Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease of the CNS, most frequently starting with a series of bouts, each followed by complete remission and then a secondary, progressive phase during which the neurological deficit increases steadily. The underlying molecular mechanisms responsible for disease progression are still unclear. Herein, we demonstrate that high mobility group box chromosomal protein 1 (HMGB1), a DNA-binding protein with proinflammatory properties, is evident in active lesions of MS and experimental autoimmune encephalomyelitis (EAE) and that HMGB1 levels correlate with active inflammation. Furthermore, the expression of the innate HMGB1 receptors—receptor for advanced glycation end products, TLR2, and TLR4—was also highly increased in MS and rodent EAE. Additionally, in vitro activation of rodent CNS-derived microglia and bone marrow-derived macrophages demonstrated that microglia were equally as capable as macrophages of translocating HMGB1 following LPS/IFN-γ stimulation. Significant expression of HMGB1 and its receptors on accumulating activated macrophages and resident microglia may thus provide a positive feedback loop that amplifies the inflammatory response during MS and EAE pathogenesis.

J. Neurochem. (2010) 114, 784–794. Positron emission tomography (PET) radioligands that bind selectively to β‐amyloid plaques (Aβ) are promising imaging tools aimed at supporting the diagnosis of Alzheimer’s disease and the evaluation of new drugs aiming to modify amyloid plaque load. For extended clinical use, there is a particular need for PET tracers labeled with fluorine‐18, a radionuclide with 110 min half‐life allowing for central synthesis followed by wide distribution. The development of fluorinated radioligands is, however, challenging because of the lipophilic nature of aromatic fluorine, rendering fluorinated ligands more prone to have high non‐specific white matter binding. We have here developed the new benzofuran‐derived radioligand containing fluorine, AZD4694 that shows high affinity for β‐amyloid fibrils in vitro (K_d = 2.3 ± 0.3 nM). In cortical sections from human Alzheimer’s disease brain [³H]AZD4694 selectively labeled β‐amyloid deposits in gray matter, whereas there was a lower level of non‐displaceable binding in plaque devoid white matter. Administration of unlabeled AZD4694 to rat showed that it has a pharmacokinetic profile consistent with good PET radioligands, i.e., it quickly entered and rapidly cleared from normal rat brain tissue. Ex vivo binding data in aged Tg2576 mice after intravenous administration of [³H]AZD4694 showed selective binding to β‐amyloid deposits in a reversible manner. In Tg2576 mice, plaque bound [³H]AZD4694 could still be detected 80 min after i.v. administration. Taken together, the preclinical profile of AZD4694 suggests that fluorine‐18 labeled AZD4694 may have potential for PET‐visualization of cerebral β‐amyloid deposits in the living human brain.

The progression of Alzheimer’s disease (AD) is associated with an increase of phosphorylated tau in the brain. One of the earliest phosphorylated sites on tau is Ser262 that is preferentially phosphorylated by microtubule affinity regulating kinase (MARK), of which four isoforms exist. Herein we investigated the expression of MARK1-4 in the hippocampus of non-demented elderly (NDE) and AD cases. In situ hybridization revealed a uniform, neuronal distribution of all four isoform mRNAs in NDE and AD. Immunohistochemical analyses using isoform-selective antibodies demonstrated that MARK4 in a phosphorylated form colocalizes with p-tau Ser262 in granulovacuolar degeneration bodies (GVDs) that progressively accumulate in AD. In contrast MARK4 is largely absent in the neuronal cytoplasm. MARK3 was localized to a subset of the GVD-containing neurons and also had a weak general cytoplasmic neuronal staining in both NDE and AD. These results suggest that in AD, phosphorylated MARK3 and MARK4 are sequestered and proteolysed in GVDs. MARK1 and MARK2 were absent in GVDs and exhibited relatively uniform neuronal expressions with no apparent differences between NDE and AD. We found that the phosphorylated and fragmented forms of MARK4 and to some extent MARK3 are present in GVDs in AD, and that this expression is highly correlated with phosphorylation of tau at Ser262. This may represent a cellular defense mechanism to remove activated MARK and p-tau Ser262 from the cytosol, thereby reducing the phosphorylating effect on tau Ser262 that appears to be a critical step for subsequent neurodegeneration.

Background: Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). It is associated with local activation of microglia and astroglia, infiltration of activated macrophages and T cells, active degradation of myelin and damage to axons and neurons. The proposed role for CX₃CL1 (fractalkine) in the control of microglia activation and leukocyte infiltration places this chemokine and its receptor CX₃CR1 in a potentially strategic position to control key aspects in the pathological events that are associated with development of brain lesions in MS. In this study, we examine this hypothesis by analyzing the distribution, kinetics, regulation and cellular origin of CX₃CL1 and CX₃CR1 mRNA expression in the CNS of rats with an experimentally induced MS-like disease, myelin oligodendrocyte glycoprotein (MOG)-induced autoimmune encephalomyelitis (EAE).Methods: The expression of CX₃CL1 and its receptor CX₃CR1 was studied within situhybridization histochemical detection of their mRNA with radio labeled cRNA probes in combination with immunohistochemical staining of phenotypic cell markers. Both healthy rat brains and brains from rats with MOG EAE were analyzed. In defined lesional stages of MOG EAE, the number of CX₃CR1 mRNA-expressing cells and the intensity of the in situ hybridization signal were determined by image analysis. Data were statistically evaluated by ANOVA, followed by Tukey\primes multiple comparison test.Results: Expression of CX₃CL1 mRNA was present within neuronal-like cells located throughout the neuraxis of the healthy rat. Expression of CX₃CL1 remained unaltered in the CNS of rats with MOG-induced EAE, with the exception of an induced expression in astrocytes within inflammatory lesions. Notably, the brain vasculature of healthy and encephalitic animals did not exhibit signs of CX₃CL1 mRNA expression. The receptor, CX₃CR1, was expressed by microglial cells in all regions of the healthy brain. Induction of MOG-induced EAE was associated with a distinct accumulation of CX₃CR1 mRNA expressing cells within the inflammatory brain lesions, the great majority of which stained positive for markers of the microglia-macrophage lineage. Analysis in time-staged brain lesions revealed elevated levels of CX₃CR1 mRNA in microglia in the periplaque zone, as well as a dramatically enhanced accumulation of CX₃CR1 expressing cells within the early-active, late-active and inactive, demyelinated lesions.Conclusion: Our data demonstrate constitutive and regulated expression of the chemokine CX₃CL1 and its receptor CX₃CR1 by neurons/astrocytes and microglia, respectively, within the normal and inflamed rat brain. Our findings propose a mechanism by which neurons and reactive astrocytes may control migration and function of the surrounding microglia. In addition, the accumulation of CX₃CR1 expressing cells other than microglia within the inflammatory brain lesions indicate a possible role for CX₃CL1 in controlling invasion of peripheral leucocytes to the brain.

Significance: Multiple sclerosis (MS) is a chronic inflammatory and degenerative disease of the central nervous system (CNS) causing paralysis. The most effective treatments for MS aim to block infiltration of inflammatory cells to the brain. However, severe side effects related to the broad-acting specificity of these treatments exist. AZD8797, a unique inhibitor of the chemokine receptor CX3CR1, provides inhibition of subpopulations of peripheral leukocytes with potential for a beneficial effect: side effect ratio. We provide evidence that blocking this receptor results in reduced paralysis, inflammation, and degeneration in the CNS in a disease model for MS. Furthermore, CX3CR1 expression analysis in the MS brain strengthens the evidence for CX3CR1 as a new target for the treatment of MS.