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Eric N Olson

Publications and source records attributed to Eric N Olson.

At least 109 records · Page 6Linked to original sources
PubMed2003

Common genomic response in different mouse models of beta-adrenergic-induced cardiomyopathy.

BACKGROUND: Although beta-adrenergic receptor (AR) blockade therapy is beneficial in the treatment of heart failure, little is known regarding the transcriptional mechanisms underlying this salutary action. METHODS AND RESULTS: In the present study, we screened mice overexpressing Gsalpha, beta1AR, beta2AR, or protein kinase A to test if a common genomic pathway exists in different models with enhanced beta-adrenergic signaling. In mice overexpressing Gsalpha, differentially expressed genes were identified by mRNA profiling. In addition to well-known markers of cardiac hypertrophy (atrial natriuretic factor, CARP, and beta-myosin heavy chain), uncoupling protein 2 (UCP2), a protein involved in the control of mitochondrial membrane potential, and four-and-a-half LIM domain protein-1 (FHL1), a member of the LIM protein family, were predicted to be upregulated. Upregulation of these genes was confirmed by quantitative reverse transcriptase-polymerase chain reaction at all time points tested during the development of cardiomyopathy in mice overexpressing Gsalpha. In mice overexpressing beta1AR, beta2AR, or protein kinase A, increased UCP2 and FHL1 expression was also observed at the onset of cardiomyopathy. BetaAR blockade treatment reversed the cardiomyopathy and suppressed the increased expression of UCP2 and FHL1 in mice overexpressing Gsalpha. CONCLUSIONS: UCP2 and FHL1 are important candidate genes that correlate with the development of betaAR-induced cardiomyopathy in different mouse models with enhanced betaAR signaling. In addition to preserving cardiac function, betaAR blockade treatment also prevents the genomic regulation that correlates with the onset of heart failure.

Adrenergic beta-Antagonists↗
PubMed2003

Control of myoblast fusion by a guanine nucleotide exchange factor, loner, and its effector ARF6.

Myoblast fusion is essential for the formation and regeneration of skeletal muscle. In a genetic screen for regulators of muscle development in Drosophila, we discovered a gene encoding a guanine nucleotide exchange factor, called loner, which is required for myoblast fusion. Loner localizes to subcellular sites of fusion and acts downstream of cell surface fusion receptors by recruiting the small GTPase ARF6 and stimulating guanine nucleotide exchange. Accordingly, a dominant-negative ARF6 disrupts myoblast fusion in Drosophila embryos and in mammalian myoblasts in culture, mimicking the fusion defects caused by loss of Loner. Loner and ARF6, which also control the proper membrane localization of another small GTPase, Rac, are key components of a cellular apparatus required for myoblast fusion and muscle development. In muscle cells, this fusigenic mechanism is coupled to fusion receptors; in other fusion-competent cell types it may be triggered by different upstream signals.

ADP-Ribosylation Factor 6↗
PubMed2003

Skeletal muscle reprogramming by activation of calcineurin improves insulin action on metabolic pathways.

The protein phosphatase calcineurin is a signaling intermediate that induces the transformation of fast-twitch skeletal muscle fibers to a slow-twitch phenotype. This reprogramming of the skeletal muscle gene expression profile may have therapeutic applications for metabolic disease. Insulin-stimulated glucose uptake in skeletal muscle is both impaired in individuals with type II diabetes mellitus and positively correlated with the percentage of slow- versus fast-twitch muscle fibers. Using transgenic mice expressing activated calcineurin in skeletal muscle, we report that skeletal muscle reprogramming by calcineurin activation leads to improved insulin-stimulated 2-deoxyglucose uptake in extensor digitorum longus (EDL) muscles compared with wild-type mice, concomitant with increased protein expression of the insulin receptor, Akt, glucose transporter 4, and peroxisome proliferator-activated receptor-gamma co-activator 1. Transgenic mice exhibited elevated glycogen deposition, enhanced amino acid uptake, and increased fatty acid oxidation in EDL muscle. When fed a high-fat diet, transgenic mice maintained superior rates of insulin-stimulated glucose uptake in EDL muscle and were protected against diet-induced glucose intolerance. These results validate calcineurin as a target for enhancing insulin action in skeletal muscle.

Animals↗
PubMed2003

The serum response factor coactivator myocardin is required for vascular smooth muscle development.

Formation of the vascular system requires differentiation and patterning of endothelial and smooth muscle cells (SMCs). Although much attention has focused on development of the vascular endothelial network, the mechanisms that control vascular SMC development are largely unknown. Myocardin is a smooth and cardiac muscle-specific transcriptional coactivator of serum response factor, a ubiquitous transcription factor implicated in smooth muscle gene expression. When expressed ectopically in nonmuscle cells, myocardin can induce smooth muscle differentiation by its association with serum response factor. Here we report that mouse embryos homozygous for a myocardin loss-of-function mutation die by embryonic day 10.5 and show no evidence of vascular SMC differentiation. Myocardin is the only transcription factor known to be necessary and sufficient for vascular SMC differentiation.

Animals↗
PubMed2003

Dose-dependent blockade to cardiomyocyte hypertrophy by histone deacetylase inhibitors.

Postnatal cardiac myocytes respond to stress signals by hypertrophic growth and activation of a fetal gene program. Recently, we showed that class II histone deacetylases (HDACs) suppress cardiac hypertrophy, and mice lacking the class II HDAC, HDAC9, are sensitized to hypertrophic signals. To further define the roles of HDACs in cardiac hypertrophy, we analyzed the effects of HDAC inhibitors on the responsiveness of primary cardiomyocytes to hypertrophic agonists. Paradoxically, HDAC inhibitors imposed a dose-dependent blockade to hypertrophy and fetal gene activation. We conclude that distinct HDACs play positive or negative roles in the control of cardiomyocyte hypertrophy. HDAC inhibitors are currently being tested in clinical trials as anti-cancer agents. Our results suggest that these inhibitors may also hold promising clinical value as therapeutics for cardiac hypertrophy and heart failure.

Adenylate Kinase↗
PubMed2003

Myocardin is a master regulator of smooth muscle gene expression.

Virtually all smooth muscle genes analyzed to date contain two or more essential binding sites for serum response factor (SRF) in their control regions. Because SRF is expressed in a wide range of cell types, it alone cannot account for smooth muscle-specific gene expression. We show that myocardin, a cardiac muscle- and smooth muscle-specific transcriptional coactivator of SRF, can activate smooth muscle gene expression in a variety of nonmuscle cell types via its association with SRF. Homodimerization of myocardin is required for maximal transcriptional activity and provides a mechanism for cooperative activation of smooth muscle genes by SRF-myocardin complexes bound to different SRF binding sites. These findings identify myocardin as a master regulator of smooth muscle gene expression and explain how SRF conveys smooth muscle specificity to its target genes.

Amino Acid Sequence↗
PubMed2003

dHAND-Cre transgenic mice reveal specific potential functions of dHAND during craniofacial development.

Most of the bone, cartilage, and connective tissue of the craniofacial region arise from cephalic neural crest cells. Presumably, patterning differences in crest cells are a result of regional action of transcription factors within the developing pharyngeal arches. The basic helix-loop-helix transcription factor dHAND/HAND2 is expressed throughout much of the neural crest-derived mesenchyme of the pharyngeal arches, suggesting that it plays a crucial role in craniofacial development. However, targeted inactivation of the dHAND gene results in embryonic lethality by E10.5 due to vascular defects, preventing further analysis of the role of dHAND in cephalic neural crest cell development. In order to examine putative roles of dHAND during later stages of embryogenesis, we have used a transgenic lineage marker approach, in which a portion of the dHAND upstream region containing an enhancer that directs dHAND expression to the pharyngeal arches is used to drive Cre recombinase expression. By crossing these dHAND-Cre transgenic mice with R26R mice, we can follow the fate of cells that expressed dHAND at any time during development by examining beta-galactosidase activity. We show that dHAND is first expressed in postmigratory cephalic neural crest cells within the pharyngeal arches. In older embryos, beta-galactosidase-labeled cells are observed in most of the neural crest-derived lower jaw skeleton and surrounding connective tissues. However, labeled cells only contribute to substructures within the middle ear, indicating that our transgene is not globally expressed in cephalic neural crest cells within the pharyngeal arches. Moreover, dHAND-Cre mice will provide a valuable tool for tissue-specific inactivation of gene expression in multiple tissue types of neural crest origin.

Animals↗
PubMed2003

Myocardin is a key regulator of CArG-dependent transcription of multiple smooth muscle marker genes.

The interactions between serum response factor (SRF) and CArG elements are critical for smooth muscle cell (SMC) marker gene transcription. However, the mechanisms whereby SRF, which is expressed ubiquitously, contributes to SMC-specific transcription are unknown. Myocardin was recently cloned as a coactivator of SRF in the heart, but its role in regulating CArG-dependent expression of SMC differentiation marker genes has not been clearly elucidated. In this study, we examined the expression and the function of myocardin in SMCs. In adult mice, myocardin mRNA was expressed in multiple smooth muscle (SM) tissues including the aorta, bladder, stomach, intestine, and colon, as well as the heart. Myocardin was also expressed in cultured rat aortic SMCs and A404 SMC precursor cells. Of particular interest, expression of myocardin was induced during differentiation of A404 cells, although it was not expressed in parental P19 cells from which A404 cells were derived. Cotransfection studies in SMCs revealed that myocardin induced the activity of multiple SMC marker gene promoters including SM alpha-actin, SM-myosin heavy chain, and SM22alpha by 9- to 60-fold in a CArG-dependent manner, whereas myocardin short interfering RNA markedly decreased activity of these promoters. Moreover, adenovirus-mediated overexpression of a dominant-negative form of myocardin significantly suppressed expression of endogenous SMC marker genes, whereas adenovirus-mediated overexpression of wild-type myocardin increased expression. Taken together, results provide compelling evidence that myocardin plays a key role as a transcriptional coactivator of SMC marker genes through CArG-dependent mechanisms.

3T3 Cells↗
PubMed2003

Galphaq and Galpha11 proteins mediate endothelin-1 signaling in neural crest-derived pharyngeal arch mesenchyme.

Endothelin-A (ET(A)) is a G-protein-coupled receptor expressed in the neural crest-derived mesenchyme of the pharyngeal arches during craniofacial development. Targeted deletion of the ET(A) receptor or its ligand endothelin-1 (ET-1) causes cleft palate and hypoplasia of the mandible, otic cup, and tympanic ring. Previously we showed that Galpha(q)/Galpha(11)-null mice die around E11.0, whereas Galpha(q)((-/-))Galpha(11)((+/-)) mice survive to birth with hypomorphic phenotypes similar to, but less severe than, ET(A) or ET-1-null mice. To determine whether ET-1 signaling is transduced by Galpha(q)/Galpha(11) proteins, we examined the expression patterns of several ET-1 dependent and independent transcription factors in Galpha(q)/Galpha(11)-deficient embryos. Expression of genes encoding the ET-1-dependent transcription factors Dlx3, Dlx6, dHAND, and eHAND was specifically downregulated in the pharyngeal arches of Galpha(q)/Galpha(11)-deficient mice. In contrast, pharyngeal arch expression of the homeobox gene Msx1, which is not regulated by ET-1 signaling, was maintained in these embryos. We conclude that the Galpha(q) and Galpha(11) proteins serve as the intracellular mediators of ET-1 signaling in the pharyngeal arch mesenchyme.

Animals↗
PubMed2003

Conditional expression of SV40 T-antigen in mouse cardiomyocytes facilitates an inducible switch from proliferation to differentiation.

Studies of cardiac muscle gene expression and signaling have been hampered by the lack of immortalized cardiomyocyte cell lines capable of proliferation and irreversible withdrawal from the cell cycle. With the goal of creating such cell lines, we generated transgenic mice using cardiac-specific cis-regulatory elements from the mouse Nkx2.5 gene to drive the expression of a simian virus 40 large T-antigen (TAg) gene flanked by sites for recombination by Cre recombinase. These transgenic mice developed tumors within the ventricular myocardium. Cells isolated from these tumors expressed cardiac markers and proliferated rapidly during serial passage in culture, without apparent senescence. However, they were unable to exit the cell cycle and failed to exhibit morphological features of terminal differentiation. Introduction of Cre recombinase to these cardiac cell lines by adenoviral delivery resulted in the elimination of TAg expression, accompanied by rapid cessation of cell division, and increase in cell size without an apparent induction of cellular differentiation. Incubation of cells lacking TAg in serum-deficient media with various pharmacological agents (norepinephrine, phenylephrine, or bone morphogenetic protein-2/4) or constitutively active calcium/calmodulin-dependent protein kinase I and/or calcineurin led to the formation of sarcomeres and up-regulation of cardiac genes involved in excitation-contraction coupling. The combination of TAg expression under the control of an early cardiac promoter and Cre-mediated recombination allowed us to derive an immortal cell line from the ventricular myocardium that could be controllably withdrawn from the cell cycle. The conditional expression of TAg in this manner permits propagation and regulated growth termination of cell types that are otherwise unable to be maintained in cell culture and may have applications for cardiac repair technologies.

Animals↗
PubMed2003

Regulation of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1 alpha ) and mitochondrial function by MEF2 and HDAC5.

The myocyte enhancer factor-2 (MEF2) transcription factor regulates muscle development and calcium-dependent gene expression. MEF2 activity is repressed by class II histone deacetylases (HDACs), which dissociate from MEF2 when phosphorylated on two serine residues in response to calcium signaling. To explore the potential importance of MEF2/HDAC interactions in the heart, we generated transgenic mice expressing a signal-resistant form of HDAC5 under cardiac-specific and doxycycline-inducible regulation. Transgene expression resulted in sudden death in male mice accompanied by loss and morphologic changes of cardiac mitochondria and down-regulation of mitochondrial enzymes. The transcriptional coactivator PGC-1 alpha, a master regulator of mitochondrial biogenesis and fatty acid oxidation, was also down-regulated in response to HDAC5 expression. Examination of the PGC-1 alpha promoter revealed two MEF2-binding sites that mediate transcriptional activation by MEF2 and repression by HDAC5. These findings identify PGC-1 alpha as a key target of the MEF2/HDAC regulatory pathway and demonstrate this pathway's importance in maintenance of cardiac mitochondrial function.

Acetylation↗
PubMed2003

Twist regulates cytokine gene expression through a negative feedback loop that represses NF-kappaB activity.

During Drosophila embryogenesis, the dorsal transcription factor activates the expression of twist, a transcription factor required for mesoderm formation. We show here that the mammalian twist proteins, twist-1 and -2, are induced by a cytokine signaling pathway that requires the dorsal-related protein RelA, a member of the NF-kappaB family of transcription factors. Twist-1 and -2 repress cytokine gene expression through interaction with RelA. Mice homozygous for a twist-2 null allele or doubly heterozygous for twist-1 and -2 alleles show elevated expression of proinflammatory cytokines, resulting in perinatal death from cachexia. These findings reveal an evolutionarily conserved signaling circuit in which twist proteins regulate cytokine signaling by establishing a negative feedback loop that represses the NF-kappaB-dependent cytokine pathway.

Animals↗
PubMed2003

Requirement of the calcineurin subunit gene canB2 for indirect flight muscle formation in Drosophila.

Calcineurin is a calcium-activated protein phosphatase involved in multiple aspects of cardiac and skeletal muscle development and disease. Genes encoding calcineurin subunit proteins are highly conserved among animal species. Toward the goal of identifying new calcineurin-interacting loci that function in myogenic processes, we expressed an activated form of mouse calcineurin A in Drosophila and screened for suppressors of the phosphatase-induced lethality. Here, we demonstrate that a mutation in the canB2 gene, which encodes a regulatory subunit of Drosophila calcineurin, can suppress a pupal developmental arrest phenotype to adult viability. As canB2 is an essential gene and rare homozygous escapers are flightless, we further analyzed canB2 expression and function in pupae and adults. The gene is expressed in the forming indirect flight muscles and central nervous system during pupal development. A canA gene is comparably expressed in these tissues. Consistent with the observed muscle expression, canB2 mutants exhibit severe defects in the organization of their indirect flight muscles, a phenotype that is likely caused by muscle hypercontractility. Together, these findings demonstrate a vital role for the phosphatase in this specific facet of Drosophila myogenesis and show conserved fly and vertebrate calcineurin genes contribute prominently to fundamental processes of muscle formation and function.

Animals↗
PubMed2003

Dual roles of modulatory calcineurin-interacting protein 1 in cardiac hypertrophy.

The calcium/calmodulin-dependent protein phosphatase calcineurin stimulates cardiac hypertrophy in response to numerous stimuli. Calcineurin activity is suppressed by association with modulatory calcineurin-interacting protein (MCIP)1DSCR1, which is up-regulated by calcineurin signaling and has been proposed to function in a negative feedback loop to modulate calcineurin activity. To investigate the involvement of MCIP1 in cardiac hypertrophy in vivo, we generated MCIP1 null mice and subjected them to a variety of stress stimuli that induce cardiac hypertrophy. In the absence of stress, MCIP1(-/-) animals exhibited no overt phenotype. However, the lack of MCIP1 exacerbated the hypertrophic response to activated calcineurin expressed from a muscle-specific transgene, consistent with a role of MCIP1 as a negative regulator of calcineurin signaling. Paradoxically, however, cardiac hypertrophy in response to pressure overload or chronic adrenergic stimulation was blunted in MCIP1(-/-) mice. These findings suggest that MCIP1 can facilitate or suppress cardiac calcineurin signaling depending on the nature of the hypertrophic stimulus. These opposing roles of MCIP have important implications for therapeutic strategies to regulate cardiac hypertrophy through modulation of calcineurin-MCIP activity.

Animals↗
PubMed2003

Transcriptional analysis of mouse skeletal myofiber diversity and adaptation to endurance exercise.

Vertebrate skeletal myofibers are heterogeneous with respect to their metabolic, contractile and morphological properties. To better understand skeletal myofiber diversity and plasticity at the transcriptional level, we carried out a whole-genome gene expression analysis of skeletal muscles composed primarily of slow/oxidative fibers (soleus) and fast fibers (extensor digitorum longus, EDL). We also followed gene expression changes in plantaris muscles from mice undergoing voluntary wheel running, a protocol that triggers transformation of glycolytic fibers into oxidative ones. Microarray analysis identified 70 genes differentially expressed by 3-fold or greater in soleus vs. EDL muscles and 15 genes up-regulated in exercised vs. sedentary plantaris muscles. A subset of these results were verified by northern blot and/or real-time RT-PCR analyses. Our results expand knowledge of the differences among various types of skeletal myofibers and their adaptation to exercise at the transcriptional level.

Animals↗
PubMed2003

Targeted deletion of a branchial arch-specific enhancer reveals a role of dHAND in craniofacial development.

The basic helix-loop-helix transcription factor dHAND is expressed in the mesenchyme of branchial arches and the developing heart. Mice homozygous for a dHAND (Hand2) null mutation die early in embryogenesis from cardiac abnormalities, precluding analysis of the potential role of dHAND in branchial arch development. Two independent enhancers control expression of dHAND in the heart and branchial arches. Endothelin-1 (ET-1) signaling regulates the branchial arch enhancer and is required for dHAND expression in the branchial arches. To determine the potential role of dHAND in branchial arch development and to assess the role of the ET-1-dependent enhancer in dHAND regulation in vivo, we deleted this enhancer by homologous recombination. Mice lacking the dHAND branchial arch enhancer died perinatally and exhibited a spectrum of craniofacial defects that included cleft palate, mandibular hypoplasia and cartilage malformations. Expression of dHAND was abolished in the ventolateral regions of the first and second branchial arches in these mutant mice, but expression was retained in a ventral domain where the related transcription factor eHAND is expressed. We conclude that dHAND plays an essential role in patterning and development of skeletal elements derived from the first and second branchial arches and that there are heterogeneous populations of cells in the branchial arches that rely on different cis-regulatory elements for activation of dHAND transcription.

Animals↗