Modest PGC-1α Overexpression in Muscle in Vivo Is Sufficient to Increase Insulin Sensitivity and Palmitate Oxidation in Subsarcolemmal, Not Intermyofibrillar, Mitochondria

Carley R Benton,James G Nickerson,James Lally,Xiao-Xia Han,Graham P Holloway,Jan F.C Glatz,Joost J F.P Luiken,Terry E Graham,John J Heikkila,Arend Bonen

doi:10.1074/jbc.m704332200

Carley R Benton, James G Nickerson + Show 8 more

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https://doi.org/10.1074/jbc.m704332200

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Abstract

PGC-1alpha overexpression in skeletal muscle, in vivo, has yielded disappointing and unexpected effects, including disrupted cellular integrity and insulin resistance. These unanticipated results may stem from an excessive PGC-1alpha overexpression in transgenic animals. Therefore, we examined the effects of a modest PGC-1alpha overexpression in a single rat muscle, in vivo, on fuel-handling proteins and insulin sensitivity. We also examined whether modest PGC-1alpha overexpression selectively targeted subsarcolemmal (SS) mitochondrial proteins and fatty acid oxidation, because SS mitochondria are metabolically more plastic than intermyofibrillar (IMF) mitochondria. Among metabolically heterogeneous rat hindlimb muscles, PGC-1alpha was highly correlated with their oxidative fiber content and with substrate transport proteins (GLUT4, FABPpm, and FAT/CD36) and mitochondrial proteins (COXIV and mTFA) but not with insulin-signaling proteins (phosphatidylinositol 3-kinase, IRS-1, and Akt2), nor with 5'-AMP-activated protein kinase, alpha2 subunit, and HSL. Transfection of PGC-1alpha into the red (RTA) and white tibialis anterior (WTA) compartments of the tibialis anterior muscle increased PGC-1alpha protein by 23-25%. This also induced the up-regulation of transport proteins (FAT/CD36, 35-195%; GLUT4, 20-32%) and 5'-AMP-activated protein kinase, alpha2 subunit (37-48%), but not other proteins (FABPpm, IRS-1, phosphatidylinositol 3-kinase, Akt2, and HSL). SS and IMF mitochondrial proteins were also up-regulated, including COXIV (15-75%), FAT/CD36 (17-30%), and mTFA (15-85%). PGC-1alpha overexpression also increased palmitate oxidation in SS (RTA, +116%; WTA, +40%) but not in IMF mitochondria, and increased insulin-stimulated phosphorylation of AKT2 (28-43%) and rates of glucose transport (RTA, +20%; WTA, +38%). Thus, in skeletal muscle in vivo, a modest PGC-1alpha overexpression up-regulated selected plasmalemmal and mitochondrial fuel-handling proteins, increased SS (not IMF) mitochondrial fatty acid oxidation, and improved insulin sensitivity.

Highlights

The abbreviations used arePPAR␥, peroxisome proliferator-activated receptor ␥; RTA, red tibialis anterior; WTA, tibialis anterior; PI, phosphatidylinositol; PI3K, phosphatidylinositol 3-kinase; SS, subsarcolemmal; IMF, intermyofibrillar; WG, white gastrocnemius; RG, red gastrocnemius; PL, plantaris; EDL, extensor digitorum longus; BSA, bovine serum albumin; TA, tibialis anterior; CPTI, carnitine palmitoyltransferase-I; AMPK␣2, 5Ј-AMP-activated protein kinase, ␣2 subunit
Skeletal muscle GLUT4 mRNA was slightly up-regulated (ϩ10%) when the PGC-1␣ mRNA increase was small (ϩ10%), whereas a 10 –13-fold increase in PGC-1␣ mRNA reduced skeletal muscle GLUT4 mRNA by up to 70%, while concomitantly reducing whole body insulin sensitivity (5)
Summary—These studies demonstrate that a modest overexpression of PGC-1␣ in rat skeletal muscle in vivo increases both fatty acid oxidation and insulin sensitivity

Summary

The abbreviations used are

PPAR␥, peroxisome proliferator-activated receptor ␥; RTA, red tibialis anterior; WTA, tibialis anterior; PI, phosphatidylinositol; PI3K, phosphatidylinositol 3-kinase; SS, subsarcolemmal; IMF, intermyofibrillar; WG, white gastrocnemius; RG, red gastrocnemius; PL, plantaris; EDL, extensor digitorum longus; BSA, bovine serum albumin; TA, tibialis anterior; CPTI, carnitine palmitoyltransferase-I; AMPK␣2, 5Ј-AMP-activated protein kinase, ␣2 subunit. In these studies (12–15) the effects of PGC-1␣ on CPTI protein expression and CPTI activity were not determined It remains to be demonstrated whether PGC-1␣ up-regulates fatty acid oxidation in mammalian skeletal muscle mitochondria in vivo. Because the effects of very large PGC-1␣ alterations in vivo have been disappointing, with respect to cardiac performance, insulin sensitivity, and dietinduced insulin resistance (5, 6, 12, 14, 18, 20), Handschin and Spiegelman (19) have recently speculated that only a moderate overexpression of PGC-1␣ may be required to observe its potential therapeutic benefits. Our study reveals for the first time that a modest overexpression of PGC-1␣ is sufficient to observe improvements in the following: (i) SS but not IMF mitochondrial fatty acid oxidation, and (ii) in insulin sensitivity in mammalian skeletal muscle

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DISCUSSION