Compensatory increases in nuclear PGC1alpha protein are primarily associated with subsarcolemmal mitochondrial adaptations in ZDF rats.
OBJECTIVE
We examined in insulin-resistant muscle if, in contrast to long-standing dogma, mitochondrial fatty acid oxidation is increased and whether this is attributed to an increased nuclear content of peroxisome proliferator-activated receptor (PPAR) gamma coactivator (PGC) 1alpha and the adaptations of specific mitochondrial subpopulations.


METHODS
Skeletal muscles from male control and Zucker diabetic fatty (ZDF) rats were used to determine 1) intramuscular lipid distribution, 2) subsarcolemmal and intermyofibrillar mitochondrial morphology, 3) rates of palmitate oxidation in subsarcolemmal and intermyofibrillar mitochondria, and 4) the subcellular localization of PGC1alpha. Electotransfection of PGC1alpha cDNA into lean animals tested the notion that increased nuclear PGC1alpha preferentially targeted subsarcolemmal mitochondria.


RESULTS
Transmission electron microscope analysis revealed that in ZDF animals the number (+50%), width (+69%), and density (+57%) of subsarcolemmal mitochondria were increased (P < 0.05). In contrast, intermyofibrillar mitochondria remained largely unchanged. Rates of palmitate oxidation were approximately 40% higher (P < 0.05) in ZDF subsarcolemmal and intermyofibrillar mitochondria, potentially as a result of the increased PPAR-targeted proteins, carnitine palmitoyltransferase-I, and fatty acid translocase (FAT)/CD36. PGC1alpha mRNA and total protein were not altered in ZDF animals; however, a greater (approximately 70%; P < 0.05) amount of PGC1alpha was located in nuclei. Overexpression of PGC1alpha only increased subsarcolemmal mitochondrial oxidation rates.


CONCLUSIONS
In ZDF animals, intramuscular lipids accumulate in the intermyofibrillar region (increased size and number), and this is primarily associated with increased oxidative capacity in subsarcolemmal mitochondria (number, size, density, and oxidation rates). These changes may result from an increased nuclear content of PGC1alpha, as under basal conditions, overexpression of PGC1alpha appears to target subsarcolemmal mitochondria.
Holloway
Graham P
GP
Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada. ghollowa@uoguelph.ca
Gurd
Brendon J
BJ
Snook
Laelie A
LA
Lally
Jamie
J
Bonen
Arend
A
D000064:Acclimatization; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002334:Carnitine O-Palmitoyltransferase / Q000235:genetics; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005786:Gene Expression Regulation; D007328:Insulin / Q000097:blood; D008297:Male; D008931:Mitochondria, Muscle / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000502:physiology; D009210:Myofibrils / Q000502:physiology; D009245:NADH Dehydrogenase / Q000235:genetics; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D016601:RNA-Binding Proteins / Q000235:genetics*; D051381:Rats; D011924:Rats, Zucker; D012016:Reference Values; D012508:Sarcolemma / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics*; D014162:Transfection; D014280:Triglycerides / Q000378:metabolism
D001786:Blood Glucose; D017931:DNA Primers; D018076:DNA, Complementary; D004272:DNA, Mitochondrial; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; C501429:Ppargc1a protein, rat; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D014280:Triglycerides; D009245:NADH Dehydrogenase; D002334:Carnitine O-Palmitoyltransferase