Recent advances in myelin biochemistry

Quantitative Evaluation of Rabbit Brain Injury after Cerebral Hemisphere Radiation Exposure Using Generalized q-Sampling Imaging

Radiation therapy is widely used for the treatment of brain tumors and may result in cellular, vascular and axonal injury and further behavioral deficits. The non-invasive longitudinal imaging assessment of brain injury caused by radiation therapy is important for determining patient prognoses. Several rodent studies have been performed using magnetic resonance imaging (MRI), but further studies in rabbits and large mammals with advanced magnetic resonance (MR) techniques are needed. Previously, we used diffusion tensor imaging (DTI) to evaluate radiation-induced rabbit brain injury. However, DTI is unable to resolve the complicated neural structure changes that are frequently observed during brain injury after radiation exposure. Generalized q-sampling imaging (GQI) is a more accurate and sophisticated diffusion MR approach that can extract additional information about the altered diffusion environments. Therefore, herein, a longitudinal study was performed that used GQI indices, including generalized fractional anisotropy (GFA), quantitative anisotropy (QA), and the isotropic value (ISO) of the orientation distribution function and DTI indices, including fractional anisotropy (FA) and mean diffusivity (MD) over a period of approximately half a year to observe long-term, radiation-induced changes in the different brain compartments of a rabbit model after a hemi-brain single dose (30 Gy) radiation exposure. We revealed that in the external capsule, the GFA right to left (R/L) ratio showed similar trends as the FA R/L ratio, but no clear trends in the remaining three brain compartments. Both the QA and ISO R/L ratios showed similar trends in the all four different compartments during the acute to early delayed post-irradiation phase, which could be explained and reflected the histopathological changes of the complicated dynamic interactions among astrogliosis, demyelination and vasogenic edema. We suggest that GQI is a promising non-invasive technique and as compared with DTI, it has better potential ability in detecting and monitoring the pathophysiological cascades in acute to early delayed radiation-induced brain injury by using clinical MR scanners.

Transcriptional analysis of glial cell differentiation in the postnatal murine spinal cord

Postnatal murine spinal cord represents a good model system to study mammalian central nervous system myelination in vivo as a basis for further studies in demyelinating diseases. Transcriptional changes were analyzed in SJL/J mice on postnatal day 0, 14, 49 and 231 (P0, P14, P49, P231) employing Affymetrix GeneChip Mouse Genome 430 2.0 Arrays. Additionally, marker gene signatures for astrocyte and oligodendrocyte lineage-stages were defined to study their gene expression in more detail. In addition, immunohistochemistry was used to quantify the abundance of commonly used glial cell markers. 6092 differentially regulated genes (DEGs) were identified. The up-regulated DEGs at P14, P49 and P231 compared to P0 exhibited significantly enriched associations to gene ontology terms such as myelination and lipid metabolic transport and down-regulated DEGs to neurogenesis and axonogenesis. Expression values of marker gene signatures for neural stem cells, oligodendrocyte precursor cells, and developing astrocytes were constantly decreasing, whereas myelinating oligodendrocyte and mature astrocyte markers showed a steady increase. Molecular findings were substantiated by immunohistochemical observations. The transcriptional changes observed are an important reference for future analysis of degenerative and inflammatory conditions in the spinal cord.

Harnessing the power of yeast to elucidate the role of sphingolipids in metabolic and signaling processes pertinent to psychiatric disorders

The development of therapies for neuropsychiatric disorders is hampered by the lack of understanding of the mechanisms underlying their pathologies. While aberrant sphingolipid metabolism is associated with psychiatric illness, the role of sphingolipids in these disorders is not understood. The genetically tractable yeast model can be exploited in order to elucidate the cellular consequences of sphingolipid perturbation. Hypotheses generated from studies in yeast and tested in mammalian cells may contribute to our understanding of the role of sphingolipids in psychiatric disorders and to the development of new treatments. Here, we compare sphingolipid metabolism in yeast and mammalian cells, discuss studies implicating sphingolipids in psychiatric disorders and propose approaches that utilize yeast in order to elucidate sphingolipid function and identify drugs that target sphingolipid synthesis.

Age- and brain region-specific effects of dietary vitamin K on myelin sulfatides

Dysregulation of myelin sulfatides is a risk factor for cognitive decline with age. Vitamin K is present in high concentrations in the brain and has been implicated in the regulation of sulfatide metabolism. Our objective was to investigate the age-related interrelation between dietary vitamin K and sulfatides in myelin fractions isolated from the brain regions of Fischer 344 male rats fed one of two dietary forms of vitamin K: phylloquinone or its hydrogenated form, 2',3'-dihydrophylloquinone (dK), for 28 days. Both dietary forms of vitamin K were converted to menaquinone-4 (MK-4) in the brain. The efficiency of dietary dK conversion to MK-4 compared to dietary phylloquinone was lower in the striatum and cortex, and was similar to that in the hippocampus. There were significant positive correlations between sulfatides and MK-4 in the hippocampus (phylloquinone-supplemented diet, 12 and 24 months; dK-supplemented diet, 12 months) and cortex (phylloquinone-supplemented diet, 12 and 24 months). No significant correlations were observed in the striatum. Furthermore, sulfatides in the hippocampus were significantly positively correlated with MK-4 in serum. This is the first attempt to establish and characterize a novel animal model that exploits the inability of dietary dK to convert to brain MK-4 to study the dietary effects of vitamin K on brain sulfatide in brain regions controlling motor and cognitive functions. Our findings suggest that this animal model may be useful for investigation of the effect of the dietary vitamin K on sulfatide metabolism, myelin structure and behavior functions.

Plasmalogen deficiency in cerebral adrenoleukodystrophy and its modulation by lovastatin

In cerebral adrenoleukodystrophy (cALD), an accumulation of very long chain fatty acids stems from a defect of the peroxisomal ALD protein (ALDP) and results in the loss of myelin/oligodendrocytes, induction of inflammatory disease and mental deterioration. In brain white matter of cALD patients, we observed not only increased levels of very long chain fatty acid but also reduced levels of plasmenylethanolamine (PlsEtn) and increased levels of reactive oxygen species (ROS). The loss of PlsEtn was greatest in the plaque area and lesser but significant at histologically normal-looking areas of the cALD brain. The reduction in PlsEtn was related to oxidative stress, as supported by increased levels of reactive lipid aldehydes (4-hydroxynonenal and acrolein) and deleterious oxidized proteins (protein carbonyl) in all areas of the cALD brain. This inverse relationship between the levels of PlsEtn and reactive oxygen species (ROS) was further supported in an in vitro study using gene-silencing for dihydroxyacetone phosphate-acyl transferase, a key enzyme for PlsEtn biosynthesis. Levels of PlsEtn were also found decreased in vitro following gene-silencing for the ALDP/ALD-related protein. Furthermore, low levels of PlsEtn were detected in brain white matter of ALDP knock out (KO) mice. A treatment of ALDP KO mice with lovastatin increased PlsEtn levels in the brain. Further, in an in vitro study, lovastatin treatment of rat C6 glial cells increased PlsEtn biosynthesis and reduced the cytokine-induced ROS accumulation. In summary, this study reports that altered metabolism of PlsEtn and ROS in cALD may be corrected by lovastatin treatment.

Fine specificity of antibodies against phospholipids and beta-2-glycoprotein I in monoclonal gammopathy associated neuropathies

Phospholipids are abundantly represented within the nervous system. Aim of our study was to evaluate the presence and fine specificity of anti phospholipid antibodies (aPLAb) among patients with monoclonal gammopathy associated neuropathy. Thirty nine percent of these patients had high titers of aPLAb, mostly associated with low levels of anti beta2 glycoprotein I, which suggests different antibody specificity compared to patients with anti phospholipid syndrome. Further 6/48 patients with dysimmune neuropathy without monoclonal gammopathy had positive aPLAb titers. APLAb strongly cross-reacted with sulfatide. These findings suggest an adjuntive role of aPLAb on nerve damage and may help to better understand the nerve binding properties of anti-sulfatide antibodies.

Deprivation of mother-pup interaction by early weaning alters myelin formation in male, but not female, ICR mice

We previously reported that early-weaned Balb/c mice develop a persistent increase in anxiety as well as aggression, and we suggested that deprivation of mother-pup interaction from postnatal days 15 to 21 might account for this phenomenon. In the present study, we investigated developmental changes in myelin formation and behavioral effects of early weaning in male and female ICR mice. Early weaning was associated with decreased numbers of open-arm entries in an elevated plus-maze for both male and female mice at 3 weeks of age (W3); this effect was persistently observed in males, but ceased after W3 in females. Compared to the brains of normally weaned mice, the brains of the early-weaned males at W8 and of the females at W5 were of lesser mass. Western blotting with whole-brain homogenates identified four isoforms of myelin basic protein (MBP; 21.5, 18.5, 17.0, and 14.0 kDa). Expression of these MBPs increased gradually in normally weaned mice. In contrast, in the early-weaned male mice, but not the early-weaned female mice, it increased robustly at W3 and then declined at W5, as compared to the normally weaned mice. These results suggest that early weaning influences not only anxiety-related behavior but also myelin formation in the brain during the developmental period, particularly between 3 and 5 weeks of age, and male mice are more vulnerable than females to early-weaning effects on behavior and myelin formation.

Vitamin K and sphingolipid metabolism: evidence to date

The brain is enriched with sphingolipids, which are important membrane constituents and major lipid signaling molecules that have a role in motor and cognitive behavior. Vitamin K has been implicated in brain sphingolipid metabolism for more than 30 years. The in vitro and in vivo studies to date suggest a role of vitamin K in the regulation of multiple enzymes involved in sphingolipid metabolism within the myelin-rich regions in the brain. However, the precise mechanisms of action are not well understood. Further, the physiological consequences of the observed effects of vitamin K on sphingolipid metabolism have not been systematically studied.

Immunointervention with cyclosporin A in autoimmune neurological disorders

Cyclosporin A has proven a remarkably effective compound in suppressing disease activity in a number of animal models of autoimmune neurological disorders. During the last decade a number of controlled clinical trials have been carried out in human neurological disorders which are considered to be immune-mediated. The results of those trials are reviewed.

Human brain proton localized NMR spectroscopy in multiple sclerosis

Localized proton spectroscopy of the brain was performed on MS patients (n = 18) and the results are compared with those of a control group (n = 17). The experiments were performed in a 1.5-T Siemens Magnetom using the stimulated echo method and selective water suppression. Acquisition parameters were TR/TE/TM = 3000/270/30 ms, NA = 256, and Acq = 13 min. Localized volumes ranged from 8 to about 80 cc. The patients (ages 25 to 66) were at various stages of the disease. Three of the eighteen patients did not show any plaques on the MR images. VOIs were chosen to contain as much plaque volume as possible in the cerebrum white matter. In the controls and in the patients with no plaques, the VOI were localized in similar white matter regions. All spectra were characterized by the presence of Cho (3.2 ppm), PCr + Cr (3.0 ppm), and NAA (2.0 ppm). The ratios NAA/Cho and NAA/(PCr + Cr) were calculated for both the MS and the control group. The results for the three MS patients with no detectable plaques did not differ significantly from the results of the control group. The former group is, however, too limited to draw any conclusion for the moment. For the MRI positive patients, the following values were found (means +/- 1 SD); NAA/Cho = 1.98 +/- 0.33 and NAA/(PCr + Cr) = 2.16 +/- 0.14. In the normals, these values were NAA/Cho = 2.54 +/- 0.39 and NAA/(PCr + Cr) = 2.76 +/- 0.25. The results quoted are TR and TE dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium reverses lidocaine-induced conduction block in rat fimbria in vitro

1. We have tested the effect of changed concentrations of Ca2+ upon lidocaine-induced conduction block in rat fimbria. 2. With bath [Ca2+] of 0.25 mM, 0.5 mM lidocaine reduced the amplitude of the compound action potential to 20.2% +/- 2.25% of baseline (n = 5). 3. On changing the bath [Ca2+] to 4.4 mM, with no change in lidocaine concentration, the compound action potential increased by 33.5 +/- 6.5%. 4. In the absence of lidocaine, changing bath [Ca2+] had opposite effects. These results replicate findings by others in peripheral nerve.

Covalent linkage of phosphoinositides to myelin basic protein: in vivo occurrence and in vitro studies with experimental allergic encephalomyelitis

We have previously reported the covalent attachment of phosphoinositides to myelin basic protein (MBP) in vitro. In this study, in vivo phosphoinositidation of MBP was observed to occur after intracerebral injection with [32p]HPO4(2-). In the in vitro study of experimental allergic encephalomyelitis, a four-fold increase in phosphoinositidation of MBP was observed in the myelin from the guinea pigs sacrificed during the development of motor dysfunction, as compared to the control group. A decrease (40%) was observed among most of the animals sacrificed before the onset of motor dysfunction.