High glucose induces podocyte injury via enhanced (pro)renin receptor-Wnt-β-catenin-snail signaling pathway

Renal Expression and Localization of the Receptor for (Pro)renin and Its Ligands in Rodent Models of Diabetes, Metabolic Syndrome, and Age-Dependent Focal and Segmental Glomerulosclerosis

The (pro)renin receptor ((P)RR), a versatile protein found in various organs, including the kidney, is implicated in cardiometabolic conditions like diabetes, hypertension, and dyslipidemia, potentially contributing to organ damage. Importantly, changes in (pro)renin/(P)RR system localization during renal injury, a critical information base, remain unexplored. This study investigates the expression and topographic localization of the full length (FL)-(P)RR, its ligands (renin and prorenin), and its target cyclooxygenase-2 and found that they are upregulated in three distinct animal models of renal injury. The protein expression of these targets, initially confined to specific tubular renal cell types in control animals, increases in renal injury models, extending to glomerular cells. (P)RR gene expression correlates with protein changes in a genetic model of focal and segmental glomerulosclerosis. However, in diabetic and high-fat-fed mice, (P)RR mRNA levels contradict FL-(P)RR immunoreactivity. Research on diabetic mice kidneys and human podocytes exposed to diabetic glucose levels suggests that this inconsistency may result from disrupted intracellular (P)RR processing, likely due to increased Munc18-1 interacting protein 3. It follows that changes in FL-(P)RR cellular content mechanisms are specific to renal disease etiology, emphasizing the need for consideration in future studies exploring this receptor's involvement in renal damage of different origins.

Cardiovascular effect of preeclampsia upon offspring development: Are (Pro) renin-renin receptor ((P)RR) and gender related?

Objectives

Preeclampsia (PE) is a complication of pregnancy that might increase progeny risk of cardiovascular and metabolic problems, mainly in males. Renin angiotensin aldosterone system is known to be involved. (Pro) renin/renin receptor ((P)RR) has been shown to participate in cardiovascular pathology. The aim of this work was to evaluate (P)RR expression and function upon cardiovascular and renal tissues from PE dams' offspring.

Materials and Methods

We used offspring from normal pregnant and preeclamptic rats, evaluating body, heart, aorta and kidney weight, length, and blood pressure along 3 months after birth. Subsets of animals received handle region peptide (HRP) (0.2 mg/Kg, sc). Another group received vehicle. Animals were sacrificed at first, second, and third months of age, tissues were extracted and processed for immunoblot to detect (P)RR, PLZF, β-catenin, DVL-1, and PKCα. (P)RR and PLZF were also measured by RT-PCR.

Results

We found that offspring developed hypertension. Male descendants remained hypertensive throughout the whole experiment. Female animals tended to recover at second month and returned to normal blood pressure at third month. HRP treatment diminished hypertension in both male and female animals. Morphological evaluations showed changes in heart, aorta, and kidney weight, and HRP reverted this effect. Finally, we found that (P)RR, PLZF, and canonical WNT transduction pathway molecules were stimulated by PE, and HRP treatment abolished this increase.

Conclusion

These findings suggest that PE can induce hypertension in offspring, and (P)RR seems to play an important role through the canonical WNT pathway and that gender seems to influence this response.

Transcriptional regulation by the NSL complex enables diversification of IFT functions in ciliated versus nonciliated cells

Members of the NSL histone acetyltransferase complex are involved in multiorgan developmental syndromes. While the NSL complex is known for its importance in early development, its role in fully differentiated cells remains enigmatic. Using a kidney-specific model, we discovered that deletion of NSL complex members KANSL2 or KANSL3 in postmitotic podocytes led to catastrophic kidney dysfunction. Systematic comparison of two primary differentiated cell types reveals the NSL complex as a master regulator of intraciliary transport genes in both dividing and nondividing cells. NSL complex ablation led to loss of cilia and impaired sonic hedgehog pathway in ciliated fibroblasts. By contrast, nonciliated podocytes responded with altered microtubule dynamics and obliterated podocyte functions. Finally, overexpression of wild-type but not a double zinc finger (ZF-ZF) domain mutant of KANSL2 rescued the transcriptional defects, revealing a critical function of this domain in NSL complex assembly and function. Thus, the NSL complex exhibits bifurcation of functions to enable diversity of specialized outcomes in differentiated cells.

Differential Methylation of Telomere-Related Genes Is Associated with Kidney Disease in Individuals with Type 1 Diabetes

Diabetic kidney disease (DKD) represents a major global health problem. Accelerated ageing is a key feature of DKD and, therefore, characteristics of accelerated ageing may provide useful biomarkers or therapeutic targets. Harnessing multi-omics, features affecting telomere biology and any associated methylome dysregulation in DKD were explored. Genotype data for nuclear genome polymorphisms in telomere-related genes were extracted from genome-wide case-control association data (n = 823 DKD/903 controls; n = 247 end-stage kidney disease (ESKD)/1479 controls). Telomere length was established using quantitative polymerase chain reaction. Quantitative methylation values for 1091 CpG sites in telomere-related genes were extracted from epigenome-wide case-control association data (n = 150 DKD/100 controls). Telomere length was significantly shorter in older age groups (p = 7.6 × 10^-6). Telomere length was also significantly reduced (p = 6.6 × 10^-5) in DKD versus control individuals, with significance remaining after covariate adjustment (p = 0.028). DKD and ESKD were nominally associated with telomere-related genetic variation, with Mendelian randomisation highlighting no significant association between genetically predicted telomere length and kidney disease. A total of 496 CpG sites in 212 genes reached epigenome-wide significance (p ≤ 10^-8) for DKD association, and 412 CpG sites in 193 genes for ESKD. Functional prediction revealed differentially methylated genes were enriched for Wnt signalling involvement. Harnessing previously published RNA-sequencing datasets, potential targets where epigenetic dysregulation may result in altered gene expression were revealed, useful as potential diagnostic and therapeutic targets for intervention.

RAGE is a critical factor of sex-based differences in age-induced kidney damage

Introduction: Advanced glycation end products (AGEs) are a heterogeneous group of molecules with potential pathophysiological effects on the kidneys. Fibrosis together with the accumulation of AGEs has been investigated for its contribution to age-related decline in renal function. AGEs mediate their effects in large parts through their interactions with the receptor for AGEs (RAGE). RAGE is a transmembrane protein that belongs to the immunoglobulin superfamily and has the ability to interact with multiple pro-inflammatory/pro-oxidative ligands. The role of RAGE in aging kidneys has not been fully characterized, especially for sex-based differences.

Methods: Therefore, we analyzed constitutive RAGE knockout (KO) mice in an age- and sex-dependent manner. Paraffin-embedded kidney sections were used for histological analysis and protein expression of fibrosis and damage markers. RNA expression analysis from the kidney cortex was done by qPCR for AGE receptors, kidney damage, and early inflammation/fibrosis factors. FACS analysis was used for immune cell profiling of the kidneys.

Results: Histological analysis revealed enhanced infiltration of immune cells (positive for B220) in aged (>70 weeks old) KO mice in both sexes. FACS analysis revealed a similar pattern of enhanced B-1a cells in aged KO mice. There was an age-based increase in pro-fibrotic and pro-inflammatory markers (IL-6, TNF, TGF-β1, and SNAIL1) in KO male mice that presumably contributed to renal fibrosis and renal damage (glomerular and tubular). In fact, in KO mice, there was an age-dependent increase in renal damage (assessed by NGAL and KIM1) that was accompanied by increased fibrosis (assessed by CTGF). This effect was more pronounced in male KO mice than in the female KO mice. In contrast to the KO animals, no significant increase in damage markers was detectable in wild-type animals at the age examined (>70 weeks old). Moreover, there is an age-based increase in AGEs and scavenger receptor MSR-A2 in the kidneys.

Discussion: Our data suggest that the loss of the clearance receptor RAGE in male animals further accelerates age-dependent renal damage; this could be in part due to an increase in AGEs load during aging and the absence of protective female hormones. By contrast, in females, RAGE expression seems to play only a minor role when compared to tissue pathology.

Urolithins Modulate the Viability, Autophagy, Apoptosis, and Nephrin Turnover in Podocytes Exposed to High Glucose

Urolithins are bioactive compounds generated in human and animal intestines because of the bacterial metabolism of dietary ellagitannins (and their constituent, ellagic acid). Due to their multidirectional effects, including anti-inflammatory, antioxidant, anti-cancer, neuroprotective, and antiglycative properties, urolithins are potential novel therapeutic agents. In this study, while considering the future possibility of using urolithins to improve podocyte function in diabetes, we assessed the results of exposing mouse podocytes cultured in normal (NG, 5.5 mM) and high (HG, 25 mM) glucose concentrations to urolithin A (UA) and urolithin B (UB). Podocytes metabolized UA to form glucuronides in a time-dependent manner; however, in HG conditions, the metabolism was lower than in NG conditions. In HG milieu, UA improved podocyte viability more efficiently than UB and reduced the reactive oxygen species level. Both types of urolithins showed cytotoxic activity at high (100 µM) concentration. The UA upregulated total and surface nephrin expression, which was paralleled by enhanced nephrin internalization. Regulation of nephrin turnover was independent of ambient glucose concentration. We conclude that UA affects podocytes in different metabolic and functional aspects. With respect to its pro-survival effects in HG-induced toxicity, UA could be considered as a potent therapeutic candidate against diabetic podocytopathy.

Kidney Injuries and Evolution of Chronic Kidney Diseases Due to Neonatal Hyperoxia Exposure Based on Animal Studies

Preterm birth interrupts the development and maturation of the kidneys during the critical growth period. The kidneys can also exhibit structural defects and functional impairment due to hyperoxia, as demonstrated by various animal studies. Furthermore, hyperoxia during nephrogenesis impairs renal tubular development and induces glomerular and tubular injuries, which manifest as renal corpuscle enlargement, renal tubular necrosis, interstitial inflammation, and kidney fibrosis. Preterm birth along with hyperoxia exposure induces a pathological predisposition to chronic kidney disease. Hyperoxia-induced kidney injuries are influenced by several molecular factors, including hypoxia-inducible factor-1α and interleukin-6/Smad2/transforming growth factor-β, and Wnt/β-catenin signaling pathways; these are key to cell proliferation, tissue inflammation, and cell membrane repair. Hyperoxia-induced oxidative stress is characterized by the attenuation or the induction of multiple molecular factors associated with kidney damage. This review focuses on the molecular pathways involved in the pathogenesis of hyperoxia-induced kidney injuries to establish a framework for potential interventions.

Mesenchymal stem cells derived from the kidney can ameliorate diabetic nephropathy through the TGF-β/Smad signaling pathway

Diabetic nephropathy (DN) has been introduced as one of the main microvascular complications in diabetic patients, the most common cause of end-stage renal disease (ESRD). Based on the therapeutic potential of mesenchymal stem cells in tissue repair, we aimed to test the hypothesis that kidney stem cells (KSCs) might be effective in the kidney regeneration process. Stem cells from rat kidney were separated, and the surface stem cell markers were determined by flow cytometry analysis. Thirty-two Sprague Dawley rats were divided into four groups (control, control that received kidney stem cells, diabetic, diabetic treated with stem cells). To establish diabetic, model STZ (streptozotocin) (60 mg/kg) was used. The KSCs were injected into experimental groups via tail vein (2 × 10⁶ cells/rat). In order to determine the impact of stem cells on the function and structure of the kidney, biochemical and histological parameters were measured. Further, the expression of miRNA-29a, miR-192, IL-1β, and TGF-β was determined through the real-time PCR technique. Phosphorylation of Smad2/3 was evaluated by using the standard western blotting. The KSCs significantly reduced blood nitrogen (BUN), serum creatinine (Scr), and 24-h urinary proteins in DN (P < 0.05). IL-1β and TGF-β significantly increased in the kidney of diabetic rats. In addition, the expression of miR-29a is significantly increased, whereas miR-192 decreased after treatment with KSCs (P < 0.05). Diabetic rats showed an increased level of phosphorylation of both Smad2 and Smad3 (P < 0.05). Periodic acid-Schiff (PAS) staining showed improved histopathological changes in the presence of KSCs. Stem cells derived from adult rat kidney may be an option for treating the early DN to improve the functions and structure of kidneys in rats with DN.

Mechanisms of podocyte injury and implications for diabetic nephropathy

Albuminuria is the hallmark of both primary and secondary proteinuric glomerulopathies, including focal segmental glomerulosclerosis (FSGS), obesity-related nephropathy, and diabetic nephropathy (DN). Moreover, albuminuria is an important feature of all chronic kidney diseases (CKDs). Podocytes play a key role in maintaining the permselectivity of the glomerular filtration barrier (GFB) and injury of the podocyte, leading to foot process (FP) effacement and podocyte loss, the unifying underlying mechanism of proteinuric glomerulopathies. The metabolic insult of hyperglycemia is of paramount importance in the pathogenesis of DN, while insults leading to podocyte damage are poorly defined in other proteinuric glomerulopathies. However, shared mechanisms of podocyte damage have been identified. Herein, we will review the role of haemodynamic and oxidative stress, inflammation, lipotoxicity, endocannabinoid (EC) hypertone, and both mitochondrial and autophagic dysfunction in the pathogenesis of the podocyte damage, focussing particularly on their role in the pathogenesis of DN. Gaining a better insight into the mechanisms of podocyte injury may provide novel targets for treatment. Moreover, novel strategies for boosting podocyte repair may open the way to podocyte regenerative medicine.

The Wnt Signaling Pathway in Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious kidney-related complication of both type 1 and type 2 diabetes mellitus (T1DM, T2DM) and the second major cause of end-stage kidney disease. DN can lead to hypertension, edema, and proteinuria. In some cases, DN can even progress to kidney failure, a life-threatening condition. The precise etiology and pathogenesis of DN remain unknown, although multiple factors are believed to be involved. The main pathological manifestations of DN include mesangial expansion, thickening of the glomerular basement membrane, and podocyte injury. Eventually, these pathological manifestations will lead to glomerulosclerosis, thus affecting renal function. There is an urgent need to develop new strategies for the prevention and treatment of DN. Existing evidence shows that the Wnt signaling cascade plays a key role in regulating the development of DN. Previous studies focused on the role of the Wnt canonical signaling pathway in DN. Subsequently, accumulated evidence on the mechanism of the Wnt non-canonical signaling indicated that Wnt/Ca²⁺ and Wnt/PCP also have essential roles in the progression of DN. In this review, we summarize the specific mechanisms of Wnt signaling in the occurrence and development of DN in podocyte injury, mesangial cell injury, and renal fibrosis. Also, to elucidate the significance of the Wnt canonical pathway in the process of DN, we uncovered evidence supporting that both Wnt/PCP and Wnt/Ca²⁺ signaling are critical for DN development.

Knockout of Nephron ATP6AP2 Impairs Proximal Tubule Function and Prevents High-Fat Diet-Induced Obesity in Male Mice

ATP6AP2 expression is increased in the nephron during high-fat diet (HFD) and its knockout (ATP6AP2 KO) reduces body weight (WT) in mice. We evaluated the contribution of ATP6AP2 to urinary glucose (UG) and albumin (Ualb) handling during HFD. We hypothesized that nephron ATP6AP2 KO increases UG and Ualb and minimizes HFD-induced obesity. Eight-week-old male C57BL/6J mice with inducible nephron-specific ATP6AP2 KO and noninduced controls were fed either normal diet (ND, 12% kcal fat) or HFD (45% kcal fat) for 6 months. ATP6AP2 KO mice on ND had 20% (P < 0.01) lower WT compared with controls. HFD-fed mice had 41% (P < 0.05) greater WT than ND-fed control mice. In contrast, ATP6AP2 KO abrogated the increase in WT induced by HFD by 40% (P < 0.05). Mice on HFD had less caloric intake compared with ND controls (P < 0.01). There were no significant differences in metabolic rate between all groups. UG and Ualb was significantly increased in ATP6AP2 KO mice on both ND and HFD. ATP6AP2 KO showed greater levels of proximal tubule apoptosis and histologic evidence of proximal tubule injury. In conclusion, our results demonstrate that nephron-specific ATP6AP2 KO is associated with glucosuria and albuminuria, most likely secondary to renal proximal tubule injury and/or dysfunction. Urinary loss of nutrients may have contributed to the reduced WT of knockout mice on ND and lack of WT gain in response to HFD. Future investigation should elucidate the mechanisms by which loss of renal ATP6AP2 causes proximal tubule injury and dysfunction.

Novel regulation of renal gluconeogenesis by Atp6ap2 in response to high fat diet via PGC1-α/AKT-1 pathway

Recent studies suggested that renal gluconeogenesis is substantially stimulated in the kidney in presence of obesity. However, the mechanisms responsible for such stimulation are not well understood. Recently, our laboratory demonstrated that mice fed high fat diet (HFD) exhibited increase in renal Atp6ap2 [also known as (Pro)renin receptor] expression. We hypothesized that HFD upregulates renal gluconeogenesis via Atp6ap2-PGC-1α and AKT pathway. Using real-time polymerase chain reaction, western blot analysis and immunostaining, we evaluated renal expression of the Atp6ap2 and renal gluconeogenic enzymes, PEPCK and G6Pase, in wild type and inducible nephron specific Atp6ap2 knockout mice fed normal diet (ND, 12 kcal% fat) or a high-fat diet (HFD, 45 kcal% fat) for 8 weeks. Compared with ND, HFD mice had significantly higher body weight (23%) (P < 0.05), renal mRNA and protein expression of Atp6ap2 (39 and 35%), PEPCK (44 and 125%) and G6Pase (39 and 44%) respectively. In addition, compared to ND, HFD mice had increased renal protein expression of PGC-1α by 32% (P < 0.05) and downregulated AKT by 33% (P < 0.05) respectively in renal cortex. Atp6ap2-KO abrogated these changes in the mice fed HFD. In conclusion, we identified novel regulation of renal gluconeogenesis by Atp6ap2 in response to high fat diet via PGC1-α/AKT-1 pathway.

The Pathological Role of Pro(Renin) Receptor in Renal Inflammation

(Pro)renin receptor (PRR) is the recently discovered component of the renin-angiotensin-aldosterone system (RAS). Many organs contain their own RAS, wherein PRR can exert organ-specific localized effects. The Binding of prorenin/renin to PRR activates angiotensin-dependent and independent pathways which leads to the development of physiological and pathological effects. Continued progress in PRR research suggests that the upregulation of PRR contributes to the development of hypertension, glomerular injury, and progression of kidney disease and inflammation. In the current review, we highlight the function of the PRR in renal inflammation in pathophysiological conditions.

(Pro)renin receptor in the kidney: function and significance

(Pro)renin receptor (PRR), a 350-amino acid receptor initially thought of as a receptor for the binding of renin and prorenin, is multifunctional. In addition to its role in the renin-angiotensin system (RAS), PRR transduces several intracellular signaling molecules and is a component of the vacuolar H⁺-ATPase that participates in autophagy. PRR is found in the kidney and particularly in great abundance in the cortical collecting duct. In the kidney, PRR participates in water and salt balance, acid-base balance, and autophagy and plays a role in development and progression of hypertension, diabetic retinopathy, and kidney fibrosis. This review highlights the role of PRR in the development and function of the kidney, namely, the macula densa, podocyte, proximal and distal convoluted tubule, and the principal cells of the collecting duct, and focuses on PRR function in body fluid volume homeostasis, blood pressure regulation, and acid-base balance. This review also explores new advances in the molecular mechanism involving PRR in normal renal health and pathophysiological states.

Protective effects of luteolin on nephrotoxicity induced by long-term hyperglycaemia in rats

Objective

This study aimed to investigate whether luteolin delays the progress of diabetic nephropathy (DN) induced by streptozotocin.

Methods

Fifty-three healthy, 8-week-old, male Sprague–Dawley rats were randomly divided into the control (n = 6), model (n = 23), and experimental groups (n = 24). The rat model of diabetic nephropathy was established by intraperitoneal injection of streptozotocin. Rats in the experimental group were administered luteolin suspension of 80 mg/kg daily for 8 weeks. Blood glucose levels and body weight were recorded until the fourth week. After intragastric administration, blood flow and the protective effect of luteolin on diabetic nephropathy were evaluated.

Results

The degree of renal apoptosis and fibrosis in the experimental group was milder, and glomerular structure was more complete compared with the model group. Nphs2 staining suggested that luteolin delayed apoptosis and deletion and fusion of podocytes under high glucose levels, and protected the filtration function of the basement membrane by upregulating Nphs2 protein expression. Time intensity curve results suggested that luteolin delayed deterioration of renal haemodynamics under hyperglycaemia.

Conclusions

This study shows that luteolin delays progression of diabetic nephropathy. This drug has potential wide applicability in future clinical application.

Sex Differences in Diabetes- and TGF-β1-Induced Renal Damage

While females are less affected by non-diabetic kidney diseases compared to males, available data on sex differences in diabetic nephropathy (DN) are controversial. Although there is evidence for an imbalance of sex hormones in diabetes and hormone-dependent mechanisms in transforming growth factor β1 (TGF-β1) signaling, causes and consequences are still incompletely understood. Here we investigated the influence of sex hormones and sex-specific gene signatures in diabetes- and TGF-β1-induced renal damage using various complementary approaches (a db/db diabetes mouse model, ex vivo experiments on murine renal tissue, and experiments with a proximal tubular cell line TKPTS). Our results show that: (i) diabetes affects sex hormone concentrations and renal expression of their receptors in a sex-specific manner; (ii) sex, sex hormones and diabetic conditions influence differences in expression of TGF-β1, its receptor and bone morphogenetic protein 7 (BMP7); (iii) the sex and sex hormones, in combination with variable TGF-β1 doses, determine the net outcome in TGF-β1-induced expression of connective tissue growth factor (CTGF), a profibrotic cytokine. Altogether, these results suggest complex crosstalk between sex hormones, sex-dependent expression pattern and profibrotic signals for the precise course of DN development. Our data may help to better understand previous contradictory findings regarding sex differences in DN.

WNT-β-catenin signalling - a versatile player in kidney injury and repair

The WNT-β-catenin system is an evolutionary conserved signalling pathway that is of particular importance for morphogenesis and cell organization during embryogenesis. The system is usually suppressed in adulthood; however, it can be re-activated in organ injury and regeneration. WNT-deficient mice display severe kidney defects at birth. Transient WNT-β-catenin activation stimulates tissue regeneration after acute kidney injury, whereas sustained (uncontrolled) WNT-β-catenin signalling promotes kidney fibrosis in chronic kidney disease (CKD), podocyte injury and proteinuria, persistent tissue damage during acute kidney injury and cystic kidney diseases. Additionally, WNT-β-catenin signalling is involved in CKD-associated vascular calcification and mineral bone disease. The WNT-β-catenin pathway is tightly regulated, for example, by proteins of the Dickkopf (DKK) family. In particular, DKK3 is released by 'stressed' tubular epithelial cells; DKK3 drives kidney fibrosis and is associated with short-term risk of CKD progression and acute kidney injury. Thus, targeting the WNT-β-catenin pathway might represent a promising therapeutic strategy in kidney injury and associated complications.

The interaction partners of (pro)renin receptor in the distal nephron

The (pro)renin receptor (PRR), a key regulator of intrarenal renin-angiotensin system (RAS), is predominantly presented in podocytes, proximal tubules, distal convoluted tubules, and the apical membrane of collecting duct A-type intercalated cells, and plays a crucial role in hypertension, cardiovascular disease, kidney disease, and fluid homeostasis. In addition to its well-known renin-regulatory function, increasing evidence suggests PRR can also act in a variety of intracellular signaling cascades independently of RAS in the renal medulla, including Wnt/β-catenin signaling, cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂ ) signaling, and the apelinergic system, and work as a component of the vacuolar H⁺ -ATPase. PRR and these pathways regulate the expression/activity of each other that controlling blood pressure and renal functions. In this review, we highlight recent findings regarding the antagonistic interaction between PRR and ELABELA/apelin, the mutually stimulatory relationship between PRR and COX-2/PGE₂ or Wnt/β-catenin signaling in the renal medulla, and their involvement in the regulation of intrarenal RAS thereby control blood pressure, renal injury, and urine concentrating ability in health and patho-physiological conditions. We also highlight the latest progress in the involvement of PRR for the vacuolar H⁺ -ATPase activity.

AGE-Induced Suppression of EZH2 Mediates Injury of Podocytes by Reducing H3K27me3

BACKGROUND

Chronic hyperglycemia, a pivotal feature of diabetes mellitus (DM), initiates the formation of advanced glycation end products (AGEs) and the dysregulation of epigenetic mechanisms, which may cause injury to renal podocytes, a central feature of diabetic kidney disease (DKD). Previous data of our group showed that AGEs significantly reduce the expression of NIPP1 (nuclear inhibitor of protein phosphatase 1) in podocytes in vitro as well as in human and murine DKD. NIPP1 was shown by others to interact with enhancer of zeste homolog 2 (EZH2), which catalyzes the repressive methylation of H3K27me3 on histone 3. Therefore, we hypothesized that AGEs can directly induce epigenetic changes in podocytes.

METHODS

We analyzed the relevance of AGEs on EZH2 expression and activity in a murine podocyte cell line. Cells were treated with 5 mg/mL glycated BSA for 24 h. To determine the meaning of EZH2 suppression, EZH2 activity was inhibited by incubating the cells with the pharmacological methyltransferase inhibitor 3-deazaneplanocin A; EZH2 expression was repressed with siRNA. mRNA expression was analyzed with real-time PCR, and protein expression with Western blot. EZH2 expression and level of H3K27 trimethylation in podocytes of diabetic db/db mice, a mouse model for type 2 DM, were analyzed using immunofluorescence.

RESULTS

Our data demonstrated that AGEs decrease EZH2 expression in podocytes and consequently reduce H3K27me3. This suppression of EZH2 mimicked the AGE effects and caused an upregulated expression of pathological factors that contribute to podocyte injury in DKD. In addition, analyses of db/db mice showed significantly reduced H3K27me3 and EZH2 expression in podocytes. Moreover, the suppression of NIPP1 and EZH2 showed similar effects regarding podocyte injury.

CONCLUSIONS

Our studies provide a novel pathway how AGEs contribute to podocyte injury and the formation of the so-called metabolic memory in DKD.

Antiproliferative Effects of Monoclonal Antibodies against (Pro)Renin Receptor in Pancreatic Ductal Adenocarcinoma

We previously reported that silencing of the PRR gene, which encodes the (pro)renin receptor [(P)RR], significantly reduced Wnt/β-catenin-dependent development of pancreatic ductal adenocarcinoma (PDAC). Here, we examined the effects of a panel of blocking mAbs directed against the (P)RR extracellular domain on proliferation of the human PDAC cell lines PK-1 and PANC-1 in vitro and in vivo We observed that four rat anti-(P)RR mAbs induced accumulation of cells in the G₀-G₁-phase of the cell cycle and significantly reduced proliferation in vitro concomitant with an attenuation of Wnt/β-catenin signaling. Systemic administration of the anti-(P)RR mAbs to nude mice bearing subcutaneous PK-1 xenografts significantly decreased tumor expression of active β-catenin and the proliferation marker Ki-67, and reduced tumor growth. In contrast, treatment with the handle region peptide of (pro)renin did not inhibit tumor growth in vitro or in vivo, indicating that the effects of the anti-(P)RR mAbs were independent of the renin-angiotensin system. These data indicate that mAbs against human (P)RR can suppress PDAC cell proliferation by hindering activation of the Wnt/β-catenin signaling pathway. Thus, mAb-mediated (P)RR blockade could be an attractive therapeutic strategy for PDAC.

Research Progress on the Pathological Mechanisms of Podocytes in Diabetic Nephropathy

Diabetic nephropathy (DN) is not only an important microvascular complication of diabetes but also the main cause of end-stage renal disease. Studies have shown that the occurrence and development of DN are closely related to morphological and functional changes in podocytes. A series of morphological changes after podocyte injury in DN mainly include podocyte hypertrophy, podocyte epithelial-mesenchymal transdifferentiation, podocyte detachment, and podocyte apoptosis; functional changes mainly involve podocyte autophagy. More and more studies have shown that multiple signaling pathways play important roles in the progression of podocyte injury in DN. Here, we review research progress on the pathological mechanism of morphological and functional changes in podocytes associated with DN, to provide a new target for delaying the occurrence and development of this disorder.

High glucose reduces expression of podocin in cultured human podocytes by stimulating TRPC6

The transient receptor potential canonical 6 (TRPC6) channel and podocin are colocalized in the glomerular slit diaphragm as an important complex to maintain podocyte function. Gain of TRPC6 function and loss of podocin function induce podocyte injury. We have previously shown that high glucose induces apoptosis of podocytes by activating TRPC6; however, whether the activated TRPC6 can alter podocin expression remains unknown. Western blot analysis and confocal microscopy were used to examine both expression levels of TRPC6, podocin, and nephrin and morphological changes of podocytes in response to high glucose. High glucose increased the expression of TRPC6 but reduced the expression of podocin and nephrin, in both cultured human podocytes and type 1 diabetic rat kidneys. The decreased podocin was diminished in TRPC6 knockdown podocytes. High glucose elevated intracellular Ca²⁺ in control podocytes but not in TRPC6 knockdown podocytes. High glucose also elevated the expression of a tight junction protein, zonula occludens-1, and induced the redistribution of zonula occludens-1 and loss of podocyte processes. These data together suggest that high glucose reduces protein levels of podocin by activating TRPC6 and induces morphological changes of cultured podocytes.

Eucalyptol Ameliorates Dysfunction of Actin Cytoskeleton Formation and Focal Adhesion Assembly in Glucose-Loaded Podocytes and Diabetic Kidney

SCOPE

Podocytes are a component of glomerular filtration barrier with interdigitating foot processes. The podocyte function depends on the dynamics of actin cytoskeletal and focal adhesion crucial for foot process structure. This study investigates the renoprotective effects of eucalyptol on the F-actin cytoskeleton formation and focal adhesion assembly in glucose-loaded podocytes and diabetic kidneys.

METHODS AND RESULTS

Eucalyptol at 1-20 µm reverses the reduction of cellular level of F-actin, ezrin, cortactin, and Arp2/3 in 33 mm glucose-loaded mouse podocytes, and oral administration of 10 mg kg^-1 eucalyptol elevates tissue levels of actin cytoskeletal proteins reduced in db/db mouse kidneys. Eucalyptol inhibits podocyte morphological changes, showing F-actin cytoskeleton formation in cortical regions and agminated F-actin along the cell periphery. Eucalyptol induces focal adhesion proteins of paxillin, vinculin, talin1, FAK, and Src in glucose-exposed podocytes and diabetic kidneys. Additionally, GTP-binding Rac1, Cdc42, Rho A, and ROCK are upregulated in glucose-stimulated podocytes and diabetic kidneys, which is attenuated by supplying eucalyptol. Rho A gene depletion partially diminishes GSK3β induction of podocytes by glucose.

CONCLUSION

Eucalyptol ameliorates F-actin cytoskeleton formation and focal adhesion assembly through blockade of the Rho signaling pathway, entailing partial involvement of GSK3β, which may inhibit barrier dysfunction of podocytes and resultant proteinuria.

A glomerulus-on-a-chip to recapitulate the human glomerular filtration barrier

In this work we model the glomerular filtration barrier, the structure responsible for filtering the blood and preventing the loss of proteins, using human podocytes and glomerular endothelial cells seeded into microfluidic chips. In long-term cultures, cells maintain their morphology, form capillary-like structures and express slit diaphragm proteins. This system recapitulates functions and structure of the glomerulus, including permselectivity. When exposed to sera from patients with anti-podocyte autoantibodies, the chips show albuminuria proportional to patients' proteinuria, phenomenon not observed with sera from healthy controls or individuals with primary podocyte defects. We also show its applicability for renal disease modeling and drug testing. A total of 2000 independent chips were analyzed, supporting high reproducibility and validation of the system for high-throughput screening of therapeutic compounds. The study of the patho-physiology of the glomerulus and identification of therapeutic targets are also feasible using this chip.

(Pro)renin receptor contributes to renal mitochondria dysfunction, apoptosis and fibrosis in diabetic mice

Recently we demonstrated that increased renal (Pro)renin receptor (PRR) expression in diabetes contributes to development of diabetic kidney disease. However, the exact mechanisms involving PRR activity and diabetic kidney dysfunction are unknown. We hypothesized that PRR is localized in renal mitochondria and contributes to renal fibrosis and apoptosis through oxidative stress-induced mitochondria dysfunction. Controls and streptozotocin-induced diabetic C57BL/6 mice were injected with scramble shRNA and PRR shRNA and followed for a period of eight weeks. At the end of study, diabetic mice showed increased expressions of PRR and NOX4 in both total kidney tissue and renal mitochondria fraction. In addition, renal mitochondria of diabetic mice showed reduced protein expression and activity of SOD2 and ATP production and increased UCP2 expression. In diabetic kidney, there was upregulation in the expressions of caspase3, phos-Foxo3a, phos-NF-κB, fibronectin, and collagen IV and reduced expressions of Sirt1 and total-FOXO3a. Renal immunostaining revealed increased deposition of PRR, collagen and fibronectin in diabetic kidney. In diabetic mice, PRR knockdown decreased urine albumin to creatinine ratio and the renal expressions of PRR, NOX4, UCP2, caspase3, phos-FOXO3a, phos-NF-κB, collagen, and fibronectin, while increased the renal mitochondria expression and activity of SOD2, ATP production, and the renal expressions of Sirt1 and total-FOXO3a. In conclusion, increased expression of PRR localized in renal mitochondria and diabetic kidney induced mitochondria dysfunction, and enhanced renal apoptosis and fibrosis in diabetes by upregulation of mitochondria NOX4/SOD2/UCP2 signaling pathway.

Oxidative Stress in the Pathogenesis and Evolution of Chronic Kidney Disease: Untangling Ariadne's Thread

Amplification of oxidative stress is present since the early stages of chronic kidney disease (CKD), holding a key position in the pathogenesis of renal failure. Induction of renal pro-oxidant enzymes with excess generation of reactive oxygen species (ROS) and accumulation of dityrosine-containing protein products produced during oxidative stress (advanced oxidation protein products—AOPPs) have been directly linked to podocyte damage, proteinuria, and the development of focal segmental glomerulosclerosis (FSGS) as well as tubulointerstitial fibrosis. Vascular oxidative stress is considered to play a critical role in CKD progression, and ROS are potential mediators of the impaired myogenic responses of afferent renal arterioles in CKD and impaired renal autoregulation. Both oxidative stress and inflammation are CKD hallmarks. Oxidative stress promotes inflammation via formation of proinflammatory oxidized lipids or AOPPs, whereas activation of nuclear factor κB transcription factor in the pro-oxidant milieu promotes the expression of proinflammatory cytokines and recruitment of proinflammatory cells. Accumulating evidence implicates oxidative stress in various clinical models of CKD, including diabetic nephropathy, IgA nephropathy, polycystic kidney disease as well as the cardiorenal syndrome. The scope of this review is to tackle the issue of oxidative stress in CKD in a holistic manner so as to provide a future framework for potential interventions.

The (pro)renin receptor: an emerging player in hypertension and metabolic syndrome

The (pro)renin receptor (PRR) is a multifunctional protein that is expressed in multiple organs. Binding of prorenin/renin to the PRR activates angiotensin II-dependent and angiotensin II-independent pathways. The PRR is also involved in autophagy and Wnt/ß catenin signaling, functions that are not contingent on prorenin binding. Emerging evidence suggests that the PRR plays an important role in blood pressure regulation and glucose and lipid metabolism. Herein, we review PRR function in health and disease, with particular emphasis on hypertension and the metabolic syndrome.

High glucose-induced ubiquitination of G6PD leads to the injury of podocytes

Oxidative stress contributes substantially to podocyte injury, which plays an important role in the development of diabetic kidney disease. The mechanism of hyperglycemia-induced oxidative stress in podocytes is not fully understood. Glucose-6-phosphate dehydrogenase (G6PD) is critical in maintaining NADPH, which is an important cofactor for the antioxidant system. Here, we hypothesized that high glucose induced ubiquitination and degradation of G6PD, which injured podocytes by reactive oxygen species (ROS) accumulation. We found that G6PD protein expression was decreased in kidneys of both diabetic patients and diabetic rodents. G6PD activity was also reduced in diabetic mice. Overexpressing G6PD reversed redox imbalance and podocyte apoptosis induced by high glucose and palmitate. Inhibition of G6PD with small interfering RNA induced podocyte apoptosis. In kidneys of G6PD-deficient mice, podocyte apoptosis was significantly increased. Interestingly, high glucose had no effect on G6PD mRNA expression. Decreased G6PD protein expression was mediated by the ubiquitin proteasome pathway. We found that the von Hippel-Lindau (VHL) protein, an E3 ubiquitin ligase subunit, directly bound to G6PD and degraded G6PD through ubiquitylating G6PD on K³⁶⁶ and K⁴⁰³. In summary, our data suggest that high glucose induces ubiquitination of G6PD by VHL E3 ubiquitin ligase, which leads to ROS accumulation and podocyte injury.-Wang, M., Hu, J., Yan, L., Yang, Y., He, M., Wu, M., Li, Q., Gong, W., Yang, Y., Wang, Y., Handy, D. E., Lu, B., Hao, C., Wang, Q., Li, Y., Hu, R., Stanton, R. C., Zhang, Z. High glucose-induced ubiquitination of G6PD leads to the injury of podocytes.

Role of mTOR signaling in the regulation of high glucose-induced podocyte injury

Podocyte injury, which promotes progressive nephropathy, is considered a key factor in the progression of diabetic nephropathy. The mammalian target of rapamycin (mTOR) signaling cascade controls cell growth, survival and metabolism. The present study investigated the role of mTOR signaling in regulating high glucose (HG)-induced podocyte injury. MTT assay and flow cytometry assay results indicated that HG significantly increased podocyte viability and apoptosis. HG effects on podocytes were suppressed by mTOR complex 1 (mTORC1) inhibitor, rapamycin, and further suppressed by dual mTORC1 and mTORC2 inhibitor, KU0063794, when compared with podocytes that received mannitol treatment. In addition, western blot analysis revealed that the expression levels of Thr-389-phosphorylated p70S6 kinase (p-p70S6K) and phosphorylated Akt (p-Akt) were significantly increased by HG when compared with mannitol treatment. Notably, rapamycin significantly inhibited HG-induced p-p70S6K expression, but did not significantly impact p-Akt expression. However, KU0063794 significantly inhibited the HG-induced p-p70S6K and p-Akt expression levels. Furthermore, the expression of ezrin was significantly reduced by HG when compared with mannitol treatment; however, α-smooth muscle actin (α-SMA) expression was significantly increased. Immunofluorescence analysis on ezrin and α-SMA supported the results of western blot analysis. KU0063794, but not rapamycin, suppressed the effect of HG on the expression levels of ezrin and α-SMA. Thus, it was suggested that the increased activation of mTOR signaling mediated HG-induced podocyte injury. In addition, the present findings suggest that the mTORC1 and mTORC2 signaling pathways may be responsible for the cell viability and apoptosis, and that the mTORC2 pathway could be primarily responsible for the regulation of cytoskeleton-associated proteins.

Effect of Baoshenfang Formula on Podocyte Injury via Inhibiting the NOX-4/ROS/p38 Pathway in Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious kidney-related complication of type 1 and type 2 diabetes. The Chinese herbal formula Baoshenfang (BSF) shows therapeutic potential in attenuating oxidative stress and apoptosis in podocytes in DN. This study evaluated the effects of BSF on podocyte injury in vivo and in vitro and explored the possible involvement of the nicotinamide adenine dinucleotide phosphate-oxidase-4/reactive oxygen species- (NOX-4/ROS-) activated p38 pathway. In the identified compounds by mass spectrometry, some active constituents of BSF were reported to show antioxidative activity. In addition, we found that BSF significantly decreased 24-hour urinary protein, serum creatinine, and blood urea nitrogen in DN patients. BSF treatment increased the nephrin expression, alleviated oxidative cellular damage, and inhibited Bcl-2 family-associated podocyte apoptosis in high-glucose cultured podocytes and/or in diabetic rats. More importantly, BSF also decreased phospho-p38, while high glucose-mediated apoptosis was blocked by p38 mitogen-activated protein kinase inhibitor in cultured podocytes, indicating that the antiapoptotic effect of BSF is p38 pathway-dependent. High glucose-induced upexpression of NOX-4 was normalized by BSF, and NOX-4 siRNAs inhibited the phosphorylation of p38, suggesting that the activated p38 pathway is at least partially mediated by NOX-4. In conclusion, BSF can decrease proteinuria and protect podocytes from injury in DN, in part through inhibiting the NOX-4/ROS/p38 pathway.

Cancer stem cells within moderately differentiated head and neck cutaneous squamous cell carcinoma express components of the renin-angiotensin system

PURPOSE

To investigate the expression of components of the renin-angiotensin system (RAS): pro-renin receptor (PRR), angiotensin converting enzyme (ACE), angiotensin II receptor 1 (ATIIR1) and angiotensin II receptor 2 (ATIIR2) by the cancer stem cell (CSC) subpopulations in moderately differentiated head and neck cutaneous squamous cell carcinoma (MDHNCSCC).

METHODOLOGY

3,3-Diaminobenzidine (DAB) immunohistochemical (IHC) staining for PRR, ACE, ATIIR1 and ATIIR2 was performed on formalin-fixed paraffin-embedded sections of ten MDHNCSCC tissue samples. Immunofluorescence (IF) IHC staining was used to localise components of the RAS. Western blotting (WB) and RT-qPCR were performed on snap-frozen MDHNCSCC tissue samples and MDHNCSCC-derived primary cell lines to investigate protein transcription expression of these proteins, respectively.

RESULTS

DAB IHC staining demonstrated the presence of PRR, ACE, ATIIR1 and ATIIR2 in all ten MDHNCSCC tissue samples. IF IHC staining showed expression of PRR and ATIIR2 by the OCT4⁺ cells, and ACE and ATIIR1 by the SOX2⁺ cells, within the tumour nests (TNs) and the peritumoural stroma (PTS). PRR, ACE, ATIIR1 and ATIIR2 were expressed by the endothelium of the microvessels within the PTS. WB confirmed protein expression for PRR, ACE and ATIIR1 in MDHNCSCC tissue samples and MDHNCSCC-derived primary cell lines. RT-qPCR showed transcriptional activation of PRR, ACE, ATIIR1 and ATIIR2 in MDHNCSCC tissue samples; and PRR, ACE, ATIIR1 but not ATIIR2, in MDHNCSCC-derived primary cell lines.

CONCLUSION

PRR, ACE, ATIIR1 and ATIIR2 are expressed by the CSC subpopulations within the TNs, the PTS, and the endothelium of the microvessels within the PTS, in MDHNCSCC.

(Pro)Renin receptor mediates obesity-induced antinatriuresis and elevated blood pressure via upregulation of the renal epithelial sodium channel

Recent studies have demonstrated that the renal (pro)renin receptor (PRR) regulates expression of the alpha subunit of the epithelial sodium channel (α-ENaC). In this study we hypothesized that the renal PRR mediates high fat diet (HFD)-induced sodium retention and elevated systolic blood pressure (SBP) by enhancing expression of the epithelial sodium channel (α-ENaC). In our study we used a recently developed inducible nephron specific PRR knockout mouse. Mice (n = 6 each group) were allocated to receive regular diet (RD, 12 kcal% fat) or a high-fat diet (HFD, 45 kcal% fat) for 10 weeks. Body weight (BW), SBP, urine volume (UV) and urine sodium (U_NaV), as well as renal interstitial Angiotensin II (Ang II), and renal medullary expression of PRR, p-SGK-1, α-ENaC were monitored in RD and HFD mice with or without PRR knockout. At baseline, there were no significant differences in BW, BP, UV or U_NaV between different animal groups. At the end of the study, HFD mice had significant increases in SBP, BW, and significant reductions in UV and U_NaV. Compared to RD, HFD significantly increased mRNA and protein expression of PRR, α-ENaC, p-SGK-1, and Ang II. Compared to HFD alone, PRR knockout mice on HFD had reduced mRNA and protein expression of PRR, p-SGK-1, and α-ENaC, as well as increased UV, U_NaV and significantly reduced SBP. RIF Ang II was significantly increased by HFD and did not change in response to PRR knockout. We conclude that obesity induced sodium retention and elevated SBP are mediated by the PRR-SGK-1- α-ENaC pathway independent of Ang II.

BMSCs and miR-124a ameliorated diabetic nephropathy via inhibiting notch signalling pathway

BMSCs are important in replacement therapy of diabetic nephropathy (DN). MiR‐124a exerts effect on the differentiation capability of pancreatic progenitor cells. The objective of this study was to explore the molecular mechanisms, the functions of miR‐124a and bone marrow mesenchymal stem cells (BMSCs) in the treatment of DN. Characterizations of BMSCs were identified using the inverted microscope and flow cytometer. The differentiations of BMSCs were analysed by immunofluorescence assay and DTZ staining. The expression levels of islet cell‐specific transcription factors, apoptosis‐related genes, podocytes‐related genes and Notch signalling components were detected using quantitative real‐time reverse transcription PCR (qRT‐PCR) and Western blot assays. The production of insulin secretion was detected by adopting radioimmunoassay. Cell proliferation and apoptosis abilities were detected by CCK‐8, flow cytometry and TUNEL assays. We found that BMSCs was induced into islet‐like cells and that miR‐124a could promote the BMSCs to differentiate into islet‐like cells. BMSCs in combination with miR‐124a regulated islet cell‐specific transcription factors, apoptosis‐related genes, podocytes‐related genes as well as the activity of Notch signalling pathway. However, BMSCs in combination with miR‐124a relieved renal lesion caused by DN and decreased podocyte apoptosis caused by HG. The protective effect of BMSCs in combination with miR‐124a was closely related to the inactivation of Notch signalling pathway. MSCs in combination with miR‐124a protected kidney tissue from impairment and inhibited nephrocyte apoptosis in DN.

Nicotine enhances mesangial cell proliferation and fibronectin production in high glucose milieu via activation of Wnt/β-catenin pathway

Diabetic nephropathy (DN) is a major complication of diabetes mellitus. Clinic reports indicate cigarette smoking is an independent risk factor for chronic kidney disease including DN; however, the underlying molecular mechanisms are not clear. Recent studies have demonstrated that nicotine, one of the active compounds in cigarette smoke, contributes to the pathogenesis of the cigarette smoking-accelerated chronic kidney disease. One of the characteristics of DN is the expansion of mesangium, a precursor of glomerular sclerosis. In the present study, we examined the involvement of Wnt/β-catenin pathway in nicotine-mediated mesangial cell growth in high glucose milieu. Primary human renal mesangial cells were treated with nicotine in the presence of normal (5 mM) or high glucose (30 mM) followed by evaluation for cell growth. In the presence of normal glucose, nicotine increased both the total cell numbers and Ki-67 positive cell ratio, indicating that nicotine stimulated mesangial cell proliferation. Although high glucose itself also stimulated mesangial cell proliferation, nicotine further enhanced the mitogenic effect of high glucose. Similarly, nicotine increased the expression of Wnts, β-catenin, and fibronectin in normal glucose medium, but further increased mesangial cell expression of these proteins in high glucose milieu. Pharmacological inhibition or genetic knockdown of β-catenin activity or expression with specific inhibitor FH535 or siRNA significantly impaired the nicotine/glucose-stimulated cell proliferation and fibronectin production. We conclude that nicotine may enhance renal mesangial cell proliferation and fibronectin production under high glucose milieus partly through activating Wnt/β-catenin pathway. Our study provides insight into molecular mechanisms involved in DN.

Wnt Signaling in Kidney Development and Disease

Wnt signal cascade is an evolutionarily conserved, developmental pathway that regulates embryogenesis, injury repair, and pathogenesis of human diseases. It is well established that Wnt ligands transmit their signal via canonical, β-catenin-dependent and noncanonical, β-catenin-independent mechanisms. Mounting evidence has revealed that Wnt signaling plays a key role in controlling early nephrogenesis and is implicated in the development of various kidney disorders. Dysregulations of Wnt expression cause a variety of developmental abnormalities and human diseases, such as congenital anomalies of the kidney and urinary tract, cystic kidney, and renal carcinoma. Multiple Wnt ligands, their receptors, and transcriptional targets are upregulated during nephron formation, which is crucial for mediating the reciprocal interaction between primordial tissues of ureteric bud and metanephric mesenchyme. Renal cysts are also associated with disrupted Wnt signaling. In addition, Wnt components are important players in renal tumorigenesis. Activation of Wnt/β-catenin is instrumental for tubular repair and regeneration after acute kidney injury. However, sustained activation of this signal cascade is linked to chronic kidney diseases and renal fibrosis in patients and experimental animal models. Mechanistically, Wnt signaling controls a diverse array of biologic processes, such as cell cycle progression, cell polarity and migration, cilia biology, and activation of renin-angiotensin system. In this chapter, we have reviewed recent findings that implicate Wnt signaling in kidney development and diseases. Targeting this signaling may hold promise for future treatment of kidney disorders in patients.

Systemic factors related to soluble (pro)renin receptor in plasma of patients with proliferative diabetic retinopathy

(Pro)renin receptor [(P)RR], a new component of the tissue renin-angiotensin system (RAS), plays a crucial role in inflammation and angiogenesis in the eye, thus contributing to the development of proliferative diabetic retinopathy (PDR). In this study, we investigated systemic factors related to plasma levels of soluble form of (P)RR [s(P)RR] in patients with PDR. Twenty type II diabetic patients with PDR and 20 age-matched, non-diabetic patients with idiopathic macular diseases were enrolled, and plasma levels of various molecules were measured by enzyme-linked immunosorbent assays. Human retinal microvascular endothelial cells were stimulated with several diabetes-related conditions to evaluate changes in gene expression using real-time quantitative PCR. Of various systemic parameters examined, the PDR patients had significantly higher blood sugar and serum creatinine levels than non-diabetic controls. Protein levels of s(P)RR, prorenin, tumor necrosis factor (TNF)-α, complement factor D (CFD), and leucine-rich α-2-glycoprotein 1 (LRG1) significantly increased in the plasma of PDR subjects as compared to non-diabetes, with positive correlations detected between s(P)RR and these inflammatory molecules but not prorenin. Estimated glomerular filtration rate and serum creatinine were also correlated with plasma s(P)RR, but not prorenin, levels. Among the inflammatory molecules correlated with s(P)RR in the plasma, TNF-α, but not CFD or LRG1, application to retinal endothelial cells upregulated the mRNA expression of (P)RR but not prorenin, while stimulation with high glucose enhanced both (P)RR and prorenin expression. These findings suggested close relationships between plasma s(P)RR and diabetes-induced factors including chronic inflammation, renal dysfunction, and hyperglycemia in patients with PDR.

Molecular mechanisms involved in podocyte EMT and concomitant diabetic kidney diseases: an update

Epithelial–mesenchymal transition (EMT) is a tightly regulated process by which epithelial cells lose their hallmark epithelial characteristics and gain the features of mesenchymal cells. For podocytes, expression of nephrin, podocin, P-cadherin, and ZO-1 is downregulated, the slit diaphragm (SD) will be altered, and the actin cytoskeleton will be rearranged. Diabetes, especially hyperglycemia, has been demonstrated to incite podocyte EMT through several molecular mechanisms such as TGF-β/Smad classic pathway, Wnt/β-catenin signaling pathway, Integrins/integrin-linked kinase (ILK) signaling pathway, MAPKs signaling pathway, Jagged/Notch signaling pathway, and NF-κB signaling pathway. As one of the most fundamental prerequisites to develop ground-breaking therapeutic options to prevent the development and progression of diabetic kidney disease (DKD), a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of podocyte EMT is compulsory. Therefore, the purpose of this paper is to update the research progress of these underlying signaling pathways and expound the podocyte EMT-related DKDs.

Effect of Huayu Tongluo Herbs on Reduction of Proteinuria via Inhibition of Wnt/β-Catenin Signaling Pathway in Diabetic Rats

The study investigated the expression of Wnt/β-catenin pathway in diabetic rats and the intervention effect of Huayu Tongluo herbs (HTH). Ten rats were randomly selected as control group and the remaining rats were established as diabetic models. The diabetic rats were randomly divided into model group and HTH treatment group. The intervention was intragastric administration in all rats for 20 weeks. At the end of every 4 weeks, fasting blood glucose and 24 h urinary total protein quantitatively were measured. At the end of the 20th week, biochemical parameters and body weight were tested. The kidney tissues were observed under light microscope and transmission electron microscopy. We examined Wnt/beta-catenin signaling pathway key proteins and renal interstitial fibrosis related molecular markers expression. The results showed that HTH could reduce urinary protein excretion and relieve renal pathological damage. Wnt4, p-GSK3β (S9), and β-catenin expression were decreased in the signaling pathway, but GSK3β level was not changed by HTH in diabetic rats. Furthermore, the expressions of TGF-β1 and ILK were decreased, but the level of E-cadherin was increased in diabetic rats after treatment with HTH. This study demonstrated that HTH could inhibit the high expression of Wnt/β-catenin pathway in kidney of diabetic rats. The effect might be one of the main ways to reduce urinary protein excretion.

(Pro)renin Receptor Is an Amplifier of Wnt/β-Catenin Signaling in Kidney Injury and Fibrosis

The (pro)renin receptor (PRR) is a transmembrane protein with multiple functions. However, its regulation and role in the pathogenesis of CKD remain poorly defined. Here, we report that PRR is a downstream target and an essential component of Wnt/β-catenin signaling. In mouse models, induction of CKD by ischemia-reperfusion injury (IRI), adriamycin, or angiotensin II infusion upregulated PRR expression in kidney tubular epithelium. Immunohistochemical staining of kidney biopsy specimens also revealed induction of renal PRR in human CKD. Overexpression of either Wnt1 or β-catenin induced PRR mRNA and protein expression in vitro Notably, forced expression of PRR potentiated Wnt1-mediated β-catenin activation and augmented the expression of downstream targets such as fibronectin, plasminogen activator inhibitor 1, and α-smooth muscle actin (α-SMA). Conversely, knockdown of PRR by siRNA abolished β-catenin activation. PRR potentiation of Wnt/β-catenin signaling did not require renin, but required vacuolar H⁺ ATPase activity. In the mouse model of IRI, transfection with PRR or Wnt1 expression vectors promoted β-catenin activation, aggravated kidney dysfunction, and worsened renal inflammation and fibrotic lesions. Coexpression of PRR and Wnt1 had a synergistic effect. In contrast, knockdown of PRR expression ameliorated kidney injury and fibrosis after IRI. These results indicate that PRR is both a downstream target and a crucial element in Wnt signal transmission. We conclude that PRR can promote kidney injury and fibrosis by amplifying Wnt/β-catenin signaling.

Vitamin D receptor deficit induces activation of renin angiotensin system via SIRT1 modulation in podocytes

Vitamin D receptor (VDR) deficient status has been shown to be associated with the activation of renin angiotensin system (RAS). We hypothesized that lack of VDR would enhance p53 expression in podocytes through down regulation of SIRT1; the former would enhance the transcription of angiotensinogen (Agt) and angiotensinogen II type 1 receptor (AT1R) leading to the activation of RAS. Renal tissues of VDR mutant (M) mice displayed increased expression of p53, Agt, renin, and AT1R. In vitro studies, VDR knockout podocytes not only displayed up regulation p53 but also displayed enhanced expression of Agt, renin and AT1R. VDR deficient podocytes also displayed an increase in mRNA expression for p53, Agt, renin, and AT1R. Interestingly, renal tissues of VDR-M as well as VDR heterozygous (h) mice displayed attenuated expression of deacetylase SIRT1. Renal tissues of VDR-M mice showed acetylation of p53 at lysine (K) 382 residues inferring that enhanced p53 expression in renal tissues could be the result of ongoing acetylation, a consequence of SIRT1 deficient state. Notably, podocytes lacking SIRT1 not only showed acetylation of p53 at lysine (K) 382 residues but also displayed enhanced p53 expression. Either silencing of SIRT1/VDR or treatment with high glucose enhanced podocyte PPAR-y expression, whereas, immunoprecipitation (IP) of their lysates with anti-retinoid X receptor (RXR) antibody revealed presence of PPAR-y. It appears that either the deficit of SIRT1 has de-repressed expression of PPAR-y or enhanced podocyte expression of PPAR-y (in the absence of VDR) has contributed to the down regulation of SIRT1.

(Pro)renin receptor contributes to regulation of renal epithelial sodium channel

BACKGROUND

Recent studies reported increased (Pro)renin receptor (PRR) expression during low-salt intake. We hypothesized that PRR plays a role in regulation of renal epithelial sodium channel (ENaC) through serum and glucocorticoid-inducible kinase isoform 1 (SGK-1)-neural precursor cell expressed, developmentally downregulated 4-2 (Nedd4-2) signaling pathway.

METHOD

Male Sprague-Dawley rats on normal-sodium diet and mouse renal inner medullary collecting duct cells treated with NaCl at 130  mmol/l (normal salt), or 63  mmol/l (low salt) were studied. PRR and α-ENaC expressions were evaluated 1 week after right uninephrectomy and left renal interstitial administration of 5% dextrose, scramble shRNA, or PRR shRNA (n = 6 each treatment).

RESULTS

In-vivo PRR shRNA significantly reduced expressions of PRR throughout the kidney and α-ENaC subunits in the renal medulla. In inner medullary collecting duct cells, low salt or angiotensin II (Ang II) augmented the mRNA and protein expressions of PRR (P < 0.05), SGK-1 (P < 0.05), and α-ENaC (P < 0.05). Low salt or Ang II increased the phosphorylation of Nedd4-2. In cells treated with low salt or Ang II, PRR siRNA significantly downregulated the mRNA and protein expressions of PRR (P < 0.05), SGK-1 (P < 0.05), and α-ENaC expression (P < 0.05).

CONCLUSION

We conclude that PRR contributes to the regulation of α-ENaC via SGK-1-Nedd4-2 signaling pathway.

Wnt/β-Catenin Signaling Mediated-UCH-L1 Expression in Podocytes of Diabetic Nephropathy

Increasing studies identified podocyte injury as a key early risk factor resulting in diabetic nephropathy (DN). The ubiquitin carboxy-terminal hydrolase 1 (UCH-L1) participates in podocyte differentiation and injury, which is elevated in the podocytes of a variety of nephritis. Whether UCH-L1 expression is positively related to podocyte injury of DN remains unclear. In this study, elevated expression of UCH-L1 and its intrinsic mechanism in high glucose (HG)-stimulated murine podocytes were investigated using western blot and real-time quantitative PCR. Kidney biopsies of DN patients and health individuals were stained by immunofluorescence (IF) method. The morphological and functional changes of podocytes were tested by F-actin staining and cell migration assay. Results demonstrated that HG induced upregulation of UCH-L1 and activation of the Wnt/β-catenin signaling pathway in podocytes. However, blocking of the Wnt pathway by dickkopf related protein 1 (DKK1) eliminated the above changes. Furthermore, IF staining confirmed that, compared with healthy individuals, the expression of UCH-L1 and β-catenin were obviously increased in kidney biopsy of DN patients. Overexpression of UCH-L1 remodeled its actin cytoskeleton, increased its cell migration and impacted its important proteins. All the findings manifested that Wnt/β-catenin/UCH-L1 may be a new potential therapy method in the treatment of DN in future.

Interaction of the renin angiotensin and cox systems in the kidney

Cyclooxygenase-2 (COX-2) plays an important role in mediating actions of the renin-angiotensin system (RAS). This review sheds light on the recent developments regarding the complex interactions between components of RAS and COX-2; and their implications on renal function and disease. COX-2 is believed to counter regulate the effects of RAS activation and therefore counter balance the vasoconstriction effect of Ang II. In kidney, under normal conditions, these systems are essential for maintaining a balance between vasodilation and vasoconstriction. However, recent studies suggested a pivotal role for this interplay in pathology. COX-2 increases the renin release and Ang II formation leading to increase in blood pressure. COX-2 is also associated with diabetic nephropathy, where its upregulation in the kidney contributes to glomerular injury and albuminuria. Selective inhibition of COX-2 retards the progression of renal injury. COX-2 also mediates the pathologic effects of the (Pro)renin receptor (PRR) in the kidney. In summary, this review discusses the interaction between the RAS and COX-2 in health and disease.

The critical role of the central nervous system (pro)renin receptor in regulating systemic blood pressure

The systemic renin-angiotensin system (RAS) has long been recognized as a critically important system in blood pressure (BP) regulation. However, extensive evidence has shown that a majority of RAS components are also present in many tissues and play indispensable roles in BP regulation. Here, we review evidence that RAS components, notably including the newly identified (pro)renin receptor (PRR), are present in the brain and are essential for the central regulation of BP. Binding of the PRR to its ligand, prorenin or renin, increases BP and promotes progression of cardiovascular diseases in an angiotensin II-dependent and -independent manner, establishing the PRR a promising antihypertensive drug target. We also review the existing PRR blockers, including handle region peptide and PRO20, and propose a rationale for blocking prorenin/PRR activation as a therapeutic approach that does not affect the actions of the PRR in vacuolar H(+)-ATPase and development. Finally, we summarize categories of currently available antihypertensive drugs and consider future perspectives.

The emerging role of fibroblast growth factor 21 in diabetic nephropathy

Diabetic nephropathy (DN), an important cause of end-stage renal diseases, brings about great social and economic burden. Due to the variable pathological changes and clinical course, the prognosis of DN is very difficult to predict. DN is also usually associated with enhanced genomic damage and cellular injury. Fibroblast growth factor 21 (FGF21), a nutritionally regulated hormone secreted mainly by the liver, plays a critical role in metabolism. Administration of FGF21 decreases blood glucose, triglyceride, and cholesterol levels, and improves insulin sensitivity, which is closely associated with the development and progression of glomerular diseases. In addition, FGF21 level was associated with renal function. However, the precise role of FGF21 in DN remains unclear. This review will give a comprehensive understanding of the underlying role of FGF21 and its possible interaction with other molecules in DN.

Critical role of serum response factor in podocyte epithelial-mesenchymal transition of diabetic nephropathy

PURPOSE

To investigate the expression and function of serum response factor in podocyte epithelial-mesenchymal transition of diabetic nephropathy.

METHODS

The expression of serum response factor, epithelial markers and mesenchymal markers was examined in podocytes or renal cortex tissues following high glucose. Serum response factor was upregulated by its plasmids and downregulated by CCG-1423 to investigate how it influenced podocyte epithelial-mesenchymal transition in diabetic nephropathy. Streptozotocin was used to generate diabetes mellitus in rats.

RESULTS

In podocytes after high glucose treatment, serum response factor and mesenchymal markers increased, while epithelial markers declined. Similar changes were observed in vivo. Serum response factor overexpression in podocytes induced expression of Snail, an important transcription factor mediating epithelial-mesenchymal transition. Blockade of serum response factor reduced Snail induction, protected podocytes from epithelial-mesenchymal transition and ameliorated proteinuria.

CONCLUSION

Together, increased serum response factor activity provokes podocytes' epithelial-mesenchymal transition and dysfunction in diabetic nephropathy. Targeting serum response factor by small-molecule inhibitor may be an attractive therapeutic strategy for diabetic nephropathy.

High-fat diet amplifies renal renin angiotensin system expression, blood pressure elevation, and renal dysfunction caused by Ceacam1 null deletion

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAMl), a substrate of the insulin receptor tyrosine kinase, regulates insulin action by promoting insulin clearance. Global null mutation of Ceacam1 gene (Cc1(-/-)) results in features of the metabolic syndrome, including insulin resistance, hyperinsulinemia, visceral adiposity, elevated blood pressure, and albuminuria. It also causes activation of the renal renin-angiotensin system (RAS). In the current study, we tested the hypothesis that high-fat diet enhances the expression of RAS components. Three-month-old wild-type (Cc1(+/+)) and Cc1(-/-) mice were fed either a regular or a high-fat diet for 8 wk. At baseline under regular feeding conditions, Cc1(-/-) mice exhibited higher blood pressure, urine albumin-to-creatinine ratio (UACR), and renal expression of angiotensinogen, renin/prorenin, angiotensin-converting enzyme, (pro)renin receptor, angiotensin subtype AT1 receptor, angiotensin II, and elevated PI3K phosphorylation, as detected by p85α (Tyr(508)) immunostaining, inflammatory response, and the expression of collagen I and collagen III. In Cc1(+/+) mice, high-fat diet increased blood pressure, UACR, the expression of angiotensin-converting enzyme and angiotensin II, PI3K phosphorylation, inflammatory response, and the expression of collagen I and collagen III. In Cc1(-/-) mice, high-fat intake further amplified these parameters. Immunohistochemical staining showed increased p-PI3K p85α (Tyr(508)) expression in renal glomeruli, proximal, distal, and collecting tubules of Cc1(-/-) mice fed a high-fat diet. Together, this demonstrates that high-fat diet amplifies the permissive effect of Ceacam1 deletion on renal expression of all RAS components, PI3K phosphorylation, inflammation, and fibrosis.