Evidence for non-traditional activation of complement factor C3 during murine liver regeneration

Complement Factor B Deficiency Is Dispensable for Female Fertility but Affects Microbiome Diversity and Complement Activity

Complement factor B (CFB) is a crucial component for the activation of the alternative pathway due to the formation of the C3 convertase with C3b, which further produces C3b to enhance the overall complement activity. Although Cfb is expressed not only in the immune tissues, but also in the reproductive tract, the physiological role of the alternative complement pathway in reproduction remains unclear. In this study, we addressed this issue by producing Cfb-knockout (KO) mice and analyzing their phenotypes. Sperm function, number of ovulated oocytes, and litter size were normal in KO mice. In contrast, the diversity of microbiomes in the gut and vaginal tract significantly increased in KO mice. Some serine protease activity in the serum from KO mice was lower than that of wild-type mice. Since the serum from KO mice showed significantly lower activity of the alternative complement pathway, CFB was found to be essential for this pathway. Our results indicate that although the alternative pathway is dispensable for normal fertility and development, it maintains the gut and vaginal microbiomes by suppressing their diversity and activating the alternative complement pathway.

Renal Epithelial Complement C3 Expression Affects Kidney Fibrosis Progression

Kidney fibrosis is a hallmark of chronic kidney diseases. Evidence shows that genetic variability and complement component 3 (C3) might influence tubulointerstitial fibrosis. Still, the role of renal C3 production in the epithelial-to-mesenchymal transition (EMT) and genetically determined fibrosis progression remains undiscovered. The kidneys of fibrosis-resistant C57Bl/6J (B6) and fibrosis-prone CBA/J (CBA) and BALB/cJ (BalbC) mice (n = 4-8/group) were subjected to unilateral ureteral obstruction (UUO) and analyzed after 1, 3, and 7 days, along with human focal glomerular sclerotic (FSGS) and healthy kidneys. Mouse primary tubular epithelial cells (PTECs) were investigated after 24 h of treatment with transforming growth factor β (TGFβ) or complement anaphylatoxin 3a (C3a) agonist (n = 4/group). UUO resulted in delayed kidney injury in fibrosis-resistant B6 mice, but very early renal C3 messenger RNA (mRNA) induction in fibrosis-prone CBA and BalbC mice, along with collagen I (Col1a1) and collagen III (Col3a1). CBA depicted the fastest fibrosis progression with the highest C3, lipocalin-2 (Lcn2), Tgfb1, and chemokine (C-C motif) ligand 2 (Ccl2) expression. Human FSGS kidneys depicted C3 mRNA over-expression and strong tubular C3 immunostaining. In PTECs, C3a agonist treatment induced pro-fibrotic early growth response protein 1 (EGR1) expression and the EMT, independent of TGFβ signaling. We conclude that de novo renal tubular C3 synthesis is associated with the genetically determined kidney fibrosis progression rate in mice and the pathogenesis of FSGS in humans. This tubular C3 overproduction can, through local pro-fibrotic effects, influence the progression of chronic kidney disease.

Crepuscular rays - The bright side of complement after tissue injury

Acute injuries trigger an intense activation of the body's defense mechanisms aiming to limit damage and initiate healing. Among the crucial components of the intravascular immune system, the complement system plays a significant role in traumatic injuries, albeit often negatively. It has been suggested that excessive activation of the complement system, transitioning from a localized and timed response to a systemic one, can lead to a loss of its host-protective characteristics. Complement activation products have been associated with the severity of injuries, which sometimes serve as predictors for the onset of organ dysfunctions. Animal studies utilizing complement-targeting agents have provided the basis for considering complement in the management of traumatic injuries in humans. However, numerous studies suggest that the spatial and temporal aspects of complement inhibition are crucial for its efficacy. Understanding the underlying mechanism of the injury is essential to determine where, when, and whether complement inhibition is warranted. Despite the detrimental effects of uncontrolled complement activation, its regulated activation may contribute to essential aspects of healing, such as waste removal and regeneration. This review focuses on the beneficial roles of complement activation in trauma, which are often overlooked or given less consideration but are of immense importance.

Complement-Coagulation Cross-talk: Factor H-mediated regulation of the Complement Classical Pathway activation by fibrin clots

The classical pathway of the complement system is activated by the binding of C1q in the C1 complex to the target activator, including immune complexes. Factor H is regarded as the key downregulatory protein of the complement alternative pathway. However, both C1q and factor H bind to target surfaces via charge distribution patterns. For a few targets, C1q and factor H compete for binding to common or overlapping sites. Factor H, therefore, can effectively regulate the classical pathway activation through such targets, in addition to its previously characterized role in the alternative pathway. Both C1q and factor H are known to recognize foreign or altered-self materials, e.g., bacteria, viruses, and apoptotic/necrotic cells. Clots, formed by the coagulation system, are an example of altered self. Factor H is present abundantly in platelets and is a well-known substrate for FXIIIa. Here, we investigated whether clots activate the complement classical pathway and whether this is regulated by factor H. We show here that both C1q and factor H bind to the fibrin formed in microtiter plates and the fibrin clots formed under in vitro physiological conditions. Both C1q and factor H become covalently bound to fibrin clots, and this is mediated via FXIIIa. We also show that fibrin clots activate the classical pathway of complement, as demonstrated by C4 consumption and membrane attack complex detection assays. Thus, factor H downregulates the activation of the classical pathway induced by fibrin clots. These results elucidate the intricate molecular mechanisms through which the complement and coagulation pathways intersect and have regulatory consequences.

Basophil Characteristics as a Marker of the Pathogenesis of Chronic Spontaneous Urticaria in Relation to the Coagulation and Complement Systems

Chronic spontaneous urticaria (CSU) is a common skin disorder characterized by daily or almost daily recurring skin edema and flare with itch and pruritus anywhere on the body for more than 6 weeks. Although basophil- and mast cell-released inflammatory mediators, such as histamine, play important roles in the pathogenesis of CSU, the detailed underlying mechanism is not clear. Since several auto-antibodies, IgGs which recognize IgE or the high-affinity IgE receptor (FcεRI) and IgEs against other self-antigens, are detected in CSU patients, they are considered to activate both mast cells in the skin and basophils circulating in the blood. In addition, we and other groups demonstrated that the coagulation and complement system also contribute to the development of urticaria. Here, we summarized the behaviors, markers and targets of basophils in relation to the coagulation-complement system, and for the treatment of CSU.

Characterization of complement C3 as a marker of alpha-amanitin toxicity by comparative secretome profiling

In the human body, proteins secreted into peripheral blood vessels are known as the secretome, and they represent the physiological or pathological status of cells. The unique response of cells to toxin exposure can be confirmed via secretome analysis, which can be used to discover toxic mechanisms or exposure markers. Alpha-amanitin (α-AMA) is the most widely studied amatoxin and inhibits transcription and protein synthesis by directly interacting with RNA polymerase II. However, secretory proteins released during hepatic failure caused by α-AMA have not been fully characterized. In this study, we analyzed the secretome of α-AMA-treated Huh-7 cells and mice using a comparative proteomics technique. Overall, 1440 and 208 proteins were quantified in cell media and mouse serum, respectively. Based on the bioinformatics results for the commonly downregulated proteins in cell media and mouse serum, we identified complement component 3 (C3) as a marker for α-AMA-induced hepatotoxicity. Through western blot in cell secretome and C3 ELISA assays in mouse serum, we validated α-AMA-induced downregulation of C3. In conclusion, using comparative proteomics and molecular biology techniques, we found that α-AMA-induced hepatotoxicity reduced C3 levels in the secretome. We expect that this study will aid in identifying new toxic mechanisms, therapeutic targets, and exposure markers of α-AMA-induced hepatotoxicity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-022-00163-z.

[The Functional Roles and the Potential as Drug Targets of Glycoproteins Regulating Complement and Coagulation Pathways]

Complement (C) activation occurs via three pathways, namely the classical, lectin, and alternative pathways. Intercommunication occurs between the complement and coagulation systems, which can trigger tissue injury and inflammation. Disseminated intravascular coagulation (DIC) is a life-threatening disease characterized by disordered coagulation and systemic inflammation; here, the intercommunication between the complement and coagulation systems contributes to the development of DIC. Extracellular histones, which are contributors to the damage-associated molecular pattern, induce severe thrombosis. C5 is a key molecule in the intercommunication between the complement and coagulation systems and is associated with the development of lethal histone-induced thrombosis. Heparin and chondroitin sulfate (CS) are negatively charged, allowing them to bind to extracellular histones. As the coagulation system is less affected by CS than heparin, CS shows potential as an effective drug for the treatment of patients with DIC who have a high risk of bleeding. Complement receptor type-1-related gene Y (Crry) inhibits the complement pathway via binding to C3b and C4b. Hence, Crry is a potent inhibitor of the classical and alternative C pathways. The expression of Crry is decreased by the endothelial damage induced by extracellular histones. Crry dysfunction promotes the activation of C on the surface of endothelial cells. The prevention of C3 cleavage on endothelial cells might be a useful therapy targeting acute lung injury.

The Aging Human Liver: The Weal and Woe of Evolutionary Legacy

Aging is characterized by the progressive decline of biological integrity and its compensatory mechanisms as well as immunological dysregulation. This goes along with an increasing risk of frailty and disease. Against this background, we here specifically focus on the aging of the human liver. For the first time, we shed light on the intertwining evolutionary underpinnings of the liver's declining regenerative capacity, the phenomenon of inflammaging, and the biotransformation capacity in the process of aging. In addition, we discuss how aging influences the risk for developing nonalcoholic fatty liver disease, hepatocellular carcinoma, and/or autoimmune hepatitis, and we describe chronic diseases as accelerators of biological aging.

The Yin and Yang of Immunity in Stem Cell Decision Guidance in Tissue Ecologies: An Infection Independent Perspective

The impact of immune system and inflammation on organ homeostasis and tissue stem cell niches in the absence of pathogen invasion has long remained a conundrum in the field of regenerative medicine. The paradoxical role of immune components in promoting tissue injury as well as resolving tissue damage has complicated therapeutic targeting of inflammation as a means to attain tissue homeostasis in degenerative disease contexts. This confound could be resolved by an integrated intricate assessment of cross-talk between inflammatory components and micro- and macro-environmental factors existing in tissues during health and disease. Prudent fate choice decisions of stem cells and their differentiated progeny are key to maintain tissue integrity and function. Stem cells have to exercise this fate choice in consultation with other tissue components. With this respect tissue immune components, danger/damage sensing molecules driving sterile inflammatory signaling cascades and barrier cells having immune-surveillance functions play pivotal roles in supervising stem cell decisions in their niches. Stem cells learn from their previous damage encounters, either endogenous or exogenous, or adapt to persistent micro-environmental changes to orchestrate their decisions. Thus understanding the communication networks between stem cells and immune system components is essential to comprehend stem cell decisions in endogenous tissue niches. Further the systemic interactions between tissue niches integrated through immune networks serve as patrolling systems to establish communication links and orchestrate micro-immune ecologies to better organismal response to injury and promote regeneration. Understanding these communication links is key to devise immune-centric regenerative therapies. Thus the present review is an integrated attempt to provide a unified purview of how inflammation and immune cells provide guidance to stem cells for tissue sculpting during development, organismal aging and tissue crisis based on the current knowledge in the field.

Advancing therapeutic complement inhibition in hematologic diseases: PNH and beyond

Complement is an elaborate system of the innate immunity. Genetic variants and autoantibodies leading to excessive complement activation are implicated in a variety of human diseases. Among them, the hematologic disease paroxysmal nocturnal hemoglobinuria (PNH) remains the prototype model of complement activation and inhibition. Eculizumab, the first-in-class complement inhibitor, was approved for PNH in 2007. Addressing some of the unmet needs, a long-acting C5 inhibitor, ravulizumab, and a C3 inhibitor, pegcetacoplan have been also now approved with PNH. Novel agents, such as factor B and factor D inhibitors, are under study with very promising results. In this era of several approved targeted complement therapeutics, selection of the proper drug needs to be based on a personalized approach. Beyond PNH, complement inhibition has also shown efficacy and safety in cold agglutinin disease (CAD), primarily with the C1s inhibitor of the classical complement pathway, sutimlimab, but also with pegcetacoplan. Furthermore, C5 inhibition with eculizumab and ravulizumab, as well as inhibition of the lectin pathway with narsoplimab, are investigated in transplant-associated thrombotic microangiopathy (TA-TMA). With this revolution of next-generation complement therapeutics, additional hematologic entities, such as delayed hemolytic transfusion reaction (DHTR) or immune thrombocytopenia (ITP), might also benefit from complement inhibitors. Therefore, this review aims to describe state-of-the-art knowledge of targeting complement in hematologic diseases focusing on: a) complement biology for the clinician, b) complement activation and therapeutic inhibition in prototypical complement-mediated hematologic diseases, c) hematologic entities under investigation for complement inhibition, and d) other complement-related disorders of potential interest to hematologists.

The Role of Coagulation and Complement Factors for Mast Cell Activation in the Pathogenesis of Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is a common skin disorder characterized by an almost daily recurrence of wheal and flare with itch for more than 6 weeks, in association with the release of stored inflammatory mediators, such as histamine, from skin mast cells and/or peripheral basophils. The involvement of the extrinsic coagulation cascade triggered by tissue factor (TF) and complement factors, such as C3a and C5a, has been implied in the pathogenesis of CSU. However, it has been unclear how the TF-triggered coagulation pathway and complement factors induce the activation of skin mast cells and peripheral basophils in patients with CSU. In this review, we focus on the role of vascular endothelial cells, leukocytes, extrinsic coagulation factors and complement components on TF-induced activation of skin mast cells and peripheral basophils followed by the edema formation clinically recognized as urticaria. These findings suggest that medications targeting activated coagulation factors and/or complement components may represent new and effective treatments for patients with severe and refractory CSU.

Emerging recognition of the complement system in hepatic ischemia/reperfusion injury, liver regeneration and recovery (Review)

Hepatic ischemia/reperfusion injury (IRI) is a result of the ischemic cascade and may occur in the settings of liver trauma, resection and transplantation. Components of the complement system have been indicated to be mediators of hepatic IRI and regulators of liver regeneration. As such, their potential to mediate both beneficial and harmful effects render them key targets for therapy. In the present study, the mechanisms of complement mediating hepatic IRI were discussed with a focus on the different functions of complement in hepatic injury and liver recovery, and an explanation for this apparent paradox is provided, i.e. that the complement products C3a and C5a have an important role in liver damage; however, C3a and C5a are also necessary for liver regeneration. Furthermore, situated at the end of the complement activation cascade, the membrane attack complex is crucial in hepatic IRI and inhibiting the complex with a site-targeted murine complement inhibitor, complement receptor 2-CD59, may improve liver regeneration after partial hepatectomy, even when hepatectomy is combined with ischemia and reperfusion.

Thrombin Inhibition by Argatroban: Potential Therapeutic Benefits in COVID-19

Thrombin is a trypsin-like serine protease with multiple physiological functions. Its role in coagulation and thrombosis is well-established. Nevertheless, thrombin also plays a major role in inflammation by activating protease-activated receptors. In addition, thrombin is also involved in angiogenesis, fibrosis, and viral infections. Considering the pathogenesis of COVID-19 pandemic, thrombin inhibitors may exert multiple potential therapeutic benefits including antithrombotic, anti-inflammatory, and antiviral activities. In this review, we describe the clinical features of COVID-19, the thrombin’s roles in various pathologies, and the potential of argatroban in COVID-19 patients. Argatroban is a synthetic, small molecule, direct, competitive, and selective inhibitor of thrombin. It is approved to parenterally prevent and/or treat heparin-induced thrombocytopenia in addition to other thrombotic conditions. Argatroban also possesses anti-inflammatory and antiviral activities and has a well-established pharmacokinetics profile. It also appears to lack a significant risk of drug–drug interactions with therapeutics currently being evaluated for COVID-19. Thus, argatroban presents a substantial promise in treating severe cases of COVID-19; however, this promise is yet to be established in randomized, controlled clinical trials.

Hallmarks of postoperative liver regeneration: An updated insight on the regulatory mechanisms

Performance and advances in liver surgery makes remarkable progress of the understanding of liver regeneration. Liver regeneration after liver resection has been widely researched, and the underlying mechanism mostly concerns proliferation of hepatocytes and the influence by inflammation through activation of Kupffer cells and the other parenchymal cells, the second regenerative pathway by hepatic progenitor cells (HPCs), inducing angiogenesis, remodeling of a extracellular matrix (ECM), and termination mechanisms. New clinical surgeries and the updated multiomics analysis are exploiting the remarkable progress, especially in immune regulation and metabolic process of two emerging hallmarks. This review briefly represents a systemic outline of eight hallmarks, including hepatocyte proliferation, contribution of hepatic progenitor cells, inducing angiogenesis, reprogramming of the extracellular matrix, apoptosis and termination of proliferation, inflammation, immune and metabolic regulation, which are set as organizing characteristics of postoperative liver regeneration and future directions of refining treatment targets.

Complementopathies and precision medicine

The renaissance of complement diagnostics and therapeutics has introduced precision medicine into a widened field of complement-mediated diseases. In particular, complement-mediated diseases (or complementopathies) with ongoing or published clinical trials of complement inhibitors include paroxysmal nocturnal hemoglobinuria, cold agglutinin disease, hemolytic uremic syndrome, nephropathies, HELLP syndrome, transplant-associated thrombotic microangiopathy, antiphospholipid antibody syndrome, myasthenia gravis, and neuromyelitis optica. Recognizing that this field is rapidly expanding, we aim to provide a state-of-the-art review of (a) current understanding of complement biology for the clinician, (b) novel insights into complement with potential applicability to clinical practice, (c) complement in disease across various disciplines (hematology, nephrology, obstetrics, transplantation, rheumatology, and neurology), and (d) the potential future of precision medicine. Better understanding of complement diagnostics and therapeutics will not only facilitate physicians treating patients in clinical practice but also provide the basis for future research toward precision medicine in this field.

The Role of Complement in Liver Injury, Regeneration, and Transplantation

The liver is both an immunologically complex and a privileged organ. The innate immune system is a central player, in which the complement system emerges as a pivotal part of liver homeostasis, immune responses, and crosstalk with other effector systems in both innate and adaptive immunity. The liver produces the majority of the complement proteins and is the home of important immune cells such as Kupffer cells. Liver immune responses are delicately tuned between tolerance to many antigens flowing in from the alimentary tract, a tolerance that likely makes the liver less prone to rejection than other solid organ transplants, and reaction to local injury, systemic inflammation, and regeneration. Notably, complement is a double-edged sword as activation is detrimental by inducing inflammatory tissue damage in, for example, ischemia-reperfusion injury and transplant rejection yet is beneficial for liver tissue regeneration. Therapeutic complement inhibition is rapidly developing for routine clinical treatment of several diseases. In the liver, targeted inhibition of damaged tissue may be a rational and promising approach to avoid further tissue destruction and simultaneously preserve beneficial effects of complement in areas of proliferation. Here, we argue that complement is a key system to manipulate in the liver in several clinical settings, including liver injury and regeneration after major surgery and preservation of the organ during transplantation.

Complement component 3 (C3): An important role in grass carp (Ctenopharyngodon idella) experimentally exposed to Aeromonas hydrophila

Complement is traditionally recognized as part of the innate immune system, defending the host against the invasion of foreign pathogens. In complement system, C3 (complement component 3) is a central component. Therefore, research into C3 can help us better understand the functions of fish complement system. In this study, we detected the grass carp C3 (gcC3) mRNA expression in all sample tissues from healthy grass carp, which was highest in the liver, followed by the heart and the spleen, and lowest in the muscle, head kidney, trunk kidney, blood and intestine. After infection with Aeromonas hydrophila, gcC3 mRNA expression levels were significantly upregulated in the gill, liver, spleen, intestine, trunk kidney and head kidney. Interestingly, C3 protein levels were downregulated and subsequently upregulated in the liver and serum. Histologically, C3 protein at 24 h pi was over expressed in necrotic liver sites, and the liver index (LI) at this point was significantly higher than that of the control. These findings are indicated that C3 plays an important role in the immune response of grass carp after A. hydrophila infection, and C3 protein may play an assistant role in repairing liver tissues from A. hydrophila injury.

Complement and coagulation cascades in trauma

Trauma remains a major cause of death throughout the world, especially for patients younger than 45 years. Due to rapid advances in clinical management, both in the acute and prehospital settings, trauma patients survive devastating injuries at unprecedented rates. However, these patients can often face life threatening complications that stem from the robust innate immune response induced by severe hemorrhage, leading to further tissue injury rather than repair. The complement and coagulation cascades are key mediators in this disordered reaction, which includes the development of trauma‐induced coagulopathy. There is increasing evidence that cross‐talk between these two pathways allows rapid amplification of their otherwise targeted responses and contributes to overwhelming and prolonged systemic inflammation. In this article, we summarize the initial steps of innate immune response to trauma and review the complex complement and coagulation cascades, as well as how they interact with each other. Despite progress in understanding these cascades, effective therapeutic targets have yet to be found and further research is needed both to improve survival rates as well as decrease associated morbidity.

Complement in Metastasis: A Comp in the Camp

The complement system represents a pillar of the innate immune response. This system, critical for host defense against pathogens, encompasses more than 50 soluble, and membrane-bound proteins. Emerging evidence underscores its clinical relevance in tumor progression and its role in metastasis, one of the hallmarks of cancer. The multistep process of metastasis entails the acquisition of advantageous functions required for the formation of secondary tumors. Thus, targeting components of the complement system could impact not only on tumor initiation but also on several crucial steps along tumor dissemination. This novel vulnerability could be concomitantly exploited with current strategies overcoming tumor-mediated immunosuppression to provide a substantial clinical benefit in the treatment of metastatic disease. In this review, we offer a tour d'horizon on recent advances in this area and their prospective potential for cancer treatment.

Natural immunoglobulin M initiates an inflammatory response important for both hepatic ischemia reperfusion injury and regeneration in mice

Complement plays a role in both hepatic ischemia reperfusion (IR) injury (IRI) and liver regeneration, but it is not clear how complement is activated in either process. We investigated the role of self-reactive immunoglobulin M (IgM) antibodies in activating complement after hepatic IR and liver resection. Natural IgM antibodies that recognize danger-associated molecular patterns (neoepitopes) activate complement following both hepatic IR and liver resection. Antibody-deficient Rag1^-/- mice were protected from hepatic IRI, but had increased hepatic injury and an impaired regenerative response after 70% partial hepatectomy (PHx). We identified two IgM monoclonal antibodies (mAbs) that specifically reversed the effect of Rag1 deficiency in both models; B4 (recognizes Annexin IV) and C2 (recognizes subset of phospholipids). Focusing on the B4-specific response, we demonstrated sinusoidal colocalization of IgM and C3d in Rag1^-/- mice that were reconstituted with B4 mAb, and furthermore that the Annexin IV neoepitope is specifically and similarly expressed after both hepatic IR and PHx in wild-type (WT) mice. A single-chain antibody construct (scFv) derived from B4 mAb blocked IgM binding and reduced injury post-IR in WT mice, although, interestingly, B4scFv did not alter regeneration post-PHx, indicating that anti-Annexin IV antibodies are sufficient, but not necessary, for the regenerative response in the context of an entire natural antibody repertoire. We also demonstrated expression of the B4 neoepitope in postischemic human liver samples obtained posttransplantation and a corollary depletion in IgM recognizing the B4 and C2 neoepitopes in patient sera following liver transplantation. Conclusion: These data indicate an important role for IgM in hepatic IRI and regeneration, with a similar cross-species injury-specific recognition system that has implications for the design of neoepitope targeted therapeutics. (Hepatology 2018;67:721-735).

Complement anaphylatoxins C3a and C5a: Emerging roles in cancer progression and treatment

Recent insights into the role of complement anaphylatoxins C3a and C5a in cancer provide new opportunities for the development of innovative biomarkers and therapeutic strategies. These two complement activation products can maintain chronic inflammation, promote an immunosuppressive microenvironment, induce angiogenesis, and increase the motility and metastatic potential of cancer cells. Still, the diverse heterogeneity of responses mediated by these peptides poses a challenge both to our understanding of the role played by these molecules in cancer progression and to the development of effective treatments. This review attempts to summarize the evidence surrounding the involvement of anaphylatoxins in the biological contexts associated with tumor progression. We also describe the recent developments that support the inhibition of anaphylatoxins, or their cognate receptors C3aR and C5aR1, as a treatment option for maximizing the clinical efficacy of current immunotherapies that target the PD-1/PD-L1 immune checkpoint.

Paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a clonal haematopoietic stem cell (HSC) disease that presents with haemolytic anaemia, thrombosis and smooth muscle dystonias, as well as bone marrow failure in some cases. PNH is caused by somatic mutations in PIGA (which encodes phosphatidylinositol N-acetylglucosaminyltransferase subunit A) in one or more HSC clones. The gene product of PIGA is required for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors; thus, PIGA mutations lead to a deficiency of GPI-anchored proteins, such as complement decay-accelerating factor (also known as CD55) and CD59 glycoprotein (CD59), which are both complement inhibitors. Clinical manifestations of PNH occur when a HSC clone carrying somatic PIGA mutations acquires a growth advantage and differentiates, generating mature blood cells that are deficient of GPI-anchored proteins. The loss of CD55 and CD59 renders PNH erythrocytes susceptible to intravascular haemolysis, which can lead to thrombosis and to much of the morbidity and mortality of PNH. The accumulation of anaphylatoxins (such as C5a) from complement activation might also have a role. The natural history of PNH is highly variable, ranging from quiescent to life-threatening. Therapeutic strategies include terminal complement blockade and bone marrow transplantation. Eculizumab, a monoclonal antibody complement inhibitor, is highly effective and the only licensed therapy for PNH.

Complement component 5 promotes lethal thrombosis

Extracellular histones promote platelet aggregation and thrombosis; this is followed by induction of coagulation disorder, which results in exhaustion of coagulation factors. Complement component 5 (C5) is known to be associated with platelet aggregation and coagulation system activation. To date, the pathological mechanism underlying liver injury has remained unclear. Here, we investigated whether C5 promotes liver injury associated with histone-induced lethal thrombosis. C5-sufficient and C5-deficient mice received single tail vein injections of purified, unfractionated histones obtained from calf thymus (45–75 μg/g). Subsequently, the mice were monitored for survival for up to 72 h. Based on the survival data, the 45 μg/g dose was used for analysis of blood cell count, liver function, blood coagulation ability, and promotion of platelet aggregation and platelet/leukocyte aggregate (PLA) production by extracellular histones. C5-deficient mice were protected from lethal thrombosis and had milder thrombocytopenia, consumptive coagulopathy, and liver injury with embolism and lower PLA production than C5-sufficient mice. These results indicate that C5 is associated with coagulation disorders, PLA production, and embolism-induced liver injury. In conclusion, C5 promotes liver injury associated with histone-induced lethal thrombosis.

Complement in the fundamental processes of the cell

Once regarded solely as an activator of innate immunity, it is now clear that the complement system acts in an assortment of cells and tissues, with immunity only one facet of a diverse array of functions under the influence of the complement proteins. Throughout development, complement activity has now been demonstrated from early sperm-egg interactions in fertilisation, to regulation of epiboly and organogenesis, and later in refinement of cerebral synapses. Complement has also been shown to regulate homeostasis of adult tissues, controlling cell processes such as migration, survival, repair, and regeneration. Given the continuing emergence of such novel actions of complement, the existing research likely represents only a fraction of the myriad of functions of this complex family of proteins. This review is focussed on outlining the current knowledge of complement family members in the regulation of cell processes in non-immune systems. It is hoped this will spur research directed towards revealing more about the role of complement in these fundamental cell processes.

Complement Factor 3 Could Be an Independent Risk Factor for Mortality in Patients with HBV Related Acute-on-Chronic Liver Failure

The complement is thought to be involved in the pathogenesis of multiple liver disorders. However, its role in patients with HBV related acute-on-chronic liver failure (HBV-ACLF) remains unclear. Serum levels of the third and fourth complement components (C3, C4) and complement function (CH50) were examined in this prospective, observational study. Associations between their expression and disease activity were analyzed. Survival was analyzed by Kaplan-Meier curves. Predictors of clinical outcome were determined by Cox regression analysis. C3, C4, and CH50 levels were significantly lower in HBV-ACLF patients compared to controls. C3, C4, and CH50 levels were negatively correlated with Tbil levels but positively associated with PTA levels. C3 levels were negatively associated with MELD-Na. C3 levels were significantly lower in HBV-ACLF patients who died compared to patients who survived. In a median hospital stay of 39 days, mortality occurred in 41 patients with a progressive increase based on C3 grade (P = 0.008). The actuarial probability of developing mortality was significantly higher in patients with low C3 grade compared to those with high C3 grade (P < 0.001). Multivariate Cox regression analysis showed that C3 levels were an independent predictor of mortality. Complement played a pathogenic role in HBV-ACLF patients and C3 was an independent predictor of mortality.

Postponing the Hypoglycemic Response to Partial Hepatectomy Delays Mouse Liver Regeneration

All serious liver injuries alter metabolism and initiate hepatic regeneration. Recent studies using partial hepatectomy (PH) and other experimental models of liver regeneration implicate the metabolic response to hepatic insufficiency as an important source of signals that promote regeneration. Based on these considerations, the analyses reported here were undertaken to assess the impact of interrupting the hypoglycemic response to PH on liver regeneration in mice. A regimen of parenteral dextrose infusion that delays PH-induced hypoglycemia for 14 hours after surgery was identified, and the hepatic regenerative response to PH was compared between dextrose-treated and control mice. The results showed that regenerative recovery of the liver was postponed in dextrose-infused mice (versus vehicle control) by an interval of time comparable to the delay in onset of PH-induced hypoglycemia. The regulation of specific liver regeneration-promoting signals, including hepatic induction of cyclin D1 and S-phase kinase-associated protein 2 expression and suppression of peroxisome proliferator-activated receptor γ and p27 expression, was also disrupted by dextrose infusion. These data support the hypothesis that alterations in metabolism that occur in response to hepatic insufficiency promote liver regeneration, and they define specific pro- and antiregenerative molecular targets whose regenerative regulation is postponed when PH-induced hypoglycemia is delayed.

Identification of an epigenetic signature of early mouse liver regeneration that is disrupted by Zn-HDAC inhibition

Liver regeneration has been well studied with hope of discovering strategies to improve liver disease outcomes. Nevertheless, the signals that initiate such regeneration remain incompletely defined, and translation of mechanism-based pro-regenerative interventions into new treatments for hepatic diseases has not yet been achieved. We previously reported the isoform-specific regulation and essential function of zinc-dependent histone deacetylases (Zn-HDACs) during mouse liver regeneration. Those data suggest that epigenetically regulated anti-proliferative genes are deacetylated and transcriptionally suppressed by Zn-HDAC activity or that pro-regenerative factors are acetylated and induced by such activity in response to partial hepatectomy (PH). To investigate these possibilities, we conducted genome-wide interrogation of the liver histone acetylome during early PH-induced liver regeneration in mice using acetyL-histone chromatin immunoprecipitation and next generation DNA sequencing. We also compared the findings of that study to those seen during the impaired regenerative response that occurs with Zn-HDAC inhibition. The results reveal an epigenetic signature of early liver regeneration that includes both hyperacetylation of pro-regenerative factors and deacetylation of anti-proliferative and pro-apoptotic genes. Our data also show that administration of an anti-regenerative regimen of the Zn-HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) not only disrupts gene-specific pro-regenerative changes in liver histone deacetylation but also reverses PH-induced effects on histone hyperacetylation. Taken together, these studies offer new insight into and suggest novel hypotheses about the epigenetic mechanisms that regulate liver regeneration.

The complement system and toll-like receptors as integrated players in the pathophysiology of atherosclerosis

Despite recent medical advances, atherosclerosis is a global burden accounting for numerous deaths and hospital admissions. Immune-mediated inflammation is a major component of the atherosclerotic process, but earlier research focus on adaptive immunity has gradually switched towards the role of innate immunity. The complement system and toll-like receptors (TLRs), and the crosstalk between them, may be of particular interest both with respect to pathogenesis and as therapeutic targets in atherosclerosis. Animal studies indicate that inhibition of C3a and C5a reduces atherosclerosis. In humans modified LDL-cholesterol activate complement and TLRs leading to downstream inflammation, and histopathological studies indicate that the innate immune system is present in atherosclerotic lesions. Moreover, clinical studies have demonstrated that both complement and TLRs are upregulated in atherosclerotic diseases, although interventional trials have this far been disappointing. However, based on recent research showing an intimate interplay between complement and TLRs we propose a model in which combined inhibition of both complement and TLRs may represent a potent anti-inflammatory therapeutic approach to reduce atherosclerosis.

Complement-Coagulation Cross-Talk: A Potential Mediator of the Physiological Activation of Complement by Low pH

The complement system is a major constituent of the innate immune system. It not only bridges innate and adaptive arms of the immune system but also links the immune system with the coagulation system. Current understanding of the role of complement has extended far beyond fighting of infections, and now encompasses maintenance of homeostasis, tissue regeneration, and pathophysiology of multiple diseases. It has been known for many years that complement activation is strongly pH sensitive, but only relatively recently has the physiological significance of this been appreciated. Most complement assays are carried out at the physiological pH 7.4. However, pH in some extracellular compartments, for example, renal tubular fluid in parts of the tubule, and extracellular fluid at inflammation loci, is sufficiently acidic to activate complement. The exact molecular mechanism of this activation is still unclear, but possible cross-talk between the contact system (intrinsic pathway) and complement may exist at low pH with subsequent complement activation. The current article reviews the published data on the effect of pH on the contact system and complement activity, the nature of the pH sensor molecules, and the clinical implications of these effects. Of particular interest is chronic kidney disease (CKD) accompanied by metabolic acidosis, in which therapeutic alkalinization of urine has been shown significantly to reduce tubular complement activation products, an effect, which may have important implications for slowing progression of CKD.

Complement: an overview for the clinician

The complement system is an essential component of the immune system. It is a highly integrative system and has a number of functions, including host defense, removal of injured cells and debris, modulation of metabolic and regenerative processes, and regulation of adaptive immunity. Complement is activated via different pathways and it is regulated tightly by several mechanisms to prevent host injury. Imbalance between complement activation and regulation can manifest in disease and injury to self. This article provides an outline of complement activation pathways, regulatory mechanisms, and normal physiologic functions of the system.

The role of the complement system in metabolic organs and metabolic diseases

Emerging evidence points to a close crosstalk between metabolic organs and innate immunity in the course of metabolic disorders. In particular, cellular and humoral factors of innate immunity are thought to contribute to metabolic dysregulation of the adipose tissue or the liver, as well as to dysfunction of the pancreas; all these conditions are linked to the development of insulin resistance and diabetes mellitus. A central component of innate immunity is the complement system. Interestingly, the classical view of complement as a major system of host defense that copes with infections is changing to that of a multi-functional player in tissue homeostasis, degeneration, and regeneration. In the present review, we will discuss the link between complement and metabolic organs, focusing on the pancreas, adipose tissue, and liver and the diverse effects of complement system on metabolic disorders.

Complement-triggered pathways orchestrate regenerative responses throughout phylogenesis

Adult tissue plasticity, cell reprogramming, and organ regeneration are major challenges in the field of modern regenerative medicine. Devising strategies to increase the regenerative capacity of tissues holds great promise for dealing with donor organ shortages and low transplantation outcomes and also provides essential impetus to tissue bioengineering approaches for organ repair and replacement. The inherent ability of cells to reprogram their fate by switching into an embryonic-like, pluripotent progenitor state is an evolutionary vestige that in mammals has been retained mostly in fetal tissues and persists only in a few organs of the adult body. Tissue regeneration reflects the capacity of terminally differentiated cells to re-enter the cell cycle and proliferate in response to acute injury or environmental stress signals. In lower vertebrates, this regenerative capacity extends to several organs and remarkably culminates in precise tissue patterning, through cellular transdifferentiation and complex morphogenetic processes that can faithfully reconstruct entire body parts. Many lessons have been learned from robust regeneration models in amphibians such as the newt and axolotl. However, the dynamic interactions between the regenerating tissue, the surrounding stroma, and the host immune response, as it adapts to the actively proliferating tissue, remain ill-defined. The regenerating zone, through a sequence of distinct molecular events, adopts phenotypic plasticity and undergoes rigorous tissue remodeling that, in turn, evokes a significant inflammatory response. Complement is a primordial sentinel of the innate immune response that engages in multiple inflammatory cascades as it becomes activated during tissue injury and remodeling. In this respect, complement proteins have been implicated in tissue and organ regeneration in both urodeles and mammals. Distinct complement-triggered pathways have been shown to modulate critical responses that promote tissue reprogramming, pattern formation, and regeneration across phylogenesis. This article will discuss the mechanistic insights underlying the crosstalk of complement with cytokine and growth factor signaling pathways that drive tissue regeneration and will provide a unified conceptual framework for considering complement modulation as a novel target for regenerative therapeutics.

Complement in animal development: unexpected roles of a highly conserved pathway

The complement pathway is most famous for its role in immunity, orchestrating an exquisitely refined system for immune surveillance. At its core lies a cascade of proteolytic events that ultimately serve to recognise microbes, infected cells or debris and target them for elimination. Mounting evidence has shown that a number of the proteolytic intermediaries in this cascade have, in themselves, other functions in the body, signalling through receptors to drive events that appear to be unrelated to immune surveillance. It seems, then, that the complement system not only functions as an immunological effector, but also has cell-cell signalling properties that are utilised by a number of non-immunological processes. In this review we examine a number of these processes in the context of animal development, all of which share a requirement for precise control of cell behaviour in time and space. As we will see, the scope of the complement system's function is indeed much greater than we might have imagined only a few years ago.

Analysis of the role of hepatic PPARγ expression during mouse liver regeneration

Mice subjected to partial hepatectomy (PH) develop hypoglycemia, followed by increased systemic lipolysis and hepatic fat accumulation, prior to onset of hepatocellular proliferation. Strategies that disrupt these metabolic events inhibit regeneration. These observations suggest that alterations in metabolism in response to hepatic insufficiency promote liver regeneration. Hepatic expression of the peroxisome proliferator-activated receptor gamma (PPARγ) influences fat accumulation in the liver. Therefore, the studies reported here were undertaken to assess the effects of disruption of hepatic PPARγ expression on hepatic fat accumulation and hepatocellular proliferation during liver regeneration. The results showed that liver regeneration was not suppressed, but rather modestly augmented in liver-specific PPARγ null mice maintained on a normal diet. These animals also exhibited accelerated hepatic cyclin D1 expression. Because hepatic PPARγ expression is increased in experimental models of fatty liver disease in which liver regeneration is impaired, regeneration in liver-specific PPARγ null mice with chronic hepatic steatosis was also examined. In contrast to the results described above, disruption of hepatic PPARγ expression in mice with diet-induced hepatic steatosis resulted in significant suppression of hepatic regeneration.

CONCLUSION

The metabolic and hepatocellular proliferative responses to PH are modestly augmented in liver-specific PPARγ null mice, thus providing additional support for a metabolic model of liver regeneration. Furthermore, regeneration is significantly impaired in liver-specific PPARγ null mice in the setting of diet-induced chronic steatosis, suggesting that pharmacological strategies to augment hepatic PPARγ activity might improve regeneration of the fatty liver.

The influence of skeletal muscle on the regulation of liver:body mass and liver regeneration

The relationship between liver and body mass is exemplified by the precision with which the liver:body mass ratio is restored after partial hepatic resection. Nevertheless, the compartments, against which liver mass is so exquisitely regulated, currently remain undefined. In the studies reported here, we investigated the role of skeletal muscle mass in the regulation of liver:body mass ratio and liver regeneration via the analysis of myostatin-null mice, in which skeletal muscle is hypertrophied. The results showed that liver mass is comparable and liver:body mass significantly diminished in the null animals compared to age-, sex-, and strain-matched controls. In association with these findings, basal hepatic Akt signaling is decreased, and the expression of the target genes of the constitutive androstane receptor and the integrin-linked kinase are dysregulated in the myostatin-null mice. In addition, the baseline expression levels of the regulators of the G1-S phase cell cycle progression in liver are suppressed in the null mice. The initiation of liver regeneration is not impaired in the null animals, although it progresses toward the lower liver:body mass set point. The data show that skeletal muscle is not the body component against which liver mass is positively regulated, and thus they demonstrate a previously unrecognized systemic compartmental specificity for the regulation of liver:body mass ratio.

Advances in assay of complement function and activation

The main function of the complement system is pattern recognition of danger. Typical exogenous danger signals are pathogen associated molecular patterns inducing a protective inflammatory response. Other examples are exposure to foreign surfaces of biomedical materials including nanoparticles, which principally induce the same inflammatory response. If a surface is "foreign" to the host, it induces complement activation. Development of monoclonal antibodies to neoepitopes on complement activation products introduced an entirely new set of methods for assay of complement activation. Activation of complement by a surface occurs by impairment of the fine balance of the control system, e.g. by preferred binding of factor B at the expense of factor H. Sensitive methods to detect complement activation on surfaces and in the fluid phase are a prerequisite for investigation of the biocompatibility of artificial materials. This information can be used to develop new materials with enhanced biocompatibility. Here we review available methods to study human and animal complement function and activation in vitro and in vivo.

Targeting of mannan-binding lectin-associated serine protease-2 confers protection from myocardial and gastrointestinal ischemia/reperfusion injury

Complement research experienced a renaissance with the discovery of a third activation route, the lectin pathway. We developed a unique model of total lectin pathway deficiency, a mouse strain lacking mannan-binding lectin-associated serine protease-2 (MASP-2), and analyzed the role of MASP-2 in two models of postischemic reperfusion injury (IRI). In a model of transient myocardial IRI, MASP-2-deficient mice had significantly smaller infarct volumes than their wild-type littermates. Mice deficient in the downstream complement component C4 were not protected, suggesting the existence of a previously undescribed lectin pathway-dependent C4-bypass. Lectin pathway-mediated activation of C3 in the absence of C4 was demonstrated in vitro and shown to require MASP-2, C2, and MASP-1/3. MASP-2 deficiency also protects mice from gastrointestinal IRI, as do mAb-based inhibitors of MASP-2. The therapeutic effects of MASP-2 inhibition in this experimental model suggest the utility of anti-MASP-2 antibody therapy in reperfusion injury and other lectin pathway-mediated disorders.

Controlling coagulation dysregulation in xenotransplantation

PURPOSE OF REVIEW

Deletion of the α1,3-galactosyltransferase (GalT) gene in pigs has removed a major xenoantigen but has not eliminated the problem of dysregulated coagulation and vascular injury. Rejecting GalT knockout organ xenografts almost invariably show evidence of thrombosis and platelet sequestration, and primate recipients frequently develop consumptive coagulopathy. This review examines recent findings that illuminate potential mechanisms of this current barrier to successful xenotransplantation.

RECENT FINDINGS

The coagulation response to xenotransplantation differs depending on the type of organ and quite likely the distinct vasculatures. Renal xenografts appear more likely to initiate consumptive coagulopathy than cardiac xenografts, possibly reflecting differential transcriptional responses. Liver xenografts induce rapid and profound thrombocytopenia resulting in recipient death within days due to bleeding; ex-vivo data suggest that liver endothelial cells and hepatocytes are responsible for platelet consumption by a coagulation-independent process.It has been proposed that expression of recipient tissue factor on platelets and monocytes is an important trigger of consumptive coagulopathy. Finally, pigs transgenic for human anticoagulants and antithrombotics are slowly but surely coming on line, but have not yet been rigorously tested to date.

SUMMARY

Successful control of coagulation dysregulation in xenotransplantation may require different combinatorial pharmacological and genetic strategies for different organs.

The development of inflammatory joint disease is attenuated in mice expressing the anticoagulant prothrombin mutant W215A/E217A

Thrombin is a positive mediator of thrombus formation through the proteolytic activation of protease-activated receptors (PARs), fibrinogen, factor XI (fXI), and other substrates, and a negative regulator through activation of protein C, a natural anticoagulant with anti-inflammatory/cytoprotective properties. Protease-engineering studies have established that 2 active-site substitutions, W215A and E217A (fII(WE)), result in dramatically reduced catalytic efficiency with procoagulant substrates while largely preserving thrombomodulin (TM)-dependent protein C activation. To explore the hypothesis that a prothrombin variant favoring antithrombotic pathways would be compatible with development but limit inflammatory processes in vivo, we generated mice carrying the fII(WE) mutations within the endogenous prothrombin gene. Unlike fII-null embryos, fII(WE/WE) mice uniformly developed to term. Nevertheless, these mice ultimately succumbed to spontaneous bleeding events shortly after birth. Heterozygous fII(WT/WE) mice were viable and fertile despite a shift toward an antithrombotic phenotype exemplified by prolonged tail-bleeding times and times-to-occlusion after FeCl₃ vessel injury. More interestingly, prothrombin(WE) expression significantly ameliorated the development of inflammatory joint disease in mice challenged with collagen-induced arthritis (CIA). The administration of active recombinant thrombin(WE) also suppressed the development of CIA in wild-type mice. These studies provide a proof-of-principle that pro/thrombin variants engineered with altered substrate specificity may offer therapeutic opportunities for limiting inflammatory disease processes.

Inhibition of complement alternative pathway suppresses experimental autoimmune anterior uveitis by modulating T cell responses

The objective of the current study was to delineate the pathway of complement activation that is crucial for the induction of experimental autoimmune anterior uveitis (EAAU). We studied the development of EAAU in melanin-associated antigen (MAA)-sensitized Lewis rats treated with antibody against C4 or factor B. Control animals received isotype IgG control. Antibody against C4 had no effect on EAAU, and all of the animals developed EAAU similar to those injected with control IgG. In contrast, EAAU was completely inhibited in all MAA-sensitized Lewis rats injected with factor B antibody. Treatment with anti-factor B antibody resulted in suppression of ocular complement activation. Adoptive transfer of T lymphocytes harvested from draining lymph nodes of donor animals treated with anti-factor B did not transfer EAAU to naïve syngenic rats. Anti-factor B antibody inhibited the ability of MAA-specific CD4(+) T cells to proliferate (in vitro) in response to MAA in a dose-dependent manner. Level of TNF-α and IFN-γ decreased in the presence of anti-factor B. Collectively, our results provide the novel finding that complement activation via the alternative pathway contributes to intraocular inflammation in EAAU, and anti-factor B-mediated inhibition of EAAU is due to diminished antigen-specific CD4(+) T cell responses to MAA. Our findings explain the interactions between the complement system and T cells that are critical for the induction of EAAU and may lead to the development of therapy for idiopathic anterior uveitis based on selective blockade of the alternative pathway.

Liver regeneration is impaired in lipodystrophic fatty liver dystrophy mice

We previously reported that mice subjected to partial hepatectomy exhibit rapid development of hypoglycemia followed by transient accumulation of fat in the early regenerating liver. We also showed that disrupting these metabolic alterations results in impaired liver regeneration. The studies reported here were undertaken to further characterize and investigate the functional importance of changes in systemic adipose metabolism during normal liver regeneration. The results showed that a systemic catabolic response is induced in each of two distinct, commonly used experimental models of liver regeneration (partial hepatectomy and carbon tetrachloride treatment), and that this response occurs in proportion to the degree of induced hepatic insufficiency. Together, these observations suggest that catabolism of systemic adipose stores may be essential for normal liver regeneration. To test this possibility, we investigated the hepatic regenerative response in fatty liver dystrophy (fld) mice, which exhibit partial lipodystrophy and have diminished peripheral adipose stores. The results showed that the development of hypoglycemia and hepatic accumulation of fat was attenuated and liver regeneration was impaired following partial hepatectomy in these animals. The fld mice also exhibited increased hepatic p21 expression and diminished plasma levels of the adipose-derived hormones adiponectin and leptin, which have each been implicated as regulators of liver regeneration.

CONCLUSION

These data suggest that the hypoglycemia that develops after partial hepatectomy induces systemic lipolysis followed by accumulation of fat derived from peripheral stores in the early regenerating liver, and that these events may be essential for initiation of normal liver regeneration.

Molecular intercommunication between the complement and coagulation systems

The complement system as well as the coagulation system has fundamental clinical implications in the context of life-threatening tissue injury and inflammation. Associations between both cascades have been proposed, but the precise molecular mechanisms remain unknown. The current study reports multiple links for various factors of the coagulation and fibrinolysis cascades with the central complement components C3 and C5 in vitro and ex vivo. Thrombin, human coagulation factors (F) XIa, Xa, and IXa, and plasmin were all found to effectively cleave C3 and C5. Mass spectrometric analyses identified the cleavage products as C3a and C5a, displaying identical molecular weights as the native anaphylatoxins C3a and C5a. Cleavage products also exhibited robust chemoattraction of human mast cells and neutrophils, respectively. Enzymatic activity for C3 cleavage by the investigated clotting and fibrinolysis factors is defined in the following order: FXa > plasmin > thrombin > FIXa > FXIa > control. Furthermore, FXa-induced cleavage of C3 was significantly suppressed in the presence of the selective FXa inhibitors fondaparinux and enoxaparin in a concentration-dependent manner. Addition of FXa to human serum or plasma activated complement ex vivo, represented by the generation of C3a, C5a, and the terminal complement complex, and decreased complement hemolytic serum activity that defines exact serum concentration that results in complement-mediated lysis of 50% of sensitized sheep erythrocytes. Furthermore, in plasma from patients with multiple injuries (n = 12), a very early appearance and correlation of coagulation (thrombin-antithrombin complexes) and the complement activation product C5a was found. The present data suggest that coagulation/fibrinolysis proteases may act as natural C3 and C5 convertases, generating biologically active anaphylatoxins, linking both cascades via multiple direct interactions in terms of a complex serine protease system.

Role of ocular complement factor H in a murine model of choroidal neovascularization

The objective of this study was to explore the relationship between local (ie, ocular) complement factor H (CFH) and choroidal neovascularization (CNV) associated with wet age-related macular degeneration (AMD), a leading cause of irreversible blindness, in laser-treated C57BL/6 mice. Immunohistochemical and RT-PCR analysis of retinal pigmented epithelium (RPE)-choroid sclera revealed that the expression of CFH was down-regulated on day 1 with a dramatic increase on days 5 and 7 postlaser injury. Flat mount and Western blot analysis further revealed that membrane attack complex (MAC) expression was up-regulated on days 1 and 3 postlaser injury; however, MAC was down-regulated on days 5 and 7 postinjury but was still higher than in non-injured mice. Similar patterns for CFH and MAC were observed for RPE cells when serial paraffin sections of the laser spots were analyzed. Subretinal injection of siRNA directed against CFH resulted in a threefold suppression of CFH in the RPE and choroid without affecting either CFH levels in the liver or the functional activity of the alternative pathway in the peripheral blood. Ocular knock-down of CFH resulted in increased MAC deposition, which leads to the early onset as well as exacerbation of laser-induced CNV. In conclusion, our findings provide evidence that CFH present on RPE and choroid regulates local MAC formation that is critical for the development of laser-induced CNV.

Complement and neutrophil function changes after liver resection in humans

BACKGROUND

Complement activation contributes to the regulation of liver regeneration after liver resection (LR) in mice.

METHODS

We hypothesized that complement activation and changes in C5a-receptors (C5aR, C5L2) on polymorphonuclear cells (PMN) and monocytes are important in clinical LR. Anaphylatoxin and C5b9 plasma levels were measured (bead-array, ELISA) (25 patients) and receptor expression was assessed after LR (19 patients) (FACS). In vitro PMN C5a-dependent chemotactic response (7 patients) as well as L-selectin shedding and Mac-1 expression (3 patients) was determined.

RESULTS

C3a increased after LR (31.1 +/- 4 before LR vs. 41.6 +/- 5 ng/ml, 30 min after LR, P < 0.01), as did C5b9 (12.7 +/- 1 before LR vs. 26.9 +/- 3 ng/ml, 60 min after LR, P < 0.001). C4a and C5a decreased after LR, by 25% 24 h after LR and 30% 2 h after LR, respectively (P < 0.01). C5L2 expression decreased at 4 h, rising at 24 h after LR (PMN: 6.3 +/- 1 before LR, 3.1 +/- 1, 4 h, 8.3 +/- 2, 24 h; P < 0.01). The receptor-related changes accompanied a diminished C5a-dependent chemotactic response by PMN (42.1 +/- 17 before LR vs. 2.1 +/- 3 4 h after LR; P < 0.01) and a reduction of activation upon C5a-R stimulation as measured by L-selectin shedding and Mac-1 expression on PMN. Changes in C5L2 expression on monocytes paralleled postoperative impairment of liver function.

CONCLUSIONS

These results indicate that complement components are released after clinical LR and subsequently PMN display altered C5a-dependent functional responses.

Oversulfated Heparin By-Products Induce Thrombin Generation in Human Plasmas Through Contact System Activation

Thrombin generation is thought to be mediated predominantly by the tissue factor or ‘‘extrinsic’’ coagulation pathway. An alternate pathway to thrombin generation (the ‘‘intrinsic’’ pathway or contact system) has been observed when blood or plasma comes in contact with artificial surfaces. Here we present evidence for a new route to thrombin formation that begins with the activation of the contact system protein prekallikrein by oversulfated heparin (OS-HB). Kallikrein, instead of activated factor X, cleaves prothrombin to form thrombin. Thrombin then cleaves fibrinogen to form fibrin clots. Moreover, we show that OS-HB by-products induce kallikrein- and thrombin-like activities in normal human plasma and in human plasma devoid of coagulation factor X or downstream contact system components factor IX or factor XI. Oversulfated heparin by-product-induced thrombin generation may have had a role in the adverse reactions associated with the recent clinical use of contaminated heparin.

Chemically oversulfated glycosaminoglycans are potent modulators of contact system activation and different cell signaling pathways

Contaminated heparin was associated with adverse reactions by activating the contact system. Chemically oversulfated/modified glycosaminoglycans (GAGs) consisting of heparan sulfate, dermatan sulfate, and chondroitin sulfate have been identified as heparin contaminants. Current studies demonstrated that each component of oversulfated GAGs was comparable with oversulfated chondroitin sulfate in activating the contact system. By testing a series of unrelated negatively charged compounds, we found that the contact system recognized negative charges rather than specific chemical structures. We further tested how oversulfated GAGs and contaminated heparins affect different cell signaling pathways. Our data showed that chemically oversulfated GAGs and contaminated heparin had higher activity than the parent compounds and authentic heparin, indicative of sulfation-dominant and GAG sequence-dependent activities in BaF cell-based models of fibroblast growth factor/fibroblast growth factor receptor, glial cell line-derived neurotrophic factor/c-Ret, and hepatocyte growth factor/c-Met signaling. In summary, these data indicate that contaminated heparins intended for blood anticoagulation not only activated the contact system but also modified different GAG-dependent cell signaling pathways.

Glycosaminoglycan (GAG) biosynthesis and GAG-binding proteins

Two major types of glycosaminoglycan (GAG) polysaccharides, heparan sulfate and chondroitin sulfate, are polymerized and modified by enzymes that are encoded by more than 40 genes in animal cells. Because of the expression repertoire of the GAG assembly and modification enzymes, each heparan sulfate and chondroitin sulfate chain has a sulfation pattern, chain length, and fine structure that is potentially unique to each animal cell. GAGs interact with hundreds of proteins. Such interactions protect growth factors, chemokines, and cytokines against proteolysis. GAGs catalyze protease (such as thrombin) inhibition by serpins. GAGs regulate multiple signaling pathways including, but not limited to, fibroblast growth factor (FGF)/FGFR, hepatocyte growth factor (HGF)/c-Met, glial cell line-derived neurotrophic factor (GDNF)/c-Ret/GFRalpha1, vascular endothelial growth factor (VEGF)/VEGFR, platelet derived growth factor (PDGF)/PDGFR, BAFF/TACI, Indian hedgehog, Wnt, and BMP signaling pathways,where genetic studies have revealed an absolute requirement for GAGs in these pathways. Most importantly, protein/GAG aggregates induce thrombin generation and immune system upregulation by activating the contact system. Abnormal protein/GAG aggregates are associated with a variety of devastating human diseases including, but not limited to, Alzheimer's, diabetes, prion or transmissible spongiform encephalopathies, Lupus, heparin-induced thrombocytopenia/thrombosis, and different kinds of cancers. Therefore, GAGs are essential components of modern molecular biology and human physiology. Understanding GAG structure and function at molecular level with regard to development and health represents a unique opportunity in combating different kinds of human diseases.