Antagonist of C5aR prevents cardiac remodeling in angiotensin II-induced hypertension

Complex regulation of cardiac fibrosis: insights from immune cells and signaling pathways

Cardiac fibrosis is a physiological process that involves the formation of scar tissue in the heart in response to injury or damage. This process is initially a protective measure characterized by enhanced fibroblasts, which are responsible for producing extracellular matrix proteins that provide structural support to the heart. However, when fibrosis becomes excessive, it can lead to adverse outcomes, including increasing tissue stiffness and impaired cardiac function, which can ultimately result in heart failure with a poor prognosis. While fibroblasts are the primary cells involved in cardiac fibrosis, immune cells have also been found to play a vital role in its progression. Recent research has shown that immune cells exert multifaceted effects besides regulation of inflammatory response. Advanced research techniques such as single-cell sequencing and multiomics have provided insights into the specific subsets of immune cells involved in fibrosis and the complex regulation of the process. Targeted immunotherapy against fibrosis is gaining traction as a potential treatment option, but it is still unclear how immune cells achieve this regulation and whether distinct subsets are involved in different roles. To better understand the role of immune cells in cardiac fibrosis, it is essential to examine the classical signaling pathways that are closely related to fibrosis formation. We have also focused on the unique properties of diverse immune cells in cardiac fibrosis and their specific intercommunications. Therefore, this review will delve into the plasticity and heterogeneity of immune cells and their specific roles in cardiac fibrosis, which propose insights to facilitate the development of anti-fibrosis therapeutic strategies.

Role of the Anaphylatoxin Receptor C5aR2 in Angiotensin II-Induced Hypertension and Hypertensive End-Organ Damage

BACKROUND

Complement activation may facilitate hypertension through its effects on immune responses. The anaphylatoxin C5a, a major inflammatory effector, binds to the C5a receptors 1 and 2 (C5aR1, C5aR2). We have recently shown that C5aR1-/- mice have reduced hypertensive renal injury. The role of C5aR2 in hypertension is unknown.

METHODS

For examination of C5aR2 expression on infiltrating and resident renal cells a tandem dye Tomato-C5aR2 knock-in reporter mouse was used. Human C5aR2 expression was analyzed in a single-cell RNAseq data set from the kidneys of hypertensive patients. Finally, we examined the effect of angiotensin II-induced hypertension in C5aR2-deficient mice.

RESULTS

Flow cytometric analysis of leukocytes isolated from kidneys of the reporter mice showed that dendritic cells are the major C5aR2-expressing population (34%) followed by monocyte/macrophages (30%) and neutrophils (14%). Using confocal microscopy C5aR2 was not detected in resident renal or cardiac cells. In the human kidney, C5aR2 was also mainly found in monocytes, macrophages, and dendritic cells with a significantly higher expression in hypertension (P < 0.05). Unilateral nephrectomy was performed followed by infusion of Ang II (0.75 ng/g/min) and a high salt diet in wildtype (n = 18) and C5aR2-deficient mice (n = 14). Blood pressure, renal injury (albuminuria, glomerular filtration rate, glomerular and tubulointerstitial injury, inflammation), and cardiac injury (cardiac fibrosis, heart weight, gene expression) did not differ between hypertensive wildtype and C5aR2-/- mice.

CONCLUSIONS

In summary, C5aR2 is mainly expressed in myeloid cells in the kidney in mice and humans but its deficiency has no effect on Ang II-induced hypertensive injury.

Deficiency of Complement C3a and C5a receptors Does Not Prevent Angiotensin II-Induced Hypertension and Hypertensive End-Organ Damage

BACKGROUND

Complement may drive the pathology of hypertension through effects on innate and adaptive immune responses. Recently an injurious role for the anaphylatoxin receptors C3aR (complement component 3a receptor) and C5aR1 (complement component 5a receptor) in the development of hypertension was shown through downregulation of Foxp3+ (forkhead box protein 3) regulatory T cells. Here, we deepen our understanding of the therapeutic potential of targeting both receptors in hypertension.

METHODS

Data from the European Renal cDNA Bank, single cell sequencing and immunohistochemistry were examined in hypertensive patients. The effect of C3aR or C3aR/C5aR1 double deficiency was assessed in two models of Ang II (angiotensin II)-induced hypertension in knockout mice.

RESULTS

We found increased expression of C3aR, C5aR1 and Foxp3 cells in kidney biopsies of patients with hypertensive nephropathy. Expression of both receptors was mainly found in myeloid cells. No differences in blood pressure, renal injury (albuminuria, glomerular filtration rate, glomerular and tubulointerstitial injury, inflammation) or cardiac injury (cardiac fibrosis, heart weight, gene expression) between control and mutant mice was discerned in C3aR-/- as well as C3aR/C5aR1-/- double knockout mice. The number of renal Tregs was not decreased in Ang II as well as in DOCA salt induced hypertension.

CONCLUSIONS

Hypertensive nephropathy in mice and men is characterized by an increase of renal regulatory T cells and enhanced expression of anaphylatoxin receptors. Our investigations do not corroborate a role for C3aR/C5aR1 axis in Ang II-induced hypertension hence challenging the concept of anaphylatoxin receptor targeting in the treatment of hypertensive disease.

The complement C3-complement factor D-C3a receptor signalling axis regulates cardiac remodelling in right ventricular failure

Failure of the right ventricle plays a critical role in any type of heart failure. However, the mechanism remains unclear, and there is no specific therapy. Here, we show that the right ventricle predominantly expresses alternative complement pathway-related genes, including Cfd and C3aR1. Complement 3 (C3)-knockout attenuates right ventricular dysfunction and fibrosis in a mouse model of right ventricular failure. C3a is produced from C3 by the C3 convertase complex, which includes the essential component complement factor D (Cfd). Cfd-knockout mice also show attenuation of right ventricular failure. Moreover, the plasma concentration of CFD correlates with the severity of right ventricular failure in patients with chronic right ventricular failure. A C3a receptor (C3aR) antagonist dramatically improves right ventricular dysfunction in mice. In summary, we demonstrate the crucial role of the C3-Cfd-C3aR axis in right ventricular failure and highlight potential therapeutic targets for right ventricular failure.

Right ventricular (RV) failure is clinically crucial, but there is no specific therapy. Here, the authors show that the complement alternative pathway is activated in RV failure and that blockade of the pathway ameliorates RV failure in mice.

Bioinformatics Analysis of Competing Endogenous RNA Network and Immune Infiltration in Atrial Fibrillation

Background

There is still no clear understanding of the pathogenesis of atrial fibrillation (AF). For this purpose, we used integrated analysis to uncover immune infiltration characteristics and investigated their relationship with competing endogenous RNA (ceRNA) network in AF.

Methods

Three AF mRNA data sets (GSE14975, GSE79768, and GSE41177) were integrated using the SVA method from Gene Expression Omnibus (GEO). Together with AF circRNA data set (GSE129409) and miRNA data set (GSE70887) from GEO database, we built a ceRNA network. Then hub genes were screened by the Cytoscape plug-in cytoHubba from a protein-protein interaction (PPI) network. As well, CIBERSORT was employed to investigate immune infiltration, followed by Pearson correlation coefficients to unravel the correlation between AF-related infiltrating immune cells and hub genes. Ulteriorly, circRNA-miRNA-mRNA regulatory axises that could be immunologically related to AF were obtained.

Results

Ten hub genes were identified from the constructing PPI network. The immune infiltration analysis revealed that the number of monocytes and neutrophils was higher, as well as the number of dendritic cells activated and T cells regulatory (Tregs) was lower in AF. Seven hub genes (C5AR1, CXCR4, HCK, LAPTM5, MPEG1, TLR8, and TNFSF13B) were associated with those 4 immune cells (P < 0.05). We found that the circ_0005299–miR-1246–C5AR1 and circRNA_0079284-miR-623-HCK/CXCR4 regulatory axises may be associated with the immune mechanism of AF.

Conclusion

The findings of our study provide insights into immuno-related ceRNA networks as potential molecular regulators of AF progression.

Fat Stem Cells Combined with Complement C3 Inhibits the Progress of Type 2 Diabetes in Rats

This study assessed the effect of fat stem cells combined with complement C3 on Wnt/β-catenin pathway in type 2 diabetic rats. 30 male rats were randomly and equally divided into group of type 2 diabetes (intraperitoneal injection of urea with cephalosporins at a dose of 30 mg/kg and fed with high sugar and fat), type 2 diabetes+adipose stem cells+C3 group (after adipose stem cells+C3 group) and control group. Rats in adipose stem cells+C3 group received administration of stem cells and C3. The model of type 2 diabetic rats was successfully constructed. The blood glucose of type 2 diabetic rats and fat stem cell+C3 group was significantly higher than 11.1 mmol/L. Adipocyte was induced to be differentiated into islet cells depending on insulin secretion and glucose concentration. The combination of complement C3 improved the glucose sensitivity in type 2 diabetic rats. Compared with diabetic group, β-catenin and TCF in fat stem cell+C3 group were significantly decreased (P < 0.05). In conclusion, fat stem cells combined with complement C3 inhibit the disease progression in type 2 diabetic rats possibly by inhibiting the activation of Wnt/β-catenin signaling pathway.

Immunomodulatory Treatment Strategies Targeting B Cells for Heart Failure

Cardio-oncology, a nascent specialty, has evolved as a concerted strategy to address the cardiovascular complications of cancer therapies. On the other hand, emerging evidence has shown that some anti-tumor drugs, such as CD20-targeted rotuximab, also have markedly cardioprotective effects in addition to treating cancers. Rituximab is a CD20-targeted monoclonal antibody and kill tumor B-cells through antibody-mediated and antibody-independent pathways, indicating that B cells participate and promote the progression of cardiovascular diseases. In this review, we mainly present the evidence that B cells contribute to the development of hypertrophy, inflammation, and maladaptive tissue remodeling, with the aim of proposing novel immunomodulatory therapeutic strategies targeting B cells and their products for the treatment of heart failure.

Role of C5a and C5aR in doxorubicin-induced cardiomyocyte senescence

Doxorubicin (DOX) is an efficacious antineoplastic drug; however, its use is limited due to its cardiotoxicity. Cardiomyocyte senescence is considered to be a key factor in the development of DOX-related cardiomyopathy. Complement component 5a (C5a) and the C5a receptor (C5aR) have been reported to play a key role in the process of cellular senescence. However, to the best of our knowledge, the exact role of C5a and C5aR in cellular senescence in the heart remains largely unknown. Reverse transcription-quantitative (RT-q)PCR and western blot assays were used to analyze the expression levels of C5a and C5aR in H9c2 embryonic rat cardiomyocytes and AC16 human cardiomyocyte-like cells. The cells were treated with DOX and a C5aR antagonist (C5aRA). The expression of TNF-α and IFN-γ was determined using ELISA and western blotting. The levels of reactive oxygen species (ROS) were also measured using ELISA. Cellular senescence was determined using senescence-associated β-galactosidase (SA-β-gal) staining and by analyzing the protein expression levels of p53, p16, p21 and insulin-like growth factor-binding protein 3 (IGFBP3). The expression levels of C5a and C5aR were found to be upregulated during the DOX-induced senescence of H9c2 and AC16 cardiomyocytes. Treatment with C5aRA downregulated TNF-α and IFN-γ expression, in addition to ROS levels. Furthermore, C5aRA prevented DOX-induced cellular senescence and decreased the levels of positive SA-β-gal staining in H9c2 and AC16 cardiomyocytes, in addition to downregulating the expression levels of p53, p16, p21 and IGFBP3. C5aRA also increased the telomere length and telomerase activity in H9c2 and AC16 cardiomyocytes following DOX stimulation. In conclusion, the findings of the present study indicated that C5a and C5aR may play a key role in cardiomyocyte senescence, and treatment with C5aRA may be an effective method for preventing DOX-induced cardiomyocyte aging.

The role of complement in arterial hypertension and hypertensive end organ damage

Increasing evidence indicates that hypertension and hypertensive end organ damage are not only mediated by haemodynamic injury but that inflammation also plays an important role. The complement system protects the host from a hostile microbial environment and maintains tissue and cell integrity through the elimination of altered or dead cells. As an important effector arm of innate immunity, it plays also central roles in the regulation of adaptive immunity. Thus, complement activation may drive the pathology of hypertension through its effects on innate and adaptive immune responses, aside from direct effects on the vasculature. Recent experimental data strongly support a role for complement in all stages of arterial hypertension. The remarkably similar clinical and histopathological features of malignant nephrosclerosis and atypical haemolytic uraemic syndrome suggest also a role for complement in the development of malignant nephrosclerosis. Here, we review the role of complement in hypertension and hypertensive end organ damage. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

Complement in Renal Disease as a Potential Contributor to Arterial Hypertension

OBJECTIVE

Complement deposition is prevalent in kidney biopsies of patients with arterial hypertension and hypertensive nephropathy, but an association of hypertension and complement deposition or involvement of complement in the pathogenesis of hypertensive nephropathy has not been shown to date.

METHODS

In this study, we analyzed complement C1q and C3c deposition in a rat model of overload and hypertension by subtotal nephrectomy (SNX) and in archival human renal biopsies from 217 patients with known hypertension and 91 control patients with no history of hypertension using semiquantitative scoring of C1q and C3c immunohistochemistry and correlation with parameters of renal function. To address whether complement was only passively deposited or actively expressed by renal cells, C1q and C3 mRNA expression were additionally analyzed.

RESULTS

Glomerular C1q and C3c complement deposition were significantly higher in kidneys of hypertensive SNX rats and hypertensive compared to nonhypertensive patients. Mean arterial blood pressure (BP) in SNX rats correlated well with the amount of glomerular C1q and C3c deposition and with left ventricular weight, as an indirect parameter of high BP. Quantitative mRNA analysis showed that C3 was not only deposited but also actively produced by glomerular cells of hypertensive SNX rats and in human renal biopsies. Of note, in patients CKD-stage correlated significantly with the intensity of glomerular C3c staining, but not with that of C1q.

CONCLUSION

Renal complement deposition correlated with experimental hypertension as well as the presence of hypertension in a variety of renal diseases. To answer the question, if and how exactly renal complement is causative for the pathogenesis of arterial hypertension in men, further studies are needed.

Myeloid cells, tissue homeostasis, and anatomical barriers as innate immune effectors in arterial hypertension

Although essential hypertension affects a large proportion of the human population and is one of the key drivers of cardiovascular mortality worldwide, we still do not have a complete understanding of its pathophysiology. More than 50 years ago, the immune system has been identified as an important part of the pathogenesis of arterial hypertension. An exceeding variety of recent publications deals with the interplay between the numerous different components of the immune system and mechanisms of arterial hypertension and has substantially contributed to our understanding of the role of immunity and inflammation in the pathogenesis of the disease. In this review, we focus on myeloid cells and anatomical barriers as particular aspects of innate immunity in arterial hypertension. Since it represents a first line of defense protecting against pathogens and maintaining tissue homeostasis, innate immunity provides many mechanistic hinge points in the area of hypertension.

Treatment of Rare Inflammatory Kidney Diseases: Drugs Targeting the Terminal Complement Pathway

The complement system comprises the frontline of the innate immune system. Triggered by pathogenic surface patterns in different pathways, the cascade concludes with the formation of a membrane attack complex (MAC; complement components C5b to C9) and C5a, a potent anaphylatoxin that elicits various inflammatory signals through binding to C5a receptor 1 (C5aR1). Despite its important role in pathogen elimination, priming and recruitment of myeloid cells from the immune system, as well as crosstalk with other physiological systems, inadvertent activation of the complement system can result in self-attack and overreaction in autoinflammatory diseases. Consequently, it constitutes an interesting target for specialized therapies. The paradigm of safe and efficacious terminal complement pathway inhibition has been demonstrated by the approval of eculizumab in paroxysmal nocturnal hematuria. In addition, complement contribution in rare kidney diseases, such as lupus nephritis, IgA nephropathy, atypical hemolytic uremic syndrome, C3 glomerulopathy, or antineutrophil cytoplasmic antibody-associated vasculitis has been demonstrated. This review summarizes the involvement of the terminal effector agents of the complement system in these diseases and provides an overview of inhibitors for complement components C5, C5a, C5aR1, and MAC that are currently in clinical development. Furthermore, a link between increased complement activity and lung damage in severe COVID-19 patients is discussed and the potential for use of complement inhibitors in COVID-19 is presented.

Angiotensin II and leukocyte trafficking: New insights for an old vascular mediator. Role of redox-signaling pathways

Inflammation and activation of the immune system are key molecular and cellular events in the pathogenesis of cardiovascular diseases, including atherosclerosis, hypertension-induced target-organ damage, and abdominal aortic aneurysm. Angiotensin II (Ang-II) is the main effector peptide hormone of the renin-angiotensin system. Beyond its role as a potent vasoconstrictor and regulator of blood pressure and fluid homeostasis, Ang-II is intimately involved in the development of vascular lesions in cardiovascular diseases through the activation of different immune cells. The migration of leukocytes from circulation to the arterial subendothelial space is a crucial immune response in lesion development that is mediated through a sequential and coordinated cascade of leukocyte-endothelial cell adhesive interactions involving an array of cell adhesion molecules present on target leukocytes and endothelial cells and the generation and release of chemoattractants that activate and guide leukocytes to sites of emigration. In this review, we outline the key events of Ang-II participation in the leukocyte recruitment cascade, the underlying mechanisms implicated, and the corresponding redox-signaling pathways. We also address the use of inhibitor drugs targeting the effects of Ang-II in the context of leukocyte infiltration in these cardiovascular pathologies, and examine the clinical data supporting the relevance of blocking Ang-II-induced vascular inflammation.

The role of B cells in heart failure and implications for future immunomodulatory treatment strategies

Despite numerous demonstrations that the immune system is activated in heart failure, negatively affecting patients' outcomes, no definitive treatment strategy exists directed to modulate the immune system. In this review, we present the evidence that B cells contribute to the development of hypertrophy, inflammation, and maladaptive tissue remodelling. B cells produce antibodies that interfere with cardiomyocyte function, which culminates as the result of recruitment and activation of a variety of innate and structural cell populations, including neutrophils, macrophages, fibroblasts, and T cells. As B cells appear as active players in heart failure, we propose here novel immunomodulatory therapeutic strategies that target B cells and their products.

Preclinical Pharmacokinetics of Complement C5a Receptor Antagonists PMX53 and PMX205 in Mice

The cyclic hexapeptides PMX53 and PMX205 are potent noncompetitive inhibitors of complement C5a receptor 1 (C5aR1). They are widely utilized to study the role of C5aR1 in mouse models, including central nervous system (CNS) disease, and are dosed through a variety of routes of administration. However, a comprehensive pharmacokinetics analysis of these drugs has not been reported. In this study, the blood and CNS pharmacokinetics of PMX53 and PMX205 were performed in mice following intravenous, intraperitoneal, subcutaneous, and oral administration at identical doses. The absorption and distribution of both drugs were rapid and followed a two-compartment model with elimination half-lives of ∼20 min for both compounds. Urinary excretion was the major route of elimination following intravenous dosing with ∼50% of the drug excreted unchanged within the first 12 h. Oral bioavailability of PMX205 was higher than that of PMX53 (23% versus 9%), and PMX205 was also more efficient than PMX53 at entering the intact CNS. In comparison to other routes, subcutaneous administration of PMX205 resulted in high bioavailability (above 90%), as well as prolonged plasma and CNS exposure. Finally, repeated daily oral or subcutaneous administration of PMX205 demonstrated no accumulation of drug in blood, the brain, or the spinal cord, promoting its safety for chronic dosing. These results will be helpful in correlating the desired therapeutic effects of these C5aR1 antagonists with their pharmacokinetic profile. It also suggests that subcutaneous dosing of PMX205 may be an appropriate route of administration for future clinical testing in neurological disease.

Complement component C3 and the TLR co-receptor CD14 are not involved in angiotensin II induced cardiac remodelling

Inflammation is centrally involved in the development of cardiac hypertrophy and the processes of remodelling. The complement system and Toll-like receptor (TLR) family, two upstream arms of the innate immune system, have previously been reported to be involved in cardiac remodelling. However, the role of complement component 3 (C3), TLR co-receptor CD14 and the synergy between them have not been addressed during pressure overload-induced cardiac remodelling. Here, we examined angiotensin II-induced cardiac hypertrophy and remodelling for 7 days in male C57Bl/6 J mice deficient in C3, CD14, or both (C3CD14), and WT controls. Angiotensin II infusion induced a mild concentric hypertrophic phenotype in WT mice with increased left ventricle weight, wall thicknesses and reduced ventricular internal diameter, associated with increased cardiac fibrosis. However, there were no differences between WT mice and mice deficient for C3, CD14 or C3CD14, as systolic blood pressure, cardiac function and structure and levels of fibrosis were comparable between WT mice and the three other genotypes. C5a did not change in angiotensin II treated mice, whereas Mac2 levels were increased in angiotensin II treated mice, but did not differ between genotypes. The inflammatory IL-6 response was comparable between WT and C3 deficient mice, however, it was decreased in CD14 and C3CD14 deficient mice. We conclude that deficiency in C3, CD14 or C3CD14 had no effect on cardiac remodelling following angiotensin II-induced pressure overload. This suggests that C3 and CD14 are not involved in angiotensin II-induced adverse cardiac remodelling.

Significance of Complement System in Ischemic Stroke: A Comprehensive Review

The complement system is an essential part of innate immunity, typically conferring protection via eliminating pathogens and accumulating debris. However, the defensive function of the complement system can exacerbate immune, inflammatory, and degenerative responses in various pathological conditions. Cumulative evidence indicates that the complement system plays a critical role in the pathogenesis of ischemic brain injury, as the depletion of certain complement components or the inhibition of complement activation could reduce ischemic brain injury. Although multiple candidates modulating or inhibiting complement activation show massive potential for the treatment of ischemic stroke, the clinical availability of complement inhibitors remains limited. The complement system is also involved in neural plasticity and neurogenesis during cerebral ischemia. Thus, unexpected side effects could be induced if the systemic complement system is inhibited. In this review, we highlighted the recent concepts and discoveries of the roles of different kinds of complement components, such as C3a, C5a, and their receptors, in both normal brain physiology and the pathophysiology of brain ischemia. In addition, we comprehensively reviewed the current development of complement-targeted therapy for ischemic stroke and discussed the challenges of bringing these therapies into the clinic. The design of future experiments was also discussed to better characterize the role of complement in both tissue injury and recovery after cerebral ischemia. More studies are needed to elucidate the molecular and cellular mechanisms of how complement components exert their functions in different stages of ischemic stroke to optimize the intervention of targeting the complement system.

Clinical Value of Complement Activation Biomarkers in Overt Diabetic Nephropathy

Background

Experimental studies support a role of complement activation in diabetic nephropathy (DN), yet few clinical correlates exist. We evaluated urinary levels of sC5b-9 membrane attack complex (MAC) in patients with overt DN, and examined its association with the glomerular filtration rate (GFR) decline, proteinuria, and inflammatory biomarkers. We explored different complement pathways and compared our findings to autoimmune glomerulonephritis.

Methods

We prospectively followed 83 patients with DN and obtained repeated measurements of proteinuria, complement fragments (sC5b-9, C4a, C1q, mannose-binding lectin–associated serine protease [MASP]-1, and factor Bb), monocyte chemoattractant protein-1 (MCP-1), and transforming growth factor (TGF)-β1. We assessed independence and interactions using general linear models and repeated measures analyses and compared levels with subjects with active focal and segmental glomerulosclerosis, ANCA-associated vasculitis, and membranous and IgA nephropathies (n = 63).

Results

The diabetic cohort had an initial GFR of 25 ± 9 ml/min per 1.73 m² and a renal function decline of 2.9 ± 3.0 ml/min per 1.73 m² per year. All complement biomarkers were strongly intercorrelated and associated with biomarker inflammation and fibrosis, proteinuria, and the rate of renal function decline. There was a significant interaction (P = 0.03) between the level of proteinuria and urinary sC5b-9: in individuals with higher levels of urinary MAC, the relationship between proteinuria and the rate of renal function decline was more pronounced than in those with low urinary MAC. Finally, patients with DN had levels of urinary sC5b-9 comparable to autoimmune glomerulonephritis, when stratified by the level of proteinuria.

Conclusion

Urinary MAC is present in patients with overt DN at levels comparable to autoimmune glomerulonephritis and correlates with the GFR decline, supporting that complement activation and its measurement are clinically relevant in DN.

Mechanisms of hypertension in autoimmune rheumatic diseases

Patients with autoimmune rheumatic diseases including rheumatoid arthritis and systemic lupus erythematosus have an increased prevalence of hypertension. There is now a large body of evidence showing that the immune system is a key mediator in both human primary hypertension and experimental models. Many of the proposed immunological mechanisms leading to primary hypertension are paralleled in autoimmune rheumatic disorders. Therefore, examining the link between autoimmunity and hypertension can be informative for understanding primary hypertension. This review examines the prevalent hypertension, the immune mediators that contribute to the prevalent hypertension and their impact on renal function and how the risk of hypertension is potentially influenced by common hormonal changes that are associated with autoimmune rheumatic diseases.

Linked Articles

This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc

Cardiomyocyte calcineurin is required for the onset and progression of cardiac hypertrophy and fibrosis in adult mice

Previous studies have demonstrated that activation of calcineurin induces pathological cardiac hypertrophy (CH). In these studies, loss-of-function was mostly achieved by systemic administration of the calcineurin inhibitor cyclosporin A. The lack of conditional knockout models for calcineurin function has impeded progress toward defining the role of this protein during the onset and the development of CH in adults. Here, we exploited a mouse model of CH based on the infusion of a hypertensive dose of angiotensin II (AngII) to model the role of calcineurin in CH in adulthood. AngII-induced CH in adult mice was reduced by treatment with cyclosporin A, without affecting the associated increase in blood pressure, and also by induction of calcineurin deletion in adult mouse cardiomyocytes, indicating that cardiomyocyte calcineurin is required for AngII-induced CH. Surprisingly, cardiac-specific deletion of calcineurin, but not treatment of mice with cyclosporin A, significantly reduced AngII-induced cardiac fibrosis and apoptosis. Analysis of profibrotic genes revealed that AngII-induced expression of Tgfβ family members and Lox was not inhibited by cyclosporin A but was markedly reduced by cardiac-specific calcineurin deletion. These results show that AngII induces a direct, calcineurin-dependent prohypertrophic effect in cardiomyocytes, as well as a systemic hypertensive effect that is independent of calcineurin activity.

Pravastatin therapy during preeclampsia prevents long-term adverse health effects in mice

Preeclampsia (PE), associates with long-term increased risk for cardiovascular disease in women, suggesting that PE is not an isolated disease of pregnancy. It is not known if increased risk for long-term diseases is due to PE-specific factors or to prepregnancy renal and cardiovascular risk factors. We used a mouse model in which a WT female with normal prepregnancy health develops PE to investigate if preeclampsia causes long-term cardiovascular consequences after pregnancy for mothers and offspring. Mothers exhibited endothelial dysfunction and hypertension after PE and had glomerular injury that not only persisted but deteriorated, leading to fibrosis. Left ventricular (LV) remodeling characterized by increased collagen deposition and MMP-9 expression and enlarged cardiomyocytes were also detected after PE. Increased LV internal wall thickness and mass, increased end diastolic and end systolic volumes, and increased stroke volume were observed after PE in the mothers. Placenta-derived bioactive factors that modulate vascular function, markers of metabolic disease, vasoconstrictor isoprostane-8, and proinflammatory mediators were increased in sera during and after a preeclamptic pregnancy in the mother. Offspring of PE mice developed endothelial dysfunction, hypertension, and signs of metabolic disease. Microglia activation was increased in the neonatal brains after PE, suggesting neurogenic hypertension in offspring. Prevention of placental insufficiency with pravastatin prevented PE-associated cardiovascular complications in both mothers and offspring. In conclusion, factors that develop during PE have long-term, cardiovascular effects in the mother and offspring independent of prepregnancy risk factors.

Complement 5a stimulates macrophage polarization and contributes to tumor metastases of colon cancer

Inflammatory cells such as macrophages can play a pro-tumorigenic role in the tumor stroma. Tumor-associated macrophages (TAMs) generally display an M2 phenotype with tumor-promoting activity; however, the mechanisms regulating the TAM phenotype remain unclear. Complement 5a (C5a) is a cytokine-like polypeptide that is generated during complement system activation and is known to promote tumor growth. Herein, we investigated the role of C5a on macrophage polarization in colon cancer metastasis in mice. We found that deficiency of the C5a receptor (C5aR) severely impairs the metastatic ability of implanted colon cancer cells. C5aR was expressed on TAMs, which exhibited an M2-like functional profile in colon cancer liver metastatic lesions. Furthermore, C5a mediated macrophage polarization and this process relied substantially on activation of the nuclear factor-kappa B (NF-κB) pathway. Finally, analysis of human colon carcinoma indicated that C5aR expression is negatively associated with tumor differentiation grade. Our results demonstrate that C5aR has a central role in regulating the M2 phenotype of TAMs, which in turn, contributes to hepatic metastasis of colon cancer through NF-κB signaling. C5a is a potential novel marker for cancer prognosis and drugs targeting complement system activation, specifically the C5aR pathway, may offer new therapeutic opportunities for colon cancer management.

Deficiency of Complement C3a and C5a Receptors Prevents Angiotensin II-Induced Hypertension via Regulatory T Cells

RATIONALE

Inflammation and immunity play crucial roles in the development of hypertension. Complement activation-mediated innate immune response is involved in the regulation of hypertension and target-organ damage. However, whether complement-mediated T-cell functions could regulate blood pressure elevation in hypertension is still unclear.

OBJECTIVE

We aim to determine whether C3aR (complement component 3a receptor) and C5aR (complement component 5a receptor) could regulate blood pressure via modulating regulatory T cells (Tregs).

METHODS AND RESULTS

We showed that angiotensin II (Ang II)-induced hypertension resulted in an elevated expression of C3aR and C5aR in Foxp3 (forkhead box P3)+ Tregs. By using C3aR and C5aR DKO (double knockout) mice, we showed that C3aR and C5aR deficiency together strikingly decreased both systolic and diastolic blood pressure in response to Ang II compared with WT (wild type), single C3aR-deficient (C3aR-/-), or C5aR-deficient (C5aR-/-) mice. Flow cytometric analysis showed that Ang II-induced Treg reduction in the kidney and blood was also blocked in DKO mice. Histological analysis indicated that renal and vascular structure remodeling and damage after Ang II treatment were attenuated in DKO mice compared with WT mice. In vitro, Ang II was able to stimulate C3aR and C5aR expression in cultured CD4+CD25+ natural Tregs. CD3 and CD28 antibody stimuli downregulated Foxp3 expression in WT but not DKO Tregs. More important, depletion of Tregs with CD25 antibody abolished the protective effects against Ang II-induced hypertension and target-organ damage in DKO mice. Adoptive transfer of DKO Tregs showed much more profound protective effects against Ang II-induced hypertension than WT Treg transfer. Furthermore, we demonstrated that C5aR expression in Foxp3+ Tregs was higher in hypertensive patients compared with normotensive individuals.

CONCLUSIONS

C3aR and C5aR DKO-mediated Treg function prevents Ang II-induced hypertension and target-organ damage. Targeting C3aR and C5aR in Tregs specifically may be an alternative novel approach for hypertension treatment.

Complement 5a Receptor deficiency does not influence adverse cardiac remodeling after pressure-overload in mice

Hypertension is one of the most common risk factors for the development heart failure in the general population. Inflammation plays a central role in this adverse remodeling and eventually to the development of heart failure. Circulating levels of Complement factor 5a (C5a) are increased in hypertensive patients and the C5a receptor is associated with the presence of cardiac fibrosis and inflammation in an experimental hypertension model. To test if C5aR is involved in adverse cardiac remodeling following pressure-overload, we induced transverse aortic constriction (TAC) in wildtype and C5a receptor deficient mice (C5aR^-/-). Six weeks after TAC, C5aR-/- animals showed a similar degree of cardiac hypertrophy and decrease in cardiac function as wild type mice (End Systolic Volume; 50.30±5.32 µl vs. 55.81±8.16 µl). In addition, other features of adverse cardiac remodeling like cardiomyocyte cell size (WGA staining), fibrosis (picrosirius red staining) or collagen degradation (matrix metalloproteinase activity assay) did not differ either. In conclusion, full body C5aR deficiency does not affect adverse cardiac remodeling after pressure-overload. However, our finding are in contrast with C5a inhibition studies. Our observations do present the role of C5a-C5aR in adverse cardiac remodeling and heart failure as controversial at the least.

Complement C5-inhibiting therapy for the thrombotic microangiopathies: accumulating evidence, but not a panacea

Thrombotic microangiopathy (TMA), characterized by organ injury occurring consequent to severe endothelial damage, can manifest in a diverse range of diseases. In complement-mediated atypical haemolytic uraemic syndrome (aHUS) a primary defect in complement, such as a mutation or autoantibody leading to over activation of the alternative pathway, predisposes to the development of disease, usually following exposure to an environmental trigger. The elucidation of the pathogenesis of aHUS resulted in the successful introduction of the complement inhibitor eculizumab into clinical practice. In other TMAs, although complement activation may be seen, its role in the pathogenesis remains to be confirmed by an interventional trial. Although many case reports in TMAs other than complement-mediated aHUS hint at efficacy, publication bias, concurrent therapies and in some cases the self-limiting nature of disease make broader interpretation difficult. In this article, we will review the evidence for the role of complement inhibition in complement-mediated aHUS and other TMAs.

Complement C5a receptors C5L2 and C5aR in renal fibrosis

Complement factor C5a has two known receptors, C5aR, which mediates proinflammatory effects, and C5L2, a potential C5a decoy receptor. We previously identified C5a/C5aR signaling as a potent profibrotic pathway in the kidney. Here we tested for the first time the role of C5L2 in renal fibrosis. In unilateral ureteral obstruction (UUO)-induced kidney fibrosis, the expression of C5aR and C5L2 increased similarly and gradually as fibrosis progressed and was particularly prominent in injured dilated tubules. Genetic deficiency of either C5aR or C5L2 significantly reduced UUO-induced tubular injury. Expression of key proinflammatory mediators, however, significantly increased in C5L2- compared with C5aR-deficient mice, but this had no effect on the number of renal infiltrating macrophages or T cells. Moreover, in C5L2^-/- mice, the cytokine and matrix metalloproteinase-inhibitor tissue inhibitor of matrix metalloproteinase-1 was specifically enhanced. Consequently, in C5L2^-/- mice the degree of renal fibrosis was similar to wild type (WT), albeit with reduced mRNA expression of some fibrosis-related genes. In contrast, C5aR^-/- mice had significantly reduced renal fibrosis compared with WT and C5L2^-/- mice in UUO. In vitro experiments with primary tubular cells demonstrated that deficiency for either C5aR or C5L2 led to a significantly reduced expression of tubular injury and fibrosis markers. Vice versa, stimulation of WT tubular cells with C5a significantly induced the expression of these markers, whereas the absence of either receptor abolished this induction. In conclusion, in experimental renal fibrosis C5L2 and C5aR both contribute to tubular injury, and, while C5aR acts profibrotic, C5L2 does not play a role in extracellular matrix accumulation, arguing against C5L2 functioning simply as a decoy receptor.

A pathogenic role of complement in arterial hypertension and hypertensive end organ damage

The self-amplifying cascade of messenger and effector molecules of the complement system serves as a powerful danger-sensing system that protects the host from a hostile microbial environment, while maintaining proper tissue and organ function through effective clearance of altered or dying cells. As an important effector arm of innate immunity, it also plays important roles in the regulation of adaptive immunity. Innate and adaptive immune responses have been identified as crucial players in the pathogenesis of arterial hypertension and hypertensive end organ damage. In line with this view, complement activation may drive the pathology of hypertension and hypertensive injury through its impact on innate and adaptive immune responses. It is well known that complement activation can cause tissue inflammation and injury and complement-inhibitory drugs are effective treatments for several inflammatory diseases. In addition to these proinflammatory properties, complement cleavage fragments of C3 and C5 can exert anti-inflammatory effects that dampen the inflammatory response to injury. Recent experimental data strongly support a role for complement in arterial hypertension. The remarkably similar clinical and histopathological features of malignant nephrosclerosis and atypical hemolytic uremic syndrome, which is driven by complement activation, suggest a role for complement also in the development of malignant nephrosclerosis. Herein, we will review canonical and noncanonical pathways of complement activation as the framework to understand the multiple roles of complement in arterial hypertension and hypertensive end organ damage.

Cadmium-induced immune abnormality is a key pathogenic event in human and rat models of preeclampsia

With increased industrial development, cadmium is an increasingly important environmental pollutant. Studies have identified various adverse effects of cadmium on human beings. However, the relationships between cadmium pollution and the pathogenesis of preeclampsia remain elusive. The objective of this study is to explore the effects of cadmium on immune system among preeclamptic patients and rats. The results showed that the cadmium levels in the peripheral blood of preeclamptic patients were significantly higher than those observed in normal pregnancy. Based on it, a novel rat model of preeclampsia was established by the intraperitoneal administration of cadmium chloride (CdCl2) (0.125 mg of Cd/kg body weight) on gestational days 9-14. Key features of preeclampsia, including hypertension, proteinuria, placental abnormalities and small foetal size, appeared in pregnant rats after the administration of low-dose of CdCl2. Cadmium increased immunoglobulin production, mainly angiotensin II type 1-receptor-agonistic autoantibodies (AT1-AA), by increasing the expression of activation-induced cytosine deaminase (AID) in B cells. AID is critical for the maturation of antibody and autoantibody responses. In addition, angiotensin II type 1-receptor-agonistic autoantibody, which emerged recently as a potential pathogenic contributor to PE, was responsible for the deposition of complement component 5 (C5) in kidneys of pregnant rats via angiotensin II type 1 receptor (AT1R) activation. C5a is a fragment of C5 that is released during C5 activation. Selectively interfering with C5a signalling by a complement C5a receptor-specific antagonist significantly attenuated hypertension and proteinuria in Cd-injected pregnant rats. Our results suggest that cadmium induces immune abnormalities that may be a key pathogenic contributor to preeclampsia and provide new insights into treatment strategies of preeclampsia.

Immune Mechanisms in Arterial Hypertension

Traditionally, arterial hypertension and subsequent end-organ damage have been attributed to hemodynamic factors, but increasing evidence indicates that inflammation also contributes to the deleterious consequences of this disease. The immune system has evolved to prevent invasion of foreign organisms and to promote tissue healing after injury. However, this beneficial activity comes at a cost of collateral damage when the immune system overreacts to internal injury, such as prehypertension. Renal inflammation results in injury and impaired urinary sodium excretion, and vascular inflammation leads to endothelial dysfunction, increased vascular resistance, and arterial remodeling and stiffening. Notably, modulation of the immune response can reduce the severity of BP elevation and hypertensive end-organ damage in several animal models. Indeed, recent studies have improved our understanding of how the immune response affects the pathogenesis of arterial hypertension, but the remarkable advances in basic immunology made during the last few years still await translation to the field of hypertension. This review briefly summarizes recent advances in immunity and hypertension as well as hypertensive end-organ damage.