Complement activation in autoimmune demyelination: Dual role in neuroinflammation and neuroprotection

Complement inhibition rapidly blocks lesion extension and facilitates remyelination in neuromyelitis optica

Cumulative disability in neuromyelitis optica spectrum disorder (NMOSD) results from incomplete recovery following inflammatory, demyelinating attacks. Retrospective case studies and current clinical practice indicate that rapid treatment of acute attacks with apheresis limits injury and improves recovery. We evaluated the effects of apheresis and complement inhibition on lesion progression and recovery in a murine ex vivo cerebellar explant model of NMOSD injury. While both strategies reduced lesion formation relative to vehicle treatment, we observed that anti-C5 complement inhibition with eculizumab rapidly halted astrocyte destruction and immediately curtailed lesion extension; whereas an experimental mimic of immunoadsorption (IA), allowed for continued low level astrocyte destruction. During lesion recovery, C5 complement inhibition resulted in a faster rate of oligodendrocyte repopulation and improved myelin repair compared to IA. Complement inhibition may offer multiple benefits for the treatment of acute NMOSD attacks.

Tg-SwDI transgenic mice: A suitable model for Alzheimer's disease and cerebral amyloid angiopathy basic research and preclinical studies

Alzheimer's disease (AD) is the most common neurodegenerative disease and the most frequent cause of dementia. Characteristic features observed in the brain of AD patients are the accumulation of amyloid beta peptide (Aβ) aggregates, neurofibrillary tangles (NFT) composed of hyperphosphorylated Tau protein, neuronal and synaptic loss, and elevated levels of oxidative stress and inflammatory markers. Cerebral amyloid angiopathy (CAA) is another common cause of cognitive decline characterized by the accumulation of Aβ in the cerebral vasculature. The precise overlapping pathogenic mechanisms underlying the co-occurrence of AD and CAA are not very well understood. However, vascular dysfunction observed at early stages is considered a key phenomenon. Tg-SwDI transgenic mice expressing human Aβ precursor protein (AβPP) harboring the Swedish K670N/M671L and vasculotropic Dutch/Iowa E693Q/D694N mutations in the brain have been extensively used to study many pathological features observed in AD/CAA patients and to design biomarkers and therapeutic strategies. The present review summarizes studies addressing different features mimicking human disease in Tg-SwDI mice: parenchymal and cerebral vascular amyloid accumulation, neuroinflammation, complement overactivation, cerebrovascular, mitochondrial and GABAergic system dysfunction, altered NO synthesis, circadian rhythm disruptions, lead exposure effect, among others. Also, reports that evaluated anti-Aβ and anti-inflammatory strategies and compounds capable of delaying or reversing vascular dysfunction and the impairment of GABAergic transmission in Tg-SwDI mice are analyzed. This review may help researchers determine this model's appropriateness for future studies of a particular mechanism or a novel treatment protocol.

In Silico Modeling of Myelin Oligodendrocyte Glycoprotein Disulfide Bond Reduction by Phosphine-Borane Complexes

BACKGROUND

Neurodegenerative diseases can cause vision loss by damaging retinal ganglion cells in the optic nerve. Novel phosphine-borane compounds (PBs) can protect these cells from oxidative stress via the reduction of disulfide bonds. However, the specific targets of these compounds are unknown. Proteomic evidence suggests that myelin oligodendrocyte glycoprotein (MOG) is a potential target. MOG is of significant interest due to its role in anti-MOG optic neuritis syndrome.

METHODS

We used in silico modeling to explore the structural consequences of cleaving the extracellular domain MOG disulfide bond, both in isolation and in complex with anti-MOG antibodies. The potential binding of PBs to this bond was examined using molecular docking.

RESULTS

Cleaving the disulfide bond of MOG altered the structure of MOG dimers and reduced their energetic favorability by 46.13 kcal/mol. The energy profiles of anti-MOG antibody complexes were less favorable when the disulfide bond of MOG was reduced in the monomeric state by 55.21 kcal/mol, but the reverse was true in the dimeric state. PBs exhibited reducing capabilities with the MOG extracellular disulfide bond, with this best-scoring compound binding with an energy of -28.54 kcal/mol to the MOG monomer and -24.97 kcal/mol to the MOG dimer.

CONCLUSIONS

These findings suggest that PBs can affect the structure of MOG dimers and the formation of antibody complexes by reducing the MOG disulfide bond. Structural changes in MOG could have implications for neurodegenerative diseases and anti-MOG syndrome.

The validity of animal models to explore the pathogenic role of the complement system in multiple sclerosis: A review

Animal models of multiple sclerosis (MS) have been extensively used to characterize the disease mechanisms in MS, as well as to identify potential pharmacologic targets for this condition. In recent years, the immune complement system has gained increased attention as an important effector in the pathogenesis of MS. Evidence from histological, serum, and CSF studies of patients supports an involvement of complement in both relapsing-remitting and progressive MS. In this review, we discuss the history and advances made on the use of MS animal models to profile the effects of the complement system in this condition. The first studies that explored the complement system in the context of MS used cobra venom factor (CVF) as a complement depleting agent in experimental autoimmune encephalomyelitis (EAE) Lewis rats. Since then, multiple mice and rat models of MS have revealed a role of C3 and the alternative complement cascade in the opsonization and phagocytosis of myelin by microglia and myeloid cells. Studies using viral vectors, genetic knockouts and pharmacologic complement inhibitors have also shown an effect of complement in synaptic loss. Antibody-mediated EAE models have revealed an involvement of the C1 complex and the classical complement as an effector of the humoral response in this disease. C1q itself may also be involved in modulating microglia activation and oligodendrocyte differentiation in these animals. In addition, animal and in vitro models have revealed that multiple complement factors may act as modulators of both the innate and adaptive immune responses. Finally, evidence gathered from mice models suggests that the membrane attack complex (MAC) may even exert protective roles in the chronic stages of EAE. Overall, this review summarizes the importance of MS animal models to better characterize the role of the complement system and guide future therapeutic approaches in this condition.

Multimodal Benefits of Exercise in Patients With Multiple Sclerosis and COVID-19

Multiple sclerosis (MS) is a demyelinating disease characterized by plaque formation and neuroinflammation. The plaques can present in various locations, causing a variety of clinical symptoms in patients with MS. Coronavirus disease-2019 (COVID-19) is also associated with systemic inflammation and a cytokine storm which can cause plaque formation in several areas of the brain. These concurring events could exacerbate the disease burden of MS. We review the neuro-invasive properties of SARS-CoV-2 and the possible pathways for the entry of the virus into the central nervous system (CNS). Complications due to this viral infection are similar to those occurring in patients with MS. Conditions related to MS which make patients more susceptible to viral infection include inflammatory status, blood-brain barrier (BBB) permeability, function of CNS cells, and plaque formation. There are also psychoneurological and mood disorders associated with both MS and COVID-19 infections. Finally, we discuss the effects of exercise on peripheral and central inflammation, BBB integrity, glia and neural cells, and remyelination. We conclude that moderate exercise training prior or after infection with SARS-CoV-2 can produce health benefits in patients with MS patients, including reduced mortality and improved physical and mental health of patients with MS.

Microglial Pruning: Relevance for Synaptic Dysfunction in Multiple Sclerosis and Related Experimental Models

Microglia, besides being able to react rapidly to a wide range of environmental changes, are also involved in shaping neuronal wiring. Indeed, they actively participate in the modulation of neuronal function by regulating the elimination (or “pruning”) of weaker synapses in both physiologic and pathologic processes. Mounting evidence supports their crucial role in early synaptic loss, which is emerging as a hallmark of several neurodegenerative diseases, including multiple sclerosis (MS) and its preclinical models. MS is an inflammatory, immune-mediated pathology of the white matter in which demyelinating lesions may cause secondary neuronal death. Nevertheless, primitive grey matter (GM) damage is emerging as an important contributor to patients’ long-term disability, since it has been associated with early and progressive cognitive decline (CD), which seriously worsens the quality of life of MS patients. Widespread synapse loss even in the absence of demyelination, axon degeneration and neuronal death has been demonstrated in different GM structures, thus raising the possibility that synaptic dysfunction could be an early and possibly independent event in the neurodegenerative process associated with MS. This review provides an overview of microglial-dependent synapse elimination in the neuroinflammatory process that underlies MS and its experimental models.

Histone Deacetylase SIRT1 Mediates C5b-9-Induced Cell Cycle in Oligodendrocytes

Sublytic levels of C5b-9 increase the survival of oligodendrocytes (OLGs) and induce the cell cycle. We have previously observed that SIRT1 co-localizes with surviving OLGs in multiple sclerosis (MS) plaques, but it is not yet known whether SIRT1 is involved in OLGs survival after exposure to sublytic C5b-9. We have now investigated the role of SIRT1 in OLGs differentiation and the effect of sublytic levels of C5b-9 on SIRT1 and phosphorylated-SIRT1 (Ser27) expression. We also examined the downstream effects of SIRT1 by measuring histone H3 lysine 9 trimethylation (H3K9me3) and the expression of cyclin D1 as a marker of cell cycle activation. OLG progenitor cells (OPCs) purified from the brain of rat pups were differentiated in vitro and treated with sublytic C5b-9 or C5b6. To investigate the signaling pathway activated by C5b-9 and required for SIRT1 expression, we pretreated OLGs with a c-jun antisense oligonucleotide, a phosphoinositide 3-kinase (PI3K) inhibitor (LY294002), and a protein kinase C (PKC) inhibitor (H7). Our data show a significant reduction in phospho-SIRT1 and SIRT1 expression during OPCs differentiation, associated with a decrease in H3K9me3 and a peak of cyclin D1 expression in the first 24 h. Stimulation of OLGs with sublytic C5b-9 resulted in an increase in the expression of SIRT1 and phospho-SIRT1, H3K9me3, cyclin D1 and decreased expression of myelin-specific genes. C5b-9-stimulated SIRT1 expression was significantly reduced after pretreatment with c-jun antisense oligonucleotide, H7 or LY294002. Inhibition of SIRT1 with sirtinol also abolished C5b-9-induced DNA synthesis. Taken together, these data show that induction of SIRT1 expression by C5b-9 is required for cell cycle activation and is mediated through multiple signaling pathways.

Promotion of microglial phagocytosis by tuftsin stimulates remyelination in experimental autoimmune encephalomyelitis

Microglia were once thought to serve a pathogenic role in demyelinating diseases, particularly in multiple sclerosis (MS). However, it has recently been shown that in the experimental autoimmune encephalomyelitis (EAE) model of MS, microglia could serve a protective role by promoting remyelination via the efficient removal of apoptotic cells, the phagocytosis of debris and the support of myelinating oligodendrocytes. The aim of the present study was to determine if the effect of microglia could promote the recovery of EAE and attenuate symptoms in EAE. The severity of EAE was assessed by clinical scores, pathologic changes revealed by luxol fast blue staining and immunohistochemical techniques. The results suggested that microglia reduced clinical scores in mice, suppressed ongoing severe EAE and promoted remyelination and recovery in EAE mice. In addition, following induction with tuftsin, the M1/M2 cytokine balance was shifted, downregulating the proinflammatory M1 response and upregulating the anti-inflammatory M2 response. Generally, microglia can stimulate remyelination, which serves a protective role in different phases of EAE and may represent a potential therapeutic strategy for the treatment of MS.

RGC-32 regulates reactive astrocytosis and extracellular matrix deposition in experimental autoimmune encephalomyelitis

Extracellular matrix (ECM) deposition in active demyelinating multiple sclerosis (MS) lesions may impede axonal regeneration and can modify immune reactions. Response gene to complement (RGC)-32 plays an important role in the mediation of TGF-β downstream effects, but its role in gliosis has not been investigated. To gain more insight into the role played by RGC-32 in gliosis, we investigated its involvement in TGF-β-induced ECM expression and the upregulation of the reactive astrocyte markers α-smooth muscle actin (α-SMA) and nestin. In cultured neonatal rat astrocytes, collagens I, IV, and V, fibronectin, α-SMA, and nestin were significantly induced by TGF-β stimulation, and RGC-32 silencing resulted in a significant reduction in their expression. Using astrocytes isolated from RGC-32 knock-out (KO) mice, we found that the expression of TGF-β-induced collagens I, IV, and V, fibronectin, and α-SMA was significantly reduced in RGC-32 KO mice when compared with wild-type (WT) mice. SIS3 inhibition of Smad3 phosphorylation was also associated with a significant reduction in RGC-32 nuclear translocation and TGF-β-induced collagen I expression. In addition, during experimental autoimmune encephalomyelitis (EAE), RGC-32 KO mouse astrocytes displayed an elongated, bipolar phenotype, resembling immature astrocytes and glial progenitors whereas those from WT mice had a reactive, hypertrophied phenotype. Taken together, our data demonstrate that RGC-32 plays an important role in mediating TGF-β-induced reactive astrogliosis in EAE. Therefore, RGC-32 may represent a new target for therapeutic intervention in MS.

The complement system as a biomarker of disease activity and response to treatment in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system. The complement system has an established role in the pathogenesis of MS, and evidence suggests that its components can be used as biomarkers of disease-state activity and response to treatment in MS. Plasma C4a levels have been found to be significantly elevated in patients with active relapsing-remitting MS (RRMS), as compared to both controls and patients with stable RRMS. C3 levels are also significantly elevated in the cerebrospinal fluid (CSF) of patients with RRMS, and C3 levels are correlated with clinical disability. Furthermore, increased levels of factor H can predict the transition from relapsing to progressive disease, since factor H levels have been found to increase progressively with disease progression over a 2-year period in patients transitioning from RRMS to secondary progressive (SP) MS. In addition, elevations in C3 are seen in primary progressive (PP) MS. Complement components can also differentiate RRMS from neuromyelitis optica. Response gene to complement (RGC)-32, a novel molecule induced by complement activation, is a possible biomarker of relapse and response to glatiramer acetate (GA) therapy, since RGC-32 mRNA expression is significantly decreased during relapse and increased in responders to GA treatment. The predictive accuracy of RGC-32 as a potential biomarker (by ROC analysis) is 90% for detecting relapses and 85% for detecting a response to GA treatment. Thus, complement components can serve as biomarkers of disease activity to differentiate MS subtypes and to measure response to therapy.

Increased soluble C5b-9 in CSF of neuromyelitis optica

Neuromyelitis optica (NMO) and multiple sclerosis (MS) are two of the autoimmune inflammatory demyelinating diseases in the central nervous system. Complement is thought to have an important role in pathogenesis of these diseases, especially in NMO. However, the change of terminal complement complex (TCC, C5b-9) in patients with NMO is still unclear. Cerebrospinal fluid (CSF) C3a, C5a, sC5b-9 were measured by enzyme-linked immunosorbent assay in patients with NMO (n = 26), MS (n = 25) and other neurological disease (OND, n = 19). CSF levels of C5a in patients with NMO were higher than patients with OND (P = 0.006). Increased CSF sC5b-9 were found in the patients with NMO compared with patients with MS (P = 0.029) and OND (P = 0.0001). CSF sC5b-9 in patients with MS were also higher than patients with OND (P = 0.030). Patients with NMO revealed a trend to an increased disease disability with increased CSF sC5b-9 during relapse but not in MS (NMO: P = 0.006, MS: P = 0.097). CSF levels of sC5b-9 are increased in patients with NMO and reflect the activation of complement in NMO.

Complement activation in the injured central nervous system: another dual-edged sword?

The complement system, a major component of the innate immune system, is becoming increasingly recognised as a key participant in physiology and disease. The awareness that immunological mediators support various aspects of both normal central nervous system (CNS) function and pathology has led to a renaissance of complement research in neuroscience. Various studies have revealed particularly novel findings on the wide-ranging involvement of complement in neural development, synapse elimination and maturation of neural networks, as well as the progression of pathology in a range of chronic neurodegenerative disorders, and more recently, neurotraumatic events, where rapid disruption of neuronal homeostasis potently triggers complement activation. The purpose of this review is to summarise recent findings on complement activation and acquired brain or spinal cord injury, i.e. ischaemic-reperfusion injury or stroke, traumatic brain injury (TBI) and spinal cord injury (SCI), highlighting the potential for complement-targeted therapeutics to alleviate the devastating consequences of these neurological conditions.

Autoimmune and inflammatory mechanisms of CNS damage

Brain morphology and function are susceptible to various psysiological influences, including changes in the immune system. Inflammation and autoimmunity are two principal immunological responses that can compromise the function of multiple organs and tissues, including the central nervous system. The present article reviews clinical and experimental evidence pointing to structural brain damage induced by chronic autoimmune and/or inflammatory processes. Largely due to the vast complexity of neuroendocrine and immune systems, most of the principal pathogenic circuits are far from elucidated. In addition to summarizing the current knowledge, this article aims to highlight the importance of interdisciplinary research and combined efforts of physicians and scientists in revealing the intricate links between immunity and mental health.

Differential expression of complement proteins in cerebrospinal fluid from active multiple sclerosis patients

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system with complex immunopathogenesis. Using the 2-D DIGE technology, we separate CSF proteins from patients with active MS and control subjects. Three of the seven differential proteins identified were related with complement system, and the network analysis of the differential proteins revealed complement activation involvement in active MS. Complement C4b (gamma chain) was confirmed elevated by performing western blotting analysis (P < 0.01). The present results are an independent quantitative proteomic measure in CSF from active MS patients. The differential expression of the complement C4b and related proteins in CSF provides potential biomarkers as well as evidence for the involvement of complement activation in the pathogenesis of MS disease.

Role of HLA class II genes in susceptibility and resistance to multiple sclerosis: studies using HLA transgenic mice

Multiple sclerosis (MS), an inflammatory and demyelinating autoimmune disease of CNS has both, a genetic and an environmental predisposition. Among all the genetic factors associated with MS susceptibility, HLA class II haplotypes such as DR2/DQ6, DR3/DQ2, and DR4/DQ8 show the strongest association. Although a direct role of HLA-DR alleles in MS have been confirmed, it has been difficult to understand the contribution of HLA-DQ alleles in disease pathogenesis, due to strong linkage disequilibrium. Population studies have indicated that DQ alleles may play a modulatory role in the progression of MS. To better understand the mechanism by which HLA-DR and -DQ genes contribute to susceptibility and resistance to MS, we utilized single and double transgenic mice expressing HLA class II gene(s) lacking endogenous mouse class II genes. HLA class II transgenic mice have helped us in identifying immunodominant epitopes of PLP in context of various HLA-DR and -DQ molecules. We have shown that HLA-DR3 transgenic mice were susceptible to PLP(91-110) induced experimental autoimmune encephalomyelitis (EAE), while DQ6 (DQB1*0601) and DQ8 (DQB1*0302) transgenic mice were resistant. Surprisingly DQ6/DR3 double transgenic mice were resistant while DQ8/DR3 mice showed higher disease incidence and severity than DR3 mice. The protective effect of DQ6 in DQ6/DR3 mice was mediated by IFNγ, while the disease exacerbating effect of DQ8 molecule was mediated by IL-17. Further, we have observed that myelin-specific antibodies play an important role in PLP(91-110) induced EAE in HLA-DR3DQ8 transgenic mice. Based on these observations, we hypothesize that epistatic interaction between HLA-DR and -DQ genes play an important role in predisposition to MS and our HLA transgenic mouse model provides a novel tool to study the effect of linkage disequilibrium in MS.

Current and future treatment approaches for neuromyelitis optica

Neuromyelitis optica (NMO) is an inflammatory disease of the central nervous system (CNS) characterized by severe attacks of optic neuritis and myelitis, and which, unlike multiple sclerosis (MS), commonly spares the brain in the early stages. NMO used to be considered as a special form of MS. During the past 10 years, however, the two diseases have been shown to be clearly different. NMO is a B-cell-mediated disease associated with anti-aquaporin-4 antibodies in many cases and its pathophysiology seems to be near the acute lesion of necrotizing vasculitis. Assessment of prevalence shows that NMO is far less frequent than MS, which explains the absence of randomized clinical trials and NMO treatment strategies validated by evidence-based medicine. Recently, many data have been published that suggest that the therapeutic option in NMO should be immunosuppressive rather than immunomodulatory drugs. In the present study, after a brief overview of NMO, we review therapeutic studies and propose new therapeutic strategies in the relapse and disease-modifying fields.

Cancer and the complement cascade

Despite significant research on the role of inflammation and immunosurveillance in the immunologic microenvironment of tumors, little attention has been given to the oncogenic capabilities of the complement cascade. The recent finding that complement may contribute to tumor growth suggests an insidious relationship between complement and cancer, especially in light of evidence that complement facilitates cellular proliferation and regeneration. We address the hypothesis that complement proteins promote carcinogenesis and suggest mechanisms by which complement can drive the fundamental features of cancer. Evidence shows that this diverse family of innate immune proteins facilitates dysregulation of mitogenic signaling pathways, sustained cellular proliferation, angiogenesis, insensitivity to apoptosis, invasion and migration, and escape from immunosurveillance. Given that the traditionally held functions for the complement system include innate immunity and cancer defense, our review suggests a new way of thinking about the role of complement proteins in neoplasia.

Complement and the central nervous system: emerging roles in development, protection and regeneration

As expanding research reveals the novel ability of complement proteins to promote proliferation and regeneration of tissues throughout the body, the concept of the complement cascade as an innate immune effector has changed rapidly. In particular, its interactions with the central nervous system have provided a wealth of information regarding the ability of complement proteins to mediate neurogenesis, synaptogenesis, cell migration, neuroprotection, proliferation and regeneration. At numerous phases of the neuronal and glial cell cycle, complement proteins exert direct or indirect influence over their behavior and fate. Neuronal stem cells differentiate and migrate in response to complement, and it prevents injury and death in adult cells in response to toxic agents. Furthermore, complement proteins promote survival via anti-apoptotic actions, and can facilitate clearance and regeneration of injured tissues in various models of CNS disease. In summary, we highlight the protean abilities of complement proteins in the central nervous system, underscoring an exciting avenue of research that has yielded greater understanding of complement's role in central nervous system health and disease.

Effector functions of antiaquaporin-4 autoantibodies in neuromyelitis optica

NMO-IgG autoantibody is now considered a useful serum biomarker of neuromyelitis optica (NMO). A series of clinical and pathological observations suggest that NMO-IgG may play a central role in NMO physiopathology. Although the exact role and function of NMO-IgG in vivo remain to be determined, recent reports suggest that this antibody that targets the aquaporin-4 (AQP-4) water channel expressed by astrocytes is able to destabilize the blood-brain barrier and contribute to astrocyte and oligodendrocyte damage. This review summarizes the latest molecular effector functions attributed to the NMO-IgG/anti-AQP4 antibody and discusses their potential role in NMO pathology.

Neuroprotection in stroke by complement inhibition and immunoglobulin therapy

Activation of the complement system occurs in a variety of neuroinflammatory diseases and neurodegenerative processes of the CNS. Studies in the last decade have demonstrated that essentially all of the activation components and receptors of the complement system are produced by astrocytes, microglia, and neurons. There is also rapidly growing evidence to indicate an active role of the complement system in cerebral ischemic injury. In addition to direct cell damage, regional cerebral ischemia and reperfusion (I/R) induces an inflammatory response involving complement activation and generation of active fragments, such as C3a and C5a anaphylatoxins, C3b, C4b, and iC3b. The use of specific inhibitors to block complement activation or their mediators such as C5a, can reduce local tissue injury after I/R. Consistent with therapeutic approaches that have been successful in models of autoimmune disorders, many of the same complement inhibition strategies are proving effective in animal models of cerebral I/R injury. One new form of therapy, which is less specific in its targeting of complement than monodrug administration, is the use of immunoglobulins. Intravenous immunoglobulin (IVIG) has the potential to inhibit multiple components of inflammation, including complement fragments, pro-inflammatory cytokine production and leukocyte cell adhesion. Thus, IVIG may directly protect neurons, reduce activation of intrinsic inflammatory cells (microglia) and inhibit transendothelial infiltration of leukocytes into the brain parenchyma following an ischemic stroke. The striking neuroprotective actions of IVIG in animal models of ischemic stroke suggest a potential therapeutic potential that merits consideration for clinical trials in stroke patients.

Complement in multiple sclerosis: its role in disease and potential as a biomarker

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system with a poorly defined and complex immunopathogenesis. Although initiated by reactive T cells, persistent inflammation is evident throughout the disease course. A contribution from complement has long been suspected, based on the results of pathological and functional studies which have demonstrated complement activation products in MS brain and biological fluids. However, the extent and nature of complement activation and its contribution to disease phenotype and long-term outcome remain unclear. Furthermore, functional polymorphisms in components and regulators of the complement system which cause dysregulation, and are known to contribute to other autoimmune inflammatory disorders, have not been investigated to date in MS in any detail. In this paper we review evidence from pathological, animal model and human functional and genetic studies, implicating activation of complement in MS. We also evaluate the potential of complement components and regulators and their polymorphic variants as biomarkers of disease, and suggest appropriate directions for future research.

Deficiency in complement C1q improves histological and functional locomotor outcome after spinal cord injury

Although studies have suggested a role for the complement system in the pathophysiology of spinal cord injury (SCI), that role remains poorly defined. Additionally, the relative contribution of individual complement pathways in SCI is unknown. Our initial studies revealed that systemic complement activation was strongly influenced by genetic background and gender. Thus, to investigate the role of the classical complement pathway in contusion-induced SCI, male C1q knock-out (KO) and wild-type (WT) mice on a complement sufficient background (BUB) received a mild-moderate T9 contusion injury with the Infinite Horizon impactor. BUB C1q KO mice exhibited greater locomotor recovery compared with BUB WT mice (p<0.05). Improved recovery observed in BUB C1q KO mice was also associated with decreased threshold for withdrawal from a mild stimulus using von Frey filament testing. Surprisingly, quantification of microglia/macrophages (F4/80) by FACS analysis showed that BUB C1q KO mice exhibited a significantly greater percentage of macrophages in the spinal cord compared with BUB WT mice 3 d post-injury (p<0.05). However, this increased macrophage response appeared to be transient as stereological assessment of spinal cord tissue obtained 28 d post-injury revealed no difference in F4/80-positive cells between groups. Stereological assessment of spinal cord tissue showed that BUB C1q KO mice had reduced lesion volume and an increase in tissue sparing compared with BUB WT mice (p<0.05). Together, these data suggest that initiation of the classical complement pathway via C1q is detrimental to recovery after SCI.

Protective autoimmunity in the nervous system

The immune system can play both detrimental and beneficial roles in the nervous system. Multiple arms of the immune system, including T cells, B cells, NK cells, mast cells, macrophages, dendritic cells, microglia, antibodies, complement and cytokines participate in limiting damage to the nervous system during toxic, ischemic, hemorrhagic, infective, degenerative, metabolic and immune-mediated insults and also assist in the process of repair after injury has occurred. Immune cells have been shown to produce neurotrophic growth factors and interact with neurons and glial cells to preserve them from injury and stimulate growth and repair. The immune system also appears to participate in proliferation of neural progenitor stem cells and their migration to sites of injury. Neural stem cells can also modify the immune response in the central and peripheral nervous system to enhance neuroprotective effects. Evidence for protective and reparative functions of the immune system has been found in diverse neurologic diseases including traumatic injury, ischemic and hemorrhagic stroke, multiple sclerosis, infection, and neurodegenerative diseases (Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis). Existing therapies including glatiramer acetate, interferon-beta and immunoglobulin have been shown to augment the protective and regenerative aspects of the immune system in humans, and other experimental interventions such as vaccination, minocycline, antibodies and neural stem cells, have shown promise in animal models of disease. The beneficent aspects of the immune response in the nervous system are beginning to be appreciated and their potential as pharmacologic targets in neurologic disease is being explored.

Complement C3 and C4 expression in C1q sufficient and deficient mouse models of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease resulting in progressive cognitive decline. Amyloid plaque deposits consisting specifically of beta-amyloid peptides that have formed fibrils displaying beta-pleated sheet conformation are associated with activated microglia and astrocytes, are colocalized with C1q and other complement activation products, and appear at the time of cognitive decline in AD. Amyloid precursor protein (APP) transgenic mouse models of AD that lack the ability to activate the classical complement pathway display less neuropathology than do the APPQ+/+ mice, consistent with the hypothesis that complement activation and the resultant inflammation may play a role in the pathogenesis of AD. Further investigation of the presence of complement proteins C3 and C4 in the brain of these mice demonstrate that both C3 and C4 deposition increase with age in APPQ+/+ transgenic mice, as expected with the age-dependent increase in fibrillar beta-amyloid deposition. In addition, while C4 is predominantly localized on the plaques and/or associated with oligodendrocytes in APPQ+/+ mice, little C4 is detected in APPQ-/- brains consistent with a lack of classical complement pathway activation because of the absence of C1q in these mice. In contrast, plaque and cell associated C3 immunoreactivity is seen in both animal models and, surprisingly, is higher in APPQ-/- than in APPQ+/+ mice, providing evidence for alternative pathway activation. The unexpected increase in C3 levels in the APPQ-/- mice coincident with decreased neuropathology provides support for the hypothesis that complement can mediate protective events as well as detrimental events in this disease. Finally, induced expression of C3 in a subset of astrocytes suggests the existence of differential activation states of these cells.

Leukemia inhibitory factor induces an antiapoptotic response in oligodendrocytes through Akt-phosphorylation and up-regulation of 14-3-3

Leukemia inhibitory factor (LIF) promotes the survival of oligodendrocytes (OLG) both in vitro and in an animal model of multiple sclerosis. Here, we show that LIF protects mature rat OLG cultures selectively against the combined insult of the proinflammatory cytokines interferon-gamma and tumor necrosis factor-alpha, but it does not protect against oxidative stress nor against staurosporine induced apoptosis. We further demonstrate that LIF activates the janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) and the phosphatidylinositol 3 kinase/Akt pathway in mature OLG. We show that LIF protection is independent of suppressors of cytokine signaling and Bcl-2 mRNA expression levels. To gain further insight into the protective mechanism, a quantitative proteomic approach (DIGE) was applied to identify differentially expressed proteins in LIF-treated OLG. Our results indicate that LIF induces a shift in the cellular machinery toward a prosurvival execution program, illustrated by an enhanced expression of isoforms of the antiapoptotic molecule 14-3-3. These data provide further insight into the mechanisms of LIF-mediated protection of mature OLGs.

Cytokines and Brain Injury: Invited Review

The brain reacts to injury or disease by cascades of cellular and molecular responses. Evidence suggests that immune-inflammatory processes are key elements in the physiopathological processes associated with brain injury or damage. Cytokines are among major mediators implicated in these processes. Cytokine responses in the initial phase of brain injury might have a role in aggravating brain damage. However, in later stages, these molecular mediators might contribute to recovery or repair. Hemodynamic stabilization and optimalization of oxygen delivery to the brain remain cornerstones in the management of acute brain injury. New approaches might use anticytokine therapy to limit progression and halt or attenuate secondary brain damage. Progress toward such novel neuroprotection strategies, however, awaits better understanding of the optimal timing and dosing of those neuromodulatory therapies and better knowledge of the numerous interactions of those mediators. This also requires understanding of how and when precisely immune mechanisms shift from noxious to protective or restorative actions.

Plaque complement activation and cognitive loss in Alzheimer's disease

BACKGROUND

Complement activation is increased in Alzheimer's disease (AD), but its significance is unclear. The objective of this study was to determine the relationship between complement activation and cognition during the development of AD.

METHODS

iC3b, C9, Bielschowsky, and Gallyas staining was performed on aged normal (n = 17), mild cognitively impaired (n = 12), and AD (n = 17-18) inferior temporal gyrus specimens. Plaques were counted in 10x fields with high numbers of Bielschowsky-stained plaques. One-way ANOVA was used to determine between-group differences for plaque counts and measures of cognitive function, and linear regression was used to evaluate global cognition as a function of Bielschowsky-stained plaques. Terms for iC3b- and C9-stained plaques were then added sequentially as additional predictors in a "mediation analysis" model.

RESULTS

Complement was detected on plaques in all groups, and on neurofibrillary tangles only in AD specimens. iC3b, C9, and Bielschowsky-stained plaque counts increased 2.5- to 3-fold in AD vs. other groups (all p < or = 0.01). C9 staining was present on some diffuse plaques, as well as on neuritic plaques. Bielschowsky-stained and complement-stained plaque counts were highly correlated, and were negatively correlated with cognitive measures. When the Bielschowsky plaque count was used as a predictor, its correlations with cognitive measures were statistically significant, but when iC3b and C9 plaque counts were added as additional predictors, these correlations were no longer significant. This loss of significance was attributed to multicollinearity, i.e., high correlations between Bielschowsky-stained and complement-stained plaque counts.

CONCLUSION

Both early-stage (iC3b) and late-stage (C9) complement activation occurs on neocortical plaques in subjects across the cognitive spectrum; contrary to previous reports, C9 is present on some diffuse plaques. Because of high correlations between complement-stained and Bielschowsky-stained plaque counts, quantitative assessment of the extent to which complement activation may mediate the relationship between plaques and cognitive function could not be performed. Additional studies with animal models of AD (if late-stage complement activation can be demonstrated), or possibly a trial in AD patients with an inhibitor of late-stage complement activation, may be necessary to determine the significance of this process in AD.

Induction of complement proteins in a mouse model for cerebral microvascular A beta deposition

The deposition of amyloid β-protein (Aβ) in cerebral vasculature, known as cerebral amyloid angiopathy (CAA), is a common pathological feature of Alzheimer's disease and related disorders. In familial forms of CAA single mutations in the Aβ peptide have been linked to the increase of vascular Aβ deposits accompanied by a strong localized activation of glial cells and elevated expression of neuroinflammatory mediators including complement proteins. We have developed human amyloid-β precursor protein transgenic mice harboring two CAA Aβ mutations (Dutch E693Q and Iowa D694N) that mimic the prevalent cerebral microvascular Aβ deposition observed in those patients, and the Swedish mutations (K670N/M671L) to increase Aβ production. In these Tg-SwDI mice, we have reported predominant fibrillar Aβ along microvessels in the thalamic region and diffuse plaques in cortical region. Concurrently, activated microglia and reactive astrocytes have been detected primarily in association with fibrillar cerebral microvascular Aβ in this model. Here we show that three native complement components in classical and alternative complement pathways, C1q, C3, and C4, are elevated in Tg-SwDI mice in regions rich in fibrillar microvascular Aβ. Immunohistochemical staining of all three proteins was increased in thalamus, hippocampus, and subiculum, but not frontal cortex. Western blot analysis showed significant increases of all three proteins in the thalamic region (with hippocampus) as well as the cortical region, except C3 that was below detection level in cortex. Also, in the thalamic region (with hippocampus), C1q and C3 mRNAs were significantly up-regulated. These complement proteins appeared to be expressed largely by activated microglial cells associated with the fibrillar microvascular Aβ deposits. Our findings demonstrate that Tg-SwDI mice exhibit elevated complement protein expression in response to fibrillar vascular Aβ deposition that is observed in patients with familial CAA.