Expression of complement messenger RNAs and proteins by human oligodendroglial cells

Potential new antiepileptogenic targets indicated by microarray analysis in a rat model for temporal lobe epilepsy

To get insight into the mechanisms that may lead to progression of temporal lobe epilepsy, we investigated gene expression during epileptogenesis in the rat. RNA was obtained from three different brain regions [CA3, entorhinal cortex (EC), and cerebellum (CB)] at three different time points after electrically induced status epilepticus (SE): acute phase [group D (1 d)], latent period [group W (1 week)], and chronic epileptic period [group M (3-4 months)]. A group that was stimulated but that had not experienced SE and later epilepsy was also included (group nS). Gene expression analysis was performed using the Affymetrix Gene Chip System (RAE230A). We used GENMAPP and Gene Ontology to identify global biological trends in gene expression data. The immune response was the most prominent process changed during all three phases of epileptogenesis. Synaptic transmission was a downregulated process during the acute and latent phases. GABA receptor subunits involved in tonic inhibition were persistently downregulated. These changes were observed mostly in both CA3 and EC but not in CB. Rats that were stimulated but that did not develop spontaneous seizures later on had also some changes in gene expression, but this was not reflected in a significant change of a biological process. These data suggest that the targeting of specific genes that are involved in these biological processes may be a promising strategy to slow down or prevent the progression of epilepsy. Especially genes related to the immune response, such as complement factors, interleukins, and genes related to prostaglandin synthesis and coagulation pathway may be interesting targets.

LRRK2 expression in normal and pathologic human brain and in human cell lines

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) have been recently identified in families with autosomal-dominant late-onset Parkinson disease. We report that by reverse transcriptase-polymerase chain reaction, the mRNA of LRRK2 is expressed in soluble extracts of human brain, liver, and heart and in cultured human astrocytes, microglia, and oligodendroglia as well as in human neuroblastoma cell lines. We find by Western blotting using a polyclonal antibody of the leucine-rich repeat kinase 2 protein (Lrrk2) specific for C-terminal residues 2,511-2,527 that an apparent full-length protein and several of its fractions are expressed in soluble extracts of normal human brain. By immunocytochemistry, the antibody recognizes neurons, and more weakly astrocytes and microglia, in normal brain tissue. It intensely labels Lewy bodies in Parkinson disease and related neurodegenerative disorders. It also labels a subset of neurofibrillary tangles in Alzheimer disease and the Parkinsonism dementia complex of Guam (PDCG). It labels thorn-shaped astrocytes and oligodendroglial coiled bodies in PDCG; oligodendroglial inclusions in multiple system atrophy; Pick bodies in Pick disease; nuclear and cytoplasmic inclusions in Huntington disease; and intraneuronal and glial inclusions in amyotrophic lateral sclerosis. In summary, LRRK2 is constitutively expressed in neurons and also in glial cells of human brain. It strongly associates with pathological inclusions in several neurodegenerative disorders.

Glial degeneration and reactive gliosis in alpha-synucleinopathies: the emerging concept of primary gliodegeneration

The concept of gliodegenerative diseases has not been widely established although there is accumulating evidence that glial cells may represent a primary target of degenerative disease processes. In the central nervous system (CNS), examples that provide a "proof of concept" include at least one alpha-synucleinopathy, multiple system atrophy (MSA), but this disease is conventionally discussed under the heading of "neurodegeneration". Additional evidence in support of primary glial affection has been reported in neurodegenerative disorders such as Parkinson's disease, Alzheimer's disease and transmissible spongiform encephalopathies. Based on biochemical, genetic and transcriptomic studies it is also becoming increasingly clear that the molecular changes measured in whole tissue extracts, e.g. obtained from Parkinson's disease brain, are not based on a purely neuronal contribution. This important evidence has been missed in cell culture or laser capture work focusing on the neuronal cell population. Studies of animal and in vitro models of disease pathogenesis additionally suggest glial accountability for some CNS degenerative processes. This review provides a critical analysis of the evidence available to date in support of the concept of gliodegeneration, which we propose to represent an essential although largely disregarded component of the spectrum of classical "neurodegeneration". Examples from the spectrum of alpha-synucleinopathies are presented.

The complement system in central nervous system diseases

The activation of complement system is important factor in inflammatory, neurodegenerative and cerebrovascular diseases. CNS cells are able to synthesize complement components, and myelin and oligodendrocytes (OLG) are known to activate the classical pathway of complement in vitro in the absence of antibodies. Although activation of the complement system is known to promote tissue injury, recent evidence has also indicated that this process can have neuroprotective effects. In particular, terminal C5b-9 complexes enhance OLG survival both in vitro and in vivo. Complement activation may also reduce the accumulation of amyloid and degenerating neurons by promoting their clearance and suggest that certain inflammatory defense mechanisms in the brain may be beneficial in neurodegenerative disease. Complement system activation plays also an important role in brain damage after ischemic injury or head trauma. These findings strongly suggest that complement activation and membrane assembly of C5b-9 can play a role in injury but can also provide neuroprotection depending on the pathophysiological context.

Therapeutic activity of C5a receptor antagonists in a rat model of neurodegeneration

The complement system is thought to be involved in the pathogenesis of numerous neurological diseases, although its precise role remains controversial. In this study we used orally active C5a receptor antagonists (PMX53 and PMX205) developed in our laboratories in a rat model of 3-nitropropionic acid (3-NP) -induced Huntington's disease. Administration of the C5a antagonists (10 mg/kg/day, oral) either 48 h pre- or 48 h post-toxin significantly reduced body weight loss, anorexia, and behavioral and motor deficits associated with 3-NP intoxication. Striatal lesion size, apoptosis, neutrophil infiltration, and hemorrhage were also significantly reduced in C5a antagonist-treated rats. Immunohistochemical analysis demonstrated marked deposition of C3 and C9, and up-regulation of C5a receptors on neuronal cells at the time of lesion formation. Inhibition of prostaglandins or TNF-alpha with ibuprofen or infliximab had no effect in this model. The C5a antagonists did not affect 3-NP-induced cell death when added directly to rat striatal neuronal cultures, indicating a secondary mechanism of action in vivo. Our findings demonstrate for the first time that complement activation in the brain, particularly C5a, is a key event in the pathogenesis of this disease model, and suggest a future role for inhibitors of C5a in the treatment of neurodegenerative diseases.

Activation of kainate receptors sensitizes oligodendrocytes to complement attack

Glutamate excitotoxicity and complement attack have both been implicated separately in the generation of tissue damage in multiple sclerosis and in its animal model, experimental autoimmune encephalomyelitis. Here, we investigated whether glutamate receptor activation sensitizes oligodendrocytes to complement attack. We found that a brief incubation with glutamate followed by exposure to complement was lethal to oligodendrocytes in vitro and in freshly isolated optic nerves. Complement toxicity was induced by activation of kainate but not of AMPA receptors and was abolished by removing calcium from the medium during glutamate priming. Dose-response studies showed that sensitization to complement attack is induced by two distinct kainate receptor populations displaying high and low affinities for glutamate. Oligodendrocyte death by complement required the formation of the membrane attack complex, which in turn increased membrane conductance and induced calcium overload and mitochondrial depolarization as well as a rise in the level of reactive oxygen species. Treatment with the antioxidant Trolox and inhibition of poly(ADP-ribose) polymerase-1, but not of caspases, protected oligodendrocytes against damage induced by complement. These findings indicate that glutamate sensitization of oligodendrocytes to complement attack may contribute to white matter damage in acute and chronic neurological disorders.

Thrombin and prothrombin are expressed by neurons and glial cells and accumulate in neurofibrillary tangles in Alzheimer disease brain

Thrombin is a serine protease that is generated by proteolytic cleavage of its precursor, prothrombin. We previously showed that thrombin proteolyses the microtubule-associated protein tau and that phosphorylation of tau inhibits this process. To characterize further the role of thrombin in the brain, we investigated prothrombin and thrombin expression in cultured brain cells and in brains of control, Alzheimer disease (AD) and parkinsonism-dementia complex of Guam (PDCG). We show by reverse transcriptase-polymerase chain reaction that prothrombin mRNA is expressed in brain tissues, neuroblastoma cells, and cultured human astrocytes, oligodendrocytes, and microglial cells. We also show by immunohistochemistry that the proteins prothrombin and thrombin are present in brain using specific monoclonal and polyclonal antibodies for both proteins. All antibodies stained residual serum in blood vessels, as well as normal pyramidal neurons and their processes, and some astrocytes. Additionally, in AD and PDCG cases, all antibodies stained extra- and intracellular neurofibrillary tangles (NFTs), senile plaques, and reactive microglial cells. The ubiquitous expression of prothrombin and thrombin in brain cells suggests that thrombin plays an important physiological role in normal brain. The accumulation of thrombin and prothrombin in NFTs supports the hypothesis that thrombin may be involved in tau proteolysis and that failure to metabolize tau may lead to its aggregation in neurodegenerative diseases.

Activation of early components of complement targets myelin and oligodendrocytes in the aged rhesus monkey brain

The disruption and loss of myelin in the white matter are some of the major changes that occur in the brain with age. In vitro studies suggest a role of the complement system in the catabolic breakdown of myelin membranes. This study presents findings on activation of the early components of complement cascade in the brains of both young and aged rhesus monkeys with evidence of increased complement activation in aged animals. Complement containing oligodendrocytes (CAOs) containing C3d and C4d complement activation products bound to oligodendrocytes and myelinated fibers were found in the brain of normal young and old animals. The CAOs, which also contained activated microglia, were distributed throughout the whole brain and in significantly greater numbers in the aged monkeys. These findings, together with the demonstration of covalent binding of the C3 fragments to myelin, suggest the initiation of the complement cascade by myelin and oligodendrocytes, which are known classical complement activators. Activation of terminal complement components was not demonstrable in the CAOs. Taken together the findings support the concept that activation of early components of complement in the brain may be a normal biological process that involves the metabolism of myelin and oligodendrocytes and up-regulates with age.

Brain microglia and blood-derived macrophages: molecular profiles and functional roles in multiple sclerosis and animal models of autoimmune demyelinating disease

Microglia and macrophages, one a brain-resident, the other a mostly hematogenous cell type, represent two related cell types involved in the brain pathology in multiple sclerosis and its autoimmune animal model, the experimental allergic encephalomyelitis. Together, they perform a variety of different functions: they are the primary sensors of brain pathology, they are rapidly recruited to sites of infection, trauma or autoimmune inflammation in experimental allergic encephalomyelitis and multiple sclerosis and they are competent presenters of antigen and interact with T cells recruited to the inflamed CNS. They also synthesise a variety of molecules, such as cytokines (TNF, interleukins), chemokines, accessory molecules (B7, CD40), complement, cell adhesion glycoproteins (integrins, selectins), reactive oxygen radicals and neurotrophins, that could exert a damaging or a protective effect on adjacent axons, myelin and oligodendrocytes. The current review will give a detailed summary on their cellular response, describe the different classes of molecules expressed and their attribution to the blood derived or brain-resident macrophages and then discuss how these molecules contribute to the neuropathology. Recent advances using chimaeric and genetically modified mice have been particularly telling about the specific, overlapping and nonoverlapping roles of macrophages and microglia in the demyelinating disease. Interestingly, they point to a crucial role of hematogenous macrophages in initiating inflammation and myelin removal, and that of microglia in checking excessive response and in the induction and maintenance of remission.

Closed head injury--an inflammatory disease?

Closed head injury (CHI) remains the leading cause of death and persisting neurological impairment in young individuals in industrialized nations. Research efforts in the past years have brought evidence that the intracranial inflammatory response in the injured brain contributes to the neuropathological sequelae which are, in large part, responsible for the adverse outcome after head injury. The presence of hypoxia and hypotension in the early resuscitative period of brain-injured patients further aggravates the inflammatory response in the brain due to ischemia/reperfusion-mediated injuries. The profound endogenous neuroinflammatory response after CHI, which is phylogenetically aimed at defending the intrathecal compartment from invading pathogens and repairing lesioned brain tissue, contributes to the development of cerebral edema, breakdown of the blood-brain barrier, and ultimately to delayed neuronal cell death. However, aside from these deleterious effects, neuroinflammation has been recently shown to mediate neuroreparative mechanisms after brain injury as well. This "dual effect" of neuroinflammation was the focus of extensive experimental and clinical research in the past years and has lead to an expanded basic knowledge on the cellular and molecular mechanisms which regulate the intracranial inflammatory response after CHI. Thus, head injury has recently evolved as an inflammatory and immunological disease much more than a pure traumatological, neurological, or neurosurgical entity. The present review will summarize the so far known mechanisms of posttraumatic neuroinflammation after CHI, based on data from clinical and experimental studies, with a special focus on the role of pro-inflammatory cytokines, chemokines, and the complement system.

Interactions between Alzheimer's disease and cerebral ischemia--focus on inflammation

Progressive memory impairment, beta-amyloid (Abeta) plaques associated with local inflammation, neurofibrillary tangles, and loss of neurons in selective brain areas are hallmarks of Alzheimer's disease (AD). Although beta-amyloid precursor protein (APP) and Abeta have a central role in the etiology of AD, it is not clear which forms of APP or Abeta are responsible for the neuronal vulnerability in AD brain. Brain ischemia, another cause of dementia in the elderly, has recently been recognized to contribute to the pathogenesis of AD and individuals with severe cognitive decline and possibly underlying AD are at increased risk for ischemic events in the brain. Moreover, the epsilon4 allele of apolipoprotein E (ApoE) is a risk factor for both AD and poor outcome following brain ischemia and hemorrhage. Several factors and molecular mechanisms that lower the threshold of neuronal death in models of AD have recently been described. Among these neuroinflammation seems to play an important role. The development and maturation of both AD neuropathology and ischemic lesions in the central nervous system are characterized by activation of glial cells and upregulation of inflammatory mediators. Indeed, anti-inflammatory approaches have proven to be beneficial in the prevention and treatment of AD-like neuropathology and ischemic injuries in vivo. This review summarizes some of the findings suggesting that neuronal overexpression of human APP renders the brain more vulnerable to ischemic injury and describes the factors that are involved in increased neuronal susceptibility to ischemic stroke.

Differential regulation of Abeta42-induced neuronal C1q synthesis and microglial activation

Expression of C1q, an early component of the classical complement pathway, has been shown to be induced in neurons in hippocampal slices, following accumulation of exogenous Aβ42. Microglial activation was also detected by surface marker expression and cytokine production. To determine whether C1q induction was correlated with intraneuronal Aβ and/or microglial activation, D-(-)-2-amino-5-phosphonovaleric acid (APV, an NMDA receptor antagonist) and glycine-arginine-glycine-aspartic acid-serine-proline peptide (RGD, an integrin receptor antagonist), which blocks and enhances Aβ42 uptake, respectively, were assessed for their effect on neuronal C1q synthesis and microglial activation. APV inhibited, and RGD enhanced, microglial activation and neuronal C1q expression. However, addition of Aβ10–20 to slice cultures significantly reduced Aβ42 uptake and microglial activation, but did not alter the Aβ42-induced neuronal C1q expression. Furthermore, Aβ10–20 alone triggered C1q production in neurons, demonstrating that neither neuronal Aβ42 accumulation, nor microglial activation is required for neuronal C1q upregulation. These data are compatible with the hypothesis that multiple receptors are involved in Aβ injury and signaling in neurons. Some lead to neuronal C1q induction, whereas other(s) lead to intraneuronal accumulation of Aβ and/or stimulation of microglia.

Human oligodendroglial cells express low levels of C1 inhibitor and membrane cofactor protein mRNAs

BACKGROUND: Oligodendrocytes, neurons, astrocytes, microglia, and endothelial cells are capable of synthesizing complement inhibitor proteins. Oligodendrocytes are vulnerable to complement attack, which is particularly observed in multiple sclerosis. This vulnerability may be related to a deficiency in their ability to express complement regulatory proteins. METHODS: This study compared the expression level of complement inhibitor mRNAs by human oligodendrocytes, astrocytes and microglia using semi-quantitative RT-PCR. RESULTS: Semi-quantitative RT-PCR analysis showed that C1 inhibitor (C1-inh) mRNA expression was dramatically lower in oligodendroglial cells compared with astrocytes and microglia. The mRNA expression level of membrane cofactor protein (MCP) by oligodendrocytes was also significantly lower than for other cell types. CONCLUSION: The lower mRNA expression of C1-inh and MCP by oligodendrocytes could contribute to their vulnerability in several neurodegenerative and inflammatory diseases of the central nervous system.

Complement synthesis and activation in the brain of SIV-infected monkeys

Complement is one of the most critical defence tools against cerebral infections, but uncontrolled complement biosynthesis and activation can induce profound brain tissue damage. To clarify the role of complement in the pathogenesis of AIDS-associated neurological disorders, we analysed the synthesis of complement in the brains of SIV-infected rhesus macaques. Using immunohistochemical staining we could show that the cerebral synthesis of complement factors C1q and C3 was strongly upregulated in SIV-infected monkeys compared to the spontaneous synthesis in uninfected control monkeys. Astrocytes, neurons, microglia, infiltrating macrophages and multinuclear giant cells all contribute to the high amounts of C1q and C3 in the brain. Secreted C1q and C3 are also deposited on the membrane of neurons, a prerequisite for formation of the membrane-driven lytic membrane attack complex. The membrane deposition thus might suggest complement-induced lysis of bystander neurons as a potential mechanism for cell damage during viral infection of the brain.

Phylogeny and regulation of four lipocalin genes clustered in the chicken genome: evidence of a functional diversification after gene duplication

A novel lipocalin gene is here reported that represents the fourth member of a cluster we have identified in the chicken genome. This cluster also includes Chondrogenesis-Associated Lipocalins beta and gamma (CAL beta, CAL gamma) and Extracellular Fatty Acid Binding Protein (Ex-FABP). The new gene codes for a 22-kDa secreted protein with three cysteine residues and a series of sequence features well conserved in the lipocalin family. All the genes in the cluster are structurally similar presenting comparable exon/intron boundary positions and exon sizes. A phylogenetic analysis indicates the monophyletic grouping of these genes, and their relationship with the lipocalins alpha-1-microglobulin (A1mg), complement factor 8 gamma chain (C8GC), prostaglandin D synthase (PGDS), and neutrophil-gelatinase-associated lipocalin (NGAL). The new cluster gene appears to be the ortholog of the mammalian C8GC and was thus named Ggal-C8GC. This orthology also suggests that this lipocalin was present in the ancestor common to reptiles and mammals. In addition to other expressing tissues, Ex-FABP, CAL beta and CAL gamma genes are highly transcribed in chondrocytes at late stages of chondrogenesis during endochondral bone formation and/or upon inflammatory stimulation. Here, we show that they are also transcriptionally induced when chondrocytes are subjected to various biological events as cell quiescence, cell shape transition, and hormonal stimulation. By contrast, Ggal-C8GC transcripts are only barely detectable in chondrocytes, but are more abundant in liver, kidney, brain, heart, skeletal muscle and particularly in skin. Moreover, no expression induction was observed neither during chondrocyte differentiation, nor upon any of the stimulations mentioned above. This indicates that the Ggal-C8GC gene was co-opted for a novel function after the duplication events that gave rise to the cluster. The peculiar coordinated regulation of Ex-FABP, CAL beta and CAL gamma, and the apparent divergent role of Ggal-C8GC suggest that these gene duplications may have been maintained during evolution by a sub-functionalization mechanism where some common function(s) are shared by several members of the cluster and some other specialized function(s) are unique to other members.

Pentoxifylline Inhibits Tumor Necrosis Factor-Alpha Induced Synthesis of Complement Component C3 in Human Endothelial Cells

Vascular endothelium is a major target for the inflammatory damage that occurs with multiple organ dysfunction associated with sepsis and other trauma. The growing appreciation of endothelium as a target of inflammation has obscured the importance of these cells as a source of inflammatory mediators. In the following study we evaluated the ability of tumor necrosis factor-alpha (TNF) to induce the synthesis of complement component C3 in human umbilical vein endothelial cells (HUVEC) and whether pentoxifylline (PTX) could reduce C3 expression. Confluent monolayers of HUVEC were treated with increasing concentrations of TNF with and without two concentrations of PTX. Concentrations of C3 were determined every 48 h for 144 h in cellular supernatants and C3 mRNA was amplified using RT-PCR. TNF increased C3 release from HUVEC in a concentration dependent manner. PTX added at the same time as TNF significantly reduced C3 release at the 96 h time point. Consistent with data on C3 release PTX inhibited the increased C3 mRNA expression associated with TNF treatment. TNF increases C3 synthesis and release from endothelial cells which were inhibited by clinical concentrations of PTX. This data further supports the potential benefit of PTX in multiple organ dysfunction and other inflammatory processes involving the endothelium by inhibiting one of the major mediators of vascular damage.