AMP-activated protein kinase controls exercise training- and AICAR-induced increases in SIRT3 and MnSOD

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.

Myokine Secretion following an Aerobic Exercise Intervention in Individuals with Type 2 Diabetes with or without Exercise Resistance

Type 2 diabetes (T2D) is characterized by muscle metabolic dysfunction that exercise can minimize, but some patients do not respond to an exercise intervention. Myokine secretion is intrinsically altered in patients with T2D, but the role of myokines in exercise resistance in this patient population has never been studied. We sought to determine if changes in myokine secretion were linked to the response to an exercise intervention in patients with T2D. The participants followed a 10-week aerobic exercise training intervention, and patients with T2D were grouped based on muscle mitochondrial function improvement (responders versus non-responders). We measured myokines in serum and cell-culture medium of myotubes derived from participants pre- and post-intervention and in response to an in vitro model of muscle contraction. We also quantified the expression of genes related to inflammation in the myotubes pre- and post-intervention. No significant differences were detected depending on T2D status or response to exercise in the biological markers measured, with the exception of modest differences in expression patterns for certain myokines (IL-1β, IL-8, IL-10, and IL-15). Further investigation into the molecular mechanisms involving myokines may explain exercise resistance with T2D; however, the role in metabolic adaptations to exercise in T2D requires further investigation.

Overexpression of manganese superoxide dismutase mitigates ACL injury-induced muscle atrophy, weakness and oxidative damage

Oxidative stress has been implicated in the etiology of skeletal muscle weakness following joint injury. We investigated longitudinal patient muscle samples following knee injury (anterior cruciate ligament tear). Following injury, transcriptomic analysis revealed downregulation of mitochondrial metabolism-related gene networks, which were supported by reduced mitochondrial respiratory flux rates. Additionally, enrichment of reactive oxygen species (ROS)-related pathways were upregulated in muscle following knee injury, and further investigation unveiled marked oxidative damage in a progressive manner following injury and surgical reconstruction. We then investigated whether antioxidant protection is effective in preventing muscle atrophy and weakness after knee injury in mice that overexpress Mn-superoxide dismutase (MnSOD+/-). MnSOD+/- mice showed attenuated oxidative damage, atrophy, and muscle weakness compared to wild type littermate controls following ACL transection surgery. Taken together, our results indicate that ROS-related damage is a causative mechanism of muscle dysfunction after knee injury, and that mitochondrial antioxidant protection may hold promise as a therapeutic target to prevent weakness and development of disability.

The multifaceted benefits of walking for healthy aging: from Blue Zones to molecular mechanisms

Physical activity, including walking, has numerous health benefits in older adults, supported by a plethora of observational and interventional studies. Walking decreases the risk or severity of various health outcomes such as cardiovascular and cerebrovascular diseases, type 2 diabetes mellitus, cognitive impairment and dementia, while also improving mental well-being, sleep, and longevity. Dose-response relationships for walking duration and intensity are established for adverse cardiovascular outcomes. Walking's favorable effects on cardiovascular risk factors are attributed to its impact on circulatory, cardiopulmonary, and immune function. Meeting current physical activity guidelines by walking briskly for 30 min per day for 5 days can reduce the risk of several age-associated diseases. Additionally, low-intensity physical exercise, including walking, exerts anti-aging effects and helps prevent age-related diseases, making it a powerful tool for promoting healthy aging. This is exemplified by the lifestyles of individuals in Blue Zones, regions of the world with the highest concentration of centenarians. Walking and other low-intensity physical activities contribute significantly to the longevity of individuals in these regions, with walking being an integral part of their daily lives. Thus, incorporating walking into daily routines and encouraging walking-based physical activity interventions can be an effective strategy for promoting healthy aging and improving health outcomes in all populations. The goal of this review is to provide an overview of the vast and consistent evidence supporting the health benefits of physical activity, with a specific focus on walking, and to discuss the impact of walking on various health outcomes, including the prevention of age-related diseases. Furthermore, this review will delve into the evidence on the impact of walking and low-intensity physical activity on specific molecular and cellular mechanisms of aging, providing insights into the underlying biological mechanisms through which walking exerts its beneficial anti-aging effects.

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.

Pinocembrin alleviates pyroptosis and apoptosis through ROS elimination in random skin flaps via activation of SIRT3

Random skin flap grafting is the most common skin grafting technique in reconstructive surgery. Despite progress in techniques, the incidence of distal flap necrosis still exceeds 3%, which limits its use in clinical practice. Current methods for treating distal flap necrosis are still lacking. Pinocembrin (Pino) can inhibit reactive oxygen species (ROS) and cell death in a variety of diseases, such as cardiovascular diseases, but the role of Pino in random flaps has not been explored. Therefore, we explore how Pino can enhance flap survival and its specific upstream mechanisms via macroscopic examination, Doppler, immunohistochemistry, and western blot. The results suggested that Pino can enhance the viability of random flaps by inhibiting ROS, pyroptosis and apoptosis. The above effects were reversed by co-administration of Pino with adeno-associated virus-silencing information regulator 2 homolog 3 (SIRT3) shRNA, proving the beneficial effect of Pino on the flaps relied on SIRT3. In addition, we also found that Pino up-regulates SIRT3 expression by activating the AMP-activated protein kinase (AMPK) pathway. This study proved that Pino can improve random flap viability by eliminating ROS, and ROS-induced cell death through the activation of SIRT3, which are triggered by the AMPK/PGC-1α signaling pathway.

Complex II Biology in Aging, Health, and Disease

Aging is associated with a decline in mitochondrial function which may contribute to age-related diseases such as neurodegeneration, cancer, and cardiovascular diseases. Recently, mitochondrial Complex II has emerged as an important player in the aging process. Mitochondrial Complex II converts succinate to fumarate and plays an essential role in both the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC). The dysfunction of Complex II not only limits mitochondrial energy production; it may also promote oxidative stress, contributing, over time, to cellular damage, aging, and disease. Intriguingly, succinate, the substrate for Complex II which accumulates during mitochondrial dysfunction, has been shown to have widespread effects as a signaling molecule. Here, we review recent advances related to understanding the function of Complex II, succinate signaling, and their combined roles in aging and aging-related diseases.

Transient changes to metabolic homeostasis initiate mitochondrial adaptation to endurance exercise

Endurance exercise is well established to increase mitochondrial content and function in skeletal muscle, a process termed mitochondrial biogenesis. Current understanding is that exercise initiates skeletal muscle mitochondrial remodeling via modulation of cellular nutrient, energetic and contractile stress pathways. These subtle changes in the cellular milieu are sensed by numerous transduction pathways that serve to initiate and coordinate an increase in mitochondrial gene transcription and translation. The result of these acute signaling events is the promotion of growth and assembly of mitochondria, coupled to a greater capacity for aerobic ATP provision in skeletal muscle. The aim of this review is to highlight the acute metabolic events induced by endurance exercise and the subsequent molecular pathways that sense this transient change in cellular homeostasis to drive mitochondrial adaptation and remodeling.

Exercise Improves the Coordination of the Mitochondrial Unfolded Protein Response and Mitophagy in Aging Skeletal Muscle

The mitochondrial unfolded protein response (UPRmt) and mitophagy are two mitochondrial quality control (MQC) systems that work at the molecular and organelle levels, respectively, to maintain mitochondrial homeostasis. Under stress conditions, these two processes are simultaneously activated and compensate for each other when one process is insufficient, indicating mechanistic coordination between the UPRmt and mitophagy that is likely controlled by common upstream signals. This review focuses on the molecular signals regulating this coordination and presents evidence showing that this coordination mechanism is impaired during aging and promoted by exercise. Furthermore, the bidirectional regulation of reactive oxygen species (ROS) and AMPK in modulating this mechanism is discussed. The hierarchical surveillance network of MQC can be targeted by exercise-derived ROS to attenuate aging, which offers a molecular basis for potential therapeutic interventions for sarcopenia.

Sirtuin-3: A potential target for treating several types of brain injury

Sirtuin-3 (SIRT3) is responsible for maintaining mitochondrial homeostasis by deacetylating substrates in an NAD+-dependent manner. SIRT3, the primary deacetylase located in the mitochondria, controls cellular energy metabolism and the synthesis of essential biomolecules for cell survival. In recent years, increasing evidence has shown that SIRT3 is involved in several types of acute brain injury. In ischaemic stroke, subarachnoid haemorrhage, traumatic brain injury, and intracerebral haemorrhage, SIRT3 is closely related to mitochondrial homeostasis and with the mechanisms of pathophysiological processes such as neuroinflammation, oxidative stress, autophagy, and programmed cell death. As SIRT3 is the driver and regulator of a variety of pathophysiological processes, its molecular regulation is significant. In this paper, we review the role of SIRT3 in various types of brain injury and summarise SIRT3 molecular regulation. Numerous studies have demonstrated that SIRT3 plays a protective role in various types of brain injury. Here, we present the current research available on SIRT3 as a target for treating ischaemic stroke, subarachnoid haemorrhage, traumatic brain injury, thus highlighting the therapeutic potential of SIRT3 as a potent mediator of catastrophic brain injury. In addition, we have summarised the therapeutic drugs, compounds, natural extracts, peptides, physical stimuli, and other small molecules that may regulate SIRT3 to uncover additional brain-protective mechanisms of SIRT3, conduct further research, and provide more evidence for clinical transformation and drug development.

Regular exercise effectively protects against the aging-associated decline in skeletal muscle NAD content

Skeletal muscle is a tissue integral to general health. Due to its high abundance and oxidative capacity, its metabolism is intimately linked to whole-body physiology. In the elderly population, mobility correlates positively with life expectancy and survival. Furthermore, regular physical activity is one of the most effective health-promoting interventions that delay the onset of aging-associated chronic diseases. Data from preclinical studies show that aging of various tissues is accompanied by a decrease in the concentration of nicotinamide adenine dinucleotide (NAD), which plays a central role in energy homeostasis. Thus, a hypothesis has emerged that normalization of its content would ameliorate the age-related decline in tissue function and therefore improve health of the elderly. This idea, along with the documented safety and high tolerability of NAD precursor supplementation, makes NAD metabolism a prospective target for anti-aging interventions. Interestingly, muscle NAD biosynthesis pathways are stimulated by exercise training, which suggests that training-induced adaptations rely on tissue NAD levels. However, while the relationship between muscle fitness and regular physical activity is well-characterized, the proposed synergy between muscle NAD replenishment and exercise training has not been established. Here, we review the published data on the role of NAD metabolism in exercise in the context of young and aged skeletal muscle and discuss the current challenges relevant to the field.

A Promising Strategy to Treat Neurodegenerative Diseases by SIRT3 Activation

SIRT3, the primary mitochondrial deacetylase, regulates the functions of mitochondrial proteins including metabolic enzymes and respiratory chain components. Although SIRT3's functions in peripheral tissues are well established, the significance of its downregulation in neurodegenerative diseases is beginning to emerge. SIRT3 plays a key role in brain energy metabolism and provides substrate flexibility to neurons. It also facilitates metabolic coupling between fuel substrate-producing tissues and fuel-consuming tissues. SIRT3 mediates the health benefits of lifestyle-based modifications such as calorie restriction and exercise. SIRT3 deficiency is associated with metabolic syndrome (MetS), a precondition for diseases including obesity, diabetes, and cardiovascular disease. The pure form of Alzheimer's disease (AD) is rare, and it has been reported to coexist with these diseases in aging populations. SIRT3 downregulation leads to mitochondrial dysfunction, neuroinflammation, and inflammation, potentially triggering factors of AD pathogenesis. Recent studies have also suggested that SIRT3 may act through multiple pathways to reduce plaque formation in the AD brain. In this review, we give an overview of SIRT3's roles in brain physiology and pathology and discuss several activators of SIRT3 that can be considered potential therapeutic agents for the treatment of dementia.

Substrate stiffness enhances human regulatory T cell induction and metabolism

Regulatory T cells (Tregs) provide an essential tolerance mechanism to suppress the immune response. Induced Tregs hold the potential to treat autoimmune diseases in adoptive therapy and can be produced with stimulating signals to CD3 and CD28 in presence of the cytokine TGF-β and IL-2. This report examines the modulation of human Treg induction by leveraging the ability of T cells to sense the mechanical stiffness of an activating substrate. Treg induction on polyacrylamide gels (PA-gels) was sensitive to the substrate's elastic modulus, increasing with greater material stiffness. Single-cell RNA-Seq analysis revealed that Treg induction on stiffer substrates involved greater use of oxidative phosphorylation (OXPHOS). Inhibition of ATP synthase significantly reduced the rate of Treg induction and abrogated the difference among gels while activation of AMPK (AMP-activated protein kinase) increased Treg induction on the softer sample but not on the harder sample. Treg induction is thus mechanosensitive and OXPHOS-dependent, providing new strategies for improving the production of these cells for cellular immunotherapy.

The Aging Heart: A Molecular and Clinical Challenge

Aging is associated with an increasing burden of morbidity, especially for cardiovascular diseases (CVDs). General cardiovascular risk factors, ischemic heart diseases, heart failure, arrhythmias, and cardiomyopathies present a significant prevalence in older people, and are characterized by peculiar clinical manifestations that have distinct features compared with the same conditions in a younger population. Remarkably, the aging heart phenotype in both healthy individuals and patients with CVD reflects modifications at the cellular level. An improvement in the knowledge of the physiological and pathological molecular mechanisms underlying cardiac aging could improve clinical management of older patients and offer new therapeutic targets.

The Role of SIRT3 in Exercise and Aging

The health benefits of regular exercise are well established. Nonetheless, the molecular mechanism(s) responsible for exercise-induced health benefits remain a topic of debate. One of the key cell-signaling candidates proposed to provide exercise-induced benefits is sirtuin 3 (SIRT3). SIRT3, an NAD+ dependent mitochondrial deacetylase, positively modulates many cellular processes, including energy metabolism, mitochondrial biogenesis, and protection against oxidative stress. Although the exercise-induced change in SIRT3 signaling is a potential mechanism contributing to the health advantages of exercise on aging, studies investigating the impact of exercise on SIRT3 abundance in cells provide conflicting results. To resolve this conundrum, this narrative review provides a detailed analysis of the role that exercise-induced changes in SIRT3 play in providing the health and aging benefits associated with regular physical activity. We begin with an overview of SIRT3 function in cells followed by a comprehensive review of the impact of exercise on SIRT3 expression in humans and other mammalians. We then discuss the impact of SIRT3 on aging, followed by a thorough analysis of the cell-signaling links between SIRT3 and exercise-induced adaptation. Notably, to stimulate future research, we conclude with a discussion of key unanswered questions related to exercise, aging, and SIRT3 expression.

Molecular mechanisms of sacubitril/valsartan in cardiac remodeling

Cardiovascular diseases have become a major clinical burden globally. Heart failure is one of the diseases that commonly emanates from progressive uncontrolled hypertension. This gives rise to the need for a new treatment for the disease. Sacubitril/valsartan is a new drug combination that has been approved for patients with heart failure. This review aims to detail the mechanism of action for sacubitril/valsartan in cardiac remodeling, a cellular and molecular process that occurs during the development of heart failure. Accumulating evidence has unveiled the cardioprotective effects of sacubitril/valsartan on cellular and molecular modulation in cardiac remodeling, with recent large-scale randomized clinical trials confirming its supremacy over other traditional heart failure treatments. However, its molecular mechanism of action in cardiac remodeling remains obscure. Therefore, comprehending the molecular mechanism of action of sacubitril/valsartan could help future research to study the drug's potential therapy to reduce the severity of heart failure.

Unbiased proteomics, histochemistry, and mitochondrial DNA copy number reveal better mitochondrial health in muscle of high-functioning octogenarians

Background

Master athletes (MAs) prove that preserving a high level of physical function up to very late in life is possible, but the mechanisms responsible for their high function remain unclear.

Methods

We performed muscle biopsies in 15 octogenarian world-class track and field MAs and 14 non-athlete age/sex-matched controls (NA) to provide insights into mechanisms for preserving function in advanced age. Muscle samples were assessed for respiratory compromised fibers, mitochondrial DNA (mtDNA) copy number, and proteomics by liquid-chromatography mass spectrometry.

Results

MA exhibited markedly better performance on clinical function tests and greater cross-sectional area of the vastus lateralis muscle. Proteomics analysis revealed marked differences, where most of the ~800 differentially represented proteins in MA versus NA pertained to mitochondria structure/function such as electron transport capacity (ETC), cristae formation, mitochondrial biogenesis, and mtDNA-encoded proteins. In contrast, proteins from the spliceosome complex and nuclear pore were downregulated in MA. Consistent with proteomics data, MA had fewer respiratory compromised fibers, higher mtDNA copy number, and an increased protein ratio of the cristae-bound ETC subunits relative to the outer mitochondrial membrane protein voltage-dependent anion channel. There was a substantial overlap of proteins overrepresented in MA versus NA with proteins that decline with aging and that are higher in physically active than sedentary individuals. However, we also found 176 proteins related to mitochondria that are uniquely differentially expressed in MA.

Conclusions

We conclude that high function in advanced age is associated with preserving mitochondrial structure/function proteins, with underrepresentation of proteins involved in the spliceosome and nuclear pore complex. Whereas many of these differences in MA appear related to their physical activity habits, others may reflect unique biological (e.g., gene, environment) mechanisms that preserve muscle integrity and function with aging.

Funding

Funding for this study was provided by operating grants from the Canadian Institutes of Health Research (MOP 84408 to TT and MOP 125986 to RTH). This work was supported in part by the Intramural Research Program of the National Institute on Aging, NIH, Baltimore, MD, USA.

AMPK and the Adaptation to Exercise

Noncommunicable diseases are chronic diseases that contribute to death worldwide, but these diseases can be prevented and mitigated with regular exercise. Exercise activates signaling molecules and the transcriptional network to promote physiological adaptations, such as fiber type transformation, angiogenesis, and mitochondrial biogenesis. AMP-activated protein kinase (AMPK) is a master regulator that senses the energy state, promotes metabolism for glucose and fatty acid utilization, and mediates beneficial cellular adaptations in many vital tissues and organs. This review focuses on the current, integrative understanding of the role of exercise-induced activation of AMPK in the regulation of system metabolism and promotion of health benefits.

Atlas of exercise metabolism reveals time-dependent signatures of metabolic homeostasis

Tissue sensitivity and response to exercise vary according to the time of day and alignment of circadian clocks, but the optimal exercise time to elicit a desired metabolic outcome is not fully defined. To understand how tissues independently and collectively respond to timed exercise, we applied a systems biology approach. We mapped and compared global metabolite responses of seven different mouse tissues and serum after an acute exercise bout performed at different times of the day. Comparative analyses of intra- and inter-tissue metabolite dynamics, including temporal profiling and blood sampling across liver and hindlimb muscles, uncovered an unbiased view of local and systemic metabolic responses to exercise unique to time of day. This comprehensive atlas of exercise metabolism provides clarity and physiological context regarding the production and distribution of canonical and novel time-dependent exerkine metabolites, such as 2-hydroxybutyrate (2-HB), and reveals insight into the health-promoting benefits of exercise on metabolism.

Do exercise-associated genes explain phenotypic variance in the three components of fitness? a systematic review & meta-analysis

The aim of this systematic review and meta-analysis was to identify a list of common, candidate genes associated with the three components of fitness, specifically cardiovascular fitness, muscular strength, and anaerobic power, and how these genes are associated with exercise response phenotype variability, in previously untrained participants. A total of 3,969 potentially relevant papers were identified and processed for inclusion. After eligibility and study selection assessment, 24 studies were selected for meta-analysis, comprising a total of 3,012 participants (male n = 1,512; females n = 1,239; not stated n = 261; age 28 ± 9 years). Meta-Essentials spreadsheet 1.4 (Microsoft Excel) was used in creating the forest plots and meta-analysis. IBM SPSS statistics V24 was implemented for the statistical analyses and the alpha was set at p ≤ 0.05. 13 candidate genes and their associated alleles were identified, which were associated with the phenotypes of interest. Analysis of training group data showed significant differential phenotypic responses. Subgroup analysis showed; 44%, 72% and 10% of the response variance in aerobic, strength and power phenotypes, respectively, were explained by genetic influences. This analysis established that genetic variability explained a significant proportion of the adaptation differences across the three components of fitness in the participants post-training. The results also showed the importance of analysing and reporting specific gene alleles. Information obtained from these findings has the potential to inform and influence future exercise-related genes and training studies.

Redox interactions of immune cells and muscle in the regulation of exercise-induced pain and analgesia: implications on the modulation of muscle nociceptor sensory neurons

The mechanistic interactions among redox status of leukocytes, muscle, and exercise in pain regulation are still poorly understood and limit targeted treatment. Exercise benefits are numerous, including the treatment of chronic pain. However, unaccustomed exercise may be reported as undesirable as it may contribute to pain. The aim of the present review is to evaluate the relationship between oxidative metabolism and acute exercise-induced pain, and as to whether improved antioxidant capacity underpins the analgesic effects of regular exercise. Preclinical and clinical studies addressing relevant topics on mechanisms by which exercise modulates the nociceptive activity and how redox status can outline pain and analgesia are discussed, in sense of translating into refined outcomes. Emerging evidence points to the role of oxidative stress-induced signaling in sensitizing nociceptor sensory neurons. In response to acute exercise, there is an increase in oxidative metabolism, and consequently, pain. Instead, regular exercise can modulate redox status in favor of antioxidant capacity and repair mechanisms, which have consequently increased resistance to oxidative stress, damage, and pain. Data indicate that acute sessions of unaccustomed prolonged and/or intense exercise increase oxidative metabolism and regulate exercise-induced pain in the post-exercise recovery period. Further, evidence demonstrates regular exercise improves antioxidant status, indicating its therapeutic utility for chronic pain disorders. An improved comprehension of the role of redox status in exercise can provide helpful insights into immune-muscle communication during pain modulatory effects of exercise and support new therapeutic efforts and rationale for the promotion of exercise.

Mitochondrial contributions to vascular endothelial dysfunction, arterial stiffness, and cardiovascular diseases

Cardiovascular disease (CVD) affects one in three adults and remains the leading cause of death in America. Advancing age is a major risk factor for CVD. Recent plateaus in CVD-related mortality rates in high-income countries after decades of decline highlight a critical need to identify novel therapeutic targets and strategies to mitigate and manage the risk of CVD development and progression. Vascular dysfunction, characterized by endothelial dysfunction and large elastic artery stiffening, is independently associated with an increased CVD risk and incidence and is therefore an attractive target for CVD prevention and management. Vascular mitochondria have emerged as an important player in maintaining vascular homeostasis. As such, age- and disease-related impairments in mitochondrial function contribute to vascular dysfunction and consequent increases in CVD risk. This review outlines the role of mitochondria in vascular function and discusses the ramifications of mitochondrial dysfunction on vascular health in the setting of age and disease. The adverse vascular consequences of increased mitochondrial-derived reactive oxygen species, impaired mitochondrial quality control, and defective mitochondrial calcium cycling are emphasized, in particular. Current evidence for both lifestyle and pharmaceutical mitochondrial-targeted strategies to improve vascular function is also presented.

Ammonium chloride administration prior to exercise has muscle-specific effects on mitochondrial and myofibrillar protein synthesis in rats

AIM

Exercise is able to increase both muscle protein synthesis and mitochondrial biogenesis. However, acidosis, which can occur in pathological states as well as during high-intensity exercise, can decrease mitochondrial function, whilst its impact on muscle protein synthesis is disputed. Thus, the aim of this study was to determine the effect of a mild physiological decrease in pH, by administration of ammonium chloride, on myofibrillar and mitochondrial protein synthesis, as well as associated molecular signaling events.

METHODS

Male Wistar rats were given either a placebo or ammonium chloride prior to a short interval training session. Rats were killed before exercise, immediately after exercise, or 3 h after exercise.

RESULTS

Myofibrillar (p = 0.036) fractional protein synthesis rates was increased immediately after exercise in the soleus muscle of the placebo group, but this effect was absent in the ammonium chloride group. However, in the gastrocnemius muscle NH4 Cl increased myofibrillar (p = 0.044) and mitochondrial protein synthesis (0 h after exercise p = 0.01; 3 h after exercise p = 0.003). This was accompanied by some small differences in protein phosphorylation and mRNA expression.

CONCLUSION

This study found ammonium chloride administration immediately prior to a single session of exercise in rats had differing effects on mitochondrial and myofibrillar protein synthesis rates in soleus (type I) and gastrocnemius (type II) muscle in rats.

Sirtuin3 in Neurological Disorders

Sirtuins are NAD+ dependent enzymes that have a predominant role in neurodegenerative disorders and also regulate the inflammatory process, protein aggregation, etc. The relation between Sirtuins with that of the nervous system and neurodegeneration are widely studied consequently. Sirtuins have a strong role in metabolic syndrome in mitochondria also. The activities of Sirtuins can be altered by using small molecules that would be developed into drugs and it is proven that manipulation of SIRT1 activity influences neurodegenerative disease models. They are especially thrilling since using small molecules, which would be developed into a drug, it is feasible to alter the activities of sirtuins. Different functions of Sirtuins are depended upon their subcellular localization. In this review paper, we are discussing different Sirtuins, differential expression of sirtuins, and expression of sirtuin in the brain and briefly about sirtuin3 (SIRT3).

Dynamic changes in DICER levels in adipose tissue control metabolic adaptations to exercise

DICER is a key enzyme in microRNA (miRNA) biogenesis. Here we show that aerobic exercise training up-regulates DICER in adipose tissue of mice and humans. This can be mimicked by infusion of serum from exercised mice into sedentary mice and depends on AMPK-mediated signaling in both muscle and adipocytes. Adipocyte DICER is required for whole-body metabolic adaptations to aerobic exercise training, in part, by allowing controlled substrate utilization in adipose tissue, which, in turn, supports skeletal muscle function. Exercise training increases overall miRNA expression in adipose tissue, and up-regulation of miR-203-3p limits glycolysis in adipose under conditions of metabolic stress. We propose that exercise training-induced DICER-miR-203-3p up-regulation in adipocytes is a key adaptive response that coordinates signals from working muscle to promote whole-body metabolic adaptations.

Reciprocity Between Skeletal Muscle AMPK Deletion and Insulin Action in Diet-Induced Obese Mice

Insulin resistance due to overnutrition places a burden on energy-producing pathways in skeletal muscle (SkM). Nevertheless, energy state is not compromised. The hypothesis that the energy sensor AMPK is necessary to offset the metabolic burden of overnutrition was tested using chow-fed and high-fat (HF)-fed SkM-specific AMPKα1α2 knockout (mdKO) mice and AMPKα1α2lox/lox littermates (wild-type [WT]). Lean mdKO and WT mice were phenotypically similar. HF-fed mice were equally obese and maintained lean mass regardless of genotype. Results did not support the hypothesis that AMPK is protective during overnutrition. Paradoxically, mdKO mice were more insulin sensitive. Insulin-stimulated SkM glucose uptake was approximately twofold greater in mdKO mice in vivo. Furthermore, insulin signaling, SkM GLUT4 translocation, hexokinase activity, and glycolysis were increased. AMPK and insulin signaling intersect at mammalian target of rapamycin (mTOR), a critical node for cell proliferation and survival. Basal mTOR activation was reduced by 50% in HF-fed mdKO mice, but was normalized by insulin stimulation. Mitochondrial function was impaired in mdKO mice, but energy charge was preserved by AMP deamination. Results show a surprising reciprocity between SkM AMPK signaling and insulin action that manifests with diet-induced obesity, as insulin action is preserved to protect fundamental energetic processes in the muscle.

Proteomics-based identification of different training adaptations of aged skeletal muscle following long-term high-intensity interval and moderate-intensity continuous training in aged rats

Aging-associated loss of skeletal muscle mass and force increases the risk of falls, impairs mobility, and leads to a reduced quality of life. High-intensity interval training (HIIT) is superior to moderate-intensity continuous training (MICT) for improving morphological and metabolic adaptations of skeletal muscle in older adults, but the underlying mechanism is unknown. Aged female rats underwent HIIT and MICT for 8 months, and their differential impacts on skeletal muscle proteome were investigated. HIIT resulted in a larger improvement in grip strength and fiber cross-sectional area, with similar increases in inclined plane performance and time to exhaustion. Proteomic analysis showed that common training adaptations of both protocols included changes to muscle contraction, focal adhesion signaling, mitochondrial function, apoptosis and regeneration, and anti-oxidation, whereas protein processing in the endoplasmic reticulum and adipocytokine signaling were specifically altered in the MICT and HIIT groups, respectively. Immunoblotting showed that upregulation of the adiponectin/AMPK signaling pathway may be associated with improvements in autophagy, oxidative stress, mitochondrial function, and apoptosis in aged skeletal muscle following HIIT. Thus, understanding the molecular differences in training adaptations from these two exercise modalities may aid in combatting sarcopenia.

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.

Effects and Mechanisms of Five Psoralea Prenylflavonoids on Aging-Related Diseases

During the aging process, senescent cells gradually accumulate in the organs; they secrete proinflammatory cytokines and other factors, collectively known as the senescence-associated secretory phenotype (SASP). SASP secretions contribute to “inflammaging,” which is a state of chronic, systemic, sterility, low-grade inflammatory microenvironment and a key risk factor in the development of aging-related diseases. Fructus psoraleae is a traditional Chinese medical herb best known for delaying aging and treating osteoporosis. Prenylflavonoids from fructus psoraleae are the main bioactive compounds responsible for its pharmacological applications, such as beaching, bavachinin, bavachalcone, isobavachalcone, and neobavaisoflavone. In previous decades, there have been some promising studies on the pharmacology of fructus psoraleae. Here, we focus on the anti-inflammatory and antiaging diseases of five psoralea prenylflavonoids, such as cardiovascular protection, diabetes and obesity intervention, neuroprotection, and osteoporosis, and discuss the mechanism of these active ingredients for better understanding the material basis and drug application of fructus psoraleae in Chinese medicine.

Alpha-synuclein-induced mitochondrial dysfunction is mediated via a sirtuin 3-dependent pathway

BACKGROUND

Misfolding and aggregation of the presynaptic protein alpha-synuclein (αsyn) is a hallmark of Parkinson's disease (PD) and related synucleinopathies. Although predominantly localized in the cytosol, a body of evidence has shown that αsyn localizes to mitochondria and contributes to the disruption of key mitochondrial processes. Mitochondrial dysfunction is central to the progression of PD and mutations in mitochondrial-associated proteins are found in familial cases of PD. The sirtuins are highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent enzymes that play a broad role in cellular metabolism and aging. Interestingly, mitochondrial sirtuin 3 (SIRT3) plays a major role in maintaining mitochondrial function and preventing oxidative stress, and is downregulated in aging and age-associated diseases such as neurodegenerative disorders. Herein, we hypothesize that αsyn is associated with decreased SIRT3 levels contributing to impaired mitochondrial dynamics and biogenesis in PD.

METHODS

The level of mitochondrial SIRT3 was assessed in cells expressing oligomeric αsyn within the cytosolic and mitochondrial-enriched fractions. Mitochondrial integrity, respiration, and health were examined using several markers of mitochondrial dynamics and stress response and by measuring the rate of oxygen consumption (OCR). Our findings were validated in a rodent model of PD as well as in human post-mortem Lewy body disease (LBD) brain tissue.

RESULTS

Here, we demonstrate that αsyn associates with mitochondria and induces a decrease in mitochondrial SIRT3 levels and mitochondrial biogenesis. We show that SIRT3 downregulation is accompanied by decreased phosphorylation of AMPK and cAMP-response element binding protein (CREB), as well as increased phosphorylation of dynamin-related protein 1 (DRP1), indicative of impaired mitochondrial dynamics. OCR was significantly decreased suggesting a mitochondria respiratory deficit. Interestingly treatment with AMPK agonist 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) restores SIRT3 expression, improves mitochondrial function, and decreases αsyn oligomer formation in a SIRT3-dependent manner.

CONCLUSIONS

Together, our findings suggest that pharmacologically increasing SIRT3 levels can counteract αsyn-induced mitochondrial dysfunction by reducing αsyn oligomers and normalizing mitochondrial bioenergetics. These data support a protective role for SIRT3 in PD-associated pathways and contribute significant mechanistic insight into the interplay of SIRT3 and αsyn.

High intensity interval training and molecular adaptive response of skeletal muscle

Increased cardiovascular fitness, V˙O_2max, is associated with enhanced endurance capacity and a decreased rate of mortality. High intensity interval training (HIIT) is one of the best methods to increase V˙O_2max and endurance capacity for top athletes and for the general public as well. Because of the high intensity of this type of training, the adaptive response is not restricted to Type I fibers, as found for moderate intensity exercise of long duration. Even with a short exercise duration, HIIT can induce activation of AMPK, PGC-1α, SIRT1 and ROS pathway as well as by the modulation of Ca²⁺ homeostasis, leading to enhanced mitochondrial biogenesis, and angiogenesis. The present review summarizes the current knowledge of the adaptive response of HIIT.

SIRT4 and Its Roles in Energy and Redox Metabolism in Health, Disease and During Exercise

NAD⁺-dependent SIRT4 has been reported to be a key regulator of metabolic enzymes and antioxidant defense mechanisms in mitochondria. It also plays an important role in regulation of mitochondrial metabolism in response to exercise. Recent studies have shown that SIRT4 is involved in a wide range of mitochondrial metabolic processes, including depressing insulin secretion in pancreatic beta cells, promoting lipid synthesis, regulating mitochondrial adenosine triphosphate (ATP) homeostasis, controlling apoptosis and regulating redox. SIRT4 also appears to have enzymatic functions involved in posttranslational modifications such as ADP-ribosylation, lysine deacetylation and lipoamidation. However, the effects on SIRT4 by metabolic diseases and changes in metabolic homeostasis such as during exercise, along with the roles of SIRT4 in the regulation of metabolism during disease, are not well understood. The main goal of this review is to critically analyse and summarise the current research evidence on the significance of the SIRT4 as a metabolic regulator and in mitochondrial function and its putative roles in relation to metabolic diseases and exercise.

Time of Exercise Specifies the Impact on Muscle Metabolic Pathways and Systemic Energy Homeostasis

While the timing of food intake is important, it is unclear whether the effects of exercise on energy metabolism are restricted to unique time windows. As circadian regulation is key to controlling metabolism, understanding the impact of exercise performed at different times of the day is relevant for physiology and homeostasis. Using high-throughput transcriptomic and metabolomic approaches, we identify distinct responses of metabolic oscillations that characterize exercise in either the early rest phase or the early active phase in mice. Notably, glycolytic activation is specific to exercise at the active phase. At the molecular level, HIF1α, a central regulator of glycolysis during hypoxia, is selectively activated in a time-dependent manner upon exercise, resulting in carbohydrate exhaustion, usage of alternative energy sources, and adaptation of systemic energy expenditure. Our findings demonstrate that the time of day is a critical factor to amplify the beneficial impact of exercise on both metabolic pathways within skeletal muscle and systemic energy homeostasis.

Exercise and Sirtuins: A Way to Mitochondrial Health in Skeletal Muscle

The sirtuins form a family of evolutionarily conserved nicotinamide adenine dinucleotide (NAD)-dependent deacetylases. Seven sirtuins (SIRT1–SIRT7) have been described in mammals, with specific intracellular localization and biological functions associated with mitochondrial energy homeostasis, antioxidant activity, proliferation and DNA repair. Physical exercise affects the expression of sirtuin in skeletal muscle, regulating changes in mitochondrial biogenesis, oxidative metabolism and the cellular antioxidant system. In this context, sirtuin 1 and sirtuin 3 have been the most studied. This review focuses on the effects of different types of exercise on these sirtuins, the molecular pathways involved and the biological effect that is caused mainly in healthy subjects. The reported findings suggest that an acute load of exercise activates SIRT1, which in turn activates biogenesis and mitochondrial oxidative capacity. Additionally, several sessions of exercise (training) activates SIRT1 and also SIRT3 that, together with the biogenesis and mitochondrial oxidative function, jointly activate ATP production and the mitochondrial antioxidant function.

Short-term high salt intake impairs hepatic mitochondrial bioenergetics and biosynthesis in SIRT3 knockout mice

High salt intake (HS) is an important factor in the development of many metabolic diseases. The liver is the metabolic center in the body. However, the effect of short-term HS on the liver mitochondria and its mechanism are still unclear. In this study, we investigated the effects of short-term HS on liver mitochondrial function. We found that HS reduced Sirtuin3 (SIRT3) protein level, increasing protein carbonylation in mice liver. HS intake decreased ATP production, mitochondrial transcription factor A (TFAM), and complex I level. SIRT3 knockout (SKO) mice exhibited similar results with HS-treated wild-type mice but with a less extent of carbonylation and ATP reduction. Our study shows that short-term HS led to increased hepatic oxidative state, impaired mitochondrial biosynthesis, and bioenergetics. HS-treated mice could still maintain hepatic glucose homeostasis by compensatory activation of Adenosine 5'-monophosphate-activated protein kinase (AMPK). However, in HS-treated SKO mice, AMPK was not activated, instead, the glycogen synthase activity increased, which caused an exceptionally increased glycogen accumulation. This study provides evidence that short-term HS intake could cause the early hepatic metabolic changes, highlighting the importance of controlling salt intake especially in those patients with defects in SIRT3. Highlights High salt intake down-regulates SIRT3 protein level and increases oxidation. High salt intake activates AMPK via AMP-dependent pathway. High salt intake impairs energy metabolism. High salt combined with SIRT3 knockout results in glycogen accumulation.

Voluntary wheel running in the late dark phase ameliorates diet-induced obesity in mice without altering insulin action

Metabolic dysfunction and Type 2 diabetes are associated with perturbed circadian rhythms. However, exercise appears to ameliorate circadian disturbances, as it can phase-shift or reset the internal clock system. Evidence is emerging that exercise at a distinct time of day can correct misalignments of the circadian clock and influence energy metabolism. This suggests that timing of exercise training can be important for the prevention and management of metabolic dysfunction. In this study, obese, high-fat diet-fed mice were subjected to voluntary wheel running (VWR) at two different periods of the day to determine the effects of time-of-day-restricted VWR on basal and insulin-stimulated glucose disposal. VWR in the late dark phase reduced body weight gain compared with VWR in the beginning of the dark phase. Conversely, time-of-day-restricted VWR did not influence insulin action and glucose disposal, since skeletal muscle and adipose tissue glucose uptake and insulin signaling remained unaffected. Protein abundance of the core clock proteins, brain-muscle arnt-like 1 (BMAL1), and circadian locomotor output control kaput (CLOCK), were increased in skeletal muscle after VWR, independent of whether mice had access to running wheels in the early or late dark phase. Collectively, we provide evidence that VWR in the late dark phase ameliorates diet-induced obesity without altering insulin action or glucose homeostasis.

NEW & NOTEWORTHY Exercise appears to ameliorate circadian disturbances as it can entrain the internal clock system. We provide evidence that voluntary wheel running increases core clock protein abundance and influences diet-induced obesity in mice in a time-of-day-dependent manner. However, the effect of time-of-day-restricted voluntary wheel running on body weight gain is not associated with enhanced basal- and insulin-stimulated glucose disposal, suggesting that time-of-day-restricted voluntary wheel running affects energy homeostasis rather than glucose homeostasis.

A physiological drop in pH decreases mitochondrial respiration, and HDAC and Akt signaling, in L6 myocytes

Exercise stimulates mitochondrial biogenesis and increases mitochondrial respiratory function and content. However, during high-intensity exercise muscle pH can decrease below pH 6.8 with a concomitant increase in lactate concentration. This drop in muscle pH is associated with reduced exercise-induced mitochondrial biogenesis, while increased lactate may act as a signaling molecule to affect mitochondrial biogenesis. Therefore, in this study we wished to determine the impact of altering pH and lactate concentration in L6 myotubes on genes and proteins known to be involved in mitochondrial biogenesis. We also examined mitochondrial respiration in response to these perturbations. Differentiated L6 myotubes were exposed to normal (pH 7.5)-, low (pH 7.0)-, or high (pH 8.0)-pH media with and without 20 mM sodium l-lactate for 1 and 6 h. Low pH and 20 mM sodium l-lactate resulted in decreased Akt (Ser473) and AMPK (T172) phosphorylation at 1 h compared with controls, while at 6 h the nuclear localization of histone deacetylase 5 (HDAC5) was decreased. When the pH was increased both Akt (Ser473) and AMPK (T172) phosphorylation was increased at 1 h. Overall increased lactate decreased the nuclear content of HDAC5 at 6 h. Exposure to both high- and low-pH media decreased basal mitochondrial respiration, ATP turnover, and maximum mitochondrial respiratory capacity. These data indicate that muscle pH affects several metabolic signaling pathways, including those required for mitochondrial function.

Skeletal Muscle Insulin Sensitivity Show Circadian Rhythmicity Which Is Independent of Exercise Training Status

Circadian rhythms can be perturbed by shift work, travel across time zones, many occupational tasks, or genetic mutations. Perturbed circadian rhythms are associated with the increasing problem of obesity, metabolic dysfunction, and insulin resistance. We hypothesized that insulin sensitivity in skeletal muscle follows a circadian pattern and that this pattern is important for overall metabolic function. This hypothesis was verified using mice as a model system. We observed circadian rhythmicity in whole body insulin tolerance, as well as in signaling pathways regulating insulin- and exercise-induced glucose uptake in skeletal muscle, including AKT, 5'-adenosine monophosphate-activated protein kinase (AMPK) and TBC1 domain family member 4 (TBC1D4) phosphorylation. Basal and insulin-stimulated glucose uptake in skeletal muscle and adipose tissues in vivo also differed between day- and nighttime. However, the rhythmicity of glucose uptake differed from the rhythm of whole-body insulin tolerance. These results indicate that neither skeletal muscle nor adipose tissue play a major role for the circadian rhythmicity in whole-body insulin tolerance. To study the circadian pattern of insulin sensitivity directly in skeletal muscle, we determined glucose uptake under basal and submaximal insulin-stimulated conditions ex vivo every sixth hour. Both insulin sensitivity and signaling of isolated skeletal muscle peaked during the dark period. We next examined the effect of exercise training on the circadian rhythmicity of insulin sensitivity. As expected, voluntary exercise training enhanced glucose uptake in skeletal muscle. Nevertheless, exercise training did not affect the circadian rhythmicity of skeletal muscle insulin sensitivity. Taken together, our results provide evidence that skeletal muscle insulin sensitivity exhibits circadian rhythmicity.

The Role of SIRT3 in the Brain Under Physiological and Pathological Conditions

Sirtuin enzymes are a family of highly seven conserved protein deacetylases, namely SIRT1 through SIRT7, whose enzymatic activities require the cofactor nicotinamide adenine dinucleotide (NAD⁺). Sirtuins reside in different compartments within cells, and their activities have been shown to regulate a number of cellular pathways involved in but not limited to stress management, apoptosis and inflammatory responses. Given the importance of mitochondrial functional state in neurodegenerative conditions, the mitochondrial SIRT3 sirtuin, which is the primary deacetylase within mitochondria, has garnered considerable recent attention. It is now clear that SIRT3 plays a major role in regulating a host of mitochondrial molecular cascades that can contribute to both normal and pathophysiological processes. However, most of the currently available knowledge on SIRT3 stems from studies in non-neuronal cells, and the consequences of the interactions between SIRT3 and its targets in the CNS are only beginning to be elucidated. In this review, we will summarize current advances relating to SIRT3, and explore how its known functions could influence brain physiology.

Elevated Nicotinamide Phosphoribosyl Transferase in Skeletal Muscle Augments Exercise Performance and Mitochondrial Respiratory Capacity Following Exercise Training

Mice overexpressing NAMPT in skeletal muscle (NamptTg mice) develop higher exercise endurance and maximal aerobic capacity (VO₂max) following voluntary exercise training compared to wild-type (WT) mice. Here, we aimed to investigate the mechanisms underlying by determining skeletal muscle mitochondrial respiratory capacity in NamptTg and WT mice. Body weight and body composition, tissue weight (gastrocnemius, quadriceps, soleus, heart, liver, and epididymal white adipose tissue), skeletal muscle and liver glycogen content, VO₂max, skeletal muscle mitochondrial respiratory capacity (measured by high-resolution respirometry), skeletal muscle gene expression (measured by microarray and qPCR), and skeletal muscle protein content (measured by Western blot) were determined following 6 weeks of voluntary exercise training (access to running wheel) in 13-week-old male NamptTg (exercised NamptTg) mice and WT (exercised WT) mice. Daily running distance and running time during the voluntary exercise training protocol were recorded. Daily running distance (p = 0.51) and running time (p = 0.85) were not significantly different between exercised NamptTg mice and exercised WT mice. VO₂max was higher in exercised NamptTg mice compared to exercised WT mice (p = 0.02). Body weight (p = 0.92), fat mass (p = 0.49), lean mass (p = 0.91), tissue weight (all p > 0.05), and skeletal muscle (p = 0.72) and liver (p = 0.94) glycogen content were not significantly different between exercised NamptTg mice and exercised WT mice. Complex I oxidative phosphorylation (OXPHOS) respiratory capacity supported by fatty acid substrates (p < 0.01), maximal (complex I+II) OXPHOS respiratory capacity supported by glycolytic (p = 0.02) and fatty acid (p < 0.01) substrates, and maximal uncoupled respiratory capacity supported by fatty acid substrates (p < 0.01) was higher in exercised NamptTg mice compared to exercised WT mice. Transcriptomic analyses revealed differential expression for genes involved in oxidative metabolism in exercised NamptTg mice compared to exercised WT mice, specifically, enrichment for the gene set related to the SIRT3-mediated signaling pathway. SIRT3 protein content correlated with NAMPT protein content (r = 0.61, p = 0.04). In conclusion, NamptTg mice develop higher exercise capacity following voluntary exercise training compared to WT mice, which is paralleled by higher mitochondrial respiratory capacity in skeletal muscle. The changes in SIRT3 targets suggest that these effects are due to remodeling of mitochondrial function.

Reversing age-associated arterial dysfunction: insight from preclinical models

Cardiovascular diseases (CVDs) remain the leading causes of death in the United States, and advancing age is a primary risk factor. Impaired endothelium-dependent dilation and increased stiffening of the arteries with aging are independent predictors of CVD. Increased tissue and systemic oxidative stress and inflammation underlie this age-associated arterial dysfunction. Calorie restriction (CR) is the most powerful intervention known to increase life span and improve age-related phenotypes, including arterial dysfunction. However, the translatability of long-term CR to clinical populations is limited, stimulating interest in the pursuit of pharmacological CR mimetics to reproduce the beneficial effects of CR. The energy-sensing pathways, mammalian target of rapamycin, AMPK, and sirtuin-1 have all been implicated in the beneficial effects of CR on longevity and/or physiological function and, as such, have emerged as potential targets for therapeutic intervention as CR mimetics. Although manipulation of each of these pathways has CR-like benefits on arterial function, the magnitude and/or mechanisms can be disparate from that of CR. Nevertheless, targeting these pathways in older individuals may provide some benefits against arterial dysfunction and CVD. The goal of this review is to provide a brief discussion of the mechanisms and pathways underlying age-associated dysfunction in large arteries, explain how these are impacted by CR, and to present the available evidence, suggesting that targets for energy-sensing pathways may act as vascular CR mimetics.

Perturbations of NAD+ salvage systems impact mitochondrial function and energy homeostasis in mouse myoblasts and intact skeletal muscle

Nicotinamide adenine dinucleotide (NAD⁺) can be synthesized by nicotinamide phosphoribosyltransferase (NAMPT). We aimed to determine the role of NAMPT in maintaining NAD⁺ levels, mitochondrial function, and metabolic homeostasis in skeletal muscle cells. We generated stable Nampt knockdown (sh Nampt KD) C2C12 cells using a shRNA lentiviral approach. Moreover, we applied gene electrotransfer to express Cre recombinase in tibialis anterior muscle of floxed Nampt mice. In sh Nampt KD C2C12 myoblasts, Nampt and NAD⁺ levels were reduced by 70% and 50%, respectively, and maximal respiratory capacity was reduced by 25%. Moreover, anaerobic glycolytic flux increased by 55%, and 2-deoxyglucose uptake increased by 25% in sh Nampt KD cells. Treatment with the NAD⁺ precursor nicotinamide riboside restored NAD⁺ levels in sh Nampt cells and increased maximal respiratory capacity by 18% and 32% in control and sh Nampt KD cells, respectively. Expression of Cre recombinase in muscle of floxed Nampt mice reduced NAMPT and NAD⁺ levels by 38% and 43%, respectively. Glucose uptake increased by 40%, and mitochondrial complex IV respiration was compromised by 20%. Hypoxia-inducible factor (HIF)-1α-regulated genes and histone H3 lysine 9 (H3K9) acetylation, a known sirtuin 6 (SIRT6) target, were increased in shNampt KD cells. Thus, we propose that the shift toward glycolytic metabolism observed, at least in part, is mediated by the SIRT6/HIF1α axis. Our findings suggest that NAMPT plays a key role for maintaining NAD⁺ levels in skeletal muscle and that NAMPT deficiency compromises oxidative phosphorylation capacity and alters energy homeostasis in this tissue.

AMPK in skeletal muscle function and metabolism

Skeletal muscle possesses a remarkable ability to adapt to various physiologic conditions. AMPK is a sensor of intracellular energy status that maintains energy stores by fine-tuning anabolic and catabolic pathways. AMPK’s role as an energy sensor is particularly critical in tissues displaying highly changeable energy turnover. Due to the drastic changes in energy demand that occur between the resting and exercising state, skeletal muscle is one such tissue. Here, we review the complex regulation of AMPK in skeletal muscle and its consequences on metabolism (e.g., substrate uptake, oxidation, and storage as well as mitochondrial function of skeletal muscle fibers). We focus on the role of AMPK in skeletal muscle during exercise and in exercise recovery. We also address adaptations to exercise training, including skeletal muscle plasticity, highlighting novel concepts and future perspectives that need to be investigated. Furthermore, we discuss the possible role of AMPK as a therapeutic target as well as different AMPK activators and their potential for future drug development.—Kjøbsted, R., Hingst, J. R., Fentz, J., Foretz, M., Sanz, M.-N., Pehmøller, C., Shum, M., Marette, A., Mounier, R., Treebak, J. T., Wojtaszewski, J. F. P., Viollet, B., Lantier, L. AMPK in skeletal muscle function and metabolism.

SIRT3 gene expression but not SIRT3 subcellular localization is altered in response to fasting and exercise in human skeletal muscle

NEW FINDINGS

What is the central question of this study? Evidence from cellular and animal models suggests that SIRT3 is involved in regulating aerobic ATP production. Thus, we investigated whether changes in fatty acid and oxidative metabolism known to accompany fasting and exercise occur in association with changes in SIRT3 mitochondrial localization and expression in human skeletal muscle. What is the main finding and its importance? We find that 48 h of fasting and acute endurance exercise decrease SIRT3 mRNA expression but do not alter SIRT3 mitochondrial localization despite marked increases in fatty acid oxidation. This suggests that SIRT3 activity is not regulated by changes in mitochondrial localization in response to cellular energy stress in human skeletal muscle. The present study examined SIRT3 expression and SIRT3 mitochondrial localization in response to acute exercise and short-term fasting in human skeletal muscle. Experiment 1 involved eight healthy men (age, 21.4 ± 2.8 years; peak O2 uptake, 47.1 ± 11.8 ml min(-1)  kg(-1) ) who performed a single bout of exercise at ∼55% of peak aerobic work rate for 1 h. Muscle biopsies were obtained at rest (Rest), immediately after exercise (EX-0) and 3 h postexercise (EX-3). Experiment 2 involved 10 healthy men (age, 22.0 ± 1.5 years; peak O2 uptake, 46.9 ± 6.0 ml min−1 kg−1) who underwent a 48 h fast, with muscle biopsies collected 1 h postprandial (Fed) and after 48 h of fasting (Fast). Mitochondrial respiration was measured using high-resolution respirometry in permeabilized muscle fibre bundles to assess substrate oxidation. Whole body fat oxidation increased after both exercise (Rest, 0.96 ± 0.32 kcal min(-1) ; Exercise, 5.66 ± 1.97 kcal min(-1) ; P < 0.001) and fasting (Fed, 0.87 ± 0.51 kcal min(-1) ; Fast, 1.30 ± 0.37 kcal min(-1) , P < 0.05). SIRT3 gene expression decreased (P < 0.05) after both exercise (-8%) and fasting (-19%); however, SIRT3 whole muscle protein content was unaltered after fasting. No changes were observed in SIRT3 mitochondrial localization following either exercise or fasting. Fasting also decreased the Vmax of glutamate [80 ± 43 versus 50 ± 21 pmol s(-1)  (mg dry weight)(-1) ; P < 0.05]. These findings suggest that SIRT3 does not appear to be regulated by changes in mitochondrial localization at the time points measured in the present study in response to cellular energy stress in human skeletal muscle.

PGC-1α and fasting-induced PDH regulation in mouse skeletal muscle

The purpose of the present study was to examine whether lack of skeletal muscle peroxisome proliferator‐activated receptor gamma coactivator 1 alpha (PGC‐1α) affects the switch in substrate utilization from a fed to fasted state and the fasting‐induced pyruvate dehydrogenase (PDH) regulation in skeletal muscle. Skeletal muscle‐specific PGC‐1α knockout (MKO) mice and floxed littermate controls were fed or fasted for 24 h. Fasting reduced PDHa activity, increased phosphorylation of all four known sites on PDH‐E1α and increased pyruvate dehydrogenase kinase (PDK4) and sirtuin 3 (SIRT3) protein levels, but did not alter total acetylation of PDH‐E1α. Lack of muscle PGC‐1α did not affect the switch from glucose to fat oxidation in the transition from the fed to fasted state, but was associated with lower and higher respiratory exchange ratio (RER) in the fed and fasted state, respectively. PGC‐1α MKO mice had lower skeletal muscle PDH‐E1α, PDK1, 2, 4, and pyruvate dehydrogenase phosphatase (PDP1) protein content than controls, but this did not prevent the fasting‐induced increase in PDH‐E1α phosphorylation in PGC‐1α MKO mice. However, lack of skeletal muscle PGC‐1α reduced SIRT3 protein content, increased total lysine PDH‐E1α acetylation in the fed state, and prevented a fasting‐induced increase in SIRT3 protein. In conclusion, skeletal muscle PGC‐1α is required for fasting‐induced upregulation of skeletal muscle SIRT3 and maintaining high fat oxidation in the fasted state, but is dispensable for preserving the capability to switch substrate during the transition from the fed to the fasted state and for fasting‐induced PDH regulation in skeletal muscle.

The effect of acute and chronic sprint-interval training on LRP130, SIRT3, and PGC-1α expression in human skeletal muscle

This study examined changes in LRP130 gene and protein expression in response to an acute bout of sprint‐interval training (SIT) and 6 weeks of SIT in human skeletal muscle. In addition, we investigated the relationships between changes in LRP130, SIRT3, and PGC‐1α gene or protein expression. Fourteen recreationally active men (age: 22.0 ± 2.4 years) performed a single bout of SIT (eight, 20‐sec intervals at ~170% of VO₂peak work rate, separated by 10 sec of rest). Muscle biopsies were obtained at rest (PRE) and 3 h post‐exercise. The same participants then underwent a 6 week SIT program with biopsies after 2 (MID) and 6 (POST) weeks of training. In response to an acute bout of SIT, PGC‐1α mRNA expression increased (284%, P < 0.001); however, LRP130 and SIRT3 remained unchanged. VO₂peak and fiber‐specific SDH activity increased in response to training (P < 0.01). LRP130, SIRT3, and PGC‐1α protein expression were also unaltered following 2 and 6 weeks of SIT. There were no significant correlations between LRP130, SIRT3, or PGC‐1α mRNA expression in response to acute SIT. However, changes in protein expression of LRP130, SIRT3, and PGC‐1α were positively correlated at several time points with large effect sizes, which suggest that the regulation of these proteins may be coordinated in human skeletal muscle. Future studies should investigate other exercise protocols known to increase PGC‐1α and SIRT3 protein, like longer duration steady‐state exercise, to identify if LRP130 expression can be altered in response to exercise.

High-intensity high-volume swimming induces more robust signaling through PGC-1α and AMPK activation than sprint interval swimming in m. triceps brachii

We aimed to test whether high-intensity high-volume training (HIHVT) swimming would induce more robust signaling than sprint interval training (SIT) swimming within the m. triceps brachii due to lower metabolic and oxidation. Nine well-trained swimmers performed the two training procedures on separate randomized days. Muscle biopsies from m. triceps brachii and blood samples were collected at three different time points: a) before the intervention (pre), b) immediately after the swimming procedures (post) and c) after 3 h of rest (3 h). Hydroperoxides, creatine kinase (CK), and lactate dehydrogenase (LDH) were quantified from blood samples, and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and the AMPK^pTHR172/AMPK ratio were quantified by Western blot analysis. PGC-1α, sirtuin 3 (SIRT3), superoxide-dismutase 2 (SOD2), and vascular endothelial growth factor (VEGF) mRNA levels were also quantified. SIT induced a higher release of LDH (p < 0.01 at all time points) and CK (p < 0.01 at post) than HIHVT, but neither SIT nor HIHVT altered systemic hydroperoxides. Additionally, neither SIRT3 nor SOD2 mRNA levels increased, while PGC-1α transcription increased at 3 h after SIT (p < 0.01) and after HIHVT (p < 0.001). However, PGC-1α protein was higher after HIHVT than after SIT (p < 0.05). Moreover, the AMPK^pTHR172/AMPK ratio increased at post after SIT (p < 0.05), whereas this effect was delayed after HIHVT as it increased after 3 h (p < 0.05). In addition, VEGF transcription was higher in response to HIHVT (p < 0.05). In conclusion, SIT induces higher muscular stress than HIHVT without increasing systemic oxidation. In addition, HIHVT may induce more robust oxidative adaptations through PGC-1α and AMPK.