Brandon J Biesiadecki

The Ohio State University, Columbus, Ohio, United States

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Publications (51)242.33 Total impact

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    ABSTRACT: Protein phosphatase 2A (PP2A) is a serine/threonine-selective holoenzyme composed of a catalytic, scaffolding, and regulatory subunit. In the heart, PP2A activity is requisite for cardiac excitation-contraction coupling and central in adrenergic signaling. We found that mice deficient in the PP2A regulatory subunit B56α (1 of 13 regulatory subunits) had altered PP2A signaling in the heart that was associated with changes in cardiac physiology, suggesting that the B56α regulatory subunit had an autoinhibitory role that suppressed excess PP2A activity. The increase in PP2A activity in the mice with reduced B56α expression resulted in slower heart rates and increased heart rate variability, conduction defects, and increased sensitivity of heart rate to parasympathetic agonists. Increased PP2A activity in B56α(+/-) myocytes resulted in reduced Ca(2+) waves and sparks, which was associated with decreased phosphorylation (and thus decreased activation) of the ryanodine receptor RyR2, an ion channel on intracellular membranes that is involved in Ca(2+) regulation in cardiomyocytes. In line with an autoinhibitory role for B56α, in vivo expression of B56α in the absence of altered abundance of other PP2A subunits decreased basal phosphatase activity. Consequently, in vivo expression of B56α suppressed parasympathetic regulation of heart rate and increased RyR2 phosphorylation in cardiomyocytes. These data show that an integral component of the PP2A holoenzyme has an important inhibitory role in controlling PP2A enzyme activity in the heart. Copyright © 2015, American Association for the Advancement of Science.
    Science Signaling 07/2015; 8(386):ra72. DOI:10.1126/scisignal.aaa5876 · 7.65 Impact Factor
  • Biophysical Journal 01/2015; 108(2):596a. DOI:10.1016/j.bpj.2014.11.3246 · 3.97 Impact Factor
  • Biophysical Journal 01/2015; 108(2):597a-598a. DOI:10.1016/j.bpj.2014.11.3251 · 3.97 Impact Factor
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    Laurin M. Hanft · Brandon J. Biesiadecki · Craig A. Emter · Kerry S. McDonald
    Biophysical Journal 01/2015; 108(2):597a. DOI:10.1016/j.bpj.2014.11.3249 · 3.97 Impact Factor
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    ABSTRACT: Excessive oxidative stress in the heart results in contractile dysfunction. While antioxidant therapies have been a disappointment clinically, exercise has shown beneficial results, in part by reducing oxidative stress. We have previously shown that neuronal nitric oxide synthase (nNOS) is essential for cardioprotective adaptations caused by exercise. We hypothesize that part of the cardioprotective role of nNOS is via the augmentation of the antioxidant defense with exercise by positively shifting the nitroso-redox balance. Our results show that nNOS is indispensable for the augmented anti-oxidant defense with exercise. Furthermore, exercise training nNOS knockout mice resulted in a negative shift in the nitroso-redox balance resulting in contractile dysfunction. Remarkably, overexpressing nNOS (conditional cardiac-specific nNOS overexpression) was able to mimic exercise by increasing VO2max. This study demonstrates that exercise results in a positive shift in the nitroso-redox balance that is nNOS-dependent. Thus, targeting nNOS signaling may mimic the beneficial effects of exercise by combating oxidative stress and may be a viable treatment strategy for heart disease. Copyright © 2015. Published by Elsevier Ltd.
    Journal of Molecular and Cellular Cardiology 01/2015; 81. DOI:10.1016/j.yjmcc.2015.01.003 · 5.22 Impact Factor
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    ABSTRACT: As the heart transitions from one exercise intensity to another, changes in cardiac output occur, which are modulated by alterations in force development and calcium handling. Although the steady-state force-calcium relationship at various heart rates is well investigated, regulation of these processes during transitions in heart rate is poorly understood. In isolated right ventricular muscle preparations from the rabbit, we investigated the beat-to-beat alterations in force and calcium during the transition from one stimulation frequency to another, using contractile assessments and confocal microscopy. We show that a change in steady-state conditions occurs in multiple phases: a rapid phase, which is characterized by a fast change in force production mirrored by a change in calcium transient amplitude, and a slow phase, which follows the rapid phase and occurs as the muscle proceeds to stabilize at the new frequency. This second/late phase is characterized by a quantitative dissociation between the calcium transient amplitude and developed force. Twitch timing kinetics, such as time to peak tension and 50% relaxation rate, reached steady-state well before force development and calcium transient amplitude. The dynamic relationship between force and calcium upon a switch in stimulation frequency unveils the dynamic involvement of myofilament-based properties in frequency-dependent activation.
    01/2015; 2015:1-12. DOI:10.1155/2015/468548
  • Brandon J Biesiadecki · Jonathan P Davis · Mark T Ziolo · Paul M L Janssen
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    ABSTRACT: Cardiac muscle relaxation is an essential step in the cardiac cycle. Even when the contraction of the heart is normal and forceful, a relaxation phase that is too slow will limit proper filling of the ventricles. Relaxation is too often thought of as a mere passive process that follows contraction. However, many decades of advancements in our understanding of cardiac muscle relaxation have shown it is a highly complex and well-regulated process. In this review, we will discuss three distinct events that can limit the rate of cardiac muscle relaxation: the rate of intracellular calcium decline, the rate of thin-filament de-activation, and the rate of cross-bridge cycling. Each of these processes are directly impacted by a plethora of molecular events. In addition, these three processes interact with each other, further complicating our understanding of relaxation. Each of these processes is continuously modulated by the need to couple bodily oxygen demand to cardiac output by the major cardiac physiological regulators. Length-dependent activation, frequency-dependent activation, and β-adrenergic regulation all directly and indirectly modulate calcium decline, thin-filament deactivation, and cross-bridge kinetics. We hope to convey our conclusion that cardiac muscle relaxation is a process of intricate checks and balances, and should not be thought of as a single rate-limiting step that is regulated at a single protein level. Cardiac muscle relaxation is a system level property that requires fundamental integration of three governing systems: intracellular calcium decline, thin filament deactivation, and cross-bridge cycling kinetics.
    Biophysical Reviews 12/2014; 6(3-):273-289. DOI:10.1007/s12551-014-0143-5
  • Circulation 11/2014; 2014(130):A18888. · 14.95 Impact Factor
  • Circulation 11/2014; 2014(130):A. · 14.95 Impact Factor
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    ABSTRACT: Troponin I (TnI), the inhibitory subunit of the troponin complex, can be phosphorylated as a key regulatory mechanism to alter the calcium regulation of contraction. Recent work has identified phosphorylation of TnI Tyr-26 in the human heart with unknown functional effects. We hypothesized that TnI Tyr-26 N-terminal phosphorylation decreases calcium sensitivity of the thin filament, similar to the desensitizing effects of TnI Ser-23/24 phosphorylation. Our results demonstrate Tyr-26 phosphorylation and pseudo-phosphorylation decrease calcium binding to Troponin C (TnC) on the thin filament and calcium sensitivity of force development to a similar magnitude as TnI Ser-23/24 pseudo-phosphorylation. To investigate the effects of TnI Tyr-26 phosphorylation on myofilament deactivation, we measured the rate of calcium dissociation from TnC. Results demonstrate filaments containing Tyr-26 pseudo-phosphorylated TnI accelerate the rate of calcium dissociation from TnC similar to that of TnI Ser-23/24. Finally, to assess functional integration of TnI Tyr-26 with Ser-23/24 phosphorylation, we generated recombinant TnI phospho-mimetic substitutions at all three residues. Our biochemical analyses demonstrated no additive effect on calcium sensitivity or calcium-sensitive force development imposed by Tyr-26 and Ser-23/24 phosphorylation integration. However, integration of Tyr-26 phosphorylation with pseudo-phosphorylated Ser-23/24 further accelerated thin filament deactivation. Our findings suggest that TnI Tyr-26 phosphorylation functions similarly to Ser-23/24 N-terminal phosphorylation to decrease myofilament calcium sensitivity and accelerate myofilament relaxation. Furthermore, Tyr-26 phosphorylation can buffer the desensitization of Ser-23/24 phosphorylation while further accelerating thin filament deactivation. Therefore, the functional integration of TnI phosphorylation may be a common mechanism to modulate Ser-23/24 phosphorylation function.
    Journal of Molecular and Cellular Cardiology 09/2014; 76. DOI:10.1016/j.yjmcc.2014.09.013 · 5.22 Impact Factor
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    ABSTRACT: The binding of Ca2 + to troponin C (TnC) in the troponin complex is a critical step regulating the thin filament, the actin-myosin interaction and cardiac contraction. Phosphorylation of the troponin complex is a key regulatory mechanism to match cardiac contraction to demand. Here we demonstrate phosphorylation of the troponin I (TnI) subunit is simultaneously increased at Ser-150 and Ser-23/24 during in vivo myocardial ischemia. Myocardial ischemia decreases intracellular pH resulting in depressed binding of Ca2 + to TnC and impaired contraction. To determine the pathological relevance of simultaneous TnI phosphorylation we measured individual TnI Ser-150 (S150D), Ser-23/24 (S23/24D) and combined (S23/24/150D) pseudo-phosphorylation effects on thin filament regulation at acidic pH similar to that in myocardial ischemia. Results demonstrate that while acidic pH decreased thin filament Ca2 + binding to TnC regardless of TnI composition, TnI S150D attenuated this decrease rendering it similar to non-phosphorylated TnI at normal pH. The dissociation of Ca2 + from TnC was unaltered by pH such that TnI S150D remained slow, S23/24D remained accelerated and the combined S23/24/150D remained accelerated. This effect of the combined TnI Ser-150 and Ser-23/24 pseudo-phosphorylation to maintain Ca2 + binding while accelerating Ca2 + dissociation represents the first post-translational modification of troponin by phosphorylation to both accelerate thin filament deactivation and maintain Ca2 + sensitive activation. These data suggest TnI Ser-150 phosphorylation attenuation of the pH-dependent decrease in Ca2 + sensitivity and its combination with Ser-23/24 phosphorylation to maintain accelerated thin filament deactivation may impart an adaptive role to preserve contraction during acidic ischemia pH without slowing relaxation.
    Journal of Molecular and Cellular Cardiology 07/2014; 72. DOI:10.1016/j.yjmcc.2014.03.010 · 5.22 Impact Factor
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    ABSTRACT: -While sinoatrial node (SAN) dysfunction is a hallmark of human heart failure (HF), the underlying mechanisms remain poorly understood. We aimed to examine the role of adenosine in SAN dysfunction and tachy-brady arrhythmias in chronic HF.
    Circulation 05/2014; 130(4). DOI:10.1161/CIRCULATIONAHA.113.007086 · 14.95 Impact Factor
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    ABSTRACT: Repeated, intense contractile activity compromises the ability of skeletal muscle to generate force and velocity, resulting in fatigue. The decrease in velocity is thought to be due, in part, to the intracellular build-up of acidosis inhibiting the function of the contractile proteins myosin and troponin, however the underlying molecular basis of this process remains poorly understood. We sought to gain novel insight into the decrease in velocity by determining if the depressive effect of acidosis could be altered by 1) introducing Ca(++)-sensitizing mutations into troponin (Tn) or 2) by agents that directly affect myosin function, including inorganic phosphate (Pi) and 2-deoxy-ATP (dATP) in an in vitro motility assay. Acidosis reduced regulated thin filament velocity (VRTF) at both maximal and sub-maximal Ca(++) levels in a pH-dependent manner. A truncated construct of the inhibitory subunit of troponin (TnI) and a Ca(++)-sensitizing mutation in the Ca(++)-binding subunit of troponin (TnC) increased VRTF at sub-maximal Ca(++) under acidic conditions, but had no effect on VRTF at maximal Ca(++) levels. In contrast, both Pi and replacement of ATP with dATP reversed much of the acidosis-induced depression of VRTF at saturating Ca(++). Interestingly, despite producing similar magnitude increases in VRTF, the combined effects of Pi and dATP were additive, suggesting different underlying mechanisms of action. These findings suggest that acidosis depresses velocity by slowing the detachment rate from actin but also by possibly slowing the attachment rate.
    Journal of Applied Physiology 03/2014; 116(9). DOI:10.1152/japplphysiol.01161.2013 · 3.43 Impact Factor
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    ABSTRACT: -Hypertrophic cardiomyopathy (HCM) is a common genetic disorder caused mainly by mutations in sarcomeric proteins and is characterized by maladaptive myocardial hypertrophy, diastolic heart failure, increased myofilament Ca(2+) sensitivity and high susceptibility to sudden death. We tested the following hypothesis: correction of the increased myofilament sensitivity can delay or prevent the development of the HCM phenotype. -We used an HCM mouse model with an E180G mutation in α-tropomyosin (Tm180) that demonstrates increased myofilament Ca(2+) sensitivity, severe hypertrophy and diastolic dysfunction. To test our hypothesis, we reduced myofilament Ca(2+) sensitivity in Tm180 mice by generating a double transgenic (DTG) mouse line. We crossed Tm180 mice with mice expressing a pseudo-phosphorylated cardiac troponin I (cTnI) (S23D and S24D; TnI-PP). TnI-PP mice demonstrated a reduced myofilament Ca(2+) sensitivity compared to wild-type mice. The development of pathological hypertrophy did not occur in mice expressing both Tm180 and TnI-PP. Left ventricle performance was improved in DTG compared to their Tm180 littermates, which express wild-type cTnI. Hearts of DTG mice demonstrated no changes in expression of phospholamban (PLN) and Serca2a, increased levels of PLN and TnT phosphorylation, and reduced phosphorylation of TnI compared to Tm180 mice. Moreover, expression of TnI-PP in Tm180 hearts inhibited modifications in the activity of ERK1/2 and GATA-4 in Tm180 hearts. -Our data strongly indicate that reduction of myofilament sensitivity to Ca(2+) and associated correction of abnormal relaxation can delay or prevent development of HCM and should be considered as a therapeutic target for HCM.
    Circulation Cardiovascular Genetics 02/2014; 7(2). DOI:10.1161/CIRCGENETICS.113.000324 · 5.34 Impact Factor
  • Biophysical Journal 01/2014; 106(2):724a. DOI:10.1016/j.bpj.2013.11.3999 · 3.97 Impact Factor
  • Biophysical Journal 01/2014; 106(2):344a. DOI:10.1016/j.bpj.2013.11.1967 · 3.97 Impact Factor
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    Bin Liu · Joseph J Lopez · Brandon J Biesiadecki · Jonathan P Davis
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    ABSTRACT: Adrenergic stimulation modulates cardiac function by altering the phosphorylation status of several cardiac proteins. The Troponin complex, which is the Ca(2+) sensor for cardiac contraction, is a hot spot for adrenergic phosphorylation. While the effect of β-adrenergic related PKA phosphorylation of troponin I at Ser23/24 is well established, the effects of α-adrenergic induced PKC phosphorylation on multiple sites of TnI (Ser43/45, Thr144) and TnT (Thr194, Ser198, Thr203 and Thr284) are much less clear. By utilizing an IAANS labeled fluorescent troponin C, [Formula: see text], we systematically examined the site specific effects of PKC phosphomimetic mutants of TnI and TnT on TnC's Ca(2+) binding properties in the Tn complex and reconstituted thin filament. The majority of the phosphomemetics had little effect on the Ca(2+) binding properties of the isolated Tn complex. However, when incorporated into the thin filament, the phosphomimetics typically altered thin filament Ca(2+) sensitivity in a way consistent with their respective effects on Ca(2+) sensitivity of skinned muscle preparations. The altered Ca(2+) sensitivity could be generally explained by a change in Ca(2+) dissociation rates. Within TnI, phosphomimetic Asp and Glu did not always behave similar, nor were Ala mutations (used to mimic non-phosphorylatable states) benign to Ca(2+) binding. Our results suggest that Troponin may act as a hub on the thin filament, sensing physiological stimuli to modulate the contractile performance of the heart.
    PLoS ONE 01/2014; 9(1):e86279. DOI:10.1371/journal.pone.0086279 · 3.53 Impact Factor
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    ABSTRACT: Recent studies suggest that proarrhythmic effects of cardiac glycosides (CGs) on cardiomyocyte Ca(2+) handling involves generation of reactive oxygen species (ROS). However, the specific pathway(s) of ROS production and the subsequent downstream molecular events that mediate CG-dependent arrhythmogenesis remain to be defined.Methods and ResultsWe examined the effects of digitoxin (DGT) on Ca(2+) handling and ROS production in cardiomyocytes using a combination of pharmacological approaches and genetic mouse models. Myocytes isolated from mice deficient in NADPH oxidase type 2 (NOX2KO) and mice transgenically overexpressing mitochondrial superoxide dismutase displayed markedly increased tolerance to the proarrhythmic action of DGT as manifested by inhibition of DGT-dependent ROS and spontaneous Ca(2+) waves (SCW). Additionally, DGT-induced mitochondrial membrane potential depolarization was abolished in NOX2KO cells. DGT-dependent ROS was suppressed by inhibition of PI3K, PKC and the mitochondrial KATP channel, suggesting roles for these proteins, respectively, in activation of NOX2 and in mitochondrial ROS generation. Western blot revealed increased levels of oxidized CaMKII in WT but not in NOX2KO hearts treated with DGT. The DGT-induced increase in SCW frequency was abolished in myocytes isolated from mice in which the Ser 2814 CaMKII phosphorylation site on RyR2 is constitutively inactivated. These results suggest that the arrhythmogenic adverse effects of CGs on Ca(2+) handling involve PI3K- and PKC-mediated stimulation of NOX2 and subsequent NOX2-dependent ROS release from the mitochondria; mitochondria-derived ROS then activate CaMKII with consequent phosphorylation of RyR2 at Ser 2814.
    Cardiovascular Research 10/2013; 101(1). DOI:10.1093/cvr/cvt233 · 5.81 Impact Factor
  • Laurin M Hanft · Brandon J Biesiadecki · Kerry S McDonald
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    ABSTRACT: According to the Frank-Starling relationship, greater end diastolic volume increases ventricular output. The Frank-Starling relationship is based, in part, on the length-tension relationship in cardiac myocytes. Recently, we identified a dichotomy in the steepness of length-tension relationships in mammalian cardiac myocytes that was dependent upon PKA-induced myofibrillar phosphorylation. Since PKA has multiple myofibrillar substrates including titin, myosin binding protein-C (MyBP-C), and cardiac troponin I (cTnI), we sought to define if phosphorylation of one of these molecules could control length-tension relationships. We focused on cTnI since troponin can be exchanged in permeabilized striated muscle cell preparations and tested the hypothesis that phosphorylation of cTnI modulates length dependence of force generation. For these experiments, we exchanged unphosphorylated recombinant cardiac troponin (cTn) into either a rat cardiac myocyte preparation or a skinned slow-twitch skeletal muscle fibre. In all cases unphosphorylated cTn yielded a shallow length-tension relationship, which was shifted to a steep relationship after PKA treatment. Furthermore, exchange with cTn having cTnI serines 23 and 24 mutated to aspartic acids to mimic phosphorylation always shifted a shallow length-tension relationship to a steep relationship. Overall, these results indicate that phosphorylation of cTnI serines 23/24 is a key regulator of length dependence of force generation in striated muscle.
    The Journal of Physiology 07/2013; 104(2). DOI:10.1113/jphysiol.2013.258400 · 4.54 Impact Factor
  • Mark T Ziolo · Brandon J Biesiadecki
    Journal of Molecular and Cellular Cardiology 06/2013; 62. DOI:10.1016/j.yjmcc.2013.06.006 · 5.22 Impact Factor

Publication Stats

542 Citations
242.33 Total Impact Points


  • 2010–2015
    • The Ohio State University
      • Department of Physiology and Cell Biology
      Columbus, Ohio, United States
  • 2007
    • Case Western Reserve University School of Medicine
      • Department of Physiology and Biophysics
      Cleveland, Ohio, United States