AMPKα₂deficiency uncovers time dependency in the regulation of contraction-induced palmitate and glucose uptake in mouse muscle

Abstract

Abbott MJ, Bogachus LD, Turcotte LP. AMPK␣2 deficiency uncovers time dependency in the regulation of contraction-induced palmitate and glucose uptake in mouse muscle. J Appl Physiol 111: 125-134, 2011. First published May 5, 2011 doi:10.1152/japplphysiol.00807.2010.-AMP-activated protein kinase (AMPK) is a fuel sensor in skeletal muscle with multiple downstream signaling targets that may be triggered by increases in intracellular Ca 2ϩ concentration ([Ca 2ϩ ]). The purpose of this study was to determine whether increases in intracellular [Ca 2ϩ ] induced by caffeine act solely via AMPK␣ 2 and whether AMPK␣2 is essential to increase glucose uptake, fatty acid (FA) uptake, and FA oxidation in contracting skeletal muscle. Hindlimbs from wild-type (WT) or AMPK␣ 2 dominant-negative (DN) transgene mice were perfused during rest (n ϭ 11), treatment with 3 mM caffeine (n ϭ 10), or muscle contraction (n ϭ 11). Time-dependent effects on glucose and FA uptake were uncovered throughout the 20-min muscle contraction perfusion period (P Ͻ 0.05). Glucose uptake rates did not increase in DN mice during muscle contraction until the last 5 min of the protocol (P Ͻ 0.05). FA uptake rates were elevated at the onset of muscle contraction and diminished by the end of the protocol in DN mice (P Ͻ 0.05). FA oxidation rates were abolished in the DN mice during muscle contraction (P Ͻ 0.05). The DN transgene had no effect on caffeine-induced FA uptake and oxidation (P Ͼ 0.05). Glucose uptake rates were blunted in caffeine-treated DN mice (P Ͻ 0.05). The DN transgene resulted in a greater use of intramuscular triglycerides as a fuel source during muscle contraction. The DN transgene did not alter caffeine-or contraction-mediated changes in the phosphorylation of Ca 2ϩ /calmodulin-dependent protein kinase I or ERK1/2 (P Ͼ 0.05). These data suggest that AMPK␣ 2 is involved in the regulation of substrate uptake in a time-dependent manner in contracting muscle but is not necessary for regulation of FA uptake and oxidation during caffeine treatment. ERK1/2; muscle contraction; caffeine; calcium/calmodulin-dependent protein kinase kinase; acetyl-CoA carboxylase EVIDENCE SUGGESTS THAT MULTIPLE cellular signals regulate the changes in substrate metabolism with muscle contraction, including the AMP-activated protein kinase (AMPK) signaling cascade (2, 34, 35, 52). During states of low energy, such as muscle contraction or exercise, it is widely accepted that liver kinase B1 (LKB1) acts as an upstream AMPK kinase that phosphorylates and activates AMPK and initiates a multitude of signaling events to maintain energy homeostasis (39 -41). Although strong evidence indicates that the LKB1-AMPK cascade is a key signaling pathway that regulates changes in glucose uptake, fatty acid (FA) uptake, and FA oxidation in contracting skeletal muscle (16,25,54,56), data also show that AMPK may not be the sole signal mediating contractioninduced changes in glucose uptake, FA uptake, and FA oxidation (35,36,56).Along with AMPK, mounting data suggest that increas...

Calcium signaling recruits substrate transporters GLUT4 and CD36 to the sarcolemma without increasing cardiac substrate uptake

“…We did not observe an increased phosphorylation of CaMKI or of CaMKII upon 7-min, 4-Hz stimulation (Fig. 2B), which is in contrast to findings in skeletal E227 CALCIUM SIGNALING AND CARDIAC SUBSTRATE UPTAKE muscle (1,48). Additionally, treatment with oligomycin or AICAR treatment did not increase phosphorylation of either kinase (Fig.…”

“…Studies describing the role of Ca 2ϩ signaling in skeletal muscle substrate uptake often have used caffeine to increase [Ca 2ϩ ] i (1,48). Specifically, it has been shown that caffeine treatment induces CaMKK␤ and CaMKII phosphorylation concomitantly with increased glucose uptake.…”

Exercise and type 2 diabetes: molecular mechanisms regulating glucose uptake in skeletal muscle

“…The ␣and ␤-subunits each exist in two isoforms (␣ 1 , ␣ 2 , ␤ 1 , and ␤ 2 ), and the ␥-subunit exists in three isoforms (␥ 1 , ␥ 2 , and ␥ 3 ). Some studies (1,28,30,33,57,69) have shown that mice overexpressing a dominant negative AMPK-␣ 2 construct in muscle or AMPK-␣ 1 and -␤ KO mice have impaired exercise-stimulated glucose uptake. A previous study (53) involving incubation with the AMP-analog 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) have shown that activation of AMPK is positively correlated with increased skeletal muscle glucose uptake.…”

The IL-6 Paradox: Context Dependent Interplay of SOCS3 and AMPK

“…Additionally, AMPKβ2 knockout mice had reduced maximal exercise capacity and AMPK activity during treadmill running compared to wild type mice [89], and muscle specific AMPKβ1β2 knockout mice showed decreased AMPKα1α2 activity and AMPK phosphorylation following exercise compared to wild type mice [90]. Following muscle contraction, glucose uptake rates did not increase until the last five minutes in hind limb muscles from AMPKα2 dominant negative mice, whereas glucose uptake rates increased rapidly and remained elevated throughout the contraction period in wild type mice [91]. A similar study on AMPKα2 dominant negative mice found that contraction induced glucose uptake was reduced by 50% in extensor digitorum longus muscle compared to the wild type mice, suggesting that AMPK activity has important role in exercise induced glucose uptake [92].…”