AMP-activated protein kinase-mediated expression of heat shock protein beta 1 enhanced insulin sensitivity in the skeletal muscle

Knockout of Hsp70 genes significantly affects locomotion speed and gene expression in leg skeletal muscles of Drosophila melanogaster

The functions of the heat shock protein 70 (Hsp70) genes were studied using a line of Drosophila melanogaster with a knockout of 6 of these genes out of 13. Namely, the effect of knockout of Hsp70 genes on negative geotaxis climbing (locomotor) speed and the ability to adapt to climbing training (0.5-1.5 h/day, 7 days/wk, 19 days) were examined. Seven- and 23-day-old Hsp70- flies demonstrated a comparable reduction (twofold) in locomotor speed and widespread changes in leg skeletal muscle transcriptome (RNA sequencing) compared with w1118 flies. To identify the functions of genes related to decreased locomotor speed, the overlapped differentially expressed genes at both time points were analyzed: the upregulated genes encoded extracellular proteins, regulators of drug metabolism, and the antioxidant response, whereas downregulated genes encoded regulators of carbohydrate metabolism and transmembrane proteins. In addition, in Hsp70- flies, activation of transcription factors related to disruption of the fibril structure and heat shock response (Hsf) was predicted, using the position weight matrix approach. In control flies, adaptation to chronic exercise training was associated mainly with gene response to a single exercise bout, whereas the predicted transcription factors were related to stress/immune (Hsf, NF-κB, etc.) and early gene response. In contrast, Hsp70- flies demonstrated no adaptation to training as well as a significantly impaired gene response to a single exercise bout. In conclusion, the knockout of Hsp70 genes not only reduced physical performance but also disrupted adaptation to chronic physical training, which is associated with changes in the leg skeletal muscle transcriptome and impaired gene response to a single exercise bout.NEW & NOTEWORTHY Knockout of six heat shock protein 70 (Hsp70) genes in Drosophila melanogaster reduced locomotion (climbing) speed that is associated with genotype-specific differences in leg skeletal muscle gene expression. Disrupted adaptation of Hsp70- flies to chronic exercise training is associated with impaired gene response to a single exercise bout.

Neuroprotective Effect of IND1316, an Indole-Based AMPK Activator, in Animal Models of Huntington Disease

Aggregation of mutant huntingtin, because of an expanded polyglutamine track, underlies the cause of neurodegeneration in Huntington disease (HD). However, it remains unclear how some alterations at the cellular level lead to specific structural changes in HD brains. In this context, the neuroprotective effect of the activation of AMP-activated protein kinase (AMPK) appears to be a determinant factor in several neurodegenerative diseases, including HD. In the present work, we describe a series of indole-derived compounds able to activate AMPK at the cellular level. By using animal models of HD (both worms and mice), we demonstrate the in vivo efficacy of one of these compounds (IND1316), confirming that it can reduce the neuropathological symptoms of this disease. Taken together, in vivo results and in silico studies of druggability, allow us to suggest that IND1316 could be considered as a promising new lead compound for the treatment of HD and other central nervous system diseases in which the activation of AMPK results in neuroprotection.

Overheating or overcooling: heat transfer in the spot to fight against the pandemic obesity

The prevalence of obesity has nearly doubled worldwide over the past three and a half decades, reaching pandemic status. Obesity is associated with decreased life expectancy and with an increased risk of metabolic, cardiovascular, nervous system diseases. Hence, understanding the mechanisms involved in the onset and development of obesity is mandatory to promote planned health actions to revert this scenario. In this review, common aspects of cold exposure, a process of heat generation, and exercise, a process of heat dissipation, will be discussed as two opposite mechanisms of obesity, which can be oversimplified as caloric conservation. A common road between heat generation and dissipation is the mobilization of Free Faty Acids (FFA) and Carbohydrates (CHO). An increase in energy expenditure (immediate effect) and molecular/metabolic adaptations (chronic effect) are responses that depend on SNS activity in both conditions of heat transfer. This cycle of using and removing FFA and CHO from blood either for heat or force generation disrupt the key concept of obesity: energy accumulation. Despite efforts in making the anti-obesity pill, maybe it is time to consider that the world's population is living at thermoneutrality since temperature-controlled places and the lack of exercise are favoring caloric accumulation.

Valdecoxib improves lipid-induced skeletal muscle insulin resistance via simultaneous suppression of inflammation and endoplasmic reticulum stress

Valdecoxib (VAL), a non-steroidal anti-inflammatory drug, has been widely used for treatment of rheumatoid arthritis, osteoarthritis, and menstrual pain. It is a selective cyclooxygenase-2 inhibitor. The suppressive effects of VAL on cardiovascular diseases and neuroinflammation have been documented; however, its impact on insulin signaling in skeletal muscle has not been studied in detail. The aim of this study was to investigate the effects of VAL on insulin resistance in mouse skeletal muscle. Treatment of C2C12 myocytes with VAL reversed palmitate-induced aggravation of insulin signaling and glucose uptake. Further, VAL attenuated palmitate-induced inflammation and endoplasmic reticulum (ER) stress in a concentration-dependent manner. Treatment with VAL concentration-dependently upregulated AMP-activated protein kinase (AMPK) and heat shock protein beta 1 (HSPB1) expression. In line with in vitro experiments, treatment with VAL augmented AMPK phosphorylation and HSPB1 expression, thereby alleviating high-fat diet-induced insulin resistance along with inflammation and ER stress in mouse skeletal muscle. However, small interfering RNA-mediated inhibition of AMPK abolished the effects of VAL on insulin resistance, inflammation, and ER stress. These results suggest that VAL alleviates insulin resistance through AMPK/HSPB1-mediated inhibition of inflammation and ER stress in skeletal muscle under hyperlipidemic conditions. Hence, VAL could be used as an effective pharmacotherapeutic agent for management of insulin resistance and type 2 diabetes.

Tiam1 mediates Rac1 activation and contraction-induced glucose uptake in skeletal muscle cells

Contraction-stimulated glucose uptake in skeletal muscle requires Rac1, but the molecular mechanism of its activation is not fully understood. Treadmill running was applied to induce C57BL/6 mouse hind limb skeletal muscle contraction in vivo and electrical pulse stimulation contracted C2C12 myotube cultures in vitro. The protein levels or activities of AMPK or the Rac1-specific GEF, Tiam1, were manipulated by activators, inhibitors, siRNA-mediated knockdown, and adenovirus-mediated expression. Activated Rac1 was detected by a pull-down assay and immunoblotting. Glucose uptake was measured using the 2-NBD-glucose fluorescent analog. Electrical pulse stimulated contraction or treadmill exercise upregulated the expression of Tiam1 in skeletal muscle in an AMPK-dependent manner. Axin1 siRNA-mediated knockdown diminished AMPK activation and upregulation of Tiam1 protein expression by contraction. Tiam1 siRNA-mediated knockdown diminished contraction-induced Rac1 activation, GLUT4 translocation, and glucose uptake. Contraction increased Tiam1 gene expression and serine phosphorylation of Tiam1 protein via AMPK. These findings suggest Tiam1 is part of an AMPK-Tiam1-Rac1 signaling pathway that mediates contraction-stimulated glucose uptake in skeletal muscle cells and tissue.

CD44, a Predominant Protein in Methylglyoxal-Induced Secretome of Muscle Cells, is Elevated in Diabetic Plasma

Methylglyoxal (MG), a glycolytic intermediate and reactive dicarbonyl, is responsible for exacerbation of insulin resistance and diabetic complication. In this study, MG-induced secretome of rat muscle cells was identified and relatively quantified by SWATH-MS. A total of 643 proteins were identified in MG-induced secretome, of which 82 proteins were upregulated and 99 proteins were downregulated by more than 1.3-fold in SWATH analysis. Further, secretory proteins from the classical secretory pathway and nonclassical secretory pathway were identified using SignalP and SecretomeP, respectively. A total of 180 proteins were identified with SignalP, and 113 proteins were identified with SecretomeP. The differentially expressed proteins were functionally annotated by KEGG pathway analysis using Cytoscape software with plugin clusterMaker. The differentially expressed proteins were found to be involved in various pathways like extracellular matrix (ECM)-receptor interaction, leukocyte transendothelial migration, fluid shear stress and atherosclerosis, complement and coagulation cascades, and lysosomal pathway. Since the MG levels are high in diabetic conditions, the presence of MG-induced secreted proteins was inspected by profiling human plasma of healthy and diabetic subjects (n = 10 each). CD44, a predominant MG-induced secreted protein, was found to be elevated in the diabetic plasma and to have a role in the development of insulin resistance.

The effect of whole-body cryostimulation on body composition and leukocyte expression of HSPA1A, HSPB1, and CRP in obese men

In recent years, the prevalence of obesity has increased dramatically and has become a 21st century epidemic. Obesity is associated with the development of many diseases, and therefore treatments that can reduce body mass are actively sought. The aim of this study was to examine the effect of 20 cryostimulation sessions on body composition in obese/high body mass (HBM, n = 12) males and normal body mass (NBM, n = 9) controls. The HBM group had a mean age = 29.08 ± 4.19 years, body fat percentage = 32.08 ± 6.16%, body mass index = 36.23 ± 8.13 kg/m²) and NBM group had a mean age = 22.00 ± 2.45 years, body fat percentage = 12.14 ± 4.93%, body mass index = 23.58 ± 2.00 kg/m². Kilocalorie intake was similar for both groups. All participants received 20 sessions of systemic cryostimulation at -120°C for 2-3 min in a cryochamber. Blood samples were collected before the first session, 1 h after the 10th session, and 1 h after the 20th cryostimulation session. C-reactive protein (CRP) plasma concentrations, and expression of the heat shock protein genes (HSPA1A, HSPB1) and CRP mRNA in leukocytes were evaluated after 10 and 20 cryostimulation sessions. In both groups, 20 sessions were associated with a significant decrease in body mass, fat mass and the percentage of body fat. CRP concentrations were significantly higher in obese people before the first session and after 10 treatments, but not at the end of study. Expression of HSPA1A and HSPB1 mRNA gradually decreased with the number of cryostimulation sessions. A significant difference in HSPA1A expression was found after 20 sessions (NBM > HBM) and for HSPB1 at baseline and after 20 sessions (HBM > NBM). Our results show that cryostimulation influences body composition and that cryostimulation-induced HSP genes expression depends on the number of cryosessions and baseline body mass, and is differentially altered in HBM individuals. Further research on the interaction between body mass and cold adaptation is warranted.

An AMPK/Axin1-Rac1 signaling pathway mediates contraction-regulated glucose uptake in skeletal muscle cells

Contraction stimulates skeletal muscle glucose uptake predominantly through activation of AMP-activated protein kinase (AMPK) and Rac1. However, the molecular details of how contraction activates these signaling proteins are not clear. Recently, Axin1 has been shown to form a complex with AMPK and liver kinase B1 during glucose starvation-dependent activation of AMPK. Here, we demonstrate that electrical pulse-stimulated (EPS) contraction of C2C12 myotubes or treadmill exercise of C57BL/6 mice enhanced reciprocal coimmunoprecipitation of Axin1 and AMPK from myotube lysates or gastrocnemius muscle tissue. Interestingly, EPS or exercise upregulated total cellular Axin1 levels in an AMPK-dependent manner in C2C12 myotubes and gastrocnemius mouse muscle, respectively. Also, direct activation of AMPK with 5-aminoimidazole-4-carboxamide ribonucleotide treatment of C2C12 myotubes or gastrocnemius muscle elevated Axin1 protein levels. On the other hand, siRNA-mediated Axin1 knockdown lessened activation of AMPK in contracted myotubes. Further, AMPK inhibition with compound C or siRNA-mediated knockdown of AMPK or Axin1 blocked contraction-induced GTP loading of Rac1, p21-activated kinase phosphorylation, and contraction-stimulated glucose uptake. In summary, our results suggest that an AMPK/Axin1-Rac1 signaling pathway mediates contraction-stimulated skeletal muscle glucose uptake.

The beneficial effects of 15 units of high-intensity circuit training in women is modified by age, baseline insulin resistance and physical capacity

AIM

To investigate the effect of a single and 15 units of high-intensity circuit training (HICT) programme on glucose metabolism, myokines' response and selected genes' expression in women.

METHODS

Thirty-three, non-active women (mean age: 38 ± 12) were split into a HICT (n = 20) or a control group (CON, n = 13). The training protocol included three circuits of nine exercises with own body weight as a workload performed 3 times a week for five weeks. The CON group performed HICT twice. Blood samples were taken before, 1 h and 24 h after the first and last unit to determine IGF-1, myostatin, irisin, decorin, HSP27, interleukin-15 concentrations using the ELISA immunoenzymatic method. To evaluate HSPB1, TNF-α and DCN mRNA, real-time PCR was used. Pre- and post-intervention, the oral glucose test and body composition assessment were completed.

RESULTS

The following parameters tended to decrease after the 5-week HICT program: insulin and HOMA-IR Training diminished insulin/IGF-1 ratio (51% CI: -63% to -34%) and induced the drop of myostatin concentration but significantly only among middle-aged women and at baseline insulin resistance.

CONCLUSION

Obtained data revealed that HICT improved an insulin sensitivity and diminished myostatin concentration among older, insulin-resistant women with lower baseline physical capacity.

LRP6 Knockdown Ameliorates Insulin Resistance via Modulation of Autophagy by Regulating GSK3β Signaling in Human LO2 Hepatocytes

Recent studies suggest that autophagy is highly involved in insulin resistance (IR). Inhibition of the PI3K/AKT/mTOR signaling pathway induces autophagy activation. Additionally, depletion of LRP6 has been shown to increase insulin sensitivity but its mechanism is still not clear. We hypothesized that LRP6 contributes to IR by regulating mTOR mediated autophagy through GSK3β in hepatocytes. LO2 hepatocytes were treated with palmitate (PA) and insulin to induced IR. Levels of LRP6 mRNA and protein expression were measured by real time-PCR and western blot analysis. LRP6 knock down was achieved by adenovirus mediated Si-LRP6 expression and its roles in IR, glucose, GSK3β, mTOR signaling, and autophagy were explored. Finally, GSK3β was overexpressed and its involvement in autophagy and IR was examined. We found that PA treatment led to a reduced glucose uptake and IR in hepatocytes, which was accompanied by an upregulation of LRP6 expression. Knocking down of LRP6 enhanced glucose uptake and insulin sensitivity in PA treated cells, probably through increasing GSK3b activity. Overexpression of GSK3b mimicked LRP6 reduction by enhancing autophagy and ameliorating IR. Our study revealed a significant molecular mechanism connecting LRP6 to insulin sensitivity through GSK3β-mTOR mediated autophagy.

In vitro experimental models for examining the skeletal muscle cell biology of exercise: the possibilities, challenges and future developments

Exercise provides a cornerstone in the prevention and treatment of several chronic diseases. The use of in vivo exercise models alone cannot fully establish the skeletal muscle-specific mechanisms involved in such health-promoting effects. As such, models that replicate exercise-like effects in vitro provide useful tools to allow investigations that are not otherwise possible in vivo. In this review, we provide an overview of experimental models currently used to induce exercise-like effects in skeletal muscle in vitro. In particular, the appropriateness of electrical pulse stimulation and several pharmacological compounds to resemble exercise, as well as important technical considerations, are addressed. Each model covered herein provides a useful tool to investigate different aspects of exercise with a level of abstraction not possible in vivo. That said, none of these models are perfect under all circumstances, and the choice of model (and terminology) used should be informed by the specific research question whilst accounting for the several inherent limitations of each model. Further work is required to develop and optimise the current experimental models used, such as combination with complementary techniques during treatment, and thereby improve their overall utility and impact within muscle biology research.

Electrical pulse stimulation induces GLUT4 translocation in C2C12 myotubes that depends on Rab8A, Rab13, and Rab14

The signals mobilizing GLUT4 to the plasma membrane in response to muscle contraction are less known than those elicited by insulin. This disparity is undoubtedly due to lack of suitable in vitro models to study skeletal muscle contraction. We generated C₂C₁₂ myotubes stably expressing HA-tagged GLUT4 (C2C12-GLUT4 HA) that contract in response to electrical pulse stimulation (EPS) and investigated molecular mechanisms regulating GLUT4 HA. EPS (60 min, 20 V, 1 Hz, 24-ms pulses at 976-ms intervals) elicited a gain in surface GLUT4 HA (GLUT4 translocation) comparably to insulin or 5-amino imidazole-4-carboxamide ribonucleotide (AICAR). A myosin II inhibitor prevented EPS-stimulated myotube contraction and reduced surface GLUT4 by 56%. EPS stimulated AMPK and CaMKII phosphorylation, and EPS-stimulated GLUT4 translocation was reduced in part by small interfering (si)RNA-mediated AMPKα1/α2 knockdown, compound C, siRNA-mediated Ca²⁺/calmodulin-dependent protein kinase (CaMKII)δ knockdown, or CaMKII inhibitor KN93. Key regulatory residues on the Rab-GAPs AS160 and TBC1D1 were phosphorylated in response to EPS. Stable expression of an activated form of the Rab-GAP AS160 (AS160-4A) diminished EPS- and insulin-stimulated GLUT4 translocation, suggesting regulation of GLUT4 vesicle traffic by Rab GTPases. Knockdown of each Rab8a, Rab13, or Rab14 reduced, in part, GLUT4 translocation induced by EPS, whereas only Rab8a, or Rab14 knockdown reduced the AICAR response. In conclusion, EPS involves Rab8a, Rab13, and Rab14 to elicit GLUT4 translocation but not Rab10; moreover, Rab10 and Rab13 are not engaged by AMPK activation alone. C2C12-GLUT4 HA cultures constitute a valuable in vitro model to investigate molecular mechanisms of contraction-stimulated GLUT4 translocation.

Effects of aquatic and land-based exercises on amyloid beta, heat shock protein 27, and pulse wave velocity in elderly women

BACKGROUND

Alzheimer's disease is a neurodegenerative brain disease resulting from the deterioration of neuronal cells and vascular dementia, the latter of which results from cerebrovascular disorders. Exercise is effective in preventing and treating degenerative brain diseases as it activates blood flow to the brain, increases nerve production in the hippocampus, and promotes the expression of synaptic plasticity-related proteins. Therefore, this study investigated the effects of 16-week aquatic and land-based exercise programs on amyloid beta (Aβ), heat shock protein (HSP) 27 levels, and pulse wave velocity (PWV).

MATERIALS AND METHODS

Forty elderly women, aged 60-70 years, voluntarily participated in the study. They were divided into control (n = 12), aquatic exercise (n = 14), and land-based exercise groups (n = 14). The variables of amyloid beta, heat shock protein 27, and pulse wave velocity were measured in all the participants before and after the 16-week study.

RESULTS

Significantly higher levels of serum HSP27 (p < 0.05) and significantly lower levels of vascular elasticity (p < 0.05) were found in the aquatic exercise group after 16 weeks of exercise compared with the control group. Aβ did not significantly differ between groups. Thirty minutes after the first exercise, Aβ in the aquatic exercise group (p < 0.01) and HSP27 in the land-based exercise group (p < 0.05) were significantly higher than the corresponding levels in the resting condition before exercise. 30 min after the last exercise, Aβ (p < 0.01) and HSP27 (p < 0.05) were significantly higher.

CONCLUSIONS

Aquatic and land-based exercises increased serum Aβ and HSP27 and decreased pulse wave velocity. Thus, they may play a positive role in the prevention of degenerative brain diseases and improvement of brain function in elderly people.

Exercise-induced GLUT4 transcription via inactivation of HDAC4/5 in mouse skeletal muscle in an AMPKα2-dependent manner

Abnormal glucose metabolism induces various metabolic disorders such as insulin resistance and type 2 diabetes. Regular exercise improved glucose uptake and enhanced glucose oxidation by increasing GLUT4 transcription in skeletal muscle. However, the regulatory mechanisms of GLUT4 transcription in response to exercise are poorly understood. AMPK is a sensor of exercise and upstream kinase of class II HDACs that act as transcriptional repressors. We used 6-week treadmill exercise or one single-bout exercise wild type or AMPKα2^-/- C57BL/6J mice to explore how HDACs regulate GLUT4 transcription and the underlying molecular mechanisms mediated by AMPK in the physiologic process of exercise. We demonstrate that regular physical exercise significantly enhanced GLUT4 transcription by inactivating HDAC4/5 in skeletal muscle by ChIP experiment. HDAC4 coordinately regulated with HDAC5 represses transcriptional activity of GLUT4 promoter in C2C12 myotubes by Luciferase assay. If either HDAC4 or HDAC5 is silenced via RNAi technology, the functional compensation by the other will occur. In addition, a single-bout of exercise decreased HDAC4/5 activity in skeletal muscle of wild type but not in AMPKα2^-/- mice, suggesting an AMPKα2-dependent manner. Those findings provide new insight into the mechanisms responsible for AMPKα2-dependent regulation of GLUT4 transcription after exercise.

Sestrin 2 induces autophagy and attenuates insulin resistance by regulating AMPK signaling in C2C12 myotubes

Impaired insulin-stimulated glucose uptake in skeletal muscle serves a critical role in the development of insulin resistance (IR), whereas the precise mechanism of the process remains unknown. Recently, the evolutionarily conserved, stress-inducible protein Sestrin2 (Sesn2) has been proposed to play a protective role against obesity-induced IR and diabetes. Activation of Sesn2 may activate AMP-activated protein kinase (AMPK) accompanied by suppression of mammalian target of rapamycin (mTOR), which may ultimately lead to autophagy induction. In view of the potential protective effects of autophagy on the physiological and the pathological regulatory processes via the regulation of energy homeostasis and metabolism, we investigated the effects of Sesn2 on the components of the insulin signaling pathway and insulin-stimulated glucose uptake in palmitate-induced insulin-resistant C2C12 myotubes. We showed that Sesn2 effectively restored the impaired insulin signaling. Moreover, autophagic activity decreased in response to palmitate, whereas Sesn2 significantly reversed the palmitate-suppressed autophagic signaling in this context. Our findings further revealed that Sesn2-induced autophagy contributed to restore the impaired insulin signaling through the activation of AMPK signal. Even in the presence of palmitate, Sesn2 up-regulation maintained insulin sensitivity and glucose metabolism via AMPK-dependent autophagic activation.