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Biomedical subjects

Andrew R Marks

Publications and source records attributed to Andrew R Marks.

At least 55 records · Page 3Linked to original sources
PubMed2003

Beta-blockers restore calcium release channel function and improve cardiac muscle performance in human heart failure.

BACKGROUND: Chronic beta-adrenergic receptor (beta-AR) blockade improves cardiac contractility and prolongs survival in patients with heart failure; however, the mechanisms underlying these favorable responses are poorly understood. Stress-induced activation of the sympathetic nervous system results in protein kinase A (PKA)-mediated phosphorylation of the calcium (Ca2+) release channel/cardiac ryanodine receptor (RyR2), required for cardiac excitation-contraction (EC) coupling, activating the RyR2 channel, and increasing cardiac contractility. The hyperadrenergic state of heart failure results in leaky RyR2 channels attributable to PKA hyperphosphorylation and depletion of the stabilizing FK506 binding protein, FKBP12.6. We tested the hypothesis that improved cardiac muscle function attributable to beta-AR blockade is associated with restoration of normal RyR2 channel function in patients with heart failure. METHODS AND RESULTS: We assessed the effects of beta-AR blockade on left ventricular volume using isolated perfused hearts and beta-agonist responsiveness using muscle strips from patients undergoing transplantation. Twenty-four human hearts were examined, 10 from patients with heart failure treated with beta-AR blockers (carvedilol, metoprolol, or atenolol), 9 from patients with heart failure without beta-AR blocker treatment, and 5 normal hearts. RyR2 PKA phosphorylation was determined by back-phosphorylation, FKBP12.6 in the RyR2 macromolecular complex was determined by coimmunoprecipitation, and channel function was assayed using planar lipid bilayers. beta-AR blockers reduced left ventricular volume (reverse remodeling) and restored beta-agonist response in cardiac muscle from patients with heart failure. Improved cardiac muscle function was associated with restoration of normal FKBP12.6 levels in the RyR2 macromolecular complex and RyR2 channel function. CONCLUSIONS: Improved cardiac muscle function during beta-AR blockade is associated with improved cardiac Ca2+ release channel function in patients with heart failure.

Adrenergic beta-Antagonists↗
PubMed2003

Use of rapamycin slows progression of cardiac transplantation vasculopathy.

BACKGROUND: Cardiac transplantation vasculopathy is the leading cause of late death in heart transplantation recipients. Rapamycin is an immunosuppressant drug with potent antiproliferative and antimigratory effects. We investigated whether rapamycin could prevent progression of graft vasculopathy in 46 patients (age, 54+/-10 years; 4.3+/-2.3 years after transplantation) with severe disease. METHODS AND RESULTS: At annual cardiac catheterization, patients were randomly assigned to treatment with rapamycin (n=22) versus continued current immunosuppression (n=24). Clinical characteristics including recipient age and sex, underlying cause of congestive heart failure, donor age and sex, and ischemic time were recorded. Cardiac catheterization was graded with the use of a semiquantitative scale and repeated annually. Clinically significant adverse events were defined as death, need for angioplasty or bypass surgery, myocardial infarction, and a >25% worsening of the catheterization score. These events were monitored as primary study end points. Anti-HLA class I and II antibody production and lymphocyte growth assays were measured with each biopsy. Patients selected for rapamycin had azathioprine or mycophenolate mofetil discontinued and were given rapamycin. Outcomes were compared by means of log-rank analysis. There were no significant differences in baseline characteristics. Duration of follow-up was comparable (rapamycin, 689+/-261; control, 630+/-207 days; NS). In the rapamycin group, 3 patients reached primary end points versus 14 patients in the control group (P<0.001). There was no difference in baseline or subsequent anti-HLA class I or II antibody production. CONCLUSIONS: In this patient cohort with cardiac vasculopathy, treatment with rapamycin slowed disease progression probably by its antiproliferative and antimigratory effects.

Arterial Occlusive Diseases↗
PubMed2003

PKA phosphorylation activates the calcium release channel (ryanodine receptor) in skeletal muscle: defective regulation in heart failure.

The type 1 ryanodine receptor (RyR1) on the sarcoplasmic reticulum (SR) is the major calcium (Ca2+) release channel required for skeletal muscle excitation-contraction (EC) coupling. RyR1 function is modulated by proteins that bind to its large cytoplasmic scaffold domain, including the FK506 binding protein (FKBP12) and PKA. PKA is activated during sympathetic nervous system (SNS) stimulation. We show that PKA phosphorylation of RyR1 at Ser2843 activates the channel by releasing FKBP12. When FKB12 is bound to RyR1, it inhibits the channel by stabilizing its closed state. RyR1 in skeletal muscle from animals with heart failure (HF), a chronic hyperadrenergic state, were PKA hyperphosphorylated, depleted of FKBP12, and exhibited increased activity, suggesting that the channels are "leaky." RyR1 PKA hyperphosphorylation correlated with impaired SR Ca2+ release and early fatigue in HF skeletal muscle. These findings identify a novel mechanism that regulates RyR1 function via PKA phosphorylation in response to SNS stimulation. PKA hyperphosphorylation of RyR1 may contribute to impaired skeletal muscle function in HF, suggesting that a generalized EC coupling myopathy may play a role in HF.

Animals↗
PubMed2003

Altered function and regulation of cardiac ryanodine receptors in cardiac disease.

In cardiac muscle, the ryanodine receptor (RyR2) on the sarcoplasmic reticulum (SR) releases the calcium required for muscle contraction. The magnitude of Ca(2+) release by RyR2, which is subject to regulation by several physiological mediators, determines cardiac contractility. In heart failure, chronic stimulation of the beta-adrenergic signaling pathway leads to hyperphosphorylation of RyR2 by protein kinase A, which dissociates calstabin2 (FKBP12.6) from the receptor. Calstabin2-depleted channels display altered channel gating and can cause diastolic Ca(2+) release from the SR. This release depletes the SR Ca(2+) stores, leading to reduced myocardial contractility. Mutant RyR2, found in patients with catecholaminergic polymorphic ventricular tachycardia, has decreased calstabin2 binding affinity, which can trigger ventricular arrhythmias and sudden cardiac death after stress and exercise. Thus, defects in RyR2 have been linked to heart failure and exercise-induced sudden cardiac death and might provide novel therapeutic targets for the treatment of these common diseases of the heart.

Death, Sudden, Cardiac↗
PubMed2003

Immunophilins and coupled gating of ryanodine receptors.

The ryanodine receptor (RyR) is the major calcium (Ca(2+)) release channel in the sarcoplasmic reticulum (SR) of skeletal and cardiac muscle and is required for excitation-contraction (EC) coupling. The 565 kDa RyR protein forms a tetrameric channel that is part of a macromolecular signaling complex that also includes four FK506 binding proteins (FKBPs). The RyR channel complex is localized on specialized regions of the SR, such that the large RyR cytoplasmic domain is closely opposed to the transverse tubule (T-tubule) of the plasma membrane. RyR channel complexes are organized in regular arrays such that neighboring RyRs are in physical contact with each other. We have shown that physical and functional association between RyR1 or RyR2 channels results in coordinated gating behavior termed coupled gating. Coupled gating requires FKBP12 or FKBP12.6 in the RyR1 or RyR2 macromolecular complexes, respectively. FKBPs are known to stabilize single RyR channel function. Coupled gating describes an additional role for FKBPs in the functional coordination of RyR channel complexes that allows clusters of channels to function as "Ca2+ release units" (CRU). In addition, the FKBP-RyR interaction is regulated by PKA phosphorylation. In failing hearts PKA hyperphosphorylation of RyR2 causes depletion of FKBP12.6 from the channel macromolecular complex and may contribute to contractile dysfunction by impairing EC coupling. As FKBPs are potent modulators of RyR channel function, the FKBP-RyR interaction is a focus for determining molecular mechanisms of coupled gating and presents an exciting pharmacologic target for restoration of RyR complex function in diseased states.

Animals↗
PubMed2002

Protein kinase A phosphorylation of the cardiac calcium release channel (ryanodine receptor) in normal and failing hearts. Role of phosphatases and response to isoproterenol.

The cardiac ryanodine receptor/calcium release channel (RyR2) on the sarcoplasmic reticulum (SR) comprises a macromolecular complex that includes a kinase and two phosphatases that are bound to the channel via targeting proteins. We previously found that the RyR2 is protein kinase A (PKA)-hyperphosphorylated in end-stage human heart failure. Because heart failure is a progressive disease that often evolves from hypertrophy, we analyzed the RyR2 macromolecular complex in several animal models of cardiomyopathy that lead to heart failure, including hypertrophy, and at different stages of disease progression. We now show that RyR2 is PKA-hyperphosphorylated in diverse models of heart failure and that the degree of RyR2 PKA phosphorylation correlates with the degree of cardiac dysfunction. Interestingly, we show that RyR2 PKA hyperphosphorylation can be lost during perfusion of isolated hearts due to the activity of the endogenous phosphatases in the RyR2 macromolecular complex. Moreover, infusion of isoproterenol resulted in PKA phosphorylation of RyR2 in rat, indicating that systemic catecholamines can activate phosphorylation of RyR2 in vivo. These studies extend our previous analyses of the RyR2 macromolecular complex, show that both the kinase and phosphatase activities in the macromolecular complex are regulated physiologically in vivo, and suggest that RyR2 PKA hyperphosphorylation is likely a general feature of heart failure.

Animals↗
PubMed2002

Protein kinase A and two phosphatases are components of the inositol 1,4,5-trisphosphate receptor macromolecular signaling complex.

The inositol 1,4,5-trisphosphate receptor (IP3R) is a ubiquitously expressed intracellular calcium (Ca(2+)) release channel on the endoplasmic reticulum. IP3Rs play key roles in controlling Ca(2+) signals that activate numerous cellular functions including T cell activation, neurotransmitter release, oocyte fertilization and apoptosis. There are three forms of IP3R, all of which are ligand-gated channels activated by the second messenger inositol 1,4,5-trisphosphate. Channel function is modulated via cross-talk with other signaling pathways including those mediated by kinases and phosphatases. In particular IP3Rs are known to be regulated by cAMP-dependent protein kinase (PKA) phosphorylation. In the present study we show that PKA and the protein phosphatases PP1 and PP2A are components of the IP3R1 macromolecular signaling complex. PKA phosphorylation of IP3R1 increases channel activity in planar lipid bilayers. These studies indicate that regulation of IP3R1 function via PKA phosphorylation involves components of a macromolecular signaling complex.

Animals↗
PubMed2002

Ryanodine receptors, FKBP12, and heart failure.

RyR2 function is regulated by highly conserved signaling pathways that modulate excitation-contraction (EC) coupling. cAMP dependent protein kinase (PKA) phosphorylation of RyR2 plays an important role in regulating channel function in response to stress signaled by the sympathetic nervous system (the classic "fight or flight response") (1). PKA phosphorylation of RyR2 induces dissociation of the regulatory protein FKBP12.6 resulting in channels with increased sensitivity to Ca2+-induced Ca2+ release. Under normal physiological conditions (no cardiac damage) PKA phosphorylation of RyR2 is part of an integrated physiological response that leads to increased EC coupling gain and increased cardiac output. PKA-hyperphosphorylation of RyR2 in failing hearts is a maladaptive response that results in depletion of FKBP12.6 from the RyR2 macromolecular complex and defective channel function (pathologically increased sensitivity to Ca2+-induced Ca2+ release) that may cause depletion of SR Ca2+ and diastolic release of SR Ca2+ that can initiate delayed after depolarizations (DADs) that trigger ventricular arrhythmias (1). RyR2 mutations in patients with catecholaminergic induced sudden cardiac death provide further evidence linking the sympathetic nervous system, RyR2 and ventricular arrhythmias (2-4). The chronic hyperadrenergic state of heart failure is associated with defective Ca2+ signaling in part due to PKA hyperphosphorylation of RyR2.

Adrenergic beta-Antagonists↗
PubMed2002

Molecular BKology: the study of splicing and dicing.

The activity of ion channels is regulated by several different mechanisms. Studies have been undertaken to determine how the large-conductance Ca(2+)-sensitive K(+) channel (the BK channel) is regulated. Fury et al. discuss how the presence or absence of alternatively spliced regions in the BK channel alpha subunit can act as a molecular switch by which different kinases activate the BK channel.

Alternative Splicing↗
PubMed2002

Requirement of a macromolecular signaling complex for beta adrenergic receptor modulation of the KCNQ1-KCNE1 potassium channel.

Sympathetic nervous system (SNS) regulation of cardiac action potential duration (APD) is mediated by beta adrenergic receptor (betaAR) activation, which increases the slow outward potassium ion current (IKS). Mutations in two human I(KS) channel subunits, hKCNQ1 and hKCNE1, prolong APD and cause inherited cardiac arrhythmias known as LQTS (long QT syndrome). We show that betaAR modulation of I(KS) requires targeting of adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase (PKA) and protein phosphatase 1 (PP1) to hKCNQ1 through the targeting protein yotiao. Yotiao binds to hKCNQ1 by a leucine zipper motif, which is disrupted by an LQTS mutation (hKCNQ1-G589D). Identification of the hKCNQ1 macromolecular complex provides a mechanism for SNS modulation of cardiac APD through IKS.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2002

Involvement of the cardiac ryanodine receptor/calcium release channel in catecholaminergic polymorphic ventricular tachycardia.

The cardiac ryanodine receptor (RyR2), the major calcium release channel on the sarcoplasmic reticulum (SR) in cardiomyocytes, has recently been shown to be involved in at least two forms of sudden cardiac death (SCD): (1) Catecholaminergic polymorphic ventricular tachycardia (CPVT) or familial polymorphic VT (FPVT); and (2) Arrhythmogenic right ventricular dysplasia type 2 (ARVD2). Eleven RyR2 missense mutations have been linked to these diseases. All eleven RyR2 mutations cluster into 3 regions of RyR2 that are homologous to the three malignant hyperthermia (MH)/central core disease (CCD) mutation regions of the skeletal muscle ryanodine receptor/calcium release channel RyR1. MH/CCD RyR1 mutations have been shown to alter calcium-induced calcium release. Sympathetic nervous system stimulation leads to phosphorylation of RyR2 by protein kinase A (PKA). PKA phosphorylation of RyR2 activates the channel. In conditions associated with high rates of SCD such as heart failure RyR2 is PKA hyperphosphorylated resulting in "leaky" channels. SR calcium leak during diastole can generate "delayed after depolarizations" that can trigger fatal cardiac arrhythmias (e.g., VT). We propose that RyR2 mutations linked to genetic forms of catecholaminergic-induced SCD may alter the regulation of the channel resulting in increased SR calcium leak during sympathetic stimulation.

Animals↗
PubMed2002

Regulation of the ryanodine receptor in heart failure.

In the heart, calcium (Ca2+) regulates muscle contraction and electrical signals that determine cardiac rhythm and cell growth pathways. The ryanodine receptor (RyR), an intracellular Ca2+ release channel, is required for excitation-contraction coupling. The cardiac RyR has a large cytoplasmic structure that serves as a scaffold for modulatory proteins that regulate the function of the channel. Protein kinase A (PKA) phosphorylation of RyR2 dissociates the regulatory protein FKBP 12.6 and regulates the open probability of the channel. In failing hearts, RyR2 is PKA hyperphosphorylated resulting in defective channel function due to increased sensitivity to Ca2+ induced activation.

Animals↗
PubMed2002

Regulation of ryanodine receptors via macromolecular complexes: a novel role for leucine/isoleucine zippers.

Defective calcium (Ca(2+)) signaling, manifest as a loss of excitation-contraction (EC) coupling gain in cardiac muscle, likely plays an important role in the pathophysiology of human heart failure. The mechanism underlying this loss of cardiac EC coupling gain involves altered regulation of the cardiac ryanodine receptor (RyR2), the major sarcoplasmic reticulum Ca(2+) release channel in the heart. This altered regulation of RyR2 is due, in part, to hyperphosphorylation of the channel by cyclic adenosine monophosphate-dependent protein kinase A (PKA). PKA phosphorylation of RyR2 is controlled by a macromolecular signaling complex that targets PKA and two phosphatases (PP1 and PP2A) to the channel. The targeting of PKA, PP1, and PP2A to RyR2 is dependent on the binding of targeting proteins to the channel via highly conserved leucine/isoleucine zippers (LIZs). Formation of an ion channel macromolecular signaling complex is a novel role of LIZs. Recognition of this new function for LIZ motifs has provided a road map for rapidly identifying components of the RyR2 macromolecular signaling complex that play a key role in regulating normal cardiac physiology as part of the "fight or flight" response. The components of the RyR2 macromolecular signaling complex are also novel targets for heart failure and cardiac arrhythmia therapeutics.

Animals↗