Age-related effects of interleukin-1 beta on polymorphonuclear neutrophil-dependent increases in blood-brain barrier permeability in rats

Stimulation of cerebellar fastigial nucleus inhibits interleukin-1beta-induced cerebrovascular inflammation

Electrical stimulation of the cerebellar fastigial nucleus (FN) in rat protects the brain against ischemia. We studied whether FN could reduce the cerebrovascular inflammation as a mechanism of protection. FN or dentate nucleus (sham controls) was electrically stimulated for 1 h, and 72 h later rats were either injected with interleukin (IL)-1beta into the striata or processed to analyze inflammatory responses in isolated brain microvessels. In striata, IL-1beta induced a recruitment of leukocytes that was reduced by 50% by FN stimulation. In isolated microvessels, IL-1beta induced the transient and dose-dependent upregulation of the mRNAs encoding for the inducible nitric oxide synthase (NOS-2), intercellular adhesion molecule 1 (ICAM-1), and inhibitory kappaB-alpha (IkappaB-alpha), an inhibitor of nuclear factor-kappaB. FN stimulation decreased the upregulation of NOS-2 and ICAM-1 mRNAs, whereas it increased IkappaB-alpha mRNA expression. Dentate nucleus stimulation did not mimic the FN actions. These findings suggest that FN stimulation may render brain microvessels refractory to IL-1beta by overproduction of IkappaB-alpha and support the hypothesis that alteration of microvascular inflammation may contribute to the central neurogenic neuroprotection elicited from the FN.

Differential blood-brain barrier breakdown and leucocyte recruitment following excitotoxic lesions in juvenile and adult rats

Acute neuronal degeneration can be induced by intracerebral injections of the glutamate receptor agonists kainic acid (KA) and NMDA (N-methyl-D-aspartate). It is accompanied by an inflammatory response that has not yet been fully investigated. We have previously demonstrated that the juvenile rat brain is more susceptible to an inflammatory challenge when compared to adult rat brain. This study set out to investigate whether this also applied to the inflammatory response associated with acute neuronal degeneration. NMDA and kainic acid were injected into the rat striatum and lesion size, leucocyte recruitment, and blood-brain barrier (BBB) breakdown were assessed after 4, 8, 12, 24, 72, and 168 h. Both NMDA and KA induced lesions of similar volume at either age and apoptotic and necrotic nuclei could be detected. NMDA induced cellular loss by 4 h, whereas KA-injected rats did not show signs of neuronal loss until 8-12 h. The inflammatory response was characterized by an infiltration of neutrophils followed by macrophages. Juvenile rats showed a greater susceptibility to leucocyte recruitment compared to adult rats. BBB breakdown in response to NMDA injection occurred in the absence of cellular recruitment at 4 h in juveniles and was significantly greater in juvenile compared to adult rats at 8 h. BBB breakdown was minimal in KA-injected animals while at 7 days an influx of serum IgG coincided with a loss of astrocytic GFAP staining within the lesion.

Alzheimer's beta-amyloid peptides induce inflammatory cascade in human vascular cells: the roles of cytokines and CD40

Accumulating evidence suggests that beta-amyloid (Abeta)-induced inflammatory reactions may partially drive the pathogenesis of Alzheimer's disease (AD). Recent data also implicate similar inflammatory processes in cerebral amyloid angiopathy (CAA). To evaluate the roles of Abeta in the inflammatory processes in vascular tissues, we have tested the ability of Abeta to trigger inflammatory responses in cultured human vascular cells. We found that stimulation with Abeta dose-dependently increased the expression of CD40, and secretion of interferon-gamma (IFN-gamma) and interleukin-1beta (IL-1beta) in endothelial cells. Abeta also induced expression of IFN-gamma receptor (IFN-gammaR) both in endothelial and smooth muscle cells. Characterization of the Abeta-induced inflammatory responses in the vascular cells showed that the ligation of CD40 further increased cytokine production and/or the expression of IFN-gammaR. Moreover, IL-1beta and IFN-gamma synergistically increased the Abeta-induced expression of CD40 and IFN-gammaR. We have recently found that Abeta induces expression of adhesion molecules, and that cytokine production and interaction of CD40-CD40 ligand (CD40L) further increase the Abeta-induced expression of adhesion molecules in these same cells. These results suggest that Abeta can function as an inflammatory stimulator to activate vascular cells and induces an auto-amplified inflammatory molecular cascade, through interactions among adhesion molecules, CD40-CD40L and cytokines. Additionally, Abeta1-42, the more pathologic form of Abeta, induces much stronger effects in endothelial cells than in smooth muscle cells, while the reverse is true for Abeta1-40. Collectively, these findings support the hypothesis that the Abeta-induced inflammatory responses in vascular cells may play a significant role in the pathogenesis of CAA and AD.

Loss of the tight junction proteins occludin and zonula occludens-1 from cerebral vascular endothelium during neutrophil-induced blood-brain barrier breakdown in vivo

The tight junctions found between cerebral vascular endothelial cells form the basis of the blood-brain barrier. Breakdown of the blood-brain barrier is a feature of a variety of CNS pathologies that are characterized by extensive leucocyte recruitment, such as multiple sclerosis and stroke. The molecular mechanisms associated with opening of the blood-brain barrier and leucocyte recruitment in vivo are currently poorly understood. We have used an in vivo rat model to investigate the molecular response of the CNS endothelium to neutrophil adhesion and migration. Injection of interleukin-1 beta into the striatum of juvenile brains results in a neutrophil-dependent increase in vessel permeability at 4 h. Only a subset of blood vessels were associated with neutrophil recruitment. These particular vessels displayed an increase in phosphotyrosine staining, loss of the tight junctional proteins, occludin and zonula occludens-1, and apparent redistribution of the adherens junction protein vinculin. Examination of these vessels under the electron microscope indicated that the cell-cell adhesions in such vessels are morphologically different from normal junctions. This study provides the first direct evidence in vivo that leucocyte recruitment can trigger signal transduction cascades leading to junctional disorganization and blood-brain barrier breakdown. Our results have established an endothelial cell molecular profile associated with leucocyte-induced blood-brain barrier breakdown in vivo, and the relevance of different in vitro cell culture models may now be viewed more objectively.

CXC chemokines generate age-related increases in neutrophil-mediated brain inflammation and blood-brain barrier breakdown

Children are at greater risk than adults of permanent brain damage and mortality following head injury or infection [1-5]. Rodent models have demonstrated a 'window of susceptibility' in young animals during which the brain parenchyma is at greater risk of acute neutrophil-mediated breakdown of the blood-brain barrier [6-7]. The exact mechanism of this age-related susceptibility to brain inflammation has yet to be defined, but animal models have revealed that the potent pro-inflammatory cytokine interleukin-1beta (IL-1beta) initiates an intense acute neutrophil-mediated inflammatory response in the brains of young rats and mice that is not seen in adults [6]. Here, we demonstrate the rapid induction of CXC chemokines (which contain a Cys-X-Cys motif), in particular the cytokine-induced neutrophil chemoattractant CINC-1, following the intracerebral administration of IL-1beta. The CXC chemokines produced a more intense neutrophil response in young rats than in adults. The IL-1beta-induced blood-brain barrier breakdown in young rats could be attenuated by an anti-CINC-1 neutralising antibody. These results show that the immature central nervous system (CNS) is dramatically more susceptible to the chemotactic effects of CXC chemokines. Blocking the CXC chemokine activity associated with brain inflammation inhibits neutrophil-mediated blood-brain barrier damage and represents a significant therapeutic possibility.

Matrix metalloproteinase expression in an experimentally-induced DTH model of multiple sclerosis in the rat CNS

In an experimentally-induced DTH model of MS, we examined mRNA and protein expression of a range of MMPs and of TNFalpha to establish the contribution that individual MMPs might make to the pathogenesis. In control rat brain, mRNA for all of the MMPs examined was detectable. However, by immunohistochemistry, only MMP-2 could be detected. In the DTH lesions, significant increases in the level of mRNA expression were observed for MMP-7, MMP-8, MMP-12, and TNFalpha. Where expression of MMP mRNA was increased, there was a corresponding increase in protein expression detected by immunohistochemistry. To determine whether the upregulated MMPs could invoke destructive events in the CNS, highly purified activated MMP-7, MMP-8, and MMP-9 were stereotaxically injected into the brain parenchyma. All provoked recruitment of leukocytes and BBB breakdown. In addition, MMPs 7 and 9 induced loss of myelin staining. In conclusion, specific MMPs are upregulated in DTH lesions; for the most part, measurement of mRNA was a predictor of increased protein expression. From our injections of MMPs, it is clear that the upregulated MMPs in the DTH lesions could participate in the disruption of the BBB, leukocyte recruitment, and tissue damage.

Central nervous system vasculitis

Central nervous system vasculitis occurs in a variety of clinical settings. Some exhibit a distinct age preference; others a tissue tropism. Most frequently encountered are giant cell arteritis (temporal arteritis) and vasculitis secondary to infections. The central nervous system may be involved in the antineutrophil cytoplasmic antibody-associated systemic vasculitides and occasionally neurologic abnormalities appear as a presenting manifestation of disease. Isolated angiitis of the central nervous system, a rare form of vasculitis that is restricted to the central nervous system, must be distinguished from other causes of central nervous system inflammation and from noninflammatory vascular disease. We are learning a great deal about the cellular mechanisms of vascular inflammation in general. Some manifestations of the clinical disease result from histologic features of the infiltrate and the size of affected vessel. However, the local consequences of inflammation, such as increased coagulation and altered vasomotor tone, as well as the systemic consequences, such as activation of the central noradrenergic systems, trigeminovascular system, and hypothalamic pituitary adrenal axis, contribute both to pathogenesis of disease and to recovery.

The blood-brain barrier and the inflammatory response

The environment of the brain is controlled by a sophisticated endothelial barrier that prevents the free entry of solutes from the blood. It is commonly assumed that this blood-brain barrier (BBB) also prevents the entry of leukocytes into the central nervous system. However, recent evidence in animal models shows that this is not the case, and leukocytes can cross an intact BBB during health and disease. Indeed, in many neurological diseases, including Alzheimer's disease, prion diseases and AIDS-related dementia, leukocytes enter the brain parenchyma without concomitant BBB breakdown. Current research is concentrating on factors that control the integrity of the BBB and the mechanisms that leukocytes use to enter the brain.