Skeletal muscle atrophy in an inevitable occurrence with advancing age, and a consequence of dise... more Skeletal muscle atrophy in an inevitable occurrence with advancing age, and a consequence of disease including cancer. Muscle atrophy in the elderly is managed by a regimen of resistance exercise and increased protein intake. Understanding the signaling that regulates muscle mass may identify potential therapeutic targets for the prevention and reversal of muscle atrophy in metabolic and neuromuscular diseases. This review covers the major anabolic and catabolic pathways that regulate skeletal muscle mass, with a focus on recent progress and potential new players.
Skeletal muscle has the remarkable ability to modulate its mass in response to changes in nutriti... more Skeletal muscle has the remarkable ability to modulate its mass in response to changes in nutritional input, functional utilization, systemic disease, and age. This is achieved by the coordination of transcriptional and post-transcriptional networks and the signaling cascades balancing anabolic and catabolic processes with energy and nutrient availability. The extent to which alternative splicing regulates these signaling networks is uncertain. Here we investigate the role of the RNA binding protein hnRNP-U on the expression and splicing of genes, and the signaling processes regulating skeletal muscle hypertrophic growth. Muscle specific Hnrnpu knockout (mKO) mice develop an adult onset myopathy characterized by the selective atrophy of glycolytic muscle, the constitutive activation of Akt, increases in cellular and metabolic stress gene expression, and changes in the expression and splicing of metabolic and signal transduction genes. These findings link Hnrnpu with the balance between anabolic signaling, cellular and metabolic stress, and physiological growth.
Skeletal muscle exhibits remarkable plasticity in its ability to modulate its mass in response to... more Skeletal muscle exhibits remarkable plasticity in its ability to modulate its mass in response to the physiologic changes associated with functional use, systemic disease, and aging. Although a gradual loss of muscle mass normally occurs with advancing age, its increasingly rapid progression results in sarcopenia in a subset of individuals. The identities of muscle-enriched, long noncoding RNAs that regulate this process are unknown. Here, we identify a long noncoding RNA, named Chronos, whose expression in muscle is positively regulated with advancing age and negatively regulated during Akt1-mediated growth. Inhibition of Chronos induces myofiber hypertrophy both in vitro and in vivo, in part, through the epigenetic modulation of Bmp7 signaling.
Biochemical and Biophysical Research Communications, 2019
Skeletal muscle regeneration following injury is a complex multi-stage process involving the recr... more Skeletal muscle regeneration following injury is a complex multi-stage process involving the recruitment of inflammatory cells, the activation of muscle resident fibroblasts, and the differentiation of activated myoblasts into myocytes. Dysregulation of these cellular processes is associated with ineffective myo-fiber repair and excessive deposition of extracellular matrix proteins leading to fibrosis. PI3K/Akt signaling is a critical integrator of intra-and intercellular signals connecting nutrient availability to cell survival and growth. Activation of the PI3K/Akt pathway in skeletal muscle leads to hypertrophic growth and a reversal of the changes in body composition associated with obesity and advanced age. Though the molecular mechanisms mediating these effects are incompletely understood, changes in paracrine signaling are thought to play a key role. Here, we utilized modified RNA to study the biological role of the transient translocation of Akt to the myonuclei of maturing myotubes. Using a conditioned medium model system, we show that ectopic myonuclear Akt suppresses fibrogenic paracrine signaling in response to oxidative stress, and that interventions that increase or restore myonuclear Akt may impair fibrosis.
MicroRNAs (miRNAs) are a class of small ∼22 nt noncoding RNAs. miRNAs regulate gene expression at... more MicroRNAs (miRNAs) are a class of small ∼22 nt noncoding RNAs. miRNAs regulate gene expression at the posttranscriptional levels by destabilization and degradation of the target mRNA or by translational repression. Numerous studies have demonstrated that miRNAs are essential for normal mammalian development and organ function. Deleterious changes in miRNA expression play an important role in human diseases. We and others have previously reported several muscle-specific miRNAs, including miR-1/206, miR-133, and miR-208. These muscle-specific miRNAs are essential for normal myoblast differentiation and proliferation, and they have also been implicated in various cardiac and skeletal muscular diseases. miRNA-based gene therapies hold great potential for the treatment of cardiac and skeletal muscle disease(s). Herein, we introduce the methods commonly applied to study the biological role of miRNAs, as well as the techniques utilized to manipulate miRNA expression.
Journal of cardiovascular translational research, 2010
MicroRNAs (miRNAs) are a large sub-group of small non-coding RNAs, which have been demonstrated t... more MicroRNAs (miRNAs) are a large sub-group of small non-coding RNAs, which have been demonstrated to post-transcriptionally regulate the expression of protein-coding genes in a wide-range biological process. miRNAs have been shown to be essential for normal heart development and cardiac function. Recent data suggest that miRNAs are involved in the etiology of cardiac disease and the remodeling of hearts, including cardiac hypertrophy, myocardial infarction, and cardiac arrhythmias. In this review, we focus on the recent progress in the understanding of the function of miRNAs in cardiac remodeling and disease. We will also discuss the diagnostic and therapeutic potential of miRNAs in heart disease.
Biochemical studies of seizures in patients and laboratory animals have monitored postictal pertu... more Biochemical studies of seizures in patients and laboratory animals have monitored postictal perturbations in cerebral metabolism with either invasive techniques or with such noninvasive techniques as nuclear medicine, MR imaging, in vivo phosphorus MR spectroscopy (MRS), and in vivo proton MRS at field strengths of 1.5 T or above. We investigated postictal metabolic changes in a generalized seizure model with in vivo proton MRS at 0.5 T, in which the combination of glutamate and glutamine resonances (denoted glx) can be modeled as a singlet. Five adult mongrel dogs underwent control and postictal experiments in which single-voxel proton MR spectra were obtained from the right frontal lobe cortex with a point-resolved spectroscopy technique approximately every 20 minutes for 3 hours. N-acetylaspartate (NAA), glx, and creatine (Cr) were quantified in absolute millimolar units with a cerebral water-referenced algorithm. Inter- and intrasubject differences in mean metabolite concentrati...
Myocardin is a serum response factor (SRF) coactivator exclusively expressed in cardiomyocytes an... more Myocardin is a serum response factor (SRF) coactivator exclusively expressed in cardiomyocytes and smooth muscle cells (SMCs). However, there is highly controversial evidence as to whether myocardin is essential for normal differentiation of these cell types, and there are no data showing whether cardiac or SMC subtypes exhibit differential myocardin requirements during development. Results of the present studies showed the virtual absence of myocardin(-/-) visceral SMCs or ventricular myocytes in chimeric myocardin knockout (KO) mice generated by injection of myocardin(-/-) embryonic stem cells (ESCs) into wild-type (WT; i.e., myocardin(+/+) ESC) blastocysts. In contrast, myocardin(-/-) ESCs readily formed vascular SMC, albeit at a reduced frequency compared with WT ESCs. In addition, myocardin(-/-) ESCs competed equally with WT ESCs in forming atrial myocytes. The ultrastructural features of myocardin(-/-) vascular SMCs and cardiomyocytes were unchanged from their WT counterparts as determined using a unique X-ray microprobe transmission electron microscopic method developed by our laboratory. Myocardin(-/-) ESC-derived SMCs also showed normal contractile properties in an in vitro embryoid body SMC differentiation model, other than impaired thromboxane A2 responsiveness. Together, these results provide novel evidence that myocardin is essential for development of visceral SMCs and ventricular myocytes but is dispensable for development of atrial myocytes and vascular SMCs in the setting of chimeric KO mice. In addition, results suggest that as yet undefined defects in development and/or maturation of ventricular cardiomyocytes may have contributed to early embryonic lethality observed in conventional myocardin KO mice and that observed deficiencies in development of vascular SMC may have been secondary to these defects.
Myosin light chain phosphatase plays a critical role in modulating smooth muscle contraction in r... more Myosin light chain phosphatase plays a critical role in modulating smooth muscle contraction in response to a variety of physiologic stimuli. A downstream target of the RhoA/Rho-ki-nase and nitric oxide (NO)/cGMP/cyclic GMP-dependent kinase (cGKI) pathways, myosin light chain phosphatase activity reflects the sum of both calcium sensitization and desensitiza-tion pathways through phosphorylation and dephosphorylation of the myosin phosphatase targeting subunit (MYPT1). As cer-ebral blood flow is highly spatio-temporally modulated under normal physiologic conditions, severe perturbations in normal cerebral blood flow, such as in cerebral vasospasm, can induce neurological deficits. In nonpermeabilized cerebral vessels stimulated with U-46619, a stable mimetic of endogenous thromboxane A 2 implicated in the etiology of cerebral vaso-spasm, we observed significant increases in contractile force, RhoA activation, regulatory light chain phosphorylation, as well as phosphorylation of MYPT1 at Thr-696, Thr-853, and surprisingly Ser-695. Inhibition of nitric oxide signaling completely abrogated basal MYPT1 Ser-695 phosphorylation and significantly increased and potentiated U-46619-induced MYPT1 Thr-853 phosphorylation and contractile force, indicating that NO/cGMP/cGKI signaling maintains basal vascular tone through active inhibition of calcium sensitization. Surprisingly, a fall in Ser-695 phosphorylation did not result in an increase in phosphorylation of the Thr-696 site. Although activation of cGKI with exogenous cyclic nucleotides inhibited thromboxane A 2-induced MYPT1 membrane association, RhoA activation, contractile force, and regulatory light chain phosphorylation, the anticipated decreases in MYPT1 phosphorylation at Thr-696/Thr-853 were not observed, indicating that the vasorelax-ant effects of cGKI are not through dephosphorylation of MYPT1. Thus, thromboxane A 2 signaling within the intact cer-ebral vasculature induces " buffered " vasoconstrictions, in which both the RhoA/Rho-kinase calcium-sensitizing and the NO/cGMP/cGKI calcium-desensitizing pathways are activated.
Skeletal muscle atrophy in an inevitable occurrence with advancing age, and a consequence of dise... more Skeletal muscle atrophy in an inevitable occurrence with advancing age, and a consequence of disease including cancer. Muscle atrophy in the elderly is managed by a regimen of resistance exercise and increased protein intake. Understanding the signaling that regulates muscle mass may identify potential therapeutic targets for the prevention and reversal of muscle atrophy in metabolic and neuromuscular diseases. This review covers the major anabolic and catabolic pathways that regulate skeletal muscle mass, with a focus on recent progress and potential new players.
Skeletal muscle has the remarkable ability to modulate its mass in response to changes in nutriti... more Skeletal muscle has the remarkable ability to modulate its mass in response to changes in nutritional input, functional utilization, systemic disease, and age. This is achieved by the coordination of transcriptional and post-transcriptional networks and the signaling cascades balancing anabolic and catabolic processes with energy and nutrient availability. The extent to which alternative splicing regulates these signaling networks is uncertain. Here we investigate the role of the RNA binding protein hnRNP-U on the expression and splicing of genes, and the signaling processes regulating skeletal muscle hypertrophic growth. Muscle specific Hnrnpu knockout (mKO) mice develop an adult onset myopathy characterized by the selective atrophy of glycolytic muscle, the constitutive activation of Akt, increases in cellular and metabolic stress gene expression, and changes in the expression and splicing of metabolic and signal transduction genes. These findings link Hnrnpu with the balance between anabolic signaling, cellular and metabolic stress, and physiological growth.
Skeletal muscle exhibits remarkable plasticity in its ability to modulate its mass in response to... more Skeletal muscle exhibits remarkable plasticity in its ability to modulate its mass in response to the physiologic changes associated with functional use, systemic disease, and aging. Although a gradual loss of muscle mass normally occurs with advancing age, its increasingly rapid progression results in sarcopenia in a subset of individuals. The identities of muscle-enriched, long noncoding RNAs that regulate this process are unknown. Here, we identify a long noncoding RNA, named Chronos, whose expression in muscle is positively regulated with advancing age and negatively regulated during Akt1-mediated growth. Inhibition of Chronos induces myofiber hypertrophy both in vitro and in vivo, in part, through the epigenetic modulation of Bmp7 signaling.
Biochemical and Biophysical Research Communications, 2019
Skeletal muscle regeneration following injury is a complex multi-stage process involving the recr... more Skeletal muscle regeneration following injury is a complex multi-stage process involving the recruitment of inflammatory cells, the activation of muscle resident fibroblasts, and the differentiation of activated myoblasts into myocytes. Dysregulation of these cellular processes is associated with ineffective myo-fiber repair and excessive deposition of extracellular matrix proteins leading to fibrosis. PI3K/Akt signaling is a critical integrator of intra-and intercellular signals connecting nutrient availability to cell survival and growth. Activation of the PI3K/Akt pathway in skeletal muscle leads to hypertrophic growth and a reversal of the changes in body composition associated with obesity and advanced age. Though the molecular mechanisms mediating these effects are incompletely understood, changes in paracrine signaling are thought to play a key role. Here, we utilized modified RNA to study the biological role of the transient translocation of Akt to the myonuclei of maturing myotubes. Using a conditioned medium model system, we show that ectopic myonuclear Akt suppresses fibrogenic paracrine signaling in response to oxidative stress, and that interventions that increase or restore myonuclear Akt may impair fibrosis.
MicroRNAs (miRNAs) are a class of small ∼22 nt noncoding RNAs. miRNAs regulate gene expression at... more MicroRNAs (miRNAs) are a class of small ∼22 nt noncoding RNAs. miRNAs regulate gene expression at the posttranscriptional levels by destabilization and degradation of the target mRNA or by translational repression. Numerous studies have demonstrated that miRNAs are essential for normal mammalian development and organ function. Deleterious changes in miRNA expression play an important role in human diseases. We and others have previously reported several muscle-specific miRNAs, including miR-1/206, miR-133, and miR-208. These muscle-specific miRNAs are essential for normal myoblast differentiation and proliferation, and they have also been implicated in various cardiac and skeletal muscular diseases. miRNA-based gene therapies hold great potential for the treatment of cardiac and skeletal muscle disease(s). Herein, we introduce the methods commonly applied to study the biological role of miRNAs, as well as the techniques utilized to manipulate miRNA expression.
Journal of cardiovascular translational research, 2010
MicroRNAs (miRNAs) are a large sub-group of small non-coding RNAs, which have been demonstrated t... more MicroRNAs (miRNAs) are a large sub-group of small non-coding RNAs, which have been demonstrated to post-transcriptionally regulate the expression of protein-coding genes in a wide-range biological process. miRNAs have been shown to be essential for normal heart development and cardiac function. Recent data suggest that miRNAs are involved in the etiology of cardiac disease and the remodeling of hearts, including cardiac hypertrophy, myocardial infarction, and cardiac arrhythmias. In this review, we focus on the recent progress in the understanding of the function of miRNAs in cardiac remodeling and disease. We will also discuss the diagnostic and therapeutic potential of miRNAs in heart disease.
Biochemical studies of seizures in patients and laboratory animals have monitored postictal pertu... more Biochemical studies of seizures in patients and laboratory animals have monitored postictal perturbations in cerebral metabolism with either invasive techniques or with such noninvasive techniques as nuclear medicine, MR imaging, in vivo phosphorus MR spectroscopy (MRS), and in vivo proton MRS at field strengths of 1.5 T or above. We investigated postictal metabolic changes in a generalized seizure model with in vivo proton MRS at 0.5 T, in which the combination of glutamate and glutamine resonances (denoted glx) can be modeled as a singlet. Five adult mongrel dogs underwent control and postictal experiments in which single-voxel proton MR spectra were obtained from the right frontal lobe cortex with a point-resolved spectroscopy technique approximately every 20 minutes for 3 hours. N-acetylaspartate (NAA), glx, and creatine (Cr) were quantified in absolute millimolar units with a cerebral water-referenced algorithm. Inter- and intrasubject differences in mean metabolite concentrati...
Myocardin is a serum response factor (SRF) coactivator exclusively expressed in cardiomyocytes an... more Myocardin is a serum response factor (SRF) coactivator exclusively expressed in cardiomyocytes and smooth muscle cells (SMCs). However, there is highly controversial evidence as to whether myocardin is essential for normal differentiation of these cell types, and there are no data showing whether cardiac or SMC subtypes exhibit differential myocardin requirements during development. Results of the present studies showed the virtual absence of myocardin(-/-) visceral SMCs or ventricular myocytes in chimeric myocardin knockout (KO) mice generated by injection of myocardin(-/-) embryonic stem cells (ESCs) into wild-type (WT; i.e., myocardin(+/+) ESC) blastocysts. In contrast, myocardin(-/-) ESCs readily formed vascular SMC, albeit at a reduced frequency compared with WT ESCs. In addition, myocardin(-/-) ESCs competed equally with WT ESCs in forming atrial myocytes. The ultrastructural features of myocardin(-/-) vascular SMCs and cardiomyocytes were unchanged from their WT counterparts as determined using a unique X-ray microprobe transmission electron microscopic method developed by our laboratory. Myocardin(-/-) ESC-derived SMCs also showed normal contractile properties in an in vitro embryoid body SMC differentiation model, other than impaired thromboxane A2 responsiveness. Together, these results provide novel evidence that myocardin is essential for development of visceral SMCs and ventricular myocytes but is dispensable for development of atrial myocytes and vascular SMCs in the setting of chimeric KO mice. In addition, results suggest that as yet undefined defects in development and/or maturation of ventricular cardiomyocytes may have contributed to early embryonic lethality observed in conventional myocardin KO mice and that observed deficiencies in development of vascular SMC may have been secondary to these defects.
Myosin light chain phosphatase plays a critical role in modulating smooth muscle contraction in r... more Myosin light chain phosphatase plays a critical role in modulating smooth muscle contraction in response to a variety of physiologic stimuli. A downstream target of the RhoA/Rho-ki-nase and nitric oxide (NO)/cGMP/cyclic GMP-dependent kinase (cGKI) pathways, myosin light chain phosphatase activity reflects the sum of both calcium sensitization and desensitiza-tion pathways through phosphorylation and dephosphorylation of the myosin phosphatase targeting subunit (MYPT1). As cer-ebral blood flow is highly spatio-temporally modulated under normal physiologic conditions, severe perturbations in normal cerebral blood flow, such as in cerebral vasospasm, can induce neurological deficits. In nonpermeabilized cerebral vessels stimulated with U-46619, a stable mimetic of endogenous thromboxane A 2 implicated in the etiology of cerebral vaso-spasm, we observed significant increases in contractile force, RhoA activation, regulatory light chain phosphorylation, as well as phosphorylation of MYPT1 at Thr-696, Thr-853, and surprisingly Ser-695. Inhibition of nitric oxide signaling completely abrogated basal MYPT1 Ser-695 phosphorylation and significantly increased and potentiated U-46619-induced MYPT1 Thr-853 phosphorylation and contractile force, indicating that NO/cGMP/cGKI signaling maintains basal vascular tone through active inhibition of calcium sensitization. Surprisingly, a fall in Ser-695 phosphorylation did not result in an increase in phosphorylation of the Thr-696 site. Although activation of cGKI with exogenous cyclic nucleotides inhibited thromboxane A 2-induced MYPT1 membrane association, RhoA activation, contractile force, and regulatory light chain phosphorylation, the anticipated decreases in MYPT1 phosphorylation at Thr-696/Thr-853 were not observed, indicating that the vasorelax-ant effects of cGKI are not through dephosphorylation of MYPT1. Thus, thromboxane A 2 signaling within the intact cer-ebral vasculature induces " buffered " vasoconstrictions, in which both the RhoA/Rho-kinase calcium-sensitizing and the NO/cGMP/cGKI calcium-desensitizing pathways are activated.
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associated with functional use, systemic disease, and aging. Although a gradual loss of muscle mass normally occurs
with advancing age, its increasingly rapid progression results in sarcopenia in a subset of individuals. The identities of
muscle-enriched, long noncoding RNAs that regulate this process are unknown. Here, we identify a long noncoding
RNA, named Chronos, whose expression in muscle is positively regulated with advancing age and negatively regulated
during Akt1-mediated growth. Inhibition of Chronos induces myofiber hypertrophy both in vitro and in vivo, in part,
through the epigenetic modulation of Bmp7 signaling.
associated with functional use, systemic disease, and aging. Although a gradual loss of muscle mass normally occurs
with advancing age, its increasingly rapid progression results in sarcopenia in a subset of individuals. The identities of
muscle-enriched, long noncoding RNAs that regulate this process are unknown. Here, we identify a long noncoding
RNA, named Chronos, whose expression in muscle is positively regulated with advancing age and negatively regulated
during Akt1-mediated growth. Inhibition of Chronos induces myofiber hypertrophy both in vitro and in vivo, in part,
through the epigenetic modulation of Bmp7 signaling.