The complement cascade in kidney disease: from sideline to center stage

Complement C3 Deficiency Enhances Renal Leptospiral Load and Inflammation While Impairing T Cell Differentiation During Chronic Leptospira interrogans Infection

Leptospirosis is a neglected zoonotic disease caused by pathogenic Leptospira spp., affecting an estimated of one million people annually and resulting in approximately 60,000 fatalities. The disease can lead to hepatic, renal, and pulmonary dysfunctions and may contribute to the development of chronic kidney disease. The Complement System plays a crucial role in eliminating bacteria by generating opsonins, anaphylotoxins, that degranulate mastocytes and basophils, and attract immune cells to the infection site, among other important functions. This study aimed to investigate the role of C3, the central protein of the Complement System, in vivo during chronic infection of L interrogans serovar Copenhageni strain FIOCRUZ L1-130 (LIC). C57BL/6 wild-type (WT) and C3 knockout (C3KO) mice were infected with 10 8 LIC and monitored at 15, 30, 60, 90 and 180 days' post-infection (d.p.i.). LIC-infected C3KO mice exhibited a significantly higher leptospiral load in the kidneys compared to WT counterparts. Both groups showed local inflammation at 15 and 30 d.p.i., but only C3KO LIC-infected mice had a higher number of Leptospira DNA copies at 30 d.p.i. At the same time point, C3KO LIC-infected mice developed a larger fibrotic area than WT mice. Interestingly, independent of C3, mice pre-treated with a nephrotoxic drug increased the renal inflammatory response; however, this pretreatment did not affect the local leptospiral load in infected mice. Additionally, levels of specific IgG2b and IgG3 antibodies were significantly higher in LIC-infected C3KO mice compared to WT mice. Proteomic analysis showed lower levels of C5/C5a in WT and C3KO LIC-infected mice, as well as in C3KO control mice. M-CSF and SDF-1 cytokine levels were reduced in both LIC-infected groups. Furthermore, naïve T lymphocytes count (both CD4 + and CD8 + ) were higher in LIC-infected C3KO mice, whereas effector CD8 + T lymphocyte numbers declined during LIC infection - a phenomenon more pronounced in C3KO mice. Overall, this study demonstrates that during LIC infection, the absence of C3 does not affect mouse survival but leads to increased renal leptospiral load and fibrosis. Additionally, it highlights the crucial role of C3 in supporting the maturation and differentiation of T lymphocytes into pre-effector cells, underscoring its importance as a key link between the innate and adaptive immune responses in leptospirosis.

Author Summary

Leptospirosis is an infectious disease with approximately one million new cases annually and is responsible for about 5% of deaths, particularly in underdeveloped countries. Our objective is to understand the immune response in leptospirosis, specifically the role of the Complement C3 protein. In this study, we observed that C3 deficiency is associated with a higher renal leptospiral load and an increased incidence of renal fibrosis after one month of chronic infection. Notably, C3 also influences the differentiation of helper and cytotoxic T lymphocytes into effector cells, potentially contributing to the increased severity of chronic leptospirosis observed in C3-deficient animals.

Intraperitoneal MASP-1 Levels are Associated with Peritoneal Solute Transport Rate in Peritoneal Dialysis Patients: A Retrospective Cohort Study

Purpose

A major limitation of long-term peritoneal dialysis (PD) is peritoneal membrane dysfunction characterized by faster peritoneal solute-transport rate (PSTR). This study aimed to identify efficient complement factors in peritoneal effluents of continuous ambulatory peritoneal dialysis (CAPD) patients that can predict the PSTR.

Methods

A multiplex suspension protein array was used to screened related complement pathways in overnight peritoneal effluents among 58 CAPD patients. Then the related complement factors in lectin and classical pathways in effluents were analyzed using ELISA kits among another cohort of 129 CAPD patients. Logistic regression modeling was fitted to predict the PSTR of PD patients.

Results

The multiplex suspension protein array showed complement factors including C2, C4b, C5, C5a, Factor D, Factor I, and MBL were detected in effluents of CAPD patients, and the effluent C2 Appearance rate (Ar) and C4b Ar levels were significantly correlated with D/P Cr and D/D0 glucose. The levels of effluents MASP-1 Ar, M-Ficolin Ar, C2 Ar and C4b Ar, which belong to the lectin pathway were also positively correlated with D/P Cr according the ELISA results and these parameters were expressed higher in the high and high-average (H/HA) groups according to the PET results. Moreover, effluent Masp-1 was independently associated with increased PSTR and adverse events related peritoneal transport function failure.

Conclusion

This study suggested that the lectin pathway may be involved in local complement activation and peritoneal injury of PD patients, intraperitoneal level of Masp-1 was an independent predictor of increased PSTR in PD patients.

A review of progress on complement and primary membranous nephropathy

Primary membranous nephropathy (PMN) is a predominant cause of adult nephrotic syndrome, with its incidence witnessing a progressive surge over time. Approximately 35% to 47% of patients progress to renal failure within 10 years, causing a huge social burden. Within China, the proportion of PMN in primary glomerular disease exhibits a gradual ascension. Recent studies have shown that the 3 activation pathways of complement: the classical pathway, mannose-binding lectin pathway, and alternative pathway, are all involved in the pathogenesis of PMN. Despite historical limitations in detecting C1q deposits on the glomeruli of PMN in the past, recent studies have confirmed the classical pathway is implicated in patients with PMN. Considering the dysregulation of the complement system has been observed in PMN, complement inhibitors become increasingly promising. Several clinical trials are presently underway to evaluate the efficacy of complement inhibitors, such as MASP2 antagonists (OMS721), C3 and C3b antagonists (APL2), FD inhibitors (BCX9930), C3aR antagonists (SB290157 and JR14a), FB inhibitors (LNP023). This article reviews the recent research progress on the role of the complement pathway in the pathogenesis of PMN, and underscores the importance of continued research into the complement pathway and its inhibitors, which may pave the way for groundbreaking advancements in the management of PMN.

Doxycycline Alters the Porcine Renal Proteome and Degradome during Hypothermic Machine Perfusion

Ischemia-reperfusion injury (IRI) is a hallmark for tissue injury in donation after circulatory death (DCD) kidneys. The implementation of hypothermic machine perfusion (HMP) provides a platform for improved preservation of DCD kidneys. Doxycycline administration has shown protective effects during IRI. Therefore, we explored the impact of doxycycline on proteolytic degradation mechanisms and the urinary proteome of perfused kidney grafts. Porcine kidneys underwent 30 min of warm ischemia, 24 h of oxygenated HMP (control/doxycycline) and 240 min of ex vivo reperfusion. A proteomic analysis revealed distinctive clustering profiles between urine samples collected at T15 min and T240 min. High-efficiency undecanal-based N-termini (HUNTER) kidney tissue degradomics revealed significantly more proteolytic activity in the control group at T-10. At T240, significantly more proteolytic activity was observed in the doxycycline group, indicating that doxycycline alters protein degradation during HMP. In conclusion, doxycycline administration during HMP led to significant proteomic and proteolytic differences and protective effects by attenuating urinary NGAL levels. Ultimately, we unraveled metabolic, and complement and coagulation pathways that undergo alterations during machine perfusion and that could be targeted to attenuate IRI induced injury.

Uromodulin aggravates renal tubulointerstitial injury through activation of the complement pathway in rats

Uromodulin (Umod) is the most abundant constituent of urine in humans and exclusively found in the kidney tubular epithelium. However, the specific role of Umod in renal tubulointerstitial injury is yet to be understood. The present study was conducted with aim of investigating the potential therapeutic mechanism of Umod in the regulation of renal tubulointerstitial injury. Protein expression of Umod in renal tubular epithelial cells was measured with the conduction of Western blot analysis. Enzyme-linked immunosorbent assay and immunofluorescence assay were performed to detect the complement activation products and the activation products of surface deposition. The expression of C1q, C2, C4, B factor, C3, C5, H factor, CD46, CD55, C3aR, and C5aR were determined with the use of reverse-transcription quantitative polymerase chain reaction and Western blot analyses. Subsequently, the unilateral ureteral obstruction (UUO) rat model was established. Renal tubulointerstitial injury was assessed with the application of hematoxylin-eosin staining and Masson staining in rats. UUO rats and normal rats were injected with si-NC or si-Umod and complement inhibitor. UUO rats were observed to have serious impairment of kidney tubule, renal tubular dilation, and epithelial atrophy, with downregulated Umod and activated complement pathway. Silencing of Umod resulted in the activation of complement system while promoting interstitial fibrosis in renal tubules. Moreover, addition of complement inhibitor significantly alleviated the renal tubule injury and fibrosis. Collectively, our study suggests that silencing of Umod mediates the complement pathway, exacerbating renal tubulointerstitial injury in rats, which provides insight into the development of novel therapeutic agents for renal tubulointerstitial injury.

The pathogenesis of diclofenac induced immunoallergic hepatitis in a canine model of liver injury

Hypersensitivity to non-steroidal anti-inflammatory drugs is a common adverse drug reaction and may result in serious inflammatory reactions of the liver. To investigate mechanism of immunoallergic hepatitis beagle dogs were given 1 or 3 mg/kg/day (HD) oral diclofenac for 28 days. HD diclofenac treatment caused liver function test abnormalities, reduced haematocrit and haemoglobin but induced reticulocyte, WBC, platelet, neutrophil and eosinophil counts. Histopathology evidenced hepatic steatosis and glycogen depletion, apoptosis, acute lobular hepatitis, granulomas and mastocytosis. Whole genome scans revealed 663 significantly regulated genes of which 82, 47 and 25 code for stress, immune response and inflammation. Immunopathology confirmed strong induction of IgM, the complement factors C3&B, SAA, SERPING1 and others of the classical and alternate pathway. Alike, marked expression of CD205 and CD74 in Kupffer cells and lymphocytes facilitate antigen presentation and B-cell differentiation. The highly induced HIF1A and KLF6 protein expression in mast cells and macrophages sustain inflammation. Furthermore, immunogenomics discovered 24, 17, 6 and 11 significantly regulated marker genes to hallmark M1/M2 polarized macrophages, lymphocytic and granulocytic infiltrates; note, the latter was confirmed by CAE staining. Other highly regulated genes included alpha-2-macroglobulin, CRP, hepcidin, IL1R1, S100A8 and CCL20. Diclofenac treatment caused unprecedented induction of myeloperoxidase in macrophages and oxidative stress as shown by SOD1/SOD2 immunohistochemistry. Lastly, bioinformatics defined molecular circuits of inflammation and consisted of 161 regulated genes.

Altogether, the mechanism of diclofenac induced liver hypersensitivity reactions involved oxidative stress, macrophage polarization, mastocytosis, complement activation and an erroneous programming of the innate and adaptive immune system.

Complement related kidney diseases: Recurrence after transplantation

The recurrence of renal disease after renal transplantation is becoming one of the main causes of graft loss after kidney transplantation. This principally concerns some of the original diseases as the atypical hemolytic uremic syndrome (HUS), the membranoproliferative glomerulonephritis (MPGN), in particular the MPGN now called C3 glomerulopathy. Both this groups of renal diseases are characterized by congenital (genetic) or acquired (auto-antibodies) modifications of the alternative pathway of complement. These abnormalities often remain after transplantation because they are constitutional and poorly influenced by the immunosuppression. This fact justifies the high recurrence rate of these diseases. Early diagnosis of recurrence is essential for an optimal therapeutically approach, whenever possible. Patients affected by end stage renal disease due to C3 glomerulopathies or to atypical HUS, may be transplanted with extreme caution. Living donor donation from relatives is not recommended because members of the same family may be affected by the same gene mutation. Different therapeutically approaches have been attempted either for recurrence prevention and treatment. The most promising approach is represented by complement inhibitors. Eculizumab, a monoclonal antibody against C5 convertase is the most promising drug, even if to date is not known how long the therapy should be continued and which are the best dosing. These facts face the high costs of the treatment. Eculizumab resistant patients have been described. They could benefit by a C3 convertase inhibitor, but this class of drugs is by now the object of randomized controlled trials.

Complement involvement in kidney diseases: From physiopathology to therapeutical targeting

Complement cascade is involved in several renal diseases and in renal transplantation. The different components of the complement cascade might represent an optimal target for innovative therapies. In the first section of the paper the authors review the physiopathology of complement involvement in renal diseases and transplantation. In some cases this led to a reclassification of renal diseases moving from a histopathological to a physiopathological classification. The principal issues afforded are: renal diseases with complement over activation, renal diseases with complement dysregulation, progression of renal diseases and renal transplantation. In the second section the authors discuss the several complement components that could represent a therapeutic target. Even if only the anti C5 monoclonal antibody is on the market, many targets as C1, C3, C5a and C5aR are the object of national or international trials. In addition, many molecules proved to be effective in vitro or in preclinical trials and are waiting to move to human trials in the future.

The role of complement in the pathogenesis of renal ischemia-reperfusion injury and fibrosis

The complement system is a major component of innate immunity and has been commonly identified as a central element in host defense, clearance of immune complexes, and tissue homeostasis. After ischemia-reperfusion injury (IRI), the complement system is activated by endogenous ligands that trigger proteolytic cleavage of complement components via the classical, lectin and/or alternative pathway. The result is the formation of terminal complement components C3a, C5a, and the membrane attack complex (C5b-9 or MAC), all of which play pivotal roles in the amplification of the inflammatory response, chemotaxis, neutrophil/monocyte recruitment and activation, and direct tubular cell injury. However, recent evidence suggests that complement activity transcends innate host defense and there is increasing data suggesting complement as a regulator in processes such as allo-immunity, stem cell differentiation, tissue repair, and progression to fibrosis. In this review, we discuss recent advances addressing the role of complement as a regulator of IRI and renal fibrosis after organ donation for transplantation. We will also briefly discuss currently approved therapies that target complement activity in kidney ischemia-reperfusion and transplantation.

The role of complement in the pathogenesis of renal ischemia-reperfusion injury and fibrosis

The complement system is a major component of innate immunity and has been commonly identified as a central element in host defense, clearance of immune complexes, and tissue homeostasis. After ischemia-reperfusion injury (IRI), the complement system is activated by endogenous ligands that trigger proteolytic cleavage of complement components via the classical, lectin and/or alternative pathway. The result is the formation of terminal complement components C3a, C5a, and the membrane attack complex (C5b-9 or MAC), all of which play pivotal roles in the amplification of the inflammatory response, chemotaxis, neutrophil/monocyte recruitment and activation, and direct tubular cell injury. However, recent evidence suggests that complement activity transcends innate host defense and there is increasing data suggesting complement as a regulator in processes such as allo-immunity, stem cell differentiation, tissue repair, and progression to fibrosis. In this review, we discuss recent advances addressing the role of complement as a regulator of IRI and renal fibrosis after organ donation for transplantation. We will also briefly discuss currently approved therapies that target complement activity in kidney ischemia-reperfusion and transplantation.

Comparison of complement activity in adult and preterm sheep serum

PROBLEM

Functional complement activity is routinely measured utilizing rabbit antibody-sensitized sheep erythrocytes. Due to complement inhibitor expression on erythrocytes, the development of an alternative method to measure complement function in sheep serum was required.

METHOD OF STUDY

Several species of target erythrocyte and sensitizing antibody were investigated for improved measurement of complement function testing.

RESULTS AND CONCLUSION

Guinea pig erythrocytes were identified as the optimal target, although sensitizing them with rabbit antiguinea pig erythrocyte antibody did not enhance the lysis by maternal sheep serum. In contrast, preterm neonatal sheep serum was unable to efficiently lyse guinea pig erythrocytes unless pre-sensitized with antibody. Further investigation revealed that maternal serum contained high levels of antibodies that cross-reacted with guinea pig and rabbit erythrocytes, while no cross-reacting antierythrocyte antibodies were found in preterm neonatal serum. Therefore, unlike primates, rabbits, and guinea pigs, no transplacental transfer of maternal IgG to foetal sheep occurs. Use of exogenous complement regulators is often used to dissect the contribution of complement to disease pathogenesis; however, we found that while full-length soluble human complement receptor 1 (sCR1, CDX-1135) was able to inhibit lysis of guinea pig erythrocytes by human and rat serum, no inhibition of sheep serum could be observed. Investigation of complement contribution to disease pathogenesis in the future will require the identification of an inhibitor that is effective against sheep complement.