Project description:Background: Beta-adrenergic receptor agonists (BA) induce skeletal muscle hypertrophy, yet specific mechanisms that lead to this effect are not well understood. The objective of this research was to identify novel genes and physiological pathways that potentially facilitate BA induced skeletal muscle growth. We chose to evaluate global changes in gene expression by utilizing the Affymetrix platform to identify gene expression changes in mouse skeletal muscle. Changes in gene expression were evaluated 24 h (1D) and 10 days (10D) after administration of the BA clenbuterol. Results: Administration of clenbuterol stimulated anabolic activity, as indicated by decreased blood urea nitrogen (BUN; P < 0.01) and increased body weight gain (P < 0.05) 24 h or 10 d, respectively, after initiation of clenbuterol treatment. A total of 22,787 probesets were evaluated with 113 probesets defined as differentially expressed based on a false discovery rate of 10%. Differential mRNA abundance of four of these genes was validated in an independent experiment by quantitative PCR. Patterns of gene expression change observed from the microarray data suggested more genes are differentially regulated after 24 h than 10 d of BA administration. Functional characterization of differentially expressed genes revealed several categories that participate in biological processes important to skeletal muscle growth, including regulators of transcription and translation, mediators of cell-signaling pathways, and genes involved in polyamine metabolism. Included within these lists were several genes previously associated with myogenic differentiation, along with multiple genes known to promote a general up-regulation of translation. Conclusions: Global evaluation of gene expression after administration of clenbuterol identified changes gene expression and overrepresented functional categories of genes that may regulate BA-induced muscle hypertrophy. Changes in the mRNA abundance of multiple genes associated with myogenic differentiation may indicate an important effect of BA on the proliferation, differentiation, and/or recruitment of satellite cells into muscle fibers to promote muscle hypertrophy. Additionally, increased mRNA abundance of genes involved in the initiation of translation suggests that increased levels of protein synthesis often associated with BA administration may result from a general up-regulation of translational initiators, rather than a sustained up-regulation of gene expression at the transcriptional level. Additionally, numerous other genes and physiological pathways were identified that will be important targets for further investigations of the hypertrophic effect of BA on skeletal muscle. Experiment Overall Design: A total of 27 mice were used to represent three treatments. Hybridizations were done using RNA pools from 3 mice, with 3 pools (replicates) per treatment. Treatments included control, 1 day of clenbuterol administration, and 10 days of clenbuterol administration. Data represent skeletal muscle gene expression.

Project description:We analyzed the functional role of DOR (Diabetes and Obesity Regulated gene) (also named Tp53inp2) in skeletal muscle. We show that DOR has a direct impact on skeletal muscle mass in vivo. Thus, using different transgenic mouse models, we demonstrate that while muscle-specific DOR gain-of-function results in reduced muscle mass, loss-of-function causes muscle hypertrophy. DOR has been described as a protein with two different functions, i.e., a nuclear coactivator and an autophagy regulator (Baumgartner et. al., PLoS One, 2007; Francis et. al., Curr Biol, 2010; Mauvezin et. al., EMBO Rep, 2010; Nowak et. al., Mol Biol Cell, 2009). This is why we decided to analyze which of these two functions could explain the phenotype observed in our mice models. In this regard, we performed a transcriptomic analysis using microarrays looking for genes differentially expressed in the quadriceps muscle of WT and SKM-Tg mice as well as in C and SKM-KO animals. Surprisingly, only a reduced number of genes were dysregulated upon DOR manipulation and most of the genes underwent mild changes in expression. These data strongly suggest that DOR does not operate as a nuclear co-factor in mouse skeletal muscle under the conditions subjected to study. In contrast, DOR enhances basal autophagy in skeletal muscle and promotes muscle wasting when autophagy is a contributor to muscle loss. To determine the functional role of DOR in skeletal muscle, we generated transgenic mice (SKM-Tg) overexpressing DOR specifically in skeletal muscle under the Myosin-Light Chain 1 promoter/enhancer. The open reading frame of DOR was introduced in an EcoRI site in the MDAF2 vector, which contains a 1.5 kb fragment of the MLC1 promoter and 0.9 kb fragment of the MLC1/3 gene containing a 3' muscle enhancer element (Rosenthal et. al., PNAS, 1989; Otaegui et. al., FASEB J, 2003). The fragment obtained after the digestion of this construct with BssHII was the one used to generate both transgenic mouse lines. Nontransgenic littermates were used as controls for the transgenic animals (Wt). In addition, a muscle-specific DOR knock-out mouse line (SKM-KO) was also generated by crossing homozygous DOR loxP/loxP mice with a mouse strain expressing Cre recombinase under the control of the Myosin-Light Chain 1 promoter (Bothe et. al., Genesis, 2000). Deletion of exons 3 and 4 driven by Cre recombinase caused the ablation of DOR expression. Non-expressing Cre DOR loxP/loxP littermates were used as controls for knockout animals (C). Four-month-old male mice were used in all experiments. Mice were in a C57BL/6J pure genetic background.

Project description:We analyzed the functional role of DOR (Diabetes and Obesity Regulated gene) (also named Tp53inp2) in skeletal muscle. We show that DOR has a direct impact on skeletal muscle mass in vivo. Thus, using different transgenic mouse models, we demonstrate that while muscle-specific DOR gain-of-function results in reduced muscle mass, loss-of-function causes muscle hypertrophy. DOR has been described as a protein with two different functions, i.e., a nuclear coactivator and an autophagy regulator (Baumgartner et. al., PLoS One, 2007; Francis et. al., Curr Biol, 2010; Mauvezin et. al., EMBO Rep, 2010; Nowak et. al., Mol Biol Cell, 2009). This is why we decided to analyze which of these two functions could explain the phenotype observed in our mice models. In this regard, we performed a transcriptomic analysis using microarrays looking for genes differentially expressed in the quadriceps muscle of WT and SKM-Tg mice as well as in C and SKM-KO animals. Surprisingly, only a reduced number of genes were dysregulated upon DOR manipulation and most of the genes underwent mild changes in expression. These data strongly suggest that DOR does not operate as a nuclear co-factor in mouse skeletal muscle under the conditions subjected to study. In contrast, DOR enhances basal autophagy in skeletal muscle and promotes muscle wasting when autophagy is a contributor to muscle loss. To determine the functional role of DOR in skeletal muscle, we generated transgenic mice (SKM-Tg) overexpressing DOR specifically in skeletal muscle under the Myosin-Light Chain 1 promoter/enhancer. The open reading frame of DOR was introduced in an EcoRI site in the MDAF2 vector, which contains a 1.5 kb fragment of the MLC1 promoter and 0.9 kb fragment of the MLC1/3 gene containing a 3' muscle enhancer element (Rosenthal et. al., PNAS, 1989; Otaegui et. al., FASEB J, 2003). The fragment obtained after the digestion of this construct with BssHII was the one used to generate both transgenic mouse lines. Nontransgenic littermates were used as controls for the transgenic animals (Wt). In addition, a muscle-specific DOR knock-out mouse line (SKM-KO) was also generated by crossing homozygous DOR loxP/loxP mice with a mouse strain expressing Cre recombinase under the control of the Myosin-Light Chain 1 promoter (Bothe et. al., Genesis, 2000). Deletion of exons 3 and 4 driven by Cre recombinase caused the ablation of DOR expression. Non-expressing Cre DOR loxP/loxP littermates were used as controls for knockout animals (C). Four-month-old male mice were used in all experiments. Mice were in a C57BL/6J pure genetic background. We used microarrays to analyze the effect of DOR gain-of-function and DOR ablation on skeletal muscle gene expression Total RNA from quadriceps muscles from 4-month-old male mice was extracted and used for hibridization on Affimetrix microarrays

Project description:Background: Beta-adrenergic receptor agonists (BA) induce skeletal muscle hypertrophy, yet specific mechanisms that lead to this effect are not well understood. The objective of this research was to identify novel genes and physiological pathways that potentially facilitate BA induced skeletal muscle growth. We chose to evaluate global changes in gene expression by utilizing the Affymetrix platform to identify gene expression changes in mouse skeletal muscle. Changes in gene expression were evaluated 24 h (1D) and 10 days (10D) after administration of the BA clenbuterol. Results: Administration of clenbuterol stimulated anabolic activity, as indicated by decreased blood urea nitrogen (BUN; P < 0.01) and increased body weight gain (P < 0.05) 24 h or 10 d, respectively, after initiation of clenbuterol treatment. A total of 22,787 probesets were evaluated with 113 probesets defined as differentially expressed based on a false discovery rate of 10%. Differential mRNA abundance of four of these genes was validated in an independent experiment by quantitative PCR. Patterns of gene expression change observed from the microarray data suggested more genes are differentially regulated after 24 h than 10 d of BA administration. Functional characterization of differentially expressed genes revealed several categories that participate in biological processes important to skeletal muscle growth, including regulators of transcription and translation, mediators of cell-signaling pathways, and genes involved in polyamine metabolism. Included within these lists were several genes previously associated with myogenic differentiation, along with multiple genes known to promote a general up-regulation of translation. Conclusions: Global evaluation of gene expression after administration of clenbuterol identified changes gene expression and overrepresented functional categories of genes that may regulate BA-induced muscle hypertrophy. Changes in the mRNA abundance of multiple genes associated with myogenic differentiation may indicate an important effect of BA on the proliferation, differentiation, and/or recruitment of satellite cells into muscle fibers to promote muscle hypertrophy. Additionally, increased mRNA abundance of genes involved in the initiation of translation suggests that increased levels of protein synthesis often associated with BA administration may result from a general up-regulation of translational initiators, rather than a sustained up-regulation of gene expression at the transcriptional level. Additionally, numerous other genes and physiological pathways were identified that will be important targets for further investigations of the hypertrophic effect of BA on skeletal muscle. Keywords: Compound administration, time course

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Mus musculus strain:C57BL/6

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