Anders Ericsson-Dahlstrand

Inflammatory response : pathway across the blood–brain barrier

Inflammatory reactions against invaders in the body call upon cytokine molecules that elicit systemic responses, such as fever, fatigue, increased pain sensitivity and appetite loss, mediated by the central nervous system. But how cytokines can induce these effects has been a mystery as they are unlikely to cross the blood–brain barrier. Here we show that cerebral vascular cells express components enabling a blood-borne cytokine to stimulate the production of prostaglandin E2, an inflammatory mediator whose small size and lipophilic properties allow it to diffuse into the brain parenchyma. As receptors for this prostaglandin are found on responsive deep neural structures, we propose that the activated immune system controls central reactions to peripheral inflammation through a prostaglandin-dependent, cytokine-mediated pathway.

Distribution of the EP3 prostaglandin E2 receptor subtype in the rat brain: Relationship to sites of interleukin-1–induced cellular responsiveness

The activation of neurosecretory neurons that express corticotropin‐releasing hormone (CRH) in response to increased circulating levels of interleukin‐1β (IL‐1β) depends on prostaglandin E2 (PGE2) acting locally within the brain parenchyma. To identify potential central targets for PGE2 relevant to pituitary‐adrenal control, the distribution of mRNA encoding the PGE2 receptor subtype EP3 (EP3R) was analyzed in rat brain. Hybridization histochemistry revealed prominent labeling of cells in discrete portions of the olfactory system, iso‐ and hippocampal cortices, and subcortical telencephalic structures in the septal region and amygdala. Labeling over the midline, intralaminar, and anterior thalamic groups was particularly prominent. EP3R expression was enriched in the median preoptic nucleus and adjoining aspects of the medial preoptic area (MPO) implicated in thermoregulatory/febrile responses and sleep induction. EP3R‐expressing cells were also prominent in brainstem cell groups involved in nociceptive information processing/modulation (periaqueductal gray, locus coeruleus (LC), parabrachial nucleus (PB), caudal raphé nuclei), arousal and wakefulness (LC, midbrain raphé and tuberomammillary nuclei); and in conveying interoceptive input, including systemic IL‐1 signals, to the endocrine hypothalamus (nucleus of the solitary tract (NTS) and rostral ventrolateral medulla [VLM]). Combined hybridization histochemical detection of EP3R mRNA with immunolocalization of IL‐1β–induced Fos protein expression identified cytokine‐sensitive, EP3R‐positive cells in the medial NTS, rostral VLM, and, to a lesser extent, aspects of the MPO. These findings are consistent with the view that increased circulating IL‐1 may stimulate central neural mechanisms, including hypothalamic CRH neurons, through an EP3R‐dependent mechanism involving PGE2‐mediated activation of cells in the caudal medulla and/or preoptic region. J. Comp. Neurol. 428:5–20, 2000.

Prostaglandins as inflammatory messengers across the blood-brain barrier

Abstract. Upon immune challenge the brain launches a wide range of responses, such as fever, anorexia, and hyperalgesia that serve to maintain homeostasis. While these responses are adaptive during acute infections, they may be destructive during chronic inflammatory conditions. Research performed during the last decade has given us insight into how the brain monitors the presence of a peripheral inflammation and the mechanisms underlying the brain-mediated acute-phase reactions. Here we give a brief review on this subject, with focus on the role of prostaglandin E2 produced in cells associated with the blood-brain barrier in immune-to-brain signaling. The recent advances in this field have not only elucidated the mechanisms behind the anti-pyretic and anti-hyperalgesic effects of cyclooxygenase inhibitors, but have also identified novel and more-selective potential drug targets.

CX3CL1 (fractalkine) and CX3CR1 expression in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis: kinetics and cellular origin

BackgroundMultiple 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).MethodsThe expression of CX3CL1 and its receptor CX3CR1 was studied with in situ hybridization 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.ResultsExpression 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.ConclusionOur 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.

Temporal expression and cellular origin of CC chemokine receptors CCR1, CCR2 and CCR5 in the central nervous system: insight into mechanisms of MOG-induced EAE

BackgroundThe CC chemokine receptors CCR1, CCR2 and CCR5 are critical for the recruitment of mononuclear phagocytes to the central nervous system (CNS) in multiple sclerosis (MS) and other neuroinflammatory diseases. Mononuclear phagocytes are effector cells capable of phagocytosing myelin and damaging axons. In this study, we characterize the regional, temporal and cellular expression of CCR1, CCR2 and CCR5 mRNA in the spinal cord of rats with myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE). While resembling human MS, this animal model allows unique access to CNS-tissue from various time-points of relapsing neuroinflammation and from various lesional stages: early active, late active, and inactive completely demyelinated lesions.MethodsThe expression of CCR1, CCR2 and CCR5 mRNA was studied with in situ hybridization using radio labelled cRNA probes in combination with immunohistochemical staining for phenotypic cell markers. Spinal cord sections from healthy rats and rats with MOG-EAE (acute phase, remission phase, relapse phase) were analysed. In defined lesion stages, the number of cells expressing CCR1, CCR2 and CCR5 mRNA was determined. Data were statistically analysed by the nonparametric Mann-Whitney U test.ResultsIn MOG-EAE rats, extensive up-regulation of CCR1 and CCR5 mRNA, and moderate up-regulation of CCR2 mRNA, was found in the spinal cord during episodes of active inflammation and demyelination. Double staining with phenotypic cell markers identified the chemokine receptor mRNA-expressing cells as macrophages/microglia. Expression of all three receptors was substantially reduced during clinical remission, coinciding with diminished inflammation and demyelination in the spinal cord. Healthy control rats did not show any detectable expression of CCR1, CCR2 or CCR5 mRNA in the spinal cord.ConclusionOur results demonstrate that the acute and chronic-relapsing phases of MOG-EAE are associated with distinct expression of CCR1, CCR2, and CCR5 mRNA by cells of the macrophage/microglia lineage within the CNS lesions. These data support the notion that CCR1, CCR2 and CCR5 mediate recruitment of both infiltrating macrophages and resident microglia to sites of CNS inflammation. Detailed knowledge of expression patterns is crucial for the understanding of therapeutic modulation and the validation of CCR1, CCR2 and CCR5 as feasible targets for therapeutic intervention in MS.

Induction of microsomal prostaglandin E synthase in the rat brain endothelium and parenchyma in adjuvant-induced arthritis

Although central nervous symptoms such as hyperalgesia, fatigue, malaise, and anorexia constitute major problems in the treatment of patients suffering from chronic inflammatory disease, little has been known about the signaling mechanisms by which the brain is activated during such conditions. Here, in an animal model of rheumatoid arthritis, we show that microsomal prostaglandin E‐synthase, the inducible terminal isomerase in the prostaglandin E2‐synthesizing pathway, is expressed in endothelial cells along the blood‐brain barrier and in the parenchyma of the paraventricular hypothalamic nucleus. The endothelial cells but not the paraventricular hypothalamic cells displayed a concomitant induction of cyclooxygenase‐2 and expressed interleukin‐1 type 1 receptors, which indicates that the induction is due to peripherally released cytokines. In contrast to cyclooxygenase‐2, microsomal prostaglandin E synthase had very sparse constitutive expression, suggesting that it could be a target for developing drugs that will carry fewer side effects than the presently available cyclooxygenase inhibitors. These findings, thus, suggest that immune‐to‐brain communication during chronic inflammatory conditions involves prostaglandin E2‐synthesis both along the blood‐brain barrier and in the parenchyma of the hypothalamic paraventricular nucleus and point to novel avenues for the treatment of the brain‐elicited disease symptoms during these conditions. J. Comp. Neurol. 452:205–214, 2002.

Differential Expression of the Chemokine Receptors CX3CR1 and CCR1 by Microglia and Macrophages in Myelin-Oligodendrocyte-Glycoprotein-Induced Experimental Autoimmune Encephalomyelitis

Chemokines are important for the recruitment of immune cells into sites of inflammation. To better understand their functional roles during inflammation we have here studied the in vivo expression of receptors for the chemokines CCL3/CCL5/CCL7 (MIP‐1α/RANTES/MCP‐3) and CX3CL1 (fractalkine), CCR1 and CX3CR1, respectively, in rat myelin oligodendrocyte glycoprotein‐induced experimental autoimmune encephalomyelitis. Combined in situ hybridization and immunohistochemistry demonstrated intensely upregulated CCR1 mRN A expression in early, actively demyelinating plaques, whereas CX3CR1 displayed a more generalized expression pattern. CX3CR1 mRNA expressing cells were identified as microglia on the basis of their cellular morphology and positive GSA/B4 lectin staining. In contrast, CCR1 mRNA was preferentially expressed by ED1+GSA/B4+ macrophages. The notion of differential chemokine receptor expression in microglia and monocyte‐derived macrophages was corroborated at the protein level by extraction and flow cytometric sorting of cells infiltrating the spinal cord using gating for the surface markers CD45, ED‐2 and CD11b. These observations suggest a differential receptor expression between microglia and monocyte‐derived macrophages and that mainly the latter cell type is responsible for active demyelination. This has great relevance for the possibility of therapeutic intervention in demyelinating diseases such as multiple sclerosis, for example by targeting signaling events leading to monocyte recruitment.

Effector stage CC chemokine receptor-1 selective antagonism reduces multiple sclerosis-like rat disease

We have studied the role of the chemokine receptor CCR1 during the effector stage of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis in DA rats. In situ hybridization histochemistry revealed local production of the CCR1 ligands CCL3 (MIP-1 alpha) and CCL5 (RANTES), as well as large numbers of CCR1 and CCR5 expressing cells within inflammatory brain lesions. A low-molecular weight CCR1 selective antagonist potently abrogated both clinical and histopathological disease signs during a 5-day treatment period, without signs of peripheral immune compromise. Thus, we demonstrate therapeutic targeting of CCR1-dependent leukocyte recruitment to the central nervous system in a multiple sclerosis (MS)-like rat model.

Activation of prostanoid EP3 and EP4 receptor mRNA-expressing neurons in the rat parabrachial nucleus by intravenous injection of bacterial wall lipopolysaccharide

Systemic inflammation activates central autonomic circuits, such as neurons in the pontine parabrachial nucleus. This activation may be the result of afferent signaling through the vagus nerve, but it may also depend on central prostaglandin‐mediated mechanisms. Recently, we have shown that neurons in the parts of the parabrachial nucleus that are activated by immune challenge express prostaglandin receptors of the EP3 and EP4 subtypes, but it remains to be determined if the prostaglandin receptor‐expressing neurons are identical to those that respond to immune stimuli. In the present study, bacterial wall lipopolysaccharide was injected intravenously in adult male rats and the expression of c‐fos mRNA and of EP3 and EP4 receptor mRNA was examined with complementary RNA probes labeled with digoxigenin and radioisotopes, respectively. Large numbers of neurons in the external lateral parabrachial subnucleus, a major target of vagal‐solitary tract efferents, expressed c‐fos mRNA. Quantitative analysis showed that about 60% (range 40%–79%) of these neurons also expressed EP3 receptor mRNA. Conversely, slightly more than 50% (range 48%–63%) of the EP3 receptor‐expressing neurons in the same subnucleus coexpressed c‐fos mRNA. In contrast, few EP4 receptor‐expressing neurons were c‐fos positive, with the exception of a small population located in the superior lateral and dorsal lateral subnuclei. These findings show that immune challenge activates central autonomic neurons that could be the target of centrally produced prostaglandin E2, suggesting that synaptic signaling and paracrine mechanisms may interact on these neurons. J. Comp. Neurol. 440:378–386, 2001.

Pharmacological inhibition of the chemokine receptor CX3CR1 attenuates disease in a chronic-relapsing rat model for multiple sclerosis

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. One hallmark of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) is infiltration of leukocytes into the CNS, where chemokines and their receptors play a major mediatory role. CX3CR1 is a chemokine receptor involved in leukocyte adhesion and migration and hence a mediator of immune defense reactions. The role of CX3CR1 in MS and EAE pathogenesis however remains to be fully assessed. Here, we demonstrate CX3CR1 mRNA expression on inflammatory cells within active plaque areas in MS brain autopsies. To test whether blocking CNS infiltration of peripheral leukocytes expressing CX3CR1 would be a suitable treatment strategy for MS, we developed a selective, high-affinity inhibitor of CX3CR1 (AZD8797). The compound is active outside the CNS and AZD8797 treatment in Dark Agouti rats with myelin oligodendrocyte glycoprotein-induced EAE resulted in reduced paralysis, CNS pathology, and incidence of relapses. The compound is effective when starting treatment before onset, as well as after the acute phase. This treatment strategy is mechanistically similar to, but more restricted than, current very late antigen-4–directed approaches that have significant side effects. We suggest that blocking CX3CR1 on leukocytes outside the CNS could be an alternative approach to treat MS.