AMP‐activated protein kinase α2 is an essential signal in the regulation of insulin‐stimulated fatty acid uptake in control‐fed and high‐fat‐fed mice

Abstract

Owing to its critical role in the regulation of skeletal muscle metabolism, AMP-activated protein kinase (AMPK) remains a central focus of research for the treatment of insulin resistance. The purpose of the present study was to determine the role of AMPKα2 activity in the regulation of glucose uptake and fatty acid (FA) metabolism in insulin-resistant skeletal muscle. Male C57BL/6 mice were divided into groups fed a control diet (CD) or high-fat (60%) diet (HFD) for 6 weeks and were either wild-type (WT) or possessed an AMPKα2 dominant negative transgene (DN). After 6 weeks, hindlimbs of CD (n = 10) and HFD mice (n = 10) were perfused with or without 450 μU ml −1 insulin. Muscles of CD (n = 8) and HFD mice (n = 8) were used for measurement of basal protein expression. In CD mice, low AMPKα2 activity did not affect basal FA uptake (FAU), but it increased basal FA oxidation (FAO) by 28% and prevented the typical insulin-mediated increase in FAU and decrease in FAO. In HFD-fed mice, low AMPKα2 activity increased basal FAU by 147% (P < 0.05). In both WT and DN mice, HFD abolished the typical insulin-mediated increase in FAU and decrease in FAO. In HFD-fed mice, low AMPKα2 activity increased SIRT1 activity and decreased Protein Tyrosine Phosphatase 1B (PTP1B) expression and AktThr308 phosphorylation (P < 0.05). Adipose tissue protein expression of interleukin-6 and tumour necrosis factor α was increased by HFD in WT mice but not in DN mice (P < 0.05). Skeletal muscle interleukin-15 expression was decreased in both feeding conditions in the DN mice (P < 0.05). The data from this study suggest that in insulin-resistant conditions low AMPKα2 activity impacts the regulation of skeletal muscle FA metabolism via changes in SIRT1 activity, PTP1B expression and Akt phosphorylation and the expression of adipose tissue proinflammatory markers. A precursor and unfavourable indicator of type 2 diabetes mellitus is insulin resistance in skeletal muscle (DeFronzo et al. 1992;Båvenholm et al. 2003). While the mechanisms leading to the development of insulin resistance have not been completely identified, there is evidence that its progression is linked to alterations in fatty acid (FA) metabolism (Laybutt et al. 1999;Chavez & Summers, 2003;Aas et al. 2004 (Winder & Hardie, 1999;Ruderman & Prentki, 2004).AMPK has been studied extensively for its role as an energy sensor during states of low energy balance, as exemplified by muscle contraction or hypoxia (Hutber et al. 1997;Mu et al. 2001). Additionally, multiple studies have linked FA intake and high-fat diets to alterations in AMPK activity in liver and skeletal muscle (Suchankova Fillmore et al. 2010). A recent study has linked the deletion of AMPKα2 activity to an exacerbation of high-fat diet-induced insulin resistance as it pertains to glucose metabolism (Fujii et al. 2008). However, in another study, it was shown that reduced AMPK activity did not affect the development of obesity-induced lipid accumulation and insulin resistance ). As such, the role of low muscle AMPK activ...

The Effects of a High Fat Diet on Mitochondrial Biogenesis and Inflammation in the Brain

“…Diets high in SF have also been shown to decrease PGC-1alpha activity thereby reducing oxidative phosphorylation of lipids (11,34). AMPK and PGC-1alpha gene expression have been shown to increase with the acute manipulation of a HFD and concomitantly SIRT1 gene expression is up regulated to enhance fatty acid metabolism during times of metabolic stress, thereby increasing mitochondrial biogenesis driving energy metabolism in times of low demand (1,19,22).…”

“…HFD's can act as a metabolic stressor by inducing an overload on the body with excess lipid accumulation and altered signaling of AMPK (1,19) causing localized oxidative stress and fatigue. Diets high in SF have been shown to impair insulin sensitivity and enzyme regulation by causing severe inflammation through the NF K B pathway increasing inflammatory cytokines IL-6 and TNF-alpha (32,33).…”

“…Peroxisome proliferator activated receptor gamma coactivator alpha (PGC-1alpha) and sirtuins one (SIRT1) are key signaling molecules that are allosterically mediated within the AMPK pathway that intrinsically regulates mitochondrial activity and mitochondrial biogenesis. In a fasted state the AMPK pathway is activated by the release of glucagon thereby stimulating SIRT1 via cAMP cascade, which deacetylates PGC-1alpha, increasing fatty acyl CoA dehydrogenase and carintine acyletransferase, driving mitochondrial biogenesis and oxidative capacity of long and short chain fatty acids (1,16,50). PGC-1alpha is considered to be a "master regulator" of mitochondrial biogenesis in skeletal muscle and has been shown to up regulate fatty acid metabolism and energy expenditure within the mitochondria, as well as to improve insulin sensitivity in times of stress (22,65).…”

“…Current research has demonstrated that chronic HFD's negatively affect mitochondrial capacity in skeletal muscle through dysfunctional enzymatic regulation and declines in the activity of molecular signalers (1,58). HFD's have also been shown to induce oxidative stress and insulin insensitivity in peripheral tissues (1,10,19,27,62,68).…”

“…HFD's have also been shown to induce oxidative stress and insulin insensitivity in peripheral tissues (1,10,19,27,62,68). Chronic inflammation has been linked as a key component in diet induced obesity and has been shown to negate cellular interactions, insulin signaling, molecular signalers, and normal cellular functioning (1,7,19). Two pro-inflammatory cytokines IL-1β and TNF-alpha are responsible for activating the NF k B pathway inducing M1 macrophage infiltration (56).…”