Elevated urinary podocyte-derived extracellular microvesicles in renovascular hypertensive patients

Exosomes secreted by podocytes regulate the differentiation of Th17/Treg cells in idiopathic nephrotic syndrome

Background

Previous studies have demonstrated that immune cells release exosomes, which act as antigen-presenting vesicles to activate T cells. In our previous study, we discovered that podocytes, a type of kidney cell, can also exhibit antigen-presenting functions to naïve CD4+ T cells in idiopathic nephrotic syndrome (INS). Building upon these findings, the objective of this study was to investigate whether podocytes can regulate the balance between Th17 and Treg cells through the release of exosomes.

Methods

We co-cultured naïve CD4+ T cells with LPS-treated bone marrow dendritic cells (LPS-BMDC), LPS-treated mouse podocyte clone 5 (LPS-MPC-5), and exosomes derived from LPS-MPC-5 (LPS-EXO). As a control group, naïve CD4+ T cells were cultured with exosomes from untreated MPC-5 (EXO). After 48 h, we analyzed the percentages of Th17 and Treg cells using flow cytometry, measured the concentrations of IL-17A, IL-10, and IL-4 were using ELISA, and examined the expressions of IL-17a, IL-10, RORC, and FOXP3 using RT-qPCR.

Results

We confirmed the presence of exosomes derived from podocytes based on their morphology, size distribution, concentrations, and the levels of exosomes-specific markers. The percentage of Th17 and Treg cells in the LPS-EXO group was significantly higher than that in the control groups, but lower than in the LPS-MPC-5 group. Furthermore, the ratio of Th17/Treg was relatively higher in the LPS-EXO group compared to the LPS-MPC-5 group.

Conclusion

This study indicated further insights into the role of exosomes released from LPS-treated podocytes in regulating the balance between Th17 and Treg cells in INS.

Frontier role of extracellular vesicles in kidney disease

Kidney diseases represent a diverse range of conditions that compromise renal function and structure which characterized by a progressive deterioration of kidney function, may ultimately necessitate dialysis or kidney transplantation as end-stage treatment options. This review explores the complex landscape of kidney diseases, highlighting the limitations of existing treatments and the pressing need for innovative strategies. The paper delves into the role of extracellular vesicles (EVs) as emerging biomarkers and therapeutic agents in the context of kidney pathophysiology. Urinary extracellular vesicles (uEVs), in particular, offer a non-invasive means of assessing renal injury and monitoring disease progression. Additionally, mesenchymal stem cell-derived EVs (MSC-EVs) are examined for their immunomodulatory and tissue repair capabilities, presenting a promising avenue for novel therapeutic interventions. And discusses the potential of engineering EVs to enhance their targeting and therapeutic efficacy. This paper systematically integrates the latest research findings and aims to provide a comprehensive overview of the role of EVs in kidney disease, providing cutting-edge insights into their potential as a diagnostic and therapeutic tool.

Future embracing: exosomes driving a revolutionary approach to the diagnosis and treatment of idiopathic membranous nephropathy

Membranous nephropathy (MN) is a leading cause of nephrotic syndrome in adults and is associated with high rates of end-stage renal disease. Early detection and precise interventions are crucial for improving patient prognosis and quality of life. However, the current diagnosis primarily relies on renal biopsies and traditional biomarkers, which have limitations. Additionally, targeted therapeutic strategies are lacking. Exosomes, small vesicles that facilitate intercellular communication, have emerged as potential noninvasive diagnostic markers due to their stability, diverse cargo, and rapid detectability. They also hold promise as carriers for gene and drug delivery, presenting innovative opportunities in renal disease prognosis and treatment. However, research on exosomes in the context of idiopathic membranous nephropathy (IMN) remains limited, with a focus on exploring urinary exosomes as IMN markers. In this review, we summarize the current status of MN diagnosis and treatment, highlight the fundamental characteristics of exosomes, and discuss recent advancements in their application to IMN diagnosis and therapy. We provide insights into the clinical prospects of exosomes in IMN and acknowledge potential challenges. This article aims to offer forward-looking insights into the future of exosome-mediated IMN diagnosis and treatment, indicating a revolutionary transformation in this field.

Podocyte-specific proteins in urinary extracellular vesicles of patients with IgA nephropathy: Vasorin and ceruloplasmin

Introduction

Urinary extracellular vesicles (uEVs) can be considered biomarkers of kidney diseases. EVs derived from podocytes may reflect podocyte damage in different glomerular diseases. IgA nephropathy (IgAN) is one of the most common forms of glomerulonephritis (GN) characterized by proteinuria and hematuria. This study aimed to analyze the uEVs of IgAN patients to understand the pathophysiological processes of the disease at the protein level.

Methods

Patients with GN [biopsy-proven IgAN (n = 16) and membranous glomerulonephritis (MGN, n = 16)], and healthy controls (n = 16) were included in this study. The uEVs were extracted, characterized, and analyzed to evaluate the protein levels of candidate markers of IgAN, including vasorin precursor, aminopeptidase N, and ceruloplasmin by western-blot analysis.

Results

Higher levels of both podocytes and EVs-related proteins were observed in the pooled urine samples of GN patients compared to the healthy controls. In IgAN patients, uEV-protein levels of vasorin were statistically lower while levels of ceruloplasmin were significantly higher compared to MGN (P = 0.002, P = 0.06) and healthy controls, respectively (P = 0.020, P= 0.001).

Conclusion

Different levels of the studied proteins in uEVs may indicate podocyte injury and represent a direct association with the pathology of IgAN and MGN.

Extracellular Vesicles in Kidney Diseases: Moving Forward

Extracellular vesicles (EVs) are evolving as novel cell mediators, biomarkers, and therapeutic targets in kidney health and disease. They are naturally derived from cells both within and outside the kidney and carry cargo which mirrors the state of the parent cell. Thus, they are potentially more sensitive and disease-specific as biomarkers and messengers in various kidney diseases. Beside their role as novel communicators within the nephron, they likely communicate between different organs affected by various kidney diseases. Study of urinary EVs (uEVs) can help to fill current knowledge gaps in kidney diseases. However, separation and characterization are challenged by their heterogeneity in size, shape, and cargo. Fortunately, more sensitive and direct EV measuring tools are in development. Many clinical syndromes in nephrology from acute to chronic kidney and glomerular to tubular diseases have been studied. Yet, validation of biomarkers in larger cohorts is warranted and simpler tools are needed. Translation from in vitro to in vivo studies is also urgently needed. The therapeutic role of uEVs in kidney diseases has been studied extensively in rodent models of AKI. On the basis of the current exponential growth of EV research, the field of EV diagnostics and therapeutics is moving forward.

Levels of serum podocalyxin in preeclampsia and relationship with maternal echocardiographic and Doppler ultrasound parameters

INTRODUCTION

Podocalyxin (PCX) is an indicator of glomerular injury. Aside from the kidney, it is expressed in the endothelial cells of various organs. Echographic examinations are useful in assessing the alterations in cardiovascular structure and function during pregnancy.

Exploring Urinary Extracellular Vesicles and Immune Mediators as Biomarkers of Kidney Injury in COVID-19 Hospitalized Patients

Kidney injury is an important outcome associated with COVID-19 severity. In this regard, alterations in urinary extracellular vesicles (uEVs) could be detected in the early phases of renal injury and may be reflective of the inflammatory process. This is an observational study performed with a case series of COVID-19 hospitalized patients presenting mild-to-critical disease. Total and podocyte-derived uEVs were identified by nanoscale flow cytometry, and urinary immune mediators were assessed by a multiplex assay. We studied 36 patients, where 24 (66.7%) were considered as mild/moderate and 12 (33.3%) as severe/critical. Increased levels of total uEVs were observed (p = 0.0001). Importantly, total uEVs were significantly higher in severe/critical patients who underwent hemodialysis (p = 0.03) and were able to predict this clinical outcome (AUC 0.93, p = 0.02). Severe/critical patients also presented elevated urinary levels (p < 0.05) of IL-1β, IL-4, IL-6, IL-7, IL-16, IL-17A, LIF, CCL-2, CCL-3, CCL-11, CXCL-10, FGFb, M-CSF, and CTAcK. Lastly, we observed that total uEVs were associated with urinary immune mediators. In conclusion, our results show that early alterations in urinary EVs could identify patients at higher risk of developing renal dysfunction in COVID-19. This could also be relevant in different scenarios of systemic and/or infectious disease.

Emerging role of extracellular vesicles in kidney diseases

Many types of renal disease eventually progress to end-stage renal disease, which can only be maintained by renal replacement therapy. Therefore, kidney diseases now contribute significantly to the health care burden in many countries. Many new advances and strategies have been found in the research involving kidney diseases; however, there is still no efficient treatment. Extracellular vesicles (EVs) are cell-derived membrane structures, which contains proteins, lipids, and nucleic acids. After internalization by downstream cells, these components can still maintain functional activity and regulate the phenotype of downstream cells. EVs drive the information exchange between cells and tissues. Majority of the cells can produce EVs; however, its production, contents, and transportation may be affected by various factors. EVs have been proved to play an important role in the occurrence, development, and treatment of renal diseases. However, the mechanism and potential applications of EVs in kidney diseases remain unclear. This review summarizes the latest research of EVs in renal diseases, and provides new therapeutic targets and strategies for renal diseases.

Exfoliated Kidney Cells from Urine for Early Diagnosis and Prognostication of CKD: The Way of the Future?

Chronic kidney disease (CKD) is a global health issue, affecting more than 10% of the worldwide population. The current approach for formal diagnosis and prognostication of CKD typically relies on non-invasive serum and urine biomarkers such as serum creatinine and albuminuria. However, histological evidence of tubulointerstitial fibrosis is the 'gold standard' marker of the likelihood of disease progression. The development of novel biomedical technologies to evaluate exfoliated kidney cells from urine for non-invasive diagnosis and prognostication of CKD presents opportunities to avoid kidney biopsy for the purpose of prognostication. Efforts to apply these technologies more widely in clinical practice are encouraged, given their potential as a cost-effective approach, and no risk of post-biopsy complications such as bleeding, pain and hospitalization. The identification of biomarkers in exfoliated kidney cells from urine via western blotting, enzyme-linked immunosorbent assay (ELISA), immunofluorescence techniques, measurement of cell and protein-specific messenger ribonucleic acid (mRNA)/micro-RNA and other techniques have been reported. Recent innovations such as multispectral autofluorescence imaging and single-cell RNA sequencing (scRNA-seq) have brought additional dimensions to the clinical application of exfoliated kidney cells from urine. In this review, we discuss the current evidence regarding the utility of exfoliated proximal tubule cells (PTC), podocytes, mesangial cells, extracellular vesicles and stem/progenitor cells as surrogate markers for the early diagnosis and prognostication of CKD. Future directions for development within this research area are also identified.

Metabolic Syndrome-Related Kidney Injury: A Review and Update

Metabolic syndrome (MetS) includes visceral obesity, hyperglycemia, dyslipidemia, and hypertension. The prevalence of MetS is 20-25%, which is an important risk factor for chronic kidney disease (CKD). MetS causes effects on renal pathophysiology, including glomerular hyperfiltration, RAAS, microalbuminuria, profibrotic factors and podocyte injury. This review compares several criteria of MetS and analyzes their differences. MetS and the pathogenesis of CKD includes insulin resistance, obesity, dyslipidemia, inflammation, oxidative stress, and endothelial dysfunction. The intervention of MetS-related renal damage is the focus of this article and includes controlling body weight, hypertension, hyperglycemia, and hyperlipidemia, requiring all components to meet the criteria. In addition, interventions such as endoplasmic reticulum stress, oxidative stress, gut microbiota, body metabolism, appetite inhibition, podocyte apoptosis, and mesenchymal stem cells are reviewed.

Microparticles in Diabetic Kidney Disease

Diabetickidneydisease(DKD)isthemostcommoncauseofrenal failure and a major contributor to the socioeconomic burden in chronic kidney disease (CKD) patients worldwide. The pathogenesis of DKD involves all the structures in the nephron, and it is indicated by proteinuria, hypertension, and progressive decline in renal function, leading tosubstantialmorbidityandmortality. Due to the limitations of currently available standard markers (albuminuria and glomerular filtration rate) in the diagnosis and clinical grading of DKD, it's time to have novel biomarkers for early detection, targeted and effective therapy to prevent the progression. Microparticles (MPs) are extracellular vesicles measuring 0.1 to 1 micron derived by cytoskeletal reorganization in the form of cytoplasmic blebs which alters the phospholipid cytochemistry of the cell membrane. They are shed during cell activation and apoptosis as well as plays an important role in cell-to-cell communication. Over the last few decades, both plasma and urinary MPs have been investigated, validated and the preliminary research looks promising. With alterations in their number and composition documented in clinical situations involving both Type1 and 2 diabetes mellitus, microparticles assay appears to be promising in early diagnosis and prognostication of DKD. WecoverthebasicsofmicroparticlesandtheirinvolvementinDKDinthisreviewarticle.

Differential and targeted vesiculation: pathologic cellular responses to elevated arterial pressure

Extracellular vesicles are small membrane-enclosed particles released during cell activation or injury. They have been investigated for several decades and found to be secreted in various diseases. Their pathogenic role is further supported by the presence of several important molecules among their cargo, including proteins, lipids, and nucleic acids. Many studies have reported enhanced and targeted extracellular vesicle biogenesis in diseases that involve chronic or transient elevation of arterial pressure resulting in endothelial dysfunction, within either the general circulatory system or specific local vascular beds. In addition, several associated pathologic processes have been studied and reported. However, the role of elevated pressure as a common pathogenic trigger across vascular domains and disease chronicity has not been previously described. This review will therefore summarize our current knowledge of the differential and targeted biogenesis of extracellular vesicles in major diseases that are characterized by elevated arterial pressure leading to endothelial dysfunction and propose a unified theory of pressure-induced extracellular vesicle-mediated pathogenesis.

Urinary extracellular vesicles: A position paper by the Urine Task Force of the International Society for Extracellular Vesicles

Urine is commonly used for clinical diagnosis and biomedical research. The discovery of extracellular vesicles (EV) in urine opened a new fast-growing scientific field. In the last decade urinary extracellular vesicles (uEVs) were shown to mirror molecular processes as well as physiological and pathological conditions in kidney, urothelial and prostate tissue. Therefore, several methods to isolate and characterize uEVs have been developed. However, methodological aspects of EV separation and analysis, including normalization of results, need further optimization and standardization to foster scientific advances in uEV research and a subsequent successful translation into clinical practice. This position paper is written by the Urine Task Force of the Rigor and Standardization Subcommittee of ISEV consisting of nephrologists, urologists, cardiologists and biologists with active experience in uEV research. Our aim is to present the state of the art and identify challenges and gaps in current uEV-based analyses for clinical applications. Finally, recommendations for improved rigor, reproducibility and interoperability in uEV research are provided in order to facilitate advances in the field.

Circulating Extracellular Vesicles As Biomarkers and Drug Delivery Vehicles in Cardiovascular Diseases

Extracellular vesicles (EVs) are composed of a lipid bilayer containing transmembrane and soluble proteins. Subtypes of EVs include ectosomes (microparticles/microvesicles), exosomes, and apoptotic bodies that can be released by various tissues into biological fluids. EV cargo can modulate physiological and pathological processes in recipient cells through near- and long-distance intercellular communication. Recent studies have shown that origin, amount, and internal cargos (nucleic acids, proteins, and lipids) of EVs are variable under different pathological conditions, including cardiovascular diseases (CVD). The early detection and management of CVD reduce premature morbidity and mortality. Circulating EVs have attracted great interest as a potential biomarker for diagnostics and follow-up of CVD. This review highlights the role of circulating EVs as biomarkers for diagnosis, prognosis, and therapeutic follow-up of CVD, and also for drug delivery. Despite the great potential of EVs as a tool to study the pathophysiology of CVD, further studies are needed to increase the spectrum of EV-associated applications.

Importance of extracellular vesicles in hypertension

Hypertension affects approximately 1.13 billion adults worldwide and is the leading global risk factor for cardiovascular, cerebrovascular, and kidney diseases. There is emerging evidence that extracellular vesicles participate in the development and progression of hypertension. Extracellular vesicles are membrane-enclosed structures released from nearly all types of eukaryotic cells. During their formation, extracellular vesicles incorporate various parent cell components, including proteins, lipids, and nucleic acids that can be transferred to recipient cells. Extracellular vesicles mediate cell-to-cell communication in a variety of physiological and pathophysiological processes. Therefore, studying the role of circulating and urinary extracellular vesicles in hypertension has the potential to identify novel noninvasive biomarkers and therapeutic targets of different hypertension phenotypes. This review discusses the classification and biogenesis of three EV subcategories (exosomes, microvesicles, and apoptotic bodies) and provides a summary of recent discoveries in the potential impact of extracellular vesicles on hypertension with a specific focus on their role in the blood pressure regulation by organs-artery and kidney, as well as renin-angiotensin-system.

Diagnostic roles of urinary kidney microvesicles in diabetic nephropathy

Background

The pathology of diabetic nephropathy (DN) broadly involves the injury of glomeruli, tubulointerstitium and endothelium. Cells from these compartments can release increased numbers of microvesicles (MVs) into urine when stressed or damaged. Currently whether urinary MVs from these three parts can help diagnose DN and reflect pathological features remain unclear.

Methods

Forty-nine patients with histologically proven DN and 29 proteinuric controls with membranous nephropathy or minimal change disease were enrolled. Urinary podocyte, proximal tubular and endothelial cell-derived MVs were quantified by flow cytometry. Renal glomerular, tubulointerstitial and vascular lesions were semi-quantitatively scored and their relevance to urinary MVs were analyzed.

Results

DN patients had greater numbers of urinary MVs from podocytes, proximal tubular and endothelial cells compared with proteinuric controls. The combination of podocyte nephrin+ MVs and diabetic retinopathy optimally diagnose DN with 89.7% specificity and 88.9% sensitivity. Moreover, positive correlations were observed between urinary levels of proximal tubular MVs and the severity of tubular injury and between urinary levels of endothelial MVs and the degree of vascular injury. Using urinary proximal tubular MVs as the indicators for tubular injury, the differences between DN patients and proteinuric controls diminished after matching the degree of renal vascular injury or when proteinuria >8 g/24 h.

Conclusions

Urinary kidney-specific cell-derived MVs might serve as noninvasive biomarkers for the diagnosis of DN in diabetic proteinuric patients. Their elevated levels could reflect corresponding renal pathological lesions, helping physicians look into the heterogeneity of DN.

Podocyte-Released Migrasomes in Urine Serve as an Indicator for Early Podocyte Injury

Background

Levels of urinary microvesicles, which are increased during various kidney injuries, have diagnostic potential for renal diseases. However, the significance of urinary microvesicles as a renal disease indicator is dampened by the difficulty to ascertain their cell source.

Objectives

The aim of this study was to demonstrate that podocytes can release migrasomes, a unique class of microvesicle with size ranging between 400 and 2,000 nm, and the urine level of migrasomes may serve as novel non-invasive biomarker for early podocyte injury.

Method

In this study, immunofluorescence labeling, electronic microscopy, nanosite, and sequential centrifugation were used to purify and analyze migrasomes.

Results

Migrasomes released by podocytes differ from exosomes as they have different content and mechanism of release. Compared to podocytes, renal tubular cells secrete markedly less migrasomes. Moreover, secretion of migrasomes by human or murine podocytes was strongly augmented during podocyte injuries induced by LPS, puromycin amino nucleoside (PAN), or a high concentration of glucose (HG). LPS, PAN, or HG-induced podocyte migrasome release, however, was blocked by Rac-1 inhibitor. Strikingly, a higher level of podocyte migrasomes in urine was detected in mice with PAN-nephropathy than in control mice. In fact, increased urinary migrasome number was detected earlier than elevated proteinuria during PAN-nephropathy, suggesting that urinary migrasomes are a more sensitive podocyte injury indicator than proteinuria. Increased urinary migrasome number was also detected in diabetic nephropathy patients with proteinuria level <5.5 g/day.

Conclusions

Our findings reveal that podocytes release the "injury-related" migrasomes during migration and provide urinary podocyte migrasome as a potential diagnostic marker for early podocyte injury.

Exosomes in Nephropathies: A Rich Source of Novel Biomarkers

The biomarkers commonly utilized in diagnostic evaluations of kidney disease suffer from low sensitivity, especially in the early stages of renal damage. On the other hand, obtaining a renal biopsy to augment clinical decision making can lead to potentially serious complications. In order to overcome the shortcomings of currently available diagnostic tools, recent studies suggest that exosomes, cell-secreted extracellular vesicles containing a large array of active molecules to facilitate cell-to-cell communication, may represent a rich source of novel disease biomarkers. Because of their endocytic origin, exosomes carry markers typical for their parent cells, which could permit the localization of biochemical cellular alterations in specific kidney compartments. Different types of exosomes can be isolated from noninvasively obtained biofluids; however, in the context of kidney disease, evidence has emerged on the role of urinary exosomes in the diagnostic and predictive modeling of renal pathology. The current review summarizes the potential application of exosomes in the detection of acute and chronic inflammatory, metabolic, degenerative, and genetic renal diseases.

Increased cellular senescence in the murine and human stenotic kidney: Effect of mesenchymal stem cells

Cell stress may give rise to insuperable growth arrest, which is defined as cellular senescence. Stenotic kidney (STK) ischemia and injury induced by renal artery stenosis (RAS) may be associated with cellular senescence. Mesenchymal stem cells (MSCs) decrease some forms of STK injury, but their ability to reverse senescence in RAS remains unknown. We hypothesized that RAS evokes STK senescence, which would be ameliorated by MSCs. Mice were studied after 4 weeks of RAS, RAS treated with adipose tissue-derived MSCs 2 weeks earlier, or sham. STK senescence-associated β-galactosidase (SA-β-Gal) activity was measured. Protein and gene expression was used to assess senescence and the senescence-associated secretory phenotype (SASP), and staining for renal fibrosis, inflammation, and capillary density. In addition, senescence was assessed as p16+ and p21+ urinary exosomes in patients with renovascular hypertension (RVH) without or 3 months after autologous adipose tissue-derived MSC delivery, and in healthy volunteers (HV). In RAS mice, STK SA-β-Gal activity increased, and senescence and SASP marker expression was markedly elevated. MSCs improved renal function, fibrosis, inflammation, and capillary density, and attenuated SA-β-Gal activity, but most senescence and SASP levels remained unchanged. Congruently, in human RVH, p21+ urinary exosomes were elevated compared to HV, and only slightly improved by MSC, whereas p16+ exosomes remained unchanged. Therefore, RAS triggers renal senescence in both mice and human subjects. MSCs decrease renal injury, but only partly mitigate renal senescence. These observations support exploration of targeted senolytic therapy in RAS.

Distinct Functional Requirements for Podocalyxin in Immature and Mature Podocytes Reveal Mechanisms of Human Kidney Disease

Dominant and recessive mutations in podocalyxin (PODXL) are associated with human kidney disease. Interestingly, some PODXL mutations manifest as anuria while others are associated with proteinuric kidney disease. PODXL heterozygosity is associated with adult-onset kidney disease and podocalyxin shedding into the urine is a common biomarker of a variety nephrotic syndromes. It is unknown, however, how various lesions in PODXL contribute to these disparate disease pathologies. Here we generated two mouse stains: one that deletes Podxl in developmentally mature podocytes (Podxl^∆Pod) and a second that is heterozygous for podocalyxin in all tissues (Podxl^+/-). We used histologic and ultrastructural analyses, as well as clinical chemistry assays to evaluate kidney development and function in these strains. In contrast to null knockout mice (Podxl^-/-), which die shortly after birth from anuria and hypertension, Podxl^∆Pod mice develop an acute congenital nephrotic syndrome characterized by focal segmental glomerulosclerosis (FSGS) and proteinuria. Podxl^+/- mice, in contrast, have a normal lifespan, and fail to develop kidney disease under normal conditions. Intriguingly, although wild-type C57Bl/6 mice are resistant to puromycin aminonucleoside (PA)-induced nephrosis (PAN), Podxl^+/- mice are highly sensitive and PA induces severe proteinuria and collapsing FSGS. In summary, we find that the developmental timepoint at which podocalyxin is ablated (immature vs. mature podocytes) has a profound effect on the urinary phenotype due to its critical roles in both the formation and the maintenance of podocyte ultrastructure. In addition, Podxl^∆Pod and Podxl^+/- mice offer powerful new mouse models to evaluate early biomarkers of proteinuric kidney disease and to test novel therapeutics.

microRNA in Extracellular Vesicles Released by Damaged Podocytes Promote Apoptosis of Renal Tubular Epithelial Cells

Tubular injury and fibrosis are associated with progressive kidney dysfunction in advanced glomerular disease. Glomerulotubular crosstalk is thought to contribute to tubular injury. microRNAs (miRNAs) in extracellular vesicles (EVs) can modulate distant cells. We hypothesized that miRNAs in EVs derived from injured podocytes lead to tubular epithelial cell damage. As proof of this concept, tubular epithelial (HK2) cells were cultured with exosomes from puromycin-treated or healthy human podocytes, and damage was assessed. Sequencing analysis revealed the miRNA repertoire of podocyte EVs. RNA sequencing identified 63 upregulated miRNAs in EVs from puromycin-treated podocytes. Among them, five miRNAs (miR-149, -424, -542, -582, and -874) were selected as candidates for inducing tubular apoptosis according to a literature-based search. To validate the effect of the miRNAs, HK2 cells were treated with miRNA mimics. EVs from injured podocytes induced apoptosis and p38 phosphorylation of HK2 cells. The miRNA-424 and 149 mimics led to apoptosis of HK2 cells. These results show that miRNAs in EVs from injured podocytes lead to damage to tubular epithelial cells, which may contribute to the development of tubular injury in glomerular disease.

Urinary Extracellular Vesicles as Biomarkers of Kidney Disease: From Diagnostics to Therapeutics

Cell-derived extracellular vesicles (EVs) can be isolated from various body fluids, including urine. Urinary EVs have gained important recognition as potential diagnostic biomarkers in renal disease since their cargo includes nucleic acids, proteins, and other cellular components, which likely mirror the physiological and possibly pathophysiological state of cells along the nephron. Accumulating evidence highlights the feasibility of using EVs as biomarkers for diagnostic, prognostic, and therapeutic purposes in several forms of renal disease, such as acute kidney injury, glomerulonephritis, and renal transplantation. Additionally, exogenous delivery of EVs released in vitro by cells in culture may have salutary benefits for renal diseases. In this review, we introduce recent studies that attempt to identify urinary EVs as candidate biomarkers for human kidney diseases and consider their potential implication as a therapeutic option in key kidney diseases.

Extracellular Vesicles as Signaling Mediators and Disease Biomarkers across Biological Barriers

Extracellular vesicles act as shuttle vectors or signal transducers that can deliver specific biological information and have progressively emerged as key regulators of organized communities of cells within multicellular organisms in health and disease. Here, we survey the evolutionary origin, general characteristics, and biological significance of extracellular vesicles as mediators of intercellular signaling, discuss the various subtypes of extracellular vesicles thus far described and the principal methodological approaches to their study, and review the role of extracellular vesicles in tumorigenesis, immunity, non-synaptic neural communication, vascular-neural communication through the blood-brain barrier, renal pathophysiology, and embryo-fetal/maternal communication through the placenta.

Acute and chronic glomerular damage is associated with reduced CD133 expression in urinary extracellular vesicles

Extracellular vesicles released into urine (uEVs) can represent interesting biomarkers of renal cell damage. CD133, a stem/progenitor cell marker expressed by renal progenitor cells, is highly expressed in uEVs of healthy individuals. In the present study, we evaluated the level of CD133 in the uEVs of patients with acute and chronic glomerular damage by cytofluorimetric analysis. The level of CD133⁺ uEVs was significantly decreased in pediatric patients with acute glomerulonephritis during the acute phase of renal damage, while it was restored after the subsequent recovery. A similar decrease was also observed in patients with chronic glomerulonephritis. Moreover, CD133⁺ uEVs significantly declined in patients with type 2 diabetes, used as validation group, with the lowest levels in patients with albuminuria with diabetic nephropathy. Indeed, receiver-operating characteristic curve analysis indicates the ability of CD133⁺ uEV values to discriminate the health condition from that of glomerular disease. In parallel, a significant decrease of CD133 in renal progenitor cells and in their derived EVs was observed in vitro after cell treatment with a combination of glucose and albumin overload, mimicking the diabetic condition. These data indicate that the level of CD133⁺ uEVs may represent an easily accessible marker of renal normal physiology and could provide information on the "reservoir" of regenerating cells within tubules.

Using Imaging Flow Cytometry to Characterize Extracellular Vesicles Isolated from Cell Culture Media, Plasma or Urine

The ability to non-invasively detect specific damage to the kidney has been limited. Identification of extracellular vesicles released by cells, especially when under duress, might allow for monitoring and identification of specific cell types within the kidney that are stressed. We have adapted a previously published traditional flow cytometry method for use with an imaging flow cytometer (Amnis FlowSight) for identifying EV released by specific cell types and excreted into the urine or blood using markers characteristic of particular cells in the kidney. Here we present a protocol utilizing the Amnis FlowSight Imaging Flow Cytometer to identify and quantify EV from the urine of patients with essential hypertension and renovascular disease. Notably, EV isolated from cell culture media and plasma can also be analyzed similarly.

Role of Podocyte Injury in Glomerulosclerosis

Finding new therapeutic targets of glomerulosclerosis treatment is an ongoing quest. Due to a living environment of various stresses and pathological stimuli, podocytes are prone to injuries; moreover, as a cell without proliferative potential, loss of podocytes is vital in the pathogenesis of glomerulosclerosis. Thus, sufficient understanding of factors and underlying mechanisms of podocyte injury facilitates the advancement of treating and prevention of glomerulosclerosis. The clinical symptom of podocyte injury is proteinuria, sometimes with loss of kidney functions progressing to glomerulosclerosis. Injury-induced changes in podocyte physiology and function are actually not a simple passive process, but a complex interaction of proteins that comprise the anatomical structure of podocytes at molecular levels. This chapter lists several aspects of podocyte injuries along with potential mechanisms, including glucose and lipid metabolism disorder, hypertension, RAS activation, micro-inflammation, immune disorder, and other factors. These aspects are not technically separated items, but intertwined with each other in the pathogenesis of podocyte injuries.

Urinary levels of podocyte-derived microparticles are associated with the progression of chronic kidney disease

Background

Podocyte-derived microparticles (MPs) could be secreted from activated or apoptotic podocytes. An increased number of podocyte-derived MPs in the urine might reflect podocyte injury in renal diseases. This study aimed to observe the change of urinary podocyte-derived MP levels in patients with chronic kidney disease (CKD) and to further explore its correlation with the progression of CKD.

Methods

A prospective, longitudinal study was conducted in eighty patients with biopsy-proven CKD. Podocyte-derived MPs (annexin V and podocalyxin positive) were detected by flow cytometry. The number of urinary podocyte-derived MPs was analyzed to evaluate the association with biochemical measurements and pathological glomerulosclerosis assessment. Patients with idiopathic membranous nephropathy (IMN) were followed up after the six-month treatment of prednisone combined with tacrolimus to evaluate the association of urinary podocyte-derived MP levels and the remission of IMN.

Results

The CKD patients had higher urinary podocyte-derived MP levels compared with healthy controls (HCs). Baseline urinary levels of podocyte-derived MPs were positively correlated with 24-hour proteinuria, while were inversely correlated with the percentage of global glomerulosclerosis. The urinary podocyte-derived MPs levels had good discrimination for glomerulosclerosis [area under curve (AUC), 0.66]. The urinary podocyte-derived MPs levels in IMN patients were significantly decreased accompanied with the recovery of abnormal clinical parameters after six-month treatment.

Conclusions

The urinary levels of podocyte-derived MPs were closely associated with podocyte injury and glomerulosclerosis, which could be useful for monitoring disease activity in CKD patients. Urinary podocyte-derived MPs might be a non-invasive biomarker for the evaluation of early CKD progression.

Urinary podocyte microparticles are associated with disease activity and renal injury in systemic lupus erythematosus

Background

New non-invasive biomarkers are demanded to identify renal damage in various autoimmune-associated kidney diseases. Glomerular podocyte damage mediated by systemic lupus erythematosus (SLE) plays an important role in the pathogenesis and progression of lupus nephritis (LN). This study evaluated whether the podocyte-derived microparticles (MPs) were novel biomarkers of clinical and histological features in SLE patients with LN.

Methods

A cross-sectional study, including 34 SLE patients and 16 healthy controls, was designed. Urinary annexin V⁺ podocalyxin⁺ MPs of all participants were quantified by flow cytometry. The correlation of podocyte-derived MPs with clinical and histological parameters of SLE patients was analysed.

Results

The number of annexin V⁺ podocalyxin⁺ MPs from urine samples were markly increased in patients with SLE. Furthermore, the level of urinary podocyte-derived MPs was positively correlated with the SLE Disease Activity Index (SLEDAI) score, anti-dsDNA antibody titre, erythrocyte sedimentation rate, and proteinuria. Conversely, it was negatively correlated with the level of complement C3 and serum albumin. The number of urinary podocyte-derived MPs was significantly increased in SLE patients with high activity indices. Receiver operating characteristic (ROC) curves were calculated to assess the power for podocyte-derived MP levels in differentiating between SLE patients with and without LN. Podocyte-derived MP levels were able to differentiate between SLE patients with mild disease activity, as well as those with moderate and above disease activity. SLE patients showed increased podocyte-derived MP excretion into the urine.

Conclusions

These findings suggest that the change in urinary podocyte-derived MP levels could be useful for evaluating and monitoring SLE disease activity.

Extracellular vesicles as a novel diagnostic and research tool for patients with HTN and kidney disease

Hypertension (HTN) affects one in three adults in the United States and is a major risk factor for cardiovascular disease and kidney failure. There is emerging evidence that more intense blood pressure lowering reduces mortality in patients with kidney disease who are at risk of cardiovascular disease and progression to end-stage renal disease. However, the ideal blood pressure threshold for patients with kidney disease remains a question of debate. Novel tools to more precisely diagnose HTN, tailor treatment, and predict the risk of end-organ damage such as kidney disease are needed. Analysis of circulating and urinary extracellular vesicles (EVs) and their cargo (protein and RNA) has the potential to identify novel noninvasive biomarkers that can also reflect a specific pathological mechanism of different HTN phenotypes. We will discuss the use of extracellular vesicles as markers of HTN severity and explain their profile change with antihypertensive medicine and potential to detect early end-organ damage. However, more studies with enhanced rigor in this field are needed to define the blood pressure threshold to prevent or delay kidney disease progression and decrease cardiovascular risk.

Senescent Kidney Cells in Hypertensive Patients Release Urinary Extracellular Vesicles

Background Hypertension may be associated with renal cellular injury. Cells in distress release extracellular vesicles (EVs), and their numbers in urine may reflect renal injury. Cellular senescence, an irreversible growth arrest in response to a noxious milieu, is characterized by release of proinflammatory cytokines. We hypothesized that EVs released by senescent nephron cells can be identified in urine of patients with hypertension. Methods and Results We recruited patients with essential hypertension (EH) or renovascular hypertension and healthy volunteers (n=14 each). Renal oxygenation was assessed using magnetic resonance imaging and blood samples collected from both renal veins for cytokine-level measurements. EVs isolated from urine samples were characterized by imaging flow cytometry based on specific markers, including p16 (senescence marker), calyxin (podocytes), urate transporter 1 (proximal tubules), uromodulin (ascending limb of Henle's loop), and prominin-2 (distal tubules). Overall percentage of urinary p16+ EVs was elevated in EH and renovascular hypertension patients compared with healthy volunteers and correlated inversely with renal function and directly with renal vein cytokine levels. Urinary levels of p16+/urate transporter 1+ were elevated in all hypertensive subjects compared with healthy volunteers, whereas p16+/prominin-2+ levels were elevated only in EH versus healthy volunteers and p16+/uromodulin+ in renovascular hypertension versus EH. Conclusions Levels of p16+ EVs are elevated in urine of hypertensive patients and may reflect increased proximal tubular cellular senescence. In EH, EVs originate also from distal tubules and in renovascular hypertension from Henle's loop. Hence, urinary EVs levels may be useful to identify intrarenal sites of cellular senescence.

Loss of Renal Peritubular Capillaries in Hypertensive Patients Is Detectable by Urinary Endothelial Microparticle Levels

Hypertension, an important cause of chronic kidney disease, is characterized by peritubular capillary (PTC) loss. Circulating levels of endothelial microparticles (EMPs) reflect systemic endothelial injury. We hypothesized that systemic and urinary PTC-EMPs levels would reflect renal microvascular injury in hypertensive patients. We prospectively measured by flow cytometry renal vein, inferior vena cava, and urinary levels of EMPs in essential (n=14) and renovascular (RVH; n=24) hypertensive patients and compared them with peripheral blood and urinary levels in healthy volunteers (n=14). PTC-EMPs were identified as urinary exosomes positive for the PTC marker plasmalemmal-vesicle-associated protein. In 7 RVH patients, PTC and fibrosis were also quantified in renal biopsy, and in 18 RVH patients, PTC-EMPs were measured again 3 months after continued medical therapy with or without stenting (n=9 each). Renal vein and systemic PTC-EMPs levels were not different among the groups, whereas their urinary levels were elevated in both RVH and essential hypertension versus healthy volunteers (56.8%±12.7% and 62.8%±10.7% versus 34.0%±17.8%; both P≤0.001). Urinary PTC-EMPs levels correlated directly with blood pressure and inversely with estimated glomerular filtration rate. Furthermore, in RVH, urinary PTC-EMPs levels correlated directly with stenotic kidney hypoxia, histological PTC count, and fibrosis and inversely with cortical perfusion. Three months after treatment, the change in urinary PTC-EMPs levels correlated inversely with a change in renal function ( r=-0.582; P=0.011). Therefore, urinary PTC-EMPs levels are increased in hypertensive patients and may reflect renal microcirculation injury, whereas systemic PTC-EMPs levels are unchanged. Urinary PTC-EMPs may be useful as novel biomarkers of intrarenal capillary loss.

Early podocyte injury and elevated levels of urinary podocyte-derived extracellular vesicles in swine with metabolic syndrome: role of podocyte mitochondria

Metabolic syndrome (MetS) is associated with nutrient surplus and kidney hyperfiltration, accelerating chronic renal failure. The potential involvement of podocyte damage in early MetS remains unclear. Mitochondrial dysfunction is an important determinant of renal damage, but whether it contributes to MetS-related podocyte injury remains unknown. Domestic pigs were studied after 16 wk of diet-induced MetS, MetS treated with the mitochondria-targeted peptide elamipretide (ELAM; 0.1 mg·kg^-1·day^-1 sc) for the last month of diet, and lean controls (n = 6 pigs/group). Glomerular filtration rate (GFR) and renal blood flow (RBF) were measured using multidetector computed tomography, and podocyte and mitochondrial injury were measured by light and electron microscopy. Urinary levels of podocyte-derived extracellular vesicles (pEVs; nephrin positive/podocalyxin positive) were characterized by flow cytometry. Body weight, blood pressure, RBF, and GFR were elevated in MetS. Glomerular size and glomerular injury score were also elevated in MetS and decreased after ELAM treatment. Evidence of podocyte injury, impaired podocyte mitochondria, and foot process width were all increased in MetS but restored with ELAM. The urinary concentration of pEVs was elevated in MetS pigs and directly correlated with renal dysfunction, glomerular injury, and fibrosis and inversely correlated with glomerular nephrin expression. Additionally, pEV numbers were elevated in the urine of obese compared with lean human patients. Early MetS induces podocyte injury and mitochondrial damage, which can be blunted by mitoprotection. Urinary pEVs reflecting podocyte injury might represent early markers of MetS-related kidney disease and a novel therapeutic target.

Extracellular vesicles in renal physiology and clinical applications for renal disease

Many cells in the nephron release extracellular vesicles (EVs). EVs envelop nucleic acids, proteins, and lipids. The surfaces of EVs express donor cell-specific markers, ligands, and major histocompatibility complex molecules. They are involved in cell-to-cell communication, immune modulation, and the removal of unwanted materials from cells. EVs have been studied as biomarkers of specific diseases and have potential therapeutic applications. Recent research has emphasized the functions of EVs in the kidney. This review provides an overview of recent findings related to the roles of EVs in the nephron, and their utility as biomarkers and therapeutic factors in renal disease.

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.

Therapeutic application of extracellular vesicles in kidney disease: promises and challenges

Extracellular vesicles (EVs) are nanosized, membrane‐bound vesicles released from different cells. Recent studies have revealed that EVs may participate in renal tissue damage and regeneration through mediating inter‐nephron communication. Thus, the potential use of EVs as therapeutic vector has gained considerable interest. In this review, we will discuss the basic characteristics of EVs and its role in nephron cellular communication. Then, the application of EVs as therapeutic vector based on its natural content or as carriers of drug, in acute and chronic kidney injury, was discussed. Finally, perspectives and challenges of EVs in therapy of kidney disease were described.

The Emerging Roles of Microparticles in Diabetic Nephropathy

Microparticles (MPs) are a type of extracellular vesicles (EVs) shed from the outward budding of plasma membranes during cell apoptosis and/or activation. These microsized particles then release specific contents (e.g., lipids, proteins, microRNAs) which are active participants in a wide range of both physiological and pathological processes at the molecular level, e.g., coagulation and angiogenesis, inflammation, immune responses. Research limitations, such as confusing nomenclature and overlapping classification, have impeded our comprehension of these tiny molecules. Diabetic nephropathy (DN) is currently the greatest contributor to end-stage renal diseases (ESRD) worldwide, and its public health impact will continue to grow due to the persistent increase in the prevalence of diabetes mellitus (DM). MPs have recently been considered as potentially involved in DN onset and progression, and this review juxtaposes some of the research updates about the possible mechanisms from several relevant aspects and insights into the therapeutic perspectives of MPs in clinical management and pharmacological treatment of DN patients.

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.