Protective role for properdin in progression of experimental murine atherosclerosis

Endothelial Gsα deficiency promotes ferroptosis and exacerbates atherosclerosis in apolipoprotein E-deficient mice via the inhibition of NRF2 signaling

The importance of ferroptosis in the occurrence and progression of atherosclerosis is gradually being recognized. The stimulatory G protein α subunit (Gsα) plays a crucial role in the physiology of endothelial cells (ECs). Our previous study showed that endothelial Gsα could regulate angiogenesis and preserve endothelial permeability. In this study, we investigated whether endothelial Gsα contributed to atherosclerosis through ferroptosis and oxidative stress. We generated endothelial Gsα-specific knockout mice in apolipoprotein E-deficient (ApoE-/-) background (ApoE-/-GsαECKO), and found that the mice exhibited aggravated atherosclerotic lesions and signs of ferroptosis compared with their wild-type littermates (ApoE-/-Gsαfl/fl). In human aortic endothelial cells (HAECs), overexpression of Gsα reduced lipid peroxidation and ferroptosis, whereas Gsα knockdown exacerbated oxidative stress and ferroptosis. Further, Gsα overexpression in HAECs increased the expression of antioxidant genes nuclear factor erythroid 2-related 2 (NRF2) and its downstream genes. Gsα regulated the expression of NRF2 through CCCTC-binding factor (CTCF). In conclusion, this study has revealed that Gsα acts as a defense factor against endothelial ferroptosis and is a potential target for the treatment of atherosclerosis and associated ischemic heart disease. A model depicting the increase in the endothelial Gsα protein level in response to atherosclerotic stimuli. Gsα regulates NRF2 expression through cAMP/Epac/CTCF-mediated transcription and inhibits ferroptosis. Endothelial Gsα deficiency alleviates antioxidative stress and exacerbates atherosclerosis.

Alternative Complement Pathway in Carotid Atherosclerosis: Low Plasma Properdin Levels Associate With Long-Term Cardiovascular Mortality

BACKGROUND

Complement activation may promote atherosclerosis. Yet, data on the to which extent complement, and more specifically the alternative complement pathway, is activated in patients with carotid atherosclerosis and related to adverse outcome in these patients, are scarce.

METHODS AND RESULTS

We measured, by ELISA, plasma levels of factor D, properdin, C3bBbP (C3 convertase), and factor H in patients with advanced carotid atherosclerosis in a Discovery (n=324) and in a Validation (n=206) cohort in relation to adverse outcome (mean follow-up 7.8 and 6.6 years, respectively). Our major findings were as follows. Compared with healthy controls, patients with carotid atherosclerosis had increased plasma levels of factor D, properdin, and C3bBbP (P<0.001), but not factor H, an inhibitor of the alternative complement pathway, compared with controls. Although patients with carotid atherosclerosis had elevated levels of properdin compared with controls, within these patients, low plasma levels of properdin (ie,

CONCLUSIONS

We show a strong and independent association of low plasma properdin levels with cardiovascular mortality in 2 cohorts. Conversely, the plaque properdin levels linked to features of plaque vulnerability, potentially reflecting increased deposition at the site of inflammation or local production of properdin in the atherosclerotic lesion indicating local enhanced alternative complement pathway activation.

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Key Words

• alternative complement pathway
• carotid atherosclerosis
• complement
• plaque vulnerability
• properdin
• stroke

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MESH Headings

• Humans
• Male
• Female
• Properdin/metabolism
• Properdin/analysis
• Carotid Artery Diseases/mortality
• Carotid Artery Diseases/blood
• Carotid Artery Diseases/immunology
• Middle Aged
• Complement Pathway, Alternative
• Aged
• Biomarkers/blood
• Risk Factors
• Prognosis
• Complement Factor D/metabolism
• Complement Factor D/analysis
• Case-Control Studies
• Time Factors
• Enzyme-Linked Immunosorbent Assay
• Complement Factor H/metabolism

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Grants

• South‐Eastern Norway Regional Health Authority
• Skåne University Hospital
• Swedish Society for Medical Research
• Swedish Stroke Association
• Swedish Foundation for Strategic Research
• Region Skåne

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Affiliation(s)

Mieke C. Louwe Research Institute of Internal Medicine, Oslo University HospitalOsloNorway
Chrysostomi Gialeli Department of Clinical Sciences MalmöLund UniversityLundSweden
Annika E. Michelsen Research Institute of Internal Medicine, Oslo University HospitalOsloNorway Institute of Clinical Medicine, Faculty of Medicine, University of OsloNorway
Sverre Holm Research Institute of Internal Medicine, Oslo University HospitalOsloNorway
Andreas Edsfeldt Department of Clinical Sciences MalmöLund UniversityLundSweden Department of CardiologyMalmö, Skåne University HospitalMalmöSweden Wallenberg Center for Molecular MedicineLund UniversityLundSweden
Karolina Skagen Institute of Clinical Medicine, Faculty of Medicine, University of OsloNorway Department of NeurologyOslo University Hospital RikshospitaletOsloNorway
Tove Lekva Research Institute of Internal Medicine, Oslo University HospitalOsloNorway
Maria Belland Olsen Research Institute of Internal Medicine, Oslo University HospitalOsloNorway
Vigdis Bjerkeli Research Institute of Internal Medicine, Oslo University HospitalOsloNorway
Therese Schjørlien Institute of Clinical Medicine, Faculty of Medicine, University of OsloNorway Department of NeurologyOslo University Hospital RikshospitaletOsloNorway
Kristine Stø Institute of Clinical Medicine, Faculty of Medicine, University of OsloNorway Department of NeurologyOslo University Hospital RikshospitaletOsloNorway
Xiang Yi Kong Research Institute of Internal Medicine, Oslo University HospitalOsloNorway
Tuva B. Dahl Research Institute of Internal Medicine, Oslo University HospitalOsloNorway
Per H. Nilsson Department of ImmunologyOslo University Hospital Rikshospitalet and University of OsloNorway Linnaeus Centre for Biomaterials ChemistryLinnaeus UniversityKalmarSweden
Peter Libby Division of Cardiovascular MedicineBrigham and Women’s Hospital, Harvard Medical SchoolBostonMAUSA
Pål Aukrust Research Institute of Internal Medicine, Oslo University HospitalOsloNorway Institute of Clinical Medicine, Faculty of Medicine, University of OsloNorway Section of Clinical Immunology and Infectious DiseasesOslo University Hospital RikshospitaletOsloNorway
Tom Eirik Mollnes Department of ImmunologyOslo University Hospital Rikshospitalet and University of OsloNorway Research LaboratoryNordland HospitalBodøNorway Centre of Molecular Inflammation ResearchNorwegian University of Science and TechnologyTrondheimNorway
Thor Ueland Research Institute of Internal Medicine, Oslo University HospitalOsloNorway Institute of Clinical Medicine, Faculty of Medicine, University of OsloNorway K. G. Jebsen Thrombosis Research and Expertise CenterUniversity of TromsøNorway
Mona Skjelland Institute of Clinical Medicine, Faculty of Medicine, University of OsloNorway Department of NeurologyOslo University Hospital RikshospitaletOsloNorway
Isabel Gonçalves Department of Clinical Sciences MalmöLund UniversityLundSweden Department of CardiologyMalmö, Skåne University HospitalMalmöSweden
Bente Halvorsen Research Institute of Internal Medicine, Oslo University HospitalOsloNorway Institute of Clinical Medicine, Faculty of Medicine, University of OsloNorway

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Collaborators Collapse

Canonical and non-canonical roles of complement in atherosclerosis

Cardiovascular diseases are the leading cause of death globally, and atherosclerosis is the major contributor to the development and progression of cardiovascular diseases. Immune responses have a central role in the pathogenesis of atherosclerosis, with the complement system being an acknowledged contributor. Chronic activation of liver-derived and serum-circulating canonical complement sustains endothelial inflammation and innate immune cell activation, and deposition of complement activation fragments on inflamed endothelial cells is a hallmark of atherosclerotic plaques. However, increasing evidence indicates that liver-independent, cell-autonomous and non-canonical complement activities are underappreciated contributors to atherosclerosis. Furthermore, complement activation can also have atheroprotective properties. These specific detrimental or beneficial contributions of the complement system to the pathogenesis of atherosclerosis are dictated by the location of complement activation and engagement of its canonical versus non-canonical functions in a temporal fashion during atherosclerosis progression. In this Review, we summarize the classical and the emerging non-classical roles of the complement system in the pathogenesis of atherosclerosis and discuss potential strategies for therapeutic modulation of complement for the prevention and treatment of atherosclerotic cardiovascular disease.

Colchicine promotes atherosclerotic plaque stability independently of inflammation

Atherosclerosis is a chronic inflammatory disease which is driven in part by the aberrant trans -differentiation of vascular smooth muscle cells (SMCs). No therapeutic drug has been shown to reverse detrimental SMC-derived cell phenotypes into protective phenotypes, a hypothesized enabler of plaque regression and improved patient outcome. Herein, we describe a novel function of colchicine in the beneficial modulation of SMC-derived cell phenotype, independent of its conventional anti-inflammatory effects. Using SMC fate mapping in an advanced atherosclerotic lesion model, colchicine induced plaque regression by converting pathogenic SMC-derived macrophage-like and osteoblast-like cells into protective myofibroblast-like cells which thickened, and thereby stabilized, the fibrous cap. This was dependent on Notch3 signaling in SMC-derived plaque cells. These findings may help explain the success of colchicine in clinical trials relative to other anti-inflammatory drugs. Thus, we demonstrate the potential of regulating SMC phenotype in advanced plaque regression through Notch3 signaling, in addition to the canonical anti-inflammatory actions of drugs to treat atherosclerosis.

Contribution of animal models to the mechanistic understanding of Alternative Pathway and Amplification Loop (AP/AL)-driven Complement-mediated Diseases

This review aimed to capture the key findings that animal models have provided around the role of the alternative pathway and amplification loop (AP/AL) in disease. Animal models, particularly mouse models, have been incredibly useful to define the role of complement and the alternative pathway in health and disease; for instance, the use of cobra venom factor and depletion of C3 provided the initial insight that complement was essential to generate an appropriate adaptive immune response. The development of knockout mice have further underlined the importance of the AP/AL in disease, with the FH knockout mouse paving the way for the first anti-complement drugs. The impact from the development of FB, properdin, and C3 knockout mice closely follows this in terms of mechanistic understanding in disease. Indeed, our current understanding that complement plays a role in most conditions at one level or another is rooted in many of these in vivo studies. That C3, in particular, has roles beyond the obvious in innate and adaptive immunity, normal physiology, and cellular functions, with or without other recognized AP components, we would argue, only extends the reach of this arm of the complement system. Humanized mouse models also continue to play their part. Here, we argue that the animal models developed over the last few decades have truly helped define the role of the AP/AL in disease.

The role of properdin and Factor H in disease

The complement system consists of three pathways (alternative, classical, and lectin) that play a fundamental role in immunity and homeostasis. The multifunctional role of the complement system includes direct lysis of pathogens, tagging pathogens for phagocytosis, promotion of inflammatory responses to control infection, regulation of adaptive cellular immune responses, and removal of apoptotic/dead cells and immune complexes from circulation. A tight regulation of the complement system is essential to avoid unwanted complement-mediated damage to the host. This regulation is ensured by a set of proteins called complement regulatory proteins. Deficiencies or malfunction of these regulatory proteins may lead to pro-thrombotic hematological diseases, renal and ocular diseases, and autoimmune diseases, among others. This review focuses on the importance of two complement regulatory proteins of the alternative pathway, Factor H and properdin, and their role in human diseases with an emphasis on: (a) characterizing the main mechanism of action of Factor H and properdin in regulating the complement system and protecting the host from complement-mediated attack, (b) describing the dysregulation of the alternative pathway as a result of deficiencies, or mutations, in Factor H and properdin, (c) outlining the clinical findings, management and treatment of diseases associated with mutations and deficiencies in Factor H, and (d) defining the unwanted and inadequate functioning of properdin in disease, through a discussion of various experimental research findings utilizing in vitro, mouse and human models.

CFP is a prognostic biomarker and correlated with immune infiltrates in Gastric Cancer and Lung Cancer

Complement factor properdin (CFP), encodes plasma glycoprotein, is a critical gene that regulates the complement pathway of the innate immune system. However, correlations of CFP in cancers remain unclear. In this study, the expression pattern and prognostic value of CFP in pan-cancer were analyzed via the Oncomine, PrognoScan, GEPIA and Kaplan-Meier plotters. In addition, we used immunohistochemical staining to validate CFP expression in clinical tissue samples. Finally, we evaluated the correlations between CFP and cancer immune infiltrates particularly in stomach adenocarcinoma (STAD) and lung adenocarcinoma (LUAD) by using GEPIA and TIMER databases. The results of database analysis and immunohistochemistry showed that the expression level of CFP in STAD and LUAD was lower than that in normal tissues. Low expression level of CFP was associated with poorer overall survival (OS), first progression (FP), post progression survival (PPS) and was detrimental to the prognosis of STAD and LUAD, specifically in stage 3, stage T3, stage N2 and N3 of STAD (P<0.05). Moreover, expression of CFP had significant positive correlations with the infiltration levels of CD8+ T cells, CD4+ T cells, macrophages, neutrophils and dendritic cells (DCs) in STAD and LUAD. Furthermore, gene markers of infiltrating immune cells exhibited different CFP-related immune infiltration patterns such as tumor-associated-macrophages (TAMs). These results suggest that CFP can serve as a prognostic biomarker for determining prognosis and immune infiltration in STAD and LUAD.

Complement Properdin Regulates the Metabolo-Inflammatory Response to a High Fat Diet

Background and objectives: Overnutrition leads to a metabolic and inflammatory response that includes the activation of Complement. Properdin is the only amplifier of complement activation and increases the provision of complement activation products. Its absence has previously been shown to lead to increased obesity in mice on a high fat diet. The aim of this study was to determine ways in which properdin contributes to a less pronounced obese phenotype. Materials and Methods: Wild type (WT) and properdin deficient mice (KO) were fed a high-fat diet (HFD) for up to 12 weeks. Results: There was a significant increase in liver triglyceride content in the KO HFD group compared to WT on HFD. WT developed steatosis. KO had an additional inflammatory component (steatohepatitis). Analysis of AKT signalling by phosphorylation array supported a decrease in insulin sensitivity which was greater for KO than WT in liver and kidney. There was a significant decrease of C5L2 in the fat membranes of the KO HFD group compared to the WT HFD group. Circulating microparticles in KO HFD group showed lower presence of C5L2. Expression of the fatty acid transporter CD36 in adipose tissue was increased in KO on HFD and was also significantly increased in plasma of KO HFD mice compared to WT on HFD. CD36 was elevated on microparticles from KO on HFD. Ultrastructural changes consistent with obesity-associated glomerulopathy were observed for both HFD fed genotypes, but tubular strain was greater in KO. Conclusion: Our work demonstrates that complement properdin is a dominant factor in limiting the severity of obesity-associated conditions that impact on liver and kidney. The two receptors, C5L2 and CD36, are downstream of the activity exerted by properdin.

Clinical and functional consequences of anti-properdin autoantibodies in patients with lupus nephritis

Properdin is the only positive regulator of the complement system. In this study, we characterize the prevalence, functional consequences and disease associations of autoantibodies against properdin in a cohort of patients with autoimmune disease systemic lupus erythematosus (SLE) suffering from lupus nephritis (LN). We detected autoantibodies against properdin in plasma of 22·5% of the LN patients (16 of 71) by enzyme-linked immunosorbent assay (ELISA). The binding of these autoantibodies to properdin was dose-dependent and was validated by surface plasmon resonance. Higher levels of anti-properdin were related to high levels of anti-dsDNA and anti-nuclear antibodies and low concentrations of C3 and C4 in patients, and also with histological signs of LN activity and chronicity. The high negative predictive value (NPV) of anti-properdin and anti-dsDNA combination suggested that patients who are negative for both anti-properdin and anti-dsDNA will not have severe nephritis. Immunoglobulin G from anti-properdin-positive patients' plasma increased the C3b deposition on late apoptotic cells by flow cytometry. Nevertheless, these IgGs did not modify substantially the binding of properdin to C3b, the C3 convertase C3bBb and the pro-convertase C3bB, evaluated by surface plasmon resonance. In conclusion, anti-properdin autoantibodies exist in LN patients. They have weak but relevant functional consequences, which could have pathological significance.

Role of Complement and Complement-Related Adipokines in Regulation of Energy Metabolism and Fat Storage

Adipose tissue releases many cytokines and inflammatory factors described as adipokines. In obesity, adipokines released from expanding adipose tissue are implicated in disease progression and metabolic dysfunction. However, mechanisms controlling the progression of adiposity and metabolic complications are not fully understood. It has been suggested that expanding fat mass and sustained release of inflammatory adipokines in adipose tissue lead to hypoxia, oxidative stress, apoptosis, and cellular damage. These changes trigger an immune response involving infiltration of adipose tissue with immune cells, complement activation and generation of factors involved in opsonization and clearance of damaged cells. Abundant evidence now indicates that adipose tissue is an active secretory source of complement and complement-related adipokines that, in addition to their inflammatory role, contribute to the regulation of metabolic function. This article highlights advances in knowledge regarding the role of these adipokines in energy regulation of adipose tissue through modulating lipogenic and lipolytic pathways. Several adipokines will be discussed including adipsin, Factor H, properdin, C3a, Acylation-Stimulating Protein, C1q/TNF-related proteins, and response gene to complement-32 (RGC-32). Interactions between these factors will be described considering their immune-metabolic roles in the adipose tissue microenvironment and their potential contribution to progression of adiposity and metabolic dysfunction. The differential expression and the role of complement factors in gender-related fat partitioning will also be addressed. Identifying lipogenic adipokines and their specific autocrine/paracrine roles may provide means for adipose-tissue-targeted therapeutic interventions that may disrupt the vicious circle of adiposity and disease progression. © 2019 American Physiological Society. Compr Physiol 9:1411-1429, 2019.

Role of complement system in pathological remodeling of the vascular wall

Cardiovascular diseases (CVD) remain the major cause of morbidity and mortality in Europe. The clinical complications associated to arterial wall rupture involve intimal cap rupture in complicated atherosclerotic plaques and medial rupture in abdominal aortic aneurysm (AAA). The mechanisms underlying pathological vascular remodeling include lipid accumulation, cell proliferation, redox imbalance, proteolysis, leukocyte infiltration, cell death, and eventually, thrombosis. The complement system could participate in vascular remodeling by several mechanisms, from an initial protective response that aims in the clearing of cell debris to a potential deleterious role participating in leukocyte chemotaxis and cell activation and bridging innate and adaptive immunity. We have reviewed the presence and distribution of complement components, as well as the triggers of complement activation in atherosclerotic plaques and AAA, to later assess the functional consequences of complement modulation in experimental models of pathological vascular remodeling and the potential role of complement components as potential circulating biomarkers of CVD. On the whole, complement system is a key mechanism involved in vascular remodelling, which could be useful in the diagnostic/prognostic setting, as well as a potential therapeutic target, of CVD.

Properdin: A multifaceted molecule involved in inflammation and diseases

Properdin, the widely known positive regulator of the alternative pathway (AP), has undergone significant investigation over the last decade to define its function in inflammation and disease, including its role in arthritis, asthma, and kidney and cardiovascular diseases. Properdin is a glycoprotein found in plasma that is mainly produced by leukocytes and can positively regulate AP activity by stabilizing C3 and C5 convertases and initiating the AP. Promotion of complement activity by properdin results in changes in the cellular microenvironment that contribute to innate and adaptive immune responses, including pro-inflammatory cytokine production, immune cell infiltration, antigen presenting cell maturation, and tissue damage. The use of properdin-deficient mouse models and neutralizing antibodies has contributed to the understanding of the mechanisms by which properdin contributes to promoting or preventing disease pathology. This review mainly focusses on the multifaceted roles of properdin in inflammation and diseases, and how understanding these roles is contributing to the development of new disease therapies.

The alternative complement pathway is longitudinally associated with adverse cardiovascular outcomes

The alternative pathway of complement activation is highly reactive and can be activated spontaneously in the vasculature. Activation may contribute to vascular damage and development of cardiovascular disease (CVD). We aimed to investigate functional components of the alternative pathway in cardiovascular risk. We studied 573 individuals who were followed-up for seven years. At baseline, we measured the enhancer properdin; the rate-limiting protease factor D (FD); and a marker of systemic activation, Bb. Using generalised estimating equations, we investigated their longitudinal associations with cardiovascular events (CVE, N=89), CVD (N=159), low-grade inflammation (LGI), endothelial dysfunction (ED) and carotid intima-media thickness (cIMT). Furthermore, we investigated associations with incident CVE (N=39) and CVD (N=73) in 342 participants free of CVD at baseline. CVE included myocardial infarction, stroke, cardiac angioplasty and/or cardiac bypass. CVD additionally included ischaemia on an electrocardiogram and/or ankle-brachial index < 0.9. In adjusted analyses, properdin was positively associated with CVE (per 1SD, longitudinal OR=1.36 [1.07; 1.74], OR for incident CVE=1.53 [1.06; 2.20]), but not with CVD. Properdin was also positively associated with ED (β=0.13 [95 %CI 0.06; 0.20]), but not with LGI or cIMT. FD and Bb were positively associated with LGI (per 1SD, FD: β=0.21 [0.12; 0.29], Bb: β=0.14 [0.07; 0.21]), and ED (FD: β=0.20 [0.11; 0.29], Bb: β=0.10 [0.03; 0.18]), but not with cIMT, CVE or CVD. Taken together, this suggests that the alternative complement pathway contributes to processes of vascular damage, and that in particular a high potential to enhance alternative pathway activation may promote unfavourable cardiovascular outcomes in humans.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Longitudinal associations of the alternative and terminal pathways of complement activation with adiposity: The CODAM study

OBJECTIVE

To investigate longitudinal associations of components of the alternative (C3, C3a, Bb, factor D [FD], factor H [FH], and properdin) and the terminal complement pathway (C5a, sC5b-9) with adiposity.

METHODS

A prospective human cohort study (n=574 at baseline, n=489 after 7 years follow-up) was analyzed. Generalized estimating equations were used to evaluate the longitudinal associations between complement components (standardized values) and adiposity (main outcome BMI [kg/m²]). Multiple linear regression models were used to investigate the associations between change in complement levels and change in BMI. Analyses were adjusted for age, sex, medication and lifestyle.

RESULTS

Over the 7-year period, baseline C3 was positively associated with BMI (β=1.72 [95% confidence interval (CI): 1.35; 2.09]). Positive associations were also observed for C3a (β=0.64 [0.31; 0.97]), FD (β=1.00 [0.59; 1.42]), FH (β=1.17 [0.82; 1.53]), and properdin (β=0.60 [0.28; 0.92]), but not for Bb, C5a or sC5b-9. Moreover, changes in C3 (β=0.52 [0.34; 0.71]) and FH (β=0.51 [0.32; 0.70]) were significantly associated with changes in BMI.

CONCLUSIONS

The complement system, particularly activation of the alternative pathway, may be involved in development of adiposity. Whether individual aspects of alternative pathway activation have a causal role in human obesity, remains to be investigated.

The IL-1RI Co-Receptor TILRR (FREM1 Isoform 2) Controls Aberrant Inflammatory Responses and Development of Vascular Disease

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The IL-1RI co-receptor, TILRR, is a potent amplifier of IL-1–induced responses.

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Blocking TILRR inhibits IL-1 receptor function and activation of inflammatory genes.

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TILRR expression is high in atherosclerotic lesions but low in healthy tissue, allowing distinct inhibition at sites of inflammation.

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Genetic deletion of TILRR and antibody blocking of TILRR function reduce plaque development and progression of atherosclerosis. Lesions exhibit low levels of macrophages and increased levels of smooth muscle cells and collagen, characteristics of stable plaques.

Expression of the interleukin-1 receptor type I (IL-1RI) co-receptor Toll-like and interleukin-1 receptor regulator (TILRR) is significantly increased in blood monocytes following myocardial infarction and in the atherosclerotic plaque, whereas levels in healthy tissue are low. TILRR association with IL-1RI at these sites causes aberrant activation of inflammatory genes, which underlie progression of cardiovascular disease. The authors show that genetic deletion of TILRR or antibody blocking of TILRR function reduces development of atherosclerotic plaques. Lesions exhibit decreased levels of monocytes, with increases in collagen and smooth muscle cells, characteristic features of stable plaques. The results suggest that TILRR may constitute a rational target for site- and signal-specific inhibition of vascular disease.

Properdin: a tightly regulated critical inflammatory modulator

The complement alternative pathway is a powerful arm of the innate immune system that enhances diverse inflammatory responses in the human host. Key to the effects of the alternative pathway is properdin, a serum glycoprotein that can both initiate and positively regulate alternative pathway activity. Properdin is produced by many different leukocyte subsets and circulates as cyclic oligomers of monomeric subunits. While the formation of non‐physiological aggregates in purified properdin preparations and the presence of potential properdin inhibitors in serum have complicated studies of its function, properdin has, regardless, emerged as a key player in various inflammatory disease models. Here, we review basic properdin biology, emphasizing the major hurdles that have complicated the interpretation of results from properdin‐centered studies. In addition, we elaborate on an emerging role for properdin in thromboinflammation and discuss the potential utility of properdin inhibitors as long‐term therapeutic options to treat diseases marked by increased formation of platelet/granulocyte aggregates. Finally, we describe the interplay between properdin and the alternative pathway negative regulator, Factor H, and how aiming to understand these interactions can provide scientists with the most effective ways to manipulate alternative pathway activation in complex systems.

Melatonin: Protection against age-related cardiac pathology

Aging is a complex and progressive process that involves physiological and metabolic deterioration in every organ and system. Cardiovascular diseases are one of the most common causes of mortality and morbidity among elderly subjects worldwide. Most age-related cardiovascular disorders can be influenced by modifiable behaviours such as a healthy diet rich in fruit and vegetables, avoidance of smoking, increased physical activity and reduced stress. The role of diet in prevention of various disorders is a well-established factor, which has an even more important role in the geriatric population. Melatonin, an indoleamine with multiple actions including antioxidant properties, has been identified in a very large number of plant species, including edible plant products and medical herbs. Among products where melatonin has been identified include wine, olive oil, tomato, beer, and others. Interestingly, consumed melatonin in plant foods or melatonin supplementation may promote health benefits by virtue of its multiple properties and it may counteract pathological conditions also related to cardiovascular disorders, carcinogenesis, neurological diseases and aging. In the present review, we summarized melatonin effects against age-related cardiac alterations and abnormalities with a special focus on heart ischemia/reperfusion (IR) injury and myocardial infarction.

The genetics of age-related macular degeneration (AMD)--Novel targets for designing treatment options?

Age-related macular degeneration (AMD) is a progressive disease of the central retina and the main cause of legal blindness in industrialized countries. Risk to develop the disease is conferred by both individual as well as genetic factors with the latter being increasingly deciphered over the last decade. Therapeutically, striking advances have been made for the treatment of the neovascular form of late stage AMD while for the late stage atrophic form of the disease, which accounts for almost half of the visually impaired, there is currently no effective therapy on the market. This review highlights our current knowledge on the genetic architecture of early and late stage AMD and explores its potential for the discovery of novel, target-guided treatment options. We reflect on current clinical and experimental therapies for all forms of AMD and specifically note a persisting lack of efficacy for treatment in atrophic AMD. We further explore the current insight in AMD-associated genes and pathways and critically question whether this knowledge is suited to design novel treatment options. Specifically, we point out that known genetic factors associated with AMD govern the risk to develop disease and thus may not play a role in its severity or progression. Treatments based on such knowledge appear appropriate rather for prevention than treatment of manifest disease. As a consequence, future research in AMD needs to be greatly focused on approaches relevant to the patients and their medical needs.

Clinical and genetic factors associated with progression of geographic atrophy lesions in age-related macular degeneration

Worldwide, age-related macular degeneration (AMD) is a serious threat to vision loss in individuals over 50 years of age with a pooled prevalence of approximately 9%. For 2020, the number of people afflicted with this condition is estimated to reach 200 million. While AMD lesions presenting as geographic atrophy (GA) show high inter-individual variability, only little is known about prognostic factors. Here, we aimed to elucidate the contribution of clinical, demographic and genetic factors on GA progression. Analyzing the currently largest dataset on GA lesion growth (N = 388), our findings suggest a significant and independent contribution of three factors on GA lesion growth including at least two genetic factors (ARMS2_rs10490924 [P < 0.00088] and C3_rs2230199 [P < 0.00015]) as well as one clinical component (presence of GA in the fellow eye [P < 0.00023]). These correlations jointly explain up to 7.2% of the observed inter-individual variance in GA lesion progression and should be considered in strategy planning of interventional clinical trials aimed at evaluating novel treatment options in advanced GA due to AMD.