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Journal of Autoimmunity May 2023Genetic deficiencies of early components of the classical complement activation pathway (especially C1q, r, s, and C4) are the strongest monogenic causal factors for the... (Review)
Review
Genetic deficiencies of early components of the classical complement activation pathway (especially C1q, r, s, and C4) are the strongest monogenic causal factors for the prototypic autoimmune disease systemic lupus erythematosus (SLE), but their prevalence is extremely rare. In contrast, isotype genetic deficiency of C4A and acquired deficiency of C1q by autoantibodies are frequent among patients with SLE. Here we review the genetic basis of complement deficiencies in autoimmune disease, discuss the complex genetic diversity seen in complement C4 and its association with autoimmune disease, provide guidance as to when clinicians should suspect and test for complement deficiencies, and outline the current understanding of the mechanisms relating complement deficiencies to autoimmunity. We focus primarily on SLE, as the role of complement in SLE is well-established, but will also discuss other informative diseases such as inflammatory arthritis and myositis.
Topics: Humans; Complement C1q; Autoimmune Diseases; Complement System Proteins; Lupus Erythematosus, Systemic; Hereditary Complement Deficiency Diseases; Complement C4; Complement C4a
PubMed: 36535812
DOI: 10.1016/j.jaut.2022.102979 -
Nature Feb 2016Schizophrenia is a heritable brain illness with unknown pathogenic mechanisms. Schizophrenia's strongest genetic association at a population level involves variation in...
Schizophrenia is a heritable brain illness with unknown pathogenic mechanisms. Schizophrenia's strongest genetic association at a population level involves variation in the major histocompatibility complex (MHC) locus, but the genes and molecular mechanisms accounting for this have been challenging to identify. Here we show that this association arises in part from many structurally diverse alleles of the complement component 4 (C4) genes. We found that these alleles generated widely varying levels of C4A and C4B expression in the brain, with each common C4 allele associating with schizophrenia in proportion to its tendency to generate greater expression of C4A. Human C4 protein localized to neuronal synapses, dendrites, axons, and cell bodies. In mice, C4 mediated synapse elimination during postnatal development. These results implicate excessive complement activity in the development of schizophrenia and may help explain the reduced numbers of synapses in the brains of individuals with schizophrenia.
Topics: Alleles; Amino Acid Sequence; Animals; Axons; Base Sequence; Brain; Complement C4; Complement Pathway, Classical; Dendrites; Gene Dosage; Gene Expression Regulation; Genetic Predisposition to Disease; Genetic Variation; Haplotypes; Humans; Major Histocompatibility Complex; Mice; Models, Animal; Neuronal Plasticity; Polymorphism, Single Nucleotide; RNA, Messenger; Risk Factors; Schizophrenia; Synapses
PubMed: 26814963
DOI: 10.1038/nature16549 -
Nature Neuroscience Feb 2021The complement component 4 (C4) gene is linked to schizophrenia and synaptic refinement. In humans, greater expression of C4A in the brain is associated with an...
The complement component 4 (C4) gene is linked to schizophrenia and synaptic refinement. In humans, greater expression of C4A in the brain is associated with an increased risk of schizophrenia. To investigate this genetic finding and address how C4A shapes brain circuits in vivo, here, we generated a mouse model with primate-lineage-specific isoforms of C4, human C4A and/or C4B. Human C4A bound synapses more efficiently than C4B. C4A (but not C4B) rescued the visual system synaptic refinement deficits of C4 knockout mice. Intriguingly, mice without C4 had normal numbers of cortical synapses, which suggests that complement is not required for normal developmental synaptic pruning. However, overexpressing C4A in mice reduced cortical synapse density, increased microglial engulfment of synapses and altered mouse behavior. These results suggest that increased C4A-mediated synaptic elimination results in abnormal brain circuits and behavior. Understanding pathological overpruning mechanisms has important therapeutic implications in disease conditions such as schizophrenia.
Topics: Animals; Behavior, Animal; Complement C4; Dendritic Spines; Depression; Female; Gene Dosage; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Microglia; Nerve Net; Psychomotor Performance; Schizophrenia; Schizophrenic Psychology; Synapses; Synaptosomes
PubMed: 33353966
DOI: 10.1038/s41593-020-00763-8 -
Frontiers in Immunology 2021Complement C4, a key molecule in the complement system that is one of chief constituents of innate immunity for immediate recognition and elimination of invading... (Review)
Review
Complement C4, a key molecule in the complement system that is one of chief constituents of innate immunity for immediate recognition and elimination of invading microbes, plays an essential role for the functions of both classical (CP) and lectin (LP) complement pathways. Complement C4 is the most polymorphic protein in complement system. A plethora of research data demonstrated that individuals with C4 deficiency are prone to microbial infections and autoimmune disorders. In this review, we will discuss the diversity of complement C4 proteins and its genetic structures. In addition, the current development of the regulation of complement C4 activation and its activation derivatives will be reviewed. Moreover, the review will provide the updates on the molecule interactions of complement C4 under the circumstances of bacterial and viral infections, as well as autoimmune diseases. Lastly, more evidence will be presented to support the paradigm that links microbial infections and autoimmune disorders under the condition of the deficiency of complement C4. We provide such an updated overview that would shed light on current research of complement C4. The newly identified targets of molecular interaction will not only lead to novel hypotheses on the study of complement C4 but also assist to propose new strategies for targeting microbial infections, as well as autoimmune disorders.
Topics: Animals; Autoimmune Diseases; Autoimmunity; Communicable Diseases; Complement Activation; Complement C4; Host-Pathogen Interactions; Humans; Signal Transduction
PubMed: 34335607
DOI: 10.3389/fimmu.2021.694928 -
Frontiers in Immunology 2022Graves' ophthalmopathy (GO), the most frequent extrathyroidal manifestation of Graves' disease (GD), can lead to a significant decline in the quality of life in...
Graves' ophthalmopathy (GO), the most frequent extrathyroidal manifestation of Graves' disease (GD), can lead to a significant decline in the quality of life in patients. Exosomes, which contain proteins, lipids and DNA, play important roles in the pathological processes of various diseases. However, their roles in Graves' ophthalmopathy are still unclear. We aimed to isolate exosomes and analyze the different exosomal proteins. Tear fluids were collected from twenty-four GO patients, twenty-four GD patients and sixteen control subjects. The numbers of tear exosomes were assayed using nanoparticle tracking analysis. A Luminex 200 kit and ELISA kit were used to confirm the different cytokine concentrations in serum. Extraocular muscle from GO patients and controls was extracted, and western blotting was used to assay the levels of Caspase-3 and complement C4A. Our study demonstrated that the number of tear exosomes differ from GD patients and control. The expression levels of cytokines, including IL-1 and IL-18, were significantly increased in the tear exosomes and serum from GO patients compared with GD patients and controls. The levels of the exosomal proteins Caspase-3, complement C4A and APOA-IV were significantly increased in GO patients compared to GD patients and controls. Orbital fibroblasts from GO patients showed significantly higher levels of Caspase-3 and complement C4A than those from controls. The levels of serum APOA-IV in GO patients were significantly higher than those in GD patients and controls. Specific proteins showed elevated expression in tear exosomes from GO patients, indicating that they may play important roles in GO pathogenesis.
Topics: Humans; Biomarkers; Caspase 3; Complement C4a; Cytokines; Graves Ophthalmopathy; Quality of Life; Tears; Exosomes
PubMed: 36561758
DOI: 10.3389/fimmu.2022.1088606 -
Clinical Journal of the American... Nov 2021Membranoproliferative GN and C3 glomerulopathy are rare and overlapping disorders associated with dysregulation of the alternative complement pathway. Specific etiologic... (Observational Study)
Observational Study
BACKGROUND AND OBJECTIVES
Membranoproliferative GN and C3 glomerulopathy are rare and overlapping disorders associated with dysregulation of the alternative complement pathway. Specific etiologic data for pediatric membranoproliferative GN/C3 glomerulopathy are lacking, and outcome data are based on retrospective studies without etiologic data.
DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS
A total of 80 prevalent pediatric patients with membranoproliferative GN/C3 glomerulopathy underwent detailed phenotyping and long-term follow-up within the National Registry of Rare Kidney Diseases (RaDaR). Risk factors for kidney survival were determined using a Cox proportional hazards model. Kidney and transplant graft survival was determined using the Kaplan-Meier method.
RESULTS
Central histology review determined 39 patients with C3 glomerulopathy, 31 with immune-complex membranoproliferative GN, and ten with immune-complex GN. Patients were aged 2-15 (median, 9; interquartile range, 7-11) years. Median complement C3 and C4 levels were 0.31 g/L and 0.14 g/L, respectively; acquired (anticomplement autoantibodies) or genetic alternative pathway abnormalities were detected in 46% and 9% of patients, respectively, across all groups, including those with immune-complex GN. Median follow-up was 5.18 (interquartile range, 2.13-8.08) years. Eleven patients (14%) progressed to kidney failure, with nine transplants performed in eight patients, two of which failed due to recurrent disease. Presence of >50% crescents on the initial biopsy specimen was the sole variable associated with kidney failure in multivariable analysis (hazard ratio, 6.2; 95% confidence interval, 1.05 to 36.6; 0.05). Three distinct C3 glomerulopathy prognostic groups were identified according to presenting eGFR and >50% crescents on the initial biopsy specimen.
CONCLUSIONS
Crescentic disease was a key risk factor associated with kidney failure in a national cohort of pediatric patients with membranoproliferative GN/C3 glomerulopathy and immune-complex GN. Presenting eGFR and crescentic disease help define prognostic groups in pediatric C3 glomerulopathy. Acquired abnormalities of the alternative pathway were commonly identified but not a risk factor for kidney failure.
Topics: Adolescent; Autoantibodies; Child; Child, Preschool; Complement C3; Complement C3b; Complement C4; Complement Factor B; Complement Factor H; Disease Progression; Female; Follow-Up Studies; Glomerular Filtration Rate; Glomerulonephritis, Membranoproliferative; Graft Survival; Humans; Kaplan-Meier Estimate; Kidney Failure, Chronic; Kidney Transplantation; Male; Phenotype; Prognosis; Proportional Hazards Models; Prospective Studies; Recurrence; Registries; Risk Factors
PubMed: 34551983
DOI: 10.2215/CJN.00320121 -
Developmental Neuroscience 2023Complex brain disorders like schizophrenia may have multifactorial origins related to mis-timed heritable and environmental factors interacting during neurodevelopment....
Complex brain disorders like schizophrenia may have multifactorial origins related to mis-timed heritable and environmental factors interacting during neurodevelopment. Infections, inflammation, and autoimmune diseases are over-represented in schizophrenia leading to immune system-centered hypotheses. Complement component C4 is genetically and neurobiologically associated with schizophrenia, and its dual activity peripherally and in the brain makes it an exceptional target for biomarker development. Studies to evaluate the biomarker potential of plasma or serum C4 in schizophrenia do so to understand how peripheral C4 might reflect central nervous system-derived neuroinflammation, synapse pruning, and other mechanisms. This effort, however, has produced mostly conflicting results, with peripheral C4 sometimes elevated, reduced, or unchanged between comparison groups. We undertook a pilot biomarker development study to systematically identify sociodemographic, genetic, and immune-related variables (autoimmune, infection-related, gastrointestinal, inflammatory), which may be associated with plasma C4 levels in schizophrenia (SCH; n = 335) and/or in nonpsychiatric comparison subjects (NCs; n = 233). As with previously inconclusive studies, we detected no differences in plasma C4 levels between SCH and NCs. In contrast, levels of general inflammation, C-reactive protein (CRP), were significantly elevated in SCH compared to NCs (ANOVA, F = 20.74, p < 0.0001), suggestive that plasma C4 and CRP may reflect different sources or causes of inflammation. In multivariate regressions of C4 gene copy number variants, plasma C4 levels were correlated only for C4A (not C4B, C4L, C4S) and only in NCs (R Coeff = 0.39, CI = 0.01-0.77, R2 = 0.18, p < 0.01; not SCH). Other variables associated with plasma C4 levels only in NCs included sex, double-stranded DNA IgG, tissue-transglutaminase (TTG) IgG, and cytomegalovirus IgG. Toxoplasma gondii IgG was the only variable significantly correlated with plasma C4 in SCH but not in NCs. Many variables were associated with plasma C4 in both groups (body mass index, race, CRP, N-methyl-D-aspartate receptor (NMDAR) NR2 subunit IgG, TTG IgA, lipopolysaccharide-binding protein (LBP), and soluble CD14 (sCD14). While the direction of most C4 associations was positive, autoimmune markers tended to be inverse, and associated with reduced plasma C4 levels. When NMDAR-NR2 autoantibody-positive individuals were removed, plasma C4 was elevated in SCH versus NCs (ANOVA, F = 5.16, p < 0.02). Our study was exploratory and confirmation of the many variables associated with peripheral C4 requires replication. Our preliminary results point toward autoimmune factors and exposure to the pathogen, T. gondii, as possibly significant contributors to variability of total C4 protein levels in plasma of individuals with schizophrenia.
Topics: Humans; Complement C4; Schizophrenia; Inflammation; Biomarkers; Immunoglobulin G
PubMed: 37734326
DOI: 10.1159/000534185 -
Nature Jun 2020Many common illnesses, for reasons that have not been identified, differentially affect men and women. For instance, the autoimmune diseases systemic lupus erythematosus...
Many common illnesses, for reasons that have not been identified, differentially affect men and women. For instance, the autoimmune diseases systemic lupus erythematosus (SLE) and Sjögren's syndrome affect nine times more women than men, whereas schizophrenia affects men with greater frequency and severity relative to women. All three illnesses have their strongest common genetic associations in the major histocompatibility complex (MHC) locus, an association that in SLE and Sjögren's syndrome has long been thought to arise from alleles of the human leukocyte antigen (HLA) genes at that locus. Here we show that variation of the complement component 4 (C4) genes C4A and C4B, which are also at the MHC locus and have been linked to increased risk for schizophrenia, generates 7-fold variation in risk for SLE and 16-fold variation in risk for Sjögren's syndrome among individuals with common C4 genotypes, with C4A protecting more strongly than C4B in both illnesses. The same alleles that increase risk for schizophrenia greatly reduce risk for SLE and Sjögren's syndrome. In all three illnesses, C4 alleles act more strongly in men than in women: common combinations of C4A and C4B generated 14-fold variation in risk for SLE, 31-fold variation in risk for Sjögren's syndrome, and 1.7-fold variation in schizophrenia risk among men (versus 6-fold, 15-fold and 1.26-fold variation in risk among women, respectively). At a protein level, both C4 and its effector C3 were present at higher levels in cerebrospinal fluid and plasma in men than in women among adults aged between 20 and 50 years, corresponding to the ages of differential disease vulnerability. Sex differences in complement protein levels may help to explain the more potent effects of C4 alleles in men, women's greater risk of SLE and Sjögren's syndrome and men's greater vulnerability to schizophrenia. These results implicate the complement system as a source of sexual dimorphism in vulnerability to diverse illnesses.
Topics: Adult; Alleles; Complement C3; Complement C4; Female; Genetic Predisposition to Disease; HLA Antigens; Haplotypes; Humans; Lupus Erythematosus, Systemic; Major Histocompatibility Complex; Male; Middle Aged; Sex Characteristics; Sjogren's Syndrome; Young Adult
PubMed: 32499649
DOI: 10.1038/s41586-020-2277-x -
Scientific Reports May 2023Triple-negative breast cancer (TNBC) subtype is characterized by aggressive clinical behavior and poor prognosis patient outcomes. Here, we show that ADAR1 is more...
Triple-negative breast cancer (TNBC) subtype is characterized by aggressive clinical behavior and poor prognosis patient outcomes. Here, we show that ADAR1 is more abundantly expressed in infiltrating breast cancer (BC) tumors than in benign tumors. Further, ADAR1 protein expression is higher in aggressive BC cells (MDA-MB-231). Moreover, we identify a novel interacting partners proteins list with ADAR1 in MDA-MB-231, using immunoprecipitation assay and mass spectrometry. Using iLoop, a protein-protein interaction prediction server based on structural features, five proteins with high iloop scores were discovered: Histone H2A.V, Kynureninase (KYNU), 40S ribosomal protein SA, Complement C4-A, and Nebulin (ranged between 0.6 and 0.8). In silico analysis showed that invasive ductal carcinomas had the highest level of KYNU gene expression than the other classifications (p < 0.0001). Moreover, KYNU mRNA expression was shown to be considerably higher in TNBC patients (p < 0.0001) and associated with poor patient outcomes with a high-risk value. Importantly, we found an interaction between ADAR1 and KYNU in the more aggressive BC cells. Altogether, these results propose a new ADAR-KYNU interaction as potential therapeutic targeted therapy in aggressive BC.
Topics: Humans; Aggression; Breast; Complement C4; Histones; Triple Negative Breast Neoplasms; Adenosine Deaminase; RNA-Binding Proteins
PubMed: 37221310
DOI: 10.1038/s41598-023-35517-6 -
American Journal of Nephrology 2019Complement activation occurs in many glomerular diseases, the exact pathway(s) of activation has been studied in detail in some diseases but not in all. C4d is generated... (Review)
Review
Complement activation occurs in many glomerular diseases, the exact pathway(s) of activation has been studied in detail in some diseases but not in all. C4d is generated by the activation of classical and lectin pathways, and its presence can point to the activation of either of these pathways. This review aims to summarize the available data with regard to the deposition of glomerular C4d in native kidney biopsies in different glomerular pathologies that may be useful for future research into the role of complement activation in glomerular diseases. While there is more information on C4d in certain diseases (e.g., Immunoglobulin A (IgA) nephropathy), there is scant data in other diseases (such as focal segmental glomerulosclerosis).
Topics: Animals; Complement C4b; Complement Pathway, Classical; Complement Pathway, Mannose-Binding Lectin; Disease Models, Animal; Glomerulonephritis, IGA; Glomerulosclerosis, Focal Segmental; Humans; Kidney Glomerulus; Peptide Fragments
PubMed: 30612132
DOI: 10.1159/000496059