Reconstitution of the complement function in C1q-deficient (C1qa-/-) mice with wild-type bone marrow cells

Determining M2 macrophages content for the anti-tumor effects of metal-organic framework-encapsulated pazopanib nanoparticles in breast cancer

Pazopanib (PAZ), an oral multi-tyrosine kinase inhibitor, demonstrates promising cytostatic activities against various human cancers. However, its clinical utility is limited by substantial side effects and therapeutic resistance. We developed a nanoplatform capable of delivering PAZ for enhanced anti-breast cancer therapy. Nanometer-sized PAZ@Fe-MOF, compared to free PAZ, demonstrated increased anti-tumor therapeutic activities in both syngeneic murine 4T1 and xenograft human MDA-MB-231 breast cancer models. High-throughput single-cell RNA sequencing (scRNAseq) revealed that PAZ@Fe-MOF significantly reduced pro-tumorigenic M2-like macrophage populations at tumor sites and suppressed M2-type signaling pathways, such as ATF6-TGFBR1-SMAD3, as well as chemokines including CCL17, CCL22, and CCL24. PAZ@Fe-MOF reprogramed the inhibitory immune microenvironment and curbed tumorigenicity by blocking the polarization of M2 phenotype macrophages. This platform offers a promising and new strategy for improving the cytotoxicity of PAZ against breast cancers. It provides a method to evaluate the immunological response of tumor cells to PAZ-mediated treatment.

Monogenic lupus: Tracing the therapeutic implications from single gene mutations

Monogenic lupus, a distinctive variant of systemic lupus erythematosus (SLE), is characterized by early onset, family-centric clustering, and heightened disease severity. So far, over thirty genetic variations have been identified as single-gene etiology of SLE and lupus-like phenotypes. The critical role of these gene mutations in disrupting various immune pathways is increasingly recognized. In particular, single gene mutation-driven dysfunction within the innate immunity, notably deficiencies in the complement system, impedes the degradation of free nucleic acid and immune complexes, thereby promoting activation of innate immune cells. The accumulation of these components in various tissues and organs creates a pro-inflammatory microenvironment, characterized by a surge in pro-inflammatory cytokines, chemokines, reactive oxygen species, and type I interferons. Concurrently, single gene mutation-associated defects in the adaptive immune system give rise to the emergence of autoreactive T cells, hyperactivated B cells and plasma cells. The ensuing spectrum of cytokines and autoimmune antibodies drives systemic disease manifestations, primarily including kidney, skin and central nervous system-related phenotypes. This review provides a thorough overview of the single gene mutations and potential consequent immune dysregulations in monogenic lupus, elucidating the pathogenic mechanisms of monogenic lupus. Furthermore, it discusses the recent advances made in the therapeutic interventions for monogenic lupus.

Identification of circulating monocytes as producers of tuberculosis disease biomarker C1q

Tuberculosis (TB) is a prevalent disease causing an estimated 1.6 million deaths and 10.6 million new cases annually. Discriminating TB disease from differential diagnoses can be complex, particularly in the field. Increased levels of complement component C1q in serum have been identified as a specific and accessible biomarker for TB disease but the source of C1q in circulation has not been identified. Here, data and samples previously collected from human cohorts, a clinical trial and a non-human primate study were used to identify cells producing C1q in circulation. Cell subset frequencies were correlated with serum C1q levels and combined with single cell RNA sequencing and flow cytometry analyses. This identified monocytes as C1q producers in circulation, with a pronounced expression of C1q in classical and intermediate monocytes and variable expression in non-classical monocytes.

The complement system and human autoimmune diseases

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.

Immune infiltration associated C1q acts as a novel prognostic biomarker of cutaneous melanoma

C1q (complement C1q A chain, complement C1q B chain, and complement C1q C chain) is a recognized component of the classical complement pathway that influences the prognosis of various cancers. However, the effects of C1q on cutaneous melanoma (SKCM) outcomes and immune infiltration remain unknown. Gene expression profiling interactive analysis 2 and the human protein atlas were used to evaluate differential expression of C1q mRNA and protein. The relationship between C1q expression and clinicopathological features was also examined. The genetic alterations of C1q and their impact on survival were analyzed using the cbioportal database. The Kaplan-Meier approach was used to assess the significance of C1q in individuals with SKCM. The cluster profiler R package and the cancer single-cell state atlas database were used to investigate the function and mechanism of C1q in SKCM. The relationship between C1q and immune cell infiltration was estimated using single-sample gene set enrichment analysis. C1q expression was increased, and predicted a favorable prognosis. High C1q expression correlated with clinicopathological T stage, pathological stage, overall survival, and disease specific survival events. Moreover, C1q genetic alterations range from 2.7% to 4%, with no impact on prognosis. According to the enrichment analysis, C1q and immune-related pathways were closely connected. The link between complement C1q B chain and the functional state of inflammation was determined using the cancer single-cell state atlas database. In particular, C1q expression was significantly associated with infiltration of most immune cells and checkpoints PDCD1, CD274, and HAVCR2. The results of this study suggest that C1q is associated with prognosis and immune cell infiltration, supporting its value as a diagnostic and prognostic biomarker.

Resolution therapy: Harnessing efferocytic macrophages to trigger the resolution of inflammation

Several chronic inflammatory diseases are associated with non-resolving inflammation. Conventional anti-inflammatory drugs fail to completely cure these diseases. Resolution pharmacology is a new therapeutic approach based on the use of pro-resolving mediators that accelerate the resolution phase of inflammation by targeting the productive phase of inflammation. Indeed, pro-resolving mediators prevent leukocyte recruitment and induce apoptosis of accumulated leukocytes. This approach is now called resolution therapy with the introduction of complex biological drugs and cell-based therapies. The main objective of resolution therapy is to specifically reduce the duration of the resolution phase to accelerate the return to homeostasis. Under physiological conditions, macrophages play a critical role in the resolution of inflammation. Indeed, after the removal of apoptotic cells (a process called efferocytosis), macrophages display anti-inflammatory reprogramming and subsequently secrete multiple pro-resolving factors. These factors can be used as resolution therapy. Here, we review the different mechanisms leading to anti-inflammatory reprogramming of macrophages after efferocytosis and the pro-resolving factors released by these efferocytic macrophages. We classify these mechanisms in three different categories: macrophage reprogramming induced by apoptotic cell-derived factors, by molecules expressed by apoptotic cells (i.e., "eat-me" signals), and induced by the digestion of apoptotic cell-derived materials. We also evoke that macrophage reprogramming may result from cooperative mechanisms, for instance, implicating the apoptotic cell-induced microenvironment (including cellular metabolites, specific cytokines or immune cells). Then, we describe a new drug candidate belonging to this resolution therapy. This candidate, called SuperMApo, corresponds to the secretome of efferocytic macrophages. We discuss its production, the pro-resolving factors present in this drug, as well as the results obtained in experimental models of chronic (e.g., arthritis, colitis) and acute (e.g., peritonitis or xenogeneic graft-versus-host disease) inflammatory diseases.

RAGE pathway activation and function in chronic kidney disease and COVID-19

The multi-ligand receptor for advanced glycation end-products (RAGE) and its ligands are contributing factors in autoimmunity, cancers, and infectious disease. RAGE activation is increased in chronic kidney disease (CKD) and coronavirus disease 2019 (COVID-19). CKD may increase the risk of COVID-19 severity and may also develop in the form of long COVID. RAGE is expressed in essentially all kidney cell types. Increased production of RAGE isoforms and RAGE ligands during CKD and COVID-19 promotes RAGE activity. The downstream effects include cellular dysfunction, tissue injury, fibrosis, and inflammation, which in turn contribute to a decline in kidney function, hypertension, thrombotic disorders, and cognitive impairment. In this review, we discuss the forms and mechanisms of RAGE and RAGE ligands in the kidney and COVID-19. Because various small molecules antagonize RAGE activity in animal models, targeting RAGE, its co-receptors, or its ligands may offer novel therapeutic approaches to slowing or halting progressive kidney disease, for which current therapies are often inadequate.

C1q as a target molecule to treat human disease: What do mouse studies teach us?

The complement system is a field of growing interest for pharmacological intervention. Complement protein C1q, the pattern recognition molecule at the start of the classical pathway of the complement cascade, is a versatile molecule with additional non-canonical actions affecting numerous cellular processes. Based on observations made in patients with hereditary C1q deficiency, C1q is protective against systemic autoimmunity and bacterial infections. Accordingly, C1q deficient mice reproduce this phenotype with susceptibility to autoimmunity and infections. At the same time, beneficial effects of C1q deficiency on disease entities such as neurodegenerative diseases have also been described in murine disease models. This systematic review provides an overview of all currently available literature on the C1q knockout mouse in disease models to identify potential target diseases for treatment strategies focusing on C1q, and discusses potential side-effects when depleting and/or inhibiting C1q.

Identification and Validation of Candidate Gene Module Along With Immune Cells Infiltration Patterns in Atherosclerosis Progression to Plaque Rupture via Transcriptome Analysis

Objective

To explore the differentially expressed genes (DEGs) along with infiltrating immune cells landscape and their potential mechanisms in the progression of atherosclerosis from onset to plaque rupture.

Methods

In this study, three atherosclerosis-related microarray datasets were downloaded from the NCBI-GEO database. The gene set enrichment analysis (GSEA) was performed for interpreting the biological insights of gene expression data. The CIBERSORTx algorithm was applied to infer the relative proportions of infiltrating immune cells of the atherosclerotic samples. DEGs of the datasets were screened using R. The protein interaction network was constructed via STRING. The cluster genes were analyzed by the Cytoscape software. Gene ontology (GO) enrichment was performed via geneontology.org. The least absolute shrinkage and selection operator (LASSO) logistic regression algorithm and receiver operating characteristics (ROC) analyses were performed to build machine learning models for differentiating atherosclerosis status. The Pearson correlation analysis was carried out to illustrate the relationship between cluster genes and immune cells. The expression levels of the cluster genes were validated in two external cohorts. Transcriptional factors and drug-gene interaction analysis were performed to investigate the promising targets for atherosclerosis intervention.

Results

Pathways related to immunoinflammatory responses were identified according to GSEA analysis, and the detailed fractions infiltrating immune cells were compared between the early and advanced atherosclerosis. Additionally, we identified 170 DEGs in atherosclerosis progression (|log2FC|≥1 and adjusted p < 0.05). They were mainly enriched in GO terms relating to inflammatory response and innate immune response. A cluster of nine genes, such as ITGB2, C1QC, LY86, CTSS, C1QA, CSF1R, LAPTM5, VSIG4, and CD163, were found to be significant, and their correlations with infiltrating immune cells were calculated. The cluster genes were also validated to be upregulated in two external cohorts. Moreover, C1QA and ITGB2 may exert pathogenic functions in the entire process of atherogenesis.

Conclusions

We reanalyzed the transcriptomic signature of atherosclerosis development from onset to plaque rupture along with the landscape of the immune cell, as well as revealed new insights and specific prospective DEGs for the investigation of disease-associated dynamic molecular processes and their regulations with immune cells.

Human C1q Regulates Influenza A Virus Infection and Inflammatory Response via Its Globular Domain

The Influenza A virus (IAV) is a severe respiratory pathogen. C1q is the first subcomponent of the complement system’s classical pathway. C1q is composed of 18 polypeptide chains. Each of these chains contains a collagen-like region located at the N terminus, and a C-terminal globular head region organized as a heterotrimeric structure (ghA, ghB and ghC). This study was aimed at investigating the complement activation-independent modulation by C1q and its individual recombinant globular heads against IAV infection. The interaction of C1q and its recombinant globular heads with IAV and its purified glycoproteins was examined using direct ELISA and far-Western blotting analysis. The effect of the complement proteins on IAV replication kinetics and immune modulation was assessed by qPCR. The IAV entry inhibitory properties of C1q and its recombinant globular heads were confirmed using cell binding and luciferase reporter assays. C1q bound IAV virions via HA, NA and M1 IAV proteins, and suppressed replication in H1N1, while promoting replication in H3N2-infected A549 cells. C1q treatment further triggered an anti-inflammatory response in H1N1 and pro-inflammatory response in H3N2-infected cells as evident from differential expression of TNF-α, NF-κB, IFN-α, IFN-β, IL-6, IL-12 and RANTES. Furthermore, C1q treatment was found to reduce luciferase reporter activity of MDCK cells transfected with H1N1 pseudotyped lentiviral particles, indicative of an entry inhibitory role of C1q against infectivity of IAV. These data appear to demonstrate the complement-independent subtype specific modulation of IAV infection by locally produced C1q.

High complement protein C1q levels in pulmonary fibrosis and non-small cell lung cancer associated with poor prognosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is the most common type of interstitial pneumonia. Lung cancer, mainly non-small cell lung cancer (NSCLC), is a complication of idiopathic pulmonary fibrosis. IPF is also an independent risk factor of lung cancer. Some studies have shown that the complement system can promote the progression of interstitial pulmonary fibrosis. In addition, C1q has also demonstrated to exert a tumor-promoting effect in many tumors. However, the role of C1q in idiopathic pulmonary fibrosis and lung cancer still remain unclear.

METHODS

We selected common differentially expressed genes in IPF and non-small cell lung cancer using datasets from GEO, and investigated common hub gene. The hub genes were validated in IPF by establishing mouse model of IPF and using another four datasets from the GEO. Multiple databases were analyzed including those of Kaplan-Meier Plotter, Tumor Immune Estimation Resource (TIMER2.0) and the Human Protein Atlas (HPA) for NSCLC.

RESULTS

In this study, 37 common DEGs were identified in IPF and NSCLC including 32 up-regulated genes and 5 down-regulated genes, and C1q was identified as common hub gene. The methylation status of C1q decreased and the expression levels of C1q increased in both lung cancer and idiopathic pulmonary fibrosis. The prognosis of non-small cell lung cancer and IPF patients with high levels of C1q is poor.

CONCLUSIONS

These results show that C1q participates in pulmonary fibrosis and non-small cell lung cancer, and may be a potential diagnostic / prognostic biomarker or a therapeutic target.

C1q inhibits differentiation of oligodendrocyte progenitor cells via Wnt/β-catenin signaling activation in a cuprizone-induced mouse model of multiple sclerosis

Multiple sclerosis (MS) is a chronic central nervous system demyelinating disease of autoimmune originate. Complement C1q, a complex glycoprotein, mediates a variety of immunoregulatory functions considered important in the prevention of autoimmunity. Although we found that the increased serum C1q level was highly associated with the Fazekas scores and T2 lesion volume of MS patients, the effect and mechanism of C1q on demyelination remains unclear. Cluster analysis and protein array results showed that serum Wnt receptors Frizzled-6 and LRP-6 levels in MS patients were both increased, we proposed that C1q may be involved in demyelination via Wnt signaling. The increased C1q protein levels in the serum and brain tissue were confirmed in a cuprizone (CPZ)-induced demyelination mice model. Moreover, CPZ treatment induced significant increase of LRP-6 and Frizzled-6 protein in mice corpus callosum. LRP-6 extra-cellular domain (LRP-6-ECD) level in the serum and cerebrospinal fluid (CSF) of CPZ mice also significantly increased. Knockdown of the subunit C1s of C1 not only substantially attenuated demyelination, promoted M2 microglia polarization and improved neurological function, but inhibited β-catenin expression and its nuclear translocation in oligodendrocyte progenitor cells (OPCs). In vitro, C1s silence reversed the increased level of LRP-6-ECD in the medium and β-catenin expression in OPCs induced by C1q treatment. Meanwhile, inhibition of C1s also markedly lowered the number of EDU positive OPCs, but enhanced the number of CNPase positive oligodendrocyte and the protein of MBP. The present study indicated that C1q was involved in demyelination in response to CPZ in mice by preventing OPC from differentiating into mature oligodendrocyte via Wnt/β-catenin signaling activation.

Circulating C1q levels in health and disease, more than just a biomarker

C1q is the recognition molecule of the classical pathway of the complement system. By binding to its targets, such as antigen-bound immunoglobulins or C-reactive protein, C1q contributes to the innate defense against infections. However, C1q also plays several other roles beyond its traditional role in complement activation. Circulating levels of C1q are determined in routine diagnostics as biomarker in several diseases. Decreased C1q levels are present in several autoimmune conditions. The decreased levels reflect the consumption of C1q by complement activation and serves as a biomarker for disease activity. In contrast, increased C1q levels are present in infectious and inflammatory diseases and may serve as a diagnostic biomarker. The increased levels of C1q are still incompletely understood but are suggested to modulate the adaptive immune response as C1q is known to impact on the maturation status of antigen-presenting cells and C1q impacts directly on T cells leading to decreased T-cell activity in high C1q conditions. In this review, we provide a comprehensive overview of the current literature on circulating levels of C1q in health and disease, and discuss how C1q can both protect against infections as well as maintain tolerance by regulating adaptive immunity.

C1r Upregulates Production of Matrix Metalloproteinase-13 and Promotes Invasion of Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the most common metastatic skin cancer with increasing incidence worldwide. Previous studies have demonstrated the role of complement system in cSCC progression. In this study we have investigated the mechanistic role of serine protease C1r, a component of the classical pathway of complement system, in cSCC. Knockout of C1r in cSCC cells using CRISPR/Cas9 resulted in significant decrease in their proliferation, migration, and invasion through collagen type I compared to wild type cSCC cells. Knockout of C1r suppressed growth and vascularization of cSCC xenograft tumors, and promoted apoptosis of tumor cells in vivo. mRNA-seq analysis after C1r knockdown revealed significantly regulated GO terms Cell-matrix adhesion, Extracellular matrix component, Basement membrane, Metalloendopeptidase activity and KEGG pathway Extracellular matrix-receptor interaction. Among the significantly regulated genes were invasion-associated matrix metalloproteinases MMP1, MMP13, MMP10, and MMP12. Knockout of C1r resulted in decreased production of MMP-1, MMP-13, MMP-10, and MMP-12 by cSCC cells in culture. Knockout of C1r inhibited expression of MMP-13 by tumor cells, suppressed invasion, and reduced the amount of degraded collagen in vivo in xenografts. These results provide evidence for the role of C1r in promoting the invasion of cSCC cells by increasing MMP production.

The Contribution of Complement to the Pathogenesis of IgA Nephropathy: Are Complement-Targeted Therapies Moving from Rare Disorders to More Common Diseases?

Primary IgA nephropathy (IgAN) is a leading cause of chronic kidney disease and kidney failure for which there is no disease-specific treatment. However, this could change, since novel therapeutic approaches are currently being assessed in clinical trials, including complement-targeting therapies. An improved understanding of the role of the lectin and the alternative pathway of complement in the pathophysiology of IgAN has led to the development of these treatment strategies. Recently, in a phase 2 trial, treatment with a blocking antibody against mannose-binding protein-associated serine protease 2 (MASP-2, a crucial enzyme of the lectin pathway) was suggested to have a potential benefit for IgAN. Now in a phase 3 study, this MASP-2 inhibitor for the treatment of IgAN could mark the start of a new era of complement therapeutics where common diseases can be treated with these drugs. The clinical development of complement inhibitors requires a better understanding by physicians of the biology of complement, the pathogenic role of complement in IgAN, and complement-targeted therapies. The purpose of this review is to provide an overview of the role of complement in IgAN, including the recent discovery of new mechanisms of complement activation and opportunities for complement inhibitors as the treatment of IgAN.

Bone marrow transplantation from a human leukocyte antigen-mismatched unrelated donor in a case with C1q deficiency associated with refractory systemic lupus erythematosus

Human C1q deficiency is frequently associated with systemic lupus erythematosus (SLE), which requires long-term systemic corticosteroid administration. We report the case of a 12-year-old female patient with C1q deficiency presenting with intractable SLE who successfully underwent bone marrow transplantation from a human leukocyte antigen (HLA)-mismatched unrelated donor with an immunosuppressive conditioning regimen based on fludarabine, melphalan, and anti-thymocyte globulin. She developed Grade I graft-versus-host disease, but did not have any transplantation-related morbidity. Complete donor chimerism has been maintained for 2 years after transplantation, leading to the restoration of C1q levels and the resolution of SLE symptoms. Normal C1q mRNA expression was observed in CD14 + cells. Hematopoietic stem cell transplantation from an HLA-mismatched donor is a feasible treatment for patients with C1q deficiency with refractory SLE that is dependent on systemic corticosteroid treatment who do not have an HLA-matched donor.

The role of phosphatidylserine recognition receptors in multiple biological functions

Apoptotic cells are rapidly engulfed and degraded by phagocytes through efferocytosis. Efferocytosis is a highly regulated process. It is triggered upon the activation of caspase-dependent apoptosis, which in turn promotes the expression of "eat me" signals on the surface of dying cells and the release of soluble "find me" signals for the recruitment of phagocytes. To date, many "eat me" signals have been recognized, including phosphatidylserine (PS), intercellular adhesion molecule-3, carbohydrates (e.g., amino sugars, mannose) and calreticulin. Among them, PS is the most studied one. PS recognition receptors are different functionally active receptors expressed by phagocytes. Various PS recognition receptors with different structure, cell type expression, and ability to bind to PS have been recognized. Although PS recognition receptors do not fall into a single classification or family of proteins due to their structural differences, they all share the common ability to activate downstream signaling pathways leading to the production of anti-inflammatory mediators. In this review, available evidence regarding molecular mechanisms underlying PS recognition receptor-regulated clearance of apoptotic cells is discussed. In addition, some efferocytosis-independent biological functions of PS recognition receptors are reviewed.

Recent advances into the role of pattern recognition receptors in transplantation

Pattern recognition receptors (PRRs) are germline-encoded sensors best characterized for their critical role in host defense. However, there is accumulating evidence that organ transplantation induces the release or display of molecular patterns of cellular injury and death that trigger PRR-mediated inflammatory responses. There are also new insights that indicate PRRs are able to distinguish between self and non-self, suggesting the existence of non-clonal mechanisms of allorecognition. Collectively, these reports have spurred considerable interest into whether PRRs or their ligands can be targeted to promote transplant survival. This review examines the mounting evidence that PRRs play in transplant-mediated inflammation. Given the large number of PRRs, we will focus on members from four families: the complement system, toll-like receptors, the formylated peptide receptor, and scavenger receptors through examining reports of their activity in experimental models of cellular and solid organ transplantation as well as in the clinical setting.

Tumour-cell-derived complement components C1r and C1s promote growth of cutaneous squamous cell carcinoma

BACKGROUND

The incidence of epidermal keratinocyte-derived cutaneous squamous cell carcinoma (cSCC) is increasing worldwide.

OBJECTIVES

To study the role of the complement classical pathway components C1q, C1r and C1s in the progression of cSCC.

METHODS

The mRNA levels of C1Q subunits and C1R and C1S in cSCC cell lines, normal human epidermal keratinocytes, cSCC tumours in vivo and normal skin were analysed with quantitative real-time polymerase chain reaction. The production of C1r and C1s was determined with Western blotting. The expression of C1r and C1s in tissue samples in vivo was analysed with immunohistochemistry and further investigated in human cSCC xenografts by knocking down C1r and C1s.

RESULTS

Significantly elevated C1R and C1S mRNA levels and production of C1r and C1s were detected in cSCC cells, compared with normal human epidermal keratinocytes. The mRNA levels of C1R and C1S were markedly elevated in cSCC tumours in vivo compared with normal skin. Abundant expression of C1r and C1s by tumour cells was detected in invasive sporadic cSCCs and recessive dystrophic epidermolysis bullosa-associated cSCCs, whereas the expression of C1r and C1s was lower in cSCC in situ, actinic keratosis and normal skin. Knockdown of C1r and C1s expression in cSCC cells inhibited activation of extracellular signal-related kinase 1/2 and Akt, promoted apoptosis of cSCC cells and significantly suppressed growth and vascularization of human cSCC xenograft tumours in vivo.

CONCLUSIONS

These results provide evidence for the role of tumour-cell-derived C1r and C1s in the progression of cSCC and identify them as biomarkers and putative therapeutic targets in cSCC. What's already known about this topic? The incidences of actinic keratosis, cutaneous squamous cell carcinoma (cSCC) in situ and invasive cSCC are increasing globally. Few specific biomarkers for progression of cSCC have been identified, and no biological markers are in clinical use to predict the aggressiveness of actinic keratosis, cSCC in situ and invasive cSCC. What does this study add? Our results provide novel evidence for the role of complement classical pathway components C1r and C1s in the progression of cSCC. What is the translational message? Our results identify complement classical pathway components C1r and C1s as biomarkers and putative therapeutic targets in cSCC.

Recombinant C1q variants modulate macrophage responses but do not activate the classical complement pathway

Complement protein C1q plays a dual role in a number of inflammatory diseases such as atherosclerosis. While in later stages classical complement pathway activation by C1q exacerbates disease progression, C1q also plays a beneficial role in early disease. Independent of its role in complement activation, we and others have identified a number of potentially beneficial interactions of C1q with phagocytes in vitro, including triggering phagocytosis of cellular and molecular debris and polarizing macrophages toward an anti-inflammatory phenotype. These interactions may also be important in preventing autoimmunity. Here, we characterize variants of recombinant human C1q (rC1q) which no longer initiate complement activation, through mutation of the C1r₂C1s₂ interaction site. For insight into the structural location of the site of C1q that is important for interaction with phagocytes, we investigated the effect of these mutations on phagocytosis and macrophage inflammatory polarization, as compared to wild-type C1q. Phagocytosis of antibody coated sheep erythrocytes and oxidized LDL was measured in human monocytes and monocyte-derived macrophages (HMDM) respectively that had interacted with rC1q wild-type or variants. Secreted levels of cytokines were also measured in C1q stimulated HMDM. All variants of C1q increased phagocytosis in HMDM compared to controls, similar to native or wild-type rC1q. In addition, levels of certain pro-inflammatory cytokines and chemokines secreted by HMDM were modulated in cells that interacted with C1q variants, similar to wild-type rC1q and native C1q. This includes downregulation of IL-1α, IL-1β, TNFα, MIP-1α, and IL-12p40 by native and rC1q in both resting and M1-polarized HMDM. This suggests that the site responsible for C1q interaction with phagocytes is independent of the C1r₂C1s₂ interaction site. Further studies with these classical pathway-null variants of C1q should provide greater understanding of the complement-independent role of C1q, and allow for potential therapeutic exploitation.

Is the Complement Protein C1q a Pro- or Anti-tumorigenic Factor? Bioinformatics Analysis Involving Human Carcinomas

C1q is the first subcomponent of the classical pathway of the complement system and belongs to the C1q/Tumor Necrosis Factor superfamily. C1q can perform a diverse range of immune and non-immune functions in a complement-dependent as well as -independent manner. Being a pattern recognition molecule of the innate immunity, C1q can recognize a number of self, non-self and altered-self ligands and bring about effector mechanisms designed to clear pathogens via opsonisation and inflammatory response. C1q is locally synthesized by macrophages and dendritic cells, and thus, can get involved in a range of biological processes, such as angiogenesis and tissue remodeling, immune modulation, and immunologic tolerance. The notion of C1q involvement in the pathogenesis of cancer is still evolving. C1q appears to have a dual role in cancer: tumor promoting as well as tumor-protective, depending on the context of the disease. In the current study, we performed a bioinformatics analysis to investigate whether C1q can serve as a potential prognostic marker for human carcinoma. We used the Oncomine database and the survival analysis platforms Kaplan-Meier plotter. Our results showed that high levels of C1q have a favorable prognostic index in basal-like breast cancer for disease-free survival, and in HER2-positive breast cancer for overall survival, while it showed a pro-tumorigenic role of C1q in lung adenocarcinoma, and in clear cell renal cell carcinoma. This in silico study, if validated via a retrospective study, can be a step forward in establishing C1q as a new tool as a prognostic biomarker for various carcinoma.

Critical Role for a Subset of Intestinal Macrophages in Shaping Gut Microbiota in Adult Zebrafish

The gut microbiota is strongly influenced by environmental factors, although host contribution is far less understood. We leveraged macrophage-deficient interferon regulatory factor irf8 zebrafish mutants to investigate the role of macrophages in this process. In conventionally raised adult irf8-deficient mutants, we found a significant loss of intestinal macrophages associated with a strikingly altered gut microbiota when compared to co-housed siblings. The destabilization of the gut commensal microbiota was associated with a severe reduction in complement C1q genes and outgrowth of a rare bacterial species. Consistent with a critical function of irf8 in adult intestinal macrophages, irf8 is abundantly expressed in these cells normally, and restoring macrophage irf8 expression in irf8 mutants was sufficient to recover commensal microbes and C1q genes expression. This study reports an important subpopulation of intestinal macrophages that requires irf8 to establish in the gut, ensure normal colonization of gut microbes, and prevent immune dysregulation.

Usefulness of Complement C1q to Predict 10-Year Mortality in Men With Diabetes Mellitus Referred for Coronary Angiography

The complement system consists of a family of proteins that play a critical role in the innate immune system. Complement activation has been implicated in many chronic inflammatory diseases, including atherosclerosis. However, a number of experimental studies have highlighted a beneficial role of component C1q in early atherosclerosis and in diabetes mellitus (DM). Despite these data, there have been no studies that have specifically examined the utility of plasma complement C1q as a clinical biomarker in patients with known or suspected coronary artery disease. In this study, baseline plasma complement C1q levels were measured in 159 men with DM who were referred for coronary angiography and who were followed up prospectively for the development of all-cause mortality for 10 years. After adjustment for baseline clinical, angiographic, and laboratory parameters, reduced plasma complement C1q levels were an independent predictor of all-cause mortality at 10 years (hazard ratio 0.66, 95% confidence interval 0.52 to 0.84, p = 0.0006). In additional multivariate models that adjusted for a variety of biomarkers with established prognostic efficacy, complement C1q remained an independent predictor of all-cause mortality at 10 years. In conclusion, reduced levels of complement C1q are associated with an increased risk of all-cause mortality at 10 years in patients with DM referred for coronary angiography. Furthermore, this association is independent of a variety of clinical, angiographic, laboratory variables, including biomarkers with established prognostic efficacy in the prediction of adverse cardiovascular outcomes.

Complement Component C1q: Historical Perspective of a Functionally Versatile, and Structurally Unusual, Serum Protein

Complement component C1q plays an important recognition role in adaptive, and innate, immunity through its ability to interact, via its six globular head regions, with both immunoglobulin and non-immunoglobulin activators of the complement system, and also in the clearance of cell debris, and by playing a role in regulation of cellular events by interacting with a wide range of cell surface molecules. The presence of collagen-like triple-helical structures within C1q appears crucial to the presentation, and multivalent binding, of the globular heads of C1q to targets, and also to its association with the proenzyme complex of C1r₂–C1s₂, to yield the C1 complex. The possible role that movement of these collagen-like structures may play in the activation of the C1 complex is a controversial area, with there still being no definitive answer as to how the first C1r proenzyme molecule becomes activated within the C1 complex, thus allowing it to activate proenzyme C1s, and initiate and the consequent cascade of events in the activation of the classical pathway of complement. The globular heads of C1q are similar to domains found within the tumor necrosis factor (TNF) superfamily of proteins, and have been shown to bind to a very wide range of ligands. In addition to its well-defined roles in infection and immunity, a variety of other functions associated with C1q include possible roles, in the development of problems in the central nervous system, which occur with aging, and perhaps in the regulation of tumor growth.

Complement C1q stimulates the progression of hepatocellular tumor through the activation of discoidin domain receptor 1

C1q is known to perform several functions in addition to the role it plays in complement activation. C1q contains a collagen-like portion and DDR1 (discoidin domain receptor 1) is a well-known collagen receptor. Accordingly, we hypothesized C1q might be a novel ligand of DDR1. This study shows for the first time C1q directly induces the activation and upregulation of DDR1, and that this leads to enhanced migration and invasion of HepG2 cells. In addition, C1q was found to induce the activations of mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinase (PI3K)/Akt signaling, and to increase the expressions of matrix metalloproteinases (MMP2 and 9). Our results reveal a relationship between C1q and DDR1 and suggest C1q-induced DDR1 activation signaling may be involved in the progression of hepatocellular carcinoma.

MafB is a critical regulator of complement component C1q

The transcription factor MafB is expressed by monocytes and macrophages. Efferocytosis (apoptotic cell uptake) by macrophages is important for inhibiting the development of autoimmune diseases, and is greatly reduced in Mafb-deficient macrophages. Here, we show the expression of the first protein in the classical complement pathway C1q is important for mediating efferocytosis and is reduced in Mafb-deficient macrophages. The efferocytosis defect in Mafb-deficient macrophages can be rescued by adding serum from wild-type mice, but not by adding serum from C1q-deficient mice. By hemolysis assay we also show that activation of the classical complement pathway is decreased in Mafb-deficient mice. In addition, MafB overexpression induces C1q-dependent gene expression and signals that induce C1q genes are less effective in the absence of MafB. We also show that Mafb-deficiency can increase glomerular autoimmunity, including anti-nuclear antibody deposition. These results show that MafB is an important regulator of C1q.

Complement components as promoters of immunological tolerance in dendritic cells

Complement and dendritic cells (DCs) share many functional features that drive the outcome of immune-inflammatory processes. Both have a sentinel function, acting as danger sensors specialized for a rapid, comprehensive and selective action against potential threats without damaging the healthy host cells. But while complement has been considered as a "master alarm" system poised for direct pathogen killing, DCs are regarded as "master regulators" or orchestrators of a vast range of effector immune cells for an effective immune response against threatening insults. The original definition of the complement system, coined to denote its auxiliary function to enhance or assist in the role of antibodies or phagocytes to clear microbes or damaged cells, envisaged an important crosstalk between the complement and the mononuclear phagocyte systems. More recent studies have shown that, depending on the microenvironmental conditions, several complement effectors are competent to influence the differentiation and/or function of different DC subsets toward immunogenicity or tolerance. In this review we will infer about the capability of complement activators and inhibitors to "condition" a tolerogenic and anti-inflammatory immune response by direct interaction with DC surface receptors, and about the implications of this knowledge to devise new complement-based therapeutic approaches for autoimmune pathologies.

Systemic lupus erythematosus with C1q deficiency: treatment with fresh frozen plasma

Treatment and outcome of systemic lupus erythematosus (SLE) in C1q deficient patients are rarely reported. The aim of this report is to share our experience about the course of management of three cases diagnosed as SLE with C1q deficiency, in light of present literature. Initial and dominant complaints of three cases from two different families were cutaneous manifestations. One patient was also diagnosed with arthritis and thrombocytopenia. Antinuclear antibody was positive in all cases, whereas anti-dsDNA was negative with normal levels of complement C3, C4 and decreased CH50 activity. C1QA gene of two patients had homozygous nonsense mutation (c.622 > T/p.Gln208Ter). Previously, all of them had been treated with steroids, hydroxychloroquine and methotrexate or azathioprine. It was learned that they had responded only to high dosage prednisolone and their symptoms flared up during dosage reduction even under methotrexate or azathioprine. All symptoms of all three cases improved by daily fresh frozen plasma (FFP) infusions, and once cutaneous lesions subsided, the infusions were reduced to a frequency that would prevent the flare up of the symptoms. Literature search revealed seven reports on fresh frozen plasma treatment in SLE with C1q deficient patients. In this report, it is concluded that severe cutaneous lesions, as seen in these C1q deficient SLE patients, cannot be controlled with conventional immunosuppressive treatment. Instead, regular fresh frozen plasma infusions are proposed as a more reasonable method of treatment.

C1q: A fresh look upon an old molecule

Originally discovered as part of C1, the initiation component of the classical complement pathway, it is now appreciated that C1q regulates a variety of cellular processes independent of complement activation. C1q is a complex glycoprotein assembled from 18 polypeptide chains, with a C-terminal globular head region that mediates recognition of diverse molecular structures, and an N-terminal collagen-like tail that mediates immune effector mechanisms. C1q mediates a variety of immunoregulatory functions considered important in the prevention of autoimmunity such as the enhancement of phagocytosis, regulation of cytokine production by antigen presenting cells, and subsequent alteration in T-lymphocyte maturation. Furthermore, recent advances indicate additional roles for C1q in diverse physiologic and pathologic processes including pregnancy, tissue repair, and cancer. Finally, C1q is emerging as a critical component of neuronal network refinement and homeostatic regulation within the central nervous system. This review summarizes the classical functions of C1q and reviews novel discoveries within the field.

Complement C1q is hydroxylated by collagen prolyl 4 hydroxylase and is sensitive to off-target inhibition by prolyl hydroxylase domain inhibitors that stabilize hypoxia-inducible factor

Complement C1q is part of the C1 macromolecular complex that mediates the classical complement activation pathway: a major arm of innate immune defense. C1q is composed of A, B, and C chains that require post-translational prolyl 4-hydroxylation of their N-terminal collagen-like domain to enable the formation of the functional triple helical multimers. The prolyl 4-hydroxylase(s) that hydroxylate C1q have not previously been identified. Recognized prolyl 4-hydroxylases include collagen prolyl-4-hydroxylases (CP4H) and the more recently described prolyl hydroxylase domain (PHD) enzymes that act as oxygen sensors regulating hypoxia-inducible factor (HIF). We show that several small-molecule prolyl hydroxylase inhibitors that activate HIF also potently suppress C1q secretion by human macrophages. However, reducing oxygenation to a level that activates HIF does not compromise C1q hydroxylation. In vitro studies showed that a C1q A chain peptide is not a substrate for PHD2 but is a substrate for CP4H1. Circulating levels of C1q did not differ between wild-type mice or mice with genetic deficits in PHD enzymes, but were reduced by prolyl hydroxylase inhibitors. Thus, C1q is hydroxylated by CP4H, but not the structurally related PHD hydroxylases. Hence, reduction of C1q levels may be an important off-target side effect of small molecule PHD inhibitors developed as treatments for renal anemia.

Local amplifiers of IL-4Rα-mediated macrophage activation promote repair in lung and liver

The type 2 immune response controls helminth infection and maintains tissue homeostasis but can lead to allergy and fibrosis if not adequately regulated. We have discovered local tissue-specific amplifiers of type 2-mediated macrophage activation. In the lung, surfactant protein A (SP-A) enhanced interleukin-4 (IL-4)-dependent macrophage proliferation and activation, accelerating parasite clearance and reducing pulmonary injury after infection with a lung-migrating helminth. In the peritoneal cavity and liver, C1q enhancement of type 2 macrophage activation was required for liver repair after bacterial infection, but resulted in fibrosis after peritoneal dialysis. IL-4 drives production of these structurally related defense collagens, SP-A and C1q, and the expression of their receptor, myosin 18A. These findings reveal the existence within different tissues of an amplification system needed for local type 2 responses.

Cell-specific deletion of C1qa identifies microglia as the dominant source of C1q in mouse brain

BACKGROUND

The complement cascade not only provides protection from infection but can also mediate destructive inflammation. Complement is also involved in elimination of neuronal synapses which is essential for proper development, but can be detrimental during aging and disease. C1q, required for several of these complement-mediated activities, is present in the neuropil, microglia, and a subset of interneurons in the brain.

METHODS

To identify the source(s) of C1q in the brain, the C1qa gene was selectively inactivated in the microglia or Thy-1⁺ neurons in both wild type mice and a mouse model of Alzheimer's disease (AD), and C1q synthesis assessed by immunohistochemistry, QPCR, and western blot analysis.

RESULTS

While C1q expression in the brain was unaffected after inactivation of C1qa in Thy-1⁺ neurons, the brains of C1qa ^FL/FL :Cx3cr1 ^CreERT2 mice in which C1qa was ablated in microglia were devoid of C1q with the exception of limited C1q in subsets of interneurons. Surprisingly, this loss of C1q occurred even in the absence of tamoxifen by 1 month of age, demonstrating that Cre activity is tamoxifen-independent in microglia in Cx3cr1 ^{CreERT2/WganJ} mice. C1q expression in C1qa ^FL/FL : Cx3cr1 ^{CreERT2/WganJ} mice continued to decline and remained almost completely absent through aging and in AD model mice. No difference in C1q was detected in the liver or kidney from C1qa ^FL/FL : Cx3cr1 ^{CreERT2/WganJ} mice relative to controls, and C1qa ^FL/FL : Cx3cr1 ^{CreERT2/WganJ} mice had minimal, if any, reduction in plasma C1q.

CONCLUSIONS

Thus, microglia, but not neurons or peripheral sources, are the dominant source of C1q in the brain. While demonstrating that the Cx3cr1 ^{CreERT2/WganJ} deleter cannot be used for adult-induced deletion of genes in microglia, the model described here enables further investigation of physiological roles of C1q in the brain and identification of therapeutic targets for the selective control of complement-mediated activities contributing to neurodegenerative disorders.

Complement Protein C1q Enhances Macrophage Foam Cell Survival and Efferocytosis

In the atherosclerotic lesion, macrophages ingest high levels of damaged modified low-density lipoproteins (LDLs), generating macrophage foam cells. Foam cells undergo apoptosis and, if not efficiently cleared by efferocytosis, can undergo secondary necrosis, leading to plaque instability and rupture. As a component of the innate immune complement cascade, C1q recognizes and opsonizes modified forms of LDL, such as oxidized or acetylated LDL, and promotes ingestion by macrophages in vitro. C1q was shown to be protective in an atherosclerosis model in vivo. Therefore, this study aimed to investigate whether ingestion of modified LDL in the presence of C1q alters macrophage foam cell survival or function. In an unbiased transcriptome analysis, C1q was shown to modulate expression of clusters of genes involved in cell death and apoptosis pathways in human monocyte-derived macrophages ingesting modified LDL; this was validated by quantitative PCR in human and murine macrophages. C1q downregulated levels and activity of active caspase-3 and PARP-1 in human and mouse macrophages during ingestion of modified LDL. This led to a measurable increase in survival and decrease in cell death, as measured by alamarBlue and propidium iodide assays, respectively. C1q opsonization also increased phagocytosis and efferocytosis in macrophage foam cells. These data suggest that C1q promotes macrophage survival during ingestion of excess cholesterol, as well as improves foam cell efferocytic function. This may be important in slowing disease progression and provides insight into the protective role of C1q in early atherosclerosis.

Tumor-host signaling interaction reveals a systemic, age-dependent splenic immune influence on tumor development

The concept of age-dependent host control of cancer development raises the natural question of how these effects manifest across the host tissue/organ types with which a tumor interacts, one important component of which is the aging immune system. To investigate this, changes in the spleen, an immune nexus in the mouse, was examined for its age-dependent interactive influence on the carcinogenesis process. The model is the C57BL/6 male mice (adolescent, young adult, middle-aged, and old or 68, 143, 551 and 736 days old respectively) with and without a syngeneic murine tumor implant. Through global transcriptome analysis, immune-related functions were found to be key regulators in the spleen associated with tumor progression as a function of age with CD2, CD3ε, CCL19, and CCL5 being the key molecules involved. Surprisingly, other than CCL5, all key factors and immune-related functions were not active in spleens from non-tumor bearing old mice. Our findings of age-dependent tumor-spleen signaling interaction suggest the existence of a global role of the aging host in carcinogenesis. Suggested is a new avenue for therapeutic improvement that capitalizes on the pervasive role of host aging in dictating the course of this disease.

Alternative functions of the complement protein C1q at embryo implantation site

Complement component C1q is one of the recognition molecules of the complement system which can serve several functions unrelated to complement activation. This molecule is produced at foeto-maternal interface by macrophages as wells as by decidual endothelial cells and invading trophoblast. Foetal trophoblast cells migrating through the decidua in the early stages of pregnancy synthesize and express C1q on their surface, which is actively involved in promoting trophoblast endovascular and interstitial invasion of the decidua. These functions are mediated by two cell surface receptors, gC1qR and α4β1 integrin, which promote trophoblast adhesion and migration through the activation of ERK1/2 MAPKs. C1q^-/- mice manifest increased frequency of foetal resorption, reduced foetal weight, and smaller litter size when compared to their wild-type counterparts, suggesting that defective local production of C1q may be involved in pregnancy disorders, such as pre-eclampsia. C1q acts also as a strong angiogenic factor and promotes neovascularization. These studies suggest novel and unexpected roles of this complement component in physiological and pathological pregnancies.

Macrophage molecular signaling and inflammatory responses during ingestion of atherogenic lipoproteins are modulated by complement protein C1q

BACKGROUND AND AIMS

This study investigated the effect of innate immune protein C1q on macrophage programmed responses during the ingestion of atherogenic lipoproteins. C1q plays a dual role in atherosclerosis where activation of complement by C1q is known to drive inflammation and promote disease progression. However, C1q is atheroprotective in early disease using mouse models. Our previous studies have highlighted a non-complement associated role for C1q in polarizing macrophages towards an M2-like anti-inflammatory phenotype during ingestion of targets such as atherogenic lipoproteins. This study aims to investigate the molecular mechanisms involved.

METHODS

We investigated the molecular signaling mechanisms involved in macrophage polarization using an unbiased examination of gene expression profiles in human monocyte derived macrophages ingesting oxidized or acetylated low density lipoproteins in the presence or absence of C1q.

RESULTS

Expression of genes involved in Janus kinase and signal transducer and activator of transcription (JAK-STAT) signaling, peroxisome proliferator activating receptor (PPAR) signaling and toll-like receptor (TLR) signaling were modulated by C1q in this screen. C1q was also shown to significantly suppress JAK-STAT pathway activation (a maximum 55% ± 13% reduction, p = 0.044) and increase transcriptional activation of PPARs (a maximum 229% ± 54% increase, p = 0.0002), consistent with an M2-like polarized response. These pathways were regulated in macrophages by C1q bound to different types of modified atherogenic lipoprotein and led to a reduction in the release of pro-inflammatory cytokine IL-6.

CONCLUSIONS

This study identifies potential molecular mechanisms for the beneficial role C1q plays in early atherosclerosis.

Roles of renin-angiotensin system and Wnt pathway in aging-related phenotypes

The renin-angiotensin system (RAS) regulates diverse cellular responses and is crucial for normal organ development and function. On the other hand, RAS exerts deleterious effects promoting cardiovascular and multiple organ damage and contributes to promoting various aging-related diseases and aging-related decline in multiple organ functions. RAS blockade has been shown to prevent the progression of aging-related phenotypes and promote longevity. Wnt signaling pathway also plays a major role in the regulation of mammalian pathophysiology and is essential for organismal survival, and furthermore, it is substantially involved in the promotion of aging process. In this way, both RAS signaling and Wnt signaling have the functions of antagonistic pleiotropy during the process of growth and aging. Our recent study has demonstrated that an anti-aging effect of RAS blockade is associated with down-regulation of canonical Wnt signaling pathway, providing evidence for the hierarchical relationship between RAS signaling and Wnt signaling in promoting aging-related phenotypes. Here, we review how RAS signaling and Wnt signaling regulate the aging process and promote aging-related diseases.

Early Components of the Complement Classical Activation Pathway in Human Systemic Autoimmune Diseases

The complement system consists of effector proteins, regulators, and receptors that participate in host defense against pathogens. Activation of the complement system, via the classical pathway (CP), has long been recognized in immune complex-mediated tissue injury, most notably systemic lupus erythematosus (SLE). Paradoxically, a complete deficiency of an early component of the CP, as evidenced by homozygous genetic deficiencies reported in human, are strongly associated with the risk of developing SLE or a lupus-like disease. Similarly, isotype deficiency attributable to a gene copy-number (GCN) variation and/or the presence of autoantibodies directed against a CP component or a regulatory protein that result in an acquired deficiency are relatively common in SLE patients. Applying accurate assay methodologies with rigorous data validations, low GCNs of total C4, and heterozygous and homozygous deficiencies of C4A have been shown as medium to large effect size risk factors, while high copy numbers of total C4 or C4A as prevalent protective factors, of European and East-Asian SLE. Here, we summarize the current knowledge related to genetic deficiency and insufficiency, and acquired protein deficiencies for C1q, C1r, C1s, C4A/C4B, and C2 in disease pathogenesis and prognosis of SLE, and, briefly, for other systemic autoimmune diseases. As the complement system is increasingly found to be associated with autoimmune diseases and immune-mediated diseases, it has become an attractive therapeutic target. We highlight the recent developments and offer a balanced perspective concerning future investigations and therapeutic applications with a focus on early components of the CP in human systemic autoimmune diseases.

C1q acts in the tumour microenvironment as a cancer-promoting factor independently of complement activation

Complement C1q is the activator of the classical pathway. However, it is now recognized that C1q can exert functions unrelated to complement activation. Here we show that C1q, but not C4, is expressed in the stroma and vascular endothelium of several human malignant tumours. Compared with wild-type (WT) or C3- or C5-deficient mice, C1q-deficient (C1qa^−/−) mice bearing a syngeneic B16 melanoma exhibit a slower tumour growth and prolonged survival. This effect is not attributable to differences in the tumour-infiltrating immune cells. Tumours developing in WT mice display early deposition of C1q, higher vascular density and an increase in the number of lung metastases compared with C1qa^−/− mice. Bone marrow (BM) chimeras between C1qa^−/− and WT mice identify non-BM-derived cells as the main local source of C1q that can promote cancer cell adhesion, migration and proliferation. Together these findings support a role for locally synthesized C1q in promoting tumour growth.

C1q is known to initiate the activation of the complement classical pathway. Here, the authors show the C1q is expressed in the tumour microenvironment and can promote cancer cell migration and adhesion in a complement activation-independent manner.

Angiotensin II receptor blockade promotes repair of skeletal muscle through down-regulation of aging-promoting C1q expression

Disruption of angiotensin II type 1 (AT₁) receptor prolonged life span in mice. Since aging-related decline in skeletal muscle function was retarded in Atgr1a^−/− mice, we examined the role of AT₁ receptor in muscle regeneration after injury. Administration of AT₁ receptor blocker irbesartan increased the size of regenerating myofibers, decreased fibrosis, and enhanced functional muscle recovery after cryoinjury. We recently reported that complement C1q, secreted by macrophages, activated Wnt/β-catenin signaling and promoted aging-related decline in regenerative capacity of skeletal muscle. Notably, irbesartan induced M2 polarization of macrophages, but reduced C1q expression in cryoinjured muscles and in cultured macrophage cells. Irbesartan inhibited up-regulation of Axin2, a downstream gene of Wnt/β-catenin pathway, in cryoinjured muscles. In addition, topical administration of C1q reversed beneficial effects of irbesartan on skeletal muscle regeneration after injury. These results suggest that AT₁ receptor blockade improves muscle repair and regeneration through down-regulation of the aging-promoting C1q-Wnt/β-catenin signaling pathway.

Wnt/β-Catenin Signaling Contributes to Skeletal Myopathy in Heart Failure via Direct Interaction With Forkhead Box O

Background—

There are changes in the skeletal muscle of patients with chronic heart failure (CHF), such as volume reduction and fiber type shift toward fatigable type IIb fiber. Forkhead box O (FoxO) signaling plays a critical role in the development of skeletal myopathy in CHF, and functional interaction between FoxO and the Wnt signal mediator β-catenin was previously demonstrated. We have recently reported that serum of CHF model mice activates Wnt signaling more potently than serum of control mice and that complement C1q mediates this activation. We, therefore, hypothesized that C1q-induced activation of Wnt signaling plays a critical role in skeletal myopathy via the interaction with FoxO.

Methods and Results—

Fiber type shift toward fatigable fiber was observed in the skeletal muscle of dilated cardiomyopathy model mice, which was associated with activation of both Wnt and FoxO signaling. Wnt3a protein activated FoxO signaling and induced fiber type shift toward fatigable fiber in C2C12 cells. Wnt3a-induced fiber type shift was inhibited by suppression of FoxO1 activity, whereas Wnt3a-independent fiber type shift was observed by overexpression of constitutively active FoxO1. Serum of dilated cardiomyopathy mice activated both Wnt and FoxO signaling and induced fiber type shift toward fatigable fiber in C2C12 cells. Wnt inhibitor and C1-inhibitor attenuated FoxO activation and fiber type shift both in C2C12 cells and in the skeletal muscle of dilated cardiomyopathy mice.

Conclusions—

C1q-induced activation of Wnt signaling contributes to fiber type shift toward fatigable fiber in CHF. Wnt signaling may be a novel therapeutic target to prevent skeletal myopathy in CHF.

Marked variability in clinical presentation and outcome of patients with C1q immunodeficiency

OBJECTIVE

Globally approximately 60 cases of C1q deficiency have been described with a high prevalence of Systemic Lupus Erythematosus (SLE). So far treatment has been guided by the clinical presentation rather than the underlying C1q deficiency. Recently, it was shown that C1q production can be restored by allogeneic hematopoietic stem cell transplantation. Current literature lacks information on disease progression and quality of life of C1q deficient persons which is of major importance to guide clinicians taking care of patients with this rare disease.

METHODS

We performed an international survey, of clinicians treating C1q deficient patients. A high response rate of >70% of the contacted clinicians yielded information on 45 patients with C1q deficiency of which 25 are published.

RESULTS

Follow-up data of 45 patients from 31 families was obtained for a median of 11 years after diagnosis. Of these patients 36 (80%) suffer from SLE, of which 16 suffer from SLE and infections, 5 (11%) suffer from infections only and 4 (9%) have no symptoms. In total 9 (20%) of the C1q deficient individuals had died. All except for one died before the age of 20 years. Estimated survival times suggest 20% case-fatality before the age of 20, and at least 50% of patients are expected to reach their middle ages.

CONCLUSION

Here we report the largest phenotypic data set on C1q deficiency to date, revealing high variance; with high mortality but also a subset of patients with an excellent prognosis. Management of C1q deficiency requires a personalized approach.

Classical pathway deficiencies - A short analytical review

Deficiencies in the classical pathway of complement activation have some common features but show also great differences. Deficiencies of each of the components (C1q, C1s, C1r, C4 and C2) imply increased susceptibility to bacterial infections. They are also associated with increased risk to develop systemic lupus erythematosus where deficiency of C1q is strongly associated to the disease while C4 less and C2 much less. Deficiency of C1q affects only activation of the classical pathway while deficiency of C4 and C2 also prevent activation of the lectin pathway. Bypass mechanisms may result in complement activation also in absence of C2 but not in absence of C1q or C4. The genes for C2 and C4 isotypes are closely located within the MHC class III region on chromosome 6p and the genes for the 3 C1q chains are on chromosome 1p. Deficiencies of C1q and of C4 show genetic heterogeneity while deficiency of C2 in the great majority of cases is caused by a specific deletion. The production of C4 and C2 is mainly by the hepatocytes in the liver while C1q is produced by monocytic bone marrow derived cells. This has implications for the possibility to treat the deficiency and hematopoietic stem cell transplantation has been tried in C1q deficiency.

Fluorescent Ly6G antibodies determine macrophage phagocytosis of neutrophils and alter the retrieval of neutrophils in mice

Fluorescently labeled Ly6G antibodies enable the tracking of neutrophils in mice, whereas purified anti-Ly6G rapidly depletes neutrophils from the circulation. The mechanisms underlying neutrophil depletion are still under debate. Here, we examined how identical Ly6G antibodies coupled to different fluorochromes affect neutrophil fate in vivo. BM cells stained with Ly6G antibodies were injected into mice. The number of retrieved anti-Ly6G-FITC(+) cells was reduced significantly in comparison with anti-Ly6G-APC(+) or anti-Ly6G-PE(+) cells. Flow cytometry and multispectral imaging flow cytometry analyses revealed that anti-Ly6G-FITC(+) neutrophils were preferentially phagocytosed by BMMs in vitro and by splenic, hepatic, and BM macrophages in vivo. Direct antibody injection of anti-Ly6G-FITC but not anti-Ly6G-PE depleted neutrophils to the same degree as purified anti-Ly6G, indicating that the FITC-coupled antibody eliminates neutrophils by a similar mechanism as the uncoupled antibody. With the use of a protein G-binding assay, we demonstrated that APC and PE but not FITC coupling inhibited access to interaction sites on the anti-Ly6G antibody. We conclude the following: 1) that neutrophil phagocytosis by macrophages is a central mechanism in anti-Ly6G-induced neutrophil depletion and 2) that fluorochrome-coupling can affect functional properties of anti-Ly6G antibodies, thereby modifying macrophage uptake of Ly6G-labeled neutrophils and neutrophil retrieval following adoptive cell transfer or injection of fluorescent anti-Ly6G.

The paradoxical roles of C1q and C3 in autoimmunity

In this review we will focus on the links between complement and autoimmune diseases and will highlight how animal models have provided insights into the manner by which C1q and C3 act to modulate both adaptive and innate immune responses. In particular we will highlight how C1q may not only act as initiator of the classical complement pathway, but can also mediate multiple immune responses in a complement activation independent manner.

Complement C1q-induced activation of β-catenin signalling causes hypertensive arterial remodelling

Hypertension induces structural remodelling of arteries, which leads to arteriosclerosis and end-organ damage. Hyperplasia of vascular smooth muscle cells (VSMCs) and infiltration of immune cells are the hallmark of hypertensive arterial remodelling. However, the precise molecular mechanisms of arterial remodelling remain elusive. We have recently reported that complement C1q activates β-catenin signalling independent of Wnts. Here, we show a critical role of complement C1-induced activation of β-catenin signalling in hypertensive arterial remodelling. Activation of β-catenin and proliferation of VSMCs were observed after blood-pressure elevation, which were prevented by genetic and chemical inhibition of β-catenin signalling. Macrophage depletion and C1qa gene deletion attenuated the hypertension-induced β-catenin signalling, proliferation of VSMCs and pathological arterial remodelling. Our findings unveil the link between complement C1 and arterial remodelling and suggest that C1-induced activation of β-catenin signalling becomes a novel therapeutic target to prevent arteriosclerosis in patients with hypertension.

The role of macrophages in hypertension-induced arterial remodeling is poorly understood. Here, Sumida et al. show that high blood pressure drives the alternatively activated macrophages to secrete complement C1q protein, which in turn elicits proliferative β-catenin signalling in the arterial smooth muscle cells.

Complement protein C1q promotes macrophage anti-inflammatory M2-like polarization during the clearance of atherogenic lipoproteins

OBJECTIVE

Innate immune protein C1q plays a dual role in the chronic inflammatory disease of atherosclerosis. Complement activation via C1q exacerbates pathology in the atherosclerotic lesion in later stages of the disease. However, in early stages of disease C1q is protective. We hypothesize that complement-independent activities of C1q are involved in reprogramming macrophage inflammatory polarization.

METHODS

The influence of C1q on macrophage inflammatory responses during clearance of oxLDL was examined. Changes in cytokines at the gene and protein level were measured by quantitative PCR and ELISA assay.

RESULTS

C1q modulated cytokine expression in Raw264.7 macrophages during ingestion of oxLDL. Levels of pro-inflammatory cytokines IL-1β and IL-6 were downregulated by C1q, whereas levels of the anti-inflammatory cytokine IL-10 were increased. In addition, data from an NFκB-luciferase gene reporter assay suggest that C1q suppresses activation of NFκB during lipoprotein clearance in macrophages, providing one mechanism by which C1q downregulates pro-inflammatory cytokine production.

CONCLUSIONS

C1q-polarization of macrophages toward an anti-inflammatory (M2-like) phenotype may be important in dampening inflammation in the early atherosclerotic lesion. Further investigation of molecular pathways targeted by C1q may provide novel therapeutic targets for this disease.

The triggering receptor expressed on myeloid cells 2 inhibits complement component 1q effector mechanisms and exerts detrimental effects during pneumococcal pneumonia

Phagocytosis and inflammation within the lungs is crucial for host defense during bacterial pneumonia. Triggering receptor expressed on myeloid cells (TREM)-2 was proposed to negatively regulate TLR-mediated responses and enhance phagocytosis by macrophages, but the role of TREM-2 in respiratory tract infections is unknown. Here, we established the presence of TREM-2 on alveolar macrophages (AM) and explored the function of TREM-2 in the innate immune response to pneumococcal infection in vivo. Unexpectedly, we found Trem-2(-/-) AM to display augmented bacterial phagocytosis in vitro and in vivo compared to WT AM. Mechanistically, we detected that in the absence of TREM-2, pulmonary macrophages selectively produced elevated complement component 1q (C1q) levels. We found that these increased C1q levels depended on peroxisome proliferator-activated receptor-δ (PPAR-δ) activity and were responsible for the enhanced phagocytosis of bacteria. Upon infection with S. pneumoniae, Trem-2(-/-) mice exhibited an augmented bacterial clearance from lungs, decreased bacteremia and improved survival compared to their WT counterparts. This work is the first to disclose a role for TREM-2 in clinically relevant respiratory tract infections and demonstrates a previously unknown link between TREM-2 and opsonin production within the lungs.

Increased complement C1q level marks active disease in human tuberculosis

Background

Complement functions as an important host defense system and complement C5 and C7 have been implicated in immunopathology of tuberculosis. However, little is known about the role of other complement components in tuberculosis.

Methods

Complement gene expression in peripheral blood mononuclear cells of tuberculosis patients and controls were determined using whole genome transcriptional microarray assays. The mRNA and protein levels of three C1q components, C1qA, C1qB, and C1qC, were further validated by qRT-PCR and enzyme-linked immunosorbent assay, respectively. The percentages of C1q expression in CD14 positive cells were determined by flow cytometry. Finally, C1qC protein level was quantified in the pleural fluid of tuberculosis and non-tuberculosis pleurisy.

Results

C1q expression increases significantly in the peripheral blood of patients with active tuberculosis compared to healthy controls and individuals with latent TB infection. The percentage of C1q-expressing CD14 positive cells is significantly increased in active TB patients. C1q expression in the peripheral blood correlates with sputum smear positivity in tuberculosis patients and is reduced after anti-tuberculosis chemotherapy. Notably, receiver operating characteristic analysis showed that C1qC mRNA levels in peripheral blood efficiently discriminate active from latent tuberculosis infection and healthy controls. Additionally, C1qC protein level in pleural effusion shows improved power in discriminating tuberculosis from non-tuberculosis pleurisy when compared to other inflammatory markers, such as IL-6 and TNF-α.

Conclusions

C1q expression correlates with active disease in human tuberculosis. C1q could be a potential diagnostic marker to discriminate active tuberculosis from latent tuberculosis infection as well as tuberculosis pleurisy from non-tuberculosis pleurisy.