Molecular mechanisms of diabetic kidney disease

A Novel Type 2 Diabetes Mouse Model of Combined Diabetic Kidney Disease and Atherosclerosis

Diabetic kidney disease and atherosclerotic disease are major causes of morbidity and mortality associated with type 2 diabetes (T2D), and diabetic kidney disease is a major cardiovascular risk factor. The black and tan, brachyury (BTBR) mouse strain with leptin deficiency (Lep^ob) has emerged as one of the best models of human diabetic kidney disease. However, no T2D mouse model of combined diabetic kidney disease and atherosclerosis exists. Our goal was to generate such a model. To this end, the low-density lipoprotein (LDL) receptor was targeted for degradation via inducible degrader of the LDL receptor (IDOL) overexpression, using liver-targeted adenoassociated virus serotype DJ/8 (AAV-DJ/8) in BTBR wild-type and BTBR Lep^ob mice. Liver-targeted IDOL-AAV-DJ/8 increased plasma LDL cholesterol compared with the control enhanced green fluorescent protein AAV-DJ/8. IDOL-induced dyslipidemia caused formation of atherosclerotic lesions of an intermediate stage, which contained both macrophages and smooth muscle cells. BTBR Lep^ob mice exhibited diabetic kidney disease. IDOL-induced dyslipidemia worsened albuminuria and glomerular macrophage accumulation but had no effect on mesangial expansion or podocyte numbers. Thus, by inducing hepatic degradation of the LDL receptor, we generated a T2D model of combined kidney disease and atherosclerosis. This model provides a new tool to study mechanisms, interactions, and treatment strategies of kidney disease and atherosclerosis in T2D.

Shifts in podocyte histone H3K27me3 regulate mouse and human glomerular disease

Histone protein modifications control fate determination during normal development and dedifferentiation during disease. Here, we set out to determine the extent to which dynamic changes to histones affect the differentiated phenotype of ordinarily quiescent adult glomerular podocytes. To do this, we examined the consequences of shifting the balance of the repressive histone H3 lysine 27 trimethylation (H3K27me3) mark in podocytes. Adriamycin nephrotoxicity and subtotal nephrectomy (SNx) studies indicated that deletion of the histone methylating enzyme EZH2 from podocytes decreased H3K27me3 levels and sensitized mice to glomerular disease. H3K27me3 was enriched at the promoter region of the Notch ligand Jag1 in podocytes, and derepression of Jag1 by EZH2 inhibition or knockdown facilitated podocyte dedifferentiation. Conversely, inhibition of the Jumonji C domain-containing demethylases Jmjd3 and UTX increased the H3K27me3 content of podocytes and attenuated glomerular disease in adriamycin nephrotoxicity, SNx, and diabetes. Podocytes in glomeruli from humans with focal segmental glomerulosclerosis or diabetic nephropathy exhibited diminished H3K27me3 and heightened UTX content. Analogous to human disease, inhibition of Jmjd3 and UTX abated nephropathy progression in mice with established glomerular injury and reduced H3K27me3 levels. Together, these findings indicate that ostensibly stable chromatin modifications can be dynamically regulated in quiescent cells and that epigenetic reprogramming can improve outcomes in glomerular disease by repressing the reactivation of developmental pathways.

Trans-resveratrol mitigates type 1 diabetes-induced oxidative DNA damage and accumulation of advanced glycation end products in glomeruli and tubules of rat kidneys

Hyperglycemia induces the formation of advanced glycation end products (AGEs) and their receptors (RAGEs), which alter several intracellular signaling mechanisms leading to the onset and progression of diabetic nephropathy. The present study focused on, i) modulatory effects of trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene) on structural changes, AGE (N^Ɛ-carboxymethyl-lysine), RAGE, oxidative stress and DNA damage, and apoptosis, and ii) localization of fibrotic changes, AGE, RAGE, 8-oxo-dG and 4-hydroxynonenal (4-HNE) in diabetic rat kidneys. Resveratrol (5mg/kg; po, administered during last 45days of 90-day-long hyperglycemic period) administration to streptozotocin-induced type 1 diabetic male Wistar rats reduced renal hypertrophy and structural changes (tubular atrophy, mesangial expansion or shrinkage, diffuse glomerulonephritis, and fibrosis), AGE accumulation, oxidative stress and DNA damage (8-oxo-dG), 4-HNE, caspase-3, and cleaved-caspase-3, but not the RAGE expression. The AGE accumulated in the mesangium, vascular endothelium, and proximal convoluted tubules and less intensely in distal convoluted tubules of diabetic rat kidneys. The RAGE expression increased in the convoluted tubules and collecting ducts of diabetic rat kidneys, but not in the mesangium. Diabetes increased the expression of 8-oxo-dG in nuclei and cytoplasm of renal cells, and 4-HNE in glomeruli, convoluted tubules, the loops of Henle and collecting ducts. Hyperglycemia-induced AGE-RAGE axis and oxidative stress in turn induced apoptosis in diabetic kidneys. Resveratrol mitigated all diabetic effects except the RAGE expression. In conclusion, Resveratrol significantly alleviates diabetes-induced glycation, oxidative damage, and apoptosis to inhibit the progression of diabetic nephropathy. Resveratrol supplementation may be useful to hinder the onset and progression of diabetic kidney diseases.

Collective and experimental research project for master's students on the pathophysiology of obesity

We describe here a collective and experimental research project-based learning (ERPBL) for master's students that can be used to illustrate some basic concepts on glucose/lipid homeostasis and renal function around a topical issue. The primary objective of this ERPBL was to strengthen students' knowledge and understanding of physiology and pathophysiology. The secondary objectives were to help students to develop technical/practical abilities and acquire transversal skills with real-world connections. Obesity is a worldwide public health problem that increases the risk for developing type 2 diabetes and nephropathies. To study the impact of western dietary habits, students evaluated the effects of a diet enriched with fat and cola [high-fat and cola diet (HFCD)] on metabolism and renal function in mice. Students mainly worked in tandem to prepare and perform experiments, but also collectively to compile, analyze, and discuss data. Students showed that HFCD-fed mice 1) developed obesity; 2) exhibited glucose homeostasis impairments associated to ectopic fat storage; and 3) displayed reduced glomerular filtration. The educational benefit of the program was estimated using three evaluation metrics: a conventional multicriteria assessment by teachers, a pre-/posttest, and a self-evaluation questionnaire. They showed that the current approach successfully strengthened scientific student knowledge and understanding of physiology/pathophysiology. In addition, it helped students develop new skills, such as technical and transversal skills. We concluded that this ERPBL dealing with the pathophysiology of obesity was strongly beneficial for master's students, thereby appearing as an efficient and performing educational tool.

Microarray analysis reveals gene and microRNA signatures in diabetic kidney disease

The current study aimed to identify therapeutic gene and microRNA (miRNA) biomarkers for diabetic kidney disease (DKD). The public expression profile GSE30122 was used. Following data preprocessing, the limma package was used to select differentially-expressed genes (DEGs) in DKD glomeruli samples and tubuli samples and they were compared with corresponding controls. Then overlapping DEGs in glomeruli and tubuli were identified and enriched analysis was performed. In addition, protein‑protein interaction (PPI) network analysis as well as sub‑network analysis was conducted. miRNAs of the overlapping DEGs were investigated using WebGestal. A total of 139 upregulated and 28 downregulated overlapping DEGs were selected, which were primarily associated with pathways involved in extracellular matrix (ECM)‑receptor interactions and cytokine‑cytokine receptor interactions. CD44, fibronectin 1, C‑C motif chemokine ligand 5 and C‑X‑C motif chemokine receptor 4 were four primary nodes in the PPI network. miRNA (miR)‑17‑5p, miR‑20a and miR‑106a were important and nuclear receptor subfamily 4 group A member 3 (NR4A3), protein tyrosine phosphatase, receptor type O (PTPRO) and Kruppel like factor 9 (KLF9) were all predicted as target genes of the three miRNAs in the integrated miRNA‑target network. Several genes were identified in DKD, which may be involved in pathways such as ECM‑receptor interaction and cytokine‑cytokine receptor interaction. Three miRNAs may also be used as biomarkers for therapy of DKD, including miR‑17‑5p, miR‑20a and miR‑106a, with the predicted targets of NR4A3, PTPRO and KLF9.

Increased Oxidative Damage of RNA in Early-Stage Nephropathy in db/db Mice

To evaluate RNA oxidation in the early stage of diabetic nephropathy, we applied an accurate method based on isotope dilution high-performance liquid chromatography-triple quadruple mass spectrometry to analyze the oxidatively generated guanine nucleosides in renal tissue and urine from db/db mice of different ages. We further investigated the relationship between these oxidative stress markers, microalbumin excretion, and histological changes. We found that the levels of 8-oxo-7,8-dihydroguanosine (8-oxoGuo) and 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo) were increased in the urine and renal tissue of db/db mice and db/db mice with early symptoms of diabetic nephropathy suffered from more extensive oxidative damage than lean littermate control db/m mice. Importantly, in contrast to the findings in db/m mice, the 8-oxoGuo levels in the urine and renal tissue of db/db mice were higher than those of 8-oxodGuo at four weeks. These results indicate that RNA oxidation is more apparent than DNA oxidation in the early stage of diabetic nephropathy. RNA oxidation may provide new insight into the pathogenesis of diabetic nephropathy, and urinary 8-oxoGuo may represent a novel, noninvasive, and easily detected biomarker of diabetic kidney diseases if further study could clarify its source and confirm these results in a large population study.

Inhibition of (pro)renin Receptor Contributes to Renoprotective Effects of Angiotensin II Type 1 Receptor Blockade in Diabetic Nephropathy

Aims: Renal renin-angiotensin system (RAS) plays a pivotal role in the development of diabetic nephropathy (DN). Angiotensin II (Ang II) type 1 receptor (AT₁R) blockade elevates (pro)renin, which may bind to (pro)renin receptor (PRR) and exert receptor-mediated, angiotensin-independent profibrotic effects. We therefore investigated whether PRR activation leads to the limited anti-fibrotic effects of AT₁R blockade on DN, and whether PRR inhibition might ameliorate progression of DN.

Methods: To address the issue, the expression of RAS components was tested in different stages of streptozotocin (STZ)-induced diabetic rats (6, 12, and 24 weeks) and 6-week AT₁R blockade (losartan) treated diabetic rats. Using the blocker for PRR, the handle region peptide (HRP) of prorenin, the effects of PRR on high glucose or Ang II-induced proliferative and profibrotic actions were evaluated by measurement of cell proliferation, matrix metalloproteinase-2 (MMP-2) activity, activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and transforming growth factor-β1 (TGF-β1) expression in rat mesangial cells (MCs).

Results: PRR was downregulated in the kidneys of different stages of diabetic rats (6, 12, and 24 weeks). Moreover, 6-week losartan treatment further suppressed PRR expression via upregulating AT₂R, and ameliorated diabetic renal injury. HRP inhibited high glucose and Ang II-induced proliferative and profibrotic effects in MCs through suppressing TGF-β1 expression and activating MMP-2. Meanwhile, HRP enhanced losartan's anti-fibrotic effects through further inhibiting phosphorylation of ERK1/2 and TGF-β1 expression. Moreover, the inhibitive effect of HRP on Ang II-induced TGF-β1 expression depended on the regulation of PRR expression by AT₂R.

Conclusions: Our findings suggest that inhibition of PRR contributes to renoprotection against diabetic nephropathy by AT₁R blockade.

Perioperative risk factors for acute kidney injury after off-pump coronary artery bypass grafting: a retrospective study

Background

Acute kidney injury (AKI) after cardiac surgery is associated with increased morbidity and mortality. Although morbidity of AKI after off-pump coronary artery bypass grafting (OPCAB) has been investigated, little is known about risk factors for AKI after OPCAB. To identify risk factors for AKI, we examined the association between perioperative variables and AKI after OPCAB.

Findings

We reviewed the medical records of consecutive adult patients who underwent isolated OPCAB between January 2010 and February 2013 in a single institute, retrospectively. The primary outcome was the incidence of AKI evaluated using Acute Kidney Injury Network classifications during the first 48 h postoperatively. We investigated preoperative and intraoperative variables, including hemodynamic parameters, as potential risk factors for AKI. The relationship between candidates of AKI and incidence of AKI was examined by multivariate logistic regression analysis.A total of 298 patients were enrolled in this study. Acute kidney injury occurred in 47 patients (15.7%). Multivariate logistic regression analysis showed that intraoperative furosemide administration (odds ratio [OR], 5.163; 95% confidence interval, 2.171 to 12.185; P < 0.001] and diabetes mellitus (OR, 1.954; 95% confidence interval, 1.004 to 3.880; P = 0.049) were significantly associated with AKI.

Conclusions

Intraoperative furosemide administration and diabetes mellitus were significantly associated with AKI in patients who had received OPCAB.

Plasma Leucine-Rich α-2-Glycoprotein 1 Predicts Rapid eGFR Decline and Albuminuria Progression in Type 2 Diabetes Mellitus

CONTEXT

Abnormal angiogenesis plays an important role in pathogenesis of diabetic kidney disease (DKD). Leucine-rich α-2 glycoprotein 1 (LRG1) is a newly identified angiogenic factor.

OBJECTIVE

To study whether plasma LRG1 may independently predict progression of DKD in individuals with type 2 diabetes mellitus (T2DM).

DESIGN AND SETTING

Prospective cohort study in a regional hospital.

PATIENTS

In total, 1226 T2DM participants were followed for a mean ± standard deviation (SD) of 3.1 ± 0.4 years.

MAIN OUTCOMES

Albuminuria progression was defined as elevation in albuminuria level to a higher category. Chronic kidney disease (CKD) progression [rapid estimated glomerular filtration rate (eGFR) decline] was defined as a 40% or greater deterioration in eGFR in 3 years.

RESULTS

Both participants with albuminuria progression and those with CKD progression had higher plasma LRG1 levels at baseline. LRG1 independently predicted albuminuria progression above traditional risk factors, including baseline eGFR and urine albumin to creatinine ratio. A 1-SD increment in LRG1 was associated with a 1.26-fold [95% confidence interval (CI), 1.04 to 1.53, P = 0.018] higher adjusted risk for albuminuria progression. The association of LRG1 with microalbuminuria to macroalbuminuria progression was stronger than its association with normoalbuminuria to microalbuminuria progression [odds ratio (OR), 1.51; 95% CI, 1.04 to 2.18, P = 0.029 vs OR, 1.09; 95% CI, 0.86 to 1.37, P = 0.486, per 1-SD LRG1 increment]. Also, LRG1 independently predicted CKD progression above traditional risk factors. A 1-SD increment in LRG1 was associated with a 1.48-fold (95% CI, 1.04 to 2.11, P = 0.032) higher adjusted risk for CKD progression.

CONCLUSIONS

Plasma LRG1 predicts both albuminuria and CKD progression beyond traditional risk factors. It may play a role in the pathologic pathway leading to progression of DKD in T2DM.

Crosstalk of Hyperglycemia and Dyslipidemia in Diabetic Kidney Disease

Background

Diabetic kidney disease (DKD) is defined by the functional, structural, and clinical abnormalities of the kidney that are caused by diabetes.

Summary

One-third of both type 1 diabetes and type 2 diabetes patients suffer from DKD, which is the leading cause of end-stage renal disease, and is also associated with cardiovascular disease and high public health care costs. Serum glucose level and lipid level are key factors in the pathogenesis of DKD and are modifiable. The goal of this review is to provide an update on the roles of glucose and lipid metabolism in DKD and their crosstalk at the molecular level. We will further discuss the recent advances regarding metabolic nuclear receptors in glucose-lipid crosstalk, which may provide new potential therapeutic targets for DKD.

Key Message

AMPK, SREBP-1, and some metabolic hormone receptors including liver X receptors, farnesoid X receptors, and peroxisome proliferator-activated receptors mediate the crosstalk of hyperglycemia and dyslipidemia in diabetic kidney disease and might be potential treatment candidates.

Therapeutic effect of human adipose-derived stem cells and their secretome in experimental diabetic pain

Painful neuropathy is one of the complications of diabetes mellitus that adversely affects patients'quality of life. Pharmacological treatments are not fully satisfactory, and novel approaches needed. In a preclinical mouse model of diabetes the effect of both human mesenchymal stromal cells from adipose tissue (hASC) and their conditioned medium (hASC-CM) was evaluated. Diabetes was induced by streptozotocin. After neuropathic hypersensitivity was established, mice were intravenously injected with either 1 × 10⁶ hASC or with CM derived from 2 × 10⁶ hASC. Both hASC and CM (secretome) reversed mechanical, thermal allodynia and thermal hyperalgesia, with a rapid and long lasting effect, maintained up to 12 weeks after treatments. In nerves, dorsal root ganglia and spinal cord of neuropathic mice we determined high IL-1β, IL-6 and TNF-α and low IL-10 levels. Both treatments restored a correct pro/antinflammatory cytokine balance and prevented skin innervation loss. In spleens of streptozotocin-mice, both hASC and hASC-CM re-established Th1/Th2 balance that was shifted to Th1 during diabetes. Blood glucose levels were unaffected although diabetic animals regained weight, and kidney morphology was recovered by treatments. Our data show that hASC and hASC-CM treatments may be promising approaches for diabetic neuropathic pain, and suggest that cell effect is likely mediated by their secretome.

Ursolic acid improves podocyte injury caused by high glucose

BACKGROUND

Autophagy plays an important role in the maintenance of podocyte homeostasis. Reduced autophagy may result in limited renal cell function during exposure to high glucose conditions. In this study we investigated the effects of ursolic acid (UA) on autophagy and podocyte injury, which were induced by high glucose.

METHODS

Conditionally immortalized murine podocytes were cultured in media supplemented with high glucose and the effects of the PI3K inhibitor LY294002 and UA on protein expression were determined. miR-21 expression was detected by real-time RT-PCR. Activation of the PTEN-PI3K/Akt/mTOR pathway, expression of autophagy-related proteins and expression of podocyte marker proteins were determined by western blot. Immunofluorescence was used to monitor the accumulation of LC3 puncta. Autophagosomes were also observed by transmission electron microscopy.

RESULTS

During exposure to high glucose conditions, the normal level of autophagy was reduced in podocytes, and this defective autophagy induced podocyte injury. Increased miR-21 expression, decreased PTEN expression and abnormal activation of the PI3K/Akt/mTOR pathway were observed in cells that were cultured in high glucose conditions. UA and LY294002 reduced podocyte injury through the restoration of defective autophagy. Our data suggest that UA inhibits miR-21 expression and increases PTEN expression, which in turn inhibits Akt and mTOR and restores normal levels of autophagy.

CONCLUSIONS

Our data suggest that podocyte injury is associated with reduced levels of autophagy during exposure to high glucose conditions, UA attenuated podocyte injury via an increase in autophagy through miR-21 inhibition and PTEN expression, which inhibit the abnormal activation of the PI3K/Akt/mTOR pathway.

Soluble epoxide hydrolase in podocytes is a significant contributor to renal function under hyperglycemia

BACKGROUND

Diabetic nephropathy (DN) is the leading cause of renal failure, and podocyte dysfunction contributes to the pathogenesis of DN. Soluble epoxide hydrolase (sEH, encoded by Ephx2) is a conserved cytosolic enzyme whose inhibition has beneficial effects on renal function. The aim of this study is to investigate the contribution of sEH in podocytes to hyperglycemia-induced renal injury.

MATERIALS AND METHODS

Mice with podocyte-specific sEH disruption (pod-sEHKO) were generated, and alterations in kidney function were determined under normoglycemia, and high-fat diet (HFD)- and streptozotocin (STZ)-induced hyperglycemia.

RESULTS

sEH protein expression increased in murine kidneys under HFD- and STZ-induced hyperglycemia. sEH deficiency in podocytes preserved renal function and glucose control and mitigated hyperglycemia-induced renal injury. Also, podocyte sEH deficiency was associated with attenuated hyperglycemia-induced renal endoplasmic reticulum (ER) stress, inflammation and fibrosis, and enhanced autophagy. Moreover, these effects were recapitulated in immortalized murine podocytes treated with a selective sEH pharmacological inhibitor. Furthermore, pharmacological-induced elevation of ER stress or attenuation of autophagy in immortalized podocytes mitigated the protective effects of sEH inhibition.

CONCLUSIONS

These findings establish sEH in podocytes as a significant contributor to renal function under hyperglycemia.

GENERAL SIGNIFICANCE

These data suggest that sEH is a potential therapeutic target for podocytopathies.

Increasing the level of peroxisome proliferator-activated receptor γ coactivator-1α in podocytes results in collapsing glomerulopathy

Inherited and acquired mitochondrial defects have been associated with podocyte dysfunction and chronic kidney disease (CKD). Peroxisome proliferator-activated receptor γ coactivator-1α (PGC1α) is one of the main transcriptional regulators of mitochondrial biogenesis and function. We hypothesized that increasing PGC1α expression in podocytes could protect from CKD. We found that PGC1α and mitochondrial transcript levels are lower in podocytes of patients and mouse models with diabetic kidney disease (DKD). To increase PGC1α expression, podocyte-specific inducible PGC1α-transgenic mice were generated by crossing nephrin-rtTA mice with tetO-Ppargc1a animals. Transgene induction resulted in albuminuria and glomerulosclerosis in a dose-dependent manner. Expression of PGC1α in podocytes increased mitochondrial biogenesis and maximal respiratory capacity. PGC1α also shifted podocytes towards fatty acid usage from their baseline glucose preference. RNA sequencing analysis indicated that PGC1α induced podocyte proliferation. Histological lesions of mice with podocyte-specific PGC1α expression resembled collapsing focal segmental glomerular sclerosis. In conclusion, decreased podocyte PGC1α expression and mitochondrial content is a consistent feature of DKD, but excessive PGC1α alters mitochondrial properties and induces podocyte proliferation and dedifferentiation, indicating that there is likely a narrow therapeutic window for PGC1α levels in podocytes.

Signal integration at the PI3K-p85-XBP1 hub endows coagulation protease activated protein C with insulin-like function

Coagulation proteases have increasingly recognized functions beyond hemostasis and thrombosis. Disruption of activated protein C (aPC) or insulin signaling impair function of podocytes and ultimately cause dysfunction of the glomerular filtration barrier and diabetic kidney disease (DKD). We here show that insulin and aPC converge on a common spliced-X-box binding protein-1 (sXBP1) signaling pathway to maintain endoplasmic reticulum (ER) homeostasis. Analogous to insulin, physiological levels of aPC maintain ER proteostasis in DKD. Accordingly, genetically impaired protein C activation exacerbates maladaptive ER response, whereas genetic or pharmacological restoration of aPC maintains ER proteostasis in DKD models. Importantly, in mice with podocyte-specific deficiency of insulin receptor (INSR), aPC selectively restores the activity of the cytoprotective ER-transcription factor sXBP1 by temporally targeting INSR downstream signaling intermediates, the regulatory subunits of PI3Kinase, p85α and p85β. Genome-wide mapping of condition-specific XBP1-transcriptional regulatory patterns confirmed that concordant unfolded protein response target genes are involved in maintenance of ER proteostasis by both insulin and aPC. Thus, aPC efficiently employs disengaged insulin signaling components to reconfigure ER signaling and restore proteostasis. These results identify ER reprogramming as a novel hormonelike function of coagulation proteases and demonstrate that targeting insulin signaling intermediates may be a feasible therapeutic approach ameliorating defective insulin signaling.

Regulating Autophagy as a Therapeutic Target for Diabetic Nephropathy

PURPOSE OF REVIEW

Autophagy promotes cellular health in response to various cellular stresses and to changes in nutrient conditions. In this review, we focus on the role of autophagy in the pathogenesis of diabetic nephropathy and discuss the regulation of autophagy as a new therapeutic target for the suppression of diabetic nephropathy.

RECENT FINDINGS

Previous studies have indicated that autophagy deficiency or insufficiency in renal cells, including podocytes, mesangial cells, endothelial cells and tubular cells, contributes to the pathogenesis of diabetic nephropathy. Alterations in the nutrient-sensing pathways, including mammalian target of rapamycin complex1 (mTORC1), AMP-activated kinase (AMPK) and Sirt1, due to excess nutrition　in diabetes are implicated in the impairment of autophagy. Maintaining both basal and adaptive autophagy against cellular stress may protect the kidney from diabetes-induced cellular stresses. Therefore, the activation of autophagy through the modulation of nutrient-sensing pathways may be a new therapeutic option for the suppression of diabetic nephropathy.

PLK2 Plays an Essential Role in High D-Glucose-Induced Apoptosis, ROS Generation and Inflammation in Podocytes

Diabetic kidney disease (DKD) is a serious complication of hyperglycemia. Currently, there is no effective therapeutic intervention for DKD. In this study, we sought to provide a set of gene profile in diabetic kidneys. We identified 338 genes altered in diabetes-induced DKD glomeruli, and PLK2 exhibited the most dramatic change. Gene set enrichment analysis (GSEA) indicated multiple signaling pathways are involved DKD pathogenesis. Here, we investigated whether PLK2 contributes to podocyte dysfunction, a characteristic change in the development of DKD. High D-glucose (HDG) significantly increased PLK2 expression in mouse podocytes. Suppressing PLK2 attenuated HDG-induced apoptosis and inflammatory responses both in vitro and in vivo. NAC, an antioxidant reagent, rescued HDG and PLK2 overexpression-induced kidney injuries. In summary, we demonstrated that silencing PLK2 attenuates HDG-induced podocyte apoptosis and inflammation, which may serve as a future therapeutic target in DKD.

Protective effect of berberine on renal fibrosis caused by diabetic nephropathy

Berberine (BBR) is a material extracted from Chinese herbs, which has been used in the treatment of diabetes in Chinese medicine for thousands of years. However, the importance of BBR in renal fibrosis remains to be elucidated. In the present study, streptozotocin-induced diabetic nephropathy (DN) rats were used to determine the effect of BBR on renal fibrosis. The pathology of the kidneys was examined using periodic acid-Schiff (PAS) and Masson staining. The expression levels of transforming growth factor-β (TGF-β) and α smooth muscle actin (α-SMA) in kidneys were observed using immunohistochemical staining. The mRNA and protein expression levels of TGF-β, α-SMA, vimentin, nuclear factor-κB were examined using reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. PAS and Masson staining revealed that there was notable glomerular hypertrophy and mesangial matrix expansion in DN rats. Immunohistochemistry revealed that there was a significant increase in TGF-β and α-SMA expression levels in the renal tubulointerstitium and the extracellular matrix. However, treatment with BBR may significantly reduce kidney injury. The protein and mRNA expression levels of TGF-β, vimentin and α-SMA were significantly increased in DN rats compared with the control group; however, this increase was reduced following treatment with BBR. The present study revealed that BBR may inhibit fibrosis and ameliorate the symptoms of DN. The current findings indicated that BBR may be used as a potential treatment for patients with DN.

Evidence for two distinct phenotypes of chronic kidney disease in individuals with type 1 diabetes mellitus

AIMS/HYPOTHESIS

In a retrospective, observational, cross-sectional, single-centre study, we assessed the prevalence and correlates of different CKD phenotypes (with and without albuminuria) in a large cohort of patients of white ethnicity with type 1 diabetes.

METHODS

From 2001 to 2009, 408 men and 369 women with type 1 diabetes (age 40.2 ± 11.7 years, diabetes duration 19.4 ± 12.2 years, HbA_1c 7.83 ± 1.17% [62.0 ± 12.9 mmol/mol]) were recruited consecutively. Albumin-to-creatinine ratio (ACR) and eGFR (Modification of Diet in Renal Disease) were obtained for all individuals, together with CKD stage. Diabetic retinopathy and peripheral polyneuropathy were detected in 41.5% and 8.1%, respectively, and cardiovascular disease (CVD) occurred in 8.5%. Adjudications of CKD phenotype were made by blinded investigators.

RESULTS

Normo- (ACR <3.4), micro- (ACR 3.4-34) or macroalbuminuria (ACR ≥34 mg/mmol) were present in 91.6%, 6.4% and 1.9% of individuals, respectively. eGFR categories 1 (≥90 ml min^-1 [1.73 m]^-2), 2 (60-89 ml min^-1 [1.73 m]^-2) and 3 (<60 ml min^-1 [1.73 m]^-2) were present in 57.3%, 39.0% and 3.7%, respectively. The majority of participants had no CKD (89.4%), while stages 1-2 and ≥3 CKD were detected in 6.8% and 3.7%, respectively. The albuminuric (Alb⁺) and non-albuminuric (Alb^-) phenotypes were present in 12 (41.4%) and 17 (58.6%) individuals with stage ≥3 CKD, respectively. Individuals with an ACR <3.4 mg/mmol were subdivided into those with normal albuminuria (<1.1 mg/mmol; 77.2%) and mildly increased albuminuria (1.1-3.4 mg/mmol; 14.4%), and individuals with stage 2 CKD were subdivided into those with eGFR 75-89 ml min^-1 [1.73 m]^-2 and 60-74 ml min^-1 [1.73 m]^-2. ACR <3.4 mg/mmol (88.7%) and even <1.1 mg/mmol (70.4%) were common in individuals with eGFR 60-74 ml min^-1 [1.73 m]^-2. The prevalence of ACR <1.1 mg/mmol was lower but still significant (34.5%) in those with stage ≥3 CKD. In logistic regression analysis, stages 1-2 and ≥3 CKD were independently associated with age, HbA_1c, γ-glutamyltransferase, fibrinogen, hypertension, but not with sex, BMI, smoking, HDL-cholesterol or triacylglycerol. Inclusion of advanced retinopathy removed HbA_1c from the model. The CKD Alb⁺ phenotype correlated with diabetes duration, HbA_1c, HDL-cholesterol, fibrinogen and hypertension, while the CKD Alb^- phenotype was associated with age and hypertension, but not with diabetes duration, HbA_1c and fibrinogen.

CONCLUSIONS/INTERPRETATION

The Alb^- CKD phenotype is present in a significant proportion of individuals with type 1 diabetes supporting the hypothesis of two distinct pathways (Alb⁺ and Alb^-) of progression towards advanced kidney disease in type 1 diabetes. These are probably distinct pathways as suggested by different sets of covariates associated with the two CKD phenotypes.

Jiangtang decoction ameliorate diabetic nephropathy through the regulation of PI3K/Akt-mediated NF-κB pathways in KK-Ay mice

Background

Jiangtang decoction (JTD) is a China patented drug which contains Euphorbia humifusa Willd, Salvia miltiorrhiza Bunge, Astragalus mongholicus Bunge, Anemarrhena asphodeloides Bunge, and Coptis chinensis Franch. For decades, it has also been used clinically to treat diabetic nephropathy (DN) effectively; however, the associated mechanisms remain unknown. Thus, the present study aimed to examine the protective efficacy of JTD in DN and elucidate the underlying molecular mechanisms.

Methods

A diabetic model using KK-Ay mice received a daily administration of JTD for 12 weeks. Body weight, blood glucose, triglycerides (TGs), total cholesterol (TC), urea nitrogen (UN), creatinine (Cr), and microalbumin/urine creatinine (MA/UCREA) was measured every 4 weeks. Furthermore, on the day of the sacrifice, blood, urine, and kidneys were collected to assess renal function according to general parameters. Pathological staining was performed to evaluate the protective renal effect of JTD. In addition, the levels of inflammatory cytokines (tumor necrosis factor-α [TNF-α], interleukin [IL]-6 and intercellular adhesion molecule [ICAM]-1), insulin receptor substrate [IRS]-1, advanced glycation end products [AGEs], and receptor of glycation end products [RAGE] were assessed. Finally, the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway and involvement of nuclear factor-κB (NF-κB) was further analyzed.

Results

After 12 weeks of metformin and JTD administration, the mice exhibited a significant amelioration in glucose and lipid metabolism dysfunction, reduced morphological changes in the renal tissue, decreased urinary albumin excretion, and normalized creatinine clearance. JTD treatment also reduced the accumulation of AGEs and RAGE, up-regulated IRS-1, and increased the phosphorylation of both PI3K (p85) and Akt, indicating that the activation of the PI3K/Akt signaling pathway was involved. Additionally, JTD administration reduced the elevated levels of renal inflammatory mediators and decreased the phosphorylation of NF-κB p65.

Conclusions

These results demonstrate that JTD might reduce inflammation in DN through the PI3K/Akt and NF-κB signaling pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s13020-017-0134-0) contains supplementary material, which is available to authorized users.

ATP-citrate lyase is essential for high glucose-induced histone hyperacetylation and fibrogenic gene upregulation in mesangial cells

The goal of this study was to address the role of ATP-citrate lyase (ACL), an enzyme that converts citrate to acetyl-CoA, in high glucose (HG)-induced histone acetylation and profibrotic gene expression. Our recent ChIP-Seq studies have demonstrated that HG induces genome-wide histone hyperacetylation in mesangial cells (MCs). Here, we showed that exposure of MCs to HG markedly increased histone acetylation at the H3K9/14 and H3K18 marks and induced the expression of potent profibrotic factors TGF-β1, TGF-β3, and connective tissue growth factor (CTGF). The induction of these profibrotic factors was further enhanced by histone deacetylase inhibitor but suppressed by histone acetyl-transferase inhibitor, confirming the importance of histone acetylation in this regulation. Interestingly, HG not only upregulated ACL expression but also promoted ACL nuclear translocation, evidenced by increased ACL concentration and activity in the nuclear extracts. Consistent with this observation, transfection of MCs with a plasmid-carrying green fluorescent protein (GFP)-ACL fusion protein led to GFP nuclear accumulation when cultured in HG condition. Silencing ACL with siRNAs alleviated HG-induced histone hyperacetylation, as well as upregulation of TGF-β1, TGF-β3, CTGF, and extracellular matrix (ECM) proteins fibronectin and collagen type IV, whereas ACL overexpression further enhanced HG induction of histone acetylation, as well as these profibrotic factors and ECM proteins. Collectively, these observations demonstrate that HG promotes ACL expression and translocation into the nucleus, where ACL converts citrate to acetyl-CoA to provide the substrate for histone acetylation, leading to upregulation of fibrogenic genes. Therefore, ACL plays a critical role in epigenetic regulation of diabetic renal fibrosis.

Role of MicroRNAs in Type 2 Diabetes and Associated Vascular Complications

Type 2 diabetes mellitus (T2DM) has become a major health threat worldwide. MicroRNAs (miRNAs) are a group of non-coding RNAs known to regulate various biological processes including the pathogenesis of T2DM. Recent studies have pointed out that specific miRNAs play a critical role in controlling β cell activities and the development of diabetic vascular complications. Their association with the disease pathogenesis and omnipresence in body fluids have made them important players for prognosis, diagnosis and management of T2DM. Owing to the limitations of classical biomarkers of diabetes such as fasting plasma glucose, glycosylated haemoglobin (HbA_1c) lack in predicting the risk of development of diabetes complications in a susceptible population. The miRNAs can act as ideal biomarkers for diabetes associated complications. Identification of specific miRNA signatures to detect diabetes and ideally to find out the risk of development of diabetes-associated complications in susceptible population is the essential requirement of the present clinical strategies for controlling diabetes worldwide. In this article, we summarize the potential miRNAs and miRNA signatures involved in the β cell activities and diabetes associated macrovascular and microvascular complications.

LncRNA MALAT1 is dysregulated in diabetic nephropathy and involved in high glucose-induced podocyte injury via its interplay with β-catenin

Metastasis associated lung adenocarcinoma transcript 1(MALAT1) is a long non-coding RNA, broadly expressed in mammalian tissues including kidney and up-regulated in a variety of cancer cells. To date, its functions in podocytes are largely unknown. β-catenin is a key mediator in the canonical and non-canonical Wnt signalling pathway; its aberrant expression promotes podocyte malfunction and albuminuria, and contributes to kidney fibrosis. In this study, we found that MALAT1 levels were increased in kidney cortices from C57BL/6 mice with streptozocin (STZ)-induced diabetic nephropathy, and dynamically regulated in cultured mouse podocytes stimulated with high glucose, which showed a trend from rise to decline. The decline of MALAT1 levels was accompanied with β-catenin translocation to the nuclei and enhanced expression of serine/arginine splicing factor 1 (SRSF1), a MALAT1 RNA-binding protein. Further we showed early interference with MALAT1 siRNA partially restored podocytes function and prohibited β-catenin nuclear accumulation and SRSF1 overexpression. Intriguingly, we showed that β-catenin was involved in MALAT1 transcription by binding to the promotor region of MALAT1; β-catenin knock-down also decreased MALAT1 levels, suggesting a novel feedback regulation between MALAT1 and β-catenin. Notably, β-catenin deletion had limited effects on SRSF1 expression, demonstrating β-catenin might serve as a downstream signal of SRSF1. These findings provided evidence for a pivotal role of MALAT1 in diabetic nephropathy and high glucose-induced podocyte damage.

Pyruvate kinase M2 activation may protect against the progression of diabetic glomerular pathology and mitochondrial dysfunction

Diabetic nephropathy (DN) is a major cause of end-stage renal disease, and therapeutic options for preventing its progression are limited. To identify novel therapeutic strategies, we studied protective factors for DN using proteomics on glomeruli from individuals with extreme duration of diabetes (ł50 years) without DN and those with histologic signs of DN. Enzymes in the glycolytic, sorbitol, methylglyoxal and mitochondrial pathways were elevated in individuals without DN. In particular, pyruvate kinase M2 (PKM2) expression and activity were upregulated. Mechanistically, we showed that hyperglycemia and diabetes decreased PKM2 tetramer formation and activity by sulfenylation in mouse glomeruli and cultured podocytes. Pkm-knockdown immortalized mouse podocytes had higher levels of toxic glucose metabolites, mitochondrial dysfunction and apoptosis. Podocyte-specific Pkm2-knockout (KO) mice with diabetes developed worse albuminuria and glomerular pathology. Conversely, we found that pharmacological activation of PKM2 by a small-molecule PKM2 activator, TEPP-46, reversed hyperglycemia-induced elevation in toxic glucose metabolites and mitochondrial dysfunction, partially by increasing glycolytic flux and PGC-1α mRNA in cultured podocytes. In intervention studies using DBA2/J and Nos3 (eNos) KO mouse models of diabetes, TEPP-46 treatment reversed metabolic abnormalities, mitochondrial dysfunction and kidney pathology. Thus, PKM2 activation may protect against DN by increasing glucose metabolic flux, inhibiting the production of toxic glucose metabolites and inducing mitochondrial biogenesis to restore mitochondrial function.

Zeaxanthin ameliorates high glucose-induced mesangial cell apoptosis through inhibiting oxidative stress via activating AKT signalling-pathway

Oxidative stress is a critical factor in the pathophysiology of diabetic kidney disease. Previous study shows that hyperglycaemia aggravates renal injury through oxidative stress in diabetic model, and antioxidants have beneficial effect on diabetic kidney disease. However, the role of antioxidants in the progression of diabetic kidney disease is poorly understood. The aim of this study was to clarify whether zeaxanthin, an antioxidant, could ameliorate mesangial cell injury and if so, identify the related mechanism underlying this protective effect. To that end, superoxide dismutase (SOD) activity and methane dicarboxylic aldehyde (MDA) levels were measured by an assay kit, and mesangial cell apoptosis and ROS levels were assessed using flow cytometry analysis. Furthermore, The levels of a phosphorylated ser/thr protein kinase (p-AKT), phosphorylated glycogen synthase kinase-3 beta (p-GSK-3β), Bcl-2 associated X protein (Bax) and cleaved cysteinyl aspartate-specific proteinase-3 (caspase-3) were detected by western blot. We found that zeaxanthin decreases MDA levels and increased SOD activity, as well as inhibits apoptosis and decreases ROS levels in mesangial cells in a high sugar environment. Furthermore, zeaxanthin increased p-AKT levels while decreased the levels of p-GSK-3β, Bax and cleaved-caspase-3. In addition, LY294002 reversed the protective effect of zeaxanthin on mesangial cells. In conclusion, zeaxanthin ameliorated mesangial cell apoptosis may be involved in inhibiting oxidative stress through activating of the AKT signalling pathway.

Influence of Dipeptidyl Peptidase-IV Inhibitor Sitagliptin on Extracellular Signal-Regulated Kinases 1/2 Signaling in Rats with Diabetic Nephropathy

The protective effects of sitagliptin on the kidneys of rats with diabetic nephropathy (DN) and its influence on extracellular signal-regulated kinases 1/2 (ERK1/2) signaling were investigated. Male Wistar rats (n = 40) were randomly assigned to normal control, DN, low-dose sitagliptin intervention (ST1), or high-dose sitagliptin intervention (ST2) groups. Animals were euthanized after a 16-week treatment, and blood glucose (BG), glycosylated hemoglobin (HbA1c), urinary albumin excretion rate (AER), serum creatinine (Scr), creatinine clearance rate (Ccr), active glucagon-like peptide-1 (GLP-1) levels, kidney hypertrophy index, and renal pathohistology were determined. Immunohistochemical methods and real-time polymerase chain reaction (PCR) were used to detect protein and mRNA expression of podocalyxin, ERK1/2, GLP-1 receptor (GLP-1R) and transforming growth factor-β (TGF-β). After 16 weeks, BG, AER, Scr, HbA1c and the kidney hypertrophy index were all significantly decreased (p < 0.05) in ST1 and ST2 groups, while Ccr and active GLP-1 levels were increased (p < 0.05), with changes more pronounced in ST2 (p < 0.05). Glomerular pathological lesions were also improved following sitagliptin treatment, especially in ST2. Immunohistochemical and real-time PCR revealed that protein and mRNA expression levels of podocalyxin and GLP-1R were increased significantly in ST1 and ST2, while expression of ERK1/2 and TGF-β was decreased (p < 0.05). Sitagliptin therefore delayed DN progression, possibly via the inhibition of ERK1/2 signaling and promotion of the interaction between GLP-1 and the GLP-1R.

Phosphodiesterase-5 inhibition preserves renal hemodynamics and function in mice with diabetic kidney disease by modulating miR-22 and BMP7

Diabetic Nephropathy (DN) is the leading cause of end-stage renal disease. Preclinical and experimental studies show that PDE5 inhibitors (PDE5is) exert protective effects in DN improving perivascular inflammation. Using a mouse model of diabetic kidney injury we investigated the protective proprieties of PDE5is on renal hemodynamics and the molecular mechanisms involved. PDE5i treatment prevented the development of DN-related hypertension (P < 0.001), the increase of urine albumin creatinine ratio (P < 0.01), the fall in glomerular filtration rate (P < 0.001), and improved renal resistive index (P < 0.001) and kidney microcirculation. Moreover PDE5i attenuated the rise of nephropathy biomarkers, soluble urokinase-type plasminogen activator receptor, suPAR and neutrophil gelatinase-associated lipocalin, NGAL. In treated animals, blood vessel perfusion was improved and vascular leakage reduced, suggesting preserved renal endothelium integrity, as confirmed by higher capillary density, number of CD31⁺ cells and pericyte coverage. Analysis of the mechanisms involved revealed the induction of bone morphogenetic protein-7 (BMP7) expression, a critical regulator of angiogenesis and kidney homeostasis, through a PDE5i-dependent downregulation of miR-22. In conclusion PDE5i slows the progression of DN in mice, improving hemodynamic parameters and vessel integrity. Regulation of miR-22/BMP7, an unknown mechanism of PDE5is in nephrovascular protection, might represent a novel therapeutic option for treatment of diabetic complications.

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

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

MicroRNA-27a promotes podocyte injury via PPARγ-mediated β-catenin activation in diabetic nephropathy

Podocyte injury has a pivotal role in the pathogenesis of diabetic nephropathy (DN). MicroRNA-27a (miR-27a), peroxisome proliferator-activated receptor γ (PPARγ) and β-catenin pathways have been involved in the pathogenesis of DN. Herein, we asked whether miR-27a mediates podocyte injury through PPARγ/β-catenin signaling in DN. The functional relevance of miR-27a, PPARγ and β-catenin were investigated in cultured podocytes and glomeruli of diabetic rats and patients using in vitro and in vivo approaches. Podocyte injury was assessed by migration, invasion and apoptosis assay. Biological parameters were analyzed using enzyme-linked immunosorbent assay. We found that high glucose stimulated miR-27a expression, which, by negatively targeting PPARγ, activated β-catenin signaling as evidenced by upregulation of β-catenin target genes, snail1 and α-smooth muscle actin (α-SMA) and downregulation of podocyte-specific markers podocin and synaptopodin. These changes caused podocyte injury as demonstrated by increased podocyte mesenchymal transition, disrupted podocyte architectural integrity and increased podocyte apoptosis. Furthermore, we provide evidence that miR-27a contributed to unfavorable renal function and increased podocyte injury in diabetic rats. Notably, miR-27a exhibited clinical and biological relevance as it was linked to elevated serum creatinine, proteinuria and reduced creatinine clearance rate. In addition, miR-27a upregulation and activation of PPARγ/β-catenin signaling were verified in renal biopsy samples from DN patients. We propose a novel role of the miR-27a/PPARγ/β-catenin axis in fostering the progression toward more deteriorated podocyte injury in DN. Targeting miR-27a could be a potential therapeutic approach for DN.

Podocyte Injury and Albuminuria in Experimental Hyperuricemic Model Rats

Although hyperuricemia is shown to accelerate chronic kidney disease, the mechanisms remain unclear. Accumulating studies also indicate that uric acid has both pro- and antioxidant properties. We postulated that hyperuricemia impairs the function of glomerular podocytes, resulting in albuminuria. Hyperuricemic model was induced by oral administration of 2% oxonic acid, a uricase inhibitor. Oxonic acid caused a twofold increase in serum uric acid levels at 8 weeks when compared to control animals. Hyperuricemia in this model was associated with the increase in blood pressure and the wall-thickening of afferent arterioles as well as arcuate arteries. Notably, hyperuricemic rats showed significant albuminuria, and the podocyte injury marker, desmin, was upregulated in the glomeruli. Conversely, podocin, the key component of podocyte slit diaphragm, was downregulated. Structural analysis using transmission electron microscopy confirmed podocyte injury in this model. We found that urinary 8-hydroxy-2'-deoxyguanosine levels were significantly increased and correlated with albuminuria and podocytopathy. Interestingly, although the superoxide dismutase mimetic, tempol, ameliorated the vascular changes and the hypertension, it failed to reduce albuminuria, suggesting that vascular remodeling and podocyte injury in this model are mediated through different mechanisms. In conclusion, vasculopathy and podocytopathy may distinctly contribute to the kidney injury in a hyperuricemic state.

Effect of Vitamin D Status on Von Willebrand Factor and ADAMTS13 in Diabetic Patients on Chronic Hemodialysis

Von Willebrand factor (vWF) is a glycoprotein with a crucial role in the formation of platelet thrombi, and ADAMTS13 is the main enzyme responsible for vWF cleavage. Both are important in the relationship between diabetic nephropathy, hypercoagulability, and cardiovascular disease. This study evaluated a potential relationship between vitamin D (vitD) levels, vWF, ADAMTS13 activity, and inflammation in diabetic patients on chronic hemodialysis (HD). Blood samples from 52 diabetic patients on chronic HD were obtained to determine vitD levels, vWF, and ADAMTS13 activity, and inflammatory markers. HD patients were grouped according to 25-hydroxyvitamin D [25(OH) VitD]<25 nmol/L (n=16) or >25 nmol/L (n=36). vWF antigen and vWF activity were elevated in both groups, with an average of 214.3±82.6% and 175.8±72.6%, respectively. Average ADAMTS13 activity was within the normal range in both groups. Blood samples from the vitD <25 nmol/L group showed a positive correlation between c-reactive protein (CRP) and vWF levels (P=0.023; r=0.564; 95% confidence interval=0.095-0.828), with a negative correlation between HbA1c and 25(OH) VitD (P=0.015; r=-0.337; 95% confidence interval=-0.337-0.19). Diabetic patients on chronic HD had elevated vWF levels and activity with no significant change in ADAMTS13 activity. The correlation between CRP and vWF levels in the 25(OH) VitD<25 nmol/L group suggests inflammatory-related endothelial dysfunction in these patients.

Critical role of the cAMP-PKA pathway in hyperglycemia-induced epigenetic activation of fibrogenic program in the kidney

Hyperglycemia is a major pathogenic factor that promotes diabetic nephropathy, but the underlying mechanism remains incompletely understood. Here, we show that high glucose induced cAMP response element-binding protein (CREB)-binding protein (CBP)-mediated H3K9/14 hyperacetylation in approximately 5000 gene promoters in glomerular mesangial cells, including those of Tgfb1, Tgfb3, and Ctgf, the major profibrotic factors that are known to drive diabetic renal fibrogenesis. In these promoters, H3K9/14 hyperacetylation was closely associated with NF-κB or CREB motifs. Chromatin immunoprecipitation assays confirmed that hyperglycemia promoted phospho-p65 or phospho-CREB and CBP bindings and RNA polymerase II recruitment to these promoters in mesangial cells as well as in glomeruli that were purified from type I and type II diabetic mice. Under hyperglycemia, cAMP production and PKA activity were markedly increased as a result of glucose transporter 1-mediated glucose influx that drives glucose metabolism and ATP production, which led to increased phosphorylation of p65 and CREB. Inhibition of adenylyl cyclase or PKA activity blocked p65 and CREB phosphorylation, CBP recruitment, and histone acetylation in these promoters. Collectively, these data demonstrate that the cAMP-PKA pathway plays a key role in epigenetic regulation of key profibrotic factors in diabetes.-Deb, D. K., Bao, R., Li, Y. C. Critical role of the cAMP-PKA pathway in hyperglycemia-induced epigenetic activation of fibrogenic program in the kidney.

Amelioration of high fat diet-induced nephropathy by cilostazol and rosuvastatin

Multiple comorbidities of metabolic disorders are associated with facilitated chronic kidney disease progression. Anti-platelet cilostazol is used for the treatment of peripheral artery disease. In this study, we investigated the potential beneficial effects of cilostazol and rosuvastatin on metabolic disorder-induced renal dysfunctions. C57BL/6 mice that received high fat diet (HFD) for 22 weeks and a low dose of streptozotocin (STZ, 40 mg/kg) developed albuminuria and had increased urinary cystatin C excretion, and cilostazol treatment (13 weeks) improved these markers. Histopathological changes, including glomerular mesangial expansion, tubular vacuolization, apoptosis, and lipid accumulation were ameliorated by cilostazol treatment. Tubulointerstitial fibrosis that was indicated by the increases in collagen and transforming growth factor-β1 subsided by cilostazol. Renoprotective effects were also observed in rosuvastatin-treated mice, and combinatorial treatment with cilostazol and rosuvastatin demonstrated enhanced ameliorative effects in histopathological evaluations. Notably, repressed renal heme oxygenase-1 (Ho-1) level in HFD/STZ mice was restored in cilostazol group. Further, we demonstrated that cilostazol enhanced Nrf2/Ho-1 signaling in cultured proximal tubular epithelial cells. Collectively, these results suggest the potential advantageous use of cilostazol as an adjunctive therapy with statins for the amelioration of metabolic disorder-associated renal injury.

Stable Isotope Labeling with Amino Acids (SILAC)-Based Proteomics of Primary Human Kidney Cells Reveals a Novel Link between Male Sex Hormones and Impaired Energy Metabolism in Diabetic Kidney Disease

Male sex predisposes to many kidney diseases. Considering that androgens exert deleterious effects in a variety of cell types within the kidney, we hypothesized that dihydrotestosterone (DHT) would alter the biology of the renal tubular cell by inducing changes in the proteome. We employed stable isotope labeling with amino acids (SILAC) in an indirect spike-in fashion to accurately quantify the proteome in DHT- and 17β-estradiol (EST)-treated human proximal tubular epithelial cells (PTEC). Of the 5043 quantified proteins, 76 were differentially regulated. Biological processes related to energy metabolism were significantly enriched among DHT-regulated proteins. SILAC ratios of 3 candidates representing glycolysis, N-acetylglucosamine metabolism and fatty acid β-oxidation, namely glucose-6-phosphate isomerase (GPI), glucosamine-6-phosphate-N-acetyltransferase 1 (GNPNAT1), and mitochondrial trifunctional protein subunit alpha (HADHA), were verified in vitro. In vivo, renal GPI and HADHA protein expression was significantly increased in males. Furthermore, male sex was associated with significantly higher GPI, GNPNAT1, and HADHA kidney protein expression in two different murine models of diabetes. Enrichment analysis revealed a link between our DHT-regulated proteins and oxidative stress within the diabetic kidney. This finding was validated in vivo, as we observed increased oxidative stress levels in control and diabetic male kidneys, compared with females. This in depth quantitative proteomics study of human primary PTEC response to sex hormone administration suggests that male sex hormone stimulation results in perturbed energy metabolism in kidney cells, and that this perturbation results in increased oxidative stress in the renal cortex. The proteome-level changes associated with androgens may play a crucial role in the development of structural and functional changes in the diseased kidney. With our findings, we propose a possible link between diabetic and non-diabetic kidney disease progression and male sex hormone levels. Data are available via ProteomeXchange (https://www.ebi.ac.uk/pride/archive/) with identifier PXD003811.

C-peptide and diabetic kidney disease

Kidney disease is a serious development in diabetes mellitus and poses an increasing clinical problem. Despite increasing incidence and prevalence of diabetic kidney disease, there have been no new therapies for this condition in the last 20 years. Mounting evidence supports a biological role for C-peptide, and findings from multiple studies now suggest that C-peptide may beneficially affect the disturbed metabolic and pathophysiological pathways leading to the development of diabetic nephropathy. Studies of C-peptide in animal models and in humans with type 1 diabetes all suggest a renoprotective effect for this peptide. In diabetic rodents, C-peptide reduces glomerular hyperfiltration and albuminuria. Cohort studies of diabetic patients with combined islet and kidney transplants suggest that maintained C-peptide secretion is protective of renal graft function. Further, in short-term studies of patients with type 1 diabetes, administration of C-peptide is also associated with a lowered hyperfiltration rate and reduced microalbuminuria. Thus, the available information suggests that type 1 diabetes should be regarded as a dual hormone deficiency disease and that clinical trials of C-peptide in diabetic nephropathy are both justified and urgently required.

Derangement of calcium metabolism in diabetes mellitus: negative outcome from the synergy between impaired bone turnover and intestinal calcium absorption

Both types 1 and 2 diabetes mellitus (T1DM and T2DM) are associated with profound deterioration of calcium and bone metabolism, partly from impaired intestinal calcium absorption, leading to a reduction in calcium uptake into the body. T1DM is associated with low bone mineral density (BMD) and osteoporosis, whereas the skeletal changes in T2DM are variable, ranging from normal to increased and to decreased BMD. However, both types of DM eventually compromise bone quality through production of advanced glycation end products and misalignment of collagen fibrils (so-called matrix failure), thereby culminating in a reduction of bone strength. The underlying cellular mechanisms (cellular failure) are related to suppression of osteoblast-induced bone formation and bone calcium accretion, as well as to enhancement of osteoclast-induced bone resorption. Several other T2DM-related pathophysiological changes, e.g., osteoblast insulin resistance, impaired productions of osteogenic growth factors (particularly insulin-like growth factor 1 and bone morphogenetic proteins), overproduction of pro-inflammatory cytokines, hyperglycemia, and dyslipidemia, also aggravate diabetic osteopathy. In the kidney, DM and the resultant hyperglycemia lead to calciuresis and hypercalciuria in both humans and rodents. Furthermore, DM causes deranged functions of endocrine factors related to mineral metabolism, e.g., parathyroid hormone, 1,25-dihydroxyvitamin D3, and fibroblast growth factor-23. Despite the wealth of information regarding impaired bone remodeling in DM, the long-lasting effects of DM on calcium metabolism in young growing individuals, pregnant women, and neonates born to women with gestational DM have received scant attention, and their underlying mechanisms are almost unknown and worth exploring.

VEGF and the diabetic kidney: More than too much of a good thing

Over a decade and a half has passed since the publication of early reports hinting at a pathogenetic role for vascular endothelial growth factor ("VEGF") in the development of diabetic kidney disease. In diabetic rats, renal mRNA levels of the VEGF-A isoform were upregulated and administration of a VEGF-A neutralizing antibody attenuated albuminuria: VEGF was "bad" in diabetic nephropathy. Since that time, our understanding of the complexity of the renal VEGF system has advanced. Unlike its experimental counterpart, human diabetic nephropathy is associated with diminished VEGF-A levels and experience in the oncological setting has taught us that VEGF blocking therapy can cause adverse renal effects in patients. Correspondingly, investigational studies in cultured cells and rodent models have demonstrated that the biological effects of the VEGF system are dependent not only on the amount of VEGF, but also the type of VEGF, its sites of action and the prevailing milieu. Here we reflect back on the discoveries that have been made since those initial reports that shone the spotlight on the importance of the VEGF system in the diabetic kidney and we consider that the role of VEGF in diabetic nephropathy extends well beyond being "too much of a good thing".

Repression of miR-217 protects against high glucose-induced podocyte injury and insulin resistance by restoring PTEN-mediated autophagy pathway

Podocyte damage is the initial hallmark of diabetic nephropathy (DN), leading to the increasing morbidity and mortality in diabetic patients. Recent researches have corroborated the critical roles of miRNAs in the pathological progression of DN. Here, elevation of miR-217 was verified in high glucose (HG)-stimulated podocytes. Moreover, blocking miR-217 expression antagonized HG-induced cell injury by attenuating the adverse role of HG on cell viability and inhibiting ROS levels and cell apoptosis. Simultaneously, miR-217 repression restored HG-disrupted insulin resistance by elevating glucose uptake and nephrin expression, an essential component for insulin-induced glucose uptake. Mechanism assay substantiated the defective autophagy in HG-treated podocytes, which was resumed by miR-217 cessation. Importantly, suppressing autophagy pathway with 3-MA alleviated the protective roles of miR-217 down-regulation in podocyte injury and insulin resistance. Luciferase reporter analysis confirmed that PTEN was a target of miR-217 in podocytes. Additionally, blocking PTEN expression restrained autophagy restoration in miR-217-decreased cells. Furthermore, PTEN down-regulation attenuated the beneficial role of miR-217 suppression in HG-induced injury and insulin resistance. Together, this study manifests that miR-217inhibition can protectively antagonize HG-induced podocyte damage and insulin resistance by restoring the defective autophagy pathway via targeting PTEN, representing a novel and promising therapeutic target against diabetic nephropathy.

Astragaloside IV Attenuates Podocyte Apoptosis Mediated by Endoplasmic Reticulum Stress through Upregulating Sarco/Endoplasmic Reticulum Ca2+-ATPase 2 Expression in Diabetic Nephropathy

Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) plays a central role in the pathogenesis of diabetes. This protein has been recognized as a potential target for diabetic therapy. In this study, we identified astragaloside IV (AS-IV) as a potent modulator of SERCA inhibiting renal injury in diabetic status. Increasing doses of AS-IV (2, 6, and 18 mg kg^-1 day^-1) were administered intragastrically to db/db mice for 8 weeks. Biochemical and histopathological approaches were conducted to evaluate the therapeutic effects of AS-IV. Cultured mouse podocytes were used to further explore the underlying mechanism in vitro. AS-IV dose-dependently increased SERCA activity and SERCA2 expression, and suppressed ER stress-mediated and mitochondria-mediated apoptosis in db/db mouse kidney. AS-IV also normalized glucose tolerance and insulin sensitivity, improved renal function, and ameliorated glomerulosclerosis and renal inflammation in db/db mice. In palmitate stimulated podocytes, AS-IV markedly improved inhibitions of SERCA activity and SERCA2 expression, restored intracellular Ca²⁺ homeostasis, and attenuated podocyte apoptosis in a dose-dependent manner with a concomitant abrogation of ER stress as evidenced by the downregulation of GRP78, cleaved ATF6, phospho-IRE1α and phospho-PERK, and the inactivation of both ER stress-mediated and mitochondria-mediated apoptotic pathways. Furthermore, SERCA2b knockdown eliminated the effect of AS-IV on ER stress and ER stress-mediated apoptotic pathway, whereas its overexpression exhibited an anti-apoptotic effect. Our data obtained from in vivo and in vitro studies demonstrate that AS-IV attenuates renal injury in diabetes subsequent to inhibiting ER stress-induced podocyte apoptosis through restoring SERCA activity and SERCA2 expression.

Inhibition of the processing of miR-25 by HIPK2-Phosphorylated-MeCP2 induces NOX4 in early diabetic nephropathy

Phosphorylated methyl-CpG binding protein2 (p-MeCP2) suppresses the processing of several microRNAs (miRNAs). Homeo-domain interacting protein kinase2 (HIPK2) phosphorylates MeCP2, a known transcriptional repressor. However, it is not known if MeCP2 and HIPK2 are involved in processing of miRNAs implicated in diabetic nephropathy. p-MeCP2 and HIPK2 levels were significantly increased, but Seven in Absentia Homolog1 (SIAH1), which mediates proteasomal degradation of HIPK2, was decreased in the glomeruli of streptozotocin injected diabetic mice. Among several miRNAs, miR-25 and its precursor were significantly decreased in diabetic mice, whereas primary miR-25 levels were significantly increased. NADPH oxidase4 (NOX4), a target of miR-25, was significantly increased in diabetic mice. Protein levels of p-MeCP2, HIPK2, and NOX4 were increased in high glucose (HG)- or TGF-β-treated mouse glomerular mesangial cells (MMCs). miR-25 (primary, precursor, and mature) and mRNA levels of genes indicated in the in vivo study showed similar trends of regulation in MMCs treated with HG or TGF-β. The HG- or TGF-β-induced upregulation of p-MeCP2, NOX4 and primary miR-25, but downregulation of precursor and mature miR-25, were attenuated by Hipk2 siRNA. These results demonstrate a novel role for the SIAH1/HIPK2/MeCP2 axis in suppressing miR-25 processing and thereby upregulating NOX4 in early diabetic nephropathy.

TGR5 suppresses high glucose-induced upregulation of fibronectin and transforming growth factor-β1 in rat glomerular mesangial cells by inhibiting RhoA/ROCK signaling

RhoA/ROCK can cause renal inflammation and fibrosis in the context of diabetes by activating nuclear factor-κB (NF-κB). TGR5 is known for its role in maintaining metabolic homeostasis and anti-inflammation, which is closely related to NF-κB inhibition. Given that TGR5 is highly enriched in kidney, we aim to investigate the regulatory role of TGR5 on fibronectin (FN) and transforming growth factor-β1 (TGF-β1) in high glucose (HG)-treated rat glomerular mesangial cells (GMCs). Both the factors are closely related to renal inflammations and mediated by NF-κB. Moreover, our study determines whether such regulation is achieved by the inhibition of RhoA/ROCK and the subsequent NF-κB suppression. Polymerase chain reaction was taken to test the mRNA level of TGR5. Western blot was used to measure the protein expressions of TGR5, FN, TGF-β1, p65, IκBα, phospho-MYPT1 (Thr853), and MYPT1. Glutathione S-transferase-pull down and immunofluorescence were conducted to test the activation of RhoA, the distribution of TGR5, and p65, respectively. Electrophoretic mobility shift assay was adopted to measure the DNA binding activity of NF-κB. In GMCs, TGR5 activation or overexpression significantly suppressed FN and TGF-β1 protein expressions, NF-κB, and RhoA/ROCK activation induced by HG or transfection of constitutively active RhoA. By contrast, TGR5 RNA interference caused enhancement of FN, TGF-β1 protein expressions, increase of RhoA/ROCK activation. However, TGR5 cannot suppress RhoA/ROCK activation when a selective Protein kinase A (PKA) inhibitor was used. This study suggests that in HG-treated GMCs, TGR5 significantly suppresses the NF-κB-mediated upregulation of FN and TGF-β1, which are hallmarks of diabetic nephropathy. These functions are closely related to the suppression of RhoA/ROCK via PKA.

HDL cholesterol and risk of diabetic nephropathy in patient with type 1 diabetes: A meta-analysis of cohort studies

A meta-analysis was conducted to assess the impact of HDL on risk of diabetic nephropathy in T1DM patients. Ten papers containing (7698) participants were included in this meta-analysis. Our meta-analysis suggest that the risk of diabetic nephropathy was decreased with HDL in type 1 diabetes.

Berberine enhances the AMPK activation and autophagy and mitigates high glucose-induced apoptosis of mouse podocytes

High glucose concentration can induce injury of podocytes and berberine has a potent activity against diabetic nephropathy. However, whether and how berberine can inhibit high glucose-mediated injury of podocytes have not been clarified. This study tested the effect of berberine on high glucose-mediated apoptosis and the AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR) activation and autophagy in podocytes. The results indicated that berberine significantly mitigated high glucose-decreased cell viability, and nephrin and podocin expression as well as apoptosis in mouse podocytes. Berberine significantly increased the AMPK activation and mitigated high glucose and/or the AMPK inhibitor, compound C-mediated mTOR activation and apoptosis in podocytes. Berberine significantly enhanced the AMPK activation and protected from high glucose-induced apoptosis in the AMPK-silencing podocytes. Furthermore, berberine significantly increased the high glucose-elevated Unc-51-like autophagy-activating kinase 1 (ULK1) S317/S555 phosphorylation, Beclin-1 expression, the ratios of LC3II to LC3I expression and the numbers of autophagosomes, but reduced ULK1 S757 phosphorylation in podocytes. In addition, berberine significantly attenuated compound C-mediated inhibition of autophagy in podocytes. The protective effect of berberine on high glucose-induced podocyte apoptosis was significantly mitigated by pre-treatment with 3-methyladenine or bafilomycin A1. Collectively, berberine enhanced autophagy and protected from high glucose-induced injury in podocytes by promoting the AMPK activation. Our findings may provide new insights into the molecular mechanisms underlying the anti-diabetic nephropathy effect of berberine and may aid in design of new therapies for intervention of diabetic nephropathy.

Diabetic nephropathy: A potential savior with 'rotten-egg' smell

Diabetic nephropathy (DN) is currently the leading cause of end-stage renal disease. Despite optimal management, DN is still a major contributor to morbidity and mortality of diabetic patients worldwide. The major pathological alterations in DN include excessive accumulation and deposition of extracellular matrix, leading to expansion of mesangial matrix, thickening of glomerular basement membrane and tubulointerstitial fibrosis. At the molecular level, accumulating evidence suggests that hyperglycemia or high glucose mediates renal injury in DN via multiple molecular mechanisms such as induction of oxidative stress, upregulation of renal transforming growth factor beta-1 expression, production of proinflammatory cytokines, activation of fibroblasts and renin angiotensin system, and depletion of adenosine triphosphate. Also worrying is the fact that existing therapies only retard the disease progression but do not prevent it. Therefore, there is urgent need to identify novel therapies to target additional disease mechanisms. Hydrogen sulfide (H₂S), the third member of the gasotransmitter family, has recently been identified and demonstrated to possess important therapeutic characteristics that prevent the development and progression of DN in experimental animals by targeting several important molecular pathways, and therefore may represent an alternative or additional therapeutic approach for DN. This review discusses recent experimental findings on the molecular mechanisms underlying the therapeutic effects of H₂S against the development and progression of DN and its clinical application in the future.