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1.  Cardiac Troponins and Autoimmunity: their role in the pathogenesis of myocarditis and of heart failure 
Despite the widespread use of cardiac troponins as biomarkers for the diagnosis and quantitation of cardiac injury, the effect of troponin release and a possible autoimmune response to the troponins is unknown. Other investigators reported that programmed cell death – 1 (PD-1) – receptor deficient mice developed severe cardiomyopathy with autoantibodies to troponin I. We found that immunization of genetically susceptible mice with troponin I but not troponin T induced a robust autoimmune response leading to marked inflammation and fibrosis in the myocardium. At later times, antibodies to cardiac myosin were detected in troponin – immunized mice. The severity of inflammation correlated with expression of chemokines RANTES, MIP-2, IP-10 and MCD-1 in the myocardium. Prior immunization with troponin I increased the severity of experimental infarctions, indicating that an autoimmune response to troponin I aggravates acute cardiac damage. Cardiac inflammation, fibrosis and functional impairment were transferred from immunized to naive recipients by CD4+ T cells, and the cytokine profile suggested both a Th2 and Th17 profile in A/J mice. Finally we identified an 18-mer of troponin I containing an immuno-dominant epitope.
doi:10.1016/j.clim.2009.04.008
PMCID: PMC2819185  PMID: 19446498
2.  The Δ14 Mutation of Human Cardiac Troponin T Enhances ATPase Activity and Alters the Cooperative Binding of S1-ADP to Regulated Actin† 
Biochemistry  2004;43(48):15276-15285.
The complex of tropomyosin and troponin binds to actin and inhibits activation of myosin ATPase activity and force production of striated muscles at low free Ca2+ concentrations. Ca2+ stimulates ATP activity, and at subsaturating actin concentrations, the binding of NEM-modified S1 to actin–tropomyosin–troponin increases the rate of ATP hydrolysis even further. We show here that the Δ14 mutation of troponin T, associated with familial hypertrophic cardiomyopathy, results in an increase in ATPase rate like that seen with wild-type troponin in the presence of NEM-S1. The enhanced ATPase activity was not due to a decreased incorporation of mutant troponin T with troponin I and troponin C to form an active troponin complex. The activating effect was more prominent with a hybrid troponin (skeletal TnI, TnC, and cardiac TnT) than with all cardiac troponin. Thus it appears that changes in the troponin–troponin contacts that result from mutations or from forming hybrids stabilize a more active state of regulated actin. An analysis of the effect of the Δ14 mutation on the equilibrium binding of S1-ADP to actin was consistent with stabilization of an active state of actin. This change in activation may be important in the development of cardiac disease.
doi:10.1021/bi048646h
PMCID: PMC1351011  PMID: 15568820
3.  Expression of the troponin complex genes: transcriptional coactivation during myoblast differentiation and independent control in heart and skeletal muscles. 
Molecular and Cellular Biology  1988;8(10):4134-4142.
We compared the developmental regulation of the three troponin genes that encode the proteins of the Ca2+ regulatory complex in striated muscles of the Japanese quail. Nuclear run-on transcription and RNA protection analyses showed that the fast skeletal troponin I, the fast skeletal troponin T, and the slow skeletal-cardiac troponin C genes were transcriptionally coactivated and that transcripts rapidly accumulated within 6 to 12 h after the initiation of myoblast differentiation. The fast-isoform mRNAs of troponin I and troponin T were coexpressed at similar levels in different skeletal muscles, whereas the slow-cardiac troponin C mRNA varied independently and was the only one of these genes expressed in embryonic and adult heart. We conclude that these troponin genes are transcriptionally coactivated during skeletal myoblast differentiation, indicating that their transcription is under precise temporal control. However, this troponin C gene is regulated independently is specialized striated muscles.
Images
PMCID: PMC365482  PMID: 3185544
4.  Troponin utilization in patients presenting with atrial fibrillation/flutter to the emergency department: retrospective chart review 
Background
There are few recommendations about the use of cardiac markers in the investigation and management of atrial fibrillation/flutter. Currently, it is unknown how many patients with atrial fibrillation/flutter undergo troponin testing, and how positive troponin results are managed in the emergency department. We sought to look at the emergency department troponin utilization patterns.
Methods
We performed a retrospective chart review of patients with atrial fibrillation/flutter presenting to the emergency department at three centers. Outcome measures included the rates of troponins ordered by emergency doctors, number of positive troponins, and those with positive troponins treated as acute coronary syndrome (ACS) by consulting services.
Results
Four hundred fifty-one charts were reviewed. A total of 388 (86%) of the patients had troponins ordered, 13.7% had positive results, and 4.9% were treated for ACS.
Conclusions
Troponin tests are ordered in a high percentage of patients with atrial fibrillation/flutter presenting to emergency departments. Five percent of our total patient cohort was diagnosed as having acute coronary syndrome by consulting services.
doi:10.1186/1865-1380-4-25
PMCID: PMC3126697  PMID: 21651774
5.  Molecular Dynamics Simulations of the Cardiac Troponin Complex Performed with FRET Distances as Restraints 
PLoS ONE  2014;9(2):e87135.
Cardiac troponin (cTn) is the Ca2+-sensitive molecular switch that controls cardiac muscle activation and relaxation. However, the molecular detail of the switching mechanism and how the Ca2+ signal received at cardiac troponin C (cTnC) is communicated to cardiac troponin I (cTnI) are still elusive. To unravel the structural details of troponin switching, we performed ensemble Förster resonance energy transfer (FRET) measurements and molecular dynamic (MD) simulations of the cardiac troponin core domain complex. The distance distributions of forty five inter-residue pairs were obtained under Ca2+-free and saturating Ca2+ conditions from time-resolved FRET measurements. These distances were incorporated as restraints during the MD simulations of the cardiac troponin core domain. Compared to the Ca2+-saturated structure, the absence of regulatory Ca2+ perturbed the cTnC N-domain hydrophobic pocket which assumed a closed conformation. This event partially unfolded the cTnI regulatory region/switch. The absence of Ca2+, induced flexibility to the D/E linker and the cTnI inhibitory region, and rotated the cTnC N-domain with respect to rest of the troponin core domain. In the presence of saturating Ca2+ the above said phenomenon were absent. We postulate that the secondary structure perturbations experienced by the cTnI regulatory region held within the cTnC N-domain hydrophobic pocket, coupled with the rotation of the cTnC N-domain would control the cTnI mobile domain interaction with actin. Concomitantly the rotation of the cTnC N-domain and perturbation of the D/E linker rigidity would control the cTnI inhibitory region interaction with actin to effect muscle relaxation.
doi:10.1371/journal.pone.0087135
PMCID: PMC3928104  PMID: 24558365
6.  The utility of troponin measurement to detect myocardial infarction: review of the current findings 
Myocardial infarction (MI) is defined by the presence of myocardial necrosis in combination with clinical evidence of myocardial ischemia. Cardiac troponins are regulatory proteins within the myocardium that are released into the circulation when damage to the myocyte has occurred. Therefore, serum troponin is an exquisitely sensitive marker of myocardial injury and is necessary for establishing the diagnosis of MI. High-sensitivity troponin assays are improving the diagnostic accuracy and rapid detection of myocardial infarction. The early identification of MI is vital for the institution of anti-thrombotic therapy to limit myocardial damage and preserve cardiac function. Troponin has both diagnostic and prognostic significance in the setting of acute coronary syndrome (ACS). Increased troponin levels in the absence of ACS should prompt an evaluation for an alternative, non-thrombotic mechanism of troponin elevation and direct management at the underlying cause. This review describes the role of troponin in the evaluation of patients with suspected myocardial infarction.
PMCID: PMC2941782  PMID: 20859540
myocardial infarction; troponin; high-sensitivity assays
7.  The clinical significance of cardiac troponins in medical practice 
Troponins are regulatory proteins that form the cornerstone of muscle contraction. The amino acid sequences of cardiac troponins differentiate them from that of skeletal muscles, allowing for the development of monoclonal antibody-based assay of troponin I (TnI) and troponin T (TnT). Along with the patient history, physical examination and electrocardiography, the measurement of highly sensitive and specific cardiac troponin has supplanted the former gold standard biomarker (creatine kinase-MB) to detect myocardial damage and estimate the prognosis of patients with ischemic heart disease. The current guidelines for the diagnosis of non-ST segment elevation myocardial infarction are largely based on an elevated troponin level. The implementation of these new guidelines in clinical practice has led to a substantial increase in the frequency of myocardial infarction diagnosis.
Automated assays using cardiac-specific monoclonal antibodies to cardiac TnI and TnT are commercially available. They play a major role in the evaluation of myocardial injury and prediction of cardiovascular outcome in cardiac and non-cardiac causes.
In this review we discuss the clinical applications of cardiac troponins and the interpretation of elevated levels in the context of various clinical settings.
doi:10.1016/j.jsha.2010.10.001
PMCID: PMC3727460  PMID: 23960628
Cardiac troponin; Myocardial injury; Reinfarction; Perioperative infarction
8.  A model of calcium-activation of the cardiac thin filament 
Biochemistry  2011;50(34):7405-7413.
The cardiac thin filament regulates actomyosin interactions through calcium-dependent alterations in the dynamics of cardiac troponin and tropomyosin. Over the past several decades many details have been discovered regarding the structure and function of the cardiac thin filament and its components. We propose a dynamic, complete model of the thin filament that encompasses known structures of cardiac troponin, tropomyosin and actin and show that it is able to capture key experimental findings. By performing molecular dynamics simulations in two conditions, one with calcium bound and the other without calcium bound to site II of cardiac troponin C (cTnC), we found that subtle changes in structure and protein contacts within cardiac troponin resulted in sweeping changes throughout the complex that alter tropomyosin (Tm) dynamics and cardiac troponin-actin interactions. Significant calcium-dependent changes in dynamics occur throughout the cardiac troponin complex resulting from the combination of: secondary structural changes in the N-lobe of cTnC at and adjacent to sites I and II and the link between them; secondary structural changes of the cardiac troponin I (cTnI) switch peptide, the mobile domain, and in the vicinity of residue 25 of the N-terminus; secondary structural changes in the cardiac troponin T (cTnT) linker and Tm-binding regions; and small changes in cTnC-cTnI and cTnT-Tm contacts. As a result of these changes, we observe large changes in the dynamics of the following regions: the N-lobe of cTnC; the mobile domain of cTnI; the I-T arm; the cTnT linker; and overlapping Tm. Our model demonstrates a comprehensive mechanism for calcium-activation of the cardiac thin filament consistent with previous, independent experimental findings. This model provides a valuable tool for research into the normal physiology of cardiac myofilaments and a template for studying cardiac thin filament mutations that cause human cardiomyopathies.
doi:10.1021/bi200506k
PMCID: PMC3165030  PMID: 21797264
9.  Genomic Organization, Expression, and Analysis of the Troponin C Gene pat-10 of Caenorhabditis elegans 
The Journal of Cell Biology  1999;146(1):193-202.
We have cloned and characterized the troponin C gene, pat-10 of the nematode Caenorhabditis elegans. At the amino acid level nematode troponin C is most similar to troponin C of Drosophila (45% identity) and cardiac troponin C of vertebrates. Expression studies demonstrate that this troponin is expressed in body wall muscle throughout the life of the animal. Later, vulval muscles and anal muscles also express this troponin C isoform. The structural gene for this troponin is pat-10 and mutations in this gene lead to animals that arrest as twofold paralyzed embryos late in development. We have sequenced two of the mutations in pat-10 and both had identical two mutations in the gene; one changes D64 to N and the other changes W153 to a termination site. The missense alteration affects a calcium-binding site and eliminates calcium binding, whereas the second mutation eliminates binding to troponin I. These combined biochemical and in vivo studies of mutant animals demonstrate that this troponin is essential for proper muscle function during development.
PMCID: PMC2199735  PMID: 10402470
troponin C; Caenorhabditis elegans; troponin I; muscle gene; gene expression
10.  An In Silico Analysis of Troponin I Mutations in Hypertrophic Cardiomyopathy of Indian Origin 
PLoS ONE  2013;8(8):e70704.
Hypertrophic Cardiomyopathy (HCM) is an autosomal dominant disorder of the myocardium which is hypertrophied resulting in arrhythmias and heart failure leading to sudden cardiac death (SCD). Several sarcomeric proteins and modifier genes have been implicated in this disease. Troponin I, being a part of the Troponin complex (troponin I, troponin C, troponin T), is an important gene for sarcomeric function. Four mutations (1 novel) were identified in Indian HCM cases, namely, Pro82Ser, Arg98Gln, Arg141Gln and Arg162Gln in Troponin I protein, which are in functionally significant domains. In order to analyse the effect of the mutations on protein stability and protein-protein interactions within the Troponin complex, an in silico study was carried out. The freely available X-ray crystal structure (PDB ID: 1JIE) was used as the template to model the protein followed by loop generation and development of troponin complex for both the troponin I wild type and four mutants (NCBI ID: PRJNA194382). The structural study was carried out to determine the effect of mutation on the structural stability and protein-protein interactions between three subunits in the complex. These mutations, especially the arginine to glutamine substitutions were found to result in local perturbations within the troponin complex by creating/removing inter/intra molecular hydrogen bonds with troponin T and troponin C. This has led to a decrease in the protein stability and loss of important interactions between the three subunits. It could have a significant impact on the disease progression when coupled with allelic heterogeneity which was observed in the cases carrying these mutations. However, this can be further confirmed by functional studies on protein levels in the identified cases.
doi:10.1371/journal.pone.0070704
PMCID: PMC3742764  PMID: 23967088
11.  Basal and Ischemia-Induced Transcardiac Troponin Release into the Coronary Circulation in Patients with Suspected Coronary Artery Disease 
PLoS ONE  2013;8(4):e60163.
Background
Cardiac troponin is a specific biomarker for cardiomyocyte necrosis in acute coronary syndromes. Troponin release from the coronary circulation remains to be determined because of the lower sensitivity of the conventional assay. We sought to determine basal and angina-induced troponin release using a highly sensitive troponin assay.
Methods and Results
The cardiac troponin T levels in serum sampled from the peripheral vein (PV), the aortic root (AO), and the coronary sinus (CS) were measured in 105 consecutive stable patients with coronary risk factor(s) and suspected coronary artery disease (CAD) and in 33 patients without CAD who underwent an acetylcholine provocation test. At baseline, there was a significant increase in the troponin levels from AO [9.0 (6.4, 13.1) pg/mL for median (25th, 75th percentiles)] to CS [10.3 (7.3, 15.5) pg/mL, p<0.001] in 96 (91.4%) patients and the difference was 1.1 (0.4, 2.1) pg/mL, which reflected basal transcardiac troponin release (TTR). TTR was positively correlated with PV levels (r = 0.22, p = 0.03). Male sex, left ventricular hypertrophy determined by echocardiography, T-wave inversion, and CAD correlated with elevated TTR defined as above: median, 1.1 pg/mL. A significant increase in TTR was noted in 17 patients with coronary spasms [0.6 (0.2, 1.2) pg/mL, p<0.01] but not in 16 patients without spasms [0.0 (−0.5, 0.9) pg/mL, p = 0.73] after the acetylcholine provocation.
Conclusion
Basal TTR in the coronary circulation was observed in most of the patients with suspected CAD and risk factor(s). This sensitive assay detected myocardial ischemia-induced increases in TTR caused by coronary spasms.
doi:10.1371/journal.pone.0060163
PMCID: PMC3615044  PMID: 23565198
12.  Concentrations of cardiac troponin T in neonates with and without respiratory distress 
Aims: To establish a practical postnatal reference range for cardiac troponin T in neonates and to investigate concentrations in neonates with respiratory distress.
Methods: Prospective investigation in a tertiary neonatal unit, recruiting infants with and without respiratory distress (sick and healthy infants respectively). Concentrations of cardiac troponin T were compared between sick and healthy infants, accounting for confounding variables.
Results: A total of 162 neonates (113 healthy and 49 sick infants) had samples taken. The median (interquartile range) cardiac troponin T concentration in the healthy infants was 0.025 (0.01–0.062) ng/ml, and the 95th centile was 0.153 ng/ml. There were no significant relations between cardiac troponin T and various variables. The median (interquartile range) cardiac troponin T concentration in the sick infants was 0.159 (0.075–0.308) ng/ml. This was significantly higher (p < 0.0001) than in the healthy infants. In a linear regression model, the use of inotropes and oxygen requirement were significant associations independent of other basic and clinical variables in explaining the variation in cardiac troponin T concentrations.
Conclusions: Cardiac troponin T is detectable in the blood of many healthy neonates, but no relation with important basic and clinical variables was found. Sick infants have significantly higher concentrations than healthy infants. The variations in cardiac troponin T concentration were significantly associated with oxygen requirement or the use of inotropic support in a regression model. Cardiac troponin T may be a useful marker of neonatal and cardiorespiratory morbidity.
doi:10.1136/adc.2002.025478
PMCID: PMC1721706  PMID: 15210673
13.  Misleading Elevation of Troponin T caused by Polymyositis 
Background:
Elevations of cardiac enzymes are commonly used to indicate myocardial ischemia, but they can be elevated due to other conditions. Different forms of Troponin (cTnT, sTnT, cTnI), can cause cross-reactivity in the Troponin T assay, leading to false positives. This report describes a patient with polymyositis who had elevated Troponin T, but no cardiac abnormalities. The purpose is to show that Troponin T, which is believed to be solely from cardiac muscle breakdown, can be seen in inflammatory muscle disease, so Troponin I should be used instead.
Description:
This is a case report of a 70-year-old woman with a history of diabetes, hypertension, gout and polymyositis, who presented with one-day history of lightheadedness and abdominal pain. To rule out myocardial ischemia, cardiac enzyme testing was ordered which showed elevated CK, CK-MB, and Troponin T. A full cardiac workup was performed which showed no signs of ischemia. Troponin I was <0.05 ng/mL, (normal).
Discussion:
In inflammatory myositis, there are elevations in many cardiac markers due to non-cardiac causes, which could be related to muscle regeneration and gene expression. This is not seen certain isoforms of Troponin I, specifically cardiac Troponin I.
Conclusion:
In patients with history of diabetes and other comorbidities, silent myocardial ischemias should be ruled out. Non-cardiac elevations in Troponin T can be seen in patients with inflammatory, so Troponin I should be ordered to get an accurate interpretation. Patients with inflammatory myopathies can have elevations in CK, CK-MB, and Troponin T, but not Troponin I.
PMCID: PMC3708267  PMID: 23847461
false positive Troponin T; Polymyositis; Troponin T; Troponin I
14.  Calcium-Regulated Conformational Change in the COOH-Terminal End Segment of Troponin I and Its Binding to Tropomyosin 
The FEBS journal  2011;278(18):3348-3359.
Summary
The troponin complex plays an essential role in the thin filament regulation of striated muscle contraction. Of the three subunits of troponin, troponin I (TnI) is the actomyosin ATPase inhibitory subunit and its effect is released upon Ca2+-binding to troponin C. The exon 8-encoded COOH-terminal end segment represented by the last 24 amino acids of cardiac TnI is highly conserved and critical to the inhibitory function of troponin. Here we investigated the function and calcium regulation of the COOH-terminal end segment of TnI. A TnI model molecule was labeled with Alexa fluor 532 at a Cys engineered at the COOH-terminal end and used to reconstitute tertiary troponin complex. A Ca2+-regulated conformational change in the COOH terminus of TnI was shown by a sigmoid-shape fluorescence intensity titration curve similar to that of the circular dichroism calcium titration curve of troponin C. Such corresponding Ca2+-responses are consistent with the function of troponin as a coordinated molecular switch. Reconstituted troponin complex containing a mini-troponin T lacking its two tropomyosin-binding sites showed a saturable binding to tropomyosin at pCa 9 but not at pCa 4. This Ca2+-regulated binding was diminished when the COOH-terminal 19 amino acids of cardiac TnI were removed. These results provided novel evidence for suggesting that the COOH-terminal end segment of TnI participates in the Ca2+-regulation of muscle thin filament through an interaction with tropomyosin.
doi:10.1111/j.1742-4658.2011.08250.x
PMCID: PMC3168705  PMID: 21777381
Troponin I; COOH-terminus; Tropomyosin; Calcium
15.  Altered cardiac troponin T in vitro function in the presence of a mutation implicated in familial hypertrophic cardiomyopathy. 
Journal of Clinical Investigation  1996;97(12):2842-2848.
Familial hypertrophic cardiomyopathy (HCM) can be caused by dominant missense mutations in cardiac troponin T (TnT), alpha-tropomyosin, C-protein, or cardiac myosin heavy chain genes. The myosin mutations are known to impair function, but any functional consequences of the TnT mutations are unknown. This report describes the in vitro function of troponin containing an IIe91Asn mutation in rat cardiac TnT, corresponding to the HCM-causing Ile79Asn mutation in man. Mutant and wild-type TnT cDNAs were expressed in bacteria and the proteins purified and reconstituted with the other troponin subunits, the mutation had no effect on troponin's affinity for tropomyosin, troponin-induced binding of tropomyosin to actin, cooperative binding of myosin subfragment 1 to the thin filament, CA(2+)-sensitive regulation of thin filament-myosin subfragment 1 ATPase activity, or the CA2+ concentration dependence of this regulation. However, the mutation resulted in 50% faster thin filament movement over a surface coated with heavy meromyosin in in vitro motility assays. The increased sliding speed suggests an unexpected role for the amino terminal region of TnT in which this mutation occurs. The relationship between this faster motility and altered cardiac contraction in patients with HCM is discussed.
PMCID: PMC507378  PMID: 8675696
16.  Cardiac Troponin Mutations and Restrictive Cardiomyopathy 
Mutations in sarcomeric proteins have recently been established as heritable causes of Restrictive Cardiomyopathy (RCM). RCM is clinically characterized as a defect in cardiac diastolic function, such as, impaired ventricular relaxation, reduced diastolic volume and increased end-diastolic pressure. To date, mutations have been identified in the cardiac genes for desmin, α-actin, troponin I and troponin T. Functional studies in skinned muscle fibers reconstituted with troponin mutants have established phenotypes consistent with the clinical findings which include an increase in myofilament Ca2+ sensitivity and basal force. Moreover, when RCM mutants are incorporated into reconstituted myofilaments, the ability to inhibit the ATPase activity is reduced. A majority of the mutations cluster in specific regions of cardiac troponin and appear to be mutational “hot spots”. This paper highlights the functional and clinical characteristics of RCM linked mutations within the troponin complex.
doi:10.1155/2010/350706
PMCID: PMC2896668  PMID: 20617149
17.  Discontinuous thoracic venous cardiomyocytes and heart exhibit synchronized developmental switch of troponin isoforms 
The FEBS journal  2013;280(3):880-891.
Cardiomyocyte-like cells have been reported in thoracic veins of rodents and other mammals, but their differentiation state and relationship to the muscle mass in the heart remain to be characterized. Here we investigated the distribution, ultrastructure, and the expression and developmental regulation of myofilament proteins in mouse and rat pulmonary and azygos venous cardiomyocytes. Tracing cardiomyocytes in transgenic mouse tissues with a lacZ reporter gene driven by cloned rat cardiac troponin T promoter demonstrated scattered distribution of cardiomyocytes discontinuous from the atrial sleeves. The longitudinal axis of venous cardiomyocytes is perpendicular to that of the vessel. These cells contain typical sarcomere structures and intercalated discs as shown in electron microscopic images and express cardiac isoforms of troponin T, troponin I and myosin. The expression of troponin I isoform genes and the alternative splicing of cardiac troponin T in thoracic venous cardiomyocytes are regulated during postnatal development in a precise synchrony with that in the heart. Nonetheless, the patterns of cardiac troponin T splicing in adult rat thoracic venous cardiomyocytes are slightly but clearly distinct from those in the atrial and ventricular muscles. The data indicate that mouse and rat thoracic venous cardiomyocytes residing in extra-cardiac tissue possess a physiologically differentiated state and an intrinsically preset developmental clock, which are apparently independent of the very different hemodynamic environments and functional features of the vessels and heart.
doi:10.1111/febs.12076
PMCID: PMC3734956  PMID: 23176202
cardiac muscle; myofilament protein; troponin isoform switch; development
18.  The unique functions of cardiac troponin I in the control of cardiac muscle contraction and relaxation 
We review development of evidence and current perceptions of the multiple and significant functions of cardiac troponin I in regulation and modulation of cardiac function. Our emphasis is on the unique structure function relations of the cardiac isoform of troponin I, especially regions containing sites of phosphorylation. The data indicate that modifications of specific regions cardiac troponin I by phosphorylations either promote or reduce cardiac contractility. Thus, a homeostatic balance in these phosphorylations is an important aspect of control of cardiac function. A new concept is the idea that the homeostatic mechanisms may involve modifications of intra-molecular interactions in cardiac troponin I.
doi:10.1016/j.bbrc.2007.12.114
PMCID: PMC2365727  PMID: 18162178
Cardiac; Sarcomeres; Adrenergic stimulation; Mechanics; Kinases; Phosphatases
19.  Identification of Cardiac Troponin I Sequence Motifs Leading to Heart Failure by Inducing Myocardial Inflammation and Fibrosis 
Circulation  2008;118(20):2063-2072.
Background
Despite the widespread use of cardiac troponins for diagnosis of myocyte injury and risk stratification in acute cardiac disorders, little is known about the long term effects of the released troponins on cardiac function. Recently, we showed that an autoimmune response to cardiac troponin I induces severe inflammation and subsequent fibrosis in the myocardium. This autoimmune disorder predisposes in mice to heart failure and cardiac death.
Methods and Results
To investigate the role of cTnI-specific T-cells, T-cells were isolated from splenocytes of mice immunized with murine cardiac troponin I (mcTnI). WT mice receiving mcTnI-specific T-cells showed high mcTnI-specific antibody titers, increased production of pro-inflammatory cytokines IL-1β and TNF-α, severe inflammation and fibrosis in the myocardium, and reduced fractional shortening. To identify the antigenic determinants of troponin I responsible for the observed inflammation, fibrosis and heart failure, 16 overlapping 16-18mer peptides covering the entire amino acid sequence of mcTnI (211 residues) were synthesized. Only mice immunized with the residues 105-122 of mcTnI developed significant inflammation and fibrosis in the myocardium with increased expression of inflammatory chemokines RANTES, MCP-1, MIP-1α, MIP-1β, MIP-2, TCA-3, eotaxin and chemokine receptors CCR1, CCR2, CCR5. Mice immunized with the corresponding human cTnI residues 104-121 and the mcTnI residues 131-148 developed milder disease.
Conclusion
Transfer of troponin I-specific T-cells can induce inflammation and fibrosis in WT mice leading to deterioration of contractile function. Furthermore, two sequence motifs of cTnI that induce inflammation and fibrosis in the myocardium are characterized.
doi:10.1161/CIRCULATIONAHA.108.788711
PMCID: PMC2774217  PMID: 18955666
inflammation; heart failure; myocarditis; immunology
20.  Single Amino Acid Substitutions Define Isoform-Specific Effects of Troponin I on Myofilament Ca2+ and pH Sensitivity 
Troponin I isoforms play a key role in determining myofilament Ca2+ sensitivity in cardiac muscle. The goal here was to identify domain clusters and residues that confer troponin I isoform-specific myofilament Ca2+ and pH sensitivities of contraction. Key domains/residues that contribute to troponin I isoform-specific Ca2+ and pH sensitivity were studied using gene transfer of a slow skeletal troponin I (ssTnI) template, with targeted cardiac troponin I (cTnI) residue substitutions. Substitutions in ssTnI with cognate cTnI residues R125Q, H132A, and V134E, studied both independently and together (ssTnIQAE), resulted in efficient stoichiometric replacement of endogenous myofilament cTnI in adult cardiac myocytes. In permeabilized myocytes, the pCa50 of tension ([Ca2+] required for half maximal force), and the acidosis-induced rightward shiftof pCa50 were converted to the cTnI phenotype in myocytes expressing ssTnIQAE or ssTnIH132A, and there was no functionally additive effect of ssTnIQAE versus ssTnIH132A. Interestingly, only the acidosis-induced shift in Ca2+ sensitivity was comparable to cTnI in myocytes expressing ssTnIV134E, while ssTnIR125Q fully retained the ssTnI phenotype. An additional ssTnIN141H substitution, which lies within the same structural region of TnI as V134, produced a shift in myofilament Ca2+ sensitivity comparable to cTnI at physiological pH, while the acidic pH response was similar to the effect of wild-type ssTnI. Analysis of sarcomere shortening in intact adult cardiac myocytes was consistent with the force measurements. Targeted substitutions in the carboxyl portion of TnI produced residue-specific influences on myofilament Ca2+ and pH sensitivity of force and give new molecular insights into the TnI isoform-dependence of myofilament function.
doi:10.1016/j.yjmcc.2007.05.017
PMCID: PMC2043486  PMID: 17602701
troponin I; heart; myocyte; Ca2+ sensitivity; contractility
21.  Troponin T Isoforms and Posttranscriptional Modifications: Evolution, Regulation and Function 
Troponin-mediated Ca2+-regulation governs the actin-activated myosin motor function which powers striated (skeletal and cardiac) muscle contraction. This review focuses on the structure-function relationship of troponin T, one of the three protein subunits of the troponin complex. Molecular evolution, gene regulation, alternative RNA splicing, and posttranslational modifications of troponin T isoforms in skeletal and cardiac muscles are summarized with emphases on recent research progresses. The physiological and pathophysiological significances of the structural diversity and regulation of troponin T are discussed for impacts on striated muscle function and adaptation in health and diseases.
doi:10.1016/j.abb.2010.10.013
PMCID: PMC3018564  PMID: 20965144
troponin T isoform genes; molecular evolution; posttranscriptional modification; striated muscle thin filament; calcium regulation of contraction
22.  Elevated Cardiac Troponin (cTnI) Levels Correlate with the Clinical and Echocardiographic Evidences of Severe Myocarditis in Scorpion Sting Envenomation 
Objective
This study was to evaluate the predictive value of the cardiac troponins in scorpion sting myocarditis at a tertiary care hospital in Raichur, (Karnataka state) India.
Methods
A total of 84 consecutive patients were prospectively studied. The data included the demographics, the time of presentation to the hospital, the clinical features, the cardiac troponin levels and the echocardiographic findings.
Results
12 patients with only local symptoms had troponin levels of less than 0.01μg/L. 12 patients with local and systemic symptoms without an echocardiac evidence of myocarditis had troponin values of 0.01 to 0.11 μg/L. 60 patients with an echocardiographic evidence of myocarditis had troponin levels of above 0.11 μg/L. 6 patients with severe myocarditis who required ventilator support or which led to death had troponin values which were higher than 10 μg/L.
Conclusions
High cardiac troponin levels predict myocarditis in scorpion sting envenomation and they can be a useful tool in guiding the therapy early.
doi:10.7860/JCDR/2012/4760.2361
PMCID: PMC3471504  PMID: 23205349
Scorpion; Myocarditis; Envenomation; Echocardiography; Troponins
23.  Intraoperative cardiac troponin T release and lactate metabolism during coronary artery surgery: comparison of beating heart with conventional coronary artery surgery with cardiopulmonary bypass 
Heart  1999;81(5):495-500.
OBJECTIVE—To compare cardiac troponin T release and lactate metabolism in coronary sinus and arterial blood during uncomplicated coronary grafting on the beating heart with conventional coronary grafting using cardiopulmonary bypass.
DESIGN—A prospective observational study with simultaneous sampling of coronary sinus and arterial blood: before and 1, 4, 10, and 20 minutes after reperfusion for analysis of cardiac troponin T and lactate. Cardiac troponin T was also analysed in venous samples taken 3, 6, 24, 48, and 72 hours after surgery.
SETTING—Cardiac surgical unit in a tertiary referral centre.
PATIENTS—18 patients undergoing coronary grafting on the beating heart (10 single vessel and eight two-vessel grafting) and eight undergoing two-vessel grafting with cardiopulmonary bypass.
RESULTS—Cardiac troponin T was detected in coronary sinus blood in all patients by 20 minutes after beating heart coronary artery surgery before arterial concentrations were consistently increased. Peak arterial and coronary sinus cardiac troponin T values on the beating heart during single (0.03 (0 to 0.05) and 0.09 (0.07 to 0.16 µg/l, respectively) and two-vessel grafting (0.1 (0.07 to 0.11) and 0.19 (0.14 to 0.25) µg/l) were lower than the values obtained during cardiopulmonary bypass (0.64 (0.52 to 0.72) and 1.4 (0.9 to 2.0) µg/l) (p < 0.05). The area under the curve of venous cardiac troponin T over 72 hours for two-vessel grafting on the beating heart was less than with cardiopulmonary bypass (13 (10 to 16) v 68 (26 to 102) µg.h/l) (p < 0.001). Lactate extraction began within one minute of snare release during beating heart coronary surgery while lactate was still being produced 20 minutes after cross clamp release following cardiopulmonary bypass.
CONCLUSIONS—Lower intraoperative and serial venous cardiac troponin T concentrations suggest a lesser degree of myocyte injury during beating heart coronary artery surgery than during cardiopulmonary bypass. Oxidative metabolism also recovers more rapidly with beating heart coronary artery surgery than with conventional coronary grafting. Coronary sinus cardiac troponin T concentrations increased earlier and were greater than arterial concentrations during beating heart surgery, suggesting that this may be a more sensitive method of intraoperative assessment of myocardial injury.


Keywords: beating heart coronary artery surgery; troponin T; cardiopulmonary bypass; intraoperative assessment; myocardial injury
PMCID: PMC1729023  PMID: 10212167
24.  A new mutation of the cardiac troponin T gene causing familial hypertrophic cardiomyopathy without left ventricular hypertrophy 
Heart  1999;82(5):621-624.
AIM—To screen for a mutation of the cardiac troponin T gene in two families where there had been sudden deaths without an increase in left ventricular mass but with myocardial disarray suggesting hypertrophic cardiomyopathy.
METHODS—DNA from affected individuals from both families was used to screen the cardiac troponin T gene on an exon by exon basis. Mutation screening was achieved by polymerase chain reaction and direct sequencing. Where appropriate, a mutation was confirmed by restriction digest.
RESULTS—A novel missense mutation of exon 9 was found in the affected individuals of one of the families. This mutation at amino acid 94 resulted in the substitution of arginine for leucine and was not found in 100 normal control samples. A mutation of the cardiac troponin T gene was excluded in the second family.
CONCLUSIONS—A mutation of the gene for the sarcomeric protein cardiac troponin T can cause familial hypertrophic cardiomyopathy with marked myocyte disarray and frequent premature sudden death in the absence of myocardial hypertrophy at clinical or macroscopic level.


Keywords: hypertrophic cardiomyopathy; troponin T
PMCID: PMC1760789  PMID: 10525521
25.  Determinants and prognostic implications of Cardiac Troponin T measured by a sensitive assay in Type 2 Diabetes Mellitus 
Background
The cardiac troponins are biomarkers used for diagnosis of myocardial injury. They are also powerful prognostic markers in many diseases and settings. Recently introduced high-sensitivity assays indicate that chronic cardiac troponin elevations are common in response to cardiovascular (CV) morbidity. Type 2 diabetes mellitus (T2DM) confers a high risk of CV disease, but little is known about chronic cardiac troponin elevations in diabetic subjects. Accordingly, we aimed to understand the prevalence, determinants, and prognostic implications of cardiac troponin T (cTnT) elevations measured with a high-sensitivity assay in patients with T2DM.
Methods
cTnT was measured in stored, frozen serum samples from 124 subjects enrolled in the Asker and Bærum Cardiovascular Diabetes trial at baseline and at 2-year follow-up, if availabe (96 samples available). Results were analyzed in relation to baseline variables, hospitalizations, and group assignment (multifactorial intensive versus conventional diabetes care for lowering CV risk).
Results
One-hundred thirteen (90 %) had detectable cTnT at baseline and of those, 22 (18 % of the total population) subjects had values above the 99th percentile for healthy controls (13.5 ng/L). Levels at baseline were associated with conventional CV risk factors (age, renal function, gender). There was a strong correlation between cTnT levels at the two time-points (r = 0.92, p > 0.001). Risk for hospitalizations during follow-up increased step-wise by quartiles of hscTnT measured at baseline (p = 0.058).
Conclusions
Elevations of cTnT above the 99th percentile measured by a highly sensitive assay were encountered frequently in a population of T2DM patients. cTnT levels appeared to be stable over time and associated with conventional CV risk factors. Although a clear trend was present, no statistically robust associations with adverse outcomes could be found.
doi:10.1186/1475-2840-9-52
PMCID: PMC2946276  PMID: 20843304

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