Christian Park
BME PhD Defense Presentation

Date: 2026-09-23
Time: 10:00 am-12:00 pm
Location / Meeting Link: HSRB I Rollins Auditorium W106; Join Zoom Meeting https://zoom.us/j/95365227692?pwd=i7CIxwzmd8g7K0pfLEFA3b91sUdlMv.1     Meeting ID: 953 6522 7692 Passcode: 467552     +14702509358 US (Atlanta) +14703812552 US (Atlanta)

Committee Members:
Dr. Hanjoong Jo (Advisor); Dr. W. Robert Taylor; Dr. Saurabh Sinha; Dr. James E. Dahlman; Dr. Gregory C. Gibson


Title: Flow-Induced Reprogramming of Endothelial Cells under Disturbed Flow and Hypercholesterolemia during Atherogenesis

Abstract:
Atherosclerosis occurs preferentially in arterial regions exposed to disturbed blood flow (d-flow), while regions exposed to stable flow (s-flow) remain atheroprotected even under hypercholesterolemia. Plaque development, however, requires both d-flow and hypercholesterolemia, and the mechanism underlying this interaction has remained unclear. This dissertation tests and defines the two-hit hypothesis that d-flow alone initiates a partial flow-induced reprogramming of endothelial cells (partial FIRE) and that the addition of hypercholesterolemia is the fuel required to drive it to complete FIRE. Single-cell RNA sequencing of arterial cells from mice subjected to d-flow alone, hypercholesterolemia alone, or their combination revealed that d-flow alone induced endothelial inflammation and endothelial-to-mesenchymal transition (EndMT) with only partial endothelial-to-immune-cell transition (partial EndIT), while hypercholesterolemia alone had minimal effect. In contrast, d-flow in the presence of hypercholesterolemia induced full EndIT along with a novel endothelial-to-foam-cell transition (EndFT). These findings were validated at the protein level by lineage tracing in endothelial cell (EC)-specific confetti mice, in which genetically labeled ECs co-expressed markers of inflammation, EndMT, EndIT, and EndFT in response to d-flow under hypercholesterolemia during atherogenesis. FIRE was further supported by reanalysis of human atherosclerotic plaque scRNA-seq datasets and by immunostaining of human coronary arteries. An in vitro FIRE platform, in which primary human aortic ECs (HAECs) are exposed to oscillatory shear stress (OSS) mimicking d-flow, the cholesterol metabolite 27-hydroxycholesterol, and a proinflammatory cytokine cocktail (IFN-γ, IL-1β, TNF-α, TGF-β1/2), recapitulated FIRE in vitro, including the novel EndIT and EndFT, at the transcript, protein, and functional levels. To identify which of the 1,291 FIRE-sensitive genes identified from the mouse scRNA-seq study drives FIRE, two independent yet complementary screens were performed. A CRISPRi-Perturb-seq screen targeting all 1,291 genes yielded 444,360 single ECs carrying a single unique guide across four flow conditions, including unidirectional laminar shear stress (ULS) mimicking s-flow, static, OSS, and FIRE, and an independent drug screening study using the FIRE platform identified 35 potential anti-FIRE inhibitors. The two independent gene-based Perturb-seq and drug-based anti-FIRE screening studies converged on a candidate FIRE driver pathway and its associated genes, and the leading FIRE inhibitor showed reduction of atherosclerotic plaque in vivo in mice. Together, these findings demonstrate that ECs are highly plastic and can transition to immune-like and foam-like cells in response to d-flow under hypercholesterolemia, and identify FIRE as a potential therapeutic target in atherosclerosis.