Abnormal metabolism flexibility in response to high palmitate concentrations in myotubes derived from obese type 2 diabetic patients

Abstract

Insulin resistance in type 2 diabetes (T2D) is associated with intramuscular lipid (IMCL) accumulation. To determine whether impaired lipid oxidation is involved in IMCL accumulation, we measured expression of genes involved in mitochondrial oxidative metabolism or biogenesis, mitochondrial content and palmitate beta-oxidation before and after palmitate overload (600μM for 16h), in myotubes derived from healthy subjects and obese T2D patients. Mitochondrial gene expression, content and network were not different between groups. Basal palmitate beta-oxidation was not affected in T2D myotubes, whereas after 16h of palmitate pre-treatment, T2D myotubes in contrast to control myotubes, showed an inability to increase palmitate beta-oxidation (p<0.05). Interestingly, acetyl-CoA carboxylase (ACC) phosphorylation was increased with a tendency for statistical significance after palmitate pre-treatment in control myotubes (p=0.06) but not in T2D myotubes which can explain their inability to increase palmitate beta-oxidation after palmitate overload. To determine whether the activation of the AMP activated protein kinase (AMPK)-ACC pathway was able to decrease lipid content in T2D myotubes, cells were treated with AICAR and metformin. These AMPK activators had no effect on ACC and AMPK phosphorylation in T2D myotubes as well as on lipid content, whereas AICAR, but not metformin, increased AMPK phosphorylation in control myotubes. Interestingly, metformin treatment and mitochondrial inhibition by antimycin induced increased lipid content in control myotubes. We conclude that T2D myotubes display an impaired capacity to respond to metabolic stimuli.

Galactose Enhances Oxidative Metabolism and Reveals Mitochondrial Dysfunction in Human Primary Muscle Cells

“…Thus, in spite of the fact that there was no difference in OCR between obese non-diabetic myotubes and post-diabetic myotubes when differentiated in LG or HG, the GAL media was able to highlight a decreased oxidative capacity in post-diabetic myotubes compared to obese non-diabetic myotubes. Other studies have described a decrease in oxidative metabolic capacity in myotubes derived from diabetic patients as indicated by a decrease in citrate synthase activity [7] and a decrease in lipid oxidation capacity [5], [9]. Myotubes derived from post-diabetic subjects are also known to have a decreased oxidative capacity when challenged with a high glucose medium (decreased mitochondrial content, decreased citrate synthase and COX activities) compared to myotubes derived from matched obese non-diabetic individuals [40].…”

“…Cell culture of human primary myotubes offers not only an excellent and dynamic model for studying metabolism under standardized conditions, but provides an excellent system for studying metabolic disorders. Indeed, a number of studies have shown that human primary muscle cells retain the same metabolic phenotype as those previously evidenced in vivo in muscle [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. The oxidative capacity of skeletal muscle is highly influenced by various genetic and environmental factors; cultured myotubes offer a unique model that separates these two influences on metabolic phenotype [7].…”

“…Mitochondrial respiration is known to be reduced in the skeletal muscle of T2DM patients [25], [26], [27] and lean insulin-resistant offspring of T2DM parents [28], [29]. Some studies, done on primary muscle cells derived from diabetic patients and matched controls have also shown a decrease in mitochondrial capacity: impaired ATP synthesis [30], [31], perturbed palmitate beta-oxidation when exposed to high level of palmitate [9], and impaired citrate synthase activity [7]. However, to our knowledge, no study has directly assessed whether myotubes derived from T2DM patients or patients with a history of T2DM retain a decrease in mitochondrial respiration when cultured in vitro .…”

Mitochondrial Plasticity in Obesity and Diabetes Mellitus

“…palmitate-overloading impaired b-oxidation and promoted intramyocellular lipid accumulation in myotubes from patients with T2DM compared with controls (37). In order to examine the time course of FFA-dependent changes in insulin sensitivity and mitochondrial plasticity, we monitored whole body glucose uptake (Fig.…”

Sensibilidade periférica à insulina e resposta inflamatória na vigência de dietas obesogênicas, suplementação com óleo de peixe e ausência de TLR-4.

“…Gene expression analyses in the skeletal muscle identified several candidates involved in carbohydrate and lipid metabolism, namely pyruvate dehydrogenase kinase 4, fructose-1,6-bisphophatase 2, and carnitine palmitoyltransferase 1b, which could be involved in the additive effects of the combined intervention [53]. On the contrary, myotubes from T2D patients when challenged with high concentrations of palmitate show a defect in palmitate b-oxidation, and this impaired response could be the result of a lack of inhibition of ACC activity by the fatty acid [54].…”