Low TGFβ1 expression prevents and high expression exacerbates diabetic nephropathy in mice

Sleeve gastrectomy links the attenuation of diabetic kidney disease to the inhibition of renal tubular ferroptosis through down-regulating TGF-β1/Smad3 signaling pathway

PURPOSE

To investigate how sleeve gastrectomy (SG), a typical operation of bariatric surgery, attenuated symptom, and progression of diabetic kidney disease (DKD).

METHODS

DKD model was induced by high-fat diet (HFD) combined with streptozocin in Wistar rats. SG was performed, and the group subjected to sham surgery served as control. The animals were euthanized 12 weeks after surgery, followed by sample collection for the subsequent experiment. The HK-2, a renal proximal tubular epithelial cell line derived from human, was utilized to investigate the potential mechanisms.

RESULTS

SG improved metabolic parameters and glucose homeostasis, and could alleviate DKD in terms of renal function indices as well as histological and morphological structures in DM rats, accompanied with a significant reduction in renal tubular injury. Compared with sham group, SG reduced the renal tubular ferroptosis. To further clarify the mechanism involved, in vitro experiments were performed. In the presence of high glucose, renal tubular TGF-β1 secretion was significantly increased in HK-2 cell line, which led to activation of ferroptosis through TGF-β1/Smad3 signaling pathway. Inhibition of TGF-β1 receptor and phosphorylation of Smad3 significantly ameliorated TGF-β1-mediated ferroptosis. In vivo experiments also found that SG improved the hyperglycemic environment, reduced renal TGF-β1 concentrations, and down-regulated the TGF-β1/Smad3 signaling pathway.

CONCLUSIONS

With the capacity to lower the glucose, SG could attenuate the ferroptosis by inhibiting TGF-β1/Smad3 signaling pathway in DKD rats, and eventually attenuated DKD.

LRG1 loss effectively restrains glomerular TGF-β signaling to attenuate diabetic kidney disease

Transforming growth factor (TGF)-β signaling is a well-established pathogenic mediator of diabetic kidney disease (DKD). However, owing to its pleiotropic actions, its systemic blockade is not therapeutically optimal. The expression of TGF-β signaling regulators can substantially influence TGF-β's effects in a cell- or context-specific manner. Among these, leucine-rich α2-glycoprotein 1 (LRG1) is significantly increased in glomerular endothelial cells (GECs) in DKD. As LRG1 is a secreted molecule that can exert autocrine and paracrine effects, we examined the effects of LRG1 loss in kidney cells in diabetic OVE26 mice by single-cell transcriptomic analysis. Gene expression analysis confirmed a predominant expression of Lrg1 in GECs, which further increased in diabetic kidneys. Loss of Lrg1 led to the reversal of angiogenic and TGF-β-induced gene expression in GECs, which were associated with DKD attenuation. Notably, Lrg1 loss also mitigated the increased TGF-β-mediated gene expression in both podocytes and mesangial cells in diabetic mice, indicating that GEC-derived LRG1 potentiates TGF-β signaling in glomerular cells in an autocrine and paracrine manner. Indeed, a significant reduction in phospho-Smad proteins was observed in the glomerular cells of OVE26 mice with LRG1 loss. These results indicate that specific antagonisms of LRG1 may be an effective approach to curb the hyperactive glomerular TGF-β signaling to attenuate DKD.

Exploring unconventional targets in myofibroblast transdifferentiation outside classical TGF-β signaling in renal fibrosis

We propose that the key initiators of renal fibrosis are myofibroblasts which originate from four predominant sources-fibroblasts, pericytes, endothelial cells and macrophages. Increased accumulation of renal interstitial myofibroblasts correlates with an increase in collagen, fibrillar proteins, and fibrosis severity. The canonical TGF-β pathway, signaling via Smad proteins, is the central molecular hub that initiates these cellular transformations. However, directly targeting these classical pathway molecules has proven challenging due their integral roles in metabolic process, and/or non-sustainable effects involving compensatory cross-talk with TGF-β. This review explores recently discovered alternative molecular targets that drive transdifferentiation into myofibroblasts. Discovering targets outside of the classical TGF-β/Smad pathway is crucial for advancing antifibrotic therapies, and strategically targeting the development of myofibroblasts offers a promising approach to control excessive extracellular matrix deposition and impede fibrosis progression.

Exercise training improves diabetic renal injury by reducing fetuin-A, oxidative stress and inflammation in type 2 diabetic rats

Background

Diabetic kidney disease (DKD) stands as a primary contributor to end-stage renal disease, associated with heightened mortality in cardiovascular diseases. This study aimed to explore the impact of an eight-week high-intensity interval training (HIIT) on renal injury in diabetic rats.

Methods

Twenty-eight male Wistar rats were randomly allocated into four groups: healthy control (CTL), diabetic control (DC), exercise (EX), and diabetes-exercise (D + EX). Induction of diabetes in the DC and D + EX groups occurred through a two-month high-fat diet followed by a single dose of 35 mg/kg streptozotocin (STZ). Rats in the EX and D + EX groups underwent 4-10 intervals of HIIT (80-100% Vmax) over 8 weeks. Subsequently, pathological and biochemical parameters were assessed in the serum and kidney tissue of the experimental groups.

Results

In the DC group, diabetes led to elevated kidney damage, glomerulosclerosis, fasting blood glucose (FBG), Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) index, animal weight, kidney dysfunction, albuminuria, and glomerular filtration rate. Additionally, serum and kidney levels of fetuin-A increased, along with kidney levels of KIM-1. Mechanistically, diabetes induction resulted in kidney inflammation by elevating levels of tumor necrosis factor-alpha (TNF-α), transforming growth factor beta (TGF-β), and interleukin 6 (IL-6), while reducing IL-10 levels and increasing the IL-6/IL-10 ratio. Furthermore, diabetes triggered renal oxidative stress, evidenced by increased Malondialdehyde (MDA) levels and decreased levels of glutathione peroxidase (GPx), catalase, and superoxide dismutase (SOD). HIIT mitigated the adverse effects of diabetes in the D + EX group compared to the DC group.

Conclusion

Our findings suggest that HIIT ameliorates type 2 diabetes (T2D)-induced kidney damage by mitigating inflammation, lowering serum levels of fetuin-A, and bolstering antioxidant defenses. This study highlights the potential of HIIT as a time-efficient intervention for diabetic nephropathy.

Circulating exosomal miR-16-5p and let-7e-5p are associated with bladder fibrosis of diabetic cystopathy

Diabetic cystopathy (DCP) is a prevalent etiology of bladder dysfunction in individuals with longstanding diabetes, frequently leading to bladder interstitial fibrosis. Research investigating the initial pathological alterations of DCP is notably scarce. To comprehend the development of fibrosis and find effective biomarkers for its diagnosis, we prepared streptozotocin-induced long-term diabetic SD rats exhibiting a type 1 diabetes phenotype and bladder fibrosis in histology detection. After observing myofibroblast differentiation from rats' primary bladder fibroblasts with immunofluorescence, we isolated fibroblasts derived exosomes and performed exosomal miRNA sequencing. The co-differentially expressed miRNAs (DEMis) (miR-16-5p and let-7e-5p) were screened through a joint analysis of diabetic rats and long-term patients' plasma data (GES97123) downloaded from the GEO database. Then two co-DEMis were validated by quantitative PCR on exosomes derived from diabetic rats' plasma. Following with a series of analysis, including target mRNAs and transcription factors (TFs) prediction, hubgenes identification, protein-protein interaction (PPI) network construction and gene enrichment analysis, a miRNA-mediated genetic regulatory network consisting of two miRNAs, nine TFs, and thirty target mRNAs were identified in relation to fibrotic processes. Thus, circulating exosomal miR-16-5p and let-7e-5p are associated with bladder fibrosis of DCP, and the crucial genes in regulatory network might hold immense significance in studying the pathogenesis and molecular mechanisms of fibrosis, which deserves further exploration.

A Programmable Oxygenation Device Facilitates Oxygen Generation and Replenishment to Promote Wound Healing

Inadequate oxygenation is one of the chief culprits for delayed wound healing. However, current oxygen therapies, such as hyperbaric oxygen therapy and topical oxygen therapy, face hurdles in providing sustained and long-term oxygenation to reverse wound hypoxia. Furthermore, their efficacy in rejuvenating wound injury is restricted by limited penetration of oxygen in the wound bed. Herein, this study proposes a programmable and portable oxygenation device (named GUFO oxydevice) by ingeniously integrating i) a controllable oxygen generation and unidirectional transmission system (COGT-UTS), and ii) a supramolecular assembled perfluorinated hyperbranched polymer/gelatin (GUF) hydrogel in which the perfluorinated hyperbranched polymer (FHBP) acts as an oxygen reservoir to ensure sustained and convenient oxygen replenishment and thus directly regulate the hypoxic wound microenvironment. Accelerating the wound healing process by GUFO oxydevice is achieved in both a diabetic rat and an acute porcine wound model without any secondary tissue damages. The present study demonstrates that the GUFO oxydevice holds promise as a practically feasible candidate for wound treatment.

Trigonelline inhibits tubular epithelial-mesenchymal transformation in diabetic kidney disease via targeting Smad7

OBJECTIVES

Diabetic kidney disease (DKD) is a prevalent microvascular complication of diabetes. Inhibiting the epithelial-mesenchymal transition (EMT) of proximal tubule epithelial cells (PTCs) can slow down renal fibrosis. Trigonelline (TRL), an alkaloid isolated from the fenugreek, has demonstrated therapeutic effects on diabetes and its complications. Nevertheless, the underlying mechanisms for the effects of TRL are still obscure. The present study was aimed to evaluate the treatment of TRL against DKD and explore the potential mechanisms.

METHODS

The db/db mice were used as a spontaneous model of DKD and TRL solution was administered by daily gavage for 8 weeks. Indicators associated with glucose metabolism, renal function and urinary albumin were tested. Renal fibrosis in diabetic mice was evaluated by histopathological staining. Kidney transcriptomics was performed after confirming therapeutic effects of TRL on DKD mice. Molecular biology techniques and in vitro experiments were utilized for final mechanism verification.

RESULTS

Biochemical tests revealed that TRL ameliorated renal damage and reduced microalbuminuria in DKD mice. TRL exhibited a protective effect on PTCs, effectively mitigating tubular EMT and renal fibrosis in diabetic kidneys. Transcriptomics analysis indicated that TRL may target Smad7, an inhibitor of TGF-β1 signaling, to alleviate fibrosis. Furthermore, in vitro experiments validated that silencing Smad7 abolished the therapeutic effect of TRL.

CONCLUSION

Our findings indicate that TRL can alleviate tubular epithelial-mesenchymal transition and renal fibrosis in db/db mice by upregulating Smad7 in PTCs, suggesting that TRL is a promising medicine against DKD.

Pathomechanisms of Diabetic Kidney Disease

The worldwide occurrence of diabetic kidney disease (DKD) is swiftly rising, primarily attributed to the growing population of individuals affected by type 2 diabetes. This surge has been transformed into a substantial global concern, placing additional strain on healthcare systems already grappling with significant demands. The pathogenesis of DKD is intricate, originating with hyperglycemia, which triggers various mechanisms and pathways: metabolic, hemodynamic, inflammatory, and fibrotic which ultimately lead to renal damage. Within each pathway, several mediators contribute to the development of renal structural and functional changes. Some of these mediators, such as inflammatory cytokines, reactive oxygen species, and transforming growth factor β are shared among the different pathways, leading to significant overlap and interaction between them. While current treatment options for DKD have shown advancement over previous strategies, their effectiveness remains somewhat constrained as patients still experience residual risk of disease progression. Therefore, a comprehensive grasp of the molecular mechanisms underlying the onset and progression of DKD is imperative for the continued creation of novel and groundbreaking therapies for this condition. In this review, we discuss the current achievements in fundamental research, with a particular emphasis on individual factors and recent developments in DKD treatment.

Jiangtang Decoction Ameliorates Diabetic Kidney Disease Through the Modulation of the Gut Microbiota

Purpose

This study aimed to elucidate the impact of Jiangtang decoction (JTD) on diabetic kidney disease (DKD) and its association with alterations in the gut microbiota.

Methods

Using a diabetic mouse model (KK-Ay mice), daily administration of JTD for eight weeks was undertaken. Weekly measurements of body weight and blood glucose were performed, while kidney function, uremic toxins, inflammation factors, and fecal microbiota composition were assessed upon sacrifice. Ultra-structural analysis of kidney tissue was conducted to observe the pathological changes.

Results

The study findings demonstrated that JTD improve metabolism, kidney function, uremic toxins and inflammation, while also exerting a modulatory effect on the gut microbiota. Specifically, the genera Rikenella, Lachnoclostridium, and unclassified_c_Bacilli exhibited significantly increased abundance following JTD treatment, accompanied by reduced abundance of norank_f_Lachnospiraceae compared to the model group. Importantly, Rikenella and unclassified_c_Bacilli demonstrated negative correlations with urine protein levels. Lachnoclostridium and norank_f_Lachnospiraceae were positively associated with creatinine (Cr), indoxyl sulfate (IS) and interleukin (IL)-6. Moreover, norank_f_Lachnospiraceae exhibited positive associations with various indicators of DKD severity, including weight, blood glucose, urea nitrogen (UN), kidney injury molecule-1 (KIM-1) levels, trimethylamine-N-oxide (TMAO), p-cresyl sulfate (pCS), nucleotide-binding oligomerization domain (Nod)-like receptor family pyrin domain-containing 3 (NLRP3) and IL-17A production.

Conclusion

These findings suggested that JTD possess the ability to modulate the abundance of Rikenella, Lachnoclostridium, unclassified_c_Bacilli and norank_f_Lachnospiraceae within the gut microbiota. This modulation, in turn, influenced metabolic processes, kidney function, uremic toxin accumulation, and inflammation, ultimately contributing to the amelioration of DKD.

The miR-143/145 cluster induced by TGF-β1 suppresses Wilms' tumor 1 expression in cultured human podocytes

Transforming growth factor (TGF)-β1 contributes to podocyte injury in various glomerular diseases, including diabetic kidney disease, probably at least in part by attenuating the expression of Wilms' tumor 1 (WT1). However, the precise mechanisms remain to be defined. We performed miRNA microarray analysis in a human podocyte cell line cultured with TGF-β1 to examine the roles of miRNAs in podocyte damage. The microarray analysis identified miR-143-3p as the miRNA with the greatest increase following exposure to TGF-β1. Quantitative RT-PCR confirmed a significant increase in the miR-143-3p/145-5p cluster in TGF-β1-supplemented cultured podocytes and demonstrated upregulation of miR-143-3p in the glomeruli of mice with type 2 diabetes. Ectopic expression of miR-143-3p and miR-145-5p suppressed WT1 expression in cultured podocytes. Furthermore, inhibition of Smad or mammalian target of rapamycin signaling each partially reversed the TGF-β1-induced increase in miR-143-3p/145-5p and decrease in WT1. In conclusion, TGF-β1 induces expression of miR-143-3p/145-5p in part through Smad and mammalian target of rapamycin pathways, and miR-143-3p/145-5p reduces expression of WT1 in cultured human podocytes. miR-143-3p/145-5p may contribute to TGF-β1-induced podocyte injury.NEW & NOTEWORTHY This study by miRNA microarray analysis demonstrated that miR-143-3p expression was upregulated in cultured human podocytes following exposure to transforming growth factor (TGF)-β1. Furthermore, we report that the miR-143/145 cluster contributes to decreased expression of Wilms' tumor 1, which represents a possible mechanism for podocyte injury induced by TGF-β1. This study is important because it presents a novel mechanism for TGF-β-associated glomerular diseases, including diabetic kidney disease (DKD), and suggests potential therapeutic strategies targeting miR-143-3p/145-5p.

Metabolic rewiring and epigenetic reprogramming in leptin receptor-deficient db/db diabetic nephropathy mice

BACKGROUND

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease in the United States. Emerging evidence suggests that mitochondrial metabolism and epigenetics play an important role in the development and progression of DN and its complications. For the first time, we investigated the regulation of cellular metabolism, DNA methylation, and transcriptome status by high glucose (HG) in the kidney of leptin receptor-deficient db/db mice using multi-omics approaches.

METHODS

The metabolomics was performed by liquid-chromatography-mass spectrometry (LC-MS), while epigenomic CpG methylation coupled with transcriptomic gene expression was analyzed by next-generation sequencing.

RESULTS

LC-MS analysis of glomerular and cortex tissue samples of db/db mice showed that HG regulated several cellular metabolites and metabolism-related signaling pathways, including S-adenosylmethionine, S-adenosylhomocysteine, methionine, glutamine, and glutamate. Gene expression study by RNA-seq analysis suggests transforming growth factor beta 1 (TGFβ1) and pro-inflammatory pathways play important roles in early DN. Epigenomic CpG methyl-seq showed HG revoked a list of differentially methylated regions in the promoter region of the genes. Integrated analysis of DNA methylation in the promoter regions of genes and gene expression changes across time points identified several genes persistently altered in DNA methylation and gene expression. Cyp2d22, Slc1a4, and Ddah1 are some identified genes that could reflect dysregulated genes involved in renal function and DN.

CONCLUSION

Our results suggest that leptin receptor deficiency leading to HG regulates metabolic rewiring, including SAM potentially driving DNA methylation and transcriptomic signaling that could be involved in the progression of DN.

Bone morphogenetic protein-7 attenuates pancreatic damage under diabetic conditions and prevents progression to diabetic nephropathy via inhibition of ferroptosis

Background

Approximately 30% of diabetic patients develop diabetic nephropathy, a representative microvascular complication. Although the etiological mechanism has not yet been fully elucidated, renal tubular damage by hyperglycemia-induced expression of transforming growth factor-β (TGF-β) is known to be involved. Recently, a new type of cell death by iron metabolism called ferroptosis was reported to be involved in kidney damage in animal models of diabetic nephropathy, which could be induced by TGF-β. Bone morphogenetic protein-7 (BMP7) is a well-known antagonist of TGF-β inhibiting TGF-β-induced fibrosis in many organs. Further, BMP7 has been reported to play a role in the regeneration of pancreatic beta cells in diabetic animal models.

Methods

We used protein transduction domain (PTD)-fused BMP7 in micelles (mPTD-BMP7) for long-lasting in vivo effects and effective in vitro transduction and secretion.

Results

mPTD-BMP7 successfully accelerated the regeneration of diabetic pancreas and impeded progression to diabetic nephropathy. With the administration of mPTD-BMP7, clinical parameters and representative markers of pancreatic damage were alleviated in a mouse model of streptozotocin-induced diabetes. It not only inhibited the downstream genes of TGF-β but also attenuated ferroptosis in the kidney of the diabetic mouse and TGF-β-stimulated rat kidney tubular cells.

Conclusion

BMP7 impedes the progression of diabetic nephropathy by inhibiting the canonical TGF-β pathway, attenuating ferroptosis, and helping regenerate diabetic pancreas.

Yishen Tongluo formula alleviates diabetic kidney disease through regulating Sirt6/TGF-β1/Smad2/3 pathway and promoting degradation of TGF-β1

ETHNOPHARMACOLOGICAL RELEVANCE

Yishen Tongluo formula (YSTLF) is formulated based on traditional Chinese medicine theory for the treatment of Diabetic kidney disease (DKD) and has been shown to be effective in improving the symptoms of DKD according to the clinical observation.

AIM OF THE STUDY

To explore the effect of YSTLF on DKD and figure out whether its effects were due to the regulation Sirt6/TGF-β1/Smad2/3 pathway and promoting degradation of TGF-β1.

MATERIALS AND METHODS

The extract of YSTLF at 1, 2.5 and 5 g/kg was orally administered to C57BLKS/J (db/db) mice for 8 weeks and db/db mice were given valsartan as a positive control. The littermate db/m and db/db mice were given vehicle as the control and model group, respectively. Blood urea nitrogen and serum creatinine were detected and the urinary albumin excretion, urea albumin creatinine ratio was calculated. The histopathological change of renal tissues in each group was determined. Simultaneously, the levels of fibrosis-related proteins and messenger RNA (mRNA) in kidney and high glucose (HG)-induced SV40-MES-13 cells were detected. The roles of YSTLF in regulating of Sirt6/TGF-β1/Smad2/3 signaling pathway were investigated in HG-stimulated SV40-MES-13 cells and validated in db/db mice. Furthermore, the effect of YSTLF on TGF-β1 degradation was investigated in HG-stimulated SV40-MES-13 cells.

RESULTS

YSTLF significantly improved the renal function in DKD mice. YSTLF dose-dependently attenuated pathological changes and suppressed the expression of type I collagen, alpha smooth muscle actin, type IV collagen, and fibronectin in vitro and in vivo, resulting in ameliorating of renal fibrosis. YSTLF positively regulated Sirt6 expression, while inhibited the activating of TGF-β1/Smad2/3 signaling pathway. TGF-β1 was steady expressed in HG-stimulated SV40-MES-13 cells, whereas was continuously degraded under YSTLF treatment.

CONCLUSIONS

YSTLF significantly ameliorates renal damages and fibrosis may via regulating Sirt6/TGF-β1/Smad2/3 signaling pathway as well as promoting the degradation of TGF-β1.

Decreased DANCR contributes to high glucose-induced extracellular matrix accumulation in human renal mesangial cell via regulating the TGF-β/Smad signaling

Glomerulosclerosis is one of the major histopathologic changes in diabetic kidney diseases (DKD), which is characterized by excessive deposition of extracellular matrix (ECM) in the glomerulus mainly produced by mesangial cells in response to transforming growth factor-β (TGF-β) stimuli under diabetic conditions. Despite TGF-β has been implicated as a major pathogenic factor in the development of diabetic glomerulosclerosis, clinical trials of monoclonal antibodies against TGF-β failed to demonstrate therapeutic benefits. Thus, developing alternative therapeutic strategies to effectively block the TGF-β/Smad signaling could be of paramount importance for DKD treatment. Emerging evidence indicates that dysregulation of certain lncRNAs can lead to aberrant activation of TGF-β/Smad signaling. Herein, we identified a novel lncRNA, named DANCR, which could efficiently function as a negative regulator of TGF-β/Smad signaling in mesangial cells. Ectopic expression of DANCR could specifically block the activation of TGF-β/Smad signaling induced by high-glucose or TGF-β in human renal mesangial cells (HRMCs). Mechanistically, DANCR functions to stabilize nemo-like kinase (NLK) mRNA through interaction with insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2), resulting in enhanced phosphorylating on the linker region of activated Smad2/3 in the nucleus. Taken together, our data have uncovered an lncRNA-based regulatory modality of the TGF-β/Smad signaling and identified DANCR as an endogenous blocker of TGF-β/Smad signaling in HRMCs, which may represent a potential therapeutic target against the diabetic glomerulosclerosis.

TGFβ instructs mTORC2 to activate PKCβII for increased TWIST1 expression in proximal tubular epithelial cell injury

The plasticity of proximal tubular epithelial cells in response to TGFβ contributes to the expression of TWIST1 to drive renal fibrosis. The mechanism of TWIST1 expression is not known. We show that both PI3 kinase and its target mTORC2 increase TGFβ-induced TWIST1 expression. TGFβ enhances phosphorylation on Ser-660 in the protein kinase C βII (PKCβII) hydrophobic motif site. Remarkably, phosphorylation-deficient PKCβIIS660A, kinase-dead PKCβII, and PKCβII knockdown blocked TWIST1 expression by TGFβ. Inhibition of TWIST1 arrested TGFβ-induced tubular cell hypertrophy and the expression of fibronectin, collagen I (α2), and α-smooth muscle actin. By contrast, TWIST1 overexpression induced these pathologies. Interestingly, the inhibition of PKCβII reduced these phenomena, which were countered by the expression of TWIST1. These results provide the first evidence for the involvement of the mTORC2-PKCβII axis in TWIST1 expression to promote tubular cell pathology.

A therapeutic target for CKD: activin A facilitates TGFβ1 profibrotic signaling

BACKGROUND

TGFβ1 is a major profibrotic mediator in chronic kidney disease (CKD). Its direct inhibition, however, is limited by adverse effects. Inhibition of activins, also members of the TGFβ superfamily, blocks TGFβ1 profibrotic effects, but the mechanism underlying this and the specific activin(s) involved are unknown.

METHODS

Cells were treated with TGFβ1 or activins A/B. Activins were inhibited generally with follistatin, or specifically with neutralizing antibodies or type I receptor downregulation. Cytokine levels, signaling and profibrotic responses were assessed with ELISA, immunofluorescence, immunoblotting and promoter luciferase reporters. Wild-type or TGFβ1-overexpressing mice with unilateral ureteral obstruction (UUO) were treated with an activin A neutralizing antibody.

RESULTS

In primary mesangial cells, TGFβ1 induces secretion primarily of activin A, which enables longer-term profibrotic effects by enhancing Smad3 phosphorylation and transcriptional activity. This results from lack of cell refractoriness to activin A, unlike that for TGFβ1, and promotion of TGFβ type II receptor expression. Activin A also supports transcription through regulating non-canonical MRTF-A activation. TGFβ1 additionally induces secretion of activin A, but not B, from tubular cells, and activin A neutralization prevents the TGFβ1 profibrotic response in renal fibroblasts. Fibrosis induced by UUO is inhibited by activin A neutralization in wild-type mice. Worsened fibrosis in TGFβ1-overexpressing mice is associated with increased renal activin A expression and is inhibited to wild-type levels with activin A neutralization.

CONCLUSIONS

Activin A facilitates TGFβ1 profibrotic effects through regulation of both canonical (Smad3) and non-canonical (MRTF-A) signaling, suggesting it may be a novel therapeutic target for preventing fibrosis in CKD.

Prenatal arsenic exposure induces immunometabolic alteration and renal injury in rats

Arsenic (As) exposure is progressively associated with chronic kidney disease (CKD), a leading public health concern present worldwide. The adverse effect of As exposure on the kidneys of people living in As endemic areas have not been extensively studied. Furthermore, the impact of only prenatal exposure to As on the progression of CKD also has not been fully characterized. In the present study, we examined the effect of prenatal exposure to low doses of As 0.04 and 0.4 mg/kg body weight (0.04 and 0.4 ppm, respectively) on the progression of CKD in male offspring using a Wistar rat model. Interestingly, only prenatal As exposure was sufficient to elevate the expression of profibrotic (TGF-β1) and proinflammatory (IL-1α, MIP-2α, RANTES, and TNF-α) cytokines at 2-day, 12- and 38-week time points in the exposed progeny. Further, alteration in adipogenic factors (ghrelin, leptin, and glucagon) was also observed in 12- and 38-week old male offspring prenatally exposed to As. An altered level of these factors coincides with impaired glucose metabolism and homeostasis accompanied by progressive kidney damage. We observed a significant increase in the deposition of extracellular matrix components and glomerular and tubular damage in the kidneys of 38-week-old male offspring prenatally exposed to As. Furthermore, the overexpression of TGF-β1 in kidneys corresponds with hypermethylation of the TGF-β1 gene-body, indicating a possible involvement of prenatal As exposure-driven epigenetic modulations of TGF-β1 expression. Our study provides evidence that prenatal As exposure to males can adversely affect the immunometabolism of offspring which can promote kidney damage later in life.

Identification of biomarkers and prediction of upstream miRNAs in diabetic nephropathy

OBJECTIVE

To explore biomarkers of diabetic nephropathy (DN) and predict upstream miRNAs.

METHODS

The data sets GSE142025 and GSE96804 were obtained from Gene Expression Omnibus database. Subsequently, common differentially expressed genes (DEGs) of renal tissue in DN and control group were identified and protein-protein interaction network (PPI) was constructed. Hub genes were screened from in DEGs and made an investigation on functional enrichment and pathway research. Finally, the target gene was selected for further study. The receiver operating characteristic (ROC) curve was used to evaluate the diagnostic efficiency of target gene and predicted its upstream miRNAs.

RESULTS

130 common DEGs were obtained through analysis, and 10 Hub genes were further identified. The function of Hub genes was mainly related to extracellular matrix (ECM), collagen fibrous tissue, transforming growth factor (TGF) -β, advanced glycosylation end product (AGE) -receptor (RAGE) and so on. Research showed that the expression level of Hub genes in DN group was significantly higher than that in control group. (all P<0.05). The target gene matrix metalloproteinase 2 (MMP2) was selected for further study, and it was found to be related to the fibrosis process and the genes regulating fibrosis. Meanwhile, ROC curve analysis showed that MMP2 had a good predictive value for DN. miRNA prediction suggested that miR-106b-5p and miR-93-5p could regulate the expression of MMP2.

CONCLUSION

MMP2 can be used as a biomarker for DN to participate in the pathogenesis of fibrosis, and miR-106b-5p and miR-93-5p may regulate the expression of MMP2 as upstream signals.

Renal fibrosis as a hallmark of diabetic kidney disease: Potential role of targeting transforming growth factor-beta (TGF-β) and related molecules

INTRODUCTION

Diabetic kidney disease (DKD) is the most common cause of end-stage renal disease (ESRD) worldwide. Currently, there is no effective treatment to completely prevent DKD progression to ESRD. Renal fibrosis and inflammation are the major pathological features of DKD, being pursued as potential therapeutic targets for DKD.

AREAS COVERED

Inflammation and renal fibrosis are involved in the pathogenesis of DKD. Anti-inflammatory drugs have been developed to combat DKD but without efficacy demonstrated. Thus, we have focused on the mechanisms of TGF-β-induced renal fibrosis in DKD, as well as discussing the important molecules influencing the TGF-β signaling pathway and their potential development into new pharmacotherapies, rather than targeting the ligand TGF-β and/or its receptors, such options include Smads, microRNAs, histone deacetylases, connective tissue growth factor, bone morphogenetic protein 7, hepatocyte growth factor, and cell division autoantigen 1.

EXPERT OPINION

TGF-β is a critical driver of renal fibrosis in DKD. Molecules that modulate TGF-β signaling rather than TGF-β itself are potentially superior targets to safely combat DKD. A comprehensive elucidation of the pathogenesis of DKD is important, which requires a better model system and access to clinical samples via collaboration between basic and clinical researchers.

Sestrin2 remedies podocyte injury via orchestrating TSP-1/TGF-β1/Smad3 axis in diabetic kidney disease

Sestrin2 is identified as a stress-induced protein and could functionate in many aspects. In our study, we investigated the latent impact of Sestrin2 on podocyte injury and its molecular mechanism in vivo and in vitro in diabetic kidney disease (DKD). Sestrin2 was low-expressed in renal biopsies from individuals with DKD, the glomeruli from diabetic mice, and mouse podocytes exposed to high glucose (HG). Sestrin2 overexpression ameliorated HG-induced phenotypic alterations, apoptosis, and oxidative stress in conditionally immortalized mouse podocytes and modulated the activity of Thrombospondin-1 (TSP-1)/transforming growth factor (TGF-β1)/Smad3 pathway in podocytes. Moreover, TSP-1 inhibitor LSKL or TGF-β blocker Pirfenidone arrested podocyte injury induced by HG. Streptozotocin (STZ) was employed to render equivalent diabetes in B6-TgN (CMV-Sestrin2) (TgN) and wild-type (WT) control mice. Sestrin2 alleviated increased levels of 24-h urinary protein, blood urea nitrogen, serum creatinine and triglyceride, and urine 8-OHdG in diabetic mice. Podocyte phenotypic alterations, increased expression of apoptosis-associated proteins and podocyte loss were observed in WT but not in diabetic TgN mice, as well as oxidative stress. Additionally, TSP-1/TGF-β1/Smad3 signaling pathway was also suppressed in glomeruli of diabetic TgN mice. Thus, Sestrin2 mitigates podocyte injury in DKD via orchestrating TSP-1/TGF-β1/Smad3 pathway, underlining Sestrin2 as a promising therapeutic target for DKD.

Oncoprotein DJ-1 interacts with mTOR complexes to effect transcription factor Hif1α-dependent expression of collagen I (α2) during renal fibrosis

Proximal tubular epithelial cells respond to transforming growth factor β (TGFβ) to synthesize collagen I (α2) during renal fibrosis. The oncoprotein DJ-1 has previously been shown to promote tumorigenesis and prevent apoptosis of dopaminergic neurons; however, its role in fibrosis signaling is unclear. Here, we show TGFβ-stimulation increased expression of DJ-1, which promoted noncanonical mTORC1 and mTORC2 activities. We show DJ-1 augmented the phosphorylation/activation of PKCβII, a direct substrate of mTORC2. In addition, coimmunoprecipitation experiments revealed association of DJ-1 with Raptor and Rictor, exclusive subunits of mTORC1 and mTORC2, respectively, as well as with mTOR kinase. Interestingly, siRNAs against DJ-1 blocked TGFβ-stimulated expression of collagen I (α2), while expression of DJ-1 increased expression of this protein. In addition, expression of dominant negative PKCβII and siRNAs against PKCβII significantly inhibited TGFβ-induced collagen I (α2) expression. In fact, constitutively active PKCβII abrogated the effect of siRNAs against DJ-1, suggesting a role of PKCβII downstream of this oncoprotein. Moreover, we demonstrate expression of collagen I (α2) stimulated by DJ-1 and its target PKCβII is dependent on the transcription factor hypoxia-inducible factor 1α (Hif1α). Finally, we show in the renal cortex of diabetic rats that increased TGFβ was associated with enhanced expression of DJ-1 and activation of mTOR and PKCβII, concomitant with increased Hif1α and collagen I (α2). Overall, we identified that DJ-1 affects TGFβ-induced expression of collagen I (α2) via an mTOR-, PKCβII-, and Hif1α-dependent mechanism to regulate renal fibrosis.

The impact of sensory neuropathy and inflammation on epithelial wound healing in diabetic corneas

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes, with several underlying pathophysiological mechanisms, some of which are still uncertain. The cornea is an avascular tissue and sensitive to hyperglycemia, resulting in several diabetic corneal complications including delayed epithelial wound healing, recurrent erosions, neuropathy, loss of sensitivity, and tear film changes. The manifestation of DPN in the cornea is referred to as diabetic neurotrophic keratopathy (DNK). Recent studies have revealed that disturbed epithelial-neural-immune cell interactions are a major cause of DNK. The epithelium is supplied by a dense network of sensory nerve endings and dendritic cell processes, and it secretes growth/neurotrophic factors and cytokines to nourish these neighboring cells. In turn, sensory nerve endings release neuropeptides to suppress inflammation and promote epithelial wound healing, while resident immune cells provide neurotrophic and growth factors to support neuronal and epithelial cells, respectively. Diabetes greatly perturbs these interdependencies, resulting in suppressed epithelial proliferation, sensory neuropathy, and a decreased density of dendritic cells. Clinically, this results in a markedly delayed wound healing and impaired sensory nerve regeneration in response to insult and injury. Current treatments for DPN and DNK largely focus on managing the severe complications of the disease. Cell-based therapies hold promise for providing more effective treatment for diabetic keratopathy and corneal ulcers.

Proteomic Analysis of Mouse Kidney Tissue Associates Peroxisomal Dysfunction with Early Diabetic Kidney Disease

Background: The absence of efficient inhibitors for diabetic kidney disease (DKD) progression reflects the gaps in our understanding of DKD molecular pathogenesis. Methods: A comprehensive proteomic analysis was performed on the glomeruli and kidney cortex of diabetic mice with the subsequent validation of findings in human biopsies and omics datasets, aiming to better understand the underlying molecular biology of early DKD development and progression. Results: LC–MS/MS was employed to analyze the kidney proteome of 2 DKD models: Ins2Akita (early and late DKD) and db/db mice (late DKD). The abundance of detected proteins was defined. Pathway analysis of differentially expressed proteins in the early and late DKD versus the respective controls predicted dysregulation in DKD hallmarks (peroxisomal lipid metabolism and β-oxidation), supporting the functional relevance of the findings. Comparing the observed protein changes in early and late DKD, the consistent upregulation of 21 and downregulation of 18 proteins was detected. Among these were downregulated peroxisomal and upregulated mitochondrial proteins. Tissue sections from 16 DKD patients were analyzed by IHC confirming our results. Conclusion: Our study shows an extensive differential expression of peroxisomal proteins in the early stages of DKD that persists regardless of the disease severity, providing new perspectives and potential markers of diabetic kidney dysfunction.

Treatment with crocin suppresses diabetic nephropathy progression via modulating TGF-β1 and oxidative stress in an experimental model of pinealectomized diabetic rats

One of the most common complications of diabetes is diabetic nephropathy (DN). Uncontrolled hyperglycemia leads to histopathologic alterations in the kidney that prevent normal renal function. This study aimed to explore the effects of crocin treatment via virtue of its numerous beneficial properties in streptozotocin-induced pinealectomized diabetic rats. The pinealectomy procedure was conducted on the first day of the study. On the 30th day following pinealectomy, streptozotocin (STZ) (50 mg/kg) was administered intraperitoneally in Wistar rats for induction of diabetes. Diabetes was confirmed on the 3rd day following STZ administration by determining the glucose levels. Daily crocin treatment intraperitoneally for 15 days (50 mg/kg) ameliorated impaired renal oxidant/antioxidant balance, reduced TGF-β1 immuno-staining around tubules, and promoted improvement of renal architecture. Moreover, crocin administration improved altered renal function parameters, including serum Cr and BUN, and also increased creatinine clearance. In conclusion, the protective effects of crocin on diabetic nephropathy might be associated with its powerful antioxidant properties, its ability to improve tissue antioxidant status, and its ability to prevent inflammatory pathways.

Mechanisms of Chinese Herbal Medicines for Diabetic Nephropathy Fibrosis Treatment

Diabetic nephropathy (DN) is a severe microvascular complication of diabetes mellitus that is one of the main causes of end-stage renal disease, causing considerable health problems as well as significant financial burden worldwide. The pathological features of DN include loss of normal nephrons, massive fibroblast and myofibroblast hyperplasia, accumulation of extracellular matrix proteins, thickening of the basement membrane, and tubulointerstitial fibrosis. Renal fibrosis is a final and critical pathological change in DN. Although progress has been made in understanding the pathogenesis of DN fibrosis, current conventional treatment strategies may not be completely effective in preventing the disease’s progression. Traditionally, Chinese herbal medicines (CHMs) composed of natural ingredients have been used for symptomatic relief of DN. Increasing numbers of studies have confirmed that CHMs can exert a renoprotective effect in DN, and antifibrosis has been identified as a key mechanism. In this review, we summarize the antifibrotic efficacy of CHM preparations, single herbal medicines, and their bioactive compounds based on their effects on diminishing the inflammatory response and oxidative stress, regulating transforming growth factor, preventing epithelial-mesenchymal transition, and modulating microRNAs. We intend to provide patients of DN with therapeutic interventions that are complementary to existing options.

TGF-β1 is involved in senescence-related pathways in glomerular endothelial cells via p16 translocation and p21 induction

p16 inhibits cyclin-dependent kinases and regulates senescence-mediated arrest as well as p21. Nuclear p16 promotes G1 cell cycle arrest and cellular senescence. In various glomerular diseases, nuclear p16 expression is associated with disease progression. Therefore, the location of p16 is important. However, the mechanism of p16 trafficking between the nucleus and cytoplasm is yet to be fully investigated. TGF-β1, a major cytokine involved in the development of kidney diseases, can upregulate p21 expression. However, the relationship between TGF-β1 and p16 is poorly understood. Here, we report the role of podocyte TGF-β1 in regulating the p16 behavior in glomerular endothelial cells. We analyzed podocyte-specific TGF-β1 overexpression mice. Although p16 was found in the nuclei of glomerular endothelial cells and led to endothelial cellular senescence, the expression of p16 did not increase in glomeruli. In cultured endothelial cells, TGF-β1 induced nuclear translocation of p16 without increasing its expression. Among human glomerular diseases, p16 was detected in the nuclei of glomerular endothelial cells. In summary, we demonstrated the novel role of podocyte TGF-β1 in managing p16 behavior and cellular senescence in glomeruli, which has clinical relevance for the progression of human glomerular diseases.

TGF-Beta as a Master Regulator of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common complications in diabetes mellitus and the leading cause of end-stage renal disease. TGF-β is a pleiotropic cytokine and has been recognized as a key mediator of DN. However, anti-TGF-β treatment for DN remains controversial due to the diverse role of TGF-β1 in DN. Thus, understanding the regulatory role and mechanisms of TGF-β in the pathogenesis of DN is the initial step towards the development of anti-TGF-β treatment for DN. In this review, we first discuss the diverse roles and signaling mechanisms of TGF-β in DN by focusing on the latent versus active TGF-β1, the TGF-β receptors, and the downstream individual Smad signaling molecules including Smad2, Smad3, Smad4, and Smad7. Then, we dissect the regulatory mechanisms of TGF-β/Smad signaling in the development of DN by emphasizing Smad-dependent non-coding RNAs including microRNAs and long-non-coding RNAs. Finally, the potential therapeutic strategies for DN by targeting TGF-β signaling with various therapeutic approaches are discussed.

Trimethylamine N-Oxide Exacerbates Renal Inflammation and Fibrosis in Rats With Diabetic Kidney Disease

The gut microbiota plays a pivotal role in the onset and development of diabetes and its complications. Trimethylamine N-oxide (TMAO), a gut microbiota-dependent metabolite of certain nutrients, is associated with type 2 diabetes and its complications. Diabetic kidney disease (DKD) is one of the most serious microvascular complications. However, whether TMAO accelerates the development of DKD remains unclear. We tested the hypothesis that TMAO accelerates the development of DKD. A high-fat diet/low-dose streptozotocin-induced diabetes rat model was established, with or without TMAO in the rats’ drinking water. Compared to the normal rats, the DKD rats showed significantly higher plasma TMAO levels at the end of the study. TMAO treatment not only exacerbated the kidney dysfunction of the DKD rats, but also renal fibrosis. Furthermore, TMAO treatment activated the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome and resulted in the release of interleukin (IL)-1β and IL-18 to accelerate renal inflammation. These results suggested that TMAO aggravated renal inflammation and fibrosis in the DKD rats, which provides a new perspective to understand the pathogenesis of DKD and a potential novel target for preventing the progression of DKD.

A novel podocyte protein, R3h domain containing-like, inhibits TGF-β-induced p38 MAPK and regulates the structure of podocytes and glomerular basement membrane

Not only in kidney glomerular physiological function but also glomerular pathology especially in diabetic condition, glomerular podocytes play pivotal roles. Therefore, it is important to increase our knowledge about the genes and proteins expressed in podocytes. Recently, we have identified a novel podocyte-expressed gene, R3h domain containing-like (R3hdml) and analyzed its function in vivo as well as in vitro. Transforming growth factor-β (TGF-β) signaling regulated the expression of R3hdml. And R3hdml inhibited p38 mitogen-activated protein kinase phosphorylation, which was induced by TGF-β, leading to the amelioration of podocyte apoptosis. Furthermore, a lack of R3hdml in mice significantly worsened glomerular function in streptozotocin (STZ)-induced diabetes, while overexpression of R3hdml ameliorated albuminuria in STZ-induced diabetes. Our results surmise that the functional analyses of R3hdml may lead to the development of novel therapeutic strategies for diabetic nephropathy in the future. KEY MESSAGES: • A novel podocyte expressed protein R3h domain containing-like was identified. • R3HDML inhibits podocyte apoptosis by inhibiting TGF-β-mediated p38 MAPK signaling. • Overexpression of R3HDML ameliorates albuminuria in STZ-induced diabetes mice. • R3HDML may prove to be a novel therapeutic strategy for diabetic nephropathy.

Mechanism of Albuminuria Reduction by Chymase Inhibition in Diabetic Mice

Chymase has several functions, such as angiotensin II formation, which can promote diabetic kidney disease (DKD). In this study, we evaluated the effect of the chymase inhibitor TY-51469 on DKD in diabetic db/db mice. Diabetic mice were administered TY-51469 (10 mg/kg/day) or placebo for 4 weeks. No significant difference was observed in body weight and fasting blood glucose between TY-51469- and placebo-treated groups. However, a significant reduction in urinary albumin/creatinine ratio was observed in the TY-51469-treated group compared with the placebo-treated group. In the renal extract, chymase activity was significantly higher in placebo-treated mice than in non-diabetic db/m mice, but it was reduced by treatment with TY-51469. Both NADPH oxidase 4 expression and the oxidative stress marker malondialdehyde were significantly augmented in the placebo-treated group, but they were attenuated in the TY-51469-treated group. Significant increases of tumor necrosis factor-α and transforming growth factor-β mRNA levels in the placebo-treated group were significantly reduced by treatment with TY-51469. Furthermore, the expression of nephrin, which is a podocyte-specific protein, was significantly reduced in the placebo-treated group, but it was restored in the TY-51469-treated group. These findings demonstrated that chymase inhibition reduced albuminuria via attenuation of podocyte injury by oxidative stress.

TGFβ acts through PDGFRβ to activate mTORC1 via the Akt/PRAS40 axis and causes glomerular mesangial cell hypertrophy and matrix protein expression

Interaction of transforming growth factor-β (TGFβ)-induced canonical signaling with the noncanonical kinase cascades regulates glomerular hypertrophy and matrix protein deposition, which are early features of glomerulosclerosis. However, the specific target downstream of the TGFβ receptor involved in the noncanonical signaling is unknown. Here, we show that TGFβ increased the catalytic loop phosphorylation of platelet-derived growth factor receptor β (PDGFRβ), a receptor tyrosine kinase expressed abundantly in glomerular mesangial cells. TGFβ increased phosphorylation of the PI 3-kinase-interacting Tyr-751 residue of PDGFRβ, thus activating Akt. Inhibition of PDGFRβ using a pharmacological inhibitor and siRNAs blocked TGFβ-stimulated phosphorylation of proline-rich Akt substrate of 40 kDa (PRAS40), an intrinsic inhibitory component of mTORC1, and prevented activation of mTORC1 in the absence of any effect on Smad 2/3 phosphorylation. Expression of constitutively active myristoylated Akt reversed the siPDGFRβ-mediated inhibition of mTORC1 activity; however, co-expression of the phospho-deficient mutant of PRAS40 inhibited the effect of myristoylated Akt, suggesting a definitive role of PRAS40 phosphorylation in mTORC1 activation downstream of PDGFRβ in mesangial cells. Additionally, we demonstrate that PDGFRβ-initiated phosphorylation of PRAS40 is required for TGFβ-induced mesangial cell hypertrophy and fibronectin and collagen I (α2) production. Increased activating phosphorylation of PDGFRβ is also associated with enhanced TGFβ expression and mTORC1 activation in the kidney cortex and glomeruli of diabetic mice and rats, respectively. Thus, pursuing TGFβ noncanonical signaling, we identified how TGFβ receptor I achieves mTORC1 activation through PDGFRβ-mediated Akt/PRAS40 phosphorylation to spur mesangial cell hypertrophy and matrix protein accumulation. These findings provide support for targeting PDGFRβ in TGFβ-driven renal fibrosis.

Preservation of microvascular barrier function requires CD31 receptor-induced metabolic reprogramming

Endothelial barrier (EB) breaching is a frequent event during inflammation, and it is followed by the rapid recovery of microvascular integrity. The molecular mechanisms of EB recovery are poorly understood. Triggering of MHC molecules by migrating T-cells is a minimal signal capable of inducing endothelial contraction and transient microvascular leakage. Using this model, we show that EB recovery requires a CD31 receptor-induced, robust glycolytic response sustaining junction re-annealing. Mechanistically, this response involves src-homology phosphatase activation leading to Akt-mediated nuclear exclusion of FoxO1 and concomitant β-catenin translocation to the nucleus, collectively leading to cMyc transcription. CD31 signals also sustain mitochondrial respiration, however this pathway does not contribute to junction remodeling. We further show that pathologic microvascular leakage in CD31-deficient mice can be corrected by enhancing the glycolytic flux via pharmacological Akt or AMPK activation, thus providing a molecular platform for the therapeutic control of EB response.

The Role of Podocytes and Podocyte-Associated Biomarkers in Diagnosis and Treatment of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is an important public health problem. Podocyte injury is a central event in the mechanism of DKD development. Podocytes are terminally differentiated, highly specialized glomerular visceral epithelial cells critical for the maintenance of the glomerular filtration barrier. Although potential mechanisms by which diabetic milieu contributes to irreversible loss of podocytes have been described, identification of markers that prognosticate either the development of DKD or the progression to end-stage kidney disease (ESKD) have only recently made it to the forefront. Currently, the most common marker of early DKD is microalbuminuria; however, this marker has significant limitations: not all diabetic patients with microalbuminuria will progress to ESKD and as many as 30% of patients with DKD have normal urine albumin levels. Several novel biomarkers indicating glomerular or tubular damage precede microalbuminuria, suggesting that the latter develops when significant kidney injury has already occurred. Because podocyte injury plays a key role in DKD pathogenesis, identification of markers of early podocyte injury or loss may play an important role in the early diagnosis of DKD. Such biomarkers in the urine include podocyte-released microparticles as well as expression of podocyte-specific markers. Here, we review the mechanisms by which podocyte injury contributes to DKD as well as key markers that have been recently implicated in the development and/or progression of DKD and might serve to identify individuals that require earlier preventative care and treatment in order to slow the progression to ESKD.

Mesenchymal stem cells modified with angiotensin-converting enzyme 2 are superior for amelioration of glomerular fibrosis in diabetic nephropathy

AIMS

This study aimed to detect the effect of angiotensin-converting enzyme (ACE) 2-modified mesenchymal stem cells (MSCs) on glomerular fibrosis in vitro and in vivo and investigate the underlying molecular mechanism.

METHODS

MSCs transduced with the ACE2 gene (MSCs-ACE2) were cocultured with glomerular mesangial cells (GMCs) following Ang II stimulation. MSCs-ACE2 were transplanted into streptozotocin-induced diabetic rats. Physical, biochemical and morphological parameters were measured, and fibrotic indicators and renin-angiotensin system (RAS) components in GMCs and kidney tissues were assessed.

RESULTS

The transduction efficiency of MSCs was as high as 85%. The modified MSCs secreted soluble ACE2 protein into the culture medium. After transplantation into rats with diabetes, MSCs-ACE2 targeted injured kidneys and enhanced local expression of ACE2. Compared with MSC treatment alone, MSC-ACE2 treatment was superior in reducing albuminuria and improving glomerulosclerosis. In vitro and in vivo, MSCs-ACE2 were more beneficial than MSCs alone in decreasing Ang II and increasing Ang1-7, thereby inhibiting the detrimental effects of Ang II accumulation by downregulating collagen I and fibronectin (FN) expression and inhibiting the transforming growth factor (TGF-β)/Smad pathway.

CONCLUSIONS

MSCs modified with ACE2 therapy have additional benefits to the progression of diabetic nephropathy (DN) by inhibiting renal RAS activation and reducing glomerular fibrosis.

Transforming Growth Factor-Beta1 in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) worldwide. Renin-angiotensin-aldosterone system (RAAS) inhibitors and sodium-glucose co-transporter 2 (SGLT2) inhibitors have shown efficacy in reducing the risk of ESRD. However, patients vary in their response to RAAS blockades, and the pharmacodynamic responses to SGLT2 inhibitors decline with increasing severity of renal impairment. Thus, effective therapy for DKD is yet unmet. Transforming growth factor-β1 (TGF-β1), expressed by nearly all kidney cell types and infiltrating leukocytes and macrophages, is a pleiotropic cytokine involved in angiogenesis, immunomodulation, and extracellular matrix (ECM) formation. An overactive TGF-β1 signaling pathway has been implicated as a critical profibrotic factor in the progression of chronic kidney disease in human DKD. In animal studies, TGF-β1 neutralizing antibodies and TGF-β1 signaling inhibitors were effective in ameliorating renal fibrosis in DKD. Conversely, a clinical study of TGF-β1 neutralizing antibodies failed to demonstrate renal efficacy in DKD. However, overexpression of latent TGF-β1 led to anti-inflammatory and anti-fibrosis effects in non-DKD. This evidence implied that complete blocking of TGF-β1 signaling abolished its multiple physiological functions, which are highly associated with undesirable adverse events. Ideal strategies for DKD therapy would be either specific and selective inhibition of the profibrotic-related TGF-β1 pathway or blocking conversion of latent TGF-β1 to active TGF-β1.

Type 2 diabetes-associated polymorphisms correlate with SIRT1 and TGF-β1 gene expression

The polymorphisms rs3758391 and rs1800470 located in SIRT1 and TGF-β1 have been associated with type 2 diabetes in different populations but its functional effect is not clear. In this study, we evaluated their effect on the expression of SIRT1 and TGF-β1 in peripheral blood as well as their participation in the formation of DNA-protein complexes in a pancreas-derived cell line. It has been described that SIRT1 and TGF-β1 participate in cell growth and regulation of production and secretion of insulin in the pancreas. Anthropometric and biochemical profiles of 127 adults were measured. Genotypes for rs3758391 and rs1800470 were determined using TaqMan assays. Expression analysis of SIRT1 and TGF-β1 were performed using real-time PCR. Gene expression of these genes increased 1.8 ± 0.6- and 1.3 ± 0.6-fold in patients carrying the TT genotype of rs3758391 and rs1800470 when compared to carriers of the CC genotype. Then, we tested whether these single-nucleotide polymorphisms (SNPs) (and rs932658, which is in linkage disequilibrium with rs3758391) are located in regulatory DNA-protein binding sites by electrophoretic mobility shift assays using nuclear extract from the pancreas-derived cell line BxPC-3. The electrophoretic mobility shift assay showed no binding of nuclear proteins to DNA. In conclusion, the genotypes of rs3758391 and rs1800470 are associated with modifications in the expression of the genes SIRT1 and TGF-β1, respectively, but none of the tested SNPs are located in regulatory DNA-protein binding sites.

Protective effect of vanillin on diabetic nephropathy by decreasing advanced glycation end products in rats

AIMS

Diabetic nephropathy (DN) is a common chronic microvascular complication of both types of diabetes mellitus, which leads to renal dysfunction and subsequent need of dialysis and organ transplantation. Advanced glycation end products (AGEs) are metabolic consequence of hyperglycemia and are main contributory factor in the DN pathogenesis through mediating establishment of oxidative status and chronic inflammatory milieu. This study aimed to explore the impact of vanillin on preventing the progression of DN.

MAIN METHODS

Experimental DN model was established in rats utilizing streptozotocin. Serum concentration of AGEs and Interleukin-6 (IL-6) and transforming growth factor β1 (TGFβ1) levels in kidney homogenate were assessed using ELISA technique. Also, we evaluated the expression of nuclear factor kappa B (NF-κB) using immunohistochemistry.

KEY FINDINGS

Treatment with vanillin for 8 weeks significantly ameliorated DN. Vanillin significantly decreased hyperglycemia and improved kidney function reflected by decreased serum levels of blood urea nitrogen, creatinine, and decreased proteinuria. Also, vanillin significantly decreased malondialdehyde content and elevated superoxide dismutase activity in renal tissues. Moreover, vanillin decreased renal expression of NF-κB and renal concentrations of IL-6, TGFβ1 and collagen. In addition, vanillin significantly decreased serum AGEs concentration. Also, vanillin attenuated histological abnormalities in kidney architecture.

SIGNIFICANCE

Vanillin, which is a cheap and abundant natural product, exhibited anti-AGEs, antioxidant, anti-inflammatory and anti-fibrotic activities. These activities might be helpful and potent mechanisms in preventing the progression of DN.

P-Coumaric acid alleviates experimental diabetic nephropathy through modulation of Toll like receptor-4 in rats

AIMS

Diabetic nephropathy (DN) is responsible for the occurrence of 30-47% of the incident cases of end-stage renal disease (ESRD) worldwide. DN is a chronic inflammatory disorder, which results from hyperglycemia-induced alterations and leads to renal fibrosis and ESRD. Toll like receptor-4 (TLR-4) participates in regulation of inflammatory response through controlling of innate immune system. P-Coumaric Acid (P-CA) is a natural hydroxycinnamic acid derivative and is widely present in vegetables, fruits, mushrooms and cereals. This study aimed to explore the renoprotective effect of P-CA, as anti-inflammatory and antioxidant natural compound, against experimental DN.

METHODS

DN was induced by single intraperitoneal injection of streptozotocin (45 mg/kg) in rats. In kidney homogenate, levels of TLR-4, interleukin-6 (IL-6) and transforming growth factor β1 (TGFβ1) were measured using ELISA technique. Also, kidney collagen content was determined colorimetrically.

KEY FINDINGS

Oral administration of P-CA (100 mg/kg) for 8 weeks significantly alleviated the DN. P-CA significantly reduced serum concentrations of glucose, creatinine, blood urea nitrogen (BUN) and reduced protein content in urine. Also, P-CA significantly increased superoxide dismutase (SOD) activity and significantly reduced kidney contents of malondialdehyde (MDA), TLR-4, IL-6, TGFβ1 and collagen when compared with DN group. Moreover, P-CA significantly improved DN-induced histopathological abnormalities.

SIGNIFICANCE

P-CA confers protection against the progression of DN. This renoprotective effect can be attributed to its ability to decrease the generation of inflammatory and fibrotic cytokines in addition to restoring oxidant/antioxidant balance through its ability to down-regulate TLR-4 activation.

Yin Yang 1 protein ameliorates diabetic nephropathy pathology through transcriptional repression of TGFβ1

Transforming growth factor–β1 (TGFβ1) has been identified as a major pathogenic factor underlying the development of diabetic nephropathy (DN). However, the current strategy of antagonizing TGFβ1 has failed to demonstrate favorable outcomes in clinical trials. To identify a different therapeutic approach, we designed a mass spectrometry–based DNA-protein interaction screen to find transcriptional repressors that bind to the TGFB1 promoter and identified Yin Yang 1 (YY1) as a potent repressor of TGFB1. YY1 bound directly to TGFB1 promoter regions and repressed TGFB1 transcription in human renal mesangial cells. In mouse models, YY1 was elevated in mesangial cells during early diabetic renal lesions and decreased in later stages, and knockdown of renal YY1 aggravated, whereas overexpression of YY1 attenuated glomerulosclerosis. In addition, although their duration of diabetic course was comparable, patients with higher YY1 expression developed diabetic nephropathy more slowly compared to those who presented with lower YY1 expression. We found that a small molecule, eudesmin, suppressed TGFβ1 and other profibrotic factors by increasing YY1 expression in human renal mesangial cells and attenuated diabetic renal lesions in DN mouse models by increasing YY1 expression. These results suggest that YY1 is a potent transcriptional repressor of TGFB1 during the development of DN in diabetic mice and that small molecules targeting YY1 may serve as promising therapies for treating DN.

Therapeutic potential of NaoXinTong Capsule on the developed diabetic nephropathy in db/db mice

The current treatment for diabetic nephropathy (DN) is still limited. NaoXinTong Capsule (NXT) is a Chinese Medicine prescribed to patients with cardiovascular disease. It can also ameliorate metabolic syndromes in patients indicating its anti-diabetic properties. Herein we report the therapeutic effects of NXT on the developed DN. The db/db diabetic mice at ˜12 weeks old, the age with DN at middle/advanced stages, were treated with NXT for 12 weeks. We found NXT treatment reduced diabetes-induced hyperglycemia and dyslipidemia, thereby substantially reduced DN progress. In the kidney, NXT reduced mesangial matrix expansion and glomerulosclerosis by inhibiting extracellular matrix accumulation through activation of matrix metalloproteinase 2/9 and inactivating transforming growth factor β1 expression. NXT reduced podocyte injury by reducing renal inflammation and expression of adhesion molecules. Mechanically, NXT potently activated AMPKα in multiple tissues thereby enhancing energy metabolism. In the liver, NXT increased glucokinase expression and insulin sensitivity by increasing insulin receptor substrate 1/2 and protein kinase B (AKT) 1/2 expression/phosphorylation. In skeletal muscle, NXT activated expression of glucose transporter type 4, AKT, glycogen synthase and peroxisome proliferator activated receptor α/γ. In adipose tissue, NXT reduced fatty acid synthase while activating hormone-sensitive lipase expression. Taken together, our study demonstrates that NXT reduced progress of the developed DN by ameliorating glucose, lipid and energy metabolism, maintaining renal structural and functional integrity. Our study also indicates the potential application of NXT for DN treatment in clinics.

Hydrogen sulfide inhibits Ca2+-induced mitochondrial permeability transition pore opening in type-1 diabetes

Hydrogen sulfide (H2S) attenuates N-methyl-d-aspartate receptor-R1 (NMDA-R1) and mitigates diabetic renal damage; however, the molecular mechanism is not well known. Whereas NMDA-R1 facilitates Ca2+ permeability, H2S is known to inhibit L-type Ca2+ channel. High Ca2+ activates cyclophilin D (CypD), a gatekeeper protein of mitochondrial permeability transition pore (MPTP), thus facilitating molecular exchange between matrix and cytoplasm causing oxidative outburst and cell death. We tested the hypothesis of whether NMDA-R1 mediates Ca2+ influx causing CypD activation and MPTP opening leading to oxidative stress and renal injury in diabetes. We also tested whether H2S treatment blocks Ca2+ channel and thus inhibits CypD and MPTP opening to prevent renal damage. C57BL/6J and Akita (C57BL/6J-Ins2Akita) mice were treated without or with H2S donor GYY4137 (0.25 mg·kg-1·day-1 ip) for 8 wk. In vitro studies were performed using mouse glomerular endothelial cells. Results indicated that low levels of H2S and increased expression of NMDA-R1 in diabetes induced Ca2+ permeability, which was ameliorated by H2S treatment. We observed cytosolic Ca2+ influx in hyperglycemic (HG) condition along with mitochondrial-CypD activation, increased MPTP opening, and oxidative outburst, which were mitigated with H2S treatment. Renal injury biomarker KIM-1 was upregulated in HG conditions and normalized following H2S treatment. Inhibition of NMDA-R1 by pharmacological blocker MK-801 revealed similar results. We conclude that NMDA-R1-mediated Ca2+ influx in diabetes induces MPTP opening via CypD activation leading to increased oxidative stress and renal injury, and H2S protects diabetic kidney from injury by blocking mitochondrial Ca2+ permeability through NMDA-R1 pathway.

Key Genes Involved in Diabetic Nephropathy Investigated by Microarray Analysis

We aimed to investigate significant genes associated with diabetic nephropathy (DN), and their potential mechanisms in the process of DN pathogenesis. We downloaded the microarray data of GSE111154 from gene expression omnibus (GEO) database. First, we analyzed differentially expressed genes (DEGs) between early diabetic nephropathy (EDN) samples and nondiabetic control samples. Functional and pathway enrichment analysis was carried out. Disease-related gene sets were analyzed. Then, we constructed the protein-protein interaction (PPI) network and predicted the relation. Finally, transcriptional regulation analyses of microRNA and transcription factors were performed. Totally 554 DEGs between EDN samples and nondiabetic control samples were obtained. Enrichment analysis of disease-related gene sets showed that transforming growth factor beta 1 (TGFB1) was significantly enriched in DN. TGFB1 was involved in more pathways, such as proteoglycans in cancer, malaria, and amebiasis. Furthermore, TGFB1 had the highest degree in PPI network. In addition, TGFB1 was correlated with miR-21-5p, miR-146a-5p, and RAD21. TGFB1, miR-146a-5p, and miR-21-5p are important for DN development. Furthermore, TGFB1 may be involved in DN progression through the regulation of miR-21-5p, miR-146a-5p, and RAD21.

Cell surface expression of 78-kDa glucose-regulated protein (GRP78) mediates diabetic nephropathy

The 78-kDa glucose-regulated protein (GRP78) is a well-established endoplasmic reticulum (ER)-resident chaperone that maintains protein homeostasis and regulates the unfolded protein response. Under conditions of ER stress, GRP78 is also expressed at the cell surface and implicated in tumorigenesis, immunity, and cellular signaling events. The role of cell surface-associated GRP78 (csGRP78) in the pathogenesis of diabetic nephropathy has not yet been defined. Here we explored the role of csGRP78 in regulating high glucose (HG)-induced profibrotic AKT Ser/Thr kinase (AKT) signaling and up-regulation of extracellular matrix proteins. Using primary kidney mesangial cells, we show that HG treatment, but not the osmotic control mannitol, induces csGRP78 expression through an ER stress-dependent mechanism. We found that csGRP78, known to be located on the outer membrane leaflet, interacts with the transmembrane protein integrin β1 and activates focal adhesion kinase and downstream PI3K/AKT signaling. Localization of GRP78 at the cell surface and its interaction with integrin β1 were also required for extracellular matrix protein synthesis in response to HG. Surprisingly, both the N and C termini of csGRP78 were necessary for this profibrotic response. Increased localization of GRP78 at the plasma membrane was also found in the glomerular mesangial area of type 1 diabetic mice in two different models (streptozotocin-induced and Akita). In freshly isolated glomeruli from Akita mice, csGRP78 co-localized with the mesangial cell surface marker α8-integrin. In conclusion, our work reveals a role for csGRP78 in HG-induced profibrotic responses in mesangial cells, informing a potential approach to treating diabetic nephropathy.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

A Glimpse of the Mechanisms Related to Renal Fibrosis in Diabetic Nephropathy

Diabetic nephropathy (DN) is a common kidney disease in people with diabetes, which is also a serious microvascular complication of diabetes and the main cause of end-stage renal disease (ESRD) in developed and developing countries. Renal fibrosis is a finally pathological change in DN. Nevertheless, the relevant mechanism of cause to renal fibrosis in DN is still complex. In this review, we summarized that the role of cell growth factors, epithelial-mesenchymal transition (EMT) in the renal fibrosis of DN, we also highlighted the miRNA and inflammatory cells, such as macrophage, T lymphocyte, and mastocyte modulate the progression of DN. In addition, there are certain other mechanisms that may yet be conclusively defined. Recent studies demonstrated that some of the new signaling pathways or molecules, such as Notch, Wnt, mTOR, Epac-Rap-1 pathway, may play a pivotal role in the modulation of ECM accumulation and renal fibrosis in DN. This review aims to elucidate the mechanism of renal fibrosis in DN and has provided new insights into possible therapeutic interventions to inhibit renal fibrosis and delay the development of DN.