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

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-ß 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-ß 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.

Expression of interferon gamma in the brain of cats with natural Borna disease virus infection.

Borna disease virus (BDV) is a neurotropic, negative-stranded RNA virus, which causes a non-suppurative meningoencephalomyelitis in a wide range of animals. In cats, BDV infection leads to staggering disease. In spite of a vigorous immune response the virus persists in the central nervous system (CNS) in both experimentally and naturally infected animals. Since the CNS is vulnerable to cytotoxic effects mediated via NK-cells and cytotoxic T-cells, other non-cytolytic mechanisms such as the interferon (IFN) system is favourable for viral clearance. In this study, IFN-γ expression in the brain of cats with clinical signs of staggering disease (N=12) was compared to the expression in cats with no signs of this disease (N=7) by quantitative RT-PCR. The IFN-γ expression was normalised against the expression of three reference genes (HPRT, RPS7, YWHAZ). Cats with staggering disease had significantly higher expression of IFN-γ compared to the control cats (p-value ≤ 0.001). There was no significant difference of the IFN-γ expression in BDV-positive (N=7) and -negative (N=5) cats having clinical signs of staggering disease. However, as BDV-RNA still could be detected, despite an intense IFN-γ expression, BDV needs to have mechanisms to evade this antiviral immune response of the host, to be able to persist.

A chemotactic gradient sequestered on endothelial heparan sulfate induces directional intraluminal crawling of neutrophils.

During infection, chemokines sequestered on endothelium induce recruitment of circulating leukocytes into the tissue where they chemotax along chemokine gradients toward the afflicted site. The aim of this in vivo study was to determine whether a chemokine gradient was formed intravascularly and influenced intraluminal neutrophil crawling and transmigration. A chemokine gradient was induced by placing a macrophage inflammatory protein-2 (MIP-2)-containing (CXCL2) gel on the cremaster muscle of anesthetized wild-type mice or heparanase-overexpressing transgenic mice (hpa-tg) with truncated heparan sulfate (HS) side chains. Neutrophil-endothelial interactions were visualized by intravital microscopy and chemokine gradients detected by confocal microscopy. Localized extravascular chemokine release (MIP-2 gel) induced directed neutrophil crawling along a chemotactic gradient immobilized on the endothelium and accelerated their recruitment into the target tissue compared with homogeneous extravascular chemokine concentration (MIP-2 superfusion). Endothelial chemokine sequestration occurred exclusively in venules and was HS-dependent, and neutrophils in hpa-tg mice exhibited random crawling. Despite similar numbers of adherent neutrophils in hpa-tg and wild-type mice, the altered crawling in hpa-tg mice was translated into decreased number of emigrated neutrophils and ultimately decreased the ability to clear bacterial infections. In conclusion, an intravascular chemokine gradient sequestered by endothelial HS effectively directs crawling leukocytes toward transmigration loci close to the infection site.