PPARδ and FOXO1 Mediate Palmitate-Induced Inhibition of Muscle Pyruvate Dehydrogenase Complex and CHO Oxidation, Events Reversed by Electrical Pulse Stimulation.

Hung-Che Chien,Dumitru Constantin-Teodosiu,Paul L Greenhaff

doi:10.3390/ijms21165942

Abstract

The mechanisms behind the reduction in muscle pyruvate dehydrogenase complex (PDC)-controlled carbohydrate (CHO) oxidation during chronic high-fat dietary intake are poorly understood, as is the basis of CHO oxidation restoration during muscle contraction. C2C12 myotubes were treated with (300 μM) palmitate or without (control) for 16 h in the presence and absence of electrical pulse stimulation (EPS, 11.5 V, 1 Hz, 2 ms). Compared to control, palmitate reduced cell glucose uptake (p < 0.05), PDC activity (p < 0.01), acetylcarnitine accumulation (p < 0.05) and glucose-derived mitochondrial ATP production (p < 0.01) and increased pyruvate dehydrogenase kinase isoform 4 (PDK4) (p < 0.01), peroxisome proliferator-activated receptor alpha (PPARα) (p < 0.01) and peroxisome proliferator-activated receptor delta (PPARδ) (p < 0.01) proteins, and reduced the whole-cell p-FOXO1/t-FOXO1 (Forkhead Box O1) ratio (p < 0.01). EPS rescued palmitate-induced inhibition of CHO oxidation, reflected by increased glucose uptake (p < 0.01), PDC activity (p < 0.01) and glucose-derived mitochondrial ATP production (p < 0.01) compared to palmitate alone. EPS was also associated with less PDK4 (p < 0.01) and PPARδ (p < 0.01) proteins, and lower nuclear p-FOXO1/t-FOXO1 ratio normalised to the cytoplasmic ratio, but with no changes in PPARα protein. Collectively, these data suggest PPARδ, and FOXO1 transcription factors increased PDK4 protein in the presence of palmitate, which limited PDC activity and flux, and blunted CHO oxidation and glucose uptake. Conversely, EPS rescued these metabolic events by modulating the same transcription factors.

Highlights

Obesity and chronically elevated levels of circulating free fatty acids (FFA) are recognised as factors contributing to the development of metabolic inflexibility (MI; defined as the inability to switch from lipid to glucose oxidation during the fasting-to-fed transition), insulin resistance (IR), and type 2 diabetes mellitus [1]
Muscle pyruvate dehydrogenase complex (PDC) activity is most potently increased during contraction, which is mediated by intra-mitochondrial calcium accumulation, which activates PDP1 [10]
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Summary

Introduction

Obesity and chronically elevated levels of circulating free fatty acids (FFA) are recognised as factors contributing to the development of metabolic inflexibility (MI; defined as the inability to switch from lipid to glucose oxidation during the fasting-to-fed transition), insulin resistance (IR), and type 2 diabetes mellitus [1]. The most common saturated fatty acid in the diet, is often used to induce cellular MI and IR in vitro and in vivo by blunting insulin signalling and decreasing cellular glucose transport and mitochondrial carbohydrate (CHO) use [6,7,8,9]. Central to this latter response is the evidence that chronically elevated palmitate directly inhibits the activity status of the pyruvate dehydrogenase complex (PDC) activity, which is the rate-limiting step in mitochondrial CHO oxidation [10]. Muscle PDC activity is most potently increased during contraction, which is mediated by intra-mitochondrial calcium accumulation, which activates PDP1 [10]

Methods

Results

Conclusion