Mammalian target of rapamycin regulates Nox4-mediated podocyte depletion in diabetic renal injury

High glucose-induced downregulation of PTEN-Long is sufficient for proximal tubular cell injury in diabetic kidney disease

During the progression of diabetic kidney disease, proximal tubular epithelial cells respond to high glucose to induce hypertrophy and matrix expansion leading to renal fibrosis. Recently, a non-canonical PTEN has been shown to be translated from an upstream initiation codon CUG (leucine) to produce a longer protein called PTEN-Long (PTEN-L). Interestingly, the extended sequence present in PTEN-L contains cell secretion/penetration signal. Role of this non-canonical PTEN-L in diabetic renal tubular injury is not known. We show that high glucose decreases expression of PTEN-L. As a mechanism of its function, we find that reduced PTEN-L activates Akt-2, which phosphorylates and inactivate tuberin and PRAS40, resulting in activation of mTORC1 in tubular cells. Antibacterial agent acriflavine and antiviral agent ATA regulate translation from CUG codon. Acriflavine and ATA, respectively, decreased and increased expression of PTEN-L to altering Akt-2 and mTORC1 activation in the absence of change in expression of canonical PTEN. Consequently, acriflavine and ATA modulated high glucose-induced tubular cell hypertrophy and lamininγ1 expression. Importantly, expression of PTEN-L inhibited high glucose-stimulated Akt/mTORC1 activity to abrogate these processes. Since PTEN-L contains secretion/penetration signals, addition of conditioned medium containing PTEN-L blocked Akt-2/mTORC1 activity. Notably, in renal cortex of diabetic mice, we found reduced PTEN-L concomitant with Akt-2/mTORC1 activation, leading to renal hypertrophy and lamininγ1 expression. These results present first evidence for involvement of PTEN-L in diabetic kidney disease.

AMPK-SP1-Guided Dynein Expression Represents a New Energy-Responsive Mechanism and Therapeutic Target for Diabetic Nephropathy

Key Points

AMP kinase senses diabetic stresses in podocytes, subsequently upregulates specificity protein 1–mediated dynein expression and promotes podocyte injury. Pharmaceutical restoration of dynein expression by targeting specificity protein 1 represents an innovative therapeutic strategy for diabetic nephropathy.

Background

Diabetic nephropathy (DN) is a major complication of diabetes. Injury to podocytes, epithelial cells that form the molecular sieve of a kidney, is a preclinical feature of DN. Protein trafficking mediated by dynein, a motor protein complex, is a newly recognized pathophysiology of diabetic podocytopathy and is believed to be derived from the hyperglycemia-induced expression of subunits crucial for the transportation activity of the dynein complex. However, the mechanism underlying this transcriptional signature remains unknown.

Methods

Through promoter analysis, we identified binding sites for transcription factor specificity protein 1 (SP1) as the most shared motif among hyperglycemia-responsive dynein genes. We demonstrated the essential role of AMP-activated protein kinase (AMPK)–regulated SP1 in the transcription of dynein subunits and dynein-mediated trafficking in diabetic podocytopathy using chromatin immunoprecipitation quantitative PCR and live cell imaging. SP1-dependent dynein-driven pathogenesis of diabetic podocytopathy was demonstrated by pharmaceutical intervention with SP1 in a mouse model of streptozotocin-induced diabetes.

Results

Hyperglycemic conditions enhance SP1 binding to dynein promoters, promoted dynein expression, and enhanced dynein-mediated mistrafficking in cultured podocytes. These changes can be rescued by chemical inhibition or genetic silencing of SP1. The direct repression of AMPK, an energy sensor, replicates hyperglycemia-induced dynein expression by activating SP1. Mithramycin inhibition of SP1-directed dynein expression in streptozotocin-induced diabetic mice protected them from developing podocytopathy and prevented DN progression.

Conclusions

Our work implicates AMPK-SP1–regulated dynein expression as an early mechanism that translates energy disturbances in diabetes into podocyte dysfunction. Pharmaceutical restoration of dynein expression by targeting SP1 offers a new therapeutic strategy to prevent DN.

Macrophage polarization and signaling in diabetic kidney disease: a catalyst for disease progression

Diabetic kidney disease (DKD) is a serious complication of diabetes affecting millions of people worldwide. Macrophages, a critical immune cell type, are central players in the development and progression of DKD. In this comprehensive review, we delve into the intricate role of macrophages in DKD, examining how they can become polarized into proinflammatory M1 or anti-inflammatory M2 phenotypes. We explore the signaling pathways involved in macrophage recruitment and polarization in the kidneys, including the key cytokines and transcription factors that promote M1 and M2 polarization. In addition, we discuss the latest clinical studies investigating macrophages in DKD and explore the potential of hypoglycemic drugs for modulating macrophage polarization. By gaining a deeper understanding of the mechanisms that regulate macrophage polarization in DKD, we may identify novel therapeutic targets for this debilitating complication of diabetes. This review provides valuable insights into the complex interplay between macrophages and DKD, shedding light on the latest developments in this important area of research. This review aims to enhance understanding of the role that macrophages play in the pathogenesis of DKD.

Nox4-SH3YL1 complex is involved in diabetic nephropathy

Nox4-derived H2O2 generation plays an important role in the pathogenesis of chronic kidney diseases (CKDs) such as diabetic nephropathy (DN). Here, we showed that SH3 domain-containing Ysc84-like 1 (SH3YL1), a Nox4 cytosolic activator, regulated DN. Streptozotocin (STZ)-induced type Ⅰ diabetic models in SH3YL1 whole-body knockout (KO) mice and podocyte-specific SH3YL1 conditional KO (Nphs2-Cre/SH3YL1fl/fl) mice were established to investigate the function of SH3YL1 in DN. The expression of fibrosis markers and inflammatory cytokines, the generation of oxidative stress, and the loss of podocytes were suppressed in diabetic SH3YL1 KO and Nphs2-Cre/SH3YL1fl/fl mice, compared to diabetic control mice. To extrapolate the observations derived from diabetic mice to clinical implication, we measured the protein level of SH3YL1 in patients DN. In fact, the SH3YL1 level was increased in patients DN. Overall, the SH3YL1-Nox4 complex was identified to play an important role in renal inflammation and fibrosis, resulting in the development of DN.

Hyperuricemia and Gout Reduction by SGLT2 Inhibitors in Diabetes and Heart Failure: JACC Review Topic of the Week

Gout is characterized by increased production of purines (through the pentose phosphate pathway), which is coupled with reduced renal or intestinal excretion of urate. Concurrent upregulation of nutrient surplus signaling (mammalian target of rapamycin and hypoxia-inducible factor-1a) and downregulation of nutrient deprivation signaling (sirtuin-1 and adenosine monophosphate-activated protein kinase) redirects glucose toward anabolic pathways (rather than adenosine triphosphate production), thus promoting heightened oxidative stress and cardiomyocyte and proximal tubular dysfunction, leading to cardiomyopathy and kidney disease. Hyperuricemia is a marker (rather than a driver) of these cellular stresses. By inducing a state of starvation mimicry in a state of nutrient surplus, sodium-glucose cotransporter-2 inhibitors decrease flux through the pentose phosphate pathway (thereby attenuating purine and urate synthesis) while promoting renal urate excretion. These convergent actions exert a meaningful effect to lower serum uric acid by ≈0.6 to 1.5 mg/dL and to reduce the risk of gout by 30% to 50% in large-scale clinical trials.

Therapeutic mechanism exploration of polysaccharides from Dendrobium officinale on unilateral ureteral obstruction operation-induced renal fibrosis based on improving oxidative stress injury mediated by AhR/NOX4 pathway

Dendrobium officinale polysaccharides (DOP) has been reported to possess remarkable effects on improving renal function, oxidative stress damage and fibrotic diseases. However, the role and mechanism of DOP in preventing and treating renal fibrosis remain unclear. The purpose of this paper was to explore the therapeutic effects and underlying mechanisms of DOP on renal fibrosis. Firstly, renal fibrosis model was induced by unilateral ureteral obstruction operation (UUO) in male BALB/c mice. Subsequently, the anti-renal fibrosis effect of DOP was evaluated. It turned out that DOP significantly attenuated UUO induced renal fibrosis. The beneficial effects of DOP on renal fibrosis were concretely manifested in the relief of clinical symptoms, improvement of renal function, reduction of extracellular matrix collagen aggregation, attenuation of structural damage and inflammation, and decrement of profibrotic factors secretion. Meanwhile, DOP could also alleviate oxidative stress injury and inhibit the AhR/NOX4 pathway proteins expression. Furthermore, multivariate statistical analysis, AhR interference and overexpression experiments showed that the effect of DOP on alleviating renal fibrosis was closely related to the improvement of oxidative stress injury mediated by the AhR/NOX4 pathway. Overall, the data in the present paper indicated that DOP could alleviate renal fibrosis through improving AhR/NOX4 mediated oxidative stress injury.

Podocyte injury of diabetic nephropathy: Novel mechanism discovery and therapeutic prospects

Diabetic nephropathy (DN) is a severe complication of diabetes mellitus, posing significant challenges in terms of early prevention, clinical diagnosis, and treatment. Consequently, it has emerged as a major contributor to end-stage renal disease. The glomerular filtration barrier, composed of podocytes, endothelial cells, and the glomerular basement membrane, plays a vital role in maintaining renal function. Disruptions in podocyte function, including hypertrophy, shedding, reduced density, and apoptosis, can impair the integrity of the glomerular filtration barrier, resulting in elevated proteinuria, abnormal glomerular filtration rate, and increased creatinine levels. Hence, recent research has increasingly focused on the role of podocyte injury in DN, with a growing emphasis on exploring therapeutic interventions targeting podocyte injury. Studies have revealed that factors such as lipotoxicity, hemodynamic abnormalities, oxidative stress, mitochondrial dysfunction, and impaired autophagy can contribute to podocyte injury. This review aims to summarize the underlying mechanisms of podocyte injury in DN and provide an overview of the current research status regarding experimental drugs targeting podocyte injury in DN. The findings presented herein may offer potential therapeutic targets and strategies for the management of DN associated with podocyte injury.

COL4A3 Mutation Induced Podocyte Apoptosis by Dysregulation of NADPH Oxidase 4 and MMP-2

Introduction

Podocyte apoptosis is a common mechanism driving progression in Alport syndrome (AS). This study aimed to investigate the mechanism of podocyte apoptosis caused by COL4A3 mutations.

Methods

We recruited patients with autosomal dominant AS (ADAS). Patients with minimal change disease (MCD) were recruited as controls. Microarray analysis was carried out on isolated glomeruli from the patients and validated. Then, corresponding mutant human podocytes (p.C1616Y) and 129 mice (p.C1615Y, the murine homolog to the human p.C1616Y) were constructed. The highest differentially expressed genes (DEGs) from microarray analysis were validated in transgenic mice and podocytes before and after administration of MMP-2 inhibitor (SB-3CT) and NOX4 inhibitor (GKT137831). We further validated NOX4/MMP-2/apoptosis pathway by real-time polymerase chain reaction (PCR), immunohistochemistry, and western blot in renal tissues from the ADAS patients.

Results

Using microarray analysis, we observed that DEGs, including NOX4/H2O2, MMP-2, and podocyte apoptosis-related genes were significantly upregulated. These genes were validated by real-time PCR, histologic analysis, and western blot in corresponding mutant human podocyte (p.C1616Y) and/or mice models (p.C1615Y). Moreover, we found podocyte apoptosis was abrogated and MMP-2 expression was down-regulated both in vivo and in vitro by NOX4 inhibition, urinary albumin-to-creatinine ratio, 24-hour proteinuria; and renal pathologic lesion was attenuated by NOX4 inhibition in vivo. Furthermore, podocyte apoptosis was attenuated whereas NOX4 expression remained the same by inhibition of MMP-2 both in vivo and in vitro.

Conclusion

These results indicated that NOX4 might induce podocyte apoptosis through the regulation of MMP-2 in patients with COL4A3 mutations. Our findings provided new insights into the mechanism of ADAS.

Rapamycin Inhibits Osteoclastogenesis and Prevents LPS-Induced Alveolar Bone Loss by Oxidative Stress Suppression

Periodontitis is a progressive inflammatory skeletal disease characterized by periodontal tissue destruction, alveolar bone resorption, and tooth loss. Chronic inflammatory response and excessive osteoclastogenesis play essential roles in periodontitis progression. Unfortunately, the pathogenesis that contributes to periodontitis remains unclear. As a specific inhibitor of the mTOR (mammalian/mechanistic target of rapamycin) signaling pathway and the most common autophagy activator, rapamycin plays a vital role in regulating various cellular processes. The present study investigated the effects of rapamycin on osteoclast (OC) formation in vitro and its effects on the rat periodontitis model. The results showed that rapamycin inhibited OC formation in a dose-dependent manner by up-regulating the Nrf2/GCLC signaling pathway, thus suppressing the intracellular redox status, as measured by 2',7'-dichlorofluorescein diacetate and MitoSOX. In addition, rather than simply increasing the autophagosome formation, rapamycin increased the autophagy flux during OC formation. Importantly, the anti-oxidative effect of rapamycin was regulated by an increase in autophagy flux, which could be attenuated by blocking autophagy with bafilomycin A1. In line with the in vitro results, rapamycin treatment attenuated alveolar bone resorption in rats with lipopolysaccharide-induced periodontitis in a dose-dependent manner, as assessed by micro-computed tomography, hematoxylin-eosin staining, and tartrate-resistant acid phosphatase staining. Besides, high-dose rapamycin treatment could reduce the serum levels of proinflammatory factors and oxidative stress in periodontitis rats. In conclusion, this study expanded our understanding of rapamycin's role in OC formation and protection from inflammatory bone diseases.

Nox4 as a novel therapeutic target for diabetic vascular complications

Diabetic vascular complications can affect both microvascular and macrovascular. Diabetic microvascular complications, such as diabetic nephropathy, diabetic retinopathy, diabetic neuropathy, and diabetic cardiomyopathy, are believed to be caused by oxidative stress. The Nox family of NADPH oxidases is a significant source of reactive oxygen species and plays a crucial role in regulating redox signaling, particularly in response to high glucose and diabetes mellitus. This review aims to provide an overview of the current knowledge about the role of Nox4 and its regulatory mechanisms in diabetic microangiopathies. Especially, the latest novel advances in the upregulation of Nox4 that aggravate various cell types within diabetic kidney disease will be highlighted. Interestingly, this review also presents the mechanisms by which Nox4 regulates diabetic microangiopathy from novel perspectives such as epigenetics. Besides, we emphasize Nox4 as a therapeutic target for treating microvascular complications of diabetes and summarize drugs, inhibitors, and dietary components targeting Nox4 as important therapeutic measures in preventing and treating diabetic microangiopathy. Additionally, this review also sums up the evidence related to Nox4 and diabetic macroangiopathy.

Unraveling the Crosstalk between Lipids and NADPH Oxidases in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a serious complication of diabetes mellitus and a leading cause of end-stage renal disease. Abnormal lipid metabolism and intrarenal accumulation of lipids have been shown to be strongly correlated with the development and progression of diabetic kidney disease (DKD). Cholesterol, phospholipids, triglycerides, fatty acids, and sphingolipids are among the lipids that are altered in DKD, and their renal accumulation has been linked to the pathogenesis of the disease. In addition, NADPH oxidase-induced production of reactive oxygen species (ROS) plays a critical role in the development of DKD. Several types of lipids have been found to be tightly linked to NADPH oxidase-induced ROS production. This review aims to explore the interplay between lipids and NADPH oxidases in order to provide new insights into the pathogenesis of DKD and identify more effective targeted therapies for the disease.

Translational Aspects of the Mammalian Target of Rapamycin Complexes in Diabetic Nephropathy

Significance: Despite the many efforts put into understanding diabetic nephropathy (DN), direct treatments for DN have yet to be discovered. Understanding the mechanisms behind DN is an essential step in the development of novel therapeutic regimens. The mammalian target of rapamycin (mTOR) pathway has emerged as an important candidate in the quest for drug discovery because of its role in regulating growth, proliferation, as well as protein and lipid metabolism. Recent Advances: Kidney cells have been found to rely on basal autophagy for survival and for conserving kidney integrity. Recent studies have shown that diabetes induces renal autophagy deregulation, leading to kidney injury. Hyper-activation of the mTOR pathway and oxidative stress have been suggested to play a role in diabetes-induced autophagy imbalance. Critical Issues: A detailed understanding of the role of mTOR signaling in diabetes-associated complications is of major importance in the search for a cure. In this review, we provide evidence that mTOR is heavily implicated in diabetes-induced kidney injury. We suggest possible mechanisms through which mTOR exerts its negative effects by increasing insulin resistance, upregulating oxidative stress, and inhibiting autophagy. Future Directions: Both increased oxidative stress and autophagy deregulation are deeply embedded in DN. However, the mechanisms controlling oxidative stress and autophagy are not well understood. Although Akt/mTOR signaling seems to play an important role in oxidative stress and autophagy, further investigation is required to uncover the details of this signaling pathway. Antioxid. Redox Signal. 37, 802-819.

Intestinal microbiota regulates diabetes and cancer progression by IL-1β and NOX4 dependent signaling cascades

Diabetes changes the host microbiota, a condition known as dysbiosis. Dysbiosis is an important factor for the pathogenesis of diabetes and colorectal cancer (CRC). We aimed at identifying the microbial signature associated with diabetes and CRC; and identifying the signaling mechanism altered by dysbiosis and leading to CRC progression in diabetes. MKR mice that can spontaneously develop type 2 diabetes were used. For CRC induction, another subset of mice was treated with azoxymethane and dextran sulfate sodium. To identify the role of microbiota, microbiota-depleted mice were inoculated with fecal microbial transplant from diabetic and CRC mice. Further, a mouse group was treated with probiotics. At the end of the treatment, 16S rRNA sequencing was performed to identify microbiota in the fecal samples. Blood was collected, and colons were harvested for molecular, anatomical, and histological analysis. Our results show that diabetes is associated with a microbial signature characterized by reduction of butyrate-forming bacteria. This dysbiosis is associated with gastrointestinal complications reflected by a reduction in colon lengths. These changes are reversed upon treatment with probiotics, which rectified the observed dysbiosis. Inoculation of control mice with diabetic or cancer microbiota resulted in the development of increased number of polyps. Our data also show that inflammatory cytokines (mainly interleukin (IL)-1β) and NADPH oxidase (NOX)4 are over-expressed in the colon tissues of diabetic mice. Collectively our data suggest that diabetes is associated with dysbiosis characterized by lower abundance of butyrate-forming bacteria leading to over-expression of IL-1β and NOX4 leading to gastrointestinal complications and CRC.

Activation of 20-HETE Synthase Triggers Oxidative Injury and Peripheral Nerve Damage in Type 2 Diabetic Mice

Diabetic Peripheral Neuropathy (DPN), highly prevalent among patients with diabetes, is characterized by peripheral nerve dysfunction. Reactive Oxygen Species (ROS) overproduction has been suggested to orchestrate diabetic complications including DPN. Untargeted antioxidant therapy has exhibited limited efficacy, highlighting a critical need to explore ROS sources altered in a cell-specific manner in DPN. Cytochromes P450 (CYP) enzymes are prominent sources of ROS. Particularly, the 20-HETE synthase, CYP4A, is reported to mediate diabetes-induced renal, retinal, and cardiovascular injuries. This work investigates the role of CYP4A/20-HETE in DPN and their mechanisms of action. Non-obese type 2 Diabetic mice (MKR) were used and treated with a CYP4A-inhibitor (HET0016) or AMPK-activator (Metformin). Peripheral nerves of MKR mice reflect increased CYP4A and 20-HETE levels, concurrent with altered myelin proteins and sensorimotor deficits. This was associated with increased ROS production and altered Beclin-1 and LC3 protein levels, indicative of disrupted autophagic responses in tandem with AMPK inactivation. AMPK activation via Metformin restored nerve integrity, reduced ROS production, and regulated autophagy. Interestingly, similar outcomes were revealed upon HET0016 treatment whereby ROS production, autophagic responses, and AMPK signaling were normalized in diabetic mice. Altogether, the results highlight hyperglycemia-mediated oxidative injury in DPN through a novel CYP4A/20-HETE/AMPK pathological axis. PERSPECTIVE: To our knowledge, this is the first study to highlight the role of CYPs/20-HETE-induced oxidative injury in the pathogenesis of diabetic peripheral neuropathy. Targeting the identified pathological axis CYP4A/20-HETE/AMPK may be of clinical potential in predicting and alleviating peripheral nerve injury in patients with Type 2 Diabetes Mellitus.

Oncoprotein DJ-1 interacts with mTOR complexes to effect transcription factor Hif1α-dependent expression of collagen I (α2) during renal fibrosis

Proximal tubular epithelial cells respond to transforming growth factor β (TGFβ) to synthesize collagen I (α2) during renal fibrosis. The oncoprotein DJ-1 has previously been shown to promote tumorigenesis and prevent apoptosis of dopaminergic neurons; however, its role in fibrosis signaling is unclear. Here, we show TGFβ-stimulation increased expression of DJ-1, which promoted noncanonical mTORC1 and mTORC2 activities. We show DJ-1 augmented the phosphorylation/activation of PKCβII, a direct substrate of mTORC2. In addition, coimmunoprecipitation experiments revealed association of DJ-1 with Raptor and Rictor, exclusive subunits of mTORC1 and mTORC2, respectively, as well as with mTOR kinase. Interestingly, siRNAs against DJ-1 blocked TGFβ-stimulated expression of collagen I (α2), while expression of DJ-1 increased expression of this protein. In addition, expression of dominant negative PKCβII and siRNAs against PKCβII significantly inhibited TGFβ-induced collagen I (α2) expression. In fact, constitutively active PKCβII abrogated the effect of siRNAs against DJ-1, suggesting a role of PKCβII downstream of this oncoprotein. Moreover, we demonstrate expression of collagen I (α2) stimulated by DJ-1 and its target PKCβII is dependent on the transcription factor hypoxia-inducible factor 1α (Hif1α). Finally, we show in the renal cortex of diabetic rats that increased TGFβ was associated with enhanced expression of DJ-1 and activation of mTOR and PKCβII, concomitant with increased Hif1α and collagen I (α2). Overall, we identified that DJ-1 affects TGFβ-induced expression of collagen I (α2) via an mTOR-, PKCβII-, and Hif1α-dependent mechanism to regulate renal fibrosis.

Modes of podocyte death in diabetic kidney disease: an update

Diabetic kidney disease (DKD) accounts for a large proportion of end-stage renal diseases that require renal replacement therapies including dialysis and transplantation. Therefore, it is critical to understand the occurrence and development of DKD. Podocytes are mainly injured during the development of DKD, ultimately leading to their extensive death and loss. In turn, the injury and death of glomerular podocytes are also the main culprits of DKD. This review introduces the characteristics of podocytes and summarizes the modes of their death in DKD, including apoptosis, autophagy, mitotic catastrophe (MC), anoikis, necroptosis, and pyroptosis. Apoptosis is characterized by nuclear condensation and the formation of apoptotic bodies, and it exerts a different effect from autophagy in mediating DKD-induced podocyte loss. MC mediates a faulty mitotic process while anoikis separates podocytes from the basement membrane. Moreover, pyroptosis activates inflammatory factors to aggravate podocyte injuries whilst necroptosis drives signaling cascades, such as receptor-interacting protein kinases 1 and 3 and mixed lineage kinase domain-like, ultimately promoting the death of podocytes. In conclusion, a thorough knowledge of the modes of podocyte death in DKD can help us understand the development of DKD and lay the foundation for strategies in DKD disease therapy.

Kidney disease in diabetes: From mechanisms to clinical presentation and treatment strategies

Metabolic and haemodynamic perturbations and their interaction drive the development of diabetic kidney disease (DKD) and its progression towards end stage renal disease (ESRD). Increased mitochondrial oxidative stress has been proposed as the central mechanism in the pathophysiology of DKD, but other mechanisms have been implicated. In parallel to increased oxidative stress, inflammation, cell apoptosis and tissue fibrosis drive the relentless progressive loss of kidney function affecting both the glomerular filtration barrier and the renal tubulointerstitium. Alteration of glomerular capillary autoregulation is at the basis of glomerular hypertension, an important pathogenetic mechanism for DKD. Clinical presentation of DKD can vary. Its classical presentation, often seen in patients with type 1 diabetes (T1DM), features hyperfiltration and albuminuria followed by progressive fall in renal function. Patients can often also present with atypical features characterised by progressive reduction in renal function without albuminuria, others in conjunction with non-diabetes related pathologies making the diagnosis, at times, challenging. Metabolic, lipid and blood pressure control with lifestyle interventions are crucial in reducing the progressive renal function decline seen in DKD. The prevention and management of DKD (and parallel cardiovascular disease) is a huge global challenge and therapies that target haemodynamic perturbations, such as inhibitors of the renin-angiotensin-aldosterone system (RAAS) and SGLT2 inhibitors, have been most successful.

Reno-Protective Effect of GLP-1 Receptor Agonists in Type1 Diabetes: Dual Action on TRPC6 and NADPH Oxidases

Diabetic kidney disease (DKD), a serious diabetic complication, results in podocyte loss and proteinuria through NADPH oxidases (NOX)-mediated ROS production. DUOX1 and 2 are NOX enzymes that require calcium for their activation which enters renal cells through the pivotal TRPC channels. Hypoglycemic drugs such as liraglutide can interfere with this deleterious mechanism imparting reno-protection. Herein, we aim to investigate the reno-protective effect of GLP1 receptor agonist (GLP1-RA), via its effect on TRPC6 and NADPH oxidases. To achieve our aim, control or STZ-induced T1DM Sprague-Dawley rats were used. Rats were treated with liraglutide, metformin, or their combination. Functional, histological, and molecular parameters of the kidneys were assessed. Our results show that treatment with liraglutide, metformin or their combination ameliorates DKD by rectifying renal function tests and protecting against fibrosis paralleled by restored mRNA levels of nephrin, DUOX1 and 2, and reduced ROS production. Treatment with liraglutide reduces TRPC6 expression, while metformin treatment shows no effect. Furthermore, TRPC6 was found to be directly interacting with nephrin, and indirectly interacting with DUOX1, DUOX2 and GLP1-R. Our findings suggest that treatment with liraglutide may prevent the progression of diabetic nephropathy by modulating the crosstalk between TRPC6 and NADPH oxidases.

Role of diabetes in lung injury from acute exposure to electronic cigarette, heated tobacco product, and combustible cigarette aerosols in an animal model

BACKGROUND

Patients with diabetes are more vulnerable to the detrimental respiratory effects of combustible cigarette smoke (CS) when compared to the general population. Electronic cigarettes (ECIG) and heated tobacco products (HTP) are marketed as less harmful alternatives to CS. In this study, we compared the effects of acute ECIG, HTP and CS exposure on the lungs of type II diabetes versus non-diabetic mice in an animal model.

METHODS

Type II Diabetic (Diab) and Non-Diabetic (Non-Diab) mice were divided into Control, ECIG, HTP and CS groups. Animals were exposed for 6 hrs./day to either air, ECIG, HTP or CS for seven days. Lung injury was determined by a) histopathology, b) wet to dry ratio, c) albumin concentration in bronchoalveolar lavage fluid, d) expression of TNF-α, IL-6, and IL-1 β, e) reactive oxygen species production (ROS), and f) assessment of cellular apoptosis.

RESULTS

Lung histology revealed increased edema and inflammatory cells in diabetic mice exposed to ECIG, HTP and CS. The expression of Inflammatory mediators was, in general, more significant in the Diabetic groups as well. TNF-α expression, for example, was upregulated in Diab + ECIG but not in Non-Diab + ECIG. ROS was significantly increased in Diab + CS, less in Non-Diab + CS and weakly noted in ECIG + Diab. Significant albumin leak was observed in Diab and Non-Diab HTP-exposed animals. CS exposure worsened lung injury in Diab when compared to Non-Diab mice.

CONCLUSION

Comorbid medical conditions like diabetes may amplify ill effects of CS, ECIG or HTP exposure.

High glucose-stimulated enhancer of zeste homolog-2 (EZH2) forces suppression of deptor to cause glomerular mesangial cell pathology

Function of mTORC1 and mTORC2 has emerged as a driver of mesangial cell pathologies in diabetic nephropathy. The mechanism of mTOR activation is poorly understood in this disease. Deptor is a constitutive subunit and a negative regulator of both mTOR complexes. Mechanistic investigation in mesangial cells revealed that high glucose decreased the expression of deptor concomitant with increased mTORC1 and mTORC2 activities, induction of hypertrophy and, expression of fibronectin and PAI-1. shRNAs against deptor mimicked these pathologic outcomes of high glucose. Conversely, overexpression of deptor significantly inhibited all effects of high glucose. To determine the mechanism of deptor suppression, we found that high glucose significantly increased the expression of EZH2, resulting in lysine-27 tri-methylation of histone H3 (H3K27Me3). Employing approaches including pharmacological inhibition, shRNA-mediated downregulation and overexpression of EZH2, we found that EZH2 regulates high glucose-induced deptor suppression along with activation of mTOR, mesangial cell hypertrophy and fibronectin/PAI-1 expression. Moreover, expression of hyperactive mTORC1 reversed shEZH2-mediated inhibition of hypertrophy and expression of fibronectin and PAI-1 by high glucose. Finally, in renal cortex of diabetic mice, we found that enhanced expression of EZH2 is associated with decreased deptor levels and increased mTOR activity and, expression of fibronectin and PAI-1. Together, our findings provide a novel mechanism for mTOR activation via EZH2 to induce mesangial cell hypertrophy and matrix expansion during early progression of diabetic nephropathy. These results suggest a strategy for leveraging the intrinsic effect of deptor to suppress mTOR activity via reducing EZH2 as a novel therapy for diabetic nephropathy.

Metformin: A Growing Journey from Glycemic Control to the Treatment of Alzheimer's Disease and Depression

Metabolic stress, transduced as an altered cellular redox and energy status, presents as the main culprit in many diseases, including diabetes. However, its role in the pathology of neurological disorders is still not fully elucidated. Metformin, a biguanide compound, is an FDA approved antidiabetic drug generally used for the treatment of type 2 diabetes. The recently described wide spectrum of action executed by this drug suggests a potential therapeutic benefit in a panoply of disorders. Current studies imply that metformin could play a neuroprotective role by reversing hallmarks of brain injury (metabolic dysfunction, neuronal dystrophy and cellular loss), in addition to cognitive and behavioral alterations that accompany the onset of certain brain diseases such as Alzheimer's disease (AD) and depression. However, the mechanisms by which metformin exerts its protective effect in neurodegenerative disorders are not yet fully elucidated. The aim of this review is to reexamine the mechanisms through which metformin performs its function while concentrating on its effect on reestablishing homeostasis in a metabolically disturbed milieu. We will also highlight the importance of metabolic stress, not only as a component of many neurological disorders, but also as a primary driving force for neural insult. Of interest, we will explore the involvement of metabolic stress in the pathobiology of AD and depression. The derangement in major metabolic pathways, including AMPK, insulin and glucose transporters, will be explored and the potential therapeutic effects of metformin administration on the reversal of brain injury in such metabolism dependent diseases will be exposed.

CYP450 Mediates Reactive Oxygen Species Production in a Mouse Model of β-Thalassemia through an Increase in 20-HETE Activity

Oxidative damage by reactive oxygen species (ROS) is one of the main contributors to cell injury and tissue damage in thalassemia patients. Recent studies suggest that ROS generation in non-transfusion-dependent (NTDT) patients occurs as a result of iron overload. Among the different sources of ROS, the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes and cytochrome P450 (CYP450) have been proposed to be major contributors for oxidative stress in several diseases. However, the sources of ROS in patients with NTDT remain poorly understood. In this study, Hbbth3/+ mice, a mouse model for β-thalassemia, were used. These mice exhibit an unchanged or decreased expression of the major NOX isoforms, NOX1, NOX2 and NOX4, when compared to their C57BL/6 control littermates. However, a significant increase in the protein synthesis of CYP4A and CYP4F was observed in the Hbbth3/+ mice when compared to the C57BL/6 control mice. These changes were paralleled by an increased production of 20-hydroxyeicosatetraenoic acid (20-HETE), a CYP4A and CYP4F metabolite. Furthermore, these changes corroborate with onset of ROS production concomitant with liver injury. To our knowledge, this is the first report indicating that CYP450 4A and 4F-induced 20-HETE production mediates reactive oxygen species overgeneration in Hbbth3/+ mice through an NADPH-dependent pathway.

COVID-19 and diabetes mellitus: how one pandemic worsens the other

In light of the most challenging public health crisis of modern history, COVID-19 mortality continues to rise at an alarming rate. Patients with co-morbidities such as hypertension, cardiovascular disease, and diabetes mellitus (DM) seem to be more prone to severe symptoms and appear to have a higher mortality rate. In this review, we elucidate suggested mechanisms underlying the increased susceptibility of patients with diabetes to infection with SARS-CoV-2 with a more severe COVID-19 disease. The worsened prognosis of COVID-19 patients with DM can be attributed to a facilitated viral uptake assisted by the host's receptor angiotensin-converting enzyme 2 (ACE2). It can also be associated with a higher basal level of pro-inflammatory cytokines present in patients with diabetes, which enables a hyperinflammatory "cytokine storm" in response to the virus. This review also suggests a link between elevated levels of IL-6 and AMPK/mTOR signaling pathway and their role in exacerbating diabetes-induced complications and insulin resistance. If further studied, these findings could help identify novel therapeutic intervention strategies for patients with diabetes comorbid with COVID-19.

Morroniside Inhibits H2O2-Induced Podocyte Apoptosis by Down-Regulating NOX4 Expression Controlled by Autophagy In Vitro

Podocyte apoptosis is the common pathological basis for the progression of various kidney diseases. The overexpression of NOX4, a key enzyme involved in oxidative stress, has been proved to participate in the occurrence of podocyte apoptosis. Autophagy is a kind of adaptive response of cells under stress. However, as a “double-edged sword”, the effect of autophagy on apoptosis in different cells and conditions is complex and variable, which has not been fully explained yet. Morroniside, extracted from the traditional medicinal plant Cornus officinalis, has remarkable antioxidant and anti-apoptosis effects, and has been proven to inhibit the overexpression of NOX4 in kidney tissue. Therefore, H₂O₂ was used in this study to explore the effects of autophagy on podocyte NOX4 overexpression and apoptosis induced by oxidative stress, as well as the protection mechanism of morroniside in podocytes. The results showed that the autophagy activator rapamycin, as well as the autophagy inhibitor chloroquine, could induce podocyte apoptosis cultured in normal condition, and chloroquine could also significantly increase the NOX4 expression. The NOX4 expression and apoptosis rate of podocytes increased after H₂O₂ treatment, the expression of LC3-II decreased, and the expressions of p62, mTOR, and p-mTOR increased. The intervention of morroniside and rapamycin improved autophagy activity and inhibited NOX4 overexpression and apoptosis induced by H₂O₂. And chloroquine reversed the inhibitory effect of morroniside on NOX4 overexpression and podocyte apoptosis. Taken together, our results suggest that the expression level of NOX4 in podocytes is regulated by autophagy activity. Morroniside can reduce oxidative stress induced podocyte apoptosis by restoring the damaged autophagy flux and inhibit the overexpression of NOX4.

High Glucose Affects the Cytotoxic Potential of Rapamycin, Metformin and Hydrogen Peroxide in Cultured Human Mesenchymal Stem Cells

BACKGROUND

Oxidative stress and chronic hyperglycemia are two major side effects of type 2 diabetes affecting all cell types including mesenchymal stem cells (MSCs). As a cell therapy choice, understanding the behavior of MSCs will provide crucial information for efficient treatment.

METHODS

Placental mesenchymal stem cells were treated with various concentrations of glucose, metformin, rapamycin, and hydrogen peroxide to monitor their viability and cell cycle distribution. Cellular viability was examined via the MTT assay. Cell cycle distribution was studied by propidium iodide staining and apoptosis was determined using Annexin Vpropidium iodide staining and flow cytometry. Involvement of potential signaling pathways was evaluated by Western blotting for activation of Akt, P70S6K, and AMPK.

RESULTS

The results indicated that high glucose augmented cell viability and reduced metformin toxic potential. However, the hydrogen peroxide and rapamycin toxicities were exacerbated.

CONCLUSION

Our findings suggest that high glucose concentration has a major effect on placental mesenchymal stem cell viability in the presence of rapamycin, metformin and hydrogen peroxide in culture.

TGFβ acts through PDGFRβ to activate mTORC1 via the Akt/PRAS40 axis and causes glomerular mesangial cell hypertrophy and matrix protein expression

Interaction of transforming growth factor-β (TGFβ)-induced canonical signaling with the noncanonical kinase cascades regulates glomerular hypertrophy and matrix protein deposition, which are early features of glomerulosclerosis. However, the specific target downstream of the TGFβ receptor involved in the noncanonical signaling is unknown. Here, we show that TGFβ increased the catalytic loop phosphorylation of platelet-derived growth factor receptor β (PDGFRβ), a receptor tyrosine kinase expressed abundantly in glomerular mesangial cells. TGFβ increased phosphorylation of the PI 3-kinase-interacting Tyr-751 residue of PDGFRβ, thus activating Akt. Inhibition of PDGFRβ using a pharmacological inhibitor and siRNAs blocked TGFβ-stimulated phosphorylation of proline-rich Akt substrate of 40 kDa (PRAS40), an intrinsic inhibitory component of mTORC1, and prevented activation of mTORC1 in the absence of any effect on Smad 2/3 phosphorylation. Expression of constitutively active myristoylated Akt reversed the siPDGFRβ-mediated inhibition of mTORC1 activity; however, co-expression of the phospho-deficient mutant of PRAS40 inhibited the effect of myristoylated Akt, suggesting a definitive role of PRAS40 phosphorylation in mTORC1 activation downstream of PDGFRβ in mesangial cells. Additionally, we demonstrate that PDGFRβ-initiated phosphorylation of PRAS40 is required for TGFβ-induced mesangial cell hypertrophy and fibronectin and collagen I (α2) production. Increased activating phosphorylation of PDGFRβ is also associated with enhanced TGFβ expression and mTORC1 activation in the kidney cortex and glomeruli of diabetic mice and rats, respectively. Thus, pursuing TGFβ noncanonical signaling, we identified how TGFβ receptor I achieves mTORC1 activation through PDGFRβ-mediated Akt/PRAS40 phosphorylation to spur mesangial cell hypertrophy and matrix protein accumulation. These findings provide support for targeting PDGFRβ in TGFβ-driven renal fibrosis.

Role of the Nox4/AMPK/mTOR signaling axe in adipose inflammation-induced kidney injury

Diabetic kidney disease is one of the most serious complications of diabetes worldwide and is the leading cause of end-stage renal disease. While research has primarily focused on hyperglycemia as a key player in the pathophysiology of diabetic complications, recently, increasing evidence have underlined the role of adipose inflammation in modulating the development and/or progression of diabetic kidney disease. This review focuses on how adipose inflammation contribute to diabetic kidney disease. Furthermore, it discusses in detail the underlying mechanisms of adipose inflammation, including pro-inflammatory cytokines, oxidative stress, and AMPK/mTOR signaling pathway and critically describes their role in diabetic kidney disease. This in-depth understanding of adipose inflammation and its impact on diabetic kidney disease highlights the need for novel interventions in the treatment of diabetic complications.

NOX4/H2O2/mTORC1 Pathway in Salt-Induced Hypertension and Kidney Injury

We have reported that a high-salt (4.0% NaCl) dietary intake activates mTORC1 and inhibition of this pathway with rapamycin blunts the chronic phase of salt-induced hypertension and renal injury in Dahl salt-sensitive (SS) rats. In SS rats, high-salt intake is known to increase the renal production of H2O2 by NOX4, the most abundant NOX isoform in the kidney, and the global knockout of NOX4 blunts salt-sensitivity in these rats. Here, we explored the hypothesis that elevations of H2O2 by NOX4 in high-salt fed SS rat stimulate mTORC1 for the full development of salt-induced hypertension and renal injury. Our in vitro studies found that H2O2 activates mTORC1 independent of PI3K/AKT and AMPK pathways. To determine the in vivo relevance of NOX4/H2O2/mTORC1 in the salt-induced hypertension, SS-Nox4 knockout (SSNox4-/-) rats were daily administrated with vehicle/rapamycin fed a high-salt diet for 21 days. Rapamycin treatment of SSNox4-/- rats had shown no augmented effect on the salt-induced hypertension nor upon indices of renal injury. Significant reductions of renal T lymphocyte and macrophage together with inhibition of cell proliferation were observed in rapamycin treated rats suggesting a role of mTORC1 independent of NOX4 in the proliferation of immune cell. Given the direct activation of mTORC1 by H2O2 and absence of any further protection from salt-induced hypertension in rapamycin-treated SSNox4-/- rats, we conclude that NOX4-H2O2 is a major upstream activator of mTORC1 that contributes importantly to salt-induced hypertension and renal injury in the SS rat model.

Targeting the NADPH Oxidase-4 and Liver X Receptor Pathway Preserves Schwann Cell Integrity in Diabetic Mice

Diabetes triggers peripheral nerve alterations at a structural and functional level, collectively referred to as diabetic peripheral neuropathy (DPN). This work highlights the role of the liver X receptor (LXR) signaling pathway and the cross talk with the reactive oxygen species (ROS)-producing enzyme NADPH oxidase-4 (Nox4) in the pathogenesis of DPN. Using type 1 diabetic (T1DM) mouse models together with cultured Schwann cells (SCs) and skin biopsies from patients with type 2 diabetes (T2DM), we revealed the implication of LXR and Nox4 in the pathophysiology of DPN. T1DM animals exhibit neurophysiological defects and sensorimotor abnormalities paralleled by defective peripheral myelin gene expression. These alterations were concomitant with a significant reduction in LXR expression and increase in Nox4 expression and activity in SCs and peripheral nerves, which were further verified in skin biopsies of patients with T2DM. Moreover, targeted activation of LXR or specific inhibition of Nox4 in vivo and in vitro to attenuate diabetes-induced ROS production in SCs and peripheral nerves reverses functional alteration of the peripheral nerves and restores the homeostatic profiles of MPZ and PMP22. Taken together, our findings are the first to identify novel, key mediators in the pathogenesis of DPN and suggest that targeting LXR/Nox4 axis is a promising therapeutic approach.

TXNIP deficiency mitigates podocyte apoptosis via restraining the activation of mTOR or p38 MAPK signaling in diabetic nephropathy

Thioredoxin-interacting protein (TXNIP), is identified as an inhibitor of the thiol oxidoreductase thioredoxin that acts endogenously, and is increased by high glucose (HG). In this study, we investigated the potential function of TXNIP on apoptosis of podocytes and its potential mechanism in vivo and in vitro in diabetic nephropathy (DN). TXNIP silencing attenuated HG-induced apoptosis and obliterated the activation of signaling pathways of mammalian target of rapamycin (mTOR) and p38 mitogen-activated protein kinase (MAPK) in conditionally immortalized mouse podocytes. Furthermore, the Raptor and Rictor shRNAs, mTOR specific inhibitor KU-0063794 and p38 MAPK inhibitor SB203580 were used to assess the role of mTOR or p38 MAPK pathway on podocyte apoptosis induced by HG. The Rictor and Raptor shRNAs and KU-0063794 appeared to reduce HG-induced apoptosis in podocytes. Simultaneously, SB203580 could also restrain HG-induced apoptosis in podocytes. Streptozotocin rendered equivalent diabetes in TXNIP-/- (TKO) and wild-type (WT) control mice. TXNIP deficiency mitigated renal injury in diabetic mice. Additionally, TXNIP deficiency also descended the apoptosis-related protein and Nox4 levels, the mTOR signaling activation and the p38 MAPK phosphorylation in podocytes of diabetic mice. All these data indicate that TXNIP deficiency may mitigate apoptosis of podocytes by inhibiting p38 MAPK or mTOR signaling pathway in DN, underlining TXNIP as a putative target for therapy.

Metformin alleviates renal injury in diabetic rats by inducing Sirt1/FoxO1 autophagic signal axis

Diabetic nephropathy (DN) is the major microvascular complication of diabetes mellitus and the most important cause of end-stage renal disease worldwide. Metformin is the preferred oral hypoglycaemic drug for type 2 diabetes mellitus (T2DM). Recent studies have shown that besides lowering blood glucose, metformin also has protective effects on renal function, but its mechanism is not clear. In this study, we established a diabetic rat model by high-fat feeding combined with intraperitoneal injection of streptozotocin. Their changes of renal function, oxidative stress, histopathology and structure, and autophagy were observed after 8 weeks of metformin treatment at different dose. Sirt1 inhibitor EX527 and metformin were used to observe whether the protective effect of metformin on DN kidney was achieved through the Sirt1/FoxO1 autophagic signalling pathway. The results showed that metformin could protect renal function by up-regulating autophagy level, alleviating oxidative stress level of renal tissue and pathological and structural changes of glomeruli, and inhibiting the expression of extracellular matrix. Sirt1 inhibitor could block the protective effect of metformin on kidney of diabetic rats, suggesting that metformin could alleviate kidney injury in diabetic rats by inducing Sirt1/FoxO1 autophagy signal axis. So metformin could alleviate renal injury in diabetic rats, which may be achieved by regulating Sirt1/FoxO1 autophagic signalling pathway and inducing renal autophagy.

Research Progress on the Pathological Mechanisms of Podocytes in Diabetic Nephropathy

Diabetic nephropathy (DN) is not only an important microvascular complication of diabetes but also the main cause of end-stage renal disease. Studies have shown that the occurrence and development of DN are closely related to morphological and functional changes in podocytes. A series of morphological changes after podocyte injury in DN mainly include podocyte hypertrophy, podocyte epithelial-mesenchymal transdifferentiation, podocyte detachment, and podocyte apoptosis; functional changes mainly involve podocyte autophagy. More and more studies have shown that multiple signaling pathways play important roles in the progression of podocyte injury in DN. Here, we review research progress on the pathological mechanism of morphological and functional changes in podocytes associated with DN, to provide a new target for delaying the occurrence and development of this disorder.

Xuesaitong Protects Podocytes from Apoptosis in Diabetic Rats through Modulating PTEN-PDK1-Akt-mTOR Pathway

Diabetic kidney disease (DKD) is a major cause of end-stage renal disease (ESRD), and therapeutic strategies for delaying its progression are limited. Loss of podocytes by apoptosis characterizes the early stages of DKD. To identify novel therapeutic options, we investigated the effects of Xuesaitong (XST), consisting of total saponins from Panax notoginseng, on podocyte apoptosis in streptozotocin- (STZ-) induced diabetic rats. XST (5 mg/kg·d) or Losartan (10 mg/kg·d) was given to diabetic rats for 12 weeks. Albuminuria, renal function markers, and renal histopathology morphological changes were examined. Podocyte apoptosis was determined by triple immunofluorescence labelling including a TUNEL assay, WT1, and DAPI. Renal expression of Nox4, miRNA-214, PTEN, PDK1, phosphorylated Akt, mTOR, and mTORC1 was detected. In diabetic rats, severe hyperglycaemia and albuminuria developed, and apoptotic podocytes were markedly increased in diabetic kidneys. However, XST attenuated albuminuria, mesangial expansion, podocyte apoptosis, and morphological changes of podocytes in diabetic rats. Decreased expression of PTEN, as well as increased expression of Nox4, miRNA-214, PDK1, phosphorylated Akt, mTOR, and mTORC1, was detected. These abnormalities were partially restored by XST treatment. Thus, XST ameliorated podocyte apoptosis partly through modulating the PTEN-PDK1-Akt-mTOR pathway. These novel findings might point the way to a natural therapeutic strategy for treating DKD.

Protective effects of glucagon-like peptide-1 on cardiac remodeling by inhibiting oxidative stress through mammalian target of rapamycin complex 1/p70 ribosomal protein S6 kinase pathway in diabetes mellitus

AIMS/INTRODUCTION

Although increased reactive oxygen species (ROS) generation is a major mechanism leading to cardiac remodeling in diabetes mellitus, research into the effects of anti-oxidation on diabetic cardiac remodeling remains scarce and controversial. Glucagon-like peptide-1 (GLP-1) shows potential anti-oxidative effects besides lowering blood glucose. The objective of this research was to investigate the effects of GLP-1 on cardiac remodeling and the molecular mechanism involved in diabetes mellitus.

MATERIALS AND METHODS

Streptozotocin-induced diabetic rats received exenatide treatment for 3 months. Cardiac function, cardiac weight index and myocardial interstitial fibrosis were measured. Cardiomyocytes were cultured in high-glucose medium with GLP-1 treatment. The ROS production, apoptosis and the levels of mammalian target of rapamycin complex 1/p70 ribosomal protein S6 kinase protein expression in cardiomyocytes were analyzed.

RESULTS

Experimental diabetes mellitus showed impaired cardiac diastolic function, increased brain natriuretic peptide expression and increased interstitial collagen deposition in the myocardium, which were ameliorated by exenatide treatment. Exenatide reduced myocardial ROS production and apoptosis in diabetes mellitus. Also, high glucose-induced ROS generation and apoptosis in cardiomyocytes were inhibited by GLP-1, as well as the levels of mammalian target of rapamycin complex 1/p70 ribosomal protein S6 kinase phosphorylation. Furthermore, GLP-1 treatment upregulated adenosine monophosphate-activated protein kinase activity in high-glucose-induced cardiomyocyte.

CONCLUSIONS

Glucagon-like peptide-1 protects the cardiomyocytes from oxidative stress and apoptosis in diabetes mellitus, which might contribute to the improvement of cardiac remodeling. The cardiac protection of GLP-1 might be dependent on inhibition of mammalian target of rapamycin complex 1/p70 ribosomal protein S6 kinase, through an adenosine monophosphate-activated protein kinase-mediated pathway.

Glucose 6-Phosphate Accumulates via Phosphoglucose Isomerase Inhibition in Heart Muscle

RATIONALE

Metabolic and structural remodeling is a hallmark of heart failure. This remodeling involves activation of the mTOR (mammalian target of rapamycin) signaling pathway, but little is known on how intermediary metabolites are integrated as metabolic signals.

OBJECTIVE

We investigated the metabolic control of cardiac glycolysis and explored the potential of glucose 6-phosphate (G6P) to regulate glycolytic flux and mTOR activation.

METHODS AND RESULTS

We developed a kinetic model of cardiomyocyte carbohydrate metabolism, CardioGlyco, to study the metabolic control of myocardial glycolysis and G6P levels. Metabolic control analysis revealed that G6P concentration is dependent on phosphoglucose isomerase (PGI) activity. Next, we integrated ex vivo tracer studies with mathematical simulations to test how changes in glucose supply and glycolytic flux affect mTOR activation. Nutrient deprivation promoted a tight coupling between glucose uptake and oxidation, G6P reduction, and increased protein-protein interaction between hexokinase II and mTOR. We validated the in silico modeling in cultured adult mouse ventricular cardiomyocytes by modulating PGI activity using erythrose 4-phosphate. Inhibition of glycolytic flux at the level of PGI caused G6P accumulation, which correlated with increased mTOR activation. Using click chemistry, we labeled newly synthesized proteins and confirmed that inhibition of PGI increases protein synthesis.

CONCLUSIONS

The reduction of PGI activity directly affects myocyte growth by regulating mTOR activation.

Arg913Gln variation of SLC12A3 gene is associated with diabetic nephropathy in type 2 diabetes and Gitelman syndrome: a systematic review

Abstract

Background

Diabetic nephropathy is a global common cause of chronic kidney disease and end-stage renal disease. A lot of research has been conducted in biomedical sciences, which has enhanced understanding of the pathophysiology of diabetic nephropathy and has expanded the potential available therapies. An increasing number of evidence suggests that genetic alterations play a major role in development and progression of diabetic nephropathy. This systematic review was focused on searching an association between Arg913Gln variation in SLC12A3 gene with diabetic nephropathy in individuals with Type 2 Diabetes and Gitelman Syndrome.

Methods

An extensive systematic review of the literature was completed using PubMed, EBSCO and Cochrane Library, from their inception to January 2018. The PRISMA guidelines were followed and the search strategy ensured that all possible studies were identified to compile the review. Inclusion criteria for this review were: 1) Studies that analyzed the SLC12A3 gene in individuals with Type 2 Diabetes and Gitelman Syndrome. 2) Use of at least one analysis investigating the association between the Arg913Gln variation of SLC12A3 gene with diabetic nephropathy. 3) Use of a case–control or follow-up design. 4) Investigation of type 2 diabetes mellitus in individuals with Gitelman’s syndrome, with a history of diabetic nephropathy.

Results

The included studies comprised 2106 individuals with diabetic nephropathy. This review shows a significant genetic association in most studies in the Arg913Gln variation of SLC12A3 gene with the diabetic nephropathy, pointing out that the mutations of this gene could be a key predictor of end-stage renal disease.

Conclusions

The results showed in this systematic review contribute to better understanding of the association between the Arg913Gln variation of SLC12A3 gene with the pathogenesis of diabetic nephropathy in individuals with T2DM and GS.

Inhibition of high mobility group box 1 (HMGB1) attenuates podocyte apoptosis and epithelial-mesenchymal transition by regulating autophagy flux

BACKGROUND

Podocyte injury, characterized by podocyte hypertrophy, apoptosis, and epithelial-mesenchymal transition (EMT), is the major causative factor of diabetic nephropathy (DN). Autophagy dysfunction is regarded as the major risk factor for podocyte injury including EMT and apoptosis. High mobility group box 1 (HMGB1) is involved in the progression of DN through the induction of autophagy. However, the underlying mechanism remains unknown.

METHODS

Plasma HMGB1 concentrations were determined in DN patients using ELISA. Apoptosis of DN serum-treated podocytes was evaluated by flow cytometry. Podocyte autophagy flux was measured using immunofluorescence. Western blotting analysis was used to investigate HMGB1 expression, EMT, and autophagy-related signaling pathways.

RESULTS

Upregulation of HMGB1 was found in DN patients and DN serum-treated podocytes. Removal of HMGB1 inhibited DN serum-mediated podocyte apoptosis by inhibiting autophagy and activating AKT/mammalian target of rapamycin (mTOR) signaling. In addition, HMGB1 depletion repressed the progression of podocyte EMT by inhibiting transforming growth factor (TGF)-β/smad1 signaling in vitro and in vivo. The combination of HMGB1 short interference (si) RNA and the autophagy activator rapamycin protected against podocyte apoptosis and EMT progression by inhibiting the AKT/mTOR and TGF-β/smad signaling pathway, respectively.

CONCLUSIONS

Although HMGB1 siRNA and rapamycin treatment had opposite effects on autophagy and AKT/mTOR signaling, there was no contradiction about the role of HMGB1 siRNA and rapamycin on AKT/mTOR pathway because autophagy and AKT/mTOR signaling play dual roles in intracellular biological processes. Based on the findings of this study, we may assume that HMGB1-initiated autophagy is harmful, whereas rapamycin is beneficial to podocyte survival. Possibly combined treatment with HMGB1 siRNA and rapamycin improved podocyte damage and EMT by regulating autophagy homeostasis.

Thioredoxin-interacting protein deficiency alleviates phenotypic alterations of podocytes via inhibition of mTOR activation in diabetic nephropathy

Thioredoxin-interacting protein (TXNIP) is induced by high glucose (HG), whereupon it acts to inhibit thioredoxin, thereby promoting oxidative stress. We have found that TXNIP knockdown in human renal tubular cells helped prevent the epithelial-to-mesenchymal transition (EMT). Here, we studied the potential effect of TXNIP on podocyte phenotypic alterations in diabetic nephropathy (DN) in vivo and in vitro. In conditionally immortalized mouse podocytes under HG conditions, knocking down TXNIP disrupted EMT, reactive oxygen species (ROS) production, and mammalian target of rapamycin (mTOR) pathway activation. Further, Raptor short hairpin RNA (shRNA), Rictor shRNA, and mTOR specific inhibitor KU-0063794 were used to assess if the mTOR signal pathway is involved in HG-induced EMT in podocytes. We found that Raptor shRNA, Rictor shRNA, and KU-0063794 could all restrain HG-induced EMT and ROS production in podocytes. In addition, antioxidant Tempol or N-acetylcysteine presented a prohibitive effect on HG-induced EMT in podocytes. Streptozotocin was utilized to render equally diabetic in wild-type (WT) control and TXNIP ^-/- (TKO) mice. Diabetes did not increase levels of 24-hr urinary protein, serum creatinine, blood urea nitrogen, and triglyceride in TXNIP ^-/- mice. Podocyte phenotypic alterations and podocyte loss were detected in WT but not in TKO diabetic mice. Oxidative stress was also suppressed in diabetic TKO mice relative to WT controls. Also, TXNIP deficiency suppresses the activation of mTOR in glomeruli of streptozotocin-induced diabetic mice. Moreover, TXNIP expression, mTOR activation, Nox1, and Nox4 could be detected in renal biopsy tissues of patients with DN. This suggests that decreased TXNIP could ameliorate phenotypic alterations of podocytes via inhibition of mTOR in DN, highlighting TXNIP as a promising therapeutic target.

High glucose increases miR-214 to power a feedback loop involving PTEN and the Akt/mTORC1 signaling axis

The mechanism of PTEN repression by high glucose in diabetic nephropathy is not known. Using proximal tubular cells, we show that inhibition of PI3 kinase/Akt and their inactive enzymes prevents high glucose-induced PTEN downregulation. Similarly, rapamycin (Rapa) and shRaptor block suppression of PTEN by high glucose. In contrast, the constitutive activation of Akt and mechanistic target of rapamycin (mTOR)C1 decrease the expression of PTEN, similarly to high glucose. Remarkably, PI3 kinase/Akt/mTORC1 inhibition significantly attenuates high glucose-stimulated increase in miR-214, which targets PTEN, while constitutively active Akt/mTORC1 increases miR-214. Furthermore, anti-miR-214 and mTORC1 inhibition block high glucose-induced hypertrophy and fibronectin expression. These results reveal the first evidence for the presence of a high glucose-forced positive feedback conduit between the three-layered kinase cascade and miR-214/ PTEN in tubular cell injury.

Huangqi decoction inhibits hyperglycemia-induced podocyte apoptosis by down-regulated Nox4/p53/Bax signaling in vitro and in vivo

BACKGROUND

Podocyte dysfunction is associated with the progression of diabetic nephropathy (DN). Huangqi decoction (HQD), a traditional Chinese medical formula, has been used to improve diabetes-related syndrome in China. The present study was to investigate the protective effect of HQD on podocyte apoptosis and the underlying molecular mechanism.

METHODS

Podocyte was used to measure the efficacy of HQD on cell apoptosis, activities of NADPH oxidases, ROS generation and mitochondrial membrane potential (MMP), and the activation of Nox4/p53/Bax signaling pathway with HQD treatment were also investigated in vitro. Renal pathological morphology, renal function, podocyte apoptosis and Nox4/p53/Bax signaling pathway were investigated with STZ-induced diabetic mice in vivo.

RESULTS

HQD increased the cell proliferation and MMP level, while the ROS production and activities of NADPH oxidases were decreased. Meanwhile, Nox4/p53/Bax signaling was down-regulated. Contrarily, overexpression of Nox4 or p53 significantly abolished those efficacies of HQD. Accordingly, in vivo study showed that the progressive albuminuria, glomerulosclerosis and loss of podocytes were significantly alleviated with HQD treatment in diabetic mice, which paralleled by the marked inhibition of Nox4/p53/Bax signaling.

CONCLUSION

Collectively, we provide further evidence that HQD had a renoprotective effect in preventing podocyte apoptosis, which was mediated at least in part by down-regulation of Nox4/p53/Bax signaling.

Novel triazine-based pyrimidines suppress glomerular mesangial cells proliferation and matrix protein accumulation through a ROS-dependent mechanism in the diabetic milieu

Diabetic nephropathy (DN) is one of the most serious complications of diabetes worldwide. It is depicted as the leading cause of end-stage renal disease. Oxidative stress plays a key role in hyperglycemia-induced DN. The preparation and characterization of novel mono-, di-, and trisubstituted-s-triazines endowed with uracil and/or thymine are described in this paper. The synthesis of the title compounds was realized through selective nucleophilic substitution reactions of cyanuric chloride with the corresponding hydrazide nucleobases. In this study, we assessed the effects of these derivatives on the progression of diabetic nephropathy. Our results show that trisubstituted-s-triazines endowed with acylhydrazides attenuate high-glucose induced glomerular mesangial cells proliferation and matrix protein accumulation in vitro. Notably, these derivatives also display anti-oxidative properties. This suggests that the novel trisubstituted-s-triazine derivatives provide renal protection through a reactive oxygen species (ROS)-dependent mechanism. Our data provide evidence that these derivatives may serve as potential therapeutic candidates in the treatment of DN.

Deacetylation of S6 kinase promotes high glucose-induced glomerular mesangial cell hypertrophy and matrix protein accumulation

S6 kinase acts as a driver for renal hypertrophy and matrix accumulation, two key pathologic signatures of diabetic nephropathy. As a post-translational modification, S6 kinase undergoes acetylation at the C terminus. The role of this acetylation to regulate kidney glomerular cell hypertrophy and matrix expansion is not known. In mesangial cells, high glucose decreased the acetylation and enhanced phosphorylation of S6 kinase and its substrates rps6 and eEF2 kinase that lead to dephosphorylation of eEF2. To determine the mechanism of S6 kinase deacetylation, we found that trichostatin A, a pan-histone deacetylase (HDAC) inhibitor, blocked all high glucose-induced effects. Furthermore, high glucose increased the expression and association of HDAC1 with S6 kinase. HDAC1 decreased the acetylation of S6 kinase and mimicked the effects of high glucose, resulting in mesangial cell hypertrophy and expression of fibronectin and collagen I (α2). In contrast, siRNA against HDAC1 inhibited these effects by high glucose. A C-terminal acetylation-mimetic mutant of S6 kinase suppressed high glucose-stimulated phosphorylation of S6 kinase, rps6 and eEF2 kinase, and inhibited the dephosphorylation of eEF2. Also, the acetylation mimetic attenuated the mesangial cell hypertrophy and fibronectin and collagen I (α2) expression. Conversely, an S6 kinase acetylation-deficient mutant induced all the above effects of high glucose. Finally, in the renal glomeruli of diabetic rats, the acetylation of S6 kinase was significantly reduced concomitant with increased HDAC1 and S6 kinase activity. In aggregate, our data uncovered a previously unrecognized role of S6 kinase deacetylation in high glucose-induced mesangial cell hypertrophy and matrix protein expression.

Prevention of kidney cell damage in hyperglycaemia condition by adiponectin

Adiponectin (APN) is an adipocytokine, secreted from adipose tissue and has anti-inflammatory, anti-ageing, and antidiabetic properties. Hyperglycaemia can damage the renal cells, and mammalian target of rapamycin (mTOR), along with Sirtuin 1 (SIRT1), have an important role in kidney cell response to hyperglycaemia. Therefore, understanding the relationship between adiponectin, mTOR, and SIRT1 proteins is beneficial for deciphering the mechanism of adiponectin function. In this study, Human Embryonic Kidney-293 (HEK-293) cells were cultured under normal and high-glucose condition, with and without APN (1, 10, and 100 ng/mL) for 48 hours. mTOR protein expression was evaluated by western blot analysis, and SIRT1 protein was assessed using ELISA method. To evaluate hyperglycaemia-mediated cytotoxicity, cell viability was determined using MTT assay. Data showed that APN in high dose (100 ng/mL) significantly reduced the expression of mTOR and p-mTOR, increased SIRT1 protein, and also improved cell viability compared with the control high glucose (p ≤ 0.05). According to this results, APN can be useful in preventing renal cell damage, by affecting on the expression of mTOR and SIRT1 proteins, as well as increasing the survival of kidney cells in hyperglycaemia conditions. SIGNIFICANCE OF THE STUDY: Adiponectin triggered mTOR/p-mTOR/SIRT1 pathway and decreased cell death in human kidney cells. Our findings provide preliminary experimental data that support further studies on the potential therapeutic role of adiponectin in diabetes and diabetic-induced metabolic complications.

The MEK Inhibitor Trametinib Ameliorates Kidney Fibrosis by Suppressing ERK1/2 and mTORC1 Signaling

BACKGROUND

During kidney fibrosis, a hallmark and promoter of CKD (regardless of the underlying renal disorder leading to CKD), the extracellular-regulated kinase 1/2 (ERK1/2) pathway, is activated and has been implicated in the detrimental differentiation and expansion of kidney fibroblasts. An ERK1/2 pathway inhibitor, trametinib, is currently used in the treatment of melanoma, but its efficacy in the setting of CKD and renal fibrosis has not been explored.

METHODS

We investigated whether trametinib has antifibrotic effects in two mouse models of renal fibrosis-mice subjected to unilateral ureteral obstruction (UUO) or fed an adenine-rich diet-as well as in cultured primary human fibroblasts. We also used immunoblot analysis, immunohistochemical staining, and other tools to study underlying molecular mechanisms for antifibrotic effects.

RESULTS

Trametinib significantly attenuated collagen deposition and myofibroblast differentiation and expansion in UUO and adenine-fed mice. We also discovered that in injured kidneys, inhibition of the ERK1/2 pathway by trametinib ameliorated mammalian target of rapamycin complex 1 (mTORC1) activation, another key profibrotic signaling pathway. Trametinib also inhibited the ERK1/2 pathway in cultured primary human renal fibroblasts stimulated by application of TGF-β1, the major profibrotic cytokine, thereby suppressing downstream mTORC1 pathway activation. Additionally, trametinib reduced the expression of myofibroblast marker α-smooth muscle actin and the proliferation of renal fibroblasts, corroborating our in vivo data. Crucially, trametinib also significantly ameliorated renal fibrosis progression when administered to animals subsequent to myofibroblast activation.

CONCLUSIONS

Further study of trametinib as a potential candidate for the treatment of chronic renal fibrotic diseases of diverse etiologies is warranted.

Akt2 causes TGFβ-induced deptor downregulation facilitating mTOR to drive podocyte hypertrophy and matrix protein expression

TGFβ promotes podocyte hypertrophy and expression of matrix proteins in fibrotic kidney diseases such as diabetic nephropathy. Both mTORC1 and mTORC2 are hyperactive in response to TGFβ in various renal diseases. Deptor is a component of mTOR complexes and a constitutive inhibitor of their activities. We identified that deptor downregulation by TGFβ maintains hyperactive mTOR in podocytes. To unravel the mechanism, we found that TGFβ -initiated noncanonical signaling controls deptor inhibition. Pharmacological inhibitor of PI 3 kinase, Ly 294002 and pan Akt kinase inhibitor MK 2206 prevented the TGFβ induced downregulation of deptor, resulting in suppression of both mTORC1 and mTORC2 activities. However, specific isoform of Akt involved in this process is not known. We identified Akt2 as predominant isoform expressed in kidney cortex, glomeruli and podocytes. TGFβ time-dependently increased the activating phosphorylation of Akt2. Expression of dominant negative PI 3 kinase and its signaling inhibitor PTEN blocked Akt2 phosphorylation by TGFβ. Inhibition of Akt2 using a phospho-deficient mutant that inactivates its kinase activity, as well as siRNA against the kinase markedly diminished TGFβ -mediated deptor suppression, its association with mTOR and activation of mTORC1 and mTORC2. Importantly, inhibition of Akt2 blocked TGFβ -induced podocyte hypertrophy and expression of the matrix protein fibronectin. This inhibition was reversed by the downregulation of deptor. Interestingly, we detected increased phosphorylation of Akt2 concomitant with TGFβ expression in the kidneys of diabetic rats. Thus, our data identify previously unrecognized Akt2 kinase as a driver of TGFβ induced deptor downregulation and sustained mTORC1 and mTORC2 activation. Furthermore, we provide the first evidence that deptor downstream of Akt2 contributes to podocyte hypertrophy and matrix protein expression found in glomerulosclerosis in different renal diseases.

miR-423-5p suppresses high-glucose-induced podocyte injury by targeting Nox4

Podocyte injury plays crucial roles in the pathogenesis of diabetic nephropathy (DN). Aberrant microRNAs (miRNAs) have been suggested to contribute to podocyte injury. However, whether miR-423-5p could alleviate high glucose (HG)-mediated podocyte injury and the underlying mechanisms remains unclear. In this study, we found that patients with DN have reduced miR-423-5p and elevated Nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) expressions in clinical renal tissues, and HG induced Nox4 but suppressed miR-423-5p expressions in cultured podocytes in a time-dependent manner. Moreover, overexpression of miR-423-5p antagonized HG-stimulated podocyte injury by enhancing cell viability, inhibiting reactive oxygen species (ROS) production, suppressing cell apoptosis, reducing inflammatory activity, and repressing cytoskeleton damage accompanied with alternations of podocyte specific proteins. Furthermore, functional assays substantiated that Nox4 was a direct target and negatively regulated by miR-423-5p. Additionally, restoration of Nox4 impeded the protective effect of miR-423-5p on podocyte injury via activation of p38 MAPK pathway. Therefore, this study manifested that miR-423-5p overexpression protected HG-induced podocyte damage by inhibiting ROS generation via targeting Nox4, providing a potential therapeutic strategy against DN.

Pharmacological inhibition of the mitochondrial NADPH oxidase 4/PKCα/Gal-3 pathway reduces left ventricular fibrosis following myocardial infarction

Although the initial reparative fibrosis after myocardial infarction (MI) is crucial for preventing rupture of the ventricular wall, an exaggerated fibrotic response and reactive fibrosis outside the injured area are detrimental. Although metformin prevents adverse cardiac remodeling, as well as provides glycemic control, the underlying mechanisms remain poorly documented. This study describes the effect of mitochondrial NADPH oxidase 4 (mitoNox) and protein kinase C-alpha (PKCα) on the cardiac fibrosis and galectin 3 (Gal-3) expression. Randomly rats underwent MI, received metformin or saline solution. A model of biomechanical strain and co-culturewas used to enable cross talk between cardiomyocytes and fibroblasts. Long-term metformin treatment after MIwas associated with (1) a reduction in myocardial fibrosis and Gal-3 levels; (2) an increase in adenosine monophosphate-activated protein kinase (AMPK) α1/α2 levels; and (3) an inhibition of both mRNA expression and enzymatic activities of mitoNox and PKCα. These findings were replicated in the cellular model, where the silencing of AMPK expression blocked the ability of metformin to protect cardiomyocytes from strain. The use of specific inhibitors or small interference RNA provided evidence that PKCα is downstream of mitoNox, and that the activation of this pathway results in Gal-3 upregulation.The Gal-3 secreted by cardiomyocytes has a paracrine effect on cardiac fibroblasts, inducing their activation. In conclusion, a metformin-induced increase in AMPK improves myocardial remodeling post-MI, which is related to the inhibition of the mitoNox/PKCα/Gal-3 pathway. Manipulation of this pathway might offer new therapeutic options against adverse cardiac remodeling, in terms of preventing the activation of the present fibroblast population.