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

Study on the Correlation Between Renal Blood Perfusion and Kidney Injury in Different Weekly-Aged Type 2 Diabetic Mice

This study aims to explore the correlation between renal blood perfusion (RBP) and diabetic nephropathy (DN).

METHODS

A total of 72 mice included db/db and db/m mice at the ages of 6, 14, and 22 weeks, forming six groups. RBP was assessed using Laser Speckle Contrast Imaging (LSCI). Kidney function markers and the extent of pathological damage were evaluated. Pearson correlation analysis was employed to predict the relationship between RBP and various indicators of kidney damage.

RESULTS

Compared to db/m mice of all ages, 6-week-old db/db mice showed no significant difference in kidney function markers and had no apparent pathological damage. However, db/db mice at other ages showed deteriorating kidney functions and evident pathological damage, which worsened with age. The RBP in db/m mice of all ages and 6-week-old db/db mice showed no significant difference; however, RBP in db/db mice demonstrated a significant declining trend with age. The correlation between RBP and kidney damage indicators was as follows: 24 h urinary microalbumin (r=-0.728), urinary transferrin (r=-0.834), urinary beta2-microglobulin (r=-0.755), urinary monocyte chemoattractant protein-1 (r=-0.786), Masson's trichrome staining (r=-0.872), and Periodic Acid-Schiff staining (r=-0.908).

CONCLUSION

RBP is strongly correlated with the extent of diabetic kidney damage.

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.

Understanding the effects of COVID-19 on patients with diabetic nephropathy: a systematic review

Background

Diabetic nephropathy is one of the consequences of diabetes mellitus that causes a continuous decline in the eGFR. After the COVID-19 pandemic, studies have shown that patients with diabetic nephropathy who had contracted COVID-19 have higher rates of morbidity and disease progression. The aim of this study was to systematically review the literature to determine and understand the effects and complications of SARS-CoV-2 on patients with diabetic nephropathy.

Materials and methods

The authors' research protocol encompassed the study selection process, search strategy, inclusion/exclusion criteria, and a data extraction plan. A systematic review was conducted by a team of five reviewers, with an additional reviewer assigned to address any discrepancies. To ensure comprehensive coverage, the authors employed multiple search engines including PubMed, ResearchGate, ScienceDirect, SDL, Ovid, and Google Scholar.

Results

A total of 14 articles meeting the inclusion criteria revealed that COVID-19 directly affects the kidneys by utilizing ACE2 receptors for cell entry, which is significant because ACE2 receptors are widely expressed in the kidney.

Conclusion

COVID-19 affects kidney health, especially in individuals with diabetic nephropathy. The mechanisms include direct viral infection and immune-mediated injury. Early recognition and management are vital for improving the outcomes.

Significance of Endothelial Dysfunction Amelioration for Sodium-Glucose Cotransporter 2 Inhibitor-Induced Improvements in Heart Failure and Chronic Kidney Disease in Diabetic Patients

Beyond lowering plasma glucose levels, sodium-glucose cotransporter 2 inhibitors (SGLT2is) significantly reduce hospitalization for heart failure (HF) and retard the progression of chronic kidney disease (CKD) in patients with type 2 diabetes. Endothelial dysfunction is not only involved in the development and progression of cardiovascular disease (CVD), but is also associated with the progression of CKD. In patients with type 2 diabetes, hyperglycemia, insulin resistance, hyperinsulinemia and dyslipidemia induce the development of endothelial dysfunction. SGLT2is have been shown to improve endothelial dysfunction, as assessed by flow-mediated vasodilation, in individuals at high risk of CVD. Along with an improvement in endothelial dysfunction, SGLT2is have been shown to improve oxidative stress, inflammation, mitochondrial dysfunction, glucotoxicity, such as the advanced signaling of glycation end products, and nitric oxide bioavailability. The improvements in endothelial dysfunction and such endothelium-derived factors may play an important role in preventing the development of coronary artery disease, coronary microvascular dysfunction and diabetic cardiomyopathy, which cause HF, and play a role in retarding CKD. The suppression of the development of HF and the progression of CKD achieved by SGLT2is might have been largely induced by their capacity to improve vascular endothelial function.

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.

Jiedu Tongluo Baoshen formula enhances podocyte autophagy and reduces proteinuria in diabetic kidney disease by inhibiting PI3K/Akt/mTOR signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM) has been applied to diabetic kidney disease (DKD). A large number of animal trials each year focus on TCM for DKD, but the evidence for these preclinical studies is not clear.

AIM OF THE STUDY

The aim of this study was to study the therapeutic effect of Jiedu Tongluo Baoshen formula (JTBF) on DKD proteinuria and renal protection. At the same time, it is verified that JTBF can reduce podocyte injury by enhancing autophagy function, and then achieve the effect of proteinuria.

MATERIALS AND METHODS

We use high performance liquid chromatography to detect and analyze the fingerprint of JTBF to find the chemical composition. Subsequently, we constructed a DKD rat model induced by high-fat diet and streptozocin (HFD + STZ). Urine and blood biochemical automatic analyzer were used to detect 24-h urine protein quantification (24 h-UP) and renal function. The renal pathological changes were observed by H&E and transmission electron microscopy (TEM), and the levels of autophagy-related proteins and mRNA in podocytes were detected by immunohistochemistry, RT-qPCR and Western Blot. The chemical composition of JTBF was screened from traditional Chinese medicine systems pharmacol (TCMSP) and PubChem databases, and the potential targets and associated pathways of JTBF were predicted using kyoto encyclopedia of genes and genomes (KEGG) and protein-protein interaction (PPI) network analysis in network pharmacology, and confirmed in animal experiments and histopathological methods.

RESULTS

We discovered 77 active ingredients of JTBF. Through animal experiments, it was found that JTBF reduced 24 h-UP and promoted the expression of podocin, nephrin, and WT-1 in podocytes, thereby reducing podocyte damage. At the same time, JTBF activates the expression of podocyte autophagy-related proteins (beclin-1, LC3 and P62). Subsequently, through network pharmacology predictions, 208 compounds were obtained from JTBF, and phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) was a potential signal pathway. JTBF was obtained in DKD rat kidney tissue to inhibit the expression of PI3K, Akt and mTOR related proteins.

CONCLUSIONS

JTBF enhance podocyte autophagy to reduce podocyte damage, thereby effectively treating DKD proteinuria and protecting kidney function.

Erythropoietin Mitigates Diabetic Nephropathy by Restoring PINK1/Parkin-Mediated Mitophagy

Diabetic nephropathy (DN), one of the most detrimental microvascular complications of diabetes, is the leading cause of end-stage renal disease. The pathogenesis of DN is complicated, including hemodynamic changes, inflammatory response, oxidative stress, among others. Recently, many studies have demonstrated that mitophagy, especially PINK1/Parkin-mediated mitophagy, plays an important role in the pathogenesis of DN. Erythropoietin (EPO), a glycoprotein hormone mainly secreted by the kidney, regulates the production of erythrocytes. This research intends to explore the beneficial effects of EPO on DN and investigate related mechanisms. In in vitro experiments, we found that EPO promoted autophagic flux and alleviated mitochondrial dysfunction in terms of mitochondrial fragmentation, elevated mitochondrial ROS as well as the loss of mitochondrial potential, and lowered the apoptosis level in high-glucose-treated mesangial cells. Moreover, EPO increased protein expressions of PINK1 and Parkin, enhanced the co-localization of LC3 with mitochondria, Parkin with mitochondria as well as LC3 with Parkin, and increased the number of GFP-LC3 puncta, resulting in increased level of PINK1/Parkin-mediated mitophagy in mesangial cells. The knockdown of PINK1 abrogated the effect of EPO on mitophagy. In addition, in vivo experiments demonstrated that EPO attenuated renal injury, reduced oxidative stress, and promoted expressions of genes related to PINK1/Parkin-mediated mitophagy in the kidneys of DN mice. In summary, these results suggest that PINK1/Parkin-mediated mitophagy is involved in the development of DN and EPO mitigates DN by restoring PINK1/Parkin-mediated mitophagy.

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.

Multi-Organ Protective Effects of Sodium Glucose Cotransporter 2 Inhibitors

Sodium glucose cotransporter 2 inhibitors (SGLT2i) block the reabsorption of glucose by inhibiting SGLT2, thus improving glucose control by promoting the renal excretion of glucose, without requiring insulin secretion. This pharmacological property of SGLT2i reduces body weight and improves insulin resistance in diabetic patients. Such beneficial metabolic changes caused by SGLT2i are expected to be useful not only for glucose metabolism, but also for the protection for various organs. Recent randomized controlled trials (RCTs) on cardiovascular diseases (EMPA-REG OUTCOME trial and CANVAS program) showed that SGLT2i prevented cardiovascular death and the development of heart failure. RCTs on renal events (EMPA-REG OUTCOME trial, CANVAS program, and CREDENCE trial) showed that SGLT2i suppressed the progression of kidney disease. Furthermore, SGLT2i effectively lowered the liver fat content, and our study demonstrated that SGLT2i reduced the degree of hepatic fibrosis in patients at high-risk of hepatic fibrosis. Such promising properties of SGLT2i for cardiovascular, renal, and hepatic protection provide us the chance to think about the underlying mechanisms for SGLT2i-induced improvement of multiple organs. SGLT2i have various mechanisms for organ protection beyond glucose-lowering effects, such as an increase in fatty acids utilization for hepatic protection, osmotic diuresis for cardiac protection, an improvement of insulin resistance for anti-atherogenesis, and an improvement of tubuloglomerular feedback for renal protection.

Abnormal Crosstalk between Endothelial Cells and Podocytes Mediates Tyrosine Kinase Inhibitor (TKI)-Induced Nephrotoxicity

Vascular endothelial growth factor A (VEGFA) and its receptor VEGFR2 are the main targets of antiangiogenic therapies, and proteinuria is one of the common adverse events associated with the inhibition of the VEGFA/VEGFR2 pathway. The proteinuric kidney damage induced by VEGFR2 tyrosine kinase inhibitors (TKIs) is characterized by podocyte foot process effacement. TKI therapy promotes the formation of abnormal endothelial‒podocyte crosstalk, which plays a key role in TKI-induced podocyte injury and proteinuric nephropathy. This review article summarizes the underlying mechanism by which the abnormal endothelial‒podocyte crosstalk mediates podocyte injury and discusses the possible molecules and signal pathways involved in abnormal endothelial‒podocyte crosstalk. What is more, we highlight the molecules involved in podocyte injury and determine the essential roles of Rac1 and Cdc42; this provides evidence for exploring the abnormal endothelial‒podocyte crosstalk in TKI-induced nephrotoxicity.

Effects of Allicin on Pathophysiological Mechanisms during the Progression of Nephropathy Associated to Diabetes

This study aimed to assess the impact of allicin on the course of diabetic nephropathy. Study groups included control, diabetes, and diabetes-treated rats. Allicin treatment (16 mg/kg day/p.o.) started after 1 month of diabetes onset and was administered for 30 days. In the diabetes group, the systolic blood pressure (SBP) increased, also, the oxidative stress and hypoxia in the kidney cortex were evidenced by alterations in the total antioxidant capacity as well as the expression of nuclear factor (erythroid-derived 2)-like 2/Kelch ECH associating protein 1 (Nrf2/Keap1), hypoxia-inducible factor 1-alpha (HIF-1α), vascular endothelial growth factor (VEGF), erythropoietin (Epo) and its receptor (Epo-R). Moreover, diabetes increased nephrin, and kidney injury molecule-1 (KIM-1) expression that correlated with mesangial matrix, the fibrosis index and with the expression of connective tissue growth factor (CTGF), transforming growth factor-β1 (TGF-β1), and α-smooth muscle actin (α-SMA). The insulin levels and glucose transporter protein type-4 (GLUT4) expression were decreased; otherwise, insulin receptor substrates 1 and 2 (IRS-1 and IRS-2) expression was increased. Allicin increased Nrf2 expression and decreased SBP, Keap1, HIF-1α, and VEGF expression. Concurrently, nephrin, KIM-1, the mesangial matrix, fibrosis index, and the fibrotic proteins were decreased. Additionally, allicin decreased hyperglycemia, improved insulin levels, and prevented changes in (GLUT4) and IRSs expression induced by diabetes. In conclusion, our results demonstrate that allicin has the potential to help in the treatment of diabetic nephropathy. The cellular mechanisms underlying its effects mainly rely on the regulation of antioxidant, antifibrotic, and antidiabetic mechanisms, which can contribute towards delay in the progression of renal disease.

Low erythropoietin levels predict faster renal function decline in diabetic patients with anemia: a prospective cohort study

Elevated erythropoietin (EPO) levels have been reported to predict poor survival in various populations including diabetic patients. However, data regarding its impact on renal outcomes are scarce. We conducted a single-center, prospective cohort study of 339 type 2 diabetic patients with anemia. The primary outcome was the estimated glomerular filtration rate (eGFR) slope for two years. We performed multiple linear regression and restricted cubic spline analyses to assess the association of serum EPO levels with the renal outcome. Chronic kidney disease (CKD) was defined as eGFR <60 mL/min/1.73 m2 or urine albumin-to-creatinine ratio >30 mg/g creatinine. Median baseline EPO and eGFR level were 14.4 IU/L and 53 mL/min/1.73 m², respectively. Inappropriately low EPO levels were observed in 73% of anemic patients and 59% of anemic patients even without CKD, suggesting that EPO deficiency precedes the onset of CKD in diabetes mellitus. Multivariable analysis revealed that iron status and hemoglobin levels were major determinants of EPO levels. Median eGFR slope was −1.3 mL/min/1.73 m²/year. We found that low EPO levels, but not low hemoglobin levels, were associated with a faster decline in eGFR, independent of clinically relevant factors. The eGFR decline was steeper, particularly when the EPO level was below the upper limit of normal. Lower EPO concentrations were associated with rapid eGFR decline, especially in patients with iron deficiency (P for interaction = 0.01). Relative EPO deficiency should be considered as a culprit in anemia of unknown etiology in diabetic patients, even those without CKD. Low EPO levels, especially when accompanied by poor iron status, are predictive of rapid loss of renal function.

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.

Heterozygosity of mitogen-activated protein kinase organizer 1 ameliorates diabetic nephropathy and suppresses epithelial-to-mesenchymal transition-like changes in db/db mice

Background

Progressive diabetic nephropathy (DN) is characterized by tubulointerstitial fibrosis that is caused by accumulation of extracellular matrix. Induced by several factors, matrix-producing myofibroblasts may to some extent originate from tubular cells by epithelial-to-mesenchymal transition (EMT). Although previous data document that activation of hypoxia-inducible factor (HIF) signalling can be renoprotective in acute kidney disease, this issue remains controversial in chronic kidney injury. Here, we studied whether DN and EMT-like changes are ameliorated in a mouse model of type 2 diabetes mellitus with increased stability and activity of the HIF.

Methods

We used db/db mice that were crossed with transgenic mice expressing reduced levels of mitogen-activated protein kinase organizer 1 (MORG1), a scaffold protein interacting with prolyl hydroxylase domain 3 (PHD3), because of deletion of one MORG1 allele.

Results

We found significantly reduced nephropathy in diabetic MORG1+/- heterozygous mice compared with the diabetic wild-types (db/dbXMORG1+/+). Furthermore, we demonstrated that EMT-like changes in the tubulointerstitium of diabetic wild-type MORG1+/+ mice are present, whereas diabetic mice with reduced expression of MORG1 showed significantly fewer EMT-like changes.

Conclusions

These findings reveal that a deletion of one MORG1 allele inhibits the development of DN in db/db mice. The data suggest that the diminished interstitial fibrosis in these mice is a likely consequence of suppressed EMT-like changes.

SGLT-2 Inhibitors and Cardiovascular Protection: Lessons and Gaps in Understanding the Current Outcome Trials and Possible Benefits of Combining SGLT-2 Inhibitors With GLP-1 Agonists

Landmark trials on diabetes control have shown variable results in terms of cardiovascular benefits, with the majority showing a favorable effect of glycemic control on microvascular and, more recently, macrovascular complications. However, some trials pointed out a CV hazard with tight diabetes mellitus (DM) control. Most of those trials were assessing the impact of glycemic control, more than evaluating the effect of a certain medication. In the last decade, food and drugs administration (FDA) has mandated that all new hypoglycemic agents run a CV outcome trial (CVOT) for safety in order to grant and sustain approval. The most stunning results came from relatively new agents in the field of diabetes management, sodium-glucose cotransporter-2 inhibitors (SGLT2i) and the glucagon-like peptide-1 agonists (GLP-1 agonists), details of these CVOTs will be addressed later in this document. SGLT2i effect on the cardiovascular system remains an area of extensive research. We aimed in this review to summarize what is the current evidence of cardiovascular protection upon using SGLT2i. Moreover, we wanted to raise a point that may be strongly adopted in the future, combining SGLT2i plus GLP-1 agonists, having a cardiovascular privilege in both molecules.

Noninvasive Real-Time Characterization of Renal Clearance Kinetics in Diabetic Mice after Receiving Danshensu Treatment

Danshensu (DSS) is an active ingredient extracted from the root of the Danshen that could ameliorate oxidative stress via upregulation of heme oxygenase- (HO-) 1. Little is known about the treatment effects of DSS on kidney function in diabetic mice. Therefore, the primary aim of the present study was to characterize the renal clearance kinetics of IRdye800CW in db/db mice after DSS treatment. The secondary aim was to measure several biomarkers of renal function and oxidative stress (urinary F2-isoprostane, HO-1 in kidney and serum bilirubin). Fourteen db/db diabetic mice were randomly assigned into two groups and received either DSS treatment (DM + DSS) or vehicle treatment (DM). A third group that comprised of db/+ nondiabetic mice (non-DM control) received no DSS treatment and served as the nondiabetic control. At the end of a 3-week intervention period, serum and urinary biomarkers of renal function and oxidative stress were assessed and the renal clearance of IRdye800CW dye in all mice was determined noninvasively using Multispectral Optoacoustic Tomography. The major finding from this study suggested that DSS treatment in db/db mice improved renal clearance. Increased expression of HO-1 after DSS treatment also suggested that DSS might represent a potential therapeutic avenue for clinical intervention in diabetic nephropathy.

CERA Attenuates Kidney Fibrogenesis in the db/db Mouse by Influencing the Renal Myofibroblast Generation

Tubulointerstitial fibrosis (TIF) is a pivotal pathophysiological process in patients with diabetic nephropathy (DN). Multiple profibrotic factors and cell types, including transforming growth factor beta 1 (TGF-β1) and interstitial myofibroblasts, respectively, are responsible for the accumulation of extracellular matrix in the kidney. Matrix-producing myofibroblasts can originate from different sources and different mechanisms are involved in the activation process of the myofibroblasts in the fibrotic kidney. In this study, 16-week-old db/db mice, a model for type 2 DN, were treated for two weeks with continuous erythropoietin receptor activator (CERA), a synthetic erythropoietin variant with possible non-hematopoietic, tissue-protective effects. Non-diabetic and diabetic mice treated with placebo were used as controls. The effects of CERA on tubulointerstitial fibrosis (TIF) as well as on the generation of the matrix-producing myofibroblasts were evaluated by morphological, immunohistochemical, and molecular biological methods. The placebo-treated diabetic mice showed significant signs of beginning renal TIF (shown by picrosirius red staining; increased connective tissue growth factor (CTGF), fibronectin and collagen I deposition; upregulated KIM1 expression) together with an increased number of interstitial myofibroblasts (shown by different mesenchymal markers), while kidneys from diabetic mice treated with CERA revealed less TIF and fewer myofibroblasts. The mechanisms, in which CERA acts as an anti-fibrotic agent/drug, seem to be multifaceted: first, CERA inhibits the generation of matrix-producing myofibroblasts and second, CERA increases the ability for tissue repair. Many of these CERA effects can be explained by the finding that CERA inhibits the renal expression of the cytokine TGF-β1.

Targeting erythropoietin protects against proteinuria in type 2 diabetic patients and in zebrafish

Objective

Adult human kidneys produce erythropoietin (EPO), which regulates red blood cell formation; however, whether EPO also functions directly on kidney development and controls diabetic kidney disease remains unknown. Here we analyzed the role of EPO in kidney development and under hyperglycemic conditions in zebrafish and in humans.

Methods

Diabetic patients and respective controls were enrolled in two cohorts. Serum EPO level and urine protein change upon human EPO administration were then analyzed. Transient knockdown and permanent knockout of EPO and EPOR in renal TG(WT1B:EGFP) zebrafish were established using the morpholino technology and CRISPR/Cas9 technology. Zebrafish embryos were phenotypically analyzed using fluorescence microscopy, and functional assays were carried out with the help of TexasRed labeled 70 kDa Dextran. Apoptosis was determined using the TUNEL assay and Annexin V staining, and caspase inhibitor zVADfmk was used for rescue experiments.

Results

In type 2 diabetic patients, serum EPO level decreased with the duration of diabetes, which was linked to reduced kidney function. Human recombinant EPO supplementation ameliorated proteinuria in diabetic nephropathy patients. In zebrafish, loss-of-function studies for EPO and EPOR, showed morphological and functional alterations within the pronephros, adversely affecting pronephric structure, leading to slit diaphragm dysfunction by increasing apoptosis within the pronephros. Induction of hyperglycemia in zebrafish embryos induced pronephros alterations which were further worsened upon silencing of EPO expression.

Conclusions

EPO was identified as a direct renal protective factor, promoting renal embryonic development and protecting kidneys from hyperglycemia induced nephropathy.

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EPO exhibited renal protective and proteinuria ameliorating function in type 2 DM patients and in hyperglycemic zebrafish embryos.

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Enhanced co-expression of EPO and EPOR was identified in both glomeruli and tubuli of DN patients.

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EPO and its receptor directly regulate physiological kidney development via repressing apoptosis.

Early low-dose erythropoiesis-stimulating agent therapy and progression of moderate chronic kidney disease: a randomized, placebo-controlled trial

Background

It is unknown whether early intervention with low-dose erythropoiesis-stimulating agents (ESAs) in non-anaemic patients delays progression of chronic kidney disease (CKD).

Methods

In a single-blind, 24-month trial, adults with estimated glomerular filtration rate (eGFR) 30–59 mL/min/1.73 m2 and either Type 2 diabetes mellitus or previous kidney transplantation were randomized to low-dose continuous erythropoiesis receptor activator (CERA; monthly dose 30–75 µg; n = 115) or placebo (n = 120). The primary endpoint was the annual change in eGFR (abbreviated Modification of Diet in Renal Disease formula).

Results

Mean (standard deviation) eGFR was 40.7 (9.8) mL/min/1.73 m2 versus 39.8 (9.2) mL/min/1.73 m2 at baseline for CERA and placebo, respectively, and 39.0 (11.6) g/dL versus 39.7 (10.6) g/dL at the final visit. The median (interquartile range) annual reduction in eGFR was 0.5 (−2.2, 3.8) mL/min/1.73 m2 with CERA versus 0.4 (−2.0, 3.2) mL/min/1.73 m2 with placebo (P = 0.657). No significant difference in the annual change in eGFR was observed between treatment groups in the subpopulations with Type 2 diabetes or kidney transplant. Adverse events with a suspected relation to study drug occurred in 22.0% and 16.2% of patients randomized to CERA or placebo, respectively, and adverse events led to study drug discontinuation in 11.0% and 8.5% of patients.

Conclusions

Patients with moderate CKD and Type 2 diabetes or previous kidney transplantation showed stable renal function that was unaffected by administration of low-dose ESA. In addition, there was no clinically meaningful effect of 2-year low-dose ESA treatment on albuminuria, an important surrogate marker of kidney injury.

Glycative Stress and Its Defense Machinery Glyoxalase 1 in Renal Pathogenesis

Chronic kidney disease is a major public health problem around the world. Because the kidney plays a role in reducing glycative stress, renal dysfunction results in increased glycative stress. In turn, glycative stress, especially that due to advanced glycated end products (AGEs) and their precursors such as reactive carbonyl compounds, exacerbates chronic kidney disease and is related to premature aging in chronic kidney disease, whether caused by diabetes mellitus or otherwise. Factors which hinder a sufficient reduction in glycative stress include the inhibition of anti-glycation enzymes (e.g., GLO-1), as well as pathogenically activated endoplasmic reticulum (ER) stress and hypoxia in the kidney. Promising strategies aimed at halting the vicious cycle between chronic kidney disease and increases in glycative stress include the suppression of AGE accumulation in the body and the enhancement of GLO-1 to strengthen the host defense machinery against glycative stress.

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.

Chronic Treatment With an Erythropoietin Receptor Ligand Prevents Chronic Kidney Disease–Induced Enlargement of Myocardial Infarct Size

Chronic kidney disease (CKD) is known to increase myocardial infarct size after ischemia/reperfusion. However, a strategy to prevent the CKD-induced myocardial susceptibility to ischemia/reperfusion injury has not been developed. Here, we examined whether epoetin β pegol, a continuous erythropoietin receptor activator (CERA), normalizes myocardial susceptibility to ischemia/reperfusion injury by its effects on protective signaling and metabolomes in CKD. CKD was induced by 5/6 nephrectomy in rats (subtotal nephrectomy, SNx), whereas sham-operated rats served controls (Sham). Infarct size as percentage of area at risk after 20-minutes coronary occlusion/2-hour reperfusion was larger in SNx than in Sham: 60.0±4.0% versus 43.9±2.2%. Administration of CERA (0.6 μg/kg SC every 7 days) for 4 weeks reduced infarct size in SNx (infarct size as percentage of area at risk=36.9±3.9%), although a protective effect was not detected for the acute injection of CERA. Immunoblot analyses revealed that myocardial phospho-Akt-Ser473 levels under baseline conditions and on reperfusion were lower in SNx than in Sham, and CERA restored the Akt phosphorylation on reperfusion. Metabolomic analyses showed that glucose 6-phosphate and glucose 1-phosphate were reduced and malate:aspartate ratio was 1.6-fold higher in SNx than in Sham, suggesting disturbed flux of malate–aspartate shuttle by CKD. The CERA improved the malate:aspartate ratio in SNx to the control level. In H9c2 cells, mitochondrial Akt phosphorylation by insulin-like growth factor-1 was attenuated by malate–aspartate shuttle inhibition. In conclusion, the results suggest that a CERA prevents CKD-induced susceptibility of the myocardium to ischemia/reperfusion injury by restoration of Akt-mediated signaling possibly via normalized malate–aspartate shuttle flux.

Hyperoside ameliorates glomerulosclerosis in diabetic nephropathy by downregulating miR-21

The purpose of this study was to investigate the therapeutic effects of hyperoside (Hyp) on glomerulosclerosis in diabetic nephropathy and its underlying mechanisms. Blood glucose, kidney mass, and renal function of mice were measured. Renal morphology was observed using hematoxylin and eosin, periodic acid - Schiff's, and Masson's trichrome stain. Fibronectin (FN) and collagen IV (COL IV) in kidney were determined by Western blot and immunohistochemical studies. Matrix metalloproteinases (MMP)-2 and -9 and tissue inhibitors of metalloproteinase (TIMP)-1 in renal tissues were detected on both the mRNA and protein levels. miRNA expression and artificial alterations by miRNA agomir transfection were evaluated to investigate the protective mechanism of Hyp in mesangial cells. Hyp effectively improved renal function and physiologic features of db/db mice. Hyp also ameliorated glomerulosclerosis by suppressing FN, COL IV, and TIMP-1 expressions and promoting MMP-9 and MMP-2 expressions. The change in MMP-9 mRNA expression was inconsistent with that in protein levels in kidney, indicating that there was a post-transcriptional regulation. Further exploration in vitro showed that miR-21 was downregulated by Hyp, increasing expression of its target, MMP-9. These results suggest that Hyp can ameliorate glomerulosclerosis in diabetic nephropathy by downregulating miR-21 to increase expression of its target, MMP-9.

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.

Restoration of Haemoglobin Level Using Hydrodynamic Gene Therapy with Erythropoietin Does Not Alleviate the Disease Progression in an Anaemic Mouse Model for TGFβ1-Induced Chronic Kidney Disease

Erythropoietin, Epo, is a 30.4 kDa glycoprotein hormone produced primarily by the fetal liver and the adult kidney. Epo exerts its haematopoietic effects by stimulating the proliferation and differentiation of erythrocytes with subsequent improved tissue oxygenation. Epo receptors are furthermore expressed in non-haematopoietic tissue and today, Epo is recognised as a cytokine with many pleiotropic effects. We hypothesize that hydrodynamic gene therapy with Epo can restore haemoglobin levels in anaemic transgenic mice and that this will attenuate the extracellular matrix accumulation in the kidneys. The experiment is conducted by hydrodynamic gene transfer of a plasmid encoding murine Epo in a transgenic mouse model that overexpresses TGF-β1 locally in the kidneys. This model develops anaemia due to chronic kidney disease characterised by thickening of the glomerular basement membrane, deposition of mesangial matrix and mild interstitial fibrosis. A group of age matched wildtype littermates are treated accordingly. After a single hydrodynamic administration of plasmid DNA containing murine EPO gene, sustained high haemoglobin levels are observed in both transgenic and wildtype mice from 7.5 ± 0.6 mmol/L to 9.4 ± 1.2 mmol/L and 10.7 ± 0.3 mmol/L to 15.5 ± 0.5 mmol/L, respectively. We did not observe any effects in the thickness of glomerular or tubular basement membrane, on the expression of different collagen types in the kidneys or in kidney function after prolonged treatment with Epo. Thus, Epo treatment in this model of chronic kidney disease normalises haemoglobin levels but has no effect on kidney fibrosis or function.

The role of hypoxia and Morg1 in renal injury

BACKGROUND

Renal hypoxia is known to play an important role in the pathophysiology of acute renal injury as well as in chronic kidney diseases. The mediators of hypoxia are the transcription factors HIF (hypoxia-inducible factors), that are highly regulated. Under normoxic conditions constitutively expressed HIF-α subunits are hydroxylated by prolyl hydroxylases (PHD1, PHD2, and PHD3) and subsequently degraded by proteasomes.

MATERIALS AND METHODS

This narrative review is based on the material searched for and obtained via PubMed and MEDLINE up to January 2015.

RESULTS

The MAPK organizer 1 (Morg1) has been identified to act as a scaffold protein of PHD3 and suppression of Morg1 leads to the stabilization of HIF-α, which forms in the absence of oxygen a heterodimer with HIF-β, translocates to the nucleus and promotes the transcription of HIF target genes.

CONCLUSIONS

This review summarizes the current knowledge regarding the role of hypoxia, HIF signalling, and Morg1 in acute and chronic renal injury.

A non-erythropoietic peptide derivative of erythropoietin decreases susceptibility to diet-induced insulin resistance in mice

BACKGROUND AND PURPOSE

The haematopoietic activity of erythropoietin (EPO) is mediated by the classic EPO receptor (EpoR) homodimer, whereas tissue-protective effects are mediated by a heterocomplex between EpoR and the β-common receptor (βcR). Here, we investigated the effects of a novel, selective ligand of this heterocomplex - pyroglutamate helix B surface peptide (pHBSP) - in mice fed a diet enriched in sugars and saturated fats.

EXPERIMENTAL APPROACH

Male C57BL/6J mice were fed a high-fat high-sucrose diet (HFHS) for 22 weeks. pHBSP (30 μg·kg(-1) s.c.) was administered for the last 11 weeks. Biochemical assays, histopathological and immunohistochemical examinations and Western blotting were performed on serum and target organs (liver, kidney and skeletal muscle).

KEY RESULTS

Mice fed with HFHS diet exhibited insulin resistance, hyperlipidaemia, hepatic lipid accumulation and kidney dysfunction. In gastrocnemius muscle, HFHS impaired the insulin signalling pathway and reduced membrane translocation of glucose transporter type 4 and glycogen content. Treatment with pHBSP ameliorated renal function, reduced hepatic lipid deposition, and normalized serum glucose and lipid profiles. These effects were associated with an improvement in insulin sensitivity and glucose uptake in skeletal muscle. Diet-induced overproduction of the myokines IL-6 and fibroblast growth factor-21 were attenuated by pHBSP and, most importantly, pHBSP markedly enhanced mitochondrial biogenesis in skeletal muscle.

CONCLUSIONS AND IMPLICATIONS

Chronic treatment of mice with an EPO derivative, devoid of haematopoietic effects, improved metabolic abnormalities induced by a high-fat high-sucrose diet, by affecting several levels of the insulin signalling and inflammatory cascades within skeletal muscle, while enhancing mitochondrial biogenesis.

Erythropoietin action in stress response, tissue maintenance and metabolism

Erythropoietin (EPO) regulation of red blood cell production and its induction at reduced oxygen tension provides for the important erythropoietic response to ischemic stress. The cloning and production of recombinant human EPO has led to its clinical use in patients with anemia for two and half decades and has facilitated studies of EPO action. Reports of animal and cell models of ischemic stress in vitro and injury suggest potential EPO benefit beyond red blood cell production including vascular endothelial response to increase nitric oxide production, which facilitates oxygen delivery to brain, heart and other non-hematopoietic tissues. This review discusses these and other reports of EPO action beyond red blood cell production, including EPO response affecting metabolism and obesity in animal models. Observations of EPO activity in cell and animal model systems, including mice with tissue specific deletion of EPO receptor (EpoR), suggest the potential for EPO response in metabolism and disease.