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The endogenous molecular clock orchestrates the temporal separation of substrate metabolism in skeletal muscle.

Hodge BA, Wen Y, Riley LA, Zhang X, England JH, Harfmann BD, Schroder EA, Esser KA - Skelet Muscle (2015)

Bottom Line: Within skeletal muscle exists an intrinsic molecular clock mechanism that regulates the timing of physiological processes.We also observed a gene signature indicative of a fast to slow fiber-type shift and a more oxidative skeletal muscle in the iMS-Bmal1 (-/-) model.These data provide evidence that the intrinsic molecular clock in skeletal muscle temporally regulates genes involved in the utilization and storage of substrates independent of circadian activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, College of Medicine, University of Kentucky, MS 508, 800 Rose Street, Lexington, KY 40536 USA ; Center for Muscle Biology, University of Kentucky, 800 Rose Street, Lexington, KY 40536 USA.

ABSTRACT

Background: Skeletal muscle is a major contributor to whole-body metabolism as it serves as a depot for both glucose and amino acids, and is a highly metabolically active tissue. Within skeletal muscle exists an intrinsic molecular clock mechanism that regulates the timing of physiological processes. A key function of the clock is to regulate the timing of metabolic processes to anticipate time of day changes in environmental conditions. The purpose of this study was to identify metabolic genes that are expressed in a circadian manner and determine if these genes are regulated downstream of the intrinsic molecular clock by assaying gene expression in an inducible skeletal muscle-specific Bmal1 knockout mouse model (iMS-Bmal1 (-/-) ).

Methods: We used circadian statistics to analyze a publicly available, high-resolution time-course skeletal muscle expression dataset. Gene ontology analysis was utilized to identify enriched biological processes in the skeletal muscle circadian transcriptome. We generated a tamoxifen-inducible skeletal muscle-specific Bmal1 knockout mouse model and performed a time-course microarray experiment to identify gene expression changes downstream of the molecular clock. Wheel activity monitoring was used to assess circadian behavioral rhythms in iMS-Bmal1 (-/-) and control iMS-Bmal1 (+/+) mice.

Results: The skeletal muscle circadian transcriptome was highly enriched for metabolic processes. Acrophase analysis of circadian metabolic genes revealed a temporal separation of genes involved in substrate utilization and storage over a 24-h period. A number of circadian metabolic genes were differentially expressed in the skeletal muscle of the iMS-Bmal1 (-/-) mice. The iMS-Bmal1 (-/-) mice displayed circadian behavioral rhythms indistinguishable from iMS-Bmal1 (+/+) mice. We also observed a gene signature indicative of a fast to slow fiber-type shift and a more oxidative skeletal muscle in the iMS-Bmal1 (-/-) model.

Conclusions: These data provide evidence that the intrinsic molecular clock in skeletal muscle temporally regulates genes involved in the utilization and storage of substrates independent of circadian activity. Disruption of this mechanism caused by phase shifts (that is, social jetlag) or night eating may ultimately diminish skeletal muscle's ability to efficiently maintain metabolic homeostasis over a 24-h period.

No MeSH data available.


Related in: MedlinePlus

Differentially expressed circadian, metabolic genes in iMS-Bmal1−/− skeletal muscle. Average expression changes of the circadian carbohydrate (A) and lipid (B) genes in iMS-Bmal1−/− gastrocnemius averaged over circadian times 18, 22, 26, 30, 34, and 38. Tibialis anterior and soleus gene expression changes (Dyar et al.) averaged over circadian times 0, 4, 8, 12, 16, and 20. The red line denotes control (iMS-Bmal1+/+) gene expression values. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001.
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Fig5: Differentially expressed circadian, metabolic genes in iMS-Bmal1−/− skeletal muscle. Average expression changes of the circadian carbohydrate (A) and lipid (B) genes in iMS-Bmal1−/− gastrocnemius averaged over circadian times 18, 22, 26, 30, 34, and 38. Tibialis anterior and soleus gene expression changes (Dyar et al.) averaged over circadian times 0, 4, 8, 12, 16, and 20. The red line denotes control (iMS-Bmal1+/+) gene expression values. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001.

Mentions: Gene expression analysis of iMS-Bmal1+/+ and iMS-Bmal1−/− muscle tissue reveals that the intrinsic molecular clock, even in constant conditions, plays a role in temporally regulating carbohydrate and lipid metabolism. We performed our transcriptome analysis at 5 weeks postrecombination to identify early gene expression changes caused by the loss of the clock mechanism in skeletal muscle. Analyzing gene expression at this time point also limits potential off-target effects of tamoxifen treatment by allowing for a sufficient wash-out period. We found that the circadian genes involved in carbohydrate metabolism were most affected by loss of Bmal1. The expression of the glycolytic enzymes, Pfkfb1, Pfkfb3, and Hk2 as well as the PDH phosphatase, Pdp1 were all significantly downregulated in the gastrocnemius (Figure 5A). In addition, expression of the adrenergic receptor, Adrb2, was also significantly decreased. These genes are convincing clock-controlled candidates in skeletal muscle as they have circadian expression patterns similar to that of known clock-controlled genes (peak expression during inactive to active phase transition), and their loss of expression following Bmal1 inactivation is indicative of direct transcriptional regulation by the clock. By targeting these genes, the molecular clock mechanism can precisely regulate the timing of carbohydrate utilization to occur during the active phase. The observation that circadian genes involved in glucose utilization are diminished in our model is in agreement with the muscle-specific Bmal1 knockout model generated by Dyar et al. in which they report significant decreases in glucose oxidation and insulin stimulated glucose uptake in their muscle tissues [43].Figure 5


The endogenous molecular clock orchestrates the temporal separation of substrate metabolism in skeletal muscle.

Hodge BA, Wen Y, Riley LA, Zhang X, England JH, Harfmann BD, Schroder EA, Esser KA - Skelet Muscle (2015)

Differentially expressed circadian, metabolic genes in iMS-Bmal1−/− skeletal muscle. Average expression changes of the circadian carbohydrate (A) and lipid (B) genes in iMS-Bmal1−/− gastrocnemius averaged over circadian times 18, 22, 26, 30, 34, and 38. Tibialis anterior and soleus gene expression changes (Dyar et al.) averaged over circadian times 0, 4, 8, 12, 16, and 20. The red line denotes control (iMS-Bmal1+/+) gene expression values. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4440511&req=5

Fig5: Differentially expressed circadian, metabolic genes in iMS-Bmal1−/− skeletal muscle. Average expression changes of the circadian carbohydrate (A) and lipid (B) genes in iMS-Bmal1−/− gastrocnemius averaged over circadian times 18, 22, 26, 30, 34, and 38. Tibialis anterior and soleus gene expression changes (Dyar et al.) averaged over circadian times 0, 4, 8, 12, 16, and 20. The red line denotes control (iMS-Bmal1+/+) gene expression values. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001.
Mentions: Gene expression analysis of iMS-Bmal1+/+ and iMS-Bmal1−/− muscle tissue reveals that the intrinsic molecular clock, even in constant conditions, plays a role in temporally regulating carbohydrate and lipid metabolism. We performed our transcriptome analysis at 5 weeks postrecombination to identify early gene expression changes caused by the loss of the clock mechanism in skeletal muscle. Analyzing gene expression at this time point also limits potential off-target effects of tamoxifen treatment by allowing for a sufficient wash-out period. We found that the circadian genes involved in carbohydrate metabolism were most affected by loss of Bmal1. The expression of the glycolytic enzymes, Pfkfb1, Pfkfb3, and Hk2 as well as the PDH phosphatase, Pdp1 were all significantly downregulated in the gastrocnemius (Figure 5A). In addition, expression of the adrenergic receptor, Adrb2, was also significantly decreased. These genes are convincing clock-controlled candidates in skeletal muscle as they have circadian expression patterns similar to that of known clock-controlled genes (peak expression during inactive to active phase transition), and their loss of expression following Bmal1 inactivation is indicative of direct transcriptional regulation by the clock. By targeting these genes, the molecular clock mechanism can precisely regulate the timing of carbohydrate utilization to occur during the active phase. The observation that circadian genes involved in glucose utilization are diminished in our model is in agreement with the muscle-specific Bmal1 knockout model generated by Dyar et al. in which they report significant decreases in glucose oxidation and insulin stimulated glucose uptake in their muscle tissues [43].Figure 5

Bottom Line: Within skeletal muscle exists an intrinsic molecular clock mechanism that regulates the timing of physiological processes.We also observed a gene signature indicative of a fast to slow fiber-type shift and a more oxidative skeletal muscle in the iMS-Bmal1 (-/-) model.These data provide evidence that the intrinsic molecular clock in skeletal muscle temporally regulates genes involved in the utilization and storage of substrates independent of circadian activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, College of Medicine, University of Kentucky, MS 508, 800 Rose Street, Lexington, KY 40536 USA ; Center for Muscle Biology, University of Kentucky, 800 Rose Street, Lexington, KY 40536 USA.

ABSTRACT

Background: Skeletal muscle is a major contributor to whole-body metabolism as it serves as a depot for both glucose and amino acids, and is a highly metabolically active tissue. Within skeletal muscle exists an intrinsic molecular clock mechanism that regulates the timing of physiological processes. A key function of the clock is to regulate the timing of metabolic processes to anticipate time of day changes in environmental conditions. The purpose of this study was to identify metabolic genes that are expressed in a circadian manner and determine if these genes are regulated downstream of the intrinsic molecular clock by assaying gene expression in an inducible skeletal muscle-specific Bmal1 knockout mouse model (iMS-Bmal1 (-/-) ).

Methods: We used circadian statistics to analyze a publicly available, high-resolution time-course skeletal muscle expression dataset. Gene ontology analysis was utilized to identify enriched biological processes in the skeletal muscle circadian transcriptome. We generated a tamoxifen-inducible skeletal muscle-specific Bmal1 knockout mouse model and performed a time-course microarray experiment to identify gene expression changes downstream of the molecular clock. Wheel activity monitoring was used to assess circadian behavioral rhythms in iMS-Bmal1 (-/-) and control iMS-Bmal1 (+/+) mice.

Results: The skeletal muscle circadian transcriptome was highly enriched for metabolic processes. Acrophase analysis of circadian metabolic genes revealed a temporal separation of genes involved in substrate utilization and storage over a 24-h period. A number of circadian metabolic genes were differentially expressed in the skeletal muscle of the iMS-Bmal1 (-/-) mice. The iMS-Bmal1 (-/-) mice displayed circadian behavioral rhythms indistinguishable from iMS-Bmal1 (+/+) mice. We also observed a gene signature indicative of a fast to slow fiber-type shift and a more oxidative skeletal muscle in the iMS-Bmal1 (-/-) model.

Conclusions: These data provide evidence that the intrinsic molecular clock in skeletal muscle temporally regulates genes involved in the utilization and storage of substrates independent of circadian activity. Disruption of this mechanism caused by phase shifts (that is, social jetlag) or night eating may ultimately diminish skeletal muscle's ability to efficiently maintain metabolic homeostasis over a 24-h period.

No MeSH data available.


Related in: MedlinePlus