Proteomic changes associated with degeneration of myelin-forming cells in the central nervous system of c-myc transgenic mice

c-Myc-dependent transcriptional regulation of cell cycle and nucleosomal histones during oligodendrocyte differentiation

Oligodendrocyte progenitor cells (OPCs) have the ability to divide or to growth arrest and differentiate into myelinating oligodendrocytes in the developing brain. Due to their high number and the persistence of their proliferative capacity in the adult brain, OPCs are being studied as potential targets for myelin repair and also as a potential source of brain tumors. This study addresses the molecular mechanisms regulating the transcriptional changes occurring at the critical transition between proliferation and cell cycle exit in cultured OPCs. Using bioinformatic analysis of existing datasets, we identified c-Myc as a key transcriptional regulator of this transition and confirmed direct binding of this transcription factor to identified target genes using chromatin immunoprecipitation. The expression of c-Myc was elevated in proliferating OPCs, where it also bound to the promoter of genes involved in cell cycle regulation (i.e. Cdc2) or chromosome organization (i.e. H2afz). Silencing of c-Myc was associated with decreased histone acetylation at target gene promoters and consequent decrease of gene transcripts. c-Myc silencing also induced a global increase of repressive histone methylation and premature peripheral nuclear chromatin compaction while promoting the progression towards differentiation. We conclude that c-Myc is an important modulator of the transition between proliferation and differentiation of OPCs, although its decrease is not sufficient to induce progression into a myelinating phenotype.

Proteomic strategies in multiple sclerosis and its animal models

The early and precise diagnosis, the prognosis, and the clinical management of multiple sclerosis, remain a considerable challenge. In recent years, the development of novel and powerful proteomic techniques prompted the use of these approaches for the search of unique biomarkers in the cerebrospinal fluid of multiple sclerosis patients. A few studies have also utilized proteomics to delineate the profile of differentially expressed proteins in animal models of the human disease in order to gain global insights into affected pathways. The identification of differentially expressed proteins may be an initial step in the discovery of novel targets and mechanisms that play critical roles in the pathology of multiple sclerosis. Based on these findings, future investigations may elucidate the events leading to demyelination, axonal damage, and neurodegeneration, providing better insights into mechanisms governing the onset and progression of the disease. Although these proteomic studies provide valuable information, they are also faced with a number of challenges. The present review discusses some of the strengths and limitations of proteomic investigations as applied to multiple sclerosis.

Proteomics: a new approach to the study of disease

The global analysis of cellular proteins has recently been termed proteomics and is a key area of research that is developing in the post-genome era. Proteomics uses a combination of sophisticated techniques including two-dimensional (2D) gel electrophoresis, image analysis, mass spectrometry, amino acid sequencing, and bio-informatics to resolve comprehensively, to quantify, and to characterize proteins. The application of proteomics provides major opportunities to elucidate disease mechanisms and to identify new diagnostic markers and therapeutic targets. This review aims to explain briefly the background to proteomics and then to outline proteomic techniques. Applications to the study of human disease conditions ranging from cancer to infectious diseases are reviewed. Finally, possible future advances are briefly considered, especially those which may lead to faster sample throughput and increased sensitivity for the detection of individual proteins.

Proteomics: a new approach to the study of disease

The global analysis of cellular proteins has recently been termed proteomics and is a key area of research that is developing in the post-genome era. Proteomics uses a combination of sophisticated techniques including two-dimensional (2D) gel electrophoresis, image analysis, mass spectrometry, amino acid sequencing, and bio-informatics to resolve comprehensively, to quantify, and to characterize proteins. The application of proteomics provides major opportunities to elucidate disease mechanisms and to identify new diagnostic markers and therapeutic targets. This review aims to explain briefly the background to proteomics and then to outline proteomic techniques. Applications to the study of human disease conditions ranging from cancer to infectious diseases are reviewed. Finally, possible future advances are briefly considered, especially those which may lead to faster sample throughput and increased sensitivity for the detection of individual proteins.

Oligodendrocyte programmed cell death and central myelination deficiency induced in transgenic mice by synergism between c-Myc and Oct-6

The basic helix-loop-helix transcription factor c-Myc is a potent trigger of programmed cell death when overexpressed during late oligodendrocyte development in transgenic mice. Here we provide evidence that c-Myc can act synergistically with the Pit, Oct, Unc homeodomain transcription factor Oct-6 to produce myelin disease pathogenesis in transgenic mice. More than 70% of c-myc/Oct-6 bitransgenic mice, obtained from crosses between phenotypically normal heterozygous mice of various My (c-Myc) and Oc (Oct-6) transgenic strains that express c-myc and oct-6 transgenes under transcriptional control of the myelin basic protein gene, developed severe neurological disturbances characterized by action tremors, recurrent seizures, and premature death. Affected bitransgenic mice exhibited multiple hypomyelinated lesions in the white matter that did not stain with myelin-specific antibodies against myelin basic protein, proteolipid protein, CNPase, and myelin-associated glycoprotein. The mice also exhibited a larger number of terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling positive cells in the white matter as well as ultrastructural evidence of glial cell death and astrogliosis. These observations indicate that the myelin lesions observed in the c-myc/oct-6 bitransgenic mice result from the untimely programmed cell death of oligodendroglia and that the c-myc and oct-6 transgenes act synergistically in producing the lesions.

Laser-assisted microdissection: applications in molecular pathology

Tissue microdissection is potentially one of the most useful techniques in molecular pathology. Laser-assisted microdissection has been developed to procure precisely the cells of interest in a tissue specimen, in a rapid and practical manner. Together with multiplex molecular approaches, it is now feasible to study genetic alterations and isolate genes and proteins in defined cell populations from complex normal and diseased tissues. The fundamental advantage of this technique is the possibility of capturing single cells from which high-quality DNA and mRNA can be isolated for analysis of sequence and quantitation of expression. Moreover, the integration of laser-assisted microdissection and proteomic analysis could identify novel protein markers for disease. The advent of laser-assisted microdissection is likely to have a profound impact on molecular pathology.

Highly basic myelin and oligodendrocyte proteins analyzed by NEPHGE-two-dimensional gel electrophoresis: recognition of novel developmentally regulated proteins

Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) provides high resolution separation of proteins and offers a powerful method for their identification and characterization. Since many myelin-specific proteins are highly basic, they cannot readily be analyzed by standard isoelectric focusing (IEF)-2D-PAGE that affords separation primarily in the isoelectric points (pI) range of 4-8. An alternative method, nonequilibrium pH gradient electrophoresis (NEPHGE)-2D-PAGE, can provide excellent resolution of highly basic proteins. In the present study, we have optimized the NEPHGE-2D-PAGE protocol for the analysis of myelin proteins with basic pIs, and provide a NEPHGE-2D-PAGE map based on size, pI, and immunoreactivity (Western blot) of myelin basic protein (MBP), 2', 3'-cyclic-nucleotide 3'-phosphodiesterase (CNP), myelin proteolipid protein (PLP), and its smaller spliced variant DM20, myelin/oligodendrocyte glycoprotein (MOG) and oligodendrocyte-specific protein (OSP). We have also demonstrated, by analyzing metabolically radiolabeled oligodendrocytes in culture at specific stages of the developmental lineage, the developmentally up-regulated expressions of several undefined, oligodendrocyte, basic membrane proteins during oligodendrocyte differentiation. We suggest that this approach offers an important tool for identifying and characterizing the plethora of uncharacterized myelin proteins.