The death ligand TRAIL in diabetic nephropathy

Advances in understanding and treating diabetic kidney disease: focus on tubulointerstitial inflammation mechanisms

Diabetic kidney disease (DKD) is a serious complication of diabetes that can lead to end-stage kidney disease. Despite its significant impact, most research has concentrated on the glomerulus, with little attention paid to the tubulointerstitial region, which accounts for the majority of the kidney volume. DKD's tubulointerstitial lesions are characterized by inflammation, fibrosis, and loss of kidney function, and recent studies indicate that these lesions may occur earlier than glomerular lesions. Evidence has shown that inflammatory mechanisms in the tubulointerstitium play a critical role in the development and progression of these lesions. Apart from the renin-angiotensin-aldosterone blockade, Sodium-Glucose Linked Transporter-2(SGLT-2) inhibitors and new types of mineralocorticoid receptor antagonists have emerged as effective ways to treat DKD. Moreover, researchers have proposed potential targeted therapies, such as inhibiting pro-inflammatory cytokines and modulating T cells and macrophages, among others. These therapies have demonstrated promising results in preclinical studies and clinical trials, suggesting their potential to treat DKD-induced tubulointerstitial lesions effectively. Understanding the immune-inflammatory mechanisms underlying DKD-induced tubulointerstitial lesions and developing targeted therapies could significantly improve the treatment and management of DKD. This review summarizes the latest advances in this field, highlighting the importance of focusing on tubulointerstitial inflammation mechanisms to improve DKD outcomes.

Profilin1 Promotes Renal Tubular Epithelial Cell Apoptosis in Diabetic Nephropathy Through the Hedgehog Signaling Pathway

Background

Profilin-1 (PFN1) regulates the dynamic balance of actin and plays an important role in cell functions as a hub protein in signaling molecule interaction networks. Dysregulation of PFN1 is related to pathologic kidney diseases. Diabetic nephropathy (DN) was recently reported as an inflammatory disorder, however, the molecular mechanisms of PFN1 in DN remain unclear. Therefore, the present study was conducted to explore the molecular and bioinformatic characteristics of PFN1 in DN.

Methods

Bioinformatics analyses were performed on the chip of database in DN kidney tissues. A cellular model of DN was established in human renal tubular epithelial cells (HK-2) induced by high glucose. The PFN1 gene was overexpressed or knocked-down to investigate its function in DN. Flow cytometry was used to detect cell proliferation and apoptosis. PFN1 and proteins in the related signaling pathways were evaluated by Western blotting.

Results

The expression of PFN1 was significantly increased in DN kidney tissues (P < 0.001) and was correlated with a high apoptosis-associated score (Pearson's correlation = 0.664) and cellular senescence-associated score (Pearson's correlation = 0.703). PFN1 protein was mainly located in cytoplasm. Overexpression of PFN1 promoted apoptosis and blocked the proliferation of HK-2 cells treated with high levels of glucose. Knockdown of PFN1 led to the opposite effects. Additionally, we found that PFN1 was correlated with the inactivation of the Hedgehog signaling pathway in HK-2 cells treated with high levels of glucose.

Conclusion

PFN1 might play an integral role in the regulation of cell proliferation and apoptosis during DN development by activating the Hedgehog signaling pathway. This study provided molecular and bioinformatic characterizations of PFN1, and contributed to the understanding of the molecular mechanisms leading to DN.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Broadening horizons in mechanisms, management, and treatment of diabetic kidney disease

Diabetic kidney disease (DKD) is the first cause of end-stage kidney disease in patients with diabetes and its prevalence is increasing worldwide. It encompasses histological alterations that mainly affect the glomerular filtration unit, which include thickening of the basement membrane, mesangial cell proliferation, endothelial alteration, and podocyte injury. These morphological abnormalities further result in a persistent increase of urinary albumin-to-creatinine ratio and in a reduction of the estimated glomerular filtration rate. Several molecular and cellular mechanisms have been recognized, up to date, as major players in mediating such clinical and histological features and many more are being under investigation. This review summarizes the most recent advances in understanding cell death mechanisms, intracellular signaling pathways and molecular effectors that play a role in the onset and progression of diabetic kidney damage. Some of those molecular and cellular mechanisms have been already successfully targeted in preclinical models of DKD and, in some cases, strategies have been tested in clinical trials. Finally, this report sheds light on the relevance of novel pathways that may become therapeutic targets for future applications in DKD.

Molecular profiling of urinary extracellular vesicles in chronic kidney disease and renal fibrosis

Chronic kidney disease (CKD) is a long-term kidney damage caused by gradual loss of essential kidney functions. A global health issue, CKD affects up to 16% of the population worldwide. Symptoms are often not apparent in the early stages, and if left untreated, CKD can progress to end-stage kidney disease (ESKD), also known as kidney failure, when the only possible treatments are dialysis and kidney transplantation. The end point of nearly all forms of CKD is kidney fibrosis, a process of unsuccessful wound-healing of kidney tissue. Detection of kidney fibrosis, therefore, often means detection of CKD. Renal biopsy remains the best test for renal scarring, despite being intrinsically limited by its invasiveness and sampling bias. Urine is a desirable source of fibrosis biomarkers as it can be easily obtained in a non-invasive way and in large volumes. Besides, urine contains biomolecules filtered through the glomeruli, mirroring the pathological state. There is, however, a problem of highly abundant urinary proteins that can mask rare disease biomarkers. Urinary extracellular vesicles (uEVs), which originate from renal cells and carry proteins, nucleic acids, and lipids, are an attractive source of potential rare CKD biomarkers. Their cargo consists of low-abundant proteins but highly concentrated in a nanosize-volume, as well as molecules too large to be filtered from plasma. Combining molecular profiling data (protein and miRNAs) of uEVs, isolated from patients affected by various forms of CKD, this review considers the possible diagnostic and prognostic value of uEVs biomarkers and their potential application in the translation of new experimental antifibrotic therapeutics.

TRAIL and EGFR Pathways Targeting microRNAs are Predominantly Regulated in Human Diabetic Nephropathy

BACKGROUND

Unbiased microRNA profiling of renal tissue and urinary extracellular vesicles (uEVs) from diabetic nephropathy (DN) subjects may unravel novel targets with diagnostic and therapeutic potential. Here we used the miRNA profile of uEVs and renal biopsies from DN subjects available on the GEO database.

METHODS

The miR expression profiles of kidney tissue (GSE51674) and urinary exosomes (GSE48318) from DN and control subjects were obtained by GEO2R tools from Gene Expression Omnibus (GEO) databases. Differentially expressed miRNAs in DN samples, relative to controls, were identified using a bioinformatic pipeline. Targets of miRs commonly regulated in both sample types were predicted by miRWalk, followed by functional gene enrichment analysis. Gene targets were identified by MiRTarBase, TargetScan and MiRDB.

RESULTS

Eight miRs, including let-7c, miR-10a, miR-10b and miR-181c, were significantly regulated in kidney tissue and uEVs in DN subjects versus controls. The top 10 significant pathways targeted by these miRs included TRAIL, EGFR, Proteoglycan syndecan, VEGF and Integrin Pathway. Gene target analysis by miRwalk upon validation using ShinyGO 70 targets with significant miRNA-mRNA interaction.

CONCLUSION

In silico analysis showed that miRs targeting TRAIL and EGFR signaling are predominately regulated in uEVs and renal tissue of DN subjects. After wet-lab validation, the identified miRstarget pairs may be explored for their diagnostic and/or therapeutic potential in diabetic nephropathy.

Repositioning the Role of Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) on the TRAIL to the Development of Diabetes Mellitus: An Update of Experimental and Clinical Evidence

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF protein superfamily, represents a multifaceted cytokine with unique biological features including both proapoptotic and pro-survival effects in different cell types depending on receptor interactions and local stimuli. Beyond its extensively studied anti-tumor and immunomodulatory properties, a growing body of experimental and clinical evidence over the past two decades suggests a protective role of TRAIL in the development of type 1 (T1DM) and type 2 (T2DM) diabetes mellitus. This evidence can be briefly summarized by the following observations: (i) acceleration and exacerbation of T1DM and T2DM by TRAIL blockade or genetic deficiency in animal models, (ii) prevention and amelioration of T1DM and T2DM with recombinant TRAIL treatment or systemic TRAIL gene delivery in animal models, (iii) significantly reduced circulating soluble TRAIL levels in patients with T1DM and T2DM both at disease onset and in more advanced stages of diabetes-related complications such as cardiovascular disease and diabetic nephropathy, (iv) increase of serum TRAIL levels in diabetic patients after initiation of antidiabetic treatment and metabolic improvement. To explore the underlying mechanisms and provide mechanistic links between TRAIL and diabetes, a number of animal and in vitro studies have reported direct effects of TRAIL on several tissues involved in diabetes pathophysiology such as pancreatic islets, skeletal muscle, adipose tissue, liver, kidney, and immune and vascular cells. Residual controversy remains regarding the effects of TRAIL on adipose tissue homeostasis. Although the existing evidence is encouraging and paves the way for investigating TRAIL-related interventions in diabetic patients with cardiometabolic abnormalities, caution is warranted in the extrapolation of animal and in vitro data to the clinical setting, and further research in humans is imperative in order to uncover all aspects of the TRAIL-diabetes relationship and delineate its therapeutic implications in metabolic disease.

Tubular epithelial cell-to-macrophage communication forms a negative feedback loop via extracellular vesicle transfer to promote renal inflammation and apoptosis in diabetic nephropathy

Background: Macrophage infiltration around lipotoxic tubular epithelial cells (TECs) is a hallmark of diabetic nephropathy (DN). However, how these two types of cells communicate remains obscure. We previously demonstrated that LRG1 was elevated in the process of kidney injury. Here, we demonstrated that macrophage-derived, LRG1-enriched extracellular vesicles (EVs) exacerbated DN.

Methods: We induced an experimental T2DM mouse model with a HFD diet for four months. Renal primary epithelial cells and macrophage-derived EVs were isolated from T2D mice by differential ultracentrifugation. To investigate whether lipotoxic TEC-derived EV (EV_e) activate macrophages, mouse bone marrow-derived macrophages (BMDMs) were incubated with EV_e. To investigate whether activated macrophage-derived EVs (EV_m) induce lipotoxic TEC apoptosis, EV_m were cocultured with primary renal tubular epithelial cells. Subsequently, we evaluated the effect of LRG1 in EV_e by investigating the apoptosis mechanism.

Results: We demonstrated that incubation of primary TECs of DN or HK-2 mTECs with lysophosphatidyl choline (LPC) increased the release of EV_e. Interestingly, TEC-derived EV_e activated an inflammatory phenotype in macrophages and induced the release of macrophage-derived EV_m. Furthermore, EV_m could induce apoptosis in TECs injured by LPC. Importantly, we found that leucine-rich α-2-glycoprotein 1 (LRG1)-enriched EV_e activated macrophages via a TGFβR1-dependent process and that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-enriched EV_m induced apoptosis in injured TECs via a death receptor 5 (DR5)-dependent process.

Conclusion: Our findings indicated a novel cell communication mechanism between tubular epithelial cells and macrophages in DN, which could be a potential therapeutic target.

Potential Role of N-Cadherin in Diagnosis and Prognosis of Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious complication of diabetes affecting about half the people with diabetes and the leading cause of end stage renal disease (ESRD). Albuminuria and creatinine levels are currently the classic markers for the diagnosis of DN. However, many shortcomings are arising from the use of these markers mainly because they are not specific to DN and their levels are altered by multiple non-pathological factors. Therefore, the aim of this study is to identify better markers for the accurate and early diagnosis of DN. The study was performed on 159 subjects including 42 control subjects, 50 T2D without DN and 67 T2D subjects with DN. Our data show that circulating N-cadherin levels are significantly higher in the diabetic patients who are diagnosed with DN (842.6 ± 98.6 mg/l) compared to the diabetic patients who do not have DN (470.8 ± 111.5 mg/l) and the non-diabetic control group (412.6 ± 41.8 mg/l). We also report that this increase occurs early during the developmental stages of the disease since N-cadherin levels are significantly elevated in the microalbuminuric patients when compared to the healthy control group. In addition, we show a significant correlation between N-cadherin levels and renal markers including creatinine (in serum and urine), urea and eGFR in all the diabetic patients. In conclusion, our study presents N-cadherin as a novel marker for diabetic nephropathy that can be used as a valuable prognostic and diagnostic tool to slow down or even inhibit ESRD.

Bone-kidney axis: A potential therapeutic target for diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD). However, its pathogenesis remains unclear, and effective prevention and treatment strategies are lacking. Recently, organ-to-organ communication has become a new focus of studies on pathogenesis. Various organs or tissues (the liver, muscle and adipose tissue) secrete a series of proteins or peptides to regulate the homeostasis of distal organs in an endocrine manner. Bone, an important part of the body, can also secrete bone-derived proteins or peptides that act on distal organs. As an organ with high metabolism, the kidney is responsible for signal and material exchange with other organs at any time through circulation. In this review, we briefly discussed bone composition and changes in bone structure and function in DN and summarized the current status of bone-derived proteins and their role in the progression of DN. We speculated that the "bone-kidney axis" is a potential target for early diagnosis and treatment of DN.

Circulating Plasma Biomarkers in Biopsy-Confirmed Kidney Disease

BACKGROUND AND OBJECTIVES

Biomarkers for noninvasive assessment of histopathology and prognosis are needed in patients with kidney disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Using a proteomics assay, we measured a multimarker panel of 225 circulating plasma proteins in a prospective cohort study of 549 individuals with biopsy-confirmed kidney diseases and semiquantitative assessment of histopathology. We tested the associations of each biomarker with histopathologic lesions and the risks of kidney disease progression (defined as ≥40% decline in eGFR or initiation of KRT) and death.

RESULTS

After multivariable adjustment and correction for multiple testing, 46 different proteins were associated with histopathologic lesions. The top-performing markers positively associated with acute tubular injury and interstitial fibrosis/tubular atrophy were kidney injury molecule-1 (KIM-1) and V-set and Ig domain-containing protein 2 (VSIG2), respectively. Thirty proteins were significantly associated with kidney disease progression, and 35 were significantly associated with death. The top-performing markers for kidney disease progression were placental growth factor (hazard ratio per doubling, 5.4; 95% confidence interval, 3.4 to 8.7) and BMP and activin membrane-bound inhibitor (hazard ratio, 3.0; 95% confidence interval, 2.1 to 4.2); the top-performing markers for death were TNF-related apoptosis-inducing ligand receptor-2 (hazard ratio, 2.9; 95% confidence interval, 2.0 to 4.0) and CUB domain-containing protein-1 (hazard ratio, 2.4; 95% confidence interval, 1.8 to 3.3).

CONCLUSION

We identified several plasma protein biomarkers associated with kidney disease histopathology and adverse clinical outcomes in individuals with a diverse set of kidney diseases.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2021_12_28_CJN09380721.mp3.

Urinary mRNA Expression of Glomerular Podocyte Markers in Glomerular Disease and Renal Transplant

The research of novel markers in urinary samples, for the description of renal damage, is of high interest, and several works demonstrated the value of urinary mRNA quantification for the search of events related to renal disease or affecting the outcome of transplant kidneys. In the present pilot study, a comparison of the urine mRNA expression of specific podocyte markers among patients who had undergone clinical indication to renal transplanted (RTx, n = 20) and native (N, n = 18) renal biopsy was performed. The aim of this work was to identify genes involved in podocytes signaling and cytoskeletal regulation (NPHS1, NPHS2, SYNPO, WT1, TRPC6, GRM1, and NEUROD) in respect to glomerular pathology. We considered some genes relevant for podocytes signaling and for the function of the glomerular filter applying an alternative normalization approach. Our results demonstrate the WT1 urinary mRNA increases in both groups and it is helpful for podocyte normalization. Furthermore, an increase in the expression of TRPC6 after all kinds of normalizations was observed. According to our data, WT1 normalization might be considered an alternative approach to correct the expression of urinary mRNA. In addition, our study underlines the importance of slit diaphragm proteins involved in calcium disequilibrium, such as TRPC6.

Hypoxia-Induced Epithelial-to-Mesenchymal Transition in Proximal Tubular Epithelial Cells through miR-545-3p-TNFSF10

Hypoxia is regarded as one of the pathophysiologic mechanisms of kidney injury and further progression to kidney failure. Epithelial-to-mesenchymal transition (EMT) in kidney tubules is a critical process of kidney fibrosis. This study utilized transcriptome analysis to investigate hypoxia-induced EMT through microRNA (miRNA)-modulated EMT in proximal tubular epithelial cells (PTECs). RNA sequencing revealed eight miRNAs were upregulated and three miRNAs were downregulated in PTECs cultured under hypoxia compared with normoxia. Among the 11 miRNAs, miR-545-3p has the highest expression in PTECs exposed to hypoxia, and miR-545-3p suppressed tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/TNFSF10) expression. Hypoxia induced EMT in PTECs through miR-545-3p–TNFSF10 modulation, and TNFSF10-attenuated EMT resulted from hypoxia or miR-545-3p mimic transfection. These findings provided new perceptions of the unique regulation of the miR-545-3p–TNFSF10 interaction and their potential therapeutic effect in kidney injury induced by hypoxia.

Decoys as potential therapeutic tools for diabetes

Current therapeutic approaches for diabetes are focused on improving glycemic control to prevent diabetes-related complications, but such approached are not completely successful. Decoy technologies such as decoy oligodeoxynucleotides (ODNs) and decoy peptides have emerged as therapeutic tools in diabetes. Decoy ODNs carry a DNA recognition motif for the binding of transcription factors in order to trap them and block their effects, whereas decoy peptides mimic the binding structure of the receptor protein, bind to the docking site of the target ligand, and prevent the interaction of the ligand and receptor. This review summarizes the technologies that have been developed to date and the studies that have investigated the therapeutic effects of decoy ODNs and peptides in diabetes.

Tacrolimus Prevents TWEAK-Induced PLA2R Expression in Cultured Human Podocytes

Primary membranous nephropathy is usually caused by antibodies against the podocyte antigen membrane M-type phospholipase A2 receptor (PLA2R). The treatment of membranous nephropathy is not fully satisfactory. The calcineurin inhibitor tacrolimus is used to treat membranous nephropathy, but recurrence upon drug withdrawal is common. TNF superfamily members are key mediators of kidney injury. We have now identified key TNF receptor superfamily members in podocytes and explored the regulation of PLA2R expression and the impact of tacrolimus. Data mining of single cell transcriptomics and glomerular transcriptomics data identified TNFRSF12a/Fn14 as the highest expressed TNF receptor superfamily gene in human membranous nephropathy, and this was confirmed by immunohistochemistry that also identified NFκB activation in membranous nephropathy podocytes. Additionally, glomerular transcriptomics identified PLA2R1 expression as being increased in membranous nephropathy in the parenteral administration of the Fn14 ligand TWEAK increased podocyte PLA2R expression in mice. Furthermore, in cultured human podocytes, TWEAK increased the expression of PLA2R as well as the expression of other genes recently identified by GWAS as linked to membranous nephropathy: NFKB1 and IRF4. Interestingly, IRF4 encodes the FK506-binding protein 52 (FKBP52), a protein associated with tacrolimus. Tacrolimus prevented the increased expression of PLA2R, NFKB1 and IRF4 induced by TWEAK in cultured podocytes. In conclusion, TWEAK upregulates the expression of PLA2R and of other genes linked to membranous nephropathy in podocytes, and this is prevented by tacrolimus. An impact of tacrolimus on the expression of PLA2R and other genes in podocytes may underlie its efficacy in treating the disease as well as the frequent recurrence of nephrotic syndrome upon tacrolimus withdrawal.

MAP3K kinases and kidney injury

Mitogen-activated protein kinases (MAP kinases) are functionally connected kinases that regulate key cellular process involved in kidney disease such as all survival, death, differentiation and proliferation. The typical MAP kinase module is composed by a cascade of three kinases: a MAP kinase kinase kinase (MAP3K) that phosphorylates and activates a MAP kinase kinase (MAP2K) which phosphorylates a MAP kinase (MAPK). While the role of MAPKs such as ERK, p38 and JNK has been well characterized in experimental kidney injury, much less is known about the apical kinases in the cascade, the MAP3Ks. There are 24 characterized MAP3K (MAP3K1 to MAP3K21 plus RAF1, BRAF and ARAF). We now review current knowledge on the involvement of MAP3K in non-malignant kidney disease and the therapeutic tools available. There is in vivo interventional evidence clearly supporting a role for MAP3K5 (ASK1) and MAP3K14 (NIK) in the pathogenesis of experimental kidney disease. Indeed, the ASK1 inhibitor Selonsertib has undergone clinical trials for diabetic kidney disease. Additionally, although MAP3K7 (MEKK7, TAK1) is required for kidney development, acutely targeting MAP3K7 protected from acute and chronic kidney injury; and targeting MAP3K8 (TPL2/Cot) protected from acute kidney injury. By contrast MAP3K15 (ASK3) may protect from hypertension and BRAF inhibitors in clinical use may induced acute kidney injury and nephrotic syndrome. Given their role as upstream regulators of intracellular signaling, MAP3K are potential therapeutic targets in kidney injury, as demonstrated for some of them. However, the role of most MAP3K in kidney disease remains unexplored.

E-cadherin and periostin in early detection and progression of diabetic nephropathy: epithelial-to-mesenchymal transition

BACKGROUND

Diabetic nephropathy (DN) is a severe complication of diabetes mellitus (DM). Many mechanisms are involved in its development; one of these mechanisms is epithelial-to-mesenchymal transition (EMT). During EMT, losing of the epithelial biomarkers like E-cadherin and increasing of mesenchymal biomarkers like periostin are very characteristic.

METHODS

The study included 19 healthy controls and 71 DN patients categorized according to their urinary albumin-to-creatinine ratio (UACR) into 19 normoalbuminuric (UACR < 30 mg/g), 37 microalbuminuric (UACR 30-300 mg/g), and 15 macroalbuminuric (UACR > 300 mg/g) patients. Fasting plasma glucose (FPG), glycated hemoglobin (HbA_1C%), serum creatinine (Cr), and urea were measured. E-cadherin and periostin were measured by ELISA and compared among groups.

RESULTS

Concerning E-cadherin levels, in comparison to control group, there were significantly decreased in all groups (0.94, 0.52, and 0.14 ng/mL in normoalbuminuria, microalbuminuria, and macroalbuminuria groups; respectively). For periostin levels, nonsignificant increase in normoalbuminuria (0.32 ng/mL) than control group (0.3 ng/mL) was observed. There was a significant increase in other groups with the highest values in macroalbuminuria group (1.66 ng/mL). E-cadherin and periostin were correlated with each other (r = - 0.353, P < 0.001). UACR was negatively correlated with E-cadherin and positively correlated with periostin. ROC curve analyses showed that the AUC to diagnose established microalbuminuria using E-cadherin was 0.998 (95% CI 0. 932-1), and using periostin was 0.833 (95% CI 0.709-0.919).

CONCLUSION

Serum E-cadherin and periostin could be considered as reliable biomarkers involved in DN pathogenesis and linked to its stages.

TRAIL, OPG, and TWEAK in kidney disease: biomarkers or therapeutic targets?

Ligands and receptors of the tumor necrosis factor (TNF) superfamily regulate immune responses and homeostatic functions with potential diagnostic and therapeutic implications. Kidney disease represents a global public health problem, whose prevalence is rising worldwide, due to the aging of the population and the increasing prevalence of diabetes, hypertension, obesity, and immune disorders. In addition, chronic kidney disease is an independent risk factor for the development of cardiovascular disease, which further increases kidney-related morbidity and mortality. Recently, it has been shown that some TNF superfamily members are actively implicated in renal pathophysiology. These members include TNF-related apoptosis-inducing ligand (TRAIL), its decoy receptor osteoprotegerin (OPG), and TNF-like weaker inducer of apoptosis (TWEAK). All of them have shown the ability to activate crucial pathways involved in kidney disease development and progression (e.g. canonical and non-canonical pathways of the transcription factor nuclear factor-kappa B), as well as the ability to regulate cell proliferation, differentiation, apoptosis, necrosis, inflammation, angiogenesis, and fibrosis with double-edged effects depending on the type and stage of kidney injury. Here we will review the actions of TRAIL, OPG, and TWEAK on diabetic and non-diabetic kidney disease, in order to provide insights into their full clinical potential as biomarkers and/or therapeutic options against kidney disease.

Antioxidant and nephroprotection activities of Combretum micranthum: A phytochemical, in-vitro and ex-vivo studies

Management of chronic renal failure is exceedingly expensive. Despite of encouraging experimental outcomes, there is a lack of potent nephroprotective drugable molecules in a clinics or market. To develop a nephroprotective phytomedicine, the present study was designed to do a literature survey on reported phytochemical and biological analysis of Combretum micranthum and to carry out chemoprofiling, in-vitro antioxidant and ex-vivo nephroprotective capacity of the title plant. The phytochemical and biological activity survey of C. micranthum has reveals the presence of many bioactive compounds such as flavonoids, terpenoids, steroids and alkaloids with many biological activities. Phytochemical investigation re-confirmed the presence of these compounds. Hydroalcoholic extract of C. micranthum (CM extract) showed a strong antioxidant activity by scavenging AAPH, DPPH, nitric oxide, hydrogen peroxide and chelating metal ions. CM extract exhibited significant (P < 0.001) dose dependent inhibition of ferric chloride-ascorbic acid induced lipid peroxidation. Diabetic nephropathy is a serious and common complication leading to end stage renal disease. Therefore, in the present study, glucose-induced toxicity was also studied in human embryonic kidney cells (HEK-293) as an in vitro model for diabetic nephropathy. The results showed that exposure of cells to high glucose (100 mM) for 72 h significantly reduced the cell viability resulting in morphological changes such as cell shrinkage, rounded cell shape and cytoplasmic vacuolation. Treatment with CM extract at 10 and 25 μg/mL resulted in significant improvement in cell viability from 10 to 23% compared to the high glucose control. This study demonstrated the potential antioxidant and nephroprotective properties of C. micranthum, justifying its traditional use in the treatment of various diseases.

Tumour necrosis factor-related apoptosis-inducing ligand expression in patients with diabetic nephropathy

Objective:

The objective of this study was to evaluate the expression profile of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) in patients with diabetic nephropathy (DN).

Methods:

A total of 126 Chinese subjects were enrolled in this study, including 42 patients with diabetes mellitus (DM), 42 patients with DN and 42 healthy controls. Real-time polymerase chain reaction was performed to analyze levels of TRAIL mRNA in peripheral blood mononuclear cells (PBMCs). Serum levels of soluble TRAIL (sTRAIL) and various cytokines were detected with a commercially available enzyme-linked immunosorbent assay kit.

Results:

Compared with the control group, the levels of TRAIL mRNA in PBMCs and sTRAIL in sera were both significantly decreased in the DM and DN patients (P < 0.05). Conversely, levels of interleukin (IL)-1, IL-6, tumour necrosis factor-α and monocyte chemotactic protein-1 were higher in the DN group than in the control group. Serum levels of TRAIL positively correlated with TRAIL mRNA levels in all of the subjects examined (P < 0.05).

Conclusions:

These results provide support and a theoretical basis for further research of TRAIL in regard to the pathogenesis of DN.

Single-cell analysis of progenitor cell dynamics and lineage specification in the human fetal kidney

The mammalian kidney develops through reciprocal interactions between the ureteric bud and the metanephric mesenchyme to give rise to the entire collecting system and the nephrons. Most of our knowledge of the developmental regulators driving this process arises from the study of gene expression and functional genetics in mice and other animal models. In order to shed light on human kidney development, we have used single-cell transcriptomics to characterize gene expression in different cell populations, and to study individual cell dynamics and lineage trajectories during development. Single-cell transcriptome analyses of 6414 cells from five individual specimens identified 11 initial clusters of specific renal cell types as defined by their gene expression profile. Further subclustering identifies progenitors, and mature and intermediate stages of differentiation for several renal lineages. Other lineages identified include mesangium, stroma, endothelial and immune cells. Novel markers for these cell types were revealed in the analysis, as were components of key signaling pathways driving renal development in animal models. Altogether, we provide a comprehensive and dynamic gene expression profile of the developing human kidney at the single-cell level.

Summary: New markers for specific cell types in the developing human kidney are identified and computational approaches infer developmental trajectories and interrogate the complex network of signaling pathways and cellular transitions.

Proteolytic processing of lysyl oxidase-like-2 in the extracellular matrix is required for crosslinking of basement membrane collagen IV

Lysyl oxidase-like-2 (LOXL2) is an enzyme secreted into the extracellular matrix that crosslinks collagens by mediating oxidative deamination of lysine residues. Our previous work demonstrated that this enzyme crosslinks the 7S domain, a structural domain that stabilizes collagen IV scaffolds in the basement membrane. Despite its relevant role in extracellular matrix biosynthesis, little is known about the structural requirements of LOXL2 that enable collagen IV crosslinking. In this study, we demonstrate that LOXL2 is processed extracellularly by serine proteases, generating a 65-kDa form lacking the first two scavenger receptor cysteine-rich domains. Site-specific mutagenesis to prevent proteolytic processing generated a full-length enzyme that is active in vitro toward a soluble substrate, but fails to crosslink insoluble collagen IV within the extracellular matrix. In contrast, the processed form of LOXL2 binds to collagen IV and crosslinks the 7S domain. Together, our data demonstrate that proteolytic processing is an important event that allows LOXL2-mediated crosslinking of basement membrane collagen IV.

Use of Proteomics To Investigate Kidney Function Decline over 5 Years

BACKGROUND AND OBJECTIVES

Using a discovery/replication approach, we investigated associations between a multiplex panel of 80 circulating proteins associated with cardiovascular pathology or inflammation, and eGFR decline per year and CKD incidence.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We used two cohorts, the Prospective Investigation of the Vasculature in Uppsala Seniors Study (PIVUS; n=687, mean age of 70 years, 51% women) and the Uppsala Longitudinal Study of Adult Men (ULSAM; n=360 men, mean age of 78 years), with 5-year follow-up data on eGFR. There were 231 and 206 incident cases of CKD during follow-up in the PIVUS and ULSAM studies, respectively. Proteomic profiling of 80 proteins was assessed by a multiplex assay (proximity extension assay). The assay uses two antibodies for each protein and a PCR step to achieve a high-specific binding and the possibility to measure multiple proteins in parallel, but gives no absolute concentrations.

RESULTS

In the discovery cohort from the PIVUS Study, 28 plasma proteins were significantly associated with eGFR decline per year, taking into account the multiple testing. Twenty of these proteins were significantly associated with eGFR decline per year in the replication cohort from the ULSAM Study after adjustment for age, sex, cardiovascular risk factors, medications, and urinary albumin-to-creatinine ratio (in order of significance: TNF-related apoptosis-inducing ligand receptor 2*, CD40L receptor, TNF receptor 1*, placenta growth factor*, thrombomodulin*, urokinase plasminogen activator surface receptor*, growth/differentiation factor 15*, macrophage colony-stimulating factor 1, fatty acid-binding protein*, cathepsin D, resistin, kallikrein 11*, C-C motif chemokine 3, proteinase-activated receptor 1*, cathepsin L, chitinase 3-like protein 1, TNF receptor 2*, fibroblast growth factor 23*, monocyte chemotactic protein 1, and kallikrein 6). Moreover, 11 of the proteins predicted CKD incidence (marked with * above). No protein consistently predicted eGFR decline per year independently of baseline eGFR in both cohorts.

CONCLUSIONS

Several circulating proteins involved in phosphate homeostasis, inflammation, apoptosis, extracellular matrix remodeling, angiogenesis, and endothelial dysfunction were associated with worsening kidney function. Multiplex proteomics appears to be a promising way of discovering novel aspects of kidney disease pathology.

Urinary DcR2 is a novel biomarker for tubulointerstitial injury in patients with diabetic nephropathy

Tubulointerstitial injury (TII) plays a crucial role in the progression of diabetic nephropathy (DN), but lack of specific and sensitive biomarkers for monitoring TII in DN management. This study is to investigate whether urinary decoy receptor 2 (uDcR2) could serve as a novel noninvasive biomarker for assessing TII in DN. We recruited 311 type 2 diabetics and 139 DN patients who were diagnosed by renal biopsy. uDcR2 levels were measured by ELISA, and renal DcR2 expression was detected immunohistochemically. Associations between uDcR2 and renal DcR2 and renal functional parameters were evaluated. Receiver operating characteristics (ROC) curve analyzed area under the curve (AUC) of uDcR2 for assessing TII. Double staining was undertaken for renal DcR2 with proximal and distal tubular markers; senescent markers p16, p21, and senescence-associated β-galactosidase (SA-β-gal); and fibrotic markers collagen I and IV. We found DcR2 was primarily expressed in renal proximal tubules; uDcR2 levels were elevated per albuminuria stratum and correlated with renal functional parameters in diabetics and were associated with percentage of tubular DcR2 and TII score in DN. The uDcR2 had an AUC of 0.909 for assessing TII in DN by ROC analysis. Almost all tubular DcR2 was coexpressed with p16 and p21, and nearly more than one-half of tubular DcR2 was positive for SA-β-gal, primarily in collagen I- and IV-positive regions of DN. Our results indicate uDcR2 could potentially serve as a novel biomarker for TII and may reflect senescence of renal proximal tubular cells in DN pathogenesis.

Bcl3: a regulator of NF-κB inducible by TWEAK in acute kidney injury with anti-inflammatory and antiapoptotic properties in tubular cells

Acute kidney injury (AKI) is characterized by tubular cell death and interstitial inflammation. TWEAK promotes experimental kidney injury and activates the transcription factor NF-κB, a key regulator of genes involved in cell survival and inflammatory response. In search of potential therapeutic targets for AKI, we compared a transcriptomics database of NF-κB-related genes from murine AKI-kidneys with a transcriptomics database of TWEAK-stimulated cultured tubular cells. Four out of twenty-four (17%) genes were significantly upregulated (false discovery rate, FDR<0.05), while nine out of twenty-four (37%) genes were significantly upregulated at FDR <0.1 in both databases. Bcl3 was the top upregulated NF-κB-related gene in experimental AKI and one of the most upregulated genes in TWEAK-stimulated tubular cells. Quantitative reverse transcription PCR (qRT-PCR), western blot and immunohistochemistry confirmed Bcl3 upregulation in both experimental conditions and localized increased Bcl3 expression to tubular cells in AKI. Transcriptomics database analysis revealed increased Bcl3 expression in numerous experimental and human kidney conditions. Furthermore, systemic TWEAK administration increased kidney Bcl3 expression. In cultured tubular cells, targeting Bcl3 by siRNA resulted in the magnification of TWEAK-induced NF-κB transcriptional activity, chemokine upregulation and Klotho downregulation, and in the sensitization to cell death induced by TWEAK/TNFα/interferon-γ. In contrast, Bcl3 overexpression decreased NF-κB transcriptional activity, inflammatory response and cell death while dampening the decrease in Klotho expression. In conclusion, Bcl3 expressed in response to TWEAK stimulation decreases TWEAK-induced inflammatory and lethal responses. Therefore, therapeutic upregulation of Bcl3 activity should be explored in kidney disease because it has advantages over chemical inhibitors of NF-κB that are known to prevent inflammatory responses but can also sensitize the cells to apoptosis.

Non-alcoholic fatty liver disease, vascular inflammation and insulin resistance are exacerbated by TRAIL deletion in mice

Non-alcoholic fatty liver disease (NAFLD) incorporates steatosis, non-alcoholic steato-hepatitis (NASH) and liver cirrhosis, associating with diabetes and cardiovascular disease (CVD). TNF-related apoptosis-inducing ligand (TRAIL) is protective of CVD. We aimed to determine whether TRAIL protects against insulin resistance, NAFLD and vascular injury. Twelve-week high fat diet (HFD)-fed Trail^−/− mice had increased plasma cholesterol, insulin and glucose compared to wildtype. Insulin tolerance was impaired with TRAIL-deletion, with reduced p-Akt, GLUT4 expression and glucose uptake in skeletal muscle. Hepatic triglyceride content, inflammation and fibrosis were increased with TRAIL-deletion, with elevated expression of genes regulating lipogenesis and gluconeogenesis. Moreover, Trail^−/− mice exhibited reduced aortic vasorelaxation, impaired insulin signaling, and >20-fold increased mRNA expression for IL-1β, IL-6, and TNF-α. In vitro, palmitate treatment of hepatocytes increased lipid accumulation, inflammation and fibrosis, with TRAIL mRNA significantly reduced. TRAIL administration inhibited palmitate-induced hepatocyte lipid uptake. Finally, patients with NASH had significantly reduced plasma TRAIL compared to control, simple steatosis or obese individuals. These findings suggest that TRAIL protects against insulin resistance, NAFLD and vascular inflammation. Increasing TRAIL levels may be an attractive therapeutic strategy, to reduce features of diabetes, as well as liver and vascular injury, so commonly observed in individuals with NAFLD.

2017 update on the relationship between diabetes and colorectal cancer: epidemiology, potential molecular mechanisms and therapeutic implications

Worldwide deaths from diabetes mellitus (DM) and colorectal cancer increased by 90% and 57%, respectively, over the past 20 years. The risk of colorectal cancer was estimated to be 27% higher in patients with type 2 DM than in non-diabetic controls. However, there are potential confounders, information from lower income countries is scarce, across the globe there is no correlation between DM prevalence and colorectal cancer incidence and the association has evolved over time, suggesting the impact of additional environmental factors. The clinical relevance of these associations depends on understanding the mechanism involved. Although evidence is limited, insulin use has been associated with increased and metformin with decreased incidence of colorectal cancer. In addition, colorectal cancer shares some cellular and molecular pathways with diabetes target organ damage, exemplified by diabetic kidney disease. These include epithelial cell injury, activation of inflammation and Wnt/β-catenin pathways and iron homeostasis defects, among others. Indeed, some drugs have undergone clinical trials for both cancer and diabetic kidney disease. Genome-wide association studies have identified diabetes-associated genes (e.g. TCF7L2) that may also contribute to colorectal cancer. We review the epidemiological evidence, potential pathophysiological mechanisms and therapeutic implications of the association between DM and colorectal cancer. Further studies should clarify the worldwide association between DM and colorectal cancer, strengthen the biological plausibility of a cause-and-effect relationship through characterization of the molecular pathways involved, search for specific molecular signatures of colorectal cancer under diabetic conditions, and eventually explore DM-specific strategies to prevent or treat colorectal cancer.

Lysyl Oxidase-like-2 Cross-links Collagen IV of Glomerular Basement Membrane

The 7S dodecamer is recognized as an important structural cross-linking domain of collagen IV networks that provide mechanical stability to basement membranes, a specialized form of extracellular matrix essential for the development and maintenance of tissue architecture. Although the 7S dodecamer is stabilized by covalent cross-linking, the molecular mechanism by which such cross-links are formed has not been revealed. Here, we aimed to identify the enzyme(s) that cross-links the 7S dodecamer and characterize its expression in the kidney glomerulus. Pharmacological inhibition of candidate extracellular matrix enzymes revealed that lysyl oxidase activity is required for cross-linking of 7S polypeptides. Among all lysyl oxidase family members, lysyl oxidase-like-2 (LOXL2) was identified as the isoform cross-linking collagen IV in mouse embryonal PFHR-9 cells. Biochemical analyses revealed that LOXL2 readily promoted the formation of lysyl-derived cross-links in the 7S dodecamer but not in the NC1 domain. We also established that LOXL2 is the main lysyl oxidase family member present in the glomerular extracellular matrix. Altogether, we demonstrate that LOXL2 is a novel component of the molecular machinery that forms cross-linked collagen IV networks, which are essential for glomerular basement membrane stability and molecular ultrafiltration function.

MXRA5 is a TGF-β1-regulated human protein with anti-inflammatory and anti-fibrotic properties

Current therapy for chronic kidney disease (CKD) is unsatisfactory because of an insufficient understanding of its pathogenesis. Matrix remodelling-associated protein 5 (MXRA5, adlican) is a human protein of unknown function with high kidney tissue expression, not present in rodents. Given the increased expression of MXRA5 in injured tissues, including the kidneys, we have suggested that MXRA5 may modulate kidney injury. MXRA5 immunoreactivity was observed in tubular cells in human renal biopsies and in urine from CKD patients. We then explored factors regulating MXRA5 expression and MXRA5 function in cultured human proximal tubular epithelial cells and explored MXRA5 expression in kidney cancer cells and kidney tissue. The fibrogenic cytokine transforming growth factor-β1 (TGFβ1) up-regulated MXRA5 mRNA and protein expression. TGFβ1-induced MXRA5 up-regulation was prevented by either interference with TGFβ1 activation of the TGFβ receptor 1 (TGFBR1, ALK5) or by the vitamin D receptor agonist paricalcitol. By contrast, the pro-inflammatory cytokine TWEAK did not modulate MXRA5 expression. MXRA5 siRNA-induced down-regulation of constitutive MXRA5 expression resulted in higher TWEAK-induced expression of chemokines. In addition, MXRA5 down-regulation resulted in a magnified expression of genes encoding extracellular matrix proteins in response to TGFβ1. Furthermore, in clear cell renal cancer, von Hippel-Lindau (VHL) regulated MXRA5 expression. In conclusion, MXRA5 is a TGFβ1- and VHL-regulated protein and, for the first time, we identify MXRA5 functions as an anti-inflammatory and anti-fibrotic molecule. This information may yield clues to design novel therapeutic strategies in diseases characterized by inflammation and fibrosis.

Cyclopropanyldehydrocostunolide LJ attenuates high glucose-induced podocyte injury by suppressing RANKL/RANK-mediated NF-κB and MAPK signaling pathways

AIMS

The aim of this research was to investigate the effects of cyclopropanyldehydrocostunolide (also named LJ), a derivative of sesquiterpene lactones (SLs), on high glucose (HG)-induced podocyte injury and the associated molecular mechanisms.

METHODS

Differentiated mouse podocytes were incubated in different treatments. The migration and albumin filtration of podocytes were examined by Transwell filters. The protein and mRNA levels of MCP-1 were measured using enzyme-linked immunosorbent assay (ELISA) and quantitative real-time PCR (q-PCR). Protein expression and phosphorylation were detected by western blot, and the nuclear translocation of NF-κB was performed with a confocal microscope. The gene expression of the receptor activator for NF-κB (RANK) was silenced by small interfering RNA (siRNA).

RESULTS

Our results showed that HG enhanced migration, albumin filtration and MCP-1 expression in podocytes. At the molecular level, HG promoted the phosphorylation of NF-κB/p65, IKKβ, IκBα, mitogen-activated protein kinase (MAPK) and the nuclear translocation of p65. LJ reversed the effects of HG in a dose-dependent manner. Furthermore, our data provided the first demonstration that the receptor activator for NF-κB ligand (RANKL) and its cognate receptor RANK were overexpressed in HG-induced podocytes and were downregulated by LJ. RANK siRNA also attenuated HG-induced podocyte injury and markedly inhibited the activation of NF-κB and MAPK signaling pathways.

CONCLUSIONS

LJ attenuates HG-induced podocyte injury by suppressing RANKL/RANK-mediated NF-κB and MAPK signaling pathways.

Clinical Application of Human Urinary Extracellular Vesicles in Kidney and Urologic Diseases

Extracellular vesicles (EVs) have been isolated in different body fluids, including urine. The cargo of urinary EVs is composed of nucleic acids and proteins reflecting the physiological and possibly pathophysiological state of cells lining the nephron and the urinary tract. Urinary EVs have been confirmed to contain low amounts of various types of RNA that play a role in intercellular communication by transferring genetic information. This communication through EV RNAs includes both continuation of normal physiological processes and conditioning in disease mechanisms. Although proteins included in urinary EVs represent only 3% of the whole-urine proteome, urinary EVs can influence cells in the renal epithelia not only by delivering RNA cargo, but also by delivering a wide range of proteins. Since urine is a readily available biofluid, the discovery of EVs has opened a new field of biomarker research. The potential use of urinary EV RNAs and proteins as diagnostic biomarkers for various kidney and urologic diseases is currently being explored. Here, we review recent studies that deal in identifying biomarker candidates for human kidney and urologic diseases using urinary EVs and might help to understand the pathophysiology.

Targeting inflammation in diabetic kidney disease: early clinical trials

INTRODUCTION

The age-standardized death rate from diabetic kidney disease increased by 106% from 1990 to 2013, indicating that novel therapeutic approaches are needed, in addition to the renin-angiotensin system (RAS) blockers currently in use. Clinical trial results of anti-fibrotic therapy have been disappointing. However, promising anti-inflammatory drugs are currently on phase 1 and 2 randomized controlled trials.

AREAS COVERED

The authors review the preclinical, phase 1 and 2 clinical trial information of drugs tested for diabetic kidney disease that directly target inflammation as a main or key mode of action. Agents mainly targeting other pathways, such as endothelin receptor or mineralocorticoid receptor blockers and vitamin D receptor activators are not discussed.

EXPERT OPINION

Agents targeting inflammation have shown promising results in the treatment of diabetic kidney disease when added on top of RAS blockade. The success of pentoxifylline in open label trials supports the concept of targeting inflammation. In early clinical trials, the pentoxifylline derivative CTP-499, the CCR2 inhibitor CCX140-B, the CCL2 inhibitor emapticap pegol and the JAK1/JAK2 inhibitor baricitinib were the most promising drugs for diabetic kidney disease. The termination of trials testing the anti-IL-1β antibody gevokizumab in 2015 will postpone the evaluation of therapies targeting inflammatory cytokines.

Renal microRNA- and RNA-profiles in progressive chronic kidney disease

BACKGROUND

MicroRNAs (miRNAs) contribute to chronic kidney disease (CKD) progression via regulating mRNAs involved in renal homeostasis. However, their association with clinical outcome remains poorly understood.

MATERIALS AND METHODS

We performed miRNA and mRNA expression profiling on renal biopsy sections by qPCR (miRNA) and microarrays (mRNA) in a discovery (n = 43) and in a validation (n = 29) cohort. miRNAs differentiating stable and progressive cases were inversely correlated with putative target mRNAs, which were further characterized by pathway analysis using KEGG pathways.

RESULTS

miR-30d, miR-140-3p, miR-532-3p, miR-194, miR-190, miR-204 and miR-206 were downregulated in progressive cases. These seven miRNAs correlated with upregulated 29 target mRNAs involved in inflammatory response, cell-cell interaction, apoptosis and intra-cellular signalling. In particular, miR-206 and miR-532-3p were associated with distinct biological processes via the expression of their target mRNAs: Reduced expression of miR-206 in progressive disease correlated with the upregulation of target mRNAs participating in inflammatory pathways (CCL19, CXCL1, IFNAR2, NCK2, PTK2B, PTPRC, RASGRP1 and TNFRSF25). Progressive cases also showed a lower expression of miR-532-3p and an increased expression of target transcripts involved in apoptosis pathways (MAP3K14, TNFRSF10B/TRAIL-R2, TRADD and TRAF2). In the validation cohort, we confirmed the decreased expression of miR-206 and miR-532-3p, and the inverse correlation of these miRNAs with the expression of nine of the 12 target genes. The levels of the identified miRNAs and the target mRNAs correlated with clinical parameters and histological damage indices.

CONCLUSIONS

These results suggest the involvement of specific miRNAs and mRNAs in biological pathways associated with the progression of CKD.

Irbesartan Ameliorates Diabetic Nephropathy by Suppressing the RANKL-RANK-NF-κB Pathway in Type 2 Diabetic db/db Mice

The receptor activator of NF-κB ligand (RANKL) and its receptor RANK are overexpressed in focal segmental glomerular sclerosis (FSGS), IgA nephropathy (IgAN), and membranous nephropathy (MN). However, the expression and the potential roles of RANKL and RANK in diabetic nephropathy (DN) remain unclear. Irbesartan (Irb) has beneficial effects against diabetes-induced renal damage, but its mechanisms are poorly understood. Our present study investigated the effects of Irb in DN and whether the renal protective effects of Irb are mediated by RANKL/RANK and the downstream NF-κB pathway in db/db mice. Our results showed that db/db mice revealed severe metabolic abnormalities, renal dysfunction, podocyte injury, and increased MCP-1; these symptoms were reversed by Irb. At the molecular level, RANKL and RANK were overexpressed in the kidneys of db/db mice and Irb downregulated RANKL and RANK and inhibited the downstream NF-κB pathway. Our study suggests that Irb can ameliorate DN by suppressing the RANKL-RANK-NF-κB pathway.

A Systems Biology Overview on Human Diabetic Nephropathy: From Genetic Susceptibility to Post-Transcriptional and Post-Translational Modifications

Diabetic nephropathy (DN), a microvascular complication occurring in approximately 20-40% of patients with type 2 diabetes mellitus (T2DM), is characterized by the progressive impairment of glomerular filtration and the development of Kimmelstiel-Wilson lesions leading to end-stage renal failure (ESRD). The causes and molecular mechanisms mediating the onset of T2DM chronic complications are yet sketchy and it is not clear why disease progression occurs only in some patients. We performed a systematic analysis of the most relevant studies investigating genetic susceptibility and specific transcriptomic, epigenetic, proteomic, and metabolomic patterns in order to summarize the most significant traits associated with the disease onset and progression. The picture that emerges is complex and fascinating as it includes the regulation/dysregulation of numerous biological processes, converging toward the activation of inflammatory processes, oxidative stress, remodeling of cellular function and morphology, and disturbance of metabolic pathways. The growing interest in the characterization of protein post-translational modifications and the importance of handling large datasets using a systems biology approach are also discussed.

Association of osteoprotegerin with impaired glucose regulation and microalbuminuria: the REACTION study

BACKGROUND

High osteoprotegerin (OPG) has been reported in association with insulin resistance and type 2 diabetes. We aimed to evaluate the association of serum OPG with impaired glucose regulation (IGR) and microalbuminuria among middle-aged and older Chinese.

METHODS

Serum OPG was measured in 599 individuals with normal glucose regulation, 730 with impaired glucose regulation and 327 newly diagnosed patients with diabetes. Serum OPG was measured using ELISA methods and urine albumin/creatinine ratio was used to determine the urinary albumin excretion.

RESULTS

Serum OPG levels were significantly higher in subjects with isolated impaired fasting glucose, isolated impaired glucose tolerance, combined impaired fasting glucose/impaired glucose tolerance and diabetes than in those with normal glucose regulation, whereas serum OPG levels were not different in the four groups with dysregulation of glucose metabolism. OPG was associated with a higher risk for IGR (OR 1.108 for each 0.1 μg/l increase in OPG, 95% CI 1.009-1.117, p = 0.01) after adjustment for gender, age, BMI, current smoking and alcohol intake, family history of diabetes, homeostasis model assessment of insulin resistance (HOMA-IR), lipid profile; the corresponding OR of combined impaired glucose regulation and type 2 diabetes was 1.121 (95% CI 1.101-1.141, p = 0.0005). OPG was associated with the risk of microalbuminuria (OR 1.025, 95% CI 1.006-1.044, p = 0.02) after adjustment for gender, age, current smoking, current alcohol intake, family history of diabetes, BMI, waist/hip ratio, HOMA-IR, eGFR and lipid profile.

CONCLUSIONS

Serum OPG level is closely and independently associated with IGR and is an independent risk factor for microalbuminuria.

CD74 in Kidney Disease

CD74 (invariant MHC class II) regulates protein trafficking and is a receptor for macrophage migration inhibitory factor (MIF) and d-dopachrome tautomerase (d-DT/MIF-2). CD74 expression is increased in tubular cells and/or glomerular podocytes and parietal cells in human metabolic nephropathies, polycystic kidney disease, graft rejection and kidney cancer and in experimental diabetic nephropathy and glomerulonephritis. Stressors like abnormal metabolite (glucose, lyso-Gb3) levels and inflammatory cytokines increase kidney cell CD74. MIF activates CD74 to increase inflammatory cytokines in podocytes and tubular cells and proliferation in glomerular parietal epithelial cells and cyst cells. MIF overexpression promotes while MIF targeting protects from experimental glomerular injury and kidney cysts, and interference with MIF/CD74 signaling or CD74 deficiency protected from crescentic glomerulonephritis. However, CD74 may protect from interstitial kidney fibrosis. Furthermore, CD74 expression by stressed kidney cells raises questions about the kidney safety of cancer therapy strategies delivering lethal immunoconjugates to CD74-expressing cells. Thus, understanding CD74 biology in kidney cells is relevant for kidney therapeutics.

Targeting Mitochondria and Reactive Oxygen Species-Driven Pathogenesis in Diabetic Nephropathy

Diabetic kidney disease is one of the major microvascular complications of both type 1 and type 2 diabetes mellitus. Approximately 30% of patients with diabetes experience renal complications. Current clinical therapies can only mitigate the symptoms and delay the progression to end-stage renal disease, but not prevent or reverse it. Oxidative stress is an important player in the pathogenesis of diabetic nephropathy. The activity of reactive oxygen and nitrogen species (ROS/NS), which are by-products of the diabetic milieu, has been found to correlate with pathological changes observed in the diabetic kidney. However, many clinical studies have failed to establish that antioxidant therapy is renoprotective. The discovery that increased ROS/NS activity is linked to mitochondrial dysfunction, endoplasmic reticulum stress, inflammation, cellular senescence, and cell death calls for a refined approach to antioxidant therapy. It is becoming clear that mitochondria play a key role in the generation of ROS/NS and their consequences on the cellular pathways involved in apoptotic cell death in the diabetic kidney. Oxidative stress has also been associated with necrosis via induction of mitochondrial permeability transition. This review highlights the importance of mitochondria in regulating redox balance, modulating cellular responses to oxidative stress, and influencing cell death pathways in diabetic kidney disease. ROS/NS-mediated cellular dysfunction corresponds with progressive disease in the diabetic kidney, and consequently represents an important clinical target. Based on this consideration, this review also examines current therapeutic interventions to prevent ROS/NS-derived injury in the diabetic kidney. These interventions, mainly aimed at reducing or preventing mitochondrial-generated oxidative stress, improving mitochondrial antioxidant defense, and maintaining mitochondrial integrity, may deliver alternative approaches to halt or prevent diabetic kidney disease.

Plasma osteoprotegerin concentrations in type 1 diabetic patients with albuminuria

BACKGROUND

Osteoprotegerin (OPG) is a recently identified inhibitor of bone resorption. Recent studies indicate that OPG is also associated with endothelial dysfunction in diabetes.

AIM

To investigate the relationship between plasma OPG levels and urinary albumin excretion (UAE) in type 1 diabetes.

METHODS

A total of 80 type 1 diabetic subjects and 40 control subjects were enrolled. Diabetic subjects were divided into a normoalbuminuric group and a microalbuminuric group according to urinary albumin excretion rate (UAER). Plasma OPG level was measured by enzyme-linked immunoassay.

RESULTS

The plasma OPG levels were significantly elevated in patients with microalbuminuria (176.39±25.05pg/ml) compared with patients with normoalbuminuria (154.73±16.66pg/ml) and control subjects (44.76±8.7pg/ml). The plasma OPG level had a positive correlation with patients' age, duration of disease, HbA1C and UAER.

CONCLUSIONS

Plasma OPG levels are significantly associated with UAE in patients with type 1 diabetes. These findings may support the concept that elevated plasma OPG may be associated with diabetic angiopathy.

Designing drugs that combat kidney damage

INTRODUCTION

Kidney disease remains one of the last worldwide frontiers in the field of non-communicable human disease. From 1990 to 2013, chronic kidney disease (CKD) was the top non-communicable cause of death with a greatest increase in global years of life lost while mortality of acute kidney injury (AKI) still hovers around 50%. This reflects the paucity (for CKD) or lack of (for AKI) therapeutic approaches beyond replacing renal function. Understanding what the barriers are and what potential pathways may facilitate the design of new drugs to combat kidney disease is a key public health priority.

AREAS COVERED

The authors discuss the hurdles and opportunities for future drug development for kidney disease in light of experience accumulated with drugs that made it to clinical trials.

EXPERT OPINION

Inflammation, cell death and fibrosis are key therapeutic targets to combat kidney damage. While the specific targeting of drugs to kidney cells would be desirable, the technology is only working at the preclinical stage and with mixed success. Nanomedicines hold promise in this respect. Most drugs undergoing clinical trials for kidney disease have been repurposed from other indications. Currently, the chemokine receptor inhibitor CCX140 holds promise for CKD and the p53 inhibitor QPI-1002 for AKI.

Cinnabar-induced subchronic renal injury is associated with increased apoptosis in rats

The aim of this study was to explore the role of apoptosis in cinnabar-induced renal injury in rats. To test this role, rats were dosed orally with cinnabar (1 g/kg/day) for 8 weeks or 12 weeks, and the control rats were treated with 5% carboxymethylcellulose solution. Levels of urinary mercury (UHg), renal mercury (RHg), serum creatinine (SCr), and urine kidney injury molecule 1 (KIM-1) were assessed, and renal pathology was analyzed. Apoptotic cells were identified and the apoptotic index was calculated. A rat antibody array was used to analyze expression of cytokines associated with apoptosis. Results from these analyses showed that UHg, RHg, and urine KIM-1, but not SCr, levels were significantly increased in cinnabar-treated rats. Renal pathological changes in cinnabar-treated rats included vacuolization of tubular cells, formation of protein casts, infiltration of inflammatory cells, and increase in the number of apoptotic tubular cells. In comparison to the control group, expression of FasL, Fas, TNF-α, TRAIL, activin A, and adiponectin was upregulated in the cinnabar-treated group. Collectively, our results suggest that prolonged use of cinnabar results in kidney damage due to accumulation of mercury and that the underlying mechanism involves apoptosis of tubular cells via a death receptor-mediated pathway.

Inflammation and renal function after a four-year follow-up in subjects with unimpaired glomerular filtration rate: results from the observational, population-based CARLA cohort

Background

There is evidence that chronic inflammation is associated with the progression/development of chronic renal failure; however, relations in subjects with preserved renal function remain insufficiently understood.

Objective

To examine the association of inflammation with the development of renal failure in a cohort of the elderly general population.

Methods

After excluding subjects with reduced estimated glomerular filtration rate (eGFR<60 mL/min/1.73 m²) and missing data, the cohort incorporated 785 men and 659 women (aged 45–83 years). Follow-up was performed four years after baseline. Covariate adjusted linear and logistic regression models were used to assess the association of plasma/serum concentrations of soluble tumour necrosis factor receptor 1 (sTNF-R1), C-reactive protein (CRP), and interleukin 6 (IL-6) with change in eGFR/creatinine. The areas under the curve (AUCs) from receiver operating characteristics (ROCs) were estimated.

Results

In adjusted models sTNF-R1 was distinctively associated with a decline in eGFR in men (0.6 mL/min/1.73 m² per 100 pg/mL sTNF-R1; 95% CI: 0.4–0.8), but not in women. A similar association could not be found for CRP or IL-6. Estimates of sTNF-R1 in the cross-sectional analyses were similar between sexes, while CRP and IL-6 were not relevantly associated with eGFR/creatinine.

Conclusion

In the elderly male general population with preserved renal function sTNF-R1 predicts the development of renal failure.

The osteoprotegerin/tumor necrosis factor related apoptosis-inducing ligand axis in the kidney

PURPOSE OF REVIEW

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a cytokine belonging to the TNF superfamily. TRAIL may modulate cell survival and proliferation through interaction with two different receptors, TRAIL-R1 and TRAIL-R2. The actions of TRAIL are regulated by three decoy receptors, TRAIL-R3, TRAIL-R4 and osteoprotegerin (OPG). There is evidence that both TRAIL and OPG are expressed by renal cells. The OPG/TRAIL axis has been recently linked to the pathogenesis of renal damage and, in particular, diabetic nephropathy.

RECENT FINDINGS

In patients with kidney diseases, serum TRAIL and OPG levels are increased in parallel and are significantly associated with each other. In diabetic nephropathy, the renal expression of TRAIL and OPG is elevated, and in tubular cells proinflammatory cytokines enhance TRAIL expression. Additionally, a high-glucose microenvironment sensitizes tubular cells to apoptosis induced by TRAIL, whereas OPG counteracts the actions of TRAIL in cultured cells.

SUMMARY

It seems that the expression and levels of TRAIL and OPG at serum and kidney levels are crucial for the pathogenesis of kidney diseases, and in particular diabetic nephropathy. Although further studies are necessary to clarify the exact role of the OPG/TRAIL axis in the kidney, this system seems to hold promise to provide therapeutic approaches for the management of renal damage.

VIDEO ABSTRACT AVAILABLE

See the Video Supplementary Digital Content 1 (http://links.lww.com/CONH/A5).

Blocking TRAIL-DR5 signaling with soluble DR5 alleviates acute kidney injury in a severely burned mouse model

Acute kidney injury (AKI) predicts high mortality in severely burned patients. Apoptosis plays a significant role during AKI; however, the apoptotic mechanisms underlying AKI induced by burn injury are not clear. Here, we report a critical role for tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-Death receptor 5 (DR5) signaling in the pathogenesis of AKI. C57BL/6 male mice were subjected to full thickness scald burn. Apoptosis was significantly up-regulated in mouse kidney 24 h after the burn. Meanwhile, the TRAIL and DR5 expression levels were significantly increased in the kidney 24 h after the burn. Soluble DR5 treatment reduced apoptotic cell death and alleviated kidney injury induced by the burn through blocking the interaction of endogenous TRAIL with DR5. These results demonstrated that TRAIL plays a deleterious role in AKI pathogenesis induced by scald burns. Inhibition of TRAIL function in the kidney may represent a novel protective strategy to treat AKI in patients with burns.

Osteoprotegerin and kidney disease

Vascular calcification in chronic kidney disease (CKD) patients is associated to increased mortality. Osteoprotegerin (OPG) is a soluble tumor necrosis factor (TNF) superfamily receptor that inhibits the actions of the cytokines receptor activator of nuclear factor kappa-B ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL) by preventing their binding to signaling receptors in the cell membrane. OPG-deficient mice display vascular calcification while OPG prevented calcification of cultured vascular smooth muscle cells and protected kidney cells from TRAIL-induced death. OPG may be a biomarker in patients with kidney disease. Circulating OPG is increased in predialysis, dialysis and transplant CKD patients and may predict vascular calcification progression and patient survival. By contrast, circulating OPG is decreased in nephrotic syndrome. In addition, free and exosome-bound urinary OPG is increased in human kidney disease. Increased urinary OPG has been associated with lupus nephritis activity. Despite the association of high OPG levels with disease, experimental functional information available suggests that OPG might be protective in kidney disease and in vascular injury in the context of uremia. Thus, tissue injury results in increased OPG, while OPG may protect from tissue injury. Recombinant OPG was safe in phase I randomized controlled trials. Further research is needed to fully define the therapeutic and biomarker potential of OPG in patients with kidney disease.

TRAIL deficiency contributes to diabetic nephropathy in fat-fed ApoE-/- mice

Background

We recently demonstrated that TNF-related apoptosis-inducing ligand (TRAIL) is protective of diet-induced diabetes in mice. While TRAIL has been implicated in chronic kidney disease, its role in vivo in diabetic nephropathy is not clear. The present study investigated the role of TRAIL in the pathogenesis of diabetic nephropathy using TRAIL^-/-ApoE^-/- mice.

Methods

TRAIL^-/-ApoE^-/- and ApoE^-/- mice were fed a high fat diet for 20 w. Plasma glucose and insulin levels were assessed over 0, 5, 8 and 20 w. At 20 w, markers of kidney function including creatinine, phosphate, calcium and cystatin C were measured. Changes in mRNA expression of MMPs, TIMP-1, IL-1β and IL-18 were assessed in the kidney. Functional and histological changes in kidneys were examined. Glucose and insulin tolerance tests were performed.

Results

TRAIL^-/-ApoE^-/- mice had significantly increased urine protein, urine protein:creatinine ratio, plasma phosphorous, and plasma cystatin C, with accelerated nephropathy. Histologically, increased extracellular matrix, mesangial expansion and mesangial cell proliferation in the glomeruli were observed. Moreover, TRAIL^-/-ApoE^-/- kidneys displayed loss of the brush border and disorganisation of tubular epithelium, with increased fibrosis. TRAIL-deficient kidneys also had increased expression of MMPs, TIMP-1, PAI-1, IL-1β and IL-18, markers of renal injury and inflammation. Compared with ApoE^-/- mice, TRAIL^-/-ApoE^-/- mice displayed insulin resistance and type-2 diabetic features with reduced renal insulin-receptor expression.

Conclusions

Here, we show that TRAIL-deficiency in ApoE^-/- mice exacerbates nephropathy and insulin resistance. Understanding TRAIL signalling in kidney disease and diabetes, may therefore lead to novel strategies for the treatment of diabetic nephropathy.

Alveolar epithelial cells in idiopathic pulmonary fibrosis display upregulation of TRAIL, DR4 and DR5 expression with simultaneous preferential over-expression of pro-apoptotic marker p53

Idiopathic pulmonary fibrosis (IPF) is a progressive, debilitating, and fatal lung disease of unknown aetiology with no current cure. The pathogenesis of IPF remains unclear but repeated alveolar epithelial cell (AEC) injuries and subsequent apoptosis are believed to be among the initiating/ongoing triggers. However, the precise mechanism of apoptotic induction is hitherto elusive. In this study, we investigated expression of a panel of pro-apoptotic and cell cycle regulatory proteins in 21 IPF and 19 control lung tissue samples. We reveal significant upregulation of the apoptosis-inducing ligand TRAIL and its cognate receptors DR4 and DR5 in AEC within active lesions of IPF lungs. This upregulation was accompanied by pro-apoptotic protein p53 overexpression. In contrast, myofibroblasts within the fibroblastic foci of IPF lungs exhibited high TRAIL, DR4 and DR5 expression but negligible p53 expression. Similarly, p53 expression was absent or negligible in IPF and control alveolar macrophages and lymphocytes. No significant differences in TRAIL expression were noted in these cell types between IPF and control lungs. However, DR4 and DR5 upregulation was detected in IPF alveolar macrophages and lymphocytes. The marker of cellular senescence p21(WAF1) was upregulated within affected AEC in IPF lungs. Cell cycle regulatory proteins Cyclin D1 and SOCS3 were significantly enhanced in AEC within the remodelled fibrotic areas of IPF lungs but expression was negligible in myofibroblasts. Taken together these findings suggest that, within the remodelled fibrotic areas of IPF, AEC can display markers associated with proliferation, senescence, and apoptotosis, where TRAIL could drive the apoptotic response. Clear understanding of disease processes and identification of therapeutic targets will direct us to develop effective therapies for IPF.

Blockade of Death Ligand TRAIL Inhibits Renal Ischemia Reperfusion Injury

Renal ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI). Many investigators have reported that cell death via apoptosis significantly contributed to the pathophysiology of renal IRI. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor superfamily, and induces apoptosis and inflammation. However, the role of TRAIL in renal IRI is unclear. Here, we investigated whether TRAIL contributes to renal IRI and whether TRAIL blockade could attenuate renal IRI. AKI was induced by unilateral clamping of the renal pedicle for 60 min in male FVB/N mice. We found that the expression of TRAIL and its receptors were highly upregulated in renal tubular cells in renal IRI. Neutralizing anti-TRAIL antibody or its control IgG was given 24 hr before ischemia and a half-dose booster injection was administered into the peritoneal cavity immediately after reperfusion. We found that TRAIL blockade inhibited tubular apoptosis and reduced the accumulation of neutrophils and macrophages. Furthermore, TRAIL blockade attenuated renal fibrosis and atrophy after IRI. In conclusion, our study suggests that TRAIL is a critical pathogenic factor in renal IRI, and that TRAIL could be a new therapeutic target for the prevention of renal IRI.