Expression and function of the Delta-1/Notch-2/Hes-1 pathway during experimental acute kidney injury

Notch3 as a novel therapeutic target for the treatment of ADPKD by regulating cell proliferation and renal cyst development

Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenic kidney disease. Emerging research indicates that the Notch signaling pathway plays an indispensable role in the pathogenesis of numerous kidney diseases, including ADPKD. Herein, we identified that Notch3 but not other Notch receptors was overexpressed in renal tissues from mice with ADPKD and ADPKD patients. Inhibiting Notch3 with γ-secretase inhibitors, which block a proteolytic cleavage required for Notch3 activation, or shRNA knockdown of Notch3 significantly delayed renal cyst growth in vitro and in vivo. Subsequent mechanistic study elucidated that the cleaved intracellular domain of Notch3 (N3ICD) and Hes1 could bind to the PTEN promoter, leading to transcriptional inhibition of PTEN. This further activated the downstream PI3K-AKT-mTOR pathway and promoted renal epithelial cell proliferation. Overall, Notch3 was identified as a novel contributor to renal epithelial cell proliferation and cystogenesis in ADPKD. We envision that Notch3 represents a promising target for ADPKD treatment.

NOTCH2 gene mutation and gamma-secretase inhibitor in mediating the malignancy of ovarian cancer

The carcinogenic mechanisms by which serous ovarian cancer (OC) occurs remain to be explored. Currently, we have conducted whole-exome sequencing (WES) and targeted deep sequencing to validate new molecular markers, including NOTCH2, that impede the progression of cell malignancy in ovarian cancer (OC). Following NOTCH2 P2113S mutation and NOTCH signaling pathway inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) treatment, the cell proliferation, migration, and invasion of A2780 and SKOV3 OC cells were examined in vitro. WES identified the P2113S point mutation in NOTCH2. The NOTCH2 mutation rate was 26.67 % among the 75 OC cases. The NOTCH2 P2113S mutation and DAPT treatment downregulated Notch-2 protein levels in the two OC cells. Functionally, interfering with NOTCH2 expression promoted the migrative, proliferative, and invasive capacities of OC cells. Western blotting further confirmed that NOTCH2-mediated tumorigenesis lies in reducing apoptosis through dysregulation of Bax/Bcl2, affecting repair of DNA damage through reducing DNA-PK and blocking the transcription factor Hes1 along with increasing immune regulator p65. Furthermore, the NOTCH2-mediated tumorigenesis was mostly reversed after NF-κB inhibitor Bay11-7082 treatment. These findings identified the NOTCH2 P2113S mutation in ovarian carcinogenesis, and NOTCH2 P2113S is a potential target in treating OC.

Liraglutide ameliorates gentamicin-induced acute kidney injury in rats via PGC-1α- mediated mitochondrial biogenesis: Involvement of PKA/CREB and Notch/Hes-1 signaling pathways

Acute kidney injury (AKI) is a challenging side effect which may clinically impede the use of gentamicin (GM). The present study explored the impact of liraglutide (Lir) on GM-induced kidney injury in rats. Lir (0.2 and 0.4 mg/kg, s.c) was given for 10 days (a dose/day) starting 3 days before giving GM (100 mg/kg, i.p) once daily for 7 days. Interestingly, Lir notably ameliorated GM-induced elevated levels of renal injury markers; urea and creatinine. Moreover, Lir remarkably mitigated malondialdehyde (MDA) level and elevated glutathione (GSH) level as well as superoxide dismutase (SOD) activity. Also, Lir pre-treatment notably diminished inflammatory markers levels; interleukin-1β (IL-1β), tumor necrosis factor alpha (TNF-α), vascular cell adhesion molecule (VCAM), monocyte chemoattractant protein 1 (MCP-1) and interferon gamma (INF-γ). In addition, Lir significantly replenished expression of Peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α), Protein kinase A (PKA), cAMP response element-binding protein (CREB), nuclear Nuclear factor erythroid 2-related factor 2 (Nrf2), heme Oxygenase-1 (HO-1), B-cell lymphoma 2 (Bcl-2), and remarkably attenuated expression of Notch homolog 1 (Notch1), Hairy and enhancer of split-1 (Hes-1), Bcl-2-associated X (Bax), cleaved caspase 3 and nuclear Nuclear factor Kappa B (NF-κB (p65)). The nephroprotective activity of Lir was further confirmed by histopathological examination as well as transmission electron microscopy (TEM). In conclusion Lir achieved its nephroprotective effects through the amelioration of oxidative stress, inflammatory and apoptotic manifestations. It is worth-mentioning that the current study is the first to focus on the involvement of mitochondrial biogenesis and its upstream regulators, PKA/CREB and Notch/Hes-1 signaling pathways in the nephroprotective potentials of Lir. The attenuation of the aforementioned injurious aspects is partially attributed to the improvement of the mitochondrial status as demonstrated by elevated PGC-1α expression via acceleration of PKA/CREB and abatement of Notch/Hes-1 signaling pathways.

NEPHROPROTECTIVE EFFECT OF GAMMA-SECRETASE INHIBITOR ON SEPSIS- INDUCED RENAL INJURY IN MOUSE MODEL OF CLP

OBJECTIVE

The aim: This study was set out to assess the potential protective impact of MK0752 (a gamma secretase inhibitor) on sepsis-induced renal injury through modulation of inflammatory and oxidative stress pathways.

PATIENTS AND METHODS

Materials and methods: Twenty-four Swiss-albino mice aged between eight and twelve week and weighted twenty to thirty-seven grams were randomly allocated into four groups (n=6 in each group). Sham group (laparotomy without cecal ligation and puncture (CLP), sepsis group (laparotomy with CLP), vehicle-treated group (equivalent volume of DMSO before the CLP), MK0752 treated group (5 mg/kg) single daily dose for three days before the CLP. Blood samples were used to assess the serum levels of urea and creatinine. The kidneys were used to assess tissue levels of the TNF-α, IL-10, IL-6, TNFR1, VEGF, notch1, jagged1 and tissue damage by histopathological analysis.

RESULTS

Results: The current study shows that pretreatment with MK0752 ameliorates the renal damage by significantly reducing the proinflammatory cytokines and notch1 signaling.

CONCLUSION

Conclusions: Taken together, these results suggest that MK0752 could be protective against the renal injury induced by sepsis through its ameliorative impact on renal architecture and modulating cytokines and Notch1 singling pathway. Further studies regarding the role of Notch signaling pathways would be worthwhile.

Gut microbial sodium butyrate alleviates renal ischemia-reperfusion injury by regulating HES1/PPARα

This study investigated the effect of gut microbial sodium butyrate (NaB) on renal ischemia-reperfusion injury (IRI) and its mechanism using a rat model of renal IRI and a HK-2 cell model of hypoxia-reoxygenation (HR) injury. The activity of malondialdehyde, superoxide dismutase, glutathione peroxidase, and catalase in kidney tissues and HK-2 cells was detected. ELISA was performed to measure the concentrations of TNF-α, IL-1β, and IL-6 in serum and cell culture supernatant. TUNEL staining and flow cytometry were used to assess apoptosis in kidney tissues and HK-2 cells, respectively. UCSC and JASPAR predicted the binding sites between HES1 and PPARα promoter, followed by experimental verification of the binding. NaB pretreatment inhibited oxidative stress, inflammation, and apoptosis following renal IRI in vivo and in vitro. NaB suppressed the expression of HES1 and promoted that of PPARα. Overexpression of HES1 or knockdown of PPARα in HR-treated HK-2 cells inhibited the protective effects of NaB. HES1 repressed the expression of PPARα by binding PPARα promoter. In conclusion, NaB may alleviate renal IRI by promoting the transcription of PPARα via downregulation of HES1.

Nephrotoxicity of perfluorooctane sulfonate (PFOS)-effect on transcription and epigenetic factors

Perfluorooctane sulfonate (PFOS) is a widespread persistent environmental pollutant implicated in nephrotoxicity with altered metabolism, carcinogenesis, and fibrosis potential. We studied the underlying epigenetic mechanism involving transcription factors of PFOS-induced kidney injury. A 14-day orally dosed mouse model was chosen to study acute influences in vivo. Messenger RNA expression analysis and gene set enrichment analysis were performed to elucidate the relationship between epigenetic regulators, transcription factors, kidney disease, and metabolism homeostasis. PFOS was found to accumulate in mouse kidney in a dose-dependent manner. Kidney injury markers Acta2 and Bcl2l1 increased in expression significantly. Transcription factors, including Nef2l2, Hes1, Ppara, and Ppard, were upregulated, while Smarca2 and Pparg were downregulated. Furthermore, global DNA methylation levels decreased and the gene expression of histone demethylases Kdm1a and Kdm4c were upregulated. Our work implicates PFOS-induced gene expression alterations in epigenetics, transcription factors, and kidney biomarkers with potential implications for kidney fibrosis and kidney carcinogenesis. Future experiments can focus on epigenetic mechanisms to establish a panel of PFOS-induced biomarkers for nephrotoxicity evaluation.

Knockout of Zeb2 ameliorates progression of renal tubulointerstitial fibrosis in a mouse model of renal ischemia-reperfusion injury

BACKGROUND

Zeb2, a zinc finger E-box-binding homeobox transcription factor, regulates transforming growth factor (TGF)-β signaling pathway. However, its role in the pathogenesis of acute kidney injury (AKI) and AKI to chronic kidney disease (CKD) transition is unclear.

METHODS

We evaluated Zeb2 function in a bilateral renal ischemia-reperfusion injury (IRI)-induced AKI model using proximal tubule-specific Zeb2 conditional knockout (Zeb2-cKO) and wild-type (WT) mice, and in renal biopsy samples.

RESULTS

In Zeb2-cKO mice, the levels of plasma creatinine and blood urea nitrogen post-IRI were significantly lower than that in WT mice. Immunohistological analysis revealed mild tubular injury, reduced neutrophil infiltration, less fibrotic changes, and reduced expression of fibrotic proteins (collagen type IV, α-smooth muscle actin [α-SMA], fibronectin, and connective tissue growth factor [CTGF]), at 3-14 days post-IRI. Zeb2 expression was upregulated in proximal tubular cells post-IRI in WT mice. Zeb2 siRNA transfection reduced TGF-β stimulated mRNA and protein expression of collagen type IV, α-SMA, fibronectin, and CTGF in cultured renal tubular cells. Patients with AKI to CKD transition exhibited high Zeb2 expression in renal tubules, as revealed by renal biopsy. Hypoxia and CoCl2-treatment upregulated Zeb2 promoter activity and mRNA and protein expression in cultured renal tubular epithelial cells, suggesting a regulatory role for hypoxia.

CONCLUSIONS

Zeb2 was upregulated in renal tissues in both mice and humans with AKI. Zeb2 regulates fibrotic pathways in the pathogenesis of AKI and AKI to CKD transition. Therefore, inhibition of Zeb2 could be a potential therapeutic strategy for AKI.

Gypenoside XLIX protects against acute kidney injury by suppressing IGFBP7/IGF1R-mediated programmed cell death and inflammation

BACKGROUND

Acute kidney injury (AKI), characterised by excessive inflammatory cell recruitment and programmed cell death, has a high morbidity and mortality; however, effective and specific therapies for AKI are still lacking.

OBJECTIVE

This study aimed to evaluate the renoprotective effects of gypenoside XLIX (Gyp XLIX) in AKI.

METHODS

The protective effects of Gyp XLIX were tested in two AKI mouse models established using male C57BL/6 mice (aged 6-8 weeks) by a single intraperitoneal injection of cisplatin (20 mg/kg) or renal ischemia-reperfusion for 40 min. Gyp XLIX was administered intraperitoneally before cisplatin administration or renal ischemia-reperfusion. Renal function, tubular injury, renal inflammation and programmed cell death were evaluated. In addition, the renoprotective effects of Gyp XLIX were also evaluated in cisplatin- or hypoxia-treated tubular epithelial cells. The mechanisms underlying these effects were then explored using RNA sequencing.

RESULTS

In vivo, Gyp XLIX substantially suppressed the increase in serum creatinine and blood urea nitrogen levels. Moreover, tubular damage was alleviated by Gyp XLIX as shown by periodic acid-Schiff staining, electron microscopy and molecular analysis of KIM-1. Consistently, we found that Gyp XLIX suppressed renal necroptosis though the RIPK1/RIPK3/MLKL pathway. The anti-inflammatory and antinecroptotic effects were further confirmed in vitro. Mechanistically, RNA sequencing showed that Gyp XLIX markedly suppressed the levels of IGF binding protein 7 (IGFBP7). Co-immunoprecipitation and western blot analysis further showed that Gyp XLIX reduced the binding of IGFBP7 to IGF1 receptor (IGF1R). Additionally, picropodophyllin, an inhibitor of IGF1R, abrogated the therapeutic effects of Gyp XLIX on cisplatin-induced renal cell injury; this finding indicated that Gyp XLIX may function by activating IGF1R-mediated downstream signalling Additionally, we also detected the metabolic distribution of Gyp XLIX after injection; Gyp XLIX had a high concentration in the kidney and exhibited a long retention time. These findings may shed light on the application of Gyp XLIX for AKI treatment clinically.

CONCLUSION

Gyp XLIX may serve as a potential therapeutic agent for AKI treatment via IGFBP7/ IGF1R-dependent mechanisms.

[Involvement of Notch1 and ALK4/5 Signaling Pathways in Renal Tubular Cell Death: Their Application to Clarification of Cadmium Toxicity]

Renal tubular cell death is caused by various extracellular stresses including toxic amounts of cadmium, an occupational and environmental pollutant metal, and is responsible for renal dysfunction. While cadmium exposure disrupts many intracellular signaling pathways, the molecular mechanism underlying cadmium-induced renal tubular cell death has not yet been fully elucidated. We have recently identified two important intracellular signaling pathways that promote cadmium-induced renal tubular cell death: the Notch1 signaling and activin receptor-like kinase (ALK) 4/5 signaling (also known as the activin-transforming growth factor β receptor pathways). In this review paper, we introduce our previous experimental findings, focusing on Notch1 and ALK4/5 signaling pathways, which may uncover the molecular mechanisms involved in cadmium-induced renal tubular cell death.

Microglia exosomal miRNA-137 attenuates ischemic brain injury through targeting Notch1

Microglia are the resident immune cells in the central nervous system and play an essential role in brain homeostasis and neuroprotection in brain diseases. Exosomes are crucial in intercellular communication by transporting bioactive miRNAs. Thus, this study aimed to investigate the function of microglial exosome in the presence of ischemic injury and related mechanism. Oxygen-glucose deprivation (OGD)-treated neurons and transient middle cerebral artery occlusion (TMCAO)-treated mice were applied in this study. Western blotting, RT-PCR, RNA-seq, luciferase reporter assay, transmission electron microscope, nanoparticle tracking analysis, immunohistochemistry, TUNEL and LDH assays, and behavioral assay were applied in mechanistic and functional studies. The results demonstrated that exosomes derived from microglia in M2 phenotype (BV2-Exo) were internalized by neurons and attenuated neuronal apoptosis in response to ischemic injury in vitro and in vivo. BV2-Exo also decreased infarct volume and behavioral deficits in ischemic mice. Exosomal miRNA-137 was upregulated in BV2-Exo and participated in the partial neuroprotective effect of BV2-Exo. Furthermore, Notch1 was a directly targeting gene of exosomal miRNA-137. In conclusion, these results suggest that BV2-Exo alleviates ischemia-reperfusion brain injury through transporting exosomal miRNA-137. This study provides novel insight into microglial exosomes-based therapies for the treatment of ischemic brain injury.

Molecular Mechanisms of Renal Progenitor Regulation: How Many Pieces in the Puzzle?

Kidneys of mice, rats and humans possess progenitors that maintain daily homeostasis and take part in endogenous regenerative processes following injury, owing to their capacity to proliferate and differentiate. In the glomerular and tubular compartments of the nephron, consistent studies demonstrated that well-characterized, distinct populations of progenitor cells, localized in the parietal epithelium of Bowman capsule and scattered in the proximal and distal tubules, could generate segment-specific cells in physiological conditions and following tissue injury. However, defective or abnormal regenerative responses of these progenitors can contribute to pathologic conditions. The molecular characteristics of renal progenitors have been extensively studied, revealing that numerous classical and evolutionarily conserved pathways, such as Notch or Wnt/β-catenin, play a major role in cell regulation. Others, such as retinoic acid, renin-angiotensin-aldosterone system, TLR2 (Toll-like receptor 2) and leptin, are also important in this process. In this review, we summarize the plethora of molecular mechanisms directing renal progenitor responses during homeostasis and following kidney injury. Finally, we will explore how single-cell RNA sequencing could bring the characterization of renal progenitors to the next level, while knowing their molecular signature is gaining relevance in the clinic.

Analysis of Differentially Expressed Long Noncoding RNA in Renal Ischemia-Reperfusion Injury

BACKGROUND

Renal ischemia-reperfusion (IR) injury is one of the major causes of acute renal failure which seriously endangers the health and life of patients. Currently, there is still lack of comprehensive knowledge of the molecular mechanism of renal IR injury, and the regulatory role of long noncoding RNA (lncRNA) in renal IR damage remains poorly understood.

AIM

The aim of this study was to analyze the expression spectrum of lncRNA in renal IR damage in mice and to explore specific lncRNA that may be involved in regulating the development of human renal IR injury.

METHODS

RNA-Seq was used to investigate the lncRNA profile of renal IR injury in a mouse model, and conservation analysis was performed on mouse lncRNAs with differential expression (fragments per kilobase of transcript per million mapped reads ≥2) by BLASTN. The potential functions and associated pathways of the differentially expressed lncRNA were explored by bioinformatics analysis. The cell hypoxia model was used to detect the expression of the candidate lncRNA.

RESULTS

Of the 45,923 lncRNA transcripts detected in the samples, and 5,868 lncRNAs were found to be significantly differentially expressed (p < 0.05 and fold change ≥ 2) in 24-h IR kidney tissue compared to the expression in the control group. It was found that 56 differently expressed mouse lncRNA transcripts have human homology by analyzing the conserved sequences. We also found that lncRNA-NONHSAT183385.1 expression significantly increased in HK2 cells after 24 h of hypoxia and increased further 6 h after reoxygenation, and after 24 h of reoxygenation it was dramatically downregulated, indicating that NONHSAT183385.1 may be involved in the pathophysiological process of renal tubular epithelial cells in response to ischemia in human renal IR.

CONCLUSION

Our study revealed differentially expressed lncRNAs in renal IR damage in mice and identified a set of conserved lncRNAs, which would help to explore lncRNAs that may play important regulatory roles in human renal IR injury.

Successful Introduction of Human Renovascular Units into the Mammalian Kidney

BACKGROUND

Cell-based therapies aimed at replenishing renal parenchyma have been proposed as an approach for treating CKD. However, pathogenic mechanisms involved in CKD such as renal hypoxia result in loss of kidney function and limit engraftment and therapeutic effects of renal epithelial progenitors. Jointly administering vessel-forming cells (human mesenchymal stromal cells [MSCs] and endothelial colony-forming cells [ECFCs]) may potentially result in in vivo formation of vascular networks.

METHODS

We administered renal tubule-forming cells derived from human adult and fetal kidneys (previously shown to exert a functional effect in CKD mice) into mice, alongside MSCs and ECFCs. We then assessed whether this would result in generation of "renovascular units" comprising both vessels and tubules with potential interaction.

RESULTS

Directly injecting vessel-forming cells and renal tubule-forming cells into the subcutaneous and subrenal capsular space resulted in self-organization of donor-derived vascular networks that connected to host vasculature, alongside renal tubules comprising tubular epithelia of different nephron segments. Vessels derived from MSCs and ECFCs augmented in vivo tubulogenesis by the renal tubule-forming cells. In vitro coculture experiments showed that MSCs and ECFCs induced self-renewal and genes associated with mesenchymal-epithelial transition in renal tubule-forming cells, indicating paracrine effects. Notably, after renal injury, renal tubule-forming cells and vessel-forming cells infused into the renal artery did not penetrate the renal vascular network to generate vessels; only administering them into the kidney parenchyma resulted in similar generation of human renovascular units in vivo.

CONCLUSIONS

Combined cell therapy of vessel-forming cells and renal tubule-forming cells aimed at alleviating renal hypoxia and enhancing tubulogenesis holds promise as the basis for new renal regenerative therapies.

Renal ischemia/reperfusion injury: An insight on in vitro and in vivo models

Optimal tissue oxygenation is essential for its normal function. Suboptimal oxygenation or ischemia contributes to increased mortalities during various pathological conditions such as stroke, acute kidney injury (AKI), cardiac failure. Despite the rapid progression of renal tissue injury, the mechanism underlying renal ischemia/reperfusion injury (IRI) remains highly unclear. Experimental in vitro and in vivo models epitomizing the fundamental process is critical to the research of the pathogenesis of IRI and the development of plausible therapeutics. In this review, we describe the in vitro and in vivo models of IRI, ranges from proximal tubular cell lines to surgery-based animal models like clamping of both renal pedicles (bilateral IRI), clamping of one renal pedicle (unilateral IRI), clamping of one/or both renal arteries/or vein, or unilateral IRI with contralateral nephrectomy (uIRIx). Also, advanced technologies like three-dimensional kidney organoids, kidney-on-a-chip are explained. This review provides thoughtful information for establishing reliable and pertinent models for studying IRI-associated acute renal pathologies.

Smad3 promotes AKI sensitivity in diabetic mice via interaction with p53 and induction of NOX4-dependent ROS production

The incidence and severity of acute kidney injury (AKI) is increased yearly in diabetic patients. Although the mechanisms for this remain unclear, the prevention of AKI in diabetic nephropathy is feasible and of value. As we detected highly activation of TGF-β/Smad3 signaling in both human biopsy and mouse model of diabetic nephropathy, we hypothesized that Smad3 activation in diabetic kidneys may increase AKI sensitivity. We tested our hypothesis in vitro using TGF-β type II receptor (TGF-βRII) disrupted tubular epithelial cells (TECs) and in vivo in mice with streptozotocin (STZ)-induced diabetic nephropathy before the induction of ischemia/reperfusion (I/R) injury. We found that high glucose (HG)-cultured TECs showed increased inflammation, apoptosis and oxidative stress following hypoxia/reoxygenation (H/R) injury. Disruption of TGF-βRII attenuated cell injury induced by H/R in HG-treated TECs. Consistently, Smad3 knockdown in diabetic kidney attenuated I/R-induced AKI. Mechanistically, Smad3 binds to p53 and enhances p53 activity in cells treated with HG and H/R, which may lead to TECs apoptosis. Additionally, ChIP assay showed that Smad3 bound with the promoter region of NOX4 and induced ROS production and inflammation. In conclusion, our results demonstrate that Smad3 promotes AKI susceptibility in diabetic mice by interacting with p53 and NOX4.

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Smad3 activation in diabetic kidneys may increase AKI sensitivity.

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Blockade of Smad3 in diabetic kidney may both prevent AKI and CKD progression.

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Smad3 interacts with p53 to enhance TECs apoptosis.

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Smad3 binds with promoter region of NOX4 to induce ROS production and inflammation.

De-Glycyrrhizinated Licorice Extract Attenuates High Glucose-Stimulated Renal Tubular Epithelial-Mesenchymal Transition via Suppressing the Notch2 Signaling Pathway

Tubulointerstitial fibrosis is a major pathological hallmark of diabetic nephropathy. Increasing evidence has shown that epithelial-to-mesenchymal transition (EMT) of renal proximal tubular cells plays a crucial role in tubulointerstitial fibrosis. Herein, we aimed to elucidate the detailed mechanism of EMT in renal tubular cells under high glucose (HG) conditions, and to investigate the potential of licorice, a medicinal herb, to inhibit HG-induced EMT. Our results showed that renal tubular epithelial cells (normal rat kidney cell clone 52E; NRK-52E) exposed to HG resulted in EMT induction characterized by increased fibronectin and α-SMA (alpha-smooth muscle actin) but decreased E-cadherin. Elevated levels of cleaved Notch2, MAML-1 (mastermind-like transcriptional coactivator 1), nicastrin, Jagged-1 and Delta-like 1 were also concomitantly detected in HG-cultured cells. Importantly, pharmacological inhibition, small interfering RNA (siRNA)-mediated depletion or overexpression of the key components of Notch2 signaling in NRK-52E cells supported that the activated Notch2 pathway is essential for tubular EMT. Moreover, we found that licorice extract (LE) with or without glycyrrhizin, one of bioactive components in licorice, effectively blocked HG-triggered EMT in NRK-52E cells, mainly through suppressing the Notch2 pathway. Our findings therefore suggest that Notch2-mediated renal tubular EMT could be a therapeutic target in diabetic nephropathy, and both LE and de-glycyrrhizinated LE could have therapeutic potential to attenuate renal tubular EMT and fibrosis.

Notch Signaling in Kidney Development, Maintenance, and Disease

Kidney development involves formation of nephrons intricately aligned with the vasculature and connected to a branched network of collecting ducts. Notch signaling plays multiple roles during kidney development involving the formation of nephrons composed of diverse epithelial cell types arranged into tubular segments, all the while maintaining a nephron progenitor niche. Here, we review the roles of Notch signaling identified from rodent kidney development and injury studies, while discussing human kidney diseases associated with aberrant Notch signaling. We also review Notch signaling requirement in maintenance of mature kidney epithelial cell states and speculate that Notch activity regulation mediates certain renal physiologic adaptations.

Found in Translation: Reasons for Optimism in the Pursuit to Prevent Chronic Kidney Disease After Acute Kidney Injury

Purpose of review:

The current review will discuss on the progress of studying the transition phase between acute kidney injury (AKI) and chronic kidney disease (CKD) through improved animal models, common AKI and CKD pathways, and how human studies may inform different translational approaches.

Sources of information:

PubMed and Google Scholar.

Methods:

A narrative review was performed using the main terms “acute kidney injury,” “chronic kidney disease,” “end-stage renal disease,” “animal models,” “review,” “decision-making,” and “translational research.”

Key findings:

The last decade has shown much progress in the study of AKI, including evidence of a pathophysiological link between AKI and CKD. We are now in a phase of redesigning animal models and discovering mechanisms that can replicate the pathological conditions of the AKI-to-CKD continuum. Translating these findings into the clinic is a barrier that must be overcome. To this end, current efforts include prediction of AKI onset and maladaptive repair, detecting patients susceptible to the progression of chronic maladaptive repair, and understanding shared signaling mechanisms between AKI and CKD.

Limitations:

This is a narrative review of the literature that is partially influenced by the knowledge, perspectives, and experiences of the authors and their research background.

Implications:

Overall, this new knowledge from the AKI-to-CKD continuum will help bridge the discontinuity that exists between animal models and patients, resulting in more effective translational biomarkers and therapeutics to test in known AKI pathologies thereby preventing the chronicity of kidney injury progression.

Modulation of Renal Parenchyma in Response to Allogeneic Adipose-Derived Mesenchymal Stem Cells Transplantation in Acute Kidney Injury

BACKGROUND AND OBJECTIVES

In regenerative medicine, mesenchymal stem cells derived from adipose tissues (Ad-MSCs) are a very attractive target to treat many diseases. In relation to nephrology, the aim of the current study is to investigate the effects of Ad-MSCs for the amelioration of acute kidney injury and to explore the mechanism of renal parenchymal changes in response to allogeneic transplantation of Ad-MSCs.

METHODS AND RESULTS

The nephrotoxicity was induced by cisplatin (CP) in balb/c mice according to RIFLE Class and AKIN Stage 3. PCR, qRT-PCR and fluorescent labeled cells infusion, histopathology, immunohistochemistry, functional analyses were used for genes and proteins expressions data acquisition respectively. We demonstrated that single intravenous infusion of 2.5×107/kg mAd-MSCs in mice pre-injected with CP recruited to the kidney, restored the renal structure, and function, which resulted in progressive survival of mice. The renal tissue morphology was recovered in terms of diminished necrosis or epithelial cells damage, protein casts formation, infiltration of inflammatory cells, tubular dilatation, and restoration of brush border protein; Megalin and decreased Kim-1 expressions in mAd-MSCs transplanted mice. Significant reduction in serum creatinine with slashed urea and urinary protein levels were observed. Anti-BrdU staining displayed enhanced tubular cells proliferation. Predominantly, downgrade expressions of TNF-α and TGF-β1 were observed post seven days in mAd-MSCs transplanted mice.

CONCLUSIONS

Ad-MSCs exerts pro-proliferative, anti-inflammatory, and anti-fibrotic effects. Ad-MSCs transplantation without any chemical or genetic manipulation can provide the evidence of therapeutic strategy for the origin of regeneration and overall an improved survival of the system in functionally deprived failed kidneys.

A novel rare CUBN variant and three additional genes identified in Europeans with and without diabetes: results from an exome-wide association study of albuminuria

AIMS/HYPOTHESIS

Identifying rare coding variants associated with albuminuria may open new avenues for preventing chronic kidney disease and end-stage renal disease, which are highly prevalent in individuals with diabetes. Efforts to identify genetic susceptibility variants for albuminuria have so far been limited, with the majority of studies focusing on common variants.

METHODS

We performed an exome-wide association study to identify coding variants in a two-stage (discovery and replication) approach. Data from 33,985 individuals of European ancestry (15,872 with and 18,113 without diabetes) and 2605 Greenlanders were included.

RESULTS

We identified a rare (minor allele frequency [MAF]: 0.8%) missense (A1690V) variant in CUBN (rs141640975, β = 0.27, p = 1.3 × 10^-11) associated with albuminuria as a continuous measure in the combined European meta-analysis. The presence of each rare allele of the variant was associated with a 6.4% increase in albuminuria. The rare CUBN variant had an effect that was three times stronger in individuals with type 2 diabetes compared with those without (p_interaction = 7.0 × 10^-4, β with diabetes = 0.69, β without diabetes = 0.20) in the discovery meta-analysis. Gene-aggregate tests based on rare and common variants identified three additional genes associated with albuminuria (HES1, CDC73 and GRM5) after multiple testing correction (p_Bonferroni < 2.7 × 10^-6).

CONCLUSIONS/INTERPRETATION

The current study identifies a rare coding variant in the CUBN locus and other potential genes associated with albuminuria in individuals with and without diabetes. These genes have been implicated in renal and cardiovascular dysfunction. The findings provide new insights into the genetic architecture of albuminuria and highlight target genes and pathways for the prevention of diabetes-related kidney disease.

Role of Krüppel-like factor-2 in kidney disease

Krüppel-like factor-2 (KLF2) is a transcription factor that plays a major role in the regulation of endothelial cell function. KLF2 protects against endothelial cell injury through its anti-inflammatory, anti-thrombotic and anti-angiogenic effects to maintain the normal vascular integrity. Our recent data indicate that KLF2 is down-regulated in glomerular endothelial cells of patients with diabetic kidney disease and that endothelial cell-specific reduction in KLF2 expression in experimental model of diabetic kidney disease exacerbates glomerular endothelial cell injury and accelerates the disease progression. KLF2 is a key transcriptional regulator of endothelial nitric oxide synthase, and its renoprotective function may be mediated through the increased endothelial nitric oxide synthase expression. As KLF2 expression is stimulated by shear stress, we also investigated the role of KLF2 in the nephrectomy mouse model, in which the endothelial KLF2 expression would be increased through glomerular hyperfiltration in the remnant kidney. Reduction of endothelial KLF2 led to increased glomerular endothelial cell injury and progressive kidney disease in uninephrectomized mice. Interestingly, KLF2 expression is also reduced in nephrectomy patients with progressive kidney disease as compared to those with the non-progressive disease. Together, these studies indicate a critical role of KLF2 in maintaining normal glomerular endothelial cell function and that deficiency of KLF2 leads to more progressive kidney disease.

Endogenous reduction of miR-185 accelerates cardiac function recovery in mice following myocardial infarction via targeting of cathepsin K

Angiogenesis is critical for re‐establishing the blood supply to the surviving myocardium after myocardial infarction (MI) in patients with acute coronary syndrome (ACS). MicroRNAs are recognised as important epigenetic regulators of endothelial function. The aim of this study was to determine the roles of microRNAs in angiogenesis. Eighteen circulating microRNAs including miR‐185‐5p were differently expressed in plasma from patients with ACS by high‐throughput RNA sequencing. The expressional levels of miR‐185‐5p were dramatically reduced in hearts isolated from mice following MI and cultured human umbilical vein endothelial cells (HUVECs) under hypoxia, as determined by fluorescence in situ hybridisation and quantitative RT‐PCR. Evidence from computational prediction and luciferase reporter gene activity indicated that cathepsin K (CatK) mRNA is a target of miR‐185‐5p. In HUVECs, miR‐185‐5p mimics inhibited cell proliferations, migrations and tube formations under hypoxia, while miR‐185‐5p inhibitors performed the opposites. Further, the inhibitory effects of miR‐185‐5p up‐regulation on cellular functions of HUVECs were abolished by CatK gene overexpression, and adenovirus‐mediated CatK gene silencing ablated these enhancive effects in HUVECs under hypoxia. In vivo studies indicated that gain‐function of miR‐185‐5p by agomir infusion down‐regulated CatK gene expression, impaired angiogenesis and delayed the recovery of cardiac functions in mice following MI. These actions of miR‐185‐5p agonists were mirrored by in vivo knockdown of CatK in mice with MI. Endogenous reductions of miR‐185‐5p in endothelial cells induced by hypoxia increase CatK gene expression to promote angiogenesis and to accelerate the recovery of cardiac function in mice following MI.

γ-secretase inhibitor DAPT mitigates cisplatin-induced acute kidney injury by suppressing Notch1 signaling

Organ toxicity, including kidney injury, limits the use of cisplatin for the treatment of multiple human cancers. Hence, interventions to alleviate cisplatin-induced nephropathy are of benefit to cancer patients. Recent studies have demonstrated that pharmacological inhibition of the Notch signaling pathway enhances cisplatin efficacy against several cancer cells. However, whether augmentation of the anti-cancer effect of cisplatin by Notch inhibition comes at the cost of increased kidney injury is unclear. We show here that treatment of mice with cisplatin resulted in a significant increase in Notch ligand Delta-like 1 (Dll1) and Notch1 intracellular domain (N1ICD) protein expression levels in the kidneys. N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), a γ-secretase inhibitor reversed cisplatin-induced increase in renal N1ICD expression and plasma or urinary levels of predictive biomarkers of acute kidney injury (AKI). DAPT also mitigated cisplatin-induced tubular injury and reduction in glomerular filtration rate. Real-time multiphoton microscopy revealed marked necrosis and peritubular vascular dysfunction in the kidneys of cisplatin-treated mice which were abrogated by DAPT. Cisplatin-induced Dll1/Notch1 signaling was recapitulated in a human proximal tubule epithelial cell line (HK-2). siRNA-mediated Dll1 knockdown and DAPT attenuated cisplatin-induced Notch1 cleavage and cytotoxicity in HK-2 cells. These data suggest that Dll1-mediated Notch1 signaling contributes to cisplatin-induced AKI. Hence, the Notch signaling pathway could be a potential therapeutic target to alleviate renal complications associated with cisplatin chemotherapy.

Jagged1/Notch2 controls kidney fibrosis via Tfam-mediated metabolic reprogramming

While Notch signaling has been proposed to play a key role in fibrosis, the direct molecular pathways targeted by Notch signaling and the precise ligand and receptor pair that are responsible for kidney disease remain poorly defined. In this study, we found that JAG1 and NOTCH2 showed the strongest correlation with the degree of interstitial fibrosis in a genome-wide expression analysis of a large cohort of human kidney samples. Transcript analysis of mouse kidney disease models, including folic-acid (FA)-induced nephropathy, unilateral ureteral obstruction (UUO), or apolipoprotein L1 (APOL1)-associated kidney disease, indicated that Jag1 and Notch2 levels were higher in all analyzed kidney fibrosis models. Mice with tubule-specific deletion of Jag1 or Notch2 (Kspcre/Jag1flox/flox and Kspcre/Notch2flox/flox) had no kidney-specific alterations at baseline but showed protection from FA-induced kidney fibrosis. Tubule-specific genetic deletion of Notch1 and global knockout of Notch3 had no effect on fibrosis. In vitro chromatin immunoprecipitation experiments and genome-wide expression studies identified the mitochondrial transcription factor A (Tfam) as a direct Notch target. Re-expression of Tfam in tubule cells prevented Notch-induced metabolic and profibrotic reprogramming. Tubule-specific deletion of Tfam resulted in fibrosis. In summary, Jag1 and Notch2 play a key role in kidney fibrosis development by regulating Tfam expression and metabolic reprogramming.

Effect of inhibition of CBP-coactivated β-catenin-mediated Wnt signalling in uremic rats with vascular calcifications

Uremic vascular calcification is a regulated cell-mediated process wherein cells in the arterial wall transdifferentiate to actively calcifying cells resulting in a process resembling bone formation. Wnt signalling is established as a major driver for vessel formation and maturation and for embryonic bone formation, and disturbed Wnt signalling might play a role in vascular calcification. ICG-001 is a small molecule Wnt inhibitor that specifically targets the coactivator CREB binding protein (CBP)/β-catenin-mediated signalling. In the present investigation we examined the effect of ICG-001 on vascular calcification in uremic rats. Uremic vascular calcification was induced in adult male rats by 5/6-nephrectomy, high phosphate diet and alfacalcidol. The presence of uremic vascular calcification in the aorta was associated with induction of gene expression of the Wnt target gene and marker of proliferation, cyclinD1; the mediator of canonical Wnt signalling, β-catenin and the matricellular proteins, fibronectin and periostin. Furthermore, genes from fibrosis-related pathways, TGF-β and activin A, as well as factors related to epithelial-mesenchymal transition, snail1 and vimentin were induced. ICG-001 treatment had significant effects on gene expression in kidney and aorta from healthy rats. These effects were however limited in uremic rats, and treatment with ICG-001 did not reduce the Ca-content of the uremic vasculature.

Notch signaling in the collecting duct regulates renal tubulointerstitial fibrosis induced by unilateral ureteral obstruction in mice

BACKGROUND/AIMS

Mind bomb-1 (Mib1) encodes an E3 ubiquitin ligase, which is required for the initiation of Notch signaling. Recently, it was demonstrated that the renal collecting duct plays an important role in renal fibrosis. Here, we investigated the role of Notch signaling in renal fibrosis using conditional knockout mice with the specific ablation of Mib1 in renal collecting duct principal cells.

METHODS

Mib1-floxed mice (Mib1f/f) were crossed with aquaporin 2 (AQP2)-Cre mice in order to generate principal cell-specific Mib1 knockout mice (Mib1f/f :AQP2-Cre+). Unilateral ureteral obstruction (UUO) was performed, and mice were sacrificed 7 days after UUO.

RESULTS

After performing the UUO, renal tubulointerstitial fibrosis and the expression of transforming growth factor β were markedly enhanced in the obstructed kidneys of Mib1f/f mice compared with the sham-operated kidney of Mib1f/f mice. These changes were shown to be even more pronounced in the obstructed kidneys of Mib1f/f :AQP2-Cre+ mice than in those of the Mib1f/f mice . Furthermore, the number of TUNNEL-positive cells in renal collecting duct was higher in the obstructed kidneys of Mib1f/f :AQP2-Cre+ mice than in the kidneys of Mib1f/f mice.

CONCLUSIONS

Notch signaling in the renal collecting duct plays an important role in the regulation of renal tubulointerstitial fibrosis and apoptosis after UUO.

Therapeutic effects of histone deacetylase inhibitors on kidney disease

Increasing evidence has shown the involvement of histone deacetylases (HDACs) in the development and progression of various renal diseases, highlighting its inhibition as a promising therapeutic strategy to prevent kidney diseases. Accordingly, numerous studies have shown that HDAC inhibitors protect the kidneys from various diseases through their effects on multiple pathways, such as suppression of transforming growth factor-β signaling pathway and nuclear factor-κB signaling pathways, augmentation of apoptosis, and inhibition of angiogenesis. To develop more effective and less toxic isoform-selective HDAC inhibitors and further improve clinical outcomes, it is necessary to identify and understand the mechanisms involved in the pathogenesis and progression of renal diseases. This review focuses on the roles of HDAC inhibitors and the mechanisms involved in their therapeutic effects in experimental models of kidney diseases including glomerulosclerosis, tubulointerstitial fibrosis, glomerular and tubulointerstitial inflammation, lupus nephritis, polycystic kidney disease, and renal cell carcinoma (RCC).

Notch-mediated Sox9+ cell activation contributes to kidney repair after partial nephrectomy

AIMS

Partial nephrectomy is a surgical technique as an alternative for traditional radical nephrectomy. The advantage of partial nephrectomy technique is nephron-sparing, however, whether the remaining kidney tissue could regenerate the lost nephron is still unknown. The current work is to investigate the kidney tissue repair process and the related cellular and molecular mechanism.

MAIN METHODS

We used a novel unilateral partial nephrectomy mouse model to study kidney repair, and focused on a population of Sox9⁺ progenitor cells to study their pivotal role in the regenerative process. Kidney function after nephrectomy was measured using creatinine and urea nitrogen assay kit. Wound healing was assessed by Masson Trichrome Staining. Tissue regeneration was tested by Sox9⁺ cells immunofluorescence staining. The differentiation potential of Sox9⁺ cells were assessed by immunoanalysis with various tubular cell markers. Notch activation was determined by qPCR and Western blotting.

KEY FINDINGS

After partial nephrectomy, we found that massive Sox9⁺ cells emerged one day after the surgery and lasted for up to 20days. The Sox9⁺ cells had proliferative capacity and could give rise to epithelial cells of proximal tubule, Henle's loop, distal tubule, collecting duct, and the parietal layer of glomerulus. We also found that the activation of Sox9⁺ cells was mediated by Notch signaling pathway.

SIGNIFICANCE

The current study reveals that Notch-mediated Sox9⁺ cell activation can contribute to kidney tubule regeneration after unilateral partial nephrectomy in mice.

Trichostatin A ameliorates renal tubulointerstitial fibrosis through modulation of the JNK-dependent Notch-2 signaling pathway

Renal fibrosis is the final common pathological feature in a variety of chronic kidney disease. Trichostatin A (TSA), a histone deacetylase inhibitor, reportedly attenuates renal fibrosis in various kidney disease models. However, the detailed molecular action of TSA in ameliorating renal fibrotic injury is not yet fully understood. In a cultured renal fibroblastic cell model, we showed that TGF-β1 triggers upregulation of α-SMA and fibronectin, two hallmarks of myofibroblastic activation. During the course of TGF-β1 treatment, activation of Smad2/3, p38, ERK, JNK and Notch-2 was also detected. Under the conditions, administration of TSA significantly decreased TGF-β1-stimulated expression of α-SMA, fibronectin, phospho-JNK, and cleaved Notch-2; however, the levels of phospho-Smad2/3, phospho-p38 and phospho-ERK remained unchanged. Pharmacological inhibition of different signaling pathways and genetic knockdown of Notch-2 further revealed JNK as an upstream effector of Notch-2 in TGF-β1-mediated renal fibrosis. Consistently, we also demonstrated that administration of TSA or a γ-secretase inhibitor RO4929097 in the mouse model of unilateral ureteral obstruction significantly ameliorated renal fibrosis through suppression of the JNK/Notch-2 signaling activation. Taken together, our findings provide further insights into the crosstalk among different signaling pathways in renal fibrosis, and elucidate the molecular action of TSA in attenuating fibrogenesis.

AKI on CKD: heightened injury, suppressed repair, and the underlying mechanisms

Acute kidney injury (AKI) and chronic kidney disease (CKD) are interconnected. Although AKI-to-CKD transition has been intensively studied, the information of AKI on CKD is very limited. Nonetheless, AKI, when occurring in patients with CKD, is known to be more severe and difficult to recover. CKD is associated with significant changes in cell signaling in kidney tissues, including the activation of transforming growth factor-β, p53, hypoxia-inducible factor, and major developmental pathways. At the cellular level, CKD is characterized by mitochondrial dysfunction, oxidative stress, and aberrant autophagy. At the tissue level, CKD is characterized by chronic inflammation and vascular dysfunction. These pathologic changes may contribute to the heightened sensitivity of, and nonrecovery from, AKI in patients with CKD.

Sirt6 deficiency exacerbates podocyte injury and proteinuria through targeting Notch signaling

Podocyte injury is a major determinant of proteinuric kidney disease and the identification of potential therapeutic targets for preventing podocyte injury has clinical importance. Here, we show that histone deacetylase Sirt6 protects against podocyte injury through epigenetic regulation of Notch signaling. Sirt6 is downregulated in renal biopsies from patients with podocytopathies and its expression correlates with glomerular filtration rate. Podocyte-specific deletion of Sirt6 exacerbates podocyte injury and proteinuria in two independent mouse models, diabetic nephropathy, and adriamycin-induced nephropathy. Sirt6 has pleiotropic protective actions in podocytes, including anti-inflammatory and anti-apoptotic effects, is involved in actin cytoskeleton maintenance and promotes autophagy. Sirt6 also reduces urokinase plasminogen activator receptor expression, which is a key factor for podocyte foot process effacement and proteinuria. Mechanistically, Sirt6 inhibits Notch1 and Notch4 transcription by deacetylating histone H3K9. We propose Sirt6 as a potential therapeutic target for the treatment of proteinuric kidney disease.

Podocytes are essential components of the renal glomerular filtration barrier and podocyte dysfunction leads to proteinuric kidney disease. Here Liu et al. show that Sirt6 protects podocytes from apoptosis and inflammation by increasing autophagic flux through inhibition of the Notch pathway.

Fibrotic Changes Mediating Acute Kidney Injury to Chronic Kidney Disease Transition

End-stage renal disease (ESRD) is common, costly, and it results from progressive chronic kidney disease (CKD). ESRD claims many lives every year. It is increasingly recognized that episodes of acute kidney injury (AKI) predispose to the future development of CKD and ESRD. While our understanding of the pathophysiology of the AKI to CKD transition is improving, there are no validated therapeutic strategies to prevent this transition. In this review, we summarize the recent progress made in defining the cellular and molecular events underlying the AKI to CKD transition and highlight potential therapeutic targets and strategies to reduce the incidence of CKD following AKI.

Paraquat poisoning induced pulmonary epithelial mesenchymal transition through Notch1 pathway

Progressive pulmonary fibrosis is the most characteristic feature of subacute PQ poisoning. Epithelial-to-mesenchymal transition (EMT) is reported to be involved in the pulmonary fibrosis after PQ exposure. Recent evidence suggested Notch signaling is required for EMT. In this study, we investigated whether Notch1 and TGF-β1/Smad3 signaling was involved in EMT caused by PQ. It is demonstrated that A549 cells underwent EMT after treated with PQ at dose of 300 μmol/L for 6 days, charactered by increasing expression of mesenchymal marker α-SMA and decreasing expression of epithelial marker E-cadherin. We found that there was an apparent increased expression of Notch1 and jagged-1 in PQ induced EMT process. EMT could be enhanced by Jagged-1 ligand of Notch1, and be blocked by DAPT, a γ-secretase inhibitor. Our data also showed that the expression of TGF-β1/Smad3 increased after Notch1 is elevated in EMT caused by PQ. Jagged-1 significantly induced SMA expression, and this induction was completely inhibited by SB431542 in A549 cells. In conclusion, we demonstrated that Notch1 pathway was important in EMT induced by PQ, and TGF-β1/Smad3 signaling partly plays a role as the downstream of Notch1.

Antagonism of profibrotic microRNA-21 improves outcome of murine chronic renal allograft dysfunction

Chronic renal allograft dysfunction (CAD) is a major limiting factor of long-term graft survival. It is characterized by interstitial fibrosis and tubular atrophy. The underlying pathomechanisms are incompletely understood. MicroRNAs are powerful regulators of gene expression and may have an impact on various diseases by direct mRNA decay or translational inhibition. A murine model of allogenic kidney transplantation was used resulting in CAD at 6 weeks after kidney transplantation. We identified fibrosis-associated miR-21a-5p by whole miRNAome expression analysis to be among the most highly upregulated miRNAs. In vitro in renal fibroblasts, miR-21a-5p was transcriptionally activated by interleukin 6-induced signal transducer and activator of transcription 3. Co-culture of LPS-activated macrophages with renal fibroblasts increased expression levels of miR-21a-5p and markers of fibrosis and inflammation. In addition, mature miR-21a-5p was secreted by macrophages in small vesicles, which were internalized by renal fibroblasts, thereby promoting profibrotic and proinflammatory effects. Notch2 receptor was identified as a potential target of miR-21a-5p and validated by luciferase gene reporter assays. Therapeutic silencing of miR-21a-5p in mice after allogenic kidney transplantation resulted in an amelioration of CAD, as indicated by a reduction in fibrosis development, inflammatory cell influx, tissue injury and BANFF lesion scoring. In a life-supporting model, miR-21a-5p antagonism had beneficial effects on kidney function. miR-21a-5p silencing may therefore be a viable therapeutic option in the treatment of patients following kidney transplantation to halt the development of CAD.

Reduced Krüppel-Like Factor 2 Aggravates Glomerular Endothelial Cell Injury and Kidney Disease in Mice with Unilateral Nephrectomy

Loss of functional nephrons induces compensatory glomerular hyperfiltration and hypertrophy, leading to the progression of chronic kidney disease. Krüppel-like factor 2 (KLF2), a shear-stress-inducible transcription factor, confers protection against endothelial injury. Because glomerular hyperfiltration is associated with shear stress, we hypothesized that KLF2 may be an important factor in the compensatory response to unilateral nephrectomy (UNX). To test this hypothesis, endothelial cell-specific Klf2 heterozygous knockout mice (KO) and their wild-type littermate control (WT) underwent either UNX or sham-operation. WT-UNX mice developed compensatory renal hypertrophy as expected, whereas KO-UNX mice did not. KO-UNX mice exhibited higher blood pressure, reduced glomerular filtration rate, and significant increase in proteinuria and glomerulosclerosis compared to WT-UNX. Expression of endothelial nitric oxide synthase (official name Nos3), a known transcriptional target gene of KLF2, was significantly reduced and dysregulation of other endothelial genes was also observed in the glomeruli of KO-UNX when compared to WT-UNX and sham-operated mice. Furthermore, both podocyte number and expression of podocyte markers were also significantly reduced in KO-UNX glomeruli, indicating a potential cross talk between glomerular endothelial cells and podocytes. Finally, decreased renal expression of KLF2 in nephrectomy patients was associated with the progression of kidney disease. Taken together, our data demonstrate a protective role of KLF2 against glomerular endothelial cell injury and progression of chronic kidney disease in the model of compensatory renal hypertrophy.

Developmental signalling pathways in renal fibrosis: the roles of Notch, Wnt and Hedgehog

Kidney fibrosis is a common histological manifestation of functional decline in the kidney. Fibrosis is a reactive process that develops in response to excessive epithelial injury and inflammation, leading to myofibroblast activation and an accumulation of extracellular matrix. Here, we describe how three key developmental signalling pathways - Notch, Wnt and Hedgehog (Hh) - are reactivated in response to kidney injury and contribute to the fibrotic response. Although transient activation of these pathways is needed for repair of injured tissue, their sustained activation is thought to promote fibrosis. Excessive Wnt and Notch expression prohibit epithelial differentiation, whereas increased Wnt and Hh expression induce fibroblast proliferation and myofibroblastic transdifferentiation. Notch, Wnt and Hh are fundamentally different signalling pathways, but their choreographed activation seems to be just as important for fibrosis as it is for embryonic kidney development. Decreasing the activity of Notch, Wnt or Hh signalling could potentially provide a new therapeutic strategy to ameliorate the development of fibrosis in chronic kidney disease.

Inhibition of Notch Signaling Ameliorates Acute Kidney Failure and Downregulates Platelet-Derived Growth Factor Receptor β in the Mouse Model

Ischemic acute kidney injury (AKI) is associated with high morbidity and frequent complications. Repeated episodes of AKI may lead to end-stage renal failure. The pathobiology of regeneration in AKI is not well understood and there is no effective clinical therapy that improves regeneration. The Notch signaling pathway plays an essential role in kidney development and has been implicated in tissue repair in the adult kidney. Here, we found that kidneys after experimental AKI in mice showed increased expression of Notch receptors, specifically Notch1-3, of the Notch ligands Jagged-1 (Jag1), Jag2 and Delta-like-4 (Dll4) and of the Notch target genes Hes1, Hey2, HeyL, Sox9 and platelet-derived growth factor receptor β (Pdgfrb). Treatment of ischemic mice with the x03B3;-secretase inhibitor DBZ blocked Notch signaling and specifically downregulated the expression of Notch3 and the Notch target genes Hes1, Hey2, HeyL and Pdgfrb. After DBZ treatment, the mice developed less interstitial edema and displayed altered interstitial inflammation patterns. Furthermore, serum urea and creatinine levels were significantly decreased from 6 h onwards when compared to control mice treated with DMSO only. Our data are consistent with an amelioration of the severity of kidney injury by blocking Notch activation following AKI, and suggest an involvement of Notch-regulated Pdgfrb in AKI pathogenesis.

Involvement of the Hippo pathway in regeneration and fibrogenesis after ischaemic acute kidney injury: YAP is the key effector

The Hippo pathway plays a stage-specific role in regeneration and fibrogenesis after ischaemia/reperfusion-induced acute kidney injury. The proper modulation of this pathway might be the key point of transition from acute kidney injury to chronic kidney disease.

Renal tubule cells can recover after they undergo AKI (acute kidney injury). An incomplete repair of renal tubules can result in progressive fibrotic CKD (chronic kidney disease). Studies have revealed the relationship between tubular epithelial cells and kidney fibrogenesis. However, the underlying mechanism remains unclear. Hippo pathway components were evaluated in complete/incomplete repair of I/R (ischaemia/reperfusion) AKI rat models, HK-2 cells and AKI human renal biopsy samples. We found that the expression levels of the Hippo pathway components changed dynamically during kidney regeneration and fibrogenesis in rat models of I/R-induced AKI and human renal biopsy samples. The transcription cofactor YAP (Yes-associated protein) might be a key effector of renal regeneration and fibrogenesis. Our results showed further that YAP might elicit both beneficial and detrimental effects on I/R AKI. After I/R injury occurred, YAP could promote the repair of the injured epithelia. The constant YAP increase and activation might be related to interstitial fibrosis and abnormal renal tubule differentiation. These results indicate that the proper modulation of the Hippo pathway, specifically the transcription cofactor YAP, during repair might be a potent therapeutic target in AKI–CKD transition after I/R injury.

Small Heat Shock Protein Beta-1 (HSPB1) Is Upregulated and Regulates Autophagy and Apoptosis of Renal Tubular Cells in Acute Kidney Injury

Background

Heat shock protein beta-1 (HSPB1, also known as HSP27) is a small heat shock protein involved in many cellular processes and reportedly protects cells against oxidative stress. Autophagy protects cells from many types of stress and is thought to play a key role in preventing stress in acute kidney injury (AKI). However, little is known about the role of HSPB1 in autophagy and apoptosis in the pathogenesis of AKI.

Methods

We used a rat ischemia/reperfusion AKI model and cultured renal tubular cells as an in vitro model. To elucidate the regulation of HSPB1, we evaluated the promoter activity and expression of HSPB1 in normal rat kidney (NRK)-52E cells in the presence of H₂O₂. To examine the regulation of autophagy by HSPB1, we established NRK-light chain 3 (NRK-LC3) cells that were stably transfected with a fusion protein of green fluorescent protein and LC3.

Results

The results of immunohistological examination showed that HSPB1 was expressed in proximal tubule cells after AKI. Real-time quantitative reverse transcription-polymerase chain reaction and western blot analysis showed that HSPB1 messenger RNA and protein expression were upregulated 6–72 h and 12–72 h, respectively, after ischemia/reperfusion injury. HSPB1 promoter activity as well as messenger RNA and protein expression indicated dose-dependent induction by H₂O₂. HSPB1 overexpression-induced autophagy in NRK-LC3 cells under normoxic conditions was confirmed with confocal microscopy, which revealed the presence of LC3-positive granules. Furthermore, H₂O₂-induced autophagy was inhibited by the transfection of small interfering RNAs for HSPB1. Overexpression of HSPB1 reduced BAX activation and H₂O₂-induced apoptosis, as measured by caspase 3 activity and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling assay.

Conclusions

We showed that HSPB1 expression increased during oxidative stress in AKI. Incremental HSPB1 expression increased autophagic flux and inhibited apoptosis in renal tubular cells. These results indicate that HSPB1 upregulation plays a role in the pathophysiology of AKI.

Kidney Regeneration: Lessons from Development

A number of genes involved in kidney development are reactivated in the adult after acute kidney injury (AKI). This has led to the belief that tissue repair mechanisms recapitulate pathways involved in embryonic development after AKI. We will discuss evidence to support this hypothesis by comparing the mechanisms of development with common pathways known to regulate post-AKI repair, or that we identified as cell-specific candidates based on public datasets from recent AKI translational profiling studies. We will argue that while many of these developmental pathways are reactivated after AKI, this is not associated with general cellular reprogramming to an embryonic state. We will show that reactivation of these developmental genes is often associated with expression in cells that are not normally involved in mediating parallel responses in the embryo, and that depending on the cellular context, these responses can have beneficial or detrimental effects on injury and repair after AKI.

Transcriptomic changes triggered by hypoxia: evidence for HIF-1α-independent, [Na+]i/[K+]i-mediated, excitation-transcription coupling

This study examines the relative impact of canonical hypoxia-inducible factor-1alpha- (HIF-1α and Na⁺_i/K⁺_i-mediated signaling on transcriptomic changes evoked by hypoxia and glucose deprivation. Incubation of RASMC in ischemic conditions resulted in ∼3-fold elevation of [Na⁺]_i and 2-fold reduction of [K⁺]_i. Using global gene expression profiling we found that Na⁺,K⁺-ATPase inhibition by ouabain or K⁺-free medium in rat aortic vascular smooth muscle cells (RASMC) led to the differential expression of dozens of genes whose altered expression was previously detected in cells subjected to hypoxia and ischemia/reperfusion. For further investigations, we selected Cyp1a1, Fos, Atf3, Klf10, Ptgs2, Nr4a1, Per2 and Hes1, i.e. genes possessing the highest increments of expression under sustained Na⁺,K⁺-ATPase inhibition and whose implication in the pathogenesis of hypoxia was proved in previous studies. In ouabain-treated RASMC, low-Na⁺, high-K⁺ medium abolished amplification of the [Na⁺]_i/[K⁺]_i ratio as well as the increased expression of all tested genes. In cells subjected to hypoxia and glucose deprivation, dissipation of the transmembrane gradient of Na⁺ and K⁺ completely eliminated increment of Fos, Atf3, Ptgs2 and Per2 mRNAs and sharply diminished augmentation expression of Klf10, Edn1, Nr4a1 and Hes1. In contrast to low-Na⁺, high-K⁺ medium, RASMC transfection with Hif-1a siRNA attenuated increments of Vegfa, Edn1, Klf10 and Nr4a1 mRNAs triggered by hypoxia but did not impact Fos, Atf3, Ptgs2 and Per2 expression. Thus, our investigation demonstrates, for the first time, that Na⁺_i/K⁺_i-mediated, Hif-1α- -independent excitation-transcription coupling contributes to transcriptomic changes evoked in RASMC by hypoxia and glucose deprivation.

Kick it up a notch: Notch signaling and kidney fibrosis

Notch is a critical regulator of kidney development, but the pathway is mostly silenced once kidney maturation is achieved. Recent reports demonstrated increased expression of Notch receptors and ligands both in acute and chronic kidney injury. In vivo studies indicated that Notch activation might contribute to regeneration after acute kidney injury; on the other hand, sustained Notch expression is causally associated with interstitial fibrosis and glomerulosclerosis. This review will summarize the current knowledge on the role of the Notch signaling with special focus on kidney fibrosis.

The deposition of Notch1 in hepatitis B virus-associated nephropathy and its role in hepatitis B virus X protein-induced epithelial-mesenchymal transdifferentiation and immunity disorder in renal tubular epithelial cells

Notch1 plays an important role in the regulation of immune responses and epithelial-mesenchymal transdifferentiation (EMT). Previous studies have observed inflammatory cell infiltration and tubulointerstitial fibrosis in the renal biopsies from patients with HBV-associated glomerulonephritis (HBV-GN). We hypothesized that Notch1 may be involved in the progression of HBV-GN. In this study, we evaluated the distribution of Notch1 in patients with HBV-GN. Our results showed that Notch1 was mainly distributed in renal tubules and the interstitial area, and the expression levels of Notch1 had a positive correlation with the renal tubular pathology. In this respect, we used human proximal tubular epithelial cells (HK-2) as target cells, which were transiently transfected with the hepatitis B virus X (HBx) gene using a eukaryotic vector. HBx expression resulted in significantly increased detection of Notch1, alpha-smooth muscle actin (α-SMA), major histocompatibility complex-II (MHC-II), CD40 and interleukin-4 (IL-4). At the same time, E-cadherin and interferon-γ (IFN-γ) expression levels were significantly inhibited. These HBx-induced phenotypes were exacerbated by upregulation of Notch1. Knock-down of Notch1 by specific shRNA caused decreases of α-SMA, MHC-II, CD40 and IL-4, and increases of E-cadherin and IFN-γ. These findings suggest that Notch1 is significantly associated with renal tubular and interstitial lesions. Notch1 can mediate HBx-induced EMT of HK-2 cells, promote HBx-induced increases in immune molecule expression and exacerbation of cytokine disorders, which may contribute to the progression of HBV-GN. Inhibitors of Notch1 signalling may be useful as new therapeutics for the treatment of HBV-GN.

Repair or progression after AKI: a role for biomarkers?

Recent progress in biomarkers represents a paradigm shift in acute kidney injury (AKI) research. Most studies have evaluated the use of these biomarkers for early diagnosis of AKI. However, the role of novel biomarkers in predicting renal recovery, though less understood, holds great clinical promise. Accurate prediction would help physicians distinguish patients with poor renal prognosis in whom further therapy is unlikely to be useful from those who are likely to have good renal prognosis. Unfortunately, current general clinical severity scores (APACHE, SOFA, etc.) and AKI-specific severity scores are not good predictors of renal recovery. The biology of renal recovery requires the repopulation by surviving renal tubular epithelial cells with the assistance of certain renal epithelial cell and specific growth factors such as neutrophil gelatinase-associated lipocalin (NGAL), hepatocyte growth factor (HGF), epidermal growth factor, and insulin-like growth factor-1 (IGF-1), etc. These markers play a major role in the recovery process. This review will describe the mechanisms of the renal recovery, epidemiology, the role of conventional clinical predictors and finally the role of novel biomarkers (NGAL, HGF, IL-8, IL-18, TNFR-1, IGF-binding protein-7 and tissue inhibitor of metalloproteinase-2) in predicting renal recovery.

Single cell dissection of early kidney development: multilineage priming

We used a single cell RNA-seq strategy to create an atlas of gene expression patterns in the developing kidney. At several stages of kidney development, histologically uniform populations of cells give rise to multiple distinct lineages. We performed single cell RNA-seq analysis of total mouse kidneys at E11.5 and E12.5, as well as the renal vesicles at P4. We define an early stage of progenitor cell induction driven primarily by gene repression. Surprising stochastic expression of marker genes associated with differentiated cell types was observed in E11.5 progenitors. We provide a global view of the polarized gene expression already present in the renal vesicle, the first epithelial precursor of the nephron. We show that Hox gene read-through transcripts can be spliced to produce intergenic homeobox swaps. We also identify a surprising number of genes with partially degraded noncoding RNA. Perhaps most interesting, at early developmental times single cells often expressed genes related to several developmental pathways. This provides powerful evidence that initial organogenesis involves a process of multilineage priming. This is followed by a combination of gene repression, which turns off the genes associated with most possible lineages, and the activation of increasing numbers of genes driving the chosen developmental direction.

Detrimental effects of Notch1 signaling activated by cadmium in renal proximal tubular epithelial cells

We examined the roles of Notch1 signaling and its cross-talk with other signaling pathways, including p53 and phosphatidylinositol-3-kinase (PI3K)/Akt, in cadmium-induced cellular damage in HK-2 human renal proximal tubular epithelial cells. Following exposure to cadmium chloride (CdCl2), the level of Notch intracellular domain (NICD), the cleaved form of the Notch1 receptor, was increased and accumulated in the nuclear fraction. Knockdown of Notch1 with siRNA or treatment with the γ-secretase inhibitor, DAPT (N-[N-(3,5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester), prevented CdCl2-induced morphological change of HK-2 cells and reduction of cell viability. Knockdown of Jagged1 or Jagged2, the ligands of the Notch1 receptor, partially suppressed cadmium cytotoxicity. Inhibition of p53 activity with pifithrin-α or inhibition of PI3K with LY294002 suppressed CdCl2-induced cellular damage and elevation of Notch1-NICD. In addition, treatment with the epidermal growth factor receptor (EGFR) inhibitor, AG1478, and the insulin-like growth factor-1 receptor inhibitor, PPP, suppressed both Notch1-NICD accumulation and Akt phosphorylation in HK-2 cells exposed to CdCl2. However, knockdown of Notch1 did not affect CdCl2-induced p53 accumulation and phosphorylation but suppressed phosphorylation of EGFR, Akt, and p70 S6 kinase. Depletion of Notch1 suppressed CdCl2-induced reduction of E-cadherin expression and elevation of Snail expression. Furthermore, treatment with SB216763, an inhibitor of glycogen synthase kinase-3, suppressed the potency of LY294002 treatment to reduce Snail expression in HK-2 cells exposed to CdCl2. Knockdown of Snail with siRNA partially prevented HK-2 cells from CdCl2-induced reduction of E-cadherin expression and cellular damage. These results suggest that cadmium exposure induces the activation of Notch1 signaling in renal proximal tubular cells with cooperative activation by the p53 and PI3K/Akt signaling pathways; the resultant expression of Snail, a repressor of E-cadherin expression, might lead to cellular damage by decreasing cell-cell adhesion.

Defining the acute kidney injury and repair transcriptome

The mammalian kidney has an intrinsic ability to repair after significant injury. However, this process is inefficient: patients are at high risk for the loss of kidney function in later life. No therapy exists to treat established acute kidney injury (AKI) per se: strategies to promote endogenous repair processes and retard associated fibrosis are a high priority. Whole-organ gene expression profiling has been used to identify repair responses initiated with AKI, and factors that may promote the transition from AKI to chronic kidney disease. Transcriptional profiling has shown molecular markers and potential regulatory pathways of renal repair. Activation of a few key developmental pathways has been reported during repair. Whether these are comparable networks with similar target genes with those in earlier nephrogenesis remains unclear. Altered microRNA profiles, persistent tubular injury responses, and distinct late inflammatory responses highlight continuing kidney pathology. Additional insights into injury and repair processes will be gained by study of the repair transcriptome and cell-specific translatome using high-resolution technologies such as RNA sequencing and translational profiling tailored to specific cellular compartments within the kidney. An enhanced understanding holds promise for both the identification of novel therapeutic targets and biomarker-based evaluation of the damage-repair process.