Role of AMP Kinase and PPARδ in the Regulation of Lipid and Glucose Metabolism in Human Skeletal Muscle

David Kitz Krämer,Lubna Al-Khalili,Bruno Guigas,Ying Leng,Pablo M Garcia-Roves,Anna Krook

doi:10.1074/jbc.m702329200

Abstract

The peroxisome proliferator-activated receptor (PPAR)delta has been implicated in the regulation of lipid metabolism in skeletal muscle. Furthermore, activation of PPARdelta has been proposed to improve insulin sensitivity and reduce glucose levels in animal models of type 2 diabetes. We recently demonstrated that the PPARdelta agonist GW501516 activates AMP-activated protein kinase (AMPK) and stimulates glucose uptake in skeletal muscle. However, the underlying mechanism remains to be clearly identified. In this study, we first confirmed that incubation of primary cultured human muscle cells with GW501516 induced AMPK phosphorylation and increased fatty acid transport and oxidation and glucose uptake. Using small interfering RNA, we have demonstrated that PPARdelta expression is required for the effect of GW501516 on the intracellular accumulation of fatty acids. Furthermore, we have shown that the subsequent increase in fatty acid oxidation induced by GW501516 is dependent on both PPARdelta and AMPK. Concomitant with these metabolic changes, we provide evidence that GW501516 increases the expression of key genes involved in lipid metabolism (FABP3, CPT1, and PDK4) by a PPARdelta-dependent mechanism. Finally, we have also demonstrated that the GW501516-mediated increase in glucose uptake requires AMPK but not PPARdelta. In conclusion, the PPARdelta agonist GW501516 promotes changes in lipid/glucose metabolism and gene expression in human skeletal muscle cells by PPARdelta- and AMPK-dependent and -independent mechanisms.

Highlights

The peroxisome proliferator-activated receptor (PPAR)␦-mediated enhancement in whole-body insulin sensitivity primarily reflects improvements in the lipid profile
Single nucleotide polymorphisms in the PPARD gene modify the conversion from impaired glucose tolerance to type 2 diabetes, in combination with single nucleotide polymorphisms identified in PPAR gamma co-activaor (PGC)1␣ and PPAR␥2 [12]
Mary Cultured Human Myotubes Requires PPAR␦—Previous expression of other genes, including DGK␦, GAPDH, nuclear results obtained with animal models indicated that activation of respiratory factor 1, and cytochrome c were unaltered by JULY 6, 2007

Summary

Introduction

The PPAR␦-mediated enhancement in whole-body insulin sensitivity primarily reflects improvements in the lipid profile. PPAR␦ activation can improve glucose homeostasis by increasing lipid oxidation to lower plasma-free fatty acid levels, which thereby relieves negative feedback on the canonical insulin signaling cascade to enhanced glucose uptake and reduce plasma glucose levels [9]. Single nucleotide polymorphisms of the human PPARD gene are associated with enhanced whole-body insulin sensitivity. Improvements in insulin sensitivity are correlated with increased PPAR␦ expression in type 2 diabetic patients performing moderate walking fatty acid-binding protein 3; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; DMEM, Dulbecco’s modified Eagle’s medium; PGC1, PPAR␥ co-activator 1; FBS, fetal bovine serum; siRNA, small interfering RNA. The contribution of AMPK to the described effects of PPAR agonists on the regulation of lipid and glucose metabolism is unknown. We endeavored to determine whether AMPK contributes to the enhanced metabolic phenotype observed in skeletal muscle conferred by PPAR␦ agonists

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