The role of interstitial macrophages in nephropathy of type 2 diabetic db/db mice

SIK2 protects against renal tubular injury and the progression of diabetic kidney disease

Despite optimal medical therapy, many patients with diabetic kidney disease (DKD) progress to end-stage renal disease. The identification of new biomarkers and drug targets for DKD is required for the development of more effective therapies. The apoptosis of renal tubular epithelial cells is a key feature of the pathogenicity associated with DKD. SIK2, a salt-inducible kinase, regulates important biological processes, such as energy metabolism, cell cycle progression and cellular apoptosis. In our current study, a notable decrease in the expression of SIK2 was detected in the renal tubules of DKD patients and murine models. Functional experiments demonstrated that deficiency or inactivity of SIK2 aggravates tubular injury and interstitial fibrosis in diabetic mice. Based on transcriptome sequencing, molecular mechanism exploration revealed that SIK2 overexpression reduces endoplasmic reticulum (ER) stress-mediated tubular epithelial apoptosis by inhibiting the histone acetyltransferase activity of p300 to activate HSF1/Hsp70. Furthermore, the specific restoration of SIK2 in tubules blunts tubular and interstitial impairments in diabetic and vancomycin-induced kidney disease mice. Together, these findings indicate that SIK2 protects against renal tubular injury and the progression of kidney disease, and make a compelling case for targeting SIK2 for therapy in DKD.

FcER1: A Novel Molecule Implicated in the Progression of Human Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a key microvascular complication of diabetes, with few therapies for targeting renal disease pathogenesis and progression. We performed transcriptional and protein studies on 103 unique blood and kidney tissue samples from patients with and without diabetes to understand the pathophysiology of DKD injury and its progression. The study was based on the use of 3 unique patient cohorts: peripheral blood mononuclear cell (PBMC) transcriptional studies were conducted on 30 patients with DKD with advancing kidney injury; Gene Expression Omnibus (GEO) data was downloaded, containing transcriptional measures from 51 microdissected glomerulous from patients with DKD. Additionally, 12 independent kidney tissue sections from patients with or without DKD were used for validation of target genes in diabetic kidney injury by kidney tissue immunohistochemistry and immunofluorescence. PBMC DKD transcriptional analysis, identified 853 genes (p < 0.05) with increasing expression with progression of albuminuria and kidney injury in patients with diabetes. GEO data was downloaded, normalized, and analyzed for significantly changed genes. Of the 325 significantly up regulated genes in DKD glomerulous (p < 0.05), 28 overlapped in PBMC and diabetic kidney, with perturbed FcER1 signaling as a significantly enriched canonical pathway. FcER1 was validated to be significantly increased in advanced DKD, where it was also seen to be specifically co-expressed in the kidney biopsy with tissue mast cells. In conclusion, we demonstrate how leveraging public and private human transcriptional datasets can discover and validate innate immunity and inflammation as key mechanistic pathways in DKD progression, and uncover FcER1 as a putative new DKD target for rational drug design.

FOXO3a Protects against Kidney Injury in Type II Diabetic Nephropathy by Promoting Sirt6 Expression and Inhibiting Smad3 Acetylation

Diabetic nephropathy (DN) is the most common cause of end-stage renal disease. Although numerous reports have demonstrated a correlation between epithelial-mesenchymal transition (EMT) and renal fibrosis, how these processes lead to tubular dysfunction remains unclear. Here, we show that FOXO3a protects kidneys from injury in type II DN by increasing Sirt6 expression, which deacetylates Smad3 and inhibits its transcriptional activity. The results showed that progressive EMT in the kidneys from db/db mice is associated with Sirt6 downregulation and involved in tubular injury and dysfunction. The reduction of Sirt6 levels in db/db mice resulted in progressive kidney injury, indicating the protective role of Sirt6. Furthermore, Sirt6 was shown to directly bind to Smad3, a key downstream mediator of TGF-β, and could deacetylate it to inhibit its nuclear accumulation and transcriptional activity in HK2 cells. Besides, we demonstrate that FOXO3a activates Sirt6 expression by binding to its promoter. shRNA-induced FOXO3a knockdown in the kidneys of db/db mice exacerbated tubular injury and renal function loss. Mechanistically, FOXO3a protects against kidney injury in type II DN through the Sirt6/Smad3 axis. Thus, the pharmacological targeting of FOXO3a-mediated Sirt6/Smad3 signaling pathways may provide a novel strategy for treating type II DN.

Transcriptome-wide association analysis identifies DACH1 as a kidney disease risk gene that contributes to fibrosis

Genome-wide association studies (GWAS) for kidney function identified hundreds of risk regions; however, the causal variants, target genes, cell types, and disease mechanisms remain poorly understood. Here, we performed transcriptome-wide association studies (TWAS), summary Mendelian randomization, and MetaXcan to identify genes whose expression mediates the genotype effect on the phenotype. Our analyses identified Dachshund homolog 1 (DACH1), a cell-fate determination factor. GWAS risk variant was associated with lower DACH1 expression in human kidney tubules. Human and mouse kidney single-cell open chromatin data (snATAC-Seq) prioritized estimated glomerular filtration rate (eGFR) GWAS variants located on an intronic regulatory region in distal convoluted tubule cells. CRISPR-Cas9-mediated gene editing confirmed the role of risk variants in regulating DACH1 expression. Mice with tubule-specific Dach1 deletion developed more severe renal fibrosis both in folic acid and diabetic kidney injury models. Mice with tubule-specific Dach1 overexpression were protected from folic acid nephropathy. Single-cell RNA sequencing, chromatin immunoprecipitation, and functional analysis indicated that DACH1 controls the expression of cell cycle and myeloid chemotactic factors, contributing to macrophage infiltration and fibrosis development. In summary, integration of GWAS, TWAS, single-cell epigenome, expression analyses, gene editing, and functional validation in different mouse kidney disease models identified DACH1 as a kidney disease risk gene.

Wnt/β-Catenin in Acute Kidney Injury and Progression to Chronic Kidney Disease

Acute kidney injury (AKI) portends a poor clinical prognosis and increases the risk for the development of chronic kidney disease (CKD). Currently, there are no therapies to treat AKI or prevent its progression to CKD. Wnt/β-catenin is a critical regulator of kidney development that is up-regulated after injury. Most of the literature support a beneficial role for Wnt/β-catenin in AKI, but suggest that this pathway promotes the progression of tubulointerstitial fibrosis, the hallmark of CKD progression. We review the role of Wnt/β-catenin in renal injury with a focus on its potential as a therapeutic target in AKI and in AKI to CKD transition.

Up-regulation of PKR pathway contributes to L-NAME induced hypertension and renal damage

Objective

Hypertension induced kidney damage is often associated with fibrosis and tubular apoptosis. Double-stranded protein kinase (PKR) is a well recognized inducer of inflammation and apoptosis. However, role of PKR in hypertension coupled renal damage is still not explored. Therefore here we sought to investigate the role of PKR in the pathogenesis of L-NAME induced hypertension and renal damage in Wistar rats and the underneath molecular mechanism.

Methods

L-NAME (40 mg/kg, p.o) and imoxin (0.5 mg/kg, i.p) was given to Wistar rats for 4 weeks. Increased eNOS expression, serum creatinine, BUN and changes in mean arterial pressure confirmed for hypertensive renal damage. Western blot and immunohistochemistry was carried out for PKR and markers for fibrosis and apoptosis. Morphological alterations were assessed by H&E staining. Sirius red and Masson's Trichrome staining was performed for collagen and fibrosis. TUNEL assay was done for tubular cell death and apoptosis.

Results

Increased expression of PKR and its downstream markers were reported in L-NAME rats, attenuation was observed with imoxin treatment. L-NAME treated rats showed a significant increase in MAP, serum calcium, creatinine and BUN along with the significant morphological changes, attenuation was reported with the imoxin treatment.

Conclusion

PKR is a core contributor in the pathogenesis of L-NAME induced renal damage and tubular apoptosis. Therapeutically targeting of PKR could be an attractive approach to treat the renal complications associated with hypertension.

Endogenous miR-204 Protects the Kidney against Chronic Injury in Hypertension and Diabetes

BACKGROUND

Aberrant microRNA (miRNA) expression affects biologic processes and downstream genes that are crucial to CKD initiation or progression. The miRNA miR-204-5p is highly expressed in the kidney but whether miR-204-5p plays any role in the development of chronic renal injury is unknown.

METHODS

We used real-time PCR to determine levels of miR-204 in human kidney biopsies and animal models. We generated Mir204 knockout mice and used locked nucleic acid-modified anti-miR to knock down miR-204-5p in mice and rats. We used a number of physiologic, histologic, and molecular techniques to analyze the potential role of miR-204-5p in three models of renal injury.

RESULTS

Kidneys of patients with hypertension, hypertensive nephrosclerosis, or diabetic nephropathy exhibited a significant decrease in miR-204-5p compared with controls. Dahl salt-sensitive rats displayed lower levels of renal miR-204-5p compared with partially protected congenic SS.13^BN26 rats. Administering anti-miR-204-5p to SS.13^BN26 rats exacerbated interlobular artery thickening and renal interstitial fibrosis. In a mouse model of hypertensive renal injury induced by uninephrectomy, angiotensin II, and a high-salt diet, Mir204 gene knockout significantly exacerbated albuminuria, renal interstitial fibrosis, and interlobular artery thickening, despite attenuation of hypertension. In diabetic db/db mice, administering anti-miR-204-5p exacerbated albuminuria and cortical fibrosis without influencing blood glucose levels. In all three models, inhibiting miR-204-5p or deleting Mir204 led to upregulation of protein tyrosine phosphatase SHP2, a target gene of miR-204-5p, and increased phosphorylation of signal transducer and activator of transcription 3, or STAT3, which is an injury-promoting effector of SHP2.

CONCLUSIONS

These findings indicate that the highly expressed miR-204-5p plays a prominent role in safeguarding the kidneys against common causes of chronic renal injury.

Automated Image Analyses of Glomerular Hypertrophy in a Mouse Model of Diabetic Nephropathy

Background

Glomerular hypertrophy is a hallmark of kidney injury in metabolically induced renal diseases such as obesity-associated glomerulopathies and diabetic nephropathy (DN).

Methods

Using light sheet fluorescent microscopy (LSFM) and 3D image analysis, we tested algorithms for automated and unbiased quantification of total glomerular numbers and individual glomerular volume in the uninephrectomized (UNx) db/db mouse model of DN.

Results

At 6 weeks after surgery, db/db and UNx db/db mice showed increased urine albumin-to-creatinine ratio (ACR) compared with db/+ control mice. Before euthanasia, glomeruli were labeled in vivo by injecting tomato lectin. Whole-kidney LSFM 3D image analysis revealed that mean glomerular volume was significantly increased in UNx db/db mice compared with db/+ mice. Moreover, analysis of individual glomerular volume showed a shift in volume distribution toward larger glomeruli and thereby demonstrated additive effects of diabetes and UNx on induction of glomerular hypertrophy. The automatized quantification showed no significant differences in glomerular numbers among db/+, db/db, and UNx db/db mice. These data correlated with glomerular numbers as quantified by subsequent stereologic quantification.

Conclusions

Overall, LSFM coupled with automated 3D histomorphometric analysis was demonstrated to be advantageous for unbiased assessment of glomerular volume and numbers in mouse whole-kidney samples. Furthermore, we showed that injection of fluorescently labeled lectin and albumin can be used as markers of nephron segments in the mouse kidneys, thus enabling functional assessment of kidney physiology, pathology, and pharmacology in preclinical rodent models of kidney disease.

1,25(OH)2D3 provides protection against diabetic kidney disease by downregulating the TLR4-MyD88-NF-κB pathway

The over-activation of Toll-like receptors (TLRs) is a typical immune response to injury. Previous work has suggested that controlling the over-activation of TLR4-MyD88-NF-κB may represent a new therapeutic option for diabetic kidney disease (DKD). 1,25(OH)₂D₃ has also been shown to exert a protective effect on DKD, although the mechanism involved has yet to be elucidated. The aim of this study was to investigate whether 1,25(OH)₂D₃ protects against DKD by down-regulating the innate immune TLR-NF-κB pathway. NRK-52E cells were cultured under normal or high-glucose conditions. We then used siRNA to knock down TLR4 expression under high-glucose conditions. NRK-52E cells cultured under high-glucose conditions, and streptozotocin (STZ)-induced diabetic rats, were treated with different doses of 1,25(OH)₂D₃ and used as in vitro and in vivo models, respectively. Renal biochemical indicators were then measured to evaluate the influence of 1,25(OH)₂D₃ treatment on DKD in diabetic rats. Histological analysis was also performed to determine the extent of infiltration by inflammatory cells and tubulointerstitial fibrosis. Using RT-qPCR, western blotting, immunohistochemistry and immunofluorescence, we determined the expression levels of TLR4, MyD88, NF-κB p65, MCP-1 and α-SMA to investigate whether 1,25(OH)₂D₃ could reduce the development of tubulointerstitial fibrosis. Knocking down TLR4 abolished the tubulointerstitial fibrosis caused by high-glucose conditions. High doses of 1,25(OH)₂D₃ consistently reduced the expression of TLR4-MyD88-NF-κB in NRK-52E cells. Moreover, high doses of 1,25(OH)₂D₃ had an obvious protective effect on kidney injury and inhibited the infiltration of inflammatory cells and tubulointerstitial fibrosis in diabetic rats. In conclusion, high doses of 1,25(OH)₂D₃ protected against tubulointerstitial fibrosis both in vitro and in vivo by downregulating the expression of TLR4-MyD88-NF-κB.

Impact of sex on diabetic nephropathy and the renal transcriptome in UNx db/db C57BLKS mice

Diabetic nephropathy (DN) is associated with albuminuria and loss of kidney function and is the leading cause of end-stage renal disease. Despite evidence of sex-associated differences in the progression of DN in human patients, male mice are predominantly being used in preclinical DN research and drug development. Here, we compared renal changes in male and female uninephrectomized (UNx) db/db C57BLKS mice using immunohistochemistry and RNA sequencing. Male and female UNx db/db mice showed similar progression of type 2 diabetes, as assessed by obesity, hyperglycemia, and HbA1c. Progression of DN was also similar between sexes as assessed by kidney and glomerular hypertrophy as well as urine albumin-to-creatinine ratio being increased in UNx db/db compared with control mice. In contrast, kidney collagen III and glomerular collagen IV were increased only in female UNx db/db as compared with respective control mice but showed a similar tendency in male UNx db/db mice. Comparison of renal cortex transcriptomes by RNA sequencing revealed 66 genes differentially expressed (p < .01) in male versus female UNx db/db mice, of which 9 genes were located on the sex chromosomes. In conclusion, male and female UNx db/db mice developed similar hallmarks of DN pathology, suggesting no or weak sex differences in the functional and structural changes during DN progression.

The diabetes pandemic suggests unmet needs for 'CKD with diabetes' in addition to 'diabetic nephropathy'-implications for pre-clinical research and drug testing

Curing 'diabetic nephropathy' is considered an unmet medical need of high priority. We propose to question the concept of 'diabetic nephropathy' that implies diabetes as the predominant cause of kidney disease, which may not apply to the majority of type 2 diabetics approaching end-stage kidney disease. With the onset of diabetes, hyperglycaemia/sodium-glucose co-transporter-2-driven glomerular hyperfiltration promotes nephron hypertrophy, which, however, on its own, causes proteinuria not before a decade later, probably because podocyte hypertrophy can usually accommodate an increase in the filtration surface. In contrast, precedent chronic kidney disease (CKD), that is, few nephrons per body mass, e.g. due to poor nephron endowment from birth, obesity, pregnancy, or renal ageing or injury-related nephron loss, usually precedes the onset of type 2 diabetes. This applies in particular in older adults, and each on its own, but especially in combination, further aggravates single nephron hyperfiltration and glomerular hypertrophy. Whenever this additional hyperglycaemia-driven enlargement of the glomerular filtration surface exceeds the capacity of podocytes for hypertrophy, podocytes detachment leads to glomerulosclerosis and nephron loss, i.e. CKD progression. Animal models of 'diabetic nephropathy' based only on hyperglycaemia do not mimic this aspect and therefore poorly predict outcomes of clinical trials usually performed on elderly CKD patients with type 2 diabetes. Thus, we advocate the use of renal mass (nephron) ablation in type 2 diabetic animals to better mimic the pathophysiology of 'CKD with diabetes' in the target patient population and the use of the glomerular filtration rate as a primary endpoint to more reliably predict trial outcomes.

Sustained Klotho delivery reduces serum phosphate in a model of diabetic nephropathy

Diabetic nephropathy (DN) is a primary cause of end-stage renal disease and is becoming more prevalent because of the global rise in type 2 diabetes. A model of DN, the db/db uninephrectomized ( db/db-uni) mouse, is characterized by obesity, as well as compromised renal function. This model also manifests defects in mineral metabolism common in DN, including hyperphosphatemia, which leads to severe endocrine disease. The FGF23 coreceptor, α-Klotho, circulates as a soluble, cleaved form (cKL) and may directly influence phosphate handling. Our study sought to test the effects of cKL on mineral metabolism in db/db-uni mice. Mice were placed into either mild or moderate disease groups on the basis of the albumin-to-creatinine ratio (ACR). Body weights of db/db-uni mice were significantly greater across the study compared with lean controls regardless of disease severity. Adeno-associated cKL administration was associated with increased serum Klotho, intact, bioactive FGF23 (iFGF23), and COOH-terminal fragments of FGF23 ( P < 0.05). Blood urea nitrogen was improved after cKL administration, and cKL corrected hyperphosphatemia in the high- and low-ACR db/db-uni groups. Interestingly, 2 wk after cKL delivery, blood glucose levels were significantly reduced in db/db-uni mice with high ACR ( P < 0.05). Interestingly, several genes associated with stabilizing active iFGF23 were also increased in the osteoblastic UMR-106 cell line with cKL treatment. In summary, delivery of cKL to a model of DN normalized blood phosphate levels regardless of disease severity, supporting the concept that targeting cKL-affected pathways could provide future therapeutic avenues in DN. NEW & NOTEWORTHY In this work, systemic and continuous delivery of the "soluble" or "cleaved" form of the FGF23 coreceptor α-Klotho (cKL) via adeno-associated virus to a rodent model of diabetic nephropathy (DN), the db/db uninephrectomized mouse, normalized blood phosphate levels regardless of disease severity. This work supports the concept that targeting cKL-affected pathways could provide future therapeutic avenues for the severe mineral metabolism defects associated with DN.

Efficacy and Safety of Safflower Yellow in Early Diabetic Nephropathy: A Meta-Analysis

Background

Diabetic nephropathy (DN) is a major cause of end-stage renal disease. In order to palliate renal function impairment and reduce kidney related mortality, it is crucial to treating DN patients at the early stage. This study aims to assess the efficacy and safety of conventional therapy combined with safflower yellow versus conventional therapy alone in early DN patients.

Methods

A meta-analysis of randomized controlled trials that compared safflower yellow plus conventional therapy with conventional therapy alone in early DN patients was conducted. Papers were searched using the electronic databases and reference lists. Two reviewers working independently extracted relevant data and carried out risk-of-bias assessments. Statistical analysis was undertaken in Review Manager 5.3.

Results

Fourteen trials (1,072 patients) were included in the meta-analysis. Conventional therapy combined with safflower yellow was associated with a higher effective rate (RD, 0.24; 95% CI, 0.17 to 0.30) and a greater decline in urinary albumin excretion rates (SMD, -1.34; 95% CI, -1.77 to -0.92), fasting blood glucose (MD, -0.57; 95% CI, -0.98 to -0.16), serum creatinine (MD, -12.36; 95% CI, -14.66 to -10.06), and blood urea nitrogen (SMD, -0.93; 95% CI, -1.13 to -0.73) in the subgroup with a follow-up time > 15 days. The incidence of adverse events did not differ significantly between these two regimens (RD, -0.01; 95% CI, -0.03 to 0.01). Findings were similar in the subgroup with a follow-up time < 15 days.

Conclusions

Conventional therapy combined with safflower yellow had a more beneficial effect than conventional therapy alone in early DN patients. There were significant differences in effective rate, urinary albumin excretion rates, fasting blood glucose, serum creatinine, and blood urea nitrogen between the two regimens and no significant difference in adverse events. More randomized controlled research using standardized protocols would be needed in the future to compare these two regimens.

Renal fibrosis: Primacy of the proximal tubule

Tubulointerstitial fibrosis (TIF) is the hallmark of chronic kidney disease and best predictor of renal survival. Many different cell types contribute to TIF progression including tubular epithelial cells, myofibroblasts, endothelia, and inflammatory cells. Previously, most of the attention has centered on myofibroblasts given their central importance in extracellular matrix production. However, emerging data focuses on how the response of the proximal tubule, a specialized epithelial segment vulnerable to injury, plays a central role in TIF progression. Several proximal tubular responses such as de-differentiation, cell cycle changes, autophagy, and metabolic changes may be adaptive initially, but can lead to maladaptive responses that promote TIF both through autocrine and paracrine effects. This review discusses the current paradigm of TIF progression and the increasingly important role of the proximal tubule in promoting TIF both in tubulointerstitial and glomerular injuries. A better understanding and appreciation of the role of the proximal tubule in TIF has important implications for therapeutic strategies to halt chronic kidney disease progression.

Inflammatory Mechanisms as New Biomarkers and Therapeutic Targets for Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of CKD and end-stage kidney disease (ESKD) worldwide. Approximately 30-40% of people with diabetes develop this microvascular complication, placing them at high risk of losing kidney function as well as of cardiovascular events, infections, and death. Current therapies are ineffective for arresting kidney disease progression and mitigating risks of comorbidities and death among patients with DKD. As the global count of people with diabetes will soon exceed 400 million, the need for effective and safe treatment options for complications such as DKD becomes ever more urgent. Recently, the understanding of DKD pathogenesis has evolved to recognize inflammation as a major underlying mechanism of kidney damage. In turn, inflammatory mediators have emerged as potential biomarkers and therapeutic targets for DKD. Phase 2 clinical trials testing inhibitors of monocyte-chemotactic protein-1 chemokine C-C motif-ligand 2 and the Janus kinase/signal transducer and activator of transcription pathway, in particular, have produced promising results.

Pharmacological Blockade of the Chemokine Receptor CCR1 Protects Mice from Systemic Candidiasis of Hematogenous Origin

Systemic candidiasis is a leading cause of nosocomial bloodstream infection with a high mortality rate despite treatment. Immune-based strategies are needed to improve outcomes. We previously reported that genetic deficiency in the chemokine receptor CCR1 improves survival and ameliorates tissue damage in Candida-infected mice. Here, we found that treatment of immunocompetent Candida-infected mice with the CCR1-selective antagonist BL5923 improves survival, decreases the kidney fungal burden, and protects from renal tissue injury.

Apolipoprotein C-I plays a role in the pathogenesis of glomerulosclerosis

Diabetic nephropathy is the leading cause of end-stage renal disease. Diabetic patients have increased plasma concentrations of apolipoprotein C-I (apoCI), and meta-analyses found that a polymorphism in APOC1 is associated with an increased risk of developing nephropathy. To investigate whether overexpressing apoCI contributes to the development of kidney damage, we studied renal tissue and peritoneal macrophages from APOC1 transgenic (APOC1-tg) mice and wild-type littermates. In addition, we examined renal material from autopsied diabetic patients with and without diabetic nephropathy and from autopsied control subjects. We found that APOC1-tg mice, but not wild-type mice, develop albuminuria, renal dysfunction, and glomerulosclerosis with increased numbers of glomerular M1 macrophages. Moreover, compared to wild-type macrophages, stimulated macrophages isolated from APOC1-tg mice have increased cytokine expression, including TNF-alpha and TGF-beta, both of which are known to increase the production of extracellular matrix proteins in mesangial cells. These results suggest that APOC1 expression induces glomerulosclerosis, potentially by increasing the cytokine response in macrophages. Furthermore, we detected apoCI in the kidneys of diabetic patients, but not in control kidneys. Moreover, patients with diabetic nephropathy have significantly more apoCI present in glomeruli compared to diabetic patients without nephropathy, suggesting that apoCI could be involved in the development of diabetic nephropathy. ApoCI co-localized with macrophages. Therefore, apoCI is a promising new therapeutic target for patients at risk of developing nephropathy. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Progression of chronic kidney disease: too much cellular talk causes damage

Tubulointerstitial fibrosis, tubular atrophy, and peritubular capillary rarefaction are major hallmarks of chronic kidney disease. The tubulointerstitium consists of multiple cell components including tubular epithelial, mesenchymal (fibroblasts and pericytes), endothelial, and inflammatory cells. Crosstalk among these cell components is a key component in the pathogenesis of this complex disease. After severe or recurrent injury, the renal tubular epithelial cells undergo changes in structure and cell cycle that are accompanied by altered expression and production of cytokines. These cytokines contribute to the initiation of the fibrotic response by favoring activation of fibroblasts, recruitment of inflammatory cells, and loss of endothelial cells. This review focuses on how augmented growth factor and cytokine production induces epithelial crosstalk with cells in the interstitium to promote progressive tubulointerstitial fibrosis after renal injury.

Inhibition of SGLT2 alleviates diabetic nephropathy by suppressing high glucose-induced oxidative stress in type 1 diabetic mice

It is unclear whether the improvement in diabetic nephropathy by sodium glucose cotransporter 2 (SGLT2) inhibitors is caused by a direct effect on SGLT2 or by the improvement in hyperglycemia. Here, we investigated the effect of dapagliflozin on early‐stage diabetic nephropathy using a mouse model of type 1 diabetes and murine proximal tubular epithelial cells. Eight‐week‐old Akita mice were treated with dapagliflozin or insulin for 12 weeks. Body weight, urinary albumin excretion, blood pressure, as well as levels of blood glucose and hemoglobin A1c were measured. Expansion of the mesangial matrix, interstitial fibrosis, and macrophage infiltration in kidneys were evaluated by histology. Oxidative stress and apoptosis were evaluated in kidneys and cultured proximal tubular epithelial cells. Compared with nontreated mice, dapagliflozin and insulin decreased blood glucose and hemoglobin A1c levels equally. Urine volume and water intake increased significantly in the dapagliflozin‐treated group compared with those in the insulin‐treated group, but there were no differences in body weight or blood pressure between the two groups. Macrophage infiltration and fibrosis in renal interstitium improved significantly in the dapagliflozin group compared with the insulin group. Oxidative stress was attenuated by dapagliflozin, and suppression occurred in a dose‐dependent manner. RNAi knockdown of SGLT2 resulted in reduced oxidative stress. Dapagliflozin ameliorates diabetic nephropathy by suppressing hyperglycemia‐induced oxidative stress in a manner independent of hyperglycemia improvement in Akita mice. Our findings suggest that dapagliflozin may be a novel therapeutic approach for the treatment of diabetic nephropathy.

Chymase inhibition protects diabetic rats from renal lesions

The present study aimed to investigate the effects of a chymase inhibitor on renal injury in diabetic rats. A total of 24 Sprague-Dawley rats were randomly divided into the following groups: The control group (n=7), the diabetes group (DM group; n=7), and the DM + chymase inhibitor group (DM + Chy-I group; n=10). Diabetes was induced via an intraperitoneal injection of streptozotocin (65 mg/kg). Rats in the DM + Chy-I group were administered 1 mg/kg chymase inhibitor [Suc-Val-Pro-Phe^P-(OPh)₂] daily for 12 weeks by intraperitoneal injection. Subsequently, kidney weight, various biochemical parameters and blood pressure were measured. In addition, the expression levels of fibronectin (FN), type IV collagen (ColIV), transforming growth factor (TGF)-β1 and vascular endothelial growth factor (VEGF) were determined by immunohistochemistry and reverse transcription polymerase chain reaction. Compared with in the DM group, the levels of serum cholesterol and urinary albumin/creatinine were decreased in the DM + Chy-I group (P<0.05). Furthermore, chymase inhibition reduced the overexpression of FN, ColIV, TGF-β1 and VEGF (P<0.05) in the renal tissue of diabetic rats. These results indicated that chymase inhibition may reduce the excretion of urinary albumin and the deposition of extracellular matrix components in the kidney of diabetic rats. These effects may be mediated by altered expression of the VEGF and TGF-β1 pathways. In conclusion, chymase inhibition may be considered a potential method for the treatment of renal damage.

Stop chronic kidney disease progression: Time is approaching

Progression of chronic kidney disease (CKD) is inevitable. However, the last decade has witnessed tremendous achievements in this field. Today we are optimistic; the dream of withholding this progression is about to be realistic. The recent discoveries in the field of CKD management involved most of the individual diseases leading the patients to end-stage renal disease. Most of these advances involved patients suffering diabetic kidney disease, chronic glomerulonephritis, polycystic kidney disease, renal amyloidosis and chronic tubulointerstitial disease. The chronic systemic inflammatory status and increased oxidative stress were also investigated. This inflammatory status influences the anti-senescence Klotho gene expression. The role of Klotho in CKD progression together with its therapeutic value are explored. The role of gut as a major source of inflammation, the pathogenesis of intestinal mucosal barrier damage, the role of intestinal alkaline phosphatase and the dietary and therapeutic implications add a novel therapeutic tool to delay CKD progression.

Selected renal cells modulate disease progression in rodent models of chronic kidney disease via NF-κB and TGF-β1 pathways

AIM

Identification of mechanistic pathways for selected renal cell (SRC) therapeutic bioactivity in rodent models of chronic kidney disease.

MATERIALS & METHODS

In vivo and in vitro functional bioassays applied to investigate regenerative outcomes associated with delivery of SRC to diseased rodent kidney.

RESULTS

In vivo, SRC reduces chronic infiltration by monocytes/macrophages. SRC attenuates NF-κB and PAI-1 responses while simultaneously promoting host tubular cell expansion through trophic cues. In vitro, SRC-derived conditioned media attenuates TNF-α-induced NF-κB response, TGF-β-mediated PAI-1 response and increases expression of transcripts associated with cell cycle regulation. Observed bioactive responses were from vesicle and nonvesicle-associated factors, including specific miRNAs.

CONCLUSION

We identify a paracrine mechanism for SRC immunomodulatory and trophic cues on host renal tissues, catalyzing long-term functional benefits in vivo.

Sitagliptin prevents inflammation and apoptotic cell death in the kidney of type 2 diabetic animals

This study aimed to evaluate the efficacy of sitagliptin, a dipeptidyl peptidase IV (DPP-IV) inhibitor, in preventing the deleterious effects of diabetes on the kidney in an animal model of type 2 diabetes mellitus; the Zucker diabetic fatty (ZDF) rat: 20-week-old rats were treated with sitagliptin (10 mg/kg bw/day) during 6 weeks. Glycaemia and blood HbA1c levels were monitored, as well as kidney function and lesions. Kidney mRNA and/or protein content/distribution of DPP-IV, GLP-1, GLP-1R, TNF-α, IL-1β, BAX, Bcl-2, and Bid were evaluated by RT-PCR and/or western blotting/immunohistochemistry. Sitagliptin treatment improved glycaemic control, as reflected by the significantly reduced levels of glycaemia and HbA1c (by about 22.5% and 1.2%, resp.) and ameliorated tubulointerstitial and glomerular lesions. Sitagliptin prevented the diabetes-induced increase in DPP-IV levels and the decrease in GLP-1 levels in kidney. Sitagliptin increased colocalization of GLP-1 and GLP-1R in the diabetic kidney. Sitagliptin also decreased IL-1β and TNF-α levels, as well as, prevented the increase of BAX/Bcl-2 ratio, Bid protein levels, and TUNEL-positive cells which indicates protective effects against inflammation and proapoptotic state in the kidney of diabetic rats, respectively. In conclusion, sitagliptin might have a major role in preventing diabetic nephropathy evolution due to anti-inflammatory and antiapoptotic properties.

Combined effect of hyperfiltration and renin angiotensin system activation on development of chronic kidney disease in diabetic db/db mice

Background

Hypertension is a major risk factor for renal disease progression. However, the mechanisms by which hypertension aggravates the effects of diabetes on the kidney are incompletely understood. We tested the hypothesis that renovascular hypertension accelerates angiotensin-II-dependent kidney damage and inflammation in the db/db mouse, a model of type II diabetes.

Methods

Renovascular hypertension was established in db/db and wild-type control mice through unilateral renal artery stenosis (RAS); the non-stenotic contralateral kidneys evaluated 2, 4 and 6 weeks later. Angiotensin-II infusion (1000 ng/kg/min), unilateral nephrectomy, or both were also performed in db/db mice to discern the contributions of hypertension versus hyperfiltration to development of chronic renal injury in db/db mice with RAS. The effect of blood pressure reduction in db/db mice with RAS was assessed using angiotensin-receptor-blocker (ARB) or hydralazine treatment.

Results

Db/db mice with renovascular hypertension developed greater and more prolonged elevation of renin activity than all other groups studied. Stenotic kidneys of db/db mice developed progressive interstitial fibrosis, tubular atrophy, and interstitial inflammation. Contralateral kidneys of wild type mice with RAS showed minimal histopathologic abnormalities, whereas db/db mice with RAS developed severe diffuse mesangial sclerosis, interstitial fibrosis, tubular atrophy, and interstitial inflammation. Db/db mice with Angiotensin II-induced hypertension developed interstitial lesions and albuminuria but not mesangial matrix expansion, while nephrectomized db/db mice exhibited modest mesangial expansion and interstitial fibrosis, but not significant albuminuria. The combination of unilateral nephrectomy and angiotensin II infusion reproduced all the features of the injury albeit in a less severe manner. ARB and hydralazine were equally effective in attenuating the development of mesangial expansion in the contralateral kidneys of db/db mice with RAS. However, only ARB prevented elevation of urinary albumin/creatinine in db/db mice with RAS.

Conclusion

Renovascular hypertension superimposed on diabetes exacerbates development of chronic renal disease in db/db mice at least in part through interaction with the renin-angiotensin system. Both ARB and hydralazine were equally effective in reducing systolic blood pressure and in preventing renal injury in the contralateral kidney of db/db mice with renal artery stenosis. ARB but not hydralazine prevented elevation of urinary albumin/creatinine in the db/db RAS model.

Low protein diet inhibits uric acid synthesis and attenuates renal damage in streptozotocin-induced diabetic rats

AIM

Several studies indicated that hyperuricemia may link to the worsening of diabetic nephropathy (DN). Meanwhile, low protein diet (LPD) retards exacerbation of renal damage in chronic kidney disease. We then assessed whether LPD influences uric acid metabolism and benefits the progression of DN in streptozotocin- (STZ-) induced diabetic rats.

METHODS

STZ-induced and control rats were both fed with LPD (5%) and normal protein diet (18%), respectively, for 12 weeks. Vital signs, blood and urinary samples for UA metabolism were taken and analyzed every 3 weeks. Kidneys were removed at the end of the experiment.

RESULTS

Diabetic rats developed into constantly high levels of serum UA (SUA), creatinine (SCr) and 24 h amounts of urinary albumin excretion (UAE), creatinine (UCr), urea nitrogen (UUN), and uric acid (UUA). LPD significantly decreased SUA, UAE, and blood glucose, yet left SCr, UCr, and UUN unchanged. A stepwise regression showed that high UUA is an independent risk factor for DN. LPD remarkably ameliorated degrees of enlarged glomeruli, proliferated mesangial cells, and hyaline-degenerated tubular epithelial cells in diabetic rats. Expression of TNF-α in tubulointerstitium significantly decreased in LPD-fed diabetic rats.

CONCLUSION

LPD inhibits endogenous uric acid synthesis and might accordingly attenuate renal damage in STZ-induced diabetic rats.

PPARγ Agonist Rosiglitazone Suppresses Renal mPGES-1/PGE2 Pathway in db/db Mice

Evidence had shown the detrimental effect of prostaglandin (PG) E2 in diabetic nephropathy (DN) of STZ-induced type-1 diabetes but its role in the development of DN of type-2 diabetes remains uncertain. The present study was undertaken to investigate the regulation of PGE2 synthetic pathway and the interaction between peroxisome proliferator-activated receptor (PPAR) γ and PGE2 synthesis in the kidneys of db/db mice. Strikingly, urinary PGE2 was remarkably elevated in db/db mice paralleled with the increased protein expressions of COX-2 and mPGES-1. In contrast, the protein expressions of COX-1, mPGES-2, cPGES, and 15-hydroxyprostaglandin dehydrogenase (15-PGDH) were not altered. Following 1-week rosiglitazone (Rosi) therapy, urinary PGE2, but not other prostanoids, was reduced by 57% in parallel with significant reduction of mPGES-1 protein and EP4 mRNA expressions. By immunohistochemistry, mPGES-1 was significantly induced in the glomeruli of db/db mice, which was almost entirely abolished by Rosi. In line with the reduction of glomerular mPGES-1, the glomerular injury score showed a tendency of improvement after 1 week of Rosi therapy. Collectively, the present study demonstrated an inhibitory effect of PPAR γ activation on renal mPGES-1/PGE2/EP4 pathway in type-2 diabetes and suggested that mPGES-1 may potentially serve as a therapeutic target for treating type-2 diabetes-associated DN.

CCR1 inhibition ameliorates the progression of lupus nephritis in NZB/W mice

Systemic lupus erythematosus is a chronic inflammatory autoimmune disease, the development of which is characterized by a progressive loss of renal function. Such dysfunction is associated with leukocyte infiltration in the glomerular and tubulointerstitial compartments in both human and experimental lupus nephritis. In this study, we investigated the role of the Ccr1 chemokine receptor in this infiltration process during the progression of nephritis in the lupus-prone New Zealand Black/New Zealand White (NZB/W) mouse model. We found that peripheral T cells, mononuclear phagocytes, and neutrophils, but not B cells, from nephritic NZB/W mice were more responsive to Ccr1 ligands than the leukocytes from younger prenephritic NZB/W mice. Short-term treatment of nephritic NZB/W mice with the orally available Ccr1 antagonist BL5923 decreased renal infiltration by T cells and macrophages. Longer Ccr1 blockade decreased kidney accumulation of effector/memory CD4(+) T cells, Ly6C(+) monocytes, and both M1 and M2 macrophages; reduced tubulointerstitial and glomerular injuries; delayed fatal proteinuria; and prolonged animal lifespan. In contrast, renal humoral immunity was unaffected in BL5923-treated mice, which reflected the unchanged numbers of infiltrated B cells in the kidneys. Altogether, these findings define a pivotal role for Ccr1 in the recruitment of T and mononuclear phagocyte cells to inflamed kidneys of NZB/W mice, which in turn contribute to the progression of renal injury.

MicroRNA-29b inhibits diabetic nephropathy in db/db mice

Inflammation and its consequent fibrosis are two main features of diabetic nephropathy (DN), but target therapy on these processes for DN remains yet ineffective. We report here that miR-29b is a novel therapeutic agent capable of inhibiting progressive renal inflammation and fibrosis in type 2 diabetes in db/db mice. Under diabetic conditions, miR-29b was largely downregulated in response to advanced glycation end (AGE) product, which was associated with upregulation of collagen matrix in mesangial cells via the transforming growth factor-β (TGF-β)/Smad3-dependent mechanism. These pathological changes were reversed by overexpressing miR-29b, but enhanced by knocking-down miR-29b. Similarly, loss of renal miR-29b was associated with progressive diabetic kidney injury, including microalbuminuria, renal fibrosis, and inflammation. Restored renal miR-29b by the ultrasound-based gene therapy was capable of attenuating diabetic kidney disease. Further studies revealed that inhibition of Sp1 expression, TGF-β/Smad3-dependent renal fibrosis, NF-κB-driven renal inflammation, and T-bet/Th1-mediated immune response may be mechanisms associated with miR-29b treatment in db/db mice. In conclusion, miR-29b may play a protective role in diabetic kidney disease and may have therapeutic potential for diabetic kidney complication.

Toll-like receptors: sensing and reacting to diabetic injury in the kidney

Accumulating evidence indicates that immunologic and inflammatory elements play an important role in initiating and orchestrating the development of diabetic nephropathy (DN), but until recently, the identity of specific innate immune pattern recognition receptors or sensors that recognize diverse diabetic 'danger signals' to trigger the proinflammatory cascade during DN remains unknown. Toll-like receptors (TLRs) are an emerging family of receptors that recognize pathogen-associated molecular patterns as well as damage-associated molecular patterns to promote the activation of leukocytes and intrinsic renal cells in non-immune kidney disease. Recent data from in vitro and in vivo studies have highlighted the critical role of TLRs, mainly TLR2 and TLR4, in the pathogenesis of DN. This review focuses on emerging findings elucidating how TLR signaling could sense and react to the metabolic stress and endogenous ligands activated by the diabetic state, thereby initiating and perpetuating renal inflammation and fibrogenesis in diabetic kidney disease. Novel strategies potentially targeting TLR signaling that could have therapeutic implications in DN are also discussed.

Danger control programs cause tissue injury and remodeling

Are there common pathways underlying the broad spectrum of tissue pathologies that develop upon injuries and from subsequent tissue remodeling? Here, we explain the pathophysiological impact of a set of evolutionary conserved danger control programs for tissue pathology. These programs date back to the survival benefits of the first multicellular organisms upon traumatic injuries by launching a series of danger control responses, i.e., 1. Haemostasis, or clotting to control bleeding; 2. Host defense, to control pathogen entry and spreading; 3. Re-epithelialisation, to recover barrier functions; and 4. Mesenchymal, to repair to regain tissue stability. Taking kidney pathology as an example, we discuss how clotting, inflammation, epithelial healing, and fibrosis/sclerosis determine the spectrum of kidney pathology, especially when they are insufficiently activated or present in an overshooting and deregulated manner. Understanding the evolutionary benefits of these response programs may refine the search for novel therapeutic targets to limit organ dysfunction in acute injuries and in progressive chronic tissue remodeling.

Immune and inflammatory role in renal disease

Chronic and acute renal diseases, irrespective of the initiating cause, have inflammation and immune system activation as a common underlying mechanism. The purpose of this review is to provide a broad overview of immune cells and inflammatory proteins that contribute to the pathogenesis of renal disease, and to discuss some of the physiological changes that occur in the kidney as a result of immune system activation. An overview of common forms of acute and chronic renal disease is provided, followed by a discussion of common therapies that have anti-inflammatory or immunosuppressive effects in the treatment of renal disease.

The TLR4 antagonist CRX-526 protects against advanced diabetic nephropathy

We recently showed that Toll-like receptor (TLR) TLR4 was overexpressed in the human diabetic kidney, which could promote tubular inflammation. Here we explored whether the TLR4 antagonist, CRX-526, has therapeutic potential to attenuate renal injuries and slow the progression of advanced diabetic nephropathy in wild-type and endothelial nitric oxide synthase (eNOS) knockout mice. In the latter, the endogenous TLR4 ligand, high-mobility group box 1, was upregulated more than in wild-type animals. Four weeks after streptozotocin induction of diabetes, mice were injected with either CRX-526 or vehicle for 8 weeks. CRX-526 significantly reduced albuminuria and blood urea nitrogen without altering blood glucose and systolic blood pressure in diabetic mice. Glomerular hypertrophy, glomerulosclerosis, and tubulointerstitial injury were attenuated by CRX-526, which was associated with decreased chemokine (C-C motif) ligand (CCL)-2, osteopontin, CCL-5 overexpression, subsequent macrophage infiltration, and collagen deposition. These effects were associated with inhibition of TGF-β overexpression and NF-κB activation. In vitro, CRX-526 inhibited high glucose-induced osteopontin upregulation and NF-κB nuclear translocation in cultured human proximal tubular epithelial cells. Thus, we provided evidence that inhibition of TLR4 with the synthetic antagonist CRX-526 conferred renoprotective effects in eNOS knockout diabetic mice with advanced diabetic nephropathy.

Inflammation and the pathogenesis of diabetic nephropathy

The most problematic issue in clinical nephrology is the relentless and progressive increase in patients with ESRD (end-stage renal disease) worldwide. The impact of diabetic nephropathy on the increasing population with CKD (chronic kidney disease) and ESRD is enormous. Three major pathways showing abnormality of intracellular metabolism have been identified in the development of diabetic nephropathy: (i) the activation of polyol and PKC (protein kinase C) pathways; (ii) the formation of advanced glycation end-products; and (iii) intraglomerular hypertension induced by glomerular hyperfiltration. Upstream of these three major pathways, hyperglycaemia is the major driving force of the progression to ESRD from diabetic nephropathy. Downstream of the three pathways, microinflammation and subsequent extracellular matrix expansion are common pathways for the progression of diabetic nephropathy. In recent years, many researchers have been convinced that the inflammation pathways play central roles in the progression of diabetic nephropathy, and the identification of new inflammatory molecules may link to the development of new therapeutic strategies. Various molecules related to the inflammation pathways in diabetic nephropathy include transcription factors, pro-inflammatory cytokines, chemokines, adhesion molecules, Toll-like receptors, adipokines and nuclear receptors, which are candidates for the new molecular targets for the treatment of diabetic nephropathy. Understanding of these molecular pathways of inflammation would translate into the development of anti-inflammation therapeutic strategies.

Resveratrol prevents renal lipotoxicity and inhibits mesangial cell glucotoxicity in a manner dependent on the AMPK-SIRT1-PGC1α axis in db/db mice

AIMS/HYPOTHESIS

Many of the effects of resveratrol are consistent with the activation of AMP-activated protein kinase (AMPK), silent information regulator T1 (SIRT1) and peroxisome proliferator-activated receptor (PPAR)γ co-activator 1α (PGC-1α), which play key roles in the regulation of lipid and glucose homeostasis, and in the control of oxidative stress. We investigated whether resveratrol has protective effects on the kidney in type 2 diabetes.

METHODS

Four groups of male C57BLKS/J db/m and db/db mice were used in this study. Resveratrol was administered via gavage to diabetic and non-diabetic mice, starting at 8 weeks of age, for 12 weeks.

RESULTS

The db/db mice treated with resveratrol had decreased albuminuria. Resveratrol ameliorated glomerular matrix expansion and inflammation. Resveratrol also lowered the NEFA and triacylglycerol content of the kidney, and this action was related to increases in the phosphorylation of AMPK and the activation of SIRT1-PGC-1α signalling and of the key downstream effectors, the PPARα-oestrogen-related receptor (ERR)-1α-sterol regulatory element-binding protein 1 (SREBP1). Furthermore, resveratrol decreased the activity of phosphatidylinositol-3 kinase (PI3K)-Akt phosphorylation and class O forkhead box (FOXO)3a phosphorylation, which resulted in a decrease in B cell leukaemia/lymphoma 2 (BCL-2)-associated X protein (BAX) and increases in BCL-2, superoxide dismutase (SOD)1 and SOD2 production. Consequently, resveratrol reversed the increase in renal apoptotic cells and oxidative stress, as reflected by renal 8-hydroxy-deoxyguanosine (8-OH-dG), urinary 8-OH-dG and isoprostane concentrations. Resveratrol prevented high-glucose-induced oxidative stress and apoptosis in cultured mesangial cells through the phosphorylation of AMPK and activation of SIRT1-PGC-1α signalling and the downstream effectors, PPARα-ERR-1α-SREBP1.

CONCLUSIONS/INTERPRETATION

The results suggest that resveratrol prevents diabetic nephropathy in db/db mice by the phosphorylation of AMPK and activation of SIRT1-PGC-1α signalling, which appear to prevent lipotoxicity-related apoptosis and oxidative stress in the kidney.

Macrophages and fibrosis: How resident and infiltrating mononuclear phagocytes orchestrate all phases of tissue injury and repair

Certain macrophage phenotypes contribute to tissue fibrosis, but why? Tissues host resident mononuclear phagocytes for their support to maintain homeostasis. Upon injury the changing tissue microenvironment alters their phenotype and primes infiltrating monocytes toward pro-inflammatory macrophages. Several mechanisms contribute to their deactivation and macrophage priming toward anti-inflammatory and pro-regenerative macrophages that produce multiple cytokines that display immunosuppressive as well as pro-regeneratory effects, such as IL-10 and TGF-beta1. Insufficient parenchymal repair creates a tissue microenvironment that becomes dominated by multiple growth factors that promote the pro-fibrotic macrophage phenotype that itself produces large amounts of such growth factors that further support fibrogenesis. However, the contribution of resident mononuclear phagocytes to physiological extracellular matrix turnover implies also their fibrolytic effects in the late stage of tissue scaring. Fibrolytic macrophages break down fibrous tissue, but their phenotypic characteristics remain to be described in more detail. Together, macrophages contribute to tissue fibrosis because the changing tissue environments prime them to assist and orchestrate all phases of tissue injury and repair. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Calcium oxalate crystals induce renal inflammation by NLRP3-mediated IL-1β secretion

Nephrocalcinosis, acute calcium oxalate (CaOx) nephropathy, and renal stone disease can lead to inflammation and subsequent renal failure, but the underlying pathological mechanisms remain elusive. Other crystallopathies, such as gout, atherosclerosis, and asbestosis, trigger inflammation and tissue remodeling by inducing IL-1β secretion, leading us to hypothesize that CaOx crystals may induce inflammation in a similar manner. In mice, intrarenal CaOx deposition induced tubular damage, cytokine expression, neutrophil recruitment, and renal failure. We found that CaOx crystals activated murine renal DCs to secrete IL-1β through a pathway that included NLRP3, ASC, and caspase-1. Despite a similar amount of crystal deposits, intrarenal inflammation, tubular damage, and renal dysfunction were abrogated in mice deficient in MyD88; NLRP3, ASC, and caspase-1; IL-1R; or IL-18. Nephropathy was attenuated by DC depletion, ATP depletion, or therapeutic IL-1 antagonism. These data demonstrated that CaOx crystals trigger IL-1β-dependent innate immunity via the NLRP3/ASC/caspase-1 axis in intrarenal mononuclear phagocytes and directly damage tubular cells, leading to the release of the NLRP3 agonist ATP. Furthermore, these results suggest that IL-1β blockade may prevent renal damage in nephrocalcinosis.

Calcium oxalate crystals induce renal inflammation by NLRP3-mediated IL-1β secretion

Nephrocalcinosis, acute calcium oxalate (CaOx) nephropathy, and renal stone disease can lead to inflammation and subsequent renal failure, but the underlying pathological mechanisms remain elusive. Other crystallopathies, such as gout, atherosclerosis, and asbestosis, trigger inflammation and tissue remodeling by inducing IL-1β secretion, leading us to hypothesize that CaOx crystals may induce inflammation in a similar manner. In mice, intrarenal CaOx deposition induced tubular damage, cytokine expression, neutrophil recruitment, and renal failure. We found that CaOx crystals activated murine renal DCs to secrete IL-1β through a pathway that included NLRP3, ASC, and caspase-1. Despite a similar amount of crystal deposits, intrarenal inflammation, tubular damage, and renal dysfunction were abrogated in mice deficient in MyD88; NLRP3, ASC, and caspase-1; IL-1R; or IL-18. Nephropathy was attenuated by DC depletion, ATP depletion, or therapeutic IL-1 antagonism. These data demonstrated that CaOx crystals trigger IL-1β-dependent innate immunity via the NLRP3/ASC/caspase-1 axis in intrarenal mononuclear phagocytes and directly damage tubular cells, leading to the release of the NLRP3 agonist ATP. Furthermore, these results suggest that IL-1β blockade may prevent renal damage in nephrocalcinosis.

Tissues use resident dendritic cells and macrophages to maintain homeostasis and to regain homeostasis upon tissue injury: the immunoregulatory role of changing tissue environments

Most tissues harbor resident mononuclear phagocytes, that is, dendritic cells and macrophages. A classification that sufficiently covers their phenotypic heterogeneity and plasticity during homeostasis and disease does not yet exist because cell culture-based phenotypes often do not match those found in vivo. The plasticity of mononuclear phagocytes becomes obvious during dynamic or complex disease processes. Different data interpretation also originates from different conceptual perspectives. An immune-centric view assumes that a particular priming of phagocytes then causes a particular type of pathology in target tissues, conceptually similar to antigen-specific T-cell priming. A tissue-centric view assumes that changing tissue microenvironments shape the phenotypes of their resident and infiltrating mononuclear phagocytes to fulfill the tissue's need to maintain or regain homeostasis. Here we discuss the latter concept, for example, why different organs host different types of mononuclear phagocytes during homeostasis. We further discuss how injuries alter tissue environments and how this primes mononuclear phagocytes to enforce this particular environment, for example, to support host defense and pathogen clearance, to support the resolution of inflammation, to support epithelial and mesenchymal healing, and to support the resolution of fibrosis to the smallest possible scar. Thus, organ- and disease phase-specific microenvironments determine macrophage and dendritic cell heterogeneity in a temporal and spatial manner, which assures their support to maintain and regain homeostasis in whatever condition. Mononuclear phagocytes contributions to tissue pathologies relate to their central roles in orchestrating all stages of host defense and wound healing, which often become maladaptive processes, especially in sterile and/or diffuse tissue injuries.

Advanced glycation endproducts stimulate renal epithelial cells to release chemokines that recruit macrophages, leading to renal fibrosis

Diabetic nephropathy is a major complication of diabetes and tubulointerstitial fibrosis is one of its manifestations. This study aimed to clarify the pathogenicity of advanced glycation endproducts (AGEs) toward NRK-52E, a tubular epithelial cell line. The AGE-exposed cells significantly increased gene expression of transforming growth factor beta, plasminogen activator inhibitor-1, and tissue transglutaminase, and a medium conditioned by them showed strong potential to recruit macrophages, partly through a chemokine, monocyte chemoattractant protein-1. Albumin denatured by maintenance at 37 °C for 120 d exhibited similar activities, but they were lower than those of the AGEs. Thus, AGEs generated in diabetic patients might exacerbate fibrosis in the kidneys directly through renal epithelial cell stimulation, and indirectly by recruitment of macrophages.

A population of selected renal cells augments renal function and extends survival in the ZSF1 model of progressive diabetic nephropathy

New treatment paradigms that slow or reverse progression of chronic kidney disease (CKD) are needed to relieve significant patient and healthcare burdens. We have shown that a population of selected renal cells (SRCs) stabilized disease progression in a mass reduction model of CKD. Here, we further define the cellular composition of SRCs and apply this novel therapeutic approach to the ZSF1 rat, a model of severe progressive nephropathy secondary to diabetes, obesity, dyslipidemia, and hypertension. Injection of syngeneic SRCs into the ZSF1 renal cortex elicited a regenerative response that significantly improved survival and stabilized disease progression to renal structure and function beyond 1 year posttreatment. Functional improvements included normalization of multiple nephron structures and functions including glomerular filtration, tubular protein handling, electrolyte balance, and the ability to concentrate urine. Improvements to blood pressure, including reduced levels of circulating renin, were also observed. These functional improvements following SRC treatment were accompanied by significant reductions in glomerular sclerosis, tubular degeneration, and interstitial inflammation and fibrosis. Collectively, these data support the utility of a novel renal cell-based approach for slowing renal disease progression associated with diabetic nephropathy in the setting of metabolic syndrome, one of the most common causes of end-stage renal disease.

Plasma leakage through glomerular basement membrane ruptures triggers the proliferation of parietal epithelial cells and crescent formation in non-inflammatory glomerular injury

Glomerular crescents are most common in rapidly progressive glomerulonephritis but also occur in non-inflammatory chronic glomerulopathies; thus, factors other than inflammation should trigger crescent formation, eg vascular damage and plasma leakage. Here we report that Alport nephropathy in Col4A3-deficient Sv129 mice is complicated by diffuse and global crescent formation in which proliferating parietal epithelial cells are the predominant cell type. Laminin staining and transmission and acellular scanning electron microscopy of acellular glomeruli documented disruptions and progressive disintegration of the glomerular basement membrane in Col4A3-deficient mice. FITC-dextran perfusion further revealed vascular leakage from glomerular capillaries into Bowman's space, further documented by fibrin deposits in the segmental crescents. Its pathogenic role was validated by showing that the fibrinolytic activity of recombinant urokinase partially prevented crescent formation. In addition, in vitro studies confirmed an additional mitogenic potential of serum on murine and human parietal epithelial cells. Furthermore, loss of parietal cell polarity and unpolarized secretion of extracellular matrix components were evident within fibrocellular crescents. Among 665 human Alport nephropathy biopsies, crescent formation was noted in 0.4%. We conclude that glomerular vascular injury and GBM breaks cause plasma leakage which triggers a wound healing programme involving the proliferation of parietal cells and their loss of polarity. This process can trigger cellular and fibrocellular crescent formation even in the absence of cellular inflammation and rupture of the Bowman's capsule.

Astragalus membranaceus inhibits inflammation via phospho-P38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB pathways in advanced glycation end product-stimulated macrophages

Advanced glycation end products (AGEs) and inflammation contribute to the development of diabetic complications. Astragalus membranaceus has properties of immunological regulation in many diseases. The aim of this study was to determine the function of A. membranaceus extract (AME) on the AGE-induced inflammatory response in Ana-1 macrophages. The viability of cells treated with AME or AGEs was evaluated with the MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide] method. The secretion and mRNA levels of IL-1β and TNF-α were measured by ELISA and RT-PCR, respectively. The activity of NF-κB was assayed by EMSA. The phosphorylation of p38 MAPK was assessed by western blotting. The results showed that AME was not toxic to macrophages. The treatment of macrophages with AME effectively inhibited AGE-induced IL-1β and TNF-α secretion and mRNA expression in macrophages. These effects may be mediated by p38 MAPK and the NF-κB pathway. The results suggest that AME can inhibit AGE-induced inflammatory cytokine production to down-regulate macrophage-mediated inflammation via p38 MAPK and NF-κB signaling pathways and indicate that AME could be an immunoregulatory agent against AGE-induced inflammation in diabetes.

Histones from dying renal cells aggravate kidney injury via TLR2 and TLR4

In AKI, dying renal cells release intracellular molecules that stimulate immune cells to secrete proinflammatory cytokines, which trigger leukocyte recruitment and renal inflammation. Whether the release of histones, specifically, from dying cells contributes to the inflammation of AKI is unknown. In this study, we found that dying tubular epithelial cells released histones into the extracellular space, which directly interacted with Toll-like receptor (TLR)-2 (TLR2) and TLR4 to induce MyD88, NF-κB, and mitogen activated protein kinase signaling. Extracellular histones also had directly toxic effects on renal endothelial cells and tubular epithelial cells in vitro. In addition, direct injection of histones into the renal arteries of mice demonstrated that histones induce leukocyte recruitment, microvascular vascular leakage, renal inflammation, and structural features of AKI in a TLR2/TLR4-dependent manner. Antihistone IgG, which neutralizes the immunostimulatory effects of histones, suppressed intrarenal inflammation, neutrophil infiltration, and tubular cell necrosis and improved excretory renal function. In summary, the release of histones from dying cells aggravates AKI via both its direct toxicity to renal cells and its proinflammatory effects. Because the induction of proinflammatory cytokines in dendritic cells requires TLR2 and TLR4, these results support the concept that renal damage triggers an innate immune response, which contributes to the pathogenesis of AKI.

Tissue microenvironments define and get reinforced by macrophage phenotypes in homeostasis or during inflammation, repair and fibrosis

Current macrophage phenotype classifications are based on distinct in vitro culture conditions that do not adequately mirror complex tissue environments. In vivo monocyte progenitors populate all tissues for immune surveillance which supports the maintenance of homeostasis as well as regaining homeostasis after injury. Here we propose to classify macrophage phenotypes according to prototypical tissue environments, e.g. as they occur during homeostasis as well as during the different phases of (dermal) wound healing. In tissue necrosis and/or infection, damage- and/or pathogen-associated molecular patterns induce proinflammatory macrophages by Toll-like receptors or inflammasomes. Such classically activated macrophages contribute to further tissue inflammation and damage. Apoptotic cells and an-tiinflammatory cytokines dominate in postinflammatory tissues which induce macrophages to produce more anti-inflammatory mediators. Similarly, tumor-associated macrophages also confer immunosuppression in tumor stroma. Insufficient parenchymal healing despite abundant growth factors pushes macrophages to gain a profibrotic phenotype and promote fibrocyte recruitment which both enforce tissue scarring. Ischemic scars are largely devoid of cytokines and growth factors so that fibrolytic macrophages that predominantly secrete proteases digest the excess extracellular matrix. Together, macrophages stabilize their surrounding tissue microenvironments by adapting different phenotypes as feed-forward mechanisms to maintain tissue homeostasis or regain it following injury. Furthermore, macrophage heterogeneity in healthy or injured tissues mirrors spatial and temporal differences in microenvironments during the various stages of tissue injury and repair.

Four danger response programs determine glomerular and tubulointerstitial kidney pathology: clotting, inflammation, epithelial and mesenchymal healing

Renal biopsies commonly display tissue remodeling with a combination of many different findings. In contrast to trauma, kidney remodeling largely results from intrinsic responses, but why? Distinct danger response programs were positively selected throughout evolution to survive traumatic injuries and to regenerate tissue defects. These are: (1) clotting to avoid major bleeding, (2) immunity to control infection, (3) epithelial repair and (4) mesenchymal repair. Collateral damages are acceptable for the sake of host survival but causes for kidney injury commonly affect the kidneys in a diffuse manner. This way, coagulation, inflammation, deregulated epithelial healing or fibrosis contribute to kidney remodeling. Here, I focus on how these ancient danger response programs determine renal pathology mainly because they develop in a deregulated manner, either as insufficient or overshooting processes that modulate each other. From a therapeutic point of view, immunopathology can be prevented by suppressing sterile renal inflammation, a useless atavism with devastating consequences. In addition, it appears as an important goal for the future to promote podocyte and tubular epithelial cell repair, potentially by stimulating the differentiation of their newly discovered intrarenal progenitor cells. By contrast, it is still unclear whether selectively targeting renal fibrogenesis can preserve or bring back lost renal parenchyma, which would be required to maintain or improve kidney function. Thus, renal pathology results from ancient danger responses that evolved because of their evolutional benefits upon trauma. Understanding these causalities may help to shape the search for novel treatments for kidney disease patients.