Brief intense interval exercise activates AMPK and p38 MAPK signaling and increases the expression of PGC-1α in human skeletal muscle

From a cell signaling perspective, short-duration intense muscular work is typically associated with resistance training and linked to pathways that stimulate growth. However, brief repeated sessions of sprint or high-intensity interval exercise induce rapid phenotypic changes that resemble traditional endurance training. We tested the hypothesis that an acute session of intense intermittent cycle exercise would activate signaling cascades linked to mitochondrialbiogenesis in human skeletal muscle. Biopsies (vastus lateralis) were obtained from six young men who performed four 30-s "all out" exercise bouts interspersed with 4 min of rest (<80 kJ total work). Phosphorylation of AMP-activated protein kinase (AMPK; subunits 1 and 2) and the p38 mitogen-activated protein kinase (MAPK) was higher (P  0.05) immediately after bout 4 vs. preexercise. Peroxisome proliferator-activated receptor- coactivator-1(PGC-1) mRNA was increased approximately twofold above rest after 3 h of recovery (P  0.05); however, PGC-1protein content was unchanged. In contrast, phosphorylation of protein kinase B/Akt (Thr³⁰⁸ and Ser⁴⁷³) tended to decrease, and downstream targets linked to hypertrophy (p70 ribosomal S6 kinase and 4E binding protein 1) were unchanged after exercise and recovery. We conclude that signaling through AMPK and p38 MAPK to PGC-1 may explain in part the metabolic remodeling induced by low-volume intense interval exercise, including mitochondrial biogenesis and an increased capacity for glucose and fatty acid oxidation.

Reduced glycogen availability is associated with increased AMPKα2 activity, nuclear AMPKα2 protein abundance, and GLUT4 mRNA expression in contracting human skeletal muscle

Glycogen availability can influence glucose transporter 4 (GLUT4) expression in skeletal muscle through unknown mechanisms. The multisubstrate enzyme AMP-activated protein kinase (AMPK) has also been shown to play an important role in the regulation of GLUT4 expression in skeletal muscle. During contraction, AMPK [alpha]2 translocates to the nucleus and the activity of this AMPK isoform is enhanced when skeletal muscle glycogen is low. In this study, we investigated if decreased pre-exercise muscle glycogen levels and increased AMPK [alpha]2 activity reduced the association of AMPK with glycogen and increased AMPK [alpha]2 translocation to the nucleus and GLUT4 mRNA expression following exercise. Seven males performed 60 min of exercise at ~70% [VO.sub.2] peak on 2 occasions: either with normal (control) or low (LG) carbohydrate pre-exercise muscle glycogen content. Muscle samples were obtained by needle biopsy before and after exercise. Low muscle glycogen was associated with elevated AMPK [alpha]2 activity and acetyl-CoA carboxylase [beta] phosphorylation, increased translocation of AMPK [alpha]2 to the nucleus, and increased GLUT4 mRNA. Transfection of primary human myotubes with a constitutively active AMPK adenovirus also stimulated GLUT4 mRNA, providing direct evidence of a role of AMPK in regulating GLUT4 expression. We suggest that increased activation of AMPK [alpha]2 under conditions of low muscle glycogen enhances AMPK [alpha]2 nuclear translocation and increases GLUT4 mRNA expression in response to exercise in human skeletal muscle.

AMPK and transcriptional regulation

The AMP-activated protein kinase (AMPK) is an energy sensing enzyme that once activated, promotes energy production and limits energy utilisation to ensure cellular survival. In addition to targeting numerous metabolic enzymes for this purpose, it is becoming apparent that AMPK can also regulate a number of transcriptional processes. These processes ensure cell survival through the inhibition of cell cycle and growth mechanisms, and also prepare the cell for future perturbations in energy balance by increasing the capacity of the cell to produce ATP. While these adaptations might be inextricably linked through regulation of the proliferation-differentiation process, recent studies have identified a number of transcriptional regulators as AMPK substrates that give insights into the regulation of transcription by AMPK in a number of metabolically active tissues.

AMPK-mediated transcription in skeletal muscle

Skeletal muscle phenotype plays a critical role in human performance and health, and skeletal muscle oxidative capacity is a key determinant of exercise tolerance. More recently, defective muscle oxidative metabolism has been implicated in a number of conditions associated with the metabolic syndrome, cardiovascular disease and muscle-wasting disorders. AMPK (AMP-activated protein kinase) is a critical regulator of cellular and organismal energy balance. AMPK has also emerged as a key regulator of skeletal muscle oxidative function, including metabolic enzyme expression, mitochondrial biogenesis and angiogenesis. AMPK mediates these processes primarily through alterations in gene expression. The present review examines the role of AMPK in skeletal muscle transcription and provides an overview of the known transcriptional substrates mediating the effects of AMPK on skeletal muscle phenotype.

Legionella pneumophila multiplication is enhanced by chronic AMPK signalling in mitochondrially diseased dictyostelium cells

Human patients with mitochondrial diseases are more susceptible to bacterial infections, particularly of the respiratory tract. To investigate the susceptibility of mitochondrially diseased cells to an intracellular bacterial respiratory pathogen, we exploited the advantages of Dictyostelium discoideum as an established model for mitochondrial disease and for Legionella pneumophila pathogenesis. Legionella infection of macrophages involves recruitment of mitochondria to the Legionella-containing phagosome. We confirm here that this also occurs in Dictyostelium and investigate the effect of mitochondrial dysfunction on host cell susceptibility to Legionella. In mitochondrially diseased Dictyostelium strains, the pathogen was taken up at normal rates, but it grew faster and reached counts that were twofold higher than in the wild-type host. We reported previously that other mitochondrial disease phenotypes for Dictyostelium are the result of the activity of an energy-sensing cellular alarm protein, AMP-activated protein kinase (AMPK). Here, we show that the increased ability of mitochondrially diseased cells to support Legionella proliferation is suppressed by antisense-inhibiting expression of the catalytic AMPKα subunit. Conversely, mitochondrial dysfunction is phenocopied, and intracellular Legionella growth is enhanced, by overexpressing an active form of AMPKα in otherwise normal cells. These results indicate that AMPK signalling in response to mitochondrial dysfunction enhances Legionella proliferation in host cells.

Differentiated mTOR but not AMPK signaling after strength vs endurance exercise in training-accustomed individuals

The influence of adenosine mono phosphate (AMP)-activated protein kinase (AMPK) vs Akt-mammalian target of rapamycin C1 (mTORC1) protein signaling mechanisms on converting differentiated exercise into training specific adaptations is not well-established. To investigate this, human subjects were divided into endurance, strength, and non-exercise control groups. Data were obtained before and during post-exercise recovery from single-bout exercise, conducted with an exercise mode to which the exercise subjects were accustomed through 10 weeks of prior training. Blood and muscle samples were analyzed for plasma substrates and hormones and for muscle markers of AMPK and Akt-mTORC1 protein signaling. Increases in plasma glucose, insulin, growth hormone (GH), and insulin-like growth factor (IGF)-1, and in phosphorylated muscle phospho-Akt substrate (PAS) of 160 kDa, mTOR, 70 kDa ribosomal protein S6 kinase, eukaryotic initiation factor 4E, and glycogen synthase kinase 3α were observed after strength exercise. Increased phosphorylation of AMPK, histone deacetylase5 (HDAC5), cAMP response element-binding protein, and acetyl-CoA carboxylase (ACC) was observed after endurance exercise, but not differently from after strength exercise. No changes in protein phosphorylation were observed in non-exercise controls. Endurance training produced an increase in maximal oxygen uptake and a decrease in submaximal exercise heart rate, while strength training produced increases in muscle cross-sectional area and strength. No changes in basal levels of signaling proteins were observed in response to training. The results support that in training-accustomed individuals, mTORC1 signaling is preferentially activated after hypertrophy-inducing exercise, while AMPK signaling is less specific for differentiated exercise.

Relação entre diferentes períodos da exposição à obesidade induzida por dieta e lipotoxidade cardíaca: papel do eixo Leptina/OB0R/AMPK/ACC/Malonil CoA

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

AKT and AMPK Activation after High-Fat and High-Glucose In Vitro Treatment of Prostate Epithelial Cells

Considering the increasing consumption of saturated fat and glucose in diets worldwide and its possible association to carcinogenesis, this investigation analysed the proliferation profile of nonmalignant human prostate epithelial cells after exposure to elevated levels of fat and glucose. PNT1A cells were cultured with palmitate (100 or 200 mu M) and/or glucose (450mg/dl) for 24 or 48 h. Treated cells were evaluated for viability test and cell proliferation (MTS assay). AKT and AMPK phosphorylation status were analysed by Western blotting. After 24 h of high-fat alone or associated with high-glucose treatment, there was an increase in AMPK and AKT activation associated to unchanged MTS-cell proliferation. Following 48 h of high-fat but not high-glucose alone, cells decreased AMPK activation and maintained elevated AKT levels. These data were associated to increased cell proliferation after further high-fat treatment. After longer high-fat exposure, MTS revealed that cells remained proliferating. High-glucose alone or associated to high-fat treatment was not able to increase cell proliferation and AKT activation. A high-fat medium containing 100 mu M of palmitate stimulates proliferation in PNT1A cells by decreasing the activation of AMPK and increasing activation of AKT after longer exposure time. These findings improve the knowledge about the negative effect of high levels of this saturated fatty acid on proliferative disorders of prostate.

Treadmill Training Increases SIRT-1 and PGC-1 alpha Protein Levels and AMPK Phosphorylation in Quadriceps of Middle-Aged Rats in an Intensity-Dependent Manner

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)