Advanced glycation end-products suppress neuropilin-1 expression in podocytes

The Functions of SARS-CoV-2 Receptors in Diabetes-Related Severe COVID-19

Angiotensin-converting enzyme 2 (ACE2) is considered a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor of high importance, but due to its non-ubiquitous expression, studies of other proteins that may participate in virus internalisation have been undertaken. To date, many alternative receptors have been discovered. Their functioning may provide an explanation for some of the events observed in severe COVID-19 that cannot be directly explained by the model in which ACE2 constitutes the central point of infection. Diabetes mellitus type 2 (T2D) can induce severe COVID-19 development. Although many mechanisms associated with ACE2 can lead to increased SARS-CoV-2 virulence in diabetes, proteins such as basigin (CD147), glucose-regulated protein 78 kDa (GRP78), cluster of differentiation 4 (CD4), transferrin receptor (TfR), integrins α5β1/αvβ3, or ACE2 co-receptors neuropilin 2 (NRP2), vimentin, and even syalilated gangliosides may also be responsible for worsening the COVID-19 course. On the other hand, some others may play protective roles. Understanding how diabetes-associated mechanisms can induce severe COVID-19 via modification of virus receptor functioning needs further extensive studies.

Potential Effects of Hyperglycemia on SARS-CoV-2 Entry Mechanisms in Pancreatic Beta Cells

The COVID-19 pandemic has revealed a bidirectional relationship between SARS-CoV-2 infection and diabetes mellitus. Existing evidence strongly suggests hyperglycemia as an independent risk factor for severe COVID-19, resulting in increased morbidity and mortality. Conversely, recent studies have reported new-onset diabetes following SARS-CoV-2 infection, hinting at a potential direct viral attack on pancreatic beta cells. In this review, we explore how hyperglycemia, a hallmark of diabetes, might influence SARS-CoV-2 entry and accessory proteins in pancreatic β-cells. We examine how the virus may enter and manipulate such cells, focusing on the role of the spike protein and its interaction with host receptors. Additionally, we analyze potential effects on endosomal processing and accessory proteins involved in viral infection. Our analysis suggests a complex interplay between hyperglycemia and SARS-CoV-2 in pancreatic β-cells. Understanding these mechanisms may help unlock urgent therapeutic strategies to mitigate the detrimental effects of COVID-19 in diabetic patients and unveil if the virus itself can trigger diabetes onset.

SiJunZi decoction ameliorates bone quality and redox homeostasis and regulates advanced glycation end products/receptor for advanced glycation end products and WNT/β-catenin signaling pathways in diabetic mice

ETHNOPHARMACOLOGICAL RELEVANCE

SiJunZi decoction (SJZD), one of the traditional Chinese medicine formulas, has been clinically and traditionally used to improve glucose and lipid metabolism and promote bone remodeling.

AIM OF THE STUDY

To study the actions and mechanisms of SJZD on bone remodeling in a type 2 diabetes mouse model.

MATERIALS AND METHODS

Diabetic mice generated with a high-fat diet (HFD) and streptozotocin (STZ) were subjected to SJZD treatment for 8 weeks. Blood glucose and lipid profile, redox status and bone metabolism were determined by ELISA or biochemical assays. Bone quality was evaluated by micro-CT, three-point bending assay and Fourier transform infrared spectrum (FTIR). Bone histomorphometry alterations were evaluated by Hematoxylin-Eosin (H&E), tartrate resistant acid phosphatase (TRAP) staining and Safranin O-fast green staining. The expressions of superoxide dismutase 1 (SOD1), advanced glycation end products (AGEs), receptor for advanced glycosylation end products (RAGE), phosphorylated nuclear factor kappa-B (p-NF-κB), NF-κB, cathepsin K, semaphorin 3A (Sema3A), insulin-like growth factor 1 (IGF1), p-GSK-3β, (p)-β-catenin, Runt-related transcription factor 2 (Runx2) and Cyclin D1 in the femurs and/or tibias were examined by Western blot or immunohistochemical staining. The main constituents in the SJZD aqueous extract were characterized by a HPLC/MS.

RESULTS

SJZD intervention improved glucose and lipid metabolism and preserved bone quality in the diabetic mice, in particular glucose tolerance, lipid profile, bone microarchitecture, strength and material composition. SJZD administration to diabetic mice preserved redox homeostasis in serum and bone marrow, and prevented an increase in AGEs, RAGE, p-NF-κB/NF-κB, cathepsin K, p-GSK-3β, p-β-catenin expressions and a decrease in Sema3A, IGF1, β-catenin, Runx2 and Cyclin D1 expressions in tibias and/or femurs. Thirteen compounds were identified in SJZD aqueous extract, including astilbin, liquiritin apioside, ononin, ginsenoside Re, Rg1, Rb1, Rb2, Ro, Rb3, Rd, notoginsenoside R2, glycyrrhizic acid, and licoricesaponin B2.

CONCLUSIONS

SJZD ameliorates bone quality in diabetic mice possibly via maintaining redox homeostasis. The mechanism governing these alterations are possibly related to effects on the AGEs/RAGE and Wnt/β-catenin signaling pathways. SJZD may offer a novel source of drug candidates for the prevention and treatment of type 2 diabetes and osteoporosis.

An update on the interaction between COVID-19, vaccines, and diabetic kidney disease

Up to now, coronavirus disease 2019 (COVID-19) is still affecting worldwide due to its highly infectious nature anrapid spread. Diabetic kidney disease (DKD) is an independent risk factor for severe COVID-19 outcomes, and they have a certain correlation in some aspects. Particularly, the activated renin–angiotensin–aldosterone system, chronic inflammation, endothelial dysfunction, and hypercoagulation state play an important role in the underlying mechanism linking COVID-19 to DKD. The dipeptidyl peptidase-4 inhibitor is considered a potential therapy for COVID-19 and has similarly shown organ protection in DKD. In addition, neuropilin-1 as an alternative pathway for angiotensin-converting enzyme 2 also contributes to severe acute respiratory syndrome coronavirus 2 entering the host cells, and its decreased expression can affect podocyte migration and adhesion. Here, we review the pathogenesis and current evidence of the interaction of DKD and COVID-19, as well as focus on elevated blood glucose following vaccination and its possible mechanism. Grasping the pathophysiology of DKD patients with COVID-19 is of great clinical significance for the formulation of therapeutic strategies.

Comparative Proteomic Analysis of Liver Tissues and Serum in db/db Mice

Background and Aims: Non-alcoholic fatty liver disease (NAFLD) affects one-quarter of individuals worldwide. Liver biopsy, as the current reliable method for NAFLD evaluation, causes low patient acceptance because of the nature of invasive sampling. Therefore, sensitive non-invasive serum biomarkers are urgently needed. Results: The serum gene ontology (GO) classification and Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed the DEPs enriched in pathways including JAK-STAT and FoxO. GO analysis indicated that serum DEPs were mainly involved in the cellular process, metabolic process, response to stimulus, and biological regulation. Hepatic proteomic KEGG analysis revealed the DEPs were mainly enriched in the PPAR signaling pathway, retinol metabolism, glycine, serine, and threonine metabolism, fatty acid elongation, biosynthesis of unsaturated fatty acids, glutathione metabolism, and steroid hormone biosynthesis. GO analysis revealed that DEPs predominantly participated in cellular, biological regulation, multicellular organismal, localization, signaling, multi-organism, and immune system processes. Protein-protein interaction (PPI) implied diverse clusters of the DEPs. Besides, the paralleled changes of the common upregulated and downregulated DEPs existed in both the liver and serum were validated in the mRNA expression of NRP1, MUP3, SERPINA1E, ALPL, and ALDOB as observed in our proteomic screening. Methods: We conducted hepatic and serum proteomic analysis based on the leptin-receptor-deficient mouse (db/db), a well-established diabetic mouse model with overt obesity and NAFLD. The results show differentially expressed proteins (DEPs) in hepatic and serum proteomic analysis. A parallel reaction monitor (PRM) confirmed the authenticity of the selected DEPs. Conclusion: These results are supposed to offer sensitive non-invasive serum biomarkers for diabetes and NAFLD.

Neuropilin (NRPs) Related Pathological Conditions and Their Modulators

Neuropilin 1 (NRP1) represents one of the two homologous neuropilins (NRP, splice variants of neuropilin 2 are the other) found in all vertebrates. It forms a transmembrane glycoprotein distributed in many human body tissues as a (co)receptor for a variety of different ligands. In addition to its physiological role, it is also associated with various pathological conditions. Recently, NRP1 has been discovered as a coreceptor for the SARS-CoV-2 viral entry, along with ACE2, and has thus become one of the COVID-19 research foci. However, in addition to COVID-19, the current review also summarises its other pathological roles and its involvement in clinical diseases like cancer and neuropathic pain. We also discuss the diversity of native NRP ligands and perform a joint analysis. Last but not least, we review the therapeutic roles of NRP1 and introduce a series of NRP1 modulators, which are typical peptidomimetics or other small molecule antagonists, to provide the medicinal chemistry community with a state-of-the-art overview of neuropilin modulator design and NRP1 druggability assessment.

Glyoxal-Lysine Dimer, an Advanced Glycation End Product, Induces Oxidative Damage and Inflammatory Response by Interacting with RAGE

The glyoxal-lysine dimer (GOLD), which is a glyoxal (GO)-derived advanced glycation end product (AGE), is produced by the glycation reaction. In this study, we evaluated the effect of GOLD on the oxidative damage and inflammatory response in SV40 MES 13 mesangial cells. GOLD significantly increased the linkage with the V-type immunoglobulin domain of RAGE, a specific receptor of AGE. We found that GOLD treatment increased RAGE expression and reactive oxygen species (ROS) production in mesangial cells. GOLD remarkably regulated the protein and mRNA expression of nuclear factor erythroid 2-related factor 2 (NRF2) and glyoxalase 1 (GLO1). In addition, mitochondrial deterioration and inflammation occurred via GOLD-induced oxidative stress in mesangial cells. GOLD regulated the mitogen-activated protein kinase (MAPK) and the release of proinflammatory cytokines associated with the inflammatory mechanism of mesangial cells. Furthermore, oxidative stress and inflammatory responses triggered by GOLD were suppressed through RAGE inhibition using RAGE siRNA. These results demonstrate that the interaction of GOLD and RAGE plays an important role in the function of mesangial cells.

Diabetic Nephropathy and COVID-19: The Potential Role of Immune Actors

Nowadays, type II diabetes mellitus, more specifically ensuing diabetic nephropathy, and severe COVID-19 disease are known to be closely associated. The exact mechanisms behind this association are less known. An implication for the angiotensin-converting enzyme 2 remains controversial. Some researchers have started looking into other potential actors, such as neuropilin-1, mitochondrial glutathione, vitamin D, and DPP4. In particular, neuropilin-1 seems to play an important role in the underlying mechanism linking COVID-19 and diabetic nephropathy. We suggest, based on the findings in this review, that its up-regulation in the diabetic kidney facilitates viral entry in this tissue, and that the engagement of both processes leads to a depletion of neuropilin-1, which was demonstrated to be strongly associated with the pathogenesis of DN. More studies are needed to confirm this hypothesis, and research should be directed towards elucidating the potential roles of all these suggested actors and eventually discovering new therapeutic strategies that could reduce the burden of COVID-19 in patients with diabetic nephropathy.

Neuropilin 1: A Novel Entry Factor for SARS-CoV-2 Infection and a Potential Therapeutic Target

The novel coronavirus disease 2019 (COVID-19) pandemic is severely challenging the healthcare systems and economies of the world, which urgently demand vaccine and therapy development to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hence, advancing our understanding of the comprehensive entry mechanisms of SARS-CoV-2, especially the host factors that facilitate viral infection, is crucial for the discovery of effective vaccines and antiviral drugs. SARS-CoV-2 has previously been documented to reach cells by binding with ACE2 and CD147 receptors in host cells that interact with the spike (S) protein of SARS-CoV-2. A novel entry factor, called neuropilin 1(NRP1), has recently been discovered as a co-receptor facilitating the entry of SARS-CoV-2. NRP1 is a single-pass transmembrane glycoprotein widely distributed throughout the tissues of the body and acts as a multifunctional co-receptor to bind with different ligand proteins and play diverse physiological roles as well as pathological and therapeutic roles in different clinical conditions/diseases, including COVID-19. The current review, therefore, briefly provides the overview of SARS-CoV-2 entry mechanisms, the structure of NRP1, and their roles in health and various diseases, as well as extensively discusses the current understanding of the potential implication of NRP1 in SARS-CoV-2 entry and COVID-19 treatment.

Glomerular Endothelial Cell Crosstalk With Podocytes in Diabetic Kidney Disease

Diabetes is the main cause of renal failure worldwide. Complications of the kidney micro-and macro-circulation are common in diabetic patients, leading to proteinuria and can progress to end-stage renal disease. Across the complex interplays aggravating diabetes kidney disease progression, lesions of the glomerular filtration barrier appear crucial. Among its components, glomerular endothelial cells are known to be central safeguards of plasma filtration. An array of evidence has recently pinpointed its intricate relations with podocytes, highly specialized pericytes surrounding glomerular capillaries. During diabetic nephropathy, endothelial cells and podocytes are stressed and damaged. Besides, each can communicate with the other, directly affecting the progression of glomerular injury. Here, we review recent studies showing how in vitro and in vivo studies help to understand pathological endothelial cells-podocytes crosstalk in diabetic kidney disease.

The Development of Maillard Reaction, and Advanced Glycation End Product (AGE)-Receptor for AGE (RAGE) Signaling Inhibitors as Novel Therapeutic Strategies for Patients with AGE-Related Diseases

Advanced glycation end products (AGEs) are generated by nonenzymatic modifications of macromolecules (proteins, lipids, and nucleic acids) by saccharides (glucose, fructose, and pentose) via Maillard reaction. The formed AGE molecules can be catabolized and cleared by glyoxalase I and II in renal proximal tubular cells. AGE-related diseases include physiological aging, neurodegenerative/neuroinflammatory diseases, diabetes mellitus (DM) and its complications, autoimmune/rheumatic inflammatory diseases, bone-degenerative diseases, and chronic renal diseases. AGEs, by binding to receptors for AGE (RAGEs), alter innate and adaptive immune responses to induce inflammation and immunosuppression via the generation of proinflammatory cytokines, reactive oxygen species (ROS), and reactive nitrogen intermediates (RNI). These pathological molecules cause vascular endothelial/smooth muscular/connective tissue-cell and renal mesangial/endothelial/podocytic-cell damage in AGE-related diseases. In the present review, we first focus on the cellular and molecular bases of AGE–RAGE axis signaling pathways in AGE-related diseases. Then, we discuss in detail the modes of action of newly discovered novel biomolecules and phytochemical compounds, such as Maillard reaction and AGE–RAGE signaling inhibitors. These molecules are expected to become the new therapeutic strategies for patients with AGE-related diseases in addition to the traditional hypoglycemic and anti-hypertensive agents. We particularly emphasize the importance of “metabolic memory”, the “French paradox”, and the pharmacokinetics and therapeutic dosing of the effective natural compounds associated with pharmacogenetics in the treatment of AGE-related diseases. Lastly, we propose prospective investigations for solving the enigmas in AGE-mediated pathological effects.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Long-term expression of glomerular genes in diabetic nephropathy

Background

Although diabetic nephropathy (DN) is the most common cause for end-stage renal disease in western societies, its pathogenesis still remains largely unclear. A different gene pattern of diabetic and healthy kidney cells is one of the probable explanations. Numerous signalling pathways have emerged as important pathophysiological mechanisms for diabetes-induced renal injury.

Methods

Glomerular cells, as podocytes or mesangial cells, are predominantly involved in the development of diabetic renal lesions. While many gene assays concerning DN are performed with whole kidney or renal cortex tissue, we isolated glomeruli from black and tan, brachyuric (BTBR) obese/obese (ob/ob) and wildtype mice at four different timepoints (4, 8, 16 and 24 weeks) and performed an mRNA microarray to identify differentially expressed genes (DEGs). In contrast to many other diabetic mouse models, these homozygous ob/ob leptin-deficient mice develop not only a severe type 2 diabetes, but also diabetic kidney injury with all the clinical and especially histologic features defining human DN. By functional enrichment analysis we were able to investigate biological processes and pathways enriched by the DEGs at different disease stages. Altered expression of nine randomly selected genes was confirmed by quantitative polymerase chain reaction from glomerular RNA.

Results

Ob/ob type 2 diabetic mice showed up- and downregulation of genes primarily involved in metabolic processes and pathways, including glucose, lipid, fatty acid, retinol and amino acid metabolism. Members of the CYP4A and ApoB family were found among the top abundant genes. But more interestingly, altered gene loci showed enrichment for processes and pathways linked to angioneogenesis, complement cascades, semaphorin pathways, oxidation and reduction processes and renin secretion.

Conclusion

The gene profile of BTBR ob/ob type 2 diabetic mice we conducted in this study can help to identify new key players in molecular pathogenesis of diabetic kidney injury.

Foxc2 is essential for podocyte function

Foxc2 is one of the earliest podocyte markers during glomerular development. To circumvent embryonic lethal effects of global deletion of Foxc2, and to specifically investigate the role of Foxc2 in podocytes, we generated mice with a podocyte-specific Foxc2 deletion. Mice carrying the homozygous deletion developed early proteinuria which progressed rapidly into end stage kidney failure and death around postnatal day 10. Conditional loss of Foxc2 in podocytes caused typical characteristics of podocyte injury, such as podocyte foot process effacement and podocyte microvillus transformation, probably caused by disruption of the slit diaphragm. These effects were accompanied by a redistribution of several proteins known to be necessary for correct podocyte structure. One target gene that showed reduced glomerular expression was Nrp1, the gene encoding neuropilin 1, a protein that has been linked to diabetic nephropathy and proteinuria. We could show that NRP1 was regulated by Foxc2 in vitro, but podocyte-specific ablation of Nrp1 in mice did not generate any phenotype in terms of proteinuria, suggesting that the gene might have more important roles in endothelial cells than in podocytes. Taken together, this study highlights a critical role for Foxc2 as an important gene for podocyte function.

Anti-neuropilin-1 monoclonal antibody suppresses the migration and invasion of human gastric cancer cells via Akt dephosphorylation

Neuropilin-1 (NRP-1) is involved in a range of physiological and pathological processes, including neuronal cell guidance, cardiovascular development, immunity, angiogenesis and the pathogenesis of cancer. Targeting of NRP-1 is considered to be a potential cancer therapy and a number of approaches have been investigated, including the use of small interfering RNA, peptides, soluble NRP antagonists and monoclonal antibodies. The present study used a novel anti-neuropilin-1 monoclonal antibody (anti-NRP-1 mAb) to investigate its potential anti-tumor effects on human gastric cancer cells in vitro and in vivo, as well as its underlying mechanisms of action. Using an MTT assay, it was observed that anti-NRP-1 mAb (<150 µg/ml) had no effects on the viability of gastric cancer cell line BGC-823, while a Boyden chamber assay indicated that treatment with anti-NRP-1 mAb suppressed the migration and invasion of BGC-823 cells. Western blot analysis also demonstrated that phosphorylation of Akt was reduced in BGC-823 cells treated with anti-NRP-1 mAb. Furthermore, anti-NRP-1 mAb suppressed the growth of gastric cancer xenograft tumors and downregulated the expression of vascular endothelial growth factor proteins within tumors in nude mice. These data indicate the potential effects of anti-NRP-1 mAb on malignant tumors and suggest that inhibition of NRP-1 function with anti-NRP-1 mAb may be a novel therapeutic approach in the treatment of cancer.

Kidney, heart and brain: three organs targeted by ageing and glycation

Advanced glycation end-product (AGE) is the generic term for a heterogeneous group of derivatives arising from a non-enzymatic reaction between reducing sugars and proteins. In recent years, evidence has accumulated that incriminates AGEs in pathogenic processes associated with both chronic hyperglycaemia and age-related diseases. Regardless of their exogenous or endogenous origin, the accumulation of AGEs and their derivatives could promote accelerated ageing by leading to protein modifications and activating several inflammatory signalling pathways via AGE-specific receptors. However, it remains to be demonstrated whether preventing the accumulation of AGEs and their effects is an important therapeutic option for successful ageing. The present review gives an overview of the current knowledge on the pathogenic role of AGEs by focusing on three AGE target organs: kidney, heart and brain. For each of these organs we concentrate on an age-related disease, each of which is a major public health issue: chronic kidney disease, heart dysfunction and neurodegenerative diseases. Even though strong connections have been highlighted between glycation and age-related pathogenesis, causal links still need to be validated. In each case, we report evidence and uncertainties suggested by animal or epidemiological studies on the possible link between pathogenesis and glycation in a chronic hyperglycaemic state, in the absence of diabetes, and with exogenous AGEs alone. Finally, we present some promising anti-AGE strategies that are currently being studied.

Growth arrest specific 2-like protein 1 expression is upregulated in podocytes through advanced glycation end-products

Background

Growth arrest specific 2-like protein 1 (GAS2L1) protein is a member of the GAS2 family of proteins, known to regulate apoptosis and cellular cytoskeleton reorganization in different cells. Recently we identified that Gas2l1 gene expression in podocytes is influenced by advanced glycation end product-bovine serum albumin(AGE-BSA).

Methods

The study was performed employing cultured podocytes and diabetic ( db/db ) mice, a model of type 2 diabetes. Akbuminuria as wellas urinary neutrophil gelatinase-associated lipocalin (NGAL) excretion as measured with specific ELISAs. Gene expression was analysed via semiquantitative and real-time polymerase chain reaction. The protein levels were determined by western blotting and immunostaining.

Results

We found that the Gas2l1 α isoform is expressed in podocytes. Treatment with AGE-BSA induced Gas2l1 α and Gas2 mRNA levels compared with controls incubated with non-glycated control BSA (Co-BSA). Moreover, application of the recombinant soluble receptor of AGEs (sRAGE), a competitor of cellular RAGE, reversed the AGE-BSA effect. Interestingly, AGE-BSA also increased the protein levels of GAS2L1α in a RAGE-dependent manner, but did not affect the GAS2 expression. Periodic acid-Schiff staining and albuminuria as well as urinary NGAL excretion revealed that db/db mice progressively developed diabetic nephropathy with renal accumulation of N ε -carboxy-methyl-lysine (immunohistochemistry, western blots). Analyses of GAS2L1α and GAS2 proteins in diabetic mice revealed that both were significantly elevated relative to their non-diabetic littermates. In addition, GAS2L1α and GAS2 proteins positively correlated with the accumulation of AGEs in the blood plasma of diabetic mice and the administration of sRAGE in diabetic mice reduced the glomerular expression of both proteins.

Conclusions

We show for the first time that the protein expression of GAS2L1α in vitro and in vivo is regulated by the AGE-RAGE axis. The suppression of AGE ligation with their RAGE in diabetic mice with progressive nephropathy reversed the GAS2L1α expression, thus suggesting a role of GAS2L1α in the development of diabetic disease, which needs to be further elucidated.

Neuropilin1 regulates glomerular function and basement membrane composition through pericytes in the mouse kidney

Neuropilin1 (Nrp1) is a co-receptor best known to regulate the development of endothelial cells and is a target of anticancer therapies. However, its role in other vascular cells including pericytes is emergent. The kidney is an organ with high pericyte density and cancer patients develop severe proteinuria following administration of NRP1B-neutralizing antibody combined with bevacizumab. Therefore, we investigated whether Nrp1 regulates glomerular capillary integrity after completion of renal development using two mouse models; tamoxifen-inducible NG2Cre to delete Nrp1 specifically in pericytes and administration of Nrp1-neutralizing antibodies. Specific Nrp1 deletion in pericytes did not affect pericyte number but mutant mice developed hematuria with glomerular basement membrane defects. Despite foot process effacement, albuminuria was absent and expression of podocyte proteins remained unchanged upon Nrp1 deletion. Additionally, these mice displayed dilation of the afferent arteriole and glomerular capillaries leading to glomerular hyperfiltration. Nidogen-1 mRNA was downregulated and collagen4α3 mRNA was upregulated with no significant effect on the expression of other basement membrane genes in the mutant mice. These features were phenocopied by treating wild-type mice with Nrp1-neutralizing antibodies. Thus, our results reveal a postdevelopmental role of Nrp1 in renal pericytes as an important regulator of glomerular basement membrane integrity. Furthermore, our study offers novel mechanistic insights into renal side effects of Nrp1 targeting cancer therapies.

A Systems Biology Overview on Human Diabetic Nephropathy: From Genetic Susceptibility to Post-Transcriptional and Post-Translational Modifications

Diabetic nephropathy (DN), a microvascular complication occurring in approximately 20-40% of patients with type 2 diabetes mellitus (T2DM), is characterized by the progressive impairment of glomerular filtration and the development of Kimmelstiel-Wilson lesions leading to end-stage renal failure (ESRD). The causes and molecular mechanisms mediating the onset of T2DM chronic complications are yet sketchy and it is not clear why disease progression occurs only in some patients. We performed a systematic analysis of the most relevant studies investigating genetic susceptibility and specific transcriptomic, epigenetic, proteomic, and metabolomic patterns in order to summarize the most significant traits associated with the disease onset and progression. The picture that emerges is complex and fascinating as it includes the regulation/dysregulation of numerous biological processes, converging toward the activation of inflammatory processes, oxidative stress, remodeling of cellular function and morphology, and disturbance of metabolic pathways. The growing interest in the characterization of protein post-translational modifications and the importance of handling large datasets using a systems biology approach are also discussed.

Role of Neuropilin-1 in Diabetic Nephropathy

Diabetic nephropathy (DN) often develops in patients suffering from type 1 or type 2 diabetes mellitus. DN is characterized by renal injury resulting in proteinuria. Neuropilin-1 (NRP-1) is a single-pass transmembrane receptor protein devoid of enzymatic activity. Its large extracellular tail is structured in several domains, thereby allowing the molecule to interact with multiple ligands linking NRP-1 to different pathways through its signaling co-receptors. NRP-1’s role in nervous system development, immunity, and more recently in cancer, has been extensively investigated. Although its relation to regulation of apoptosis and cytoskeleton organization of glomerular vascular endothelial cells was reported, its function in diabetes mellitus and the development of DN is less clear. Several lines of evidence demonstrate a reduced NRP-1 expression in glycated-BSA cultured differentiated podocytes as well as in glomeruli from db/db mice (a model of type 2 Diabetes) and in diabetic patients diagnosed with DN. In vitro studies of podocytes implicated NRP-1 in the regulation of podocytes’ adhesion to extracellular matrix proteins, cytoskeleton reorganization, and apoptosis via not completely understood mechanisms. However, the exact role of NRP-1 during the onset of DN is not yet understood. This review intends to shed more light on NRP-1 and to present a link between NRP-1 and its signaling complexes in the development of DN.

Semaphorin 3A serum levels are influenced by haemodialysis: what clinical significance?

AIM

Semaphorin 3A urinary levels represent an early, predictive biomarker of acute kidney injury and positively correlate with albumin-to-creatinine ratio and serum creatinine in hypertensive patients with chronic kidney disease. Our purpose has been to evaluate semaphorin 3A serum levels in a cohort of haemodialysis (HD) patients, the influence of a single HD session on its concentrations, and the potential correlation with clinical and biochemical parameters.

METHODS

We enrolled 18 patients receiving HD with Acetate-Free Biofiltration technique and 16 healthy subjects as controls. Peripheral venous blood samples were obtained from patients at different intervals: start of dialysis (pre-HD), middle, and end of the treatment (post-HD). We also collected dialysate samples by the Quantiscan monitoring system (Hospal, Bologna, Italy).

RESULTS

Semaphorin 3A was significantly lower in HD patients at baseline compared to controls (median 19.50 (interquartile range 1.00-65.00) versus 97.50 (23.50-161.00) ng/mL, P = 0.0237). A statistically significant reduction was seen during a single HD session (from 19.50 (1.00-65.00) to 0.86 (0.82-4.21) ng/mL, P < 0.0001), with a reduction ratio of 65.92 ± 33.51%. The median concentration in dialysate was 54.00 (15.00-102.00) ng/mL. Pre-HD values were directly related to serum vitamin D (r = 0.872; P = 0.001) and inversely correlated with calcium levels (r = -0.426; P = 0.012) and calcium × phosphate product (r = -0.422; P = 0.0252).

CONCLUSION

Semaphorin 3A removal during HD may be clinically relevant due to its involvement in different aspects of cell physiology and in bone remodelling. Semaphorin 3A both inhibits osteoclastic bone reabsorption and increases osteoblastic new bone formation, thus playing a dual osteoprotective role.

Activation of the receptor for advanced glycation end products induces nuclear inhibitor of protein phosphatase-1 suppression

The activation of the receptor for advanced glycation end products (RAGE) is involved in the development of diabetic nephropathy. Analysis of protein phosphatase-1 indicated that advanced glycation end products did not affect its expression, but increased its phosphatase activity. Using differential display analysis we previously demonstrated that stimulation of RAGE in podocytes modulates the expression of numerous genes, among others nuclear inhibitor of protein phosphatase-1 (NIPP1). Here we found that silencing of NIPP1 induced podocyte hypertrophy, cell cycle arrest, and significantly increased protein phosphatase-1 activity. NIPP1 downregulation was associated with increased p27(Kip1) protein expression. Reporter assays revealed a transcriptional activation of nuclear factor-κB in podocytes after suppression of NIPP1. The protein level of NIPP1 was also significantly reduced in podocytes of diabetic mice. Blocking the RAGE in vivo by a soluble analog elevated the NIPP1 protein in podocytes of diabetic mice. Thus, activation of the RAGE by advanced glycation end products or other ligands suppresses NIPP1 expression in diabetic nephropathy, contributes to podocyte hypertrophy, and glomerular inflammation.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Erythropoietin ameliorates podocyte injury in advanced diabetic nephropathy in the db/db mouse

Podocyte damage and accumulation of advanced glycation end products (AGEs) are characteristics of diabetic nephropathy (DN). The pathophysiology of AGE-challenged podocytes, such as hypertrophy, apoptosis, and reduced cell migration, is closely related to the induction of the cell cycle inhibitor p27Kip1 and to the inhibition of neuropilin 1 (NRP1). We have previously demonstrated that treatment with erythropoietin is associated with protective effects for podocytes in vitro. db/ db mice with overt DN aged 15–16 wk were treated with either placebo, epoetin-β, or continuous erythropoietin receptor activator (CERA) for 2 wk. db/ db mice compared with nondiabetic db/ m control mice revealed the expected increases in body weight, blood glucose, albumin-to-creatinine ratio, and AGE accumulation. Whereas there were no differences in body weight, hyperglycemia and AGEs were observed among diabetic mice that received epoetin-β compared with CERA and placebo treatment, indicating that epoetin-β/CERA treatment does not interfere with the development of diabetes in this model. However, the albumin-to-creatinine ratio was significantly lower in db/ db mice treated with epoetin-β or CERA. Furthermore, kidney weights in db/ db mice were increased compared with db/ m control mice, indicating renal hypertrophy, whereas the increase in renal weight in epoetin-β- or CERA-treated db/ db mice was significantly lower than in placebo-treated control mice. Induction of p27Kip1 and suppression of NRP1 were significantly reduced in the epoetin-β treatment group versus the CERA treatment group. Furthermore, erythropoietin treatment diminished the diabetes-induced podocyte loss. Together, independently from hematopoetic effects, epoetin-β or CERA treatment was associated with protective changes in DN, especially that NRP1 and p27Kip1 expressions as well as numbers of podocytes returned to normal levels. Our data show, for the first time, that medication of overt DN with erythropoietin for a short time can ameliorate albuminuria and podocyte loss.

Excess podocyte semaphorin-3A leads to glomerular disease involving plexinA1-nephrin interaction

Semaphorin-3A (Sema3a), a guidance protein secreted by podocytes, is essential for normal kidney patterning and glomerular filtration barrier development. Here, we report that podocyte-specific Sema3a gain-of-function in adult mice leads to proteinuric glomerular disease involving the three layers of the glomerular filtration barrier. Reversibility of the glomerular phenotype upon removal of the transgene induction provided proof-of-principle of the cause-and-effect relationship between podocyte Sema3a excess and glomerular disease. Mechanistically, excess Sema3a induces dysregulation of nephrin, matrix metalloproteinase 9, and αvβ3 integrin in vivo. Sema3a cell-autonomously disrupts podocyte shape. We identified a novel direct interaction between the Sema3a signaling receptor plexinA1 and nephrin, linking extracellular Sema3a signals to the slit-diaphragm signaling complex. We conclude that Sema3a functions as an extracellular negative regulator of the structure and function of the glomerular filtration barrier in the adult kidney. Our findings demonstrate a crosstalk between Sema3a and nephrin signaling pathways that is functionally relevant both in vivo and in vitro.

Glycemic memories and the epigenetic component of diabetic nephropathy

A strong case for the deregulation of epigenetic chromatin modifications in the development and progression of various chronic complications of diabetes has emerged from recent experimental observations. Clinical trials of type 1 and type 2 diabetes patients highlight the importance of early and intensive treatment and the prolonged damage of hyperglycemia on organs such as the kidney. The functional relationship between the regulation of chromatin architecture and persistent gene expression changes conferred by prior hyperglycemia represents an important avenue of investigation for explaining diabetic nephropathy. While several studies implicate epigenetic changes at the chromatin template in the deregulated gene expression associated with diabetic nephropathy, the molecular determinants of metabolic memory in renal cells remain poorly understood. There is now strong evidence from experimental animals and cell culture of persistent glucose-driven changes in vascular endothelial gene expression that may also have relevance for the microvasculature of the kidney. Exploration of epigenetic mechanisms underlying the hyperglycemic cue mediating persistent transcriptional changes in renal cells holds novel therapeutic potential for diabetic nephropathy.

δ-Opioid receptor activation modified microRNA expression in the rat kidney under prolonged hypoxia

Hypoxic/ischemic injury to kidney is a frequently encountered clinical problem with limited therapeutic options. Since microRNAs are differentially involved in hypoxic/ischemic events and δ-opioid receptor (DOR) activation is known to protect against hypoxic/ischemic injury, we speculated on the involvement of DOR activation in altering the microRNA (miRNA) expression in kidney under hypoxic condition. We selected 31 miRNAs based on microarray data for quantitative PCR analysis. Among them, 14 miRNAs were significantly altered after prolonged hypoxia, DOR activation or a combination of both. We found that 1) DOR activation alters miRNA expression profiles in normoxic conditions; 2) hypoxia differentially alters miRNA expression depending on the duration of hypoxia; and 3) DOR activation can modify hypoxia-induced changes in miRNA expression. For example, 10-day hypoxia reduced the level of miR-212 by over 70%, while DOR activation could mimic such reduction even in normoxic kidney. In contrast, the same stress increased miR-29a by >100%, which was reversed following DOR activation. These first data suggest that hypoxia comprehensively modifies the miRNA profile within the kidney, which can be mimicked or modified by DOR activation. Ascertaining the targeted pathways that regulate the diverse cellular and molecular functions of miRNA may provide new insights into potential therapies for hypoxic/ischemic injury of the kidney.

Neuropilins: expression and roles in the epithelium

Initially found expressed in neuronal and then later in endothelial cells, it is well established that the transmembrane glycoproteins neuropilin-1 (NRP1) and neuropilin-2 (NRP2) play essential roles in axonal growth and guidance and in physiological and pathological angiogenesis. Neuropilin expression and function in epithelial cells has received little attention when compared with neuronal and endothelial cells. Overexpression of NRPs is shown to enhance growth, correlate with invasion and is associated with poor prognosis in various tumour types, especially those of epithelial origin. The contribution of NRP and its ligands to tumour growth and metastasis has spurred a strong interest in NRPs as novel chemotherapy drug targets. Given NRP's role as a multifunctional co-receptor with an ability to bind with disparate ligand families, this has sparked new areas of research implicating NRPs in diverse biological functions. Here, we review the growing body of research demonstrating NRP expression and role in the normal and neoplastic epithelium.

Angiotensin II differentially regulates Morg1 expression in kidney cells

BACKGROUND

The mitogen-activated protein kinase organizer 1 (Morg1) belongs to the WD-40 repeat protein family and is a scaffold molecule for the extracellular regulated kinase signaling pathway. Morg1 also binds to prolyl-hydroxylase 3 (PHD3) and regulates the hypoxia-inducible factor-1α (HIF-1α) expression via PHD3 stabilization. Morg1 has been detected in the kidney as well as in other cell tissues but its expression in renal cells has not been well investigated. It has been widely shown that angiotensin II (ANG II) mediates renal damage. We have previously shown that ANG II downregulates the expression of PHD3 in PC12 cells. The aim of this study was to analyze whether ANG II regulates Morg1 expression in mouse mesangial cells (MMC), mouse proximal tubular cells (MTC) and in differentiated podocytes. The correlation between the expression of Morg1 and PHD3 activity was also addressed.

METHODS

Effect of ANG II on the Morg1 mRNA expression level was assessed by real-time PCR. Morg1 and HIF-1α cellular localization was analyzed by immunohistochemistry. HIF-1α promoter activity was investigated using a reporter gene system. PHD3 hydroxylase activity test was measured with a hydroxylation-coupled decarboxylation assay.

RESULTS

ANG II differentially regulates Morg1 expression in MMC, MTC and differentiated podocytes. We detected a biphasic effect of ANG II on Morg1 mRNA expression which was time dependent. While 9-hour ANG II treatment downregulated Morg1 expression in MMC, it induced Morg1 expression in MTC. Conversely, 24-hour ANG II stimulation upregulated the expression of Morg1 mRNA in MMC, but showed an opposite effect in MTC and differentiated podocytes. In addition, we found that ANG II signals mostly through the AT(1) receptor subtype in MMC and via the AT(2) subtype in MTC. PHD3 activity correlated to Morg1 expression patterns. Our data also demonstrate that HIF-1α transcriptional activity in MTC contrasted to PHD3 activity at 9 and 24 h, whereas in the MMC and in podocytes we did not find any correlation between PHD3 HIF-1α hydroxylation ability and HIF-1α transcriptional activation, suggesting a different mechanism of regulation in these cell types. Interestingly, the reduced expression of Morg1 in mesangial cells isolated from Morg1 (+/-) heterozygous mice correlated with a reduced PHD3 enzymatic activity and an increased HIF-1α transcriptional activity compared with mesangial cells originated from wild-type (Morg1 +/+) mice.

CONCLUSIONS

We show for the first time in various renal cells that ANG II modulates Morg1 expression and HIF-1α transcriptional activity via cell type-specific mechanisms, demonstrating a novel mechanism by which ANG II may contribute to renal disease.

Impaired neurovascular repair in subjects with diabetes following experimental intracutaneous axotomy

Diabetic complications and vascular disease are closely intertwined. Diabetes mellitus is a well-established risk factor for both large and small vessel vascular changes, and conversely other vascular risk factors confer increased risk for diabetic complications such as peripheral neuropathy, nephropathy and retinopathy. Furthermore, axons and blood vessels share molecular signals for purposes of navigation, regeneration and terminal arborizations. We examined blood vessel, Schwann cell and axonal regeneration using validated axotomy models to study and compare patterns and the relationship of regeneration among these different structures. Ten subjects with diabetes mellitus complicated by neuropathy and 10 healthy controls underwent 3 mm distal thigh punch skin biopsies to create an intracutaneous excision axotomy followed by a concentric 4-mm overlapping biopsy at different time points. Serial sections were immunostained against a pan-axonal marker (PGP9.5), an axonal regenerative marker (GAP43), Schwann cells (p75) and blood vessels (CD31) to visualize regenerating structures in the dermis and epidermis. The regenerative and collateral axonal sprouting rates, blood vessel growth rate and Schwann cell density were quantified using established stereology techniques. Subjects also underwent a chemical 'axotomy' through the topical application of capsaicin, and regenerative sprouting was assessed by the return of intraepidermal nerve fibre density through regenerative regrowth. In the healed 3 mm biopsy sites, collateral and dermal regenerative axonal sprouts grew into the central denervated area in a stereotypic pattern with collateral sprouts growing along the dermal-epidermal junction while regenerative dermal axons, blood vessels and Schwann cells grew from their transected proximal stumps into the deep dermis. Vessel growth preceded axon and Schwann cell migration into the denervated region, perhaps acting as scaffolding for axon and Schwann cell growth. In control subjects, Schwann cell growth was more robust and extended into the superficial dermis, while among subjects with diabetes mellitus, Schwann tubes appeared atrophic and were limited to the mid-dermis. Rates of collateral (P=0.0001), dermal axonal regenerative sprouting (P=0.02), Schwann cell migration (P<0.05) and blood vessel growth (P=0.002) were slower among subjects with diabetes mellitus compared with control subjects. Regenerative deficits are a common theme in diabetes mellitus and may underlie the development of neuropathy. We observed that blood vessel growth recapitulated the pattern seen in ontogeny and preceded regenerating nerve fibres, suggesting that enhancement of blood vessel growth might facilitate axonal regeneration. These models are useful tools for the efficient investigation of neurotrophic and regenerative drugs, and also to explore factors that may differentially affect axonal regeneration.

Advanced glycation end products inhibit adhesion ability of differentiated podocytes in a neuropilin-1-dependent manner

Podocyte injury can occur by a number of stimuli. Maintaining of an intact podocyte structure is essential for glomerular filtration; therefore, podocyte damage severely impairs renal function. Recently, we have reported that addition of glycated BSA [advanced glycation end products (AGE)-BSA] to differentiated murine podocytes inhibited neuropilin-1 (NRP1) expression and dramatically influenced podocyte migration ability (Bondeva T, Ruster C, Franke S, Hammerschmid E, Klagsbrun M, Cohen CD, Wolf G. Kidney Int 75: 605-616, 2009; Bondeva T, Wolf G. Am J Nephrol 30: 336-345, 2009). The present study analyzes the influence of AGEs and NRP1 on podocyte adhesion and cytoskeleton reorganization. We show that treatment with AGE-BSA significantly reduced podocyte adhesion to collagen IV, laminin, and fibronectin compared with Co-BSA (nonglycated BSA)-incubated cells, which was further augmented by transient inhibition of NRP1 expression using NRP1 short interference (si) RNA. On the other hand, forced overexpression of NRP1 markedly increased the adhesion ability of podocytes to the ECMs despite the AGE-BSA treatment. No changes were observed when podocyte adhesion to collagen I was assayed. These findings were also manifested with disorganization of podocyte actin stress fibers and decreased lamellipodia formation processes due to AGE-BSA treatment or NRP1 suppression. In addition, AGE-BSA or suppression of NRP1 both reduced the phosphorylation of focal adhesion kinase (FAK) and Erk1/2 in PMA-stimulated differentiated podocytes. Analysis of RhoA family GTPase activity demonstrated that treatment with AGE-BSA or NRP1 depletion inhibited as well the activation of the Rac-1 and Cdc42 but did not affect RhoA activity. All these effects were reversed by forced overexpression of full-length NRP1 cloned into the pcDNA3 vector in differentiated podocytes. Our study demonstrates that AGEs, in part via suppression of NRP1 expression, decreased podocyte adhesion and contribute to reduction of Rac-1 and Cdc42 GTPase activity. These effects may be further responsible for the podocytes damage and loss in diabetic nephropathy. Our findings suggest a role for NRP1 in regulating the podocyte actin cytoskeleton, and therefore reduction of NRP1 expression could be critical for podocyte function.

Podocyte vascular endothelial growth factor (Vegf₁₆₄) overexpression causes severe nodular glomerulosclerosis in a mouse model of type 1 diabetes

AIMS/HYPOTHESIS

The pathogenic role of excessive vascular endothelial growth factor (VEGF)-A in diabetic nephropathy has not been defined. We sought to test whether increased podocyte VEGF-A signalling determines the severity of diabetic glomerulopathy.

METHODS

Podocyte-specific, doxycycline-inducible Vegf₁₆₄ (the most abundant Vegfa isoform) overexpressing adult transgenic mice were made diabetic with low doses of streptozotocin and examined 12 weeks after onset of diabetes. We studied diabetic and non-diabetic transgenic mice fed a standard or doxycycline-containing diet. VEGF-A and albuminuria were measured by ELISA, creatinine was measured by HPLC, renal morphology was examined by light and electron microscopy, and gene expression was assessed by quantitative PCR, immunoblotting and immunohistochemistry.

RESULTS

Podocyte Vegf₁₆₄ overexpression in our mouse model of diabetes resulted in advanced diabetic glomerulopathy, characterised by Kimmelstiel-Wilson-like nodular glomerulosclerosis, microaneurysms, mesangiolysis, glomerular basement membrane thickening, podocyte effacement and massive proteinuria associated with hyperfiltration. It also led to increased VEGF receptor 2 and semaphorin3a levels, as well as nephrin and matrix metalloproteinase-2 downregulation, whereas circulating VEGF-A levels were similar to those in control diabetic mice.

CONCLUSIONS/INTERPRETATION

Collectively, these data demonstrate that increased podocyte Vegf₁₆₄ signalling dramatically worsens diabetic nephropathy in a streptozotocin-induced mouse model of diabetes, resulting in nodular glomerulosclerosis and massive proteinuria. This suggests that local rather than systemic VEGF-A levels determine the severity of diabetic nephropathy and that semaphorin3a signalling and matrix metalloproteinase-2 dysregulation are mechanistically involved in severe diabetic glomerulopathy.

Gene expression of neuropilin-1 and its receptors, VEGF/Semaphorin 3a, in normal and cancer cells

Extracellular domains of the transmembrane glycoprotein, neuropilin-1 (Np1), specifically bind an array of factors and co-receptors including class-3 semaphorins (Sema3a), vascular endothelial growth factor (VEGF), hepatocyte growth factor, platelet-derived growth factor BB, transforming growth factor-β 1 (TGF-β1), and fibroblast growth factor2 (FGF2). Np1 may have a role in immune response, tumor cell growth, and angiogenesis, but its relative expression in comparison to its co-primary receptors, VEGF and Sema3a, is not known. In this study we determined the mRNA expression of Np1 and its co-receptors, VEGF and Sema3a, and the ratio of VEGF/Sema3a in different human and rodent cell lines. Expression of Np1, VEGF and Sema3a is very low in cells derived from normal tissues, but these proteins are highly expressed in tumor-derived cells. Furthermore, the ratio of VEGF/Sema3a is highly variable in different tumor cells. The elevated mRNA expression of Np1 and its putative receptors in tumor cells suggests a role for these proteins in tumor cell migration and angiogenesis. As different tumor cells exhibit varying VEGF/Sema3a ratios, it appears that cancer cells show differential response to angiogenic factors. These results bring to light the individual variation among the cancer-related genes, Np1, VEGF, and Sema3a, and provide an important impetus for the possible personalized therapeutic approaches for cancer patients.

ExprEssence--revealing the essence of differential experimental data in the context of an interaction/regulation net-work

Background

Experimentalists are overwhelmed by high-throughput data and there is an urgent need to condense information into simple hypotheses. For example, large amounts of microarray and deep sequencing data are becoming available, describing a variety of experimental conditions such as gene knockout and knockdown, the effect of interventions, and the differences between tissues and cell lines.

Results

To address this challenge, we developed a method, implemented as a Cytoscape plugin called ExprEssence. As input we take a network of interaction, stimulation and/or inhibition links between genes/proteins, and differential data, such as gene expression data, tracking an intervention or development in time. We condense the network, highlighting those links across which the largest changes can be observed. Highlighting is based on a simple formula inspired by the law of mass action. We can interactively modify the threshold for highlighting and instantaneously visualize results. We applied ExprEssence to three scenarios describing kidney podocyte biology, pluripotency and ageing: 1) We identify putative processes involved in podocyte (de-)differentiation and validate one prediction experimentally. 2) We predict and validate the expression level of a transcription factor involved in pluripotency. 3) Finally, we generate plausible hypotheses on the role of apoptosis, cell cycle deregulation and DNA repair in ageing data obtained from the hippocampus.

Conclusion

Reducing the size of gene/protein networks to the few links affected by large changes allows to screen for putative mechanistic relationships among the genes/proteins that are involved in adaptation to different experimental conditions, yielding important hypotheses, insights and suggestions for new experiments. We note that we do not focus on the identification of 'active subnetworks'. Instead we focus on the identification of single links (which may or may not form subnetworks), and these single links are much easier to validate experimentally than submodules. ExprEssence is available at http://sourceforge.net/projects/expressence/.

Advanced glycation end-products and the kidney

BACKGROUND

Advanced glycation end-products (AGEs) are increased in situations with hyperglycemia and oxidative stress such as diabetes mellitus. They are products of nonenzymatic glycation and oxidation of proteins and lipids. The kidney plays an important role in clearance and metabolism of AGEs.

METHODS

Medline and other relevant databases were searched. In addition, key review articles were scanned for relevant original publication. Finally, original data from our research group were also included.

RESULTS

Kidney podocytes and endothelial cells express specific receptors for AGEs. Their activation leads to multiple pathophysiological effects including hypertrophy with cell cycle arrest and apoptosis, altered migration, and generation of proinflammatory cytokines. AGEs have been primarily implicated in the pathophysiology of diabetic nephropathy and diabetic microvascular complications. AGEs are also involved in other primary renal diseases as well as in the development and progression of atherosclerosis. However, serum or plasma concentrations of AGEs do not correlate well with cardiovascular events in patients with chronic kidney disease (CKD). This is likely due to the fact that serum concentrations failed to correlate with AGEs deposited in target tissues. Several inhibitors of the AGE-RAGE axis are currently tested for various indications.

CONCLUSION

AGEs and their receptors are involved in the pathogenesis of vascular and kidney disease. The role of circulating AGEs as biomarkers for cardiovascular risk estimation is questionable. Whether putative inhibitors of AGEs will get the maturity for its therapeutic use in the future remains open.

Insights to the genetics of diabetic nephropathy through a genome-wide association study of the GoKinD collection

The Genetics of Kidneys in Diabetes (GoKinD) study was initiated to facilitate research aimed at identifying genes involved in diabetic nephropathy (DN) in type 1 diabetes. In this review, we present an overview of this study and the various reports that have used its collection. At the forefront of these efforts is the recent genome-wide association scan implemented on the GoKinD collection. We highlight the results from our analysis of these data and describe compelling evidence from animal models that further support the potential role of associated loci in the susceptibility of DN. To enhance our analysis of genetic associations in GoKinD, using genome-wide imputation, we expanded our analysis of this collection to include genotype data from more than 2.4 million common single nucleotide polymorphisms. We illustrate the added utility of this enhanced dataset through the comprehensive fine-mapping of candidate genomic regions previously linked with DN and the targeted investigation of genes involved in candidate pathways implicated in its pathogenesis. Collectively, genome-wide association and genome-wide imputation data from the GoKinD collection will serve as a springboard for future investigations into the genetic basis of DN in type 1 diabetes.

Neuropilin-1 and neuropilin-2 are differentially expressed in human proteinuric nephropathies and cytokine-stimulated proximal tubular cells

Neuropilin-1 (NRP1) and neuropilin-2 (NRP2) are transmembrane glycoproteins with large extracellular domains that interact with class 3 semaphorins, vascular endothelial growth factor (VEGF) family members, and ligands, such as hepatocyte growth factor, platelet-derived growth factor BB, transforming growth factor-beta1 (TGF-beta1), and fibroblast growth factor2 (FGF2). Neuropilins (NRPs) have been implicated in tumor growth and vascularization, as novel mediators of the primary immune response and in regeneration and repair; however, their role in renal pathophysiology is largely unknown. Here, we report upregulation of tubular and interstitial NRP2 protein expression in patients with focal segmental glomerulosclerosis (FSGS). In an additional cohort of patients with minimal change disease (MCD), membranous nephropathy (MN), and FSGS, elevated NRP2 mRNA expression in kidney biopsies inversely correlated with estimated glomerular filtration rate (eGFR) at the time of biopsy. Furthermore, upregulation of NRP2 mRNA correlated with post-bioptic decline of kidney function. Expression of NRP1 and NRP2 in human proximal tubular cells (PTCs) was differentially affected after stimulation with TGF-beta1, interleukin-1beta (IL-1beta), and oncostatin M (OSM). Although the pro-fibrotic mediators, TGF-beta1 and IL-1beta, induced upregulation of NRP2 expression but downregulation of NRP1 expression, OSM stimulated the expression of both NRP1 and NRP2. Basal and OSM-induced NRP1 mRNA expression, as well as TGF-beta1-induced NRP2 mRNA and protein expression were partially mediated by MEK1/2-ERK1/2 signaling. This is the first report suggesting a differential role of NRP1 and NRP2 in renal fibrogenesis, and TGF-beta1, IL-1beta, and OSM represent the first ligands known to stimulate NRP2 expression in mammalian cells.

The monocyte chemoattractant protein-1/CCR2 loop, inducible by TGF-beta, increases podocyte motility and albumin permeability

The role of monocyte chemoattractant protein-1 (MCP-1) in diabetic nephropathy is typically viewed through the lens of inflammation, but MCP-1 might exert noninflammatory effects on the kidney cells directly. Glomerular podocytes in culture, verified to express the marker nephrin, were exposed to diabetic mediators such as high glucose or angiotensin II and assayed for MCP-1. Only transforming growth factor-beta (TGF-beta) significantly increased MCP-1 production, which was prevented by SB431542 and LY294002, indicating that signaling proceeded through the TGF-beta type I receptor kinase and the phosphatidylinositol 3-kinase pathway. The TGF-beta-induced MCP-1 was found to activate the podocyte's cysteine-cysteine chemokine receptor 2 (CCR2) and, as a result, enhance the cellular motility, cause rearrangement of the actin cytoskeleton, and increase podocyte permeability to albumin in a Transwell assay. The preceding effects of TGF-beta were replicated by treatment with recombinant MCP-1 and blocked by a neutralizing anti-MCP-1 antibody or a specific CCR2 inhibitor, RS102895. In conclusion, this is the first description that TGF-beta signaling through PI3K induces the podocyte expression of MCP-1 that can then operate via CCR2 to increase cellular migration and alter albumin permeability characteristics. The pleiotropic effects of MCP-1 on the resident kidney cells such as the podocyte may exacerbate the disease process of diabetic albuminuria.