Myelin basic protein-diverse conformational states of an intrinsically unstructured protein and its roles in myelin assembly and multiple sclerosis

Citrullinated isomer of myelin basic protein can induce inflammatory responses in astrocytes

Purpose

During the course of demyelinating inflammatory diseases, myelin-derived proteins, including myelin basic protein(MBP), are secreted into extracellular space. MBP shows extensive post-translational modifications, including deimination/citrullination. Deiminated MBP is structurally less ordered, susceptible to proteolytic attack, and more immunogenic than unmodified MBP. This study investigated the effect of the deiminated/citrullinated isomer of MBP(C8) and the unmodified isomer of MBP(C1) on cultured primary astrocytes.

Methods

MBP charge isomers were isolated/purified from bovine brain. Primary astrocyte cultures were prepared from the 2-day-old Wistar rats. For evaluation of glutamate release/uptake a Fluorimetric glutamate assay was used. Expression of peroxisome proliferator-activated receptor-gamma(PPAR-γ), excitatory amino acid transporter 2(EAAT2), the inhibitor of the nuclear factor kappa-B(ikB) and high mobility group-B1(HMGB1) protein were assayed by Western blot analysis. IL-17A expression was determined in cell medium by ELISA.

Results

We found that MBP(C8) and MBP(C1) acted differently on the uptake/release of glutamate in astrocytes: C1 increased glutamate uptake and did not change its release, whereas C8 decreased glutamate release but did not change its uptake. Both isomers increased the expression of PPAR-γ and EAAT2 to the same degree. Western blots of cell lysates revealed decreased expression of ikB and increased expression of HMGB1 proteins after treatment of astrocytes by C8. Moreover, C8-treated cells released more nitric oxide and proinflammatory IL-17A than C1-treated cells.

Conclusions

These data suggest that the most immunogenic deiminated isomer C8, in parallel to the decreases in glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B(NF-kB).

Summary statement

The most modified-citrullinated myelin basic protein charge isomer decreases glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B in astrocytes.

Celastrol ameliorates hypoxic-ischemic brain injury in neonatal rats by reducing oxidative stress and inflammation

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is caused by perinatal hypoxia and subsequent reductions in cerebral blood flow and is one of the leading causes of severe disability or death in newborns. Despite its prevalence, we currently lack an effective drug therapy to combat HIE. Celastrol (Cel) is a pentacyclic triterpene extracted from Tripterygium Wilfordi that can protect against oxidative stress, inflammation, and cancer. However, whether Cel can alleviate neonatal hypoxic-ischemic (HI) brain damage remains unclear.

METHODS

Here, we established both in vitro and in vivo models of HI brain damage using CoCl2-treated PC12 cells and neonatal rats, respectively, and explored the neuroprotective effects of Cel in these models.

RESULTS

Analyses revealed that Cel administration reduced brain infarction size, microglia activation, levels of inflammation factors, and levels of oxidative stress markers by upregulating levels of p-AMPKα, Nrf2, HO-1, and by downregulating levels of TXNIP and NLRP3. Conversely, these beneficial effects of Cel on HI brain damage were largely inhibited by AMPKα inhibitor Compound C and its siRNA.

CONCLUSIONS

We present compelling evidence that Cel decreases inflammation and oxidative stress through the AMPKα/Nrf2/TXNIP signaling pathway, thereby alleviating neonatal HI brain injury. Cel therefore represents a promising therapeutic agent for treating HIE.

IMPACT

We firstly report that celastrol can ameliorate neonatal hypoxic-ischemic brain injury both in in vivo and in vitro, which represents a promising therapeutic agent for treating related brain injuries. Celastrol activates the AMPKα/Nrf2/TXNIP signaling pathway to relieve oxidative stress and inflammation and thereby alleviates neonatal hypoxic-ischemic brain injury.

Synthesis and biological evaluation of radioiodinated benzoxazole and benzothiazole derivatives for imaging myelin in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system that results from destruction of the myelin sheath. Due to heterogeneity of the symptoms and course of MS, periodic monitoring of disease activity is important for diagnosis and treatment. In the present study, we synthesized four radioiodinated benzoxazole (BO) and benzothiazole (BT) derivatives, and evaluated their utility as novel myelin imaging probes for single photon emission computed tomography (SPECT). In a biodistribution study using normal mice, three compounds ([125I]BO-1, [125I]BO-2, and [125I]BT-2) displayed moderate brain uptake (2.7, 2.9, and 2.8% ID/g, respectively) at 2 min postinjection. On ex vivo autoradiography using normal mice, [125I]BO-2 showed the most preferable ratio of radioactivity accumulation in white matter (myelin-rich region) versus gray matter (myelin-deficient region). In addition, the radioactivity of [125I]BO-2 was reduced in the lysophosphatidylcholine-induced demyelination region. In conclusion, [123I]BO-2 demonstrated the fundamental characteristics of a myelin imaging probe for SPECT.

PAD2 dysregulation and aberrant protein citrullination feature prominently in reactive astrogliosis and myelin protein aggregation in sporadic ALS

Alteration in protein citrullination (PC), a common posttranslational modification (PTM), contributes to pathogenesis in various inflammatory disorders. We previously reported that PC and protein arginine deiminase 2 (PAD2), the predominant enzyme isoform that catalyzes this PTM in the central nervous system (CNS), are altered in mouse models of amyotrophic lateral sclerosis (ALS). We now demonstrate that PAD2 expression and PC are altered in human postmortem ALS spinal cord and motor cortex compared to controls, increasing in astrocytes while trending lower in neurons. Furthermore, PC is enriched in protein aggregates that contain the myelin proteins PLP and MBP in ALS. These results confirm our findings in ALS mouse models and suggest that altered PAD2 and PC contribute to neurodegeneration in ALS.

Myelin basic proteins charge isomers interact differently with the peptidyl arginine deiminase-2

The deamination of arginine and its conversion to citrulline is a modification observed in positively charged proteins such as histones or myelin basic protein (MBP). This reaction is catalyzed by peptidyl arginine deiminase (PAD), whose abnormal activation is associated with autoimmune diseases like rheumatoid arthritis and multiple sclerosis. However, the mechanisms that trigger PAD activation and the pathophysiological processes involved in hypercitrullination remain unknown. In this study, we investigated the interaction between PAD and various charged isomers of MBP, each differing in the degree of post-translational modification. Immunoprecipitation experiments were conducted to examine the binding between PAD and the different charge isomers of MBP. Our findings revealed that the phosphorylated forms of MBP (C3 and C4) exhibited a higher affinity for PAD compared to the unmodified (C1) and fully citrullinated forms (C8). Additionally, we observed that only in the presence of the unmodified C1 isomer did PAD undergo autocitrullination, which was inhibited by the endogenous guanidine-containing component, creatine. In the presence of other isomers, PAD did not undergo autocitrullination. Furthermore, we found that the unmodified isomer of MBP-C1 contains methylated arginines, which were not affected by the pre-treatment with PAD. Based on our findings, we propose that the increased phosphorylation of central threonines in the original MBP may trigger PAD activation, leading to increased citrullination of the protein and subsequent disorganization of the myelin sheath. These insights contribute to a better understanding of the underlying mechanisms in autoimmune diseases associated with hypercitrullination, potentially opening new avenues for therapeutic interventions.

Phase-Dependent Adsorption of Myelin Basic Protein to Phosphatidylcholine Lipid Bilayers

The dense packing of opposite cytoplasmic surfaces of the lipid-enriched myelin membrane, responsible for the proper saltatory conduction of nerve impulses through axons, is ensured by the adhesive properties of myelin basic protein (MBP). Although preferentially interacting with negatively charged phosphatidylserine (PS) lipids, as an intrinsically disordered protein, it can easily adapt its shape to its immediate environment and thus adsorb to domains made of zwitterionic phosphatidylcholine (PC) lipids. As the molecular-level interaction pattern between MBP and PC lipid membranes suffers from scarce characterization, an experimental and computational study of multilamellar liposomes (MLVs) composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in the presence of bovine MBP is presented here. Calorimetric and temperature-dependent UV-Vis measurements identified DPPC pretransition temperature (Tp) and calorimetric enthalpy (ΔHcal) as the physicochemical parameters most responsive to the presence of MBP. Besides suggesting an increase in β-sheet fractions of structured MBP segments as DPPC lipids undergo from the gel (20 °C) to the fluid (50 °C) phase, FTIR spectra unraveled the significant contribution of lysine (Lys) residues in the adsorption pattern, especially when DPPC is in the fluid (50 °C) phase. In addition to highlighting the importance of Lys residues in the MBP adsorption on DPPC lipid bilayer, employing salt bridges (SBs) and hydrogen bonds (HBs), MD data suggest the crucial importance of the orientation of MBP with respect to the surface of the DPPC lipid bilayer.

Characterization of membrane-interaction mechanisms of proteins using vacuum-ultraviolet circular dichroism spectroscopy

Protein-membrane interactions play an important role in various biological phenomena, such as material transport, demyelinating diseases, and antimicrobial activity. We combined vacuum-ultraviolet circular dichroism (VUVCD) spectroscopy with theoretical (e.g., molecular dynamics and neural networks) and polarization experimental (e.g., linear dichroism and fluorescence anisotropy) methods to characterize the membrane interaction mechanisms of three soluble proteins (or peptides). α1 -Acid glycoprotein has the drug-binding ability, but the combination of VUVCD and neural-network method revealed that the membrane interaction causes the extension of helix in the N-terminal region, which reduces the binding ability. Myelin basic protein (MBP) is an essential component of the myelin sheath with a multi-layered structure. Molecular dynamics simulations using a VUVCD-guided system showed that MBP forms two amphiphilic and three non-amphiphilic helices as membrane interaction sites. These multivalent interactions may allow MBP to interact with two opposing membrane leaflets, contributing to the formation of a multi-layered myelin structure. The antimicrobial peptide magainin 2 interacts with the bacterial membrane, causing damage to its structure. VUVCD analysis revealed that the M2 peptides assemble in the membrane and turn into oligomers with a β-strand structure. Linear dichroism and fluorescence anisotropy suggested that the oligomers are inserted into the hydrophobic core of the membrane, disrupting the bacterial membrane. Overall, our findings demonstrate that VUVCD and its combination with theoretical and polarization experimental methods pave the way for unraveling the molecular mechanisms of biological phenomena related to protein-membrane interactions.

Shaping membrane interfaces in lipid vesicles mimicking the cytoplasmic leaflet of myelin through variation of cholesterol and myelin basic protein contents

Myelin basic protein (MBP) is an intrinsically disordered protein and in the central nervous system (CNS) mainly responsible for connecting the cytoplasmic surfaces of the multilamellar, compact myelin. Increased posttranslational modification of MBP is linked to both, the natural development (from adolescent to adult brains) of myelin, and features of multiple sclerosis. Here, we study how a combination of this intrinsically disordered myelin protein with varying the natural cholesterol content may alter the characteristics of myelin-like membranes and interactions between these membranes. Large unilamellar vesicles (LUVs) with a composition mimicking the cytoplasmic leaflet of myelin were chosen as the model system, in which different parameters contributing to the interactions between the lipid membrane and MBP were investigated. While we use cryo-transmission electron microscopy (TEM) for imaging, dynamic light scattering (DLS) and electrophoretic measurements through continuously-monitored phase-analysis light scattering (cmPALS) were used for a more global overview of particle size and charge, and electron paramagnetic resonance (EPR) spectroscopy was utilized for local behavior of lipids in the vesicles' membranes in aqueous solution. The cholesterol content was varied from 060 % in these LUVs and measurements were performed in the presence and absence of MBP. We find that the composition of the lipid layers is relevant to the interaction with MBP. Not only the size, the shape and the aggregation behavior of the vesicles depend on the cholesterol content, but also within each membrane, cholesterol's freedom of movement, its environmental polarity and its distribution were found to depend on the content using the EPR-active spin-labeled cholesterol (CSOSL). In addition, DLS and EPR measurements probing the transition temperatures of the lipid phases allow a correlation of specific behavior with the human body temperature of 37 °C. Overall, our results aid in understanding the importance of the native cholesterol content in the healthy myelin membrane, which serves as the basis for stable and optimum protein-bilayer interactions. Although studied in this specific myelin-like system, from a more general and materials science-oriented point of view, we could establish how membrane and vesicle properties depend on cholesterol and/or MBP content, which might be useful generally when specific membrane and vesicle characteristics are sought for.

Roadmap for Postnatal Brain Maturation: Changes in Gray and White Matter Composition during Development Measured by Fourier Transformed Infrared Microspectroscopy

Key events in postnatal brain development, such as neuronal migration, synaptogenesis, and myelination, shape the adult brain. These events are reflected in changes in gray and white matter (GM and WM) occurring during this period. Therefore, precise knowledge of GM and WM composition in perinatal brain development is crucial to characterizing brain formation as well as the neurodevelopmental disruption observed in diseases such as autism and schizophrenia. In this study, we combined histochemical and immunohistochemical staining with biochemical and biophysical analyses using Fourier transform infrared (IR) microspectroscopy (μFTIR) to better understand the chemical changes during postnatal developmental myelination. For this purpose, we analyzed the GM and WM in the mouse brain and cerebellum (strain C57BL/6) from postnatal day 0 (P0) to day P28 and established presumed correlations between staining and IR data. IR spectra allowed the (i) quantification of lipid and protein content through the CH2/amide I ratio, (ii) determination of chemical characteristics of lipids, such as the presence of unsaturated bonds in the carbonate chain or carbonyls from ester groups in the polar head, and (iii) determination of the protein secondary structure (α-helix and intramolecular β-sheets). The results indicate that the increase in the CH2/amide I ratio calculated from the μFTIR data correlates well with lipid histochemical staining. IR data indicated a change in the lipid composition in WM since carbonyl and unsaturated olefinic groups do not increase when lipids accumulate during myelination. Our correlation analysis between IR data and immunohistochemical staining of myelin-associated proteins revealed that myelin oligodendrocyte protein correlated well with lipid accumulation, while myelin basic protein appeared before lipid modifications, which indicated that myelin-associated proteins and lipid deposition were not synchronic. These events were related to a decrease in the intramolecular β/α protein ratio. Our results indicate that lipids and proteins in WM substantially change their composition due to primary myelination, and according to results obtained from staining, these modifications are better described by lipid histochemical staining than by immunohistochemistry against myelin-related proteins. In conclusion, μFTIR can be a useful technique to study WM during perinatal development and provide detailed information about alterations in the chemical composition related to neurodevelopmental diseases.

Citrullination of myelin basic protein induces a Th17-cell response in healthy individuals and enhances the presentation of MBP85-99 in patients with multiple sclerosis

The post-translational modification citrullination has been proposed to play a role in the pathogenesis of multiple sclerosis (MS). Myelin basic protein (MBP) is a candidate autoantigen which is citrullinated to a minor extent under physiological conditions and hypercitrullinated in MS. We examined immune cell responses elicited by hypercitrullinated MBP (citMBP) in cultures of mononuclear cells from 18 patients with MS and 42 healthy donors (HDs). The immunodominant peptide of MBP, MBP85-99, containing citrulline in position 99, outcompeted the binding of native MBP85-99 to HLA-DR15, which is strongly linked to MS. Moreover, using the monoclonal antibody MK16 as probe, we observed that B cells and monocytes from HLA-DR15+ patients with MS presented MBP85-99 more efficiently after challenge with citMBP than with native MBP. Both citMBP and native MBP induced proliferation of CD4+ T cells from patients with MS as well as TNF-α production by their B cells and CD4+ T cells, and citrullination of MBP tended to enhance TNF-α secretion by CD4+ T cells from HLA-DR15+ patients. Unlike native MBP, citMBP induced differentiation into Th17 cells in cultures from HDs, while neither form of MBP induced Th17-cell differentiation in cultures from patients with MS. These data suggest a role for citrullination in the breach of tolerance to MBP in healthy individuals and in maintenance of the autoimmune response to MBP in patients with MS.

The intrinsically disordered protein glue of the myelin major dense line: Linking AlphaFold2 predictions to experimental data

Numerous human proteins are classified as intrinsically disordered proteins (IDPs). Due to their physicochemical properties, high-resolution structural information about IDPs is generally lacking. On the other hand, IDPs are known to adopt local ordered structures upon interactions with e.g. other proteins or lipid membrane surfaces. While recent developments in protein structure prediction have been revolutionary, their impact on IDP research at high resolution remains limited. We took a specific example of two myelin-specific IDPs, the myelin basic protein (MBP) and the cytoplasmic domain of myelin protein zero (P0ct). Both of these IDPs are crucial for normal nervous system development and function, and while they are disordered in solution, upon membrane binding, they partially fold into helices, being embedded into the lipid membrane. We carried out AlphaFold2 predictions of both proteins and analysed the models in light of experimental data related to protein structure and molecular interactions. We observe that the predicted models have helical segments that closely correspond to the membrane-binding sites on both proteins. We furthermore analyse the fits of the models to synchrotron-based X-ray scattering and circular dichroism data from the same IDPs. The models are likely to represent the membrane-bound state of both MBP and P0ct, rather than the conformation in solution. Artificial intelligence-based models of IDPs appear to provide information on the ligand-bound state of these proteins, instead of the conformers dominating free in solution. We further discuss the implications of the predictions for mammalian nervous system myelination and their relevance to understanding disease aspects of these IDPs.

Amyloid-PET of the white matter: Relationship to free water, fiber integrity, and cognition in patients with dementia and small vessel disease

White matter (WM) injury is frequently observed along with dementia. Positron emission tomography with amyloid-ligands (Aβ-PET) recently gained interest for detecting WM injury. Yet, little is understood about the origin of the altered Aβ-PET signal in WM regions. Here, we investigated the relative contributions of diffusion MRI-based microstructural alterations, including free water and tissue-specific properties, to Aβ-PET in WM and to cognition. We included a unique cohort of 115 participants covering the spectrum of low-to-severe white matter hyperintensity (WMH) burden and cognitively normal to dementia. We applied a bi-tensor diffusion-MRI model that differentiates between (i) the extracellular WM compartment (represented via free water), and (ii) the fiber-specific compartment (via free water-adjusted fractional anisotropy [FA]). We observed that, in regions of WMH, a decrease in Aβ-PET related most closely to higher free water and higher WMH volume. In contrast, in normal-appearing WM, an increase in Aβ-PET related more closely to higher cortical Aβ (together with lower free water-adjusted FA). In relation to cognitive impairment, we observed a closer relationship with higher free water than with either free water-adjusted FA or WM PET. Our findings support free water and Aβ-PET as markers of WM abnormalities in patients with mixed dementia, and contribute to a better understanding of processes giving rise to the WM PET signal.

Myricetin attenuates hypoxic-ischemic brain damage in neonatal rats via NRF2 signaling pathway

Introduction: Hypoxic-ischemic encephalopathy (HIE) is a crucial cause of neonatal death and neurological sequelae, but currently there is no effective therapy drug for HIE. Both oxidative stress and apoptosis play critical roles in the pathological development of HIE. Myricetin, a naturally extracted flavonol compound, exerts remarkable effects against oxidative stress, apoptosis, and inflammation. However, the role and underlying molecular mechanism of myricetin on HIE remain unclear. Methods: In this study, we established the neonatal rats hypoxic-ischemic (HI) brain damage model in vivo and CoCl₂ induced PC1₂ cell model in vitro to explore the neuroprotective effects of myricetin on HI injury, and illuminate the potential mechanism. Results: Our results showed that myricetin intervention could significantly reduce brain infarction volume, glia activation, apoptosis, and oxidative stress marker levels through activating NRF2 (Nuclear factor-E2-related factor 2) and increase the expressions of NRF2 downstream proteins NQO-1 and HO-1. In addition, the NRF2 inhibitor ML385 could significantly reverse the effects of myricetin. Conclusion: This study found that myricetin might alleviate oxidative stress and apoptosis through NRF2 signaling pathway to exert the protective role for HI injury, which suggested that myricetin might be a promising therapeutic agent for HIE.

Implications of Post-Translational Modifications in Autoimmunity with Emphasis on Citrullination, Homocitrullination and Acetylation for the Pathogenesis, Diagnosis and Prognosis of Rheumatoid Arthritis

Post-translational modifications (PTMs) influence cellular processes and consequently, their dysregulation is related to the etiologies of numerous diseases. It is widely known that a variety of autoimmune responses in human diseases depend on PTMs of self-proteins. In this review we summarize the latest findings about the role of PTMs in the generation of autoimmunity and, specifically, we address the most relevant PTMs in rheumatic diseases that occur in synovial tissue. Citrullination, homocitrullination (carbamylation) and acetylation are responsible for the generation of Anti-Modified Protein/Peptide Antibodies (AMPAs family), autoantibodies which have been implicated in the etiopathogenesis, diagnosis and prognosis of rheumatoid arthritis (RA). Synthetic peptides provide complete control over the exact epitopes presented as well as the specific positions in their sequence where post-translationally modified amino acids are located and are key to advancing the detection of serological RA biomarkers that could be useful to stratify RA patients in order to pursue a personalized rheumatology. In this review we specifically address the latest findings regarding synthetic peptides post-translationally modified for the specific detection of autoantibodies in RA patients.

Intrinsic Disorder as a Natural Preservative: High Levels of Intrinsic Disorder in Proteins Found in the 2600-Year-Old Human Brain

Proteomic analysis revealed the preservation of many proteins in the Heslington brain (which is at least 2600-year-old brain tissue uncovered within the skull excavated in 2008 from a pit in Heslington, Yorkshire, England). Five of these proteins-"main proteins": heavy, medium, and light neurofilament proteins (NFH, NFM, and NFL), glial fibrillary acidic protein (GFAP), and myelin basic (MBP) protein-are engaged in the formation of non-amyloid protein aggregates, such as intermediate filaments and myelin sheath. We used a wide spectrum of bioinformatics tools to evaluate the prevalence of functional disorder in several related sets of proteins, such as the main proteins and their 44 interactors, all other proteins identified in the Heslington brain, as well as the entire human proteome (20,317 manually curated proteins), and 10,611 brain proteins. These analyses revealed that all five main proteins, half of their interactors and almost one third of the Heslington brain proteins are expected to be mostly disordered. Furthermore, most of the remaining Heslington brain proteins are expected to contain sizable levels of disorder. This is contrary to the expected substantial (if not complete) elimination of the disordered proteins from the Heslington brain. Therefore, it seems that the intrinsic disorder of NFH, NFM, NFL, GFAP, and MBP, their interactors, and many other proteins might play a crucial role in preserving the Heslington brain by forming tightly folded brain protein aggregates, in which different parts are glued together via the disorder-to-order transitions.

Protein citrullination marks myelin protein aggregation and disease progression in mouse ALS models

Increased protein citrullination (PC) and dysregulated protein arginine deiminase (PAD) activity have been observed in several neurodegenerative diseases. PC is a posttranslational modification catalyzed by the PADs. PC converts peptidyl-arginine to peptidyl-citrulline, thereby reducing the positive charges and altering structure and function of proteins. Of the five PADs, PAD2 is the dominant isoform in the central nervous system (CNS). Abnormal PC and PAD dysregulation are associated with numerous pathological conditions, including inflammatory diseases and neurodegeneration. Animal model studies have shown therapeutic efficacy from inhibition of PADs, thus suggesting a role of PC in pathogenesis. To determine whether PC contribute to amyotrophic lateral sclerosis (ALS), a deadly neurodegenerative disease characterized by loss of motor neurons, paralysis, and eventual death, we investigated alterations of PC and PAD2 in two different transgenic mouse models of ALS expressing human mutant SOD1^G93A and PFN1^C71G, respectively. PC and PAD2 expression are altered dynamically in the spinal cord during disease progression in both models. PC and PAD2 increase progressively in astrocytes with the development of reactive astrogliosis, while decreasing in neurons. Importantly, in the spinal cord white matter, PC accumulates in protein aggregates that contain the myelin proteins PLP and MBP. PC also accumulates progressively in insoluble protein fractions during disease progression. Finally, increased PC and PAD2 expression spatially correlate with areas of the CNS with the most severe motor neuron degeneration. These results suggest that altered PC is an integral part of the neurodegenerative process and potential biomarkers for disease progression in ALS. Moreover, increased PC may contribute to disease-associated processes such as myelin protein aggregation, myelin degeneration, and astrogliosis.

Variation of Structural and Dynamical Flexibility of Myelin Basic Protein in Response to Guanidinium Chloride

Myelin basic protein (MBP) is intrinsically disordered in solution and is considered as a conformationally flexible biomacromolecule. Here, we present a study on perturbation of MBP structure and dynamics by the denaturant guanidinium chloride (GndCl) using small-angle scattering and neutron spin–echo spectroscopy (NSE). A concentration of 0.2 M GndCl causes charge screening in MBP resulting in a compact, but still disordered protein conformation, while GndCl concentrations above 1 M lead to structural expansion and swelling of MBP. NSE data of MBP were analyzed using the Zimm model with internal friction (ZIF) and normal mode (NM) analysis. A significant contribution of internal friction was found in compact states of MBP that approaches a non-vanishing internal friction relaxation time of approximately 40 ns at high GndCl concentrations. NM analysis demonstrates that the relaxation rates of internal modes of MBP remain unaffected by GndCl, while structural expansion due to GndCl results in increased amplitudes of internal motions. Within the model of the Brownian oscillator our observations can be rationalized by a loss of friction within the protein due to structural expansion. Our study highlights the intimate coupling of structural and dynamical plasticity of MBP, and its fundamental difference to the behavior of ideal polymers in solution.

Phenytoin promotes the proliferation of oligodendrocytes and enhances the expression of myelin basic protein in the corpus callosum of mice demyelinated by cuprizone

Oligodendrocyte loss and myelin sheet destruction are crucial characteristics of demyelinating diseases. Phenytoin promotes the proliferation of endogenous neural precursor cells in the ventricular-subventricular zone in the postnatal brain that help restore the oligodendroglial population. This study aimed to evaluate whether phenytoin promotes myelin recovery of the corpus callosum of demyelinated adult mice. CD1 male mice were exposed to a demyelinating agent (0.2% cuprizone) for 8 weeks. We assembled two groups: the phenytoin-treated group and the control-vehicle group. The treated group received oral phenytoin (10 mg/kg) for 4 weeks. We quantified the number of Olig2 + and NG2 + oligodendrocyte precursor cells (OPCs), Rip + oligodendrocytes, the expression level of myelin basic protein (MBP), and the muscle strength and motor coordination. The oligodendroglial lineage (Olig2 + cells, NG2 + cells, and RIP + cells) significantly increases by the phenytoin administration when compared to the control-vehicle group. The phenytoin-treated group also showed an increased expression of MBP in the corpus callosum and better functional scores in the horizontal bar test. These findings suggest that phenytoin stimulates the proliferation of OPCs, re-establishes the oligodendroglial population, promotes myelin recovery in the corpus callosum, and improves motor coordination and muscle strength.

ATP synthase FOF1 structure, function, and structure-based drug design

ATP synthases are unique rotatory molecular machines that supply biochemical reactions with adenosine triphosphate (ATP)-the universal "currency", which cells use for synthesis of vital molecules and sustaining life. ATP synthases of F-type (FOF1) are found embedded in bacterial cellular membrane, in thylakoid membranes of chloroplasts, and in mitochondrial inner membranes in eukaryotes. The main functions of ATP synthases are control of the ATP synthesis and transmembrane potential. Although the key subunits of the enzyme remain highly conserved, subunit composition and structural organization of ATP synthases and their assemblies are significantly different. In addition, there are hypotheses that the enzyme might be involved in the formation of the mitochondrial permeability transition pore and play a role in regulation of the cell death processes. Dysfunctions of this enzyme lead to numerous severe disorders with high fatality levels. In our review, we focus on FOF1-structure-based approach towards development of new therapies by using FOF1 structural features inherited by the representatives of this enzyme family from different taxonomy groups. We analyzed and systematized the most relevant information about the structural organization of FOF1 to discuss how this approach might help in the development of new therapies targeting ATP synthases and design tools for cellular bioenergetics control.

Characterization of Radioiodinated Diaryl Oxadiazole Derivatives as SPECT Probes for Detection of Myelin in Multiple Sclerosis

Multiple sclerosis (MS) is an intractable disease of the central nervous system that results from destruction of the myelin sheath. Direct measurement of de- and remyelination is required for monitoring the disease stage of MS, but no useful method has been established. In this study, we characterized four diaryl oxadiazole derivatives as novel myelin-imaging probes for single photon emission computed tomography (SPECT). All the diaryl oxadiazole derivatives penetrated the blood-brain barrier in normal mice. Among them, the highest ratio of radioactivity accumulation in the white matter (myelin-rich region) against the gray matter (myelin-deficient region) was observed at 60 min postinjection of [¹²⁵I]1,3,4-PODP-DM in ex vivo autoradiography using normal mice. In the blocking study with ex vivo autoradiography, the radioactivity accumulation of [¹²⁵I]1,3,4-PODP-DM in the white matter markedly reduced. [¹²⁵I]1,3,4-PODP-DM detected demyelination in the ex vivo autoradiographic images of not only the spinal cord of the experimental autoimmune encephalomyelitis mice but also the brain after lysophosphatidylcholine (LPC) injection. In addition, [¹²³I]1,3,4-PODP-DM could image LPC-induced demyelination in the mouse brain with SPECT. These results suggest that [¹²³I]1,3,4-PODP-DM may be a potential SPECT probe for imaging myelin in MS.

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.

Serum and Saliva Myelin Basic Protein as Multiple Sclerosis Biomarker

Introduction:

Multiple Sclerosis (MS) is presented with motor and sensory function loss. It is caused by demyelination and following axonal lesion. As Myelin Basic Protein (MBP) is one of the key elements of the myelin cover, we examined the level of MBP in serum, stimulated, and unstimulated saliva as a suitable biomarker for detecting MS.

Methods:

A case-control study was performed in 29 healthy women and 32 definitive relapsing-remitting MS patients hospitalized in Imam Reza hospital, Tehran, Iran. MBP level was assayed in serum and stimulated and unstimulated whole saliva.

Results:

MBP was expressed at a lower level in serum and stimulated saliva of MS patients compared to the control group. The serum MBP level had a considerable correlation with its stimulated saliva level. The receiver operating characteristic analysis showed significant diagnostic ability for MBP to discriminate MS patients with serum and stimulated saliva from controls.

Conclusion:

Serum and saliva level of MBP is lower in MS, so it may be considered a potential biomarker in MS.

Comprehensive Atlas of the Myelin Basic Protein Interaction Landscape

Intrinsically disordered myelin basic protein (MBP) is one of the key autoantigens in autoimmune neurodegeneration and multiple sclerosis particularly. MBP is highly positively charged and lacks distinct structure in solution and therefore its intracellular partners are still mostly enigmatic. Here we used combination of formaldehyde-induced cross-linking followed by immunoprecipitation and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to elucidate the interaction network of MBP in mammalian cells and provide the list of potential MBP interacting proteins. Our data suggest that the largest group of MBP-interacting proteins belongs to cellular proteins involved in the protein translation machinery, as well as in the spatial and temporal regulation of translation. MBP interacts with core ribosomal proteins, RNA helicase Ddx28 and RNA-binding proteins STAU1, TDP-43, ADAR-1 and hnRNP A0, which are involved in various stages of RNA biogenesis and processing, including specific maintaining MBP-coding mRNA. Among MBP partners we identified CTNND1, which has previously been shown to be necessary for myelinating Schwann cells for cell-cell interactions and the formation of a normal myelin sheath. MBP binds proteins MAGEB2/D2 associated with neurotrophin receptor p75NTR, involved in pathways that promote neuronal survival and neuronal death. Finally, we observed that MBP interacts with RNF40–a component of heterotetrameric Rnf40/Rnf20 E3 ligase complex, recruited by Egr2, which is the central transcriptional regulator of peripheral myelination. Concluding, our data suggest that MBP may be more actively involved in myelination not only as a main building block but also as a self-regulating element.

Expression of Oligodendrocyte and Oligoprogenitor Cell Proteins in Frontal Cortical White and Gray Matter: Impact of Adolescent Development and Ethanol Exposure

Adolescent development of prefrontal cortex (PFC) parallels maturation of executive functions as well as increasing white matter and myelination. Studies using MRI and other methods find that PFC white matter increases across adolescence into adulthood in both humans and rodents. Adolescent binge drinking is common and has been found to alter adult behaviors and PFC functions. This study examines development of oligoprogenitor (OPC) and oligodendrocytes (OLs) in Wistar rats from adolescence to adulthood within PFC white matter, corpus callosum forceps minor (fmi), PFC gray matter, and the neurogenic subventricular zone (SVZ) using immunohistochemistry for marker proteins. In addition, the effects of adolescent intermittent ethanol exposure [AIE; 5.0 g/kg/day, intragastric, 2 days on/2 days off on postnatal day (P)25-54], which is a weekend binge drinking model, were determined. OPC markers NG2+, PDGFRα+ and Olig2+IHC were differentially impacted by both age and PFC region. In both fmi and SVZ, NG2+IHC cells declined from adolescence to adulthood with AIE increasing adult NG2+IHC cells and their association with microglial marker Iba1. PFC gray matter decline in NG2+IHC in adulthood was not altered by AIE. Both adult maturation and AIE impacted OL expression of PLP+, MBP+, MAG+, MOG+, CNPase+, Olig1+, and Olig2+IHC in all three PFC regions, but in region- and marker-specific patterns. These findings are consistent with PFC region-specific changes in OPC and OL markers from adolescence to adulthood as well as following AIE that could contribute to lasting changes in PFC function.

The Role of Lipids, Lipid Metabolism and Ectopic Lipid Accumulation in Axon Growth, Regeneration and Repair after CNS Injury and Disease

Axons in the adult mammalian nervous system can extend over formidable distances, up to one meter or more in humans. During development, axonal and dendritic growth requires continuous addition of new membrane. Of the three major kinds of membrane lipids, phospholipids are the most abundant in all cell membranes, including neurons. Not only immature axons, but also severed axons in the adult require large amounts of lipids for axon regeneration to occur. Lipids also serve as energy storage, signaling molecules and they contribute to tissue physiology, as demonstrated by a variety of metabolic disorders in which harmful amounts of lipids accumulate in various tissues through the body. Detrimental changes in lipid metabolism and excess accumulation of lipids contribute to a lack of axon regeneration, poor neurological outcome and complications after a variety of central nervous system (CNS) trauma including brain and spinal cord injury. Recent evidence indicates that rewiring lipid metabolism can be manipulated for therapeutic gain, as it favors conditions for axon regeneration and CNS repair. Here, we review the role of lipids, lipid metabolism and ectopic lipid accumulation in axon growth, regeneration and CNS repair. In addition, we outline molecular and pharmacological strategies to fine-tune lipid composition and energy metabolism in neurons and non-neuronal cells that can be exploited to improve neurological recovery after CNS trauma and disease.

Noncovalent Association and Partitioning of Some Perfume Components at Infinite Dilution with Myelin Basic Protein Pseudophase in Normal Saline

Myelin basic protein (MBP), one of the major protein constituents of the myelin sheath, possesses unique ligand-binding features. We present a novel equilibrium headspace gas chromatographic technique to examine the thermodynamics of noncovalent interactions between common perfume components: Lilial, Hedione, Hexylcinnamic aldehyde, and Versalide with MBP monomers and its hexameric MBP-pseudophase. A general theoretical model is used to calculate the critical aggregation concentration (cac) of MBP, perfume component binding constants with monomeric MBP, K₁₁, and MBP as pseudophase, K_n1, and free energies for perfume component binding with monomeric MBP, ΔG_b,11, and MBP as pseudophase, ΔG_b,n1. In addition, the pseudophase-water partition coefficients, K_x, the free energies of transfer of perfume from bulk water to the MBP-pseudophase, ΔG_t, and the intra-aggregate activity coefficients, γ_m^∞, at infinite dilution were also determined. The cac value measured by the method of fractional distribution is a unique and precise approach in understanding the aggregation phenomenon. Within the experimental error, the 1:1 binding free energies did not differ by more than 1 kJ/mol among the perfume components but favored the MBP pseudophase binding by 6 kJ/mol. Therefore, that protein aggregation can enhance the binding of small molecules is probably a general conclusion. While the magnitudes of K₁₁, K_n1, ΔG_b, K_x, and ΔG_t show weak trends, the γ_m^∞ values show a strong and distinct trend in interaction, spanning 4 orders of magnitude among the perfume components.

N-acetylcysteine Provides Cytoprotection in Murine Oligodendrocytes through Heme Oxygenase-1 Activity

Oligodendrocytic injury by oxidative stress can lead to demyelination, contributing to neurodegeneration. We investigated the mechanisms by which an antioxidant, N-acetylcysteine (NAC), reduces oxidative stress in murine oligodendrocytes. We used normal 158N and mutant 158JP cells with endogenously high reactive oxygen species (ROS) levels. Oxidative stress was induced in 158N cells using hydrogen peroxide (H₂O₂, 500 μM), and both cells were treated with NAC (50 µM to 500 µM). ROS production, total glutathione (GSH) and cell survival were measured 24 h after treatment. In normal cells, H₂O₂ treatment resulted in a ~5.5-fold increase in ROS and ~50% cell death. These deleterious effects of oxidative stress were attenuated by NAC, resulting in improved cell survival. Similarly, NAC treatment resulted in decreased ROS levels in 158JP cells. Characterization of mechanisms underlying cytoprotection in both cell lines revealed an increase in GSH levels by NAC, which was partially blocked by an inhibitor of GSH synthesis. Interestingly, we observed heme oxygenase-1 (HO-1), a cytoprotective enzyme, play a critical role in cytoprotection. Inhibition of HO-1 activity abolished the cytoprotective effect of NAC with a corresponding decrease in total antioxidant capacity. Our results indicate that NAC promotes oligodendrocyte survival in oxidative stress-related conditions through multiple pathways.

Myelin Basic Protein Phospholipid Complexation Likely Competes with Deimination in Experimental Autoimmune Encephalomyelitis Mouse Model

Multiple sclerosis has complex pathogenesis encompassing a variety of components (immunologic, genetic, and environmental). The autoimmunogenicity against the host's myelin basic protein is a major contributor. An increase in myelin basic protein deimination (a post-translational modification) and a change in phospholipid composition have been associated with multiple sclerosis. The interaction of myelin basic protein with phospholipids in the myelin membrane is an important contributor to the stability and maintenance of proper myelin sheath function. The study of this aspect of multiple sclerosis is an area that has yet to be fully explored and that the present study seeks to understand. Several biochemical methods, a capillary electrophoresis coupled system and mass spectrometry, were used in this study. These methods identified four specific phospholipids complexing with myelin basic protein. We show that lysophosphatidylcholine 18:1 provides a robust competitive effect against hyper-deimination. Our data suggest that lysophosphatidylcholine 18:1 has a different biochemical behavior when compared to other phospholipids and lysophosphatidylcholines 14:0, 16:0, and 18:0.

Information theoretic measures for quantifying sequence-ensemble relationships of intrinsically disordered proteins

Intrinsically disordered proteins (IDPs) contribute to a multitude of functions. De novo design of IDPs should open the door to modulating functions and phenotypes controlled by these systems. Recent design efforts have focused on compositional biases and specific sequence patterns as the design features. Analysis of the impact of these designs on sequence-function relationships indicates that individual sequence/compositional parameters are insufficient for describing sequence-function relationships in IDPs. To remedy this problem, we have developed information theoretic measures for sequence–ensemble relationships (SERs) of IDPs. These measures rely on prior availability of statistically robust conformational ensembles derived from all atom simulations. We show that the measures we have developed are useful for comparing sequence-ensemble relationships even when sequence is poorly conserved. Based on our results, we propose that de novo designs of IDPs, guided by knowledge of their SERs, should provide improved insights into their sequence–ensemble–function relationships.

Myelin basic protein dynamics from out-of-equilibrium functional state to degraded state in myelin

Living matter is a quasi-stationary out-of-equilibrium system; in this physical condition, structural fluctuations at nano- and meso-scales are needed to understand the physics behind its biological functionality. Myelin has a simple ultrastructure whose fluctuations show correlated disorder in its functional out-of-equilibrium state. However, there is no information on the relationship between this correlated disorder and the dynamics of the intrinsically disordered Myelin Basic Protein (MBP) which is expected to influence the membrane structure and overall functionality. In this work, we have investigated the role of this protein structural dynamics in the myelin ultrastructure fluctuations in various conditions, by using synchrotron Scanning micro X Ray Diffraction and Small Angle X ray Scattering. We have induced the crossover from out-of-equilibrium functional state to in-equilibrium degeneration changing the pH to values far from physiological condition. The observed compression of the cytosolic layer thickness probes that the intrinsic large MBP fluctuations preserve the cytosol structure also in the degraded state. Thus, the transition of myelin ultrastructure from correlated to uncorrelated disordered state, is principally affected by the deformation of the membrane and extracellular domain.

Effect of Cholesterol and Myelin Basic Protein (MBP) Content on Lipid Monolayers Mimicking the Cytoplasmic Membrane of Myelin

Myelin basic protein (MBP) is located in the insulating covers of nerve cells in the brain and spinal cord. By interacting with lipid membranes, it is responsible for compaction of the myelin sheath in the central nervous system, which is weakened in demyelinating diseases. The lipid composition of the myelin leaflet has a high impact on the interaction between the membrane and MBP. Cholesterol is present in the cytoplasmic leaflet with a rather high amount of 44% (mol%). In this study, the focus is on the effect of cholesterol, mainly by varying its content, on the interaction of MBP with a lipid monolayer. Therefore, Langmuir lipid monolayers mimicking the cytoplasmic membrane of myelin and monolayers with variations of cholesterol content between 0% and 100% were measured at the air/water interface with additional imaging by fluorescence microscopy. All experiments were performed with and without bovine MBP to study the dependence of the interaction of the protein with the monolayers on the cholesterol content. The native amount of 44% cholesterol in the monolayer combines optima in the order of the monolayer (presumably correlating to compaction and thermodynamic stability) and protein interaction and shows unique features in comparison to lower or higher cholesterol contents.

Flexible Players within the Sheaths: The Intrinsically Disordered Proteins of Myelin in Health and Disease

Myelin ensheathes selected axonal segments within the nervous system, resulting primarily in nerve impulse acceleration, as well as mechanical and trophic support for neurons. In the central and peripheral nervous systems, various proteins that contribute to the formation and stability of myelin are present, which also harbor pathophysiological roles in myelin disease. Many myelin proteins have common attributes, including small size, hydrophobic segments, multifunctionality, longevity, and regions of intrinsic disorder. With recent advances in protein biophysical characterization and bioinformatics, it has become evident that intrinsically disordered proteins (IDPs) are abundant in myelin, and their flexible nature enables multifunctionality. Here, we review known myelin IDPs, their conservation, molecular characteristics and functions, and their disease relevance, along with open questions and speculations. We place emphasis on classifying the molecular details of IDPs in myelin, and we correlate these with their various functions, including susceptibility to post-translational modifications, function in protein–protein and protein–membrane interactions, as well as their role as extended entropic chains. We discuss how myelin pathology can relate to IDPs and which molecular factors are potentially involved.

Oligodendrocyte dysfunction and regeneration failure: A novel hypothesis of delayed encephalopathy after carbon monoxide poisoning

Carbon monoxide (CO) poisoning usually causes brain lesions and delayed encephalopathy, also known as delayed neurological sequelae (DNS). Demyelination of white matter (WM) is one of the most common sites of abnormalities in patients with DNS, but its mechanisms remain unclear. Oligodendrocytes (OLs) are myelinated cells that ensure the rapid conduction of neuronal axon signals and provide the nutritional factors necessary for maintaining nerve integrity in the central nervous system (CNS). OLs readily regenerate and replace damaged myelin membranes around axons in the adult mammalian CNS following demyelination. The ability to regenerate OLs depends on the availability of precursor cells (OPCs) in the CNS of adults. Multiple injury-related signals can induce OPC expansion followed by OL differentiation, axonal contact and myelin regeneration (remyelination). Therefore, OL dysfunction and regeneration failure in the deep WM of the brain are the key pathophysiological mechanisms leading to delayed brain injury after CO poisoning. CO-induced toxicity may interfere with OL function and render OPCs unable to regenerate OLs through some unclear mechanisms, leading to progressive demyelinating damage and resulting in DNS. In the future, combination therapies to reduce OL damage and promote OPC differentiation and remyelination may be important for the prevention and treatmentof DNS after CO poisoning.

Myelin in the Central Nervous System: Structure, Function, and Pathology

Oligodendrocytes generate multiple layers of myelin membrane around axons of the central nervous system to enable fast and efficient nerve conduction. Until recently, saltatory nerve conduction was considered the only purpose of myelin, but it is now clear that myelin has more functions. In fact, myelinating oligodendrocytes are embedded in a vast network of interconnected glial and neuronal cells, and increasing evidence supports an active role of oligodendrocytes within this assembly, for example, by providing metabolic support to neurons, by regulating ion and water homeostasis, and by adapting to activity-dependent neuronal signals. The molecular complexity governing these interactions requires an in-depth molecular understanding of how oligodendrocytes and axons interact and how they generate, maintain, and remodel their myelin sheaths. This review deals with the biology of myelin, the expanded relationship of myelin with its underlying axons and the neighboring cells, and its disturbances in various diseases such as multiple sclerosis, acute disseminated encephalomyelitis, and neuromyelitis optica spectrum disorders. Furthermore, we will highlight how specific interactions between astrocytes, oligodendrocytes, and microglia contribute to demyelination in hereditary white matter pathologies.

Label-Free Potentiometric Ion Flux Immunosensor for Determination of Recombinant Human Myelin Basic Protein: Application to Downstream Purification from Transgenic Milk

Recombinant human myelin basic protein (rhMBP) produced in the milk of transgenic cows was found exclusively associated with milk caseins. This hindered its direct determination without extensive sample pretreatment. Here, a label-free potentiometric immunosensor was developed and validated for the determination of rhMBP. An ion flux was generated under zero-current based on surface blocking of the polymeric membrane ion-selective electrode by anti-hMBP antibody and tetrabutylammonium bromide as a marker ion. The immunosensor was successfully employed in the quantitative determination of hMBP in the range of 0.10-20.00 μg/mL with a limit of detection of 50.00 ng/mL. The applicability of the passive ion flux immunosensor for determination of target analyte in complex matrices was investigated. Downstream purification of rhMBP from the milk of transgenic cows was achieved using cation exchange chromatography, immobilized metal affinity chromatography, and immunoaffinity chromatography. The specificity of the immunosensor along with matrix effect of milk proteins were demonstrated. Results obtained using the rhMBP immunosensor were further cross-validated using an orthogonal testing protocol assembled of RP-HPLC and SE-HPLC. It should be noted that the proposed ion flux immunosensor provided a feasible and specific tool for monitoring rhMBP concentration/purity, immunogenic activity, and stability. Such approach provides an attractive economic alternative to sophisticated biosensors required for in-process quality control of biopharmaceutical products.

A novel myelin basic protein transcript variant in the murine central nervous system

Myelin basic protein is a multifunctional protein whose primary role is to adhere membranes of the myelin sheath. There are various isoforms that have been identified, 6 distinct isoforms in human and 13 distinct isoforms in mice. These distinct isoforms are the product of alternative splicing of a single gene. The present study sought out to identify the different isoforms found in the murine central nervous system. Neuronal tissue (brain) from five different C57BL6/J mice at 2 months of age was harvested and used for mRNA extraction. mRNA was reversed transcribed to cDNA and transcripts were detected through PCR amplification and DNA agarose gel separation. Primers for exon 1, exon 5b and exon 11 of the myelin basic protein gene were used to capture all the possible transcripts that are naturally found in the murine central nervous system. Unknown transcript was sequenced at Genewiz facilities (South Plainfield, NJ) and mass spectrometry protein sequence analysis demonstrated the presence of a novel myelin basic protein transcript variant. We identified a novel transcript variant of myelin basic protein. This novel transcript variant corresponds to a myelin basic protein of 32.5 kDa which has not been previously reported. This novel transcript variant presents relevant clinical significance to various demyelinating diseases due to its contribution to the understanding of the natural state of the murine central nervous system.

Structural disorder in the proteome and interactome of Alkhurma virus (ALKV)

Infection by the Alkhurma virus (ALKV) leading to the Alkhurma hemorrhagic fever is a common thread in Saudi Arabia, with no efficient treatment or prevention available as of yet. Although the rational drug design traditionally uses information on known 3D structures of viral proteins, intrinsically disordered proteins (i.e., functional proteins that do not possess unique 3D structures), with their multitude of disorder-dependent functions, are crucial for the biology of viruses. Here, viruses utilize disordered regions in their invasion of the host organisms and in hijacking and repurposing of different host systems. Furthermore, the ability of viruses to efficiently adjust and accommodate to their hostile habitats is also intrinsic disorder-dependent. However, little is currently known on the level of penetrance and functional utilization of intrinsic disorder in the ALKV proteome. To fill this gap, we used here multiple computational tools to evaluate the abundance of intrinsic disorder in the ALKV genome polyprotein. We also analyzed the peculiarities of intrinsic disorder predisposition of the individual viral proteins, as well as human proteins known to be engaged in interaction with the ALKV proteins. Special attention was paid to finding a correlation between protein functionality and structural disorder. To the best of our knowledge, this work represents the first systematic study of the intrinsic disorder status of ALKV proteome and interactome.

Myelin basic protein charge isomers change macrophage polarization

Purpose

During a neuronal injury, a variety of immune cells infiltrate into the local microenvironment at the demyelination site. After the destruction of the intact myelin sheath, its major constituent myelin basic protein (MBP) dissociates from the plasma membrane and acts as a free ligand on the infiltrated immune cells. MBP exhibits charge microheterogeneity as a result of post-translational modifications, but the effect of various isomers of MBP on the activity of macrophages is not known.

Materials and methods

MBP was isolated and purified from bovine brain white matter. RAW 264.7 macrophages were cultured in DMEM supplemented with heat-inactivated fetal bovine serum. For evaluation of macrophage polarization following treatment of RAW 264.7 cells with MBP charge isomers, inducible nitric oxide synthase (iNOS) expression (M1 phenotype marker) and arginase-1 expression (M2 phenotype marker) were determined in cell lysates by ELISA. To assess Rac activity, G-LISA Rac Activation Assay system was used. The expression of receptor for advanced glycation end-products (RAGE) and high mobility group box 1 (HMGB1) protein were assayed by Western blot analysis.

Results

Our results have shown that minimally modified C1 component of MBP increases the expression of arginase-1 in cells, decreases the expression of iNOS, does not change the secretion of HMGB1 protein, but significantly elevates surface expression of RAGE, and in parallel, increases the activity of small GTPase Rac. On the other hand, highly modified deiminated isomer C8-MBP increases the secretion of HMGB1 protein but does not change the expression of arginase-1 or the content of RAGE.

Conclusion

These data indicate that deiminated C8 isomer of MBP tends to polarize RAW macrophages into M1 phenotypes, whereas C1 enhances the activity of M2 phenotype markers.

Structural homology of myelin basic protein and muscarinic acetylcholine receptor: Significance in the pathogenesis of complex regional pain syndrome

Complex regional pain syndrome is an extremely painful condition that develops after trauma to a limb. Complex regional pain syndrome exhibits autoimmune features in part mediated by autoantibodies against muscarinic‐2 acetylcholine (M2) receptor. The mechanisms underlying the M2 receptor involvement in complex regional pain syndrome remain obscure. Based on our recent work demonstrating that limb nerve trauma releases a potent proalgesic, immunodominant myelin basic protein fragment, our present sequence database analyses reveal an unexpected and previously undescribed structural homology of the proalgesic myelin basic protein fragment with the M2 receptor. As both complex regional pain syndrome and the proalgesic myelin basic protein activity are prevalent in females, this myelin basic protein/M2 homology presents an inviting hypothesis explaining the mechanisms of autoimmune pathogenesis and sexual dimorphism that underlies vulnerability toward developing complex regional pain syndrome and other pain states with neuropathic features. This hypothesis may aid in the development of novel diagnostic and therapeutic strategies to chronic pain.

Interaction of the cryptic fragment of myelin basic protein with mitochondrial voltage-dependent anion-selective channel-1 affects cell energy metabolism

In demyelinating nervous system disorders, myelin basic protein (MBP), a major component of the myelin sheath, is proteolyzed and its fragments are released in the neural environment. Here, we demonstrated that, in contrast with MBP, the cellular uptake of the cryptic 84-104 epitope (MBP84-104) did not involve the low-density lipoprotein receptor-related protein-1, a scavenger receptor. Our pull-down assay, mass spectrometry and molecular modeling studies suggested that, similar with many other unfolded and aberrant proteins and peptides, the internalized MBP84-104 was capable of binding to the voltage-dependent anion-selective channel-1 (VDAC-1), a mitochondrial porin. Molecular modeling suggested that MBP84-104 directly binds to the N-terminal α-helix located midway inside the 19 β-blade barrel of VDAC-1. These interactions may have affected the mitochondrial functions and energy metabolism in multiple cell types. Notably, MBP84-104 caused neither cell apoptosis nor affected the total cellular ATP levels, but repressed the aerobic glycolysis (lactic acid fermentation) and decreased the l-lactate/d-glucose ratio (also termed as the Warburg effect) in normal and cancer cells. Overall, our findings implied that because of its interactions with VDAC-1, the cryptic MBP84-104 peptide invoked reprogramming of the cellular energy metabolism that favored enhanced cellular activity, rather than apoptotic cell death. We concluded that the released MBP84-104 peptide, internalized by the cells, contributes to the reprogramming of the energy-generating pathways in multiple cell types.

Interaction of Myelin Basic Protein with Myelin-like Lipid Monolayers at Air-Water Interface

Interaction of myelin basic protein (MBP) and the cytoplasmic leaflets of the oligodendrocyte membrane is essential for the formation and compaction of the myelin sheath of the central nervous system and is altered aberrantly and implicated in the pathogenesis of neurodegenerative diseases like multiple sclerosis. To gain more detailed insights into this interaction, the adsorption of MBP to model lipid monolayers of similar composition to the myelin of the central nervous system was studied at the air-water interface with monolayer adsorption experiments. Measuring the surface pressure and the related maximum insertion pressure of MBP for different myelin-like lipid monolayers provided information about the specific role of each of the single lipids in the myelin. Depending on the ratio of negatively charged lipids to uncharged lipids and the distance between charges, the adsorption process was found to be determined by two counteracting effects: (i) protein incorporation, resulting in an increasing surface pressure and (ii) lipid condensation due to electrostatic interaction between the positively charged protein and negatively charged lipids, resulting in a decreasing surface pressure. Although electrostatic interactions led to high insertion pressures, the associated lipid condensation lowered the fluidity of the myelin-like monolayer.

A sensitive and selective ELISA methodology quantifies a demyelination marker in experimental and clinical samples

Sciatic nerve chronic constriction injury (CCI) in rodents produces nerve demyelination via proteolysis of myelin basic protein (MBP), the major component of myelin sheath. Proteolysis releases the cryptic MBP epitope, a demyelination marker, which is hidden in the native MBP fold. It has never been established if the proteolytic release of this cryptic MBP autoantigen stimulates the post-injury increase in the respective circulating autoantibodies. To measure these autoantibodies, we developed the ELISA that employed the cryptic 84-104 MBP sequence (MBP84-104) as bait. This allowed us, for the first time, to quantify the circulating anti-MBP84-104 autoantibodies in rat serum post-CCI. The circulating IgM (but not IgG) autoantibodies were detectable as soon as day 7 post-CCI. The IgM autoantibody level continually increased between days 7 and 28 post-injury. Using the rat serum samples, we established that the ELISA intra-assay (precision) and inter-assay (repeatability) variability parameters were 2.87% and 4.58%, respectively. We also demonstrated the ELISA specificity by recording the autoantibodies to the liberated MBP84-104 epitope alone, but not to intact MBP in which the 84-104 region is hidden. Because the 84-104 sequence is conserved among mammals, we tested if the ELISA was applicable to detect demyelination and quantify the respective autoantibodies in humans. Our limited pilot study that involved 16 female multiple sclerosis and fibromyalgia syndrome patients demonstrated that the ELISA was efficient in measuring both the circulating IgG- and IgM-type autoantibodies in patients exhibiting demyelination. We believe that the ELISA measurements of the circulating autoantibodies against the pathogenic MBP84-104 peptide may facilitate the identification of demyelination in both experimental and clinical settings. In clinic, these measurements may assist neurologists to recognize patients with painful neuropathy and demyelinating diseases, and as a result, to personalize their treatment regimens.

Thioredoxin-1 Protects Spinal Cord from Demyelination Induced by Methamphetamine through Suppressing Endoplasmic Reticulum Stress and Inflammation

Methamphetamine (METH) is a psychostimulant abused around the world. Emerging evidence indicates that METH causes brain damage. However, there are very few reports on METH-induced demyelination. Thioredoxin-1 (Trx-1) is a redox regulating protein and plays the roles in protecting neurons from various stresses. However, whether Trx-1 resists demyelination induced by METH has not been reported. In this study, we found that METH-induced thin myelin sheaths in spinal cord, whereas Trx-1 overexpression transgenic (TG) mice restored the myelin sheaths thickness. The expressions of myelin-associated glycoprotein, myelin basic protein, and cyclin-dependent kinase 5 were decreased by METH, whereas these alterations were blocked in Trx-1 TG mice. The expressions of procaspase-12 and procaspase-3 were decreased by METH, the expression of calpain1 was increased by METH, whereas the alterations were suppressed in Trx-1 TG mice. As same as, the expressions of the extracellular signal-regulated kinase, nuclear factor κB, tumor necrosis factor-alpha, and interleukin-1beta were induced by METH, which were suppressed in Trx-1 TG mice. These data suggest that Trx-1 may play a critical role in resisting the METH-mediated demyelination in spinal cord through regulating endoplasmic reticulum stress and inflammation pathways.

Behavioral impairment in SHATI/NAT8L knockout mice via dysfunction of myelination development

We have identified SHATI/NAT8L in the brain of mice treated with methamphetamine. Recently, it has been reported that SHATI is N-acetyltransferase 8-like protein (NAT8L) that produces N-acetylaspatate (NAA) from aspartate and acetyl-CoA. We have generated SHATI/NAT8L knockout (Shati^−/−) mouse which demonstrates behavioral deficits that are not rescued by single NAA supplementation, although the reason for which is still not clarified. It is possible that the developmental impairment results from deletion of SHATI/NAT8L in the mouse brain, because NAA is involved in myelination through lipid synthesis in oligodendrocytes. However, it remains unclear whether SHATI/NAT8L is involved in brain development. In this study, we found that the expression of Shati/Nat8l mRNA was increased with brain development in mice, while there was a reduction in the myelin basic protein (MBP) level in the prefrontal cortex of juvenile, but not adult, Shati^−/− mice. Next, we found that deletion of SHATI/NAT8L induces several behavioral deficits in mice, and that glyceryltriacetate (GTA) treatment ameliorates the behavioral impairments and normalizes the reduced protein level of MBP in juvenile Shati^−/− mice. These findings suggest that SHATI/NAT8L is involved in myelination in the juvenile mouse brain via supplementation of acetate derived from NAA. Thus, reduction of SHATI/NAT8L induces developmental neuronal dysfunction.

Continuous Elution Proteoform Identification of Myelin Basic Protein by Superficially Porous Reversed-Phase Liquid Chromatography and Fourier Transform Mass Spectrometry

Myelin basic protein (MBP) plays an important structural and functional role in the neuronal myelin sheath. Translated MBP exhibits extreme microheterogeneity with numerous alternative splice variants (ASVs) and post-translational modifications (PTMs) reportedly tied to central nervous system maturation, myelin stability, and the pathobiology of various de- and dys-myelinating disorders. Conventional bioanalytical tools cannot efficiently examine ASV and PTM events simultaneously, which limits understanding of the role of MBP microheterogeneity in human physiology and disease. To address this need, we report on a top-down proteomics pipeline that combines superficially porous reversed-phase liquid chromatography (SPLC), Fourier transform mass spectrometry (FTMS), data-independent acquisition (DIA) with nozzle-skimmer dissociation (NSD), and aligned data processing resources to rapidly characterize abundant MBP proteoforms within murine tissue. The three-tier proteoform identification and characterization workflow resolved four known MBP ASVs and hundreds of differentially modified states from a single 90 min SPLC-FTMS run on ∼0.5 μg of material. This included 323 proteoforms for the 14.1 kDa ASV alone. We also identified two novel ASVs from an alternative transcriptional start site (ATSS) of the MBP gene as well as a never before characterized S-acylation event linking palmitic acid, oleic acid, and stearic acid at C78 of the 17.125 kDa ASV.

Reorganization of Lipid Diffusion by Myelin Basic Protein as Revealed by STED Nanoscopy

Myelin is a multilayered membrane that ensheathes axonal fibers in the vertebrate nervous system, allowing fast propagation of nerve action potentials. It contains densely packed lipids, lacks an actin-based cytocortex, and requires myelin basic protein (MBP) as its major structural component. This protein is the basic constituent of the proteinaceous meshwork that is localized between adjacent cytoplasmic membranes of the myelin sheath. Yet, it is not clear how MBP influences the organization and dynamics of the lipid constituents of myelin. Here, we used optical stimulated emission depletion super-resolution microscopy in combination with fluorescence correlation spectroscopy to assess the characteristics of diffusion of different fluorescent lipid analogs in myelin membrane sheets of cultured oligodendrocytes and in micrometer-sized domains that were induced by MBP in live epithelial PtK2 cells. Lipid diffusion was significantly faster and less anomalous both in oligodendrocytes and inside the MBP-rich domains of PtK2 cells compared with undisturbed live PtK2 cells. Our data show that MBP reorganizes lipid diffusion, possibly by preventing the buildup of an actin-based cytocortex and by preventing most membrane proteins from entering the myelin sheath region. Yet, in contrast to myelin sheets in oligodendrocytes, the MBP-induced domains in epithelial PtK2 cells demonstrate no change in lipid order, indicating that segregation of long-chain lipids into myelin sheets is a process specific to oligodendrocytes.