Hypoxia Induces Renal Epithelial Injury and Activates Fibrotic Signaling Through Up-Regulation of Arginase-II

The ureohydrolase, type-II arginase (Arg-II), is a mitochondrial enzyme metabolizing L-arginine into urea and L-ornithine and is highly expressed in renal proximal tubular cells (PTC) and upregulated by renal ischemia. Recent studies reported contradictory results on the role of Arg-II in renal injury. The aim of our study is to investigate the function of Arg-II in renal epithelial cell damage under hypoxic conditions. Human renal epithelial cell line HK2 was cultured under hypoxic conditions for 12–48 h. Moreover, ex vivo experiments with isolated kidneys from wild-type (WT) and genetic Arg-II deficient mice (Arg-II–/–) were conducted under normoxic and hypoxic conditions. The results show that hypoxia upregulates Arg-II expression in HK2 cells, which is inhibited by silencing both hypoxia-inducible factors (HIFs) HIF1α and HIF2α. Treatment of the cells with dimethyloxaloylglycine (DMOG) to stabilize HIFα also enhances Arg-II. Interestingly, hypoxia or DMOG upregulates transforming growth factor β1 (TGFβ1) levels and collagens Iα1, which is prevented by Arg-II silencing, while TGFβ1-induced collagen Iα1 expression is not affected by Arg-II silencing. Inhibition of mitochondrial complex-I by rotenone abolishes hypoxia-induced reactive oxygen species (mtROS) and TGFβ1 elevation in the cells. Ex vivo experiments show elevated Arg-II and TGFβ1 expression and the injury marker NGAL in the WT mouse kidneys under hypoxic conditions, which is prevented in the Arg-II–/– mice. Taking together, the results demonstrate that hypoxia activates renal epithelial HIFs-Arg-II-mtROS-TGFβ1-cascade, participating in hypoxia-associated renal injury and fibrosis.

Metabolic and Lipidomic Assessment of Kidney Cells Exposed to Nephrotoxic Vancomycin Dosages

Vancomycin is a glycopeptide antibiotic used against multi-drug resistant gram-positive bacteria such as Staphylococcus aureus (MRSA). Although invaluable against resistant bacteria, vancomycin harbors adverse drug reactions including cytopenia, ototoxicity, as well as nephrotoxicity. Since nephrotoxicity is a rarely occurring side effect, its mechanism is incompletely understood. Only recently, the actual clinically relevant concentration the in kidneys of patients receiving vancomycin was investigated and were found to exceed plasma concentrations by far. We applied these clinically relevant vancomycin concentrations to murine and canine renal epithelial cell lines and assessed metabolic and lipidomic alterations by untargeted and targeted gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry analyses. Despite marked differences in the lipidome, both cell lines increased anabolic glucose reactions, resulting in higher sorbitol and lactate levels. To the best of our knowledge, this is the first endometabolic profiling of kidney cells exposed to clinically relevant vancomycin concentrations. The presented study will provide a valuable dataset to nephrotoxicity researchers and might add to unveiling the nephrotoxic mechanism of vancomycin.

In Vitro Cell Culture Models of Hyperoxaluric States: Calcium Oxalate and Renal Epithelial Cell Interactions

Urolithiasis is a multifactorial disease with a high incidence and high recurrence rate, characterized by formation of solid deposits in the urinary tract. The most common type of these stones are calcium oxalate stones. Calcium oxalate crystals can, in hyperoxaluric states, interact with renal epithelial cells, causing injury to the renal epithelia. Pathogenesis of urolithiasis is widely investigated, but underlying mechanisms are still not completely clarified. In vitro models offer insight into molecular processes which lead to renal stone formation and are significant for evaluation of prophylactic and therapeutic management of patients with urolithiasis. In this review, we summarize recently published data from in vitro studies investigating interactions of calcium oxalate crystals with renal epithelial cell lines, anti-urolithiatic mechanisms, and the results from studies exploring possible therapeutic and prophylactic options for calcium oxalate urolithiasis in cell cultures.

A bacterial "shield and sword": A previously uncharacterized two-component system protects uropathogenic Escherichia coli from host-derived oxidative insults and promotes hemolysin-mediated host cell pyroptosis

Uropathogenic Escherichia coli (UPEC) deploys an array of virulence factors to successfully establish urinary tract infections. Coordinated expression of these various virulence factors is critical for UPEC's overall fitness in the host. Two-component signaling systems (TCSs) are a major mechanism by which bacteria sense environmental cues and initiate adaptive responses. Here, we report a previously uncharacterized TCS encoded on a pathogenicity island in UPEC that directly activates the expression of a putative methionine sulfoxide reductase system (C3566/C3567) and a pore-forming hemolysin in response to host-derived hydrogen peroxide (H2O2) exposure. The TCS increases UPEC resistance to H2O2 in vitro and survival in macrophages in tissue culture via C3566/C3567. Additionally, the TCS mediates hemolysin-induced renal epithelial cell and macrophage death via a pyroptosis pathway. Taken together, our data suggest a paradigm in which this signal transduction system coordinates both bacterial pathogen defensive and offensive traits in the presence of host-derived signals.

Non-Coding RNAs in Hereditary Kidney Disorders

Single-gene defects have been revealed to be the etiologies of many kidney diseases with the recent advances in molecular genetics. Autosomal dominant polycystic kidney disease (ADPKD), as one of the most common inherited kidney diseases, is caused by mutations of PKD1 or PKD2 gene. Due to the complexity of pathophysiology of cyst formation and progression, limited therapeutic options are available. The roles of noncoding RNAs in development and disease have gained widespread attention in recent years. In particular, microRNAs in promoting PKD progression have been highlighted. The dysregulated microRNAs modulate cyst growth through suppressing the expression of PKD genes and regulating cystic renal epithelial cell proliferation, mitochondrial metabolism, apoptosis and autophagy. The antagonists of microRNAs have emerged as potential therapeutic drugs for the treatment of ADPKD. In addition, studies have also focused on microRNAs as potential biomarkers for ADPKD and other common hereditary kidney diseases, including HNF1β-associated kidney disease, Alport syndrome, congenital abnormalities of the kidney and urinary tract (CAKUT), von Hippel–Lindau (VHL) disease, and Fabry disease. This review assembles the current understanding of the non-coding RNAs, including microRNAs and long noncoding RNAs, in polycystic kidney disease and these common monogenic kidney diseases.

Long non-coding RNA GAS5 aggravate renal epithelial cell apoptosis in cisplatin-induced AKI by regulating miR-205-5p

Introduction: The present study focuses on the interaction between long non-coding RNA GAS5 and microRNA-205-5p and their roles in cisplatin-induced acute kidney injury. Methods: Human kidney tubular cells (HK-2) were used to simulate acute renal injury induced by cisplatin with the consequent fluctuating expression levels of GAS5 and MIR-205-5p being determined respectively. Furthermore, the modulating effects of miR-205-5p and GAS5 in cisplatin-induced apoptosis of renal tubular epithelial cells and the possible binding sites between them were evaluated. Results: The results depicted that the expression of GAS5 was significantly up-regulated after AKI induced by cisplatin, while inhibiting the increase of expression would alleviate the apoptotic-promoting effect of cisplatin on renal tubular epithelial cells. MIR-205-5p is negatively regulated by GAS5, thus down-regulation of GAS5 will consequently elevate the expression of miR-205-5p and further alleviate the damage of HK-2 cells induced by cisplatin. Conclusions: In conclusion, in cisplatin-induced AKI, the expression of GAS5 was increased and consequently inhibited that of miR-205-5p by direct binding, which eventually aggravate the renal tubular epithelial injury, indicating their potential of being important diagnostic markers and therapeutic targets in the treatment of cisplatin-induced AKI.

Long Noncoding RNA PRNCR1 Reduces Renal Epithelial Cell Apoptosis in Cisplatin-Induced AKI by Regulating miR-182-5p/EZH1

<b><i>Background/Aims:</i></b> This study was designed to examine the role of long noncoding RNA PRNCR1 in cisplatin-induced acute kidney injury (AKI) in vitro and in vivo. <b><i>Methods:</i></b> The expression levels of PRNCR1 and miR-182-5p in cisplatin-induced AKI mice were examined. HK-2 cells were treated with cisplatin to induce cell damage. Then, the effects of PRNCR1 and miR-182-5p on cisplatin-stimulated HK-2 cell viability and apoptosis were detected by the CCK-8 and annexin V-FITC/PI method. Target genes of PRNCR1 and miR-182-5p were analyzed by bioinformatics analysis and luciferase. <b><i>Results:</i></b> The expression level of PRNCR1 was significantly reduced in cisplatin-induced AKI mice. In addition, overexpression of PRNCR1 attenuated the damage of cisplatin to HK-2. The expression level of miR-182-5p was significantly raised in cisplatin-induced AKI mice. MiR-182-5p was negatively regulated by PRNCR1 and leaded to an upregulation of EZH1 expression. Overexpression of PRNCR1 attenuated cisplatin-induced apoptosis by downregulating the miR-182-5p/EZH1 axis. <b><i>Conclusion:</i></b> LncPRNCR1 reduced the apoptosis of renal epithelial cells induced by cisplatin by modulating miR-182-5p/EZH1.

Negative regulators of TGF-β1 signaling in renal fibrosis; pathological mechanisms and novel therapeutic opportunities

Elevated expression of the multifunctional cytokine transforming growth factor β1 (TGF-β1) is causatively linked to kidney fibrosis progression initiated by diabetic, hypertensive, obstructive, ischemic and toxin-induced injury. Therapeutically relevant approaches to directly target the TGF-β1 pathway (e.g., neutralizing antibodies against TGF-β1), however, remain elusive in humans. TGF-β1 signaling is subjected to extensive negative control at the level of TGF-β1 receptor, SMAD2/3 activation, complex assembly and promoter engagement due to its critical role in tissue homeostasis and numerous pathologies. Progressive kidney injury is accompanied by the deregulation (loss or gain of expression) of several negative regulators of the TGF-β1 signaling cascade by mechanisms involving protein and mRNA stability or epigenetic silencing, further amplifying TGF-β1/SMAD3 signaling and fibrosis. Expression of bone morphogenetic proteins 6 and 7 (BMP6/7), SMAD7, Sloan–Kettering Institute proto-oncogene (Ski) and Ski-related novel gene (SnoN), phosphate tensin homolog on chromosome 10 (PTEN), protein phosphatase magnesium/manganese dependent 1A (PPM1A) and Klotho are dramatically decreased in various nephropathies in animals and humans albeit with different kinetics while the expression of Smurf1/2 E3 ligases are increased. Such deregulations frequently initiate maladaptive renal repair including renal epithelial cell dedifferentiation and growth arrest, fibrotic factor (connective tissue growth factor (CTGF/CCN2), plasminogen activator inhibitor type-1 (PAI-1), TGF-β1) synthesis/secretion, fibroproliferative responses and inflammation. This review addresses how loss of these negative regulators of TGF-β1 pathway exacerbates renal lesion formation and discusses the therapeutic value in restoring the expression of these molecules in ameliorating fibrosis, thus, presenting novel approaches to suppress TGF-β1 hyperactivation during chronic kidney disease (CKD) progression.