Up-regulation of Nrf2 is involved in FGF21-mediated fenofibrate protection against type 1 diabetic nephropathy

Salvianolic Acid A Protects the Kidney against Oxidative Stress by Activating the Akt/GSK-3β/Nrf2 Signaling Pathway and Inhibiting the NF-κB Signaling Pathway in 5/6 Nephrectomized Rats

Salvianolic acid A (SAA) is a bioactive polyphenol extracted from Salviae miltiorrhizae Bunge, which possesses a variety of pharmacological activities. In our previous study, we have demonstrated that SAA effectively attenuates kidney injury and inflammation in an established animal model of 5/6 nephrectomized (5/6Nx) rats. However, there has been limited research regarding the antioxidative effects of SAA on chronic kidney disease (CKD). Here, we examined the antioxidative effects and underlying mechanisms of SAA in 5/6Nx rats. The rats were injected with SAA (2.5, 5, and 10 mg·kg⁻¹·d⁻¹, ip) for 28 days. Biochemical, flow cytometry, and Western blot analyses showed that SAA significantly increased the activities of total superoxide dismutase (T-SOD), glutathione peroxidase (GPx), and catalase (CAT) and lowered the levels of malondialdehyde (MDA), reactive oxygen species (ROS), and NADPH oxidase 4 (NOX-4) in a dose-dependent manner in 5/6Nx rats and in H₂O₂-induced HK-2 cells in vitro. Moreover, SAA enhanced the activation of the protein kinase B/glycogen synthase kinase-3β/nuclear factor-erythroid-2-related factor 2 (Akt/GSK-3β/Nrf2) signaling pathway in a dose-dependent manner and subsequently increased the expression of heme oxygenase-1 (HO-1) in the kidney of 5/6Nx rats, which were consistent with those obtained in H₂O₂-induced HK-2 cells in vitro shown by Western blot analysis. Furthermore, SAA significantly increased the expression of intranuclear Nrf2 and HO-1 proteins compared to HK-2 cells stimulated by LPS on the one hand, which can be enhanced by QNZ to some extent; on the other hand, SAA significantly lowered the expression of p-NF-κB p65 and ICAM-1 proteins compared to HK-2 cells stimulated by H₂O₂, which can be abrogated by ML385 to some extent. In conclusion, our results demonstrated that SAA effectively protects the kidney against oxidative stress in 5/6Nx rats. One of the pivotal mechanisms for the protective effects of SAA on kidney injury was mainly related with its antioxidative roles by activating the Akt/GSK-3β/Nrf2 signaling pathway and inhibiting the NF-κB signaling pathway.

Fu Brick Tea Alleviates Chronic Kidney Disease of Rats with High Fat Diet Consumption through Attenuating Insulin Resistance in Skeletal Muscle

Fu brick tea is a unique post-fermented dark tea product which undergoes controlled fermentation by "golden flower" fungus Eurotium cristatum. This study examined the effects of Fu brick tea aqueous extract (FTE) to alleviate insulin resistance, chronic kidney disease (CKD), and its regulatory mechanism in high fat diet (HFD)-induced obese rats. Sixteen-week administration of FTE at 400 mg/kg bw in rats significantly antagonized HFD-induced insulin resistance and CKD with elevations in serum leptin, TC, TG, LDL-C, blood urea nitrogen, uric acid, and creatinine levels, respectively ( p < 0.05). FTE treatment decreased the glomerular area, the thickness of basement membrane of renal tubules, and kidney fibrosis in HFD-fed rats. FTE alleviated insulin resistance through down-regulation of SIRP-α expression and activation of the insulin signaling Akt/GLUT4, FoxO1, and mTOR/S6K1 pathways in skeletal muscle. Furthermore, FTE prevented the HFD-caused kidney dysfunction and lipid or collagen accumulation, which was accompanied by the inhibition of GSK-3β phosphorylation and the action of PI3K/Akt and nuclear accumulation of Nrf2 in kidney. These results indicated that FTE alleviated insulin resistance and CKD through modulating insulin signal transduction cascades in skeletal muscle and enhanced the Nrf2 expression in kidney.

Retinal Neurodegeneration as an Early Manifestation of Diabetic Eye Disease and Potential Neuroprotective Therapies

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is a major cause of visual impairment and blindness throughout the world. Microvascular changes have long been regarded central to disease pathogenesis. In recent years, however, retinal neurodegeneration is increasingly being hypothesized to occur prior to the vascular changes classically associated with DR and contribute to disease pathogenesis.

RECENT FINDINGS

There is growing structural and functional evidence from human and animal studies that suggests retinal neurodegeneration to be an early component of DR. Identification of new therapeutic targets is an ongoing area of research with several different molecules undergoing testing in animal models for their neuroprotective properties and for possible use in humans. Retinal neurodegeneration may play a central role in DR pathogenesis. As new therapies are developed, it will be important to develop criteria for clinically defining retinal neurodegeneration. A standardization of the methods for monitoring neurodegeneration along with more sensitive means of detecting preclinical damage is also needed.

Role of sirtuin-1 in diabetic nephropathy

Diabetic nephropathy (DN) is a research priority for scientists around the world because of its high prevalence and poor prognosis. Although several mechanisms have been shown to be involved in its pathogenesis and many useful drugs have been developed, the management of DN remains challenging. Increasing amounts of evidence show that silent information regulator 2 homolog 1 (sirtuin-1), a nicotinamide adenine dinucleotide (NAD+)–dependent protein deacetylase, plays a crucial role in the pathogenesis and development of DN. Clinical data show that gene polymorphisms of sirtuin-1 affect patient vulnerability to DN. In addition, upregulation of sirtuin-1 attenuates DN in various experimental models of diabetes and in renal cells, including podocytes, mesangial cells, and renal proximal tubular cells, incubated with high concentrations of glucose or advanced glycation end products. Mechanistically, sirtuin-1 has its renoprotective effects by modulating metabolic homeostasis and autophagy, resisting apoptosis and oxidative stress, and inhibiting inflammation through deacetylation of histones and the transcription factors p53, forkhead box group O, nuclear factor-κB, hypoxia-inducible factor-1α, and others. Furthermore, some microRNAs have been implicated in the progression of DN because they target sirtuin-1 mRNA. Several synthetic drugs and natural compounds have been identified that upregulate the expression and activity of sirtuin-1, which protects against DN. The present review will summarize advances in knowledge regarding the role of sirtuin-1 in the pathogenesis of DN. The available evidence implies that sirtuin-1 has great potential as a clinical target for the prevention and treatment of diabetes.

Salutary effect of fenofibrate on type 1 diabetic retinopathy via inhibiting oxidative stress-mediated Wnt/β-catenin pathway activation

Fenofibrate has been shown to have therapeutic effects on diabetic retinopathy (DR). Our previous studies demonstrated that the oxidative stress-activated Wnt/β-catenin pathway plays a pathogenic role in diabetic complications. In the present study, we evaluate the effect and mechanism of fenofibrate on regulating the oxidative stress-activated Wnt/β-catenin pathway by using the genetic type 1 diabetes model of C57BL/6J-Ins2^Akita mice and high glucose (HG)-treated ARPE-19. Our results demonstrated that retinal phosphorylation of LRP6 and nuclear β-catenin were increased in C57BL/6J-Ins2^Akita mice suggesting activation of Wnt/β-catenin signaling. Meanwhile, C57BL/6J-Ins2^Akita showed upregulation of oxidant enzyme Nox4 and Nox2 and downregulation of antioxidant enzyme SOD1 and SOD2. All these alterations were reversed in C57BL/6J-Ins2^Akita mice with fenofibrate treatment. Moreover, fenofibrate significantly ameliorated diabetes-induced retinal vascular leakage in C57BL/6J-Ins2^Akita mice. In cultured ARPE-19, fenofibrate decreased HG-induced Nox2 and Nox4 upregulation, attenuated SOD1 and SOD2 downregulation and inhibited LRP6 phosphorylation. Moreover, activation of Wnt/β-catenin by Wnt3a conditional medium (WCM) reduced SOD1 and SOD2 and did not affect Nox2 and Nox4. Fenofibrate suppressed WCM-induced LRP6 phosphorylation and reversed SOD downregulation. Importantly, Nox4 overexpression directly phosphorylated LPR6 in ARPE19; conversely, Nox4 knockdown suppressed HG-induced LPR6 phosphorylation. Taken together, Nox-mediated oxidative stress contributes to Wnt/β-catenin activation in DR. Fenofibrate ameliorated DR through coordinate attenuation of oxidative stress and blockade of Wnt/β-catenin signaling.

Genetic Variants Flanking the FGF21 Gene Were Associated with Renal Function in Chinese Patients with Type 2 Diabetes

AIMS

Fibroblast growth factor 21 (FGF21) is closely linked with metabolic disorders including diabetes. Evidences suggested that FGF21 may play a protective role against diabetic kidney disease (DKD). However, the relationship between genetic variants in the FGF21 gene region and DKD remains unknown. In our study, we aimed to investigate the association of genetic variations in this gene region with DKD and DKD-related clinical traits.

MATERIALS AND METHODS

We recruited 1340 Han Chinese participants with type 2 diabetes, including 596 DKD patients and 744 patients who was diagnosed with diabetes for more than 5 years but did not progress to DKD. Three single-nucleotide polymorphisms were selected (rs2071699, rs838136, and rs499765) and genotyped. The association between these SNPs and DKD as well as DKD-related quantitative traits was analyzed.

RESULTS

We did not find any significant association between these SNPs and susceptibility to DKD in the present study. However, a significant association with estimated glomerular filtration rate (eGFR) was detected: in the non-DKD group, rs838136 was significantly associated with eGFR under an additive model (β = 0.013 ± 0.006, P = 0.0295, β was calculated for log₁₀eGFR) as well as a recessive model (P = 0.0385) and rs499765 was associated with eGFR under a dominant model (P = 0.0411) and in the DKD group, rs499765 showed a trend toward association with eGFR under an additive model (β = -0.022 ± 0.012, P = 0.0820, β was calculated for log₁₀eGFR) and showed a significant association with eGFR under a dominant model (P = 0.0182).

CONCLUSIONS

Our findings indicated that genetic variations adjacent to FGF21 were associated with eGFR in Chinese diabetic patients.

Clopidogrel Reduces Fibronectin Accumulation and Improves Diabetes-Induced Renal Fibrosis

Hyperglycemia-induced renal fibrosis causes end-stage renal disease. Clopidogrel, a platelet inhibitor, is often administered to decrease cardiovascular events in diabetic patients. We investigated whether clopidogrel can reduce diabetes-induced renal fibrosis in a streptozotocin-induced type 1 diabetes murine model and fibronectin involvement in this protective response. Diabetic and age-matched controls were sacrificed three months after the onset of diabetes, and additional controls and diabetic animals were further treated with clopidogrel or vehicle for three months. Diabetes induced renal morphological changes and fibrosis after three months. Clopidogrel, administered during the last three months, significantly decreased blood glucose, collagen and fibronectin expression compared to vehicle-treated diabetic mice. Diabetes increased TGF-β expression, inducing fibrosis via Smad-independent pathways, MAP kinases, and Akt activation at three months but returned to baseline at six months, whereas the expression of fibronectin and collagen remained elevated. Our results suggest that activation of TGF-β, CTGF, and MAP kinases are early profibrotic signaling events, resulting in significant fibronectin accumulation at the early time point and returning to baseline at a later time point. Akt activation at the three-month time point may serve as an adaptive response in T1D. Mechanisms of clopidogrel therapeutic effect on the diabetic kidney remain to be investigated as this clinically approved compound could provide novel approaches to prevent diabetes-induced renal disease, therefore improving patients' survival.

Fibroblast growth factor 21 facilitates peripheral nerve regeneration through suppressing oxidative damage and autophagic cell death

Seeking for effective drugs which are beneficial to facilitating axonal regrowth and elongation after peripheral nerve injury (PNI) has gained extensive attention. Fibroblast growth factor 21 (FGF21) is a metabolic factor that regulates blood glucose and lipid homeostasis. However, there is little concern for the potential protective effect of FGF21 on nerve regeneration after PNI and revealing related molecular mechanisms. Here, we firstly found that exogenous FGF21 administration remarkably promoted functional and morphologic recovery in a rat model of sciatic crush injury, manifesting as persistently improved motor and sensory function, enhanced axonal remyelination and regrowth and accelerated Schwann cells (SCs) proliferation. Furthermore, local FGF21 application attenuated the excessive activation of oxidative stress, which was accompanied with the activation of nuclear factor erythroid‐2‐related factor 2 (Nrf‐2) transcription and extracellular regulated protein kinases (ERK) phosphorylation. We detected FGF21 also suppressed autophagic cell death in SCs. Additionally, treatment with the ERK inhibitor U0126 or autophagy inhibitor 3‐MA partially abolishes anti‐oxidant effect and reduces SCs death. Taken together, these results indicated that the role of FGF21 in remyelination and nerve regeneration after PNI was probably related to inhibit the excessive activation of ERK/Nrf‐2 signalling‐regulated oxidative stress and autophagy‐induced cell death. Overall, our work suggests that FGF21 administration may provide a new therapy for PNI.

Nrf2, a novel molecular target to reduce type 1 diabetes associated secondary complications: The basic considerations

Oxidative stress and inflammation are the mediators of diabetes and related secondary complications. Oxidative stress arises because of the excessive production of reactive oxygen species and diminished antioxidant production due to impaired Nrf2 activation, the master regulator of endogenous antioxidant. It has been established from various animal models that the transcription factor Nrf2 provides cytoprotection, ameliorates oxidative stress, inflammation and delays the progression of diabetes and its associated complications. Whereas, deletion of the transcription factor Nrf2 amplifies tissue level pathogenic alterations. In addition, Nrf2 also regulates the expression of numerous cellular defensive genes and protects against oxidative stress-mediated injuries in diabetes. The present review provides an overview on the role of Nrf2 in type 1 diabetes and explores if it could be a potential target for the treatment of diabetes and related complications. Further, the rationality of different agent's intervention has been discussed to mitigate organ damages induced by diabetes.

Protective role of fenofibrate in sepsis-induced acute kidney injury in BALB/c mice

Acute kidney injury (AKI) is a severe complication of sepsis, which largely contributes to the associated high mortality rate. Fenofibrate, a peroxisome proliferator activated receptor α (PPARα) agonist, has received considerable attention because of its effects related to renal damage-related energy metabolism and inflammation. The present study investigated the effects of fenofibrate on sepsis-associated AKI in BALB/c mice subjected to caecal ligation and puncture (CLP). Eight-week-old male BALB/c mice were divided into four groups: control group, fenofibrate group, caecal ligation and puncture (CLP) group, and fenofibrate + CLP group. CLP was performed after mice were gavaged with fenofibrate for 2 weeks. After 48 hours, we measured the histopathological alterations of the kidney tissue and plasma levels of serum creatinine (CRE), neutrophil gelatinase-associated lipocalin (NGAL), reactive oxygen species (ROS), ATP, and ADP. We evaluated PPARα and P53 protein levels as well as interleukin (IL)-1β, IL-6, and tumour necrosis factor-α mRNA levels. Our results showed that administering fenofibrate significantly reduced kidney histological alterations caused by CLP. Fenofibrate inhibited the plasma levels of ROS, CRE, NGAL, and increased the ATP/ADP ratio. Fenofibrate significantly inhibited elevations in P53, IL-1β, IL-6, and tumour necrosis factor-α expression. The results suggest that fenofibrate administration effectively modulates energy metabolism and may be a novel approach to treat sepsis-induced renal damage.

The role of FGF21 in type 1 diabetes and its complications

Data from the International Diabetes Federation show that 347 million people worldwide have diabetes, and the incidence is still rising. Although the treatment of diabetes has been advanced, the current therapeutic options and outcomes, e.g. complications, are yet far from ideal. Therefore, an urgent need exists for the development of more effective therapies. Numerous studies have been conducted to establish and confirm whether FGF21 exerts beneficial effects on obesity and diabetes along with its complications. However, most of the studies associated with FGF21 were conducted in the patients with type 2 diabetes. Subsequently, the effect of FGF21 in the prevention or treatment of type 1 diabetes and its complications were also increasingly reported. In this review, we summarize the findings available on the function of FGF21 and the status of FGF21's treatment for type 1 diabetes. Based on the available information, we found that FGF21 exerts a hypoglycemic effect, restores the function of brown fat, and inhibits various complications in type 1 diabetes patients. Although these features are predominantly similar to those observed in the studies that showed the beneficial impact of FGF21 on type 2 diabetes and its complications, there are also certain distinct features and findings that may be of provide important and instructive for us to understand mechanistic insights and further promote the prevention and treatment of type 1 diabetes.

Fibroblast Growth Factor 21 Protects Photoreceptor Function in Type 1 Diabetic Mice

Retinal neuronal abnormalities occur before vascular changes in diabetic retinopathy. Accumulating experimental evidence suggests that neurons control vascular pathology in diabetic and other neovascular retinal diseases. Therefore, normalizing neuronal activity in diabetes may prevent vascular pathology. We investigated whether fibroblast growth factor 21 (FGF21) prevented retinal neuronal dysfunction in insulin-deficient diabetic mice. We found that in diabetic neural retina, photoreceptor rather than inner retinal function was most affected and administration of the long-acting FGF21 analog PF-05231023 restored the retinal neuronal functional deficits detected by electroretinography. PF-05231023 administration protected against diabetes-induced disorganization of photoreceptor segments seen in retinal cross section with immunohistochemistry and attenuated the reduction in the thickness of photoreceptor segments measured by optical coherence tomography. PF-05231023, independent of its downstream metabolic modulator adiponectin, reduced inflammatory marker interleukin-1β (IL-1β) mRNA levels. PF-05231023 activated the AKT-nuclear factor erythroid 2-related factor 2 pathway and reduced IL-1β expression in stressed photoreceptors. PF-05231023 administration did not change retinal expression of vascular endothelial growth factor A, suggesting a novel therapeutic approach for the prevention of early diabetic retinopathy by protecting photoreceptor function in diabetes.

MDM2 controls NRF2 antioxidant activity in prevention of diabetic kidney disease

Oxidative stress and P53 contribute to the pathogenesis of diabetic kidney disease (DKD). Nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of cellular antioxidant defense system, is negatively regulated by P53 and prevents DKD. Recent findings revealed an important role of mouse double minute 2 (MDM2) in protection against DKD. However, the mechanism remained unclear. We hypothesized that MDM2 enhances NRF2 antioxidant signaling in DKD given that MDM2 is a key negative regulator of P53. The MDM2 inhibitor nutlin3a elevated renal P53, inhibited NRF2 signaling and induced oxidative stress, inflammation, fibrosis, DKD-like renal pathology and albuminuria in the wild-type (WT) non-diabetic mice. These effects exhibited more prominently in nutlin3a-treated WT diabetic mice. Interestingly, nutlin3a failed to induce greater renal injuries in the Nrf2 knockout (KO) mice under both the diabetic and non-diabetic conditions, indicating that NRF2 predominantly mediates MDM2's action. On the contrary, P53 inhibition by pifithrin-α activated renal NRF2 signaling and the expression of Mdm2, and attenuated DKD in the WT diabetic mice, but not in the Nrf2 KO diabetic mice. In high glucose-treated mouse mesangial cells, P53 gene silencing completely abolished nutlin3a's inhibitory effect on NRF2 signaling. The present study demonstrates for the first time that MDM2 controls renal NRF2 antioxidant activity in DKD via inhibition of P53, providing MDM2 activation and P53 inhibition as novel strategies in the management of DKD.

Anticancer Properties of Fenofibrate: A Repurposing Use

Cancer is a leading cause of death throughout the world, and cancer therapy remains a big medical challenge in terms of both its therapeutic efficacy and safety. Therefore, to find out a safe anticancer drug has been long goal for oncologist and medical scientists. Among clinically used medicines with no or little toxicity, fenofibrate is a drug of the fibrate class that plays an important role in lowering the levels of serum cholesterol and triglycerides while elevating the levels of high-density lipoproteins. Recently, several studies have implied that fenofibrate may exert anticancer effects via a variety of pathways involved in apoptosis, cell-cycle arrest, invasion, and migration. Given the great potential that fenofibrate may have anticancer effects, this review was to investigate all published works which directly or indirectly support the anticancer activity of fenofibrate. These studies provide evidence that fenofibrate exerted antitumor effects in several human cancer cell lines, such as breast, liver, glioma, prostate, pancreas, and lung cancer cell lines. Among these studies some have further confirmed the possibility and efficacy of fenofibrate anticancer in xenograft mouse models. In the last part of this review, we also discuss the potential mechanisms of action of fenofibrate based on the available information. Overall, we may repurpose fenofibrate as an anticancer drug in cancer treatment, which urgently need further and comprehensively investigated.

Gastrodin and Isorhynchophylline Synergistically Inhibit MPP+-Induced Oxidative Stress in SH-SY5Y Cells by Targeting ERK1/2 and GSK-3β Pathways: Involvement of Nrf2 Nuclear Translocation

The pathogenesis of Parkinson's disease (PD) is multifactorial event. Combination therapies might be more effective in controlling the disease. Thus, the studies reported were designed to test the hypothesis that gastrodin (GAS)-induced de novo synthesis of nuclear factor E2-related factor 2 (Nrf2) and isorhynchophylline (IRN) inhibition of Nrf2 nuclear export contribute to their additive or synergistic neuroprotective effect. Here, we have demonstrated that the combination of GAS and IRN (GAS/IRN) protects SH-SY5Y cells against 1-methyl-4-phenylpyridinium (MPP⁺) toxicity in a synergistic manner. Concomitantly, GAS/IRN led to a statistically significant reduction of oxidative stress, as assessed by reactive oxygen species (ROS) and lipid hydroperoxides (LPO), and enhancement of both glutathione (GSH) and thioredoxin (Trx) systems compared with treatment with either agent alone in MPP⁺-challenged SH-SY5Y cells. Interestingly, GAS but not IRN activated extracellular signal-regulated kinases 1 and 2 (ERK1/2), leading to a increase in de novo synthesis of Nrf2 and nuclear import of Nrf2. Simultaneously, IRN but not GAS suppressed both constitutive glycogen synthase kinase (GSK)-3β and Fyn activation, which inhibited nuclear export of Nrf2. Importantly, simultaneous inhibition of GSK-3β pathway by IRN and activation of ERK1/2 pathway by GAS synergistically induced accumulation of Nrf2 in the nucleus in SH-SY5Y cells challenged with MPP⁺. Furthermore, the activation of the ERK1/2 pathway and inhibition of GSK-3β pathway by GAS/IRN are mediated by independent mechanisms. Collectively, these novel findings suggest an in vitro model of synergism between IRN and GAS in the induction of neuroprotection warrant further investigations in vivo.

Mitochondrial dysfunction in diabetic kidney disease

Globally, diabetes is the leading cause of chronic kidney disease and end-stage renal disease, which are major risk factors for cardiovascular disease and death. Despite this burden, the factors that precipitate the development and progression of diabetic kidney disease (DKD) remain to be fully elucidated. Mitochondrial dysfunction is associated with kidney disease in nondiabetic contexts, and increasing evidence suggests that dysfunctional renal mitochondria are pathological mediators of DKD. These complex organelles have a broad range of functions, including the generation of ATP. The kidneys are mitochondrially rich, highly metabolic organs that require vast amounts of ATP for their normal function. The delivery of metabolic substrates for ATP production, such as fatty acids and oxygen, is altered by diabetes. Changes in metabolic fuel sources in diabetes to meet ATP demands result in increased oxygen consumption, which contributes to renal hypoxia. Inherited factors including mutations in genes that impact mitochondrial function and/or substrate delivery may also be important risk factors for DKD. Hence, we postulate that the diabetic milieu and inherited factors that underlie abnormalities in mitochondrial function synergistically drive the development and progression of DKD.

Fibroblast growth factor-21 prevents diabetic cardiomyopathy via AMPK-mediated antioxidation and lipid-lowering effects in the heart

Our previous studies showed that both exogenous and endogenous FGF21 inhibited cardiac apoptosis at the early stage of type 1 diabetes. Whether FGF21 induces preventive effect on type 2 diabetes-induced cardiomyopathy was investigated in the present study. High-fat-diet/streptozotocin-induced type 2 diabetes was established in both wild-type (WT) and FGF21-knockout (FGF21-KO) mice followed by treating with FGF21 for 4 months. Diabetic cardiomyopathy (DCM) was diagnosed by significant cardiac dysfunction, remodeling, and cardiac lipid accumulation associated with increased apoptosis, inflammation, and oxidative stress, which was aggravated in FGF21-KO mice. However, the cardiac damage above was prevented by administration of FGF21. Further studies demonstrated that the metabolic regulating effect of FGF21 is not enough, contributing to FGF21-induced significant cardiac protection under diabetic conditions. Therefore, other protective mechanisms must exist. The in vivo cardiac damage was mimicked in primary neonatal or adult mouse cardiomyocytes treated with HG/Pal, which was inhibited by FGF21 treatment. Knockdown of AMPKα1/2, AKT2, or NRF2 with their siRNAs revealed that FGF21 protected cardiomyocytes from HG/Pal partially via upregulating AMPK–AKT2–NRF2-mediated antioxidative pathway. Additionally, knockdown of AMPK suppressed fatty acid β-oxidation via inhibition of ACC–CPT-1 pathway. And, inhibition of fatty acid β-oxidation partially blocked FGF21-induced protection in cardiomyocytes. Further, in vitro and in vivo studies indicated that FGF21-induced cardiac protection against type 2 diabetes was mainly attributed to lipotoxicity rather than glucose toxicity. These results demonstrate that FGF21 functions physiologically and pharmacologically to prevent type 2 diabetic lipotoxicity-induced cardiomyopathy through activation of both AMPK–AKT2–NRF2-mediated antioxidative pathway and AMPK–ACC–CPT-1-mediated lipid-lowering effect in the heart.

Protection by dimethyl fumarate against diabetic cardiomyopathy in type 1 diabetic mice likely via activation of nuclear factor erythroid-2 related factor 2

Oxidative stress and inflammation play key roles in the development of diabetic cardiomyopathy (DCM). Dimethyl fumarate (DMF), an FDA approved medicine for relapsing multiple sclerosis, has manifested its antioxidant and anti-inflammatory function mostly in the central nervous system. In this study, we investigated whether DMF could attenuate the development of DCM. Type 1 diabetes mouse model was established using multiple low-dose streptozotocin, and the diabetic mice were treated with DMF (10 mg/kg body weight) for 3 months. Cardiac functions were determined using echocardiography. Oxidative stress, pro-inflammatory cytokines and pro-fibrotic markers were determined with commercially available kits, real-time quantitative PCR or western blot techniques. DCM was characterized by diminished cardiac function, accompanied by oxidative stress and enhanced expression of pro-inflammatory cytokines. Diabetic cardiac tissue exhibited marked fibrosis, revealed by extracellular matrix deposition as determined by Sirius red staining of the myocardial tissues. Furthermore, Nrf2 and its downstream effectors were repressed in diabetic myocardium. On the contrary, diabetic animals treated with DMF exhibited blunted oxidative stress, inflammation, fibrosis and this correlated with Nrf2 activation. Our findings suggest that DMF could potentially thwart diabetes-induced myocardial tissue injury, likely via activation of Nrf2 function, providing firm impetus for future repurposing of DMF in the management of DCM.

Fenofibrate ameliorates diabetic retinopathy by modulating Nrf2 signaling and NLRP3 inflammasome activation

Oxidative stress and neuroinflammation contribute significantly to the development and progression of diabetic retinopathy. Fenofibrate has received great attention as it benefits diabetic patients by reducing retinal laser requirement. Nuclear factor erythroid-2-related factor 2 (Nrf2) is a master regulator of anti-oxidative defense. Activation of nucleotide binding domain, leucine-rich repeat-containing receptor (NLR), pyrin domain-containing 3 (NLRP3) inflammasome plays a pivotal role in neuroinflammation. The purpose of this study is to determine whether fenofibrate protects retinas from oxidative damage and neuroinflammation via modulating the Nrf2 pathway and blocking NLRP3 inflammasome activation during diabetes. Diabetes is induced by intraperitoneal injection of streptozotocin in mice. Fenofibrate was given to mice in rodent chow. Upregulation of Nrf2 and NLRP3 inflammasome, enhanced ROS formation, and increased leukostasis and vascular leakage were observed in diabetic mouse retinas. Notably, Nrf2 and Caspase-1 were mainly colocalized with glutamine synthetase, one of the Mȕller cell markers. Fenofibrate further increased the expression of Nrf2 and its target gene NQO-1 and HO-1 and reduced ROS formation in diabetic retinas. In addition, retinal expression of NLRP3, Caspase-1 p20, IL-1β p17, and ICAM-1 were dramatically increased in vehicle-treated diabetic mice, which were abolished by fenofibrate intervention. Moreover, fenofibrate treatment also attenuated diabetes-induced retinal leukostasis and vascular leakage in mice. Taken together, fenofibrate attenuates oxidative stress and neuroinflammation in diabetic retinas, which is at least partially through modulating Nrf2 expression and NLRP3 inflammasome activation.

Fibroblast growth factor 21 in chronic kidney disease

The association between fibroblast growth factor 21 (FGF21) and kidney function has been extensively studied in recent years in both animal and human studies. However, the exact functional role of FGF21 in the kidney remains unclear. Previous animal studies have shown that administration of FGF21 ameliorates kidney function, morphological glomerular abnormalities, dyslipidemia, hyperglycemia, insulin resistance, oxidative stress and obesity. In human studies, FGF21 levels negatively correlated with estimated glomerular filtration rate. FGF21 levels were elevated in patients with end-stage renal disease. The elevation of FGF21 levels in presence of kidney disease has also raised questions as to whether FGF21 is a potential biomarker for detecting a decline in renal function. In recent clinical trials, an FGF21 analogue reduced insulin levels and body weight, and ameliorated dyslipidemia in patients with type 2 diabetes mellitus and obesity, all of which are well-known risk factors for kidney disease. Thus, FGF21 may be a potential therapeutic target for the treatment of kidney disease, although adverse side effects should also be considered when administering FGF21 since FGF21 may affect bone development and reproduction. This review will assess current knowledge on the relationship between FGF21 and kidney function.

Epigenetics and type 1 diabetes: mechanisms and translational applications

Type 1 diabetes (T1D) is an irreversible degenerative disease with severe complications such as heart disease, nephropathy, neuropathy, and retinopathy. Although exogenous insulin administration is a life-saving therapy, it does not cure the disease. This review addresses the epigenetic mechanisms responsible for the development of T1D and discusses epigenetic-based strategies for prevention and treatment of the disease. We describe novel epigenetic biomarkers for the identification of susceptible individuals and the establishment of innovative therapies with epidrugs and cell therapy to regenerate the lost β-cells. Despite the wealth of promising data regarding the potential benefits of epigenetic tools to reduce the burden of T1D, clinical trials are still very few, and this issue needs to be resolved in the near future.

Bamboo leaf extract ameliorates diabetic nephropathy through activating the AKT signaling pathway in rats

Diabetic nephropathy (DN) is one of the most severe diabetic complication and it is becoming become a worldwide epidemic, accounting for approximately one-third of all case of end-stage renal disease. However, the underlying mechanism and strategy to alleviate renal injury remain unclear. In the present study, we assessed the protective effect of bamboo leaf extract on the DN, and investigated the underlying mechanism by which bamboo leaf extract ameliorating DN. Diabetic rats were induced by 4 weeks high sugar and high fat diet, and then injected a single dose of STZ (35mg/kg) into abdominal cavity. Different dose of bamboo extract (50mg/kg, 100mg/kg and 200mg/kg) were orally administered every day for a period of 12 weeks. Body weight, blood glucose, glycosylated hemoglobin A1c (HbAlc), blood urea nitrogen (BUN), serum creatinine (Scr), and 24-hour urinary protein (24 h-UP) were assessed. Total superoxide dismutase (T-SOD) activity and MDA (methane dicarboxylic aldehyde, MDA) level were tested by assay kit. Microstructural changes were observed by hematoxylin-eosin (HE) staining and electron microscopy. Expression of phosphorylated ser/thr protein kinase (P-AKT), phosphorylated glycogen synthase kinase-3 beta (P-GSK-3β), B cell lymphoma/leukemia 2-associated X protein (BAX) and cleaved-cysteinyl aspartate-specific proteinase-3 (Cleaved Caspase-3) were measured by Western-Blotting (WB). Results showed that diabetic rats had weight loss, high blood glucose, HbAlc, BUN, Scr and 24-UP and T-SOD activity were increased and MDA level was decreased in diabetic rats. Moreover, hyperglycemia could injury renal tissue ultrastructure, inhibit P-AKT level and increase P-GSK-3β, BAX and Cleaved Caspase-3 levels in rats. However, bamboo leaf extract treatment could reduce body weight loss, BUN, Scr, 24 h-UP and MDA level, improve T-SOD activity and alleviate renal injury in diabetic rats. Furthermore, bamboo leaf extract increased P-AKT level, decreased P-GSK-3β, BAX and Cleaved Caspase-3 levels in STZ-diabetic rats. In conclusion, our study suggested that bamboo leaf extract ameliorated DN in diabetic rats, and this protective effect is possibly related to suppressing oxidative stress through activating AKT signaling pathway. Bamboo leaf extract treatment may be a potential promising therapy for DN.

Elevating CXCR7 Improves Angiogenic Function of EPCs via Akt/GSK-3β/Fyn-Mediated Nrf2 Activation in Diabetic Limb Ischemia

RATIONALE

Endothelial progenitor cells (EPCs) respond to stromal cell-derived factor 1 (SDF-1) through chemokine receptors CXCR7 and CXCR4. Whether SDF-1 receptors involves in diabetes mellitus-induced EPCs dysfunction remains unknown.

OBJECTIVE

To determine the role of SDF-1 receptors in diabetic EPCs dysfunction.

METHODS AND RESULTS

CXCR7 expression, but not CXCR4 was reduced in EPCs from db/db mice, which coincided with impaired tube formation. Knockdown of CXCR7 impaired tube formation of EPCs from normal mice, whereas upregulation of CXCR7 rescued angiogenic function of EPCs from db/db mice. In normal EPCs treated with oxidized low-density lipoprotein or high glucose also reduced CXCR7 expression, impaired tube formation, and increased oxidative stress and apoptosis. The damaging effects of oxidized low-density lipoprotein or high glucose were markedly reduced by SDF-1 pretreatment in EPCs transduced with CXCR7 lentivirus but not in EPCs transduced with control lentivirus. Most importantly, EPCs transduced with CXCR7 lentivirus were superior to EPCs transduced with control lentivirus for therapy of ischemic limbs in db/db mice. Mechanistic studies demonstrated that oxidized low-density lipoprotein or high glucose inhibited protein kinase B and glycogen synthase kinase-3β phosphorylation, nuclear export of Fyn and nuclear localization of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), blunting Nrf2 downstream target genes heme oxygenase-1, NAD(P)H dehydrogenase (quinone 1) and catalase, and inducing an increase in EPC oxidative stress. This destructive cascade was blocked by SDF-1 treatment in EPCs transduced with CXCR7 lentivirus. Furthermore, inhibition of phosphatidylinositol 3-kinase/protein kinase B prevented SDF-1/CXCR7-mediated Nrf2 activation and blocked angiogenic repair. Moreover, Nrf2 knockdown almost completely abolished the protective effects of SDF-1/CXCR7 on EPC function in vitro and in vivo.

CONCLUSIONS

Elevated expression of CXCR7 enhances EPC resistance to diabetes mellitus-induced oxidative damage and improves therapeutic efficacy of EPCs in treating diabetic limb ischemia. The benefits of CXCR7 are mediated predominantly by a protein kinase B/glycogen synthase kinase-3β/Fyn pathway via increased activity of Nrf2.

Role of Nuclear Factor Erythroid 2-Related Factor 2 in Diabetic Nephropathy

Diabetic nephropathy (DN) is manifested as increased urinary protein level, decreased glomerular filtration rate, and final renal dysfunction. DN is the leading cause of end-stage renal disease worldwide and causes a huge societal healthcare burden. Since satisfied treatments are still limited, exploring new strategies for the treatment of this disease is urgently needed. Oxidative stress takes part in the initiation and development of DN. In addition, nuclear factor erythroid 2-related factor 2 (Nrf2) plays a key role in the cellular response to oxidative stress. Thus, activation of Nrf2 seems to be a new choice for the treatment of DN. In current review, we discussed and summarized the therapeutic effects of Nrf2 activation on DN from both basic and clinical studies.

ISN Forefronts Symposium 2015: Nuclear Receptors and Diabetic Nephropathy

Diabetic nephropathy (DN) is the major reason for end stage renal disease in the western world. Patients with DN developed more severe cardiovascular complications with worse prognosis. In spite of tight blood pressure and glucose control through applying angiotensin II receptor antagonism, angiotensin receptor inhibitors and even direct renin inhibitors, the progression and development of DN has continued to accelerate. Nuclear receptors are, with few exceptions, ligand-depended transcription factors some of which modulate genes involved in the transportation and metabolism of carbohydrate or lipid, and inflammation. Considering the diverse biological functions of nuclear receptors, efforts have been made to explore their contributions to the pathogenesis of DN and potential therapeutic strategies. This review is mainly focused on the association between various nuclear receptors and the pathogenesis of DN, the potential beneficial effects of targeting these receptors for preventing the progress of DN, and the important role that nuclear receptors may play in future therapeutic strategies for DN.

Methionine restriction improves renal insulin signalling in aged kidneys

Dietary methionine restriction (MR) leads to loss of adiposity, improved insulin sensitivity and lifespan extension. The possibility that dietary MR can protect the kidney from age-associated deterioration has not been addressed. Aged (10-month old) male and female mice were placed on a MR (0.172% methionine) or control diet (0.86% methionine) for 8-weeks and blood glucose, renal insulin signalling, and gene expression were assessed. Methionine restriction lead to decreased blood glucose levels compared to control-fed mice, and enhanced insulin-stimulated phosphorylation of PKB/Akt and S6 in kidneys, indicative of improved glucose homeostasis. Increased expression of lipogenic genes and downregulation of PEPCK were observed, suggesting that kidneys from MR-fed animals are more insulin sensitive. Interestingly, renal gene expression of the mitochondrial uncoupling protein UCP1 was upregulated in MR-fed animals, as were the anti-ageing and renoprotective genes Sirt1, FGF21, klotho, and β-klotho. This was associated with alterations in renal histology trending towards reduced frequency of proximal tubule intersections containing vacuoles in mice that had been on dietary MR for 190days compared to control-fed mice, which exhibited a pre-diabetic status. Our results indicate that dietary MR may offer therapeutic potential in ameliorating the renal functional decline related to ageing and other disorders associated with metabolic dysfunction by enhancing renal insulin sensitivity and renoprotective gene expression.