Modelling diabetic nephropathy in mice

Revisiting Experimental Models of Diabetic Nephropathy

Diabetes prevalence is constantly increasing and, nowadays, it affects more than 350 million people worldwide. Therefore, the prevalence of diabetic nephropathy (DN) has also increased, becoming the main cause of end-stage renal disease (ESRD) in the developed world. DN is characterized by albuminuria, a decline in glomerular filtration rate (GFR), hypertension, mesangial matrix expansion, glomerular basement membrane thickening, and tubulointerstitial fibrosis. The therapeutic advances in the last years have been able to modify and delay the natural course of diabetic kidney disease (DKD). Nevertheless, there is still an urgent need to characterize the pathways that are involved in DN, identify risk biomarkers and prevent kidney failure in diabetic patients. Rodent models provide valuable information regarding how DN is set and its progression through time. Despite the utility of these models, kidney disease progression depends on the diabetes induction method and susceptibility to diabetes of each experimental strain. The classical DN murine models (Streptozotocin-induced, Akita, or obese type 2 models) do not develop all of the typical DN features. For this reason, many models have been crossed to a susceptible genetic background. Knockout and transgenic strains have also been created to generate more robust models. In this review, we will focus on the description of the new DN rodent models and, additionally, we will provide an overview of the available methods for renal phenotyping.

Systematic review and meta-analysis of mouse models of diabetes-associated ulcers

Mouse models are frequently used to study diabetes-associated ulcers, however, whether these models accurately simulate impaired wound healing has not been thoroughly investigated. This systematic review aimed to determine whether wound healing is impaired in mouse models of diabetes and assess the quality of the past research. A systematic literature search was performed of publicly available databases to identify original articles examining wound healing in mouse models of diabetes. A meta-analysis was performed to examine the effect of diabetes on wound healing rate using random effect models. A meta-regression was performed to examine the effect of diabetes duration on wound healing impairment. The quality of the included studies was also assessed using two newly developed tools. 77 studies using eight different models of diabetes within 678 non-diabetic and 720 diabetic mice were included. Meta-analysis showed that wound healing was impaired in all eight models. Meta-regression suggested that longer duration of diabetes prior to wound induction was correlated with greater degree of wound healing impairment. Pairwise comparisons suggested that non-obese diabetic mice exhibited more severe wound healing impairment compared with db/db mice, streptozotocin-induced diabetic mice or high-fat fed mice at an intermediate stage of wound healing (p<0.01). Quality assessment suggested that the prior research frequently lacked incorporation of key clinically relevant characteristics. This systematic review suggested that impaired wound healing can be simulated in many different mouse models of diabetes but these require further refinement to become more clinically relevant.

Using Genetic and Species Diversity to Tackle Kidney Disease

Progress in the identification of causal genes and understanding of the mechanism underlying kidney disease is hindered by the almost exclusive use of a few animal models with restrictive monogenic backgrounds that may be more resistant to kidney disease compared with humans and, therefore, poor models. Exploring the large genetic diversity in classical animal models, such as mice and rats, and leveraging species diversity will allow us to use the genetic advantages of zebrafish, Drosophila, and other species, to develop both new animal models that are more relevant to the study of human kidney disease and potential therapies.

Therapeutic Renin Inhibition in Diabetic Nephropathy-A Review of the Physiological Evidence

The purpose of this systematic review was to investigate the scientific evidence to support the use of direct renin inhibitors (DRIs) in diabetic nephropathy (DN). MEDLINE was searched for articles reported until 2018. A standardized dataset was extracted from articles describing the effects of DRIs on plasma renin activity (PRA) in DN. A total of three clinical articles studying PRA as an outcome measure for DRIs use in DN were identified. These clinical studies were randomized controlled trials (RCTs): one double-blind crossover, one post hoc of a double-blind and placebo-controlled study, and one open-label and parallel-controlled study. Two studies reported a significant decrease of albuminuria associated with PRA reduction. One study had a DRI as monotherapy compared with placebo, and two studies had DRI as add-in to an angiotensin II (Ang II) receptor blocker (ARB). Of 10,393 patients with DN enrolled in five studies with DRI, 370 (3.6%) patients had PRA measured. Only one preclinical study was identified that determined PRA when investigating the effects of aliskiren in DN. Moreover, most of observational preclinical and clinical studies identified report on a low PRA or hyporeninemic hypoaldosteronism in DM. Renin inhibition has been suggested for DN, but proof-of-concept studies for this are scant. A small number of clinical and preclinical studies assessed the PRA effects of DRIs in DN. For a more successful translational research for DRIs, specific patient population responsive to the treatment should be identified, and PRA may remain a biomarker of choice for patient stratification.

Sex Differences in Diabetic Kidney Disease

While the global prevalence of both type 1 and type 2 diabetes mellitus is similar in men and women, the consequences of diabetes on associated end-organ complications, including diabetic kidney disease appear to be more sex-specific. Particularly, women with diabetes have higher mortality rates for diabetes-related deaths, and higher prevalence of diabetic kidney disease risk factors such as hypertension, hyperglycemia, obesity, and dyslipidemia. However, the evidence for the impact of sex on diabetic kidney disease prevalence and disease progression is limited and inconsistent. Although most studies agree that the protective effect of the female sex against the development of kidney disease is diminished in the setting of diabetes, the reasons for this observation are unclear. Whether or not sex differences exist in the risk of diabetic kidney disease is also unclear, with studies reporting either higher risk in men, women, or no sex differences. Despite the remaining controversies, some of the factors that associate with sex differences in the risk of diabetic kidney disease are age at onset, and type and duration of diabetes. There is growing appreciation of the importance of sex hormones in the regulation of renal function, with estrogens generally considered to be renoprotective. Although some progress has been made towards better understanding of the mechanisms by which sex hormones play a role in the pathophysiology of diabetic kidney disease, the translational potential of this knowledge is still underappreciated. A better understanding of sex differences in diabetic kidney disease may provide basis for personalized and sex-specific treatment of diabetic kidney disease.

Exploring the role of the metabolite-sensing receptor GPR109a in diabetic nephropathy

Alterations in gut homeostasis may contribute to the progression of diabetic nephropathy. There has been recent attention on the renoprotective effects of metabolite-sensing receptors in chronic renal injury, including the G protein-coupled receptor (GPR)109a, which ligates the short-chain fatty acid butyrate. However, the role of GPR109a in the development of diabetic nephropathy, a milieu of diminished microbiome-derived metabolites, has not yet been determined. The present study aimed to assess the effects of insufficient GPR109a signaling, via genetic deletion of GPR109a, on the development of renal injury in diabetic nephropathy. Gpr109a^-/- mice or their wild-type littermates (Gpr109a^+/+) were rendered diabetic with streptozotocin. Mice received a control diet or an isocaloric high-fiber diet (12.5% resistant starch) for 24 wk, and gastrointestinal permeability and renal injury were determined. Diabetes was associated with increased albuminuria, glomerulosclerosis, and inflammation. In comparison, Gpr109a^-/- mice with diabetes did not show an altered renal phenotype. Resistant starch supplementation did not afford protection from renal injury in diabetic nephropathy. While diabetes was associated with alterations in intestinal morphology, intestinal permeability assessed in vivo using the FITC-dextran test was unaltered. GPR109a deletion did not worsen gastrointestinal permeability. Furthermore, 12.5% resistant starch supplementation, at physiological concentrations, had no effect on intestinal permeability or morphology. The results of this study indicate that GPR109a does not play a critical role in intestinal homeostasis in a model of type 1 diabetes or in the development of diabetic nephropathy.

Practical Considerations when Using Mouse Models of Diabetes

Mouse models of diabetes are important tools used in preclinical diabetes research. However, when working with these models, it is important to consider factors that could influence experimental outcome. This is particularly important given the wide variety of models available, each with specific characteristics that could be influenced by extrinsic or intrinsic factors. Blood glucose concentrations, a commonly used and valid endpoint in these models, are particularly susceptible to manipulation by these factors. These include potential effects of intrinsic factors such as strain, sex, and age and extrinsic factors such as husbandry practices and experimental protocols. These variables should therefore be taken into consideration when the model is chosen and the experiments are designed. This chapter outlines common variables that can impact the phenotype of a model, as well as describes the methods used for assessing onset of diabetes and monitoring diabetic mice.

Over-expression of arginine vasopressin in magnocellular neurosecretory cells of hypothalamus and its potential relationship with development of diabetic nephropathy

INTRODUCTION

We aimed to assess our hypothesis that the expression changes of arginine vasopressin (AVP) in the magnocellular neurosecretory cells (MNCs) of hypothalamus and V2 receptor for AVP (RVP) in kidney may contribute to the pathogenesis of diabetic nephropathy (DN).

MATERIAL AND METHODS

Twenty-five male Wistar rats were randomly assigned to the control group and the diabetes mellitus (DM) group. Periodic acid-Schiff (PAS) staining and electron microscopy were used for morphological studies. Immunohistochemical staining for glial fibrillary acidic protein (GFAP) is standard for visualization of reactive astrocytes in the hypothalamus. Hypothalamus was used for immunofluorescence of AVP. Kidney was used for immunohistochemical staining of RVP. Quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR) was used for quantitative determinations of AVP mRNA in hypothalamus and RVP mRNA in kidney. Western blot was used to measure the protein expression of AVP in hypothalamus and RVP in kidney.

RESULTS

Morphological studies showed abnormalities in kidney and hypothalamus in the DM group. The number of neurons and the gray value of astrocytes in hypothalamus in the DM group were markedly decreased. The expression level of AVP in hypothalamus and the expression level of RVP in kidney of DM rats were significantly increased. The positive correlations between the proteinuria and expression (mRNA and protein) of AVP, proteinuria and expression (mRNA and protein) of RVP, and the expression of AVP and RVP levels were found.

CONCLUSIONS

AVP was upregulated in the MNCs of hypothalamus and RVP was upregulated in kidney in streptozotocin-induced DM rats, indicating their potential roles in the development of DN.

Sex differences in progression of diabetic nephropathy in OVE26 type 1 diabetic mice

AIMS

OVE26 mice (FVB background), genetically overexpressing calmodulin in pancreatic beta cells, develop early onset type 1 diabetes, leading to progressive diabetic nephropathy (DN), with features of established human DN. The role of gender in characteristics of renal lesions has remained unexplored.

METHODS

Male and female OVE26 mice were compared to age and sex matched wild-type, nondiabetic FVB mice at ages of 4, 12, 24 and 36 weeks. Nephropathy was examined by measuring urine albumin-to-creatinine ratio, histopathology, expression of pathological markers and immunochemistry in the same cohort of mice.

RESULTS

Progression of diabetic kidney disease was evident first in the OVE26 glomerulus, initially as mesangial matrix expansion at 4 weeks followed by loss of podocytes, glomerular volume expansion and severe albuminuria at 12 weeks. Tubule dilation and initiation of interstitial fibrosis did not become significant until 24 weeks. T-lymphocyte infiltration into the renal parenchyma appeared at 36 weeks. OVE26 female mice developed more advanced DN than male OVE26 mice, such as more severe albuminuria, greater podocyte loss, additional fibrosis and significantly more inflammatory cell infiltration. The female OVE26 mice had lowest level of plasma estradiol in all 36 weeks old mice, as well as renal estrogen receptors.

CONCLUSIONS

This demonstration of the role of gender, combined with the detailed characterization of DN progression illustrates the value of OVE26 mice for understanding gender effects on DN and provides the basis for researchers to better select the age and sex of OVE26 mice in future studies of type 1 DN.

RESEARCH IN CONTEXT

What is already known about this subject? What is the key question? What are the new findings? How might this impact on clinical practice in the foreseeable future?

Sugar-Lowering Drugs for Type 2 Diabetes Mellitus and Metabolic Syndrome-Strategies for In Vivo Administration: Part-II

Diabetes is a complex disease characterized by hyperglycemia, together with polyuria, polydipsia, and polyphagia. While Type 1 diabetes mellitus (T1DM) results from genetic, environmental, or immune dysfunction factors leading to pancreatic β-cell destruction depriving the organism from endogenous insulin, Type 2 diabetes mellitus (T2DM) is characterized by peripheral insulin resistance. Depending on the type of diabetes mellitus and drug mechanism to study, the animal model should be carefully selected among the wide variety of the currently available ones. This review discusses the most common animal models currently employed to study T1DM and T2DM. Moreover, an overview on the administration routes that could be used is also discussed.

Coro2b, a podocyte protein downregulated in human diabetic nephropathy, is involved in the development of protamine sulphate-induced foot process effacement

Podocytes have an important role in the pathogenesis of diabetic nephropathy (DN). Podocyte foot process effacement, mediated largely by the actin-based cytoskeleton of foot processes, is commonly detected in DN and is believed to be a key pathogenic event in the development of proteinuria. In this study, we identified coronin 2b (Coro2b), a member of known actin-regulating proteins, the coronins, as a highly podocyte-enriched molecule located at the cytoplasmic side of the apical plasma membrane. Studies in human renal biopsies show that glomerular Coro2b expression is significantly down-regulated in patients with DN. Studies in knockout mice indicate that Coro2b is not required for the development or maintenance of the glomerular filtration barrier. Moreover, inactivation of Coro2b specifically in podocytes does not affect the outcome of nephropathy in a streptozotocin-induced diabetes model. However, Coro2b seems to modulate the reorganization of foot processes under pathological conditions as Coro2b knockout podocytes are partially protected from protamine sulfate perfusion-induced foot process effacement. Taken together, our study suggests a role for Coro2b in the pathogenesis of glomerulopathies. Further studies regarding the involvement of Coro2b in podocyte health and diseases are warranted.

Activation of 20-HETE/PPARs involved in reno-therapeutic effect of naringenin on diabetic nephropathy

Naringenin is a flavanone compound found in citrus fruits. Recent researches showed that naringenin has many potentially pharmacological effects. However, the therapeutic effect and the potential mechanism of naringenin on diabetic nephropathy (DN) remain to be elucidated. DN model was established by a high-fat diet combined with streptozotocin (STZ), which was confirmed by the levels of fasting blood glucose (FBG, more than 11.1 mmol/L) and urinary albumin (10 times higher than the normal mice). After 5 weeks of STZ injection, the DN was developed in model mice. Then naringenin (25 or 75 mg/kg·d) were supplemented for 4 weeks. At the end of the experiment, the injury of the renal function and structure was deteriorated. Concomitantly, peroxisome proliferators-activated receptors (PPARs) protein expression was down-regulated, and CYP4A expression and 20-hydroxyeicosatetraenoic acid (20-HETE) level were reduced in DN mice. Naringenin administration improved the renal damage of DN mice, and up-regulated PPARs expression, increased CYP4A-20-HETE level. Consistent with the results of in vivo, glucose at 30 mmol/L (high glucose, HG) significantly induced cell proliferation and hypertrophy in NRK-52E cells, following the reductive PPARs protein expression and the downward CYP4A-20-HETE level. Naringenin (0.01, 0.1, 1 μmol/L) reversed these changes induced by HG in a dose-dependent manner. HET0016, a selective inhibitor of 20-HETE synthase, partially blocked the effects of naringenin. In conclusion, naringenin has a therapeutic effect on DN, which may be, at least partly, related to the activation of CYP4A-20-HETE and the up-regulation of PPARs.

Diabetes-Induced DUSP4 Reduction Promotes Podocyte Dysfunction and Progression of Diabetic Nephropathy

Diabetic nephropathy (DN) remains the leading cause of end-stage renal disease. Hyperglycemia-induced podocyte dysfunction is a major contributor of renal function impairment in DN. Previous studies showed that activation of mitogen-activated protein kinase (MAPK) in diabetes promotes podocyte dysfunction and cell death. Dual specificity phosphatases (DUSPs) are a family of phosphatases mainly responsible for MAPK inhibition. In this study, we demonstrated that diabetes and high glucose exposure decreased DUSP4 expression in cultured podocytes and glomeruli. Diabetes-induced DUSP4 reduction enhanced p38 and c-Jun N-terminal kinase (JNK) activity and podocyte dysfunction. The overexpression of DUSP4 prevented the activation of p38, JNK, caspase 3/7 activity, and NADPH oxidase 4 expression induced by high glucose level exposure. Deletion of DUSP4 exacerbated albuminuria and increased mesangial expansion and glomerular fibrosis in diabetic mice. These morphological changes were associated with profound podocyte foot process effacement, cell death, and sustained p38 and JNK activation. Moreover, inhibition of protein kinase C-δ prevented DUSP4 expression decline and p38/JNK activation in the podocytes and renal cortex of diabetic mice. Analysis of DUSP4 expression in the renal cortex of patients with diabetes revealed that decreased DUSP4 mRNA expression correlated with reduced estimated glomerular filtration rate (<60 mL/min/1.73 m²). Thus, this study demonstrates that preserving DUSP4 expression could protect against podocyte dysfunction and preserve glomerular function in DN.

Rat models of colistin nephrotoxicity: previous experimental researches and future perspectives

Colistin is an old antibiotic, which is abandoned decades ago because of high nephrotoxicity rates. However, it is reintroduced to clinical medicine due to lack of newly discovered antibiotics and is still widely used for the treatment of resistant gram-negative infections. Discovering mechanisms to reduce nephrotoxicity risk is of significant importance since exposed patients may have many other factors that alter kidney functions. Several agents were evaluated in animal models of colistin nephrotoxicity as a means to prevent kidney injury. Considerable heterogeneity exists in terms of reporting colistin dosing and experimental designs. This issue leads clinicians to face difficulties in designing studies and sometimes may lead to report dosing strategies inadequately. Here, we present a review according to animal models of colistin nephrotoxicity using data gathered from previous experiments to draw attention on possible complexities that researchers may encounter.

Ergosterol Ameliorates Diabetic Nephropathy by Attenuating Mesangial Cell Proliferation and Extracellular Matrix Deposition via the TGF-β1/Smad2 Signaling Pathway

(1) Background: Diabetic nephropathy, a microvascular complication of diabetes, is one of the principal causes of end-stage renal disease worldwide. The aim of this study was to explore the therapeutic effects of ergosterol on diabetic nephropathy. (2) Methods: Streptozotocin (STZ)-induced C57BL/6 diabetic mice were treated with ergosterol (10, 20, 40 mg/kg/day) for 8 weeks by oral gavage. The in vitro study employed rat mesangial cells exposed to 30 mM glucose for 48 h in the presence of 10 or 20 μM ergosterol. (3) Results: Ergosterol treatment improved body weights, ameliorated the majority of biochemical and renal functional parameters and histopathological changes, and reduced extracellular matrix (ECM) deposition in diabetic mice. In vitro, ergosterol suppressed proliferation, reduced the levels of ECM proteins, and increased the expression of matrix metalloproteinase-2 and -9 in high glucose-induced mesangial cells; Furthermore, ergosterol markedly improved transforming growth factor-β1 (TGF-β1) expression, enhanced phosphorylation levels of drosophila mothers against decapentaplegic 2 (Smad2), and regulated the downstream factors in vivo and in vitro. (4) Conclusions: Ergosterol alleviated mesangial cell proliferation and the subsequent ECM deposition by regulating the TGF-β1/Smad2 signaling pathway.

Effect of a novel nonsteroidal selective mineralocorticoid receptor antagonist, esaxerenone (CS-3150), on blood pressure and renal injury in high salt-treated type 2 diabetic mice

Although beneficial antihypertensive and antialbuminuric effects of steroidal mineralocorticoid receptor (MR) antagonists have been shown, the use of these drugs has been clinically limited in diabetic kidney disease (DKD) because of the high incidence of side effects. Here, we aimed to examine the effect of a novel nonsteroidal selective mineralocorticoid receptor antagonist, esaxerenone, on blood pressure and renal injury in high salt-treated type 2 diabetic KK-A^y mice, a model of human hypertensive DKD. KK-A^y mice were treated with a normal salt diet (NS: 0.3% NaCl, n = 5), high salt diet (HS: 4% NaCl, n = 8), HS + esaxerenone (1 mg/kg/day, p.o., n = 8), or HS + spironolactone, a steroidal non-selective MR antagonist (20 mg/kg/day, p.o., n = 7) for 8 weeks. Renal tissue oxidative stress was evaluated by dihydroethidium florescence intensity. HS-treated diabetic KK-A^y mice showed higher blood pressure and severe albuminuria, glomerular injury, tubulointerstitial fibrosis, renal inflammation, and oxidative stress than NS-treated diabetic KK-A^y mice. Treatment with esaxerenone or spironolactone decreased blood pressure to a similar extent in HS-treated KK-A^y mice. Conversely, esaxerenone elicited a greater attenuation of albuminuria, glomerular injury, tubulointerstitial fibrosis, and renal inflammation than spironolactone, which were associated with reduction in renal oxidative stress. These data indicate for the first time that a nonsteroidal MR antagonist elicits renoprotective effects in DKD mice.

Assessing urinary levels of IL-18, NGAL and albumin creatinine ratio in patients with diabetic nephropathy

AIMS

Diabetic nephropathy (DN) is a serious microvascular complication of a longstanding hyperglycemia. This study aims to evaluate whether urinary neutrophil gelatinase-associated lipocalin (NGAL) and urinary Interleukin-18 possess a better diagnostic value than albumin creatinine ratio in assessing the severity of nephropathy in patients with type 2 diabetes mellitus (T2DM).

MATERIAL & METHODS

Ninety participants diagnosed with T2DM were recruited and they were divided into three study groups according to their albumin/creatinine ratio (ACR): (Normoalbuminuria group, Microalbuminuria group, and Macroalbuminuria group). A matching of Ninety healthy subjects were included as controls. Blood and urine samples were collected to measure various markers of glycemic control and kidney function.

RESULTS

IL-18 levels were not changed significantly between all study groups (P > 0.05), despite a significant positive correlation between IL-18 and urinary albumin levels. NGAL levels were significantly increased in Microalbuminuria group and Macroalbuminuria group as compared to the control and Normoalbuminuria groups. NGAL was also positively correlated with urinary albumin and ACR, but negatively correlated with the age and body mass index. Receiver Operating Characteristic curves revealed that for early detection of DN, the best cutoff values to discriminate DN and diabetic without nephropathy groups were ˃ 21.4 ng/ml for NGAL (94.67 sensitivity, 26.67% specificity), ≤0.34 pg/mL for IL-18 (72% sensitivity, 53.33% specificity), and ˃29.8 mg/g for ACR (80% sensitivity, 100% specificity).

CONCLUSION

We conclude that the urinary ACR is a more accurate individual biomarker of DN when compared to both NGAL and IL-18.

Early Enhanced Leucine-Rich α-2-Glycoprotein-1 Expression in Glomerular Endothelial Cells of Type 2 Diabetic Nephropathy Model Mice

Abnormal angiogenesis plays a major role in the development of early stage diabetic nephropathy. Vascular endothelial growth factor (VEGF) is a classical proangiogenic factor that regulates abnormal glomerular angiogenesis linked to glomerular hypertrophy in the early stage of diabetic nephropathy. Leucine-rich α-2-glycoprotein-1 (LRG1) was recently reported as a novel proangiogenic factor that is expressed in endothelial cells and promotes angiogenesis by modulating the transforming growth factor-β signaling pathway. However, the pathophysiology of LRG1 in diabetic nephropathy remains largely unknown. In the present study, we investigated intrarenal expression of the novel proangiogenic factor LRG1 in diabetic db/db mice by immunohistochemistry and a laser capture microdissection method during the development of diabetic nephropathy. We hypothesized that glomerular LRG1 expression is increased earlier than VEGF expression under conditions of pathological angiogenesis in the early stage of diabetic nephropathy. Thus, we compared glomerular expression of VEGF and LRG1 in diabetic db/db mice at 16 and 24 weeks of age. At 16 weeks, diabetic db/db mice exhibited glomerular hypertrophy with abnormal angiogenesis characterized by endothelial cell proliferation, which was concomitant with an increase in LRG1 expression of glomerular endothelial cells. However, glomerular VEGF expression was not increased at this early stage. At 24 weeks, the features of early diabetic nephropathy in db/db mice had developed further, along with further enhanced glomerular LRG1 expression. At this late stage, glomerular VEGF and fibrosis-related-gene expression was also significantly increased compared with nondiabetic db/m mice. These results suggest that LRG1 plays a pivotal role in the initial development of diabetic nephropathy by promoting abnormal angiogenesis, thereby suggesting that LRG1 is a potential preemptive therapeutic target of diabetic nephropathy.

Targeting inflammation in diabetic nephropathy: a tale of hope

INTRODUCTION

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD). Beyond the new anti-diabetic drugs that possess markedly cardiovascular and renal protective effects, no novel direct therapies for DN have become available on the market in the last twenty years. Recently well-designed clinical trials for the treatment of DN, with attractive pathogenetic rationale, e.g. bardoxolone and atrasentan, were canceled or stopped because of safety concerns or lack of reaching the end points, respectively.

AREAS COVERED

In this review, we focus on the involvement of inflammation in the pathogenesis of DN. We update information from recent experimental and clinical studies that reported beneficial effects of several agents targeting chemokines, cytokines, transcription factors and kinases as well as several compounds with anti-inflammatory properties on DN.

EXPERT OPINION

Inflammation plays a key role in the DN progression. Preclinical studies have identified several anti-inflammatory molecules that effective decrease albuminuria and/or proteinuria. However, limited clinical trials in humans have been performed to confirm these results. Inhibitors of CCL2/CCR2, IL-1β and JAK/STAT pathways, and Nrf2 inducers are promising therapeutic options to improve the renal outcome of patients with DN, but appropriate clinical trials are necessary.

Inflammation and Immunity Pathways Regulate Genetic Susceptibility to Diabetic Nephropathy

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease worldwide, but its molecular pathogenesis is not well defined, and there are no specific treatments. In humans, there is a strong genetic component determining susceptibility to DN. However, specific genes controlling DN susceptibility in humans have not been identified. In this study, we describe a mouse model combining type 1 diabetes with activation of the renin-angiotensin system (RAS), which develops robust kidney disease with features resembling human DN: heavy albuminuria, hypertension, and glomerulosclerosis. Additionally, there is a powerful effect of genetic background regulating susceptibility to nephropathy; the 129 strain is susceptible to kidney disease, whereas the C57BL/6 strain is resistant. To examine the molecular basis of this differential susceptibility, we analyzed the glomerular transcriptome of young mice early in the course of their disease. We find dramatic differences in regulation of immune and inflammatory pathways, with upregulation of proinflammatory pathways in the susceptible (129) strain and coordinate downregulation in the resistant (C57BL/6) strain. Many of these pathways are also upregulated in rat models and in humans with DN. Our studies suggest that genes controlling inflammatory responses, triggered by hyperglycemia and RAS activation, may be critical early determinants of susceptibility to DN.

Aberrant activation of Notch-1 signaling inhibits podocyte restoration after islet transplantation in a rat model of diabetic nephropathy

Signaling abnormalities play important roles during podocyte injury and have been indicated as crucial events for triggering many glomerular diseases. There is emerging evidence demonstrating significant improvements in preventing renal injury and restoring podocytes after islet transplantation. However, whether signaling abnormalities affect the therapeutic efficacy of islet transplantation remain unclear. This study was established to investigate the impact of Notch-1 signaling activation on renal injury and podocyte restoration after islet transplantation. Experiments were performed in vivo and in vitro under conditions of diabetic nephropathy and high-glucose medium, respectively. Podocyte injury in vitro was induced by high-glucose concentration, and expression levels of genes associated with the Notch-1 pathway were also regulated by Jagged-1/FC and N-[N-(3,5-Difluorophenacetyl)-L-alanyl]- S-phenylglycine t-butyl ester (DAPT). Podocytes were co-cultured with islets to investigate the protective effect of islets in high-glucose conditions. Histopathological staining and transmission electron microscopy were performed to assess pathological changes in podocytes in glomeruli. The results from this study showed that Notch-1 signaling in podocytes was significantly decreased by functional islet cells in vivo and in vitro. Compared with the co-cultured group and transplanted group, highly activated Notch-1 signaling significantly moderated the effect of islets in affecting podocyte restoration and renal injury. Renal damage and podocyte injury were alleviated after DAPT treatment. Furthermore, the balance between apoptosis and autophagy was diverse under different treatments. All the data in this study showed that highly activated Notch-1 signaling could affect the therapeutic efficacy of islet transplantation on renal injury and podocyte restoration in high-glucose conditions. The balance between apoptosis and autophagy was also closely associated with the degree of podocyte restoration. This finding may suggest that the in vivo microenvironment plays a critical role in podocyte restoration after islet transplantation, which provides a promising and individual assessment and targeting treatment for different diabetic nephropathy patients after islet transplantation into the future.

ERp44 depletion exacerbates ER stress and aggravates diabetic nephropathy in db/db mice

Diabetic nephropathy (DN) is a major complication of diabetes, and the dysfunction of endoplasmic reticulum (ER) plays an important role in its pathogenesis. ERp44, an ER resident chaperone protein, has been implicated in the modulation of ER stress, however, its role and mechanism in DN are not determined. Here, we show that ERp44 expression is upregulated in the glomeruli of db/db mice, a rodent model of type 2 diabetes. When ERp44 is depleted by in vivo shRNA-mediated knockdown, the features associated with DN including albuminuria level and glomerular basement membrane (GBM) thickness are aggravated, therefore suggesting a detrimental role of ERp44 depletion in DN progression. We further show that ERp44 depletion exacerbates ER stress in DN in db/db mice, and that attenuating ER stress with the chemical chaperone TUDCA remarkably diminishes the aggravated DN features caused by ERp44 depletion. These results suggest that the exacerbated ER stress is a critical factor for the detrimental effect of ERp44 depletion on DN progression in db/db mice. Thus, our study links the role of ERp44 in DN with ER stress regulation and may offer a potential therapeutic strategy to interfere DN progression.

LincRNA 1700020I14Rik alleviates cell proliferation and fibrosis in diabetic nephropathy via miR-34a-5p/Sirt1/HIF-1α signaling

Long intergenic noncoding RNAs (lincRNAs) have been gradually identified to be functional in a variety of different mechanisms associating with development and epigenetic regulation of cellular homeostasis. However, the study of lincRNAs in diabetic nephropathy (DN) is still in its infancy. Here, we have found dysexpressed long noncoding RNAs (lncRNAs) in renal tissues of db/db DN mice compared with db/m mice by RNA sequencing. In this study, 5 lincRNAs were confirmed to express in a consistent trend among these DN-related lncRNAs both in vivo and in vitro. Particularly, 1700020I14Rik was the downregulated one. Moreover, our data showed overexpression or knockdown of 1700020I14Rik could regulate cell proliferation and fibrosis in mouse mesangial cells (MCs). Furthermore, 1700020I14Rik was found to interact with miR-34a-5p via both the directly targeting way by bioinformatic investigation and luciferase assay and the Ago2-dependent manner by RIP assay. Results also displayed that overexpression of 1700020I14Rik inhibited cell proliferation and expressions of renal fibrosis markers through miR-34a-5p/Sirt1/HIF-1α pathway in MCs under high glucose condition, while knockdown of 1700020I14Rik could increase cell proliferation and expressions of renal fibrosis markers. In conclusion, these results provide new insights into the regulation between 1700020I14Rik and miR-34a-5p/Sirt1/HIF-1α signaling pathway during the progression of DN.

HIF1α deletion facilitates adipose stem cells to repair renal fibrosis in diabetic mice

Adipose stem cell (ASC) transplantation is a promising therapeutic strategy for diabetic renal fibrosis. Hypoxia-inducible factor 1α (HIF1α) is a negative regulatory factor of mitochondrial function. In the current study, we aimed to explore if HIF1α deletion protects against hyperglycemia-induced ASC damage and enhances the therapeutic efficiency of ASCs in diabetic renal fibrosis. Our data indicated that HIF1α was upregulated in ASCs in response to high glucose stimulation. Higher HIF1α expression was associated with ASC apoptosis and proliferation arrest. Loss of HIF1α activated mitophagy protecting ASCs against high glucose-induced apoptosis via preserving mitochondrial function. Transplanting HIF1α-deleted ASCs in db/db mice improved the abnormalities in glucose metabolic parameters, including the levels of glucose, insulin, C-peptide, HbA1c, and inflammatory markers. In addition, the engraftment of HIF1α-modified ASCs also reversed renal function, decreased renal hypertrophy, and ameliorated renal histological changes in db/db mice. Functional studies confirmed that HIF1α-modified ASCs reduced renal fibrosis. Collectively, our results demonstrate that ASCs may be a promising therapeutic treatment for ameliorating diabetes and the development of renal fibrosis and that the loss of HIF1α in ASCs may further increase the efficiency of stem cell-based therapy. These findings provide a new understanding about the protective effects of HIF1α silencing on ASCs and offer a new strategy for promoting the therapeutic efficacy of ASCs in diabetic renal fibrosis.

Lipoxins Regulate the Early Growth Response-1 Network and Reverse Diabetic Kidney Disease

Background The failure of spontaneous resolution underlies chronic inflammatory conditions, including microvascular complications of diabetes such as diabetic kidney disease. The identification of endogenously generated molecules that promote the physiologic resolution of inflammation suggests that these bioactions may have therapeutic potential in the context of chronic inflammation. Lipoxins (LXs) are lipid mediators that promote the resolution of inflammation.Methods We investigated the potential of LXA₄ and a synthetic LX analog (Benzo-LXA₄) as therapeutics in a murine model of diabetic kidney disease, ApoE^-/- mice treated with streptozotocin.Results Intraperitoneal injection of LXs attenuated the development of diabetes-induced albuminuria, mesangial expansion, and collagen deposition. Notably, LXs administered 10 weeks after disease onset also attenuated established kidney disease, with evidence of preserved kidney function. Kidney transcriptome profiling defined a diabetic signature (725 genes; false discovery rate P≤0.05). Comparison of this murine gene signature with that of human diabetic kidney disease identified shared renal proinflammatory/profibrotic signals (TNF-α, IL-1β, NF-κB). In diabetic mice, we identified 20 and 51 transcripts regulated by LXA₄ and Benzo-LXA₄, respectively, and pathway analysis identified established (TGF-β1, PDGF, TNF-α, NF-κB) and novel (early growth response-1 [EGR-1]) networks activated in diabetes and regulated by LXs. In cultured human renal epithelial cells, treatment with LXs attenuated TNF-α-driven Egr-1 activation, and Egr-1 depletion prevented cellular responses to TGF-β1 and TNF-αConclusions These data demonstrate that LXs can reverse established diabetic complications and support a therapeutic paradigm to promote the resolution of inflammation.

Novel differences in renal gene expression in a diet-induced obesity model

Obesity is a significant risk factor for both chronic kidney disease and end-stage renal disease. To better understand disease development, we sought to identify novel genes differentially expressed early in disease progression. We first confirmed that mice fed a high-fat (HF) diet exhibit early signs of renal injury including hyperfiltration. We then performed RNA-Seq using renal cortex RNA from C57BL6/J male mice fed either HF or control (Ctrl) diet. We identified 1,134 genes differentially expressed in the cortex on HF vs. Ctrl, of which 31 genes were selected for follow-up analysis. This included the 9 most upregulated, the 11 most downregulated, and 11 genes of interest (primarily sensory receptors and G proteins). Quantitative (q)RT-PCR for these 31 genes was performed on additional male renal cortex and medulla samples, and 11 genes (including all 9 upregulated genes) were selected for further study based on qRT-PCR. We then examined expression of these 11 genes in Ctrl and HF male heart and liver samples, which demonstrated that these changes are relatively specific to the renal cortex. These 11 genes were also examined in female renal cortex, where we found that the expression changes seen in males on a HF diet are not replicated in females, even when the females are started on the diet sooner to match weight gain of the males. In sum, these data demonstrate that in a HF-diet model of early disease, novel transcriptional changes occur that are both sex specific and specific to the renal cortex.