C1-Inhibitor Decreases the Release of Vasculitis-Like Chemotactic Endothelial Microvesicles

The dark side of foetal bovine serum in extracellular vesicle studies

Extracellular vesicles (EVs) have been shown to be involved in cell-cell communication and to take part in both physiological and pathological processes. Thanks to their exclusive cargo, which includes proteins, lipids, and nucleic acids from the originating cells, they are gaining interest as potential biomarkers of disease. In recent years, their appealing features have been fascinating researchers from all over the world, thus increasing the number of in vitro studies focused on EV release, content, and biological activities. Cultured cell lines are the most-used source of EVs; however, the EVs released in cell cultures are influenced by the cell culture conditions, such as the use of foetal bovine serum (FBS). FBS is the most common supplement for cell culture media, but it is also a source of contaminants, such as exogenous bovine EVs, RNA, and protein aggregates, that can contaminate the cell-derived EVs and influence their cargo composition. The presence of FBS contaminants in cell-derived EV samples is a well-known issue that limits the clinical applications of EVs, thus increasing the need for standardization. In this review, we will discuss the pros and cons of using FBS in cell cultures as a source of EVs, as well as the protocols used to remove contaminants from FBS.

Analysis of microRNAs in Small Urinary Extracellular Vesicles and Their Potential Roles in Pathogenesis of Renal ANCA-Associated Vasculitis

Antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) represents an autoimmunity disease characterized by high mortality. For successful treatment, the detailed knowledge of its complex pathogenesis and the set of biomarkers for differential diagnostics are desired. Analysis of molecular content of small urinary extracellular vesicles (uEV) offers the possibility to find markers in the form of microRNAs (miRNAs) and study the pathways involved in pathogenesis. We used next-generation sequencing in the first preliminary study to detect the miRNAs with altered expression in uEVs of patients with AAV in comparison with age-matched controls. We confirmed the results using single-target quantitative polymerase chain reaction tests on different sets of samples and found five miRNAs (miR-30a-5p, miR-31-3p, miR-99a-5p, miR-106b-5p, miR-182-5p) with highly elevated levels in uEVs of patients. We performed the comparison of their targets with the differentially expressed proteins in uEVs of patients included in the first phase. We realized that upregulated miRNAs and proteins in uEVs in AAV patients target different biological pathways. The only overlap was detected in pathways regulating the actin cytoskeleton assembly and thus potentially affecting the glomerular functions. The associations of upregulated miRNAs with pathways that were neglected as components of complex AAV pathogenesis, e.g., the epidermal growth factor receptor signaling pathway, were found.

Extracellular Vesicles and Acute Kidney Injury: Potential Therapeutic Avenue for Renal Repair and Regeneration

Acute kidney injury (AKI) is a sudden decline of renal function and represents a global clinical problem due to an elevated morbidity and mortality. Despite many efforts, currently there are no treatments to halt this devastating condition. Extracellular vesicles (EVs) are nanoparticles secreted by various cell types in both physiological and pathological conditions. EVs can arise from distinct parts of the kidney and can mediate intercellular communication between various cell types along the nephron. Besides their potential as diagnostic tools, EVs have been proposed as powerful new tools for regenerative medicine and have been broadly studied as therapeutic mediators in different models of experimental AKI. In this review, we present an overview of the basic features and biological relevance of EVs, with an emphasis on their functional role in cell-to-cell communication in the kidney. We explore versatile roles of EVs in crucial pathophysiological mechanisms contributing to AKI and give a detailed description of the renoprotective effects of EVs from different origins in AKI. Finally, we explain known mechanisms of action of EVs in AKI and provide an outlook on the potential clinical translation of EVs in the setting of AKI.

Interactions amongst inflammation, renin-angiotensin-aldosterone and kallikrein-kinin systems: suggestive approaches for COVID-19 therapy

Coronavirus disease 2019 (COVID-19) is a rapid-spread infectious disease caused by the SARS-CoV-2 virus, which can culminate in the renin-angiotensin-aldosterone (RAAS) and kallikrein-kinin (KKS) systems imbalance, and in serious consequences for infected patients. This scoping review of published research exploring the RAAS and KKS was undertaken in order to trace the history of the discovery of both systems and their multiple interactions, discuss some aspects of the viral-cell interaction, including inflammation and the system imbalance triggered by SARS-CoV-2 infection, and their consequent disorders. Furthermore, we correlate the effects of continued use of the RAAS blockers in chronic diseases therapies with the virulence and physiopathology of COVID-19. We also approach the RAAS and KKS-related proposed potential therapies for treatment of COVID-19. In this way, we reinforce the importance of exploring both systems and the application of their components or their blockers in the treatment of coronavirus disease.

Crosstalk between the renin-angiotensin, complement and kallikrein-kinin systems in inflammation

During severe inflammatory and infectious diseases, various mediators modulate the equilibrium of vascular tone, inflammation, coagulation and thrombosis. This Review describes the interactive roles of the renin–angiotensin system, the complement system, and the closely linked kallikrein–kinin and contact systems in cell biological functions such as vascular tone and leakage, inflammation, chemotaxis, thrombosis and cell proliferation. Specific attention is given to the role of these systems in systemic inflammation in the vasculature and tissues during hereditary angioedema, cardiovascular and renal glomerular disease, vasculitides and COVID-19. Moreover, we discuss the therapeutic implications of these complex interactions, given that modulation of one system may affect the other systems, with beneficial or deleterious consequences.

The renin–angiotensin, complement and kallikrein–kinin systems comprise a multitude of mediators that modulate physiological responses during inflammatory and infectious diseases. This Review investigates the complex interactions between these systems and how these are dysregulated in various conditions, including cardiovascular diseases and COVID-19, as well as their therapeutic implications.

Associations Between Plasma Kinin B1 Receptor Levels and the Presence and Severity of Coronary Artery Disease

Aim: Kinin B1 receptor (KB1R) was shown to be up-regulated in human carotid atherosclerotic lesions. Serum KB1R levels were also reported to be high in patients with stroke. However, KB1R deficiency increased atherosclerotic lesions. Therefore, the role of KB1R in atherosclerosis remains unclear. Moreover, no study has reported blood KB1R levels in patients with coronary artery disease (CAD).

Methods: We measured plasma KB1R levels in 375 patients undergoing coronary angiography. The severity of CAD was represented as the numbers of ＞50% stenotic vessels and segments and the severity score.

Results: CAD was found in 197 patients, of whom 89 had 1-vessel disease (1-VD), 62 had 2-VD, and 46 had 3-VD. Plasma KB1R levels were higher in 197 patients with CAD than in 178 without CAD (median 83.3 vs. 73.7 pg/mL, p ＜0.01). A stepwise increase in KB1R levels was found depending on the number of stenotic vessels: 77.1 in 1-VD, 87.8 in 2-VD, and 88.5 pg/mL in 3-VD ( p ＜0.025). A high KB1R level (＞90.0 pg/mL) was present in 30% of patients with CAD(-), 39% of 1-VD, 50% of 2-VD, and 48% of 3-VD ( p ＜0.025). KB1R levels correlated with the number of stenotic segments and the severity score (r=0.14 and r=0.17, p ＜0.01). In multivariate analysis, KB1R levels were an independent factor associated with CAD. Odds ratio for CAD was 1.62 (95%CI=1.02-2.58) for high KB1R level ＞90.0 pg/mL.

Conclusion: Plasma KB1R levels in patients with CAD were high and were associated with the presence and severity of CAD independent of atherosclerotic risk factors.

Extracellular vesicles in renal inflammatory and infectious diseases

Extracellular vesicles can mediate cell-to-cell communication, or relieve the parent cell of harmful substances, in order to maintain cellular integrity. The content of extracellular vesicles includes miRNAs, mRNAs, growth factors, complement factors, cytokines, chemokines and receptors. These may contribute to inflammatory and infectious diseases by the exposure or transfer of potent effectors that induce vascular inflammation by leukocyte recruitment and thrombosis. Furthermore, vesicles release cytokines and induce their release from cells. Extracellular vesicles possess immune modulatory and anti-microbial properties, and induce receptor signaling in the recipient cell, not least by the transfer of pro-inflammatory receptors. Additionally, the vesicles may carry virulence factors systemically. Extracellular vesicles in blood and urine can contribute to the development of kidney diseases or exhibit protective effects. In this review we will describe the role of EVs in inflammation, thrombosis, immune modulation, angiogenesis, oxidative stress, renal tubular regeneration and infection. Furthermore, we will delineate their contribution to renal ischemia/reperfusion, vasculitis, glomerulonephritis, lupus nephritis, thrombotic microangiopathies, IgA nephropathy, acute kidney injury, urinary tract infections and renal transplantation. Due to their content of miRNAs and growth factors, or when loaded with nephroprotective modulators, extracellular vesicles have the potential to be used as therapeutics for renal regeneration.

Recent advances in Extracellular Vesicles and their involvements in vasculitis

Systemic vasculitis is a heterogeneous group of multisystem autoimmune disorders characterized by inflammation of blood vessels. Although many progresses in diagnosis and immunotherapies have been achieved over the past decades, there are still many unanswered questions about vasculitis from pathological understanding to more advanced therapies. Extracellular vesicles (EVs) are double-layer phospholipid membrane vesicles harboring various cargoes. EVs can be classified into exosomes, microvesicles (MVs), and apoptotic bodies depending on their size and origin of cellular compartment. EVs can be released by almost all cell types and may be involved in physical and pathological processes including inflammation and autoimmune responses. In systemic vasculitis, EVs may have pathogenic involvement in inflammation, autoimmune responses, thrombosis, endothelium injury, angiogenesis and intimal hyperplasia. EV-associated redox reaction may also be involved in vasculitis pathogenesis by inducing inflammation, endothelial injury and thrombosis. Additionally, EVs may serve as specific biomarkers for diagnosis or monitoring of disease activity and therapeutic efficacy, i.e. AAV-associated renal involvement. In this review, we have discussed the recent advances of EVs, especially their roles in pathogenesis and clinical involvements in vasculitis.

Extracellular vesicles in kidneys and their clinical potential in renal diseases

Extracellular vesicles (EVs), such as exosomes and microvesicles, are cell-derived lipid bilayer membrane particles, which deliver information from host cells to recipient cells. EVs are involved in various biological processes including the modulation of the immune response, cell-to-cell communications, thrombosis, and tissue regeneration. Different types of kidney cells are known to release EVs under physiologic as well as pathologic conditions, and recent studies have found that EVs have a pathophysiologic role in different renal diseases. Given the recent advancement in EV isolation and analysis techniques, many studies have shown the diagnostic and therapeutic potential of EVs in various renal diseases, such as acute kidney injury, polycystic kidney disease, chronic kidney disease, kidney transplantation, and renal cell carcinoma. This review updates recent clinical and experimental findings on the role of EVs in renal diseases and highlights the potential clinical applicability of EVs as novel diagnostics and therapeutics.

Potential role of extracellular vesicles in the pathophysiology of glomerular diseases

Extracellular vesicles (EVs) are membrane-bound vesicles released by most cells and are found in diverse biological fluids. The release of EVs provides a new mechanism for intercellular communication, allowing cells to transfer their functional cargoes to target cells. Glomerular diseases account for a large proportion of end-stage renal disease (ESRD) worldwide. In recent years, an increasing number of research groups have focused their effort on identifying the functional role of EVs in renal diseases. However, the involvement of EVs in the pathophysiology of glomerular diseases has not been comprehensively described and discussed. In this review, we first briefly introduce the characteristics of EVs. Then, we describe the involvement of EVs in the mechanisms underlying glomerular diseases, including immunological and fibrotic processes. We also discuss what functions EVs derived from different kidney cells have in glomerular diseases and how EVs exert their effects through different signaling pathways. Furthermore, we summarize recent advances in the knowledge of EV involvement in the pathogenesis of various glomerular diseases. Finally, we propose future research directions for identifying better management strategies for glomerular diseases.

Circulating extracellular vesicles from patients with valvular heart disease induce neutrophil chemotaxis via FOXO3a and the inhibiting role of dexmedetomidine

We previously demonstrated that circulating extracellular vesicles (EVs) from patients with valvular heart disease (VHD; vEVs) contain inflammatory components and inhibit endothelium-dependent vasodilation. Neutrophil chemotaxis plays a key role in renal dysfunction, and dexmedetomidine (DEX) can reduce renal dysfunction in cardiac surgery. However, the roles of vEVs in neutrophil chemotaxis and effects of DEX on vEVs are unknown. Here, we investigated the impact of vEVs on neutrophil chemotaxis in kidneys and the influence of DEX on vEVs. Circulating EVs were isolated from healthy subjects and patients with VHD. The effects of EVs on chemokine generation, forkhead box protein O3a (FOXO3a) pathway activation and neutrophil chemotaxis on cultured human umbilical vein endothelial cells (HUVECs) and kidneys in mice and the influence of DEX on EVs were detected. vEVs increased FOXO3a expression, decreased phosphorylation of Akt and FOXO3a, promoted FOXO3a nuclear translocation, and activated the FOXO3a signaling pathway in vitro. DEX pretreatment reduced vEV-induced CXCL4 and CCL5 expression and neutrophil chemotaxis in cultured HUVECs via the FOXO3a signaling pathway. vEVs were also found to suppress Akt phosphorylation and activate FOXO3a signaling to increase plasma levels of CXCL4 and CCL5 and neutrophil accumulation in kidney. The overall mechanism was inhibited in vivo with DEX pretreatment. Our data demonstrated that vEVs induced CXCL4-CCL5 to stimulate neutrophil infiltration in kidney, which can be inhibited by DEX via the FOXO3a signaling. Our findings reveal a unique mechanism involving vEVs in inducing neutrophils chemotaxis and may provide a novel basis for using DEX in reducing renal dysfunction in valvular heart surgery.

Update on C1 Esterase Inhibitor in Human Solid Organ Transplantation

Complement plays important roles in both ischemia-reperfusion injury (IRI) and antibody-mediated rejection (AMR) of solid organ allografts. One approach to possibly improve outcomes after transplantation is the use of C1 inhibitor (C1-INH), which blocks the first step in both the classical and lectin pathways of complement activation and also inhibits the contact, coagulation, and kinin systems. C1-INH can also directly block leukocyte-endothelial cell adhesion. C1-INH contrasts with eculizumab and other distal inhibitors, which do not affect C4b or C3b deposition or noncomplement pathways. Authors of reports on trials in kidney transplant recipients have suggested that C1-INH treatment may reduce IRI and delayed graft function, based on decreased requirements for dialysis in the first month after transplantation. This effect was particularly marked with grafts with Kidney Disease Profile Index ≥ 85. Other clinical studies and models suggest that C1-INH may decrease sensitization and donor-specific antibody production and might improve outcomes in AMR, including in patients who are refractory to other modalities. However, the studies have been small and often only single-center. This article reviews clinical data and ongoing trials with C1-INH in transplant recipients, compares the results with those of other complement inhibitors, and summarizes potentially productive directions for future research.

Kinin B1 Receptor Is Important in the Pathogenesis of Myeloperoxidase-Specific ANCA GN

BACKGROUND

Myeloperoxidase-specific ANCA (MPO-ANCA) are implicated in the pathogenesis of vasculitis and GN. Kinins play a major role during acute inflammation by regulating vasodilatation and vascular permeability and by modulating adhesion and migration of leukocytes. Kinin system activation occurs in patients with ANCA vasculitis. Previous studies in animal models of GN and sclerosing kidney diseases have demonstrated protective effects of bradykinin receptor 1 (B1R) blockade via interference with myeloid cell trafficking.

METHODS

To investigate the role of B1R in a murine model of MPO-ANCA GN, we evaluated effects of B1R genetic ablation and pharmacologic blockade. We used bone marrow chimeric mice to determine the role of B1R in bone marrow-derived cells (leukocytes) versus nonbone marrow-derived cells. We elucidated mechanisms of B1R effects using in vitro assays for MPO-ANCA-induced neutrophil activation, endothelial adherence, endothelial transmigration, and neutrophil adhesion molecule surface display.

RESULTS

B1R deficiency or blockade prevented or markedly reduced ANCA-induced glomerular crescents, necrosis, and leukocyte influx in mice. B1R was not required for in vitro MPO-ANCA-induced neutrophil activation. Leukocyte B1R deficiency, but not endothelial B1R deficiency, decreased glomerular neutrophil infiltration induced by MPO-ANCA in vivo. B1R enhanced ANCA-induced neutrophil endothelial adhesion and transmigration in vitro. ANCA-activated neutrophils exhibited changes in Mac-1 and LFA-1, important regulators of neutrophil endothelial adhesion and transmigration: ANCA-activated neutrophils increased surface expression of Mac-1 and increased shedding of LFA-1, whereas B1R blockade reduced these effects.

CONCLUSIONS

The leukocyte B1R plays a critical role in the pathogenesis of MPO-ANCA-induced GN in a mouse model by modulating neutrophil-endothelial interaction. B1R blockade may have potential as a therapy for ANCA GN and vasculitis.

Current State of Precision Medicine in Primary Systemic Vasculitides

Precision medicine (PM) is an emerging data-driven health care approach that integrates phenotypic, genomic, epigenetic, and environmental factors unique to an individual. The goal of PM is to facilitate diagnosis, predict effective therapy, and avoid adverse reactions specific for each patient. The forefront of PM is in oncology; nonetheless, it is developing in other fields of medicine, including rheumatology. Recent studies on elucidating the genetic architecture of polygenic and monogenic rheumatological diseases have made PM possible by enabling physicians to customize medical treatment through the incorporation of clinical features and genetic data. For complex inflammatory disorders, the prevailing paradigm is that disease susceptibility is due to additive effects of common reduced-penetrance gene variants and environmental factors. Efforts have been made to calculate cumulative genetic risk score (GRS) and to relate specific susceptibility alleles for use of target therapies. The discovery of rare patients with single-gene high-penetrance mutations informed our understanding of pathways driving systemic inflammation. Here, we review the advances in practicing PM in patients with primary systemic vasculitides (PSVs). We summarize recent genetic studies and discuss current knowledge on the contribution of epigenetic factors and extracellular vesicles (EVs) in disease progression and treatment response. Implementation of PM in PSVs is a developing field that will require analysis of a large cohort of patients to validate data from genomics, transcriptomics, metabolomics, proteomics, and epigenomics studies for accurate disease profiling. This multi-omics approach to study disease pathogeneses should ultimately provide a powerful tool for stratification of patients to receive tailored optimal therapies and for monitoring their disease activity.

Blockade of the kallikrein-kinin system reduces endothelial complement activation in vascular inflammation

Background

The complement and kallikrein-kinin systems (KKS) are activated during vascular inflammation. The aim of this study was to investigate if blockade of the KKS can affect complement activation on the endothelium during inflammation.

Methods

Complement deposition on endothelial microvesicles was assayed in vasculitis patient plasma samples and controls. Plasma was perfused over glomerular endothelial cells and complement deposition assayed by flow cytometry. The effect of the kinin system was assessed using kinin receptor antagonists and C1-inhibitor. The in vivo effect was assessed in kidney sections from mice with nephrotoxic serum-induced glomerulonephritis treated with a kinin receptor antagonist.

Findings

Vasculitis patient plasma had significantly more C3- and C9-positive endothelial microvesicles than controls. Perfusion of patient acute-phase plasma samples over glomerular endothelial cells induced the release of significantly more complement-positive microvesicles, in comparison to remission or control plasma. Complement activation on endothelial microvesicles was reduced by kinin B1- and B2-receptor antagonists or by C1-inhibitor (the main inhibitor of the classical pathway and the KKS). Likewise, perfusion of glomerular endothelial cells with C1-inhibitor-depleted plasma induced the release of complement-positive microvesicles, which was significantly reduced by kinin-receptor antagonists or C1-inhibitor. Mice with nephrotoxic serum-induced glomerulonephritis exhibited significantly reduced glomerular C3 deposition when treated with a B1-receptor antagonist.

Interpretation

Excessive complement deposition on the endothelium will promote endothelial injury and the release of endothelial microvesicles. This study demonstrates that blockade of the KKS can reduce complement activation and thereby the inflammatory response on the endothelium.

Funding

Full details are provided in the Acknowledgements/Funding section.

The complex functioning of the complement system in xenotransplantation

The role of complement in xenotransplantation is well-known and is a topic that has been reviewed previously. However, our understanding of the immense complexity of its interaction with other constituents of the innate immune response and of the coagulation, adaptive immune, and inflammatory responses to a xenograft is steadily increasing. In addition, the complement system plays a function in metabolism and homeostasis. New reviews at intervals are therefore clearly warranted. The pathways of complement activation, the function of the complement system, and the interaction between complement and coagulation, inflammation, and the adaptive immune system in relation to xenotransplantation are reviewed. Through several different mechanisms, complement activation is a major factor in contributing to xenograft failure. In the organ-source pig, the detrimental influence of the complement system is seen during organ harvest and preservation, for example, in ischemia-reperfusion injury. In the recipient, the effect of complement can be seen through its interaction with the immune, coagulation, and inflammatory responses. Genetic-engineering and other therapeutic methods by which the xenograft can be protected from the effects of complement activation are discussed. The review provides an updated source of reference to this increasingly complex subject.

Extracellular vesicles in autoimmune vasculitis - Little dirts light the fire in blood vessels

Systemic vasculitis is diverse group of autoimmune disorders which are characterized by inflammation of blood vessel walls with deep aching and burning pain. Their underlying etiology and pathophysiology still remain poorly understood. Extracellular vesicles (EVs), including exosomes, microvesicles (MVs), and apoptotic bodies, are membrane vesicular structures that are released either during cell activation, or when cells undergo programmed cell death, including apoptosis, necroptosis, and pyroptosis. Although EVs were thought as cell dusts, but now they have been found to be potently active since they harbor bioactive molecules, such as proteins, lipids, nucleic acids, or multi-molecular complexes. EVs can serve as novel mediators for cell-to-cell communications by delivery bioactive molecules from their parental cells to the recipient cells. Earlier studies mainly focused on MVs budding from membrane surface. Recent studies demonstrated that EVs may also carry molecules from cytoplasm or even from nucleus of their parental cells, and these EVs may carry autoantigens and are important in vasculitis. EVs may play important roles in vasculitis through their potential pathogenic involvements in inflammation, autoimmune responses, procoagulation, endothelial dysfunction/damage, angiogenesis, and intimal hyperplasia. EVs have also been used as specific biomarkers for diagnostic use or disease severity monitoring. In this review, we have focused on the aspects of EV biology most relevant to the pathogenesis of vasculitis, discussed their perspective insights, and summarized the exist literature on EV relevant studies in vasculitis, therefore provides an integration of current knowledge regarding the novel role of EVs in systemic vasculitis.

Extracellular Vesicles: Opportunities and Challenges for the Treatment of Renal Diseases

Extracellular vesicles (EVs) are lipid-based membrane-bound particles secreted by virtually all types of cells under both physiological and pathological conditions. Given their unique biological and pharmacological properties, EVs have spurred a renewed interest in their utility for therapeutics. Herein, efforts are made to give a comprehensive overview on the recent advances of EV-based therapy in renal diseases. The fact that EVs are implicated in various renal diseases provides us with new therapeutic modalities by eliminating these pathogenic entities. Strategies that target EVs to inhibit their production, release, and uptake will be discussed. Further, EVs-derived predominantly from stem cells can stimulate tissue repair and ameliorate renal injury via transferring proteins and nucleic acids to injured cells. Such EVs can be exploited as agents in renal regenerative medicine. Finally, we will focus on the specific application of EVs as a novel drug delivery system and highlight the challenges of EVs-based therapies for renal diseases.

Platelets release proinflammatory microparticles in anti-neutrophil cytoplasmic antibody-associated vasculitis

OBJECTIVES

The biological functions of the platelets contributing to ANCA-associated vasculitis (AAV) are largely unclear. The current study aimed to investigate the potential role of platelet-derived microparticles (PMPs) in AAV.

METHODS

In the current study, microparticles in AAV patients were analysed by flow cytometry, and PMPs were probed for relative levels of 640 bioactive proteins secreted from patients' platelets using antibody microarrays. These data were then correlated with clinical and pathological parameters.

RESULTS

PMPs were significantly increased in 69 AAV patients, predominantly MPO-ANCA positive patients in active stage compared with in remission [4406.8/μl (2135.4, 5485.0) vs 549.7/μl (350, 708.5), P < 0.0001], and 43% of microparticles in active AAV were PMPs. Compared with 15 patients in remission, highly expressed proinflammatory molecules in the microparticles from platelets in 15 AAV patients in active stage revealed that potential functions of PMPs were promotion of the effect of chemotaxis, adhesion, growth and apoptosis (all the patients for array analysis were MPO-ANCA positive). The level of PMPs had a significant association with disease activity, inflammation, and renal damage.

CONCLUSION

PMPs may serve as inflammatory propagators through their wide production of proinflammatory cytokines in AAV, potentially providing a novel therapeutic target.

Extracellular Vesicles: Opportunities and Challenges for the Treatment of Renal Fibrosis

Extracellular vesicles (EVs) are small lipid-based membrane-bound vesicles secreted by most cells under both physiological and pathological conditions. A key function of EVs is to mediate cell-cell communication via transferring mRNAs, miRNAs and proteins from parent cells to recipient cells. These unique features of EVs have spurred a renewed interest in their utility for therapeutics. Given the growing evidence for EV-mediated renal diseases, strategies that could block the release or uptake of pathogenic EVs will be discussed in this review. Then, the therapeutic potential of EVs predominantly from stem cells in renal diseases will be outlined. Finally, we will focus on the specific application of EVs as a novel drug delivery system and highlight the challenges of EVs-based therapies for renal diseases.

Exosomes and microvesicles in normal physiology, pathophysiology, and renal diseases

Extracellular vesicles are cell-derived membrane particles ranging from 30 to 5,000 nm in size, including exosomes, microvesicles, and apoptotic bodies. They are released under physiological conditions, but also upon cellular activation, senescence, and apoptosis. They play an important role in intercellular communication. Their release may also maintain cellular integrity by ridding the cell of damaging substances. This review describes the biogenesis, uptake, and detection of extracellular vesicles in addition to the impact that they have on recipient cells, focusing on mechanisms important in the pathophysiology of kidney diseases, such as thrombosis, angiogenesis, tissue regeneration, immune modulation, and inflammation. In kidney diseases, extracellular vesicles may be utilized as biomarkers, as they are detected in both blood and urine. Furthermore, they may contribute to the pathophysiology of renal disease while also having beneficial effects associated with tissue repair. Because of their role in the promotion of thrombosis, inflammation, and immune-mediated disease, they could be the target of drug therapy, whereas their favorable effects could be utilized therapeutically in acute and chronic kidney injury.

New insight into the role of extracellular vesicles in kidney disease

Extracellular vesicles (EVs) are released to maintain cellular homeostasis as well as to mediate cell communication by spreading protective or injury signals to neighbour or remote cells. In kidney, increasing evidence support that EVs are signalling vesicles for different segments of tubules, intra‐glomerular, glomerular‐tubule and tubule‐interstitial communication. EVs released by kidney resident and infiltrating cells can be isolated from urine and were found to be promising biomarkers for kidney disease, reflecting deterioration of renal function and histological change. We have here summarized the recent progress about the functional role of EVs in kidney disease as well as challenges and future directions involved.

The role of complement inhibition in kidney transplantation

INTRODUCTION AND BACKGROUND

The complement system which belongs to the innate immune system acts both as a first line of defence against various pathogens and as a guardian of host homeostasis. The role of complement has been recently highlighted in several aspects of kidney transplantation: ischaemia-reperfusion, antibody-mediated rejection and native kidney disease recurrence.

SOURCES OF DATA

Experimental data, availability of complement-blocking molecules (mainly the anti-C5 monoclonal antibody, eculizumab) and several trials in human kidney transplant recipients has led to some areas of agreement and some disappointment.

AREAS OF AGREEMENT AND CONTROVERSIES

So far, eculizumab has shown great efficacy in treatment and prevention of atypical haemolytic and uraemic syndrome, some efficacy in the prevention of antibody-mediated and so far no efficacy in the prevention of delayed graft function.

GROWING POINTS

Among the numerous potentially available drugs potentially interfering with complement, recent focus has been made on C1 blockers in the setting of antibody-mediated rejection with promising results.

AREAS TIMELY FOR DEVELOPING RESEARCH

Complement is now recognized as a major player in transplant immunology, several targets are going to be tested to define precisely which ones may be potentially useful in clinical practice.

Microvesicle Involvement in Shiga Toxin-Associated Infection

Shiga toxin is the main virulence factor of enterohemorrhagic Escherichia coli, a non-invasive pathogen that releases virulence factors in the intestine, causing hemorrhagic colitis and, in severe cases, hemolytic uremic syndrome (HUS). HUS manifests with acute renal failure, hemolytic anemia and thrombocytopenia. Shiga toxin induces endothelial cell damage leading to platelet deposition in thrombi within the microvasculature and the development of thrombotic microangiopathy, mostly affecting the kidney. Red blood cells are destroyed in the occlusive capillary lesions. This review focuses on the importance of microvesicles shed from blood cells and their participation in the prothrombotic lesion, in hemolysis and in the transfer of toxin from the circulation into the kidney. Shiga toxin binds to blood cells and may undergo endocytosis and be released within microvesicles. Microvesicles normally contribute to intracellular communication and remove unwanted components from cells. Many microvesicles are prothrombotic as they are tissue factor- and phosphatidylserine-positive. Shiga toxin induces complement-mediated hemolysis and the release of complement-coated red blood cell-derived microvesicles. Toxin was demonstrated within blood cell-derived microvesicles that transported it to renal cells, where microvesicles were taken up and released their contents. Microvesicles are thereby involved in all cardinal aspects of Shiga toxin-associated HUS, thrombosis, hemolysis and renal failure.

Extracellular vesicles in renal disease

Extracellular vesicles, such as exosomes and microvesicles, are host cell-derived packages of information that allow cell-cell communication and enable cells to rid themselves of unwanted substances. The release and uptake of extracellular vesicles has important physiological functions and may also contribute to the development and propagation of inflammatory, vascular, malignant, infectious and neurodegenerative diseases. This Review describes the different types of extracellular vesicles, how they are detected and the mechanisms by which they communicate with cells and transfer information. We also describe their physiological functions in cellular interactions, such as in thrombosis, immune modulation, cell proliferation, tissue regeneration and matrix modulation, with an emphasis on renal processes. We discuss how the detection of extracellular vesicles could be utilized as biomarkers of renal disease and how they might contribute to disease processes in the kidney, such as in acute kidney injury, chronic kidney disease, renal transplantation, thrombotic microangiopathies, vasculitides, IgA nephropathy, nephrotic syndrome, urinary tract infection, cystic kidney disease and tubulopathies. Finally, we consider how the release or uptake of extracellular vesicles can be blocked, as well as the associated benefits and risks, and how extracellular vesicles might be used to treat renal diseases by delivering therapeutics to specific cells.