Evidence for a role of transforming growth factor (TGF)-beta1 in the induction of postglomerular albuminuria in diabetic nephropathy: amelioration by soluble TGF-beta type II receptor

Therapeutic potential of SMAD7 targeting miRNA in the pathogenesis of diabetic nephropathy

Diabetic nephropathy (DN) is a common complication of diabetes and a leading cause of end-stage renal disease, characterized by progressive kidney fibrosis and inflammation. The transforming growth factor-beta (TGF-β) signaling pathway plays a crucial role in the pathogenesis of diabetes nephropathy, and SMAD7 is a key negative regulator of this pathway. Recent studies have highlighted the involvement of miRNA in the progression of DN. Computational analysis identified 11 potential miRNAs such as miR-424, miR-195, miR-216a, miR-503, miR-15a-5p, miR-15b-5p, miR-665, miR-520h, miR16-5p, miR-21 and miR-32-5p which are predicted to target 3'UTR of SMAD7 mRNA. This review aims to explore the role of these miRNAs in the progression of DN. Notably, these miRNAs have shown therapeutic potential in mitigating fibrosis and inflammation by modulating SMAD7 expression in DN. Future directions can be to investigate the mechanistic pathways through which these miRNAs exert their effects, as well as optimizing delivery systems for effective clinical application. Targeting miRNAs that modulate SMAD7 expression represents a promising strategy for developing specific and effective therapies for diabetic nephropathy.

A human stem cell-derived model reveals pathologic extracellular matrix remodeling in diabetic podocyte injury

Diabetic nephropathy results from chronic (or uncontrolled) hyperglycemia and is the leading cause of kidney failure. The kidney's glomerular podocytes are highly susceptible to diabetic injury and subsequent non-reversible degeneration. We generated a human induced pluripotent stem (iPS) cell-derived model of diabetic podocytopathy to investigate disease pathogenesis and progression. The model recapitulated hallmarks of podocytopathy that precede proteinuria including retraction of foot processes and podocytopenia (detachment from the extracellular matrix (ECM)). Moreover, hyperglycemia-induced injury to podocytes exacerbated remodeling of the ECM. Specifically, mature podocytes aberrantly increased expression and excessively deposited collagen (IV)α1α1α2 that is normally abundant in the embryonic glomerulus. This collagen (IV) imbalance coincided with dysregulation of lineage-specific proteins, structural abnormalities of the ECM, and podocytopenia - a mechanism not shared with endothelium and is distinct from drug-induced injury. Intriguingly, repopulation of hyperglycemia-injured podocytes on decellularized ECM scaffolds isolated from healthy podocytes attenuated the loss of synaptopodin (a mechanosensitive protein associated with podocyte health). These results demonstrate that human iPS cell-derived podocytes can facilitate in vitro studies to uncover the mechanisms of chronic hyperglycemia and ECM remodeling and guide disease target identification.

Urinary Vitamin D Binding Protein: A Marker of Kidney Tubular Dysfunction in Patients at Risk for Type 2 Diabetes

Context

Recent studies have reported elevated urinary vitamin D binding protein (uVDBP) concentrations in patients with diabetic kidney disease, although the utility of uVDBP to predict deterioration of kidney function over time has not been examined.

Objective

Our objective was to assess the association of uVDBP with longitudinal changes in kidney function.

Methods

Adults at-risk for type 2 diabetes from the Prospective Metabolism and Islet Cell Evaluation (PROMISE) study had 3 assessments over 6 years (n = 727). Urinary albumin-to-creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) were used as measures of kidney function. Measurements of uVDBP were performed with enzyme-linked immunosorbent assay and normalized to urine creatinine (uVDBP:cr). Generalized estimating equations (GEEs) evaluated longitudinal associations of uVDBP and uVDBP:cr with measures of kidney function, adjusting for covariates.

Results

Renal uVDBP loss increased with ACR severity at baseline. Individuals with normoalbuminuria, microalbuminuria, and macroalbuminuria had median log uVDBP:cr concentrations of 1.62 μg/mmol, 2.63 μg/mmol, and 2.48 μg/mmol, respectively, and ACR positively correlated with uVDBP concentrations (r = 0.37; P < .001). There was no significant association between uVDBP and eGFR at baseline. Adjusted longitudinal GEE models indicated that each SD increase both in baseline and longitudinal uVDBP:cr was significantly associated with higher ACR over 6 years (β = 30.67 and β = 32.91, respectively). Conversely, neither baseline nor longitudinal uVDBP:cr measures showed a significant association with changes in eGFR over time. These results suggest that loss of uVDBP:cr over time may be a useful marker for predicting renal tubular damage in individuals at risk for diabetes.

Urinary exosomal miRNA-663a shows variable expression in diabetic kidney disease patients with or without proteinuria

Heterogeneity in the Diabetic Kidney Disease (DKD) diagnosis makes its rational therapeutics challenging. Although albuminuria characterizes DKD, reports also indicate its prevalence among non-proteinuric. Recent understanding of disease progression has thus inclined the focus on proximal tubular cell damage besides the glomeruli. A non-invasive approach exploiting exosomal miRNA derived from human kidney proximal tubular cell line was, hence, targeted. Upon miRNA profiling, three miRNAs, namely, hsa-miR-155-5p, hsa-miR-28-3p, and hsa-miR-425-5p were found to be significantly upregulated, while hsa-miR-663a was downregulated under diabetic conditions. Among these, hsa-miR-663a downregulation was more pronounced in non-proteinuric than proteinuric DKD subjects and was thus selected for the bioinformatics study. Ingenuity Pathway Analysis (IPA) narrowed on to IL-8 signaling and inflammatory response as the most enriched 'canonical pathway' and 'disease pathway' respectively, during DKD. Further, the putative gene network generated from these enriched pathways revealed experimentally induced diabetes, renal tubular injury, and decreased levels of albumin as part of mapping under 'disease and function'. Genes target predictions and annotations by IPA reiterated miR-663a's role in the pathogenesis of DKD following tubular injury. Overall, the observations might offer an indirect reflection of the underlying mechanism between patients who develop proteinuria and non-proteinuria.

TGF-β Inhibitors for Therapeutic Management of Kidney Fibrosis

Kidney fibrosis is a common pathophysiological mechanism of chronic kidney disease (CKD) progression caused by several underlying kidney diseases. Among various contributors to kidney fibrosis, transforming growth factor-β1 (TGF-β1) is the major factor driving fibrosis. TGF-β1 exerts its profibrotic attributes via the activation of canonical and non-canonical signaling pathways, which induce proliferation and activation of myofibroblasts and subsequent accumulation of extracellular matrix. Over the past few decades, studies have determined the TGF-β1 signaling pathway inhibitors and evaluated whether they could ameliorate the progression of CKD by hindering kidney fibrosis. However, therapeutic strategies that block TGF-β1 signaling have usually demonstrated unsatisfactory results. Herein, we discuss the therapeutic concepts of the TGF-β1 signaling pathway and its inhibitors and review the current state of the art regarding regarding TGF-β1 inhibitors in CKD management.

Megalin and Vitamin D Metabolism—Implications in Non-Renal Tissues and Kidney Disease

Megalin is an endocytic receptor abundantly expressed in proximal tubular epithelial cells and other calciotropic extrarenal cells expressing vitamin D metabolizing enzymes, such as bone and parathyroid cells. The receptor functions in the uptake of the vitamin D-binding protein (DBP) complexed to 25 hydroxyvitamin D3 (25(OH)D3), facilitating the intracellular conversion of precursor 25(OH)D3 to the active 1,25 dihydroxyvitamin D3 (1,25(OH)2D3). The significance of renal megalin-mediated reabsorption of 25(OH)D3 and 1,25(OH)2D3 has been well established experimentally, and other studies have demonstrated relevant roles of extrarenal megalin in regulating vitamin D homeostasis in mammary cells, fat, muscle, bone, and mesenchymal stem cells. Parathyroid gland megalin may regulate calcium signaling, suggesting intriguing possibilities for megalin-mediated cross-talk between calcium and vitamin D regulation in the parathyroid; however, parathyroid megalin functionality has not been assessed in the context of vitamin D. Within various models of chronic kidney disease (CKD), megalin expression appears to be downregulated; however, contradictory results have been observed between human and rodent models. This review aims to provide an overview of the current knowledge of megalin function in the context of vitamin D metabolism, with an emphasis on extrarenal megalin, an area that clearly requires further investigation.

Vaccination against connective tissue growth factor attenuates the development of renal fibrosis

There is a critical need for efficient treatment of chronic kidney disease (CKD). Renal fibrosis is a final common pathway to end-stage renal disease independent of the underlying etiology, and connective tissue growth factor (CTGF) is a well-recognized profibrotic factor in fibrosis of various organ systems. Here, we developed a novel peptide vaccine against CTGF to attenuate the development of renal fibrosis. Three inoculations with this CTGF vaccine at 2-week intervals elicited antibodies specifically binding to human full-length CTGF, and the antigen-specific serum IgG antibody titers were maintained for > 30 weeks. The efficacy of the CTGF vaccine on renal fibrosis was evaluated in adenine-induced CKD and unilateral ureteral obstruction (UUO) murine models. In adenine-induced CKD model, immunization with the CTGF vaccine attenuated renal interstitial fibrosis. Vaccinated mice showed low levels of serum creatinine and urea nitrogen and low urine albumin–creatinine ratio compared with vehicle-treated mice. In UUO model, the CTGF vaccination also suppressed the onset of renal fibrosis. In an in vitro study, CTGF vaccine-elicited IgG antibodies efficiently suppressed CTGF-induced- and transforming growth factor-β-induced α-smooth muscle actin expression in kidney fibroblasts. These results demonstrate that the CTGF vaccine is a promising strategy to attenuate the development of renal fibrosis.

Exploring the multifaceted role of TGF-β signaling in diabetic complications

Diabetes is one of the most comprehensive metabolic disorders and is spread across the globe. The data from IDF Diabetes Atlas and National Diabetes Statistics mentions that the number of patients with diabetes is increasing at an exponential rate which is challenging the current therapeutics used for the management of diabetes. However, current therapies used for the treatment may provide symptomatic relief but lack in preventing the progression of the disease and thereby limiting the treatment of diabetes-associated complications. A thorough review and analysis were conducted using various databases including EMBASE, MEDLINE, and Google Scholar to extract the available information on challenges faced by current therapies which have triggered the development of novel molecules or drugs. From the analysis, it was analyzed that transforming growth factor βs (TGF-βs) have been shown to exhibit pleiotropic activity and are responsible for maintaining homeostasis and its overexpression is convoluted in the pathogenesis of various disorders. Therefore, developing drugs that block TGF-β signaling may provide therapeutic benefits. This extensive review concluded that drugs targeting TGF-β signaling pathway and its subsequent blockade have shown promising results and hold the potential to become drugs of choice in the management of diabetes and associated complications.

TGF-Beta as a Master Regulator of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common complications in diabetes mellitus and the leading cause of end-stage renal disease. TGF-β is a pleiotropic cytokine and has been recognized as a key mediator of DN. However, anti-TGF-β treatment for DN remains controversial due to the diverse role of TGF-β1 in DN. Thus, understanding the regulatory role and mechanisms of TGF-β in the pathogenesis of DN is the initial step towards the development of anti-TGF-β treatment for DN. In this review, we first discuss the diverse roles and signaling mechanisms of TGF-β in DN by focusing on the latent versus active TGF-β1, the TGF-β receptors, and the downstream individual Smad signaling molecules including Smad2, Smad3, Smad4, and Smad7. Then, we dissect the regulatory mechanisms of TGF-β/Smad signaling in the development of DN by emphasizing Smad-dependent non-coding RNAs including microRNAs and long-non-coding RNAs. Finally, the potential therapeutic strategies for DN by targeting TGF-β signaling with various therapeutic approaches are discussed.

Role of ARK5 in cancer and other diseases (Review)

Malignant tumors are often exposed to hypoxic and glucose-starved microenvironments. AMP-activated protein kinase (AMPK) is an energy sensor that is stimulated during energy-deficient conditions and protects cells from hypoxic injury by regulating metabolism. AMPK-related protein kinase 5 (ARK5) is a member of the catalytic sub-unit of the AMPK family and has an important role in energy regulation and hypoxia. ARK5 is regulated by Akt and liver kinase B1 and is associated with numerous tumor-related molecules to exert the negative effects of tumors. Studies have revealed ARK5 overexpression in cases of tumor invasion and metastasis and a positive association with the degree of cancer cell malignancy, which is regarded as a key element in determining cancer prognosis. Furthermore, ARK5 downregulation improves drug sensitivity through the epithelial-mesenchymal transition pathway, indicating that it may be a potential therapeutic target. In other non-cancer conditions, ARK5 has various roles in neurodegenerative diseases (Alzheimer's and Huntington's disease), renal disorders (diabetic nephropathy and renal fibrosis) and physiological processes (striated muscle generation). In the present review, the upstream and downstream molecular pathways of ARK5 in cancer and other diseases are described and potential therapeutic strategies are discussed.

Diabetic fibrosis

Diabetes-associated morbidity and mortality is predominantly due to complications of the disease that may cause debilitating conditions, such as heart and renal failure, hepatic insufficiency, retinopathy or peripheral neuropathy. Fibrosis, the excessive and inappropriate deposition of extracellular matrix in various tissues, is commonly found in patients with advanced type 1 or type 2 diabetes, and may contribute to organ dysfunction. Hyperglycemia, lipotoxic injury and insulin resistance activate a fibrotic response, not only through direct stimulation of matrix synthesis by fibroblasts, but also by promoting a fibrogenic phenotype in immune and vascular cells, and possibly also by triggering epithelial and endothelial cell conversion to a fibroblast-like phenotype. High glucose stimulates several fibrogenic pathways, triggering reactive oxygen species generation, stimulating neurohumoral responses, activating growth factor cascades (such as TGF-β/Smad3 and PDGFs), inducing pro-inflammatory cytokines and chemokines, generating advanced glycation end-products (AGEs) and stimulating the AGE-RAGE axis, and upregulating fibrogenic matricellular proteins. Although diabetes-activated fibrogenic signaling has common characteristics in various tissues, some organs, such as the heart, kidney and liver develop more pronounced and clinically significant fibrosis. This review manuscript summarizes current knowledge on the cellular and molecular pathways involved in diabetic fibrosis, discussing the fundamental links between metabolic perturbations and fibrogenic activation, the basis for organ-specific differences, and the promises and challenges of anti-fibrotic therapies for diabetic patients.

WITHDRAWN: Effect of 2-dodecyl-6-methoxycyclohexa-2, 5-diene-1, 4-dione, isolated from Averrhoa carambola L. (Oxalidaceae) roots, on advanced glycation end-product-mediated renal injury in type 2 diabetic KKAy mice

The Publisher regrets that this article is an accidental duplication of an article that has already been published in [Toxicology Letters, 339C (2021) 88–96], https://doi.org/10.1016/j.toxlet.2020.11.022. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal

NQO1 Deficiency Aggravates Renal Injury by Dysregulating Vps34/ATG14L Complex during Autophagy Initiation in Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the causes of end-stage renal failure, featuring renal fibrosis. However, autophagy, a vital process for intracellular homeostasis, can counteract renal fibrosis. Moreover, NAD(P)H: quinone dehydrogenase 1 (NQO1) modulates the ratios of reduced/oxidized nicotinamide nucleotides, exerting a cytoprotective function. Here, to examine the role of NQO1 genes in DN progression, the levels of autophagy-related proteins and pro-fibrotic markers were assessed in silencing or overexpression of NQO1 in human proximal tubular cells (HK2), and C57BL/6 (wild-type) and Nqo1 knockout (KO) mice injected to streptozotocin (50 mg/kg). NQO1 deficiency impaired the autophagy process by suppressing basal expression of ClassⅢ PI 3-kinase (Vps34) and autophagy-related (ATG)14L and inducing the expressions of transforming growth factor beta (TGF-β1), Smad3, and matrix metallopeptidase9 (MMP9) in high-glucose (HG) -treated HK2 cells. Meanwhile, NQO1 overexpression increased the expression of Vps34 and ATG14L, while, reducing TGF-β1, Smad3 and MMP9 expression. In vivo, the expression of Vps34 and ATG14L were suppressed in Nqo1 KO mice indicating aggravated glomerular changes and interstitial fibrosis. Therefore, NQO1 deficiency dysregulated autophagy initiation in HK2 cells, with consequent worsened renal cell damage under HG condition. Moreover, STZ-treated Nqo1 KO mice showed that NQO1 deficiency aggravated renal fibrosis by dysregulating autophagy.

Soluble (pro)renin receptor promotes the fibrotic response in renal proximal tubule epithelial cells in vitro via the Akt/β-catenin/Snail signaling pathway

Tubulointerstitial fibrosis has been regarded as a critical event in the pathogenesis of chronic kidney disease. The soluble form of (pro)renin receptor (sPRR), generated by site-1 protease (S1P) cleavage of full-length PRR, can be detected in biological fluid and elevated under certain pathological conditions. The present study was designed to evaluate the potential role of sPRR in the regulation of the fibrotic response in a cultured human renal proximal tubular cell line (HK-2 cells) in the setting of transforming growth factor (TGF)-β or sPRR-His treatment. The TGF-β-induced fibrotic response of HK-2 cells was indicated by upregulation of fibronectin (FN) expression; meanwhile, TGF-β could also induce the generation of sPRR, due to enhanced cleavage of full-length PRR. To explore the role of sPRR in the fibrotic response of HK-2 cells, we blocked the production of sPRR with a the S1P inhibitor PF429242 and found that PF429242 remarkably suppressed TGF-β-induced sPRR generation and FN expression in HK-2 cells. Administration of sPRR-His restored the PF429242-attenuated FN expression in HK-2 cells, indicating that sPRR could promote the TGF-β-induced fibrotic response. Furthermore, sPRR-His alone also increased the abundance of FN in HK-2 cells. These data suggested that sPRR was sufficient and necessary for the TGF-β-induced fibrotic response of HK-2 cells. Mechanistically, sPRR activated the AKT and β-catenin pathway in HK-2 cells, and blockade of the AKT or β-catenin pathway significantly abrogated sPRR-induced FN and Snail expression. Taking together, sPRR promoted the fibrotic response of HK-2 cells by activating Akt/β-catenin/Snail signaling, and it may serve as a potential therapeutic target in renal fibrosis.

RIPK3: A New Player in Renal Fibrosis

Chronic kidney disease (CKD) is the end result of a plethora of renal insults, including repeated episodes of acute or toxic kidney injury, glomerular, or diabetic kidney disease. It affects a large number of the population worldwide, resulting in significant personal morbidity and mortality and economic cost to the community. Hence it is appropriate to focus on treatment strategies that interrupt the development of kidney fibrosis, the end result of all forms of CKD, in addition to upstream factors that may be specific to certain diseases. However, the current clinical approach to prevent or manage renal fibrosis remains unsatisfactory. The rising importance of receptor-interacting serine/threonine-protein kinase (RIPK) 3 in the inflammatory response and TGF-β1 signaling is increasingly recognized. We discuss here the biological functions of RIPK3 and its role in the development of renal fibrosis.

Megalin: A bridge connecting kidney, the renin-angiotensin system, and atherosclerosis

Megalin is a member of the low-density lipoprotein receptor superfamily. It has been recognized as an endocytic receptor for a large spectrum of ligands. As a consequence, megalin regulates homeostasis of many molecules and affects multiple physiological and pathophysiological functions. The renin-angiotensin system is a hormonal system. A number of studies have reported contributions of the renin-angiotensin system to atherosclerosis. There is evolving evidence that megalin is a regulator of the renin-angiotensin system, and contributes to atherosclerosis. This brief review provides contemporary insights into effects of megalin on renal functions, the renin-angiotensin system, and atherosclerosis.

Differential Roles of Cysteinyl Cathepsins in TGF-β Signaling and Tissue Fibrosis

Transforming growth factor beta (TGF-β) signaling contributes to tissue fibrosis. Here we demonstrate that TGF-β enhances CatS and CatK expression but reduces CatB and CatL expression in mouse kidney tubular epithelial cells (TECs). CatS- and CatK deficiency reduces TEC nuclear membrane importer importin-β expression, Smad-2/3 activation, and extracellular matrix (ECM) production. Yet CatB- and CatL-deficiency displays the opposite observations with reduced nuclear membrane exporter RanBP3 expression. CatS and CatK form immunocomplexes with the importin-β and RanBP3 more effectively than do CatB and CatL. On the plasma membrane, CatS and CatK preferentially form immunocomplexes with and activate TGF-β receptor-2, whereas CatB and CatL form immunocomplexes with and inactivate TGF-β receptor-1. Unilateral ureteral obstruction-induced renal injury tests differential cathepsin activities in TGF-β signaling and tissue fibrosis. CatB- or CatL-deficiency exacerbates fibrosis, whereas CatS- or CatK-deficiency protects kidneys from fibrosis. These cathepsins exert different effects in the TGF-β signaling cascade independent of their proteolytic properties.

Systemic Inflammation Precedes Microalbuminuria in Diabetes

Aim

The aim of the case-control study was to investigate if serum biomarkers indicative of vascular inflammation and endothelial dysfunction can predict the development of microalbuminuria in patients with diabetes mellitus type 2.

Methods

Among participants enrolled in the ROADMAP (Randomized Olmesartan And Diabetes MicroAlbuminuria Prevention) and observational follow-up (OFU) studies, a panel of 15 serum biomarkers was quantified from samples obtained at initiation of the study and tested for associations with the development of new-onset microalbuminuria during follow-up. A case-control study was conducted with inclusion of 172 patients with microalbuminuria and 188 matched controls. Nonparametric inferential, nonlinear regression, mediation, and bootstrapping statistical methods were used for the analysis.

Results

The median follow-up time was 37 months. At baseline, mean concentrations of C-X-C motif chemokine ligand 16 (CXCL-16), transforming growth factor (TGF)–β1 and angiopoietin-2 were higher in patients with subsequent microalbuminuria. In the multivariate analysis, after adjustment for age, sex, body mass index, glycated hemoglobin, duration of diabetes, low-density lipoprotein (LDL), smoking status, blood pressure, baseline urine albumin-to-creatinine ratio (UACR), estimated glomerular filtration rate (eGFR), time of follow-up and cardiovascular disease, CXCL-16 (odds ratio [OR] 2.60, 95% confidence interval [CI] 1.71–3.96), angiopoietin-2 (OR 1.50, 95% CI 1.14–1.98) and TGF-β1 (OR 1.03, 95% CI 1.01–1.04) remained significant predictors of new-onset microalbuminuria (P < 0.001). Inclusion of these biomarkers in conventional clinical risk models for prediction of microalbuminuria increased the area under the curve (AUC) from 0.638 to 0.760 (P < 0.001).

Conclusion

In patients with type 2 diabetes, elevated plasma levels of CXCL-16, angiopoietin-2, and TGF-β1 are independently predictive of microalbuminuria. Thus, these serum markers improve renal risk models beyond established clinical risk factors.

Participation of the SMAD2/3 signalling pathway in the down regulation of megalin/LRP2 by transforming growth factor beta (TGF-ß1)

Megalin/LRP2 is a receptor that plays important roles in the physiology of several organs, such as kidney, lung, intestine, and gallbladder and also in the physiology of the nervous system. Megalin expression is reduced in diseases associated with fibrosis, including diabetic nephropathy, hepatic fibrosis and cholelithiasis, as well as in some breast and prostate cancers. One of the hallmarks of these conditions is the presence of the cytokine transforming growth factor beta (TGF-ß). Although TGF-ß has been implicated in the reduction of megalin levels, the molecular mechanism underlying this regulation is not well understood. Here, we show that treatment of two epithelial cell lines (from kidney and gallbladder) with TGF-ß1 is associated with decreased megalin mRNA and protein levels, and that these effects are reversed by inhibiting the TGF-ß1 type I receptor (TGF-ßRI). Based on in silico analyses, the two SMAD-binding elements (SBEs) in the megalin promoter are located at positions -57 and -605. Site-directed mutagenesis of the SBEs and chromatin immunoprecipitation (ChIP) experiments revealed that SMAD2/3 transcription factors interact with SBEs. Both the presence of SMAD2/3 and intact SBEs were associated with repression of the megalin promoter, in the absence as well in the presence of TGF-ß1. Also, reduced megalin expression and promoter activation triggered by high concentration of albumin are dependent on the expression of SMAD2/3. Interestingly, the histone deacetylase inhibitor Trichostatin A (TSA), which induces megalin expression, reduced the effects of TGF-ß1 on megalin mRNA levels. These data show the significance of TGF-ß and the SMAD2/3 signalling pathway in the regulation of megalin and explain the decreased megalin levels observed under conditions in which TGF-ß is upregulated, including fibrosis-associated diseases and cancer.

Angiotensin blockade attenuates diabetic nephropathy in hypogonadal adult male rats

This study examined the effect of the aromatase inhibitor letrozole (0.5 mg/kg) alone or in combination with the angiotensin-receptor blocker valsartan (30 mg/kg) against streptozocin-induced diabetic nephropathy (DN) in hypogonadal (HG) rats for 12 weeks. First, we tested the HG effect on hormone levels, inflammatory cytokines, and oxidative stress in nondiabetic (ND) and diabetic (D) rats. HG was induced with the luteinizing hormone-releasing hormone antagonist cetrorelix (0.71 mg/kg). Diabetes enhanced hormonal hypogonadism and increased inflammation and oxidative stress. Next, experiments examined the effect of early letrozole and valsartan intervention on DN in HG rats. HG-ND and HG-D rats were treated with letrozole alone or in combination with valsartan. HG-D rats developed proteinuria and had increased blood urea nitrogen and creatinine, and histopathological evidence of renal injury, including glomerular hypertrophy and mesangial expansion. Valsartan alone or in combination with letrozole reduced proteinuria, improved renal functions, and reduced diabetes-induced renal angiotensin II. Both agents ameliorated nuclear factor kappa light chain enhancer of activated B cells, interleukin 1β, interleukin 6, and tumor necrosis factor alpha levels. The combination decreased superoxide dismutase, malondialdehyde, and glutathione peroxidase levels, and prevented glomerular hypertrophy. In HG-D rats, valsartan reduced renal collagen IV and transforming growth factor-beta 1, especially when the testosterone level was corrected by letrozole. Thus, normalizing testosterone and inhibiting renal angiotensin II have a renoprotective effect against DN in HG male rats.

Coumarin glycosides from Hydrangea paniculata slow down the progression of diabetic nephropathy by targeting Nrf2 anti-oxidation and smad2/3-mediated profibrosis

BACKGROUND

Water extract of Hydrangea paniculata (HP) stem, rich in coumarin glycosides, has been demonstrated to have renal protective effect in several experimental kidney injury animal models. Currently, it is under pre-clinical development as a class 5 herbal drug against membranous nephropathy. However, whether it also benefits diabetic nephropathy (DN) is not clear.

PURPOSE

This study was performed to investigate the protective effect of HP on streptozotocin-induced experimental DN, and further understand its molecular mechanisms.

METHODS

In the present study, type 1 diabetes rat model was established by the intraperitoneal injection of streptozotocin. HP was orally administered every day for three months. Biochemical analysis and histopathological staining were conducted to evaluate the renal functions. In vivo pharmacokinetic study was conducted to analyse the metabolites of HP with high blood drug concentration. In vitro assay using these metabolites was performed to analyse their ability to reduce reactive oxygen species (ROS) production induced under high glucose (HG) condition by flow cytometry. Reverse transcription-polymerase chain reaction was conducted to analyse the mRNA level of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and IL6 and western blot was performed to analyse the phosphorylation status of smad 2/3 in HK2 cells under TGFβ1 stimulation.

RESULTS

The treatment with HP significantly reduced the blood urea nitrogen and serum creatinine content, and urine albumin excretion in diabetic rats, and increased the creatinine clearance rate. Periodic acid-schiff and methenamine staining and immunohistochemistry revealed that HP also ameliorated glomerulosclerosis and tubular vacuolar degeneration, as well as the deposition of fibronectin and collagen IV in the glomeruli. Pharmacokinetic study results revealed that the major coumarin compounds from HP were metabolised into umbelliferone and esculetin. By in vitro assay, umbelliferone and esculetin were found to significantly decrease ROS production induced by HG content, as well as increase the mRNA level of Nrf2. HP and its metabolites also can down-regulate fibronectin secretion in HK2 cells stimulated by TGFβ1 and inhibit smad2/3 phosphorylation.

CONCLUSION

HP has beneficial effect on DN by increasing Nrf2 expression and inhibiting TGF-smad signal activation. Further, it can be a novel herbal drug against DN.

Exploring macrophage cell therapy on Diabetic Kidney Disease

Alternatively activated macrophages (M2) have regenerative properties and shown promise as cell therapy in chronic kidney disease. However, M2 plasticity is one of the major hurdles to overcome. Our previous studies showed that genetically modified macrophages stabilized by neutrophil gelatinase‐associated lipocalin (NGAL) were able to preserve their M2 phenotype. Nowadays, little is known about M2 macrophage effects in diabetic kidney disease (DKD). The aim of the study was to investigate the therapeutic effect of both bone marrow‐derived M2 (BM‐фM2) and ф‐NGAL macrophages in the db/db mice. Seventeen‐week‐old mice with established DKD were divided into five treatment groups with their controls: D+BM‐фM2; D+ф‐BM; D+ф‐NGAL; D+ф‐RAW; D+SHAM and non‐diabetic (ND) (db/‐ and C57bl/6J) animals. We infused 1 × 10⁶ macrophages twice, at baseline and 2 weeks thereafter. BM‐фM2 did not show any therapeutic effect whereas ф‐NGAL significantly reduced albuminuria and renal fibrosis. The ф‐NGAL therapy increased the anti‐inflammatory IL‐10 and reduced some pro‐inflammatory cytokines, reduced the proportion of M1 glomerular macrophages and podocyte loss and was associated with a significant decrease of renal TGF‐β1. Overall, our study provides evidence that ф‐NGAL macrophage cell therapy has a therapeutic effect on DKD probably by modulation of the renal inflammatory response caused by the diabetic milieu.

The preventive and therapeutic implication for renal fibrosis by targetting TGF-β/Smad3 signaling

It is well established that Smad3 is a key downstream effector of transforming growth factor-β (TGF-β) signaling in tissue fibrogenesis. We reported here that targetting Smad3 specifically with a Smad3 inhibitor SIS3 is able to prevent or halt the progression of renal fibrosis in a mouse model of unilateral ureteral obstructive nephropathy (UUO). We found that preventive treatment with SIS3 at the time of disease induction largely suppressed progressive renal fibrosis by inhibiting α-smooth muscle actin (α-SMA) + myofibroblast accumulation and extracellular matrix (collagen I (Col.I) and fibronectin (FN)) production. Importantly, we also found that treatment with SIS3 on established mouse model of UUO from day 4 after UUO nephropathy halted the progression of renal fibrosis. Mechanistically, the preventive and therapeutic effects of SIS3 on renal fibrosis were associated with the inactivation of Smad3 signaling and inhibition of TGF-β1 expression in the UUO kidney. In conclusion, results from the present study suggest that targetting Smad3 may be a specific and effective therapy for renal fibrosis.

Transforming growth factor-β signalling in renal fibrosis: from Smads to non-coding RNAs

Transforming growth factor-β (TGF-β) is the key player in tissue fibrosis. However, antifibrotic therapy targeting this multifunctional protein may interfere with other physiological processes to cause side effects. Thus, precise therapeutic targets need to be identified by further understanding the underlying mechanisms of TGF-β1 signalling during fibrogenesis. Equilibrium of Smad signalling is crucial for TGF-β-mediated renal fibrosis, where Smad3 is pathogenic but Smad2 and Smad7 are protective. The activation of TGF-β1/Smad signalling triggers extracellular matrix deposition, and local myofibroblast generation and activation. Mechanistic studies have shown that TGF-β/Smad3 transits the microRNA profile from antifibrotic to profibrotic and therefore promotes renal fibrosis via regulating non-coding RNAs at transcriptional levels. More importantly, disease-specific Smad3-dependent long non-coding RNAs have been recently uncovered from mouse kidney disease models and may represent novel precision therapeutic targets for chronic kidney disease. In this review, mechanisms of TGF-β-driven renal fibrosis via non-coding RNAs and their translational capacities will be discussed in detail.

Increased megalin expression in early type 2 diabetes: role of insulin-signaling pathways

The megalin/cubilin complex is responsible for the majority of serum protein reclamation in the proximal tubules. The current study examined if decreases in their renal expression, along with the albumin recycling protein neonatal Fc receptor (FcRn) could account for proteinuria/albuminuria in the Zucker diabetic fatty rat model of type 2 diabetes. Immunoblots of renal cortex samples obtained at worsening disease stages demonstrated no loss in megalin, cubilin, or FcRn, even when proteinuria was measured. Additionally, early diabetic rats exhibited significantly increased renal megalin expression when compared with controls (adjusted P < 0.01). Based on these results, the ability of insulin to increase megalin was examined in a clonal subpopulation of the opossum kidney proximal tubule cell line. Insulin treatments (24 h, 100 nM) under high glucose conditions significantly increased megalin protein ( P < 0.0001), mRNA ( P < 0.0001), and albumin endocytosis. The effect on megalin expression was prevented with inhibitors against key effectors of insulin intracellular signaling, phosphatidylinositide 3-kinase and Akt. Studies using rapamycin to inhibit the mechanistic target of rapamycin complex 1 (mTORC1) resulted in a loss of insulin-induced megalin expression. However, subsequent evaluation demonstrated these effects were independent of initial mTORC1 suppression. The presented results provide insight into the expression of megalin, cubilin, and FcRn in type 2 diabetes, which may be impacted by elevated insulin and glucose. Furthermore, proximal tubule endocytic activity in early diabetics may be enhanced, a process that could have a significant role in proteinuria-induced renal damage.

Oxidative stress increases megalin expression in the renal proximal tubules during the normoalbuminuric stage of diabetes mellitus

Megalin, an endocytic receptor expressed in proximal tubule cells, plays a critical role in renal tubular protein reabsorption and is associated with the albuminuria observed in diabetic nephropathy. We have previously reported increased oxidant production in the renal cortex during the normoalbuminuric stage of diabetes mellitus (DM); however, the relationship between oxidative stress and renal megalin expression during the normoalbuminuric stage of DM remains unclear. In the present study, we evaluated whether oxidative stress affects megalin expression in the normoalbuminuric stage of DM in a streptozotocin-induced diabetic rat model and in immortalized human proximal tubular cells (HK-2). We demonstrated that increased expression of renal megalin accompanies oxidative stress during the early stage of DM, before albuminuria development. Telmisartan treatment prevented the diabetes-induced elevation in megalin level, possibly through an oxidative stress-dependent mechanism. In HK-2 cells, hydrogen peroxide significantly increased megalin levels in a dose- and time-dependent manner; however, the elevation in megalin expression was decreased following prolonged exposure to severe oxidative stress induced by 0.4 mmol/l hydrogen peroxide. High-glucose treatment also significantly increased megalin expression in HK-2 cells. Concurrent administration of the antioxidant N-acetyl-cysteine blocked the effects of high glucose on megalin expression. Furthermore, the hydrogen peroxide-induced increase in megalin expression was blocked by treatment with phosphatidylinositol 3-kinase and Akt inhibitors. Increase of phosphorylated Akt expression was also seen in the renal cortex of diabetic rats. Taken together, our results indicate that mild oxidative stress increases renal megalin expression through the phosphatidylinositol 3-kinase-Akt pathway in the normoalbuminuric stage of DM.

Protective effects of allicin on streptozotocin-induced diabetic nephropathy in rats

BACKGROUND

Studies in animal models have shown that allicin, a major biologically active component of garlic, can play a role in the prevention of tissue fibrosis in the liver, lung and heart, mainly related to the inhibition of fibroblast proliferation, fibrogenic cytokine secretion and extracellular matrix synthesis. This study aimed to investigate the protective effects of allicin on renal damage in streptozotocin (STZ)-induced diabetic rats. STZ-induced diabetic rats were administered allicin (15, 30 and 45 mg · kg^-1  · day^-1 ) via daily intra-gastric gavage for 12 weeks. The levels of fasting blood glucose (FBG), blood urea nitrogen (BUN), serum creatinine (sCr), lipid and 24 h urine albumin excretion (UAE) were measured at the end of weeks 4, 8 and 12. The renal histopathology and the expression levels of collagen I, transforming growth factor β1 (TGF-β1) and phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) were measured using immunohistochemistry and/or western blotting.

RESULTS

In 12 week STZ-induced diabetic rats, severe hyperglycemia and albuminuria were markedly developed. Treatment with allicin for 12 weeks ameliorated diabetes-induced morphological alterations of the kidney and decreased FBG, BUN, sCr, triglyceride (TG) and 24 h UAE in diabetic rats. The expression levels of collagen I, TGF-β1 and p-ERK1/2 were significantly decreased by allicin treatment.

CONCLUSION

These results suggested that allicin may play a protective role in diabetic nephropathy via the TGF-β1/ERK pathway in diabetic rats. © 2016 Society of Chemical Industry.

Structured DAG oil ameliorates renal injury in streptozotocin-induced diabetic rats through inhibition of NF-κB and activation of Nrf2 pathway

Accumulating evidence suggested that inflammatory processes are involved in the development of diabetic nephropathy (DN). Here, we have tested the hypothesis that Caprylic Acid (Cy)-diacylglycerol (DAG) oil (Cy-DAG), a novel structurally formulated lipid with high nutritional value, ameliorated DN in streptozotocin (STZ)-induced diabetic rats through the anti-inflammatory mechanisms. Basic hematological, biochemical parameters, immunoblotting, immunofluorescence and flow cytometry analysis were performed to observe the anti-inflammatory potential of Cy-DAG oil. The data revealed that STZ significantly increased the renal oxidative stress markers and decreased the levels of renal enzymatic and non-enzymatic antioxidants. Moreover, renal nitric oxide (NO), tissue necrosis factor-α (TNF-α), interleukin-6 (IL-6) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) were also increased in the renal tissue of STZ-treated rats. Further, DAG oil pretreatment produced a significant improvement in renal antioxidant status, reduced the lipid peroxidation and the levels of inflammatory markers in STZ-treated kidney. Similarly, results of protein expression showed that DAG oil pretreatment normalized the renal expression of Nrf2/Keap1 and its downstream regulatory proteins in STZ-treated condition. Immunohistochemical observations provided further evidence that DAG oil effectively protected the kidney from STZ-mediated oxidative damage. These results suggested that the DAG oil ameliorated STZ-induced oxidative renal injury by the activation of AKT/Nrf2/HO-1 pathway and the inhibition of ROS/MAPK/NF-κB pathway.

Diabetes and Kidney Disease: Role of Oxidative Stress

Intrarenal oxidative stress plays a critical role in the initiation and progression of diabetic kidney disease (DKD). Enhanced oxidative stress results from overproduction of reactive oxygen species (ROS) in the context of concomitant, insufficient antioxidant pathways. Renal ROS production in diabetes is predominantly mediated by various NADPH oxidases (NOXs), but a defective antioxidant system as well as mitochondrial dysfunction may also contribute. Recent Advances: Effective agents targeting the source of ROS generation hold the promise to rescue the kidney from oxidative damage and prevent subsequent progression of DKD. Critical Issues and Future Directions: In the present review, we summarize and critically analyze molecular and cellular mechanisms that have been demonstrated to be involved in NOX-induced renal injury in diabetes, with particular focus on the role of increased glomerular injury, the development of albuminuria, and tubulointerstitial fibrosis, as well as mitochondrial dysfunction. Furthermore, novel agents targeting NOX isoforms are discussed. Antioxid. Redox Signal. 25, 657-684.

TGF-β: the master regulator of fibrosis

Transforming growth factor-β (TGF-β) is the primary factor that drives fibrosis in most, if not all, forms of chronic kidney disease (CKD). Inhibition of the TGF-β isoform, TGF-β1, or its downstream signalling pathways substantially limits renal fibrosis in a wide range of disease models whereas overexpression of TGF-β1 induces renal fibrosis. TGF-β1 can induce renal fibrosis via activation of both canonical (Smad-based) and non-canonical (non-Smad-based) signalling pathways, which result in activation of myofibroblasts, excessive production of extracellular matrix (ECM) and inhibition of ECM degradation. The role of Smad proteins in the regulation of fibrosis is complex, with competing profibrotic and antifibrotic actions (including in the regulation of mesenchymal transitioning), and with complex interplay between TGF-β/Smads and other signalling pathways. Studies over the past 5 years have identified additional mechanisms that regulate the action of TGF-β1/Smad signalling in fibrosis, including short and long noncoding RNA molecules and epigenetic modifications of DNA and histone proteins. Although direct targeting of TGF-β1 is unlikely to yield a viable antifibrotic therapy due to the involvement of TGF-β1 in other processes, greater understanding of the various pathways by which TGF-β1 controls fibrosis has identified alternative targets for the development of novel therapeutics to halt this most damaging process in CKD.

Elevation of Non-Classical (CD14+/lowCD16++) Monocytes Is Associated with Increased Albuminuria and Urine TGF-β1 in HIV-Infected Individuals on Stable Antiretroviral Therapy

OBJECTIVE

High rates of albuminuria are observed among HIV-infected individuals on stable antiretroviral therapy (ART). Though pro-inflammatory and pro-fibrotic responses are described as components of albuminuria in the general population, it is unclear how these responses are associated to albuminuria in ART-treated chronic HIV. We investigated the relationship of monocyte subsets and urine inflammatory and fibrotic biomarkers to albuminuria in ART-treated HIV-infected participants.

DESIGN AND METHODS

Cross-sectional analyses were performed on Hawaii Aging with HIV-cardiovascular disease study cohort participants who were required at entry to be ≥40 years old and on ART ≥3 months. Monocyte subpopulations were determined in banked peripheral blood mononuclear cells (PBMC) using multi-parametric flow-cytometry. Entry random urine samples were assessed for albumin-to-creatinine ratios (UACR). Urine samples were measured for inflammatory and fibrotic biomarkers using Luminex technology.

RESULTS

Among 96 HIV-infected subjects with measured UACR (87% male, 59% Caucasian, and 89% undetectable HIV RNA with median CD4 of 495.5 cells/μL), 18 patients (19%) had albuminuria. Non-classical (CD14low/+CD16++) monocytes were significantly elevated in subjects with albuminuria (p = 0.034) and were correlated to UACR (r = 0.238, p = 0.019). Elevated non-classical monocyte counts were significant predictors of worsening albuminuria, independent of traditional- and ART-associated risk factors (β = 0.539, p = 0.007). Urine TGF-β1 and collagen-IV were significantly higher in albuminuric compared to non-albuminuric participants (TGF-β1; p = 0.039 and collagen-IV; p = 0.042). Urine TGF-β1 was significantly correlated with non-classical monocyte counts (r = 0.464, p = 0.017).

CONCLUSION

Alterations in monocyte subpopulations and urine pro-fibrotic factors may play a role in kidney dysfunction during chronic HIV infection and warrants further study.

Role of IGFBP7 in Diabetic Nephropathy: TGF-β1 Induces IGFBP7 via Smad2/4 in Human Renal Proximal Tubular Epithelial Cells

Tubular injury is one of the important determinants of progressive renal failure in diabetic nephropathy (DN), and TGF-β1 has been implicated in the pathogenesis of tubulointerstitial disease that characterizes proteinuric renal disease. The aim of this study was to identify novel therapeutic target molecules that play a role in the tubule damage of DN. We used an LC-MS/MS-based proteomic technique and human renal proximal epithelial cells (HRPTECs). Urine samples from Japanese patients with type 2 diabetes (n = 46) were used to quantify the candidate protein. Several proteins in HRPTECs in cultured media were observed to be driven by TGF-β1, one of which was 33-kDa IGFBP7, which is a member of IGFBP family. TGF-β1 up-regulated the expressions of IGFBP7 mRNA and protein in a dose- and time-dependent fashion via Smad2 and 4, but not MAPK pathways in HRPTECs. In addition, the knockdown of IGFBP7 restored the TGF-β1-induced epithelial to mesenchymal transition (EMT). In the immunohistochemical analysis, IGFBP7 was localized to the cytoplasm of tubular cells but not that of glomerular cells in diabetic kidney. Urinary IGFBP7 levels were significantly higher in the patients with macroalbuminuria and were correlated with age (r = 0.308, p = 0.037), eGFR (r = −0.376, p = 0.01), urinary β₂-microglobulin (r = 0.385, p = 0.008), and urinary N-acetyl-beta-D-glucosaminidase (NAG) (r = 0.502, p = 0.000). A multivariate regression analysis identified urinary NAG and age as determinants associated with urinary IGFBP7 levels. In conclusion, our data suggest that TGF-β1 enhances IGFBP7 via Smad2/4 pathways, and that IGFBP7 might be involved in the TGF-β1-induced tubular injury in DN.

Serum TGF-β1 as a Biomarker for Type 2 Diabetic Nephropathy: A Meta-Analysis of Randomized Controlled Trials

Background

Abnormal expression of serum TGF-β1 was found in patients with diabetic nephropathy. However, the association of TGF-β1 with the risk of diabetic nephropathy remains unknown. The present study was undertaken to investigate whether such an association exists.

Methods

We searched the Chinese VIP, Wangfang, China National Knowledge Infrastructure, PubMed, Embase, and Google Scholar databases for relevant studies and extracted all eligible data. Stata12 software was used for statistical analysis.

Results

Nine reports met our criteria and were used for data extraction. There were 264 patients and 227 healthy controls from qualified reports in this meta-analysis. The results suggested that serum TGF-β1 levels were significantly up-regulated in patients with diabetic nephropathy; the instrumental variable was 3.94 (95% confidence interval 3.20–4.68, p<0.01).

Conclusions

Meta-analysis suggested that elevated serum TGF-β level in patients with diabetes is associated with a high risk of nephropathy. Further studies are required to validate these observations.

New molecular insights in diabetic nephropathy

Diabetes mellitus represents one of the major causes of functional kidney impairment. The review highlights the most significant steps made over the last decades in understanding the molecular basis of diabetic nephropathy (DN), which may provide reliable biomarkers for early diagnosis and prognosis, along with new molecular targets for personalized medicine. There is an increased interest in developing new therapeutic strategies to slow DN progression for improving patients' quality of life and reducing all-cause morbidity and disease-associated mortality. It is highly important to have a science-based medical attitude when facing diabetic patients with associated comorbidities and risk of rapid evolution toward end-stage renal disease. The data discussed herein were mainly from MEDLINE and PubMed articles published in English from 1990 to 2015 and from up-to-date. The search term was "diabetic nephropathy and oxidative stress".

Transforming growth factor-β1 and diabetic nephropathy

Transforming growth factor-β1 (TGF-β1) is established to be involved in the pathogenesis of diabetic nephropathy. The diabetic milieu enhances oxidative stress and induces the expression of TGF-β1. TGF-β1 promotes cell hypertrophy and extracellular matrix accumulation in the mesangium, which decreases glomerular filtration rate and leads to chronic renal failure. Recently, TGF-β1 has been demonstrated to regulate urinary albumin excretion by both increasing glomerular permeability and decreasing reabsorption in the proximal tubules. TGF-β1 also increases urinary excretion of water, electrolytes and glucose by suppressing tubular reabsorption in both normal and diabetic conditions. Although TGF-β1 exerts hypertrophic and fibrogenic effects in diabetic nephropathy, whether suppression of the function of TGF-β1 can be an option to prevent or treat the complication is still controversial. This is partly because adrenal production of mineralocorticoids could be augmented by the suppression of TGF-β1. However, differentiating the molecular mechanisms for glomerulosclerosis from those for the suppression of the effects of mineralocorticoids by TGF-β1 may assist in developing novel therapeutic strategies for diabetic nephropathy. In this review, we discuss recent findings on the role of TGF-β1 in diabetic nephropathy.

Kidney Injury Molecule-1 Enhances Endocytosis of Albumin in Renal Proximal Tubular Cells

Receptor-mediated endocytosis plays an important role in albumin reabsorption by renal proximal tubule epithelial cells. Kidney injury molecule-1 (KIM-1) is a scavenger receptor that is upregulated on the apical membrane of proximal tubules in proteinuric kidney disease. In this study, we examined the cellular localization and functional role of KIM-1 in cultured renal tubule epithelial cells (TECs). Confocal immunofluorescence microscopy reveals intracellular and cell surface localization of KIM-1 in primary renal TECs. Albumin stimulation resulted in a redistribution of KIM-1 and tight junction protein zonula occludens-1 in primary TEC monolayer. An increase in albumin internalization was observed in both primary TECs expressing endogenous KIM-1 and rat kidney cell line (NRK-52E) overexpressing exogenous KIM-1. KIM-1-induced albumin accumulation was abolished by its specific antibody. Moreover, endocytosed KIM-1 and its cargo proteins were delivered from endosomes to lysosomes for degradation in a clathrin-dependent pathway. Supportive evidence includes (1) detection of KIM-1 in Rab5-positive early endosomes, Rab7-positive late endosomes/multivesicular bodies, and LAMP1-positive lysosomes, (2) colocalization of KIM-1 and clathrin in the intracellular vesicles, and (3) blockade of KIM-1-mediated albumin internalization by chlorpromazine, an inhibitor of clathrin-dependent endocytosis. KIM-1 expression was upregulated by albumin but downregulated by transforming growth factor-β1. Taken together, our data indicate that KIM-1 increases albumin endocytosis in renal tubule epithelial cells, at least partially via a clathrin-dependent mechanism. J. Cell. Physiol. 231: 896-907, 2016. © 2015 Wiley Periodicals, Inc.

Chronic administration of AM251 improves albuminuria and renal tubular structure in obese rats

Modulation of the endocannabinoid system as an anti-obesity therapeutic is well established; however, the direct effects of cannabinoid receptor 1 (CB1) antagonism on renal function and structure in a model of diet-induced obesity (DIO) are unknown. The aim of this study was to characterise the renal effects of the CB1 antagonist AM251 in a model of DIO. Male Sprague-Dawley rats were fed a low- or high-fat diet (HFD: 40% digestible energy from lipids) for 10 weeks to elicit DIO (n=9). In a different cohort, rats were fed a HFD for 15 weeks. After 9 weeks consuming a HFD, rats were injected daily for 6 weeks with 3 mg/kg AM251 (n=9) or saline via i.p. injection (n=9). After 10 weeks consuming a HFD, CB1 and megalin protein expression were significantly increased in the kidneys of obese rats. Antagonism of CB1 with AM251 significantly reduced weight gain, systolic blood pressure, plasma leptin, and reduced albuminuria and plasma creatinine levels in obese rats. Importantly, there was a significant reduction in tubular cross-section diameter in the obese rats treated with AM251. An improvement in albuminuria was likely due to the reduction in tubular size, reduced leptinaemia and maintenance of megalin expression levels. In obese rats, AM251 did not alter diastolic blood pressure, sodium excretion, creatinine clearance or expression of the fibrotic proteins VEGFA, TGFB1 and collagen IV in the kidney. This study demonstrates that treatment with CB1 antagonist AM251 improves renal outcomes in obese rats.

Present and future in the treatment of diabetic kidney disease

Diabetic kidney disease is the leading cause of end-stage renal disease. Albuminuria is recognized as the most important prognostic factor for chronic kidney disease progression. For this reason, blockade of renin-angiotensin system remains the main recommended strategy, with either angiotensin converting enzyme inhibitors or angiotensin II receptor blockers. However, other antiproteinuric treatments have begun to be studied, such as direct renin inhibitors or aldosterone blockers. Beyond antiproteinuric treatments, other drugs such as pentoxifylline or bardoxolone have yielded conflicting results. Finally, alternative pathogenic pathways are being explored, and emerging therapies including antifibrotic agents, endothelin receptor antagonists, or transcription factors show promising results. The aim of this review is to explain the advances in newer agents to treat diabetic kidney disease, along with the background of the renin-angiotensin system blockade.

Do tubular changes in the diabetic kidney affect the susceptibility to acute kidney injury?

Diabetes is the single largest contributor to the growing prevalence of chronic kidney disease (CKD), and episodes of acute kidney injury (AKI) increase the risk of advanced CKD in diabetic patients. Here we discuss whether the pathophysiological changes that occur in the tubular system of the diabetic kidney affect the intrinsic susceptibility to AKI. There is abundant data showing that drug-induced nephrotoxicity is attenuated in rodents with experimental diabetes mellitus, and some mechanistic explanations have been provided, in particular in response to aminoglycosides. Besides downregulation in proximal tubular megalin, which mediates the aminoglycoside uptake in proximal tubules, a role for hyperglycemia-induced activation of regenerative mechanisms has been proposed. The available clinical data, however, indicates that diabetes is a risk factor for AKI, including aminoglycoside nephrotoxicity. While much needs to be learned about this disconnect, the isolated induction of diabetes in otherwise healthy young adult rodents may simply not fully mimic the influence that diabetes exerts in the setting of a critically ill and often elderly patient. We speculate that diabetic tubular growth and the associated molecular signature (including upregulation of TGF-β, senescence, and inflammation) set up the development of diabetic nephropathy and renal failure in part by increasing the susceptibility to AKI, which further promotes hypoxia and apoptosis. Considering the strong association between AKI episodes and the cumulative risk of developing advanced CKD in diabetes, strategies that reduce AKI in these patients are expected to help reduce the growing burden of end-stage renal disease.

The endocytic receptor megalin and its associated proteins in proximal tubule epithelial cells

Receptor-mediated endocytosis in renal proximal tubule epithelial cells (PTECs) is important for the reabsorption and metabolization of proteins and other substances, including carrier-bound vitamins and trace elements, in glomerular filtrates. Impairment of this endocytic process results in the loss of such substances and development of proteinuria, which is an important clinical indicator of kidney diseases and is also a risk marker for cardiovascular disease. Megalin, a member of the low-density lipoprotein receptor gene family, is a multiligand receptor expressed in the apical membrane of PTECs and plays a central role in the endocytic process. Megalin interacts with various intracellular adaptor proteins for intracellular trafficking and cooperatively functions with other membrane molecules, including the cubilin-amnionless complex. Evidence suggests that megalin and the cubilin-amnionless complex are involved in the uptake of toxic substances into PTECs, which leads to the development of kidney disease. Studies of megalin and its associated molecules will be useful for future development of novel strategies for the diagnosis and treatment of kidney diseases.

Clinical therapeutic strategies for early stage of diabetic kidney disease

Diabetic kidney disease (DKD) is the most common cause of chronic kidney disease, leading to end-stage renal disease and cardiovascular disease. The overall number of patients with DKD will continue to increase in parallel with the increasing global pandemic of type 2 diabetes. Based on landmark clinical trials, DKD has become preventable by controlling conventional factors, including hyperglycemia and hypertension, with multifactorial therapy; however, the remaining risk of DKD progression is still high. In this review, we show the importance of targeting remission/regression of microalbuminuria in type 2 diabetic patients, which may protect against the progression of DKD and cardiovascular events. To achieve remission/regression of microalbuminuria, several steps are important, including the early detection of microalbuminuria with continuous screening, targeting HbA1c < 7.0% for glucose control, the use of renin angiotensin system inhibitors to control blood pressure, the use of statins or fibrates to control dyslipidemia, and multifactorial treatment. Reducing microalbuminuria is therefore an important therapeutic goal, and the absence of microalbuminuria could be a pivotal biomarker of therapeutic success in diabetic patients. Other therapies, including vitamin D receptor activation, uric acid-lowering drugs, and incretin-related drugs, may also be promising for the prevention of DKD progression.

Therapeutic approaches to diabetic nephropathy--beyond the RAS

Despite improvements in glycaemic and blood pressure control, and the efficacy of renin-angiotensin system (RAS) blockade for proteinuria reduction, diabetic nephropathy is the most frequent cause of end-stage renal disease in developed countries. This finding is consistent with the hypothesis that key pathogenetic mechanisms leading to progression of renal disease are not modified or inactivated by current therapeutic approaches. Although extensive research has elucidated molecular signalling mechanisms that are involved in progression of diabetic kidney disease, a number of high-profile clinical trials of potentially nephroprotective agents have failed, highlighting an insufficient understanding of pathogenic pathways. These include trials of paricalcitol in early diabetic kidney disease and bardoxolone methyl in advanced-stage disease. Various strategies based on encouraging data from preclinical studies that showed renoprotective effects of receptor antagonists, neutralizing antibodies, kinase inhibitors, small compounds and peptide-based technologies are currently been tested in randomized controlled trials. Phase II clinical trials are investigating approaches targeting inflammation, fibrosis and signalling pathways. However, only one trial that aims to provide evidence for marketing approval of a potentially renoprotective drug (atrasentan) is underway-further research into the potential nephroprotective effects of novel glucose-lowering agents is required.

Sequoyitol ameliorates diabetic nephropathy in diabetic rats induced with a high-fat diet and a low dose of streptozotocin

Sequoyitol decreases blood glucose, improves glucose intolerance, and enhances insulin signaling in ob/ob mice. The aim of this study was to investigate the effects of sequoyitol on diabetic nephropathy in rats with type 2 diabetes mellitus and the mechanism of action. Diabetic rats, induced with a high-fat diet and a low dose of streptozotocin, and were administered sequoyitol (12.5, 25.0, and 50.0 mg·(kg body mass)−1·d−1) for 6 weeks. The levels of fasting blood glucose (FBG), serum insulin, blood urea nitrogen (BUN), and serum creatinine (SCr) were measured. The expression levels of p22phox, p47phox, NF-κB, and TGF-β1 were measured using immunohistochemisty, real-time PCR, and (or) Western blot. The total antioxidative capacity (T-AOC), as well as the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) were also determined. The results showed that sequoyitol significantly decreased FBG, BUN, and SCr levels, and increased the insulin levels in diabetic rats. The level of T-AOC was significantly increased, while ROS and MDA levels and the expression of p22phox, p47phox, NF-κB, and TGF-β1 were decreased with sequoyitol treatment both in vivo and in vitro. These results suggested that sequoyitol ameliorates the progression of diabetic nephropathy in rats, as induced by a high-fat diet and a low dose of streptozotocin, through its glucose-lowering effects, antioxidant activity, and regulation of TGF-β1 expression.

Renoprotection of Danshen Injection on streptozotocin-induced diabetic rats, associated with tubular function and structure

ETHNOPHARMACOLOGICAL RELEVANCE

Danshen Injection, the aqueous extracts of Radix Salvia miltiorrhiza (S. miltiorrhiza), is one of the most commonly used traditional Chinese herbs in chronic renal failure treatment. In present study, the mechanism of the renoprotective effect of Danshen Injection was analyzed on streptozocin (STZ)-induced diabetic rats.

MATERIALS AND METHODS

Diabetic experimental model was established in male Sprague-Dawley (SD) rats by intraperitoneal injection of STZ. Rats with blood glucose concentration of higher than 300 mg/dl were intraperitoneally administered with Danshen Injection at a dose of 0.78 ml/kgday. The blood glucose, 24h urinary protein excretion, serum creatinine (sCr), blood urea nitrogen (BUN), advanced glycation end products (AGEs), lipid peroxide (LPO), antioxidant enzyme of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), transforming growth factor-β1 (TGF-β1), and histomorphological changes in kidney of diabetic rats were analyzed during the course of Danshen Injection administration, as well as the tubular function index of albumin reabsorption of fluorescein isothiocyanate labeled bovine serum albumin (FITC-BSA).

RESULTS

The intraperitoneal administration of Danshen Injection could ameliorate the physiological dysfunctions of increased 24h urinary protein excretion((48.21 ± 8.04)%), sCr((39.4 ± 3.7)%), and BUN((43.37 ± 6.74)%), alleviate the ultrastructural abnormalities of hypertrophy, matrix expansion, and fibrosis in glomerulus, decrease the TGF-β1 expression, AGEs and LPO accumulation, and increase the activity of SOD and GSH-Px in kidney of diabetic rats, but did not significantly influence the blood glucose. Besides these, the Danshen Injection administration also partly restored the decrease of megalin expression in tubules and reabsorptive function of FITC-BSA, in diabetic rats.

CONCLUSION

The renoprotection of Danshen Injection on diabetic rats was associated with the preservation of tubular function and structure from the hyperglycemia induced toxicities of inappropriate cytokines secretion, oxidative stress, advanced glycation stress, and megalin expression deletion.

The genetics of diabetic nephropathy

Up to 40% of patients with type 1 and type 2 diabetes will develop diabetic nephropathy (DN), resulting in chronic kidney disease and potential organ failure. There is evidence for a heritable genetic susceptibility to DN, but despite intensive research efforts the causative genes remain elusive. Recently, genome-wide association studies have discovered several novel genetic variants associated with DN. The identification of such variants may potentially allow for early identification of at risk patients. Here we review the current understanding of the key molecular mechanisms and genetic architecture of DN, and discuss the merits of employing an integrative approach to incorporate datasets from multiple sources (genetics, transcriptomics, epigenetic, proteomic) in order to fully elucidate the genetic elements contributing to this serious complication of diabetes.

Biomolecular basis of the role of diabetes mellitus in osteoporosis and bone fractures

Osteoporosis has become a serious health problem throughout the world which is associated with an increased risk of bone fractures and mortality among the people of middle to old ages. Diabetes is also a major health problem among the people of all age ranges and the sufferers due to this abnormality increasing day by day. The aim of this review is to summarize the possible mechanisms through which diabetes may induce osteoporosis. Diabetes mellitus generally exerts its effect on different parts of the body including bone cells specially the osteoblast and osteoclast, muscles, retina of the eyes, adipose tissue, endocrine system specially parathyroid hormone (PTH) and estrogen, cytokines, nervous system and digestive system. Diabetes negatively regulates osteoblast differentiation and function while positively regulates osteoclast differentiation and function through the regulation of different intermediate factors and thereby decreases bone formation while increases bone resorption. Some factors such as diabetic neuropathy, reactive oxygen species, Vitamin D, PTH have their effects on muscle cells. Diabetes decreases the muscle strength through regulating these factors in various ways and ultimately increases the risk of fall that may cause bone fractures.