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Tikunova SB, Thuma J, Davis JP. Mouse Models of Cardiomyopathies Caused by Mutations in Troponin C. Int J Mol Sci 2023; 24:12349. [PMID: 37569724 PMCID: PMC10419064 DOI: 10.3390/ijms241512349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2023] [Revised: 07/27/2023] [Accepted: 08/01/2023] [Indexed: 08/13/2023] Open
Abstract
Cardiac muscle contraction is regulated via Ca2+ exchange with the hetero-trimeric troponin complex located on the thin filament. Binding of Ca2+ to cardiac troponin C, a Ca2+ sensing subunit within the troponin complex, results in a series of conformational re-arrangements among the thin filament components, leading to an increase in the formation of actomyosin cross-bridges and muscle contraction. Ultimately, a decline in intracellular Ca2+ leads to the dissociation of Ca2+ from troponin C, inhibiting cross-bridge cycling and initiating muscle relaxation. Therefore, troponin C plays a crucial role in the regulation of cardiac muscle contraction and relaxation. Naturally occurring and engineered mutations in troponin C can lead to altered interactions among components of the thin filament and to aberrant Ca2+ binding and exchange with the thin filament. Mutations in troponin C have been associated with various forms of cardiac disease, including hypertrophic, restrictive, dilated, and left ventricular noncompaction cardiomyopathies. Despite progress made to date, more information from human studies, biophysical characterizations, and animal models is required for a clearer understanding of disease drivers that lead to cardiomyopathies. The unique use of engineered cardiac troponin C with the L48Q mutation that had been thoroughly characterized and genetically introduced into mouse myocardium clearly demonstrates that Ca2+ sensitization in and of itself should not necessarily be considered a disease driver. This opens the door for small molecule and protein engineering strategies to help boost impaired systolic function. On the other hand, the engineered troponin C mutants (I61Q and D73N), genetically introduced into mouse myocardium, demonstrate that Ca2+ desensitization under basal conditions may be a driving factor for dilated cardiomyopathy. In addition to enhancing our knowledge of molecular mechanisms that trigger hypertrophy, dilation, morbidity, and mortality, these cardiomyopathy mouse models could be used to test novel treatment strategies for cardiovascular diseases. In this review, we will discuss (1) the various ways mutations in cardiac troponin C might lead to disease; (2) relevant data on mutations in cardiac troponin C linked to human disease, and (3) all currently existing mouse models containing cardiac troponin C mutations (disease-associated and engineered).
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Affiliation(s)
- Svetlana B. Tikunova
- Department of Physiology and Cell Biology, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH 43210, USA (J.P.D.)
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Dong S, Zheng W, Pinkerton N, Hansen J, Tikunova SB, Davis JP, Heissler SM, Kudryashova E, Egelman EH, Kudryashov DS. Photorhabdus luminescens TccC3 Toxin Targets the Dynamic Population of F-Actin and Impairs Cell Cortex Integrity. Int J Mol Sci 2022; 23:7026. [PMID: 35806028 PMCID: PMC9266650 DOI: 10.3390/ijms23137026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 06/17/2022] [Accepted: 06/22/2022] [Indexed: 12/30/2022] Open
Abstract
Due to its essential role in cellular processes, actin is a common target for bacterial toxins. One such toxin, TccC3, is an effector domain of the ABC-toxin produced by entomopathogenic bacteria of Photorhabdus spp. Unlike other actin-targeting toxins, TccC3 uniquely ADP-ribosylates actin at Thr-148, resulting in the formation of actin aggregates and inhibition of phagocytosis. It has been shown that the fully modified F-actin is resistant to depolymerization by cofilin and gelsolin, but their effects on partially modified actin were not explored. We found that only F-actin unprotected by tropomyosin is the physiological TccC3 substrate. Yet, ADP-ribosylated G-actin can be produced upon cofilin-accelerated F-actin depolymerization, which was only mildly inhibited in partially modified actin. The affinity of TccC3-ADP-ribosylated G-actin for profilin and thymosin-β4 was weakened moderately but sufficiently to potentiate spontaneous polymerization in their presence. Interestingly, the Arp2/3-mediated nucleation was also potentiated by T148-ADP-ribosylation. Notably, even partially modified actin showed reduced bundling by plastins and α-actinin. In agreement with the role of these and other tandem calponin-homology domain actin organizers in the assembly of the cortical actin network, TccC3 induced intense membrane blebbing in cultured cells. Overall, our data suggest that TccC3 imposes a complex action on the cytoskeleton by affecting F-actin nucleation, recycling, and interaction with actin-binding proteins involved in the integration of actin filaments with each other and cellular elements.
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Affiliation(s)
- Songyu Dong
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
| | - Weili Zheng
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22903, USA; (W.Z.); (E.H.E.)
| | - Nicholas Pinkerton
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Jacob Hansen
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Svetlana B. Tikunova
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Jonathan P. Davis
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Sarah M. Heissler
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Edward H. Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22903, USA; (W.Z.); (E.H.E.)
| | - Dmitri S. Kudryashov
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
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3
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Cool AM, Lindert S. Computational Methods Elucidate Consequences of Mutations and Post-translational Modifications on Troponin I Effective Concentration to Troponin C. J Phys Chem B 2021; 125:7388-7396. [PMID: 34213339 DOI: 10.1021/acs.jpcb.1c03844] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ca2+ binding to cardiac troponin C (cTnC) causes a conformational shift that exposes a hydrophobic patch (cTnCHP) for binding of the cTnI switch peptide (cTnISP), ultimately resulting in contraction of the heart. The inhibitory peptide (cTnIIP), attached at the N-terminal end of the cTnISP, serves as a tether for the cTnISP to the rest of the troponin complex. Due to this tethered nature, the cTnISP remains within proximity of the hydrophobic patch region, resulting in the cTnCHP experiencing an elevated "effective concentration" of the cTnISP. Mutations to the cTnIIP region have been hypothesized to cause disease by affecting the ability of the cTnISP to "find" the hydrophobic patch, resulting in alterations to the heart's ability to contract normally. We tested this hypothesis using molecular dynamics (MD) simulations of the troponin complex using a model that contained all three subunits of troponin: C, I, and T. We developed methods that allowed us to quantitatively measure the effective concentration of the cTnISP from the simulations. A significant reduction in the cTnISP effective concentration was observed when the cTnIIP was removed from the system, showcasing the importance of a tethered cTnISP. Through accelerated MD methods, we proposed the minimum effective concentration of a tethered cTnISP to be approximately 21 mM. Modification of the cTnIIP via PKC-mediated phosphorylation of T143 was shown to significantly increase the estimated effective concentration of cTnISP, help the cTnISP find the cTnCHP more effectively, and maintain the relative shape of the cTnIIP when compared to the native model. All of these data indicate that pT143 may be able to help promote binding of cTnISP to the cTnCHP. We then tested six mutations within the cTnIIP region that are known cTnC Ca2+-sensitizing mutations and have been linked with cardiomyopathy. We did not observe a significant reduction in the effective concentration upon the introduction of these mutations; however, we did observe increased variability in the flexibility and dynamics of the cTnIIP region when compared to native. Our observations led us to hypothesize that the mechanism by which these cardiomyopathic mutations affect Ca2+ sensitivity is by altering the off rate of cTnISP from the hydrophobic patch.
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Affiliation(s)
- Austin M Cool
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
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Barrick SK, Greenberg L, Greenberg MJ. A troponin T variant linked with pediatric dilated cardiomyopathy reduces the coupling of thin filament activation to myosin and calcium binding. Mol Biol Cell 2021; 32:1677-1689. [PMID: 34161147 PMCID: PMC8684737 DOI: 10.1091/mbc.e21-02-0082] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Dilated cardiomyopathy (DCM) is a significant cause of pediatric heart failure. Mutations in proteins that regulate cardiac muscle contraction can cause DCM; however, the mechanisms by which molecular-level mutations contribute to cellular dysfunction are not well understood. Better understanding of these mechanisms might enable the development of targeted therapeutics that benefit patient subpopulations with mutations that cause common biophysical defects. We examined the molecular- and cellular-level impacts of a troponin T variant associated with pediatric-onset DCM, R134G. The R134G variant decreased calcium sensitivity in an in vitro motility assay. Using stopped-flow and steady-state fluorescence measurements, we determined the molecular mechanism of the altered calcium sensitivity: R134G decouples calcium binding by troponin from the closed-to-open transition of the thin filament and decreases the cooperativity of myosin binding to regulated thin filaments. Consistent with the prediction that these effects would cause reduced force per sarcomere, cardiomyocytes carrying the R134G mutation are hypocontractile. They also show hallmarks of DCM that lie downstream of the initial insult, including disorganized sarcomeres and cellular hypertrophy. These results reinforce the importance of multiscale studies to fully understand mechanisms underlying human disease and highlight the value of mechanism-based precision medicine approaches for DCM.
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Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
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Boldt K, Rios JL, Joumaa V, Herzog W. Mechanical function of cardiac fibre bundles is partly protected by exercise in response to diet-induced obesity in rats. Appl Physiol Nutr Metab 2020; 46:46-54. [PMID: 32598858 DOI: 10.1139/apnm-2020-0275] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Decrements in contractile function resulting from obesity are thought to be major reasons for the link between obesity and cardiovascular disease, while exercise has been shown to improve cardiac muscle contractile function. The purpose of this study was to evaluate cardiac contractile properties following obesity induction and the potential protective effect of exercise. Twelve-week-old rats (n = 30) were organized into either a chow diet or a high-fat, high-sucrose (HFHS) diet group. Following 12 weeks of obesity induction the HFHS group animals were stratified and grouped into sedentary (HFHS+Sed) and exercise (HFHS+Ex) groups for an additional 12 weeks. Following 24 weeks of diet intervention, with 12 weeks of aerobic exercise (25 m/min, 30 min/day, 5 days/week) for the HFHS+Ex group, skinned cardiac fibre bundle testing was used to evaluate cardiac contractile properties. Body fat and mass were significantly greater in the HFHS-fed animals compared with the chow controls (p < 0.043). Hearts from rats in the HFHS+Sed group had significantly greater mass (p < 0.03), significantly slower maximum shortening velocity (p = 0.001), and tended to have lower calcium sensitivity (p = 0.077) and a lower proportion of α-myosin heavy chain composition (p = 0.074) than the sedentary chow animals. However, 12 weeks of moderate aerobic exercise partially prevented these decrements in contractile properties. Novelty Cardiac muscle from animals exposed to an obesogenic diet for 24 weeks had impaired contractile properties compared with controls. Obesity-induced impairment of contractile properties of the heart were partially prevented by a 12-week aerobic exercise regime.
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Affiliation(s)
- Kevin Boldt
- Faculty of Kinesiology, University of Calgary, Calgary, AB T2N 1N4, Canada.,Human Performance Laboratory, University of Calgary, Calgary, AB T2N 1N4, Canada
| | - Jaqueline Lourdes Rios
- Faculty of Kinesiology, University of Calgary, Calgary, AB T2N 1N4, Canada.,Human Performance Laboratory, University of Calgary, Calgary, AB T2N 1N4, Canada
| | - Venus Joumaa
- Faculty of Kinesiology, University of Calgary, Calgary, AB T2N 1N4, Canada.,Human Performance Laboratory, University of Calgary, Calgary, AB T2N 1N4, Canada
| | - Walter Herzog
- Faculty of Kinesiology, University of Calgary, Calgary, AB T2N 1N4, Canada.,Human Performance Laboratory, University of Calgary, Calgary, AB T2N 1N4, Canada.,Biomechanics Laboratory, School of Sports, Federal University of Santa Catarina, SC 88040-900, Brazil
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6
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Abstract
This article focuses on three "bins" that comprise sets of biophysical derangements elicited by cardiomyopathy-associated mutations in the myofilament. Current therapies focus on symptom palliation and do not address the disease at its core. We and others have proposed that a more nuanced classification could lead to direct interventions based on early dysregulation changing the trajectory of disease progression in the preclinical cohort. Continued research is necessary to address the complexity of cardiomyopathic progression and develop efficacious therapeutics.
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Affiliation(s)
- Melissa L Lynn
- Department of Medicine, University of Arizona, Room 317, 1656 East Mabel Street, Tucson, AZ 85724, USA
| | - Sarah J Lehman
- Department of Physiological Sciences, University of Arizona, Room 317, 1656 East Mabel Street, Tucson, AZ 85724, USA
| | - Jil C Tardiff
- Department of Medicine, University of Arizona, Room 312, 1656 East Mabel Street, Tucson, AZ 85724, USA.
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Baxley T, Johnson D, Pinto JR, Chalovich JM. Troponin C Mutations Partially Stabilize the Active State of Regulated Actin and Fully Stabilize the Active State When Paired with Δ14 TnT. Biochemistry 2017; 56:2928-2937. [PMID: 28530094 DOI: 10.1021/acs.biochem.6b01092] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Striated muscle contraction is regulated by the actin-associated proteins tropomyosin and troponin. The extent of activation of myosin ATPase activity is lowest in the absence of both Ca2+ and activating cross-bridges (i.e., S1-ADP or rigor S1). Binding of activating species of myosin to actin at a saturating Ca2+ concentration stabilizes the most active state (M state) of the actin-tropomyosin-troponin complex (regulated actin). Ca2+ binding alone produces partial stabilization of the active state. The extent of stabilization at a saturating Ca2+ concentration depends on the isoform of the troponin subunits, the phosphorylation state of troponin, and, in the case of cardiac muscle, the presence of hypertrophic cardiomyopathy-producing mutants of troponin T and troponin I. Cardiac dysfunction is also associated with mutations of troponin C (TnC). Troponin C mutants A8V, C84Y, and D145E increase the Ca2+ sensitivity of ATPase activity. We show that these mutants change the distribution of regulated actin states. The A8V and C84Y TnC mutants decreased the inactive B state distribution slightly at low Ca2+ concentrations, but the D145E mutants had no effect on that state. All TnC mutants increased the level of the active M state compared to that of the wild type, at a saturating Ca2+ concentration. Troponin complexes that contained two mutations that stabilize the active M state, A8V TnC and Δ14 TnT, appeared to be completely in the active state in the presence of only Ca2+. Because Ca2+ gives full activation, in this situation, troponin must be capable of positioning tropomyosin in the active M state without the need for rigor myosin binding.
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Affiliation(s)
- Tamatha Baxley
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
| | - Dylan Johnson
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine , Tallahassee, Florida 32304, United States
| | - Joseph M Chalovich
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
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Siddiqui JK, Tikunova SB, Walton SD, Liu B, Meyer M, de Tombe PP, Neilson N, Kekenes-Huskey PM, Salhi HE, Janssen PML, Biesiadecki BJ, Davis JP. Myofilament Calcium Sensitivity: Consequences of the Effective Concentration of Troponin I. Front Physiol 2016; 7:632. [PMID: 28066265 PMCID: PMC5175494 DOI: 10.3389/fphys.2016.00632] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Accepted: 12/05/2016] [Indexed: 12/04/2022] Open
Abstract
Control of calcium binding to and dissociation from cardiac troponin C (TnC) is essential to healthy cardiac muscle contraction/relaxation. There are numerous aberrant post-translational modifications and mutations within a plethora of contractile, and even non-contractile, proteins that appear to imbalance this delicate relationship. The direction and extent of the resulting change in calcium sensitivity is thought to drive the heart toward one type of disease or another. There are a number of molecular mechanisms that may be responsible for the altered calcium binding properties of TnC, potentially the most significant being the ability of the regulatory domain of TnC to bind the switch peptide region of TnI. Considering TnI is essentially tethered to TnC and cannot diffuse away in the absence of calcium, we suggest that the apparent calcium binding properties of TnC are highly dependent upon an “effective concentration” of TnI available to bind TnC. Based on our previous work, TnI peptide binding studies and the calcium binding properties of chimeric TnC-TnI fusion constructs, and building upon the concept of effective concentration, we have developed a mathematical model that can simulate the steady-state and kinetic calcium binding properties of a wide assortment of disease-related and post-translational protein modifications in the isolated troponin complex and reconstituted thin filament. We predict that several TnI and TnT modifications do not alter any of the intrinsic calcium or TnI binding constants of TnC, but rather alter the ability of TnC to “find” TnI in the presence of calcium. These studies demonstrate the apparent consequences of the effective TnI concentration in modulating the calcium binding properties of TnC.
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Affiliation(s)
- Jalal K Siddiqui
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Svetlana B Tikunova
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Shane D Walton
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Bin Liu
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Meredith Meyer
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Pieter P de Tombe
- Cell and Molecular Physiology, Loyola University Chicago Maywood, IL, USA
| | - Nathan Neilson
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | | | - Hussam E Salhi
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Paul M L Janssen
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Brandon J Biesiadecki
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Jonathan P Davis
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
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Salhi HE, Hassel NC, Siddiqui JK, Brundage EA, Ziolo MT, Janssen PML, Davis JP, Biesiadecki BJ. Myofilament Calcium Sensitivity: Mechanistic Insight into TnI Ser-23/24 and Ser-150 Phosphorylation Integration. Front Physiol 2016; 7:567. [PMID: 28018230 PMCID: PMC5156683 DOI: 10.3389/fphys.2016.00567] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 11/08/2016] [Indexed: 11/14/2022] Open
Abstract
Troponin I (TnI) is a major regulator of cardiac muscle contraction and relaxation. During physiological and pathological stress, TnI is differentially phosphorylated at multiple residues through different signaling pathways to match cardiac function to demand. The combination of these TnI phosphorylations can exhibit an expected or unexpected functional integration, whereby the function of two phosphorylations are different than that predicted from the combined function of each individual phosphorylation alone. We have shown that TnI Ser-23/24 and Ser-150 phosphorylation exhibit functional integration and are simultaneously increased in response to cardiac stress. In the current study, we investigated the functional integration of TnI Ser-23/24 and Ser-150 to alter cardiac contraction. We hypothesized that Ser-23/24 and Ser-150 phosphorylation each utilize distinct molecular mechanisms to alter the TnI binding affinity within the thin filament. Mathematical modeling predicts that Ser-23/24 and Ser-150 phosphorylation affect different TnI affinities within the thin filament to distinctly alter the Ca2+-binding properties of troponin. Protein binding experiments validate this assertion by demonstrating pseudo-phosphorylated Ser-150 decreases the affinity of isolated TnI for actin, whereas Ser-23/24 pseudo-phosphorylation is not different from unphosphorylated. Thus, our data supports that TnI Ser-23/24 affects TnI-TnC binding, while Ser-150 phosphorylation alters TnI-actin binding. By measuring force development in troponin-exchanged skinned myocytes, we demonstrate that the Ca2+ sensitivity of force is directly related to the amount of phosphate present on TnI. Furthermore, we demonstrate that Ser-150 pseudo-phosphorylation blunts Ser-23/24-mediated decreased Ca2+-sensitive force development whether on the same or different TnI molecule. Therefore, TnI phosphorylations can integrate across troponins along the myofilament. These data demonstrate that TnI Ser-23/24 and Ser-150 phosphorylation regulates muscle contraction in part by modulating different TnI interactions in the thin filament and it is the combination of these differential mechanisms that provides understanding of their functional integration.
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Affiliation(s)
| | | | | | | | | | | | | | - Brandon J. Biesiadecki
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State UniversityColumbus, OH, USA
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Cheng Y, Regnier M. Cardiac troponin structure-function and the influence of hypertrophic cardiomyopathy associated mutations on modulation of contractility. Arch Biochem Biophys 2016; 601:11-21. [PMID: 26851561 PMCID: PMC4899195 DOI: 10.1016/j.abb.2016.02.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Revised: 01/30/2016] [Accepted: 02/02/2016] [Indexed: 11/29/2022]
Abstract
Cardiac troponin (cTn) acts as a pivotal regulator of muscle contraction and relaxation and is composed of three distinct subunits (cTnC: a highly conserved Ca(2+) binding subunit, cTnI: an actomyosin ATPase inhibitory subunit, and cTnT: a tropomyosin binding subunit). In this mini-review, we briefly summarize the structure-function relationship of cTn and its subunits, its modulation by PKA-mediated phosphorylation of cTnI, and what is known about how these properties are altered by hypertrophic cardiomyopathy (HCM) associated mutations of cTnI. This includes recent work using computational modeling approaches to understand the atomic-based structural level basis of disease-associated mutations. We propose a viewpoint that it is alteration of cTnC-cTnI interaction (rather than the Ca(2+) binding properties of cTn) per se that disrupt the ability of PKA-mediated phosphorylation at cTnI Ser-23/24 to alter contraction and relaxation in at least some HCM-associated mutations. The combination of state of the art biophysical approaches can provide new insight on the structure-function mechanisms of contractile dysfunction resulting cTnI mutations and exciting new avenues for the diagnosis, prevention, and even treatment of heart diseases.
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Affiliation(s)
- Yuanhua Cheng
- University of Washington, Department of Bioengineering, Seattle, WA, USA
| | - Michael Regnier
- University of Washington, Department of Bioengineering, Seattle, WA, USA.
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11
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Shettigar V, Zhang B, Little SC, Salhi HE, Hansen BJ, Li N, Zhang J, Roof SR, Ho HT, Brunello L, Lerch JK, Weisleder N, Fedorov VV, Accornero F, Rafael-Fortney JA, Gyorke S, Janssen PML, Biesiadecki BJ, Ziolo MT, Davis JP. Rationally engineered Troponin C modulates in vivo cardiac function and performance in health and disease. Nat Commun 2016; 7:10794. [PMID: 26908229 PMCID: PMC4770086 DOI: 10.1038/ncomms10794] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Accepted: 01/21/2016] [Indexed: 12/26/2022] Open
Abstract
Treatment for heart disease, the leading cause of death in the world, has progressed little for several decades. Here we develop a protein engineering approach to directly tune in vivo cardiac contractility by tailoring the ability of the heart to respond to the Ca(2+) signal. Promisingly, our smartly formulated Ca(2+)-sensitizing TnC (L48Q) enhances heart function without any adverse effects that are commonly observed with positive inotropes. In a myocardial infarction (MI) model of heart failure, expression of TnC L48Q before the MI preserves cardiac function and performance. Moreover, expression of TnC L48Q after the MI therapeutically enhances cardiac function and performance, without compromising survival. We demonstrate engineering TnC can specifically and precisely modulate cardiac contractility that when combined with gene therapy can be employed as a therapeutic strategy for heart disease.
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Affiliation(s)
- Vikram Shettigar
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Bo Zhang
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Sean C Little
- Bristol-Myers Squibb, Department of Discovery Biology, Wallingford, Connecticut 06492, USA
| | - Hussam E Salhi
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Brian J Hansen
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Ning Li
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Jianchao Zhang
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | | | - Hsiang-Ting Ho
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Lucia Brunello
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Jessica K Lerch
- Center for Brain and Spinal Cord Repair, Department of Neuroscience, The Ohio State University College of Medicine, Columbus, Ohio 43210, USA
| | - Noah Weisleder
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Vadim V Fedorov
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Federica Accornero
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Jill A Rafael-Fortney
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Sandor Gyorke
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Paul M L Janssen
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Brandon J Biesiadecki
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Mark T Ziolo
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
| | - Jonathan P Davis
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Columbus, Ohio 43210, USA
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12
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Designing proteins to combat disease: Cardiac troponin C as an example. Arch Biochem Biophys 2016; 601:4-10. [PMID: 26901433 DOI: 10.1016/j.abb.2016.02.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Accepted: 02/04/2016] [Indexed: 01/18/2023]
Abstract
Throughout history, muscle research has led to numerous scientific breakthroughs that have brought insight to a more general understanding of all biological processes. Potentially one of the most influential discoveries was the role of the second messenger calcium and its myriad of handling and sensing systems that mechanistically control muscle contraction. In this review we will briefly discuss the significance of calcium as a universal second messenger along with some of the most common calcium binding motifs in proteins, focusing on the EF-hand. We will also describe some of our approaches to rationally design calcium binding proteins to palliate, or potentially even cure cardiovascular disease. Considering not all failing hearts have the same etiology, genetic background and co-morbidities, personalized therapies will need to be developed. We predict designer proteins will open doors for unprecedented personalized, and potentially, even generalized medicines as gene therapy or protein delivery techniques come to fruition.
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13
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McConnell BK, Singh S, Fan Q, Hernandez A, Portillo JP, Reiser PJ, Tikunova SB. Knock-in mice harboring a Ca(2+) desensitizing mutation in cardiac troponin C develop early onset dilated cardiomyopathy. Front Physiol 2015; 6:242. [PMID: 26379556 PMCID: PMC4550777 DOI: 10.3389/fphys.2015.00242] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 08/11/2015] [Indexed: 12/05/2022] Open
Abstract
The physiological consequences of aberrant Ca(2+) binding and exchange with cardiac myofilaments are not clearly understood. In order to examine the effect of decreasing Ca(2+) sensitivity of cTnC on cardiac function, we generated knock-in mice carrying a D73N mutation (not known to be associated with heart disease in human patients) in cTnC. The D73N mutation was engineered into the regulatory N-domain of cTnC in order to reduce Ca(2+) sensitivity of reconstituted thin filaments by increasing the rate of Ca(2+) dissociation. In addition, the D73N mutation drastically blunted the extent of Ca(2+) desensitization of reconstituted thin filaments induced by cTnI pseudo-phosphorylation. Compared to wild-type mice, heterozygous knock-in mice carrying the D73N mutation exhibited a substantially decreased Ca(2+) sensitivity of force development in skinned ventricular trabeculae. Kaplan-Meier survival analysis revealed that median survival time for knock-in mice was 12 weeks. Echocardiographic analysis revealed that knock-in mice exhibited increased left ventricular dimensions with thinner walls. Echocardiographic analysis also revealed that measures of systolic function, such as ejection fraction (EF) and fractional shortening (FS), were dramatically reduced in knock-in mice. In addition, knock-in mice displayed electrophysiological abnormalities, namely prolonged QRS and QT intervals. Furthermore, ventricular myocytes isolated from knock-in mice did not respond to β-adrenergic stimulation. Thus, knock-in mice developed pathological features similar to those observed in human patients with dilated cardiomyopathy (DCM). In conclusion, our results suggest that decreasing Ca(2+) sensitivity of the regulatory N-domain of cTnC is sufficient to trigger the development of DCM.
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Affiliation(s)
- Bradley K. McConnell
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Sonal Singh
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Qiying Fan
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Adriana Hernandez
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Jesus P. Portillo
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Peter J. Reiser
- Division of Biosciences, College of Dentistry, The Ohio State UniversityColumbus, OH, USA
| | - Svetlana B. Tikunova
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
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14
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E. Rohrback S, Wheatly MG, Gillen CM. Calcium binding to Procambarus clarkii sarcoplasmic calcium binding protein splice variants. Comp Biochem Physiol B Biochem Mol Biol 2015; 179:57-63. [DOI: 10.1016/j.cbpb.2014.09.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 09/22/2014] [Accepted: 09/23/2014] [Indexed: 10/24/2022]
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15
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Salhi HE, Walton SD, Hassel NC, Brundage EA, de Tombe PP, Janssen PML, Davis JP, Biesiadecki BJ. Cardiac troponin I tyrosine 26 phosphorylation decreases myofilament Ca2+ sensitivity and accelerates deactivation. J Mol Cell Cardiol 2014; 76:257-64. [PMID: 25252176 DOI: 10.1016/j.yjmcc.2014.09.013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Revised: 09/09/2014] [Accepted: 09/12/2014] [Indexed: 10/24/2022]
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-26N-terminal phosphorylation decreases calcium sensitivity of the thin filament, similar to the desensitizing effects of TnI Ser-23/24 phosphorylation. Our results demonstrate that 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 that 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-23/24N-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.
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Affiliation(s)
- Hussam E Salhi
- The Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA; The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Shane D Walton
- The Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA; The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Nathan C Hassel
- The Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA; The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Elizabeth A Brundage
- The Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA; The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Pieter P de Tombe
- The Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, IL 60153, USA
| | - Paul M L Janssen
- The Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA; The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Jonathan P Davis
- The Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA; The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Brandon J Biesiadecki
- The Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA; The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA.
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16
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Nixon BR, Walton SD, Zhang B, Brundage EA, Little SC, Ziolo MT, Davis JP, Biesiadecki BJ. Combined troponin I Ser-150 and Ser-23/24 phosphorylation sustains thin filament Ca(2+) sensitivity and accelerates deactivation in an acidic environment. J Mol Cell Cardiol 2014; 72:177-85. [PMID: 24657721 PMCID: PMC4075059 DOI: 10.1016/j.yjmcc.2014.03.010] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Revised: 03/10/2014] [Accepted: 03/13/2014] [Indexed: 01/09/2023]
Abstract
The binding of Ca(2+) 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 that 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 Ca(2+) to TnC and impaired contraction. To determine the pathological relevance of these simultaneous TnI phosphorylations 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 Ca(2+) 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 Ca(2+) 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-phosphorylations to maintain Ca(2+) binding while accelerating Ca(2+) dissociation represents the first post-translational modification of troponin by phosphorylation to both accelerate thin filament deactivation and maintain Ca(2+) sensitive activation. These data suggest that TnI Ser-150 phosphorylation induced attenuation of the pH-dependent decrease in Ca(2+) 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.
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Affiliation(s)
- Benjamin R Nixon
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Shane D Walton
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Bo Zhang
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Elizabeth A Brundage
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Sean C Little
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Mark T Ziolo
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Jonathan P Davis
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Brandon J Biesiadecki
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA.
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17
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Sheng JJ, Jin JP. Gene regulation, alternative splicing, and posttranslational modification of troponin subunits in cardiac development and adaptation: a focused review. Front Physiol 2014; 5:165. [PMID: 24817852 PMCID: PMC4012202 DOI: 10.3389/fphys.2014.00165] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Accepted: 04/10/2014] [Indexed: 12/19/2022] Open
Abstract
Troponin plays a central role in regulating the contraction and relaxation of vertebrate striated muscles. This review focuses on the isoform gene regulation, alternative RNA splicing, and posttranslational modifications of troponin subunits in cardiac development and adaptation. Transcriptional and posttranscriptional regulations such as phosphorylation and proteolysis modifications, and structure-function relationships of troponin subunit proteins are summarized. The physiological and pathophysiological significances are discussed for impacts on cardiac muscle contractility, heart function, and adaptations in health and diseases.
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Affiliation(s)
- Juan-Juan Sheng
- Department of Physiology, Wayne State University School of Medicine Detroit, MI, USA
| | - Jian-Ping Jin
- Department of Physiology, Wayne State University School of Medicine Detroit, MI, USA
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18
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Longyear TJ, Turner MA, Davis JP, Lopez J, Biesiadecki B, Debold EP. Ca++-sensitizing mutations in troponin, P(i), and 2-deoxyATP alter the depressive effect of acidosis on regulated thin-filament velocity. J Appl Physiol (1985) 2014; 116:1165-74. [PMID: 24651988 DOI: 10.1152/japplphysiol.01161.2013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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 whether 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 submaximal Ca(++) levels in a pH-dependent manner. A truncated construct of the inhibitory subunit of Tn (TnI) and a Ca(++)-sensitizing mutation in the Ca(++)-binding subunit of Tn (TnC) increased VRTF at submaximal 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.
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Affiliation(s)
- Thomas J Longyear
- Department of Kinesiology, University of Massachusetts, Amherst, Massachusetts
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19
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Swindle N, Albury ANJ, Baroud B, Burney M, Tikunova SB. Molecular and functional consequences of mutations in the central helix of cardiac troponin C. Arch Biochem Biophys 2014; 548:46-53. [PMID: 24650606 DOI: 10.1016/j.abb.2014.03.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 03/04/2014] [Accepted: 03/05/2014] [Indexed: 01/28/2023]
Abstract
The objective of this work was to investigate the role of acidic residues within the exposed middle segment of the central helix of cTnC in (1) cTnC-cTnI interactions, (2) Ca(2+) binding and exchange with the regulatory N-domain of cTnC in increasingly complex biochemical systems, and (3) ability of the cTn complex to regulate actomyosin ATPase. In order to achieve this objective, we introduced the D87A/D88A and E94A/E95A/E96A mutations into the central helix of cTnC. The D87A/D88A and E94A/E95A/E96A mutations decreased affinity of cTnC for the regulatory region of cTnI. The Ca(2+) sensitivity of the regulatory N-domain of isolated cTnC was decreased by the D87A/D88A, but not E94A/E95A/E96A mutation. However, both the D87A/D88A and E94A/E95A/E96A mutations desensitized the cTn complex and reconstituted thin filaments to Ca(2+). Decreases in the Ca(2+) sensitivity of the cTn complex and reconstituted thin filaments were, at least in part, due to faster rates of Ca(2+) dissociation. In addition, the D87A/D88A and E94A/E95A/E96A mutations desensitized actomyosin ATPase to Ca(2+), and decreased maximal actomyosin ATPase activity. Thus, our results indicate that conserved acidic residues within the exposed middle segment of the central helix of cTnC are important for the proper regulatory function of the cTn complex.
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Affiliation(s)
- Nicholas Swindle
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Acchia N J Albury
- Department of Biology, Wingate University, Wingate, NC 28174, United States
| | - Belal Baroud
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Maryam Burney
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Svetlana B Tikunova
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States.
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20
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Poggesi C, Ho CY. Muscle dysfunction in hypertrophic cardiomyopathy: what is needed to move to translation? J Muscle Res Cell Motil 2014; 35:37-45. [PMID: 24493262 DOI: 10.1007/s10974-014-9374-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Accepted: 01/02/2014] [Indexed: 02/04/2023]
Abstract
Hypertrophic cardiomyopathy (HCM) is caused by mutations in sarcomere genes. As such, HCM provides remarkable opportunities to study how changes to the heart's molecular motor apparatus may influence cardiac structure and function. Although the genetic basis of HCM is well-described, there is much more limited understanding of the precise consequences of sarcomere mutations--how they remodel the heart, and how these changes lead to the dramatic clinical consequences associated with HCM. More precise characterization of the mechanisms leading from sarcomere mutation to altered cardiac muscle function is critical to gain insight into fundamental disease biology and phenotypic evolution. Such knowledge will help foster development of novel treatment strategies aimed at correcting and preventing disease development in HCM.
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Affiliation(s)
- Corrado Poggesi
- Department of Experimental and Clinical Medicine, University of Florence, Viale Morgagni 63, 50134, Florence, Italy,
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21
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Liu B, Lopez JJ, Biesiadecki BJ, Davis JP. Protein kinase C phosphomimetics alter thin filament Ca2+ binding properties. PLoS One 2014; 9:e86279. [PMID: 24466001 PMCID: PMC3899258 DOI: 10.1371/journal.pone.0086279] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 12/10/2013] [Indexed: 11/18/2022] Open
Abstract
Adrenergic stimulation modulates cardiac function by altering the phosphorylation status of several cardiac proteins. The Troponin complex, which is the Ca2+ 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, , we systematically examined the site specific effects of PKC phosphomimetic mutants of TnI and TnT on TnC’s Ca2+ binding properties in the Tn complex and reconstituted thin filament. The majority of the phosphomemetics had little effect on the Ca2+ binding properties of the isolated Tn complex. However, when incorporated into the thin filament, the phosphomimetics typically altered thin filament Ca2+ sensitivity in a way consistent with their respective effects on Ca2+ sensitivity of skinned muscle preparations. The altered Ca2+ sensitivity could be generally explained by a change in Ca2+ 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 Ca2+ 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.
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Affiliation(s)
- Bin Liu
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio, United States of America
| | - Joseph J. Lopez
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio, United States of America
| | - Brandon J. Biesiadecki
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio, United States of America
| | - Jonathan P. Davis
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail:
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22
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Kaushik G, Engler AJ. From stem cells to cardiomyocytes: the role of forces in cardiac maturation, aging, and disease. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 126:219-42. [PMID: 25081620 DOI: 10.1016/b978-0-12-394624-9.00009-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Stem cell differentiation into a variety of lineages is known to involve signaling from the extracellular niche, including from the physical properties of that environment. What regulates stem cell responses to these cues is there ability to activate different mechanotransductive pathways. Here, we will review the structures and pathways that regulate stem cell commitment to a cardiomyocyte lineage, specifically examining proteins within muscle sarcomeres, costameres, and intercalated discs. Proteins within these structures stretch, inducing a change in their phosphorylated state or in their localization to initiate different signals. We will also put these changes in the context of stem cell differentiation into cardiomyocytes, their subsequent formation of the chambered heart, and explore negative signaling that occurs during disease.
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Affiliation(s)
- Gaurav Kaushik
- Department of Bioengineering, University of California, San Diego, La Jolla, California, USA
| | - Adam J Engler
- Department of Bioengineering, University of California, San Diego, La Jolla, California, USA
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23
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Torres CAA, Varian KD, Canan CH, Davis JP, Janssen PML. The positive inotropic effect of pyruvate involves an increase in myofilament calcium sensitivity. PLoS One 2013; 8:e63608. [PMID: 23691074 PMCID: PMC3655183 DOI: 10.1371/journal.pone.0063608] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Accepted: 04/04/2013] [Indexed: 01/26/2023] Open
Abstract
Pyruvate is a metabolic fuel that is a potent inotropic agent. Despite its unique inotropic and antioxidant properties, the molecular mechanism of its inotropic mechanism is still largely unknown. To examine the inotropic effect of pyruvate in parallel with intracellular calcium handling under near physiological conditions, we measured pH, myofilament calcium sensitivity, developed force, and calcium transients in ultra thin rabbit heart trabeculae at 37 °C loaded iontophoretically with the calcium indicator bis-fura-2. By contrasting conditions of control versus sarcoplasmic reticulum block (with either cyclopiazonic acid and ryanodine or with thapsigargin) we were able to characterize and isolate the effects of pyruvate on sarcoplasmic reticulum calcium handling and developed force. A potassium contracture technique was subsequently utilized to assess the force-calcium relationship and thus the myofilament calcium sensitivity. Pyruvate consistently increased developed force whether or not the sarcoplasmic reticulum was blocked (16.8±3.5 to 24.5±5.1 vs. 6.9±2.6 to 12.5±4.4 mN/mm(2), non-blocked vs. blocked sarcoplasmic reticulum respectively, p<0.001, n = 9). Furthermore, the sensitizing effect of pyruvate on the myofilaments was demonstrated by potassium contractures (EC50 at baseline versus 20 minutes of pyruvate infusion (peak force development) was 701±94 vs. 445±65 nM, p<0.01, n = 6). This study is the first to demonstrate that a leftward shift in myofilament calcium sensitivity is an important mediator of the inotropic effect of pyruvate. This finding can have important implications for future development of therapeutic strategies in the management of heart failure.
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Affiliation(s)
- Carlos A. A. Torres
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America
| | - Kenneth D. Varian
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America
| | - Cynthia H. Canan
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America
| | - Jonathan P. Davis
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America
| | - Paul M. L. Janssen
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail:
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24
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Tropomyosin Ser-283 pseudo-phosphorylation slows myofibril relaxation. Arch Biochem Biophys 2012; 535:30-8. [PMID: 23232082 DOI: 10.1016/j.abb.2012.11.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2012] [Revised: 11/21/2012] [Accepted: 11/22/2012] [Indexed: 12/15/2022]
Abstract
Tropomyosin (Tm) is a central protein in the Ca(2+) regulation of striated muscle. The αTm isoform undergoes phosphorylation at serine residue 283. While the biochemical and steady-state muscle function of muscle purified Tm phosphorylation have been explored, the effects of Tm phosphorylation on the dynamic properties of muscle contraction and relaxation are unknown. To investigate the kinetic regulatory role of αTm phosphorylation we expressed and purified native N-terminal acetylated Ser-283 wild-type, S283A phosphorylation null and S283D pseudo-phosphorylation Tm mutants in insect cells. Purified Tm's regulate thin filaments similar to that reported for muscle purified Tm. Steady-state Ca(2+) binding to troponin C (TnC) in reconstituted thin filaments did not differ between the 3 Tm's, however disassociation of Ca(2+) from filaments containing pseudo-phosphorylated Tm was slowed compared to wild-type Tm. Replacement of pseudo-phosphorylated Tm into myofibrils similarly prolonged the slow phase of relaxation and decreased the rate of the fast phase without altering activation kinetics. These data demonstrate that Tm pseudo-phosphorylation slows deactivation of the thin filament and muscle force relaxation dynamics in the absence of dynamic and steady-state effects on muscle activation. This supports a role for Tm as a key protein in the regulation of muscle relaxation dynamics.
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