Yin and Yang: complement activation and regulation in Alzheimer's disease

Complement-mediated synapse loss in Alzheimer's disease: mechanisms and involvement of risk factors

The complement system is increasingly recognized as a key player in the synapse loss and cognitive impairments observed in Alzheimer's disease (AD). In particular, the process of complement-dependent synaptic pruning through phagocytosis is over-activated in AD brains, driving detrimental excessive synapse elimination and contributing to synapse loss, which is the strongest neurobiological correlate of cognitive impairments in AD. Herein we review recent advances in characterizing complement-mediated synapse loss in AD, summarize the underlying mechanisms, and discuss the possible involvement of AD risk factors such as aging and various risk genes. We conclude with an overview of key questions that remain to be addressed.

Association of KDR (rs2071559, rs1870377), CFH (rs1061170, rs1410996) genes variants and serum levels with pituitary adenoma

INTRODUCTION

Pituitary adenomas (PA) are slow-growing, benign tumors that usually do not metastasize to other body organs. Although they are referred to as benign, tumor growth can eventually put pressure on nearby structures, spread to surrounding tissues, and cause symptoms. The exact cause of PA is unknown, and the pathogenesis is multifactorial.

METHODS

Our study included PA patients and healthy volunteers. Genomic DNA was extracted using the DNA salting-out method. All participants were genotyped for the KDR rs2071559, rs1870377, CFH rs1061170, and rs1410996 polymorphisms. Serum levels of KDR and CFH were examined using the ELISA method.

RESULTS

The results of the present study showed that KDR rs2071559 A allele was associated with the occurrence of PA, hormonally active PA, invasive PA, and PA without recurrence development. KDR rs1870377 increased the probability of invasive PA and PA recurrence. CFH rs1061170 C allele was associated with hormonally active PA and the T allele was associated with non-invasive PA development.

CONCLUSION

KDR rs2071559, rs1870377, and CFH rs1061170 could be potential biomarkers associated with PA.

Reduced binding of apoE4 to complement factor H promotes amyloid-β oligomerization and neuroinflammation

The APOE4 variant of apolipoprotein E (apoE) is the most prevalent genetic risk allele associated with late-onset Alzheimer's disease (AD). ApoE interacts with complement regulator factor H (FH), but the role of this interaction in AD pathogenesis is unknown. Here we elucidate the mechanism by which isoform-specific binding of apoE to FH alters Aβ1-42-mediated neurotoxicity and clearance. Flow cytometry and transcriptomic analysis reveal that apoE and FH reduce binding of Aβ1-42 to complement receptor 3 (CR3) and subsequent phagocytosis by microglia which alters expression of genes involved in AD. Moreover, FH forms complement-resistant oligomers with apoE/Aβ1-42 complexes and the formation of these complexes is isoform specific with apoE2 and apoE3 showing higher affinity to FH than apoE4. These FH/apoE complexes reduce Aβ1-42 oligomerization and toxicity, and colocalize with complement activator C1q deposited on Aβ plaques in the brain. These findings provide an important mechanistic insight into AD pathogenesis and explain how the strongest genetic risk factor for AD predisposes for neuroinflammation in the early stages of the disease pathology.

Review of the unique and dominant lectin pathway of complement activation in agnathans

As the most primitive vertebrates, lampreys are significant in understanding the early origin and evolution of the vertebrate innate and adaptive immune systems. The complement system is a biological response system with complex and precise regulatory mechanisms and plays an important role in innate and adaptive immunity. It consists of more than 30 distinct components, including intrinsic components, regulatory factors, and complement receptors. Complement system is the humoral backbone of the innate immune defense and complement-like factors have also been found in cyclostomes. Our knowledge as such in lamprey has dramatically increased in the recent years. The searching for complement components in the reissner lamprey Lethenteron reissneri genome database, together with published data, has unveiled the existence of all the orthologues of mammalian complement components identified thus far, including the complement regulatory proteins and complement receptors, in lamprey. This review, summarizes the key themes and recent updates on the complement system of agnathans and discusses the individual complement components of lampreys, and critically compare their functions to that of mammalian complement components. Interestingly, the adaptive immune system of agnathans differs from that of gnathostomes. Lamprey complement components also display some distinctive features, such as lampreys are characterized by the variable lymphocyte receptors (VLRs)-based alternative adaptive immunity. This review may serve as important literature for deducing the evolution of the immune system from invertebrates to vertebrates.

Targeting the Complement-Sphingolipid System in COVID-19 and Gaucher Diseases: Evidence for a New Treatment Strategy

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2)-induced disease (COVID-19) and Gaucher disease (GD) exhibit upregulation of complement 5a (C5a) and its C5aR1 receptor, and excess synthesis of glycosphingolipids that lead to increased infiltration and activation of innate and adaptive immune cells, resulting in massive generation of pro-inflammatory cytokines, chemokines and growth factors. This C5a-C5aR1-glycosphingolipid pathway- induced pro-inflammatory environment causes the tissue damage in COVID-19 and GD. Strikingly, pharmaceutically targeting the C5a-C5aR1 axis or the glycosphingolipid synthesis pathway led to a reduction in glycosphingolipid synthesis and innate and adaptive immune inflammation, and protection from the tissue destruction in both COVID-19 and GD. These results reveal a common involvement of the complement and glycosphingolipid systems driving immune inflammation and tissue damage in COVID-19 and GD, respectively. It is therefore expected that combined targeting of the complement and sphingolipid pathways could ameliorate the tissue destruction, organ failure, and death in patients at high-risk of developing severe cases of COVID-19.

Integrated bioinformatics-based identification of diagnostic markers in Alzheimer disease

Alzheimer disease (AD) is a progressive neurodegenerative disease resulting from the accumulation of extracellular amyloid beta (Aβ) and intracellular neurofibrillary tangles. There are currently no objective diagnostic measures for AD. The aim of this study was to identify potential diagnostic markers for AD and evaluate the role of immune cell infiltration in disease pathogenesis. AD expression profiling data for human hippocampus tissue (GSE48350 and GSE5281) were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were identified using R software and the Human Protein Atlas database was used to screen AD-related DEGs. We performed functional enrichment analysis and established a protein-protein interaction (PPI) network to identify disease-related hub DEGs. The fraction of infiltrating immune cells in samples was determined with the Microenvironment Cell Populations-counter method. The random forest algorithm was used to develop a prediction model and receiver operating characteristic (ROC) curve analysis was performed to validate the diagnostic utility of the candidate AD markers. The correlation between expression of the diagnostic markers and immune cell infiltration was also analyzed. A total of 107 AD-related DEGs were screened in this study, including 28 that were upregulated and 79 that were downregulated. The DEGs were enriched in the Gene Ontology terms GABAergic synapse, Morphine addiction, Nicotine addiction, Phagosome, and Synaptic vesicle cycle. We identified 10 disease-related hub genes and 20 candidate diagnostic genes. Synaptophysin (SYP) and regulator of G protein signaling 4 (RGS4) (area under the ROC curve = 0.909) were verified as potential diagnostic markers for AD in the GSE28146 validation dataset. Natural killer cells, B lineage cells, monocytic lineage cells, endothelial cells, and fibroblasts were found to be involved in AD; additionally, the expression levels of both SYP and RGS4 were negatively correlated with the infiltration of these immune cell types. These results suggest that SYP and RGS4 are potential diagnostic markers for AD and that immune cell infiltration plays an important role in AD development and progression.

Microglia in Alzheimer’s Disease: A Favorable Cellular Target to Ameliorate Alzheimer’s Pathogenesis

Microglial cells serve as molecular sensors of the brain that play a role in physiological and pathological conditions. Under normal physiology, microglia are primarily responsible for regulating central nervous system homeostasis through the phagocytic clearance of redundant protein aggregates, apoptotic cells, damaged neurons, and synapses. Furthermore, microglial cells can promote and mitigate amyloid β phagocytosis and tau phosphorylation. Dysregulation of the microglial programming alters cellular morphology, molecular signaling, and secretory inflammatory molecules that contribute to various neurodegenerative disorders especially Alzheimer’s disease (AD). Furthermore, microglia are considered primary sources of inflammatory molecules and can induce or regulate a broad spectrum of cellular responses. Interestingly, in AD, microglia play a double-edged role in disease progression; for instance, the detrimental microglial effects increase in AD while microglial beneficiary mechanisms are jeopardized. Depending on the disease stages, microglial cells are expressed differently, which may open new avenues for AD therapy. However, the disease-related role of microglial cells and their receptors in the AD brain remain unclear. Therefore, this review represents the role of microglial cells and their involvement in AD pathogenesis.

Deep post-GWAS analysis identifies potential risk genes and risk variants for Alzheimer's disease, providing new insights into its disease mechanisms

Alzheimer’s disease (AD) is a genetically complex, multifactorial neurodegenerative disease. It affects more than 45 million people worldwide and currently remains untreatable. Although genome-wide association studies (GWAS) have identified many AD-associated common variants, only about 25 genes are currently known to affect the risk of developing AD, despite its highly polygenic nature. Moreover, the risk variants underlying GWAS AD-association signals remain unknown. Here, we describe a deep post-GWAS analysis of AD-associated variants, using an integrated computational framework for predicting both disease genes and their risk variants. We identified 342 putative AD risk genes in 203 risk regions spanning 502 AD-associated common variants. 246 AD risk genes have not been identified as AD risk genes by previous GWAS collected in GWAS catalogs, and 115 of 342 AD risk genes are outside the risk regions, likely under the regulation of transcriptional regulatory elements contained therein. Even more significantly, for 109 AD risk genes, we predicted 150 risk variants, of both coding and regulatory (in promoters or enhancers) types, and 85 (57%) of them are supported by functional annotation. In-depth functional analyses showed that AD risk genes were overrepresented in AD-related pathways or GO terms—e.g., the complement and coagulation cascade and phosphorylation and activation of immune response—and their expression was relatively enriched in microglia, endothelia, and pericytes of the human brain. We found nine AD risk genes—e.g., IL1RAP, PMAIP1, LAMTOR4—as predictors for the prognosis of AD survival and genes such as ARL6IP5 with altered network connectivity between AD patients and normal individuals involved in AD progression. Our findings open new strategies for developing therapeutics targeting AD risk genes or risk variants to influence AD pathogenesis.

Alzheimer's Disease: A Molecular View of β-Amyloid Induced Morbific Events

Amyloid-β (Aβ) is a dynamic peptide of Alzheimer’s disease (AD) which accelerates the disease progression. At the cell membrane and cell compartments, the amyloid precursor protein (APP) undergoes amyloidogenic cleavage by β- and γ-secretases and engenders the Aβ. In addition, externally produced Aβ gets inside the cells by receptors mediated internalization. An elevated amount of Aβ yields spontaneous aggregation which causes organelles impairment. Aβ stimulates the hyperphosphorylation of tau protein via acceleration by several kinases. Aβ travels to the mitochondria and interacts with its functional complexes, which impairs the mitochondrial function leading to the activation of apoptotic signaling cascade. Aβ disrupts the Ca²⁺ and protein homeostasis of the endoplasmic reticulum (ER) and Golgi complex (GC) that promotes the organelle stress and inhibits its stress recovery machinery such as unfolded protein response (UPR) and ER-associated degradation (ERAD). At lysosome, Aβ precedes autophagy dysfunction upon interacting with autophagy molecules. Interestingly, Aβ act as a transcription regulator as well as inhibits telomerase activity. Both Aβ and p-tau interaction with neuronal and glial receptors elevate the inflammatory molecules and persuade inflammation. Here, we have expounded the Aβ mediated events in the cells and its cosmopolitan role on neurodegeneration, and the current clinical status of anti-amyloid therapy.

Proteomic Profiling of Plasma and Brain Tissue from Alzheimer's Disease Patients Reveals Candidate Network of Plasma Biomarkers

BACKGROUND

Alzheimer's disease (AD) is the most prevalent form of dementia with two pathological hallmarks of tau-containing neurofibrillary tangles and amyloid-β protein (Aβ)-containing neuritic plaques. Although Aβ and tau have been explored as potential biomarkers, levels of these pathological proteins in blood fail to distinguish AD from healthy control subjects.

OBJECTIVE

We aim to discover potential plasma proteins associated with AD pathology by performing tandem mass tag (TMT)-based quantitative proteomic analysis of proteins from peripheral and central nervous system compartments.

METHODS

We performed comparative proteomic analyses of plasma collected from AD patients and cognitively normal subjects. In addition, proteomic profiles from the inferior frontal cortex, superior frontal cortex, and cerebellum of postmortem brain tissue from five AD patients and five non-AD controls were compared with plasma proteomic profiles to search for common biomarkers. Liquid chromatography-mass spectrometry was used to analyze plasma and brain tissue labeled with isobaric TMT for relative protein quantification.

RESULTS

Our results showed that the proteins in complement coagulation cascade and interleukin-6 signaling were significantly altered in both plasma and brains of AD patients.

CONCLUSION

Our results demonstrate the relevance in immune responses between the peripheral and central nervous systems. Those differentially regulated plasma proteins are explored as candidate biomarker profiles that illustrate chronic neuroinflammation in brains of AD patients.

Function and Dysfunction of Complement Factor H During Formation of Lipid-Rich Deposits

Complement-mediated inflammation or dysregulation in lipid metabolism are associated with the pathogenesis of several diseases. These include age-related macular degeneration (AMD), C3 glomerulonephritis (C3GN), dense deposit disease (DDD), atherosclerosis, and Alzheimer’s disease (AD). In all these diseases, formation of characteristic lipid-rich deposits is evident. Here, we will discuss molecular mechanisms whereby dysfunction of complement, and especially of its key regulator factor H, could be involved in lipid accumulation and related inflammation. The genetic associations to factor H polymorphisms, the role of factor H in the resolution of inflammation in lipid-rich deposits, modification of macrophage functions, and complement-mediated clearance of apoptotic and damaged cells indicate that the function of factor H is crucial in limiting inflammation in these diseases.

Neuroinflammation in Alzheimer's Disease: Microglia, Molecular Participants and Therapeutic Choices

Alzheimer's disease is the world's most common dementing illness. It is pathologically characterized by β-amyloid accumulation, extracellular senile plaques and intracellular neurofibrillary tangles formation, and neuronal necrosis and apoptosis. Neuroinflammation has been widely recognized as a crucial process that participates in AD pathogenesis. In this review, we briefly summarized the involvement of microglia in the neuroinflammatory process of Alzheimer's disease. Its roles in the AD onset and progression are also discussed. Numerous molecules, including interleukins, tumor necrosis factor alpha, chemokines, inflammasomes, participate in the complex process of AD-related neuroinflammation and they are selectively discussed in this review. In the end of this paper from an inflammation- related perspective, we discussed some potential therapeutic choices.

Complement: Bridging the innate and adaptive immune systems in sterile inflammation

The complement system is a collection of soluble and membrane-bound proteins that together act as a powerful amplifier of the innate and adaptive immune systems. Although its role in infection is well established, complement is becoming increasingly recognized as a key contributor to sterile inflammation, a chronic inflammatory process often associated with noncommunicable diseases. In this context, damaged tissues release danger signals and trigger complement, which acts on a range of leukocytes to augment and bridge the innate and adaptive immune systems. Given the detrimental effect of chronic inflammation, the complement system is therefore well placed as an anti-inflammatory drug target. In this review, we provide a general outline of the sterile activators, effectors, and targets of the complement system and a series of examples (i.e., hypertension, cancer, allograft transplant rejection, and neuroinflammation) that highlight complement's ability to bridge the 2 arms of the immune system.

Synaptic Elimination in Neurological Disorders

Synapses are well known as the main structures responsible for transmitting information through the release and recognition of neurotransmitters by pre- and post-synaptic neurons. These structures are widely formed and eliminated throughout the whole lifespan via processes termed synaptogenesis and synaptic pruning, respectively. Whilst the first pro-cess is needed for ensuring proper connectivity between brain regions and also with the periphery, the second phenomenon is important for their refinement by eliminating weaker and unnecessary synapses and, at the same time, maintaining and fa-voring the stronger ones, thus ensuring proper synaptic transmission. It is well-known that synaptic elimination is modulated by neuronal activity. However, only recently the role of the classical complement cascade in promoting this phenomenon has been demonstrated. Specifically, microglial cells recognize activated complement component 3 (C3) bound to synapses tar-geted for elimination, triggering their engulfment. As this is a highly relevant process for adequate neuronal functioning, dis-ruptions or exacerbations in synaptic pruning could lead to severe circuitry alterations that could underlie neuropathological alterations typical of neurological and neuropsychiatric disorders. In this review, we focus on discussing the possible in-volvement of excessive synaptic elimination in Alzheimer’s disease, as it has already been reported dendritic spine loss in post-synaptic neurons, increased association of complement proteins with its synapses and, hence, augmented microglia-mediated pruning in animal models of this disorder. In addition, we briefly discuss how this phenomenon could be related to other neurological disorders, including multiple sclerosis and schizophrenia.

Stress and Systemic Inflammation: Yin-Yang Dynamics in Health and Diseases

Studies in psychoneuroimmunology (PNI) would provide better insights into the "whole mind-body system." Systems biology models of the complex adaptive systems (CASs), such as a conceptual framework of "Yin-Yang dynamics," may be helpful for identifying systems-based biomarkers and targets for more effective prevention and treatment. The disturbances in the Yin-Yang dynamical balance may result in stress, inflammation, and various disorders including insomnia, Alzheimer's disease, obesity, diabetes, cardiovascular diseases, skin disorders, and cancer. At the molecular and cellular levels, the imbalances in the cytokine pathways, mitochondria networks, redox systems, and various signaling pathways may contribute to systemic inflammation. In the nervous system, Yin and Yang may represent the dynamical associations between the progressive and regressive processes in aging and neurodegenerative diseases. In response to the damages to the heart, the Yin-Yang dynamical balance between proinflammatory and anti-inflammatory cytokine networks is crucial. The studies of cancer have revealed the importance of the Yin-Yang dynamics in the tumoricidal and tumorigenic activities of the immune system. Stress-induced neuroimmune imbalances are also essential in chronic skin disorders including atopic dermatitis and psoriasis. With the integrative framework, the restoration of the Yin-Yang dynamics can become the objective of dynamical systems medicine.

Human Cord Blood Serum-Derived APP α-Secretase Cleavage Activity is Mediated by C1 Complement

Alzheimer's Disease (AD) is the leading cause of dementia in the elderly. In healthy individuals, amyloid precursor protein (APP) is cleaved by α-secretase, generating soluble α-amyloid precursor protein (sAPPα), which contributes neuroprotective functions in the neuronal environment. In contrast, in the neurodegenerative environment of AD patients, amyloid-β-peptide (Aβ) of either 40 or 42 residues are generated by increased activity of β- and γ-secretase. These proteins amalgamate in specific regions of the brain, which disrupts neuronal functions and leads to cognitive impairment. Human umbilical cord blood cells (HUCBC) have proven useful as potential immunomodulatory therapies in various models of neurodegenerative diseases, including AD. Our most recent work studied the impact of umbilical cord blood serum (CBS) on modulation of sAPPα production. Heat-sensitive CBS significantly promoted sAPPα production, indicating that heat-sensitive factor(s) play(s) a role in this process. Liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis was used to determine the molecular source of α-secretase in purified CBS and aged blood serum (AgBS) fraction. Of the proteins identified, the subunits of C1 complex (C1q, C1r, and C1s) and alpha-2-macroglobulin showed significantly greater levels in purified α-CBS fraction (α-CBSF) compared with the AgBS fraction (AgBSF). Specifically, C1 markedly increased sAPPα and alpha-carboxyl-terminal fragment (α-CTF) production in a dose-dependent fashion, whereas C1q alone only minimally increased and C3 did not increase sAPPα production in the absence of sera. Furthermore, C1q markedly increased sAPPα and α-CTF, while decreasing Aβ, in CHO/APPwt cells cultured in the presence of whole sera. These results confirm our initial assumption that APP α-secretase activity in human blood serum is mediated by complement C1, opening a potential therapeutic modality for the future of AD.

"Immune Gate" of Psychopathology-The Role of Gut Derived Immune Activation in Major Psychiatric Disorders

Interaction between the gastrointestinal tract (GI) and brain functions has recently become a topic of growing interest in psychiatric research. These multidirectional interactions take place in the so-called gut-brain axis or more precisely, the microbiota-gut-brain axis. The GI tract is the largest immune organ in the human body and is also the largest surface of contact with the external environment. Its functions and permeability are highly influenced by psychological stress, which are often a precipitating factor in the first episode, reoccurrence and/or deterioration of symptoms of psychiatric disorders. In recent literature there is growing evidence that increased intestinal permeability with subsequent immune activation has a major role in the pathophysiology of various psychiatric disorders. Numerous parameters measured in this context seem to be aftermaths of those mechanisms, yet at the same time they may be contributing factors for immune mediated psychopathology. For example, immune activation related to gut-derived bacterial lipopolysaccharides (LPS) or various food antigens and exorphins were reported in major depression, schizophrenia, bipolar disorder, alcoholism and autism. In this review the authors will summarize the evidence and roles of such parameters and their assessment in major psychiatric disorders.

Complement as a diagnostic tool in immunopathology

The complement system is a complex and autoregulated multistep cascade at the interface of innate and adaptive immunity. It is activated by immune complexes or apoptotic cells (classical pathway), pathogen-associated glycoproteins (lectin pathway) or a variety of molecular and cellular surfaces (alternative pathway). Upon activation, complement triggers the generation of proteolytic fragments that allow the elimination of the activating surface by enhancing inflammation, opsonization, phagocytosis, and cellular lysis. Moreover, complement efficiently discriminates self from non-self surfaces by means of soluble and membrane-bound complement regulators which are critical for innate self-tolerance. Complement deficiency or dysfunction disturb complement homeostasis and give rise to diseases as diverse as bacterial infections, autoimmunity, or renal and neurological disorders. Research on complement-targeted therapies is an expanding field that has already improved the prognosis of severe diseases such as atypical Haemolytic Uremic syndrome or Paroxysmal Nocturnal Haemoglobinuria. Therefore, complement analysis and monitoring provides valuable information with deep implications for diagnosis and therapy. In addition to its important role as an extracellular defense system, it has now become evident that complement is also present intracellularly, and its activation has profound implications for leukocyte survival and function. In this review, we summarize the essential, up-to-date information on the use of complement as a diagnostic and therapeutic tool in the clinics.

Targeting neuroinflammation in Alzheimer's disease

Almost 47 million people suffer from dementia worldwide, with an estimated new case diagnosed every 3.2 seconds. Alzheimer’s disease (AD) accounts for approximately 60%–80% of all dementia cases. Given this evidence, it is clear dementia represents one of the greatest global public health challenges. Currently used drugs alleviate the symptoms of AD but do not treat the underlying causes of dementia. Hence, a worldwide quest is under way to find new treatments to stop, slow, or even prevent AD. Besides the classic targets of the oldest therapies, represented by cholinergic and glutamatergic systems, β-amyloid (Aβ) plaques, and tau tangles, new therapeutic approaches have other targets. One of the newest and most promising strategies is the control of reactive gliosis, a multicellular response to brain injury. This phenomenon occurs as a consequence of a persistent glial activation, which leads to cellular dysfunctions and neuroinflammation. Reactive gliosis is now considered a key abnormality in the AD brain. It has been demonstrated that reactive astrocytes surround both Aβ plaques and tau tangles. In this condition, glial cells lose some of their homeostatic functions and acquire a proinflammatory phenotype amplifying neuronal damage. So, molecules that are able to restore their physiological functions and control the neuroinflammatory process offer new therapeutic opportunities for this devastating disease. In this review, we describe the role of neuroinflammation in the AD pathogenesis and progression and then provide an overview of the recent research with the aim of developing new therapies to treat this disorder.

Inhibition of the classical pathway of the complement cascade prevents early dendritic and synaptic degeneration in glaucoma

Background

Glaucoma is a complex, multifactorial disease characterised by the loss of retinal ganglion cells and their axons leading to a decrease in visual function. The earliest events that damage retinal ganglion cells in glaucoma are currently unknown. Retinal ganglion cell death appears to be compartmentalised, with soma, dendrite and axon changes potentially occurring through different mechanisms. There is mounting evidence from other neurodegenerative diseases suggesting that neuronal dendrites undergo a prolonged period of atrophy, including the pruning of synapses, prior to cell loss. In addition, recent evidence has shown the role of the complement cascade in synaptic pruning in glaucoma and other diseases.

Results

Using a genetic (DBA/2J mouse) and an inducible (rat microbead) model of glaucoma we first demonstrate that there is loss of retinal ganglion cell synapses and dendrites at time points that precede axon or soma loss. We next determine the role of complement component 1 (C1) in early synaptic loss and dendritic atrophy during glaucoma. Using a genetic knockout of C1qa (D2.C1qa^-/- mouse) or pharmacological inhibition of C1 (in the rat bead model) we show that inhibition of C1 is sufficient to preserve dendritic and synaptic architecture.

Conclusions

This study further supports assessing the potential for complement-modulating therapeutics for the prevention of retinal ganglion cell degeneration in glaucoma.

Slowing the progression of Alzheimer's disease; what works?

Alzheimer's disease (AD) is an age-related progressive dementia, which is increasing in prevalence world-wide. Typically affecting short-term memory at onset, this devastating illness advances to impair all aspects of cognition, as well as non-cognitive domains. Although much effort has been made in recent years to develop disease-modifying treatments, medications which provided promising results in pre-clinical research have so far faltered in human clinical trials. Attention has recently shifted into trying to identify preventative measures that may delay the onset of the illness. Preventative factors include physical activity, proper diet, cognitive stimulation and the management of conditions such as hypertension, diabetes and obesity. However, it remains imperative to identify approaches that may help patients already diagnosed with the illness. Alongside pharmacological research, much work has been done on uncovering strategies which may slow down the progression of AD. This review aims to summarize evidence supporting or refuting methods impacting on the progression of the disease. AD remains a chronic and serious condition, therefore any intervention delaying the onset of moderate/severe symptoms will have a significant impact on patients and their families.

Inflammation in Alzheimer's Disease and Molecular Genetics: Recent Update

Alzheimer's disease (AD) is a complex age-related neurodegenerative disorder of the central nervous system. Since the first description of AD in 1907, many hypotheses have been established to explain its causes. The inflammation theory is one of them. Pathological and biochemical studies of brains from AD individuals have provided solid evidence of the activation of inflammatory pathways. Furthermore, people with long-term medication of anti-inflammatory drugs have shown a reduced risk to develop the disease. After three decades of genetic study in AD, dozens of loci harboring genetic variants influencing inflammatory pathways in AD patients has been identified through genome-wide association studies (GWAS). The most well-known GWAS risk factor that is responsible for immune response and inflammation in AD development should be APOE ε4 allele. However, a growing number of other GWAS risk AD candidate genes in inflammation have recently been discovered. In the present study, we try to review the inflammation in AD and immunity-associated GWAS risk genes like HLA-DRB5/DRB1, INPP5D, MEF2C, CR1, CLU and TREM2.

Upregulation of glycolytic enzymes, mitochondrial dysfunction and increased cytotoxicity in glial cells treated with Alzheimer's disease plasma

Alzheimer's disease (AD) is a neurodegenerative disorder associated with increased oxidative stress and neuroinflammation. Markers of increased protein, lipid and nucleic acid oxidation and reduced activities of antioxidant enzymes have been reported in AD plasma. Amyloid plaques in the AD brain elicit a range of reactive inflammatory responses including complement activation and acute phase reactions, which may also be reflected in plasma. Previous studies have shown that human AD plasma may be cytotoxic to cultured cells. We investigated the effect of pooled plasma (n = 20 each) from healthy controls, individuals with amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD) on cultured microglial cells. AD plasma and was found to significantly decrease cell viability and increase glycolytic flux in microglia compared to plasma from healthy controls. This effect was prevented by the heat inactivation of complement. Proteomic methods and isobaric tags (iTRAQ) found the expression level of complement and other acute phase proteins to be altered in MCI and AD plasma and an upregulation of key enzymes involved in the glycolysis pathway in cells exposed to AD plasma. Altered expression levels of acute phase reactants in AD plasma may alter the energy metabolism of glia.

Genetic deletion of TNFRII gene enhances the Alzheimer-like pathology in an APP transgenic mouse model via reduction of phosphorylated IκBα

Tumor necrosis factor receptor II (TNFRII) is one of the TNF receptor superfamily members and our recent pathological studies show that TNFRII is deficient in the brains of Alzheimer's disease (AD). However, the mechanisms of TNFRII in AD pathogenesis remain unclear. In the present study, by using the gene-targeting approach to delete TNFRII in AD transgenic mouse model, we found that, in the brain of APP23 mice with TNFRII deletion (APP23/TNFRII(-/-)), AD-like pathology, i.e. plaque formation and microglial activation, occurs as early as 6 months of age. To test whether the increased levels of Aβ plaques was due to elevated Aβ, we measured Aβ and found that Aβ levels indeed were significantly increased at this age. Because β-secretase, BACE1, is critical enzyme for Aβ production, we have examined BACE1 and found that BACE1 is increased in both protein levels and enzymatic activity as early as 6 months of age; Having shown that BACE1 promoter region contains NF-κB binding sites, we found that cytoplasmic NF-κB was elevated and SUMO1 binding to IκBα was decreased. To further verify these findings, we have overexpressed TNFRII and identified that overexpressing TNFRII can reverse the findings from APP23/TNFRII(-/-) mice. Altogether, our results demonstrate novel roles of TNFRII in the regulation of Aβ production, suggesting a potential therapeutic strategy for AD by up-regulating TNFRII levels and elevating phosphorylated IκBα by SUMOylation.

What does complement do in Alzheimer's disease? Old molecules with new insights

Increasing evidence suggests that inflammatory and immune components in brain are important in Alzheimer's disease (AD) and anti-inflammatory and immunotherapeutic approaches may be amenable to AD treatment. It is known that complement activation occurs in the brain of patients with AD, and contributes to a local inflammatory state development which is correlated with cognitive impairment. In addition to the complement's critical role in the innate immune system recognizing and killing, or targeting for destruction, complement proteins can also interact with cell surface receptors to promote a local inflammatory response and contributes to the protection and healing of the host. On the other hand, complement activation also causes inflammation and cell damage as an essential immune function to eliminate cell debris and potentially toxic protein aggregates. It is the balance of these seemingly competing events that influences the ultimate state of neuronal function. Our mini review will be focusing on the unique molecular interactions happening in the AD development, the functional outcomes of those interactions, as well as the contribution of each element to AD.

Fibrinogen and altered hemostasis in Alzheimer's disease

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) plaques, tau tangles, brain atrophy, and vascular pathology. Vascular defects include cerebrovascular dysfunction, decreased cerebral blood flow, and blood brain barrier (BBB) disruption, among others. Here, we review the evidence that links Aβ with the vascular pathology present in AD, with a specific focus on the hemostatic system and the clotting protein fibrinogen. Fibrinogen is normally found circulating in blood, but in AD it deposits with Aβ in the brain parenchyma and cerebral blood vessels. We found that Aβ and fibrin(ogen) interact, and their binding leads to increased fibrinogen aggregation, Aβ fibrillization, and the formation of degradation-resistant fibrin clots. Decreasing fibrinogen levels not only lessens cerebral amyloid angiopathy and BBB permeability, but it also reduces microglial activation and improves cognitive performance in AD mouse models. Moreover, a prothrombotic state in AD is evidenced by increased clot formation, decreased fibrinolysis, and elevated levels of coagulation factors and activated platelets. Abnormal deposition and persistence of fibrin(ogen) in AD may result from Aβ-fibrin(ogen) binding and altered hemostasis and could thus contribute to Aβ deposition, decreased cerebral blood flow, exacerbated neuroinflammation, and eventual neurodegeneration. Blocking the interaction between fibrin(ogen) and Aβ may be a promising therapeutic target for AD.

The role of the innate immune system in Alzheimer's disease and frontotemporal lobar degeneration: an eye on microglia

In the last few years, genetic and biomolecular mechanisms at the basis of Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) have been unraveled. A key role is played by microglia, which represent the immune effector cells in the central nervous system (CNS). They are extremely sensitive to the environmental changes in the brain and are activated in response to several pathologic events within the CNS, including altered neuronal function, infection, injury, and inflammation. While short-term microglial activity has generally a neuroprotective role, chronic activation has been implicated in the pathogenesis of neurodegenerative disorders, including AD and FTLD. In this framework, the purpose of this review is to give an overview of clinical features, genetics, and novel discoveries on biomolecular pathogenic mechanisms at the basis of these two neurodegenerative diseases and to outline current evidence regarding the role played by activated microglia in their pathogenesis.

Cellular and molecular mediators of neuroinflammation in the pathogenesis of Parkinson's disease

Neuroinflammation is a host-defense mechanism associated with restoration of normal structure and function of the brain and neutralization of an insult. Increasing neuropathological and biochemical evidence from the brains of individuals with Parkinson's disease (PD) provides strong evidence for activation of neuroinflammatory pathways. Microglia, the resident innate immune cells, may play a major role in the inflammatory process of the diseased brain of patients with PD. Although microglia forms the first line of defense for the neural parenchyma, uncontrolled activation of microglia may directly affect neurons by releasing various molecular mediators such as inflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-6, and IL-1β), nitric oxide, prostaglandin E2, and reactive oxygen and nitrogen species. Moreover, recent studies have reported that activated microglia phagocytose not only damaged cell debris but also intact neighboring cells. This phenomenon further supports their active participation in self-enduring neuronal damage cycles. As the relationship between PD and neuroinflammation is being studied, there is a realization that both cellular and molecular mediators are most likely assisting pathological processes leading to disease progression. Here, we discuss mediators of neuroinflammation, which are known activators released from damaged parenchyma of the brain and result in neuronal degeneration in patients with PD.

Younger siblings, C-reactive protein, and risk of age-related macular degeneration

In this study, we examined the relationship between exposure to siblings and 1) the risk of age-related macular degeneration (AMD) and 2) C-reactive protein levels. We retrospectively analyzed pooled cross-sectional data from 2 studies: the Cardiovascular Health and Age-Related Maculopathy Study (2001-2002) and the Age-Related Maculopathy Statin Study (2004-2006). Associations between number of siblings and AMD were assessed by using multinomial logistic regression. Associations between number of siblings and C-reactive protein levels were examined by using a generalized linear model for γ distribution. A higher number of younger siblings was associated with significantly lower odds of early AMD in those with a family history of AMD (odds ratio = 0.2, 95% confidence interval: 0.1, 0.8) (P = 0.022) but was unrelated to AMD for those who had no family history of the disease (odds ratio = 1.0, 95% confidence interval: 0.9, 1.2) (P = 0.874). A higher number of younger siblings correlated with lower C-reactive protein levels (β = -0.19, 95% confidence interval: -0.38, -0.01) (P = 0.036). This supports the theory that immune modulation contributes to AMD pathogenesis and suggests that exposure to younger siblings might be protective when there is a family history of AMD.

The senescence hypothesis of disease progression in Alzheimer disease: an integrated matrix of disease pathways for FAD and SAD

Alzheimer disease (AD) is a progressive, neurodegenerative disease characterised in life by cognitive decline and behavioural symptoms and post-mortem by the neuropathological hallmarks including the microtubule-associated protein tau-reactive tangles and neuritic plaques and amyloid-beta-protein-reactive senile plaques. Greater than 95 % of AD cases are sporadic (SAD) with a late onset and <5 % of AD cases are familial (FAD) with an early onset. FAD is associated with various genetic mutations in the amyloid precursor protein (APP) and the presenilins (PS)1 and PS2. As yet, no disease pathway has been fully accepted and there are no treatments that prevent, stop or reverse the cognitive decline associated with AD. Here, we review and integrate available environmental and genetic evidence associated with all forms of AD. We present the senescence hypothesis of AD progression, suggesting that factors associated with AD can be seen as partial stressors within the matrix of signalling pathways that underlie cell survival and function. Senescence pathways are triggered when stressors exceed the cells ability to compensate for them. The APP proteolytic system has many interactions with pathways involved in programmed senescence and APP proteolysis can both respond to and be driven by senescence-associated signalling. Disease pathways associated with sporadic disease may be different to those involving familial genetic mutations. The interpretation we provide strongly points to senescence as an additional underlying causal process in dementia progression in both SAD and FAD via multiple disease pathways.

The transcriptomic response of mixed neuron-glial cell cultures to 1,25-dihydroxyvitamin d3 includes genes limiting the progression of neurodegenerative diseases

Seasonal or chronic vitamin D deficiency and/or insufficiency is highly prevalent in the human population. Receptors for 1,25-dihydroxyvitamin D3, the hormonal metabolite of vitamin D, are found throughout the brain. To provide further information on the role of this hormone on brain function, we analyzed the transcriptomic profiles of mixed neuron-glial cell cultures in response to 1,25-dihydroxyvitamin D3. 1,25-dihydroxyvitamin D3 treatment increases the mRNA levels of 27 genes by at least 1.9 fold. Among them, 17 genes were related to neurodegenerative and psychiatric diseases, or brain morphogenesis. Notably, 10 of these genes encode proteins potentially limiting the progression of Alzheimer's disease. These data provide support for a role of 1,25-dihydroxyvitamin D3 in brain disease prevention. The possible consequences of circannual or chronic vitamin D insufficiencies on a tissue with a low regenerative potential such as the brain should be considered.

Complement factor C5a and C5a receptor contribute to morphine tolerance and withdrawal-induced hyperalgesia in rats

Morphine is a potent opioid analgesic. However, the repeated use of morphine causes tolerance and hyperalgesia. Neuroinflammation has been reported to be involved in morphine tolerance and withdrawal-induced hyperalgesia. The complement system is a crucial effector mechanism of immune responses. The present study investigated the roles of complement factor C5a and C5a receptor (C5aR) in the development of morphine tolerance and withdrawal-induced hyperalgesia. In the present study, the levels of C5a and C5aR were increased in the L5 lumbar spinal cords of morphine-tolerant rats. The administration of C5a promoted the development of hyperalgesia and the expression of spinal antinociceptive tolerance to intrathecal morphine in both mechanical and thermal test. However, these phenomena caused by morphine were significantly attenuated by the C5aR antagonist PMX53. These results suggest that complement activation within the spinal cord is involved in morphine tolerance and withdrawal-induced hyperalgesia. C5a and C5aR may serve as novel targets for the control of morphine tolerance and withdrawal-induced hyperalgesia.

A review: inflammatory process in Alzheimer's disease, role of cytokines

Alzheimer's disease (AD) is the most common neurodegenerative disorder to date. Neuropathological hallmarks are β-amyloid (Aβ) plaques and neurofibrillary tangles, but the inflammatory process has a fundamental role in the pathogenesis of AD. Inflammatory components related to AD neuroinflammation include brain cells such as microglia and astrocytes, the complement system, as well as cytokines and chemokines. Cytokines play a key role in inflammatory and anti-inflammatory processes in AD. An important factor in the onset of inflammatory process is the overexpression of interleukin (IL)-1, which produces many reactions in a vicious circle that cause dysfunction and neuronal death. Other important cytokines in neuroinflammation are IL-6 and tumor necrosis factor (TNF)-α. By contrast, other cytokines such as IL-1 receptor antagonist (IL-1ra), IL-4, IL-10, and transforming growth factor (TGF)-β can suppress both proinflammatory cytokine production and their action, subsequently protecting the brain. It has been observed in epidemiological studies that treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) decreases the risk for developing AD. Unfortunately, clinical trials of NSAIDs in AD patients have not been very fruitful. Proinflammatory responses may be countered through polyphenols. Supplementation of these natural compounds may provide a new therapeutic line of approach to this brain disorder.

Human Cytokine Response to ex vivo Amyloid-β Stimulation is Mediated by Genetic Factors

Through its ability to induce the enhanced release and production of cytokines, amyloid-β is responsible for the chronic inflammatory response that contributes to Alzheimer's disease (AD). Determining whether the response of monocytes to amyloid-β stimulation is under genetic control may help understand the basis of why some people are more prone to develop neuronal degeneration than others. In the current study we investigated the heritability of the cytokine (IL-10, IL-6, IL-1β, IL-1ra, TNF-[.alpha]) production capacity upon ex vivo stimulation with amyloid-β in whole blood samples of 222 twins and 85 singleton siblings from 139 extended twin families. It was found that individual differences in amyloid-β-induced cytokine production capacity are to a large extent of genetic origin, with heritability estimates ranging from 55% (IL-1β) to 68% (IL-6). We conclude that genes influencing amyloid-β-induced cytokine response may provide clues to the progression of AD pathology.

Microglia function in Alzheimer's disease

Contrary to early views, we now know that systemic inflammatory/immune responses transmit to the brain. The microglia, the resident "macrophages" of the brain's innate immune system, are most responsive, and increasing evidence suggests that they enter a hyper-reactive state in neurodegenerative conditions and aging. As sustained over-production of microglial pro-inflammatory mediators is neurotoxic, this raises great concern that systemic inflammation (that also escalates with aging) exacerbates or possibly triggers, neurological diseases (Alzheimer's, prion, motoneuron disease). It is known that inflammation has an essential role in the progression of Alzheimer's disease (AD), since amyloid-β (Aβ) is able to activate microglia, initiating an inflammatory response, which could have different consequences for neuronal survival. On one hand, microglia may delay the progression of AD by contributing to the clearance of Aβ, since they phagocyte Aβ and release enzymes responsible for Aβ degradation. Microglia also secrete growth factors and anti-inflammatory cytokines, which are neuroprotective. In addition, microglia removal of damaged cells is a very important step in the restoration of the normal brain environment, as if left such cells can become potent inflammatory stimuli, resulting in yet further tissue damage. On the other hand, as we age microglia become steadily less efficient at these processes, tending to become over-activated in response to stimulation and instigating too potent a reaction, which may cause neuronal damage in its own right. Therefore, it is critical to understand the state of activation of microglia in different AD stages to be able to determine the effect of potential anti-inflammatory therapies. We discuss here recent evidence supporting both the beneficial or detrimental performance of microglia in AD, and the attempt to find molecules/biomarkers for early diagnosis or therapeutic interventions.

Plasma biomarkers of brain atrophy in Alzheimer's disease

Peripheral biomarkers of Alzheimer's disease (AD) reflecting early neuropathological change are critical to the development of treatments for this condition. The most widely used indicator of AD pathology in life at present is neuroimaging evidence of brain atrophy. We therefore performed a proteomic analysis of plasma to derive biomarkers associated with brain atrophy in AD. Using gel based proteomics we previously identified seven plasma proteins that were significantly associated with hippocampal volume in a combined cohort of subjects with AD (N = 27) and MCI (N = 17). In the current report, we validated this finding in a large independent cohort of AD (N = 79), MCI (N = 88) and control (N = 95) subjects using alternative complementary methods—quantitative immunoassays for protein concentrations and estimation of pathology by whole brain volume. We confirmed that plasma concentrations of five proteins, together with age and sex, explained more than 35% of variance in whole brain volume in AD patients. These proteins are complement components C3 and C3a, complement factor-I, γ-fibrinogen and alpha-1-microglobulin. Our findings suggest that these plasma proteins are strong predictors of in vivo AD pathology. Moreover, these proteins are involved in complement activation and coagulation, providing further evidence for an intrinsic role of these pathways in AD pathogenesis.

Resilient emotionality and molecular compensation in mice lacking the oligodendrocyte-specific gene Cnp1

Altered oligodendrocyte structure and function is implicated in major psychiatric illnesses, including low cell number and reduced oligodendrocyte-specific gene expression in major depressive disorder (MDD). These features are also observed in the unpredictable chronic mild stress (UCMS) rodent model of the illness, suggesting that they are consequential to environmental precipitants; however, whether oligodendrocyte changes contribute causally to low emotionality is unknown. Focusing on 2'-3'-cyclic nucleotide 3'-phosphodiesterase (Cnp1), a crucial component of axoglial communication dysregulated in the amygdala of MDD subjects and UCMS-exposed mice, we show that altered oligodendrocyte integrity can have an unexpected functional role in affect regulation. Mice lacking Cnp1 (knockout, KO) displayed decreased anxiety- and depressive-like symptoms (i.e., low emotionality) compared with wild-type animals, a phenotypic difference that increased with age (3-9 months). This phenotype was accompanied by increased motor activity, but was evident before neurodegenerative-associated motor coordination deficits (≤ 9-12 months). Notably, Cnp1(KO) mice were less vulnerable to developing a depressive-like syndrome after either UCMS or chronic corticosterone exposure. Cnp1(KO) mice also displayed reduced fear expression during extinction, despite normal amygdala c-Fos induction after acute stress, together implicating dysfunction of an amygdala-related neural network, and consistent with proposed mechanisms for stress resiliency. However, the Cnp1(KO) behavioral phenotype was also accompanied by massive upregulation of oligodendrocyte- and immune-related genes in the basolateral amygdala, suggesting an attempt at functional compensation. Together, we demonstrate that the lack of oligodendrocyte-specific Cnp1 leads to resilient emotionality. However, combined with substantial molecular changes and late-onset neurodegeneration, these results suggest the low Cnp1 seen in MDD may cause unsustainable and maladaptive molecular compensations contributing to the disease pathophysiology.

Age-related macular degeneration: genetic and clinical findings

Age-related macular degeneration (AMD) is a sight threatening eye disease that affects millions of humans over the age of 65 years. It is considered to be the major cause of irreversible blindness in the elderly population in the developed world. The disease is prevalent in Europe and the United States, which has a large number of individuals of European descent. AMD is characterized by a progressive loss of central vision attributable to degenerative and neovascular changes that occur in the interface between the neural retina and the underlying choroid. This location contains the retinal photoreceptors, the retinal pigmented epithelium, a basement membrane complex known as Bruch's membrane and a network of choroidal capillaries. AMD is increasingly recognized as a complex genetic disorder where one or more genes contribute to an individual's susceptibility to development of the condition, while the prevailing view is that the disease stems from the interaction of multiple genetic and environmental factors. Although it has been proposed that a threshold event occurs during normal aging, the sequelae of biochemical, cellular, and molecular events leading to AMD are not fully understood. Here, we review the clinical aspects of AMD and summarize the genes which have been reported to have a positive association with the disease.

Functional variant in complement C3 gene promoter and genetic susceptibility to temporal lobe epilepsy and febrile seizures

Background

Human mesial temporal lobe epilepsies (MTLE) represent the most frequent form of partial epilepsies and are frequently preceded by febrile seizures (FS) in infancy and early childhood. Genetic associations of several complement genes including its central component C3 with disorders of the central nervous system, and the existence of C3 dysregulation in the epilepsies and in the MTLE particularly, make it the C3 gene a good candidate for human MTLE.

Methodology/Principal Findings

A case-control association study of the C3 gene was performed in a first series of 122 patients with MTLE and 196 controls. Four haplotypes (HAP1 to 4) comprising GF100472, a newly discovered dinucleotide repeat polymorphism [(CA)8 to (CA)15] in the C3 promoter region showed significant association after Bonferroni correction, in the subgroup of MTLE patients having a personal history of FS (MTLE-FS+). Replication analysis in independent patients and controls confirmed that the rare HAP4 haplotype comprising the minimal length allele of GF100472 [(CA)8], protected against MTLE-FS+. A fifth haplotype (HAP5) with medium-size (CA)11 allele of GF100472 displayed four times higher frequency in controls than in the first cohort of MTLE-FS+ and showed a protective effect against FS through a high statistical significance in an independent population of 97 pure FS. Consistently, (CA)11 allele by its own protected against pure FS in a second group of 148 FS patients. Reporter gene assays showed that GF100472 significantly influenced C3 promoter activity (the higher the number of repeats, the lower the transcriptional activity). Taken together, the consistent genetic data and the functional analysis presented here indicate that a newly-identified and functional polymorphism in the promoter of the complement C3 gene might participate in the genetic susceptibility to human MTLE with a history of FS, and to pure FS.

Conclusions/Significance

The present study provides important data suggesting for the first time the involvement of the complement system in the genetic susceptibility to epileptic seizures and to epilepsy.

Neuroinflammatory processes in Alzheimer's disease

Generation of neurotoxic amyloid beta peptides and their deposition along with neurofibrillary tangle formation represent key pathological hallmarks in Alzheimer's disease (AD). Recent evidence suggests that inflammation may be a third important component which, once initiated in response to neurodegeneration or dysfunction, may actively contribute to disease progression and chronicity. Various neuroinflammatory mediators including complement activators and inhibitors, chemokines, cytokines, radical oxygen species and inflammatory enzyme systems are expressed and released by microglia, astrocytes and neurons in the AD brain. Degeneration of aminergic brain stem nuclei including the locus ceruleus and the nucleus basalis of Meynert may facilitate the occurrence of inflammation in their projection areas given the antiinflammatory and neuroprotective action of their key transmitters norepinephrine and acetylcholine. While inflammation has been thought to arise secondary to degeneration, recent experiments demonstrated that inflammatory mediators may stimulate amyloid precursor protein processing by various means and therefore can establish a vicious cycle. Despite the fact that some aspects of inflammation may even be protective for bystander neurons, antiinflammatory treatment strategies should therefore be considered. Non-steroidal anti-inflammatory drugs have been shown to reduce the risk and delay the onset to develop AD. While, the precise molecular mechanism underlying this effect is still unknown, a number of possible mechanisms including cyclooxygenase 2 or gamma-secretase inhibition and activation of the peroxisome proliferator activated receptor gamma may alone or, more likely, in concert account for the epidemiologically observed protection.

Microglia and neuroprotection: from in vitro studies to therapeutic applications

Microglia are the main immune cells in the brain, playing a role in both physiological and pathological conditions. Microglial involvement in neurodegenerative diseases is well-established, being microglial activation and neuroinflammation common features of these neuropathologies. Microglial activation has been considered harmful for neurons, but inflammatory state is not only associated with neurotoxic consequences, but also with neuroprotective effects, such as phagocytosis of dead neurons and clearance of debris. This brought to the idea of protective autoimmunity in the brain and to devise immunomodulatory therapies, aimed to specifically increase neuroprotective aspects of microglia. During the last years, several data supported the intrinsic neuroprotective function of microglia through the release of neuroprotective molecules. These data led to change the traditional view of microglia in neurodegenerative diseases: from the idea that these cells play an detrimental role for neurons due to a gain of their inflammatory function, to the proposal of a loss of microglial neuroprotective function as a causing factor in neuropathologies. This "microglial dysfunction hypothesis" points at the importance of understanding the mechanisms of microglial-mediated neuroprotection to develop new therapies for neurodegenerative diseases. In vitro models are very important to clarify the basic mechanisms of microglial-mediated neuroprotection, mainly for the identification of potentially effective neuroprotective molecules, and to design new approaches in a gene therapy set-up. Microglia could act as both a target and a vehicle for CNS gene delivery of neuroprotective factors, endogenously produced by microglia in physiological conditions, thus strengthening the microglial neuroprotective phenotype, even in a pathological situation.

Oxidative stress and the regulation of complement activation in human glaucoma

PURPOSE

As part of ongoing studies on proteomic alterations during glaucomatous neurodegeneration, this study focused on the complement system.

METHODS

Human retinal protein samples obtained from donor eyes with (n = 10) or without (n = 10) glaucoma were analyzed by a quantitative proteomic approach using mass spectrometry. Cellular localization of protein expression for different complement components and regulators were also determined by immunohistochemical analysis of an additional group of human donor eyes with glaucoma (n = 34) compared with age-matched control eyes without glaucoma (n = 20). In addition, to determine the regulation of complement factor H (CFH) by oxidative stress, in vitro experiments were performed using rat retinal cell cultures incubated in the presence and absence of an oxidant treatment.

RESULTS

Proteomic analysis detected the expression and differential regulation of several complement components in glaucomatous samples, which included proteins involved in the classical and the lectin pathways of complement activation. In addition, several complement regulatory proteins were detected in the human retinal proteome, and glaucomatous samples exhibited a trend toward downregulation of CFH expression. In vitro experiments revealed that oxidative stress, which was also prominently detectable in the glaucomatous human retinas, downregulated CFH expression in retinal cells.

CONCLUSIONS

These findings expand the current knowledge of complement activation by presenting new evidence in human glaucoma and support that despite important roles in tissue cleaning and healing, a potential deficiency in intrinsic regulation of complement activation, as is evident in the presence of oxidative stress, may lead to uncontrolled complement attack with neurodestructive consequences.

Expression of complement system components during aging and amyloid deposition in APP transgenic mice

Background

A causal role of the complement system in Alzheimer's disease pathogenesis has been postulated based on the identification of different activated components up to the membrane attack complex at amyloid plaques in brain. However, histological studies of amyloid plaque bearing APP transgenic mice provided only evidence for an activation of the early parts of the complement cascade. To better understand the contribution of normal aging and amyloid deposition to the increase in complement activation we performed a detailed characterization of the expression of the major mouse complement components.

Methods

APP23 mice expressing human APP751 with the Swedish double mutation as well as C57BL/6 mice were used at different ages. mRNA was quantified by Realtime PCR and the age- as well as amyloid induced changes determined. The protein levels of complement C1q and C3 were analysed by Western blotting. Histology was done to test for amyloid plaque association and activation of the complement cascade.

Results

High mRNA levels were detected for C1q and some inhibitory complement components. The expression of most activating components starting at C3 was low. Expression of C1q, C3, C4, C5 and factor B mRNA increased with age in control C57BL/6 mice. C1q and C3 mRNA showed a substantial additional elevation during amyloid formation in APP23 mice. This increase was confirmed on the protein level using Western blotting, whereas immunohistology indicated a recruitment of complement to amyloid plaques up to the C3 convertase.

Conclusion

Early but not late components of the mouse complement system show an age-dependent increase in expression. The response to amyloid deposition is comparatively smaller. The low expression of C3 and C5 and failure to upregulate C5 and downstream components differs from human AD brain and likely contributes to the lack of full complement activation in APP transgenic mice.

Gain in brain immunity in the oldest-old differentiates cognitively normal from demented individuals

Background

Recent findings suggest that Alzheimer's disease (AD) neuropathological features (neuritic plaques and NFTs) are not strongly associated with dementia in extreme old (over 90 years of age) and compel a search for neurobiological indices of dementia in this rapidly growing segment of the elderly population. We sought to characterize transcriptional and protein profiles of dementia in the oldest-old.

Methods and Findings

Gene and protein expression changes relative to non-demented age-matched controls were assessed by two microarray platforms, qPCR and Western blot in different regions of the brains of oldest-old and younger old persons who died at mild or severe stages of dementia. Our results indicate that: i) consistent with recent neuropathological findings, gene expression changes associated with cognitive impairment in oldest-old persons are distinct from those in cognitively impaired youngest-old persons; ii) transcripts affected in young-old subjects with dementia participate in biological pathways related to synaptic function and neurotransmission while transcripts affected in oldest-old subjects with dementia are associated with immune/inflammatory function; iii) upregulation of immune response genes in cognitively intact oldest-old subjects and their subsequent downregulation in dementia suggests a potential protective role of the brain immune-associated system against dementia in the oldest-old; iv) consistent with gene expression profiles, protein expression of several selected genes associated with the inflammatory/immune system in inferior temporal cortex is significantly increased in cognitively intact oldest-old persons relative to cognitively intact young-old persons, but impaired in cognitively compromised oldest-old persons relative to cognitively intact oldest-old controls.

Conclusions

These results suggest that disruption of the robust immune homeostasis that is characteristic of oldest-old individuals who avoided dementia may be directly associated with dementia in the oldest-old and contrast with the synaptic and neurotransmitter system failures that typify dementia in younger old persons.

Clusterin: a forgotten player in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a versatile chaperone molecule which contains several amphipathic and coiled-coil alpha-helices, typical characteristics of small heat shock proteins. In addition, clusterin has three large intrinsic disordered regions, so-called molten globule domains, which can stabilize stressed protein structures. Twenty years ago, it was demonstrated that the expression of clusterin was clearly increased in Alzheimer's disease (AD). Later it was observed that clusterin can bind amyloid-beta peptides and prevent their fibrillization. Clusterin is also involved in the clearance of amyloid-beta peptides and fibrils by binding to megalin receptors and enhancing their endocytosis within glial cells. Clusterin is a complement inhibitor and can suppress complement activation observed in AD. Clusterin is also present in lipoprotein particles and regulates cholesterol and lipid metabolism of brain which is disturbed in AD. Clusterin is a stress-induced chaperone which is normally secreted but in conditions of cellular stress, it can be transported to cytoplasm where it can bind to Bax protein and inhibit neuronal apoptosis. Clusterin can also bind to Smad2/3 proteins and potentiate the neuroprotective TGFbeta signaling. An alternative splicing can produce a variant isoform of clusterin which can be translocated to nuclei where it induces apoptosis. The role of nuclear clusterin in AD needs to be elucidated. We will review here the extensive literature linking clusterin to AD and examine the recent progress in clusterin research with the respect to AD pathology. Though clusterin can be viewed as a multipotent guardian of brain, it is unable to prevent the progressive neuropathology in chronic AD.

Para-inflammation in the aging retina

Para-inflammation is a tissue adaptive response to noxious stress or malfunction and has characteristics that are intermediate between basal and inflammatory states (Medzhitov, 2008). The physiological purpose of para-inflammation is to restore tissue functionality and homeostasis. Para-inflammation may become chronic or turn into inflammation if tissue stress or malfunction persists for a sustained period. Chronic para-inflammation contributes to the initiation and progression of many human diseases including obesity, type 2 diabetes, atherosclerosis, and age-related neurodegenerative diseases. Evidence from our studies and the studies of some others suggests that para-inflammation also exists in the aging retina in physiological conditions and might contribute to age-related retinal pathologies. The purpose of this review is to introduce the notion of "para-inflammation" as a state between frank, overt destructive inflammation and the non-inflammatory removal of dead or dying cells by apoptosis, to the retinal community. In diabetes and atherosclerosis, leukocytes particularly monocytes and vascular endothelial cells are constantly under noxious stress due to glycaemic and/or lipidaemic dysregulation. These blood-borne stresses trigger para-inflammatory responses in leukocytes and endothelial cells by up-regulating the expression of adhesion molecules or releasing cytokines/chemokines, which in turn cause abnormal leukocyte-endothelial interactions and ultimately vascular damage. In the aging retina, on the other hand, oxidized lipoproteins and free radicals are considered to be major causes of tissue stress and serve as local triggers for retinal para-inflammation. Microarray analysis has revealed the up-regulation of a large number of inflammatory genes, including genes involved in complement activation and inflammatory cytokine/chemokine production, in the aging retina. Para-inflammatory responses in the neuroretina of aged mice are characterized by microglial activation and subretinal migration, and breakdown of blood-retinal barrier. At the retinal/choroidal interface para-inflammation is manifested by complement activation in Bruch's membrane and RPE cells, and microglia accumulation in subretinal space. With age, para-inflammatory changes have also been observed in the choroidal tissue, evidenced by 1) increased thickness of choroid; 2) increased number of CD45(+)CRIg(+) macrophages; 3) morphological abnormalities in choroidal melanocytes; and 4) fibrosis in choroidal tissue. An increased knowledge of contribution of retinal para-inflammation to various pathological conditions is essential for the better understanding of the pathogenesis of various age-related retinal diseases including diabetic retinopathy, glaucoma and age-related macular degeneration.