Skeletal muscle transcriptional coactivator PGC-1α mediates mitochondrial, but not metabolic, changes during calorie restriction - PubMed (original) (raw)
Skeletal muscle transcriptional coactivator PGC-1α mediates mitochondrial, but not metabolic, changes during calorie restriction
Lydia W S Finley et al. Proc Natl Acad Sci U S A. 2012.
Abstract
Calorie restriction (CR) is a dietary intervention that extends lifespan and healthspan in a variety of organisms. CR improves mitochondrial energy production, fuel oxidation, and reactive oxygen species (ROS) scavenging in skeletal muscle and other tissues, and these processes are thought to be critical to the benefits of CR. PGC-1α is a transcriptional coactivator that regulates mitochondrial function and is induced by CR. Consequently, many of the mitochondrial and metabolic benefits of CR are attributed to increased PGC-1α activity. To test this model, we examined the metabolic and mitochondrial response to CR in mice lacking skeletal muscle PGC-1α (MKO). Surprisingly, MKO mice demonstrated a normal improvement in glucose homeostasis in response to CR, indicating that skeletal muscle PGC-1α is dispensable for the whole-body benefits of CR. In contrast, gene expression profiling and electron microscopy (EM) demonstrated that PGC-1α is required for the full CR-induced increases in mitochondrial gene expression and mitochondrial density in skeletal muscle. These results demonstrate that PGC-1α is a major regulator of the mitochondrial response to CR in skeletal muscle, but surprisingly show that neither PGC-1α nor mitochondrial biogenesis in skeletal muscle are required for the whole-body metabolic benefits of CR.
Conflict of interest statement
The authors declare no conflict of interest.
Figures
Fig. 1.
FLOX and MKO mice have equivalent whole-body metabolic responses to CR. (A) Body weights of FLOX and MKO mice on control (C) and calorie restricted (CR) diets. (B) Basal blood glucose levels of control and CR FLOX and MKO mice. (C) Glucose tolerance tests were performed on fasted FLOX and MKO mice and glucose was monitored at the indicated intervals. Glucose levels relative to baseline (0 min, 100%) are shown. Glucose tolerance was measured as the area under the curve in D. (E–G) Metabolic cage analyses showed that FLOX and MKO mice have similar metabolic responses to CR. (E) Oxygen consumption was measured by indirect calorimetry. (F) Respiratory exchange ratio (RER) was significantly decreased by CR in both FLOX and MKO mice. (G) Both FLOX and MKO CR mice had a burst of activity before feeding time (5:00 PM), but no changes in total activity with CR. All experiments were performed on two independent cohorts of mice. Both cohorts showed equivalent results. All results shown are from a single cohort, n = 4–8 per group. All bars, SEM. Significance was assessed by two-way ANOVA followed by Bonferroni posttest. *P < 0.05, **P < 0.01.
Fig. 2.
Metabolite profiling underscores the similar metabolic responses of FLOX and MKO mice to CR. (A) Lactate and (B) glucose were measured by LC/MS in serum from FLOX and MKO mice on control or CR diets. Fold decrease with CR represents the fold change with CR relative to control mice of the same genotype. All experiments were performed on two independent cohorts of mice. Both cohorts showed equivalent results. For metabolomics, data from both cohorts were pooled, n = 9–16 per group. All bars, SEM. *P < 0.05, **P < 0.01.
Fig. 3.
CR induces a mitochondrial gene expression program in skeletal muscle through PGC-1α. Gene expression profiling was performed on RNA extracted from the tibialis anterior and extensor digitorum longus (TA/EDL) muscles of control (C) and calorie restricted (CR) mice. (A) Heat map showing relative levels of the 402 genes in the mitochondrial pathway. Scale is based on changes in log2 expression relative to the median. (B) GSEA analysis revealed that the mitochondrial pathway is highly enriched in skeletal muscle of FLOX relative to MKO animals on a control diet. (C) The mitochondrial pathway is highly enriched in skeletal muscle of FLOX CR animals relative to FLOX control animals, and PGC-1α deletion blunts the enrichment of the mitochondrial pathway in CR animals. See
SI Materials and Methods
for details on GSEA enrichment plots. (D) Average log2 expression of the 402 mitochondrial genes is graphed as a box and whisker plot, with whiskers showing minimum to maximum values. Significance was assessed by two-way ANOVA followed by Bonferroni posttest. NS, not significant. ***P < 0.001, n = 6–7. (E) Gene expression was analyzed using qRT-PCR of RNA from TA/EDL muscles. *P < 0.05, **P < 0.005. Bars, SEM. n = 4–8.
Fig. 4.
PGC-1α is required for the increase in mitochondrial density in red muscle fibers during CR. (A_–_F) Electron microscopy (EM) was used to analyze red and white muscle fibers from the TA/EDL muscles of FLOX and MKO mice on control or CR diets. Images were taken from both the center of the myofiber and the periphery, and these regions were analyzed separately. Three separate fibers were imaged from each mouse, and three to four mice per group were analyzed. Mitochondrial number per unit area was quantified in white fibers (A) and red fibers (B). (C) Representative images of the center of red muscle fibers of control and CR FLOX and MKO animals. In each image, two representative mitochondria are indicated with an arrowhead. Increased magnification is shown on the Right, including one representative mitochondrion indicated by an arrowhead. (Scale bar, 1 μm.) (D and E) There is a trend of increased mitochondrial width (D) and length (E) with CR in the center of red muscle fibers of FLOX, but not MKO animals. (F) Mitochondrial density was calculated as the percentage of the total area covered by mitochondria using ImageJ software. Images from three separate fibers from each mouse and a total of six to eight mice per group were analyzed. All bars, SEM.
References
- Ristow M, Schmeisser S. Extending life span by increasing oxidative stress. Free Radic Biol Med. 2011;51:327–336. - PubMed
- Nisoli E, et al. Calorie restriction promotes mitochondrial biogenesis by inducing the expression of eNOS. Science. 2005;310:314–317. - PubMed
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