Reduced force production during low blood flow to the heart correlates with altered troponin I phosphorylation

Christopher, Bridgette; Pizarro, Gresin O.; Nicholson, Bryson; Yuen, Samantha L.; Hoit, Brian D.; Ogut, Ozgur

doi:10.1007/s10974-009-9180-2

Cited by 11 publications

(21 citation statements)

References 43 publications

(59 reference statements)

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“…These data also suggest function may deteriorate more rapidly if there is a loss of secondary or “compensating” myofilament protein phosphorylation. The enhanced S43/45 and diminished S23/24 phosphorylation of cTnI associated with human HF is consistent with this idea (8,47,50). The ongoing changes in cellular function produced by phospho-mimetic S43/45 also are consistent with systolic dysfunction accompanied by variable changes in diastolic function reported in existing animal models expressing phospho-mimetic substitutions at S43/45 combined with S23/24 and/or T144 (3,20,24,37).…”

Section: Introductionsupporting

confidence: 78%

Functional communication between PKC-targeted cardiac troponin I phosphorylation sites

Lang

Stevenson

Schatz

et al. 2017

Archives of Biochemistry and Biophysics

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Increased protein kinase C (PKC) activity is associated with heart failure, and can target multiple cardiac troponin I (cTnI) residues in myocytes, including S23/24, S43/45 and T144. In earlier studies, cTnI-S43D and/or -S45D augmented S23/24 and T144 phosphorylation, which suggested there is communication between clusters. This communication is now explored by evaluating the impact of phospho-mimetic cTnI S43/45D combined with S23/24D (cTnIS4D) or T144D (cTnISDTD). Gene transfer of epitope-tagged cTnIS4D and cTnISDTD into adult cardiac myocytes progressively replaced endogenous cTnI. Partial replacement with cTnISDTD or cTnIS4D accelerated the time to peak (TTP) shortening and time to 50% re-lengthening (TTR50%) on day 2, but peak shortening was only diminished by cTnIS4D. Extensive cTnIS4D replacement continued to accelerate TTP, and decrease shortening amplitude, while TTR50% returned to baseline levels on day 4. In contrast, cTnISDTD modestly reduced shortening amplitude and continued to accelerate myocyte TTP and TTR50%. These results indicate cTnIS43/45 communicates with S23/24 and T144, with S23/24 exacerbating and T144 attenuating the S43/45D-dependent functional deficit. In addition, more severe functional alterations in cTnIS4D myocytes were accompanied by higher levels of secondary phosphorylation compared to cTnISDTD. These results suggest that secondary phosphorylation helps to maintain steady-state contractile function during chronic cTnI phosphorylation at PKC sites.

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Section: Introductionsupporting

confidence: 78%

Functional communication between PKC-targeted cardiac troponin I phosphorylation sites

Lang

Stevenson

Schatz

et al. 2017

Archives of Biochemistry and Biophysics

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“…PKC-mediated phosphorylation of cTnI at Ser42/44 has been implicated in several forms of cardiac disease in rodents and humans. 13–16 An increase in Ser42/44 phosphorylation has been reported in rodent models of pressure-overload of the heart, 14 low myocardial blood flow 15 and myocardial infarction. 16 In human, phosphorylation was not 9 or slightly 13 increased in ischemic and dilated end-stage failing hearts compared to non-failing donor hearts.…”

Section: Discussionmentioning

confidence: 97%

“…14–16 It has been demonstrated via top-down mass spectrometry (MS) that cTnI-Ser42/44 phosphorylation is induced by pressure overload of the heart (hypertension-induced heart failure) in rats. 14 In addition, in a rat model of low myocardial blood flow (impaired myocardial perfusion), increased cTnI phosphorylation at Ser42/44 was detected by LC-MS. 15 In a mouse model of myocardial infarction, enhanced phosphorylation of Ser42 was detected using a phospho-specific antibody at 2 and 14 days after myocardial infarction, which returned to control levels after 2 months. 16 Studies in failing human hearts showed either no phosphorylation at PKC sites 9 or a slightly higher Ser42 and Ser44 phosphorylation compared to non-failing donor hearts.…”

Section: Introductionmentioning

confidence: 97%

Phosphorylation of protein kinase C sites Ser42/44 decreases Ca2+-sensitivity and blunts enhanced length-dependent activation in response to protein kinase A in human cardiomyocytes

Wijnker

Sequeira

Witjas-Paalberends

et al. 2014

Archives of Biochemistry and Biophysics

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Protein kinase C (PKC)-mediated phosphorylation of troponin I (cTnI) at Ser42/44 is increased in heart failure. While studies in rodents demonstrated that PKC-mediated Ser42/44 phosphorylation decreases maximal force and ATPase activity, PKC incubation of human cardiomyocytes did not affect maximal force. We investigated whether Ser42/44 pseudo-phosphorylation affects force development and ATPase activity using troponin exchange in human myocardium. Additionally, we studied if pseudo-phosphorylated Ser42/44 modulates length-dependent activation of force, which is regulated by protein kinase A (PKA)-mediated cTnI-Ser23/24 phosphorylation. Isometric force was measured in membrane-permeabilized cardiomyocytes exchanged with human recombinant wild-type troponin or troponin mutated at Ser42/44 or Ser23/24 into aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. In troponin-exchanged donor cardiomyocytes experiments were repeated after PKA incubation. ATPase activity was measured in troponin-exchanged cardiac muscle strips. Compared to wild-type, 42D/44D decreased Ca2+-sensitivity without affecting maximal force in failing and donor cardiomyocytes. In donor myocardium, 42D/44D did not affect maximal ATPase activity or tension cost. Interestingly, 42D/44D blunted the length-dependent increase in Ca2+-sensitivity induced upon PKA-mediated phosphorylation. Since the drop in Ca2+-sensitivity at physiological Ca2+-concentrations is relatively large phosphorylation of Ser42/44 may result in a decrease of force and associated ATP utilization in the human heart.

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“…Several kinases phosphorylate cTnI S23/24 [3,4], and this phosphorylation accelerates Ca 2+ dissociation from troponin (Tn), and reduces the myofilament Ca 2+ sensitivity [5-7]. This reduced Ca 2+ sensitivity translates into accelerated cardiac relaxation to improve or preserve diastolic function [5,7,8], and reduced phosphorylation at this site is linked to diastolic dysfunction during end-stage heart failure [9,10]. In contrast, enhanced phosphorylation of a second cluster of residues at Ser43/45 (S43/45) in cTnI is associated with cardiac dysfunction [11-14].…”

Section: Introductionmentioning

confidence: 99%

Independent modulation of contractile performance by cardiac troponin I Ser43 and Ser45 in the dynamic sarcomere

Lang

Schwank

Stevenson

et al. 2015

Journal of Molecular and Cellular Cardiology

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Protein kinase C (PKC) targets cardiac troponin I (cTnI) S43/45 for phosphorylation in addition to other residues. During heart failure, cTnI S43/45 phosphorylation is elevated, and yet there is ongoing debate about its functional role due, in part, to the emergence of complex phenotypes in animal models. The individual functional influences of phosphorylated S43 and S45 also are not yet known. The present study utilizes viral gene transfer of cTnI with phosphomimetic S43D and/or S45D substitutions to evaluate their individual and combined influences on function in intact adult cardiac myocytes. Partial replacement (≤40%) with either cTnIS43D or cTnIS45D reduced the amplitude of contraction, and cTnIS45D slowed contraction and relaxation rates, while there were no significant changes in function with cTnIS43/45D. More extensive replacement (≥70%) with cTnIS43D, cTnIS45D, and cTnIS43/45D each reduced the amplitude of contraction. Additional experiments also showed cTnIS45D reduced myofilament Ca2+ sensitivity of tension. At the same time, shortening rates returned toward control values with cTnIS45D and the later stages of relaxation also became accelerated in myocytes expressing cTnIS43D and/or S45D. Further studies demonstrated this behavior coincided with adaptive changes in myofilament protein phosphorylation. Taken together, the results observed in myocytes expressing cTnIS43D and/or S45D suggest these 2 residues reduce function via independent mechanism(s). The changes in function associated with the onset of adaptive myofilament signaling suggest the sarcomere is capable of fine tuning PKC-mediated cTnIS43/45 phosphorylation and contractile performance. This modulatory behavior also provides insight into divergent phenotypes reported in animal models with cTnI S43/45 phosphomimetic substitutions.

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Reduced force production during low blood flow to the heart correlates with altered troponin I phosphorylation

Cited by 11 publications

References 43 publications

Functional communication between PKC-targeted cardiac troponin I phosphorylation sites

Functional communication between PKC-targeted cardiac troponin I phosphorylation sites

Phosphorylation of protein kinase C sites Ser42/44 decreases Ca2+-sensitivity and blunts enhanced length-dependent activation in response to protein kinase A in human cardiomyocytes

Independent modulation of contractile performance by cardiac troponin I Ser43 and Ser45 in the dynamic sarcomere

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