Overview of glucose signaling in mesangial cells in diabetic nephropathy

Chinese botanical drugs targeting mitophagy to alleviate diabetic kidney disease, a comprehensive review

Diabetic kidney disease (DKD) is one of the chronic microvascular complications caused by diabetes, which is characterized by persistent albuminuria and/or progressive decline of estimated glomerular filtration rate (eGFR), and has been the major cause of dialysis around the world. At present, although the treatments for DKD including lifestyle modification, glycemic control and even using of Sodium-glucose cotransporter 2 (SGLT2) inhibitors can relieve kidney damage caused to a certain extent, there is still a lack of effective treatment schemes that can prevent DKD progressing to ESRD. It is urgent to find new complementary and effective therapeutic agents. Growing animal researches have shown that mitophagy makes a great difference to the pathogenesis of DKD, therefore, exploration of new drugs that target the restoration of mitophagy maybe a potential perspective treatment for DKD. The use of Chinese botanical drugs (CBD) has been identified to be an effective treatment option for DKD. There is growing concern on the molecular mechanism of CBD for treatment of DKD by regulating mitophagy. In this review, we highlight the current findings regarding the function of mitophagy in the pathological damages and progression of DKD and summarize the contributions of CBD that ameliorate renal injuries in DKD by interfering with mitophagy, which will help us further explain the mechanism of CBD in treatment for DKD and explore potential therapeutic strategies for DKD.

Selective induction of human renal interstitial progenitor-like cell lineages from iPSCs reveals development of mesangial and EPO-producing cells

Recent regenerative studies using human pluripotent stem cells (hPSCs) have developed multiple kidney-lineage cells and organoids. However, to further form functional segments of the kidney, interactions of epithelial and interstitial cells are required. Here we describe a selective differentiation of renal interstitial progenitor-like cells (IPLCs) from human induced pluripotent stem cells (hiPSCs) by modifying our previous induction method for nephron progenitor cells (NPCs) and analyzing mouse embryonic interstitial progenitor cell (IPC) development. Our IPLCs combined with hiPSC-derived NPCs and nephric duct cells form nephrogenic niche- and mesangium-like structures in vitro. Furthermore, we successfully induce hiPSC-derived IPLCs to differentiate into mesangial and erythropoietin-producing cell lineages in vitro by screening differentiation-inducing factors and confirm that p38 MAPK, hypoxia, and VEGF signaling pathways are involved in the differentiation of mesangial-lineage cells. These findings indicate that our IPC-lineage induction method contributes to kidney regeneration and developmental research.

Apabetalone Downregulates Fibrotic, Inflammatory and Calcific Processes in Renal Mesangial Cells and Patients with Renal Impairment

Epigenetic mechanisms are implicated in transcriptional programs driving chronic kidney disease (CKD). Apabetalone is an orally available inhibitor of bromodomain and extraterminal (BET) proteins, which are epigenetic readers that modulate gene expression. In the phase 3 BETonMACE trial, apabetalone reduced risk of major adverse cardiac events (MACE) by 50% in the CKD subpopulation, indicating favorable effects along the kidney-heart axis. Activation of human renal mesangial cells (HRMCs) to a contractile phenotype that overproduces extracellular matrix (ECM) and inflammatory cytokines, and promotes calcification, frequently accompanies CKD to drive pathology. Here, we show apabetalone downregulated HRMC activation with TGF-β1 stimulation by suppressing TGF-β1-induced α-smooth muscle actin (α-SMA) expression, α-SMA assembly into stress fibers, enhanced contraction, collagen overproduction, and expression of key drivers of fibrosis, inflammation, or calcification including thrombospondin, fibronectin, periostin, SPARC, interleukin 6, and alkaline phosphatase. Lipopolysaccharide-stimulated expression of inflammatory genes IL6, IL1B, and PTGS2 was also suppressed. Transcriptomics confirmed apabetalone affected gene sets of ECM remodeling and integrins. Clinical translation of in vitro results was indicated in CKD patients where a single dose of apabetalone reduced plasma levels of key pro-fibrotic and inflammatory markers, and indicated inhibition of TGF-β1 signaling. While plasma proteins cannot be traced to the kidney alone, anti-fibrotic and anti-inflammatory effects of apabetalone identified in this study are consistent with the observed decrease in cardiovascular risk in CKD patients.

Protein O-GlcNAcylation and the regulation of energy homeostasis: lessons from knock-out mouse models

O-GlcNAcylation corresponds to the addition of N-Acetylglucosamine (GlcNAc) on serine or threonine residues of cytosolic, nuclear and mitochondrial proteins. This reversible modification is catalysed by a unique couple of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). OGT uses UDP-GlcNAc produced in the hexosamine biosynthesis pathway, to modify proteins. UDP-GlcNAc is at the cross-roads of several cellular metabolisms, including glucose, amino acids and fatty acids. Therefore, OGT is considered as a metabolic sensor that post-translationally modifies proteins according to nutrient availability. O-GlcNAcylation can modulate protein–protein interactions and regulate protein enzymatic activities, stability or subcellular localization. In addition, it can compete with phosphorylation on the same serine or threonine residues, or regulate positively or negatively the phosphorylation of adjacent residues. As such, O-GlcNAcylation is a major actor in the regulation of cell signaling and has been implicated in numerous physiological and pathological processes. A large body of evidence have indicated that increased O-GlcNAcylation participates in the deleterious effects of glucose (glucotoxicity) in metabolic diseases. However, recent studies using mice models with OGT or OGA knock-out in different tissues have shown that O-GlcNAcylation protects against various cellular stresses, and indicate that both increase and decrease in O-GlcNAcylation have deleterious effects on the regulation of energy homeostasis.

Influence of zinc levels and Nrf2 expression in the clinical and pathological changes in patients with diabetic nephropathy

Objective

We investigated the correlation between zinc levels and Nrf2 expression and potential effects on the clinicopathology of patients with diabetic nephropathy (DN).

Methods

We selected 30 patients with DN, diagnosed via renal biopsy at our hospital from March 2018 to November 2019, and enrolled 30 healthy individuals from a medical examination center as the control group. Patients with DN were divided into normal-zinc and low-zinc groups. We detected the levels of zinc, copper, and Nrf2 mRNA in their serum, and collected the clinical and pathological data of DN patients.

Results

Serum zinc level and Nrf2 mRNA expression were significantly decreased in patients with DN compared to those of healthy people (P < 0.05). Of the 30 patients, 16 had low zinc (53.3%) and 14 had normal zinc levels (46.7%). There was no significant difference in the blood Nrf2 mRNA expression between the two groups (P > 0.05). However, the expression of Nrf2 in the kidney tissue of the low-zinc group was significantly lower compared to the normal-zinc group (P < 0.05). Diastolic blood pressure and copper levels were significantly higher in the low-zinc group (P < 0.05). In contrast, body mass index, red blood cell count, Hb level, and the ratio of zinc to copper were significantly lower in the low-zinc group (P < 0.05). The pathological classifications of the low-zinc group were more severe (P < 0.05).

Conclusion

Patients with DN were more likely to have zinc deficiency and lower expression of Nrf2. Additionally, DN patients with zinc deficiency were prone to have more severe clinical and pathological manifestations.

N-type calcium channel and renal injury

Accumulating evidences indicated that voltage-gated calcium channels (VDCC), including L-, T-, N-, and P/Q-type, are present in kidney and contribute to renal injury during various chronic diseases trough different mechanisms. As a voltage-gated calcium channel, N-type calcium channel was firstly been founded predominately distributed on nerve endings which control neurotransmitter releases. Since sympathetic nerve is distributed along renal afferent and efferent arterioles, N-type calcium channel blockade on sympathetic nerve terminals would bring renal dynamic improvement by dilating both arterioles and reducing glomerular pressure. In addition, large body of scientific research indicated that neurotransmitters, such as norepinephrine, releases by activating N-type calcium channel can trigger inflammatory and fibrotic signaling pathways in kidney. Interestingly, we recently demonstrated that N-type calcium channel is also expressed on podocytes and may directly contribute to podocyte injury in denervated animal models. In this paper, we will summarize our current knowledge regarding renal N-type calcium channels, and discuss how they might contribute to the river that terminates in renal injury.

Characteristic of Streptozotocin-Nicotinamide-Induced Inflammation in A Rat Model of Diabetes-Associated Renal Injury

Background: Chemical agents such as streptozotocin (STZ) and nicotinamide (NAD) are used in animal models of diabetes mellitus and their related consequences in the kidneys. Several studies have been conducted to determine the modeling, however, the results are still unclear. Moreover, diabetic nephropathy is considered to begin with an inflammatory reaction in the kidneys.  Objectives: This study aims to investigate the metabolic profile STZ and NAD induce inflammation in the kidney.  Methods: The male Wistar rats used were divided into control and STZ-induced diabetes. Half of the diabetes group received a single dose of nicotinamide (230 mg/Kg) 15 minutes after STZ injection and all groups were monitored for 6 weeks. Furthermore, the profiles of creatinine, urea, and uric acid from serum and urine were observed and the kidney inflammation was tested by immunohistochemistry (IHC) with IL-6 and TNF-α parameters.  Results: The result shows that the administration of a single dose of 230 mg/kg NAD in diabetic rats induced with 50 mg/kg and 65 mg/kg STZ affects body weight and kidney organ index. For 6 weeks of testing, both doses of STZ were enhanced several parameters of kidney damage in diabetic rats in blood and urine chemical parameters. Furthermore, the use of NAD to promote inflammation in STZ-induced diabetic rats gave no significant difference. However, NAD can help mice live longer and avoid problems throughout the test.  Conclusions: The use of NAD leads to inflammation in Streptozotocin-induced diabetic rats. Therefore, the administration of Nicotinamide is recommended since it helps the rats live longer during the experiment. 

Therapeutic potential of pro-resolving mediators in diabetic kidney disease

Renal microvascular disease associated with diabetes [Diabetic kidney disease - DKD] is the leading cause of chronic kidney disease. In DKD, glomerular basement membrane thickening, mesangial expansion, endothelial dysfunction, podocyte cell loss and renal tubule injury contribute to progressive glomerulosclerosis and tubulointerstitial fibrosis. Chronic inflammation is recognized as a major pathogenic mechanism for DKD, with resident and circulating immune cells interacting with local kidney cell populations to provoke an inflammatory response. The onset of inflammation is driven by the release of well described proinflammatory mediators, and this is typically followed by a resolution phase. Inflammation resolution is achieved through the bioactions of endogenous specialized pro-resolving lipid mediators (SPMs). As our understanding of SPMs advances 'resolution pharmacology' based approaches using these molecules are being explored in DKD.

Insulin resistance in glomerular podocytes: Potential mechanisms of induction

Glomerular podocytes are a target for the actions of insulin. Accumulating evidence indicates that exposure to nutrient overload induces insulin resistance in these cells, manifested by abolition of the stimulatory effect of insulin on glucose uptake. Numerous recent studies have investigated potential mechanisms of the induction of insulin resistance in podocytes. High glucose concentrations stimulated reactive oxygen species production through NADPH oxidase activation, decreased adenosine monophosphate-activated protein kinase (AMPK) phosphorylation, and reduced deacetylase sirtuin 1 (SIRT1) protein levels and activity. Calcium signaling involving transient receptor potential cation channel C, member 6 (TRPC6) also was demonstrated to play an essential role in the regulation of insulin-dependent signaling and glucose uptake in podocytes. Furthermore, podocytes exposed to diabetic environment, with elevated insulin levels become insulin resistant as a result of degradation of insulin receptor (IR), resulting in attenuation of insulin signaling responsiveness. Also elevated levels of palmitic acid appear to be an important factor and contributor to podocytes insulin resistance. This review summarizes cellular and molecular alterations that contribute to the development of insulin resistance in glomerular podocytes.

Bone morphogenetic protein (BMP) 7 expression is regulated by the E3 ligase UBE4A in diabetic nephropathy

Mesangial cells played a central role in the pathophysiology of diabetic nephropathy (DN). Our goal was to evaluate the molecular mechanism that regulates loss of BMP7 protein expression in DN. The mRNA and protein levels of BMP7 or UBE4A were detected using qRT-PCR and Western blot respectively. Mass spectrometry and co-immunoprecipitation were used to explore the E3 ligase which regulated BMP7 post-translationally. We initially confirmed that BMP7 protein, but not mRNA, is downregulated when cultured under high glucose mimicking DN conditions, which was rescued by MG-132 treatment. Proteomic analysis of NRK-52E cells ± MG-132 revealed a list of ubiquitin ligases associated with BMP7. Knockdown of the ubiquitin ligase UBE4A stabilized BMP7 expression in NRK-52E cells grown under high glucose conditions. Concurrent overexpression experiments confirmed that UBE4A is the ubiquitin ligase that degrades BMP7. Co-immunoprecipitation analysis confirmed that BMP7 and UBE4A interact. BMP7 expression in DN is regulated by post-translational mechanism.

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

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

Metabolomic Changes of Human Proximal Tubular Cell Line in High Glucose Environment

Hyperglycemia causes mitochondrial damage renal tubular cells, which contribute to the progression of diabetic kidney disease. However, the metabolic aberration of renal tubular cells in an hyperglycemic milieu has not been fully elucidated. In this study, human proximal renal tubular cell line (HK-2 cell) are incubated in glucose and mannitol at 5 mM or 25 mM. Cellular metabolome was determined by capillary electrophoresis time of flight mass spectrometer (CE-TOF/MS) and capillary electrophoresis-triple quadrupole mass spectrometry (CE-QqQMS). A total of 116 metabolites were quantified. Principal component analysis (PCA) revealed excellent clustering of metabolomic changes for different treatment conditions, and exposure to glucose at 5 and 25 mM lead to distinct metabolomic profiles as compared to samples treated with serum-free medium or mannitol as osmotic control. Hierarchical clustering analysis showed a number of characteristic changes in metabolic profile following exposure to 5 mM or 25 mM glucose. Notably, lactate-to-pyruvate ratio was significantly increased, while cellular levels of citric acid, α-ketoglutaric acid (i.e. 2-oxoglutaric acid), and fumaric acid were significantly reduced after exposure to glucose at 25 mM but not 5 mM. Moreover, cellular levels of reduced glutathione and total glutathione were significantly decreased, and S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH) ratio was significantly increased after exposure to glucose 25 mM but not 5 mM. We conclude that in response to high glucose, HK-2 cells characteristic metabolomic changes, including increase in lactate-to-pyruvate ratio, reduction in Krebs cycle metabolites, reduction in glutathione antioxidant activity, and increase in cellular methylation potential. Our results may shed light on the pathogenesis of diabetic kidney disease, but the expression of glucose metabolism-related protein and enzyme activity in HK-2 cells after hyperglycemia condition need to be confirmed by further studies.

Identification of potential therapeutic target genes in mouse mesangial cells associated with diabetic nephropathy using bioinformatics analysis

The aim of the present study was to identify genes under the effect of transforming growth factor-β (TGF-β1), high glucose (HG) and glucosamine (GlcN) in MES-13 mesangial cells and elucidate the molecular mechanisms of diabetic nephropathy (DN). The gene expression datasets GSE2557 and GSE2558 were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were independently screened using the GEO2R online tool. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using the Database for Annotation, Visualization, and Integrated Discovery. The protein-protein interaction (PPI) network was constructed using the Search Tool for the Retrieval of Interacting Genes and Cytoscape software. The hub genes were identified by the NetworkAnalyzer plugin. Overlapping genes were subjected to molecular docking analysis using SystemsDock. A total of 202 upregulated and 158 downregulated DEGs from the HG-treated groups, 138 upregulated and 103 downregulated DEGs from the GlcN-treated groups, and 81 upregulated and 44 downregulated DEGs from the TGF-β1-treated groups were identified. The majority of the DEGs were independently enriched in 'nucleosome assembly', 'chromatin silencing' and 'xenobiotic glucuronidation'. In addition, KEGG pathways were significantly enriched in 'systemic lupus erythematosus', 'protein processing in endoplasmic reticulum' and 'aldarate metabolism pathway', and 'TNF signaling pathway' intersected in the TGF-β1-treated and HG-treated groups. In total, eight hub genes, Jun, prostaglandin-endoperoxide synthase 2 (Ptgs2), fibronectin 1 (Fn1), cyclin-dependent kinase (Cdk)2, Fos, heat shock protein family A (Hsp70) member 5 (Hspa5), Hsp90b1 and homo sapiens hypoxia upregulated 1 (Hyou1), and three overlapping genes, Ras homolog gene family, member B (RHOB), complement factor H (CFH) and Krüppel-like factor 15 (KLF15), were selected. Valsartan with RHOB, and fosinopril with CFH and KLF15 had preferential binding activity. In conclusion, Jun, Ptgs2, Fn1, Cdk2, Fos, Hspa5, Hsp90b1, Hyou1, RHOB, CFH and KLF15 may be potential therapeutic targets for mesangial cells associated with DN, which may provide insight into DN treatment strategies.

Proteasome subunit-α type-6 protein is post-transcriptionally repressed by the microRNA-4490 in diabetic nephropathy

A common complication of both type I and type II diabetes is nephropathy, characterized by accumulation of extracellular matrix in the glomerular mesangium. This indicates a central role of mesangial cells in the pathophysiology of diabetic nephropathy. Using the proteomic approach, it was earlier elucidated in a rat model that the proteasome subunit-α type-6 protein (PSMA6) is suppressed in the renal cortex in nephropathic kidney. However, the underlying mechanism effecting suppression of PSMA6 protein in the renal cortex is not yet known. Twenty diabetic patients were enrolled and the expression level of PSMA6 in them was detected by immunohistochemistry. The protein and mRNA expression levels of PSMA6 in NRK-52E cells under high glucose condition were determined by Western blot and quantitative real-time PCR, respectively. Dual luciferase assay was used to detect the relationship of PSMA6 and miR-4490. Our results show that PSMA6 protein is down-regulated in patients with diabetic nephropathy compared with healthy control. Using the NRK-52E cell line cultured under high glucose condition as an in vitro model of diabetic nephropathy, we show that loss of PSMA6 protein expression occured independent of changes the in PSMA6 mRNA expression. We next elucidate that PSMA6 mRNA is post-transcriptionally regulated by the microRNA (miRNA)-4490, whose expression is inversely correlated to PSMA6 protein expression. Using reporter assays we show that PSMA6 is a direct target of the miR-4490. Exogenous manipulation of miR-4490 levels modulated expression of PSMA6, indicating that miR-4490 can be tested as a biomarker for nephropathy in diabetic patients.

Sex dimorphism in ANGII-mediated crosstalk between ACE2 and ACE in diabetic nephropathy

Angiotensin-converting enzyme (ACE) and ACE2 play a critical role in the renin-angiotensin system (RAS) by altering angiotensin II (ANGII) levels, thus governing its deleterious effects. Both enzymes are altered by sex and diabetes, and play an important role in the development of diabetic nephropathy (DN). Importantly, previous evidence in diabetic and ACE2-deficient (ACE2KO) males suggest a sex-dependent crosstalk between renal ACE and ACE2. In the present work, we aimed to study the sex-specific susceptibility to diabetes and direct infusion of ANGII in kidney disease progression, with a special focus on its link to ACE2 and ACE. In our mouse model, ANGII promoted hypertension, albuminuria, reduced glomerular filtration, and glomerular histological alterations. ANGII adverse effects were accentuated by diabetes and ACE2 deficiency, in a sex-dependent fashion: ACE2 deficiency accentuated ANGII-induced hypertension, albuminuria, and glomerular hypertrophy in diabetic females, whereas in diabetic males exacerbated ANGII-mediated glomerular hypertrophy, mesangial expansion, and podocyte loss. At the molecular level, ANGII downregulated renal ACE gene and enzymatic activity levels, as well as renin gene expression in ACE2KO mice. Interestingly, male sex and diabetes accentuated this effect. Here we show sex dimorphism in the severity of diabetes- and ANGII-related renal lesions, and demonstrate that ACE2- and ACE-related compensatory mechanisms are sex-specific. Supporting our previous findings, the modulation and ANGII-mediated crosstalk between ACE2 and ACE in DN progression was more evident in males. This work increases the understanding of the sex-specific role of ACE2 and ACE in DN, reinforcing the necessity of more personalized treatments targeting RAS.

TXNIP mediated the oxidative stress response in glomerular mesangial cells partially through AMPK pathway

BACKGROUND

Thioredoxin-interacting protein (TXNIP) plays an important role in the development of diabetic nephropathy. In the present study, we investigated role of TXNIP on oxidative stress in glomerular mesangial cells (GMCs) cultured in high glucose or normal glucose, and explored the potential mechanism related to TXNIP as well.

METHODS

Oxidative stress in GMCs under high or normal glucose was detected. TXNIP knockdown by specific siRNA or over expression by pcDNA3.0-TXNIP vector was performed to evaluate the role of TXNIP on injury of GMCs caused by oxidative stress. Activator of AMPK AICAR and AMPK inhibitor Compound C were treated the GMCs. Reactive oxygen species (ROS) and mitochondrial membrane potential were detected by flow cytometry. Activities of superoxide dismutase (SOD) and superoxide dismutase (CAT) were measured by ELISA. Activity of thioredoxin (Trx) was determined using Trx activity assay kit. mRNA expression of AMPK, TXNIP, Trx1 and Trx2 were tested by qRT-PCR. Expressions of P-AMPK, TXNIP and fibronectin proteins were detected by Western blotting.

RESULTS

High glucose induced the increase of ROS level, activation of TXNIP, but restricted mitochondrial membrane potential and activities of p-AMPK, SOD and CAT, and Trx. TXNIP siRNA and AICAR inhibited high glucose-induced oxidative stress response in GMCs and fibronectin expression, but promoted cell viability. In contrast, pcDNA3.0-TXNIP and Compound C increased oxidative stress response in normal glucose cultured GMCs, but decreased cell viability. The combined effect of TXNIP siRNA and AICAR on the inhibition of oxidative stress was obviously stronger than that of single use of TXNIP siRNA.

CONCLUSION

TXNIP facilitates the oxidative stress response in GMCs partially through AMPK pathway, which may provide potential therapeutic target for diabetic nephropathy treatment.

Administration of cytokine-induced myeloid-derived suppressor cells ameliorates renal fibrosis in diabetic mice

Background

Diabetes is a proinflammatory state. Fibrosis of the renal glomerulus is the most common cause of end-stage renal disease. Glomerulosclerosis is caused by the accumulation of extracellular matrix (ECM) proteins in the mesangial interstitial space. Mesangial cells are unique stromal cells in the renal glomerulus that form the vascular pole of the renal corpuscle along with the mesangial matrix. Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cells that rapidly expand to regulate host immunity during inflammation, infection, and cancer. High concentrations of granulocyte–macrophage colony-stimulating factor (GM-CSF) alone or in combination with other molecules represent the most common ex-vivo protocol for differentiating MDSCs from bone marrow or from peripheral blood mononuclear cells. In this study, we analyzed and characterized the functions of MDSCs under the influence of mouse mesangial cells (MMCs) in a hyperglycemic environment and investigated whether cytokine-induced MDSCs ameliorated renal glomerulosclerosis in diabetic mice.

Methods

Cytokine-induced MDSCs were propagated from bone marrow cells cultured with mouse recombinant GM-CSF, IL-6, and IL-1β. Diabetic mice were induced with streptozotocin (STZ) and maintained at a blood glucose concentration exceeding 350 mg/dl. The ECM of the renal cortex and fibronectin expression of MMCs were analyzed through immunohistochemistry and western blotting. Arginase 1 and inducible NO synthase expressions of MDSCs were evaluated using quantitative reverse-transcriptase PCR. Cytokines released from MMCs were examined using a cytokine array assay.

Results

MDSCs in the diabetic mice were redistributed from the bone marrow into peripheral organs. An increase in fibronectin production was also observed in the renal glomerulus. MMCs in vitro produced more fibronectin and proinflammatory cytokines, such as macrophage inflammatory protein-2, RANTES, and stromal-cell-derived factor-1, under hyperglycemic conditions. The adoptive transfer of cytokine-induced MDSCs into STZ-induced mice normalized the glomerular filtration rate to reduce the kidney to body weight ratio and decrease fibronectin production in the renal glomerulus, ameliorating renal fibrosis. These results demonstrate the anti-inflammatory properties of cytokine-induced MDSCs and offer an alternative immunotherapy protocol for the management of diabetic nephropathy.

Conclusions

The application of cytokine-induced MDSCs provides a promising treatment for renal fibrosis and the prevention of diabetic nephropathy.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0915-0) contains supplementary material, which is available to authorized users.

Carnosine scavenging of glucolipotoxic free radicals enhances insulin secretion and glucose uptake

The worldwide prevalence of diabetes has risen to 8.5% among adults, which represents a staggering rise in prevalence from 4.7% in 1980. Whilst some treatments work by increasing insulin secretion, over time their effectiveness decreases. We aim to increase insulin secretion by developing strategies that work through mechanisms independent of current treatment options. Isolated CD1 mouse islets, INS-1 pancreatic β-cells, or C2C12 mouse myotubes were incubated in standard tissue culture media, or media supplemented with 28 mM glucose, 200 μM palmitic acid, and 200 μM oleic acid as a cellular model of diabetic glucolipotoxicity. Intracellular reactive species content was assayed using 2′,7′-dichlorofluorescein diacetate dye, inducible nitric oxide synthase levels determined by Western blot, 3-nitrotyrosine and 4-hydrpxnonenal both assayed by ELISA, insulin secretion quantified using ELISA or radioimmunoassay, and glucose uptake determined through 2-deoxy glucose 6 phosphate luminescence. Our data indicate that carnosine, a histidine containing dipeptide available through the diet, is an effective scavenger of each of the aforementioned reactive species. This results in doubling of insulin secretion from isolated mouse islets or INS-1 β-cells. Crucially, carnosine also reverses glucolipotoxic inhibition of insulin secretion and enhances glucose uptake into skeletal muscle cells. Thus, carnosine, or non-hydrolysable carnosine analogs, may represent a new class of therapeutic agent to fight type 2 diabetes.

Diabetes and risk of Kaposi's sarcoma: effects of high glucose on reactivation and infection of Kaposi's sarcoma-associated herpesvirus

Patients with diabetes are generally prone to pathogen infection and tumor progression. Here, we investigated the potential association between diabetes and Kaposi's sarcoma (KS), a tumor linked to infection with Kaposi's sarcoma-associated herpesvirus (KSHV). By using Taiwan's National Health Insurance Research Database, we found that diabetes is statistically associated with increased risk of KS in a case-control study. Since a high level of blood sugar is the hallmark of diabetes, we determined whether high glucose promotes both KSHV reactivation and infection, which are crucial for KS pathogenesis. Our results showed that high glucose significantly increases lytic reactivation of KSHV but not Epstein-Barr virus, another related human oncogenic gammaherpesvirus, in latently infected cells. Activation of the transcription factor AP1 by high glucose is critically required for the onset of KSHV lytic reactivation. We also demonstrated that high glucose enhances susceptibility of various target cells to KSHV infection. Particularly, in endothelial and epithelial cells, levels of specific cellular receptors for KSHV entry, including integrin α3β1 and xCT/CD98, are elevated under high glucose conditions, which correlate with the enhanced cell susceptibility to infection. Taken together, our studies implicate that the high-glucose microenvironment may be an important predisposing factor for KS development.

Cellular and Molecular Mechanisms of Diabetic Atherosclerosis: Herbal Medicines as a Potential Therapeutic Approach

An increasing number of patients diagnosed with diabetes mellitus eventually develop severe coronary atherosclerosis disease. Both type 1 and type 2 diabetes mellitus increase the risk of cardiovascular disease associated with atherosclerosis. The cellular and molecular mechanisms affecting the incidence of diabetic atherosclerosis are still unclear, as are appropriate strategies for the prevention and treatment of diabetic atherosclerosis. In this review, we discuss progress in the study of herbs as potential therapeutic agents for diabetic atherosclerosis.

Tongxinluo Inhibits Renal Fibrosis in Diabetic Nephropathy: Involvement of the Suppression of Intercellular Transfer of TGF-β1-Containing Exosomes from GECs to GMCs

Glomerular mesangial cells (GMCs) activation is implicated in the pathogenesis of diabetic nephropathy (DN). Our previous study revealed that high glucose (HG)-treated glomerular endothelial cells (GECs) produce an increased number of TGF-[Formula: see text]1-containing exosomes to activate GMCs through the TGF-[Formula: see text]1/Smad3 signaling pathway. We also identified that Tongxinluo (TXL), a traditional Chinese medicine, has beneficial effects on the treatment of DN in DN patients and type 2 diabetic mice. However, it remained elusive whether TXL could ameliorate renal structure and function through suppression of intercellular transfer of TGF-[Formula: see text]1-containing exosomes from GECs to GMCs. In this study, we demonstrate that TXL can inhibit the secretion of TGF-[Formula: see text]1-containing exosomes from HG-treated GECs. Furthermore, exosomes produced by HG induced-GECs treated with TXL cannot trigger GMC activation, proliferation and extracellular matrix (ECM) overproduction both in vitro and in vivo. These results suggest that TXL can prevent the transfer of TGF-[Formula: see text]1 from GECs to GMCs via exosomes, which may be one of the mechanisms of TXL in the treatment of DN.

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.

The promotion of nephropathy by Porphyromonas gingivalis lipopolysaccharide via toll-like receptors

BACKGROUND

Recently, we reported that toll-like receptor (TLR)2 and TLR4 localized on the glomerular endothelium in the glomeruli of streptozotocin (STZ)-induced type 1 diabetic mice and high fat diet feed-induced type 2 diabetic mice, and that periodontal pathogen Porphyromonas gingivalis LPS (Pg-LPS) administration lowered the survival rate of diabetic mice. The present study aims to examine the effect of TLR4 blocking on the suppression of Pg-LPS-induced diabetic nephropathy.

METHODS

The survival rate and morphological/biochemical features for streptozotocin-induced diabetic mice with Pg-LPS and TLR4 blocker eritoran administration were investigated by reporter gene assay, urine and blood analysis, immunohistochemistry, and real time-PCR.

RESULTS AND CONCLUSIONS

All of the diabetic mice administered Pg-LPS were euthanized within the survival period of almost all of the diabetic mice. The blood urea nitrogen and creatinine, expression of TLR2 and TGF-b, and type 1 collagen accumulation, in the diabetic mice increased significantly with the Pg-LPS administration. In spite of the limited TLR4 activation with Pg-LPS, the TLR4 blocker eritoran decreased blood urea nitrogen and creatinine, and raised the survival rate of the Pg-LPS-administered diabetic mice slightly. The high expression levels of TLR2, TGF-b, and type 1 collagen in Pg-LPS-administered diabetic mice decreased with eritoran. Nuclear STAT3 which enhances TLR2 expression was detected in the TLR2-expressing glomeruli of diabetic mice. The TLR2 and STAT3 gene expression increased by the Pg-LPS administration but decreased with eritoran. These may suggest that Pg-LPS-induced diabetic nephropathy is mainly dependent on TLR2 signaling on glomerular endothelial cells, and that TLR4 blocker eritoran may play a role to slow the progress of diabetic nephropathy.

Developing Treatments for Chronic Kidney Disease in the 21st Century

Chronic kidney disease (CKD) is a lethal and rapidly increasing burden on society. Despite this, there are relatively few therapies in development for the treatment of CKD. Several recent costly phase 3 trials have failed to provide improved renal outcomes, diminishing interest in pharmaceutical investment. Furthermore, poor patient, physician, and payer awareness of CKD as a diagnosis has contributed to slow trial enrollment and successful implementation of these trials. Nevertheless, several therapeutics remain in development for the treatment of CKD, including mineralocorticoid-receptor antagonists, sodium/glucose cotransporter 2 inhibitors, anti-inflammatory drugs, and drugs that mitigate oxidative injury. Success of future CKD therapeutic trials will depend not only on improved understanding of disease pathogenesis, but also on improved trial enrollment rates, through increasing awareness of this disease by the public, policy makers, and the greater medical community.

The Effect of Short-Term Hyperglycemia on the Innate Immune System

BACKGROUND

Diabetes mellitus increases the susceptibility to infection by altering both the innate and the adaptive immune systems. Hyperglycemia has been associated with adverse outcomes in hospitalized patients, especially critically ill patients; these poor outcomes are explained in part by hospital-associated infections.

MATERIALS AND METHODS

PubMed, EMBASE and Google Scholar were searched to identify studies published between 1970 and 2014 reporting short-term effects of hyperglycemia on the innate immune system. MeSH database search terms included hyperglycemia, immune system, inflammation, inflammation mediators, neutrophils, endothelial dysfunction, complement system proteins and diabetes. Pertinent articles reported studies in healthy volunteers and diabetic patients, using in vitro laboratory experiments, and with animal models.

RESULTS

Hyperglycemia activates protein kinase C, and this inhibits neutrophil migration, phagocytosis, superoxide production and microbial killing. High glucose concentrations decrease the formation of neutrophil extracellular traps. Hyperglycemia can also induce Toll-like receptor expression and inhibit neutrophil function and apoptosis. High glucose concentrations decrease vascular dilation and increase permeability during the initial inflammatory responses, possibly through protein kinase C activation. Hyperglycemia can cause direct glycosylation of proteins and alter the tertiary structure of complement; these changes inhibit immunoglobulin-mediated opsonization of bacteria and complement fixation to bacteria and decreases phagocytosis. Hyperglycemia also stimulates the production and release of cytokines. Several trials have demonstrated that better glycemic control reduces nosocomial infections in critically ill patients and surgical site infections.

CONCLUSIONS

In summary, acute hyperglycemia can significantly alter innate immune responses to infection, and this potentially explains some of the poor outcomes in hospitalized patients who develop hyperglycemia.

High glucose induces platelet-derived growth factor-C via carbohydrate response element-binding protein in glomerular mesangial cells

Persistent high concentration of glucose causes cellular stress and damage in diabetes via derangement of gene expressions. We previously reported high glucose activates hypoxia‐inducible factor‐1α and downstream gene expression in mesangial cells, leading to an extracellular matrix expansion in the glomeruli. A glucose‐responsive transcription factor carbohydrate response element‐binding protein (ChREBP) is a key mediator for such perturbation of gene regulation. To provide insight into glucose‐mediated gene regulation in mesangial cells, we performed chromatin immunoprecipitation followed by DNA microarray analysis and identified platelet‐derived growth factor‐C (PDGF‐C) as a novel target gene of ChREBP. In streptozotocin‐induced diabetic mice, glomerular cells showed a significant increase in PDGF‐C expression; the ratio of PDGF‐C‐positive cells to the total number glomerular cells demonstrated more than threefold increase when compared with control animals. In cultured human mesangial cells, high glucose enhanced expression of PDGF‐C protein by 1.9‐fold. Knock‐down of ChREBP abrogated this induction response. Upregulated PDGF‐C contributed to the production of type IV and type VI collagen, possibly via an autocrine mechanism. Interestingly, urinary PDGF‐C levels in diabetic model mice were significantly elevated in a fashion similar to urinary albumin. Taken together, we hypothesize that a high glucose‐mediated induction of PDGF‐C via ChREBP in mesangial cells contributes to the development of glomerular mesangial expansion in diabetes, which may provide a platform for novel predictive and therapeutic strategies for diabetic nephropathy.

Calcium-permeable ion channels in the kidney

Calcium ions (Ca(2+)) are crucial for a variety of cellular functions. The extracellular and intracellular Ca(2+) concentrations are thus tightly regulated to maintain Ca(2+) homeostasis. The kidney, one of the major organs of the excretory system, regulates Ca(2+) homeostasis by filtration and reabsorption. Approximately 60% of the Ca(2+) in plasma is filtered, and 99% of that is reabsorbed by the kidney tubules. Ca(2+) is also a critical signaling molecule in kidney development, in all kidney cellular functions, and in the emergence of kidney diseases. Recently, studies using genetic and molecular biological approaches have identified several Ca(2+)-permeable ion channel families as important regulators of Ca(2+) homeostasis in kidney. These ion channel families include transient receptor potential channels (TRP), voltage-gated calcium channels, and others. In this review, we provide a brief and systematic summary of the expression, function, and pathological contribution for each of these Ca(2+)-permeable ion channels. Moreover, we discuss their potential as future therapeutic targets.

The kidney and type 2 diabetes mellitus: therapeutic implications of SGLT2 inhibitors

Understanding the role of the kidneys in type 2 diabetes mellitus (T2DM) has taken on an increased importance in recent years with the arrival of sodium-glucose co-transporter 2 (SGLT2) inhibitors - antihyperglycemic agents (AHAs) that specifically target the kidneys. This review includes an update on the physiology of the kidneys, their role in the pathophysiology of T2DM, and the mechanisms implicated in the development and progression of diabetic kidney disease, such as glomerular hyperfiltration and inflammation. It also discusses renal issues that could influence the choice of AHA for patients with T2DM, including special populations such as patients with concomitant chronic kidney disease. The most recent data published on the clinical efficacy and safety of the SGLT2 inhibitors canagliflozin, dapagliflozin, and empagliflozin and their effects on renal function are presented, showing how the renally mediated mechanisms of action of these agents translate into clinical benefits, including the potential for renoprotection. The observed positive effects of these agents on measures such as glucose control, estimated glomerular filtration rate, albumin-to-creatinine ratio, blood pressure, and body weight in patients both with and without impaired renal function suggest that SGLT2 inhibitors represent an important extension to the diabetes treatment armamentarium.

Protection from diabetes-induced atherosclerosis and renal disease by D-carnosine-octylester: effects of early vs late inhibition of advanced glycation end-products in Apoe-null mice

AIMS/HYPOTHESIS

AGEs are involved in diabetic complications and might be responsible for the phenomenon of 'hyperglycaemic memory'. D-Carnosine-octylester (DCO) has been shown to attenuate AGE formation and vascular and renal injury induced by high-fat diet in Apoe-null mice. This study aimed to verify the protective effect of DCO in atherosclerosis and renal disease induced by experimental diabetes and to discover whether reduction of AGE formation by early vs late DCO treatment provides better macro and microvascular protection.

METHODS

Apoe-null mice were rendered diabetic by streptozotocin and were left untreated or were treated with DCO for 20 weeks (DCO-Extended), from week 1 to 11 (DCO-Early) or from week 9 to 19 (DCO-Late). Non-diabetic Apoe-null mice served as controls. Aortic and renal lesions were evaluated by morphometry and protein and gene expression of disease markers were assessed by immunohistochemistry and real-time PCR.

RESULTS

DCO-Extended treatment produced a more stable plaque phenotype by markedly attenuating diabetes-induced increases in lesion size, necrotic core area and plaque content of Nε-carboxymethyllysine, levels of apoptotic cells and markers of inflammation and oxidative stress and also reductions in collagen and smooth muscle cells. DCO treatment for 11 weeks afforded partial protection and this was significantly better in DCO-Early mice than in DCO-Late mice. Renal disease was attenuated in DCO-Extended mice and to a lesser extent in those treated for 11 weeks, with no significant difference between DCO-Early mice and DCO-Late mice.

CONCLUSIONS/INTERPRETATION

These data show that DCO protects mice from diabetes-induced vascular and renal disease and that protection against atherosclerosis is more effectively achieved by early treatment than by late treatment, thus suggesting that early inhibition of AGE formation attenuates progression of macroangiopathy and favours development of more stable lesions.

Expression of toll-like receptor 2 in glomerular endothelial cells and promotion of diabetic nephropathy by Porphyromonas gingivalis lipopolysaccharide

The toll-like receptor (TLR) has been suggested as a candidate cause for diabetic nephropathy. Recently, we have reported the TLR4 expression in diabetic mouse glomerular endothelium. The study here investigates the effects of the periodontal pathogen Porphyromonas gingivalis lipopolysaccharide (LPS) which is a ligand for TLR2 and TLR4 in diabetic nephropathy. In laser-scanning microscopy of glomeruli of streptozotocin- and a high fat diet feed-induced type I and type II diabetic mice, TLR2 localized on the glomerular endothelium and proximal tubule epithelium. The TLR2 mRNA was detected in diabetic mouse glomeruli by in situ hybridization and in real-time PCR of the renal cortex, the TLR2 mRNA amounts were larger in diabetic mice than in non-diabetic mice. All diabetic mice subjected to repeated LPS administrations died within the survival period of all of the diabetic mice not administered LPS and of all of the non-diabetic LPS-administered mice. The LPS administration promoted the production of urinary protein, the accumulation of type I collagen in the glomeruli, and the increases in IL-6, TNF-α, and TGF-β in the renal cortex of the glomeruli of the diabetic mice. It is thought that blood TLR ligands like Porphyromonas gingivalis LPS induce the glomerular endothelium to produce cytokines which aid glomerulosclerosis. Periodontitis may promote diabetic nephropathy.

Akt and RhoA activation in response to high glucose require caveolin-1 phosphorylation in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic renal disease. Serine/threonine kinase PKC-β1 mediates glucose-induced Akt S473 phosphorylation, RhoA activation, and transforming growth factor (TGF)-β1 upregulation and finally leads to matrix upregulation in mesangial cells (MCs). It has been reported that glucose-induced PKC-β1 activation is dependent on caveolin-1 and the presence of intact caveolae in MCs; however, whether activated PKC-β1 regulates caveolin-1 expression and phosphorylation are unknown. Here, we showed that, although the caveolin-1 protein level had no significant change, the PKC-β-specific inhibitor LY-333531 blocked caveolin-1 Y14 phosphorylation in high glucose (HG)-treated MCs and in the renal cortex of diabetic rats. The Src-specific inhibitor SU-6656 prevented the HG-induced association between PKC-β1 and caveolin-1 and PKC-β1 membrane translocation, whereas PKC-β1 small interfering RNA failed to block Src activation, indicating that Src kinase is upstream of PKC-β1 activation. Although LY-333531 blocked PKC-β1 membrane translocation, it had no effect on the PKC-β1/caveolin-1 association, suggesting that PKC-β1 activation requires the interaction of caveolin-1 and PKC-β1. PKC-β1-mediated Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation in response to HG were prevented by SU-6656 and nonphosphorylatable mutant caveolin-1 Y14A. In conclusion, Src activation by HG mediates the PKC-β1/caveolin-1 association and PKC-β1 activation, which assists in caveolin-1 Y14 phosphorylation by Src kinase. The downstream effects, including Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation, require caveolin-1 Y14 phosphorylation. Caveolin-1 is thus an important mediator of the profibrogenic process in diabetic renal disease.

Increase in AMPK brought about by cocoa is renoprotective in experimental diabetes mellitus by reducing NOX4/TGFβ-1 signaling

The aims of the present study were to investigate, in diabetes mellitus (DM), the mechanism of NOX4 up-regulation, its link with 5' adenosine monophosphate-activated protein kinase (AMPK) inactivation and transforming growth factor (TGF) ß-1 signaling in determining the accumulation of kidney extracellular matrix (ECM), and the possible action of cocoa enriched with polyphenols (CH) in these events. After 16 weeks of DM, spontaneously hypertensive rats showed increased kidney TGFβ-1 levels and expression of phosphorylated smad2, collagen IV and fibronectin in parallel with elevated NOX4 expression and reduced phosphorylated AMPK. CH treatment in diabetic rats prevented all of these abnormalities. In immortalized human mesangial cells exposed to high glucose (HG), or TGFβ-1, CH, nicotinamide adenine dinucleotide phosphate blocker, or silencing NOX4 ameliorated enhanced phosphorylated smad2 and collagen IV. Reduction in phosphorylated AMPK induced by HG or TGFβ-1 was ameliorated by CH or activation of AMPK, which reduced phosphorylation of smad2 and collagen IV via reduction in NOX4 expression. The effects of CH were abolished by AMPK blockade. These results suggest that inactivation in AMPK leads to NOX4 up-regulation, activation of TGFβ-1 signaling and increased ECM accumulation. Additionally, increased TGF-ß1 per se leads to the amplification of ECM production by reducing AMPK and promoting the activation of NOX4. It is suggested that the activation of AMPK by CH followed by reduction in NOX4/TGFβ-1 signaling may have a therapeutic potential in diabetic nephropathy.

p21(WAF1/CIP1) Expression is Differentially Regulated by Metformin and Rapamycin

The mammalian target of rapamycin (mTOR) pathway plays an important role in the development of diabetic nephropathy and other age-related diseases. One of the features of DN is the elevated expression of p21^WAF1/CIP1. However, the importance of the mTOR signalling pathway in p21 regulation is poorly understood. Here we investigated the effect of metformin and rapamycin on mTOR-related phenotypes in cell lines of epithelial origin. This study reports that metformin inhibits high glucose-induced p21 expression. High glucose opposed metformin in regulating cell size, proliferation, and protein synthesis. These effects were associated with reduced AMPK activation, affecting downstream mTOR signalling. However, the inhibition of the mTOR pathway by rapamycin did not have a negative effect on p21 expression, suggesting that metformin regulates p21 upstream of mTOR. These findings provide support for the hypothesis that AMPK activation may regulate p21 expression, which may have implications for diabetic nephropathy and other age-related pathologies.

Heparin prevents intracellular hyaluronan synthesis and autophagy responses in hyperglycemic dividing mesangial cells and activates synthesis of an extensive extracellular monocyte-adhesive hyaluronan matrix after completing cell division

Growth-arrested rat mesangial cells (RMCs) at a G0/G1 interphase stimulated to divide in hyperglycemic medium initiate intracellular hyaluronan synthesis that induces autophagy/cyclin D3-induced formation of a monocyte-adhesive extracellular hyaluronan matrix after completing cell division. This study shows that heparin inhibits the intracellular hyaluronan synthesis and autophagy responses, but at the end of cell division it induces synthesis of a much larger extracellular monocyte-adhesive hyaluronan matrix. Heparin bound to RMC surfaces by 1 h, internalizes into the Golgi/endoplasmic reticulum region by 2 h, and was nearly gone by 4 h. Treatment by heparin for only the first 4 h was sufficient for its function. Streptozotocin diabetic rats treated daily with heparin showed similar results. Glomeruli in sections of diabetic kidneys showed extensive accumulation of autophagic RMCs, increased hyaluronan matrix, and influx of macrophages over 6 weeks. Hyaluronan staining in the glomeruli of heparin-treated diabetic rats was very high at week 1 and decreased to near control level by 6 weeks without any RMC autophagy. However, the influx of macrophages by 6 weeks was as pronounced as in diabetic glomeruli. The results are as follows: 1) heparin blocks synthesis of hyaluronan in intracellular compartments, which prevents the autophagy and cyclin D3 responses thereby allowing RMCs to complete cell division and sustain function; 2) interaction of heparin with RMCs in early G1 phase is sufficient to induce signaling pathway(s) for its functions; and 3) influxed macrophages effectively remove the hyaluronan matrix without inducing pro-fibrotic responses that lead to nephropathy and proteinurea in diabetic kidneys.

O-GlcNAcylation and Inflammation: A Vast Territory to Explore

O-GlcNAcylation is a reversible post-translational modification that regulates the activities of cytosolic and nuclear proteins according to glucose availability. This modification appears to participate in several hyperglycemia-associated complications. An important feature of metabolic diseases such as diabetes and obesity is the presence of a low-grade chronic inflammation that causes numerous complications. Hyperglycemia associated with the metabolic syndrome is known to promote inflammatory processes through different mechanisms including oxidative stress and abnormally elevated protein O-GlcNAcylation. However, the role of O-GlcNAcylation on inflammation remains contradictory. O-GlcNAcylation associated with hyperglycemia has been shown to increase nuclear factor κB (NFκB) transcriptional activity through different mechanisms. This could contribute in inflammation-associated diabetic complications. However, in other conditions such as acute vascular injury, O-linked N-acetyl glucosamine (O-GlcNAc) also exerts anti-inflammatory effects via inhibition of the NFκB pathway, suggesting a complex regulation of inflammation by O-GlcNAc. Moreover, whereas macrophages and monocytes exposed to high glucose for a long-term period developed a pro-inflammatory phenotype, the impact of O-GlcNAcylation in these cells remains unclear. A future challenge will be to clearly establish the role of O-GlcNAcylation in pro- and anti-inflammatory functions in macrophages.

Inhibition of Src kinase blocks high glucose-induced EGFR transactivation and collagen synthesis in mesangial cells and prevents diabetic nephropathy in mice

Chronic exposure to high glucose leads to diabetic nephropathy characterized by increased mesangial matrix protein (e.g., collagen) accumulation. Altered cell signaling and gene expression accompanied by oxidative stress have been documented. The contribution of the tyrosine kinase, c-Src (Src), which is sensitive to oxidative stress, was examined. Cultured rat mesangial cells were exposed to high glucose (25 mmol/L) in the presence and absence of Src inhibitors (PP2, SU6656), Src small interfering RNA (siRNA), and the tumor necrosis factor-α-converting enzyme (TACE) inhibitor, TAPI-2. Src was investigated in vivo by administration of PP2 to streptozotocin (STZ)-induced diabetic DBA2/J mice. High glucose stimulated Src, TACE, epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK1/2, p38), and collagen IV accumulation in mesangial cells. PP2 and SU6656 blocked high glucose-stimulated phosphorylation of Src Tyr-416, EGFR, and MAPKs. These inhibitors and Src knockdown by siRNA, as well as TAPI-2, also abrogated high glucose-induced phosphorylation of these targets and collagen IV accumulation. In STZ-diabetic mice, albuminuria, increased Src pTyr-416, TACE activation, ERK and EGFR phosphorylation, glomerular collagen accumulation, and podocyte loss were inhibited by PP2. These data indicate a role for Src in a high glucose-Src-TACE-heparin-binding epidermal growth factor-EGFR-MAPK-signaling pathway to collagen accumulation. Thus, Src may provide a novel therapeutic target for diabetic nephropathy.

Altered dynamics in the renal lymphatic circulation of type 1 and type 2 diabetic mice

The dynamics of the renal lymphatic circulation in diabetic nephropathy is not fully elucidated. The present study evaluated the effect of diabetic nephropathy on the renal lymphatic circulation in streptozotocin (STZ)-induced type 1 diabetic mice (ICR-STZ) and in type 2 diabetic KK/Ta mice which were fed a high fat diet (KK/Ta-HF). The diabetic mouse kidneys developed edema because of the nephropathy. In control mice renal lymphatic vessels distributed in the cortex but rarely in the medulla while in ICR-STZ and KK/Ta-HF mice, there were many lymphatic vessels with small lumen in both cortex and medulla. Total numbers and areas of renal blood vessels in the diabetic mice were similar to those in the controls while the total numbers and areas of renal lymphatic vessels were larger in diabetic mice than in the controls. There were statistically significant differences in the numbers of lymphatic vessels with diameters of 50–100 µm between the ICR-STZ and the control ICR mice, and in the numbers of lymphatic capillaries with diameters smaller than 50 µm between the KK/Ta-HF and the control KK/Ta mice. The diabetic nephropathy may induce the lymphangiogenesis or result in at least the renal lymphatic vessel expansion.

Transforming growth factor beta 1 and monocyte chemoattractant protein-1 as prognostic markers of diabetic nephropathy

We aimed to find the relationship between serum transforming growth factor beta 1(TGF-β1) and urinary monocyte chemoattractant protein-1 (MCP-1) throughout the course of diabetic nephropathy (DN) and to assess the relationship between both levels and other parameters of renal injury such as albumin/creatinine ratio and estimated glomerular filtration rate (eGFR). Serum TGF-β1, urinary MCP-1, eGFR, and glycosylated hemoglobin (HbA1c) were measured in 60 patients with type II diabetes mellitus with different degrees of nephropathy (20 patients with normoalbuminuria, 20 patients with microalbuminuria, and 20 patients with macroalbuminuria) and compared with 20 matched healthy control subjects. Both the levels of serum TGF-β1 and urinary MCP-1 were significantly higher in patients with micro- and macroalbuminuria (137.8 ± 69.5 and 329.25 ± 41.46 ng/dl, respectively, for TGF-β1 and 167.41 ± 50.23 and 630.87 ± 318.10 ng/g creatinine, respectively, for MCP-1) compared with normoalbuminuric patients and healthy controls (33.25 ± 17.5 and 29.64 ± 10.57 ng/dl, respectively, for TGF-β1 and 63.85 ± 21.15 and 61.50 ± 24.81 ng/g creatinine, respectively, for MCP-1; p < 0.001). There was a positive significant correlation between the levels of serum TGF-β1 and those of urinary MCP-1 ( r = 0.73, p < 0.001). Also, serum TGF-β1 and urinary MCP-1 correlated positively with HbA1c ( r = 0.49 and 0.55, respectively, p < 0.05 for both) and inversely with eGFR ( r = −0.69 and −0.60, respectively, p < 0.001 for both). We can conclude that serum TGF-β1 and urinary MCP-1 can be used as the markers for detection of progression of DN. Antagonizing TGF-β1 and MCP-1 might be helpful in attenuating the progression of nephropathy in diabetic patients.

Expression of Toll-Like Receptor 4 in Glomerular Endothelial Cells under Diabetic Conditions

Diabetic conditions promote glomerulosclerosis by mesangial cells but the mechanisms are not fully elucidated. The present study evaluated the expression of toll-like receptor 4 in glomerular endothelial cells in the streptozotocin (STZ)-induced type 1 diabetic mouse (ICR-STZ) and the type 2 diabetic KK/TaJcl mouse which were fed a high fat diet feed (KK/Ta-HF). In the ICR-STZ and KK/Ta-HF almost glomeruli were immunostained with anti-TLR4 but there was no glomerulus immunostained by ani-TLR4 in the control ICR and KK/Ta. Laser-scanning confocal microscopy showed that the TLR4-positive region did not coincide with the podoplanin-positive region but coincide with the PECAM-1- and VE-cadherin-positive regions in the glomeruli of the ICR-STZ and KK/Ta-HF. The in situ hybridization showed that almost signals for TLR4 mRNA were present in the glomerulus of the ICR-STZ and KK/Ta-HF to a stronger extent than in the control ICR and KK/Ta. These suggest that glomerular endothelial cells usually express the TLR4 gene and hyperglycemia in the diabetic condition induces the TLR4 protein expression in the glomerular capillary endothelial cells. Cytokine productions through the TLR signaling pathway in glomerular endothelial cells may allow mesangial cells to produce extracellular matrix proteins in the diabetic milieu.

Molecular mechanisms in the pathogenesis of diabetic nephropathy: an update

Diabetes mellitus is known to trigger retinopathy, neuropathy and nephropathy. Diabetic nephropathy, a long-term major microvascular complication of uncontrolled hyperglycemia, affects a large population worldwide. Recent findings suggest that numerous pathways are activated during the course of diabetes mellitus and that these pathways individually or collectively play a role in the induction and progression of diabetic nephropathy. However, clinical strategies targeting these pathways to manage diabetic nephropathy remain unsatisfactory, as the number of diabetic patients with nephropathy is increasing yearly. To develop ground-breaking therapeutic options to prevent the development and progression of diabetic nephropathy, a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of the disease is mandatory. Therefore, the purpose of this paper is to discuss the underlying mechanisms and downstream pathways involved in the pathogenesis of diabetic nephropathy.

Hyperglycemia induces Toll like receptor 4 expression and activity in mouse mesangial cells: relevance to diabetic nephropathy

Diabetes is a proinflammatory state. The pattern recognition receptors, Toll-like receptors (TLRs), are increased in diabetic patients and have been suggested to play a role in diabetic nephropathy (DN). Progression of DN involves altered mesangial cell (MC) function with an expansion of the mesangial matrix. There is a paucity of data examining the role of TLR and its expression in MC. We hypothesize the expression of TLRs in the mesangium might be an important factor contributing to mesangium expansion and nephropathy. Thus we evaluated the effect of high glucose on TLR2 and TLR4 expression in mouse mesangial cells (MMC) in vitro. Exposure of MMC to 25 mM glucose for 24 h resulted in increased TLR4 mRNA and cell surface receptor expression compared with 5.5 mM glucose (P < 0.05). Interestingly, we were not able to detect expression of TLR2 in MMC. Furthermore, expression of a TLR4 downstream signaling cascade including myeloid differentiation factor 88 (MyD88), interferon regulatory factor 3 (IRF3), and Toll interleukin receptor domain containing adaptor inducing interferon-β (TRIF)-related adaptor molecule (TRAM) were significantly increased in cells exposed to 25 mM glucose (P < 0.05). There was also a significant increase in NF-κB activation along with increased secretion of inflammatory cytokines IL-6 and monocyte chemotactic protein-1. Levels of transforming growth factor-β were also significantly increased in the presence of 25 mM glucose (P < 0.05). Collectively, these data suggest that hyperglycemia activates TLR4 expression and activity in MC and could contribute to DN.

Tinospora cordifolia consumption ameliorates changes in kidney chondroitin sulphate/dermatan sulphate in diabetic rats

Diabetes is known to alter kidney extracellular matrix (ECM) components. Chondroitin sulphate (CS)/dermatan sulphate (DS), an ECM component, which plays an essential role in kidney is altered during diabetes. The focus of this study has been to examine the effect of Tinospora cordifolia (TC) consumption, a potent plant widely used to treat diabetes, on kidney CS/DS. Experimentally induced diabetic rats were fed with diet containing TC at 2·5 and 5 % levels and the effect of it on kidney CS/DS was examined. The CS/DS content and CS:heparan sulphate ratio which was decreased during diabetic condition were ameliorated in TC-fed groups. Disaccharide composition analysis of CS/DS by HPLC showed that decreases in 'E' units and degree of sulphation were modulated in 5 % TC-fed groups. Apparent molecular weight of purified CS/DS from the control rat kidney was found to be 38 kDa which was decreased to 29 kDa in diabetic rat kidney. Rats in 5 % TC-fed groups showed chain length of 38 kDa akin to control rats. Expression of chondroitin 4-O-sulfotransferase-1, dermatan 4-O-sulfotransferase-1 and N-acetylgalactosamine 4 sulphate 6-O-sulfotransferase, enzymes involved in the synthesis of 'E' units which was reduced during diabetic condition, was significantly contained in the 5 % TC-fed group. Purified CS/DS from 5 % TC-fed group was able to bind higher amounts of ECM components, namely type IV collagen and laminin, when compared with untreated diabetic rats. The present results demonstrate that consumption of a diet containing TC at the 5 % level modulates changes in kidney CS/DS which were due to diabetes.

Genipin inhibits mitochondrial uncoupling protein 2 expression and ameliorates podocyte injury in diabetic mice

Diabetic nephropathy (DN) is one of the most common causes of end stage renal disease (ESRD) in China, which requires renal replacement therapy. Recent investigations have suggested an essential role of podocyte injury in the initial stage of DN. This study investigated the potential therapeutic role of genipin, an active extract from a traditional Chinese medicine, on progression of DN in diabetic mice induced by intraperitoneally injection of streptozocin (STZ). In diabetic mice, orally administration of genipin postponed the progression of DN, as demonstrated by ameliorating body weight loss and urine albumin leakage, attenuating glomerular basement membrane thickness, restoring the podocyte expression of podocin and WT1 in diabetic mice. The protective role of genipin on DN is probably through suppressing the up-regulation of mitochondrial uncoupling protein 2 (UCP2) in diabetic kidneys. Meanwhile, through inhibiting the up-regulation of UCP2, genipin restores podocin and WT1 expression in cultured podocytes and attenuates glucose-induced albumin leakage through podocytes monolayer. Therefore, these results revealed that genipin inhibited UCP2 expression and ameliorated podocyte injury in DN mice.