Urinary extracellular vesicular release of aquaporins in patients with renal transplantation

Urinary extracellular vesicles in childhood kidney diseases

Most biological fluids contain extracellular vesicles (EVs). EVs are surrounded by a lipid bilayer and contain biological macromolecules such as proteins, lipids, RNA, and DNA. They lack a functioning nucleus and are incapable of replicating. The physiological characteristics and molecular composition of EVs in body fluids provide valuable information about the status of originating cells. Consequently, they could be effectively utilized for diagnostic and prognostic applications. Urine contains a heterogeneous population of EVs. To date, these urinary extracellular vesicles (uEVs) have been ignored in the standard urinalysis. In recent years, knowledge has accumulated on how uEVs should be separated and analyzed. It has become clear how uEVs reflect the expression of each molecule in cells in nephron segments and how they are altered in disease states such as glomerular/tubular disorders, rare congenital diseases, acute kidney injury (AKI), and chronic kidney disease (CKD). Significant promise exists for the molecular expression signature of uEVs detected by simple techniques such as enzyme-linked immunosorbent assay (ELISA), making them more applicable in clinical settings. This review presents the current understanding regarding uEVs, emphasizing the potential for non-invasive diagnostics, especially for childhood kidney diseases.

Diurnal rhythm of urinary aquaporin-2 in children with primary monosymptomatic nocturnal enuresis

Background/aim

Nocturnal enuresis can be frustrating for children and their families as the child ages. Our aim is to evaluate urine aquaporin 2 (AQP-2) as a noninvasive biomarker of water balance in children with primary monosymptomatic nocturnal enuresis (PMNE).

Material and methods

The study included 90 children; sixty-eight children suffering from PMNE aged (9.57 ± 2.16) years and 22 healthy children with good toilet control, matched sex and age. All enuretic children were subjected to complete history taking, clinical evaluation, and bed wetting diary. Serum arginine vasopressin (AVP) and urine AQP-2 were tested in the morning (at 9-11 am) and evening (at 9-11 pm). Blood urea, creatinine, Na, glucose, urine osmolality, Ca/Cr, Alb/Cr and specific gravity were tested simultaneously.

Results

Serum AVP, urine AQP-2, and urine osmolality were statistically lower in patients than controls. Patients had a significantly lower level of night serum AVP concentrations, urine AQP-2, and urine osmolality than the corresponding morning level. Urine AQP-2 was significantly correlated with urine osmolality (p < 0.05). AQP-2 had a sensitivity of 90% and a specificity of 70%. However, no statistically significant correlation was found between serum AVP and urine AQP-2.

Conclusion

Primary monosymptomatic nocturnal enuresis in children could be associated with reduction of urine excretion of AQP-2 at night. Urine AQP-2 is significantly correlated with urine osmolality. Therefore, it may be a noninvasive biomarker of hydration status in children with PMNE, with good sensitivity and specificity.

Update on current and potential application of extracellular vesicles in kidney transplantation

Kidney transplantation (KT) is the best treatment for end-stage kidney disease. However, early diagnosis of graft injury remains challenging, mainly because of the lack of accurate and noninvasive diagnostic techniques. Improving graft outcomes is equally demanding, as is the development of innovative therapies. Many research efforts are focusing on extracellular vesicles, cellular particles free in each body fluid that have shown promising results as precise markers of damage and potential therapeutic targets in many diseases, including the renal field. In fact, through their receptors and cargo, they act in damage response and immune modulation. In transplantation, they may be used to determine organ quality and aging, the presence of delayed graft function, rejection, and many other transplant-related pathologies. Moreover, their low immunogenicity and safe profile make them ideal for drug delivery and the development of therapies to improve KT outcomes. In this review, we summarize current evidence about extracellular vesicles in KT, starting with their characteristics and major laboratory techniques for isolation and characterization. Then, we discuss their use as potential markers of damage and as therapeutic targets, discussing their promising use in clinical practice as a form of liquid biopsy.

Extracellular Vesicles: The Future of Diagnosis in Solid Organ Transplantation?

Solid organ transplantation (SOT) is a life-saving treatment for end-stage organ failure, but it comes with several challenges, the most important of which is the existing gap between the need for transplants and organ availability. One of the main concerns in this regard is the lack of accurate non-invasive biomarkers to monitor the status of a transplanted organ. Extracellular vesicles (EVs) have recently emerged as a promising source of biomarkers for various diseases. In the context of SOT, EVs have been shown to be involved in the communication between donor and recipient cells and may carry valuable information about the function of an allograft. This has led to an increasing interest in exploring the use of EVs for the preoperative assessment of organs, early postoperative monitoring of graft function, or the diagnosis of rejection, infection, ischemia-reperfusion injury, or drug toxicity. In this review, we summarize recent evidence on the use of EVs as biomarkers for these conditions and discuss their applicability in the clinical setting.

Urinary Extracellular Vesicles in Chronic Kidney Disease: From Bench to Bedside?

Extracellular vesicles are a diverse group of particles that include exosomes, microvesicles, and apoptotic bodies and are defined by size, composition, site of origin, and density. They incorporate various bioactive molecules from their cell of origin during formation, such as soluble proteins, membrane receptors, nucleic acids (mRNAs and miRNAs), and lipids, which can then be transferred to target cells. Extracellular vesicles/exosomes have been extensively studied as a critical factor in pathophysiological processes of human diseases. Urinary extracellular vesicles could be a promising liquid biopsy for determining the pattern and/or severity of kidney histologic injury. The signature of urinary extracellular vesicles may pave the way for noninvasive methods to supplement existing testing methods for diagnosing kidney diseases. We discuss the potential role of urinary extracellular vesicles in various chronic kidney diseases in this review, highlighting open questions and discussing the potential for future research.

Extracellular Vesicles as Theranostic Tools in Kidney Disease

Extracellular vesicles are important vectors for cell-cell communication and show potential value for diagnosis and treatment of kidney diseases. The pathologic diagnosis of kidney diseases relies on kidney biopsy, whereas collection of extracellular vesicles from urine or circulating blood may constitute a less invasive diagnostic tool. In particular, urinary extracellular vesicles released mainly from resident kidney cells might provide an alternative tool for detection of kidney injury. Because extracellular vesicles mirror many features of their parent cells, cargoes of several populations of urinary extracellular vesicles are promising biomarkers for disease processes, like diabetic kidney disease, kidney transplant, and lupus nephritis. Contrarily, extracellular vesicles derived from reparative cells, such as mesenchymal stem cells, tubular epithelial progenitor cells, and human umbilical cord blood represent promising regenerative tools for treatment of kidney diseases. Furthermore, induced pluripotent stem cells-derived and engineered extracellular vesicles are being developed for specific applications for the kidney. Nevertheless, some assumptions regarding the specificity and immunogenicity of extracellular vesicles remain to be established. This review focuses on the utility of extracellular vesicles as therapeutic and diagnostic (theranostic) tools in kidney diseases and future directions for studies.

Extracellular vesicle-bound DNA in urine is indicative of kidney allograft injury

Extracellular vesicle‐bound DNA (evDNA) is an understudied extracellular vesicle (EV) cargo, particularly in cancer‐unrelated research. Although evDNA has been detected in urine, little is known about its characteristics, localization, and biomarker potential for kidney pathologies. To address this, we enriched EVs from urine of well‐characterized kidney transplant recipients undergoing allograft biopsy, characterized their evDNA and its association to allograft injury. The SEC‐based method enriched pure EVs from urine of kidney transplant recipients, regardless of the allograft injury. Urinary evDNA represented up to 29.2 ± 8% (mean ± SD) of cell‐free DNA (cfDNA) and correlated with cfDNA in several characteristics but was less fragmented (P < 0.001). Importantly, using DNase treatment and immunogold labelling TEM, we demonstrated that evDNA was bound to the surface of urinary EVs. Normalised evDNA yield (P = 0.042) and evDNA copy number (P = 0.027) significantly differed between patients with normal histology, rejection injury and non‐rejection injury, the later groups having significantly larger uEVs (mean diameter, P = 0.045) and more DNA bound per uEV. ddDNA is detectable in uEV samples of kidney allograft recipients, but its quantity is highly variable. In a proof‐of‐principle study, several evDNA characteristics correlated with clinical and histological parameters (P = 0.040), supporting that the potential of evDNA as a biomarker for kidney allograft injury should be further investigated.

Urinary extracellular vesicles and tubular transport

Tubular transport is a key function of the kidney to maintain electrolyte and acid-base homeostasis. Urinary extracellular vesicles (uEVs) harbor water, electrolyte, and acid-base transporters expressed at the apical plasma membrane of tubular epithelial cells. Within the uEV proteome, the correlations between kidney and uEV protein abundances are strongest for tubular transporters. Therefore, uEVs offer a non-invasive approach to probe tubular transport in health and disease. Here, we will review how kidney tubular physiology is reflected in uEVs and, conversely, how uEVs may modify tubular transport. Clinically, uEV tubular transporter profiling has been applied to rare diseases such as inherited tubulopathies, but also to more common conditions such as hypertension and kidney disease. Although uEVs hold the promise to advance the diagnosis of kidney disease to the molecular level, several biological and technical complexities still need to be addressed. The future will tell if uEV analysis will mainly be a powerful tool to study tubular physiology in humans or if it will move forward to become a diagnostic bedside test.

Extracellular vesicles in kidney transplantation: a state-of-the-art review

Kidney transplantation is the optimal treatment for patients with kidney failure; however, early detection and timely treatment of graft injury remain a challenge. Precise and noninvasive techniques of graft assessment and innovative therapeutics are required to improve kidney transplantation outcomes. Extracellular vesicles (EVs) are lipid bilayer-delimited particles with unique biosignatures and immunomodulatory potential, functioning as intermediaries of cell signalling. Promising evidence exists for the potential of EVs to develop precision diagnostics of graft dysfunction, and prognostic biomarkers for clinician decision making. The inherent targeting characteristics of EVs and their low immunogenic and toxicity profiles combined with their potential as vehicles for drug delivery make them ideal targets for development of therapeutics to improve kidney transplant outcomes. In this review, we summarize the current evidence for EVs in kidney transplantation, discuss common methodological principles of EV isolation and characterization, explore upcoming innovative approaches in EV research, and discuss challenges and opportunities to enable translation of research findings into clinical practice.

Urinary Extracellular Vesicles Are a Novel Tool to Monitor Allograft Function in Kidney Transplantation: A Systematic Review

Extracellular vesicles (EVs) are nanoparticles that transmit molecules from releasing cells to target cells. Recent studies link urinary EVs (uEV) to diverse processes such as infection and rejection after kidney transplantation. This, and the unmet need for biomarkers diagnosing kidney transplant dysfunction, has led to the current high level of interest in uEV. uEV provide non-intrusive access to local protein, DNA, and RNA analytics without invasive biopsy. To determine the added value of uEV measurements for detecting allograft dysfunction after kidney transplantation, we systematically included all related literature containing directly relevant information, with the addition of indirect evidence regarding urine or kidney injury without transplantation. According to their varying characteristics, uEV markers after transplantation could be categorized into kidney-specific, donor-specific, and immune response-related (IR-) markers. A few convincing studies have shown that kidney-specific markers (PODXL, ion cotransporters, SYT17, NGAL, and CD133) and IR-markers (CD3, multi-mRNA signatures, and viral miRNA) could diagnose rejection, BK virus-associated nephropathy, and calcineurin inhibitor nephrotoxicity after kidney transplantation. In addition, some indirect proof regarding donor-specific markers (donor-derived cell-free DNA) in urine has been demonstrated. Together, this literature review provides directions for exploring novel uEV markers' profiling complications after kidney transplantation.

Reduced urinary release of AQP1- and AQP2-bearing extracellular vesicles in patients with advanced chronic kidney disease

Although several studies have shown that release of water channel proteins, aquaporin 1 (AQP1) and AQP2 in urinary extracellular vesicles (uEV-AQP1 and -AQP2), were altered in experimental kidney injury models, their release in human chronic kidney disease (CKD) has been largely unexplored. The aim of the present study was to clarify whether the release of uEV-AQP1 and -AQP2 is altered in patients with CKD. Urine samples were collected from 15 healthy volunteers (normal group) and 62 CKD patients who were categorized into six glomerular filtration rate (GFR) categories (G1, G2, G3a, G3b, G4, and G5) in between 2005 and 2016 at Miyazaki Prefectural Miyazaki Hospital, Japan. uEV-proteins were evaluated by immunoblot analysis. The release of AQP1 and AQP2 were significantly decreased in patients with both CKD G4 and G5, in comparison with the normal group. The area under the receiver operating characteristic (ROC) curve (AUC) values for AQP1 and AQP2 in patients with CKD G4 and G5 were 0.926 and 0.881, respectively. On the other hand, the AUC values in patients with CKD G1-G3 were 0.512 for AQP1 and 0.680 for AQP2. Multiple logistic regression analysis showed that AQP1 and AQP2 in combination were useful for detecting CKD G4 and G5, with a higher AUC value of 0.945. These results suggest that the release of uEV-AQP1 and -AQP2 was decreased in patients with CKD G4 and G5, and these proteins might be helpful to detect advanced CKD.

The proteomic landscape of small urinary extracellular vesicles during kidney transplantation

Kidney transplantation is the preferred renal replacement therapy available. Yet, long-term transplant survival is unsatisfactory, partially due to insufficient possibilities of longitudinal monitoring and understanding of the biological processes after transplantation. Small urinary extracellular vesicles (suEVs) - as a non-invasive source of information - were collected from 22 living donors and recipients. Unbiased proteomic analysis revealed temporal patterns of suEV protein signature and cellular processes involved in both early response and longer-term graft adaptation. Complement activation was among the most dynamically regulated components. This unique atlas of the suEV proteome is provided through an online repository allowing dynamic interrogation by the user. Additionally, a correlative analysis identified putative prognostic markers of future allograft function. One of these markers - phosphoenol pyruvate carboxykinase (PCK2) - could be confirmed using targeted MS in an independent validation cohort of 22 additional patients. This study sheds light on the impact of kidney transplantation on urinary extracellular vesicle content and allows the first deduction of early molecular processes in transplant biology. Beyond that our data highlight the potential of suEVs as a source of biomarkers in this setting.

Decreased Excretion of Urinary Exosomal Aquaporin-2 in a Puromycin Aminonucleoside-Induced Nephrotic Syndrome Model

Urinary exosomes, small extracellular vesicles present in urine, are secreted from all types of renal epithelial cells. Aquaporin-2 (AQP2), a vasopressin-regulated water channel protein, is known to be selectively excreted into the urine through exosomes (UE-AQP2), and its renal expression is decreased in nephrotic syndrome. However, it is still unclear whether excretion of UE-AQP2 is altered in nephrotic syndrome. In this study, we examined the excretion of UE-AQP2 in an experimental rat model of nephrotic syndrome induced by the administration of puromycin aminonucleoside (PAN). Rats were assigned to two groups: a control group administered saline and a PAN group given a single intraperitoneal injection of PAN (125 mg/kg) at day 0. The experiment was continued for 8 days, and samples of urine, blood, and tissue were collected on days 2, 5, and 8. The blood and urine parameters revealed that PAN induced nephrotic syndrome on days 5 and 8, and decreases in the excretion of UE-AQP2 were detected on days 2 through 8 in the PAN group. Immunohistochemistry showed that the renal expression of AQP2 was decreased on days 5 and 8. The release of exosomal marker proteins into the urine through UEs was decreased on day 5 and increased on day 8. These data suggest that UE-AQP2 is decreased in PAN-induced nephrotic syndrome and that this reflects its renal expression in the marked proteinuria phase after PAN treatment.

Roles for Exosome in Various Kidney Diseases and Disorders

Exosome is a nanoscale vesicle with a size range of 30–100 nm. It is secreted from cell to extracellular space by exocytosis after fusion of multivesicular body (MVB) (formed by endocytic vesicles) with plasma membrane. Exosome plays several important roles in cellular homeostasis and intercellular communications. During the last two decades, exosome has acquired a wide attention to explore its additional roles in various aspects of cell biology and function in several organ systems. For the kidney, several lines of evidence have demonstrated 1that exosome is involved in the renal physiology and pathogenic mechanisms of various kidney diseases/disorders. This article summarizes roles of the exosome as the potential source of biomarkers, pathogenic molecules, and therapeutic biologics that have been extensively investigated in many kidney diseases/disorders, including lupus nephritis (LN), other glomerular diseases, acute kidney injury (AKI), diabetic nephropathy (DN), as well as in the process of renal fibrosis and chronic kidney disease (CKD) progression, in addition to polycystic kidney disease (PKD), kidney transplantation, and renal cell carcinoma (RCC). Moreover, the most recent evidence has shown its emerging role in kidney stone disease (or nephrolithiasis), involving inflammasome activation and inflammatory cascade frequently found in kidney stone pathogenesis.