Total Skeletal Muscle PGC-1 Deficiency Uncouples Mitochondrial Derangements from Fiber Type Determination and Insulin Sensitivity

“Interest- ingly, expression of the gene encoding nuclear respiratory factor 1 (NRF-1), a PGC-1a target (Wu et al., 1999) involved in regu- lating OXPHOS genes and coordinating nuclear and mitochon- drial genomes, was similar among the groups.”

“Originally discovered in brown adipose tissue (Puigserver et al., 1998), PGC-1a enhances transcription by interacting directly with target transcription factors, including PPARg and other members of the nuclear receptor superfamily (reviewed in”

“Plasma free fatty acids were also determined by a colorimetric assay (Lin et al., 2002b).”

“The transcriptional coactivators PPARg coactivator-1a (PGC-1a) and PGC-1b serve as regulators of mitochondrial biogenesis and cellular energy metabolism (Kelly and Scarpulla, 2004; Lin et al., 2005).”

“In addition, several studies in humans have shown reduced expression of PGC-1a (Mootha et al., 2003; Patti et al., 2003) in skeletal muscle of insulin-resistant and diabetic subjects.”

“…discovered in brown adipose tissue (Puigserver et al., 1998), PGC-1a enhances transcription by interacting directly with target transcription factors, including PPARg and other members of the nuclear receptor superfamily (reviewed in Cell M Finck and Kelly, 2006; Handschin and Spiegelman, 2006).”

“This latter function has been ascribed to the ongoing dynamics of fusion and fission, which serve to maintain mitochondrial quality control (Chen et al., 2005; Waterham et al., 2007; Zhang and Chan, 2007).”

“The PGC-1 coactivators are enriched in tissues with high capacity for mitochondrial respiratory function, such as brown adipose tissue, heart, and skeletal muscle, and are highly inducible in response to physiological stimuli, including exercise, fasting, and cold exposure (Wu et al., 1999; Goto et al., 2000; Lehman e…”

“The transcriptional coactivators PPARg coactivator-1a (PGC-1a) and PGC-1b serve as regulators of mitochondrial biogenesis and cellular energy metabolism (Kelly and Scarpulla, 2004; Lin et al., 2005).”

“PGC-1bf/f mice were crossed with mice expressing Cre under control of a MLC1f promoter (Bothe et al., 2000) or the MCK promoter (Brüning et al., 1998) to achieve muscle-specific deletion of PGC-1b.”

“…discovered in brown adipose tissue (Puigserver et al., 1998), PGC-1a enhances transcription by interacting directly with target transcription factors, including PPARg and other members of the nuclear receptor superfamily (reviewed in Cell M Finck and Kelly, 2006; Handschin and Spiegelman, 2006).”

“The PGC-1 coactivators are enriched in tissues with high capacity for mitochondrial respiratory function, such as brown adipose tissue, heart, and skeletal muscle, and are highly inducible in response to physiological stimuli, including exercise, fasting, and cold exposure (Wu et al., 1999; Goto et al., 2000; Lehman e…”

“The PGC-1 coactivators are enriched in tissues with high capacity for mitochondrial respiratory function, such as brown adipose tissue, heart, and skeletal muscle, and are highly inducible in response to physiological stimuli, including exercise, fasting, and cold exposure (Wu et al., 1999; Goto et al., 2000; Lehman e…”

“Significant evidence suggests a link between skeletal muscle mitochondrial dysfunction and the development of insulin resis- tance (Lowell and Shulman, 2005; Morino et al., 2005; Petersen et al., 2005).”

“This latter function has been ascribed to the ongoing dynamics of fusion and fission, which serve to maintain mitochondrial quality control (Chen et al., 2005; Waterham et al., 2007; Zhang and Chan, 2007).”

“This latter result is consistent with the findings of a previous study showing no effect of loss of PGC-1a on NRF-1 expression in the heart (Arany et al., 2005) or skeletal muscle (Geng et al., 2010).”

“We and others have shown that PGC-1a-deficient mice exhibit a mild exercise performance phenotype (Leone et al., 2005; Handschin et al., 2007; Lai et al., 2008).”

“Quantitative real-time PCR was performed on total RNA as previously described (Huss et al., 2004).”

“PGC-1b has been shown to drive formation of type IIx fibers (Arany et al., 2007).”

“Others have recently shown that PGC-1a and PGC-1b are capable of activating transcription of the Mfn2 gene by coacti- vating the nuclear receptor ERRa (Soriano et al., 2006; Liesa et al., 2008).”

“We and others have shown that PGC-1a-deficient mice exhibit a mild exercise performance phenotype (Leone et al., 2005; Handschin et al., 2007; Lai et al., 2008).”

“Significant evidence suggests a link between skeletal muscle mitochondrial dysfunction and the development of insulin resis- tance (Lowell and Shulman, 2005; Morino et al., 2005; Petersen et al., 2005).”

“…mouse ‘‘knockout’’ studies to date have been limited due to the functionally redundant actions of PGC-1a and PGC-1b; single PGC-1 gene deletion lines exhibit relatively minimal phenotypes (Lin et al., 2004; Leone et al., 2005; Lelliott et al., 2006; Vianna et al., 2006; Sonoda et al., 2007).”

“…PGC-1a or PGC-1b ‘‘knockout’’ mouse etabolism 12, 633–642, December 1, 2010 ª2010 Elsevier Inc. 633 models have generally not demonstrated insulin-resistant or glucose-intolerant phenotypes (Lin et al., 2004; Leone et al., 2005; Lelliott et al., 2006; Vianna et al., 2006; Sonoda et al., 2007).”

“This latter result is consistent with the findings of a previous study showing no effect of loss of PGC-1a on NRF-1 expression in the heart (Arany et al., 2005) or skeletal muscle (Geng et al., 2010).”

“…such as brown adipose tissue, heart, and skeletal muscle, and are highly inducible in response to physiological stimuli, including exercise, fasting, and cold exposure (Wu et al., 1999; Goto et al., 2000; Lehman et al., 2000; Baar et al., 2002; Pilegaard et al., 2003; Finck and Kelly, 2006).”

“SDH stains were performed as described previously (Wende et al., 2007).”

“PGC-1 overexpression in mice has been shown to inhibit the protein degrada- tion known to occur in disuse atrophy (Wenz et al., 2009; Brault et al., 2010).”

“Muscles for MHC immunofluorescence (IF) analysis were embedded in OCT Compound (Tissue-Tek), and IF was performed as described previously (Waters et al., 2004).”

“Consistent with the type II fiber specificity of the MLC-1f promoter (Donoghue et al., 1991; Parsons et al., 2004), PGC-1b gene expression was markedly reduced in gastrocnemius (GC) (residual levels 10.9% ± 1.3% of PGC-1bf/f) and white vastus (9.0% ± 1.5% of PGC-1bf/f) muscles of PGC-1bf/f/MLC-Cre…”

“Others have recently shown that PGC-1a and PGC-1b are capable of activating transcription of the Mfn2 gene by coactivating the nuclear receptor ERRa (Soriano et al., 2006; Liesa et al., 2008).”

“models have generally not demonstrated insulin-resistant or glucose-intolerant phenotypes (Lin et al., 2004; Leone et al., 2005; Lelliott et al., 2006; Vianna et al., 2006; Sonoda et al., 2007).”

“One caveat to our conclusions is that a small amount of a mutant form of a naturally occurring, alterna- tively spliced form of PGC-1a, referred to as NT-PGC-1a (Zhang et al., 2009), could be theoretically expressed in the PGC-1a-defi- cient line used in this study.”

“This latter function has been ascribed to the ongoing dynamics of fusion and fission, which serve to maintain mitochondrial quality control (Chen et al., 2005; Waterham et al., 2007; Zhang and Chan, 2007).”

“For the assessment of forelimb grip strength, a grip strength meter was used as previously described (Wozniak et al., 2007).”

“Mitochondrial Respiration Mitochondrial respiration was assessed in isolated mitochondria from the hindlimb muscle with pyruvate or palmitoylcarnitine as substrate, as described previously (Bhattacharya et al., 1991).”

“Consistent with the type II fiber specificity of the MLC-1f promoter (Donoghue et al., 1991; Parsons et al., 2004), PGC-1b gene expression was markedly reduced in gastrocnemius (GC) (residual levels 10.9% ± 1.3% of PGC-1bf/f) and white vastus (9.0% ± 1.5% of PGC-1bf/f) muscles of PGC-1bf/f/MLC-Cre…”

“Mice were euthanized by CO2 inhalation after 10 weeks on high-fat diet, and plasma and tissue triglyceride concentrations were determined by colorimetric assays as previously described (Chen et al., 2008).”

“Plasma free fatty acids were also determined by a colorimetric assay (Lin et al., 2002b).”

“To test this, we examined primary myotubes from PGC-1a/b knockout (KO) mice (Zechner et al., 2010) and from PGC-1a muscle-specific null mice (Handschin et al.”

“…of Pgc1a in mice leads to muscle fiber type switching from fast-twitching glycolytic fibers to slow-twitching oxidative fibers (Lin et al., 2002), it is still unclear how important PGC1a is for muscle fiber type determination in wild-type mice (Handschin et al., 2007; Zechner et al., 2010).”