Myelin protein metabolism in demyelination and remyelination in the sciatic nerve

Lysophosphatidylcholine (LPC) was injected intraneurally into the right sciatic nerve of a series of rats, leaving the left nerve as a control. At various time points up to 30 days after LPC treatment, the injected and control nerves were removed and incubated with [3H]amino acids, then purified myelin was prepared from the nerves. At all time points investigated the uptake of labeled amino acids was much higher in myelin proteins from the LPC-treated nerve than in those from the intact control nerve. [3H]Fucose uptake was also slightly increased. In the first week after LPC injection the increased amino acid incorporation was much greater in the myelin proteins of molecular weight higher than P0. From 10 days on, the smaller myelin proteins including P0, 19K, P1 and P2 showed the largest increase. From comparison of the morphology and biochemistry at 3 and 7 days after LPC injection, we propose that in the first 7 days, while myelin is degenerating, those proteins associated with Schwann cell or myelin reaction, interaction, and recognition functions are most stimulated metabolically, while after ten days the structural myelin proteins are actively resynthesized and the axon is remyelinated.     

Overlapping features of extrapontine myelinolysis and acquired chronic (non-Wilsonian) hepatocerebral degeneration

Central pontine myelinolysis (CPM, osmotic demyelination syndrome) and acquired chronic hepatocerebral degeneration (ACHD) both occur in patients with liver failure, but are not thought to be caused by similar etiopathogenic mechanisms despite the fact that occasional patients exhibit both disorders. In our autopsy practice we have recently encountered three patients with the pontine lesions of acute or subacute osmotic demyelination syndrome, coupled with superimposed non-Wilsonian ACHD. All three patients had well-documented rapid elevations in serum sodium proximate to their demise, as well as terminal liver failure. A close intermingling and juxtaposition of lesions with severe demyelination and macrophage breakdown [thought to represent extrapontine myelinolysis (EPM)] to those with vacuolization of myelin but no cellular reaction or myelin loss (ACHD) was noted within some of the same anatomic areas. Particular overlap was seen in lesions at the cerebral cortical gray–white junction and in pencil fibers of the striatum. In these areas it was difficult to be certain whether the lesions were due to EPM or ACHD. We concluded that there was a synergism between the two disorders and raise the possibility that there may be factors common to both disorders that lead to similar anatomic sites for involvement.Presented (in abstract format) at XVIth International Congress of Neuropathology, San Francisco, Sept 10–15, 2006.     

Chemokine receptor antagonism as a new therapy for multiple sclerosis

New information about the role of tissue inflammation in the pathogenesis of multiple sclerosis (MS) has driven a search for effective and specific therapeutics that address leukocyte trafficking. These developments in understanding MS are complemented by advances in clarifying the molecular mechanisms of leukocyte extravasation and providing the knowledge base needed to modulate tissue inflammation. Of particular interest are the chemokines and their receptors. Chemokines constitute a large family of chemoattractant peptides that regulate the vast spectrum of leukocyte migration events. This review discusses MS and proposes that identifying the chemokines and receptors involved in the inflammation associated with this disorder may lead to therapeutic intervention.     

慢性血管性痴呆模型大鼠脑胶质细胞反应及基质金属蛋白酶9的表达

背景：胶质细胞及炎性细胞因子参与了血管性痴呆慢性脑缺血的炎性反应过程。目的：观察慢性脑缺血致血管性痴呆大鼠的脑组织中胶质细胞反应及基质金属蛋白酶9的表达。方法：雄性Wistar大鼠随机分为正常组、假手术组和模型组3组。模型组通过永久性结扎大鼠的双侧颈总动脉导致慢性脑缺血建立动物模型,假手术组除不结扎双侧颈总动脉外,其余处理与模型组相同。各组大鼠行Morris水迷宫试验检测大鼠的学习记忆能力。采用病理染色、免疫组化的方法,观察大鼠在缺血后不同时间点脑组织中胶质细胞及基质金属蛋白酶9的病理改变。结果与结论：缺血早期的病理变化主要发生在皮质、基底前脑、海马、胼胝体、颞叶皮质及视束,部分出现小的梗死灶。缺血1个月后,白质髓鞘脱失、间质疏松呈空泡样改变逐渐明显,神经轴索连续性完好。小胶质细胞、星形胶质细胞及基质金属蛋白酶9的表达在缺血早期以皮质及海马为主,缺血后期以室周白质及白质疏松处更为明显,海马区表达则减少。     

Selective tonicity-induced expression of the neutral amino-acid transporter SNAT2 in oligodendrocytes in rat brain following systemic hypertonicity

Sodium-coupled neutral amino-acid transporter member 2 (SNAT2) belongs to the family of neutral amino-acid transporters. SNAT2 is encoded by the gene Slc38a2, whose expression was reported to increase in vitro in fibroblasts, endothelial and renal cells exposed to a hypertonic medium. SNAT2 tonicity-induced expression brings about cellular accumulation of amino-acid, which contributes to osmoadaptation to hypertonicity. Since brain osmoadaptation is observed in relationship to neurological disorders resulting from pathological osmotic imbalances in blood plasma, we have investigated, through immunocytochemistry, SNAT2 expression in brain of rats subjected to systemic hypertonicity. Following prolonged systemic hypertonicity (24 h), small, strongly immunolabeled elements were observed that were not present in sham-treated animals. They were evenly distributed in the gray matter, with a lower density in the forebrain and a higher density in the brain stem. However the highest density by far was observed in white matter, where they were frequently aligned in chain-like rows. These observations suggested an oligodendrocyte location that was further established by double immunofluorescent labeling, using the oligodendrocyte phenotypic markers 2'-3'-cyclic nucleotide 3'phosphodiesterase and carbonic anhydrase II. SNAT2-positive elements were found associated with oligodendrocyte cell bodies, while oligodendrocyte processes were devoid of labeling. A quantitative analysis performed in the cerebral cortex indicated that virtually all SNAT2-positive elements were associated with oligodendrocyte cell bodies and conversely that the overwhelming majority of oligodendrocytes showed SNAT2 immunolabeling. The tonicity-induced expression of SNAT2 was not observed following acute systemic hypertonicity (6 h). Our results suggest that the osmoadaptation of brain oligodendrocytes to hypertonicity relies upon amino-acid accumulation through the tonicity-induced expression of SNAT2. The possible significance of these findings in relationship to the selective loss of oligodendrocytes observed in osmotic demyelination syndrome is discussed.     

Axonal injury detected by in vivo diffusion tensor imaging correlates with neurological disability in a mouse model of multiple sclerosis

Recent studies have suggested that axonal damage, and not demyelination, is the primary cause of long-term neurological impairment in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). The axial and radial diffusivities derived from diffusion tensor imaging have shown promise as non-invasive surrogate markers of axonal damage and demyelination, respectively. In this study, in vivo diffusion tensor imaging of the spinal cords from mice with chronic EAE was performed to determine if axial diffusivity correlated with neurological disability in EAE assessed by the commonly used clinical scoring system. Axial diffusivity in the ventrolateral white matter showed a significant negative correlation with EAE clinical score and was significantly lower in mice with severe EAE than in mice with moderate EAE. Furthermore, the greater decreases in axial diffusivity were associated with greater amounts of axonal damage, as confirmed by quantitative staining for non-phosphorylated neurofilaments (SMI32). Radial diffusivity and relative anisotropy could not distinguish between the groups of mice with moderate EAE and those with severe EAE. The results further the notion that axial diffusivity is a non-invasive marker of axonal damage in white matter and could provide the necessary link between pathology and neurological disability.     

Elevated activity and microglial expression of myeloperoxidase in demyelinated cerebral cortex in multiple sclerosis

Recent studies have revealed extensive cortical demyelination in patients with progressive multiple sclerosis (MS). Demyelination in gray matter lesions is associated with activation of microglia. Macrophages and microglia are known to express myeloperoxidase (MPO) and generate reactive oxygen species during myelin phagocytosis in the white matter. In the present study we examined the extent of microglial activation in the cerebral cortex and the relationship of microglial activation and MPO activity to cortical demyelination. Twenty-one cases of neuropathologically confirmed multiple sclerosis, with 34 cortical lesions, were used to assess microglial activation. HLA-DR immunolabeling of activated microglia was significantly higher in demyelinated MS cortex than control cortex and, within the MS cohort, was significantly greater within cortical lesions than in matched non-demyelinated areas of cortex. In homogenates of MS cortex, cortical demyelination was associated with significantly elevated MPO activity. Immunohistochemistry revealed MPO in CD68-positive microglia within cortical plaques, particularly toward the edge of the plaques, but not in microglia in adjacent non-demyelinated cortex. Cortical demyelination in MS is associated with increased activity of MPO, which is expressed by a CD68-positive subset of activated microglia, suggesting that microglial production of reactive oxygen species is likely to be involved in cortical demyelination.     

S1P1 receptor subtype inhibits demyelination and regulates chemokine release in cerebellar slice cultures

Sphingosine-1-phosphate receptors (S1PRs) are drug targets for the compound FTY720, which is the first oral therapy developed for treatment of relapsing-remitting multiple sclerosis. S1PRs play a variety of functional roles in the differentiation, proliferation, survival and/or migration of neurons and glia. In this study, rat organotypic cerebellar slice cultures were used to assess whether S1PRs play a role in demyelination induced by lysolecithin (LPC). The data demonstrated that FTY720 and SEW2871 (a S1P1R-specific agonist) inhibited LPC-induced demyelination as assessed by myelin basic protein (MBP) immunofluorescence. Treatment with both drugs for 48 h also induced an increase in S1P1R expression in astrocytes. Moreover, FTY720 and SEW2871 inhibited the release of several chemokines in conditions of LPC-induced demyelination, including LIX (CXCL5), MIP-1alpha, and MIP-3alpha. Taken together, the data suggest that activation of S1P1Rs prevents LPC-induced demyelination via a mechanism involving a reduction of chemotactic chemokine release. The study supports the concept that FTY720 attenuates demyelination by not only preventing S1PR-mediated T cell migration into the CNS but also by limiting cytokine communication between cells of the immune system and the CNS.     

Diosgenin promotes oligodendrocyte progenitor cell differentiation through estrogen receptor-mediated ERK1/2 activation to accelerate remyelination

Differentiation of oligodendrocyte progenitor cells (OPCs) into mature oligodendrocytes is a prerequisite for remyelination after demyelination, and impairment of this process is suggested to be a major reason for remyelination failure. Diosgenin, a plant-derived steroid, has been implicated for therapeutic use in many diseases, but little is known about its effect on the central nervous system. In this study, using a purified rat OPC culture model, we show that diosgenin significantly and specifically promotes OPC differentiation without affecting the viability, proliferation, or migration of OPC. Interestingly, the effect of diosgenin can be blocked by estrogen receptor (ER) antagonist ICI 182780 but not by glucocorticoid and progesterone receptor antagonist RU38486, nor by mineralocorticoid receptor antagonist spirolactone. Moreover, it is revealed that both ER-alpha and ER-beta are expressed in OPC, and diosgenin can activate the extracellular signal-regulated kinase 1/2 (ERK1/2) in OPC via ER. The pro-differentiation effect of diosgenin can also be obstructed by the ERK inhibitor PD98059. Furthermore, in the cuprizone-induced demyelination model, it is demonstrated that diosgenin administration significantly accelerates/enhances remyelination as detected by Luxol fast blue stain, MBP immunohistochemistry and real time RT-PCR. Diosgenin also increases the number of mature oligodendrocytes in the corpus callosum while it does not affect the number of OPCs. Taking together, our results suggest that diosgenin promotes the differentiation of OPC into mature oligodendrocyte through an ER-mediated ERK1/2 activation pathway to accelerate remyelination, which implicates a novel therapeutic usage of this steroidal natural product in demyelinating diseases such as multiple sclerosis (MS).