Studies on protein methyltransferase in human cerebrospinal fluid

Deep Dive on the Proteome of Human Cerebrospinal Fluid: A Valuable Data Resource for Biomarker Discovery and Missing Protein Identification

Cerebrospinal fluid (CSF) is a body fluid of choice for biomarker studies of brain disorders but remains relatively under-studied compared with other biological fluids such as plasma, partly due to the more invasive means of its sample collection. The present study establishes an in-depth CSF proteome through the analysis of a unique CSF sample from a pool of donors. After immunoaffinity depletion, the CSF sample was fractionated using off-gel electrophoresis and analyzed with liquid chromatography tandem mass spectrometry (MS) using the latest generation of hybrid Orbitrap mass spectrometers. The shotgun proteomic analysis allowed the identification of 20 689 peptides mapping on 3379 proteins. To the best of our knowledge, the obtained data set constitutes the largest CSF proteome published so far. Among the CSF proteins identified, 34% correspond to genes whose transcripts are highly expressed in brain according to the Human Protein Atlas. The principal Alzheimer's disease biomarkers (e.g., tau protein, amyloid-β, apolipoprotein E, and neurogranin) were detected. Importantly, our data set significantly contributes to the Chromosome-centric Human Proteome Project (C-HPP), and 12 proteins considered as missing are proposed for validation in accordance with the HPP guidelines. Of these 12 proteins, 8 proteins are based on 2 to 6 uniquely mapping peptides from this CSF analysis, and 4 match a new peptide with a "stranded" single peptide in PeptideAtlas from previous CSF studies. The MS proteomic data are available to the ProteomeXchange Consortium ( http://www.proteomexchange.org/ ) with the data set identifier PXD009646.

Emerging Role for Methylation in Multiple Sclerosis: Beyond DNA

Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system. The inflammatory and neurodegenerative pathways driving MS are modulated by DNA, lysine, and arginine methylation, as evidenced by studies made possible by novel tools for methylation detection or loss of function. We present evidence that MS is associated with genetic variants and metabolic changes that impact on methylation. Further, we comprehensively review current understanding of how methylation can impact on central nervous system (CNS) resilience and neuroregenerative potential, as well as inflammatory versus regulatory T helper (Th) cell balance. These findings are discussed in the context of therapeutic relevance for MS, with broad implications in other neurologic and immune-mediated diseases.

Biological methylation of myelin basic protein: enzymology and biological significance

Myelin is a membrane characteristic of the nervous tissue and functions as an insulator to increase the velocity of the stimuli being transmitted between a nerve cell body and its target. Myelin isolated from human and bovine nervous tissue is composed of approximately 80% lipid and 20% protein, and 30% of the protein fraction constitutes myelin basic protein (MBP). MBP has an unusual amino acid at Res-107 as a mixture of NG-monomethylarginine and NG, N'G-dimethylarginine. The formation of these methylarginine derivatives is catalysed by one of the subtypes of protein methylase I, which specifically methylates Res-107 of this protein. Evidence is presented to demonstrate an involvement of this biological methylation in the integrity and maintenance of myelin.

Urinary excretion of NG-dimethylarginines in multiple sclerosis patients: preliminary observations

The concentrations of NG,N'G-dimethylarginine [Me2(sym)Arg] and NG,NG-dimethylarginine [Me2(asym)Arg] were determined in the urine samples from multiple sclerosis (MS) and control subjects, using a highly sensitive HPLC post-column o-phthaldialdehyde derivatization method. The presence of approximately equal amounts of both dimethylarginine isomers, of Arg concentration nearly half of Me2Arg, and of the undetectable amount of NG-monomethylarginine were the characteristic urinary excretion pattern in all human samples studied. The urinary excretion of Me2(asym)Arg and Me2(sym)Arg from MS (n = 9) and control (n = 7) were analyzed: the mean values from the samples were approximately 20% (for all MS) and 33% (for chronic-progressive MS) lower than those from the control for both dimethylarginine-derivatives when compared to the respective compounds. Although there were contrasting trends between controls and MS patients in the relationship of urinary NG-dimethylarginines and myelin basic protein like material (MBPLM), the correlations were not significant. Differences in the ratios of the concentrations of the two dimethyl derivatives, Me2(sym)Arg/Me2(asym)Arg, were not significantly different between MS and control groups. These findings warrant further investigation of possible links between urinary excretion of NG-dimethylarginine and MBPLM in MS. The possible significance of myelin metabolism in relation to urinary NG-dimethylarginines in MS is discussed.

An enzyme-linked immunosorbent assay for myelin basic protein-specific protein methylase I

A sandwich enzyme-linked immunosorbent assay (ELISA) has been developed to determine myelin basic protein (MBP)-specific protein methylase I. Rabbit immunoglobulin anti-bovine MBP-specific protein methylase I, purified by Sepharose-A affinity chromatography, was utilized as the primary antibodies, while the same antibodies which had been conjugated to peroxidase were employed as the indicator antibodies. This assay method was about 280 times more sensitive than the conventional trichloracetic acid (TCA) precipitation method. Employing the ELISA, the level of MBP-specific protein methylase I during mouse brain development was examined; the peak level of the methylase was shown to be at 16th postnatal day, indicating temporal correlation with myelination. Among several species of brains examined, human showed the highest and carp the least amount of MBP-specific protein methylase I; 6.33 micrograms and 0.33 micrograms per mg of brain cytosol protein, respectively. Dysmyelinating jimpy hemizygous mouse brain showed the immunoreactive MBP-specific protein methylase only 60% that of the control at 20 days of age. The high sensitivity of the method together with the fact that MBP-specific protein methylase is present in human cerebrospinal fluid suggests a possible clinical application of this method for evaluating demyelinating disorders.