Dual Immunoglobulin Domain-Containing Cell Adhesion Molecule Increases Early in Renal Tubular Cell Injury and Plays Anti-Inflammatory Role

Dual immunoglobulin domain-containing cell adhesion molecule (DICAM) is a type I transmembrane protein that presents in various cells including renal tubular cells. This study evaluated the expression and protective role of DICAM in renal tubular cell injury. HK-2 cells were incubated and treated with lipopolysaccharide (LPS, 30 μg/mL) or hydrogen peroxide (H2O2, 100 μM) for 24 h. To investigate the effect of the gene silencing of DICAM, small interfering RNA of DICAM was used. Additionally, to explain its role in cellular response to injury, DICAM was overexpressed using an adenoviral vector. DICAM protein expression levels significantly increased following treatment with LPS or H2O2 in HK-2 cells. In response to oxidative stress, DICAM showed an earlier increase (2-4 h following treatment) than neutrophil gelatinase-associated lipocalin (NGAL) (24 h following treatment). DICAM gene silencing increased the protein expression of inflammation-related markers, including IL-1β, TNF-α, NOX4, integrin β1, and integrin β3, in H2O2-induced HK-2 cell injury. Likewise, in the LPS-induced HK-2 cell injury, DICAM knockdown led to a decrease in occludin levels and an increase in integrin β3, IL-1β, and IL-6 levels. Furthermore, DICAM overexpression followed by LPS-induced HK-2 cell injury resulted in an increase in occludin levels and a decrease in integrin β1, integrin β3, TNF-α, IL-1β, and IL-6 levels, suggesting an alleviating effect on inflammatory responses. DICAM was elevated in the early stage of regular tubular cell injury and may protect against renal tubular injury through its anti-inflammatory properties. DICAM has a potential as an early diagnostic marker and therapeutic target for renal cell injury.

Urinary matrix metalloproteinase-7 is a sensitive biomarker to evaluate renal tubular injury in patients with minimal change disease and focal segmental glomerulosclerosis

Objective

To explore the advantages of urinary matrix metalloproteinase-7 (MMP-7) in evaluating renal tubular injury in minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) patients compared with urinary cystatin C (CysC) and retinol-binding protein (RBP).

Methods

Serum and urine samples were collected from 20 healthy volunteers, and 40 MCD and 20 FSGS patients. Serum and urinary MMP-7 levels were measured by enzyme-linked immunosorbent assay. Urinary total protein, CysC and RBP levels were measured by automatic specific protein analyzer and compared with urinary creatinine level for calibration. The renal tissue serial sections were stained by MMP-7 immunohistochemistry and periodic acid-Schiff.

Results

Under light microscopy, MMP-7 granular weak positive expression was showed sporadically in the cytoplasm of a few renal tubular epithelial cells without obvious morphological changes in MCD patients, and MMP-7-positive expression was observed in the cytoplasm of some renal tubular epithelial cells in FSGS patients. There was no significant difference in serum MMP-7 level among the three groups. Compared with the control group, the urinary MMP-7 level in MCD patients was higher, but urinary CysC and RBP levels were not increased significantly. Compared with the control group and MCD patients, urinary MMP-7, CysC and RBP levels in FSGS patients were upregulated significantly.

Conclusions

Urinary MMP-7 could not only evaluate the mild renal tubular epithelial cells injury in MCD patients with massive proteinuria, but also evaluate the continuous renal tubular epithelial cells injury in FSGS patients.

The Molecular Mechanism of Renal Tubulointerstitial Inflammation Promoting Diabetic Nephropathy

Diabetic nephropathy (DN) is a common complication affecting many diabetic patients, leading to end-stage renal disease. However, its pathogenesis still needs to be fully understood to enhance the effectiveness of treatment methods. Traditional theories are predominantly centered on glomerular injuries and need more explicit explanations of recent clinical observations suggesting that renal tubules equally contribute to renal function and that tubular lesions are early features of DN, even occurring before glomerular lesions. Although the conventional view is that DN is not an inflammatory disease, recent studies indicate that systemic and local inflammation, including tubulointerstitial inflammation, contributes to the development of DN. In patients with DN, intrinsic tubulointerstitial cells produce many proinflammatory factors, leading to medullary inflammatory cell infiltration and activation of inflammatory cells in the interstitial region. Therefore, understanding the molecular mechanism of renal tubulointerstitial inflammation contributing to DN injury is of great significance and will help further identify key factors regulating renal tubulointerstitial inflammation in the high glucose environment. This will aid in developing new targets for DN diagnosis and treatment and expanding new DN treatment methods.

Inhibition of ferroptosis of renal tubular cells with total flavones of Abelmoschus manihot alleviates diabetic tubulopathy

Ferroptosis-related renal tubular lesions play important roles in diabetic kidney disease (DKD) progression, and these pathophysiological responses are collectively described as diabetic tubulopathy (DT), which lacks an effective treatment. Total flavones from Abelmoschus manihot (TFA), a natural extract that extensively used in patients with chronic kidney disease, has been used for treatment of renal tubular injury in DKD; however, whether TFA alleviates DT and its potential mechanisms remain unclear. Hence, we investigated the effects of TFA, compared to dapagliflozin, in DT management both in vivo and in vitro, using a DKD rat model and the NRK-52 E cells. Following modeling, the DKD rats received TFA, dapagliflozin, or vehicle for 6 weeks. For the in vitro research, the NRK-52 E cells were exposed to advanced glycation end products (AGEs) plus ferrostatin-1 (Fer-1), dapagliflozin, or TFA. Changes in biochemical parameters and renal tubular injury were analyzed in vivo, while changes in ferroptosis of renal tubular cells and the ferroptosis-related proteins expression were analyzed both in vivo and in vitro. We found that TFA and dapagliflozin improved biochemical parameters, renal tubular injury, and ferroptosis in the DKD rats. Moreover, TFA and dapagliflozin inhibited ferroptosis by ameliorating iron deposition, lipid peroxidation capacity, and ferroptosis-related proteins expression in vitro, which was similar to the effects of Fer-1. Collectively, this study demonstrated that TFA treated DT in a manner similar to dapagliflozin by inhibiting ferroptosis of renal tubular cells via improving iron deposition and antioxidant capacity. Our findings provide new pharmacological evidence for TFA application in DT treatment.

Basigin is released in extracellular vesicles derived from the renal tubular epithelium in response to albuminuria

AIM

Irrespective of the cause, albumin/proteinuria induces tubulointerstitial damage and accelerates the progression of kidney diseases. Our series of studies demonstrated that proteinuria, an independent prognostic factor for chronic kidney disease (CKD), is correlated with urinary basigin/CD147 (Bsg) levels. We examined the morphology and origin of Bsg in the tubular lumen through the effects of filtered glucose and protein solutes on the tubules.

METHODS

Diabetic kidney disease (DKD) patients (N = 50) were treated with spironolactone 25 mg for 4 weeks or by conservative treatment. The associations between urinary Bsg values and clinical indicators were examined. Primary-cultured proximal tubular epithelial cells (PTECs) from human adult kidneys were exposed to high glucose or bovine serum albumin (BSA).

RESULTS

In patients with early phase DKD, urinary Bsg levels were closely correlated with proteinuria but not HbA1c. Full-length Bsg on extracellular vesicles (EVs) was investigated primarily in urine collected from DKD patients. EVs obtained from the urine of DKD patients included Bsg and SGLT2 proteins. Notably, spironolactone treatment concomitantly suppressed the release of Bsg-bearing EVs in correlation with decreased albuminuria. Exposure of PTECs to BSA (but not high glucose) enhanced the storage of supernatant Bsg in EVs despite the absence of exposure-specific changes in Bsg transcription.

CONCLUSION

Proteinuria induces the release of Bsg-bearing EVs derived from PTECs into the tubular lumen.

Research progress on extracellular vesicles in the renal tubular injury of diabetic kidney disease

Diabetic kidney disease (DKD) is a severe microvascular complication of diabetes and is a chronic progressive condition. It is also a common cause of end-stage renal disease (ESRD), which is characterized by proteinuria or a progressive decline in the glomerular filtration rate. Due to their dependence on high-energy and aerobic metabolism, renal tubules are more susceptible to the metabolic disturbances associated with DKD, leading to inflammation and fibrosis. Consequently, tubular injury has become a recent research focus, and significant advancements have been made in studying the role of extracellular vesicles in DKD-associated tubular injury. This review aimed to elucidate the mechanisms and potential applications of different types of extracellular vesicles in tubular injury in DKD to provide new insights for the prevention and treatment of DKD.

Artemether attenuates renal tubular injury by targeting mitochondria in adriamycin nephropathy mice

Chronic kidney disease (CKD) is complex and current treatment remains limited. As we know, glomerular injury plays a dominant role in kidney disease progression. However, accumulating evidence demonstrated that renal tubules, rather than being victims or bystanders, are major initiators in renal fibrosis progression. Renal tubules are rich in mitochondria and mitochondrial dysfunction may participate in renal tubular phenotypic changes and ultimately promote renal fibrosis. Previous studies have proved that artemether displayed renal protective effects, but the mechanisms remain unclear. In this experiment, we showed that artemether reduced urinary protein/creatinine ratio and attenuated renal tubular injury. Both in vivo and in vitro results indicated that artemether could restore renal tubular phenotypic alterations. Meanwhile, the unbalanced expressions of Bax and Bcl-xL in renal tubules were restored by artemether. In addition, artemether also regulated mitochondrial pyruvate metabolism, increased mitochondrial biogenesis, and improved mitochondrial function. Taken together, this study suggested that artemether could attenuate renal tubular injury by regulating mitochondrial biogenesis and function. It has great potential to be translated to the clinic as a therapeutic agent for treating kidney diseases, especially those associated with renal tubular injury.

NAD+ ameliorates endotoxin-induced acute kidney injury in a sirtuin1-dependent manner via GSK-3β/Nrf2 signalling pathway

Acute kidney injury (AKI) is a substantial worldwide public health concern with no specific and effective therapies in clinic. NAD⁺ is a pivotal determinant of cellular energy metabolism involved in the progression of AKI; however, its mechanism in kidney injury remains poorly understood. Sirtuin 1 (SIRT1) is an NAD⁺‐dependent deacetylase associated with renal protection and acute stress resistance. In this study, we have investigated the role of NAD⁺ in AKI and the potential mechanism(s) involved in its renoprotective effect. NAD⁺ was notably decreased and negatively correlated with kidney dysfunction in AKI, restoring NAD⁺ with NMN significantly ameliorates LPS‐induced oxidative stress and apoptosis and attenuates renal damage. We also found that the protection of NAD⁺ is associated with SIRT1 expressions and performs in a SIRT1‐dependent manner. Inhibition of SIRT1 blunted the protective effect of NAD⁺ and up‐regulated the activity of glycogen synthase kinase‐3β (GSK‐3β) that was concomitant with mitigated Nrf2 nuclear accumulation, thereby exacerbates AKI. These findings suggest that NAD⁺/SIRT1/GSK‐3β/Nrf2 axis is an important mechanism that can protect against AKI which might be a potential therapeutic target for the treatment of AKI.

Melatonin alleviates renal injury by activating mitophagy in diabetic nephropathy

Diabetic nephropathy (DN) causes serious renal tubule and interstitial damage, but effective prevention and treatment measures are lacking. Abnormal mitophagy may be involved in the progression of DN, but its upstream and downstream regulatory mechanisms remain unclear. Melatonin, a pineal hormone associated with circadian rhythms, is involved in regulating mitochondrial homeostasis. Here, we demonstrated abnormal mitophagy in the kidneys of DN mice or high glucose (HG)-treated HK-2 cells, which was accompanied by increased oxidative stress and inflammation. At the same time, the melatonin treatment alleviated kidney damage. After mitochondrial isolation, we found that melatonin promoted AMPK phosphorylation and accelerated the translocation of PINK1 and Parkin to the mitochondria, thereby activating mitophagy, reducing oxidative stress, and inhibiting inflammation. Interestingly, the renal protective effect of melatonin can be partially blocked by downregulation of PINK1 and inhibition of AMPK. Our studies demonstrated for the first time that melatonin plays a protective role in DN through the AMPK-PINK1-mitophagy pathway.

LncRNA MALAT1 Aggravates Renal Tubular Injury via Activating LIN28A and the Nox4/AMPK/mTOR Signaling Axis in Diabetic Nephropathy

BACKGROUND

Diabetic nephropathy (DN) is a serious complication among patients with diabetes. Elucidating its pathogenesis is crucial for identifying novel biomarkers and therapeutic targets for DN.

METHODS

DN tissues were harvested for examining MALAT1, LIN28A and Nox4. Human kidney-2 (HK-2) cells were treated with high glucose (HG) for establishing a cell model of DN. Cell viability was examined by MTT assay. HG-induced cell apoptosis and secretion of TNF-α and IL-6 were analyzed by TUNEL and ELISA assays, respectively. RIP and RNA pull-down assays were applied to analyze the interaction between MALAT1, LIN28A and Nox4 in HK-2 and human embryonic kidney 293T (HEK-293T) cells. A rat model of DN was established to determine the role of MALAT1 in DN in vivo.

RESULTS

MALAT1, LIN28A and Nox4 were upregulated in DN tissues and HG-treated HK-2 cells. Overexpression of MALAT1, LIN28A or Nox4 reduced cell viability and enhanced cell apoptosis, ROS generation and secretion of inflammatory cytokines in HG-treated HK-2 cells, whereas knockdown of MALAT1, LIN28A or Nox4 exerted opposite effects. Furthermore, MALAT1 directly interacted with LIN28A. Moreover, MALAT1 facilitated the interaction between LIN28A and Nox4 to increase Nox4 stability. Knockdown of Nox4 relieved HG-induced injury by suppressing the AMPK/mTOR signaling in HK-2 cells. Knockdown of MALAT1 alleviated renal tubular epithelial injury by suppressing LIN28A and the Nox4/AMPK/TOR signaling in DN.

CONCLUSION

MALAT1 activates the AMPK/mTOR signaling via interacting with LIN28A to stabilize Nox4 mRNA, thereby aggravating high glucose-induced renal tubular epithelial injury. Our findings provide potential therapeutic targets for DN.

Glucagon-Like Peptide 1 Receptor Agonist Improves Renal Tubular Damage in Mice with Diabetic Kidney Disease

PURPOSE

This study aims to investigate the renal protective effect of glucagon-like peptide 1 receptor agonist (GLP-1RA) on improving renal tubular damage in diabetic kidney disease (DKD) and to explore the potential mechanism of GLP-1RA on renal tubular protection.

METHODS

Long-acting GLP-1RA was used to treat DKD mice for 12 weeks. The label-free quantitative proteomic analysis of renal proteins was conducted to explore the differentially expressed proteins (DEPs) in the renal tissues of the control, DKD and GLP-1RA groups. The DEPs and markers of renal tubular injury were verified by qPCR in vivo and in vitro. The expression of glucagon-likepeptide-1 receptor (GLP-1R) in renal tubules was determined by immunofluorescence staining.

RESULTS

GLP-1RA treatment significantly improved the tubular damages in kidney tissues of DKD mice and mTEC cells stimulated by high glucose (HG). Proteomics analysis revealed that 30 proteins in kidney tissue were differentially expressed among three groups. Seminal vesicle secretory protein 6 (SVS6) was the most differentially expressed protein in kidney tissues among three groups of mice. The expression changes of Svs6 mRNA in vitro and in vivo detected by qPCR were consistent with the results of proteomic analysis. Furthermore, reduction of Svs6 expression by SVS6 siRNA could attenuate HG-stimulated tubular injury in mTEC cells. Immunofluorescence staining also found that GLP-1R was widely expressed in renal tubules in vitro and in vivo.

CONCLUSION

GLP-1RA significantly improved renal tubular damage in DKD mice. SVS6 may be a potential therapeutic target for GLP-1RA in the treatment of DKD.

Long-Term Clinical and Immunological Impact of Severe COVID-19 on a Living Kidney Transplant Recipient - A Case Report

The long-term impact of COVID-19 on transplant recipients remains unknown. We describe the case of a 30-year-old male kidney transplant recipient from Wuhan, China that was treated for severe COVID-19 in February 2020. He suffered an acute lung and renal injury and required systemic treatment including adjustment of his immunosuppressant regime. He was followed up to 1-year after discharge. No chronic lung fibrosis or deterioration of his pulmonary function was observed. Despite COVID-19 mediated damage to his renal tubular cells, no transplant rejection occurred. His immunological profile demonstrated both cellular anti-SARS-CoV-2 reactivity and specific humoral immunity, indicating that it is beneficial for the transplanted patients to be immunized with SARS-CoV-2 virus vaccine. This case will help guide clinical decision making for immunocompromised individuals that become infected with SARS-CoV-2.

LncRNA NEAT1 accelerates renal tubular epithelial cell damage by modulating mitophagy via miR-150-5p-DRP1 axis in diabetic nephropathy

NEW FINDINGS

What is the central question of this study? Diabetic nephropathy (DN) is a severe complication of diabetes correlated with a higher mortality rate in diabetic patients. Renal tubular injury participates in the pathogenesis of DN. We aimed to uncover the biological function of the NEAT1-miR-150-5p-DRP1 axis in an in vitro model of DN and elaborate the potential mechanisms. What is the main finding and its importance? NEAT1 facilitated high glucose-induced damage in HK-2 cells by reducing mitophagy via the miR-150-5p-DRP1 axis, which sheds light on DN pathogenesis and reveals a potential treatment for DN.

ABSTRACT

Diabetic nephropathy (DN) is a severe complication in diabetic patients, with a high mortality rate. Renal tubular injury is involved in the pathogenesis of DN. In this study, we aimed to uncover the regulatory roles of the NEAT1-miR-150-5p-DRP1 axis in an in vitro model of DN and its possible mechanisms. High glucose-challenged HK-2 cells were used as an in vitro DN model. NEAT1, miR-150-5p and DRP1 levels were assessed by RT-qPCR. Cell viability was determined by the MTT assay. MitoSOX Red and JC-1 were used to evaluate intracellular production of reactive oxygen species and mitochondrial membrane potential, respectively. Lactate dehydrogenase release and superoxide dismutase activity were assessed with commercial kits. The protein levels of DRP1, p62, BECN1(beclin 1) and BNIP3 were determined by western blotting. The interaction between NEAT1 (DRP1) and miR-150-5p was verified by a dual-luciferase reporter assay and an RNA immunoprecipitation assay. Our results showed that in response to high glucose the NEAT1 and DRP1 levels were upregulated, whereas the miR-150-5p level was downregulated in HK-2 cells. Knockdown of NEAT1 or DRP1 in high glucose-challenged HK-2 cells inhibited excessive reactive oxygen species production and lactate dehydrogenase release, increased cell viability, mitochondrial membrane potential and superoxide dismutase activity and enhanced mitophagy. Inhibition of miR-150-5p resulted in the opposite results. Mechanistically, NEAT1 sponged miR-150-5p to increase the DRP1 level. Moreover, silencing of NEAT1 or DRP1 could counteract miR-150-5p inhibition-induced deleterious effects. Collectively, our findings indicate that NEAT1 facilitates high glucose-induced damage in HK-2 cells by suppressing mitophagy via the miR-150-5p-DRP 1 axis, which sheds light on a novel mechanism of DN.

Positive correlation between renal tubular flattening and renal tubular injury/interstitial fibrosis in murine kidney disease models

The number of patients with chronic kidney disease (CKD) is growing continuously globally. In order to study pathogenesis and mechanisms, many animal models have been developed, including spontaneous, genetic, and induced models. Although each type of CKD shows disease-specific tissue changes in the early stages, tubular disorder and interstitial fibrosis histologically occur in the course of progression to end-stage renal failure. Therefore, the quantification of tubular disorder and interstitial fibrosis in CKD research using animal models is essential for measuring the degree of CKD severity and, thus, efficacy of therapeutic agents. Several strategies have been used to quantify interstitial fibrosis. Among scoring factors, renal tubular flattening can be quantitatively evaluated easily and inexpensively. However, the diagnostic value of renal tubular flattening evaluation has not been investigated previously. Therefore, in this study, we investigated the correlation between renal tubular flattening and interstitial fibrosis or renal tubular injury markers. We observed a strong correlation between the degree of tubular injury/interstitial fibrosis and renal tubular flattening in three types of mouse renal disease model. This is advantageous because rapidly advancing technologies such as artificial intelligence and image processing can be easily applied; hence, a more precise, objective, and quantitative diagnosis should be possible in the future.

Critically ill, tubular injury, delayed early recovery: characteristics of acute kidney disease with renal oxalosis

Objects

This study aimed to analyze the clinicopathological features of acute kidney disease (AKD) with renal oxalosis.

Methods

Data for biopsy-proven AKD with oxalosis diagnosed from Jan 2011 to Oct 2018 was collected. The underlying diseases, dietary habits, clinical and pathological characteristics of newly emerging kidney disease were analyzed. The long-term renal prognosis was observed.

Results

A total of 23 patients were included, comprised of 18 men and 5 women with a mean age of 51.6 ± 15.9 years. The peak Scr was 669.9 ± 299.8 μmol/L, and 95.7% of patients had stage 3 acute kidney injury (AKI). Drug-induced tubulointerstitial nephritis (TIN) was the most common cause (65.2%) of AKD, followed by severe nephrotic syndrome (17.4%). All patients had pathological changes indicating TIN, and 11 patients were complicated with the newly emerging glomerular disease (GD). The risk of oxalosis caused by increased enterogenous oxalate absorption accounted for only 26.1%, and others came from new kidney diseases. The majority (75%) of abundant (medium to severe) oxalosis occurred in patients without GD. There were no significant differences in the score for tubular injury (T-IS) and interstitial inflammation with different severities of oxalosis. Rate of Scr decrease (ΔScr%) at 2 weeks was negatively correlated with the severity of oxalosis (R = −0.542, p = 0.037), score for T-IS (R = −0.553, p = 0.033), and age (R = −0.736, p = 0.002). The decrease in Scr at 4 weeks was correlated with T-IS (R = −0.433), but had no correlation with oxalosis.

Conclusions

The present findings revealed that 95.7% of AKD with secondary renal oxalosis occurred in critically ill patients. AKD from tubular injury was the prominent cause. Severe oxalosis contributed to delayed early recovery of AKD.

Aortic Aneurysms, Chronic Kidney Disease and Metalloproteinases

Metalloproteinases (MPs) are proteolytic enzymes involved in extracellular matrix deposition, regulation of cellular signals of inflammation, proliferation, and apoptosis. Metalloproteinases are classified into three families: Matrix-MPs (MMPs), A-Disintegrin-and-Metalloprotease (ADAMs), and the A-Disintegrin-and-Metalloproteinase-with-Thrombospondin-1-like-Domains (ADAMTS). Previous studies showed that MPs are involved in the development of aortic aneurysms (AA) and, concomitantly, in the onset of chronic kidney disease (CKD). CKD has been, per se, associated with an increased risk for AA. The aim of this review is to examine the pathways that may associate MPs with CKD and AA. Several MMPs, such as MMP-2, -8, -9, and TIMP-1 have been shown to damage the AA wall and to have a toxic effect on renal tubular cells, leading to fibrosis. Similarly, ADAM10 and 17 have been shown to degrade collagen in the AA wall and to worsen kidney function via pro-inflammatory stimuli, the impairment of the Renin-Angiotensin-Aldosterone System, and the degradation of structural proteins. Moreover, MMP-2 and -9 inhibitors reduced aneurysm growth and albuminuria in experimental and human studies. It would be important, in the future, to expand research on MPs from both a prognostic, namely, to refine risk stratification in CKD patients, and a predictive perspective, likely to improve prognosis in response to targeted treatments.

Ferroptosis Enhanced Diabetic Renal Tubular Injury via HIF-1α/HO-1 Pathway in db/db Mice

BACKGROUND

Ferroptosis is a recently identified iron-dependent form of cell death as a result of increased reactive oxygen species (ROS) and lipid peroxidation. In this study, we investigated whether ferroptosis aggravated diabetic nephropathy (DN) and damaged renal tubules through hypoxia-inducible factor (HIF)-1α/heme oxygenase (HO)-1 pathway in db/db mice.

METHODS

Db/db mice were administered with or without ferroptosis inhibitor Ferrostatin-1 treatment, and were compared with db/m mice.

RESULTS

Db/db mice showed higher urinary albumin-to-creatinine ratio (UACR) than db/m mice, and Ferrostatin-1 reduced UACR in db/db mice. Db/db mice presented higher kidney injury molecular-1 and neutrophil gelatinase-associated lipocalin in kidneys and urine compared to db/m mice, with renal tubular basement membranes folding and faulting. However, these changes were ameliorated in db/db mice after Ferrostatin-1 treatment. Fibrosis area and collagen I were promoted in db/db mouse kidneys as compared to db/m mouse kidneys, which was alleviated by Ferrostatin-1 in db/db mouse kidneys. HIF-1α and HO-1 were increased in db/db mouse kidneys compared with db/m mouse kidneys, and Ferrostatin-1 decreased HIF-1α and HO-1 in db/db mouse kidneys. Iron content was elevated in db/db mouse renal tubules compared with db/m mouse renal tubules, and was relieved in renal tubules of db/db mice after Ferrostatin-1 treatment. Ferritin was increased in db/db mouse kidneys compared with db/m mouse kidneys, but Ferrostatin-1 reduced ferritin in kidneys of db/db mice. Diabetes accelerated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived ROS formation in mouse kidneys, but Ferrostatin-1 prevented ROS formation derived by NADPH oxidases in db/db mouse kidneys. The increased malondialdehyde (MDA) and the decreased superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GSH-Px) were detected in db/db mouse kidneys compared to db/m mouse kidneys, whereas Ferrostatin-1 suppressed MDA and elevated SOD, CAT, and GSH-Px in db/db mouse kidneys. Glutathione peroxidase 4 was lower in db/db mouse kidneys than db/m mouse kidneys, and was exacerbated by Ferrostatin-1 in kidneys of db/db mice.

CONCLUSIONS

Our study indicated that ferroptosis might enhance DN and damage renal tubules in diabetic models through HIF-1α/HO-1 pathway.

Salvianolic Acid B Protects Against Fatty Acid-Induced Renal Tubular Injury via Inhibition of Endoplasmic Reticulum Stress

Background/Aims: Obesity-related kidney disease is associated with elevated levels of saturated free fatty acids (SFA). SFA lipotoxicity in tubular cells contributes to significant cellular apoptosis and injury. Salvianolic acid B (SalB) is the most abundant bioactive molecule from Radix Salviae Miltiorrhizae. In this study, we investigated the effect of SalB on SFA-induced renal tubular injury and endoplasmic reticulum (ER) stress, in vivo and in vitro. Methods: C57BL/6 mice were assigned to five groups: a control group with normal diet (Nor), high-fat diet group (HFD), and HFD with three different SalB treatment doses, low (SalBL; 3 mg/kg), medium (SalBM; 6.25 mg/kg), and high (SalBH; 12.5 mg/kg) doses. SalB was intraperitoneally injected daily for 4 weeks after 8 weeks of HFD. After 12 weeks, mice were sacrificed and kidneys and sera were collected. Apoptosis and ER stress were induced in human proximal tubule epitelial (HK2) cells by palmitic acid (PA, 0.6 mM), tunicamycin (TM, 1 μg/ml), or thapsigargin (TG, 200 nM) in vitro. Results: C57BL/6 mice fed a high-fat diet (HFD) for 12 weeks exhibited increased apoptosis (Bax and cleaved caspase-3) and ER stress (BIP, P-eIF2α, ATF4, CHOP, ATF6, IRE1α, and XBP1s) markers expression in the kidney, compared with control mice, which were remarkably suppressed by SalB treatment. In vitro studies showed that PA (0.6 mM) induced apoptosis and ER stress in cultured HK2 cells. SalB treatment attenuated all the adverse effects of PA. However, SalB failed to inhibit TM or TG-induced ER stress in HK2 cells. Conclusion: The study indicated that SalB may play an important role in obesity-related kidney injury via mediating SFA-induced ER stress.

GADD45B Promotes Glucose-Induced Renal Tubular Epithelial-Mesenchymal Transition and Apoptosis via the p38 MAPK and JNK Signaling Pathways

Growth arrest and DNA damage-inducible beta (GADD45B) is closely linked with cell cycle arrest, DNA repair, cell survival, or apoptosis in response to stress and is known to regulate the mitogen-activated protein kinase (MAPK) pathway. Here, using an RNA sequencing approach, we determined that GADD45B was significantly upregulated in diabetic kidneys, which was accompanied by renal tubular epithelial-mesenchymal transition (EMT) and apoptosis, as well as elevated MAPK pathway activation. In vitro, GADD45B expression in cultured human kidney proximal tubular epithelial cells (HK-2 cells) was also stimulated by high glucose (HG). In addition, overexpression of GADD45B in HK-2 cells exacerbated renal tubular EMT and apoptosis and increased p38 MAPK and c-Jun N-terminal kinases (JNK) activation, whereas knockdown of GADD45B reversed these changes. Notably, the activity of extracellular regulated kinase (ERK) was not affected by GADD45B expression. Furthermore, inhibitors of p38 MAPK (SB203580) and JNK (SP600125) alleviated HG‐ and GADD45B overexpression-induced renal tubular epithelial-mesenchymal transition and apoptosis. These findings indicate a role of GADD45B in diabetes-induced renal tubular EMT and apoptosis via the p38 MAPK and JNK pathways, which may be an important mechanism of diabetic kidney injury.

PNPLA3 rs738409 is associated with renal glomerular and tubular injury in NAFLD patients with persistently normal ALT levels

BACKGROUND & AIMS

Patatin-like phospholipase domain-containing protein 3 (PNPLA3) rs738409 polymorphism is associated with NAFLD severity and the PNPLA3 gene is expressed in the kidneys, but whether PNPLA3 rs738409 polymorphism is also associated with renal tubular injury (RTI) is uncertain. We assessed the effect of PNPLA3 genotypes on biomarkers of RTI and glomerular function in subjects with NAFLD who had either normal (nALT) or abnormal (abnALT) alanine aminotransaminase levels.

METHODS

Two hundred and seventeen patients with histologically proven NAFLD of which 75 had persistently nALT (below upper limit of normal for 3 months) were included. Multivariable regression analyses were undertaken to test associations between PNPLA3 genotype and biomarkers of kidney dysfunction.

RESULTS

The nALT patient group had higher urinary neutrophil gelatinase-associated lipocalin levels (u-NGAL, a biomarker of RTI) (P < .001), higher albuminuria (P = .039) and greater prevalence of chronic kidney disease (CKD; P = .046) than the abnALT group. The association between PNPLA3 GG genotype and risk of CKD and abnormal albuminuria remained significant after adjustment for kidney risk factors and severity of NAFLD histology, mostly in the nALT group. Similarly, PNPLA3 GG genotype was associated with higher u-NGAL levels in the nALT group, even after adjustment for the aforementioned risk factors and glomerular filtration-based markers (β-coefficient: 22.29, 95% CI: 0.99-43.60, P = .041).

CONCLUSION

Patients with NAFLD and persistently nALT, who carry the PNPLA3 rs738409 G allele, are at higher risk of early glomerular and tubular damage. We suggest PNPLA3 genotyping may help identify patients with NAFLD at higher risk of RTI.

Neutrophil gelatinase-associated lipocalin accurately predicts renal tubular injury in patients with chronic hepatitis B treated with nucleos(t)ide analogs

AIM

Little is known about the impact of long-term use of nucleos(t)ide analogs on tubular function in patients with chronic hepatitis B. Previous studies showed that neutrophil gelatinase-associated lipocalin (NGAL) elevation was associated with renal tubular injury. We evaluated renal function markers and bone mineral density in patients treated long-term with adefovir dipivoxil (ADV) or entecavir (ETV).

METHODS

In this cross-sectional study, we enrolled 78 patients (ADV, 36; ETV: 42), and 21 patients matched for age, observation time, and baseline estimated glomerular filtration rate from each group.

RESULTS

Patients treated with ADV showed a significant increase in serum creatinine and urine β₂ -microglobulin, and decreased estimated glomerular filtration rate and bone mineral density. Furthermore, the median levels of NGAL in patients treated with ADV were significantly higher than those of ETV (12.5 ng/mL vs. 2.5 ng/mL, P = 0.020). The proportions of patients with proteinuria and phosphate <1 mmol/L in the ADV group were higher than those in the ETV group. Additionally, age, β₂ -microglobulin, phosphate, and ADV use were associated with altered NGAL levels on multivariate analysis. Among the commonly used biomarkers, NGAL was the most useful (odds ratio = 5.72; P = 0.005) and specific (92% specificity at 18.1 ng/mL cut-off) in predicting low bone mass.

CONCLUSIONS

Patients with chronic hepatitis B treated long-term with ADV showed elevated urinary NGAL levels. Neutrophil gelatinase-associated lipocalin was more specific in predicting low bone mass during therapy compared with β₂ -microglobulin, phosphate, and creatinine. In general, this analysis examined the value of NGAL as a renal tubular injury indicator, resulting from ADV use.

Transcriptional and Translational Modulation of myo-Inositol Oxygenase (Miox) by Fatty Acids: IMPLICATIONS IN RENAL TUBULAR INJURY INDUCED IN OBESITY AND DIABETES

The kidney is one of the target organs for various metabolic diseases, including diabetes, metabolic syndrome, and obesity. Most of the metabolic studies underscore glomerular pathobiology, although the tubulo-interstitial compartment has been underemphasized. This study highlights mechanisms concerning the pathobiology of tubular injury in the context of myo-inositol oxygenase (Miox), a tubular enzyme. The kidneys of mice fed a high fat diet (HFD) had increased Miox expression and activity, and the latter was related to phosphorylation of serine/threonine residues. Also, expression of sterol regulatory element-binding protein1 (Srebp1) and markers of cellular/nuclear damage was increased along with accentuated apoptosis and loss of tubular brush border. Similar results were observed in cells treated with palmitate/BSA. Multiple sterol-response elements and E-box motifs were found in the miox promoter, and its activity was modulated by palmitate/BSA. Electrophoretic mobility and ChIP assays confirmed binding of Srebp to consensus sequences of the miox promoter. Exposure of palmitate/BSA-treated cells to rapamycin normalized Miox expression and prevented Srebp1 nuclear translocation. In addition, rapamycin treatment reduced p53 expression and apoptosis. Like rapamycin, srebp siRNA reduced Miox expression. Increased expression of Miox was associated with the generation of reactive oxygen species (ROS) in kidney tubules of mice fed an HFD and cell exposed to palmitate/BSA. Both miox and srebp1 siRNAs reduced generation of ROS. Collectively, these findings suggest that HFD or fatty acids modulate transcriptional, translational, and post-translational regulation of Miox expression/activity and underscore Miox being a novel target of the transcription factor Srebp1. Conceivably, activation of the mTORC1/Srebp1/Miox pathway leads to the generation of ROS culminating into tubulo-interstitial injury in states of obesity.

Mitochondrial dysfunction confers albumin-induced NLRP3 inflammasome activation and renal tubular injury

Proteinuria is involved in the development of tubular lesions and in the progressive loss of renal function in chronic kidney diseases via uncertain mechanisms. Growing evidence suggests a pathogenic role of mitochondrial dysfunction in chronic kidney diseases. Therefore, the present study aimed to define the roles of mitochondria in proteinuria-induced renal tubular injury and their underlying mechanisms. Using the albumin-overload mouse model, we observed severe tubular structure damage and striking tubular cell apoptosis. Furthermore, tubular epithelial cells displayed a loss of E-cadherin expression and gained expression of α-smooth muscle actin and vimentin, indicating a cellular phenotypic alteration. Strikingly, these albumin overload-induced abnormalities were robustly blocked by a mitochondrial SOD2 mimic, Mn(III) tetrakis (4-benzoic acid)porphyrin chloride (MnTBAP). In agreement with these results, we observed a marked change in mitochondrial morphology accompanied by mitochondrial cytochrome c release and a copy number reduction of mitochondrial DNA. These alterations were largely reversed by MnTBAP, suggesting a key role for mitochondria-derived oxidative stress in mediating the albumin effect on mitochondrial dysfunction and subsequent tubular injury. Moreover, the NOD-like receptor family, pyrin domain-containing 3 (NLRP3)/caspase-1/cytokine cascade was activated in the kidney by albumin overload and was entirely abolished by MnTBAP. In albumin-treated mouse proximal tubular cells, albumin directly induced ROS production, mitochondrial dysfunction, NLRP3/caspase-1/cytokine cascade activation, cell apoptosis, and cellular phenotypic transition. Similar to our in vivo results, treatment with either MnTBAP or cyclosporin A, a mitochondrial permeability transition pore inhibitor, remarkably attenuated these abnormalities in cells. Taken together, these novel findings demonstrate a potential role for the mitochondrial dysfunction/NLRP3 inflammasome axis in the pathogenesis of proteinuria-induced renal tubular injury.

Exendin-4 attenuates renal tubular injury by decreasing oxidative stress and inflammation in streptozotocin-induced diabetic mice

In this study, we aimed to research the restorative effects of exendin-4, a GLP-1 analog, on renal tubular injury in streptozotocin-induced diabetes model. BALB/c male mice were divided into four groups: non-diabetic, non-diabetic + exendin-4 (3 μg/kg), diabetic and diabetic + exendin-4. In our diabetic model, we observed renal injury mainly in tubular area rather than glomeruli and exendin-4 decreased tubular injury with its glucose lowering effect. Besides, PCNA positive tubular cells, activities of LDH and Na(+)-K(+)-ATPase were also significantly declined by the administration of exendin-4. Furthermore, exendin-4 attenuated the levels of ROS, MDA, 8-OHdG, proinflammatory cytokines (TNF-α, IL-1β), chemokine MCP-1, ICAM-1, and fibrosis-related molecules (transforming growth factor β1 and fibronectin). In consistent with reducing tubular injury, macrophage infiltration and both MCP-1 and ICAM-1 production in tubular cells were decreased. These results indicate that exendin-4 may decrease renal tubular injury seen in the beginning of diabetic nephropathy by decreasing ROS production and inflammation.

Urine neutrophil gelatinase-associated lipocalin and risk of cardiovascular disease and death in CKD: results from the Chronic Renal Insufficiency Cohort (CRIC) Study

BACKGROUND

Chronic kidney disease is common and is associated with increased cardiovascular disease risk. Currently, markers of renal tubular injury are not used routinely to describe kidney health and little is known about the risk of cardiovascular events and death associated with these biomarkers independent of glomerular filtration-based markers (such as serum creatinine or albuminuria).

STUDY DESIGN

Cohort study, CRIC (Chronic Renal Insufficiency Cohort) Study.

SETTING & PARTICIPANTS

3,386 participants with estimated glomerular filtration rate of 20 to 70mL/min/1.73m(2) enrolled from June 2003 through August 2008.

PREDICTOR

Urine neutrophil gelatinase-associated lipocalin (NGAL) concentration.

OUTCOMES

Adjudicated heart failure event, ischemic atherosclerotic event (myocardial infarction, ischemic stroke, or peripheral artery disease), and death through March 2011.

MEASUREMENTS

Urine NGAL measured at baseline with a 2-step assay using chemiluminescent microparticle immunoassay technology on an ARCHITECT i2000SR (Abbott Laboratories).

RESULTS

There were 428 heart failure events (during 16,383 person-years of follow-up), 361 ischemic atherosclerotic events (during 16,584 person-years of follow-up), and 522 deaths (during 18,214 person-years of follow-up). In Cox regression models adjusted for estimated glomerular filtration rate, albuminuria, demographics, traditional cardiovascular disease risk factors, and cardiac medications, higher urine NGAL levels remained associated independently with ischemic atherosclerotic events (adjusted HR for the highest [>49.5ng/mL] vs lowest [≤6.9ng/mL] quintile, 1.83 [95% CI, 1.20-2.81]; HR per 0.1-unit increase in log urine NGAL, 1.012 [95% CI, 1.001-1.023]), but not heart failure events or deaths.

LIMITATIONS

Urine NGAL was measured only once.

CONCLUSIONS

Among patients with chronic kidney disease, urine levels of NGAL, a marker of renal tubular injury, were associated independently with future ischemic atherosclerotic events, but not with heart failure events or deaths.