Bioinformatics analysis of potential key ferroptosis-related genes involved in tubulointerstitial injury in patients with diabetic nephropathy

Diabetic nephropathy (DN) is the primary complication of diabetes mellitus. Ferroptosis is a form of cell death that plays an important role in DN tubulointerstitial injury, but the specific molecular mechanism remains unclear. Here, we downloaded the DN tubulointerstitial datasets GSE104954 and GSE30529 from the Gene Expression Omnibus database. We examined the differentially expressed genes (DEGs) between DN patients and healthy controls, and 36 ferroptosis-related DEGs were selected. Pathway-enrichment analyses showed that many of these genes are involved in metabolic pathways, phosphoinositide 3-kinase/Akt signaling, and hypoxia-inducible factor-1 signaling. Ten of the 36 ferroptosis-related DEGs (CD44, PTEN, CDKN1A, DPP4, DUSP1, CYBB, DDIT3, ALOX5, VEGFA, and NCF2) were identified as key genes. Expression patterns for six of these (CD44, PTEN, DDIT3, ALOX5, VEGFA, and NCF2) were validated in the GSE30529 dataset. Nephroseq data indicated that the mRNA expression levels of CD44, PTEN, ALOX5, and NCF2 were negatively correlated with the glomerular filtration rate (GFR), while VEGFA and DDIT3 mRNA expression levels were positively correlated with GFR. Immune infiltration analysis demonstrated altered immunity in DN patients. Real-time quantitative PCR (qPCR) analysis showed that ALOX5, PTEN, and NCF2 mRNA levels were significantly upregulated in high-glucose-treated human proximal tubular (HK-2) cells, while DDIT3 and VEGFA mRNA levels were significantly downregulated. Immunohistochemistry analysis of human renal biopsies showed positive staining for ALOX5 and NCF2 protein in DN samples but not the controls. These key genes may be involved in the molecular mechanisms underlying ferroptosis in patients with DN, potentially through specific metabolic pathways and immune/inflammatory mechanisms.

Clinical characteristics and prognosis of patients with idiopathic membranous nephropathy with kidney tubulointerstitial damage

BACKGROUND

To investigate the clinical and kidney pathological features and prognosis of idiopathic membranous nephropathy (IMN) with kidney tubulointerstitial damage (TID).

METHODS

Based on the presence or absence of kidney TID by kidney biopsy, 300 patients diagnosed with IMN were categorized into non-TID (TID-) and tubulointerstitial injury (TID+) groups. The clinical and pathological data were analyzed retrospectively. All patients were followed up for 6-24 months after treatment with glucocorticoids (GCs) combined with cyclophosphamide or GCs combined with calcineurin inhibitors (CNIs) to observe treatment effects on patient prognosis.

RESULTS

The patients in the TID + group were older and more likely to be male. The 24-h urine protein, blood urea nitrogen, serum creatinine, cystatin C, β2-microglobulin, and antiphospholipase A2 receptor antibody levels were higher than those in the TID - group and the pathological manifestations were more severe. After 1 year of follow-up, the overall response rate (complete response + partial response) in the TID + group was lower (66.67% vs. 80.89%, p = .022) than in the other. After combined GC and CNI therapy, the complete remission rate in the TID + group was significantly lower than that in the TID - group (13.79% vs. 35.46%, p = .022). The 24-h urine protein level was an independent risk factor for worsening kidney condition (p = .038).

CONCLUSION

Patients with IMN with TID have more severe clinical manifestations and pathological damage and lower remission rates. IMN with TID is a risk factor for worsening kidney condition; however, it is not an independent risk factor.

Kidney injury molecule 1 (KIM-1): a potential biomarker of acute kidney injury and tubulointerstitial injury in patients with ANCA-glomerulonephritis

Background

Kidney injury molecule 1 (KIM-1) is a transmembrane glycoprotein expressed by proximal tubular cells, recognized as an early, sensitive and specific urinary biomarker for kidney injury. Blood KIM-1 was recently associated with the severity of acute and chronic kidney damage but its value in antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis with glomerulonephritis (ANCA-GN) has not been studied. Thus, we analyzed its expression at ANCA-GN diagnosis and its relationship with clinical presentation, kidney histopathology and early outcomes.

Methods

We assessed KIM-1 levels and other pro-inflammatory molecules (C-reactive protein, interleukin-6, tumor necrosis factor α, monocyte chemoattractant protein-1 and pentraxin 3) at ANCA-GN diagnosis and after 6 months in patients included in the Maine-Anjou registry, which gathers data patients from four French Nephrology Centers diagnosed since January 2000.

Results

Blood KIM-1 levels were assessed in 54 patients. Levels were elevated at diagnosis and decreased after induction remission therapy. KIM-1 was associated with the severity of renal injury at diagnosis and the need for kidney replacement therapy. In opposition to other pro-inflammatory molecules, KIM-1 correlated with the amount of acute tubular necrosis and interstitial fibrosis/tubular atrophy (IF/TA) on kidney biopsy, but not with interstitial infiltrate or with glomerular involvement. In multivariable analysis, elevated KIM-1 predicted initial estimated glomerular filtration rate (β = -19, 95% CI -31, -7.6, P = .002).

Conclusion

KIM-1 appears as a potential biomarker for acute kidney injury and for tubulointerstitial injury in ANCA-GN. Whether KIM-1 is only a surrogate marker or is a key immune player in ANCA-GN pathogenesis remain to be determined.

Effects of a High-Protein Diet on Kidney Injury under Conditions of Non-CKD or CKD in Mice

Considering the prevalence of obesity and global aging, the consumption of a high-protein diet (HPD) may be advantageous. However, an HPD aggravates kidney dysfunction in patients with chronic kidney disease (CKD). Moreover, the effects of an HPD on kidney function in healthy individuals are controversial. In this study, we employed a remnant kidney mouse model as a CKD model and aimed to evaluate the effects of an HPD on kidney injury under conditions of non-CKD and CKD. Mice were divided into four groups: a sham surgery (sham) + normal diet (ND) group, a sham + HPD group, a 5/6 nephrectomy (Nx) + ND group and a 5/6 Nx + HPD group. Blood pressure, kidney function and kidney tissue injury were compared after 12 weeks of diet loading among the four groups. The 5/6 Nx groups displayed blood pressure elevation, kidney function decline, glomerular injury and tubular injury compared with the sham groups. Furthermore, an HPD exacerbated glomerular injury only in the 5/6 Nx group; however, an HPD did not cause kidney injury in the sham group. Clinical application of these results suggests that patients with CKD should follow a protein-restricted diet to prevent the exacerbation of kidney injury, while healthy individuals can maintain an HPD without worrying about the adverse effects.

Positive association of serum FUT8 activity with renal tubulointerstitial injury in IgA nephropathy patients

BACKGROUND

α-1,6 Fucosyltransferase (FUT8) appears to play an essential role in the pathogenesis of renal fibrosis. However, it remained unknown whether FUT8 also contributed to renal fibrosis in immunoglobulin A nephropathy (IgAN). In the present study, we explored the association of serum FUT8 activity with renal tubulointerstitial injury in IgAN patients.

METHODS

Serum FUT8 activity was measured in 135 IgAN patients and 68 healthy controls from January 2016 to December 2018. The relationships of serum FUT8 activity with clinical and pathological features were analyzed.

RESULTS

Relative to healthy controls, IgAN patients had significantly higher serum FUT8 activity and upregulation of renal FUT8 protein (p < .05). Among IgAN patients, there was a positive correlation of serum FUT8 activity with renal FUT8 protein expression (p < .05). Multivariable logistic regression analyses showed that serum FUT8 activity was significantly associated with serum creatinine and eGFR (p < .05). Based on a cut-off value determined from ROC curve analysis, we divided IgAN patients into a low serum FUT8 activity group (≤12.2 pmol/h/mL, n = 40) and a high serum FUT8 activity group (>12.2 pmol/h/ml, n = 95). The high serum FUT8 activity group had a higher Oxford T score, increased inflammatory cell infiltration, more severe fibrosis and poor renal function (p < .05).

CONCLUSION

Serum FUT8 activity was positive association with renal tubulointerstitial injury in IgAN patients.

Activation of Complement Pathways in Kidney Tissue May Mediate Tubulointerstitial Injury in Diabetic Nephropathy

Introduction

Key genes involved in tubulointerstitial injury may influence the development and progression of diabetic nephropathy (DN). We investigated whether complement-related genes are linked to the mechanism underlying tubulointerstitial injury in DN.

Methods

We analyzed the microarray data of 17 tubulointerstitial tissue samples from DN patients and 21 normal controls from the Gene Expression Omnibus. A gene co-expression network was constructed, and genes were divided into modules by weighted gene co-expression network analysis (WGCNA). We also investigated the association of C3 and C1q deposits in kidney tissues with a composite outcome of end-stage renal disease or a 50% reduction in the estimated glomerular filtration rate (eGFR) in DN patients. Finally, we performed immunohistochemical analyses of C3, C1q, C5b-9, mannose-binding lectin (MBL), and factor B in kidney tissues.

Results

Nine co-expression modules were constructed using 12,075 genes from the 38 human tubulointerstitial tissue samples. Black module with more genes was positively correlated with tubulointerstitial injury in DN. C3, one of the top 10 genes in tubulointerstitial injury, was verified in an independent dataset; C3 was significantly overexpressed in tubulointerstitial tissue from patients with DN compared to the normal controls. The mRNA level of C3 in renal tubulointerstitium was negatively correlated with eGFR in DN patients (r = −0.75; p = 0.001). Analysis of the follow-up data of 54 DN patients demonstrated that codeposits of C3 and C1q in kidney tissues were independently associated with the renal outcome in DN (hazard ratio, 2.3, 95% confidence interval, 1.01–5.2, p < 0.05). Immunohistochemical analysis showed that patients with higher C1q, C3, C5b-9, MBL, or factor B expression in renal tubulointerstitium were more likely to progress to kidney failure.

Conclusion

Local complement activation of the classical, lectin and alternative pathways appears linked to tubulointerstitial injury and disease progression in DN.

High Doses of Essential Oil of Croton Zehntneri Induces Renal Tubular Damage

The essential oil of Croton zehntneri (EOCZ) and its major compounds are known to have several biological activities. However, some evidence shows potential toxic effects of high doses of EOCZ (>300 mg/kg) in amphibian and human kidneys. The aim of the present work was to investigate the effects on renal function of EOCZ at 300 mg/kg/day in healthy Swiss mice and a subclinical acute kidney injury (subAKI) animal model, which presents tubule-interstitial injury (TII). Four experimental groups were generated: (1) CONT group (control); (2) EOCZ, mice treated with EOCZ; (3) subAKI; (4) subAKI+EOCZ, subAKI treated simultaneously with EOCZ. EOCZ treatment induced TII measured by increases in (1) proteinuria; (2) cortical tubule-interstitial space; (3) macrophage infiltration; (4) collagen deposition. A decrease in tubular sodium reabsorption was also observed. These results were similar and nonadditive to those observed in the subAKI group. These data suggest that treatment with EOCZ at higher concentrations induces TII in mice, which could be mediated by protein overload in the proximal tubule.

Dysbiosis of intestinal microbiota mediates tubulointerstitial injury in diabetic nephropathy via the disruption of cholesterol homeostasis

Background: Our previous study demonstrated that the disruption of cholesterol homeostasis promotes tubulointerstitial injury in diabetic nephropathy (DN). This study aimed to further investigate the effects of gut microbiota dysbiosis on this process and explored its potential mechanism.

Methods: Diabetic rats treated with broad-spectrum oral antibiotics or faecal microbiota transplantation (FMT) from the healthy donor group and human kidney 2 (HK-2) cells stimulated with sodium acetate were used to observe the effects of gut microbiota on cholesterol homeostasis. The gut microbiota distribution was measured by 16S rDNA sequencing with faeces. Serum acetate level was examined by gas chromatographic analysis. Protein expression of G protein coupled receptor 43 (GPR43) and molecules involved in cholesterol homeostasis were assessed by immunohistochemical staining, immunofluorescence staining, and Western Blotting.

Results: Depletion of gut microbiota significantly attenuated albuminuria and tubulointerstitial injury. Interestingly, serum acetate levels were also markedly decreased in antibiotics-treated diabetic rats and positively correlated with the cholesterol contents in kidneys. An in vitro study demonstrated that acetate significantly increased cholesterol accumulation in HK-2 cells, which was caused by increased expression of proteins mainly modulating cholesterol synthesis and uptake. As expected, FMT effectively decreased serum acetate levels and alleviated tubulointerstitial injury in diabetic rats through overriding the disruption of cholesterol homeostasis. Furthermore, GPR43 siRNA treatment blocked acetate-mediated cholesterol homeostasis dysregulation in HK-2 cells through decreasing the expression of proteins governed cholesterol synthesis and uptake.

Conclusion: Our studies for the first time demonstrated that the acetate produced from gut microbiota mediated the dysregulation of cholesterol homeostasis through the activation of GPR43, thereby contributing to the tubulointerstitial injury of DN, suggesting that gut microbiota reprogramming might be a new strategy for DN prevention and therapy.

Tumor necrosis factor-α blockade ameliorates diabetic nephropathy in rats

Background

Tubular injury plays a critical role in the development of diabetic nephropathy (DN), but current DN therapies do not combat tubular injury. This study was conducted to investigate if tumor necrosis factor (TNF)-α inhibition protects against tubular injury in diabetic rats and to examine the associated mechanisms.

Methods

Kidney biopsy tissues were collected and analyzed from 12 patients with DN and 5 control subjects. Streptozotocin (STZ)-induced diabetic rats were treated with a TNF-α inhibitor for 12 weeks. Renal function, albuminuria, histological injury, renal TNF-α messenger RNA (mRNA) and the NOD- (nucleotide-binding), LRR- (domain-like receptor) and pyrin domain-containing protein 3 (NLRP3) inflammasome were assessed.

Results

Diabetic patients with tubulointerstitial injury (TIN) presented with higher renal tubular expression of TNF-α mRNA and the NLRP3 inflammasome (P < 0.05). TNF-α inhibition reduced albuminuria, glomerular injury and tubular injury in STZ-induced diabetic rats (P < 0.05). Importantly, TNF-α inhibition significantly reduced the NLRP3 inflammasome in tubules (P < 0.05). Moreover, TNF-α inhibition decreased expression of tubular interleukin (IL)-6 and IL-17A mRNA.

Conclusions

TNF-α inhibition protects against TIN by suppressing the NLRP3 inflammasome in DN rats. Future studies may focus on the clinical protective effects of TNF-α inhibition using prospective observation.

Nephroprotective effect of losartan in IgA model rat

Objective

This study was performed to investigate the possible nephroprotective effects of losartan in a rat model of experimental IgA nephropathy (IgAN).

Methods

Thirty male Sprague–Dawley rats were randomly divided into three groups. The rats in the model group were treated with bovine serum albumin (oral gavage), lipopolysaccharide (tail vein injection), and carbon tetrachloride (subcutaneous injection); rats in the losartan group received treatments similar to those of the model group, and were orally gavaged with losartan; and rats in the control group received phosphate-buffered saline alone (both orally and intravenously).

Results

Losartan treatment lowered the 24-hour urinary protein, serum blood urea nitrogen, and serum creatinine levels. Proliferating mesangial cells with a variable increase in the mesangial matrix were detected in the model group, whereas injury in the losartan group was significantly attenuated. Immunohistochemistry revealed that the expression levels of transforming growth factor (TGF)-β1 and α-smooth muscle actin were significantly elevated in the model group but reduced in the losartan group. The expression levels of TGF-β1 and monocyte chemoattractant protein-1 were minimal in the control group, significantly increased in the model group, and reduced in the losartan group.

Conclusion

Losartan has a protective effect against tubulointerstitial injury in IgAN.

Gelofusine Attenuates Tubulointerstitial Injury Induced by cRGD-Conjugated siRNA by Regulating the TLR3 Signaling Pathway

Integrin αvβ3, which is selectively targeted by cyclic arginine-glycine-aspartic acid (cRGD) peptides, is significantly upregulated in tumors. Previous studies showed that small interfering RNA (siRNA) modified with cRGD (cRGD-siRNA) could significantly inhibit tumor growth through RNAi with oncogene expression. However, cRGD-siRNA is partially reabsorbed and trapped in the kidneys, causing renal injury in an unpredictable manner. This study aimed to investigate the influence of Gelofusine on tubulointerstitial injury induced by cRGD-siRNA in vitro and in vivo. The effect of Gelofusine on the distribution of cRGD-siRNA in tumor-bearing nude mice and wild-type mice was also explored. We found that Gelofusine inhibited apoptosis and activation of the innate immune response of human tubular epithelial cells induced by cRGD-siRNA in vitro. In addition, co-injection of Gelofusine efficiently reduced renal retention of cRGD-siRNA without affecting its tumor targeting in vivo. Further in vivo studies indicated that Gelofusine significantly attenuated tubulointerstitial injury induced by cRGD-siRNA through regulating Toll-like receptor 3 (TLR3)-mediated activation of the nuclear factor κ B (NF-κB) and caspase-3 apoptotic pathway. In conclusion, Gelofusine, acting as a novel and effective renal protective agent, could form a compound preparation with siRNA drugs for future clinical applications.

Protection against age-dependent renal injury in the F344xBrown Norway male rat is associated with maintained nitric oxide synthase

Age-dependent renal damage is influenced by genetic background and the Fisher344xBrown Norway (F344xBN) rat is resistant to glomerular injury. In vulnerable strains, a fall in renal nitric oxide synthase (NOS) contributes to age-dependent renal damage. Here, we investigated renal NOS in young (3 months) and old (30 months) male F344xBN to test the hypothesis that renal NOS is maintained in "protected" strains. We also examined if 6 months of renin-angiotensin system (RAS) blockade using angiotensin converting enzyme inhibition (ACEI) and angiotensin receptor blockade (ARB) provides further benefit in these "protected" old rats. Aging increased tubulointerstitial injury but glomerular sclerosis was minimal and NOS and superoxide dismutase abundance increased. There was no change in the NOS inhibitor, ADMA (asymmetric dimethylarginine) or its regulatory enzymes. RAS blockade with ARB protected against tubulointerstitial injury and increased nNOSα, but ACEI, which also increased nNOSα, had no protective effect on the tubulointerstitium. We conclude that the glomerular sclerosis-resistant aged male F344xBN rat maintains renal NOS, thus reinforcing our hypothesis that progressive glomerular injury is related to renal NOS deficiency. The tubulointerstitial injury seen with aging is reversed with 6 months of ARB but not ACEI and is not associated with renal NOS.