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Astrogliosis during acute and chronic cuprizone demyelination and implications for remyelination.

ABSTRACT: In multiple sclerosis, microglia/macrophage activation and astrocyte reactivity are important components of the lesion environment that can impact remyelination. The current study characterizes these glial populations relative to expression of candidate regulatory molecules in cuprizone demyelinated corpus callosum. Importantly, periods of recovery after acute or chronic cuprizone demyelination are examined to compare conditions of efficient versus limited remyelination, respectively. Microglial activation attenuates after early demyelination. In contrast, astrocyte reactivity persists throughout demyelination and a 6-week recovery period following either acute or chronic demyelination. This astrocyte reaction is characterized by (a) early proliferation, (b) increased expression of GFAP (glial fibrillary acidic protein), Vim (vimentin), Fn1 (fibronectin) and CSPGs (chondroitin sulphate proteoglycans) and (c) elaboration of a dense network of processes. Glial processes elongated in the axonal plane persist throughout lesion areas during both the robust remyelination that follows acute demyelination and the partial remyelination that follows chronic demyelination. However, prolonged astrocyte reactivity with chronic cuprizone treatment does not progress to barrier formation, i.e. dense compaction of astrocyte processes to wall off the lesion area. Multiple candidate growth factors and inflammatory signals in the lesion environment show strong correlations with GFAP across the acute cuprizone demyelination and recovery time course, yet there is more divergence across the progression of chronic cuprizone demyelination and recovery. However, differential glial scar formation does not appear to be responsible for differential remyelination during recovery in the cuprizone model. The astrocyte phenotype and lesion characteristics in this demyelination model inform studies to identify triggers of non-remyelinating sclerosis in chronic multiple sclerosis lesions.

SUBMITTER: Hibbits N

PROVIDER: S-EPMC3483617 | biostudies-literature | 2012 Oct

REPOSITORIES: biostudies-literature

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Astrogliosis during acute and chronic cuprizone demyelination and implications for remyelination.

Hibbits Norah N Yoshino Jun J Le Tuan Q TQ Armstrong Regina C RC

ASN neuro 20121030 6

In multiple sclerosis, microglia/macrophage activation and astrocyte reactivity are important components of the lesion environment that can impact remyelination. The current study characterizes these glial populations relative to expression of candidate regulatory molecules in cuprizone demyelinated corpus callosum. Importantly, periods of recovery after acute or chronic cuprizone demyelination are examined to compare conditions of efficient versus limited remyelination, respectively. Microglial ...[more]

PMID: 23025787

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Project description:Phospholipases A(2) (PLA(2)) are the enzymatic keys for the activation of the arachidonic acid (AA) cascade and the subsequent synthesis of pro-inflammatory prostanoids (prostaglandins and tromboxanes). Prostanoids play critical roles in the initiation and modulation of inflammation and their levels have been reported increased in several neurological and neurodegenerative disorders, including multiple sclerosis (MS). Here, we aimed to determine whether brain expression PLA(2) enzymes and the terminal prostagland in levels are changed during cuprizone-induced demyelination and in the subsequent remyelination phase. Mice were given the neurotoxicant cuprizone through the diet for six weeks to induce brain demyelination. Then, cuprizone was withdrawn and mice were returned to a normal diet for 6 weeks to allow spontaneous remyelination. We found that after 4-6 weeks of cuprizone, sPLA(2)(V) and cPLA(2), but not iPLA(2)(VI), gene expression was upregulated in the cortex, concomitant with an increase in the expression of astrocyte and microglia markers. Cyclooxygenase (COX)-2 gene expression was consistently upregulated during all the demyelination period, whereas COX-1 sporadically increased only at week 5 of cuprizone exposure. However, we found that at the protein level only sPLA(2)(V) and COX-1 were elevated during demyelination, with COX-1 selectively expressed by activated and infiltrated microglia/macrophages and astrocytes. Levels of PGE(2), PGD(2), PGI(2) and TXB(2) were also increased during demyelination. During remyelination, none of the PLA(2) isoforms was significantly changed, whereas COX-1 and -2 were sporadically upregulated only at the gene expression level. PGE(2), PGI(2) and PGD(2) levels returned to normal, whereas TXB(2) was still upregulated after 3 weeks of cuprizone withdrawal. Our study characterizes for the first time time-dependent changes in the AA metabolic pathway during cuprizone-induced demyelination and the subsequent remyelination and suggests that sPLA(2)(V) is the major isoform contributing to AA release.

Project description:BACKGROUND:Various studies by MRI exhibit that the corpus callosum (CC) is the most vulnerable to cuprizone administration, detecting the demyelination and remyelination process using different MRI parameters are, however, lacking. PURPOSE:To investigate the sensitivity of multiparametric MRI both in vivo and ex vivo for demyelination and remyelination. STUDY TYPE:Prospective. ANIMAL MODEL:A cuprizone mice model with an age-matched control group (n = 5), 4-week cuprizone exposure group followed by 9-week on a normal diet (n = 6), and a 13-week cuprizone exposure group (n = 6). FIELD STRENGTH/SEQUENCE:3D gradient recalled echo, T2 -weighted, and diffusion tensor imaging (DTI) at 7.0T and 9.4T. ASSESSMENT:Quantification of DTI metrics, quantitative susceptibility mapping (QSM), and T2 -weighted imaging intensity in major white matter bundles. STATISTICAL TESTS:Nonparametric permutation tests were used with a cluster-forming threshold as 3.09 (equivalent to P = 0.001), and the significant level as P = 0.05 with family-wise correction. RESULTS:In vivo susceptibility values increased from -11.7 to -0.7 ppb (P < 0.001) in CC and from -13.7 to -5.1 ppb (P < 0.001) in the anterior commissure (AC) after the 13-week cuprizone exposure. Ex vivo susceptibility values increased from -25.4 to 7.4 ppb (P < 0.001) in CC and from -41.6 to -15.8 ppb (P < 0.001) in AC. Susceptibility values showed high variations to demyelination for in vivo studies (94.0% in CC, 62.8% in AC). Susceptibility values exhibited higher variations than radial diffusivity for ex vivo studies (129.1% vs. 28.3% in CC, 62.0% vs. 25.0% in AC). In addition to the differential susceptibility variations in different white matter tracts, intraregional demyelination variation was also present not only in CC but also in the AC area by voxel-based analysis. DATA CONCLUSION:QSM is sensitive to the demyelination process of cuprizone exposure, which can be a complementary technique to conventional T2 -weighted images and DTI metrics. LEVEL OF EVIDENCE:2 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019;50:1852-1865.

Project description:Although MRI is the gold standard for the diagnosis and monitoring of multiple sclerosis (MS), current conventional MRI techniques often fail to detect cortical alterations and provide little information about gliosis, axonal damage and myelin status of lesioned areas. Diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) provide sensitive and complementary measures of the neural tissue microstructure. Additionally, specific white matter tract integrity (WMTI) metrics modelling the diffusion in white matter were recently derived. In the current study we used the well-characterized cuprizone mouse model of central nervous system demyelination to assess the temporal evolution of diffusion tensor (DT), diffusion kurtosis tensor (DK) and WMTI-derived metrics following acute inflammatory demyelination and spontaneous remyelination. While DT-derived metrics were unable to detect cuprizone induced cortical alterations, the mean kurtosis (MK) and radial kurtosis (RK) were found decreased under cuprizone administration, as compared to age-matched controls, in both the motor and somatosensory cortices. The MK remained decreased in the motor cortices at the end of the recovery period, reflecting long lasting impairment of myelination. In white matter, DT, DK and WMTI-derived metrics enabled the detection of cuprizone induced changes differentially according to the stage and the severity of the lesion. More specifically, the MK, the RK and the axonal water fraction (AWF) were the most sensitive for the detection of cuprizone induced changes in the genu of the corpus callosum, a region less affected by cuprizone administration. Additionally, microgliosis was associated with an increase of MK and RK during the acute inflammatory demyelination phase. In regions undergoing severe demyelination, namely the body and splenium of the corpus callosum, DT-derived metrics, notably the mean diffusion (MD) and radial diffusion (RD), were among the best discriminators between cuprizone and control groups, hence highlighting their ability to detect both acute and long lasting changes. Interestingly, WMTI-derived metrics showed the aptitude to distinguish between the different stages of the disease. Both the intra-axonal diffusivity (Da) and the AWF were found to be decreased in the cuprizone treated group, Da specifically decreased during the acute inflammatory demyelinating phase whereas the AWF decrease was associated to the spontaneous remyelination and the recovery period. Altogether our results demonstrate that DKI is sensitive to alterations of cortical areas and provides, along with WMTI metrics, information that is complementary to DT-derived metrics for the characterization of demyelination in both white and grey matter and subsequent inflammatory processes associated with a demyelinating event.

Dataset Information

Astrogliosis during acute and chronic cuprizone demyelination and implications for remyelination.

Publications

Astrogliosis during acute and chronic cuprizone demyelination and implications for remyelination.

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