Human Kidney Proximal Tubular Cells Research Articles

Kidney-targeted antioxidant salvianolic acid B nanoparticles restoring lysosome homeostasis for acute kidney injury therapy

Acute kidney injury (AKI) is highly correlated with oxidative stress, and the application of antioxidants is one of the promising treatments. Salvianolic acid B (SAB) is a natural polyphenol with powerful antioxidant effects. Due to its inherent characteristic of inferior bioavailability, its clinical application is impeded. In this study, small SAB-incorporated nanoparticles (SFA) were synthesized via the self-assembly of SAB, ferric ions, and bovine serum albumin (BSA). Apart from antioxidant activity, the SFA nanoparticles were found to efficiently restore lysosome dysfunction induced by reactive oxygen species (ROS) in human kidney proximal tubular epithelial HK-2 cells. The small size and BSA incorporation make the SFA nanoparticles to be promising AKI-targeting nanoparticles. They are rapidly accumulated and long-term retained in injured kidneys of glycerol-induced AKI mice, especially in the proximal tubules which are the key lesion location during AKI. In vivo studies indicate that SFA nanoparticles show a superior protective effect compared with the free drug by suppressing oxidative stress and maintaining lysosome homeostasis indicated by enhanced heme oxygenase-1 (HO-1) expression and restored cathepsin B (CTSB) activity, respectively. In summary, this study develops a delivery system for the antioxidant SAB enhancing local delivery and offering an additional lysosome restoring mechanism for AKI therapy.

Multi-omics and imaging mass cytometry characterization of human kidneys to identify pathways and phenotypes associated with impaired kidney function

Despite the recent advances in our understanding of the role of lipids, metabolites and related enzymes in mediating kidney injury, there is limited integrated multi-omics data identifying potential metabolic pathways driving impaired kidney function. The limited availability of kidney biopsies from living donors with acute kidney injury has remained a major constraint. Here, we validated the use of deceased transplant donor kidneys as a good model to study acute kidney injury in humans and characterized these kidneys using imaging and multi-omics approaches. We noted consistent changes in kidney injury and inflammatory markers in donors with reduced kidney function. Neighborhood and correlation analyses of imaging mass cytometry data showed that subsets of kidney cells (proximal tubular cells and fibroblasts) are associated with the expression profile of kidney immune cells, potentially linking these cells to kidney inflammation. Integrated transcriptomic and metabolomic analysis of human kidneys showed that kidney arachidonic acid metabolism and seven other metabolic pathways were upregulated following diminished kidney function. To validate the arachidonic acid pathway in impaired kidney function we demonstrated increased levels of cytosolic phospholipase A2 protein and related lipid mediators (prostaglandin E2) in the injured kidneys. Further, inhibition of cytosolic phospholipase A2 reduced injury and inflammation in human kidney proximal tubular epithelial cells in vitro. Thus, our study identified cell types and metabolic pathways that may be critical for controlling inflammation associated with impaired kidney function in humans.

Dextrin conjugation to colistin inhibits its toxicity, cellular uptake and acute kidney injury in vivo.

The acute kidney injury (AKI) and dose-limiting nephrotoxicity, which occurs in 20-60% of patients following systemic administration of colistin, represents a challenge in the effective treatment of multi-drug resistant Gram-negative infections. To reduce clinical toxicity of colistin and improve targeting to infected/inflamed tissues, we previously developed dextrin-colistin conjugates, whereby colistin is designed to be released by amylase-triggered degradation of dextrin in infected and inflamed tissues, after passive targeting by the enhanced permeability and retention effect. Whilst it was evident in vitro that polymer conjugation can reduce toxicity and prolong plasma half-life, without significant reduction in antimicrobial activity of colistin, it was unclear how dextrin conjugation would alter cellular uptake and localisation of colistin in renal tubular cells in vivo. We discovered that dextrin conjugation effectively reduced colistin's toxicity towards human kidney proximal tubular epithelial cells (HK-2) in vitro, which was mirrored by significantly less cellular uptake of Oregon Green (OG)-labelled dextrin-colistin conjugate, when compared to colistin. Using live-cell confocal imaging, we revealed localisation of both, free and dextrin-bound colistin in endolysosome compartments of HK-2 and NRK-52E cells. Using a murine AKI model, we demonstrated dextrin-colistin conjugation dramatically diminishes both proximal tubular injury and renal accumulation of colistin. These findings reveal new insight into the mechanism by which dextrin conjugation can overcome colistin's renal toxicity and show the potential of polymer conjugation to improve the side effect profile of nephrotoxic drugs.

Polystyrene nanoplastics induce apoptosis of human kidney proximal tubular epithelial cells via oxidative stress and MAPK signaling pathways.

Polystyrene nanoplastics (PS-NPs) have recently been found to be present in human blood and kidney. However, the renal toxicity of PS-NPs and the underlying mechanisms have not been fully elucidated. Here, we found that exposure of PS-NPs induced apoptosis of human renal proximal tubular epithelial cells (HK-2) in a size- and dose-dependent manner as revealed by AnnexinV-FITC assay. In addition, PS-NPs promoted ROS production and caused structure changes of mitochondrial and endoplasmic reticulum. Mechanistically, transcriptional sequencing indicated the involvement of MAPK pathway in apoptosis, which was further confirmed by the upregulation of p-p38, p-ERK, CHOP, BAX, cytochrome C, and caspase 3 expression. This study clarified the molecular mechanism underlying PS-NP-induced apoptosis in HK-2 cells and contributed to our risk estimation of PS-NPs in human kidney.

Long Non-coding RNA ZFAS1 Regulates Fibrosis and Scortosis in the Cell Model of Diabetic Nephropathy Through miR-525-5p/SGK1 Axis.

Diabetic nephropathy (DN) is a common clinical syndrome in diabetic patients. Functional characterization of non-coding (ncRNAs) involved in the progression of DN can provide insights into the diagnosis and therapeutic management of DN. Human kidney proximal tubular epithelial cells (HK-2) were challenged by high glucose (HG, 50mM) as a cell model of DN. The expression level of long non-coding RNA (lncRNA) ZFAS1 was quantified by qRT-PCR. The proteins and cytokines related to fibrosis and scortosis in DN (NLRP3, GSDMD-N, IL-1β and Caspase 1, fibronectin, collagen I, collagen III, IL-1β, and IL-18) were examined by western blot or ELISA. RNA precipitation and luciferase reporter activity experiments were conducted to assess the molecular associations. ZFAS1 and SGK1 were highly induced in HK-2 cells challenged with HG, while miR-525-5p downregulated upon HG treatment. ZFAS1 knockdown attenuated HG-induced fibrosis and scortosis in HK-2 cells by reducing the levels of NLRP3, GSDMD-N, Caspase 1, fibronectin, collagen I/III, IL-1β, and IL-18. Mechanically, ZFAS1 knockdown protected HK-2 cells from HG-induced injury by upregulating miR-525-5p and repressing SGK1 expression. Overall, our results suggest that knocking down ZFAS1 may be formulated as a protective strategy in ameliorating DN progression through regulating miR-525-5p/SGK1 pathway. Targeting ZFAS1 could be further explored as a potential approach for the management of DN.

Signaling pathways upregulating glutathione‑specific γ‑glutamylcyclotransferase 1 by 3‑(5'‑hydroxymethyl‑2'‑furyl)‑1‑benzylindazole.

Glutathione‑specific γ‑glutamylcyclotransferase1 (CHAC1), is an unfolded protein response‑induced gene. Although it has been previously reported that CHAC1 transcription is regulated by activating transcription factor (ATF)4, ATF3 and CCAAT/enhancer‑binding protein β (C/EBPβ), the signaling pathways that regulate CHAC1 are largely unknown. It was revealed that 3‑(5'‑hydroxymethyl‑2'‑furyl)‑1‑benzylindazole (YC‑1; PubChem ID: 5712), a nitric oxide‑independent activator ofsoluble guanylyl cyclase (sGC), increases CHAC1 levels in cultured human kidney proximal tubular cells (HK‑2). Therefore, in the present study, the signaling pathways that induce CHAC1 by YC‑1 were investigated in HK‑2 cells. YC‑1 induced CHAC1 expression in a dose‑ and time‑dependent manner. KT5823, an inhibitor of cGMP‑dependent protein kinase (PKG), partially inhibited CHAC1 upregulation, indicating that the sGC‑cGMP‑PKG pathway participates in CHAC1 regulation. These results also suggested that other signaling pathways are involved in the regulation of CHAC1. Since antibody array analysis showed the activation of p38, mTOR and Akt, the involvement of these factors was further investigated. Although LY294002 and KU0063794 (inhibitors of Akt and mTOR, respectively) inhibited YC‑1‑induced CHAC1 expression, SB203580 (an inhibitor of p38) did not. These results indicated that CHAC1 is regulated by the Akt‑mTOR pathway. In addition, YC‑1 induced endoplasmic reticulum (ER) stress, a regulator of CHAC1 induction. These findings suggested that CHAC1 is regulated by YC‑1 through the sGC‑cGMP‑PKG, Akt‑mTOR and ER stress pathways. The present study demonstrated that CHAC1 induction reduced the intracellular glutathione concentration, indicating that CHAC1 plays an important role in intracellular redox homeostasis in tubular cells.

Impact of hypoxia and reoxygenation on the extra/intracellular metabolome and on transporter expression in a human kidney proximal tubular cell line.

Ischemia-reperfusion injury (IRI) induces several perturbations that alter immediate kidney graft function after transplantation and may affect long-term graft outcomes. Given the IRI-dependent metabolic disturbances previously reported, we hypothesized that proximal transporters handling endo/exogenous substrates may be victims of such lesions. This study aimed to determine the impact of hypoxia/reoxygenation on the human proximal transport system through two semi-targeted omics analyses. Human proximal tubular cells were cultured in hypoxia (6 or 24h), each followed by 2, 24 or 48-h reoxygenation. We investigated the transcriptomic modulation of transporters. Using semi-targeted LC-MS/MS profiling, we characterized the extra/intracellular metabolome. Statistical modelling was used to identify significant metabolic variations. The expression profile of transporters was impacted during hypoxia (y + LAT1 and OCTN2), reoxygenation (MRP2, PEPT1/2, rBAT, and OATP4C1), or in both conditions (P-gp and GLUT1). The P-gp and GLUT1 transcripts increased (FC (fold change) = 2.93 and 4.11, respectively) after 2-h reoxygenation preceded by 24-h hypoxia. We observed a downregulation (FC = 0.42) of y+LAT1 after 24-h hypoxia, and of PEPT2 after 24-h hypoxia followed by 2-h reoxygenation (FC = 0.40). Metabolomics showed that hypoxia altered the energetic pathways. However, intracellular metabolic homeostasis and cellular exchanges were promptly restored after reoxygenation. This study provides insight into the transcriptomic response of the tubular transporters to hypoxia/reoxygenation. No correlation was found between the expression of transporters and the metabolic variations observed. Given the complexity of studying the global tubular transport systems, we propose that further studies focus on targeted transporters.

Serum myoglobin modulates kidney injury via inducing ferroptosis after exertional heatstroke.

Myoglobin released by rhabdomyolysis (RM) is considered to be involved in pathogenesis of kidney disease caused by crush injury, but whether high level of serum myoglobin predisposes patients to acute kidney injury (AKI) and its molecular mechanisms are still unclear in exertional heatstroke (EHS). We aimed to determine the association and potential mechanism of myoglobin and AKI, and further investigate the targeted therapeutic agents for myoglobinemia. Serum myoglobin concentrations in patients with EHS were measured at admission, 24 h and 48 h after admission and discharge. The risk of AKI at 48 h was the primary outcome; the secondary outcome was composite outcome events with myoglobin levels and AKI at discharge and death at 90 days. In experimental studies, we further investigated the mechanisms of human kidney proximal tubular (HK-2) cells that were exposed to human myoglobin under heat stress conditions and the effect of baicalein. Our measurements showed that the highest myoglobin quartile (vs. the lowest) had an adjusted odds ratio (OR) of 18.95 (95% confidence interval [CI], 6.00-59.83) for AKI and that the OR (vs. quartile 2) was 7.92 (95% CI, 1.62-38.89) for the secondary outcome. The survival rate of HK-2 cells treated with myoglobin under heat stress was significantly decreased, and the production of Fe2+ and reactive oxygen species (ROS) was markedly increased, accompanied by changes in ferroptosis proteins, including increased p53, decreased SLC7A11 and GPX4, and alterations in endoplasmic reticulum stress (ERS) marker proteins. Treatment with baicalein attenuated HK-2 cell ferroptosis induced by myoglobin under heat stress through inhibition of ERS. High myoglobin was associated with AKI in the EHS, and its mechanisms involved ERS-associated ferroptosis. Baicalein may be a potential therapeutic drug for the treatment of AKI in patients with high myoglobin induced by rhabdomyolysis following EHS.

#3680 CALPAIN INHIBITION PREVENTS FIBROSIS IN PROGRESSIVE CHRONIC KIDNEY DISEASE

Abstract Background and Aims Kidney fibrosis is one of the main pathological processes of chronic kidney disease (CKD), although the pathogenesis of renal scar formation is not fully understood. Calpains (CAPN) are intracellular cysteine ​​proteases that play a key role in multiple biological processes linked to tissue damage and repair mechanisms, such as fibrosis and epithelial-mesenchymal transition. However, CAPN contribution in CKD genesis and progression remains to be fully elucidated. The aim of this study was to investigate the possible role of CAPN in the development of CKD and renal fibrosis in an experimental model of CKD induced by adenine and in human kidney proximal tubular cells (HK-2). Method C57BL/6 wild-type mice were fed a 0.2% adenine-rich diet (WTA) for 5 days and 2 weeks to induce tubulointerstitial damage resembling what occurs in human CKD. Mice with a standard diet were used as controls (WT). WT and 5 days WTA mice were injected intraperitoneally for 5 consecutive days with a dose of calpain inhibitor III (20 mg/kg). In vitro experiments were performed in HK-2 cells in the presence or absence of TGF-β (1 ng/ml, different times) and calpain inhibitor III (50 µM). Mice renal function was assessed by measuring plasma BUN and creatinine. Interstitial fibrosis was evaluated in kidney samples embedded in paraffin by Sirius red staining of the collagen renal cortex content. Fibrosis markers were determined by RT-qPCR. CAPN localization in the kidney was assessed by immunofluorescence. CAPN 2 and 5 protein content were analyzed by western blot. CAPN activity was determined by fluorescence assays. All data were analyzed using non-parametric statistics for comparisons, applying the Kruskal-Wallis with Mann-Whitney post-test. A value of p<0.05 was considered statistically significant. Results Our results show a progressive worsening of renal function and structure in adenine-fed mice, with increased BUN, creatinine and COL I mRNA expression being significantly higher at 2 weeks of treatment. CAPN 2 and 5 protein content was significantly higher in animals that received adenine for 2 weeks compared to control, with a statistically significant increased renal CAPN activity. Our results point out that CAPN 2 and 5 content in renal tissue increases as CKD and fibrosis progress. To verify this potential relationship, we treated kidney tubular cells, where we observed a greater calpain expression compared to other kidney cells, with TGF-β to induce fibrosis. This treatment increased COL I mRNA expression, as well as CAPN 2 and 5 levels in HK-2 cells. However, calpain inhibitor III administration prevents increased COL I expression, both in vitro and in vivo. Conclusion We suggest a direct relationship between the cellular content of CAPN and the renal fibrosis observed in CKD, being involved in the genesis or progression of kidney disease. Thus, effective CAPN blockade or downregulation could be helpful as a therapeutic strategy to prevent CKD.

#6496 CYCLIN D1 AMELIORATES ACUTE KIDNEY INJURY BY IMPROVING FATTY ACID OXIDATION VIA AMPK PATHWAY

Abstract Background and Aims Acute Kidney Injury (AKI) is a critical condition that is caused by the absence of oxygen during the acute ischemic phase, leading to energy metabolism disturbance and kidney tubular epithelial cell damage. Fatty Acid Oxidation (FAO) is the main source of energy production of renal proximal tubular epithelial cells. Timely promoting FAO, increasing supplies of energy, and promoting cell proliferation are essential to improve kidney injury. However, there is no clinically recognized effective treatment for this. Cyclin D1(CCND1), a member of the cell cycle family, plays a vital role in cell proliferation. Our previous study showed that CCND1 improved AKI by increasing FAO. This study aimed to investigate the role and molecular basis of CCND1 involvement in fatty acid oxidation of AKI. Method CCND1 was evaluated in human kidney proximal tubular epithelial cells (HK-2 cells) and in male C57BL/6J mice (wild type). We investigated the protective role of CCND1 in AKI using a mouse model of ischemia-reperfusion injury, which was treated by transferring CCND1-expressing plasmids in male C57BL/6J mice (wild type) by ultrasound and microbubble-mediated delivery. Eight-week-old male C57BL/6J mice (wild type) were subjected to bilateral renal artery occlusion for 30min followed by 24h of reperfusion. We evaluated FAO, proliferation, and autophagy in vitro and in vivo. In addition, we evaluated the concentrations of blood urea nitrogen and creatinine, evaluated kidney ultrastructure and so on. Results In vivo studies showed that activation of CCND1 prevented AKI-induced lipid accumulation, kidney tubule injury and kidney function declined after ischemia-reperfusion injury. Compared to test control, the treatment significantly (p<0.05) reduced the concentrations of blood urea nitrogen and creatinine. Kidney-specific overexpression of CCND1 increased FAO, promoted proliferation and reduced apoptosis. Mechanistically, CCND1 activated the AMPK pathway, which increased the expression of phosphorylation AMP activated protein kinase (p-AMPK) and upregulated FAO. On the other hand, inhibiting the expression of CCND1 worsened the impairment of FAO and disturbed energy metabolism. Conclusion CCND1 improved FAO and reduced lipid accumulation through the active AMPK pathway in kidney proximal tubular epithelial cells (PTECs). Hence, restoring of the expression of CCND1 may offer a novel therapeutic strategy for treating AKI.

#5349 CYCLIN D1 AMELIORATES ACUTE KIDNEY INJURY BY IMPROVING FATTY ACID OXIDATION VIA AMPK PATHWAY

Abstract Background and Aims Acute kidney injury (AKI) is a life-threatening condition. The absence of oxygen during the acute ischemic phase would disturb energy metabolism and cause kidney tubular epithelial cell damage. Fatty Acid Oxidation (FAO) is the main source of energy production of renal proximal tubular epithelial cells. Timely promoting FAO, increasing supplies of energy, and promoting cell proliferation are essential to improve kidney injury, but there is no clinically recognized effective treatment for this. Cyclin D1(CCND1), a member of the cell cycle family, plays a vital role in cell proliferation. Our previous study found that CCND1 improved AKI accompanied with increased fatty acid oxidation. Therefore, we investigated the role and molecular basis for CCND1 involvement in fatty acid oxidation of AKI. Method CCND1 was evaluated in AKI in human kidney proximal tubular epithelial cells (HK-2 cells) and male C57BL/6J mice (wild type). The protective role of CCND1 in AKI was investigated in a mouse model of ischemia-reperfusion AKI treated by ultrasound-microbubble-mediated kidney-specifically transferring CCND1-expressing plasmids in male C57BL/6J mice (wild type). Eight-week-old male C57BL/6J mice (wild type) were subjected to bilateral renal artery occlusion for 30min followed by 24h of reperfusion. We evaluated FAO, proliferation, and autophagy in vitro and in vivo. In addition, we evaluated the concentrations of blood urea nitrogen and creatinine, evaluated kidney ultrastructure and so on. Results In vivo studies had shown that activation of CCND1 can prevent AKI-induced lipid accumulation, kidney tubule injury and kidney function declined after ischemia-reperfusion injury. Compared to test control, the treatment significantly (p < 0.05) lowered the concentrations of blood urea nitrogen and creatinine. Kidney specific overexpression of CCND1 promoted FAO, promoted proliferation and reduced apoptosis. Mechanistically, CCND1 activated the AMPK pathway, which increased the expression of phosphorylation AMP activated protein kinase (p-AMPK) and upregulated FAO. On the contrary, inhibiting the expression of CCND1 exacerbated impairment of FAO and disturbed energy metabolism. Conclusion Thus, CCND1 improved FAO and reduced lipid accumulation via active AMPK pathway in kidney proximal tubular epithelial cells (PTECs). Hence, reconstruction of the expression of CCND1 may be a novel therapeutic strategy for treating AKI.

#5330 CYCLIN D1 AMELIORATES ISCHEMIA/REPERFUSION-INDUCED ACUTE KIDNEY INJURY

Abstract Background and Aims Acute kidney injury (AKI) is a life-threatening condition. The absence of oxygen during the acute ischemic phase would disturb energy metabolism and cause kidney tubular epithelial cell damage. Fatty Acid Oxidation (FAO) is the main source of energy production of renal proximal tubular epithelial cells. Timely promoting FAO, increasing supplies of energy, and promoting cell proliferation are essential to improve kidney injury, but there is no clinically recognized effective treatment for this. Cyclin D1(CCND1), a member of the cell cycle family, plays a vital role in cell proliferation. Our previous study found that CCND1 improved AKI accompanied with increased fatty acid oxidation. Therefore, we investigated the role and molecular basis for CCND1 involvement in fatty acid oxidation of AKI. Method CCND1 was evaluated in AKI in human kidney proximal tubular epithelial cells (HK-2 cells) and male C57BL/6J mice (wild type). The protective role of CCND1 in AKI was investigated in a mouse model of ischemia-reperfusion AKI treated by ultrasound-microbubble-mediated kidney-specifically transferring CCND1-expressing plasmids in male C57BL/6J mice (wild type). Eight-week-old male C57BL/6J mice (wild type) were subjected to bilateral renal artery occlusion for 30min followed by 24h of reperfusion. We evaluated FAO, proliferation, and autophagy in vitro and in vivo. In addition, we evaluated the concentrations of blood urea nitrogen and creatinine, evaluated kidney ultrastructure and so on. Results In vivo studies had shown that activation of CCND1 can prevent AKI-induced lipid accumulation, kidney tubule injury and kidney function declined after ischemia-reperfusion injury. Compared to test control, the treatment significantly (p<0.05) lowered the concentrations of blood urea nitrogen and creatinine. Kidney specific overexpression of CCND1 promoted FAO, promoted proliferation and reduced apoptosis. Mechanistically, CCND1 activated the AMPK pathway, which increased the expression of phosphorylation AMP activated protein kinase (p-AMPK) and upregulated FAO. On the contrary, inhibiting the expression of CCND1 exacerbated impairment of FAO and disturbed energy metabolism. Conclusion Thus, CCND1 improved FAO and reduced lipid accumulation via active AMPK pathway in kidney proximal tubular epithelial cells (PTECs). Hence, reconstruction of the expression of CCND1 may be a novel therapeutic strategy for treating AKI.

FUT1-mediated terminal fucosylation acts as a new target to attenuate renal fibrosis

BackgroundsRenal fibrosis is a common pathologic process of most chronic kidney diseases (CKDs), becoming one of the major public health problems worldwide. Terminal fucosylation plays an important role in physiological homeostasis and pathological development. The present study aimed to explore the role of terminal fucosylation during kidney fibrogenesis and propose a possible anti-fibrosis treatment via suppressing aberrant terminal fucosylation.MethodsWe investigated the expression level of fucosyltransferase1 (FUT1) in CKD patients by using public database. Then, we further confirmed the level of terminal fucosylation by UEA-I staining and FUT1 expression in unilateral ureteral obstruction (UUO)-induced renal fibrosis mice. Immunostaining, qPCR, western blotting and wound healing assay were applied to reveal the effect of FUT1 overexpression in human kidney proximal tubular epithelial cell (HK-2). What’s more, we applied terminal fucosylation inhibitor, 2-Deoxy-D-galactose (2-D-gal), to determine whether suppressing terminal fucosylation ameliorates renal fibrosis progression in vitro and in vivo.ResultsHere, we found that the expression of FUT1 significantly increased during renal fibrosis. In vitro experiments showed upregulation of epithelial-mesenchymal transition (EMT) after over-expression of FUT1 in HK-2. Furthermore, in vivo and in vitro experiments indicated that suppression of terminal fucosylation, especially on TGF-βR I and II, could alleviate fibrogenesis via inhibiting transforming growth factor-β (TGF-β)/Smad signaling.ConclusionsThe development of kidney fibrosis is attributed to FUT1-mediated terminal fucosylation, shedding light on the inhibition of terminal fucosylation as a potential therapeutic treatment against renal fibrosis.

Urinary exosomal miRNA-663a shows variable expression in diabetic kidney disease patients with or without proteinuria

Heterogeneity in the Diabetic Kidney Disease (DKD) diagnosis makes its rational therapeutics challenging. Although albuminuria characterizes DKD, reports also indicate its prevalence among non-proteinuric. Recent understanding of disease progression has thus inclined the focus on proximal tubular cell damage besides the glomeruli. A non-invasive approach exploiting exosomal miRNA derived from human kidney proximal tubular cell line was, hence, targeted. Upon miRNA profiling, three miRNAs, namely, hsa-miR-155-5p, hsa-miR-28-3p, and hsa-miR-425-5p were found to be significantly upregulated, while hsa-miR-663a was downregulated under diabetic conditions. Among these, hsa-miR-663a downregulation was more pronounced in non-proteinuric than proteinuric DKD subjects and was thus selected for the bioinformatics study. Ingenuity Pathway Analysis (IPA) narrowed on to IL-8 signaling and inflammatory response as the most enriched ‘canonical pathway’ and ‘disease pathway’ respectively, during DKD. Further, the putative gene network generated from these enriched pathways revealed experimentally induced diabetes, renal tubular injury, and decreased levels of albumin as part of mapping under ‘disease and function’. Genes target predictions and annotations by IPA reiterated miR-663a’s role in the pathogenesis of DKD following tubular injury. Overall, the observations might offer an indirect reflection of the underlying mechanism between patients who develop proteinuria and non-proteinuria.

Reducing GEF-H1 Expression Inhibits Renal Cyst Formation, Inflammation, and Fibrosis via RhoA Signaling in Nephronophthisis.

Nephronophthisis (NPHP) is the most prevalent monogenic disease leading to end-stage renal failure in childhood. RhoA activation is involved in NPHP pathogenesis. This study explored the role of the RhoA activator guanine nucleotide exchange factor (GEF)-H1 in NPHP pathogenesis. We analyzed the expression and distribution of GEF-H1 in NPHP1 knockout (NPHP1KO) mice using Western blotting and immunofluorescence, followed by GEF-H1 knockdown. Immunofluorescence and renal histology were used to examine the cysts, inflammation, and fibrosis. A RhoA GTPase activation assay and Western blotting were used to detect the expression of downstream GTP-RhoA and p-MLC2, respectively. In NPHP1 knockdown (NPHP1KD) human kidney proximal tubular cells (HK2 cells), we detected the expressions of E-cadherin and α-smooth muscle actin (α-SMA). In vivo, increased expression and redistribution of GEF-H1, and higher levels of GTP-RhoA and p-MLC2 in renal tissue of NPHP1KO mice were observed, together with renal cysts, fibrosis, and inflammation. These changes were alleviated by GEF-H1 knockdown. In vitro, the expression of GEF-H1 and activation of RhoA were also increased, with increased expression of α-SMA and decreased E-cadherin. GEF-H1 knockdown reversed these changes in NPHP1KD HK2 cells. Thus, the GEF-H1/RhoA/MLC2 axis is activated in NPHP1 defects and may play a pivotal role in NPHP pathogenesis.

Toxicity and efficacy of green tea catechin derivative-based micellar nanocomplexes for anticancer protein delivery.

Toxicity towards non-tumor cells during anticancer therapy can be reduced by using nanoscale systems for anticancer drug delivery. Usually only the loaded drug has anticancer activity. Recently, micellar nanocomplexes (MNCs) comprising green tea catechin derivatives for the delivery of the anticancer proteins, such as Herceptin, have been developed. Herceptin as well as the MNCs without the drug were effective against HER2/neu-overexpressing human tumor cells and had synergistic anticancer effects in vitro and in vivo. It remained unclear which kinds of negative effects the MNCs had on tumor cells exactly, and which of their components mediated them. Also, it was unclear if MNC has any toxicity effects on the normal cells of vital human organ systems. Herein we examined the effects of Herceptin-MNCs and their individual components on human breast cancer cells and on normal primary human endothelial and kidney proximal tubular cells. We applied a novel in vitro model that predicts nephrotoxicity in humans with high accuracy, as well as high-content screening and microfluidic mono- and co-culture models to thoroughly address effects on various cell types. The results showed that MNCs alone were profoundly toxic for breast cancer cells, and induced apoptosis regardless of HER2/neu expression levels. Apoptosis was induced by both green tea catechin derivatives contained within MNCs. In contrast, MNCs were not toxic for normal human cells, and the probability was low that MNCs would be nephrotoxic in humans. Together, the results supported the hypothesis that green tea catechin derivative-based MNCs could improve efficacy and safety of therapies with anticancer proteins.

Upregulation of Thioredoxin Reductase 1 Expression by Flavan-3-Ols Protects Human Kidney Proximal Tubular Cells from Hypoxia-Induced Cell Death.

Renal hypoxia and its associated oxidative stress is a common pathway for the development of kidney diseases, and using dietary antioxidants such as flavan-3-ols to prevent kidney failure has received much attention. This study investigates the molecular mechanism by which flavan-3-ols prevent hypoxia-induced cell death in renal tubular epithelial cells. Human kidney proximal tubular cells (HKC-8) were exposed to hypoxia (1% O2) in the presence of flavan-3-ols (catechin, epicatechin, procyanidin B1, and procyanidin B2). Cell death was examined using flow cytometric analysis. Gene expression was determined using a PCR array and Western blotting, and its network and functions were investigated using STRING databases. Here, we show that the cytoprotective activity of catechin was the highest among these flavan-3-ols against hypoxia-induced cell death in cultured HKC-8 cells. Exposure of HKC-8 cells to hypoxia induced oxidative stress leading to up-regulation of DUOX2, NOX4, CYBB and PTGS2 and down-regulation of TXNRD1 and HSP90AA1. Treatment with catechin or other flavan-3-ols prevented the down-regulation of TXNRD1 expression in hypoxic HKC-8 cells. Overexpression of TXNRD1 prevented hypoxia-induced cell death, and inactivation of TXNRD1 with TRi-1, a specific TXNRD1 inhibitor, reduced the catechin cytoprotection against hypoxia-induced HKC-8 cell death. In conclusion, flavan-3-ols prevent hypoxia-induced cell death in human proximal tubular epithelial cells, which might be mediated by their maintenance of TXNRD1 expression, suggesting that enhancing TXNRD1 expression or activity may become a novel therapeutic strategy to prevent hypoxia-induced kidney damage.

ZIP14 is involved in iron deposition and triggers ferroptosis in diabetic nephropathy.

Ferroptosis is caused by lipid peroxidation and iron accumulation and can cause cell death. Abnormally expressed iron transporters are involved in ferroptosis in a variety of diseases. ZRT/IRT-like protein 14 (ZIP14) is a transport protein that can mediate cellular uptake of iron, zinc, and manganese. Herein, we have tested the hypothesis that the divalent metal transporter ZIP14 is involved in the initiation of ferroptosis in diabetic nephropathy (DN). DN was induced in 8-week-old male rats by streptozotocin before analysis of the degree of renal tubular injury. In addition, an in vitro model of DN in human kidney proximal tubular cell line was used. We showed that ZIP14 was up-regulated and ferrous iron (Fe2+) levels increased both in vivo and in vitro. Expression of glutathioneperoxidase4 and the level of glutathione were reduced, whereas that of malondialdehyde (MDA) increased. Ferrostatin-1 (Fer-1) treatment reduced the expression of ZIP14 and the levels of Fe2+ and MDA, which is consistent with ferroptosis. Fer-1 improved kidney function in DN rats. This was characterized by urine levels of protein-to-creatinine ratio, α1-microglobulin, and N-acetyl-β-D-glucosaminidase. Our study demonstrates a novel role for ZIP14 in diabetic kidney injury mediated by ferroptosis, and suggests a potential new therapeutic approach for the treatment of diabetic nephropathy.

Fatty acid amide hydrolase (FAAH) inhibition mitigates TGF‐β1‐induced fibrogenesis via the anandamide‐COX‐2‐dependent pathway

Chronic proximal tubular injury with subsequent fibrosis is the key factor in the transition of acute kidney injury (AKI) to chronic kidney disease (CKD). An increasing body of evidence has shown that endocannabinoids such as anandamide (AEA) and 2‐arachidonoylglycerol (2AG) and their cannabinoid receptors (CBs) play important roles in renal diseases. It remains unclear whether substrates or metabolites of AEA‐metabolizing enzyme FAAH participate in fibrogenesis of kidneys. Though AEA binds the CB1 receptor with high binding affinity, its in vivo pharmacological effects mediated by cannabinoid receptors are of short duration. Likely, active metabolites produced from the rapid catabolism of AEA exert physiological actions. We have previously showed that inhibition of FAAH protects against TGF‐β1‐induced damages via actions independent of CBs in renal tubular cells. Therefore, our aims are to study the effects of downstream metabolites derived from FAAH as well as AEA‐ cyclooxygenase‐2 (COX‐2) pathways on TGF‐β1‐induced renal fibrogenesis. To produce the AKI to CKD transition model, male wild type (WT) C57BL6 and Faah−/− mice were subjected to post ischemia‐reperfusion injury (PIR) by unilateral kidney ischemia‐reperfusion and contralateral nephrectomy 10 days after ischemia‐reperfusion. Our previous studies showed that Faah−/− mice protected against PIR‐induced renal fibrogenesis. Here, LC‐MS/MS assay demonstrated that PIR‐injured WT mice had a significant downregulation of renal AEA level, which was blocked in Faah−/−‐PIR mice (68% reduction in WT‐PIR versus 12% in Faah−/−‐PIR mice compared with WT‐sham group, p<0.001), whereas 2AG showed no difference between WT‐PIR and Faah−/−‐PIR mice (1.2‐fold versus 1.1‐fold increase, p>0.9). In addition, Faah−/− mice did not show difference in the levels of arachidonic acid (AA) (1.13‐fold to WT‐sham, p=0.25), the downstream metabolites of FAAH. Our previous in vitro studies showed that TGF‐β1‐induced profibrotic effects in HK‐2 cells (human kidney proximal tubular epithelial cells) were abolished after the treatment of FAAH inhibitor (PF‐04457845, PF, 1μM) in a CB2‐independent manner. In the current study, blockage of AEA‐COX‐2 derived prostamides pathway by a substrate‐selective COX‐2 inhibitor (LM‐4131, 300nM) reversed the decreased level of a profibrotic marker α‐smooth muscle actin (α‐SMA) caused by PF (1.9‐fold in TGF‐β1, 0.83‐fold in PF+TGF‐β1 and 2.88‐fold in PF+LM‐4131+TGF‐β1 compared to the control group, p<0.0001). Further, supplement of AA did not reverse the protection of FAAH inhibition against TGF‐β1‐induced expression of α‐SMA (2.53‐fold in TGF‐β1, 0.62‐fold in PF+TGF‐β1 versus 0.48‐fold in AA+PF+TGF‐β1 compared to the control group, p>0.99). The AEA‐COX‐2 metabolite, prostamide E2 mimicked the protective effect of FAAH inhibition against TGF‐β1‐induced α‐SMA expression (2.17‐fold in TGF‐β1 vs. 0.9‐fold in prostamide E2 +TGF‐β1 compared to the control group, p<0.0001). Overall, the present study suggests that inactivation of FAAH augments the actions of downstream metabolites of AEA‐COX‐2, which mediates the protection against TGF‐β1‐induced renal fibrogenesis.

Cigarette Smoke Exposure Increases Glucose-6-phosphate Dehydrogenase, Autophagy, Fibrosis, and Senescence in Kidney Cells In Vitro and In Vivo.

Cigarette smoke (CS) is a risk factor for chronic obstructive pulmonary disease. We attempted to investigate fully the possible effects of CS on kidney cells. We found that the viability of a human kidney proximal tubular epithelial cell line (HK-2 cells) was decreased after treatment with CS extract (CSE). In particular, the effects of CSE at low concentrations did not change the expression of apoptosis and necrosis. Furthermore, CSE increased autophagy- and fibrosis-related proteins in HK-2 cells. Senescence-related proteins and the senescence-associated secretory phenotype (SASP) increased after HK-2 cells were treated with CSE. In addition, both RNA sequencing and gene set enrichment analysis data revealed that glucose-6-phosphate dehydrogenase (G6PD) in the reactive oxygen species (ROS) pathway is responsible for the changes in CSE-treated HK-2 cells. CSE increased G6PD expression and its activity. Moreover, the inhibition of G6PD activity increased senescence in HK-2 cells. The inhibition of autophagy reinforced senescence in the CSE-treated cells. In a mouse model of CS exposure, CS caused kidney damage, including tubular injury and glomerulosclerosis. CS increased fibrosis, autophagy, and G6PD expression in kidney tissue sections. In conclusion, CS induced G6PD expression, autophagy, fibrosis, and senescence in kidney cells. G6PD has a protective role in CS-induced nephrotoxicity.