Arctigenin efficiently enhanced sedentary mice treadmill endurance

Physical inactivity is considered as one of the potential risk factors for the development of type 2 diabetes and other metabolic diseases, while endurance exercise training could enhance fat oxidation that is associated with insulin sensitivity improvement in obesity. AMP-activated protein kinase (AMPK) as an energy sensor plays pivotal roles in the regulation of energy homeostasis, and its activation could improve glucose uptake, promote mitochondrial biogenesis and increase glycolysis. Recent research has even suggested that AMPK activation contributed to endurance enhancement without exercise. Here we report that the natural product arctigenin from the traditional herb Arctium lappa L. (Compositae) strongly increased AMPK phosphorylation and subsequently up-regulated its downstream pathway in both H9C2 and C2C12 cells. It was discovered that arctigenin phosphorylated AMPK via calmodulin-dependent protein kinase kinase (CaMKK) and serine/threonine kinase 11(LKB1)-dependent pathways. Mice treadmill based in vivo assay further indicated that administration of arctigenin improved efficiently mice endurance as reflected by the increased fatigue time and distance, and potently enhanced mitochondrial biogenesis and fatty acid oxidation (FAO) related genes expression in muscle tissues. Our results thus suggested that arctigenin might be used as a potential lead compound for the discovery of the agents with mimic exercise training effects to treat metabolic diseases.     

GLP-1 regulates exercise endurance and skeletal muscle remodeling via GLP-1R/AMPK pathway

Exercise-induced physical endurance enhancement and skeletal muscle remodeling can prevent and delay the development of multiple diseases, especially metabolic syndrome. Herein, the study explored the association between glucagon-like peptide-1 (GLP-1) secretion and exercise, and its effect on skeletal muscle remodeling to enhance endurance capacity. We found both acute exercise and short-term endurance training significantly increased the secretion of GLP-1 in mice. Recombinant adeno-associated virus (AAV) encoding Gcg (proglucagon) was used to induce the overexpression of GLP-1 in skeletal muscle of mice. Overexpression of GLP-1 in skeletal muscle enhanced endurance capacity. Meanwhile, glycogen synthesis, glucose uptake, type I fibers proportion, and mitochondrial biogenesis were augmented in GLP-1-AAV skeletal muscle. Furthermore, the in vitro experiment showed that exendin-4 (a GLP-1 receptor agonist) treatment remarkably promoted glucose uptake, type I fibers formation, and mitochondrial respiration. Mechanistically, the knockdown of AMPK could reverse the effects imposed by GLP-1R activation in vitro. Taken together, these results verify that GLP-1 regulates skeletal muscle remodeling to enhance exercise endurance possibly via GLP-1R signaling-mediated phosphorylation of AMPK.     

TRPV1 activation improves exercise endurance and energy metabolism through PGC-1α upregulation in mice

Impaired aerobic exercise capacity and skeletal muscle dysfunction are associated with cardiometabolic diseases. Acute administration of capsaicin enhances exercise endurance in rodents, but the long-term effect of dietary capsaicin is unknown. The capsaicin receptor, the transient receptor potential vanilloid 1 (TRPV1) cation channel has been detected in skeletal muscle, the role of which remains unclear. Here we report the function of TRPV1 in cultured C2C12 myocytes and the effect of TRPV1 activation by dietary capsaicin on energy metabolism and exercise endurance of skeletal muscles in mice. In vitro, capsaicin increased cytosolic free calcium and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) expression in C2C12 myotubes through activating TRPV1. In vivo, PGC-1α in skeletal muscle was upregulated by capsaicin-induced TRPV1 activation or genetic overexpression of TRPV1 in mice. TRPV1 activation increased the expression of genes involved in fatty acid oxidation and mitochondrial respiration, promoted mitochondrial biogenesis, increased oxidative fibers, enhanced exercise endurance and prevented high-fat diet-induced metabolic disorders. Importantly, these effects of capsaicin were absent in TRPV1-deficient mice. We conclude that TRPV1 activation by dietary capsaicin improves energy metabolism and exercise endurance by upregulating PGC-1α in skeletal muscles. The present results indicate a novel therapeutic strategy for managing metabolic diseases and improving exercise endurance.     

Physical exercise regulates p53 activity targeting SCO2 and increases mitochondrial COX biogenesis in cardiac muscle with age

The purpose of this study was to outline the timelines of mitochondrial function, oxidative stress and cytochrome c oxidase complex (COX) biogenesis in cardiac muscle with age, and to evaluate whether and how these age-related changes were attenuated by exercise. ICR/CD-1 mice were treated with pifithrin-μ (PFTμ), sacrificed and studied at different ages; ICR/CD-1 mice at younger or older ages were randomized to endurance treadmill running and sedentary conditions. The results showed that mRNA expression of p53 and its protein levels in mitochondria increased with age in cardiac muscle, accompanied by increased mitochondrial oxidative stress, reduced expression of COX subunits and assembly proteins, and decreased expression of most markers in mitochondrial biogenesis. Most of these age-related changes including p53 activity targeting cytochrome oxidase deficient homolog 2 (SCO2), p53 translocation to mitochondria and COX biogenesis were attenuated by exercise in older mice. PFTμ, an inhibitor blocking p53 translocation to mitochondria, increased COX biogenesis in older mice, but not in young mice. Our data suggest that physical exercise attenuates age-related changes in mitochondrial COX biogenesis and p53 activity targeting SCO2 and mitochondria, and thereby induces antisenescent and protective effects in cardiac muscle.     

Resveratrol induces Sirt1-dependent apoptosis in 3T3-L1 preadipocytes by activating AMPK and suppressing AKT activity and survivin expression

Resveratrol is a natural polyphenolic compound with anti-inflammatory, antioxidant and neuroprotective properties, and it serves as a chemopreventive and chemotherapeutic agent. However, only very limited data have been obtained regarding the effects of resveratrol on preadipocytes, and the mechanisms of these effects remain largely unknown. In this study, murine 3T3-L1 preadipocytes were incubated with resveratrol, and cell apoptosis was investigated. Resveratrol caused S-phase arrest to inhibit cell proliferation and significantly increased the lactate dehydrogenase leaking ratio. Hoechst 33258 staining and transmission electron microscopy revealed the ultrastructural changes in nuclear chromatins of apoptotic cells. Furthermore, resveratrol activated the mitochondrial signaling with decreases in the mitochondrial membrane potential, cytochrome c release and the activation of caspase 9 and caspase 3. Resveratrol treatment also increased the protein level of Sirt1. By using small interfering RNAs of Sirt1, adenosine-monophosphate-activated protein kinase (AMPK) α, survivin and the AMPK agonist (5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside) and specific inhibitors for protein kinase B (AKT) or caspases, it was demonstrated that activation of Sirt1 inhibited AKT activation and further decreased the expression of survivin. It could also increase AMPK activation. Both signaling pathways activated mitochondrion-mediated pathway. Our findings clarified the apoptotic effects of resveratrol in 3T3-L1 preadipocytes and revealed the involved pathway including AMPK, AKT and survivin, suggesting its potential therapeutic application in the treatment or prevention of obesity and related metabolic symptoms.     

NAMPT regulates mitochondria biogenesis via NAD metabolism and calcium binding proteins during skeletal muscle contraction

[Purpose]

The purpose of this study was to investigate the effect that muscle contraction induced NAD metabolism via NAMPT has on mitochondrial biogenesis.

[Methods]

Primary skeletal muscle cells were isolated from the gastrocnemius in C57BL/6 mice. The muscle cells were stimulated by electrical current at 1Hz for 3 minutes in conditions of normal or NAD metabolism related inhibitor treatment. NAD/NADH level, Sirt1 and mitochondria biogenesis related signal factor’s changes were examined in normal or NAD metabolism related inhibitor treated cells.

[Results]

Electrical stimulation (ES) induced muscle contractions significantly increased NAD/NADH levels, NAMPT inhibitor FK-866 inhibited ES-induced NAD formation, which caused SIRT1 expression and PGC-1α deacetylation to decrease. Moreover, NAMPT inhibition decreased mitochondrial biogenesis related mRNA, COX-1 and Tfam levels. Along with AMPK inhibitor, compound C decreases SIRT1 expression, PGC-1α deacetylation and muscle contraction induced mitochondrial biogenesis related mRNA increment. These results indicated that the AMPK-NAMPT signal is a key player for muscle contraction induced SIRT1 expression and PGC-1α deacetylation, which influences mitochondrial biogenesis. Inhibition of the AMPK upregulator, Camkkβ, STO-609 decreased AMPK phosphorylation and SIRT1 expression but did not decrease PGC-1α deacetylation. However, CAMKII inhibition via AIP decreased PGC-1α deacetylation.

[Conclusion]

In conclusion, the results indicate that NAMPT plays an important role in NAD metabolism and mitochondrial biogenesis. However, mitochondrial biogenesis is also controlled by different calcium binding protein signals including Camkkβ and CAMKII. [Keyword] Muscle contraction, NAD metabolism, SIRT1, PGC-1 α, mitochondria biogenesis.     

Aging-associated reductions in AMP-activated protein kinase activity and mitochondrial biogenesis

Recent studies have demonstrated a strong relationship between aging-associated reductions in mitochondrial function, dysregulated intracellular lipid metabolism, and insulin resistance. Given the important role of the AMP-activated protein kinase (AMPK) in the regulation of fat oxidation and mitochondrial biogenesis, we examined AMPK activity in young and old rats and found that acute stimulation of AMPK-alpha(2) activity by 5'-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) and exercise was blunted in skeletal muscle of old rats. Furthermore, mitochondrial biogenesis in response to chronic activation of AMPK with beta-guanidinopropionic acid (beta-GPA) feeding was also diminished in old rats. These results suggest that aging-associated reductions in AMPK activity may be an important contributing factor in the reduced mitochondrial function and dysregulated intracellular lipid metabolism associated with aging.     

Effects of Resveratrol and SIRT1 on PGC-1α Activity and Mitochondrial Biogenesis: A Reevaluation

It has been reported that feeding mice resveratrol activates AMPK and SIRT1 in skeletal muscle leading to deacetylation and activation of PGC-1α, increased mitochondrial biogenesis, and improved running endurance. This study was done to further evaluate the effects of resveratrol, SIRT1, and PGC-1α deacetylation on mitochondrial biogenesis in muscle. Feeding rats or mice a diet containing 4 g resveratrol/kg diet had no effect on mitochondrial protein levels in muscle. High concentrations of resveratrol lowered ATP concentration and activated AMPK in C₂C₁₂ myotubes, resulting in an increase in mitochondrial proteins. Knockdown of SIRT1, or suppression of SIRT1 activity with a dominant-negative (DN) SIRT1 construct, increased PGC-1α acetylation, PGC-1α coactivator activity, and mitochondrial proteins in C₂C₁₂ cells. Expression of a DN SIRT1 in rat triceps muscle also induced an increase in mitochondrial proteins. Overexpression of SIRT1 decreased PGC-1α acetylation, PGC-1α coactivator activity, and mitochondrial proteins in C₂C₁₂ myotubes. Overexpression of SIRT1 also resulted in a decrease in mitochondrial proteins in rat triceps muscle. We conclude that, contrary to some previous reports, the mechanism by which SIRT1 regulates mitochondrial biogenesis is by inhibiting PGC-1α coactivator activity, resulting in a decrease in mitochondria. We also conclude that feeding rodents resveratrol has no effect on mitochondrial biogenesis in muscle.     

Sirt1 and the Mitochondria

Sirt1 is the most prominent and extensively studied member of sirtuins, the family of mammalian class III histone deacetylases heavily implicated in health span and longevity. Although primarily a nuclear protein, Sirt1’s deacetylation of Peroxisome proliferator-activated receptor Gamma Coactivator-1α (PGC-1α) has been extensively implicated in metabolic control and mitochondrial biogenesis, which was proposed to partially underlie Sirt1’s role in caloric restriction and impacts on longevity. The notion of Sirt1’s regulation of PGC-1α activity and its role in mitochondrial biogenesis has, however, been controversial. Interestingly, Sirt1 also appears to be important for the turnover of defective mitochondria by mitophagy. I discuss here evidences for Sirt1’s regulation of mitochondrial biogenesis and turnover, in relation to PGC-1α deacetylation and various aspects of cellular physiology and disease.     

The AMPK-PPARGC1A pathway is required for antimicrobial host defense through activation of autophagy

AMP-activated protein kinase (AMPK) is a crucial energy sensor and plays a key role in integration of cellular functions to maintain homeostasis. Despite this, it is largely unknown whether targeting the AMPK pathway can be used as a therapeutic strategy for infectious diseases. Herein, we show that AMPK activation robustly induces antibacterial autophagy, which contributes to antimicrobial defense against Mycobacterium tuberculosis (Mtb). AMPK activation led to inhibition of Mtb-induced phosphorylation of the mechanistic target of rapamycin (MTOR) in macrophages. In addition, AMPK activation increased the genes involved in oxidative phosphorylation, mitochondrial ATP production, and biogenesis in Mtb-infected macrophages. Notably, peroxisome proliferator-activated receptor-gamma, coactivator 1α (PPARGC1A) was required for AMPK-mediated antimicrobial activity, as well as enhancement of mitochondrial function and biogenesis, in macrophages. Further, the AMPK-PPARGC1A pathway was involved in the upregulation of multiple autophagy-related genes via CCAAT/enhancer binding protein (C/EBP), β (CEBPB). PPARGC1A knockdown inhibited the AMPK-mediated induction of autophagy and impaired the fusion of phagosomes with MAP1LC3B (LC3B) autophagosomes in Mtb-infected macrophages. The link between autophagy, mitochondrial function, and antimicrobial activity was further demonstrated by studying LysMCre-mediated knockout of atg7, demonstrating mitochondrial ultrastructural defects and dysfunction, as well as blockade of antimicrobial activity against mycobacteria. Collectively, our results identify the AMPK-PPARGC1A axis as contributing to autophagy activation leading to an antimicrobial response, as a novel host defense mechanism.     

Mitochonic acid-5 attenuates TNF-α-mediated neuronal inflammation via activating Parkin-related mitophagy and augmenting the AMPK–Sirt3 pathways

Mitochondrial dysfunction has been found to be associated with neuronal inflammation; however, no effective drug is available to attenuate neuroinflammation via sustaining mitochondrial function. In the current study, experiments were performed to understand the beneficial effects of mitochonic acid 5 (MA-5) on tumor necrosis factor-α (TNF-α)-mediated neuronal injury and mitochondrial damage. Our data illustrated that MA-5 pretreatment reduced inflammation response induced by TNF-α in CATH.a cells. Molecular investigations demonstrated that MA-5 pretreatment repressed oxidative stress, inhibited endoplasmic reticulum stress, sustained cellular energy metabolism, and blocked cell apoptosis induced by TNF-α stress. Further, we found that MA-5 treatment elevated the expression of Sirtuin 3 (Sirt3) and this effect was dependent on the activation of AMP-activated protein kinase (AMPK) pathway. Blockade of AMPK abolished the promotive action of MA-5 on Sirt3 and thus mediated mitochondrial damage and cell death. Besides, we also found that MA-5 treatment augmented Parkin-related mitophagy and increased mitophagy promoted CATH.a cells survival via improving mitochondrial function. Knockdown of Parkin abolished the beneficial action of MA-5 on mitochondrial homeostasis and CATH.a cell survival. Altogether, our results confirm that MA-5 is an effective drug to attenuate neuroinflammation via sustaining mitochondrial damage and promoting CATH.a cell survival. The protective action of MA-5 on neuronal damage is associated with Parkin-related mitophagy and the activation of AMPK–Sirt3 pathways.     

Berberine protects against high fat diet-induced dysfunction in muscle mitochondria by inducing SIRT1-dependent mitochondrial biogenesis

Berberine (BBR) has recently been shown to improve insulin sensitivity in rodent models of insulin resistance. Although this effect was explained partly through an observed activation of AMP-activated protein kinase (AMPK), the upstream and downstream mediators of this phenotype were not explored. Here, we show that BBR supplementation reverts mitochondrial dysfunction induced by High Fat Diet (HFD) and hyperglycemia in skeletal muscle, in part due to an increase in mitochondrial biogenesis. Furthermore, we observe that the prevention of mitochondrial dysfunction by BBR, the increase in mitochondrial biogenesis, as well as BBR-induced AMPK activation, are blocked in cells in which SIRT1 has been knocked-down. Taken together, these data reveal an important role for SIRT1 and mitochondrial biogenesis in the preventive effects of BBR on diet-induced insulin resistance.     

Berberine protects against high fat diet-induced dysfunction in muscle mitochondria by inducing SIRT1-dependent mitochondrial biogenesis

Berberine (BBR) has recently been shown to improve insulin sensitivity in rodent models of insulin resistance. Although this effect was explained partly through an observed activation of AMP-activated protein kinase (AMPK), the upstream and downstream mediators of this phenotype were not explored. Here, we show that BBR supplementation reverts mitochondrial dysfunction induced by High Fat Diet (HFD) and hyperglycemia in skeletal muscle, in part due to an increase in mitochondrial biogenesis. Furthermore, we observe that the prevention of mitochondrial dysfunction by BBR, the increase in mitochondrial biogenesis, as well as BBR-induced AMPK activation, are blocked in cells in which SIRT1 has been knocked-down. Taken together, these data reveal an important role for SIRT1 and mitochondrial biogenesis in the preventive effects of BBR on diet-induced insulin resistance.     

An acute bout of high-intensity interval training increases the nuclear abundance of PGC-1α and activates mitochondrial biogenesis in human skeletal muscle

Low-volume, high-intensity interval training (HIT) increases skeletal muscle mitochondrial capacity, yet little is known regarding potential mechanisms promoting this adaptive response. Our purpose was to examine molecular processes involved in mitochondrial biogenesis in human skeletal muscle in response to an acute bout of HIT. Eight healthy men performed 4 × 30-s bursts of all-out maximal intensity cycling interspersed with 4 min of rest. Muscle biopsy samples (vastus lateralis) were obtained immediately before and after exercise, and after 3 and 24 h of recovery. At rest, the majority of peroxisome proliferator-activated receptor γ coactivator (PGC)-1α, a master regulator of mitochondrial biogenesis, was detected in cytosolic fractions. Exercise activated p38 MAPK and AMPK in the cytosol. Nuclear PGC-1α protein increased 3 h into recovery from exercise, a time point that coincided with increased mRNA expression of mitochondrial genes. This was followed by an increase in mitochondrial protein content and enzyme activity after 24 h of recovery. These findings support the hypothesis that an acute bout of low-volume HIT activates mitochondrial biogenesis through a mechanism involving increased nuclear abundance of PGC-1α.