultaneously select for oligodendrocytes (OLs) and Schwann cells (SCs), transgenic mice were generated that expressed a bacterial beta-galactosidase (beta-gal) and neomycin phosphotransferase fusion protein (betageo) under the control of murine 2'3'-cyclic nucleotide 3'-phosphodiesterase (muCNP) promoters I and II. Transgenic beta-gal activity was detected at embryonic day 12.5 in the ventral region of the rhombencephalon and spinal cord and in the neural crest. When cells from the rhombencephalon were cultured in the presence of G418, surviving cells differentiated into OLs, indicating that during development this brain region provides one source of OL progenitors. Postnatally, robust beta-gal activity was localized to OLs throughout the brain and was absent from astrocytes, neurons, and microglia or monocytes. In the sciatic nerve beta-gal activity was localized exclusively to SCs. Cultures from postnatal day 10 brain or sciatic nerve were grown in the presence of G418, and within 8-9 d exposure to antibiotic, 99% of all surviving cells were beta-gal-positive OLs or SCs. These studies demonstrate that the muCNP-betageo transgenic mice are useful for identifying OLs and SCs beginning at early stages of the glial cell lineage and throughout their development. This novel approach definitively establishes that the beta-gal-positive cells identified in vivo are glial progenitors, as defined by their ability to survive antibiotic selection and differentiate into OLs or SCs in vitro. Moreover, this experimental paradigm facilitates the rapid and efficient selection of pure populations of mouse OLs and SCs and further underscores the use of cell-specific promoters in the purification of distinct cell types.

Expression of autoimmune disease-related antigens by cells of the immune system

The process of thymic selection is critical for the generation of the mature T-cell repertoire, yet the nature of the self-peptides that serve this function is not known. Several studies suggest that tissue-specific auto-antigens are expressed in the thymus. We initiated this study to examine the expression of a panel of auto-antigens related to several autoimmune diseases in the thymus, peripheral lymphoid organs, and various cell lines. We looked for the expression of these antigens by reverse transcriptase-polymerase chain reaction, fluorescence-activated cell sorter (FACS) analysis, immunoblotting, and immunoprecipitation. We found that in the thymus there is evidence for the expression of a wide variety of disease-related self-antigens including myelin antigens, insulin, cardiac myosin, and retinal S antigen. By FACS analysis, several monoclonal anti-myelin basic protein antibodies were found to bind to immune cells. In Western blotting, we could find in the thymus and other lymphoid organs the expression of myelin basic protein, proteolipid protein, and cyclic nucleotide phosphodiesterase; in contrast, the staining for myelin oligodendrocyte glycoprotein, microtubule-associated Tau protein, and insulin were negative in these organs. The results of these studies confirm that there is evidence for the expression of a variety of auto-antigens in the immune system, both at the mRNA and protein levels, potentially enabling them to participate in the process of thymic education.

Myelin protein expression in lymphoid tissues: implications for peripheral tolerance

During chronic relapsing experimental autoimmune encephalomyelitis (EAE), T lymphocytes specific for myelin protein epitopes are stimulated in vivo. When epitopes are unique from the disease-initiating myelin protein epitope, this phenomenon has been termed "epitope spreading". These T-lymphocyte responses have been detected primarily in lymph node and spleen during the relapsing phase of disease. If myelin proteins are sequestered behind the blood brain barrier, a fundamental question arises: where does the in vivo stimulation of T lymphocytes occur during relapsing EAE? While it has been thought that epitope spreading may occur within the central nervous system (CNS), here we present data supporting a novel hypothesis. Epitope spreading during EAE may not occur within the CNS, but rather within lymphoid tissues. Both myelin basic protein (MBP) and proteolipid protein (PLP) are expressed at the RNA and protein level in lymph node, thymus and spleen of SJL mice with relapsing EAE. This myelin protein expression occurs within T lymphocytes, B lymphocytes and macrophages. Further, T-lymphocyte lines from SJL mice specific for the immunodominant and subdominant epitopes of MBP and PLP can recognize endogenous protein within cells derived from lymphoid tissues. Thus, immunologically relevant myelin proteins are endogenously produced and presented within lymphoid tissues. The hypothesis that epitope spreading occurs within lymphoid tissues would explain how myelin protein-specific T lymphocytes become activated outside the CNS to allow their passage through the blood brain barrier to form new CNS lesions during relapses.