Modulating the Integrated Stress Response Pathway to Treat Contractile Dysfunction

The integrated stress response (ISR) is an evolutionarily conserved signaling pathway used by eukaryotic cells to maintain cellular homeostasis in response to stress (e.g., accumulation of misfolded proteins, mitochondrial dysfunction, amino acid deprivation, viral infection). Activation of the ISR leads to the autophosphorylation of four stress-sensor kinases that phosphorylates eukaryotic translation initiation factor 2 alpha (elF2α), leading to the inhibition of global protein synthesis while paradoxically increasing the translation of stress-response genes. Dysregulation of the ISR has been described in various diseases, including cancer, neurodegenerative disorders, metabolic disease, and aging. However, it is unclear how the ISR is altered in cardiac diseases. My preliminary data suggest that the ISR is activated in a heart cell model with reduced contractile function. Contrarily, the ISR is inhibited in a similar cell model harboring a mutation associated with increased contractile function from initial gene and protein analysis. Thus, there seems to be a correlation between the ISR activation state and the contractile function of CMs. My goal is to understand how modulation of the ISR alters contractile function in heart cells and determine if pharmacological activation or inhibition of the ISR can rescue function in two cardiac disease models. To test the hypothesis that direct modulation of the ISR alters the contractile function of heart cells (cardiomyocytes), I will utilize single-cell human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CMs) models. I will first treat cells with two well-established pharmacological agents that can activate (increase the phosphorylation of elF2α) or inhibit (reduce elF2α phosphorylation) the ISR pathway. I will assess changes to the contractile function of hiPSC-CMs with live-cell imaging techniques that enable me to quantitatively determine the amount of contractile force generated by these cells. To determine if the direct modulation of the ISR can serve as a therapeutic target for treating cardiac dysfunction, I will utilize two contractile dysfunction models. The first is a hiPSC-CM cardiotoxicity model that demonstrates a reduction in contractile force when exposed to the cancer drug doxorubicin. The second is an hiPSC-CM model with a protein mutation associated with higher contractile force, ultimately leading to contractile dysfunction. I will treat these cells with the ISR modulators to determine if pharmacological regulation of the ISR can rescue contractile function. Application to biomedical research and potential impact. The ability of the heart to pump blood is directly proportional to the ability of individual heart cells to contract and produce force. A reduction or constant increase in the contractile force of these cells can lead to heart failure (HF), a clinical syndrome that costs our healthcare system ~30 billion annually. Currently, there is no cure for HF. Thus, there is a great need for biomedical research exploring molecular mechanisms and therapeutic interventions. The findings of my study will 1) provide insight into the molecular mechanisms that regulate contractile force and 2) demonstrate whether pharmacological modulation of the ISR can serve as a therapeutic target to rescue contractile function in patients suffering from HF.