Early alteration of urinary exosomal aquaporin 1 and transforming growth factor β1 after release of unilateral pelviureteral junction obstruction

Emerging roles for AQP in mammalian extracellular vesicles

Recent research in the aquaporin (AQP) field has identified a role for diverse AQPs in extracellular vesicles (EV). Though still in its infancy, there is a growing body of knowledge in the area; AQPs in EV have been suggested as biomarkers for disease, as drug targets and show potential as therapeutics. To advance further in this field, AQPs in EV must be better understood. Here we summarize current knowledge of the presence and function of AQPs in EV and hypothesise their roles in health and disease.

iTRAQ-based proteomics and in vitro experiments reveals essential roles of ACE and AP-N in the renin-angiotensin system-mediated congenital ureteropelvic junction obstruction

OBJECTIVE

Ureteropelvic junction obstruction (UPJO) is a common renal obstructive disorder, but its pathogenic mechanisms remain largely unclear. We aimed to investigate the potential involvement of the renin-angiotensin system in congenital UPJO pathogenesis.

METHODS

Differentially expressed proteins in exosomes isolated from amniotic fluid of patients with congenital UPJO were characterized using iTRAQ (isobaric tags for relative and absolute quantification)-based proteomics. The expressions of angiotensin-converting enzyme (ACE) and aminopeptidase N (AP-N) in HK2 cells were inhibited by quinapril and siRNA, respectively. Cell proliferation and reactive oxygen species were measured by EdU staining and flow cytometry, respectively. Gene expression was detected by Western blot or qRT-PCR. The inflammatory factors were measured through ELISA. Mice that underwent unilateral ureteral obstruction were used as the animal model.

RESULTS

The identity of exosomes from amniotic fluids was confirmed by the expression of CD9 and CD26. In total, 633 differentially expressed proteins were identified in the amniotic fluid-derived exosomes from patients with UPJO, including 376 up- and 257 down-regulated proteins associated with multiple biological processes. Of them, ACE and AP-N were significantly decreased in the amniotic fluid exosomes. Inhibition of ACE and AP-N resulted in suppressed cell proliferation; repressed IARP, AT1R, and MAS1 expression; elevated ROS production; and increased IL-1β, TNF-α, and IL-6 levels in HK2 cells. Decreased ACE expression and elevated IL-1β levels were also observed in the mouse model.

CONCLUSION

Suppression of ACE and AP-N expression mediates congenital UPJO pathogenesis by repressing renal tubular epithelial proliferation, promoting ROS production, and enhancing inflammatory factor expression.

Melatonin therapy protects against renal injury before and after release of bilateral ureteral obstruction in rats

AIM

Blockage of the urinary tract is often connected with renal function impediment, including reductions in glomerular filtration rate (GFR) and the power to control sodium as well as water elimination through urination. Melatonin, known to be the primary product of the pineal gland, prevents renal damage caused by ischemic reperfusion. However, the effects of melatonin on urinary obstruction, as well as release of obstruction induced kidney injury are still largely unknown. The aim of present study was to investigate the effect of melatonin on mediating protection against renal injury triggered from either bilateral ureteral obstruction (BUO) or BUO release (BUO-R).

MAIN METHODS

Adult male Sprague-Dawley rats (n = 60) were clustered into six treatment groups: sham treated-1; BUO-non-treated (24 h BUO only); BUO + melatonin; sham treated-2; BUO-48hR (24 h of BUO and then release for 2 days); and BUO-48hR + melatonin. Kidney tissues, blood and urine samples were obtained for further assessment.

KEY FINDINGS

It was found that melatonin treatment remarkably promoted the recovery of the handling capacity of urinary excretion of water as well as sodium in BUO and BUO-48hR models. Melatonin treatment partially inhibited inflammatory cytokine expression and the downregulation of aquaporin (AQPs, AQP-1, -2 and -3) expression in these two models. Moreover, the cytoarchitecture of BUO rats exposed to melatonin was well preserved.

SIGNIFICANCE

Melatonin treatment potently prevents BUO or BUO-R induced renal injury, which may be partially attributed to restoring the expression of AQPs and inhibition of inflammatory response, as well as preserving renal ultrastructural integrity.

The Expanding Role of Vesicles Containing Aquaporins

In animals and plants, membrane vesicles containing proteins have been defined as key for biological systems involving different processes such as trafficking or intercellular communication. Docking and fusion of vesicles to the plasma membrane occur in living cells in response to different stimuli, such as environmental changes or hormones, and therefore play an important role in cell homeostasis as vehicles for certain proteins or other substances. Because aquaporins enhance the water permeability of membranes, their role as proteins immersed in vesicles formed of natural membranes is a recent topic of study. They regulate numerous physiological processes and could hence serve new biotechnological purposes. Thus, in this review, we have explored the physiological implications of the trafficking of aquaporins, the mechanisms that control their transit, and the proteins that coregulate the migration. In addition, the importance of exosomes containing aquaporins in the cell-to-cell communication processes in animals and plants have been analyzed, together with their potential uses in biomedicine or biotechnology. The properties of aquaporins make them suitable for use as biomarkers of different aquaporin-related diseases when they are included in exosomes. Finally, the fact that these proteins could be immersed in biomimetic membranes opens future perspectives for new biotechnological applications.

Risk factors for postobstructive diuresis in pediatric patients with ureteropelvic junction obstruction, following open pyeloplasty in three high complexity institutions

INTRODUCTION

Postobstructive diuresis (POD) is a polyuric state in which large quantities of salt and water are eliminated after solving a urinary tract obstruction. These patients are at increased risk of severe dehydration, electrolytic disturbances, hypovolemic shock, and death. Ureteropelvic junction obstruction (UPJO) is the most common etiology of collecting system dilatation in the fetal kidney, and a significant number of patients require pyeloplasty. There are limited data regarding prognostic risk factors for POD in this scenario.

OBJECTIVE

To describe possible clinical risk factors for POD in the pediatric population after open pyeloplasty.

STUDY DESIGN

This was a retrospective case series study of consecutive patients diagnosed with UPJO at three high complexity centers, managed with open pyeloplasty from 2006 to 2016. Multiple qualitative and quantitative variables possibly associated with POD were included according to the literature review. They were statistically analyzed with STATA 14 software.

RESULTS

A total of 88 patients with UPJO following open pyeloplasty were analyzed. Twenty-seven patients (30%) had POD. A tendency to present POD in younger patients was found, with a mean age of 20.2 months vs. 72.3 months. There was also an increased risk of POD in patients with previous diagnosis of tubular acidosis.

CONCLUSIONS

There are no data about prognostic clinical risk factors for POD after open pyeloplasty in the pediatric population. Our study corresponds to one of the larger series reported so far. It suggests that younger patients and patients with a previous diagnosis of tubular acidosis could be at greater risk of POD. Consequently, prospective studies are required for validation of our results, and possible impact on patient follow-up.

Urine Exosomes: An Emerging Trove of Biomarkers

Exosomes are released by most cells and can be isolated from all biofluids including urine. Exosomes are small vesicles formed as part of the endosomal pathway that contain cellular material surrounded by a lipid bilayer that can be traced to the plasma membrane. Exosomes are potentially a more targeted source of material for biomarker discovery than unfractionated urine, and provide diagnostic and pathophysiological information without an invasive tissue biopsy. Cytoplasmic contents including protein, mRNA, miRNA, and lipids have all been studied within the exosomal fraction. Many prospective urinary exosomal biomarkers have been successfully identified for a variety of kidney or genitourinary tract conditions; detection of systemic conditions may also be possible. Isolation and analysis of exosomes can be achieved by several approaches, although many require specialized equipment or involve lengthy protocols. The need for timely analysis in the clinical setting has driven considerable innovation with several promising options recently emerging. Consensus on exosome isolation, characterization, and normalization procedures would resolve critical clinical translational bottlenecks for existing candidate exosomal biomarkers and provide a template for additional discovery studies.

Aquaporins in Urinary Extracellular Vesicles (Exosomes)

Since the successful characterization of urinary extracellular vesicles (uEVs) by Knepper’s group in 2004, these vesicles have been a focus of intense basic and translational research worldwide, with the aim of developing novel biomarkers and therapeutics for renal disease. Along with these studies, there is growing evidence that aquaporins (AQPs), water channel proteins, in uEVs have the potential to be diagnostically useful. In this review, we highlight current knowledge of AQPs in uEVs from their discovery to clinical application.

Exosomes in urine biomarker discovery

Nanovesicles present in urine the so-called urinary exosomes have been found to be secreted by every epithelial cell type lining the urinary tract system in human. Urinary exosomes are an appealing source for biomarker discovery as they contain molecular constituents of their cell of origin, including proteins and genetic materials, and they can be isolated in a non-invasive manner. Following the discovery of urinary exosomes in 2004, many studies have been performed using urinary exosomes as a starting material to identify biomarkers in various renal, urogenital, and systemic diseases. Here, we describe the discovery of urinary exosomes and address the issues on the collection, isolation, and normalization of urinary exosomes as well as delineate the systems biology approach to biomarker discovery using urinary exosomes.