Adult skeletal muscle peroxisome proliferator-activated receptor γ -related coactivator 1 is involved in maintaining mitochondrial content

Abstract

The peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) family of transcriptional coactivators are regulators of mitochondrial oxidative capacity and content in skeletal muscle. Many of these conclusions are based primarily on gain-of-function studies using muscle-specific overexpression of PGC1s. We have previously reported that genetic deletion of both PGC-1α and PGC-1β in adult skeletal muscle resulted in a significant reduction in oxidative capacity with no effect on mitochondrial content. However, the contribution of PGC-1-related coactivator (PRC), the third PGC-1 family member, in regulating skeletal muscle mitochondria is unknown. Therefore, we generated an inducible skeletal muscle-specific PRC knockout mouse (iMS-PRC-KO) to assess the contribution of PRC in skeletal muscle mitochondrial function. We measured mRNA expression of electron transport chain (ETC) subunits as well as markers of mitochondrial content in the iMS-PRC-KO animals and observed an increase in ETC gene expression and mitochondrial content. Furthermore, the increase in ETC gene expression and mitochondrial content was associated with increased expression of PGC-1α and PGC-1β. We therefore generated an adult-inducible PGC-1 knockout mouse in which all PGC-1 family members are deleted (iMS-PGC-1TKO). The iMS-PGC-1TKO animals exhibited a reduction in ETC mRNA expression and mitochondrial content. These data suggest that in the absence of PRC alone, compensation occurs by increasing PGC-1α and PGC-1β to maintain mitochondrial content. Moreover, the removal of all three PGC-1s in skeletal muscle results in a reduction in both ETC mRNA expression and mitochondrial content. Taken together, these results suggest that PRC plays a role in maintaining baseline mitochondrial content in skeletal muscle.

Keywords: PGC-1-related coactivator; mitochondria; mitochondrial biogenesis; skeletal muscle.

Figure 1.

Effect of adult deletion of PRC on skeletal muscle ETC expression and mitochondrial content. PRC mRNA expression (A), nuclear-encoded ETC mRNA expression (B), protein expression of ETC subunits (C), densitometry quantification of ETC subunits protein expression to Ponceau S staining in gastrocnemius muscle (D), time to exhaustion (E), citrate synthase activity (F), mtDNA-to-nDNA (mtDNA/nDNA) ratio (G), VDAC protein expression (H), densitometry quantification of VDAC protein expression normalized to Tuba protein expression (I) and PGC-1α and PGC-1β mRNA expression in gastrocnemius muscle in adult-inducible skeletal muscle-specific PRC knockouts (iMS-PRC-KO) and control littermates (J). Data are presented as means ± SE; n = 4–5 per group; *P < 0.05, **P < 0.01, ***P < 0.001 compared with control as determined by unpaired t test. ETC, electron transport chain; KO, knockout; mtDNA, mitochondrial DNA; nDNA, nuclear DNA; PGC-1, peroxisome proliferator-activated receptor γ coactivator-1; PRC, PGC-1-related coactivator; VDAC, voltage-dependent anion channel.

Figure 2.

Effect of adult deletion of PRC and PGC-1α on skeletal muscle ETC expression and mitochondrial content. PGC-1α, PGC-1β, and PRC mRNA expression (A); nuclear-encoded ETC mRNA expression (B); protein expression of ETC subunits (C); densitometry quantification of ETC subunits protein expression to Ponceau S staining in gastrocnemius muscle (D); time to exhaustion (E); citrate synthase activity (F); mtDNA-to-nDNA (mtDNA/nDNA) ratio (G); VDAC protein expression (H); densitometry quantification of VDAC protein expression normalized to Tuba protein expression in gastrocnemius muscle in adult-inducible skeletal muscle-specific PGC-1α/PRC knockouts (iMS-PGC-1α/PRC-DKO) and control littermates (I). Data are presented as means ± SE; n = 4–5 per group; *P < 0.05, **P < 0.01, ***P < 0.001 compared with control as determined by unpaired t test. ETC, electron transport chain; KO, knockout; mtDNA, mitochondrial DNA; nDNA, nuclear DNA; PGC-1, peroxisome proliferator-activated receptor γ coactivator-1; PRC, PGC-1-related coactivator; VDAC, voltage-dependent anion channel.

Figure 3.

Effect of adult deletion of PRC and PGC-1β on skeletal muscle ETC expression and mitochondrial content. PGC-1α, PGC-1β, and PRC mRNA expression (A); nuclear-encoded ETC mRNA expression (B); protein expression of ETC subunits (C); densitometry quantification of ETC subunits protein expression to Ponceau S staining in gastrocnemius muscle (D); time to exhaustion (E); citrate synthase activity (F); mtDNA-to-nDNA (mtDNA/nDNA) ratio (G); VDAC protein expression (H); densitometry quantification of VDAC protein expression normalized to Tuba protein expression in gastrocnemius muscle in adult-inducible skeletal muscle-specific PGC-1β/PRC knockouts (iMS-PGC-1β/PRC-DKO) and control littermates (I). Data are presented as means ± SE; n = 4–5 per group; *P < 0.05, **P < 0.01, ***P < 0.001 compared with control as determined by unpaired t test. ETC, electron transport chain; KO, knockout; mtDNA, mitochondrial DNA; nDNA, nuclear DNA; PGC-1, peroxisome proliferator-activated receptor γ coactivator-1; PRC, PGC-1-related coactivator; VDAC, voltage-dependent anion channel.

Figure 4.

Effect of adult deletion of all three PGC-1s on skeletal muscle ETC expression and mitochondrial content. PGC-1α, PGC-1β, and PRC mRNA expression (A); nuclear-encoded ETC mRNA expression (B); protein expression of ETC subunits (C); densitometry quantification of ETC subunits protein expression to Ponceau S staining in gastrocnemius muscle (D); time to exhaustion (E); citrate synthase activity (F); mtDNA-to-nDNA (mtDNA/nDNA) ratio (G); VDAC protein expression (H); densitometry quantification of VDAC protein expression normalized to Tuba protein expression in gastrocnemius muscle in adult-inducible skeletal muscle-specific PGC-1α/PGC-1β/PRC knockouts (iMS-PGC-1-TKO) and control littermates (I). Data are presented as means ± SE; n = 4–5 per group; *P < 0.05, **P < 0.01, ***P < 0.001 compared with control as determined by unpaired t test. ETC, electron transport chain; KO, knockout; mtDNA, mitochondrial DNA; nDNA, nuclear DNA; PGC-1, peroxisome proliferator-activated receptor γ coactivator-1; PRC, PGC-1-related coactivator; VDAC, voltage-dependent anion channel.