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Heparanase overexpression impairs inflammatory response and macrophage-mediated clearance of amyloid-? in murine brain.

ABSTRACT: Neuroinflammation is typically observed in neurodegenerative diseases such as Alzheimer's disease, as well as after traumatic injury and pathogen infection. Resident immune cells, microglia and astrocytes, are activated and joined by blood-borne monocytes that traverse the blood-brain barrier and convert into activated macrophages. The activated cells express various cytokines, chemokines and proteolytic enzymes. To study the role of heparan sulfate proteoglycans in neuroinflammation, we employed a transgenic mouse overexpressing heparanase, an endoglucuronidase that specifically degrades heparan sulfate side chains. Neuroinflammation was induced by systemic challenge with lipopolysaccharide, or by localized cerebral microinjection of aggregated amyloid-? peptide, implicated in Alzheimer's disease. Lipopolysaccharide-treated control mice showed massive activation of resident microglia as well as recruitment of monocyte-derived macrophages into the brain parenchyma. Microinjection of aggregated amyloid-? elicited a similar inflammatory response, albeit restricted to the injection site, which led to dispersion and clearance of the amyloid. In the heparanase-overexpressing mice, all aspects of immune cell recruitment and activation were significantly attenuated in both inflammation models, as was amyloid dispersion. Accordingly, an in vitro blood-brain barrier model constructed from heparanase-overexpressing cerebral vascular cells showed impaired transmigration of monocytes compared to a corresponding assembly of control cells. Our data indicate that intact heparan sulfate chains are required at multiple sites to mediate neuroinflammatory responses, and further point to heparanase as a modulator of this process, with potential implications for Alzheimer's disease.

SUBMITTER: Zhang X

PROVIDER: S-EPMC3444710 | biostudies-literature | 2012 Oct

REPOSITORIES: biostudies-literature

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Heparanase overexpression impairs inflammatory response and macrophage-mediated clearance of amyloid-β in murine brain.

Zhang Xiao X Wang Bo B O'Callaghan Paul P Hjertström Elina E Jia Juan J Gong Feng F Zcharia Eyal E Nilsson Lars N G LN Lannfelt Lars L Vlodavsky Israel I Lindahl Ulf U Li Jin-Ping JP

Acta neuropathologica 20120613 4

Neuroinflammation is typically observed in neurodegenerative diseases such as Alzheimer's disease, as well as after traumatic injury and pathogen infection. Resident immune cells, microglia and astrocytes, are activated and joined by blood-borne monocytes that traverse the blood-brain barrier and convert into activated macrophages. The activated cells express various cytokines, chemokines and proteolytic enzymes. To study the role of heparan sulfate proteoglycans in neuroinflammation, we employe ...[more]

PMID: 22692572

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Project description:Osteopontin (OPN), a matricellular immunomodulatory cytokine highly expressed by myelomonocytic cells, is known to regulate immune cell migration, communication, and response to brain injury. Enhanced cerebral recruitment of monocytes achieved through glatiramer acetate (GA) immunization or peripheral blood enrichment with bone marrow (BM)-derived CD115+ monocytes (MoBM) curbs amyloid β-protein (Aβ) neuropathology and preserves cognitive function in murine models of Alzheimer's disease (ADtg mice). To elucidate the beneficial mechanisms of these immunomodulatory approaches in AD, we focused on the potential role of OPN in macrophage-mediated Aβ clearance. Here, we found extensive OPN upregulation along with reduction of vascular and parenchymal Aβ burden in cortices and hippocampi of GA-immunized ADtg mice. Treatment combining GA with blood-grafted MoBM further increased OPN levels surrounding residual Aβ plaques. In brains from AD patients and ADtg mice, OPN was also elevated and predominantly expressed by infiltrating GFP+- or Iba1+-CD45high monocyte-derived macrophages engulfing Aβ plaques. Following GA immunization, we detected a significant increase in a subpopulation of inflammatory blood monocytes (CD115+CD11b+Ly6Chigh) expressing OPN, and subsequently, an elevated population of OPN-expressing CD11b+Ly6C+CD45high monocyte/macrophages in the brains of these ADtg mice. Correlogram analyses indicate a strong linear correlation between cerebral OPN levels and macrophage infiltration, as well as a tight inverse relation between OPN and Aβ-plaque burden. In vitro studies corroborate in vivo findings by showing that GA directly upregulates OPN expression in BM-derived macrophages (MФBM). Further, OPN promotes a phenotypic shift that is highly phagocytic (increased uptake of Aβ fibrils and surface scavenger receptors) and anti-inflammatory (altered cell morphology, reduced iNOS, and elevated IL-10 and Aβ-degrading enzyme MMP-9). Inhibition of OPN expression in MФBM, either by siRNA, knockout (KOOPN), or minocycline, impairs uptake of Aβ fibrils and hinders GA's neuroprotective effects on macrophage immunological profile. Addition of human recombinant OPN reverses the impaired Aβ phagocytosis in KOOPN-MФBM. This study demonstrates that OPN has an essential role in modulating macrophage immunological profile and their ability to resist pathogenic forms of Aβ.

Dataset Information

Heparanase overexpression impairs inflammatory response and macrophage-mediated clearance of amyloid-? in murine brain.

Publications

Heparanase overexpression impairs inflammatory response and macrophage-mediated clearance of amyloid-β in murine brain.

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