Abstract 15554: Heart Failure-Related Hyperphosphorylation of Ser199 on Cardiac Troponin I Causes Divergent Effects on Cardiac Function at Baseline and During Ischemia-Reperfusion
Background: Phosphorylation of cardiac troponin I (cTnI) on Ser199 is significantly increased in human heart failure (HF), however its cardiac impact in vivo remains unknown. In addition, selective proteolysis of cTnI is a marker of myocardial injury and contributes to cardiac dysfunction in ischemia/reperfusion (I/R), and Ser199 phosphorylation affects cTnI proteolysis in vitro, thus whether Ser199 phosphorylation affects cardiac performance during I/R is of great interest.
Methods and Results: We generated transgenic mice (TgS200D) carrying cTnI S200D mutation to mimic the site-specific hyperphosphorylation of murine Ser200 (equivalent to human Ser199). Cardiac function was first assessed in vivo using echocardiography. TgS200D mice demonstrated unaltered ejection fraction (EF), significantly prolonged isovolumic relaxation time, and normal left ventricular (LV) chamber size and wall thickness (n=10). LV pressure-volume studies showed preserved dp/dtmax, significantly decreased -dp/dtmin and increased relaxation time constant in TgS200D when compared to non-transgenic (NTg) control group at baseline (n=10). With increasing heart rates, the two groups showed similar enhancement in both systolic and diastolic function, suggesting the positive force-frequency relation is preserved in TgS200D (n=5). After isoproterenol injection (i.v. 40ng/min/kg), although a comparable increase in dp/dtmax was observed in both groups, there was no enhancement of -dp/dtmin in TgS200D in contrast to 15% of increase in NTg (n=5, p=0.019). After ischemia (30 min)/reperfusion (60 min), LV developed pressure was recovered by ~90% in isolated TgS200D hearts but only ~40% in NTg (n=5, p=0.003). Immunoblotting detected cTnI cleavage only in NTg hearts.
Conclusions: Our results indicate that hyperphosphorylation of cTnI Ser199 1) impairs basal diastolic function but preserves systolic function, without LV hypertrophy or dilation; 2) blunts cardiac lusitropic response to β-adrenergic stimulation with isoproterenol; 3) protects heart against I/R injury, likely via preventing cTnI degradation. We propose a dual role of cTnI Ser199 hyperphosphorylaiton: contributing to HF with preserved EF but protecting heart during I/R.
- diastiolic function
- myofilament protein
- post-translational modification
- heart failure
Author Disclosures: Y. Li: None. G. Zhu: None. C. Takahashi: None. D. Bedja: None. G. Ramirez-Correa: None. N. Paolocci: None. D.A. Kass: None. A.M. Murphy: None.
- © 2015 by American Heart Association, Inc.