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Biomedical subjects

Gerald W Dorn

Publications and source records attributed to Gerald W Dorn.

At least 37 records · Page 2Linked to original sources
PubMed2004

Increased particulate partitioning of PKC epsilon reverses susceptibility of phospholamban knockout hearts to ischemic injury.

Cytosolic Ca(2+) overload is a critical mediator of myocardial damage following cardiac ischemia-reperfusion. It has therefore been proposed that normalization of sarcoplasmic reticulum Ca(2+) cycling through inhibition or ablation of the Ca(2+) ATP-ase inhibitor phospholamban (PLN), which shows promise as a treatment for heart failure, could be beneficial in ischemic heart disease. However, a recent study has shown that globally ischemic PLN-deficient hearts exhibit increased ischemic injury, with impaired contractile, ATP, and phosphocreatine recoveries, compared to wild-type hearts. Since protein kinase C (PKC) family members are widely recognized as mediators of both post-ischemic injury and ischemic preconditioning, we assessed PKC levels in PLN-deficient hearts. Compared to genetically normal hearts, PLN-deficient hearts exhibited diminished particulate partitioning of PKC, a known cardioprotective PKC isoform, without alterations in the levels of membrane-associated PKC delta nor PKC alpha. To determine if decreased particulate partitioning of cardioprotective PKC epsilon was a cause of increased ischemic injury in PLN-deficient hearts, PLN-deficient mice were mated with mice expressing a myocardial-specific PKC epsilon translocation activator peptide, pseudo-epsilon receptor for activated kinase C (psi epsilon RACK). In psi epsilon RACK/PLN knockout (KO) hearts, PKC epsilon translocation to membranous cellular structures was augmented and this was associated with a significant acceleration of post-ischemic contraction and relaxation rates, as well as reduction of creatine phosphokinase release, compared to PLN-deficient hearts. Importantly, post-ischemic functional recovery reached pre-ischemic hyperdynamic values in psi epsilon RACK/PLN KO hearts, indicating super-rescue by the combination of PLN ablation and psi epsilon RACK expression. These findings suggest that diminished PKC epsilon particulate partitioning in PLN-deficient hearts is associated with attenuated contractile recovery upon ischemia-reperfusion and that increased translocation of PKC to membranous cellular structures confers full cardioprotection.

Animals↗
PubMed2004

Genetic factors in cardiac hypertrophy.

Cardiac hypertrophy is an adaptive response to any cardiac insult or stress that increases hemodynamic load. Cardiac hypertrophy can exist in a state of compensation or progress to a decompensated state (i.e., heart failure) over time. It has been established through transgenic overexpression and gene ablation studies that multiple signaling pathways are involved in the induction of hypertrophy as well as its decompensation. This article reviews the role of G alpha q in the development of pressure overload hypertrophy and discusses the relationships between G alpha q and beta-adrenergic receptors, RGS proteins, and the proapoptotic factor, Nix/Bnip3L.

Apoptosis↗
PubMed2003

Inhibition of cardiac myocyte apoptosis improves cardiac function and abolishes mortality in the peripartum cardiomyopathy of Galpha(q) transgenic mice.

BACKGROUND: Although the occurrence of cardiac myocyte apoptosis during heart failure has been documented, its importance in pathogenesis is unknown. Transgenic mice with cardiac-restricted overexpression of Galpha(q) exhibit a lethal, peripartum cardiomyopathy accompanied by apoptosis. To test whether apoptosis is causally linked to heart failure, we assessed whether inhibiting this cell death would improve left ventricular function and survival in the Galpha(q) peripartum cardiomyopathy model. METHODS AND RESULTS: The potent polycaspase inhibitor IDN-1965 or vehicle was administered subcutaneously to Galpha(q) mice by osmotic minipump beginning on day 12 of pregnancy and continuing through euthanasia at day 14 postpartum. As expected, IDN-1965 markedly suppressed cardiac caspase-3-like activity (86.5%; P<0.01), accompanied by reduction in the frequency of cardiac myocyte apoptosis from 1.9+/-0.3% to 0.2+/-0.1% (P<0.01). Animals receiving IDN-1965 exhibited significant improvements in left ventricular end-diastolic dimension (vehicle, 4.7+/-0.1 mm; IDN-1965, 4.2+/-0.1 mm; P<0.01), fractional shortening (vehicle, 30.7+/-1.2%; IDN-1965, 38.9+/-1.0%; P<0.01), positive (vehicle, 3972+/-412; IDN-1965, 5870+/-295; P<0.01) and negative (vehicle, 2365+/-213; IDN-1965, 3413+/-201; P<0.01) dP/dt, and complete suppression of mortality (vehicle, 6 of 20 died; IDN-1965, 0 of 14 died; P<0.05). CONCLUSIONS: Reduction in cardiac myocyte apoptosis by caspase inhibition improved left ventricular function and survival in pregnant Galpha(q) mice. These data indicate that cardiac myocyte apoptosis plays a causal role in the pathogenesis of cardiomyopathy in this model. Caspase inhibition may provide a novel therapeutic target for heart failure.

Animals↗
PubMed2003

Protein kinase Calpha negatively regulates systolic and diastolic function in pathological hypertrophy.

The protein kinase C (PKC) family is implicated in cardiac hypertrophy, contractile failure, and beta-adrenergic receptor (betaAR) dysfunction. Herein, we describe the effects of gain- and loss-of-PKCalpha function using transgenic expression of conventional PKC isoform translocation modifiers. In contrast to previously studied PKC isoforms, activation of PKCalpha failed to induce cardiac hypertrophy, but instead caused betaAR insensitivity and ventricular dysfunction. PKCalpha inhibition had opposite effects. Because PKCalpha is upregulated in human and experimental cardiac hypertrophy and failure, its effects were also assessed in the context of the Galphaq overexpression model (in which PKCalpha is transcriptionally upregulated). Normalization (inhibition) of PKCalpha activity in Galpha(q) hearts improved systolic and diastolic function, whereas further activation of PKCalpha caused a lethal restrictive cardiomyopathy with marked interstitial fibrosis. These results define pathological roles for PKCalpha as a negative regulator of ventricular systolic and diastolic function.

Adrenergic beta-Agonists↗
PubMed2003

Beta 1-adrenergic receptor polymorphisms confer differential function and predisposition to heart failure.

Catecholamines stimulate cardiac contractility through beta(1)-adrenergic receptors (beta(1)-ARs), which in humans are polymorphic at amino acid residue 389 (Arg/Gly). We used cardiac-targeted transgenesis in a mouse model to delineate mechanisms accounting for the association of Arg389 with human heart failure phenotypes. Hearts from young Arg389 mice had enhanced receptor function and contractility compared with Gly389 hearts. Older Arg389 mice displayed a phenotypic switch, with decreased beta-agonist signaling to adenylyl cyclase and decreased cardiac contractility compared with Gly 389 hearts. Arg389 hearts had abnormal expression of fetal and hypertrophy genes and calcium-cycling proteins, decreased adenylyl cyclase and G alpha(s) expression, and fibrosis with heart failure This phenotype was recapitulated in homozygous, end-stage, failing human hearts. In addition, hemodynamic responses to beta-receptor blockade were greater in Arg389 mice, and homozygosity for Arg389 was associated with improvement in ventricular function during carvedilol treatment in heart failure patients. Thus the human Arg389 variant predisposes to heart failure by instigating hyperactive signaling programs leading to depressed receptor coupling and ventricular dysfunction, and influences the therapeutic response to beta-receptor blockade.

Adrenergic beta-Antagonists↗
PubMed2003

Akt-mediated cardiomyocyte survival pathways are compromised by G alpha q-induced phosphoinositide 4,5-bisphosphate depletion.

Expression of the wild type alpha subunit of Gq (GqWT) in cardiomyocytes induces hypertrophy, whereas a constitutively active G alpha q subunit (GqQ209L) induces apoptosis. Akt phosphorylation increases with GqWT expression but is markedly attenuated in cardiomyocytes expressing GqQ209L or in those expressing GqWT and treated with agonist. A membrane-targeted Akt rescues GqQ209L-expressing cardiomyocytes from apoptotic cell death. In contrast, leukemia inhibitory factor fails to activate Akt or promote cell survival in these cells. Association of Akt and PDK-1 with the membrane is also diminished in GqQ209L-expressing cardiomyocytes. Phosphatidylinositol 3,4,5-trisphosphate (PIP3), the primary regulator of Akt, increases significantly in GqWT-expressing cells but not in cardiomyocytes expressing GqQ209L. Levels of phosphatidylinositol 4,5-bisphosphate (PIP2), the immediate precursor of PIP3, are also markedly lower in GqQ209L-expressing compared to control cells. Expression of a GqQ209L mutant that has diminished capacity to activate phospholipase C does not decrease PIP2 or Akt or induce apoptosis. In transgenic mice with cardiac G alpha q overexpression, heart failure and increased cardiomyocyte apoptosis develop during the peripartal period. Akt phosphorylation and PIP2 levels decrease concomitantly. Our findings suggest that an Akt-mediated cell survival pathway is compromised by the diminished availability of PIP2 elicited by pathological levels of Gq activity.

Animals↗
PubMed2003

Additive protection of the ischemic heart ex vivo by combined treatment with delta-protein kinase C inhibitor and epsilon-protein kinase C activator.

BACKGROUND: Protein kinase C (PKC) plays a major role in cardioprotection from ischemia/reperfusion injury. Using an HIV-1 Tat protein-derived peptide to mediate rapid and efficient transmembrane delivery of peptide regulators of PKC translocation and function, we examined the cardioprotective effect of selective delta-PKC inhibitor (deltaV1-1) and epsilon-PKC activator (psi(epsilon)RACK) peptides for ischemia/reperfusion damage in isolated perfused rat hearts. Furthermore, we examined the protective effects of these PKC isozymes in isolated perfused hearts subjected to ischemia/reperfusion damage using transgenic mice expressing these peptides specifically in their cardiomyocytes. METHODS AND RESULTS: In isolated perfused rat hearts, administration of deltaV1-1 but not psi(epsilon)RACK during reperfusion improved cardiac function and decreased creatine phosphokinase release. In contrast, pretreatment with psi(epsilon)RACK but not deltaV1-1, followed by a 10-minute washout before ischemia/reperfusion, also improved cardiac function and decreased creatine phosphokinase release. Furthermore, administration of psi(epsilon)RACK before ischemia followed by deltaV1-1 during reperfusion only conferred greater cardioprotective effects than that obtained by each peptide treatment alone. Both the delta-PKC inhibitor and epsilon-PKC activator conferred cardioprotection against ischemia/reperfusion injury in transgenic mice expressing these peptides in the heart, and coexpression of both peptides conferred greater cardioprotective effects than that obtained by the expression of each peptide alone. CONCLUSIONS: delta-PKC inhibitor prevents reperfusion injury, and epsilon-PKC activator mimics ischemic preconditioning. Furthermore, treatment with both peptides confers additive cardioprotective effects. Therefore, these peptides mediate cardioprotection by regulating ischemia/reperfusion damage at distinct time points.

Amino Acid Sequence↗
PubMed2003

Transforming growth factor beta in cardiovascular development and function.

Transforming growth factor betas (TGFbetas) are pleiotropic cytokines involved in many biological processes. Genetic engineering and tissue explanation studies have revealed specific non-overlapping roles for TGFbeta ligands and their signaling molecules in development and in normal function of the cardiovascular system in the adult. In the embryo, TGFbetas appear to be involved in epithelial-mesenchymal transformations (EMT) during endocardial cushion formation, and in epicardial epithelial-mesenchymal transformations essential for coronary vasculature, ventricular myocardial development and compaction. In the adult, TGFbetas are involved in cardiac hypertrophy, vascular remodeling and regulation of the renal renin-angiotensin system. The evidence for TGFbeta activities during cardiovascular development and physiologic function will be given and areas which need further investigation will be discussed.

Animals↗
PubMed2003

Rescue of cardiomyocyte dysfunction by phospholamban ablation does not prevent ventricular failure in genetic hypertrophy.

Cardiac hypertrophy, either compensated or decompensated, is associated with cardiomyocyte contractile dysfunction from depressed sarcoplasmic reticulum (SR) Ca(2+) cycling. Normalization of Ca(2+) cycling by ablation or inhibition of the SR inhibitor phospholamban (PLN) has prevented cardiac failure in experimental dilated cardiomyopathy and is a promising therapeutic approach for human heart failure. However, the potential benefits of restoring SR function on primary cardiac hypertrophy, a common antecedent of human heart failure, are unknown. We therefore tested the efficacy of PLN ablation to correct hypertrophy and contractile dysfunction in two well-characterized and highly relevant genetic mouse models of hypertrophy and cardiac failure, Galphaq overexpression and human familial hypertrophic cardiomyopathy mutant myosin binding protein C (MyBP-C(MUT)) expression. In both models, PLN ablation normalized the characteristically prolonged cardiomyocyte Ca(2+) transients and enhanced unloaded fractional shortening with no change in SR Ca(2+) pump content. However, there was no parallel improvement in in vivo cardiac function or hypertrophy in either model. Likewise, the activation of JNK and calcineurin associated with Galphaq overexpression was not affected. Thus, PLN ablation normalized contractility in isolated myocytes, but failed to rescue the cardiomyopathic phenotype elicited by activation of the Galphaq pathway or MyBP-C mutations.

Animals↗
PubMed2003

Human phospholamban null results in lethal dilated cardiomyopathy revealing a critical difference between mouse and human.

In human disease and experimental animal models, depressed Ca(2+) handling in failing cardiomyocytes is widely attributed to impaired sarcoplasmic reticulum (SR) function. In mice, disruption of the PLN gene encoding phospholamban (PLN) or expression of dominant-negative PLN mutants enhances SR and cardiac function, but effects of PLN mutations in humans are unknown. Here, a T116G point mutation, substituting a termination codon for Leu-39 (L39stop), was identified in two families with hereditary heart failure. The heterozygous individuals exhibited hypertrophy without diminished contractile performance. Strikingly, both individuals homozygous for L39stop developed dilated cardiomyopathy and heart failure, requiring cardiac transplantation at ages 16 and 27. An over 50% reduction in PLN mRNA and no detectable PLN protein were noted in one explanted heart. The expression of recombinant PLN-L39stop in human embryonic kidney (HEK) 293 cells and adult rat cardiomyocytes showed no PLN inhibition of SR Ca(2+)-ATPase and the virtual absence of stable PLN expression; where PLN was expressed, it was misrouted to the cytosol or plasma membrane. These findings describe a naturally-occurring loss-of-function human PLN mutation (PLN null). In contrast to reported benefits of PLN ablation in mouse heart failure, humans lacking PLN develop lethal dilated cardiomyopathy.

Animals↗
PubMed2003

RAS point mutations and PAX8-PPAR gamma rearrangement in thyroid tumors: evidence for distinct molecular pathways in thyroid follicular carcinoma.

A series of 88 conventional follicular and Hürthle cell thyroid tumors were analyzed for RAS mutations and PAX8-PPAR gamma rearrangements using molecular methods and for galectin-3 and HBME-1 expression by immunohistochemistry. A novel LightCycler technology-based method was developed to detect point mutations in codons 12/13 and 61 of the H-RAS, K-RAS, and N-RAS genes. Forty-nine percent of conventional follicular carcinomas had RAS mutations, 36% had PAX8-PPAR gamma rearrangement, and only one (3%) had both. In follicular adenomas, 48% had RAS mutations, 4% had PAX8-PPAR gamma rearrangement, and 48% had neither. Follicular carcinomas with PAX8-PPAR gamma typically showed immunoreactivity for galectin-3 but not for HBME-1, tended to present at a younger patient age and be smaller size, and were almost always overtly invasive. In contrast, follicular carcinomas with RAS mutations most often displayed an HBME-1-positive/galectin-3-negative immunophenotype and were either minimally or overtly invasive. Hürthle cell tumors infrequently had PAX8-PPAR gamma rearrangement or RAS mutations. These results suggest that conventional follicular thyroid carcinomas develop through at least two distinct and virtually nonoverlapping molecular pathways initiated by either RAS point mutation or PAX8-PPAR gamma rearrangement.

Adenocarcinoma, Follicular↗
PubMed2002

Ischemic protection and myofibrillar cardiomyopathy: dose-dependent effects of in vivo deltaPKC inhibition.

To delineate the in vivo cardiac functions requiring normal delta protein kinase C (PKC) activity, we pursued loss-of-function through transgenic expression of a deltaPKC-specific translocation inhibitor protein fragment, deltaV1, in mouse hearts. Initial results using the mouse alpha-myosin heavy chain (alphaMHC) promoter resulted in a lethal heart failure phenotype. Viable deltaV1 mice were therefore obtained using novel attenuated mutant alphaMHC promoters lacking one or the other thyroid response element (TRE-1 and -2). In transgenic mouse hearts, deltaV1 decorated cytoskeletal elements and inhibited ischemia-induced deltaPKC translocation. At high levels, deltaV1 expression was uniformly lethal, with depressed cardiac contractile function, increased expression of fetal cardiac genes, and formation of intracardiomyocyte protein aggregates. Ultrastructural and immunoconfocal analyses of these aggregates revealed focal cytoskeletal disruptions and localized concentrations of desmin and alphaB-crystallin. In individual cardiomyocytes, cytoskeletal abnormalities correlated with impaired contractile function. Whereas desmin and alphaB-crystallin protein were increased approximately 4-fold in deltaV1 hearts, combined overexpression of these proteins at these levels was not sufficient to cause any detectable cardiac pathology. At low levels, deltaV1 expression conferred striking resistance to postischemic dysfunction, with no measurable effects on basal cardiac structure, function, or gene expression. Intermediate expression of deltaV1 conferred modest basal contractile depression with less ischemic protection, associated with abnormal cardiac gene expression, and a histological picture of infrequent cardiomyocyte cytoskeletal deformities. These results validate an approach of deltaPKC inhibition to protect against myocardial ischemia, but indicate that there is a threshold level of deltaPKC activation that is necessary to maintain normal cardiomyocyte cytoskeletal integrity.

Animals↗
PubMed2002

Novel and nondetected human signaling protein polymorphisms.

The frequency of single nucleotide polymorphisms (SNPs) in downstream signaling proteins was determined by combination heteroduplex HPLC and double-stranded sequencing of genomic DNA from 96-144 congestive heart failure (CHF) patients. Analysis of 56 coding exons in 9 signaling genes revealed 17 novel and 8 previously reported synonymous (no change in amino acid) SNPs, as well as one novel nonsynonymous SNP in the Rad small G protein. Because this initial analysis failed to detect numerous SNPs reported in the NCBI and Celera databases, double-strand sequencing of relevant exons from 74-91 CHF patients was used to confirm the absence of 10 previously reported nonsynonymous SNPs. Our results show that synonymous SNPs are frequent in signaling protein genes, whereas nonsynonymous SNPs are rare, suggesting a high degree of evolutionary conservation among these downstream signaling molecules. Comparisons of our results to the NCBI and Celera databases indicates that 56% of their SNP entries are not detected in our cohort. Importantly, while 31% of database SNPs were verified, 69% of SNPs detected in our cohort are not included in these databases. These findings indicate that caution may be warranted in relying exclusively on SNP databases as catalogs for polymorphic signaling protein genes.

Age of Onset↗
PubMed2002

Mitochondrial death protein Nix is induced in cardiac hypertrophy and triggers apoptotic cardiomyopathy.

Loss of cardiomyocytes through programmed cell death is a key event in the development of heart failure, but the inciting molecular mechanisms are largely unknown. We used microarray analysis to identify a genetic program for myocardial apoptosis in Gq-mediated and pressure-overload cardiac hypertrophy. A critical component of this apoptotic program was Nix/Bnip3L. Nix localized to mitochondria and caused release of cytochrome c, activation of caspase-3 and apoptotic cell death, when expressed in HEK293 fibroblasts. A previously undescribed truncated Nix isoform, termed sNix, was not targeted to mitochondria but heterodimerized with Nix and protected against Nix-mediated apoptosis. Forced in vivo myocardial expression of Nix resulted in apoptotic cardiomyopathy and rapid death. Conversely, sNix protected against apoptotic peripartum cardiomyopathy in G(alpha)q-overexpressors. Thus, Nix/Bnip3L is upregulated in myocardial hypertrophy, and is both necessary and sufficient for Gq-mediated apoptosis of cardiomyocytes and resulting hypertrophy decompensation.

Animals↗
PubMed2002

Adrenergic pathways and left ventricular remodeling.

BACKGROUND: Cardiac insufficiency, acute or chronic, engenders an increase in systemic and local myocardial sympathetic tone with release of the endogenous sympathetic hormones epinephrine and norepinephrine. These catecholamines activate cardiomyocyte alpha- and beta-adrenergic receptors which, although responsive to the same hormonal ligands, stimulate almost entirely distinct signaling pathways with different end organ results. METHODS: Minute-by-minute cardiac function is regulated by the beta-adrenergic receptor system, coupled to the adenylate cyclase and protein kinase (PK) A pathway via the Gs heterotrimeric G protein. In contrast, activation of alpha-adrenergic receptors and the Gq/phospholipase C/PKC pathway has little acute effect on instantaneous myocardial contractility, but can be a potent stimulus for cardiac hypertrophy. RESULTS: The distinct effects of alpha- and beta-adrenergic pathways in the in vivo heart, which are difficult to dissociate using conventional pharmacologic techniques, have been delineated through the use of cardiac-specific transgenic overexpression of individual components of their respective signaling pathways. Ventricular remodeling resulting from overexpression of alpha-adrenergic receptors or the alpha subunit of the Gq heterotrimeric G protein takes the form of concentric or eccentric hypertrophy without ventricular dilation or myocardial fibrosis. Cardiomyocyte cell size is increased and a panel of hypertrophy-associated embryonic cardiac genes is reexpressed. These phenotypic features are characteristic of pressure overload hypertrophy, and inhibition of Gq signaling can, in fact, prevent pressure overload hypertrophy in mice. Increased signaling through Gq exceeding that which causes hypertrophy results in cardiomyocyte apoptosis and progression from compensated hypertrophy to dilated cardiomyopathy. CONCLUSION: Transgenic overexpression of beta-adrenergic receptors or the alpha subunit of the Gs heterotrimeric G protein results in the expected increase in myocardial contractility, but also causes a progressive cardiomyocyte loss resulting in a delayed fibrotic cardiomyopathy, thus recapitulating the clinical syndrome of catecholamine cardiomyopathy as seen with pheochromocytoma or iatrogenic catecholamine infusion. These effects of beta-adrenergic receptors are concentration-dependent, and appear to be much more severe for the beta 1 than the beta 2 subtype, perhaps because of beta 2 coupling to inhibitory Gi.

Animals↗