Effects of different exercise durations on Keap1-Nrf2-ARE pathway activation in mouse skeletal muscle

Effects of Sulforaphane Treatment on Skeletal Muscle from Exhaustive Exercise-Induced Inflammation and Oxidative Stress Through the Nrf2/HO-1 Signaling Pathway

Skeletal muscle is primarily involved in exercise performance and health promotion. Sulforaphane (SFN) is a naturally occurring isothiocyanate that indirectly activates the transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2), thus inducing the expression of Nrf2 target genes, including antioxidant enzymes. This study aimed to identify the effects of a single dose of SFN administration on exhaustive exercise-induced inflammation and oxidative stress in skeletal muscle tissue and elucidate the underlying mechanisms. Thirty-six mice were divided into four groups: control, SFN, exercise (Ex), and SFN + Ex. The SFN group and SFN + Ex group received SFN orally (50 mg/kg body weight) 2 h before the running test. Exercise significantly reduced plasma glucose levels, while the SFN-treated group exhibited a smaller reduction. Acute exhaustive exercise increased the expression of pro-inflammatory cytokines in muscle tissue, while the SFN + Ex group exhibited significantly reduced expression of pro-inflammatory cytokines. The gene expression of Nrf2 and its target enzymes, including heme oxygenase (HO)-1, superoxide dismutase (SOD)-1, catalase (CAT), and glutathione peroxidase (GPx)-1, was measured in the gastrocnemius and soleus muscle tissue. Compared with the Ex group, the SFN + Ex group showed upregulated expression of all these parameters, including Nrf2. SFN treatment reduced acute exhaustive exercise-induced oxidative stress and inflammation via activation of the Nrf2/HO-1 signaling pathway.

Unlocking peak performance: The role of Nrf2 in enhancing exercise outcomes and training adaptation in humans

Since the discovery of the nuclear factor erythroid-derived 2-like 2 (Nrf2) transcription factor thirty years ago, it has been shown that it regulates more than 250 genes involved in a multitude of biological processes, including redox balance, mitochondrial biogenesis, metabolism, detoxification, cytoprotection, inflammation, immunity, autophagy, cell differentiation, and xenobiotic metabolism. In skeletal muscle, Nrf2 signalling is primarily activated in response to perturbation of redox balance by reactive oxygen species or electrophiles. Initial investigations into human skeletal muscle Nrf2 responses to exercise, dating back roughly a decade, have consistently indicated that exercise-induced ROS production stimulates Nrf2 signalling. Notably, recent studies employing Nrf2 knockout mice have revealed impaired skeletal muscle contractile function characterised by reduced force output and increased fatigue susceptibility compared to wild-type counterparts. These deficiencies partially stem from diminished basal mitochondrial respiratory capacity and an impaired capacity to upregulate specific mitochondrial proteins in response to training, findings corroborated by inducible muscle-specific Nrf2 knockout models. In humans, baseline Nrf2 expression in skeletal muscle correlates with maximal oxygen uptake and high-intensity exercise performance. This manuscript delves into the mechanisms underpinning Nrf2 signalling in response to acute exercise in human skeletal muscle, highlighting the involvement of ROS, antioxidants and Keap1/Nrf2 signalling in exercise performance. Furthermore, it explores Nrf2's role in mediating adaptations to chronic exercise and its impact on overall exercise performance. Additionally, the influence of diet and certain supplements on basal Nrf2 expression and its role in modulating acute and chronic exercise responses are briefly addressed.

The impact of aerobic exercise timing on BMAL1 protein expression and antioxidant responses in skeletal muscle of mice

It is well known that the adaptations of muscular antioxidant system to aerobic exercise depend on the frequency, intensity, duration, type of the exercise. Nonetheless, the timing of aerobic exercise, related to circadian rhythms or biological clock, may also affect the antioxidant defense system, but its impact remains uncertain. Bain and muscle ARNT-like 1 (BMAL1) is the core orchestrator of molecular clock, which can maintain cellular redox homeostasis by directly controlling the transcriptional activity of nuclear factor erythroid 2-related factor 2 (NRF2). So, our research objective was to evaluate the impacts of aerobic exercise training at various time points of the day on BMAL1 and NRF2-mediated antioxidant system in skeletal muscle. C57BL/6J mice were assigned to the control group, the group exercising at Zeitgeber Time 12 (ZT12), and the group exercising at ZT24. Control mice were not intervened, while ZT12 and ZT24 mice were trained for four weeks at the early and late time point of their active phase, respectively. We observed that the skeletal muscle of ZT12 mice exhibited higher total antioxidant capacity and lower reactive oxygen species compared to ZT24 mice. Furthermore, ZT12 mice improved the colocalization of BMAL1 with nucleus, the protein expression of BMAL1, NRF2, NAD(P)H quinone oxidoreductase 1, heme oxygenase 1, glutamate-cysteine ligase modifier subunit and glutathione reductase in comparison to those of ZT24 mice. In conclusion, the 4-week aerobic training performed at ZT12 is more effective for enhancing NRF2-mediated antioxidant responses of skeletal muscle, which may be attributed to the specific activation of BMAL1.

Antioxidant enzymes and Nrf2/Keap1 in human skeletal muscle: Influence of age, sex, adiposity and aerobic fitness

Ageing, a sedentary lifestyle, and obesity are associated with increased oxidative stress, while regular exercise is associated with an increased antioxidant capacity in trained skeletal muscles. Whether a higher aerobic fitness is associated with increased expression of antioxidant enzymes and their regulatory factors in skeletal muscle remains unknown. Although oestrogens could promote a higher antioxidant capacity in females, it remains unknown whether a sex dimorphism exists in humans regarding the antioxidant capacity of skeletal muscle. Thus, the aim was to determine the protein expression levels of the antioxidant enzymes SOD1, SOD2, catalase and glutathione reductase (GR) and their regulatory factors Nrf2 and Keap1 in 189 volunteers (120 males and 69 females) to establish whether sex differences exist and how age, VO2max and adiposity influence these. For this purpose, vastus lateralis muscle biopsies were obtained in all participants under resting and unstressed conditions. No significant sex differences in Nrf2, Keap1, SOD1, SOD2, catalase and GR protein expression levels were observed after accounting for VO2max, age and adiposity differences. Multiple regression analysis indicates that the VO2max in mL.kg LLM-1.min-1can be predicted from the levels of SOD2, Total Nrf2 and Keap1 (R = 0.58, P < 0.001), with SOD2 being the main predictor explaining 28 % of variance in VO2max, while Nrf2 and Keap1 explained each around 3 % of the variance. SOD1 protein expression increased with ageing in the whole group after accounting for differences in VO2max and body fat percentage. Overweight and obesity were associated with increased pSer40-Nrf2, pSer40-Nrf2/Total Nrf2 ratio and SOD1 protein expression levels after accounting for differences in age and VO2max. Overall, at the population level, higher aerobic fitness is associated with increased basal expression of muscle antioxidant enzymes, which may explain some of the benefits of regular exercise.

Determinants of the maximal functional reserve during repeated supramaximal exercise by humans: The roles of Nrf2/Keap1, antioxidant proteins, muscle phenotype and oxygenation

When high-intensity exercise is performed until exhaustion a "functional reserve" (FR) or capacity to produce power at the same level or higher than reached at exhaustion exists at task failure, which could be related to reactive oxygen and nitrogen species (RONS)-sensing and counteracting mechanisms. Nonetheless, the magnitude of this FR remains unknown. Repeated bouts of supramaximal exercise at 120% of VO2max interspaced with 20s recovery periods with full ischaemia were used to determine the maximal FR. Then, we determined which muscle phenotypic features could account for the variability in functional reserve in humans. Exercise performance, cardiorespiratory variables, oxygen deficit, and brain and muscle oxygenation (near-infrared spectroscopy) were measured, and resting muscle biopsies were obtained from 43 young healthy adults (30 males). Males and females had similar aerobic (VO2max per kg of lower extremities lean mass (LLM): 166.7 ± 17.1 and 166.1 ± 15.6 ml kg LLM-1.min-1, P = 0.84) and anaerobic fitness (similar performance in the Wingate test and maximal accumulated oxygen deficit when normalized to LLM). The maximal FR was similar in males and females when normalized to LLM (1.84 ± 0.50 and 2.05 ± 0.59 kJ kg LLM-1, in males and females, respectively, P = 0.218). This FR depends on an obligatory component relying on a reserve in glycolytic capacity and a putative component generated by oxidative phosphorylation. The aerobic component depends on brain oxygenation and phenotypic features of the skeletal muscles implicated in calcium handling (SERCA1 and 2 protein expression), oxygen transport and diffusion (myoglobin) and redox regulation (Keap1). The glycolytic component can be predicted by the protein expression levels of pSer40-Nrf2, the maximal accumulated oxygen deficit and the protein expression levels of SOD1. Thus, an increased capacity to modulate the expression of antioxidant proteins involved in RONS handling and calcium homeostasis may be critical for performance during high-intensity exercise in humans.

Effects of Six Weeks of Hypoxia Exposure on Hepatic Fatty Acid Metabolism in ApoE Knockout Mice Fed a High-Fat Diet

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease with a characteristic of abnormal lipid metabolism. In the present study, we employed apolipoprotein E knockout (ApoE KO) mice to investigate the effects of hypoxia exposure on hepatic fatty acid metabolism and to test whether a high-fat diet (HFD) would suppress the beneficial effect caused by hypoxia treatment. ApoE KO mice were fed a HFD for 12 weeks, and then were forwarded into a six-week experiment with four groups: HFD + normoxia, normal diet (ND) + normoxia, HFD + hypoxia exposure (HE), and ND + HE. The C57BL/6J wild type (WT) mice were fed a ND for 18 weeks as the baseline control. The hypoxia exposure was performed in daytime with normobaric hypoxia (11.2% oxygen, 1 h per time, three times per week). Body weight, food and energy intake, plasma lipid profiles, hepatic lipid contents, plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and molecular/biochemical makers and regulators of the fatty acid synthesis and oxidation in the liver were measured at the end of interventions. Six weeks of hypoxia exposure decreased plasma triglycerides (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) contents but did not change hepatic TG and non-esterified fatty acid (NEFA) levels in ApoE KO mice fed a HFD or ND. Furthermore, hypoxia exposure decreased the mRNA expression of Fasn, Scd1, and Srebp-1c significantly in the HFD + HE group compared with those in the HFD + normoxia group; after replacing a HFD with a ND, hypoxia treatment achieved more significant changes in the measured variables. In addition, the protein expression of HIF-1α was increased only in the ND + HE group but not in the HFD + HE group. Even though hypoxia exposure did not affect hepatic TG and NEFA levels, at the genetic level, the intervention had significant effects on hepatic metabolic indices of fatty acid synthesis, especially in the ND + HE group, while HFD suppressed the beneficial effect of hypoxia on hepatic lipid metabolism in male ApoE KO mice. The dietary intervention of shifting HFD to ND could be more effective in reducing hepatic lipid accumulation than hypoxia intervention.

Diabetes Mellitus: An Overview in Relationship to Charcot Neuroarthropathy

Diabetes mellitus with the lack of glycemic control increases risks for developing comorbidities affecting organ systems responsible for critical function. The development of diabetic neuropathy predisposes patients to the onset of Charcot neuroarthropathy (CN). There is significant complexity with treatment of diabetic-induced CN, which can have an often delayed or missed diagnosis. Supervision and treatment from trained specialists are required to provide care for this multifaceted disease process. It is essential for patients to partner with glucose control, comorbidity prevention and care, as well as lower extremity management. Ultimately, CN can result in significant lower extremity deformity placing patients at risk of limb and life.

Aerobic exercise training combined with probiotic supplement improves antioxidant defence of cardiomyocytes by regulating Nrf2 and caspase3 gene expression in type 2 diabetic rats

This study aimed to evaluate the effect of four weeks of aerobic exercise training combined with probiotic supplementation on mRNA levels of Nrf-2 and caspase-3 genes, superoxide dismutase (SOD), and serum total antioxidant capacity (TAC) in rats with type 2 diabetes. 40 male Wistar diabetic rats were divided into five groups: healthy placebo control group (NC), diabetic control group without supplement (DC), diabetic control group with supplement (SDC), diabetic aerobic training group without supplement (DT), and diabetic aerobic training group with probiotic supplement (SDT). Each training group performed training five days per week for four weeks and each session of training consisted of 30 min running on a treadmill with an intensity of 65-60% of maximum speed. Simultaneously, rats were fed probiotic supplements. Serum glucose, SOD, and TAC were analysed. The real-time PCR technique was used to determine the gene expression of Nrf-2 and caspase-3. Both aerobic exercise training and probiotic supplementation interactively reduced caspase 3 gene expression, increased Nrf-2 gene expression and enhanced TAC in the left ventricle of diabetic rats. Also, the reduction of caspase-3 mRNA in the left ventricle was more effective in the SDT group than in other diabetic groups. There was no interaction effect on SOD. However, a simultaneous effect of training and supplementation was observed on increasing TAC levels when compared to the DC group. Pearson’s correlation showed that the heart weight gain in the SDT group occurred only by decreasing the expression of the caspase-3 gene. Based on these results, probiotics combined with exercise training can be a strategy for improving the antioxidant defence system and preventing risk factors of diabetic cardiomyocytes, especially cell death and myocardial ischemia.

Oxidative stress in the pathophysiology of type 2 diabetes and related complications: Current therapeutics strategies and future perspectives

Type 2 diabetes (T2DM) is a persistent metabolic disorder rising rapidly worldwide. It is characterized by pancreatic insulin resistance and β-cell dysfunction. Hyperglycemia induced reactive oxygen species (ROS) production and oxidative stress are correlated with the pathogenesis and progression of this metabolic disease. To counteract the harmful effects of ROS, endogenous antioxidants of the body or exogenous antioxidants neutralise it and maintain bodily homeostasis. Under hyperglycemic conditions, the imbalance between the cellular antioxidant system and ROS production results in oxidative stress, which subsequently results in the development of diabetes. These ROS are produced in the endoplasmic reticulum, phagocytic cells and peroxisomes, with the mitochondrial electron transport chain (ETC) playing a pivotal role. The exacerbated ROS production can directly cause structural and functional modifications in proteins, lipids and nucleic acids. It also modulates several intracellular signaling pathways that lead to insulin resistance and impairment of β-cell function. In addition, the hyperglycemia-induced ROS production contributes to micro- and macro-vascular diabetic complications. Various in-vivo and in-vitro studies have demonstrated the anti-oxidative effects of natural products and their derived bioactive compounds. However, there is conflicting clinical evidence on the beneficial effects of these antioxidant therapies in diabetes prevention. This review article focused on the multifaceted role of oxidative stress caused by ROS overproduction in diabetes and related complications and possible antioxidative therapeutic strategies targeting ROS in this disease.

Physical-Exercise-Induced Antioxidant Effects on the Brain and Skeletal Muscle

Erythroid-related nuclear factor 2 (NRF2) and the antioxidant-responsive-elements (ARE) signaling pathway are the master regulators of cell antioxidant defenses, playing a key role in maintaining cellular homeostasis, a scenario in which proper mitochondrial function is essential. Increasing evidence indicates that the regular practice of physical exercise increases cellular antioxidant defenses by activating NRF2 signaling. This manuscript reviewed classic and ongoing research on the beneficial effects of exercise on the antioxidant system in both the brain and skeletal muscle.

The Role of Nrf2 in Skeletal Muscle on Exercise Capacity

Nuclear factor erythroid 2-related factor 2 Nfe2l2 (Nrf2) is believed to play a crucial role in protecting cells against oxidative stress. In addition to its primary function of maintaining redox homeostasis, there is emerging evidence that Nrf2 is also involved in energy metabolism. In this review, we briefly discuss the role of Nrf2 in skeletal muscle metabolism from the perspective of exercise physiology. This article is part of a special issue “Mitochondrial Function, Reactive Oxygen/Nitrogen Species and Skeletal Muscle” edited by Håkan Westerblad and Takashi Yamada.

A Quantitative Proteomics Approach to Gain Insight into NRF2-KEAP1 Skeletal Muscle System and Its Cysteine Redox Regulation

Mammalian skeletal muscle (SkM) tissue engages the Nrf2-Keap1-dependent antioxidant defense mechanism to respond adaptively to stress. Redox homeostasis mediated by the reversible modification of selective cysteines is the prevalent mode of regulation. The protein targets of SkM redox regulation are largely unknown. We previously reported the proteomic profiles of soleus (Sol) and extensor digitorum longus (EDL) with Nrf2 or Keap1 gene deletion, using SkM-specific Nrf2 or Keap1 knockout models; iMS-Nrf2flox/flox; and iMS-Keap1flox/flox. Here, we employed these two animal models to understand the global expression profile of red tibialis anterior (RTA) using a label free approach and its redox proteomics using iodoacetyl tandem mass tag (iodoTMTTM)-labeled cysteine quantitation. We quantified 298 proteins that were significantly altered globally in the RTA with Nrf2 deficiency but only 21 proteins in the Keap1 KO samples. These proteins are involved in four intracellular signaling pathways: sirtuin signaling, Nrf2 mediated oxidative stress response, oxidative phosphorylation, and mitochondrion dysfunction. Moreover, we identified and quantified the cysteine redox peptides of 34 proteins, which are associated with mitochondrial oxidative phosphorylation, energy metabolism, and extracellular matrix. Our findings suggest that Nrf2-deficient RTA is implicated in metabolic myopathy, mitochondrial disorders, and motor dysfunction, possibly due to an enhanced oxidative modification of the structure and functional proteins in skeletal myocytes.

High intensity muscle stimulation activates a systemic Nrf2-mediated redox stress response

High intensity exercise is a popular mode of exercise to elicit similar or greater adaptive responses compared to traditional moderate intensity continuous exercise. However, the molecular mechanisms underlying these adaptive responses are still unclear. The purpose of this pilot study was to compare high and low intensity contractile stimulus on the Nrf2-mediated redox stress response in mouse skeletal muscle. An intra-animal design was used to control for variations in individual responses to muscle stimulation by comparing a stimulated limb (STIM) to the contralateral unstimulated control limb (CON). High Intensity (HI - 100Hz), Low Intensity (LI - 50Hz), and Naïve Control (NC - Mock stimulation vs CON) groups were used to compare these effects on Nrf2-ARE binding, Keap1 protein, and downstream gene and protein expression of Nrf2 target genes. Muscle stimulation significantly increased Nrf2-ARE binding in LI-STIM compared to LI-CON (p = 0.0098), while Nrf2-ARE binding was elevated in both HI-CON and HI-STIM compared to NC (p = 0.0007). The Nrf2-ARE results were mirrored in the downregulation of Keap1, where Keap1 expression in HI-CON and HI-STIM were both significantly lower than NC (p = 0.008) and decreased in LI-STIM compared to LI-CON (p = 0.015). In addition, stimulation increased NQO1 protein compared to contralateral control regardless of stimulation intensity (p = 0.019), and HO1 protein was significantly higher in high intensity compared to the Naïve control group (p = 0.002). Taken together, these data suggest a systemic redox signaling exerkine is activating Nrf2-ARE binding and is intensity gated, where Nrf2-ARE activation in contralateral control limbs were only seen in the HI group. Other research in exercise induced Nrf2 signaling support the general finding that Nrf2 is activated in peripheral tissues in response to exercise, however the specific exerkine responsible for the systemic signaling effects is not known. Future work should aim to delineate these redox sensitive systemic signaling mechanisms.

Reactive oxygen species in exercise and insulin resistance: Working towards personalized antioxidant treatment

Reactive oxygen species (ROS) are well known for their role in insulin resistance and the development of cardiometabolic disease including type 2 diabetes mellitus (T2D). Conversely, evidence supports the notion that ROS are a necessary component for glucose cell transport and adaptation to physiological stress including exercise and muscle contraction. Although genetic rodent models and cell culture studies indicate antioxidant treatment to be an effective strategy for targeting ROS to promote health, human findings are largely inconsistent. In this review we discuss human research that has investigated antioxidant treatment and glycemic control in the context of health (healthy individuals and during exercise) and disease (insulin resistance and T2D). We have identified key factors that are likely to influence the effectiveness of antioxidant treatment: 1) the context of treatment including whether oxidative distress or eustress is present (e.g., hyperglycemia/lipidaemia or during exercise and muscle contraction); 2) whether specific endogenous antioxidant deficiencies are identified (redox screening); 3) whether antioxidant treatment is specifically designed to target and restore identified deficiencies (antioxidant specificity); 4) and the bioavailability and bioactivity of the antioxidant which are influenced by treatment dose, duration, and method of administration. The majority of human research has failed to account for these factors, limiting their ability to robustly test the effectiveness of antioxidants for health promotion and disease prevention. We propose that a modern "redox screening" and "personalized antioxidant treatment" approach is required to robustly explore redox regulation of human physiology and to elicit more effective antioxidant treatment in humans.

Skeletal Muscle Nrf2 Contributes to Exercise-Evoked Systemic Antioxidant Defense Via Extracellular Vesicular Communication

This review explores the hypothesis that the repetitive contraction-relaxation that occurs during chronic exercise activates skeletal myocyte nuclear factor erythroid-derived 2-like 2 (Nrf2) to upregulate antioxidant enzymes. These proteins are secreted into the circulation within extracellular vesicles and taken up by remote cells, thus providing remote organs with cytoprotection against subsequent oxidative stress.

Effect of Running Exercise on Oxidative Stress Biomarkers: A Systematic Review

Background: Exercise induced health benefits are limited by the overaccumulation of reactive oxygen species (ROS). ROS and further oxidative stress could potentially induce muscle damage which could result in poor exercise performance. However, predicting ROS induced oxidative stress in response to endurance training has several limitations in terms of selecting biomarkers that are used to measure oxidative stress.

Objective: The purpose of this study was to systematically investigate the suitable biomarkers that predict oxidative stress status among runners.

Methods: According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, a search for relevant articles was carried out on PubMed/Medline, ISI Web of Science, and Google Scholar using related search terms such as oxidative damage, ROS, exercise, physical training, running, marathon, and ultramarathon.

Results: Outcomes included (1) running programs like a half-marathon, ultramarathon, and iron-man race, (2) measuring biochemical assessment of oxidative damage markers such as malondialdehyde (MDA), protein carbonyl (PC), total antioxidant capacity (TAC), thiobarbituric acid reactive substances (TBARS), 8-Oxo-2'-deoxyguanosine (8-OH-dG), 4-hydroxynonenal (HNE), and F1-isoprostones, and enzymatic and non-enzymatic antioxidants level.

Conclusions: This study concluded that a running exercise does not elicit a response to specific biomarkers of oxidative stress, instead, oxidative damage markers of lipids, proteins, and various enzymatic and non-enzymatic antioxidants are expressed according to the training status of the individual.

Physical Activity Level Influences MTHFR Gene Methylation Profile in Diabetic Patients

Introduction

MTHFR methylation status is associated with microvascular complications in diabetes, but the factors influencing this profile remain unknown.

Objective

The aim of this study was to evaluate the influence of physical activity level and nutritional status on the methylation profile of the MTHFR gene in patients with type 2 diabetes mellitus (T2DM).

Methods

A total of 111 patients, 43 men and 68 women diagnosed with DM (7.0 ± 2.3 years), answered the International Physical Activity Questionnaire (IPAQ) and underwent blood collection for biochemical analysis, DNA extraction, and MTHFR gene methylation profile determination.

Result

The comparison of the methylation pattern showed that the partially methylated profile predominates in the insufficiently active group (85%), which does not occur in the sufficiently active group (54%) (p = 0.012). No differences were found in the nutritional status comparison. Logistic regression including overweight, waist circumference, gender, age, time of DM, hypertension, dyslipidemia, smoking, alcoholism, and family DM revealed that the association of the level of physical activity with methylation profile proved to be independent of these confounding variables. Considering the partially methylated profile as a result, being physically inactive favors the partially methylated MTHFR pattern in patients with DM.

Conclusion

We concluded that insufficient physical activity is associated with partially methylated pattern of MTHFR promoter.

Functional, proteomic and bioinformatic analyses of Nrf2- and Keap1- null skeletal muscle

KEY POINTS

Nrf2 is a master regulator of endogenous cellular defences, governing the expression of more than 200 cytoprotective proteins, including a panel of antioxidant enzymes. Nrf2 plays an important role in redox haemostasis of skeletal muscle in response to the increased generation of reactive oxygen species during contraction. Employing skeletal muscle-specific transgenic mouse models with unbiased-omic approaches, we uncovered new target proteins, downstream pathways and molecular networks of Nrf2 in skeletal muscle following Nrf2 or Keap1 deletion. Based on the findings, we proposed a two-way model to understand Nrf2 function: a tonic effect through a Keap1-independent mechanism under basal conditions and an induced effect through a Keap1-dependent mechanism in response to oxidative and other stresses.

ABSTRACT

Although Nrf2 has been recognized as a master regulator of cytoprotection, its functional significance remains to be completely defined. We hypothesized that proteomic/bioinformatic analyses from Nrf2-deficient or overexpressed skeletal muscle tissues will provide a broader spectrum of Nrf2 targets and downstream pathways than are currently known. To this end, we created two transgenic mouse models; the iMS-Nrf2flox/flox and iMS-Keap1flox/flox , employing which we demonstrated that selective deletion of skeletal muscle Nrf2 or Keap1 separately impaired or improved skeletal muscle function. Mass spectrometry revealed that Nrf2-KO changed expression of 114 proteins while Keap1-KO changed expression of 117 proteins with 10 proteins in common between the groups. Gene ontology analysis suggested that Nrf2 KO-changed proteins are involved in metabolism of oxidoreduction coenzymes, purine ribonucleoside triphosphate, ATP and propanoate, which are considered as the basal function of Nrf2, while Keap1 KO-changed proteins are involved in cellular detoxification, NADP metabolism, glutathione metabolism and the electron transport chain, which belong to the induced effect of Nrf2. Canonical pathway analysis suggested that Keap1-KO activated four pathways, whereas Nrf2-KO did not. Ingenuity pathway analysis further revealed that Nrf2-KO and Keap1-KO impacted different signal proteins and functions. Finally, we validated the proteomic and bioinformatics data by analysing glutathione metabolism and mitochondrial function. In conclusion, we found that Nrf2-targeted proteins are assigned to two groups: one mediates the tonic effects evoked by a low level of Nrf2 at basal condition; the other is responsible for the inducible effects evoked by a surge of Nrf2 that is dependent on a Keap1 mechanism.

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and exercise

Chronic metabolic health diseases are increasing worldwide placing strain on healthcare systems and importantly, impacting individuals' quality of life. It is well established that many chronic diseases are associated with inflammation and oxidative stress. Exercise is a known strategy to manage and treat inflammation in animals and humans. Understanding the mechanisms which cause acute and chronic changes to systems via various exercise protocols may provide insights into how we can better clinically manage patients with inflammatory and oxidative stress associated diseases. Nrf2 is a basic leucine transcription factor which regulates the expression of antioxidant proteins to protect against damage caused by electrophilic or oxidative stress. The aim of this narrative review is to provide an overview of the literature which has investigated the relationship between acute and chronic exercise training and Nrf2 protein, mRNA and Nrf2-ARE binding activity. This narrative review presents analysis of twenty-nine articles presenting studies using animals and humans. Findings from animal models suggest that exercise increases all molecular aspects of the Nrf2-ARE pathway in all tissues studied. It was noted that there seems to be an age-related decline in Nrf2 protein upregulation with exercise training. In humans, however, there is a lack of evidence to support this claim.

Forced exercise activates the NrF2 pathway in the striatum and ameliorates motor and behavioral manifestations of Parkinson's disease in rotenone-treated rats

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by progressive loss of nigrostriatal dopaminergic neurons leading to dopamine depletion and problems of movement, emotions, and cognition. While the pathogenesis of PD is not clear, damage of dopaminergic neurons by oxygen-derived free radicals is considered an important contributing mechanism. This study aimed to evaluate the role of treadmill exercise in male Wister rats as a single treatment and as an aid-therapy with L-dopa for rotenone-induced PD. To study the role of the Nrf2- ARE pathway as a mechanism involved in exercise-associated improvement in rotenone-induced PD in rats.

METHOD

Animals were divided into 5 groups, (Control, rotenone, rotenone\exercise, rotenone\L-dopa, and rotenone\exercise\L-dopa (combination)groups). After the PD induction, rats in the rotenone\exercise and combination groups were daily treadmill exercised for 4 weeks.

RESULTS

Treadmill exercise significantly improved behavioral and motor aspects of rotenone-induced PD. When treadmill exercise was introduced as a single intervention, it amended most behavioral aspects of PD, gait fully corrected, short-term memory, and motor coordination. Where L-dopa corrected locomotor activity and motor coordination but failed to improve short-term memory and only partially corrected the gait of rotenone-treated rats. When treadmill exercise was combined with L-dopa, all features of PD were corrected. It was found that exercise upregulated some of its associative genes to Nrf2 pathways such as TFAM, Nrf2 and NQO.1 mRNA expression.

CONCLUSION

This study suggests that forced exercise improved parkinsonian like features by activating the Nrf2 pathway.

Manganese Superoxide Dismutase Dysfunction and the Pathogenesis of Kidney Disease

The mitochondria are a major source of reactive oxygen species (ROS). Superoxide anion (O₂^•–) is produced by the process of oxidative phosphorylation associated with glucose, amino acid, and fatty acid metabolism, resulting in the production of adenosine triphosphate (ATP) in the mitochondria. Excess production of reactive oxidants in the mitochondria, including O₂^•–, and its by-product, peroxynitrite (ONOO^–), which is generated by a reaction between O₂^•– with nitric oxide (NO^•), alters cellular function via oxidative modification of proteins, lipids, and nucleic acids. Mitochondria maintain an antioxidant enzyme system that eliminates excess ROS; manganese superoxide dismutase (Mn-SOD) is one of the major components of this system, as it catalyzes the first step involved in scavenging ROS. Reduced expression and/or the activity of Mn-SOD results in diminished mitochondrial antioxidant capacity; this can impair the overall health of the cell by altering mitochondrial function and may lead to the development and progression of kidney disease. Targeted therapeutic agents may protect mitochondrial proteins, including Mn-SOD against oxidative stress-induced dysfunction, and this may consequently lead to the protection of renal function. Here, we describe the biological function and regulation of Mn-SOD and review the significance of mitochondrial oxidative stress concerning the pathogenesis of kidney diseases, including chronic kidney disease (CKD) and acute kidney injury (AKI), with a focus on Mn-SOD dysfunction.

Regulation of Nrf2/Keap1 signalling in human skeletal muscle during exercise to exhaustion in normoxia, severe acute hypoxia and post-exercise ischaemia: Influence of metabolite accumulation and oxygenation

The Nrf2 transcription factor is induced by reactive oxygen and nitrogen species and is necessary for the adaptive response to exercise in mice. It remains unknown whether Nrf2 signalling is activated by exercise in human skeletal muscle. Here we show that Nrf2 signalling is activated by exercise to exhaustion with similar responses in normoxia (P_IO₂: 143 mmHg) and severe acute hypoxia (P_IO₂: 73 mmHg). CaMKII and AMPKα phosphorylation were similarly induced in both conditions. Enhanced Nrf2 signalling was achieved by raising Nrf2 total protein and Ser⁴⁰ Nrf2 phosphorylation, accompanied by a reduction of Keap1. Keap1 protein degradation is facilitated by the phosphorylation of p62/SQSTM1 at Ser³⁴⁹ by AMPK, which targets Keap1 for autophagic degradation. Consequently, the Nrf2-to-Keap1 ratio was markedly elevated and closely associated with a 2-3-fold increase in Catalase protein. No relationship was observed between Nrf2 signalling and SOD1 and SOD2 protein levels. Application of ischaemia immediately at the end of exercise maintained these changes, which were reverted within 1 min of recovery with free circulation. While SOD2 did not change significantly during either exercise or ischaemia, SOD1 protein expression was marginally downregulated and upregulated during exercise in normoxia and hypoxia, respectively. We conclude that Nrf2/Keap1/Catalase pathway is rapidly regulated during exercise and recovery in human skeletal muscle. Catalase emerges as an essential antioxidant enzyme acutely upregulated during exercise and ischaemia. Post-exercise ischaemia maintains Nrf2 signalling at the level reached at exhaustion and can be used to avoid early post-exercise recovery, which is O₂-dependent.

The Potential for Reducing Lynch Syndrome Cancer Risk with Nutritional Nrf2 Activators

Lynch syndrome (LS), is an autosomal dominant disorder predisposing patients to multiple cancers, predominantly colorectal (CRC) and endometrial, and is implicated in 2-4% of all CRC cases. LS is characterized by mutations of four mismatch repair (MMR) genes which code for proteins responsible for recognizing and repairing DNA lesions occurring through multiple mechanisms including oxidative stress (OS). Increased OS can cause DNA mutations and is considered carcinogenic. Due to reduced MMR activity, LS patients have an increased risk of cancer as a result of a decreased ability to recognize and repair DNA lesions caused by OS. Due to its carcinogenic properties, reducing the level of OS may reduce the risk of cancer. Nutritional Nrf2 activators have been shown to reduce the risk of carcinogenesis in the general population through activation of the endogenous antioxidant system. Common nutritional Nrf2 activators include sulforaphane, curcumin, DATS, quercetin, resveratrol, and EGCG. Since LS patients are more susceptible to carcinogenesis caused by OS, it is hypothesized that nutritional Nrf2 activators may have the potential to reduce the risk of cancer in those with LS by modulating OS and inflammation. The purpose of this paper is to review the available evidence in support of this statement.

Desflurane Preconditioning Protects Against Renal Ischemia-Reperfusion Injury and Inhibits Inflammation and Oxidative Stress in Rats Through Regulating the Nrf2-Keap1-ARE Signaling Pathway

OBJECTIVE

Kidney is sensitive to ischemia-reperfusion (I/R) injury because of its special structure and function. In this study, we aimed to explore the mechanism of desflurane (DFE) preconditioning effecting on renal I/R injury in rats.

METHODS

Renal I/R injury rats model was constructed, and the expressions of serum renal function parameters (blood urea nitrogen (BUN) and serum creatinine (SCr)) and lipid peroxidation-related factors were detected using corresponding commercial kits to assess the degrees of renal functional damage and oxidative stress. Hematoxylin--eosin (HE) staining and Masson trichrome staining were applied to measure the renal histologic damage. The expressions of inflammation-related factors were determined by ELISA assay. The cell apoptosis was analyzed using TUNEL, Western blot and immunohistochemistry (IHC). IHC was also used to detect the number of myeloperoxidase (MPO)-positive cells. The expressions of proteins associated with the Nrf2-Keap1-ARE pathway were assessed by Western blot and IHC.

RESULTS

DFE preconditioning inhibited I/R injury-induced BUN and SCr increase and renal histologic injury in rats. Also, DFE suppressed the inflammation, apoptosis and oxidative stress caused by renal I/R injury in vivo. In addition, DFE preconditioning repressed peroxide-related factors (MDA, MPO and NO) expressions and promoted antioxidant-related factors (GSH, SOD, GPx and CAT) expressions. In addition, DFE promoted Nrf2-Keap1-ARE-related proteins including Nrf2, NQO1, HO-1, γ-GCS, GSR and GCLc expressions.

CONCLUSION

DFE preconditioning protected the kidney as well as inhibited the inflammation, cell apoptosis and oxidative stress in renal I/R injury rats by activating the Nrf2-Keap1-ARE signaling pathway.

The impact of acute and chronic exercise on Nrf2 expression in relation to markers of mitochondrial biogenesis in human skeletal muscle

PURPOSE

To examine the relationship between changes in nuclear factor erythroid 2-related factor 2 (Nrf2) expression and markers of mitochondrial biogenesis in acutely and chronically exercised human skeletal muscle.

METHODS

The impact of acute submaximal endurance (END) and supramaximal interval (Tabata) cycling on the upregulation of Nrf2 (and its downstream targets), nuclear respiratory factor-1 (NRF-1) and mitochondrial transcription factor A (TFAM) mRNA expression was examined in healthy young males (n = 10). The relationship between changes in citrate synthase (CS) maximal activity and the protein content of Nrf2, heme oxygenase 1 (HO-1), NRF-1, and TFAM was also investigated following 4 weeks of Tabata in a separate group of males (n = 21).

RESULTS

Nrf2, NRF-1, and HO-1 mRNA expression increased after acute exercise (p < 0.05), whereas the increase in superoxide dismutase 2 (SOD2) mRNA expression approached significance (p = 0.08). Four weeks of Tabata increased CS activity and Nrf2, NRF-1, and TFAM protein content (p < 0.05), but decreased HO-1 protein content (p < 0.05). Training-induced changes in Nrf2 protein were strongly correlated with NRF-1 (r = 0.63, p < 0.01). When comparing protein content changes between individuals with the largest (HI: + 23%) and smallest (LO: - 1%) observed changes in CS activity (n = 8 each), increases in Nrf2 and TFAM protein content were apparent in the HI group only (p < 0.02) with medium-to-large effect sizes for between-group differences in changes in Nrf2 (η_p²₌0.15) and TFAM (η_p² = 0.12) protein content.

CONCLUSION

Altogether, our findings support a potential role for Nrf2 in exercise-induced mitochondrial biogenesis in human skeletal muscle.

Effects of Dietary Zinc on Carcass Traits, Meat Quality, Antioxidant Status, and Tissue Zinc Accumulation of Pekin Ducks

This study investigated the effects of dietary zinc on carcass traits, meat quality, antioxidant capacity, and tissue zinc accumulation of Pekin ducks. A total of 768 1-day-old Pekin ducks were randomly allocated to six dietary treatments and penned in groups of 16 with 8 pens per treatment. Ducks were fed a basal corn-soybean meal diet supplemented with graded levels of zinc sulfate (0, 15, 30, 60, 120, 240 mg zinc/kg) for 35 days. The slaughter weight, carcass weight, eviscerated weight, and breast and leg muscle weight of Pekin ducks were increased with increasing dietary zinc levels (P < 0.05). Zinc supplementation increased the pH value at 24-h postmortem and the intramuscular fat (IMF) (P < 0.05), but decreased the lightness value, drip loss, and shear force in breast meat of ducks (P < 0.05). Increasing dietary zinc increased the activity of superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione reductase (GR), catalase (CAT), and the content of glutathione (GSH), as well as decreased the malondialdehyde (MDA) level in breast muscle (P < 0.05). RT-qPCR analysis demonstrated that supplemental zinc notably enhanced the transcription of SOD, GPX, GR, CAT, and nuclear factor erythroid 2-related factor 2 (Nrf2) (P < 0.05). Meanwhile, zinc accumulation in plasma, breast muscle, liver, and tibia were linearly increased with increasing zinc supplementation (P < 0.05). These results indicated that zinc supplementation could improve carcass traits and meat quality and increase the activities and mRNA levels of antioxidant enzymes in breast muscle of Pekin duck. Base on broken-line regression analysis that 91.32 mg/kg of dietary zinc was suggested for optimal carcass traits, meat quality, antioxidant capacity, and zinc deposition of Pekin duck.

Looking beyond PGC-1α: emerging regulators of exercise-induced skeletal muscle mitochondrial biogenesis and their activation by dietary compounds

Despite its widespread acceptance as the "master regulator" of mitochondrial biogenesis (i.e., the expansion of the mitochondrial reticulum), peroxisome proliferator-activated receptor (PPAR) gamma coactivator-1 alpha (PGC-1α) appears to be dispensable for the training-induced augmentation of skeletal muscle mitochondrial content and respiratory function. In fact, a number of regulatory proteins have emerged as important players in skeletal muscle mitochondrial biogenesis and many of these proteins share key attributes with PGC-1α. In an effort to move past the simplistic notion of a "master regulator" of mitochondrial biogenesis, we highlight the regulatory mechanisms by which nuclear factor erythroid 2-related factor 2 (Nrf2), estrogen-related receptor gamma (ERRγ), PPARβ, and leucine-rich pentatricopeptide repeat-containing protein (LRP130) may contribute to the control of skeletal muscle mitochondrial biogenesis. We also present evidence supporting/refuting the ability of sulforaphane, quercetin, and epicatechin to promote skeletal muscle mitochondrial biogenesis and their potential to augment mitochondrial training adaptations. Targeted activation of specific pathways by these compounds may allow for greater mechanistic insight into the molecular pathways controlling mitochondrial biogenesis in human skeletal muscle. Dietary activation of mitochondrial biogenesis may also be useful in clinical populations with basal reductions in mitochondrial protein content, enzyme activities, and/or respiratory function as well as individuals who exhibit a blunted skeletal muscle responsiveness to contractile activity. Novelty The existence of redundant pathways leading to mitochondrial biogenesis refutes the simplistic notion of a "master regulator" of mitochondrial biogenesis. Dietary activation of specific pathways may provide greater mechanistic insight into the exercise-induced mitochondrial biogenesis in human skeletal muscle.

Antioxidant responses to salinity stress in an invasive species, the red-eared slider (Trachemys scripta elegans) and involvement of a TOR-Nrf2 signaling pathway

The red-eared slider (Trachemys scripta elegans), a freshwater turtle, is an invasive species in many parts of the world where it survives in both freshwater and coastal saline habitats. High salinity can induce reactive oxygen species (ROS) production and lead to oxidative damage. In this study, we investigate the antioxidant defense mechanisms of T. s. elegans in response to salinity stress. The results showed that the mRNA expression levels of superoxide dismutase (SODs), catalase (CAT) and glutathione peroxidase (GSH-PXs) were significantly increased in both 5 psu and 15 psu groups at the early stages of salinity exposure (generally 6-48 h), but typically returned to control levels after the longest 30 d exposure. In addition, hepatic and cardiac mRNA levels of the NF-E2-related factor 2 (Nrf2), showed a similar upregulation as an early response to stress, but decreased at 30 d in the 5 psu and 15 psu groups. The mRNA levels of the negative regulator of Nrf2, kelch-like ECH associating protein 1 (Keap1), exhibited the opposite pattern. Moreover, mRNA expression levels of target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1) in liver and heart showed roughly similar patterns to those for Nrf2. Furthermore, the content of malondialdehyde (MDA) was significantly increased in liver, especially in the 15 psu group by ~2.5-fold. Taken together, these results indicate that T. s. elegans may activate the TOR-Nrf2 pathway to modulate antioxidant genes transcription in order to promote enhanced antioxidant defense in response to salinity stress.

Effects of acute hypoxia exposure with different durations on activation of Nrf2-ARE pathway in mouse skeletal muscle

BACKGROUND

Hypoxia training enhances the endurance capacity of athletes. This response may in part be attributed to the hypoxia-induced increase in antioxidant capacity in skeletal muscles. Nuclear factor erythroid 2-related factor 2 (Nrf2), a key transcription factor which regulates the expression of genes via binding to the antioxidant-response element (ARE) of these genes, plays a crucial role in stimulating the body's defense system and potentially responds to hypoxia. Meanwhile, hypoxia-inducible factor-1α (HIF-1α) is an important player in protecting cells from hypoxic stress. The purpose of this study was to investigate the effects of acute hypoxia exposure with different durations on the activation of Nrf2-ARE pathway and a possible regulatory role of HIF-1α in these responses.

METHODS

C57BL/6J mice were allocated into the non-hypoxia 0-hour, 6-hour, 24-hour, and 48-hour hypoxic exposure (11.2% oxygen) groups. The quadriceps femoris was collected immediately after hypoxia. Further, to investigate the possible role of HIF-1α, C2C12 myoblasts with HIF-1α knockdown by small interfering RNA (siRNA) and the inducible HIF-1α transgenic mice were employed.

RESULTS

The results showed that 48-hour hypoxia exposure up-regulated protein expression of Nrf2, Nrf2/ARE binding activity and the transcription of antioxidative genes containing ARE (Sod1 and others) in mouse skeletal muscle. Moreover, HIF-1α siRNA group of C2C12 myoblasts showed a remarkable inhibition of Nrf2 protein expression and nuclear accumulation in hypoxia exposure for 72 hours compared with that in siRNA-Control group of the cells. In addition, HIF-1α transgenic mice gave higher Nrf2 protein expression, Nrf2/ARE binding activity and expressions of Nrf2-mediated antioxidative genes in their skeletal muscle, compared with those in the wild-type mice.

CONCLUSIONS

The findings suggested that the acute hypoxia exposure could trigger the activation of Nrf2-ARE pathway, with longer duration associated with higher responses, and HIF-1α expression might be involved in promoting the Nrf2-mediated antioxidant responses in skeletal muscle.

Curcumin improves exercise performance of mice with coronary artery ligation-induced HFrEF: Nrf2 and antioxidant mechanisms in skeletal muscle

A hallmark of chronic heart failure (HF) with low ejection fraction (HFrEF) is exercise intolerance. We hypothesized that reduced expression of nuclear factor E2-related factor 2 (Nrf2) in skeletal muscle contributes to impaired exercise performance. We further hypothesized that curcumin, a Nrf2 activator, would preserve or increase exercise capacity in HF. Experiments were carried out in mice with coronary artery ligation-induced HFrEF. Curcumin was deliveried by a subcutaneous osmotic minipump at a dose of 50 mg·kg^-1·day^-1 for 8 weeks. In vivo, in situ, and in vitro experiments were employed to evaluate exercise capacity, muscle function, and molecular mechanisms. We found that: 1) the maximal speed, running distance to exhaustion, and limb grip force were significantly lower in HFrEF mice compared with sham. Curcumin-treated HF mice displayed enhanced exercise performance compared with vehicle-treated HF mice; 2) both soleus (Sol) and extensor digitorum longus (EDL) muscles of HFrEF mice exhibited reduced force and rapid fatigue, which were ameliorated by curcumin; and 3) protein expression of Nrf2, hemeoxygenase-1, SOD2, myogenin, and MyoD were significantly lower, but total ubiquitinated proteins, MURF1, and atrogen-1 were higher in Sol and EDL of HFrEF compared with sham mice, whereas these alterations in Nrf2 signaling and antioxidant defenses in HFrEF were attenuated by curcumin, which had no effect on cardiac function per se in mice with severe HFrEF. These data suggest that impaired Nrf2 signaling intrinsic to skeletal muscle contributes to exercise intolerance in HFrEF. Skeletal muscle Nrf2 should be considered as a novel therapeutic target in severe HF. NEW & NOTEWORTHY These studies suggest that impaired nuclear factor E2-related factor 2 (Nrf2) signaling is a critical mechanism underlying the enhanced oxidative stress in skeletal muscle in heart failure with low ejection fraction (HFrEF). Curcumin prevents the decline in running performance in HFrEF mice by upregulating antioxidant defenses in skeletal muscle, likely mediated by activating Nrf2 signaling. These findings suggest a novel therapeutic target for the improvement of exercise capacity and quality of life in HFrEF patients.

Astaxanthin ameliorates experimental diabetes-induced renal oxidative stress and fibronectin by upregulating connexin43 in glomerular mesangial cells and diabetic mice

Oxidative stress is the major cause of renal fibrosis in the progression of DN. Connexin43 (Cx43) exerts an anti-fibrosis effect on diabetic kidneys. The current study aimed to investigate whether astaxanthin (AST) could ameliorate the pathological progression of DN by upregulating Cx43 and activating the Nrf2/ARE signaling, which is a pivotal anti-oxidative stress system, to strengthen the cellular anti-oxidative capacity and diminish fibronectin (FN) accumulation in HG-induced glomerular mesangial cells (GMCs). Our hypothesis was verified in GMCs and the kidneys from db/db mice by western blot, immunofluorescence, immunohistochemistry, immunoprecipitation, dual luciferase reporter assay and reactive oxygen related detection kits. Results showed that AST simultaneously upregulated the Cx43 protein level and promoted the Nrf2/ARE signaling activity in the kidney of db/db mice and HG-treated GMCs. However, Cx43 depletion abrogated the Nrf2/ARE signaling activation induced by AST. AST reduced the interaction between c-Src and Nrf2 in the nuclei of GMCs cultured with HG, thereby enhancing the Nrf2 accumulation in the nuclei of GMCs. Our data suggested that AST promoted the Nrf2/ARE signaling by upregulating the Cx43 protein level to prevent renal fibrosis triggered by HG in GMCs and db/db mice. c-Src acted as a mediator in these processes.

Induction of brain Nrf2-HO-1 pathway and antinociception after different physical training paradigms in mice

AIM

Activation of the Nrf2-antioxidant response element signaling pathway is a major mechanism in the cellular defense against oxidative or electrophilic stress through conjugative reactions and by enhancing cellular antioxidant capacity. Although exercise training up-regulates antioxidant defenses system, while information regarding the intensity levels of physical exercise that acts on the cellular protection systems is limited.

MAIN METHODS

The present study evaluated the effects of different durations and intensities of physical exercise on the hippocampus, cortex and hypothalamus Nrf2 and HO-1 gene expression and related protein content and the nociception thresholds in adult C57Bl male mice. Exercise training consisted of daily running on a 10-lane rodent motor-driven treadmill for either 3 or 7 weeks at three different intensities. Pain responses were evaluated after exercise and in untrained mice by Von Frey hair test and cold plate test.

KEY FINDINGS

This study confirmed that only vigorous and longer duration aerobic exercise increased Nrf2 protein level in the hippocampus and HO-1 protein level in the cortex and reduced pain perception. Mechanical and thermal hypoalgesia were only observed in exercise groups after 7 weeks of physical training.

SIGNIFICANCE

The overall findings in this study confirm that only the long duration intensive forced exercise reduced inflammatory pain by induction of Nrf2/HO-1 antioxidant signaling pathway.

Cardiovascular Adaptive Homeostasis in Exercise

Adaptive Homeostasis has been defined as, "The transient expansion or contraction of the homeostatic range in response to exposure to sub-toxic, non-damaging, signaling molecules or events, or the removal or cessation of such molecules or events." (Davies, 2016). I propose that one of the most significant examples of adaptive homeostasis may be the adaptation of the cardiovascular system to exercise training. In particular, endurance type training involves the generation of increased levels of free radicals such as ubisemiquinone, superoxide, nitric oxide, and other (non-radical) reactive oxygen species such as hydrogen peroxide (H2O2), in a repetitive manner, typically several times per week. As long as the training intensity and duration are sub-maximal and not exhaustive these reactive species do not cause damage, but rather activate signal transduction pathways to induce mitochondrial biogenesis-the foundation of increased exercise endurance. Particularly important are the NFκB and Nrf2 signal transduction pathways which respond to reactive oxygen and nitrogen species generated during exercise. As with other examples of adaptive homeostasis the effects are transient, lasting only as long as the training is maintained. Unfortunately, the ability to adapt to exercise training declines with age, perhaps as a result of impaired Nrf2 and NFκB signaling, as does adaptive homeostasis capacity in general. Since this is an Hypothesis/Theory Paper and not a review, I have not tried to provide a comprehensive discussion of all the literature relating to exercise adaptation and the cardiovascular system. Rather, I have attempted to develop the Hypothesis or Theory that adaptive homeostasis is the foundation for adaptation of the cardiovascular system to exercise training, largely based on work from my own laboratory, that of close collaborators, and that of key contributors over a period of almost 40 years.

Astaxanthin Promotes Nrf2/ARE Signaling to Inhibit HG-Induced Renal Fibrosis in GMCs

Oxidative stress is the main cause of diabetic nephropathy (DN) progression. Nuclear factor-erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling is a crucial cellular defense system to cope with oxidative stress. Astaxanthin (AST) is a fat-soluble xanthophyll carotenoid with remarkable antioxidative capacity. AST exerted renal protective in diabetic rats. This study aimed to determine whether AST could alleviate the pathological progress of DN by activating Nrf2/ARE signaling and diminishing the excessive oxidative stress and fibronectin (FN) accumulation in glomerular mesangial cells (GMCs) challenged with high glucose (HG). In the current study, we found that AST treatment alleviated the metabolic parameters, renal morphology and extracellular matrix (ECM) accumulation in streptozotocin-induced diabetic rats. Additionally, HG induced the adaptively activated Nrf2/ARE signaling and increased the expression of FN, intercellular adhesion molecule-1 (ICAM-1) and transforming growth factor-β1 (TGF-β1), as well as the intracellular reactive oxygen species (ROS) generation in GMCs. However, AST treatment strongly promoted the nuclear translocation and transcriptional activity of Nrf2 as well as upregulated the expression of superoxide dismutase (SOD1), NAD(P)H: quinone oxidoreductase (NQO1) and heme oxygenase-1 (HO-1), ultimately quenching the higher level of ROS and inhibiting the FN, ICAM-1 and TGF-β1 expression induced by HG. Collectively, our data suggest that the renoprotective effect of AST on DN depends on Nrf2/ARE signaling activation, which could be a potentially therapeutic strategy in the treatment of DN.

Testosterone a key factor in gender related metabolic syndrome

Metabolic syndrome (MetS) is highly correlated with cardiovascular diseases. Although an excess of body fat is a determinant factor for MetS development, a reduced level of testosterone plays a fundamental role in its regulation. Low testosterone level is highly related to insulin resistance, visceral obesity and MetS. We have searched in Pubmed clinical trial with the password: testosterone and insulin resistance, and testosterone and MetS. We found 19 studies on the correlation between testosterone level with insulin resistance and 18 on the effect of testosterone therapy on MetS. A high correlation between low testosterone and insulin resistance has been found in men, but not in women. Testosterone administration in hypogonadal men improved MetS and reduced the mortality risk. Androgen and oestrogen receptors are expressed in adipocytes, muscle and liver tissue, and their activation is necessary to improve metabolic control. Normalization of testosterone level should be the primary treatment in men, along with caloric restriction and physical exercise. These findings come mainly from correlative data, and there remains a need for randomized trials to strengthen this evidence. This review will consider the effects of testosterone on the regulation and development of MetS in men and women.

Oxidative Stress: A Unifying Mechanism for Cell Damage Induced by Noise, (Water-Pipe) Smoking, and Emotional Stress-Therapeutic Strategies Targeting Redox Imbalance

SIGNIFICANCE

Modern technologies have eased our lives but these conveniences can impact our lifestyles in destructive ways. Noise pollution, mental stresses, and smoking (as a stress-relieving solution) are some environmental hazards that affect our well-being and healthcare budgets. Scrutinizing their pathophysiology could lead to solutions to reduce their harmful effects. Recent Advances: Oxidative stress plays an important role in initiating local and systemic inflammation after noise pollution, mental stress, and smoking. Lipid peroxidation and release of lysolipid by-products, disturbance in activation and function of nuclear factor erythroid 2-related factor 2 (Nrf2), induction of stress hormones and their secondary effects on intracellular kinases, and dysregulation of intracellular Ca²⁺ can all potentially trigger other vicious cycles. Recent clinical data suggest that boosting the antioxidant system through nonpharmacological measures, for example, lifestyle changes that include exercise have benefits that cannot easily be achieved with pharmacological interventions alone.

CRITICAL ISSUES

Indiscriminate manipulation of the cellular redox network could lead to a new series of ailments. An ideal approach requires meticulous scrutiny of redox balance mechanisms for individual pathologies so as to create new treatment strategies that target key pathways while minimizing side effects.

FUTURE DIRECTIONS

Extrapolating our understanding of redox balance to other debilitating conditions such as diabetes and the metabolic syndrome could potentially lead to devising a unifying therapeutic strategy. Antioxid. Redox Signal. 28, 741-759.

Nutritional Ketosis and Mitohormesis: Potential Implications for Mitochondrial Function and Human Health

Impaired mitochondrial function often results in excessive production of reactive oxygen species (ROS) and is involved in the etiology of many chronic diseases, including cardiovascular disease, diabetes, neurodegenerative disorders, and cancer. Moderate levels of mitochondrial ROS, however, can protect against chronic disease by inducing upregulation of mitochondrial capacity and endogenous antioxidant defense. This phenomenon, referred to as mitohormesis, is induced through increased reliance on mitochondrial respiration, which can occur through diet or exercise. Nutritional ketosis is a safe and physiological metabolic state induced through a ketogenic diet low in carbohydrate and moderate in protein. Such a diet increases reliance on mitochondrial respiration and may, therefore, induce mitohormesis. Furthermore, the ketone β-hydroxybutyrate (BHB), which is elevated during nutritional ketosis to levels no greater than those resulting from fasting, acts as a signaling molecule in addition to its traditionally known role as an energy substrate. BHB signaling induces adaptations similar to mitohormesis, thereby expanding the potential benefit of nutritional ketosis beyond carbohydrate restriction. This review describes the evidence supporting enhancement of mitochondrial function and endogenous antioxidant defense in response to nutritional ketosis, as well as the potential mechanisms leading to these adaptations.

Myricetin alleviates cuprizone-induced behavioral dysfunction and demyelination in mice by Nrf2 pathway

Multiple sclerosis (MS) is a demyelinating disease occurring in the central nervous system. In the present study, we evaluated the function of myricetin on the alleviation of behavioral dysfunction and myelin protection in the cuprizone-induced demyelination model. Mice were daily fed with fodder including 0.2% cuprizone and were administrated myricetin (100 mg kg^-1) by gavage administration for 5 weeks. The treatment of myricetin ameliorated hyper-locomotion and behavior impairment induced by cuprizone toxicity. With the administration of myricetin, the demyelinating lesion was lessened via increasing the LFB staining area and myelin phosphatide protein (MBP) expression. In addition, myricetin evidently promoted Nrf2 translocation in the nuclear fraction and enhanced the HO-1 and NQO1 expression levels. Our data revealed that myricetin may be a potential candidate for mitigating motor defects and demyelination in a cuprizone-induced mouse model via activating the Nrf2 pathway.

Systemic response of the stony coral Pocillopora damicornis against acute cadmium stress

Heavy metals have become one of the main pollutants in the marine environment and a major threat to the growth and reproduction of stony corals. In the present study, the density of symbiotic zooxanthellae, levels of crucial physiological activities and the transcriptome were investigated in the stony coral Pocillopora damicornis after the acute exposure to elevated cadmium concentration. The density of symbiotic zooxanthellae decreased significantly during 12-24h period, and reached lowest at 24h after acute cadmium stress. No significant changes were observed in the activity of glutathione S-transferase during the entire stress exposure. The activities of superoxide dismutase and catalase, and the concentration of glutathione decreased significantly, but the activation level of caspase3 increased significantly after cadmium exposure. Furthermore, transcriptome sequencing and bioinformatics analysis revealed 3538 significantly upregulated genes and 8048 significantly downregulated genes at 12h after the treatment. There were 12 overrepresented GO terms for significantly upregulated genes, mostly related to unfolded protein response, endoplasmic reticulum stress and apoptosis. In addition, a total of 32 GO terms were overrepresented for significantly downregulated genes, and mainly correlated with macromolecular metabolic processes. These results collectively suggest that acute cadmium stress could induce apoptosis by repressing the production of the antioxidants, elevating oxidative stress and activating the unfolded protein response. This cascade of reactions would result to the collapse of the coral-zooxanthella symbiosis and the expulsion of symbiotic zooxanthellae in the stony coral P. damicornis, ultimately leading to coral bleaching.

Does resistance exercise performed during dialysis modulate Nrf2 and NF-κB in patients with chronic kidney disease?

Studies have shown that nuclear factor erythroid 2-related factor 2 (Nrf2) can be modulated by physical exercise. However, the impact of resistance exercise has never been investigated in patients with chronic kidney disease (CKD). The aim of this study was to evaluate the effects of resistance exercise programs on the expression of transcription factors Nrf2 and nuclear factor κB (NF-κB) in CKD patients on hemodialysis (HD). Patients on an HD program were randomly assigned to an exercise group of 25 patients (54.5% women, aged 45.7±15.2years and time on dialysis=71.2±45.5months) or a control group of 19 patients who had no exercise intervention (61.5% women, aged 42.5±13.5years and time on dialysis=70.1±49.9months). A strength exercise program was performed 3 times a week during the HD sessions. Peripheral blood mononuclear cells were isolated and processed for the expression of Nrf2 and NF-κB by quantitative real-time polymerase chain reaction 3months before and after the exercise program. Using an enzyme-linked immunosorbent assay, the activity of glutathione peroxidase (GPx) as well as the products of high-sensitivity C-reactive protein and nitric oxide (NO) were assessed. Nrf2 expression (ranging from 0.86±0.4 to 1.76±0.8) and GPx activity were significantly increased after exercise intervention. In the exercise group, no difference in the levels of NO was observed; however, there was a significant reduction in the control group. In conclusion, these data suggest that resistance exercises seem to be capable of inducing Nrf2 activation in CKD patients on HD.

Environmental/lifestyle factors in the pathogenesis and prevention of type 2 diabetes

BACKGROUND

Environmental and lifestyle changes, in addition to the ageing of populations, are generally believed to account for the rapid global increase in type 2 diabetes prevalence and incidence in recent decades.

DISCUSSION

In this review, we present a comprehensive overview of factors contributing to diabetes risk, including aspects of diet quality and quantity, little physical activity, increased monitor viewing time or sitting in general, exposure to noise or fine dust, short or disturbed sleep, smoking, stress and depression, and a low socioeconomic status. In general, these factors promote an increase in body mass index. Since loss of β-cell function is the ultimate cause of developing overt type 2 diabetes, environmental and lifestyle changes must have resulted in a higher risk of β-cell damage in those at genetic risk. Multiple mechanistic pathways may come into play.

CONCLUSIONS

Strategies of diabetes prevention should aim at promoting a 'diabetes-protective lifestyle' whilst simultaneously enhancing the resistance of the human organism to pro-diabetic environmental and lifestyle factors. More research on diabetes-protective mechanisms seems warranted.

Environmental/lifestyle factors in the pathogenesis and prevention of type 2 diabetes

BACKGROUND

Environmental and lifestyle changes, in addition to the ageing of populations, are generally believed to account for the rapid global increase in type 2 diabetes prevalence and incidence in recent decades.

DISCUSSION

In this review, we present a comprehensive overview of factors contributing to diabetes risk, including aspects of diet quality and quantity, little physical activity, increased monitor viewing time or sitting in general, exposure to noise or fine dust, short or disturbed sleep, smoking, stress and depression, and a low socioeconomic status. In general, these factors promote an increase in body mass index. Since loss of β-cell function is the ultimate cause of developing overt type 2 diabetes, environmental and lifestyle changes must have resulted in a higher risk of β-cell damage in those at genetic risk. Multiple mechanistic pathways may come into play.

CONCLUSIONS

Strategies of diabetes prevention should aim at promoting a 'diabetes-protective lifestyle' whilst simultaneously enhancing the resistance of the human organism to pro-diabetic environmental and lifestyle factors. More research on diabetes-protective mechanisms seems warranted.

Exercise and Glycemic Control: Focus on Redox Homeostasis and Redox-Sensitive Protein Signaling

Physical inactivity, excess energy consumption, and obesity are associated with elevated systemic oxidative stress and the sustained activation of redox-sensitive stress-activated protein kinase (SAPK) and mitogen-activated protein kinase signaling pathways. Sustained SAPK activation leads to aberrant insulin signaling, impaired glycemic control, and the development and progression of cardiometabolic disease. Paradoxically, acute exercise transiently increases oxidative stress and SAPK signaling, yet postexercise glycemic control and skeletal muscle function are enhanced. Furthermore, regular exercise leads to the upregulation of antioxidant defense, which likely assists in the mitigation of chronic oxidative stress-associated disease. In this review, we explore the complex spatiotemporal interplay between exercise, oxidative stress, and glycemic control, and highlight exercise-induced reactive oxygen species and redox-sensitive protein signaling as important regulators of glucose homeostasis.

Nrf2 mediates redox adaptations to exercise

The primary aim of this review is to summarize the current literature on the effects of acute exercise and regular exercise on nuclear factor erythroid 2-related factor 2 (Nrf2) activity and downstream targets of Nrf2 signaling. Nrf2 (encoded in humans by the NFE2L2 gene) is the master regulator of antioxidant defenses, a transcription factor that regulates expression of more than 200 cytoprotective genes. Increasing evidence indicates that Nrf2 signaling plays a key role in how oxidative stress mediates the beneficial effects of exercise. Episodic increases in oxidative stress induced through bouts of acute exercise stimulate Nrf2 activation and when applied repeatedly, as with regular exercise, leads to upregulation of endogenous antioxidant defenses and overall greater ability to counteract the damaging effects of oxidative stress. The evidence of Nrf2 activation in response to exercise across variety of tissues may be an important mechanism of how exercise exerts its well-known systemic effects that are not limited to skeletal muscle and myocardium. Additionally there are emerging data that results from animal studies translate to humans.

Mitochondria in the middle: exercise preconditioning protection of striated muscle

Cellular and physiological adaptations to an atmosphere which became enriched in molecular oxygen spurred the development of a layered system of stress protection, including antioxidant and stress response proteins. At physiological levels reactive oxygen and nitrogen species regulate cell signalling as well as intracellular and intercellular communication. Exercise and physical activity confer a variety of stressors on skeletal muscle and the cardiovascular system: mechanical, metabolic, oxidative. Transient increases of stressors during acute bouts of exercise or exercise training stimulate enhancement of cellular stress protection against future insults of oxidative, metabolic and mechanical stressors that could induce injury or disease. This phenomenon has been termed both hormesis and exercise preconditioning (EPC). EPC stimulates transcription factors such as Nrf-1 and heat shock factor-1 and up-regulates gene expression of a cadre of cytosolic (e.g. glutathione peroxidase and heat shock proteins) and mitochondrial adaptive or stress proteins (e.g. manganese superoxide dismutase, mitochondrial KATP channels and peroxisome proliferator activated receptor γ coactivator-1 (PGC-1)). Stress response and antioxidant enzyme inducibility with exercise lead to protection against striated muscle damage, oxidative stress and injury. EPC may indeed provide significant clinical protection against ischaemia-reperfusion injury, Type II diabetes and ageing. New molecular mechanisms of protection, such as δ-opioid receptor regulation and mitophagy, reinforce the notion that mitochondrial adaptations (e.g. heat shock proteins, antioxidant enzymes and sirtuin-1/PGC-1 signalling) are central to the protective effects of exercise preconditioning.