Abstract
Ablation of peroxisome proliferator activated receptor (PPAR) alpha, a lipid-activated transcription factor that regulates expression of beta-oxidative genes, results in profound metabolic abnormalities in liver and heart. In the present study we used PPAR alpha knockout (KO) mice to determine whether this transcription factor is essential for regulating fuel metabolism in skeletal muscle. When animals were challenged with exhaustive exercise or starvation, KO mice exhibited lower serum levels of glucose, lactate, and ketones and higher nonesterified fatty acids than wild type (WT) littermates. During exercise, KO mice exhausted earlier than WT and exhibited greater rates of glycogen depletion in liver but not skeletal muscle. Fatty acid oxidative capacity was similar between muscles of WT and KO when animals were fed and only 28% lower in KO muscles when animals were starved. Exercise-induced regulation and starvation-induced regulation of pyruvate-dehydrogenase kinase 4 and uncoupling protein 3, two classical and robustly responsive PPAR alpha target genes, were similar between WT and KO in skeletal muscle but markedly different between genotypes in heart. Real time quantitative PCR analyses showed that unlike in liver and heart, in mouse skeletal muscle PPAR delta is severalfold more abundant than either PPAR alpha or PPAR gamma. In both human and rodent myocytes, the highly selective PPAR delta agonist GW742 increased fatty acid oxidation about 2-fold and induced expression of several lipid regulatory genes, including pyruvate-dehydrogenase kinase 4 and uncoupling protein 3, responses that were similar to those elicited by the PPAR alpha agonist GW647. These results show redundancy in the functions of PPARs alpha and delta as transcriptional regulators of fatty acid homeostasis and suggest that in skeletal muscle high levels of the delta-subtype can compensate for deficiency of PPAR alpha.
Highlights
Ablation of peroxisome proliferator activated receptor (PPAR) ␣, a lipid-activated transcription factor that regulates expression of -oxidative genes, results in profound metabolic abnormalities in liver and heart
Here we report that skeletal muscles from KO mice exhibited only minor changes in fatty acid homeostasis and, that neither constitutive nor inducible mRNA expression of known PPAR␣ target genes was negatively affected by its absence
Metabolic Responses to Exercise and Starvation Are Altered in PPAR␣ KO Mice—Consistent with earlier reports [4], we found that the body weights of older KO mice (23.4 Ϯ 0.73 g) were greater than their wild type (WT) littermates (21.7 Ϯ 0.98 g)
Summary
Materials—Bovine serum albumin, carnitine, and sodium oleate were from Sigma. Fetal bovine serum and Hanks’ balanced salt solution were from Invitrogen. Determination of Fatty Acid Oxidation in Cultured Myocytes—Following treatments with vehicle or PPAR-selective compounds, the myotubes were incubated at 37 °C in sealed 12- or 24-well plates containing 500 or 750 l of DFM plus 12.5 mM HEPES, 0.25% bovine serum albumin, 1.0 mM carnitine, 100 M sodium oleate, 50 g/ml gentamycin, and 1.0 Ci/ml [14C]oleate (PerkinElmer Life Sciences ). Relative quantitation of PPAR target genes in cultured myocytes was calculated by using the 2⌬CT formula, in which ⌬CT equals the difference between CT values for vehicle (Me2SO) and drug-treated cells This formula was validated for each primer/probe set using six-point serial standard curves as described previously [24]. In HSkMC and L6 myocytes differences in FAO rates and mRNA expression (CT values) were analyzed by Student’s t test for paired data
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
