GM‐CSF promotes migration of human monocytes across the blood brain barrier

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). Infiltration of monocytes into the CNS is crucial for disease onset and progression. Animal studies indicate that granulocyte‐macrophages colony‐stimulating factor (GM‐CSF) may play an essential role in this process, possibly by acting on the migratory capacities of myeloid cells across the blood–brain barrier. This study describes the effect of GM‐CSF on human monocytes, macrophages, and microglia. Furthermore, the expression of GM‐CSF and its receptor was investigated in the CNS under healthy and pathological conditions. We show that GM‐CSF enhances monocyte migration across human blood–brain barrier endothelial cells in vitro. Next, immunohistochemical analysis on human brain tissues revealed that GM‐CSF is highly expressed by microglia and macrophages in MS lesions. The GM‐CSF receptor is expressed by neurons in the rim of combined gray/white matter lesions and astrocytes. Finally, the effect of GM‐CSF on human macrophages was determined, revealing an intermediate activation status, with a phenotype similar to that observed in active MS lesions. Together our data indicate that GM‐CSF is a powerful stimulator of monocyte migration, and is abundantly present in the inflamed CNS where it may act as an activator of macrophages and microglia.     

Upregulation of Immunoglobulin‐related Genes in Cortical Sections from Multiple Sclerosis Patients

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS). Microarray‐based global gene expression profiling is a promising method, used to study potential genes involved in the pathogenesis of the disease. In the present study, we have examined global gene expression in normal‐appearing gray matter and gray matter lesions from the cortex of MS patients, and compared them with cortical gray matter samples from controls. We observed a massive upregulation of immunoglobulin (Ig)‐related genes in cortical sections of MS patients. Using immunohistochemistry, the activation of Ig genes seems to occur within plasma cells in the meninges. As synthesis of oligoclonal IgGs has been hypothesized to be caused by the activation of Epstein–Barr virus (EBV)‐infected B‐cells, we screened the brain samples for the presence of EBV by real‐time quantitative polymerase chain reaction (qPCR) and immunohistochemistry, but no evidence of active or latent EBV infection was detected. This study demonstrates that genes involved in the synthesis of Igs are upregulated in MS patients and that this activation is caused by a small number of meningeal plasma cells that are not infected by EBV. The findings indicate that the Ig‐producing B‐cells found in the cerebrospinal fluid (CSF) of MS patients could have meningeal origin.     

Magnetic resonance imaging under isoflurane anesthesia alters cortical cyclooxygenase‐2 expression and glial cell morphology during sepsis‐associated neurological dysfunction in rats

BackgroundMagnetic resonance imaging (MRI) of rodents combined with histology allows to determine what mechanisms underlie functional and structural brain changes during sepsis‐associated encephalopathy. However, the effects of MRI performed in isoflurane‐anesthetized rodents on modifications of the blood‐brain barrier and the production of vasoactive prostaglandins and glia cells, which have been proposed to mediate sepsis‐associated brain dysfunction, are unknown.MethodsThis study addressed the effect of MRI under isoflurane anesthesia on blood‐brain barrier integrity, cyclooxygenase‐2 expression, and glial cell activation during cecal ligature and puncture‐induced sepsis‐associated brain dysfunction in rats.ResultsCecal ligature and puncture reduced food intake and the righting reflex. MRI under isoflurane anesthesia reduced blood‐brain barrier breakdown, decreased circularity of white matter astrocytes, and increased neuronal cyclooxygenase‐2 immunoreactivity in the cortex 24 hours after laparotomy. In addition, it annihilated cecal ligature and puncture‐induced increased circularity of white matter microglia. MRI under isoflurane anesthesia, however, did not alter sepsis‐associated perivascular cyclooxygenase‐2 induction.ConclusionThese findings indicate that MRI under isoflurane anesthesia of rodents can modify neurovascular and glial responses and should, therefore, be interpreted with caution.     

Spinal cord gray matter demyelination in multiple sclerosis-a novel pattern of residual plaque morphology

The extent and pattern of gray matter (GM) demyelination in the spinal cord in multiple sclerosis (MS) has not been examined in detail. Human autopsy material was obtained from 36 MS cases and 12 controls. Transverse sections were taken from five levels of the spinal cord (upper cervical, lower cervical, upper thoracic, lower thoracic and lumbar levels) and the extent of GM and white matter (WM) demyelination evaluated using proteolipid protein immunohistochemistry (IHC). The proportion of the GM that was demyelinated (33%) was significantly greater than the proportion of demyelinated WM (20%) (P < 0.0001). Similarly, demyelination was more extensive in the GM than in the WM at each of the five cord levels. The extent of GM demyelination was not significantly different between the five cord levels while WM demyelination was greatest at the upper cervical level. Morphologically, the borders of a proportion of the GM plaques show a strict respect for the GM/WM boundary. We demonstrate that extensive demyelination occurs in the GM of the spinal cord in MS. Myelin protein IHC reveals a novel pattern of residual plaque morphology challenging previous work suggesting that MS plaques display a total disregard for anatomical boundaries.     

Wallerian Degeneration: A Major Component of Early Axonal Pathology in Multiple Sclerosis

Axonal loss is a major component of the pathology of multiple sclerosis (MS) and the morphological basis of permanent clinical disability. It occurs in demyelinating plaques but also in the so‐called normal‐appearing white matter (NAWM). However, the contribution of Wallerian degeneration to axonal pathology is not known. Here, we analyzed the extent of Wallerian degeneration and axonal pathology in periplaque white matter (PPWM) and lesions in early multiple sclerosis biopsy tissue from 63 MS patients. Wallerian degeneration was visualized using an antibody against the neuropeptide Y receptor Y1 (NPY‐Y1R). The number of SMI‐32‐positive axons with non‐phosphorylated neurofilaments was significantly higher in both PPWM and plaques compared to control white matter. APP‐positive, acutely damaged axons were found in significantly higher numbers in plaques compared to PPWM. Strikingly, the number of NPY‐Y1R‐positive axons undergoing Wallerian degeneration was significantly higher in PPWM and plaques than in control WM. NPY‐Y1R‐positive axons in PPWM were strongly correlated to those in the lesions. Our results show that Wallerian degeneration is a major component of axonal pathology in the periplaque white matter in early MS. It may contribute to radiological changes observed in early MS and most likely plays a major role in the development of disability.     

Expression of CD1d by astrocytes corresponds with relative activity in multiple sclerosis lesions

The CD1 protein family present lipid antigens to the immune system. CD1d has been observed in the CNS of MS patients, yet no studies have quantitatively characterized this expression and related it to inflammatory demyelinative activity in MS plaques. In this study, we set out to localize and quantify the presence of CD1d expression by astrocytes in MS brain tissue lesions. Formalin‐fixed, paraffin‐embedded MS and control brain tissues were examined. Lesions were classified as active, chronic active or chronic silent. Using immunofluorescence, the density of CD1d‐positive cells was determined in active lesions, chronic active lesion edges and chronic active lesion centers. The percentage of CD1d‐positive cells that were GFAP‐positive was also determined in each of these regions. CD1d immunoreactivity was significantly increased in MS compared to control tissue, was significantly more prevalent in areas of active demyelination, and colocalized with GFAP‐positive reactive astrocytes. Increases of CD1d immunoreactivity in the CNS of MS patients being greatest in areas of active demyelination and localized to GFAP‐positive astrocytes lend support to the hypothesis of a lipid‐targeted autoimmune process contributing to the pathogenesis of MS.     

Glial Fibrillary Acidic Protein in Astrocytes in the Human Neocortex

Glial fibrillary acidic protein (GFAP), expressed in the brain by astrocytes, is one of the major immunocytochemical markers of these cells. The aim of the present work was to study the structure of GFAP-positive astrocytes in the human neocortex. Immunocytochemical confocal laser microscopy was used to characterize the main types of GFAP-immunoreactive astrocytes in the human neocortex. These were astrocytes of layer I, forming the superficial glial delimiting membrane, along with transmembrane astrocytes of layer I, with very long processes penetrating several layers of the cortex, astrocytes of the middle layers of the neocortex, mostly of the protoplasmic type and involved in forming perivascular delimiting membranes, and typical white matter fibrous astrocytes. These data may help unify assessments of histopathological processes seen in various types of gliosis in the CNS.__________Translated from Morfologiya, Vol. 126, No. 5, pp. 7–10, September–October, 2004.Corresponding Member of the Russian Academy of Medical Sciences V. A. Otellin)     

CNS inflammation after natalizumab therapy for multiple sclerosis: A retrospective histopathological and CSF cohort study

Natalizumab, a recombinant humanized monoclonal antibody directed against the α4 subunit of the integrins α4ß1 and α4ß7, has been approved for the treatment of active relapsing‐remitting MS. Although natalizumab is a highly beneficial drug that effectively reduces the risk of sustained disability progression and the rate of clinical relapses, some patients do not respond to it, and some are at higher risk of developing progressive multifocal leukoencephalopathy (PML). The histopathological effects after natalizumab therapy are still unknown. We, therefore, performed a detailed histological characterization of the CNS inflammatory cell infiltrate of 24 brain specimens from natalizumab treated patients, consisting of 20 biopsies and 4 autopsies and 21 MS controls. To complement the analysis, immune cells in blood and cerebrospinal fluid (CSF) of 30 natalizumab‐treated patients and 42 MS controls were quantified by flow cytometry. Inflammatory infiltrates within lesions were mainly composed of T cells and macrophages, some B cells, plasma cells, and dendritic cells. There was no significant difference in the numbers of T cells or macrophages and microglial cells in lesions of natalizumab‐treated patients as compared to controls. A shift towards cytotoxic T cells of a memory phenotype was observed in the CSF. Plasma cells were significantly increased in active demyelinating lesions of natalizumab‐treated patients, but no correlation to clinical disability was observed. Dendritic cells within lesions were found to be reduced with longer ongoing therapy duration. Our findings suggest that natalizumab does not completely prevent immune cells from entering the CNS and is associated with an accumulation of plasma cells, the pathogenic and clinical significance of which is not known. As B cells are considered to serve as a reservoir of the JC virus, the observed plasma cell accumulation and reduction in dendritic cells in the CNS of natalizumab‐treated patients may potentially play a role in PML development.     

Ephrin A receptors and ligands in lesions and normal-appearing white matter in multiple sclerosis

Complexes of the tyrosine kinase ephrin ligands (ephrins) and their receptors (Ephs) provide critical cell recognition signals in CNS development. Complementary ephrin/Eph expression gradients present topographic guidance cues that may either stimulate or repulse axon growth. Some ephrin/Ephs are upregulated in adult CNS injury models. To assess their involvement in multiple sclerosis (MS), ephrin A1-5 and Eph A1-8 expression was analyzed in CNS tissues using immunohistochemistry. Control samples showed distinct expression patterns for each ephrin/Eph on different cell types. Perivascular mononuclear inflammatory cells, reactive astrocytes and macrophages expressed ephrin A1-4, Eph A1, -A3, -A4, -A6 and -A7 in active MS lesions. Axonal ephrin A1 and Eph A3, -A4, and -A7 expression was increased in active lesions and was greater in normal-appearing white matter (NAWM) adjacent to active lesions than within or adjacent to chronic MS lesions, in contralateral NAWM, or in control samples. As in development, therefore, there are temporally dynamic, lesion-associated axonal ephrin/Eph A expression gradients in the CNS of MS patients. These results indicate that ephrin/Eph As are useful cell markers in human CNS tissue samples; they likely are involved in the immunopathogenesis of active lesions and in neurodegeneration in MS NAWM; and they represent potential therapeutic targets in MS.     

Distinct changes in all major components of the neurovascular unit across different neuropathological stages of Alzheimer's disease

In the brain capillaries, endothelial cells, pericytes, astrocytes and microglia form a structural and functional complex called neurovascular unit (NVU) which is critically involved in maintaining neuronal homeostasis. In the present study, we applied a comprehensive immunohistochemical approach to investigate the structural alterations in the NVU across different Alzheimer''s disease (AD) neuropathological stages. Post‐mortem human cortical and hippocampal samples derived from AD patients and non‐demented elderly control individuals were immunostained using a panel of markers representing specific components of the NVU including Collagen IV (basement membrane), PDGFR‐β (pericytes), GFAP (astrocytes), Iba1 (microglia), MRC1 (perivascular macrophages) and lectin as an endothelial cell label. Astrocytes (GFAP) and microglia (Iba1) were quantified both in the whole visual‐field and specifically within the NVU, and the sample set was additionally analyzed using anti‐tau (AT8) and three different anti‐Aβ (clones G2‐10, G2‐11, 4G8) antibodies. Analyses of lectin labeled sections showed an altered vascular distribution in AD patients as revealed by a reduced nearest distance between capillaries. Within the NVU, a Braak‐stage dependent reduction in pericyte coverage was identified as the earliest structural alteration during AD progression. In comparison to non‐demented elderly controls, AD patients showed a significantly higher astrocyte coverage within the NVU, which was paralleled by a reduced microglial coverage around capillaries. Assessment of perivascular macrophages moreover demonstrated a relocation of these cells from leptomeningeal arteries to penetrating parenchymal vessels in AD patients. Collectively, the results of our study represent a comprehensive first in‐depth analysis of AD‐related structural changes in the NVU and suggest distinct alterations in all components of the NVU during AD progression.     

Chronic Inflammation and the Role for Cofactors (Hepatitis C,Drug Abuse,Antiretroviral Drug Toxicity,Aging) in HAND Persistence

HIV-associated neurocognitive disorders (HAND) is a group of syndromes of varying degrees of cognitive impairment affecting up to 50 % of HIV-infected individuals. The neuropathogenesis of HAND is thought to be driven by HIV invasion and productive replication within brain perivascular macrophages and endogenous microglia, and to some degree by restricted infection of astrocytes. The persistence of HAND in individuals experiencing suppression of systemic HIV viral load with antiretroviral therapy (ART) is incompletely explained, and suggested factors include chronic inflammation, persistent HIV replication in brain macrophages, effects of aging on brain vulnerability, and co-morbid conditions including hepatitis C (HCV) co-infection, substance abuse, and CNS toxicity of ART, among other factors. This review discusses several of these conditions: chronic inflammation, co-infection with HCV, drugs of abuse, aging, and antiretroviral drug effects. Effectively managing these co-morbid conditions in individuals with and without HAND is critical for improving neurocognitive outcomes and decreasing HIV-associated morbidity.     

Microglia‐Derived Macrophage Colony Stimulating Factor Promotes Generation of Proinflammatory Cytokines by Astrocytes in the Periventricular White Matter in the Hypoxic Neonatal Brain

Inflammation in the periventricular white matter (PWM) of hypoxic neonatal brain causes myelination disturbances. In this connection, macrophage colony‐stimulating factor (M‐CSF) has been reported to regulate release of proinflammatory cytokines that may be linked to PWM damage. We sought to determine if M‐CSF derived from amoeboid microglial cells (AMC) would promote proinflammatory cytokine production by astrocytes in the PWM following hypoxic exposure, and, if so, whether it is associated with axon degeneration and myelination disturbances. In 1‐day hypoxic rats, expression of M‐CSF was upregulated in AMC. This was coupled with increased expression of CSF‐1 receptor, tumor necrosis factor‐α (TNF‐α) and interleukin‐1β (IL‐1β) in astrocytes, and TNF‐receptor 1 and IL‐receptor 1 on the axons. Neurofilament‐200 immunopositive axons and myelin basic protein immunopositive processes appeared to undergo disruption in 14‐days hypoxic rats. By electron microscopy, some axons showed degenerative changes affecting the microtubules and myelin sheath. Primary cultured microglial cells subjected to hypoxia showed enhanced release of M‐CSF. Remarkably, primary cultured astrocytes treated with conditioned‐medium derived from hypoxic microglia or M‐CSF exhibited increased production of TNF‐α and IL‐1β. Our results suggest that AMC‐derived M‐CSF promotes astrocytes to generate proinflammatory cytokines, which may be involved in axonal damage following a hypoxic insult.     

Brain tissue volumes in the general elderly population. The Rotterdam Scan Study

We investigated how volumes of cerebrospinal fluid (CSF), grey matter (GM) and white matter (WM) varied with age, sex, small vessel disease and cardiovascular risk factors in the Rotterdam Scan Study. Participants (n = 490; 60–90 years) were non-demented and 51.0% had hypertension, 4.9% had diabetes mellitus, 17.8% were current smoker and 54.0% were former smoker. We segmented brain MR-images into GM, normal WM, white matter lesion (WML) and CSF. Brain infarcts were rated visually. Volumes were expressed as percentage of intra-cranial volume. With increasing age, volumes of total brain, normal WM and total WM decreased; that of GM remained unchanged; and that of WML increased, in both men and women. Excluding persons with infarcts did not alter these results. Persons with larger load of small vessel disease had smaller brain volume, especially normal WM volume. Diastolic blood pressure, diabetes mellitus and current smoking were also related to smaller brain volume. In the elderly, higher age, small vessel disease and cardiovascular risk factors are associated with smaller brain volume, especially WM volume.     

Morphometric changes in the spinal cord during prenatal life: a stereological study in sheep

This study describes the volumetric changes in the spinal cord during prenatal life in sheep using quantitative stereological methods. Twenty healthy sheep fetuses were included in the present study, divided into four groups representing 9–11, 12–14, 15–17, and 18–20 weeks of gestation. In each group, the spinal cord was dissected out and sampled according to the unbiased systematic random sampling method then used for stereological estimations. The total volume of spinal cord, volume of gray matter (GM), volume of white matter (WM), ratio of GM volume to WM volume, and volume of central canal (CC) were estimated in the whole spinal cord and its various regions using Cavalieri’s principle. The total volume of the spinal cord increased 8 times from week 9 to week 20. The cervical region showed the greatest (9.7 times) and the sacral region the least (6.3 times) volumetric change. The CC volume of the whole spinal cord increased 5.8 times from week 9 to week 20. The cervical region developed faster (8.2 times) and the thoracic region slower (4.4 times) than the total spinal cord. During development, the volume ratio of GM to WM decreased from lower toward upper regions. The greatest volume changes occurred mostly in weeks 9–11 and 12–14. The cervical region showed the greatest volume changes in comparison with other regions of the spinal cord.     

Proteomic analysis of human hippocampal subfields provides new insights into the pathogenesis of Alzheimer’s disease and the role of glial cells

The hippocampus and entorhinal cortex (EC), the earliest affected areas, are considered relative to early memory loss in Alzheimer''s disease (AD). The hippocampus is composed of heterogeneous subfields that are affected in a different order and varying degrees during AD pathogenesis. In this study, we conducted a comprehensive proteomic analysis of the hippocampal subfields and EC region in human postmortem specimens obtained from the Chinese human brain bank. Bioinformatics analysis identified region‐consistent differentially expressed proteins (DEPs) which associated with astrocytes, and region‐specific DEPs which associated with oligodendrocytes and the myelin sheath. Further analysis illuminated that the region‐consistent DEPs functioned as connection of region‐specific DEPs. Moreover, in region‐consistent DEPs, the expression level of S100A10, a marker of protective astrocytes, was increased in both aging and AD patients. Immunohistochemical analysis confirmed an increase in the number of S100A10‐positive astrocytes in all hippocampal subfields and the EC region of AD patients. Dual immunofluorescence results further showed that S100A10‐positive astrocytes contained apoptotic neuron debris in AD patients, suggesting that S100A10‐positive astrocytes may protect brain through phagocytosis of apoptotic neurons. In region‐specific DEPs, the proteome showed a specific reduction of oligodendrocytes and myelin markers in CA1, CA3, and EC regions of AD patients. Immunohistochemical analysis confirmed the loss of myelin in EC region. Above all, these results highlight the role of the glial cells in AD and provide new insights into the pathogenesis of AD and potential therapeutic strategies.     

Temporal overexpression of IL‐22 and Reg3γ differentially impacts the severity of experimental autoimmune encephalomyelitis

IL‐22 is an alpha‐helical cytokine which belongs to the IL‐10 family of cytokines. IL‐22 is produced by RORγt+ innate and adaptive lymphocytes, including ILC3, γδ T, iNKT, Th17 and Th22 cells and some granulocytes. IL‐22 receptor is expressed primarily by non‐haematopoietic cells. IL‐22 is critical for barrier immunity at the mucosal surfaces in the steady state and during infection. Although IL‐22 knockout mice were previously shown to develop experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis (MS), how temporal IL‐22 manipulation in adult mice would affect EAE course has not been studied previously. In this study, we overexpressed IL‐22 via hydrodynamic gene delivery or blocked it via neutralizing antibodies in C57BL/6 mice to explore the therapeutic impact of IL‐22 modulation on the EAE course. IL‐22 overexpression significantly decreased EAE scores and demyelination, and reduced infiltration of IFN‐γ+IL‐17A+Th17 cells into the central nervous system (CNS). The neutralization of IL‐22 did not alter the EAE pathology significantly. We show that IL‐22‐mediated protection is independent of Reg3γ, an epithelial cell‐derived antimicrobial peptide induced by IL‐22. Thus, overexpression of Reg3γ significantly exacerbated EAE scores, demyelination and infiltration of IFN‐γ+IL‐17A+ and IL‐17A+GM‐CSF+Th17 cells to CNS. We also show that Reg3γ may inhibit IL‐2‐mediated STAT5 signalling and impair expansion of Treg cells in vivo and in vitro. Finally, Reg3γ overexpression dramatically impacted intestinal microbiota during EAE. Our results provide novel insight into the role of IL‐22 and IL‐22‐induced antimicrobial peptide Reg3γ in the pathogenesis of CNS inflammation in a murine model of MS.     

FLT-3 expression and function on microglia in multiple sclerosis

Inflammatory cell infiltration and resident microglial activation within the central nervous system (CNS) are pathological events in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). While MS therapies target the peripheral immune system, no treatment is currently known to also modulate microglia. FMS-like tyrosine-3 (FLT-3) is expressed on hematopoietic and dendritic cells. We reported that FLT-3 inhibition ameliorates early actively induced EAE by predominantly modulating dendritic cell function as compared to microglia. We demonstrate in this report that FLT-3 is expressed in perivascular cuffs, brain parenchyma and in non-lesioned gray and white matter within MS brain but not in these regions within control brain. Furthermore, we demonstrate that FLT-3 is expressed on two populations of cells within MS brain; one which expresses the dendritic cell marker CD209, and the other which does not, suggesting that FLT-3 within MS brain is expressed on infiltrating dendritic cells and a non-dendritic cell such as microglia. Additionally, we report that FLT-3 inhibition in murine microglia blocks, in a dose-dependent manner, IFN-γ-induced expression of MHC class II and CD86, and LPS-induced secretion of IL-6. These data suggest that FLT-3 is involved in microglial cells' capacity to respond to environmental cues to function as antigen presenting cells and mediate CNS inflammation. Furthermore these data suggest that FLT-3 may be a therapeutic target on microglia to mitigate CNS inflammation.     

Loss of capillary pericytes and the blood–brain barrier in white matter in poststroke and vascular dementias and Alzheimer’s disease

White matter (WM) disease is associated with disruption of the gliovascular unit, which involves breach of the blood–brain barrier (BBB). We quantified pericytes as components of the gliovascular unit and assessed their status in vascular and other common dementias. Immunohistochemical and immunofluorescent methods were developed to assess the distribution and quantification of pericytes connected to the frontal lobe WM capillaries. Pericytes with a nucleus were identified by collagen 4 (COL4) and platelet‐derived growth factor receptor‐β (PDGFR‐β) antibodies with further verification using PDGFR‐β‐specific ELISA. We evaluated a total of 124 post‐mortem brains from subjects with post‐stroke dementia (PSD), vascular dementia (VaD), Alzheimer’s disease (AD), AD‐VaD (Mixed) and post‐stroke non‐demented (PSND) stroke survivors as well as normal aging controls. COL4 and PDGFR‐β reactive pericytes adopted the characteristic “crescent” or nodule‐like shapes around capillary walls. We estimated densities of pericyte somata to be 225 ±38 and 200 ±13 (SEM) per COL4 mm² area or 2.0 ± 0.1 and 1.7 ± 0.1 per mm capillary length in young and older aging controls. Remarkably, WM pericytes were reduced by ~35%–45% in the frontal lobe of PSD, VaD, Mixed and AD subjects compared to PSND and controls subjects (P < 0.001). We also found pericyte numbers were correlated with PDGFR‐β reactivity in the WM. Our results first demonstrate a reliable method to quantify COL4‐positive pericytes and then, indicate that deep WM pericytes are decreased across different dementias including PSD, VaD, Mixed and AD. Our findings suggest that downregulation of pericytes is associated with the disruption of the BBB in the deep WM in several aging‐related dementias.     

Clusterin levels are increased in Alzheimer's disease and influence the regional distribution of Aβ

Clusterin, also known as apoJ, is a lipoprotein abundantly expressed within the CNS. It regulates Aβ fibril formation and toxicity and facilitates amyloid‐β (Aβ) transport across the blood‐brain barrier. Genome‐wide association studies have shown variations in the clusterin gene (CLU) to influence the risk of developing sporadic Alzheimer''s disease (AD). To explore whether clusterin modulates the regional deposition of Aβ, we measured levels of soluble (NP40‐extracted) and insoluble (guanidine‐HCl‐extracted) clusterin, Aβ40 and Aβ42 by sandwich ELISA in brain regions with a predilection for amyloid pathology—mid‐frontal cortex (MF), cingulate cortex (CC), parahippocampal cortex (PH), and regions with little or no pathology—thalamus (TH) and white matter (WM). Clusterin level was highest in regions with plaque pathology (MF, CC, PH and PC), approximately mirroring the regional distribution of Aβ. It was significantly higher in AD than controls, and correlated positively with Aβ42 and insoluble Aβ40. Soluble clusterin level rose significantly with severity of cerebral amyloid angiopathy, and in MF and PC regions was highest in APOE ɛ4 homozygotes. In the TH and WM (areas with little amyloid pathology) clusterin was unaltered in AD and did not correlate with Aβ level. There was a significant positive correlation between the concentration of clusterin and the regional levels of insoluble Aβ42; however, the molar ratio of clusterin : Aβ42 declined with insoluble Aβ42 level in a region‐dependent manner, being lowest in regions with predilection for Aβ plaque pathology. Under physiological conditions, clusterin reduces aggregation and promotes clearance of Aβ. Our findings indicate that in AD, clusterin increases, particularly in regions with most abundant Aβ, but because the increase does not match the rising level of Aβ42, the molar ratio of clusterin : Aβ42 in those regions falls, probably contributing to Aβ deposition within the tissue.