The Role of Endoplasmic Reticulum Stress in Diabetic Nephropathy

Sodium-Glucose Cotransporter-2 Inhibitor Suppresses Endoplasmic Reticulum Stress and Oxidative Stress in Diabetic Nephropathy Through Nrf2 Signaling: A Clinical and Experimental Study

Diabetic nephropathy (DN), a severe complication of type 2 diabetes mellitus (T2DM), is marked by heightened endoplasmic reticulum stress (ERS) and oxidative stress (OS) due to protein misfolding and free radical generation. We investigated the sodium-glucose co-transporter-2 inhibitor (SGLT2i), canagliflozin (Cana), in alleviating ERS and OS in DN patients and THP-1 cells under hyperglycemic condition. A total of 120 subjects were divided into four groups, with 30 subjects in each group: healthy controls, T2DM individuals, DN patients receiving standard treatment, and those treated with Cana. The control group had no history of diabetes, cardiovascular or renal diseases, or other comorbidities. Cana was administered at doses of either 100 or 300 mg per day based on the estimated glomerular filtration rate (eGFR) value of DN individuals, with a mean follow-up of 6 months. Additionally, THP-1 monocytes were exposed to HGM (33.3 mM glucose with a cytokine cocktail of TNF-α and IFN-γ at 50 ng/mL each) to evaluate the relative levels of ERS, OS markers, and nuclear factor erythroid 2-related factor 2 (Nrf2), the transcription factor regulating cellular redox, which is downregulated in diabetes. Our results revealed that ERS markers GRP78 and PERK, as well as OS markers TXNIP and p22phox, were elevated in both DN patients and HGM-treated THP-1 monocytes and were reduced by Cana intervention. Furthermore, Cana regulated the phosphorylation of Nrf2, Akt, and EIF2α in HGM-treated monocytes. In conclusion, our findings highlight the role of Cana in activating Nrf2, thereby attenuating ERS and OS to mitigate DN progression.

(+)-Catechin ameliorates diabetic nephropathy injury by inhibiting endoplasmic reticulum stress-related NLRP3-mediated inflammation

Endoplasmic reticulum (ER) stress and chronic sterile inflammation are associated with the pathogenesis of diabetic nephropathy (DN). Catechins are natural polyphenolic compounds found in green tea that possess some health benefits. However, whether (+)-catechin can reduce tubular injury in DN by regulating ER stress and NLRP3-associated inflammation remains uncertain. This study examined the effects of (+)-catechin on streptozotocin (STZ)-induced diabetic mice and on palmitic acid (PA)-treated HK-2 cells. In vivo, a DN mouse model was generated by injecting STZ. The biochemical indicators of serum and urine, as well as renal histopathology and ultrastructure were analysed. To predict the mechanisms associated with (+)-catechin, network pharmacology and molecular docking were used. Finally, quantitative real-time PCR (qPCR), western blot analysis and immunofluorescence analysis were performed to measure the mRNA and protein expressions of specific targets in the renal tissue of DN mice and PA-treated HK-2 cells to validate the predicted results. (+)-Catechin significantly ameliorated renal function and pathological changes associated with tubular injury by inhibiting ER stress by downregulating of GRP78, PEAK, CHOP, ATF6 and XBP1. In addition, (+)-catechin inhibited renal inflammation by suppressing NLRP3 associated inflammation, which was characterized by the downregulation of NLRP3, ASC, AIM2, Caspase1, IL-1β and IL-18 in DN mice and PA-treated HK-2 cells. Collectively, these findings suggested that (+)-catechin exerted a renoprotective effect against DN by inhibiting ER stress and NLRP3-related inflammation to ameliorate tubular injury, suggesting the therapeutic potential of (+)-catechin.

Crosstalk among podocytes, glomerular endothelial cells and mesangial cells in diabetic kidney disease: an updated review

Diabetic kidney disease (DKD) is a long-term and serious complication of diabetes that affects millions of people worldwide. It is characterized by proteinuria, glomerular damage, and renal fibrosis, leading to end-stage renal disease, and the pathogenesis is complex and involves multiple cellular and molecular mechanisms. Among three kinds of intraglomerular cells including podocytes, glomerular endothelial cells (GECs) and mesangial cells (MCs), the alterations in one cell type can produce changes in the others. The cell-to-cell crosstalk plays a crucial role in maintaining the glomerular filtration barrier (GFB) and homeostasis. In this review, we summarized the recent advances in understanding the pathological changes and interactions of these three types of cells in DKD and then focused on the signaling pathways and factors that mediate the crosstalk, such as angiopoietins, vascular endothelial growth factors, transforming growth factor-β, Krüppel-like factors, retinoic acid receptor response protein 1 and exosomes, etc. Furthermore, we also simply introduce the application of the latest technologies in studying cell interactions within glomerular cells and new promising mediators for cell crosstalk in DKD. In conclusion, this review provides a comprehensive and updated overview of the glomerular crosstalk in DKD and highlights its importance for the development of novel intervention approaches.

Neuroprotective role of vitamin B12 in streptozotocin-induced type 1 diabetic rats

Chronic hyperglycemia-induced neuropathological changes include neuronal apoptosis, astrogliosis, decrease in neurotrophic support, impaired synaptic plasticity, and impaired protein quality control (PQC) system. Vitamin B12 is indispensable for neuronal development and brain function. Several studies reported the neuroprotective effect of B12 supplementation in diabetic patients. However, the underlying molecular basis for the neuroprotective effect of B12 supplementation in diabetes needs to be thoroughly investigated. Two-month-old Sprague-Dawley rats were randomly assigned into three groups: Control (CN), diabetes (D; induced with streptozotocin; STZ), and diabetic rats supplemented with vitamin B12 (DBS; vitamin B12; 50 μg/kg) for four months. At the end of 4 months of experimentation, the brain was dissected to collect the cerebral cortex (CC). The morphology of CC was investigated with H&E and Nissl body staining. Neuronal apoptosis was determined with TUNEL assay. The components of neurotrophic support, astrogliosis, synaptic plasticity, and PQC processes were investigated by immunoblotting and immunostaining methods. H& E, Nissl body, and TUNEL staining revealed that diabetes-induced neuronal apoptosis and degeneration. However, B12 supplementation ameliorated the diabetes-induced neuronal apoptosis. Further, B12 supplementation restored the markers of neurotrophic support (BDNF, NGF, and GDNF), and synaptic plasticity (SYP, and PSD-95) in diabetic rats. Interestingly, B12 supplementation also attenuated astrogliosis, ER stress, and ameliorated autophagy-related proteins in diabetic rats. Overall, these findings suggest that B12 acts as a neuroprotective agent by inhibiting the neuropathological changes in STZ-induced type 1 diabetes. Thus, B12 supplementation could produce beneficial outcomes including neuroprotective effects in diabetic patients.

Antifibrotic effects of sodium-glucose cotransporter-2 inhibitors: A comprehensive review

BACKGROUND AND AIMS

Scar tissue accumulation in organs is the underlying cause of many fibrotic diseases. Due to the extensive array of organs affected, the long-term nature of fibrotic processes and the large number of people who suffer from the negative impact of these diseases, they constitute a serious health problem for modern medicine and a huge economic burden on society. Sodium-glucose cotransporter-2 inhibitors (SGLT2is) are a relatively new class of anti-diabetic pharmaceuticals that offer additional benefits over and above their glucose-lowering properties; these medications modulate a variety of diseases, including fibrosis. Herein, we have collated and analyzed all available research on SGLT2is and their effects on organ fibrosis, together with providing a proposed explanation as to the underlying mechanisms.

METHODS

PubMed, ScienceDirect, Google Scholar and Scopus were searched spanning the period from 2012 until April 2023 to find relevant articles describing the antifibrotic effects of SGLT2is.

RESULTS

The majority of reports have shown that SGLT2is are protective against lung, liver, heart and kidney fibrosis as well as arterial stiffness. According to the results of clinical trials and animal studies, many SGLT2 inhibitors are promising candidates for the treatment of fibrosis. Recent studies have demonstrated that SGLT2is affect an array of cellular processes, including hypoxia, inflammation, oxidative stress, the renin-angiotensin system and metabolic activities, all of which have been linked to fibrosis.

CONCLUSION

Extensive evidence indicates that SGLT2is are promising treatments for fibrosis, demonstrating protective effects in various organs and influencing key cellular processes linked to fibrosis.

Pharmacological potential of Astragali Radix for the treatment of kidney diseases

BACKGROUND

With the increasing prevalence of hypertension, diabetes, and obesity, the incidence of kidney diseases is also increasing, resulting in a serious public burden. Conventional treatments for kidney diseases have unsatisfactory effects and are associated with adverse reactions. Traditional Chinese medicines have good curative effects and advantages over conventional treatments for preventing and treating kidney diseases. Astragali Radix is a Chinese herbal medicine widely used to treat kidney diseases.

PURPOSE

To review the potential applications and molecular mechanisms underlying the renal protective effects of Astragali Radix and its components and to provide direction and reference for new therapeutic strategies and future research and development of Astragali Radix.

STUDY DESIGN AND METHODS

PubMed, Google Scholar, and Web of Science were searched using keywords, including "Astragali Radix," "Astragalus," "Astragaloside IV" (AS-IV), "Astragali Radix polysaccharide" (APS), and "kidney diseases." Reports on the effects of Astragali Radix and its components on kidney diseases were identified and reviewed.

RESULTS

The main components of Astragali Radix with kidney-protective properties include AS-IV, APS, calycosin, formononetin, and hederagenin. Astragali Radix and its active components have potential pharmacological effects for the treatment of kidney diseases, including acute kidney injury, diabetic nephropathy, hypertensive renal damage, chronic glomerulonephritis, and kidney stones. The pharmacological effects of Astragali Radix are manifested through the inhibition of inflammation, oxidative stress, fibrosis, endoplasmic reticulum stress, apoptosis, and ferroptosis, as well as the regulation of autophagy.

CONCLUSION

Astragali Radix is a promising drug candidate for treating kidney diseases. However, current research is limited to animal and cell studies, underscoring the need for further verifications using high-quality clinical data.

IL-33/ST2L signaling alleviates diabetic nephropathy by regulating endoplasmic reticulum stress and apoptosis

OBJECTIVE

Diabetic nephropathy (DN) is a serious chronic complication of diabetes mellitus (DM). Endoplasmic reticulum (ER) stress is an important factor in the regulation of pathological processes in DN, and excessive ER stress can lead to apoptosis. Although the IL-33/ST2 axis is known to be involved in diabetic kidney disease or related nephropathy, its role and molecular mechanisms remain poorly understood in terms of DN. The purpose of this study was to investigate the effects of IL-33/ST2 signaling on DN and to characterize the roles that ER stress and apoptosis play in DN.

METHODS

To investigate this study, mice were randomly assigned into DN (induced by 0.1% STZ) and Control groups. Biochemical indices (FBG, BUN, UPR, UCE) were measured in serum and urine samples to reflect blood glucose and kidney damage. Quantitative real-time PCR, western blot, and immunofluorescence were used to assess gene and protein expression of the IL-33/ST2 axis and ER stress relative signaling molecule. Apoptosis was analyzed by flow cytometry.

RESULTS

IL-33 levels are significantly increased in the kidneys of patients and mice with DN. Double immunofluorescence staining showed that IL-33 colocalized with CD31-positive endothelial cells. Treatment with IL-33 attenuated kidney injury in Streptozotocin (STZ)-treated mice. In vitro, we showed that IL-33 attenuated ER stress and apoptosis in glomerular endothelial cells. However, sST2 treatment significantly reversed these effects of IL-33.

CONCLUSION

Together, these data suggest that IL-33/ST2 signaling mitigates STZ-induced renal damage, partly at least, by suppressing ER stress and apoptosis. Therefore, IL-33 may be an effective therapeutic target in DN.

[Research Progress in Stress-Induced Senescence of Renal Tubular Cells in Diabetic Nephropathy]

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Renal tubulointerstitial injury is an important pathophysiological basis that contributes to the progression of DN to end-stage renal disease. Stress-induced senescence of renal tubular epithelial cells (RTECs) forms a key link that causes tubulointerstitial injury. In recent years, it has been reported that organelles, such as endoplasmic reticulum, mitochondria, and lysosomes, in RTECs are damaged to varying degrees in DN, and that their functional imbalance may lead to stress-induced senescence of RTECs, thereby causing sustained cellular and tissue-organ damage, which in turn promotes the progression of the disease. However, the core mechanism underlying changes in the senescence microenvironment caused by stress-induced senescence of RTECs in DN is still not understood. In addition, the mechanism by which organelles lose homeostasis also needs to be further investigated. Herein, we described the specific pathophysiological mechanisms of renal tubular injury, stress-induced senescence of RTECs, and their association with organelles in the context of DN in order to provide reference for the next-step research, as well as the development of new therapeutic strategies.

CTRP4 attenuates apoptosis and epithelial-mesenchymal transition markers in podocytes through an AMPK/autophagy-dependent pathway

Hyperglycemia, characterized by high blood glucose levels resulting from pancreatic beta cell dysfunction or impaired insulin signaling, is a contributing factor in the development of diabetic nephropathy. This study aimed to investigate the effects of C1q/TNF-related protein 4 (CTRP4), known for its anti-obesity and anti-inflammatory properties in various disease models, on podocyte apoptosis and endoplasmic reticulum (ER) stress in the presence of elevated glucose levels. The expression levels of various proteins in podocytes and adipocytes were evaluated by Western blotting. Autophagosomes in podocytes were stained by MDC. Chromatin condensation in podocytes was examined by Hoechst staining. The research revealed increased expression of CTRP4 in 3T3-L1 adipocytes and CIHP-1 podocytes exposed to high glucose (HG) conditions. Treatment with CTRP4 effectively mitigated HG-induced apoptosis and ER stress and normalized epithelial-to-mesenchymal transition (EMT) markers in CIHP-1 cells. Furthermore, elevated levels of AMPK phosphorylation and autophagy were observed in CIHP-1 cells treated with CTRP4. Silencing of AMPK or the use of 3-methyl adenine (3 MA) reduced the impacts of CTRP4 on apoptosis, EMT markers and ER stress in CIHP-1 cells. In conclusion, these findings suggest that CTRP4 alleviates ER stress in podocytes under hyperglycemic conditions, leading to the suppression of apoptosis and the restoration of EMT through AMPK/autophagy-mediated signaling. These insights provide valuable information for the development of therapeutic strategies for diabetic nephropathy.

BM-MSCs alleviate diabetic nephropathy in male rats by regulating ER stress, oxidative stress, inflammation, and apoptotic pathways

Introduction: Diabetic nephropathy (DN), a chronic kidney disease, is a major cause of end-stage kidney disease worldwide. Mesenchymal stem cells (MSCs) have become a promising option to mitigate several diabetic complications. Methods: In this study, we evaluated the therapeutic potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) in a rat model of STZ-induced DN. After the confirmation of diabetes, rats were treated with BM-MSCs and sacrificed at week 12 after treatment. Results: Our results showed that STZ-induced DN rats had extensive histopathological changes, significant upregulation in mRNA expression of renal apoptotic markers, ER stress markers, inflammatory markers, fibronectin, and intermediate filament proteins, and reduction of positive immunostaining of PCNA and elevated P53 in kidney tissue compared to the control group. BM-MSC therapy significantly improved renal histopathological changes, reduced renal apoptosis, ER stress, inflammation, and intermediate filament proteins, as well as increased positive immunostaining of PCNA and reduced P53 in renal tissue compared to the STZ-induced DN group. Conclusion: In conclusion, our study indicates that BM-MSCs may have therapeutic potential for the treatment of DN and provide important insights into their potential use as a novel therapeutic approach for DN.

ShenQiWan ameliorates renal injury in type 2 diabetic mice by modulating mitochondrial fusion and endoplasmic reticulum stress

Background: ShenQiWan is commonly used in traditional Chinese medicine for the treatment of diabetic nephropathy, which is closely related to mitochondrial fusion and endoplasmic reticulum stress. This study aimed to investigate the intervention effect and molecular mechanisms of ShenQiWan on renal injury in KKAy mice. Methods: C57BL/6J mice (11 weeks old) were fed a regular diet upon arrival, while KKAy mice (11 weeks old) were fed a high-fat diet upon arrival. At 12 weeks of age, KKAy mice with random blood glucose ≥13.9 mmol/L were identified as diabetic mice and randomly divided into the model group (n = 30) and the treatment group (n = 30), while C57BL/6J mice of 12 weeks old (n = 30) served as the control group. The treatment group received daily aqueous decoction of ShenQiWan (13.5 g/kg), while the control group and model group received daily equal amounts of saline from 12 weeks old to 24 weeks old. The general status of mice was observed regularly, and fasting blood glucose and 24-hour urine microalbumin were measured. Ten mice were euthanized in each group at the age of 16, 20, and 24 weeks, serum samples were used for biochemical indexes and kidney tissues were used for morphological studies. GRP78, OPA1, MFN1, MFN2 mRNA and protein expression were detected by Real-time PCR, immunohistochemistry and Western blot. Results: The mice in the model group exhibited symptoms of lethargy, slow movement, obesity, polyuria and proteinuria. Morphological observation revealed pathological changes, including thickening of the glomerular basement membrane and interstitial fibrosis. After treatment with ShenQiWan, the fasting blood glucose level of KKAy mice was significantly reduced, urinary albuminuria was decreased, serum biochemical indexes were improved, renal tissue pathological changes were significantly alleviated. The results also showed a significant reduction in the expression of endoplasmic reticulum stress-related factor GRP78 and an increase in the expression of mitochondrial fusion-related factors OPA1, MFN1 and MFN2 after treatment with ShenQiWan. Conclusion: ShenQiWan can protect diabetic mice from renal damage by modulating mitochondrial fusion and alleviating endoplasmic reticulum stress, exerting its protective effects.

Beyond Glucose: The Dual Assault of Oxidative and ER Stress in Diabetic Disorders

Diabetes mellitus, a prevalent global health concern, is characterized by hyperglycemia. However, recent research reveals a more intricate landscape where oxidative stress and endoplasmic reticulum (ER) stress orchestrate a dual assault, profoundly impacting diabetic disorders. This review elucidates the interplay between these two stress pathways and their collective consequences on diabetes. Oxidative stress emanates from mitochondria, where reactive oxygen species (ROS) production spirals out of control, leading to cellular damage. We explore ROS-mediated signaling pathways, which trigger β-cell dysfunction, insulin resistance, and endothelial dysfunction the quintessential features of diabetes. Simultaneously, ER stress unravels, unveiling how protein folding disturbances activate the unfolded protein response (UPR). We dissect the UPR's dual role, oscillating between cellular adaptation and apoptosis, significantly influencing pancreatic β-cells and peripheral insulin-sensitive tissues. Crucially, this review exposes the synergy between oxidative and ER stress pathways. ROS-induced UPR activation and ER stress-induced oxidative stress create a detrimental feedback loop, exacerbating diabetic complications. Moreover, we spotlight promising therapeutic strategies that target both stress pathways. Antioxidants, molecular chaperones, and novel pharmacological agents offer potential avenues for diabetes management. As the global diabetes burden escalates, comprehending the dual assault of oxidative and ER stress is paramount. This review not only unveils the intricate molecular mechanisms governing diabetic pathophysiology but also advocates a holistic therapeutic approach. By addressing both stress pathways concurrently, we may forge innovative solutions for diabetic disorders, ultimately alleviating the burden of this pervasive health issue.

Research progress on multiple cell death pathways of podocytes in diabetic kidney disease

Diabetic kidney disease (DKD) is the main cause of end-stage renal disease, and its clinical manifestations are progressive proteinuria, decreased glomerular filtration rate, and renal failure. The injury and death of glomerular podocytes are the keys to DKD. Currently, a variety of cell death modes have been identified in podocytes, including apoptosis, autophagy, endoplasmic reticulum (ER) stress, pyroptosis, necroptosis, ferroptosis, mitotic catastrophe, etc. The signaling pathways leading to these cell death processes are interconnected and can be activated simultaneously or in parallel. They are essential for cell survival and death that determine the fate of cells. With the deepening of the research on the mechanism of cell death, more and more researchers have devoted their attention to the underlying pathologic research and the drug therapy research of DKD. In this paper, we discussed the podocyte physiologic role and DKD processes. We also provide an overview of the types and specific mechanisms involved in each type of cell death in DKD, as well as related targeted therapy methods and drugs are reviewed. In the last part we discuss the complexity and potential crosstalk between various modes of cell death, which will help improve the understanding of podocyte death and lay a foundation for new and ideal targeted therapy strategies for DKD treatment in the future.

Identification of endoplasmic reticulum stress-related biomarkers of diabetes nephropathy based on bioinformatics and machine learning

Backgrounds

Diabetes nephropathy (DN) is a growing public health concern worldwide. Renal dysfunction impairment in DN is intimately linked to ER stress and its related signaling pathways. Nonetheless, the underlying mechanism and biomarkers for this function of ER stress in the DN remain unknown.

Methods

Microarray datasets were retrieved from the Gene Expression Omnibus (GEO) database, and ER stress-related genes (ERSRGs) were downloaded from the MSigDB and GeneCards database. We identified hub ERSRGs for DN progression by intersecting ERSRGs with differentially expressed genes and significant genes in WGCNA, followed by a functional analysis. After analyzing hub ERSRGs with three machine learning techniques and taking the intersection, we did external validation as well as developed a DN diagnostic model based on the characteristic genes. Immune infiltration was performed using CIBERSORT. Moreover, patients with DN were then categorized using a consensus clustering approach. Eventually, the candidate ERSRGs-specific small-molecule compounds were defined by CMap.

Results

Several biological pathways driving pathological injury of DN and disordered levels of immune infiltration were revealed in the DN microarray datasets and strongly related to deregulated ERSRGs by bioinformatics multi-chip integration. Moreover, CDKN1B, EGR1, FKBP5, GDF15, and MARCKS were identified as ER stress signature genes associated with DN by machine learning algorithms, demonstrating their potential as DN biomarkers.

Conclusions

Our research sheds fresh light on the function of ER stress in DN pathophysiology and the development of early diagnostic and ER stress-related treatment targets in patients with DN.

Potential role of microRNA-503 in Icariin-mediated prevention of high glucose-induced endoplasmic reticulum stress

BACKGROUND

Dysregulated microRNA (miRNA) is crucial in the progression of diabetic nephropathy (DN).

AIM

To investigate the potential molecular mechanism of Icariin (ICA) in regulating endoplasmic reticulum (ER) stress-mediated apoptosis in high glucose (HG)-induced primary rat kidney cells (PRKs), with emphasis on the role of miR-503 and sirtuin 4 (SIRT4) in this process.

METHODS

Single intraperitoneal injection of streptozotocin (65 mg/kg) in Sprague-Dawley rats induce DN in the in vivo hyperglycemic model. Glucose-treated PRKs were used as an in vitro HG model. An immunofluorescence assay identified isolated PRKs. Cell Counting Kit-8 and flow cytometry analyzed the effect of ICA treatment on cell viability and apoptosis, respectively. Real-time quantitative polymerase chain reaction and western blot analyzed the levels of ER stress-related proteins. Dual luciferase analysis of miR-503 binding to downstream SIRT4 was performed.

RESULTS

ICA treatment alleviated the upregulated miR-503 expression in vivo (DN) and in vitro (HG). Mechanistically, ICA reduced HG-induced miR-503 overexpression, thereby counteracting its function in downregulating SIRT4 levels. ICA regulated the miR-503/SIRT4 axis and subsequent ER stress to alleviate HG-induced PRKs injury.

CONCLUSION

ICA reduced HG-mediated inhibition of cell viability, promotion of apoptosis, and ER stress in PRKs. These effects involved regulation of the miR-503/SIRT4 axis. These findings indicate the potential of ICA to treat DN, and implicate miR-503 as a viable target for therapeutic interventions in DN.

Tubular injury in diabetic kidney disease: molecular mechanisms and potential therapeutic perspectives

Diabetic kidney disease (DKD) is a chronic complication of diabetes and the leading cause of end-stage renal disease (ESRD) worldwide. Currently, there are limited therapeutic drugs available for DKD. While previous research has primarily focused on glomerular injury, recent studies have increasingly emphasized the role of renal tubular injury in the pathogenesis of DKD. Various factors, including hyperglycemia, lipid accumulation, oxidative stress, hypoxia, RAAS, ER stress, inflammation, EMT and programmed cell death, have been shown to induce renal tubular injury and contribute to the progression of DKD. Additionally, traditional hypoglycemic drugs, anti-inflammation therapies, anti-senescence therapies, mineralocorticoid receptor antagonists, and stem cell therapies have demonstrated their potential to alleviate renal tubular injury in DKD. This review will provide insights into the latest research on the mechanisms and treatments of renal tubular injury in DKD.

Human complement component C3 N-glycome changes in type 1 diabetes complications

Aim

Changes in N-glycosylation have been described in numerous diseases and are being considered as biomarkers of ongoing pathological condition. Previous studies demonstrated the interrelation of N-glycosylation and type 1 diabetes (T1D), particularly linking serum N-glycan changes with complications accompanying the disease. Moreover, the role of complement component C3 in diabetic nephropathy and retinopathy has been implicated, and C3 N-glycome was found to be altered in young T1D patients. Therefore, we investigated associations between C3 N-glycan profiles and albuminuria and retinopathy accompanying T1D, as well as glycosylation connection with other known T1D complication risk factors.

Research design and methods

Complement component C3 N-glycosylation profiles have been analyzed from 189 serum samples of T1D patients (median age 46) recruited at a Croatian hospital centre. Using our recently developed high-throughput method, relative abundances of all six of the C3 glycopeptides have been determined. Assessment of C3 N-glycome interconnection with T1D complications, hypertension, smoking status, estimated glomerular filtration rate (eGFR), glycaemic control and duration of the disease was done using linear modelling.

Results

Significant changes of C3 N-glycome in severe albuminuria accompanying type 1 diabetes were observed, as well as in T1D subjects with hypertension. All except one of the C3 glycopeptides proved to be associated with measured HbA1c levels. One of the glycoforms was shown to be changed in non-proliferative T1D retinopathy. Smoking and eGFR showed no effect on C3 N-glycome. Furthermore, C3 N-glycosylation profile was shown to be independent of disease duration.

Conclusion

This study empowered the role of C3 N-glycosylation in T1D, showing value in distinguishing subjects with different diabetic complications. Being independent of the disease duration, these changes may be associated with the disease onset, making C3 N-glycome a potential novel marker of the disease progression and severity.

The beneficial effects of astragaloside IV on ameliorating diabetic kidney disease

Diabetic kidney disease (DKD) has become the major cause of chronic kidney disease or end-stage renal disease. There is still a need for innovative treatment strategies for preventing, arresting, treating, and reversing DKD, and a plethora of scientific evidence has revealed that Chinese herbal monomers can attenuate DKD in multiple ways. Astragaloside IV (AS-IV) is one of the active ingredients of Astragalus membranaceus and was selected as a chemical marker in the Chinese Pharmacopeia for quality control purposes. An increasing amount of studies indicate that AS-IV is a promising novel drug for the treatment of DKD. AS-IV has been shown to improve DKD by combating oxidative stress, attenuating endoplasmic reticulum stress, regulating calcium homeostasis, alleviating inflammation, improving vascular function, improving epithelial to mesenchymal transition and so on. This review briefly summarizes the pathogenesis of DKD, systematically reviews the mechanisms by which AS-IV improves DKD, and aims to facilitate related pharmacological research and development to promote the utilization of Chinese herbal monomers in DKD.

Endoplasmic Reticulum Stress in Renal Cell Carcinoma

The endoplasmic reticulum is an organelle exerting crucial functions in protein production, metabolism homeostasis and cell signaling. Endoplasmic reticulum stress occurs when cells are damaged and the capacity of this organelle to perform its normal functions is reduced. Subsequently, specific signaling cascades, together forming the so-called unfolded protein response, are activated and deeply impact cell fate. In normal renal cells, these molecular pathways strive to either resolve cell injury or activate cell death, depending on the extent of cell damage. Therefore, the activation of the endoplasmic reticulum stress pathway was suggested as an interesting therapeutic strategy for pathologies such as cancer. However, renal cancer cells are known to hijack these stress mechanisms and exploit them to their advantage in order to promote their survival through rewiring of their metabolism, activation of oxidative stress responses, autophagy, inhibition of apoptosis and senescence. Recent data strongly suggest that a certain threshold of endoplasmic reticulum stress activation needs to be attained in cancer cells in order to shift endoplasmic reticulum stress responses from a pro-survival to a pro-apoptotic outcome. Several endoplasmic reticulum stress pharmacological modulators of interest for therapeutic purposes are already available, but only a handful were tested in the case of renal carcinoma, and their effects in an in vivo setting remain poorly known. This review discusses the relevance of endoplasmic reticulum stress activation or suppression in renal cancer cell progression and the therapeutic potential of targeting this cellular process for this cancer.

Soluble Klotho protects against glomerular injury through regulation of ER stress response

αKlotho (Klotho) has well established renoprotective effects; however, the molecular pathways mediating its glomerular protection remain incompletely understood. Recent studies have reported that Klotho is expressed in podocytes and protects glomeruli through auto- and paracrine effects. Here, we examined renal expression of Klotho in detail and explored its protective effects in podocyte-specific Klotho knockout mice, and by overexpressing human Klotho in podocytes and hepatocytes. We demonstrate that Klotho is not significantly expressed in podocytes, and transgenic mice with either a targeted deletion or overexpression of Klotho in podocytes lack a glomerular phenotype and have no altered susceptibility to glomerular injury. In contrast, mice with hepatocyte-specific overexpression of Klotho have high circulating levels of soluble Klotho, and when challenged with nephrotoxic serum have less albuminuria and less severe kidney injury compared to wildtype mice. RNA-seq analysis suggests an adaptive response to increased endoplasmic reticulum stress as a putative mechanism of action. To evaluate the clinical relevance of our findings, the results were validated in patients with diabetic nephropathy, and in precision cut kidney slices from human nephrectomies. Together, our data reveal that the glomeruloprotective effects of Klotho is mediated via endocrine actions, which increases its therapeutic potential for patients with glomerular diseases.

Role of advanced glycation end products and insulin resistance in diabetic nephropathy

Metabolic syndrome (MetS), i.e. a cluster of physiological and biochemical abnormalities can lead to diabetic nephropathy (DN). Insulin resistance, impaired fasting glucose are the main signs and symptoms of MetS. Excess sugar can induce various substantial structural changes like formation of advanced glycation end products (AGEs). AGEs are formed due to reaction of reducing sugars with amino groups of proteins, lipids and nucleic acids. AGEs when bound to the receptor for advanced glycation end products (RAGE) activate increased production of pro-inflammatory markers like interleukin-6 (IL-6), tumour necrosis factor alpha (TNF-α) along with induction of endoplasmic reticulum (ER) stress. Accumulation of AGEs, enhanced reactive oxygen species (ROS) generation and activation of protein kinase C (PKC), are considered to induce glomerular hypertrophy, podocyte apoptosis, therefore contributing to the development and progression of DN. In this review, we decipher different biochemical and physiological factors that link AGEs and DN.

High-Throughput Human Complement C3 N-Glycoprofiling Identifies Markers of Early Onset Type 1 Diabetes Mellitus in Children

Recently, it was shown that children at the onset of type 1 diabetes (T1D) have a higher proportion of oligomannose glycans in their total plasma protein N-glycome compared to their healthy siblings. The most abundant complement component, glycoprotein C3, contains two N-glycosylation sites occupied exclusively by this type of glycans. Furthermore, complement system, as well as C3, was previously associated with T1D. It is also known that changes in glycosylation can modulate inflammatory responses, so our aim was to characterize the glycosylation profile of C3 in T1D. For this purpose, we developed a novel high-throughput workflow for human C3 concanavalin A lectin affinity enrichment and subsequent LC-MS glycopeptide analysis which enables protein-specific N-glycosylation profiling. From the Danish Childhood Diabetes Register, plasma samples of 61 children/adolescents newly diagnosed with T1D and 84 of their unaffected siblings were C3 N-glycoprofiled. Significant changes of C3 N-glycan profiles were found. T1D was associated with an increase in the proportion of unprocessed glycan structures with more mannose units. A regression model including C3 N-glycans showed notable discriminative power between children with early onset T1D and their healthy siblings with area under curve of 0.879. This study confirmed our previous findings of plasma high-mannose glycan changes in a cohort of recent onset T1D cases, suggesting the involvement of C3 N-glycome in T1D development. Our C3 glycan-based discriminative model could be valuable in assessment of T1D risk in children.

Pan-Src kinase inhibitor treatment attenuates diabetic kidney injury via inhibition of Fyn kinase-mediated endoplasmic reticulum stress

Src family kinases (SFKs) have been implicated in the pathogenesis of kidney fibrosis. However, the specific mechanism by which SFKs contribute to the progression of diabetic kidney disease (DKD) remains unclear. Our preliminary transcriptome analysis suggested that SFK expression was increased in diabetic kidneys and that the expression of Fyn (a member of the SFKs), along with genes related to unfolded protein responses from the endoplasmic reticulum (ER) stress signaling pathway, was upregulated in the tubules of human diabetic kidneys. Thus, we examined whether SFK-induced ER stress is associated with DKD progression. Mouse proximal tubular (mProx24) cells were transfected with Fyn or Lyn siRNA and exposed to high glucose and palmitate (HG-Pal). Streptozotocin-induced diabetic rats were treated with KF-1607, a novel pan-Src kinase inhibitor (SKI) with low toxicity. The effect of KF-1607 was compared to that of losartan, a standard treatment for patients with DKD. Among the SFK family members, the Fyn and Lyn kinases were upregulated under diabetic stress. HG-Pal induced p70S6 kinase and JNK/CHOP signaling and promoted tubular injury. Fyn knockdown but not Lyn knockdown inhibited this detrimental signaling pathway. In addition, diabetic rats treated with KF-1607 showed improved kidney function and decreased ER stress, inflammation, and fibrosis compared with those treated with losartan. Collectively, these findings indicate that Fyn kinase is a specific member of the SFKs implicated in ER stress activation leading to proximal tubular injury in the diabetic milieu and that pan-SKI treatment attenuates kidney injury in diabetic rats. These data highlight Fyn kinase as a viable target for the development of therapeutic agents for DKD.

Insights into a signaling pathway that promotes diabetic kidney disease could lead to new therapies that protect against this major cause of kidney failure. Past studies have suggested that the various Src family kinase (SFK) signaling proteins play a part in the cell death and scar tissue formation associated with diabetic kidney disease. Hunjoo Ha of Ewha Womans University, Seoul, South Korea, and colleagues have now focused on one particular SFK, Fyn, as a direct driver of the kidney damage seen in mouse models of diabetes. Genetic interventions that selectively inhibit Fyn suppressed this damage, as did treatment with an oral drug that broadly inactivates SFKs. This experimental drug proved as effective as controlling inflammation and oxidative damage in the kidney as an already clinically approved treatment, confirming the significance of SFK signaling in this condition.

MBTPS2 exacerbates albuminuria in streptozotocin-induced type I diabetic nephropathy by promoting endoplasmic reticulum stress-mediated renal damage

BACKGROUND

The membrane-bound transcription factor protease site 2 (MBTPS2) is an intramembranous metalloprotease involved in the regulation of ER stress response, however, whether it is associated with DN is unknown.

RESULTS

We report that MBTPS2 expression is upregulated in the renal cortex of diabetic mice induced by streptozotocin (STZ), a murine model of insulinopenic type 1 DN. Functionally, in vivo, MBTPS2 overexpression exacerbates and its knockdown attenuates albuminuria, which indicate a detrimental role of MBTPS2 played in albuminuria development in DN mice. We further show that MBTPS2 promotes ER stress and renal damage in DN mice, and that reducing ER stress via a chemical chaperone 4-phenylbutyric acid (4-PBA) markedly rescues MBTPS2-exacerbated renal damage and albuminuria severity.

CONCLUSIONS

Collectively, our study associates the function of MBTPS2 in DN albuminuria with ER stress regulation, thus underscoring the notorious role of maladaptive ER response in influencing DN albuminuria.

Diosmin mitigates high glucose-induced endoplasmic reticulum stress through PI3K/AKT pathway in HK-2 cells

BACKGROUND

Diosmin has been reported to treat diabetes, but its role in diabetic nephropathy (DN) remains unclear. This research investigated the mechanism by which diosmin alleviated high glucose (HG)-induced HK-2 cell injury.

METHODS

First, we used CCK-8 to detect the effect of 0.1, 1, or 10 μg/mL diosmin on the viability of HK-2 cells treated with normal glucose or HG. Next, we used flow cytometry, automatic biochemical analyzer, ELISA, immunofluorescence, and colorimetric assay kit to examine the apoptosis, oxidative stress, inflammatory factors, and Caspase-3 expression in HK-2 cells. Thereafter, we used the western blot and qRT-PCR to examine the expression of the endoplasmic reticulum stress-, oxidative stress-, inflammation-, apoptosis-, and autophagy, and PI3K/AKT pathway-related factors.

RESULTS

Diosmin was non-cytotoxic to normal HK-2 cells and enhanced the HK-2 cell viability suppressed by HG. Meanwhile, diosmin restrained apoptosis, the contents of MDA, pro-inflammatory factors, and Caspase-3 but intensified the contents of SOD and CAT induced by HG. We further confirmed that diosmin blunted oxidative stress-, inflammation-, apoptosis-, and autophagy-related factors expression induced by HG via restraining the CHOP and GRP78 expressions. Further, we also discovered that PTEN level was restrained and the ratios of p-PI3K/PI3K and p-AKT/AKT were enhanced in HK-2 cells induced by HG, which was reversed by co-treatment of HG and diosmin.

CONCLUSIONS

Our study manifested that diosmin alleviated the HG-mediated endoplasmic reticulum stress injury in HK-2 cells via restraining the PI3K/AKT pathway.

Alterations in Protein Translation and Carboxylic Acid Catabolic Processes in Diabetic Kidney Disease

Diabetic kidney disease (DKD) remains the leading cause of end-stage kidney disease despite decades of study. Alterations in the glomerulus and kidney tubules both contribute to the pathogenesis of DKD although the majority of investigative efforts have focused on the glomerulus. We sought to examine the differential expression signature of human DKD in the glomerulus and proximal tubule and corroborate our findings in the db/db mouse model of diabetes. A transcriptogram network analysis of RNAseq data from laser microdissected (LMD) human glomerulus and proximal tubule of DKD and reference nephrectomy samples revealed enriched pathways including rhodopsin-like receptors, olfactory signaling, and ribosome (protein translation) in the proximal tubule of human DKD biopsy samples. The translation pathway was also enriched in the glomerulus. Increased translation in diabetic kidneys was validated using polyribosomal profiling in the db/db mouse model of diabetes. Using single nuclear RNA sequencing (snRNAseq) of kidneys from db/db mice, we prioritized additional pathways identified in human DKD. The top overlapping pathway identified in the murine snRNAseq proximal tubule clusters and the human LMD proximal tubule compartment was carboxylic acid catabolism. Using ultra-performance liquid chromatography–mass spectrometry, the fatty acid catabolism pathway was also found to be dysregulated in the db/db mouse model. The Acetyl-CoA metabolite was down-regulated in db/db mice, aligning with the human differential expression of the genes ACOX1 and ACACB. In summary, our findings demonstrate that proximal tubular alterations in protein translation and carboxylic acid catabolism are key features in both human and murine DKD.

Dioscin relieves diabetic nephropathy via suppressing oxidative stress and apoptosis, and improving mitochondrial quality and quantity control

Dioscin is a steroidal saponin isolated from various kinds of vegetables and herbs and possesses various biological activities. In this study, the protective effect of dioscin on diabetic nephropathy (DN) was explored. Dioscin and metformin (positive control) were administered orally to diabetic rats daily for 8 weeks. The biochemistry parameters, pancreas and kidney histological changes, oxidative stress, inflammation, apoptosis, autophagy, and mitochondrial quality and quantity control (mitophagy and mitochondrial fission/fusion) were measured. Our results showed that dioscin effectively reduced blood glucose, pancreatic injury, renal function markers and renal pathological changes in DN rat kidneys. Dioscin reduced O^2- and H₂O₂ levels, decreased MDA levels, enhanced antioxidant enzyme (SOD, CAT) activities, and reduced inflammatory factor expressions. Moreover, NOX4 expression and the disorder of the mitochondrial respiratory chain were reversed by dioscin. Furthermore, apoptosis mediated by the mitochondria and ER stress was inhibited by dioscin through downregulating the expressions of Bax, CytC, Apaf-1, caspase 9, p-PERK, p-EIF2α, IRE1, p-IRE1, XBP1s, ATF4, p-CHOP and caspase 12. In addition, autophagy was enhanced by dioscin via an AMPK-mTOR pathway. Mitophagy and mitochondrial fission/fusion belong to the mitochondrial quality and quantity control process, which was improved by dioscin via regulating Parkin, PINK1, DRP1, p-DRP1 and MFN2 expressions. Collectively, these results suggested that dioscin protected against DN through inhibiting oxidative stress, inflammation, and apoptosis mediated by the mitochondria and ER stress. Autophagy and mitochondrial quality and quantity control (mitophagy and mitochondrial fission/fusion) were also improved by dioscin.

Matrine alleviates spatial learning and memory impairment in diabetic mice by inhibiting endoplasmic reticulum stress and through modulation of PK2/PKRs pathway

Clinical and epidemiological studies indicate that diabetic cognitive impairment often occurs in diabetes mellitus patients. Matrine (Mat), an active component of Sophora flavescens Ait root extracts, has widely pharmacological activities including anti-tumor, anti-diabetes, cardioprotective and neuroprotective effects. The present study was designed to elucidate the possibly neuroprotective effects of Mat against diabetic spatial learning and memory impairment caused by high-fat diet and streptozotocin injection in mice. The results showed that Mat treatment significantly ameliorated fasting blood glucose level, impaired glucose tolerance, and lipid metabolism disorder in diabetic mice. In addition, diabetic mice exhibited spatial learning and memory impairment in the Morris water maze test, which could be attenuated by Mat treatment. Moreover, administration of Mat remarkably alleviated histological damage in diabetic hippocampus. Also, further investigations showed that Mat treatment abated endoplasmic reticulum stress induced hippocampal ultra-structure injury as evidenced by increasing the numbers of rough endoplasmic reticulum and mitochondria, as well as down-regulating endoplasmic reticulum stress related protein levels (GRP78, CHOP, ATF6 and Caspase-12). Furthermore, administration of Mat enhanced hippocampal protein expressions of PK2, PKR1 and PKR2, which decreased significantly in diabetic mice. Collectively, these findings suggested that Mat could ameliorate diabetes-induced spatial learning and memory impairment, possibly by alleviating ER stress, and partly through modulation of PK2/PKRs pathway.

Deciphering the Pharmacological Mechanisms of Qidan Dihuang Decoction in Ameliorating Renal Fibrosis in Diabetic Nephropathy through Experimental Validation In Vitro and In Vivo

OBJECTIVE

QiDan DiHuang decoction (QDD) has been proven to have good efficacy in decreasing albuminuria levels, improving renal function, and inhibiting renal fibrosis in diabetic nephropathy (DN). However, the potential mechanism remains unclear. The purpose of this study was to explore the underlying mechanism of QDD for treating DN in vitro and in vivo.

METHODS

Db/db mice were treated with QDD or saline intragastrically for 12 weeks. Non-diabetic db/m mice were used as controls. Rat renal tubular epithelial cells (NRK-52E) were cultured in high glucose conditions. ATF4 siRNA was transfected into NRK-52E cells. Different indicators were detected via UPLC, RT-PCR, western blotting, cell viability assays and apoptosis, transmission electron microscopy, histology, and immunofluorescence staining.

RESULTS

Db/db mice experienced severe kidney damage and fibrosis, increased levels of PERK, eIF2α, and ATF4, and suppression of renal autophagy compared with db/m mice. The results showed a significant improvement in glucose intolerance, blood urea nitrogen, urine albumin, serum creatinine, and renal fibrosis in db/db mice with QDD treatment. Meanwhile, the application of QDD resulted in the downregulation of PERK, eIF2α, and ATF4 and the upregulation of autophagy in diabetic kidneys. In vitro, the exposure of NRK-52E cells to high glucose resulted in downregulation of the ratio of LC3-II/LC3-I and upregulation of P62, a reduction in the number of autophagosomes and upregulation of fibronectin (FN), collagen IV and TGF-β1 protein, which was reversed by QDD treatment through inhibiting ATF4 expression.

CONCLUSIONS

Taken together, our results suggest that QDD effectively alleviates diabetic renal injuries and fibrosis by inhibiting the PERK-eIF2α-ATF4 pathway and promoting autophagy in diabetic nephropathy.

Mitophagy in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the most common cause of end-stage kidney disease worldwide and is the main microvascular complication of diabetes. The increasing prevalence of diabetes has increased the need for effective treatment of DKD and identification of new therapeutic targets for better clinical management. Mitophagy is a highly conserved process that selectively removes damaged or unnecessary mitochondria via the autophagic machinery. Given the important role of mitophagy in the increased risk of DKD, especially with the recent surge in COVID-19-associated diabetic complications, in this review, we provide compelling evidence for maintaining homeostasis in the glomeruli and tubules and its underlying mechanisms, and offer new insights into potential therapeutic approaches for treatment of DKD.

A new view of macula densa cell protein synthesis

Macula densa (MD) cells, a chief sensory cell type in the nephron, are endowed with unique microanatomic features including a high density of protein synthetic organelles and secretory vesicles in basal cell processes ("maculapodia") that suggest a so far unknown high rate of MD protein synthesis. This study aimed to explore the rate and regulation of MD protein synthesis and their effects on glomerular function using novel transgenic mouse models, newly established fluorescence cell biology techniques, and intravital microscopy. Sox2-tdTomato kidney tissue sections and an O-propargyl puromycin incorporation-based fluorescence imaging assay showed that MD cells have the highest level of protein synthesis within the kidney cortex followed by intercalated cells and podocytes. Genetic gain of function of mammalian target of rapamycin (mTOR) signaling specifically in MD cells (in MD-mTORgof mice) or their physiological activation by low-salt diet resulted in further significant increases in the synthesis of MD proteins. Specifically, these included both classic and recently identified MD-specific proteins such as cyclooxygenase 2, microsomal prostaglandin E2 synthase 1, and pappalysin 2. Intravital imaging of the kidney using multiphoton microscopy showed significant increases in afferent and efferent arteriole and glomerular capillary diameters and blood flow in MD-mTORgof mice coupled with an elevated glomerular filtration rate. The presently identified high rate of MD protein synthesis that is regulated by mTOR signaling is a novel component of the physiological activation and glomerular hemodynamic regulatory functions of MD cells that remains to be fully characterized.NEW & NOTEWORTHY This study discovered the high rate of protein synthesis in macula densa (MD) cells by applying direct imaging techniques with single cell resolution. Physiological activation and mammalian target of rapamycin signaling played important regulatory roles in this process. This new feature is a novel component of the tubuloglomerular cross talk and glomerular hemodynamic regulatory functions of MD cells. Future work is needed to elucidate the nature and (patho)physiological role of the specific proteins synthesized by MD cells.

Recent Advances in Diabetic Kidney Diseases: From Kidney Injury to Kidney Fibrosis

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease and end-stage renal disease. The natural history of DKD includes glomerular hyperfiltration, progressive albuminuria, declining estimated glomerular filtration rate, and, ultimately, kidney failure. It is known that DKD is associated with metabolic changes caused by hyperglycemia, resulting in glomerular hypertrophy, glomerulosclerosis, and tubulointerstitial inflammation and fibrosis. Hyperglycemia is also known to cause programmed epigenetic modification. However, the detailed mechanisms involved in the onset and progression of DKD remain elusive. In this review, we discuss recent advances regarding the pathogenic mechanisms involved in DKD.

LncRNA TUG1/miR-29c-3p/SIRT1 axis regulates endoplasmic reticulum stress-mediated renal epithelial cells injury in diabetic nephropathy model in vitro

Long non-coding RNAs (lncRNAs) are important regulators in diabetic nephropathy. In this study, we investigated the potential role of lncRNA TUG1 in regulating endoplasmic reticulum stress (ERS)-mediated apoptosis in high glucose induced renal tubular epithelial cells. Human renal tubular epithelial cell line HK-2 was challenged with high glucose following transfection with lncRNA TUG1, miR-29c-3p mimics or inhibitor expression plasmid, either alone or in combination, for different experimental purposes. Potential binding effects between TUG1 and miR-29c-3p, as well as between miR-29c-3p and SIRT1 were verified. High glucose induced apoptosis and ERS in HK-2 cells, and significantly decreased TUG1 expression. Overexpressed TUG1 could prevent high glucose-induced apoptosis and alleviated ERS via negatively regulating miR-29c-3p. In contrast, miR-29c-3p increased HK-2 cells apoptosis and ERS upon high glucose-challenge. SIRT1 was a direct target gene of miR-29c-3p in HK-2 cells, which participated in the effects of miR-29c-3p on HK-2 cells. Mechanistically, TUG1 suppressed the expression of miR-29c-3p, thus counteracting its function in downregulating the level of SIRT1. TUG1 regulates miR-29c-3p/SIRT1 and subsequent ERS to relieve high glucose induced renal epithelial cells injury, and suggests a potential role for TUG1 as a promising diagnostic marker of diabetic nephropathy.

Cassia auriculata leaf extract ameliorates diabetic nephropathy by attenuating autophagic necroptosis via RIP-1/RIP-3-p-p38MAPK signaling

Diabetic nephropathy (DN) is the most common manifestation of high glucose induced diabetes mellitus. In this study, we report the effects of Cassia auriculata ethanol leaf extract (CALE) on DN-associated cell toxicity and complications. The effects of CALE were screened in vitro using RGE cells. Cell viability was assessed using MTT and flow cytometry. Male Sprague-Dawley rats were divided into control, DN and treatment groups (n = 8). The DN and treatment groups received 60 mg/kg/bw of streptozotocin in citrate buffer, while the treatment group was administered 150 mg/kg/bw of CALE for 10 weeks. Biochemical analysis was conducted using spectrophotometry. Kidney tissues were analyzed using hematoxylin and eosin staining and transmission electron microscopy. CD365-KIM-1 expression was assessed using flow cytometry and signalling proteins were detected using western blotting. Treatment with 30-mM glucose reduced the viability of RGE cells in a time-dependent manner and increased the population of dead RGE cells. Cotreatment with CALE reduced cell death and glucose induced protein expression of LC3-II, RIP-1 and RIP-3 in a dose-dependent manner. In addition, CALE improved the biochemical complications, renal dysfunction and pathophysiology of rats with DN and partially or fully restored the expression of key DN-associated signalling proteins, such as KIM-1 LC3-II, RIP-1, RIP-3 and p-p38MAPK in kidney cells. CALE showed protective effects, and improved DN-associated complications in RGE cells under high glucose stress conditions, potentially by inhibiting autophagic-necroptosis signals. Additionally, CALE improved the biochemical and pathological features of kidney injury while reducing autophagic-necroptosis in rat renal cells via the LC3-II-RIP-p38MAPK pathway. PRACTICAL APPLICATIONS: Results from the current investigation will add information to the literature on glucose induced renal toxicity and the protective effects of CALE over the complications of diabetic nephropathy (DN). The mechanistic investigations of the study will add light on the autophagic/necroptosis signals in DN and open new routes of investigations to study the efficacy of CALE in diabetes-related complications.

LncRNA TUG1 ameliorates diabetic nephropathy via inhibition of PU.1/RTN1 signaling pathway

Diabetic nephropathy (DN) is a leading cause of end-stage renal failure. The study aimed to investigate whether long noncoding RNA taurine-upregulated gene 1 (TUG1) can ameliorate the endoplasmic reticulum stress (ERS) and apoptosis of renal tubular epithelial cells in DN, and the underlying mechanism. The DN mouse model was established by streptozocin injection, and the human renal tubular epithelial cell line HK-2 was treated with high glucose (HG) to mimic DN in vitro. The molecular mechanism was explored through dual-luciferase activity assay, RNA pull-down assay, RNA immunoprecipitation (RIP), and chromatin immunoprecipitation (CHIP) assay. The expression of TUG1 was significantly decreased in the renal tubules of DN model mice. Overexpression of TUG1 reduced the levels of ERS markers and apoptosis markers by inhibiting reticulon-1 (RTN1) expression in HG-induced HK-2 cells. Furthermore, TUG1 down-regulated RTN1 expression by inhibiting the binding of transcription factor PU.1 to the RTN1 promoter, thereby reducing the levels of ERS markers and apoptosis markers. Meanwhile, TUG1-overexpression adenovirus plasmids injection significantly alleviated tubular lesions, and reduced RTN1 expression, ERS markers and apoptosis markers, whereas these results were reversed by injection of PU.1-overexpression adenovirus plasmids. TUG1 restrains the ERS and apoptosis of renal tubular epithelial cells and ameliorates DN through inhibition of transcription factor PU.1.

Systematic investigation of the pharmacological mechanism for renal protection by the leaves of Eucommia ulmoides Oliver using UPLC-Q-TOF/MS combined with network pharmacology analysis

Bark is the traditional medicinal component of Eucommia ulmoides Oliver (E. ulmoides). However, the demand for E. ulmoides medicinal materials seriously limits their sustainability. To alleviate resource constraints, the bioactivity of E. ulmoides leaves and its pharmacodynamic basis were investigated. In the present study, extracts of E. ulmoides leaves were found to display potential renal protective properties in rat glomerular mesangial (HBZY-1) cells treated with high levels of glucose, suggesting that they possess potential factors capable of treating diabetic nephropathy. Ultra-performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) was used to comprehensively characterize the chemical components of E. ulmoides leaves. A total of 83 possible chemical components, including 12 iridoids, 13 flavonoids, 14 lignans, 20 phenylpropanoids, 14 phenolic acids, and 10 additional components, were identified in E. ulmoides leaves. Network pharmacology was used for a preliminary exploration of the potential mechanism of action of renal protection afforded by E. ulmoides leaves towards diabetic nephropathy. The network pharmacology results were verified using a series of biological experiments. The present study provided the basis for the comprehensive development and utilization of E. ulmoides leaves and the discovery of potential drugs.

Role of UPP pathway in amelioration of diabetes-associated complications

Type 2 diabetes (T2D) is one of the most widely spread metabolic disorder also called as "life style" disease. Due to the alarming number of patients, there is great need to therapies targeting functions which can help in maintaining the homeostasis of glucose levels and improving insulin sensitivity. Detailed analysis was done through various research and review papers which was searched using MEDLINE, BIOSIS, and EMBASE using various keywords. This search retrieved the most appropriate content on these molecules targeting UPP pathway. From this extensive review involving UPP pathway, it was concluded that the role of ubiquitin's is not only limited to neurodegenerative disorders but also plays a critical role in progression of diabetes including obesity, insulin resistance, and various neurogenerative disorders but it also targets proteasomal degradation including mediation of cellular signaling pathways. Thus, drugs targeting UPP not only may show effect against diabetes but also are therapeutically beneficial in the treatment of diabetes-associated complications which may be obtained. Thus, based on the available information and data on UPP functions, it can be concluded that regulation of UPP pathway via downstream regulators mainly E1, E2, and E3 may bring promising results. Drugs targeting these transcriptional factors may emerge as a novel therapy in the treatment of diabetes and diabetes-associated complications.

Ginkgo Biloba Extract EGB761 Ameliorates the Extracellular Matrix Accumulation and Mesenchymal Transformation of Renal Tubules in Diabetic Kidney Disease by Inhibiting Endoplasmic Reticulum Stress

The study is aimed at investigating the effects of Ginkgo biloba extract EGB761 on renal tubular damage and endoplasmic reticulum stress (ERS) in diabetic kidney disease (DKD). A total of 50 C57BL/6 N mice were randomly divided into the normal group, DKD group, DKD+EGB761 group (36 mg/kg), and DKD+4-phenylbutyrate (4-PBA) group (1 g/kg). The DKD model was replicated by high-fat diet combined with intraperitoneal injection of streptozotocin (STZ). Renal tubular epithelial cells (HK-2) were divided into the control group, high-glucose group (30 mmol/L), EGB761 group (40 mg/L, 20 mg/L, 10 mg/L), TM group, and TM+4-PBA group. After 8 weeks of administration, expressions of serum creatinine (Scr), blood urea nitrogen (BUN), 24 h urinary protein (24 h Pro), fasting blood glucose (FBG), β 2-microglobulin (β 2-MG), and retinol binding protein 4 (RBP4) of mice were tested. The pathological changes of renal tissue were observed. The expressions of extracellular matrix (ECM) accumulation and epithelial-mesenchymal transition (EMT) markers α-smooth muscle actin (α-SMA), E-cadherin, fibronectin, and collagen IV, as well as the ERS markers GRP78 and ATF6, were tested by Western blot, qPCR, immunohistochemistry, or immunofluorescence. EGB761 could decrease the Scr, BUN, 24 h Pro, and FBG levels in the DKD group, alleviate renal pathological injury, decrease urine β 2-MG, RBP4 levels, and decrease the expression of α-SMA, collagen IV, fibronectin, and GRP78, as well as ATF6, while increase the expression of E-cadherin. These findings demonstrate that EGB761 can improve renal function, reduce tubular injury, and ameliorate ECM accumulation and EMT in DKD kidney tubules, and the mechanism may be related to the inhibition of ERS.

Organelle stress and glycation in kidney disease

Glycation of proteins is a non-enzymatic posttranslational modification. Such random modification often deranges the structure and function of a wide range of proteins, and in turn leads to cellular dysfunction and organ damage. Protein glycation is thus an important topic in understanding the molecular mechanisms of the development or progression of various kinds of diabetes-related diseases. Meanwhile, organelle stress, such as mitochondrial or endoplasmic reticulum (ER) damage, is a causal factor for cellular dysfunction. Under pathogenic conditions, mitochondrial stress and ER stress are induced by glycated proteins. Intensive research has revealed the molecular mechanism of how glycation contributes to cell fate via organelle stress. This article will summarize the most recent evidence on organelle stress and glycation in kidney disease, especially diabetic kidney disease (DKD) associated with high glycation status.

Diabetic nephropathy induced by methylglyoxal: gallic acid regulates kidney microRNAs and glyoxalase1-Nrf2 in male mice

BACKGROUND

Methylglyoxal (MG) has been reported to be a toxic by-product of glycolysis and intracellular stressor compound. This study investigated the effects of gallic acid (GA) against diabetic nephropathy (DN) induced by MG in male mice.

METHODS

DN was induced by methylglyoxal (600 mg/kg/day, p.o.) treated for 28 consecutive days. The animals received GA (30 mg/kg/day, p.o.) and metformin (MT) (150 mg/kg/day, p.o.) for 7 consecutive days after diabetes induction. Biochemical assays, antioxidant evaluation, microRNAs associated with fibrosis, endoplasmic reticulum stress, and histopathological analysis were examined.

RESULTS

MG increased malondialdehyde, albuminuria, Nrf2, miR-192 and miR-204 expression in diabetic groups and GA decreased them. Superoxide dismutase, catalase, glyoxalase1, and miR-29a expression decreased in diabetic groups and increased in treatment with GA.

CONCLUSION

Our results revealed that GA has improved DN induced by MG via amelioration of biochemical indices, histopathological aspects, oxidative stress and microRNAs associated with endoplasmic reticulum stress and fibrosis.

Role of Glucose Metabolism and Mitochondrial Function in Diabetic Kidney Disease

PURPOSE OF REVIEW

Diabetic kidney disease (DKD) continues to be the primary cause of chronic kidney disease in the USA and around the world. The numbers of people with DKD also continue to rise despite current treatments. Certain newer hypoglycemic drugs offer a promise of slowing progression, but it remains to be seen how effective these will be over time. Thus, continued exploration of the mechanisms underlying the development and progression of DKD is essential in order to discover new treatments. Hyperglycemia is the main cause of the cellular damage seen in DKD. But, exactly how hyperglycemia leads to the activation of processes that are ultimately deleterious is incompletely understood.

RECENT FINDINGS

Studies primarily over the past 10 years have provided novel insights into the interplay of hyperglycemia, glucose metabolic pathways, mitochondrial function, and the potential importance of what has been called the Warburg effect on the development and progression of DKD. This review will provide a brief overview of glucose metabolism and the hypotheses concerning the pathogenesis of DKD and then discuss in more detail the supporting data that indicate a role for the interplay of glucose metabolic pathways and mitochondrial function.

Tanshinone IIA Ameliorates Streptozotocin-Induced Diabetic Nephropathy, Partly by Attenuating PERK Pathway-Induced Fibrosis

Purpose

Tanshinone IIA (Tan IIA), a compound extracted from Salvia miltiorrhiza, can improve type II diabetes, while the molecular mechanisms underlying Tan IIA-mediated protective effects in diabetic nephropathy are unclear. This study explored the protective actions of Tan IIA on renal tissues in streptozotocin (STZ)-induced diabetic nephropathy.

Materials and Methods

Tan IIA (2, 4, 8 mg/kg/day) was daily administered to STZ-treated rats by intraperitoneal injection for 42 days. The morphologic pathology was evaluated by hematoxylin-eosin and Masson’s trichrome staining, and transmission electron microscopy. The protein expression levels in renal tissues were evaluated by Western blotting and immunohistochemistry; the mRNA expression level was determined by quantitative real-time PCR.

Results

Tan IIA at 2 and 4 mg/kg attenuated the increase in the levels of uric acid and blood urea nitrogen and restored the reduction in the superoxide dismutase activity in the serum of the diabetic rats. Tan IIA at 2 and 4 mg/kg, but not 8 mg/kg, ameliorated the thickening of renal tubule in the diabetic rats; Tan IIA at 2 and 4 and 8 mg/kg attenuated the thickening of glomerular basement membrane and the collagen deposition in the renal tissues of the diabetic rats. Tan IIA treatment at 2, 4, 8 mg/kg decreased the expression levels of transforming growth factor-beta1, TSP-1, Grp78 and CHOP in the diabetic rats. Tan IIA at 2 and 4 and 8 mg/kg attenuated the increase in the protein levels of p-PERK, p-elf2α and ATF-4 from the renal tissues of diabetic rats, while the protein level of AFT-6 and the mRNA expression levels of XBP-1t, XBP-1s and p58IPK in the renal tissues were not affected by STZ or Tan IIA treatment.

Conclusion

Tan IIA-mediated protective effects on the STZ-induced diabetic nephropathy may be associated with the reduced endoplasmic reticulum stress via attenuating PERK signaling activities.

ATF4 promotes renal tubulointerstitial fibrosis by suppressing autophagy in diabetic nephropathy

AIM

Diabetic nephropathy (DN) is the dominant cause of end-stage renal disease which is characterized by extracellular matrix accumulation. The purpose of this study was to investigate the role of activating transcription factor 4 (ATF4) in regulating renal fibrosis and autophagy in DN.

MAIN METHOD

Streptozotocin (STZ) was administered to heterozygous ATF4 knockout (KO) and wild-type (WT) mice via an intraperitoneal injection to induce DN. NRK-52E cells were cultured in high glucose to mimic diabetic pathological. qRT-PCR, western blot, immunofluorescence, histology and electron microscopic analysis were performed. The autophagy flux was observed by tandem mRFP-GFP-LC3 fluorescence microscopy.

KEY FINDINGS

DN mice experienced severe renal injury and fibrosis and showed increased expression of ATF4 and inhibition of autophagy in kidney tissues. We found that STZ-induced ATF4 KO mice showed significant improvement in urinary albumin, serum creatinine and blood urea nitrogen and the pathological changes of renal tubulointerstitial fibrosis compared with STZ-induced WT mice. Furthermore, inhibition of ATF4 could restore autophagy in DN mice. Similar results were shown in vitro. Overexpression of ATF4 in NRK-52E cells cultured in high glucose condition suppressed autophagy and upregulated Collagen type 4 (Col-IV) expression, while inhibition of ATF4 could increase the number of the autophagosomes, improve autophagic flux and decrease Col-IV level.

SIGNIFICANCE

Our study provided the evidence of a crucial role for ATF4 in inhibiting autophagy against diabetic kidney damage. Suppression of ATF4 may be an effective therapy in restraining renal tubulointerstitial fibrosis in DN.

Resveratrol decreases high glucose‑induced apoptosis in renal tubular cells via suppressing endoplasmic reticulum stress

Diabetic nephropathy (DN) is the second most common complication of diabetes mellitus after cardiovascular complications. Endoplasmic reticulum (ER) stress is known to be associated with DN. Resveratrol (RSV) exhibits anti-oxidative, anti-inflammatory and cytoprotective effects. Therefore, the aims of the present study were to investigate the role of RSV in the inhibition of high concentration glucose (HG)-induced apoptosis in renal tubular cells, as well as to examine the protective effects of RSV against diabetes-mediated renal damage via inhibition of ER stress in DN. RSV was orally administered to diabetic db/db mice once a day for 12 consecutive weeks. Compared with untreated db/db mice, treating db/db mice with RSV significantly decreased urine albumin excretion and the urine albumin to creatinine ratio, and attenuated renal histopathological injury. Furthermore, RSV treatment resulted in decreased expression levels of glucose-regulated protein of 78 kDa and C/EBP-homologous protein (two ER stress markers) and caspase12 in murine kidneys. RSV administration also inhibited the apoptosis of NRK-52E cells and activation of the ER stress signal transduction pathway induced by HG treatment in vitro. Collectively, the present results indicated that RSV protected renal tubular cells against HG-induced apoptosis in DN by suppressing ER stress.

Beneficial Effect of Chloroquine and Amodiaquine on Type 1 Diabetic Tubulopathy by Attenuating Mitochondrial Nox4 and Endoplasmic Reticulum Stress

BACKGROUND

Oxidative stress induced by chronic hyperglycemia is recognized as a significant mechanistic contributor to the development of diabetic kidney disease (DKD). Nonphagocytic nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) is a major source of reactive oxygen species (ROS) in many cell types and in the kidney tissue of diabetic animals. We designed this study to explore the therapeutic potential of chloroquine (CQ) and amodiaquine (AQ) for inhibiting mitochondrial Nox4 and diabetic tubular injury.

METHODS

Human renal proximal tubular epithelial cells (hRPTCs) were cultured in high-glucose media (30 mM D-glucose), and diabetes was induced with streptozotocin (STZ, 50 mg/kg i.p. for 5 days) in male C57BL/6J mice. CQ and AQ were administered to the mice via intraperitoneal injection for 14 weeks.

RESULTS

CQ and AQ inhibited mitochondrial Nox4 and increased mitochondrial mass in hRPTCs under high-glucose conditions. Reduced mitochondrial ROS production after treatment with the drugs resulted in decreased endoplasmic reticulum (ER) stress, suppressed inflammatory protein expression and reduced cell apoptosis in hRPTCs under high-glucose conditions. Notably, CQ and AQ treatment diminished Nox4 activation and ER stress in the kidneys of STZ-induced diabetic mice. In addition, we observed attenuated inflammatory protein expression and albuminuria in STZ-induced diabetic mice after CQ and AQ treatment.

CONCLUSION

We substantiated the protective actions of CQ and AQ in diabetic tubulopathy associated with reduced mitochondrial Nox4 activation and ER stress alleviation. Further studies exploring the roles of mitochondrial Nox4 in the pathogenesis of DKD could suggest new therapeutic targets for patients with DKD.

Histone deacetylase inhibitor valproic acid attenuates high glucose‑induced endoplasmic reticulum stress and apoptosis in NRK‑52E cells

Previous studies have demonstrated that valproic acid (VPA), a histone deacetylase inhibitor, alleviates diabetic nephropathy (DN). However, the biological mechanisms underlying this protective effect remains unclear. This study aimed to investigate the effects of histone deacetylase inhibitor VPA on hyperglycemic induction of NRK‑52E cell ERS and apoptosis. Endoplasmic reticulum stress (ERS)‑related apoptosis is involved in DN, and improving ERS may delay the symptoms of DN. Histone deacetylase regulates gene transcription or expression of ERS‑related proteins. The present study established an ERS model by treating the rat renal tubular epithelial cells NRK‑52E with high glucose (HG) and investigated the effects of VPA on the apoptosis of the NRK‑52E cells. HG stimulation significantly increased the protein levels of the ERS‑related proteins including glucose regulated protein 78 (GRP78), activating transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), caspase‑12 and phosphorylated (p)‑JNK. VPA treatment further upregulated GRP78 expression and attenuated the levels of ATF4, CHOP, caspase‑12 and p‑JNK. Notably, HG markedly promoted apoptosis of NRK‑52E cells by regulating the protein levels of Bax, cleaved caspase‑3 and Bcl‑2, which was attenuated by simultaneous VPA treatment. Mechanistically, VPA increased the total acetylation levels of histone H4 in NRK‑52E cells and increased the histone H4 acetylation of the GRP78 promoter region. In conclusion, VPA attenuated HG‑induced ERS and apoptosis in NRK‑52E cells, which may be due to the regulation of acetylation levels of ERS‑related proteins. In addition, the present study suggested that HDACIs are promising drugs for treating patients with DN.

Mitochondria-Associated Endoplasmic Reticulum Membranes (MAMs) and Their Prospective Roles in Kidney Disease

Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) serve as essential hubs for interorganelle communication in eukaryotic cells and play multifunctional roles in various biological pathways. A defect in ER-mitochondria signaling or MAMs dysfunction has pleiotropic effects on a variety of intracellular events, which results in disturbances of the mitochondrial quality control system, Ca2+ dyshomeostasis, apoptosis, ER stress, and inflammasome activation, which all contribute to the onset and progression of kidney disease. Here, we review the structure and molecular compositions of MAMs as well as the experimental methods used to study these interorganellar contact sites. We will specifically summarize the downstream signaling pathways regulated by MAMs, mainly focusing on mitochondrial quality control, oxidative stress, ER-mitochondria Ca2+ crosstalk, apoptosis, inflammasome activation, and ER stress. Finally, we will discuss how alterations in MAMs integrity contribute to the pathogenesis of kidney disease and offer directions for future research.

AdipoRon Protects against Tubular Injury in Diabetic Nephropathy by Inhibiting Endoplasmic Reticulum Stress

Endoplasmic reticulum (ER) stress has been reported to play a pivotal role in diabetic nephropathy (DN). AdipoRon is a newly developed adiponectin receptor agonist that provides beneficial effects for diabetic mice; however, its underlying mechanism remains to be delineated. Here, we demonstrated increased expression levels of ER stress markers, accompanied by upregulated levels of proinflammatory cytokines and increased expression of collagen I, fibronectin, Bax, and cleaved caspase 3 in the kidneys of db/db mice compared with control mice. Decreased expression of adiponectin receptor 1 (AdipoR1) and phosphorylated 5′AMP-activated kinase (p-AMPK) was also observed in the kidneys of db/db mice. However, these alterations were partially reversed by intragastric gavage with AdipoRon. In vitro, AdipoRon alleviated high-glucose-induced ER stress, oxidative stress, and apoptosis in HK-2 cells, a human tubular cell line. Moreover, AdipoRon restored the expression of AdipoR1 and p-AMPK in HK-2 cells exposed to high-glucose conditions. Additionally, these effects were partially abrogated by pretreatment with AdipoR1 siRNA, but this abrogation was ameliorated by cotreatment with AICAR, an AMPK activator. Furthermore, the effects of AdipoRon were also partially abolished by cotreatment with compound C. Together, these results suggest that AdipoRon exerts favorable effects on diabetes-induced tubular injury in DN by inhibiting ER stress mediated by the AdipoR1/p-AMPK pathway.

Involvement of miR-27a-3p in diabetic nephropathy via affecting renal fibrosis, mitochondrial dysfunction, and endoplasmic reticulum stress

Diabetic nephropathy (DN) is acknowledged as a serious chronic complication of diabetes mellitus. Nevertheless, its pathogenesis is complicated and unclear. Thus, in this study, the role of miR-27a-3p-prohibitin/TMBIM6 signaling axis in the progression of DN was elucidated. Type 2 diabetic db/db mice and high glucose (HG)-challenged HK-2 cells were used as in vivo and in vitro models. Our results showed that miR-27a-3p was upregulated and prohibitin or transmembrane BAX inhibitor motif containing 6 (TMBIM6) was downregulated in the kidney tissues of db/db mice and HG-treated HK-2 cells. Silencing miR-27a-3p enhanced the expression of prohibitin and TMBIM6 in the kidney tissues and HK-2 cells. Inhibition of miR-27a-3p improved functional injury, as evidenced by decreased blood glucose, urinary albumin, serum creatinine, and blood urea nitrogen levels. MiR-27a-3p silencing ameliorated renal fibrosis, reflected by reduced profibrogenic genes (e.g., transforming growth factor β1, fibronectin, collagen I and III, and α-smooth muscle actin). Furthermore, inhibition of miR-27a-3p relieved mitochondrial dysfunction in the kidney of db/db mice, including upregulation of mitochondrial membrane potential, complex I and III activities, adenosine triphosphate, and mitochondrial cytochrome C, as well as suppressing reactive oxygen species production. In addition, miR-27a-3p silencing attenuated endoplasmic reticulum (ER) stress, reflected by reduced expression of p-IRE1α, p-eIF2α, XBP1s, and CHOP. Mechanically, we identified prohibitin and TMBIM6 as direct targets of miR-27a-3p. Inhibition of miR-27a-3p protected HG-treated HK-2 cells from apoptosis, extracellular matrix accumulation, mitochondrial dysfunction, and ER stress by regulating prohibitin or TMBIM6. Taken together, we reveal that miR-27a-3p-prohibitin/TMBIM6 signaling axis regulates the progression of DN, which can be a potential therapeutic target.

Myo-inositol Oxygenase (MIOX) Overexpression Drives the Progression of Renal Tubulointerstitial Injury in Diabetes

Conceivably, upregulation of myo-inositol oxygenase (MIOX) is associated with altered cellular redox. Its promoter includes oxidant-response elements, and we also discovered binding sites for XBP1, a transcription factor of endoplasmic reticulum (ER) stress response. Previous studies indicate that MIOX's upregulation in acute tubular injury is mediated by oxidant and ER stress. Here, we investigated whether hyperglycemia leads to accentuation of oxidant and ER stress while these boost each other's activities, thereby augmenting tubulointerstitial injury/fibrosis. We generated MIOX-overexpressing transgenic (MIOX-TG) and MIOX knockout (MIOX-KO) mice. A diabetic state was induced by streptozotocin administration. Also, MIOX-KO were crossbred with Ins2 ^Akita to generate Ins2 ^Akita/KO mice. MIOX-TG mice had worsening renal functions with kidneys having increased oxidant/ER stress, as reflected by DCF/dihydroethidium staining, perturbed NAD-to-NADH and glutathione-to-glutathione disulfide ratios, increased NOX4 expression, apoptosis and its executionary molecules, accentuation of TGF-β signaling, Smads and XBP1 nuclear translocation, expression of GRP78 and XBP1 (ER stress markers), and accelerated tubulointerstitial fibrosis. These changes were not seen in MIOX-KO mice. Interestingly, such changes were remarkably reduced in Ins2 ^Akita/KO mice and, likewise, in vitro experiments with XBP1 siRNA. These findings suggest that MIOX expression accentuates, while its deficiency shields kidneys from, tubulointerstitial injury by dampening oxidant and ER stress, which mutually enhance each other's activity.