Microphysiological Systems to Study Hypoxic Cardiac Injury

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Project Summary/Abstract Following the onset of an acute myocardial infarction (MI) with coronary artery occlusion, the restricted blood supply limits oxygenation of the myocardium, resulting in the formation of a steep oxygen (O2) gradient from normoxic, viable tissue to hypoxic, damaged tissue. A site of regional dysfunction exists at the interface between the normoxic and hypoxic tissue, known as the border zone. Reperfusion restores the flow of blood and O2 to the tissue, but also induces ischemia reperfusion injury (IRI), a pathophysiology resulting in further tissue damage. The pathological processes underlying these hypoxic cardiac injuries are not definitively established, in part due to a lack of experimental tools to recapitulate the diverse spatiotemporal O2 gradients characteristic of MI and IRI. The goal of this proposal is to engineer microphysiological systems with tight O2 control to investigate the molecular pathways activated in O2 gradients, and the resulting effects on cardiomyocyte (CM) function, to obtain a comprehensive view of the cardiac response to hypoxic injury. The aims outlined in this proposal will build on the expertise of Dr. Rexius in controlling O2 levels using microfluidics and integrate Heart- on-a-Chip technologies to advance the functional and mechanistic understanding of hypoxic cardiac injury. In the mentored phase, Dr. Rexius will use engineering and pharmacological approaches to control paracrine interactions in an MI border zone microdevice model and determine the role of paracrine-mediated hypoxic- normoxic intercellular communication in defining the spatial metabolic heterogeneity across an O2 gradient (Aim 1). Proteomic and miRNA analysis will be used to identify and validate transfer of exosome cargo as a paracrine mechanism altering CM metabolism. The existing O2 control framework will be utilized to engineer a microphysiological system to model IRI and multiplex measurements of traction force, sarcomere shortening, and calcium transients, and their dependence on O2 tension, to monitor dysfunction with live imaging (Aim 2). In the independent phase, modified versions of these systems will examine the effect of O2 reperfusion rate on CM function and the regulation of autophagy, a process by which cellular material is degraded and recycled (Aim 3). The project and mentorship plan will allow Dr. Rexius to develop skills in (1) non-invasive optical measurements of metabolic parameters, (2) bioinformatics analysis of exosome proteomic and miRNA datasets, (3) traction force microscopy, and (4) communication, mentoring, and laboratory management to prepare to lead an independent research program in academia. Dr. Rexius will be co-mentored by Dr. Megan McCain at the University of Southern California (USC) and Dr. Ching-Ling (Ellen) Lien at the Keck School of Medicine of USC and Children’s Hospital Los Angeles. Dr. Rexius has also enlisted Dr. Keyue Shen (USC) and Dr. Jennifer Van Eyk (Cedars-Sinai) as advisors to support her scientific and professional development. Completion of the aims will reveal novel insights into CM responses in heterogeneous O2 landscapes.