Thioredoxin-interacting protein: a potential therapeutic target for treatment of progressive fibrosis in diabetic nephropathy

TXNIP deficiency attenuates renal fibrosis by modulating mTORC1/TFEB-mediated autophagy in diabetic kidney disease

Thioredoxin-interacting protein (TXNIP) is an important regulatory protein for thioredoxin (TRX) that elicits the generation of reactive oxygen species (ROS) by inhibiting the redox function of TRX. Abundant evidence suggests that TXNIP is involved in the fibrotic process of diabetic kidney disease (DKD). However, the potential mechanism of TXNIP in DKD is not yet well understood. In this study, we found that TXNIP knockout suppressed renal fibrosis and activation of mammalian target of rapamycin complex 1 (mTORC1) and restored transcription factor EB (TFEB) and autophagy activation in diabetic kidneys. Simultaneously, TXNIP interference inhibited epithelial-to-mesenchymal transformation (EMT), collagen I and fibronectin expression, and mTORC1 activation, increased TFEB nuclear translocation, and promoted autophagy restoration in HK-2 cells exposed to high glucose (HG). Rapamycin, an inhibitor of mTORC1, increased TFEB nuclear translocation and autophagy in HK-2 cells under HG conditions. Moreover, the TFEB activators, curcumin analog C1 and trehalose, effectively restored HG-induced autophagy, and abrogated HG-induced EMT and collagen I and fibronectin expression in HK-2 cells. Taken together, these findings suggest that TXNIP deficiency ameliorates renal fibrosis by regulating mTORC1/TFEB-mediated autophagy in diabetic kidney diseases.

The role of innate immunity in diabetic nephropathy and their therapeutic consequences

Diabetic nephropathy (DN) is an enduring condition that leads to inflammation and affects a substantial number of individuals with diabetes worldwide. A gradual reduction in glomerular filtration and emergence of proteins in the urine are typical aspects of DN, ultimately resulting in renal failure. Mounting evidence suggests that immunological and inflammatory factors are crucial for the development of DN. Therefore, the activation of innate immunity by resident renal and immune cells is critical for initiating and perpetuating inflammation. Toll-like receptors (TLRs) are an important group of receptors that identify patterns and activate immune responses and inflammation. Meanwhile, inflammatory responses in the liver, pancreatic islets, and kidneys involve inflammasomes and chemokines that generate pro-inflammatory cytokines. Moreover, the activation of the complement cascade can be triggered by glycated proteins. This review highlights recent findings elucidating how the innate immune system contributes to tissue fibrosis and organ dysfunction, ultimately leading to renal failure. This review also discusses innovative approaches that can be utilized to modulate the innate immune responses in DN for therapeutic purposes.

Relaxin elicits renoprotective actions accompanied by increasing bile acid levels in streptozotocin-induced diabetic mice

BACKGROUND

The peptide hormone relaxin has potent anti-fibrotic and anti-inflammatory properties in various organs, including the kidneys. However, the protective effects of relaxin in the context of diabetic kidney complications remain controversial. Here, we aimed to evaluate the effects of relaxin treatment on key markers of kidney fibrosis, oxidative stress, and inflammation and their subsequent impact on bile acid metabolism in the streptozotocin-induced diabetes mouse model.

METHODS AND RESULTS

Male mice were randomly allocated to placebo-treated control, placebo-treated diabetes or relaxin-treated diabetes groups (0.5 mg/kg/d, final 2 weeks of diabetes). After 12 weeks of diabetes or sham, the kidney cortex was harvested for metabolomic and gene expression analyses. Diabetic mice exhibited significant hyperglycaemia and increased circulating levels of creatine, hypoxanthine and trimethylamine N-oxide in the plasma. This was accompanied by increased expression of key markers of oxidative stress (Txnip), inflammation (Ccl2 and Il6) and fibrosis (Col1a1, Mmp2 and Fn1) in the diabetic kidney cortex. Relaxin treatment for the final 2 weeks of diabetes significantly reduced these key markers of renal fibrosis, inflammation, and oxidative stress in diabetic mice. Furthermore, relaxin treatment significantly increased the levels of bile acid metabolites, deoxycholic acid and sodium glycodeoxycholic acid, which may in part contribute to the renoprotective action of relaxin in diabetes.

CONCLUSION

In summary, this study shows the therapeutic potential of relaxin and that it may be used as an adjunctive treatment for diabetic kidney complications.

The Pathogenesis of Diabetes

Diabetes is the most common metabolic disorder, with an extremely serious effect on health systems worldwide. It has become a severe, chronic, non-communicable disease after cardio-cerebrovascular diseases. Currently, 90% of diabetic patients suffer from type 2 diabetes. Hyperglycemia is the main hallmark of diabetes. The function of pancreatic cells gradually declines before the onset of clinical hyperglycemia. Understanding the molecular processes involved in the development of diabetes can provide clinical care with much-needed updates. This review provides the current global state of diabetes, the mechanisms involved in glucose homeostasis and diabetic insulin resistance, and the long-chain non-coding RNA (lncRNA) associated with diabetes.

NLRP3-mediated pyroptosis in diabetic nephropathy

Diabetic nephropathy (DN) is the main cause of end-stage renal disease (ESRD), which is characterized by a series of abnormal changes such as glomerulosclerosis, podocyte loss, renal tubular atrophy and excessive deposition of extracellular matrix. Simultaneously, the occurrence of inflammatory reaction can promote the aggravation of DN-induced kidney injury. The most important processes in the canonical inflammasome pathway are inflammasome activation and membrane pore formation mediated by gasdermin family. Converging studies shows that pyroptosis can occur in renal intrinsic cells and participate in the development of DN, and its activation mechanism involves a variety of signaling pathways. Meanwhile, the activation of the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome can not only lead to the occurrence of inflammatory response, but also induce pyroptosis. In addition, a number of drugs targeting pyroptosis-associated proteins have been shown to have potential for treating DN. Consequently, the pathogenesis of pyroptosis and several possible activation pathways of NLRP3 inflammasome were reviewed, and the potential drugs used to treat pyroptosis in DN were summarized in this review. Although relevant studies are still not thorough and comprehensive, these findings still have certain reference value for the understanding, treatment and prognosis of DN.

Urinary Thioredoxin as a Biomarker of Renal Redox Dysregulation and a Companion Diagnostic to Identify Responders to Redox-Modulating Therapeutics

Significance: The development and progression of renal diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), are the result of heterogeneous pathophysiology that reflects a range of environmental factors and, in a lesser extent, genetic mutations. The pathophysiology specific to most kidney diseases is not currently identified; therefore, these diseases are diagnosed based on non-pathological factors. For that reason, pathophysiology-based companion diagnostics for selection of pathophysiology-targeted treatments have not been available, which impedes personalized medicine in kidney disease. Recent Advances: Pathophysiology-targeted therapeutic agents are now being developed for the treatment of redox dysregulation. Redox modulation therapeutics, including bardoxolone methyl, suppresses the onset and progression of AKI and CKD. On the other hand, pathophysiology-targeted diagnostics for renal redox dysregulation are also being developed. Urinary thioredoxin (TXN) is a biomarker that can be used to diagnose tubular redox dysregulation. AKI causes oxidation and urinary excretion of TXN, which depletes TXN from the tubules, resulting in tubular redox dysregulation. Urinary TXN is selectively elevated at the onset of AKI and correlates with the progression of CKD in diabetic nephropathy. Critical Issues: Diagnostic methods should provide information about molecular mechanisms that aid in the selection of appropriate therapies to improve the prognosis of kidney disease. Future Directions: A specific diagnostic method enabling detection of redox dysregulation based on pathological molecular mechanisms is much needed and could provide the first step toward personalized medicine in kidney disease. Urinary TXN is a candidate for a companion diagnostic method to identify responders to redox-modulating therapeutics. Antioxid. Redox Signal. 36, 1051-1065.

Novel insights into NOD-like receptors in renal diseases

Nucleotide-binding oligomerization domain-like receptors (NLRs), including NLRAs, NLRBs (also known as NAIPs), NLRCs, and NLRPs, are a major subfamily of pattern recognition receptors (PRRs). Owing to a recent surge in research, NLRs have gained considerable attention due to their involvement in mediating the innate immune response and perpetuating inflammatory pathways, which is a central phenomenon in the pathogenesis of multiple diseases, including renal diseases. NLRs are expressed in different renal tissues during pathological conditions, which suggest that these receptors play roles in acute kidney injury, obstructive nephropathy, diabetic nephropathy, IgA nephropathy, lupus nephritis, crystal nephropathy, uric acid nephropathy, and renal cell carcinoma, among others. This review summarises recent progress on the functions of NLRs and their mechanisms in the pathophysiological processes of different types of renal diseases to help us better understand the role of NLRs in the kidney and provide a theoretical basis for NLR-targeted therapy for renal diseases.

Metabolic Dysfunction in the Regulation of the NLRP3 Inflammasome Activation: A Potential Target for Diabetic Nephropathy

Metabolic dysfunction plays a key role in the development of diabetic nephropathy (DN). However, the exact effects and mechanisms are still unclear. The pyrin domain-containing protein 3 (NLRP3) inflammasome, a member of the nod-like receptor family, is considered a crucial inflammatory regulator and plays important roles in the progress of DN. A growing body of evidence suggests that high glucose, high fat, or other metabolite disorders can abnormally activate the NLRP3 inflammasome. Thus, in this review, we discuss the potential function of abnormal metabolites such as saturated fatty acids (SFAs), cholesterol crystals, uric acid (UA), and homocysteine in the NLRP3 inflammasome activation and explain the potential function of metabolic dysfunction regulation of NLRP3 activation in the progress of DN via regulation of inflammatory response and renal interstitial fibrosis (RIF). In addition, the potential mechanisms of metabolism-related drugs, such as metformin and sodium glucose cotransporter (SGLT2) inhibitors, which have served as the suppressors of the NLRP3 inflammasomes, in DN, are also discussed. A better understanding of NLRP3 inflammasome activation in abnormal metabolic microenvironment may provide new insights for the prevention and treatment of DN.

Cardiomyocyte-specific Txnip C247S mutation improves left ventricular functional reserve in streptozotocin-induced diabetic mice

Underlying molecular mechanisms for the development of diabetic cardiomyopathy remain to be determined. Long-term exposure to hyperglycemia causes oxidative stress, which leads to cardiomyocyte dysfunction. Previous studies established the importance of thioredoxin-interacting protein (Txnip) in cellular redox homeostasis and glucose metabolism. Txnip is a highly glucose-responsive molecule that interacts with the catalytic center of reduced thioredoxin and inhibits the antioxidant function of thioredoxin. Here, we show that the molecular interaction between Txnip and thioredoxin plays a pivotal role in the regulation of redox balance in the diabetic myocardium. High glucose increased Txnip expression, decreased thioredoxin activities, and caused oxidative stress in cells. The Txnip-thioredoxin complex was detected in cells with overexpressing wild-type Txnip but not Txnip cysteine 247 to serine (C247S) mutant that disrupts the intermolecular disulfide bridge. Then, diabetes was induced in cardiomyocyte-specific Txnip C247S knock-in mice and their littermate control animals by injections of streptozotocin (STZ). Prolonged hyperglycemia upregulated myocardial Txnip expression in both genotypes. The absence of Txnip's inhibition of thioredoxin in Txnip C247S mutant hearts promoted mitochondrial antioxidative capacities in cardiomyocytes, thereby protecting the heart from oxidative damage by diabetes. Stress hemodynamic analysis uncovered that Txnip C247S knock-in hearts have a greater left ventricular contractile reserve than wild-type hearts under STZ-induced diabetic conditions. These results provide novel evidence that Txnip serves as a regulator of hyperglycemia-induced cardiomyocyte toxicities through direct inhibition of thioredoxin and identify the single cysteine residue in Txnip as a therapeutic target for diabetic injuries.NEW & NORTEWORTHY Thioredoxin-interacting protein (Txnip) has been of great interest as a molecular mechanism to mediate diabetic organ damage. Here, we provide novel evidence that a single mutation of Txnip confers a defense mechanism against myocardial oxidative stress in streptozotocin-induced diabetic mice. The results demonstrate the importance of Txnip as a cysteine-containing redox protein that regulates antioxidant thioredoxin via disulfide bond-switching mechanism and identify the cysteine in Txnip as a therapeutic target for diabetic cardiomyopathy.

Coordinated Contribution of NADPH Oxidase- and Mitochondria-Derived Reactive Oxygen Species in Metabolic Syndrome and Its Implication in Renal Dysfunction

Metabolic syndrome (MetS), a complex of interrelated risk factors for cardiovascular disease and diabetes, is comprised of central obesity (increased waist circumference), hyperglycemia, dyslipidemia (high triglyceride blood levels, low high-density lipoprotein blood levels), and increased blood pressure. Oxidative stress, caused by the imbalance between pro-oxidant and endogenous antioxidant systems, is the primary pathological basis of MetS. The major sources of reactive oxygen species (ROS) associated with MetS are nicotinamide-adenine dinucleotide phosphate (NADPH) oxidases and mitochondria. In this review, we summarize the current knowledge regarding the generation of ROS from NADPH oxidases and mitochondria, discuss the NADPH oxidase- and mitochondria-derived ROS signaling and pathophysiological effects, and the interplay between these two major sources of ROS, which leads to chronic inflammation, adipocyte proliferation, insulin resistance, and other metabolic abnormalities. The mechanisms linking MetS and chronic kidney disease are not well known. The role of NADPH oxidases and mitochondria in renal injury in the setting of MetS, particularly the influence of the pyruvate dehydrogenase complex in oxidative stress, inflammation, and subsequent renal injury, is highlighted. Understanding the molecular mechanism(s) underlying MetS may lead to novel therapeutic approaches by targeting the pyruvate dehydrogenase complex in MetS and prevent its sequelae of chronic cardiovascular and renal diseases.

Role and mechanism of TXNIP in ageing-related renal fibrosis

Kidney ageing, which is always accompanied by renal fibrosis, drives the progression of renal fibrosis. Thioredoxin-interacting protein (TXNIP) is an endogenous suppressor of the reactive oxygen species-scavenging protein thioredoxin, which has been implicated in the ageing of some organs and is involved in renal fibrosis. However, the expression of TXNIP in ageing kidneys has not been examined, and the relationship between TXNIP and ageing-related renal fibrosis is unclear. We found that TXNIP expression was upregulated in aged mouse kidneys, and this upregulation was accompanied by ageing-related renal fibrosis phenotypes. We demonstrated that the ageing biomarkers were downregulated in TXNIP-knockout mice, and these effects resulted in the alleviation of renal fibrosis and impairments in kidney function. TXNIP overexpression in tubular cells upregulated senescence markers, promoted a profibrotic response and activated STAT3 signalling, and these parameters were inhibited by the silencing of TXNIP. Similarly, the TXNIP-mediated profibrotic response was significantly suppressed by a STAT3 inhibitor. By coimmunoprecipitation, we verified that TXNIP directly bound to STAT3, which suggested that TXNIP exacerbates renal tubular epithelial fibrosis by activating the STAT3 pathway. In summary, TXNIP plays an important role in age-related renal fibrosis and might be a therapeutic target for preventing ageing-associated renal fibrosis.

Chronic advanced-glycation end products treatment induces TXNIP expression and epigenetic changes in glomerular podocytes in vivo and in vitro

Advanced glycation end products (AGEs) play an important role in oxidative stress and inflammation, processes implicated in the development and progression of kidney dysfunction. In the present study, we investigated the participation of the pro-oxidant protein thioredoxin-interacting protein (TXNIP) and of epigenetic mechanisms on kidney tissue (in vivo, in non-diabetic rats) and on terminally differentiated glomerular podocytes (in vitro) chronically exposed to AGEs. AGEs induced total kidney and glomerular TXNIP expression and decreased H3K27me3 content. Concomitant treatment with the antioxidant N-acetyl-cysteine (NAC) reversed only the increased TXNIP expression. TXNIP expression positively correlated with proteinuria and negatively correlated with H3K27me3 content. In vitro studies in podocytes showed that 72 h exposure to AGEs decreased nephrin expression and increased Txnip, Nox4, Col4a1, and epithelial-to-mesenchymal transition (EMT) markers (Acta2, Snail1, and Tgfb1). Podocytes treatment with NAC reversed Nox4, Col4a1, Acta2, and Tgfb1 increased expression but did not abrogate the reduced expression of nephrin. MiR-29a expression was downregulated by AGEs in vivo, but not in vitro. In conclusion, treatment of non-diabetic rats with AGEs induced TXNIP expression and decreased the contents of the repressive epigenetic mark H3K27me3 and of miR-29a, potentially driving injury to glomerular filtration barrier and podocytes dysfunction.

Role of Inflammasomes in Kidney Diseases via Both Canonical and Non-canonical Pathways

Inflammasomes, multiprotein complex induced by harmful factors in the body, play a crucial role in innate immunity. Activation of inflammasomes lead to the activation of casepase-1 and then the secretion of inflammatory cytokines, including IL-1β and IL-18, subsequently leading to a type of cell death called pyroptosis. There are two types of signaling pathways involved in the process of inflammasome activation: the canonical and the non-canonical signaling pathway. The canonical signaling pathway is mainly dependent on casepase-1; the non-canonical signal pathway, which was recently discovered, is mainly dependent on caspase-11, but is also meditated by caspase-4, caspase-5, and caspase-8. Kidney inflammation is basically associated with inflammatory factor exudation and inflammatory cell infiltration. Several studies have showed that inflammasomes are closely related to kidney diseases, especially the NOD-, LRR- and pyrin domain-containing 3 (NLRP3) inflammasome, which play a role in regulating kidney inflammation and fibrosis. In this review, we focus on the relationship between inflammasomes and kidney diseases, especially the role of the NLRP3 inflammasome in different kinds of kidney disease via both canonical and non-canonical signal pathways.

Nicorandil ameliorates bleomycin-induced pulmonary fibrosis in rats through modulating eNOS, iNOS, TXNIP and HIF-1α levels

Bleomycin (BLM) is one of the most common anti-cancer drugs used to treat numerous types of tumors. However, pulmonary toxicity is considered the most dramatic effect of BLM. Therefore, BLM has been frequently used for induction of pulmonary fibrosis. This study aimed to evaluate the effect of nicorandil on BLM-induced pulmonary fibrosis and explore the possible mechanisms. BLM was instilled intratracheally into male Sprague-Dawley rats as a single dose (5 mg/kg) and oral nicorandil was given (30 mg/kg/day) for 6 weeks after BLM challenge. At the end of experimental period, rats were sacrificed, and lung histopathology and biochemical parameters were evaluated. Nicorandil therapy attenuated lung inflammation and fibrosis elicited by BLM. Nicorandil significantly reduced total protein content, lactate dehydrogenase (LDH) activity and total and differential cell counts. Moreover, nicorandil diminished lung levels of malondialdehyde and total nitrite/nitrate, in addition to increasing lung contents of reduced glutathione and superoxide dismutase activity. Nicorandil reduced lung and bronchoalveolar lavage fluid contents of hypoxia inducible factor-1α (HIF-1α) and lung content of thioredoxin-interacting protein (TXNIP). Besides, nicorandil significantly improved histological lesions and reduced collagen deposition as well as hydroxyproline content. Immunohistochemical examination revealed that nicorandil-treated rats exhibited significant diminutions in protein expression levels of transforming growth factor beta-1(TGF-β1) and inducible nitric oxide synthase (iNOS) and enhanced pulmonary protein expression of endothelial NOS (eNOS). In conclusion, these results illustrate the possible potential effects of nicorandil for managing pulmonary fibrosis caused by BLM.

Mitochondria, the NLRP3 Inflammasome, and Sirtuins in Type 2 Diabetes: New Therapeutic Targets

SIGNIFICANCE

Type 2 diabetes mellitus and hyperglycemia can lead to the development of comorbidities such as atherosclerosis and microvascular/macrovascular complications. Both type 2 diabetes and its complications are related to mitochondrial dysfunction and oxidative stress. Type 2 diabetes is also a chronic inflammatory condition that leads to inflammasome activation and the release of proinflammatory mediators, including interleukins (ILs) IL-1β and IL-18. Moreover, sirtuins are energetic sensors that respond to metabolic load, which highlights their relevance in metabolic diseases, such as type 2 diabetes. Recent Advances: Over the past decade, great progress has been made in clarifying the signaling events regulated by mitochondria, inflammasomes, and sirtuins. Nod-like receptor family pyrin domain containing 3 (NLRP3) is the best characterized inflammasome, and the generation of oxidant species seems to be critical for its activation. NLRP3 inflammasome activation and altered sirtuin levels have been observed in type 2 diabetes. Critical Issue: Despite increasing evidence of the relationship between the NLRP3 inflammasome, mitochondrial dysfunction, and oxidative stress and of their participation in type 2 diabetes physiopathology, therapeutic strategies to combat type 2 diabetes that target NLRP3 inflammasome and sirtuins are yet to be consolidated.

FUTURE DIRECTIONS

In this review article, we attempt to provide an overview of the existing literature concerning the crosstalk between mitochondrial impairment and the inflammasome, with particular attention to cellular and mitochondrial redox metabolism and the potential role of the NLRP3 inflammasome and sirtuins in the pathogenesis of type 2 diabetes. In addition, we discuss potential targets for therapeutic intervention based on these molecular interactions. Antioxid. Redox Signal. 29, 749-791.

Dihydromyricetin attenuated Ang II induced cardiac fibroblasts proliferation related to inhibitory of oxidative stress

Dihydromyricetin (DMY) is one of the most important flavonoids in vine tea, which showed several pharmacological effects. However, information about the potential role of DMY on angiotensin II (Ang II) induced cardiac fibroblasts proliferation remains unknown. In the present study, cardiac fibroblasts isolated from neonatal Sprague-Dawley rats were pretreated with different concentrations of DMY (0-320μM) for 4h, or DMY (80μM) for different time (0-24h), followed by Ang II (100nM) stimulation for 24h, Then number of cardiac fibroblasts and content of hydroxyproline was measured. The level of cellular reactive oxygen species, malondialdehyde (MDA), activity of superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) were also evaluated. Expression of type I, type III collagen, α-smooth muscle actin (α-SMA), p22^phox (one vital subunit of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase), SOD and thioredoxin (Trx) were detected with real time PCR or/and western blot. We found that pre-incubation with DMY (20μM, 40μM, 80μM) for 4h, 12h or 24h attenuated the proliferation of cardiac fibroblasts induced by Ang II. Expression of type I and type III collagen, as well as α-SMA were inhibited by DMY at both mRNA and protein level. DMY also significantly decreased cellular reactive oxygen species production and MDA level, while increased the SOD activity and T-AOC. DMY suppressed p22^phox, while enhanced antioxidant SOD and Trx expression in Ang II stimulated cardiac fibroblasts. Thus, dihydromyricetin attenuated Ang II induced cardiac fibroblasts proliferation related to inhibitory of oxidative stress.

Thioredoxin-interacting protein regulates lipid metabolism via Akt/mTOR pathway in diabetic kidney disease

Abnormal lipid metabolism contributes to the renal lipid accumulation, which is associated with diabetic kidney disease, but its precise mechanism remains unclear. The growing evidence demonstrates that thioredoxin-interacting protein is involved in regulating cellular glucose and lipid metabolism. Here, we investigated the effects of thioredoxin-interacting protein on lipid accumulation in diabetic kidney disease. In contrast to the diabetic wild-type mice, the physical and biochemical parameters were improved in the diabetic thioredoxin-interacting protein knockout mice. The increased renal lipid accumulation, expression of acetyl-CoA carboxylase, fatty acid synthase and sterol regulatory element binding protein-1, and phosphorylated Akt and mTOR associated with diabetes in wild-type mice was attenuated in diabetic thioredoxin-interacting protein knockout mice. Furthermore, thioredoxin-interacting protein knockout significantly increased the expression of peroxisome proliferator-activated receptor-α, acyl-coenzyme A oxidase 1 and carnitine palmitoyltransferaser 1 in diabetic kidneys. In vitro experiments, using HK-2 cells, revealed that knockdown of thioredoxin-interacting protein inhibited high glucose-mediated lipid accumulation, expression of acetyl-CoA carboxylase, fatty acid synthase and sterol regulatory element binding protein-1, as well as activation of Akt and mTOR. Moreover, knockdown of thioredoxin-interacting protein reversed high glucose-induced reduction of peroxisome proliferator-activated receptor-α, acyl-coenzyme A oxidase 1 and carnitine palmitoyltransferaser 1 expression in HK-2 cells. Importantly, blockade of Akt/mTOR signaling pathway with LY294002, a specific PI3K inhibitor, replicated these effects of thioredoxin-interacting protein silencing. Taken together, these data suggest that thioredoxin-interacting protein deficiency alleviates diabetic renal lipid accumulation through regulation of Akt/mTOR pathway, thioredoxin-interacting protein may be a potential therapeutic target for diabetic kidney disease.

Thioredoxin interacting protein (TXNIP) regulates tubular autophagy and mitophagy in diabetic nephropathy through the mTOR signaling pathway

Hyperglycemia upregulates thioredoxin interacting protein (TXNIP) expression, which in turn induces ROS production, inflammatory and fibrotic responses in the diabetic kidney. Dysregulation of autophagy contributes to the development of diabetic nephropathy. However, the interaction of TXNIP with autophagy/mitophagy in diabetic nephropathy is unknown. In this study, streptozotocin-induced diabetic rats were given TXNIP DNAzyme or scrambled DNAzyme for 12 weeks respectively. Fibrotic markers, mitochondrial function and mitochondrial reactive oxygen species (mtROS) were assessed in kidneys. Tubular autophagy and mitophagy were determined in kidneys from both human and rats with diabetic nephropathy. TXNIP and autophagic signaling molecules were examined. TXNIP DNAzyme dramatically attenuated extracellular matrix deposition in the diabetic kidneys compared to the control DNAzyme. Accumulation of autophagosomes and reduced autophagic clearance were shown in tubular cells of human diabetic compared to non-diabetic kidneys, which was reversed by TXNIP DNAzyme. High glucose induced mitochondrial dysfunction and mtROS production, and inhibited mitophagy in proximal tubular cells, which was reversed by TXNIP siRNA. TXNIP inhibition suppressed diabetes-induced BNIP3 expression and activation of the mTOR signaling pathway. Collectively, hyperglycemia-induced TXNIP contributes to the dysregulation of tubular autophagy and mitophagy in diabetic nephropathy through activation of the mTOR signaling pathway.

Cepharanthine and Piperine ameliorate diabetic nephropathy in rats: role of NF-κB and NLRP3 inflammasome

AIMS

Hyperglycemia leads to elevation of oxidative stress and proinflammatory cytokines which are the main causes of diabetic nephropathy (DN). NLRP3 inflammasome and thioredoxin-interacting protein (TXNIP) are recently assumed to participate in the development of DN. We aimed to investigate the effects of Cepharanthine (CEP), Piperine (Pip) and their combination in streptozotocin (STZ)-induced DN focusing on their role to modulate NLRP3 and TXNIP induced inflammation.

MAIN METHODS

Diabetic rats were treated with intraperitoneal (i.p.) injection of CEP (10mg/kg/day), Pip (30mg/kg/day) or their combination for 8weeks. Nuclear factor kappa B (NF-κB), tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) were assessed by ELISA technique. TXNIP and NLRP3 genes expressions were evaluated by real time-PCR.

KEY FINDINGS

Diabetic rats showed significant increase in renal TXNIP and NLRP3 expression. CEP, Pip or their combination significantly decreased TXNIP and NLRP3 expression in diabetic kidneys. Hyperglycemia induced NF-κB activation leading to increased IL-1β and TNF-α levels. CEP, Pip or their combination showed significant inhibition of NF-κB together with decreased IL-1β and TNF-α levels in diabetic rats. Also, diabetic rats showed significant decrease in creatinine clearance and increase in blood glucose, serum creatinine, blood urea nitrogen, malondialdehyde, proteinuria, and kidney weight to body Weight ratio. All of these changes were reversed by CEP, Pip or their combination.

SIGNIFICANCE

The antioxidant and anti-inflammatory effects of CEP and Pip which were accompanied by inhibition of NF-κB and NLRP3 activation might be helpful mechanisms to halt the progression of DN.

KCa3.1 mediates dysfunction of tubular autophagy in diabetic kidneys via PI3k/Akt/mTOR signaling pathways

Autophagy is emerging as an important pathway in many diseases including diabetic nephropathy. It is acknowledged that oxidative stress plays a critical role in autophagy dysfunction and diabetic nephropathy, and KCa3.1 blockade ameliorates diabetic renal fibrosis through inhibiting TGF-β1 signaling pathway. To identify the role of KCa3.1 in dysfunctional tubular autophagy in diabetic nephropathy, human proximal tubular cells (HK2) transfected with scrambled or KCa3.1 siRNAs were exposed to TGF-β1 for 48 h, then autophagosome formation, the autophagy marker LC3, signaling molecules PI3K, Akt and mTOR, and oxidative stress marker nitrotyrosine were examined respectively. In vivo, LC3, nitrotyrosine and phosphorylated mTOR were examined in kidneys of diabetic KCa3.1+/+ and KCa3.1-/- mice. The results demonstrated that TGF-β1 increased the formation of autophagic vacuoles, LC3 expression, and phosphorylation of PI3K, Akt and mTOR in scrambled siRNA transfected HK2 cells compared to control cells, which was reversed in KCa3.1 siRNA transfected HK2 cells. In vivo, expression of LC3 and nitrotyrosine, and phosphorylation of mTOR were significantly increased in kidneys of diabetic KCa3.1+/+ mice compared to non-diabetic mice, which were attenuated in kidneys of diabetic KCa3.1-/- mice. These results suggest that KCa3.1 activation contributes to dysfunctional tubular autophagy in diabetic nephropathy through PI3K/Akt/mTOR signaling pathways.

Timosaponin B-II ameliorates diabetic nephropathy via TXNIP, mTOR, and NF-κB signaling pathways in alloxan-induced mice

Background

Many synthesized drugs with clinical severe side effects have been used for diabetic nephropathy (DN) treatment. Therefore, it is urgent and necessary to identify natural and safe agents to remedy DN. Timosaponin B-II (TB-II), a major steroidal saponin constituent in Anemarrhena asphodeloides Bunge, exhibits various activities, including anti-inflammatory and hypoglycemic functions. However, the anti-DN effects and potential mechanism(s) of TB-II have not been previously reported.

Purpose

To investigate the effect of TB-II on DN in alloxan-induced diabetic mice.

Methods

TB-II was isolated and purified from A. asphodeloides Bunge using macroporous adsorption resin and preparative high-performance liquid chromatography. The effect of TB-II on DN was evaluated in alloxan-induced diabetic mice using an assay kit and immunohistochemical determination in vivo. The expression of mammalian target of rapamycin (mTOR), thioredoxin-interacting protein (TXNIP), and nuclear transcription factor-κB (NF-κB) signaling pathways was also measured using Western blot analysis.

Results

TB-II significantly decreased the blood glucose levels and ameliorated renal histopathological injury in alloxan-induced diabetic mice. In addition, TB-II remarkably decreased the levels of renal function biochemical factors, such as kidney index, blood urea nitrogen, serum creatinine, urinary uric acid, urine creatinine, and urine protein, and it reduced lipid metabolism levels of total cholesterol and triglycerides and the levels of inflammatory cytokines interleukin-6 and tumor necrosis factor-α in alloxan-induced mice. Furthermore, TB-II inhibited the expression of mTOR, TXNIP, and NF-κB.

Conclusion

The results revealed that TB-II plays an important role in DN via TXNIP, mTOR, and NF-κB signaling pathways. Overall, TB-II exhibited a prominently ameliorative effect on alloxan-induced DN.