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Biomedical subjects

Mark E Anderson

Publications and source records attributed to Mark E Anderson.

At least 19 recordsLinked to original sources
PubMed2007

Polymorphic ventricular tachycardia and abnormal Ca2+ handling in very-long-chain acyl-CoA dehydrogenase null mice.

Patients with mutations in the mitochondrial very-long-chain acyl-CoA dehydrogenase (VLCAD) gene are at risk for cardiomyopathy, myocardial dysfunction, ventricular tachycardia (VT), and sudden cardiac death. The mechanism is not known. Here we report a novel mechanism of VT in mice lacking VLCAD (VLCAD(-/-)). These mice exhibited polymorphic VT and increased incidence of VT after isoproterenol infusion. Polymorphic VT was induced in 10 out of 12 VLCAD(-/-) mice (83%) when isoproterenol was used. One out of 10 VLCAD(-/-) mice with polymorphic VT had VT with the typical bidirectional morphology. At the molecular level, VLCAD(-/-) cardiomyocytes showed increased levels of cardiac ryanodine receptor 2, phospholamban, and calsequestrin with increased [(3)H]ryanodine binding in heart microsomes. At the single cardiomyocyte level, VLCAD(-/-) cardiomyocytes showed significant increase in diastolic indo 1 and fura 2 fluorescence, with increased Ca(2+) transient amplitude. These changes were associated with altered Ca(2+) dynamics, to include: faster sarcomere contraction, larger time derivative of the upstroke, and shorter time-to-minimum sarcomere length compared with VLCAD(+/+) control cells. The L-type Ca(2+) current characteristics were not different under voltage-clamp conditions in the two VLCAD genotypes. Sarcoplasmic reticulum Ca(2+) load measured as normalized integrated Na(+)/Ca(2+) exchange current after rapid caffeine application was increased by 48% in VLCAD(-/-) cells. We conclude that intracellular Ca(2+) handling represents a possible molecular mechanism of arrhythmias in mice and perhaps in VLCAD-deficient humans.

Acyl-CoA Dehydrogenase, Long-Chain↗
PubMed2006

Novel n-3 fatty acid oxidation products activate Nrf2 by destabilizing the association between Keap1 and Cullin3.

Consumption of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can mitigate the progression of diseases in which oxidative stress represents a common underlying biochemical process. Nrf2-regulated gene expression regulates detoxification of reactive oxygen species. EPA and DHA were subjected to an in vitro free radical oxidation process that models in vivo conditions. Oxidized n-3 fatty acids reacted directly with the negative regulator of Nrf2, Keap1, initiating Keap1 dissociation with Cullin3, thereby inducing Nrf2-directed gene expression. Liquid chromatography-tandem mass spectrometry analyses of oxidized EPA demonstrated the presence of novel cyclopentenone-containing molecules termed J3-isoprostanes in vitro and in vivo and were shown to induce Nrf2-directed gene expression. These experiments provide a biochemical basis for the hypothesis that formation of J-ring compounds generated from oxidation of EPA and DHA in vivo can reach concentrations high enough to induce Nrf2-based cellular defense systems.

Animals↗
PubMed2006

CaMKII, an emerging molecular driver for calcium homeostasis, arrhythmias, and cardiac dysfunction.

Maintenance of cytoplasmic calcium homeostasis is critical for all cells. An exciting field has emerged in elucidating the multiple roles that Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) plays in regulating Ca(2+) cycling in normal cardiac myocytes and in pathophysiological states. Moreover, CaMKII was recently identified as a potential drug target in cardiac disease. This work has given us a closer view of the complexity and therapeutic possibilities of CaMKII regulation of Ca(2+) signaling in cardiac myocytes.

Animals↗
PubMed2006

Calmodulin kinase II inhibition shortens action potential duration by upregulation of K+ currents.

The multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is activated by elevated intracellular Ca(2+) (Ca(2+)(i)), and mice with chronic myocardial CaMKII inhibition (Inh) resulting from transgenic expression of a CaMKII inhibitory peptide (AC3-I) unexpectedly showed action potential duration (APD) shortening. Inh mice exhibit increased L-type Ca(2+) current (I(Ca)), because of upregulation of protein kinase A (PKA) activity, and decreased CaMKII-dependent phosphorylation of phospholamban (PLN). We hypothesized that CaMKII is a molecular signal linking Ca(2+)(i) to repolarization. Whole cell voltage-clamp recordings revealed that the fast transient outward current (I(to,f)) and the inward rectifier current (I(K1)) were selectively upregulated in Inh, compared with wild-type (WT) and transgenic control, mice. Breeding Inh mice with mice lacking PLN returned I(to,f) and I(K1) to control levels and equalized the APD and QT intervals in Inh mice to control and WT levels. Dialysis of AC3-I into WT cells did not result in increased I(to,f) or I(K1), suggesting that enhanced cardiac repolarization in Inh mice is an adaptive response to chronic CaMKII inhibition rather than an acute effect of reduced CaMKII activity. Increasing PKA activity, by cell dialysis with cAMP, or inhibition of PKA did not affect I(K1) in WT cells. Dialysis of WT cells with cAMP also reduced I(to,f), suggesting that PKA upregulation does not increase repolarizing K(+) currents in Inh mice. These findings provide novel in vivo and cellular evidence that CaMKII links Ca(2+)(i) to cardiac repolarization and suggest that PLN may be a critical CaMKII target for feedback regulation of APD in ventricular myocytes.

Action Potentials↗
PubMed2006

Death, cardiac dysfunction, and arrhythmias are increased by calmodulin kinase II in calcineurin cardiomyopathy.

BACKGROUND: Activation of cellular Ca2+ signaling molecules appears to be a fundamental step in the progression of cardiomyopathy and arrhythmias. Myocardial overexpression of the constitutively active Ca2+-dependent phosphatase calcineurin (CAN) causes severe cardiomyopathy marked by left ventricular (LV) dysfunction, arrhythmias, and increased mortality rate, but CAN antagonist drugs primarily reduce hypertrophy without improving LV function or risk of death. METHODS AND RESULTS: We found that activity and expression of a second Ca2+-activated signaling molecule, calmodulin kinase II (CaMKII), were increased in hearts from CAN transgenic mice and that CaMKII-inhibitory drugs improved LV function and suppressed arrhythmias. We devised a genetic approach to "clamp" CaMKII activity in CAN mice to control levels by interbreeding CAN transgenic mice with mice expressing a specific CaMKII inhibitor in cardiomyocytes. We developed transgenic control mice by interbreeding CAN transgenic mice with mice expressing an inactive version of the CaMKII-inhibitory peptide. CAN mice with CaMKII inhibition had reduced risk of death and increased LV and ventricular myocyte function and were less susceptible to arrhythmias. CaMKII inhibition did not reduce transgenic overexpression of CAN or expression of endogenous CaMKII protein or significantly reduce most measures of cardiac hypertrophy. CONCLUSIONS: CaMKII is a downstream signal in CAN cardiomyopathy, and increased CaMKII activity contributes to cardiac dysfunction, arrhythmia susceptibility, and longevity during CAN overexpression.

Amino Acid Sequence↗
PubMed2006

L-type Ca2+ channel facilitation mediated by phosphorylation of the beta subunit by CaMKII.

L-type Ca(2+) channels (LTCCs) are major entry points for Ca(2+) in many cells. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is associated with cardiac LTCC complexes and increases channel open probability (P(O)) to dynamically increase Ca(2+) current (I(Ca)) and augment cellular Ca(2+) signaling by a process called facilitation. However, the critical molecular mechanisms for CaMKII localization to LTCCs and I(Ca) facilitation in cardiomyocytes have not been defined. We show CaMKII binds to the LTCC beta(2a) subunit and preferentially phosphorylates Thr498 in beta(2a). Mutation of Thr498 to Ala (T498A) in beta(2a) prevents CaMKII-mediated increases in the P(O) of recombinant LTCCs. Moreover, expression of beta(2a)(T498A) in adult cardiomyocytes ablates CaMKII-mediated I(Ca) facilitation, demonstrating that phosphorylation of beta(2a) at Thr498 modulates native calcium channels. These findings reveal a molecular mechanism for targeting CaMKII to LTCCs and facilitating I(Ca) that may modulate Ca(2+) entry in diverse cell types coexpressing CaMKII and the beta(2a) subunit.

Amino Acid Sequence↗
PubMed2006

Mice with the R176Q cardiac ryanodine receptor mutation exhibit catecholamine-induced ventricular tachycardia and cardiomyopathy.

Mutations in the cardiac ryanodine receptor 2 (RyR2) have been associated with catecholaminergic polymorphic ventricular tachycardia and a form of arrhythmogenic right ventricular dysplasia. To study the relationship between RyR2 function and these phenotypes, we developed knockin mice with the human disease-associated RyR2 mutation R176Q. Histologic analysis of hearts from RyR2(R176Q/+) mice revealed no evidence of fibrofatty infiltration or structural abnormalities characteristic of arrhythmogenic right ventricular dysplasia, but right ventricular end-diastolic volume was decreased in RyR2(R176Q/+) mice compared with controls, indicating subtle functional impairment due to the presence of a single mutant allele. Ventricular tachycardia (VT) was observed after caffeine and epinephrine injection in RyR2(R176Q/+), but not in WT, mice. Intracardiac electrophysiology studies with programmed stimulation also elicited VT in RyR2(R176Q/+) mice. Isoproterenol administration during programmed stimulation increased both the number and duration of VT episodes in RyR2(R176Q/+) mice, but not in controls. Isolated cardiomyocytes from RyR2(R176Q/+) mice exhibited a higher incidence of spontaneous Ca(2+) oscillations in the absence and presence of isoproterenol compared with controls. Our results suggest that the R176Q mutation in RyR2 predisposes the heart to catecholamine-induced oscillatory calcium-release events that trigger a calcium-dependent ventricular arrhythmia.

Animals↗
PubMed2006

Calmodulin kinase II inhibition protects against myocardial cell apoptosis in vivo.

Inhibition of the multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) or depletion of sarcoplasmic reticulum (SR) Ca(2+) stores protects against apoptosis from excessive isoproterenol (Iso) stimulation in cultured ventricular myocytes, suggesting that CaMKII inhibition could be a novel approach to reducing cell death in conditions of increased adrenergic tone, such as myocardial infarction (MI), in vivo. We used mice with genetic myocardial CaMKII inhibition due to transgenic expression of a highly specific CaMKII inhibitory peptide (AC3-I) to test whether CaMKII was important for apoptosis in vivo. A second line of mice expressed a scrambled, inactive form of AC3-I (AC3-C). AC3-C and wild-type (WT) littermates were used as controls. AC3-I mice have reduced SR Ca(2+) content and are resistant to Iso- and MI-induced apoptosis compared with AC3-C and WT mice. Phospholamban (PLN) is a target for modulation of SR Ca(2+) content by CaMKII. PLN(-/-) mice have increased susceptibility to Iso-induced apoptosis. Verapamil pretreatment prevented Iso-induced apoptosis in PLN(-/-) mice, indicating the involvement of a Ca(2+)-dependent pathway. AC3-I and AC3-C mice were bred into a PLN(-/-) background. Loss of PLN increased and equalized SR Ca(2+) content in AC3-I, AC3-C, and WT mice and abolished the resistance to apoptosis in AC3-I mice after MI. There was a trend (P = 0.07) for increased Iso-induced apoptosis in AC3-I mice lacking PLN compared with AC3-I mice with PLN. These findings indicate CaMKII is proapoptotic in vivo and suggest that regulation of SR Ca(2+) content by PLN contributes to the antiapoptotic mechanism of CaMKII inhibition.

Adrenergic beta-Agonists↗
PubMed2006

Suppression of dynamic Ca(2+) transient responses to pacing in ventricular myocytes from mice with genetic calmodulin kinase II inhibition.

The multifunctional Ca(2+) and calmodulin-dependent protein kinase II (CaMKII) is important for regulating L-type Ca(2+) current (I(Ca)) and cytoplasmic Ca(2+) (Ca(2+)(i)) uptake and release from the sarcoplasmic reticulum (SR), key elements of the 'Ca(2+)-induced Ca(2+) release' (CICR) mechanism. However, the effects of chronic CaMKII inhibition on Ca(2+)(i) responses during CICR are unknown. We hypothesized that chronic CaMKII inhibition significantly affects CICR in ventricular myocytes. We studied CICR by simultaneously measuring Ca(2+)(i) transients and I(Ca) in voltage-clamped ventricular myocytes isolated from a recently developed genetic mouse model of cardiac CaMKII inhibition. These measurements were repeated in ventricular myocytes from novel mice with cardiac CaMKII inhibition lacking phospholamban (PLN), a known CaMKII substrate and a negative regulator of Ca(2+)(i) uptake into the SR Ca(2+) store. CaMKII inhibition eliminated a pattern of I(Ca) increases called facilitation and significantly reduced beat-to-beat and cell-to-cell variability of peak Ca(2+)(i) transients in ventricular myocytes with PLN. PLN ablation eliminated I(Ca) facilitation even in the absence of CaMKII inhibition and the effects of CaMKII inhibition to reduce SR Ca(2+) content and slow SR Ca(2+) uptake were lost in the absence of PLN. PLN ablation significantly reduced I(Ca) beat-to-beat variability in cells with CaMKII inhibition. These findings show that chronic CaMKII inhibition reduces variability of CICR responses in a manner that is partly dependent on the presence of PLN.

Animals↗
PubMed2006

Disease mechanisms and emerging therapies: protein kinases and their inhibitors in myocardial disease.

Most clinically validated drugs for treating patients with cardiovascular disease target G-protein-coupled receptors (GPCRs) in the cell membrane. GPCRs engage and activate multiple intracellular signaling cascades, which are regulated by serine/threonine protein kinases. These protein kinases are cytoplasmic, more abundant than GPCRs, and have rapidly emerged as drug targets in cardiovascular diseases. One exciting potential advantage to targeting serine/threonine protein kinases rather than GPCRs is the capability of influencing more precisely the diverse biological responses that are initiated by a common GPCR. On the other hand, highly specific targeting of individual protein kinases for drug therapy presents some medicinal chemistry challenges. This concise review focuses on the biology of serine/threonine protein kinases in the cardiovascular system, discusses the current state of protein kinase inhibitor drug development for myocardial diseases, and illustrates some of the unique medicinal chemistry considerations in targeting protein kinases.

Adenosine Triphosphate↗
PubMed2006

A case study of tire crumb use on playgrounds: risk analysis and communication when major clinical knowledge gaps exist.

Physicians and public health professionals working with the U.S. Environmental Protection Agency's Region 8 Pediatric Environmental Health Specialty Unit (PEHSU) received several telephone calls requesting information regarding the safety of recycled tire crumb as a playground surface constituent placed below children's play structures. There were no reported symptoms or adverse health effects in exposed children. The literature available on the safety and risk of exposure to crumb rubber constituents was limited and revealed no information quantifying exposures associated with product use. Callers were informed by the PEHSU that no evidence existed suggesting harm from intended use of the product, but gaps in knowledge about the product were identified and communicated. Here the case of crumb rubber on playgrounds is used as a model to present an approach to similar environmental medicine questions. From defining the question, to surveying traditional and nontraditional resources for information, synthesis of findings, and risk communication, the case provides a model to approach similar questions.

Child↗
PubMed2005

Oxidative mediated lipid peroxidation recapitulates proarrhythmic effects on cardiac sodium channels.

Sudden cardiac death attributable to ventricular tachycardia/fibrillation (VF) remains a catastrophic outcome of myocardial ischemia and infarction. At the same time, conventional antagonist drugs targeting ion channels have yielded poor survival benefits. Although pharmacological and genetic models suggest an association between sodium (Na+) channel loss-of-function and sudden cardiac death, molecular mechanisms have not been identified that convincingly link ischemia to Na+ channel dysfunction and ventricular arrhythmias. Because ischemia can evoke the generation of reactive oxygen species, we explored the effect of oxidative stress on Na+ channel function. We show here that oxidative stress reduces Na+ channel availability. Both the general oxidant tert-butyl-hydroperoxide and a specific, highly reactive product of the isoprostane pathway of lipid peroxidation, E2-isoketal, potentiate inactivation of cardiac Na+ channels in human embryonic kidney (HEK)-293 cells and cultured atrial (HL-1) myocytes. Furthermore, E2-isoketals were generated in the epicardial border zone of the canine healing infarct, an arrhythmogenic focus where Na+ channels exhibit similar inactivation defects. In addition, we show synergistic functional effects of flecainide, a proarrhythmic Na+ channel blocker, and oxidative stress. These data suggest Na+ channel dysfunction evoked by lipid peroxidation is a candidate mechanism for ischemia-related conduction abnormalities and arrhythmias.

Aldehydes↗
PubMed2005

A dynamic alpha-beta inter-subunit agonist signaling complex is a novel feedback mechanism for regulating L-type Ca2+ channel opening.

L-type Ca2+ channels are macromolecular protein complexes in neurons and myocytes that open in response to cell membrane depolarization to supply Ca2+ for regulating gene transcription and vesicle secretion and triggering cell contraction. L-type Ca2+ channels include a pore-forming alpha and an auxiliary beta subunit, and alpha subunit openings are regulated by cellular Ca2+ through a mechanism involving the Ca2+-sensing protein calmodulin (CaM) and CaM binding motifs in the alpha subunit cytoplasmic C terminus. Here we show that these CaM binding motifs are "auto-agonists" that increase alpha subunit openings by binding the beta subunit. The CaM binding domains are necessary and sufficient for the alpha subunit C terminus to bind the beta subunit in vitro, and excess CaM blocks this interaction. Addition of CaM binding domains to native cardiac L-type Ca2+ channels in excised cell membrane patches increases openings, and this agonist effect is prevented by excess CaM. Recombinant LTCC openings are also increased by exogenous CaM binding domains by a mechanism requiring the beta subunit, and excess CaM blocks this effect. Thus, the bifunctional ability of the alpha subunit CaM binding motifs to competitively associate with the beta subunit or CaM provides a novel paradigm for feedback control of cellular Ca2+ entry.

Amino Acid Motifs↗
PubMed2005

Atrial fibrillation in KCNE1-null mice.

Although atrial fibrillation is the most common serious cardiac arrhythmia, the fundamental molecular pathways remain undefined. Mutations in KCNQ1, one component of a sympathetically activated cardiac potassium channel complex, cause familial atrial fibrillation, although the mechanisms in vivo are unknown. We show here that mice with deletion of the KCNQ1 protein partner KCNE1 have spontaneous episodes of atrial fibrillation despite normal atrial size and structure. Isoproterenol abolishes these abnormalities, but vagomimetic interventions have no effect. Whereas loss of KCNE1 function prolongs ventricular action potentials in humans, KCNE1-/- mice displayed unexpectedly shortened atrial action potentials, and multiple potential mechanisms were identified: (1) K+ currents (total and those sensitive to the KCNQ1 blocker chromanol 293B) were significantly increased in atrial cells from KCNE1-/- mice compared with controls, and (2) when CHO cells expressing KCNQ1 and KCNE1 were pulsed very rapidly (at rates comparable to the normal mouse heart and to human atrial fibrillation), the sigmoidicity of IKs activation prevented current accumulation, whereas cells expressing KCNQ1 alone displayed marked current accumulation at these very rapid rates. Thus, KCNE1 deletion in mice unexpectedly leads to increased outward current in atrial myocytes, shortens atrial action potentials, and enhances susceptibility to atrial fibrillation.

Action Potentials↗
PubMed2005

Calmodulin kinase II inhibition protects against structural heart disease.

Beta-adrenergic receptor (betaAR) stimulation increases cytosolic Ca(2+) to physiologically augment cardiac contraction, whereas excessive betaAR activation causes adverse cardiac remodeling, including myocardial hypertrophy, dilation and dysfunction, in individuals with myocardial infarction. The Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is a recently identified downstream element of the betaAR-initiated signaling cascade that is linked to pathological myocardial remodeling and to regulation of key proteins involved in cardiac excitation-contraction coupling. We developed a genetic mouse model of cardiac CaMKII inhibition to test the role of CaMKII in betaAR signaling in vivo. Here we show CaMKII inhibition substantially prevented maladaptive remodeling from excessive betaAR stimulation and myocardial infarction, and induced balanced changes in excitation-contraction coupling that preserved baseline and betaAR-stimulated physiological increases in cardiac function. These findings mark CaMKII as a determinant of clinically important heart disease phenotypes, and suggest CaMKII inhibition can be a highly selective approach for targeting adverse myocardial remodeling linked to betaAR signaling.

Adrenergic beta-Antagonists↗
PubMed2005

Calmodulin kinase signaling in heart: an intriguing candidate target for therapy of myocardial dysfunction and arrhythmias.

The multifunctional Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII) has emerged as a proarrhythmic and procardiomyopathic signal in a wide range of structural heart diseases. This review discusses CaMKII structure and function and recent evidence implicating CaMKII inhibition as a potential strategy for treating myocardial dysfunction and arrhythmias in the setting of structural heart disease.

Animals↗