HAX-1 Fragment Improves Cardiomyocyte Survival Upon ER and Oxidative Stresses

• Somin Park, Biomedical Engineering, University of Delaware

• Chi Keung Lam, Department of Biological Sciences, University of Delaware

The endoplasmic reticulum (ER) is an essential organelle that regulates cell survival and apoptosis by detecting disturbances in protein folding. When misfolded and unfolded proteins accumulate in the ER lumen, the ER is put under stress, activating the Unfolded Protein Response (UPR) to handle the cellular dysfunction and apoptosis. Managing ER stress in cardiomyocytes is especially crucial since heightened ER stress leads to increased risk of cardiac dysfunction and disease¹. Furthermore, ER stress and oxidative stress are interconnected, as the production of reactive oxygen species (ROS) may disrupt ER homeostasis², and an increased production of ROS alters the pH and creates further disorder in the ER. To better regulate the UPR, heat shock protein 90 (HSP90), a cytosolic chaperone protein, helps stabilize and regulate the activity of inositol-requiring enzyme type 1 (IRE1)—a key sensor in the UPR that promotes cell survival by restoring ER homeostasis. HSP90, however, also interacts with hematopoietic lineage substrate-1-associated protein X-1 (HAX-1), which competes with its binding to IRE1. Previous studies linked increased HAX-1/HSP90 interactions to decreased HSP90/IRE1 interactions, resulting in reduced cardiomyocyte survival under stress¹. Thus, we investigated the minimum binding domain of HSP90 and HAX-1 to increase the binding of IRE1 to HSP90 instead. Using the minimum binding domain, we designed HAX-1 peptides and found the minimum binding domain to be amino acids 203-245. Our lab has shown that treating cells with the minimum binding domain fragment demonstrates greater viability under Brefeldin A-induced ER stress and H2O2-induced oxidative stress, potentially due to increased HSP90/IRE1 interactions, leading to an enhanced IRE1-mediated cardioprotective ER stress response. By redirecting HSP90 toward pro-survival interactions with IRE1, HAX-1 fragment could serve as a promising therapeutic strategy to enhance cardiomyocyte viability under ER and oxidative stresses, reducing the risk of cardiac diseases.