Project Summary Myocardial infarction (MI) is a major cause of death and disability worldwide, affecting ~800,000 Americans annually. Optimal healing of the damaged tissue requires the delicate balance, both spatially and temporally, of inflammatory and reparative mechanisms to create the fibrotic scar. Cardiac fibroblasts (CFs) are the main contributor to fibrotic remodeling. Following ischemic injury, CFs transition into an activated phenotype that is characterized by increased proliferation, migration to the infarct region, and secretion of fibrotic proteins and paracrine signals. At the same time, dysregulation of the CF response to injury can promote pathological fibrosis, increased risk for arrhythmia, and cardiac dysfunction. While there has been many studies exploring the diverse signaling cascades and stressors that cause CF activation, how these stressors regulate the CF phenotype and paracrine signal generation, both spatially and temporally, remain elusive. Recent work identified stress-induced loss of the cytoskeletal protein, βIV-spectrin, to be an important step in CF activation and fibrosis3. Further, loss of βIV-spectrin was found to depend on Ca2+/ calmodulin-dependent protein kinase II (CaMKII). A broader role has been identified for βIV-spectrin/CaMKII in regulating CF gene expression through an interaction with signal transducer and activation of transcription 3 (STAT3)3,4, a signaling molecule and transcription factor that promotes profibrotic mechanisms. Specifically, CaMKII is activated and promotes loss of βIV-spectrin and redistribution of STAT3 to the nucleus that lead to changes in gene expression. Together, this leads to the hypothesis that the βIV-spectrin/STAT3 complex acts as a signaling node that is necessary for regulating cardiac fibroblast activation, recruitment, and scar formation post MI. To evaluate this hypothesis, Aim 1 will identify the role of the βIV-spectrin/STAT3 complex in CF activation and long-range communication. CFs will be subjected to both biomechanical stretch and neurohormonal stimuli, correlating to MI pathophysiology, to evaluate the effects on CF activation and exosome secretion. To understand how remote CFs migrate to the infarct area, long-range communication signals from spectrin-deficient CFs will be characterized and cultured with fresh CFs to see if they lead to activation. Additionally, this project will offer mechanistic insight into the spatiotemporal regulatory role of spectrin-based proteins in modulating exosome secretion following chronic stress. Lastly, Aim 2 will subject spectrin-preserved and spectrin-deficient mice to MI and evaluate the effects on scar formation and maturation. These studies will offer insight into how specific stress combinations tune the process of fibrotic remodeling following MI, and how these regulatory proteins can affect the overall outcome of MI patients.