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Biomedical subjects

Kenneth R Chien

Publications and source records attributed to Kenneth R Chien.

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

Myotonic dystrophy protein kinase phosphorylates phospholamban and regulates calcium uptake in cardiomyocyte sarcoplasmic reticulum.

Myotonic dystrophy (DM) is caused by a CTG expansion in the 3'-untranslated region of a protein kinase gene (DMPK). Cardiovascular disease is one of the most prevalent causes of death in DM patients. Electrophysiological studies in cardiac muscles from DM patients and from DMPK(-/-) mice suggested that DMPK is critical to the modulation of cardiac contractility and to the maintenance of proper cardiac conduction activity. However, there are no data regarding the molecular signaling pathways involved in DM heart failure. Here we show that DMPK expression in cardiac myocytes is highly enriched in the sarcoplasmic reticulum (SR) where it colocalizes with the ryanodine receptor and phospholamban (PLN), a muscle-specific SR Ca(2+)-ATPase (SERCA2a) inhibitor. Coimmunoprecipitation studies showed that DMPK and PLN can physically associate. Furthermore, purified wild-type DMPK, but not a kinase-deficient mutant (K110A DMPK), phosphorylates PLN in vitro. Subsequent studies using the DMPK(-/-) mice demonstrated that PLN is hypo-phosphorylated in SR vesicles from DMPK(-/-) mice compared with wild-type mice both in vitro and in vivo. Finally, we show that Ca(2+) uptake in SR is impaired in ventricular homogenates from DMPK(-/-) mice. Together, our data suggest the existence of a novel regulatory DMPK pathway for cardiac contractility and provide a molecular mechanism for DM heart pathology.

Adenoviridae↗
PubMed2004

Tcap gene mutations in hypertrophic cardiomyopathy and dilated cardiomyopathy.

OBJECTIVES: We sought to explore the relationship between a Tcap gene (TCAP) abnormality and cardiomyopathy. BACKGROUND: Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) cause severe heart failure and sudden death. Recent genetic investigations have revealed that mutations of genes encoding Z-disc components, including titin and muscle LIM protein (MLP), are the primary cause of both HCM and DCM. The Z-disc plays a role in establishing the mechanical coupling of sarcomeric contraction and stretching, with the titin/Tcap/MLP complex serving as a mechanical stretch sensor. Tcap interacts with the calsarcin, which tethers the calcineurin to the Z-disc. METHODS: The TCAP was analyzed in 346 patients with HCM (236 familial and 110 sporadic cases) and 136 patients with DCM (34 familial and 102 sporadic cases). Two different in vitro qualitative assays-yeast two-hybrid and glutathion S-transferase pull-down competition-were performed in order to investigate functional changes in Tcap's interaction with MLP, titin, and calsarcin-1 caused by the identified mutations and a reported DCM-associated mutation, R87Q. RESULTS: Two TCAP mutations, T137I and R153H, were found in patients with HCM, and another TCAP mutation, E132Q, was identified in a patient with DCM. It was demonstrated by the qualitative assays that the HCM-associated mutations augment the ability of Tcap to interact with titin and calsarcin-1, whereas the DCM-associated mutations impair the interaction of Tcap with MLP, titin, and calsarcin-1. CONCLUSIONS: These observations suggest that the difference in clinical phenotype (HCM or DCM) may be correlated with the property of altered binding among the Z-disc components.

Asian People↗
PubMed2004

Small proline-rich protein 1A is a gp130 pathway- and stress-inducible cardioprotective protein.

The interleukin-6 cytokines, acting via gp130 receptor pathways, play a pivotal role in the reduction of cardiac injury induced by mechanical stress or ischemia and in promoting subsequent adaptive remodeling of the heart. We have now identified the small proline-rich repeat proteins (SPRR) 1A and 2A as downstream targets of gp130 signaling that are strongly induced in cardiomyocytes responding to biomechanical/ischemic stress. Upregulation of SPRR1A and 2A was markedly reduced in the gp130 cardiomyocyte-restricted knockout mice. In cardiomyocytes, MEK1/2 inhibitors prevented SPRR1A upregulation by gp130 cytokines. Furthermore, binding of NF-IL6 (C/EBPbeta) and c-Jun to the SPRR1A promoter was observed after CT-1 stimulation. Histological analysis revealed that SPRR1A induction after mechanical stress of pressure overload was restricted to myocytes surrounding piecemeal necrotic lesions. A similar expression pattern was found in postinfarcted rat hearts. Both in vitro and in vivo ectopic overexpression of SPRR1A protected cardiomyocytes against ischemic injury. Thus, this study identifies SPRR1A as a novel stress-inducible downstream mediator of gp130 cytokines in cardiomyocytes and documents its cardioprotective effect against ischemic stress.

Adenoviridae↗
PubMed2004

Genetic depletion of cardiac myocyte STAT-3 abolishes classical preconditioning.

OBJECTIVE: To evaluate the functional requirement of signal transducer and activator of transcription-3 (STAT-3) in cardiac myocyte tolerance to ischemia (I) and in classical preconditioning. METHODS: Cardiac myocyte STAT-3 was depleted in mice using Cre-lox p technology. Isolated cardiomyocytes from wild-type (WT) and STAT-3-deficient mice were evaluated for viability following simulated ischemia (SI; 26 h). Cardiomyocytes were then preconditioned by exposure to transient simulated ischemia or via the administration of preconditioning mimetics (100 microM adenosine, 100 microM diazoxide and 0.5 ng ml(-1) TNFalpha, individually and in combination) prior to index ischemia. To evaluate the effect of cardiac myocyte depletion of STAT-3 in the context of the intact heart, these experiments were performed in isolated perfused Langendorff heart preparations which were exposed to an index insult of 30-min global ischemia and 45-min reperfusion. Ischemic preconditioning was achieved by subjecting the hearts to four cycles of 5-min ischemia followed by 5-min reperfusion prior to index ischemia. Infarct size was measured following reperfusion. RESULTS: Cell viability was diminished equally in wild-type and STAT-3-depleted cardiomyocytes. In contrast, ischemic and pharmacological preconditioning protected wild-type cardiomyocytes but not STAT-3-deficient cardiomyocytes. These results were mirrored in the intact heart. CONCLUSION: The depletion of functional STAT-3 does not modulate tolerance to ischemic injury in cardiomyocytes. This signaling molecule, however, is crucial for the ischemic and all the tested pharmacological preconditioning programs.

Animals↗
PubMed2004

Asymmetric septal hypertrophy in heterozygous cMyBP-C null mice.

OBJECTIVE: Cardiac myosin-binding protein C (cMyBP-C) gene mutations are involved in familial hypertrophic cardiomyopathy (FHC). Many of these mutations produce truncated proteins, which are unstable in the cardiac tissue of patients, suggesting that haploinsufficiency could account for the development of the phenotype. However, existing mouse models of cMyBP-C gene mutations have represented hypomorphic alleles without evidence of asymmetric septal hypertrophy, a key FHC phenotypic feature. In the present study, we generated a new model of cMyBP-C null mice and characterized the phenotype in both homozygotes and heterozygotes at different ages. METHODS: The mouse model was based upon the targeted deletion of exons 1 and 2, which contain the transcription initiation site, and the phenotype was determined by molecular, functional and morphological analyses. RESULTS: Herein, we demonstrate that inactivation of one or two mouse cMyBP-C alleles leads to different cardiac disorders at different post-natal time windows. The homozygous cMyBP-C null mice do not express the cMyBP-C gene, develop eccentric left ventricular hypertrophy with decreased fractional shortening at 3-4 months of age and a markedly impaired relaxation after 9 months. This is associated with myocardial disarray and an increase of interstitial fibrosis. The heterozygous cMyBP-C null mice present a slight but significant decrease of cMyBP-C amount and develop asymmetric septal hypertrophy associated with fibrosis at 10-11 months of age. CONCLUSION: These data provide evidence that heterozygous cMyBP-C null mice represent the first model with a key feature of human FHC that is asymmetric septal hypertrophy.

Animals↗
PubMed2004

Socs3 deficiency in the brain elevates leptin sensitivity and confers resistance to diet-induced obesity.

Leptin is an adipocyte-derived hormone that plays a key role in energy homeostasis, yet resistance to leptin is a feature of most cases of obesity in humans and rodents. In vitro analysis suggested that the suppressor of cytokine signaling-3 (Socs3) is a negative-feedback regulator of leptin signaling involved in leptin resistance. To determine the functional significance of Socs3 in vivo, we generated neural cell-specific SOCS3 conditional knockout mice using the Cre-loxP system. Compared to their wild-type littermates, Socs3-deficient mice showed enhanced leptin-induced hypothalamic Stat3 tyrosine phosphorylation as well as pro-opiomelanocortin (POMC) induction, and this resulted in a greater body weight loss and suppression of food intake. Moreover, the Socs3-deficient mice were resistant to high fat diet-induced weight gain and hyperleptinemia, and insulin-sensitivity was retained. These data indicate that Socs3 is a key regulator of diet-induced leptin as well as insulin resistance. Our study demonstrates the negative regulatory role of Socs3 in leptin signaling in vivo, and thus suppression of Socs3 in the brain is a potential therapy for leptin-resistance in obesity.

Animals↗
PubMed2004

Nkx2-5 pathways and congenital heart disease; loss of ventricular myocyte lineage specification leads to progressive cardiomyopathy and complete heart block.

Human mutations in Nkx2-5 lead to progressive cardiomyopathy and conduction defects via unknown mechanisms. To define these pathways, we generated mice with a ventricular-restricted knockout of Nkx2-5, which display no structural defects but have progressive complete heart block, and massive trabecular muscle overgrowth found in some patients with Nkx2-5 mutations. At birth, mutant mice display a hypoplastic atrioventricular (AV) node and then develop selective dropout of these conduction cells. Transcriptional profiling uncovered the aberrant expression of a unique panel of atrial and conduction system-restricted target genes, as well as the ectopic, high level BMP-10 expression in the adult ventricular myocardium. Further, BMP-10 is shown to be necessary and sufficient for a major component of the ventricular muscle defects. Accordingly, loss of ventricular muscle cell lineage specification into trabecular and conduction system myocytes is a new mechanistic pathway for progressive cardiomyopathy and conduction defects in congenital heart disease.

Acetylcholinesterase↗
PubMed2004

BMP10 is essential for maintaining cardiac growth during murine cardiogenesis.

During cardiogenesis, perturbation of a key transition at mid-gestation from cardiac patterning to cardiac growth and chamber maturation often leads to diverse types of congenital heart disease, such as ventricular septal defect (VSD), myocardium noncompaction, and ventricular hypertrabeculation. This transition, which occurs at embryonic day (E) 9.0-9.5 in murine embryos and E24-28 in human embryos, is crucial for the developing heart to maintain normal cardiac growth and function in response to an increasing hemodynamic load. Although, ventricular trabeculation and compaction are key morphogenetic events associated with this transition, the molecular and cellular mechanisms are currently unclear. Initially, cardiac restricted cytokine bone morphogenetic protein 10 (BMP10) was identified as being upregulated in hypertrabeculated hearts from mutant embryos deficient in FK506 binding protein 12 (FKBP12). To determine the biological function of BMP10 during cardiac development, we generated BMP10-deficient mice. Here we describe an essential role of BMP10 in regulating cardiac growth and chamber maturation. BMP10 null mice display ectopic and elevated expression of p57(kip2) and a dramatic reduction in proliferative activity in cardiomyocytes at E9.0-E9.5. BMP10 is also required for maintaining normal expression levels of several key cardiogenic factors (e.g. NKX2.5 and MEF2C) in the developing myocardium at mid-gestation. Furthermore, BMP10-conditioned medium is able to rescue BMP10-deficient hearts in culture. Our data suggest an important pathway that involves a genetic interaction between BMP10, cell cycle regulatory proteins and several major cardiac transcription factors in orchestrating this transition in cardiogenesis at mid-gestation. This may provide an underlying mechanism for understanding the pathogenesis of both structural and functional congenital heart defects.

Animals↗
PubMed2004

The cardiovascular physiologic actions of urocortin II: acute effects in murine heart failure.

Corticotropin-releasing factor (CRF) and its paralogues urocortin (Ucn)I, -II, and -III signal by activating their receptors, CRF receptors (CRFR)1 and -2, to maintain homeostasis through endocrine, autonomic, and behavioral responses. CRFR2 is found in cardiomyocytes and in endothelial and smooth muscle cells of the systemic vasculature. Echocardiography and cardiac catheterization were used in mice to assess the physiologic effects of i.v. UcnII and CRFR2 deficiency on left ventricular function and the systemic vasculature. UcnII treatment augmented heart rate, exhibited potent inotropic and lusitropic actions on the left ventricle, and induced a downward shift of the diastolic pressure-volume relation. UcnII also reduced systemic arterial pressure, associated with a lowering of systemic arterial elastance (end-systolic pressure/stroke volume) and systemic vascular resistance. CRFR2-deficient mice showed no alteration in cardiac contractility or blood pressure in response to UcnII administration, suggesting that the effects of UcnII are specific to CRFR2 function. Pretreatment with a beta-adrenergic receptor antagonist, esmalol, had no effect on the inotropic or lusitropic effects of UcnII in vivo, indicating that its actions are independent of beta-adrenergic receptors. Single i.v. bolus administration of UcnII to a heart failure model (muscle-specific LIM protein-deficient mice) produced significant enhancement of inotropic and lusitropic effects on left ventricular function and improved cardiac output. These results demonstrate the potent cardiovascular physiologic actions of UcnII in both wild-type and cardiomyopathic mice and support a potential beneficial use of this peptide in therapy of congestive heart failure.

Animals↗
PubMed2004

Essential role for mitochondrial thioredoxin reductase in hematopoiesis, heart development, and heart function.

Oxygen radicals regulate many physiological processes, such as signaling, proliferation, and apoptosis, and thus play a pivotal role in pathophysiology and disease development. There are at least two thioredoxin reductase/thioredoxin/peroxiredoxin systems participating in the cellular defense against oxygen radicals. At present, relatively little is known about the contribution of individual enzymes to the redox metabolism in different cell types. To begin to address this question, we generated and characterized mice lacking functional mitochondrial thioredoxin reductase (TrxR2). Ubiquitous Cre-mediated inactivation of TrxR2 is associated with embryonic death at embryonic day 13. TrxR2(TrxR2(-/-)minus;/TrxR2(-/-)minus;) embryos are smaller and severely anemic and show increased apoptosis in the liver. The size of hematopoietic colonies cultured ex vivo is dramatically reduced. TrxR2-deficient embryonic fibroblasts are highly sensitive to endogenous oxygen radicals when glutathione synthesis is inhibited. Besides the defect in hematopoiesis, the ventricular heart wall of TrxR2(TrxR2(-/-)minus;/TrxR2(-/-)minus;) embryos is thinned and proliferation of cardiomyocytes is decreased. Cardiac tissue-restricted ablation of TrxR2 results in fatal dilated cardiomyopathy, a condition reminiscent of that in Keshan disease and Friedreich's ataxia. We conclude that TrxR2 plays a pivotal role in both hematopoiesis and heart function.

Animals↗
PubMed2004

p38alpha mitogen-activated protein kinase plays a critical role in cardiomyocyte survival but not in cardiac hypertrophic growth in response to pressure overload.

The molecular mechanism for the transition from cardiac hypertrophy, an adaptive response to biomechanical stress, to heart failure is poorly understood. The mitogen-activated protein kinase p38alpha is a key component of stress response pathways in various types of cells. In this study, we attempted to explore the in vivo physiological functions of p38alpha in hearts. First, we generated mice with floxed p38alpha alleles and crossbred them with mice expressing the Cre recombinase under the control of the alpha-myosin heavy-chain promoter to obtain cardiac-specific p38alpha knockout mice. These cardiac-specific p38alpha knockout mice were born normally, developed to adulthood, were fertile, exhibited a normal life span, and displayed normal global cardiac structure and function. In response to pressure overload to the left ventricle, they developed significant levels of cardiac hypertrophy, as seen in controls, but also developed cardiac dysfunction and heart dilatation. This abnormal response to pressure overload was accompanied by massive cardiac fibrosis and the appearance of apoptotic cardiomyocytes. These results demonstrate that p38alpha plays a critical role in the cardiomyocyte survival pathway in response to pressure overload, while cardiac hypertrophic growth is unaffected despite its dramatic down-regulation.

Animals↗
PubMed2004

Chronic phospholamban inhibition prevents progressive cardiac dysfunction and pathological remodeling after infarction in rats.

Ablation or inhibition of phospholamban (PLN) has favorable effects in several genetic murine dilated cardiomyopathies, and we showed previously that a pseudophosphorylated form of PLN mutant (S16EPLN) successfully prevented progressive heart failure in cardiomyopathic hamsters. In this study, the effects of PLN inhibition were examined in rats with heart failure after myocardial infarction (MI), a model of acquired disease. S16EPLN was delivered into failing hearts 5 weeks after MI by transcoronary gene transfer using a recombinant adeno-associated virus (rAAV) vector. In treated (MI-S16EPLN, n = 16) and control (MI-saline, n = 18) groups, infarct sizes were closely matched and the left ventricle was similarly depressed and dilated before gene transfer. At 2 and 6 months after gene transfer, MI-S16EPLN rats showed an increase in left ventricular (LV) ejection fraction and a much smaller rise in LV end-diastolic volume, compared with progressive deterioration of LV size and function in MI-saline rats. Hemodynamic measurements at 6 months showed lower LV end-diastolic pressures, with enhanced LV function (contractility and relaxation), lowered LV mass and myocyte size, and less fibrosis in MI-S16EPLN rats. Thus, PLN inhibition by in vivo rAAV gene transfer is an effective strategy for the chronic treatment of an acquired form of established heart failure.

Animals↗
PubMed2004

Cardiac-specific disruption of the c-raf-1 gene induces cardiac dysfunction and apoptosis.

The Raf/MEK/extracellular signal-regulated kinase (ERK) signaling pathway regulates diverse cellular processes such as proliferation, differentiation, and apoptosis and is implicated as an important contributor to the pathogenesis of cardiac hypertrophy and heart failure. To examine the in vivo role of Raf-1 in the heart, we generated cardiac muscle-specific Raf-1-knockout (Raf CKO) mice with Cre-loxP-mediated recombination. The mice demonstrated left ventricular systolic dysfunction and heart dilatation without cardiac hypertrophy or lethality. The Raf CKO mice showed a significant increase in the number of apoptotic cardiomyocytes. The expression level and activation of MEK1/2 or ERK showed no difference, but the kinase activity of apoptosis signal-regulating kinase 1 (ASK1), JNK, or p38 increased significantly compared with that in controls. The ablation of ASK1 rescued heart dysfunction and dilatation as well as cardiac fibrosis. These results indicate that Raf-1 promotes cardiomyocyte survival through a MEK/ERK-independent mechanism.

Animals↗
PubMed2003

SOCS3 is a physiological negative regulator for granulopoiesis and granulocyte colony-stimulating factor receptor signaling.

The suppressor of cytokine signaling-3 (SOCS3/CIS3) has been shown to be an important negative regulator of cytokines, especially cytokines that activate STAT3. To examine the role of SOCS3 in neutrophils and the granulocyte colony-stimulating factor (G-CSF) signaling in vivo, we compared neutrophils from two types of conditional knockout mice, LysM-Cre:SOCS3(fl/fl) mice and Tie2-Cre:SOCS3(fl/fl) mice, in which the Socs3 gene had been deleted in mature neutrophils and hematopoietic stem cells, respectively. The size of the G-CSF-dependent colonies from Tie2-Cre:SOCS3(fl/fl) mouse bone marrow was much larger than that of colonies from control wild-type mice, while the size of interleukin-3-dependent colonies was similar. Moreover, LysM-Cre:SOCS3(fl/fl) mice had more neutrophils than SOCS3(fl/fl) mice, suggesting that SOCS3 is a negative regulator of G-CSF signaling in neutrophils. Consistent with this notion, G-CSF-induced STAT3 as well as mitogen-activated protein kinase activation was much stronger and prolonged in SOCS3-deficient mature neutrophils than in wild-type neutrophils. The preventive effect of G-CSF on apoptosis was more prominent in SOCS3-deficient mature neutrophils than in control neutrophils. These data indicate that SOCS3 negatively regulates granulopoiesis and G-CSF signaling in neutrophils and may contribute to neutrophilia or neutropenia.

Animals↗
PubMed2003

Sarcoplasmic reticulum calcium defect in Ras-induced hypertrophic cardiomyopathy heart.

The small G protein Ras-mediated signaling pathway has been implicated in the development of hypertrophy and diastolic dysfunction in the heart. Earlier cellular studies have suggested that the Ras pathway is responsible for reduced L-type calcium channel current and sarcoplasmic reticulum (SR) calcium uptake associated with sarcomere disorganization in neonatal cardiomyocytes. In the present study, we investigated the in vivo effects of Ras activation on cellular calcium handling and sarcomere organization in adult ventricular myocytes using a newly established transgenic mouse model with targeted expression of the H-Ras-v12 mutant. The transgenic hearts expressing activated Ras developed significant hypertrophy and postnatal lethal heart failure. In adult ventricular myocytes isolated from the transgenic hearts, the calcium transient was significantly depressed but membrane L-type calcium current was unchanged compared with control littermates. The expressions of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2a and phospholamban (PLB) were significantly reduced at mRNA levels. The amount of SERCA2a protein was also modestly reduced. However, the expression of PLB protein and gross sarcomere organization remained unchanged in the hypertrophic Ras hearts, whereas Ser(16) phosphorylation of PLB was dramatically inhibited in the Ras transgenic hearts compared with controls. Hypophosphorylation of PLB was also associated with a significant induction of protein phosphatase 1 expression. Therefore, our results from this in vivo model system suggest that Ras-induced contractile defects do not involve decreased L-type calcium channel activities or disruption of sarcomere structure. Rather, suppressed SR calcium uptake due to reduced SERCA2a expression and hypophosphorylation of PLB due to changes in protein phosphatase expression may play important roles in the diastolic dysfunction of Ras-mediated hypertrophic cardiomyopathy.

Animals↗