Factor XII signaling via uPAR-integrin β1 axis promotes tubular senescence in diabetic kidney disease

Coagulation factor XII (FXII) conveys various functions as an active protease that promotes thrombosis and inflammation, and as a zymogen via surface receptors like urokinase-type plasminogen activator receptor (uPAR). While plasma levels of FXII are increased in diabetes mellitus and diabetic kidney disease (DKD), a pathogenic role of FXII in DKD remains unknown. Here we show that FXII is locally expressed in kidney tubular cells and that urinary FXII correlates with kidney dysfunction in DKD patients. F12-deficient mice (F12-/-) are protected from hyperglycemia-induced kidney injury. Mechanistically, FXII interacts with uPAR on tubular cells promoting integrin β1-dependent signaling. This signaling axis induces oxidative stress, persistent DNA damage and senescence. Blocking uPAR or integrin β1 ameliorates FXII-induced tubular cell injury. Our findings demonstrate that FXII-uPAR-integrin β1 signaling on tubular cells drives senescence. These findings imply previously undescribed diagnostic and therapeutic approaches to detect or treat DKD and possibly other senescence-associated diseases.

Application of Proteomics and Machine Learning Methods to Study the Pathogenesis of Diabetic Nephropathy and Screen Urinary Biomarkers

Diabetic nephropathy (DN) has become the main cause of end-stage renal disease worldwide, causing significant health problems. Early diagnosis of the disease is quite inadequate. To screen urine biomarkers of DN and explore its potential mechanism, this study collected urine from 87 patients with type 2 diabetes mellitus (which will be classified into normal albuminuria, microalbuminuria, and macroalbuminuria groups) and 38 healthy subjects. Twelve individuals from each group were then randomly selected as the screening cohort for proteomics analysis and the rest as the validation cohort. The results showed that humoral immune response, complement activation, complement and coagulation cascades, renin-angiotensin system, and cell adhesion molecules were closely related to the progression of DN. Five overlapping proteins (KLK1, CSPG4, PLAU, SERPINA3, and ALB) were identified as potential biomarkers by machine learning methods. Among them, KLK1 and CSPG4 were positively correlated with the urinary albumin to creatinine ratio (UACR), and SERPINA3 was negatively correlated with the UACR, which were validated by enzyme-linked immunosorbent assay (ELISA). This study provides new insights into disease mechanisms and biomarkers for early diagnosis of DN.

Bradykinin induces acute kidney injury after hypothermic circulatory arrest through the repression of the Nrf2-xCT pathway

Postoperative acute kidney injury (AKI) is a common complication in patients undergoing deep hypothermic circulatory arrest (HCA); however, its underlying pathogenesis is unclear. In this study, we established a rat cardiopulmonary bypass model and demonstrated that hypothermia during HCA, rather than circulatory arrest, was responsible for the occurrence of AKI. By recruiting 56 patients who underwent surgery with HCA and analyzing the blood samples, we found that post-HCA AKI was associated with an increase in bradykinin. Animal experiments confirmed this and showed that hypothermia during HCA increased bradykinin levels by increasing kallikrein expression. Mechanistically, bradykinin inhibited the Nrf2-xCT pathway through B2R and caused renal oxidative stress damage. Application of Icatibant, a B2R inhibitor, reversed changes in the Nrf2-xCT pathway and oxidative stress damage. Finally, Icatibant reversed hypothermia-induced AKI in vivo. This finding reveals the pathogenesis of AKI after HCA and helps to provide therapeutic strategy for patients with post-HCA AKI.

Efficacy and safety of Huangkui capsule for diabetic nephropathy: A systematic review and meta-analysis

BACKGROUND

To systematically evaluate the efficacy and safety of Huangkui capsule (HKC) in the treatment of diabetic nephropathy (DN).

METHODS

A computerized search of 8 online databases, CNKI, VIP, WANGFANG, CBM, ChiCTR, Embase, PubMed, and Cochrane Library, was conducted from the time of database construction to June 23, 2023, and randomized controlled trials of HKC for the treatment of DN were included according to the predefined screening criteria. Literature quality was evaluated with the help of Cochrane Risk of Bias Assessment Tool, and data were analyzed by STATA/MP17 and RevMan 5.3 software.

RESULTS

A total of 1543 articles were retrieved, and 45 studies were finally included, all in Chinese, with a total sample size of 4297 cases, including 2168 cases in the experimental group and 2129 cases in the control group, and the quality of all the included studies was generally low. Meta-analysis showed that (1) efficacy: effective rate: [relative risk = 1.24, 95% confidence interval (CI) (1.20, 1.29), P < .001], SCR: [standard mean difference (SMD) = -1.19, 95% CI (-1.47, -0.91), P < .001], 24 h-UTP: [SMD = -1.27, 95% CI (-1.66, -0.88), P < .001]. Other renal function, glucose metabolism, lipid metabolism, and inflammatory factors related indicators improved compared with the control group. But in the outcome index of estimated glomerular filtration rate, the addition of HKC did not have an advantage over conventional treatment alone. Estimated glomerular filtration rate: [SMD = -0.21, 95% CI (-0.80, 0.39), P = .50]. (2) Safety: There was no statistical significance in the incidence of adverse reactions between the study group with the addition of HKC and the control group.

CONCLUSION

The clinical efficacy and safety of DN treated with the combination of HKC is better than that of conventional western medicine alone, but to better evaluate the efficacy and safety of HKC as an adjunctive intervention for DN, more rigorously designed large-sample, multicenter randomized controlled trials are needed to provide evidence support in the future.

The role of innate immunity in diabetic nephropathy and their therapeutic consequences

Diabetic nephropathy (DN) is an enduring condition that leads to inflammation and affects a substantial number of individuals with diabetes worldwide. A gradual reduction in glomerular filtration and emergence of proteins in the urine are typical aspects of DN, ultimately resulting in renal failure. Mounting evidence suggests that immunological and inflammatory factors are crucial for the development of DN. Therefore, the activation of innate immunity by resident renal and immune cells is critical for initiating and perpetuating inflammation. Toll-like receptors (TLRs) are an important group of receptors that identify patterns and activate immune responses and inflammation. Meanwhile, inflammatory responses in the liver, pancreatic islets, and kidneys involve inflammasomes and chemokines that generate pro-inflammatory cytokines. Moreover, the activation of the complement cascade can be triggered by glycated proteins. This review highlights recent findings elucidating how the innate immune system contributes to tissue fibrosis and organ dysfunction, ultimately leading to renal failure. This review also discusses innovative approaches that can be utilized to modulate the innate immune responses in DN for therapeutic purposes.

The Molecular Mechanism of Renal Tubulointerstitial Inflammation Promoting Diabetic Nephropathy

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

Inhibition of MD2 by natural product-drived JM-9 attenuates renal inflammation and diabetic nephropathy in mice

Diabetic kidney disease (DKD) is one of the severe complications of diabetes mellitus-related microvascular lesions, which remains the leading cause of end-stage kidney disease. The genesis and development of DKD is closely related to inflammation. Myeloid differentiation 2 (MD2) mediates hyperlyciemia-induced renal inflammation and DKD development and is considered as a potential therapeutic target of DKD. Here, we identified a new small-molecule MD2 inhibitor, JM-9. In vitro, JM-9 suppressed high glucose (HG) and palmitic acid (PA)-induced inflammation in MPMs, accompanied by inhibition of MD2 activation and the downstream TLR4/MyD88-MAPKs/NFκB pro-inflammatory signaling pathway. Macrophage-derived factors increased the fibrotic and inflammatory responses in renal tubular epithelial cells, which were inhibited by treating macrophages with JM-9. Then, we investigated the therapeutic effects against DKD in streptozotocin-induced type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) mouse models. Treatment with JM-9 prevented renal inflammation, fibrosis, and dysfunction by targeting MD2 in both T1DM and T2DM models. Our results show that JM-9, a new small-molecule MD2 inhibitor, protects against DKD by targeting MD2 and inhibiting MD2-mediated inflammation. In summary, JM-9 is a potential therapeutic agent for DKD.

Multifaceted relationship between diabetes and kidney diseases: Beyond diabetes

Diabetes mellitus is one of the most common causes of chronic kidney disease. Kidney involvement in patients with diabetes has a wide spectrum of clinical presentations ranging from asymptomatic to overt proteinuria and kidney failure. The development of kidney disease in diabetes is associated with structural changes in multiple kidney compartments, such as the vascular system and glomeruli. Glomerular alterations include thickening of the glomerular basement membrane, loss of podocytes, and segmental mesangiolysis, which may lead to microaneurysms and the development of pathognomonic Kimmelstiel-Wilson nodules. Beyond lesions directly related to diabetes, awareness of the possible coexistence of nondiabetic kidney disease in patients with diabetes is increasing. These nondiabetic lesions include focal segmental glomerulosclerosis, IgA nephropathy, and other primary or secondary renal disorders. Differential diagnosis of these conditions is crucial in guiding clinical management and therapeutic approaches. However, the relationship between diabetes and the kidney is bidirectional; thus, new-onset diabetes may also occur as a complication of the treatment in patients with renal diseases. Here, we review the complex and multifaceted correlation between diabetes and kidney diseases and discuss clinical presentation and course, differential diagnosis, and therapeutic oppor-tunities offered by novel drugs.

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.

What's New in the Molecular Mechanisms of Diabetic Kidney Disease: Recent Advances

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease, including end-stage kidney disease, and increases the risk of cardiovascular mortality. Although the treatment options for DKD, including angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, sodium-glucose cotransporter 2 inhibitors, and mineralocorticoid receptor antagonists, have advanced, their efficacy is still limited. Thus, a deeper understanding of the molecular mechanisms of DKD onset and progression is necessary for the development of new and innovative treatments for DKD. The complex pathogenesis of DKD includes various different pathways, and the mechanisms of DKD can be broadly classified into inflammatory, fibrotic, metabolic, and hemodynamic factors. Here, we summarize the recent findings in basic research, focusing on each factor and recent advances in the treatment of DKD. Collective evidence from basic and clinical research studies is helpful for understanding the definitive mechanisms of DKD and their regulatory systems. Further comprehensive exploration is warranted to advance our knowledge of the pathogenesis of DKD and establish novel treatments and preventive strategies.

Activation of Stimulator of IFN Genes (STING) Causes Proteinuria and Contributes to Glomerular Diseases

BACKGROUND

The signaling molecule stimulator of IFN genes (STING) was identified as a crucial regulator of the DNA-sensing cyclic GMP-AMP synthase (cGAS)-STING pathway, and this signaling pathway regulates inflammation and energy homeostasis under conditions of obesity, kidney fibrosis, and AKI. However, the role of STING in causing CKD, including diabetic kidney disease (DKD) and Alport syndrome, is unknown.

METHODS

To investigate whether STING activation contributes to the development and progression of glomerular diseases such as DKD and Alport syndrome, immortalized human and murine podocytes were differentiated for 14 days and treated with a STING-specific agonist. We used diabetic db/db mice, mice with experimental Alport syndrome, C57BL/6 mice, and STING knockout mice to assess the role of the STING signaling pathway in kidney failure.

RESULTS

In vitro, murine and human podocytes express all of the components of the cGAS-STING pathway. In vivo, activation of STING renders C57BL/6 mice susceptible to albuminuria and podocyte loss. STING is activated at baseline in mice with experimental DKD and Alport syndrome. STING activation occurs in the glomerular but not the tubulointerstitial compartment in association with autophagic podocyte death in Alport syndrome mice and with apoptotic podocyte death in DKD mouse models. Genetic or pharmacologic inhibition of STING protects from progression of kidney disease in mice with DKD and Alport syndrome and increases lifespan in Alport syndrome mice.

CONCLUSION

The activation of the STING pathway acts as a mediator of disease progression in DKD and Alport syndrome. Targeting STING may offer a therapeutic option to treat glomerular diseases of metabolic and nonmetabolic origin or prevent their development, progression, or both.

Mannose-binding lectin activates the nuclear factor-κB and renal inflammation in the progression of diabetic nephropathy

Increased serum mannose-binding lectin (MBL) level has been proven to correlate with the development of diabetic nephropathy (DN). Here, we aim to find the role and mechanism of MBL involved in the progression of DN. Patients with DN were recruited and divided into two groups according to different rs1800450 genotypes of the MBL2 gene, and inflammatory profiles in monocytes/macrophages were compared between the two groups. MBL was given to treat macrophages, HK2, and HMC, and a co-culture transwell system was then employed. Renal inflammation and fibrosis parameters were measured after knocking down or overexpressing MBL genes in mice. Proinflammatory profile, manifesting as enhanced IL-1β production and M1 polarization, was found in monocytes/macrophages from DN with a rs1800450 GG genotype of MBL2 gene who had higher MBL level, compared with those with a rs1800450 GA genotype. In mechanism, MBL directly induced inflammatory responses in macrophages, which promoted inflammatory and fibrotic markers in HK2 and HMCs during co-culture. Further experiments showed that MBL can promote macrophages transforming to the M1 subset mainly by activating the nuclear factor-κB pathway. After downregulation of MBL, the blood glucose, triglyceride, urine protein, injuries of glomerulus and tubules, and the degree of renal inflammation and fibrosis were ameliorated in db/db mice treated with AAV-MBL1/2-shRNA. Overexpression of MBL promoted macrophage infiltration in the kidney. In conclusion, MBL is a crucial mediator in the progression of DN via activating the nuclear factor-κB pathway in macrophages. This will serve as a genetic base for some patients with DN who have poor outcomes and provide a direction for the screening.

Nicotinamide N-methyltransferase ameliorates renal fibrosis by its metabolite 1-methylnicotinamide inhibiting the TGF-β1/Smad3 pathway

Chronic kidney disease (CKD), a disease involving damage to the kidney structure and function, is a global public health problem. Tubulointerstitial fibrosis (TIF) is both an inevitable pathological change in individuals with CKD and a driving force in the progression of renal fibrosis. Nicotinamide N-methyltransferase (NNMT) and its metabolite 1-methylnicotinamide (MNAM) have been shown to protect against lipotoxicity-induced kidney tubular injury. However, the biological roles of NNMT and MNAM in regulating TIF remain elusive. This study aimed to investigate the protective effect of NNMT and MNAM on TIF and the mechanisms involved. We explored the functions and mechanisms of NNMT and MNAM in TIF, as well as the interaction between NNMT and MNAM, using unilateral ureteral obstruction (UUO) mice and cultured mouse tubular epithelial cells (mTECs) stimulated with transforming growth factor-β1 (TGF-β1). Several important findings were obtained as follows: (1) NNMT expression was upregulated in the kidneys of UUO mice and TGF-β1-induced mTECs, and this upregulation was proposed to be a protective compensatory response to TIF. (2) MNAM was a potentially effective antifibrotic and anti-inflammatory medication in UUO mice. (3) The antifibrotic effect of NNMT overexpression was exerted by increasing the concentration of MNAM. (4) The renoprotective role of MNAM depended on the selective blockade of the interaction of Smad3 with TGFβ receptor I. Overall, our study shows that NNMT is involved in the development and progression of CKD and that its metabolite MNAM may be a novel inhibitor of the TGF-β1/Smad3 pathway with great therapeutic potential for CKD.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Diabetic proximal tubulopathy: Can we mimic the disease for in vitro screening of SGLT inhibitors?

Diabetic kidney disease (DKD) is the foremost cause of renal failure. While the glomeruli are severely affected in the course of the disease, the main determinant for disease progression is the tubulointerstitial compartment. DKD does not develop in the absence of hyperglycemia. Since the proximal tubule is the major player in glucose reabsorption, it has been widely studied as a therapeutic target for the development of new therapies. Currently, there are several proximal tubule cell lines available, being the human kidney-2 (HK-2) and human kidney clone-8 (HKC-8) cell lines the ones widely used for studying mechanisms of DKD. Studies in these models have pushed forward the understanding on how DKD unravels, however, these cell culture models possess limitations that hamper research, including lack of transporters and dedifferentiation. The sodium-glucose cotransporters (SGLT) are identified as key players in glucose reabsorption and pharmacological inhibitors have shown to be beneficial for the long-term clinical outcome in DKD. However, their mechanism of action has, as of yet, not been fully elucidated. To comprehend the protective effects of SGLT inhibitors, it is essential to understand the complete functional, structural, and molecular features of the disease, which until now have been difficult to recapitulate. This review addresses the molecular events of diabetic proximal tubulopathy. In addition, we evaluate the protective role of SGLT inhibitors in cardiovascular and renal outcomes, and provide an overview of various in vitro models mimicking diabetic proximal tubulopathy used so far. Finally, new insights on advanced in vitro systems to surpass past limitations are postulated.

Usefulness of Adding Pre-procedural Glycemia to the Mehran Score to Enhance Its Ability to Predict Contrast-induced Kidney Injury in Patients Undergoing Percutaneous Coronary Intervention Development and Validation of a Predictive Model

The Mehran score is the most widely accepted tool for predicting contrast-induced acute kidney injury (CI-AKI), a major complication of percutaneous coronary intervention (PCI). Similarly, abnormal fasting pre-procedural glycemia (FPG) represents a modifiable risk factor for CI-AKI, but it is not included in current risk models for CI-AKI prediction. We sought to analyze whether adding FPG to the Mehran score improves its ability to predict CI-AKI following PCI. We analyzed 671 consecutive patients undergoing PCI (age 69 [63,75] years, 23% females), regardless of their diabetic status, to derive a revised Mehran score obtained by including FPG in the original Mehran score (Derivation Cohort). The new risk model (GlyMehr) was externally validated in 673 consecutive patients (Validation Cohort) (age 69 [62,76] years, 21% females). In the Derivation Cohort, both FPG and the original Mehran score predicted CI-AKI (AUC 0.703 and 0.673, respectively). The GlyMehr score showed a better predictive ability when compared with the Mehran score both in the Derivation Cohort (AUC 0.749, 95%CI 0.662 to 0.836; p = 0.0016) and the Validation Cohort (AUC 0.848, 95%CI, 0.792 to 0.903; p = 0.0008). In the overall population (n = 1344), the GlyMehr score confirmed its independent and incremental predictive ability regardless of diabetic status (p ≤0.0034) or unstable/stable coronary syndromes (p ≤0.0272). In conclusion, adding FPG to the Mehran score significantly enhances our ability to predict CI-AKI. The GlyMehr score may contribute to improve the clinical management of patients undergoing PCI by identifying those at high risk of CI-AKI and potentially detecting modifiable risk factors.

Inhibition of Renal Tubular Epithelial Mesenchymal Transition and Endoplasmic Reticulum Stress-Induced Apoptosis with Shenkang Injection Attenuates Diabetic Tubulopathy

Background: The proximal renal tubule plays a critical role in diabetic kidney disease (DKD) progression. Early glomerular disease in DKD triggers a cascade of injuries resulting in renal tubulointerstitial disease. These pathophysiological responses are collectively described as diabetic tubulopathy (DT). Thus, therapeutic strategies targeting DT hold significant promise for early DKD treatment. Shenkang injection (SKI) has been widely used to treat renal tubulointerstitial fibrosis in patients with chronic kidney disease in China. However, it is still unknown whether SKI can alleviate DT. We designed a series of experiments to investigate the beneficial effects of SKI in DT and the mechanisms that are responsible for its effect on epithelial-to-mesenchymal transition (EMT) and endoplasmic reticulum (ER) stress-induced apoptosis in DT.

Methods: The modified DKD rat models were induced by uni-nephrectomy, streptozotocin intraperitoneal injection, and a high-fat diet. Following the induction of renal injury, these animals received either SKI, rosiglitazone (ROS), or vehicle, for 42 days. For in vitro research, we exposed NRK-52E cells to high glucose (HG) and 4-phenylbutyric acid (4-PBA) with or without SKI or ROS. Changes in parameters related to renal tubular injury and EMT were analyzed in vivo. Changes in the proportion of apoptotic renal tubular cells and ER stress, and the signaling pathways involved in these changes, were analyzed both in vivo and in vitro.

Results: SKI and ROS improved the general condition, the renal morphological appearance and the key biochemical parameters, and attenuated renal injury and EMT in the rat model of DKD. In addition, SKI and ROS alleviated apoptosis, inhibited ER stress, and suppressed PERK-eIF2α-ATF4-CHOP signaling pathway activation both in vivo and in vitro. Notably, our data showed that the regulatory in vitro effects of SKI on PERK-eIF2α-ATF4-CHOP signaling were similar to those of 4-PBA, a specific inhibitor of ER stress.

Conclusion: This study confirmed that SKI can alleviate DT in a similar manner as ROS, and SKI achieves this effect by inhibiting EMT and ER stress-induced apoptosis. Our findings thereby provide novel information relating to the clinical value of SKI in the treatment of DT.

Rosiglitazone attenuates high glucose-induced proliferation, inflammation, oxidative stress and extracellular matrix accumulation in mouse mesangial cells through the Gm26917/miR-185-5p pathway

Rosiglitazone (RSG) is widely used to reduce the amount of sugar in the blood of patients with diabetes mellitus. Diabetic nephropathy is the most common microvascular complication of diabetes. The role of RSG in diabetic nephropathy is not fully understood. Diabetic nephropathy model was constructed in high glucose (HG)-treated mouse mesangial cells. The effects of RSG on cell viability and cell cycle were investigated using cell counting kit-8 (CCK-8) assay and flow cytometry assay. Oxidative stress was assessed according to ROS production and SOD activity in cells. Inflammatory responses were assessed according to the releases of inflammatory cytokines. Extracellular matrix (ECM) accumulation was determined by the levels of fibronectin and collagen IV using western blot. The expression of Gm26917 and microRNA-185-5p (miR-185-5p) was detected by quantitative real-time polymerase chain reaction (qPCR). The interaction between Gm26917 and miR-185-5p was validated by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and pull-down assay. RSG significantly inhibited HG-induced proliferation, oxidative stress, inflammatory responses and ECM accumulation in mouse mesangial cells. The expression of Gm26917 was induced by HG but weakened by RSG. Gm26917 knockdown alleviated HG-induced proliferation, oxidative stress, inflammatory responses and ECM accumulation in mouse mesangial cells, and Gm26917 overexpression partly abolished the effects of RSG. Moreover, miR-185-5p was a target of Gm26917, and miR-185-5p inhibition recovered proliferation, oxidative stress, inflammatory responses and ECM accumulation in mouse mesangial cells that were alleviated by Gm26917 knockdown. RSG ameliorated HG-induced mouse mesangial cell proliferation, oxidative stress, inflammation and ECM accumulation partially by governing the Gm26917/miR-185-5p pathway.

MicroRNA-10 negatively regulates inflammation in diabetic kidney via targeting activation of the NLRP3 inflammasome

NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) inflammasome activation has emerged as a central mediator of kidney inflammation in diabetic kidney disease (DKD). However, the mechanism underlying this activation in DKD remains poorly defined. In this study, we found that kidney-enriched microRNA-10a and -10b (miR-10a/b), predominantly expressed in podocytes and tubular epithelial cells, were downregulated in kidney from diabetic mice and patients with DKD. High glucose decreased miR-10a/b expression in vitro in an osmolarity-independent manner. miR-10a/b functioned as negative regulators of the NLRP3 inflammasome through targeting the 3'untranslated region of NLRP3 mRNA, inhibiting assembly of the NLRP3 inflammasome and decreasing caspase-1-dependent release of pro-inflammatory cytokines. Delivery of miR-10a/b into kidney prevented NLRP3 inflammasome activation and renal inflammation, and it reduced albuminuria in streptozotocin (STZ)-treated mice, whereas knocking down miR-10a/b increased NLRP3 inflammasome activation. Restoration of miR-10a/b expression in established DKD ameliorated kidney inflammation and mitigated albuminuria in both db/db and STZ-treated mice. These results suggest a novel intervention strategy for inhibiting kidney inflammation in DKD by targeting the NLRP3 inflammasome.

The Emerging Role of Renal Tubular Epithelial Cells in the Immunological Pathophysiology of Lupus Nephritis

Systemic lupus erythematosus (SLE) is a systemic, autoimmune disease that can involve virtually any organ of the body. Lupus nephritis (LN), the clinical manifestation of this disease in the kidney, is one of the most common and severe outcomes of SLE. Although a key pathological hallmark of LN is glomerular inflammation and damage, tubulointerstitial lesions have been recognized as an important component in the pathology of LN. Renal tubular epithelial cells are resident cells in the tubulointerstitium that have been shown to play crucial roles in various acute and chronic kidney diseases. In this context, recent progress has been made in examining the functional role of tubular epithelial cells in LN pathogenesis. This review summarizes recent advances in our understanding of renal tubular epithelial cells in LN, the potential role of tubular epithelial cells as biomarkers in the diagnosis, prognosis, and treatment of LN, and the future therapeutic potential of targeting the tubulointerstitium for the treatment of patients with LN.

Targeting NLRP3 inflammasome as a promising approach for treatment of diabetic nephropathy: Preclinical evidences with therapeutic approaches

Diabetes mellitus is an increasingly prevalent disease around the globe. The epidemic of diabetes mellitus and its complications pretenses the foremost health threat globally. Diabetic nephropathy is the notable complication in diabetes, leading to end-stage renal disease (ESRD) and premature death. Abundant experimental evidence indicates that oxidative stress and inflammation are the important mediators in diabetic kidney diseases and interlinked with various signal transduction molecular mechanisms. Inflammasomes are the critical components of innate immunity and are recognized as a critical mediator of inflammation and autoimmune disorders. NOD-like receptor protein 3 (NLRP3) inflammasome is the well-characterized protein and it exhibits the sterile inflammation through the regulation of pro-inflammatory cytokines interleukin (IL)-1β and IL-18 production in tissues. In recent years, the role of NLRP3 inflammasome in the pathophysiology of diabetic kidney diseases in both clinical and experimental studies has generated great interest. In the current review, we focused on and discussed the role of NLRP3 inflammasome in diabetic nephropathy. A literature review was performed using online databases namely, PubMed, Scopus, Google Scholar and Web of science to explore the possible pharmacological interventions that blunt the NLRP3 inflammasome-caspase-1-IL-1β/IL-18 axis and shown to have a beneficial effect in diabetic kidney diseases. This review describes the inhibition of NLRP3 inflammasome activation as a promising therapeutic target for drug discovery in future.

Innate immunity in diabetic kidney disease

Increasing evidence suggests that renal inflammation contributes to the pathogenesis and progression of diabetic kidney disease (DKD) and that anti-inflammatory therapies might have renoprotective effects in DKD. Immune cells and resident renal cells that activate innate immunity have critical roles in triggering and sustaining inflammation in this setting. Evidence from clinical and experimental studies suggests that several innate immune pathways have potential roles in the pathogenesis and progression of DKD. Toll-like receptors detect endogenous danger-associated molecular patterns generated during diabetes and induce a sterile tubulointerstitial inflammatory response via the NF-κB signalling pathway. The NLRP3 inflammasome links sensing of metabolic stress in the diabetic kidney to activation of pro-inflammatory cascades via the induction of IL-1β and IL-18. The kallikrein-kinin system promotes inflammatory processes via the generation of bradykinins and the activation of bradykinin receptors, and activation of protease-activated receptors on kidney cells by coagulation enzymes contributes to renal inflammation and fibrosis in DKD. In addition, hyperglycaemia leads to protein glycation and activation of the complement cascade via recognition of glycated proteins by mannan-binding lectin and/or dysfunction of glycated complement regulatory proteins. Data from preclinical studies suggest that targeting these innate immune pathways could lead to novel therapies for DKD.

Associations of ACE I/D polymorphism with the levels of ACE, kallikrein, angiotensin II and interleukin-6 in STEMI patients

This study aimed to compare the plasma levels of angiotensin-I converting enzyme (ACE), Angiotensin II (AngII), kallikrein (KLK1) and interleukin-6 (IL-6) in ST segment elevation myocardial infarction (STEMI) patients with different ACE Insertion/deletion (I/D) polymorphisms in a Chinese population. The ACE genotypes were determined in the 199 STEMI patients and 216 control subjects. STEMI patients were divided into three groups based on the ACE genotypes. Single polymerase chain reaction (PCR) was performed to characterize ACE I/D polymorphisms. Plasma levels of ACE, AngII, KLK1 and IL-6 were measured by enzyme-linked immunosorbent assay (ELISA). We found that the DD or ID genotype was significantly independently associated with high ACE (OR = 4.697; 95% CI = 1.927–11.339), KLK1 (3.339; 1.383–8.063) and IL-6 levels (OR = 2.10; 1.025–4.327) in STEMI patients. However, there was no statistical significance between the ACE I/D polymorphism and AngII plasma levels whether in univariate or multivariate logistic regression. Additionally, we detected a significantly positive correlation between plasma KLK1 levels and IL-6 levels in STEMI patients (r = 0.584, P < 0.001). The study showed high levels of ACE, KLK1 and IL-6 were detected when the D allele was present, but AngII plasma levels was not influenced by the ACE I/D polymorphism.

Human mesenchymal stromal cells broadly modulate high glucose-induced inflammatory responses of renal proximal tubular cell monolayers

BACKGROUND

Renal proximal tubular epithelial cells (RPTEC) are dysfunctional in diabetic kidney disease (DKD). Mesenchymal stromal cells (MSC) may modulate DKD pathogenesis through anti-inflammatory mediators. This study aimed to investigate the pro-inflammatory effect of extended exposure to high glucose (HG) concentration on stable RPTEC monolayers and the influence of MSC on this response.

METHODS

Morphologically stable human RPTEC/TERT1 cell monolayers were exposed to 5 mM and 30 mM (HG) D-glucose or to 5 mM D-glucose + 25 mM D-mannitol (MAN) for 5 days with sequential immunoassays of supernatants and end-point transcriptomic analysis by RNA sequencing. Under the same conditions, MSC-conditioned media (MSC-CM) or MSC-containing transwells were added for days 4-5. Effects of CM from HG- and MAN-exposed RPTEC/MSC co-cultures on cytokine secretion by monocyte-derived macrophages were determined.

RESULTS

After 72-80 h, HG resulted in increased RPTEC/TERT1 release of interleukin (IL)-6, IL-8, monocyte chemoattractant protein (MCP)-1 and neutrophil gelatinase-associated lipocalin (NGAL). The HG pro-inflammatory effect was attenuated by concentrated (10×) MSC-CM and, to a greater extent, by MSC transwell co-culture. Bioinformatics analysis of RNA sequencing data confirmed a predominant effect of HG on inflammation-related mediators and biological processes/KEGG pathways in RPTEC/TERT1 stable monolayers as well as the non-contact-dependent anti-inflammatory effect of MSC. Finally, CM from HG-exposed RPTEC/MSC transwell co-cultures was associated with attenuated secretion of inflammatory mediators by macrophages compared to CM from HG-stimulated RPTEC alone.

CONCLUSIONS

Stable RPTEC monolayers demonstrate delayed pro-inflammatory response to HG that is attenuated by close proximity to human MSC. In DKD, this MSC effect has potential to modulate hyperglycemia-associated RPTEC/macrophage cross-talk.

BMP-7 inhibits renal fibrosis in diabetic nephropathy via miR-21 downregulation

Epithelial-mesenchymal transition (EMT) and extracellular matrix (ECM) deposition in renal tubular epithelial cells are critical to diabetic nephropathy (DN) pathogenesis, but the underlying mechanisms remain undefined. Bone morphogenetic protein 7 (BMP-7) inhibits EMT and ECM accumulation in renal tubular epithelial cells cultured in presence of high glucose. Meanwhile, miRNA-21 (miR-21) downregulates Smad7, promoting EMT and ECM deposition. However, the association of BMP-7 with miR-21/Smad7 in DN is unknown. Here, NRK-52E cells incubated in presence of high glucose and STZ-induced C57BL diabetic mice were considered in vitro and in vivo models of DN, respectively. In both models, BMP-7 (mRNA/protein) amounts were decreased as well as Smad7 protein expression, while miR-21 expression and TGF-β1/Smad3 pathway activation were enhanced, accompanied by enhanced EMT and ECM deposition. Further, addition of BMP-7 human recombinant cytokine (rhBMP-7) and injection of the BMP-7 overexpression plasmid in diabetic mice markedly downregulated miR-21 and upregulated Smad7, reduced Smad3 activation without affecting TGF-β1 amounts, and prevented EMT and ECM accumulation. MiR-21 overexpression in the in vitro model downregulated Smad7, promoted EMT and ECM accumulation without affecting BMP-7 amounts, and miR-21 downregulation reversed it. By interfering with BMP-7 and miR-21 expression in high glucose conditions, miR-21 amounts and Smad3 phosphorylation were further decreased. Smad7 was then upregulated, and EMT and ECM deposition were inhibited; these effects were reversed after miR-21 overexpression. These findings suggest that BMP-7 decreases renal fibrosis in DN by regulating miR-21/Smad7 signaling, providing a theoretical basis for the development of novel and effective therapeutic drugs for DN.

The classic signalling and trans-signalling of interleukin-6 are both injurious in podocyte under high glucose exposure

Interleukin‐6 (IL‐6) is a multifunctional cytokine that employs IL‐6 classic and trans‐signalling pathways, and these two signal channels execute different or even opposite effects in certain diseases. As a cardinal event of diabetic kidney disease (DKD), whether the podocyte abnormalities are associated with IL‐6 signalling, especially classic or trans‐signalling respectively, remains unclear. In this study, we identified that the circulatory IL‐6, soluble IL‐6R (sIL‐6R) and soluble glycoprotein 130 (sgp130) levels are elevated in patients with DKD. The expressions of membrane‐bound IL‐6R (mIL‐6R), sIL‐6R and gp130 are enhanced in kidney cortex of diabetic mice accompanying with activated STAT3 by tyrosine 705 residue phosphorylation, while not serine 727. Above data infer both classic signalling and trans‐signalling of IL‐6 are activated during DKD. In cultured podocyte, high glucose (HG) up‐regulates the expression of mIL‐6R and gp130, as well as STAT3 tyrosine 705 phosphorylation, in a time‐dependent manner. Entirely blocking IL‐6 signalling by gp130 shRNA, gp130 or IL‐6 neutralizing antibodies attenuates HG‐induced podocyte injury. Interestingly, either inhibiting IL‐6 classic signalling by mIL‐6R shRNA or suppressing its trans‐signalling using sgp130 protein dramatically alleviates HG‐induced podocyte injury, suggesting both IL‐6 classic signalling and trans‐signalling play a detrimental role in HG‐induced podocyte injury. Additionally, activation of IL‐6 classic or trans‐signalling aggravates podocyte damage in vitro. In summary, our observations demonstrate that the activation of either IL‐6 classic or trans‐signalling advances podocyte harming under hyperglycaemia. Thus, suppressing IL‐6 classic and trans‐signalling simultaneously may be more beneficial in podocyte protection and presents a novel therapeutic target for DKD.

Performance of urinary neutrophil gelatinase-associated lipocalin, clusterin, and cystatin C in predicting diabetic kidney disease and diabetic microalbuminuria: a consecutive cohort study

Background

Tubular biomarkers have been regarded as emerging and promising markers for early diagnosis of diabetic kidney disease (DKD). The study was to determine the diagnostic capabilities of tubular biomarkers (urinary neutrophil gelatinase-associated lipocalin [NGAL], clusterin, and cystatin C) for DKD and diabetic microalbuminuria, and whether or not the tubular biomarkers appear earlier than microalbuminuria.

Methods

In this consecutive cohort study, 146 type 2 diabetes mellitus (T2DM) patients with a disease duration of ≥6 years were enrolled. Thirty age- and gender-matched subjects without any systemic diseases were recruited as the control group. Urinary samples collected before treatment were tested for NGAL, clusterin, and cystatin C.

Results

The levels of biomarkers were higher in patients with DKD (p < 0.001); and positively correlated with the urinary albumin creatinine ratio (UACR; p < 0.001). With respect to the diagnosis of DKD, the areas under the receiver operating characteristic curve (AUCs) for urinary NGAL, clusterin, and cystatin C were 0.816 (95% confidence interval [CI], 0.741–0.891), 0.775 (95% CI: 0.694–0.857), and 0.803 (95% CI: 0.722–0.884), respectively. The levels of urinary NGAL and cystatin C in the normoalbuminuria group (UACR <30 mg /g•Cr) were elevated compared with the control group, unlike urinary clusterin. There was no statistical difference in the levels of the three biomarkers between groups with different levels of haemoglobin A_1C (HbA_1c). The diagnostic AUCs for urinary NGAL, clusterin, and cystatin C in patients with diabetic microalbuminuria were 0.841 (95% CI: 0.775–0.907), 0.783(95% CI: 0.710–0.856), and 0.805 (95% CI: 0.733–0.877), respectively.

Conclusions

Urinary NGAL, clusterin, and cystatin C may be promising biomarkers for diagnosing DKD and diabetic microalbuminuria. It is possible that urinary NGAL and cystatin C increase before the onset of microalbuminuria in T2DM patients.

Kallistatin protects against diabetic nephropathy in db/db mice by suppressing AGE-RAGE-induced oxidative stress

Kallistatin is a serine protease inhibitor with anti-inflammatory, anti-angiogenic, and anti-oxidative properties. Since oxidative stress plays a critical role in the pathogenesis of diabetic nephropathy, we studied the effect and mechanisms of action of kallistatin superinduction. Using ultrasound-microbubble-mediated gene transfer, kallistatin overexpression was induced in kidney tubules. In db/db mice, kallistatin overexpression reduced serum creatinine and BUN levels, ameliorated glomerulosclerosis and tubulointerstitial injury, and attenuated renal fibrosis by inhibiting TGF-β signaling. Additionally, downstream PAI-1 and collagens I and IV expression were reduced and kallistatin partially suppressed renal inflammation by inhibiting NF-κB signaling and decreasing tissue kallikrein activity. Kallistatin lowered blood pressure and attenuated oxidative stress as evidenced by suppressed levels of NADPH oxidase 4, and oxidative markers (nitrotyrosine, 8-hydroxydeoxyguanosine, and malondialdehyde) in diabetic renal tissue. Kallistatin also inhibited RAGE expression in the diabetic kidney and AGE-stimulated cultured proximal tubular cells. Reduced AGE-induced reactive oxygen species generation reflected an anti-oxidative mechanism via the AGE-RAGE-reactive oxygen species axis. These results indicate a renoprotective role of kallistatin against diabetic nephropathy by multiple mechanisms including suppression of oxidative stress, anti-fibrotic and anti-inflammatory actions, and blood pressure lowering.

PGC1α Activators Mitigate Diabetic Tubulopathy by Improving Mitochondrial Dynamics and Quality Control

Purpose. In this study, we investigated the effect of PGC1α activators on mitochondrial fusion, fission, and autophagic quality control in renal tubular cells in a diabetic environment in vivo and in vitro. We also examined whether the upregulation of PGC1α attenuates diabetic tubulopathy by normalizing mitochondrial homeostasis. Methods. HKC8 cells were subjected to high-glucose conditions (30 mM D-glucose). Diabetes was induced with streptozotocin (STZ, 50 mg/kg i.p. for 5 days) in male C57/BL6J mice. AICAR or metformin was used as a PGC1α activator. Results. Treatment with the PGC1α activators AICAR and metformin improved functional mitochondrial mass in HKC8 cells in high-glucose conditions. Moreover, in renal proximal tubular cells, increased PGC1α activity correlated with the reversal of changes in Drp1, Mfn1, and LC3-II protein expression in a high-glucose environment. Normalized mitochondrial life cycles resulted in low ROS production and reduced apoptosis. AICAR and metformin treatment effectively mitigated albuminuria and renal histopathology and decreased the expression of TGFβ1 and αSMA in the kidneys of diabetic mice. Conclusions. Our results demonstrate that increases in PGC1α activity improve diabetic tubulopathy by modulating mitochondrial dynamics and autophagy.

Peroxisome proliferator-activated receptor γ prevents the production of NOD-like receptor family, pyrin domain containing 3 inflammasome and interleukin 1β in HK-2 renal tubular epithelial cells stimulated by monosodium urate crystals

Recent evidence showed that peroxisome proliferator‑activated receptor γ (PPARγ) ameliorates a variety of inflammatory conditions. The present study aimed to investigate the role of PPARγ in regulating NOD-like receptor family, pyrin domain containing 3 (NALP3) inflammasome and interleukin (IL)‑1β levels during monosodium urate (MSU) crystal‑induced inflammation. HK‑2 cells were incubated with or without 200 µg/ml MSU crystals, and mRNA and protein levels of PPARγ were determined using reverse transcription quantitative polymerase chain reaction and western blot analysis, respectively. To verify the role of PPARγ, HK‑2 cells were pre‑treated with PPARγ agonist pioglitazone, and the levels of NALP3 inflammasome and IL‑1β were detected by western blot analysis and ELISA. The results showed that MSU crystals increased PPARγ expression in HK‑2 cells at 24 h, while the expression decreased to normal levels at 48 h. It was also demonstrated that although the PPARγ agonist pioglitazone did not alter the mRNA and protein levels of PPARγ, it significantly reduced the MSU crystal‑induced production of NALP3 inflammasome and IL‑1β in HK‑2 cells, possibly by increasing the level of PPARγ activity. In conclusion, the results of the present study indicated that PPARγ prevented NALP3 inflammasome formation and IL‑1β production in HK‑2 cells stimulated by MSU crystals, which indicated that PPARγ may represent a novel target for the treatment of hyperuricemic nephropathy.

BMP7 reduces inflammation and oxidative stress in diabetic tubulopathy

Bone morphogenetic protein 7 (BMP7) has been reported to confer renoprotective effects in acute and chronic kidney disease models, but its potential role in Type 2 diabetic nephropathy remains unknown. In cultured human proximal tubular epithelial cells (PTECs), exposure to advanced glycation end-products (AGEs) induced overexpression of intercellular adhesion molecule 1 (ICAM1), monocyte chemoattractant protein 1 (MCP1), interleukin 8 (IL-8) and interleukin 6 (IL-6), involving activation of p44/42 and p38 mitogen-activated protein kinase (MAPK) signalling. BMP7 dose-dependently attenuated AGE-induced up-regulation of ICAM1, MCP1, IL-8 and IL-6 at both mRNA and protein levels. Moreover, BMP7 suppressed AGE-induced p38 and p44/42 MAPK phosphorylation and reactive oxygen species production in PTECs. Compared with vehicle control, uninephrectomized db/db mice treated with BMP7 for 8 weeks had significantly lower urinary albumin-to-creatinine ratio (3549±816.2 μg/mg compared with 8612±2037 μg/mg, P=0.036), blood urea nitrogen (33.26±1.09 mg/dl compared with 37.49±0.89 mg/dl, P=0.006), and renal cortical expression of ICAM1 and MCP1 at both gene and protein levels. In addition, BMP7-treated animals had significantly less severe tubular damage, interstitial inflammatory cell infiltration, renal cortical p38 and p44/42 phosphorylation and lipid peroxidation. Our results demonstrate that BMP7 attenuates tubular pro-inflammatory responses in diabetic kidney disease by suppressing oxidative stress and multiple inflammatory signalling pathways including p38 and p44/42 MAPK. Its potential application as a therapeutic molecule in diabetic nephropathy warrants further investigation.

Renal tubular damage may contribute more to acute hyperglycemia induced kidney injury in non-diabetic conscious rats

AIMS

Growing evidences suggest that acute hyperglycemia is strongly related to kidney injury. Our study aimed to investigate the effects of acute hyperglycemia on kidney glomerular and tubular impairment in non-diabetic conscious rats.

METHODS

Non-diabetic conscious rats were randomly subjected to 6h of saline (control group) or high glucose (acute hyperglycemia group) infusion. Blood glucose was maintained at 16.0-18.0 mmol/L in acute hyperglycemia group. Renal structure and function alterations, systemic/renal inflammation and oxidative stress markers were assessed, and apoptosis markers of renal inherent cells were evaluated.

RESULTS

Acute hyperglycemia caused significant injury to structure of glomerular filtration barrier, tubular epithelial cells and peritubular vascular endothelial cells. It increased urinary microalbumin (68.01 ± 27.09 μg/24h vs 33.81 ± 13.81 μg/24h , P=0.014), β2-microglobulin, Cystatin C, urinary and serous neutrophil gelatinase-associated lipocalin levels (P < 0.05). Acute hyperglycemia decreased megalin and cubilin expression, activated systemic and renal oxidative stress as well as inflammation and promoted renal inherent cell apoptosis.

CONCLUSIONS

Acute hyperglycemia causes significant injury to kidney function and structure. Compared with damages of glomerular filtration barrier, renal tubular injury may contribute more to acute hyperglycemia induced proteinuria. Activation of inflammation especially renal inflammation, oxidative stress and enhanced apoptosis may be the underlying mechanisms.

Diabetic nephropathy and proximal tubular damage

Diabetic nephropathy (DN) is a major cause of uremia in developed societies. Inflammation is emerging as an important mechanism for its pathogenesis and progression. Herein, we review 4 recently described cellular receptors that have been shown to mediate diabetic interstitial kidney disease. Peroxisome proliferator-activated receptor-γ attenuates STAT-1 activation and has shown promise in renoprotection. Its clinical utility is limited mainly by fluid retention through upregulation of sodium-hydrogen exchanger-3 and aquaporin-1 channels in the proximal tubule. The bradykinin receptor 2 of the kallikrein-kinin system has been shown to mediate diabetic kidney injury and its blockade conferred renoprotective effects in animal models of DN. The related protease-activated receptor, especially receptor 4, has recently been shown to participate in DN. Further studies are required to confirm its role. Finally, the toll-like receptor, especially TLR4 and TLR2, has been verified in multiple models to be a significant sensor of and reactor to hyperglycemia and other diabetic substrates that orchestrate interstitial inflammation in DN.

Angiotensin converting enzyme is involved in the cardiac hypertrophy induced by sinoaortic denervation in rats

INTRODUCTION

The present study was designed to test the hypothesis that local angiotensin converting enzyme (ACE) was involved in the cardiac hypertrophy induced by sinoaortic denervation (SAD) in rats.

METHODS

Experiment 1: Six weeks after SAD of rats, components of renin-angiotensin system (RAS) in left ventricles were assayed by quantitative real-time PCR and Western blotting analysis. Experiment 2: Rats were divided into five groups treated as follows: (1) sham-operated group; (2) SAD group; (3) SAD group treated with angiotensin II type 1 receptor (AT1R) antagonist losartan (10 mg·kg(-1)·day(-1), orally); (4) SAD group treated by ACE inhibitor ramipril (1 mg·kg(-1)·day(-1), orally); (5) SAD group treated by ramipril and the B2-kinin receptor selective antagonist HOE-140 (0.25 mg·kg(-1)·day(-1), subcutaneously).

RESULTS

SAD led to augmentation of the mRNA levels and protein expression of left ventricular ACE and AT1R. Both losartan and ramipril ameliorated SAD-induced left ventricular hypertrophy. Both losartan and ramipril abated oxidative stress, suppressed inflammation, and reduced expression TGFβ-R in left ventricles. In addition, the protective effect of ramipril could be abolished by HOE-140.

CONCLUSION

Local ACE is involved in the left ventricular hypertrophy induced by sinoaortic denervation in rats, via both angiotensin II/AT1R and bradykinin/B2R pathways.

Tribbles homolog 3 attenuates mammalian target of rapamycin complex-2 signaling and inflammation in the diabetic kidney

The endoplasmic reticulum (ER) stress response is activated in the diabetic kidney and functions to reduce ER protein accumulation and improve cellular function. We previously showed that tribbles homolog 3 (TRB3), an ER stress-associated protein, is upregulated in the diabetic kidney. Here, we investigated whether absence of TRB3 alters outcomes in diabetic nephropathy. Type 1 diabetes was induced in TRB3 wild-type and knockout ((-/-)) mice by low-dose streptozotocin, and the mice were followed for 12 weeks. Diabetic TRB3(-/-) mice developed higher levels of albuminuria and increased expression of inflammatory cytokine and chemokine mRNA in renal cortices relative to wild-type littermates, despite similar hyperglycemia. Diabetic TRB3(-/-) mice also expressed higher levels of ER stress-associated molecules in both the renal cortices and glomeruli. This change was associated with higher renal cortical phosphorylation of AKT at serine 473 (Ser(473)), which is the AKT site phosphorylated by mammalian target of rapamycin complex-2 (mTORC2). We show in renal tubular cells that TRB3 binds to mTOR and the rapamycin-insensitive companion of mTOR (Rictor), a protein specific to mTORC2. Finally, we demonstrate in murine tubular cells that TRB3 can inhibit secretion of IL-6. Thus, TRB3 reduces albuminuria and inflammatory gene expression in diabetic kidney disease by a mechanism that may involve inhibition of the mTORC2/AKT pathway and may prove to be a novel therapeutic target.

Mesenchymal stem cells modulate albumin-induced renal tubular inflammation and fibrosis

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have recently shown promise as a therapeutic tool in various types of chronic kidney disease (CKD) models. However, the mechanism of action is incompletely understood. As renal prognosis in CKD is largely determined by the degree of renal tubular injury that correlates with residual proteinuria, we hypothesized that BM-MSCs may exert modulatory effects on renal tubular inflammation and epithelial-to-mesenchymal transition (EMT) under a protein-overloaded milieu. Using a co-culture model of human proximal tubular epithelial cells (PTECs) and BM-MSCs, we showed that concomitant stimulation of BM-MSCs by albumin excess was a prerequisite for them to attenuate albumin-induced IL-6, IL-8, TNF-α, CCL-2, CCL-5 overexpression in PTECs, which was partly mediated via deactivation of tubular NF-κB signaling. In addition, albumin induced tubular EMT, as shown by E-cadherin loss and α-SMA, FN and collagen IV overexpression, was also prevented by BM-MSC co-culture. Albumin-overloaded BM-MSCs per se retained their tri-lineage differentiation capacity and overexpressed hepatocyte growth factor (HGF) and TNFα-stimulating gene (TSG)-6 via P38 and NF-κB signaling. Albumin-induced tubular CCL-2, CCL-5 and TNF-α overexpression were suppressed by recombinant HGF treatment, while the upregulation of α-SMA, FN and collagen IV was attenuated by recombinant TSG-6. Neutralizing HGF and TSG-6 abolished the anti-inflammatory and anti-EMT effects of BM-MSC co-culture in albumin-induced PTECs, respectively. In vivo, albumin-overloaded mice treated with mouse BM-MSCs had markedly reduced BUN, tubular CCL-2 and CCL-5 expression, α-SMA and collagen IV accumulation independent of changes in proteinuria. These data suggest anti-inflammatory and anti-fibrotic roles of BM-MSCs on renal tubular cells under a protein overloaded condition, probably mediated via the paracrine action of HGF and TSG-6.

Tissue kallikrein mediates pro-inflammatory pathways and activation of protease-activated receptor-4 in proximal tubular epithelial cells

Tissue kallikrein (KLK1) expression is up-regulated in human diabetic kidney tissue and induced by high glucose (HG) in human proximal tubular epithelial cells (PTEC). Since the kallikrein-kinin system (KKS) has been linked to cellular inflammatory process in many diseases, it is likely that KLK1 expression may mediate the inflammatory process during the development of diabetic nephropathy. In this study, we explored the role of KLK1 in tubular pro-inflammatory responses under the diabetic milieu. Recombinant KLK1 stimulated the production of inflammatory cytokines in PTEC via the activation of p42/44 and p38 MAPK signaling pathways. Molecular knockdown of endogenous KLK1 expression by siRNA transfection in PTEC attenuated advanced glycation end-products (AGE)-induced IL-8 and ICAM-1 productions in vitro. Interestingly, exposure of PTEC to KLK1 induced the expression of protease-activated receptors (PARs). There was a 2.9-fold increase in PAR-4, 1.4-fold increase in PAR-1 and 1.2-fold increase in PAR-2 mRNA levels. Activation of PAR-4 by a selective agonist was found to elicit the pro-inflammatory and pro-fibrotic phenotypes in PTEC while blockade of the receptor by specific antagonist attenuated high glucose-induced IL-6, CCL-2, CTGF and collagen IV expression. Calcium mobilization by the PAR-4 agonist in PTEC was desensitized by pretreatment with KLK1. Consistent with these in vitro findings, there was a markedly up-regulation of tubular PAR-4 expression in human diabetic renal cortical tissues. Together, these results suggest that up-regulation of KLK1 in tubular epithelial cells may mediate pro-inflammatory pathway and PAR activation during diabetic nephropathy and provide a new therapeutic target for further investigation.

Tissue kallikrein-kinin therapy in hypertension and organ damage

Tissue kallikrein is a serine proteinase that cleaves low molecular weight kininogen to produce kinin peptides, which in turn activate kinin receptors to trigger multiple biological functions. In addition to its kinin-releasing activity, tissue kallikrein directly interacts with the kinin B2 receptor, protease-activated receptor-1, and gamma-epithelial Na channel. The tissue kallikrein-kinin system (KKS) elicits a wide spectrum of biological activities, including reducing hypertension, cardiac and renal damage, restenosis, ischemic stroke, and skin wound injury. Both loss-of-function and gain-of-function studies have shown that the KKS plays an important endogenous role in the protection against health pathologies. Tissue kallikrein/kinin treatment attenuates cardiovascular, renal, and brain injury by inhibiting oxidative stress, apoptosis, inflammation, hypertrophy, and fibrosis and promoting angiogenesis and neurogenesis. Approaches that augment tissue kallikrein-kinin activity might provide an effective strategy for the treatment of hypertension and associated organ damage.

Plasma kininogen and kininogen fragments are biomarkers of progressive renal decline in type 1 diabetes

The ability of microalbuminuria to predict early progressive renal function decline in type-1 diabetic patients has been questioned. To resolve this, we determined the plasma proteome differences between microalbuminuric patients with type-1 diabetes and stable renal function (controls) and patients at risk for early progressive renal function decline (cases) and asked whether these differences have value as surrogate biomarkers. Mass spectrometry was used to analyze small (less than 3 kDa) plasma peptides isolated from well-matched case and control plasma obtained at the beginning of an 8-12 year follow-up period. Spearman analysis of plasma peptide abundance and the rate of renal function decline during follow-up identified seven masses with a significant negative correlation with early progressive renal function decline. Tandem mass spectrometry identified three fragments of high molecular weight kininogen. Increased plasma high molecular weight kininogen in the cases was confirmed by immunoblot. One peptide, des-Arg9-BK(1-8), induced Erk1/2 phosphorylation when added apically to two proximal tubular cell lines grown on permeable inserts. Thus, we have identified plasma protein fragments, some of which have biological activity with moderate to strong correlation, with early progressive renal function decline in microalbuminuric patients with type-1 diabetes. Other peptides are candidates for validation as candidate biomarkers of diabetes-associated renal dysfunction.

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.

The high glucose-induced stimulation of B1R and B2R expression via CB(1)R activation is involved in rat podocyte apoptosis

AIMS

We examined renal kallikrein-kinin system (KKS) apoptosis and its related signaling pathway in rat podocytes. In addition, we studied the relationship of cannabinoid receptor 1 (CB(1)R) with high glucose and BK receptors.

MAIN METHODS

Cell viability was determined by an MTT assay and apoptosis by DNA fragmentation assay, while gene expression was investigated by RT-PCR. Protein expression was analyzed by Western blot analysis. A chemical inhibitor or siRNA transfection was used to inhibit B1R, B2R, and CB(1)R signaling.

KEY FINDINGS

High glucose (25 mM) treatment decreased cell viability and increased DNA fragmentation. High glucose-induced DNA fragmentation and PARP and caspase-3 activations were blocked by both [des-Arg(10)]-HOE 140 (a B1R antagonist) and HOE 140 (a B2R antagonist). High glucose also increased Akt phosphorylation, ER stress-related protein expression, and NF-κB/I-κB phosphorylation in podocytes, which was blocked by both [des-Arg(10)]-HOE 140 and HOE 140. In addition, B1R and B2R siRNA transfections prevented high glucose-induced Akt and NF-κB activations in rat podocytes. Moreover, AM251 (a CB(1)R antagonist) treatment and CB(1)R siRNA transfection blocked the high glucose-induced stimulation of BK receptor expression, Akt activation, and NF-κB activation.

SIGNIFICANCE

Our study suggests that hyperglycemia induces apoptosis via the stimulation of B1R and B2R expression through CB(1)R activation in rat podocytes in vitro, which is associated with the development of diabetic nephropathy.

The pathogenic role of the renal proximal tubular cell in diabetic nephropathy

A growing body of evidence indicates that the renal proximal tubular epithelial cell (PTEC) plays an important role in the pathogenesis of diabetic nephropathy (DN). Microalbuminuria that intensifies over time to overt proteinuria, a hallmark of DN, is already known to activate the PTEC to induce tubulointerstitial inflammation. In addition to proteins, a number of diabetic substrates including high glucose per se, advanced glycation end-products and their carbonyl intermediates, angiotensin II, and ultrafiltered growth factors activate a number of signaling pathways including nuclear factor kappa B, protein kinase C, extracellular signal-regulated kinase 1/2, p38, signal transducer and activator of transcription-1 and the generation of reactive oxygen species, to culminate in tubular cell hypertrophy and the accumulation in the interstitium of a repertoire of chemokines, cytokines, growth factors and adhesion molecules capable of orchestrating further inflammation and fibrosis. More recently, the kallikrein-kinin system (KKS) and toll-like receptors (TLRs) in PTECs have been implicated in this process. While in vitro data suggest that the KKS contributes to the progression of DN, there are conflicting in vivo results on its precise role, which may in part be strain-dependent. On the other hand, there are both in vitro and in vivo data to suggest a role for both TLR2 and TLR4 in DN. In this review, we offer a critical appraisal of the events linking the participation of the PTEC to the pathogenesis of DN, which we believe may be collectively termed diabetic tubulopathy.

Bradykinin inhibits high glucose- and growth factor-induced collagen synthesis in mesangial cells through the B2-kinin receptor

Mesangial matrix expansion is an early lesion leading to glomeruloclerosis and chronic renal diseases. A beneficial effect is achieved with angiotensin I-converting enzyme inhibitors (ACEI), which also favor bradykinin (BK) B2 receptor (B2R) activation. To define the underlying mechanism, we hypothesized that B2R activation could be a negative regulator of collagen synthesis in mesangial cells (MC). We investigated the effect of BK on collagen synthesis and signaling in MC. Inflammation was evaluated by intercellular adhesion molecule-1 (ICAM-1) expression. BK inhibited collagen I and IV synthesis stimulated by high glucose, epithelial growth factor (EGF), and transforming growth factor-β (TGF-β) but did not alter ICAM-1. Inhibition of collagen synthesis was B2R but not B1R mediated. PKC or phosphatidylinositol 3-kinase (PI3K) inhibitors mimicked the BK effect. B2R activation inhibited TGF-β- and EGF-induced Erk1/2, Smad2/3, Akt S473, and EGFR phosphorylation. A phosphatase inhibitor prevented BK effects. The in vivo impact of B2R on mesangial matrix expansion was assessed in streptozotocin-diabetic rodents. Deletion of B2R increased mesangial matrix expansion and albuminuria in diabetic mice. In diabetic rats, matrix expansion and albuminuria were prevented by ACEI but not by ACEI and B2R antagonist cotreatment. Consistently, the lowered BK content of diabetic glomeruli was restored by ACEI. In conclusion, deficient B2R activation aggravated mesangial matrix expansion in diabetic rodents whereas B2R activation reduced MC collagen synthesis by a mechanism targeting Erk1/2 and Akt, common pathways activated by EGF and TGF-β. Taken together, the data support the hypothesis of an antifibrosing effect of B2R activation.

Toll-like receptor 4 promotes tubular inflammation in diabetic nephropathy

Inflammation contributes to the tubulointerstitial lesions of diabetic nephropathy. Toll-like receptors (TLRs) modulate immune responses and inflammatory diseases, but their role in diabetic nephropathy is not well understood. In this study, we found increased expression of TLR4 but not of TLR2 in the renal tubules of human kidneys with diabetic nephropathy compared with expression of TLR4 and TLR2 in normal kidney and in kidney disease from other causes. The intensity of tubular TLR4 expression correlated directly with interstitial macrophage infiltration and hemoglobin A1c level and inversely with estimated glomerular filtration rate. The tubules also upregulated the endogenous TLR4 ligand high-mobility group box 1 in diabetic nephropathy. In vitro, high glucose induced TLR4 expression via protein kinase C activation in a time- and dose-dependent manner, resulting in upregulation of IL-6 and chemokine (C-C motif) ligand 2 (CCL-2) expression via IκB/NF-κB activation in human proximal tubular epithelial cells. Silencing of TLR4 with small interfering RNA attenuated high glucose-induced IκB/NF-κB activation, inhibited the downstream synthesis of IL-6 and CCL-2, and impaired the ability of conditioned media from high glucose-treated proximal tubule cells to induce transmigration of mononuclear cells. We observed similar effects using a TLR4-neutralizing antibody. Finally, streptozotocin-induced diabetic and uninephrectomized TLR4-deficient mice had significantly less albuminuria, renal dysfunction, renal cortical NF-κB activation, tubular CCL-2 expression, and interstitial macrophage infiltration than wild-type animals. Taken together, these data suggest that a TLR4-mediated pathway may promote tubulointerstitial inflammation in diabetic nephropathy.

Additive renoprotective effects of B2-kinin receptor blocker and PPAR-γ agonist in uninephrectomized db/db mice

We recently showed that the bradykinin B2 receptor (B2R) blocker icatibant (Icat) and the peroxisome proliferator-activated receptor-γ agonist rosiglitazone (Ros) exerted anti-inflammatory effects in renal tubular cells exposed to a diabetic milieu. This study aims to explore whether these effects can be translated to an experimental model of type 2 diabetic nephropathy (DN). db/db mice and their nondiabetic db/m littermates underwent sham operation or uninephrectomy (Unx) at 10 weeks and received vehicle (Veh), metformin (Met), Icat, Ros, or Icat plus Ros for 8 weeks before killing. Among the db/db group with Unx, mice that received Icat or Ros had significantly lower serum creatinine and albuminuria, which was further reduced when Icat and Ros were given in combination. These beneficial effects were not observed in the Met group that achieved similar glycemic control as Ros-treated animals. Likewise, the severity of reactive glomerular and proximal tubular hypertrophy, glomerulosclerosis, interstitial injury, cortical F4/80 and α-smooth muscle actin immunostaining, and CCL-2, ICAM-1 and TGF-β overexpression were all attenuated by Icat and Ros, and these effects were enhanced when both agents were combined. Immunohistochemical staining confirmed the proximal tubular expression of CCL-2 (inflammation) and TGF-β (fibrosis). Treatment with Icat was associated with decreased B2R, but increased, B1R expression, which was exaggerated in Unx animals. At the signaling level, Icat and Ros reduced extracellular signal-regulated kinase 1/2 and STAT1 activation, respectively. Our results suggest a deleterious role of the kallikrein-kinin system in murine-accelerated DN, which can be ameliorated by the B2R blocker Icat and enhanced by the addition of Ros. This calls for further evaluation of this novel therapeutic approach in more animal models of diabetic nephropathy.

Differential effects of advanced glycation end-products on renal tubular cell inflammation

AIM

The authors recently showed that advanced glycation end-products (AGE) in the form of glycated albumin (GA) upregulated renal tubular expression of interleukin (IL)-8 and soluble intercellular adhesion molecule-1 (sICAM-1), but not other important cytokines known to mediate diabetic nephropathy. This implies that other molecules such as the carbonyl intermediates of AGE or other modified protein lysine-albumin may participate in diabetic tubular injury.

METHODS

Human proximal tubular epithelial cells (PTEC) were growth-arrested and exposed to methylglyoxal (MG), MG-bovine serum albumin (BSA)-AGE, carboxymethyllysine (CML)-BSA, AGE-BSA or BSA with or without prior addition of rosiglitazone that was previously shown to attenuate the pro-inflammatory effect of GA alone.

RESULTS

MG-BSA-AGE and AGE-BSA upregulated tubular expression of connective tissue growth factor (CTGF), transforming growth factor (TGF)-β, and vascular endothelial growth factor (VEGF), whereas CML-BSA stimulated expression of IL-6, CCL-2, CTGF, TGF-β and VEGF. These AGE compounds also activated nuclear factor (NF)-κB and their effects were attenuated by pre-incubation with anti-RAGE antibody. MG and BSA did not affect the expression of any of these molecules. Rosiglitazone did not affect the in vitro biological effects of MG, MG-BSA-AGE, AGE-BSA or CML-BSA on PTEC.

CONCLUSION

AGE exhibit differential inflammatory and fibrotic effects on PTEC via RAGE activation and NF-κB signal transduction. Rosiglitazone had no effect on these responses. Further investigations on compounds that nullify the downstream effects of these AGE are warranted.