Mortality from myocardial infarction is decreasing; however, survivors are at high risk of developing ischemic cardiomyopathy (ICM). Understanding the mechanisms involved in that transition may help develop methods to prevent it. Ischemic damage produces a form of dyssynchronous contraction that cannot be treated with conventional therapies (Cardiac Resynchronization Therapy, CRT). However, the Principal Investigator previously discovered a critical molecular mechanism of CRT: it reactivates glycogen synthase kinase 3? (GSK-3?) and thus restores myofilament function. This proposal will leverage the molecular mechanism discovered in CRT in a patient population that cannot respond to it, ICM patients. Preliminary data reveals that human and mouse ICM samples exhibit myofilament calcium desensitization, and exogenous treatment with GSK-3? restores calcium sensitivity, suggesting the functional defect is linked to deactivation of GSK-3?. Further, new preliminary data has identified an independently regulated pool of GSK-3? localized to the myofilament that decreases significantly in human ICM, which correlates with the decrease in calcium sensitivity. Importantly, additional preliminary data suggest the localization of GSK-3? to the myofilament is mediated by phosphorylation of GSK-3? at tyrosine 216. This could allow targeted modulation of the myofilament pool of GSK-3? as a therapeutic strategy to improve myofilament function. Thus, based on these new preliminary data, this proposal addresses the central hypothesis that ischemia de-activates a myofilament pool of GSK-3? via altering tyrosine 216 (Y216) phosphorylation, decreasing phosphorylation of its myofilament targets and depressing myofilament function. There are three specific aims.
Aim 1 will address the hypothesis that ICM decreases myofilament function in a GSK-3? dependent manner. Genetic mouse models that alter GSK-3? activity will be subjected to surgical induction of myocardial infarction to generate ICM and then myofilament function and GSK-3? activity will assayed. Human tissue from ICM patients will be studied similarly.
Aim 2 will address the the hypothesis that phosphorylation at Y216 on GSK-3? modulates its binding to the myofilament and ICM decreases the amount and activity of GSK- 3? at the myofilament. Mutant forms of GSK-3? where the Y216 site is unphosphorylatable or mimic constitutive phosphorylation will be expressed in cardiac myocytes to determine where and how GSK-3? binds to the myofilament. Myofilament function will also be assessed to determine whether these mutant forms of GSK-3? can restore function in the GSK-3? knock-out mouse. The last aim will address the hypothesis that GSK-3? can normalize the myofilament phospho-proteome in ICM patients and ICM mouse tissue using state of the art mass spectrometry approaches. The long-term objective of this project is to identify the mechanisms by which GSK-3? affects myofilament function in the ICM heart, with the goal of discovering a therapeutic approach to prevent the transition to ischemic cardiomyopathy after a myocardial infarction.
Mortality from myocardial infarction (heart attack) is decreasing; however, survivors are at high risk of developing ischemic cardiomyopathy (ICM). We have discovered the protein glycogen synthase kinase 3? (GSK-3?) binds to the structure inside heart cells that generates force, the myofilament, but this interaction decreases in ICM and the myofilament becomes weaker. This proposal will investigate the mechanisms by which these effects occur to identify a therapeutic target to prevent the deterioration to heart failure after a myocardial infarction.
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| Papadaki, Maria; Holewinski, Ronald J; Previs, Samantha Beck et al. (2018) Diabetes with heart failure increases methylglyoxal modifications in the sarcomere, which inhibit function. JCI Insight 3: |
