Date of Award

Spring 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (Biomedical Science)

Department

Biomedical Sciences

First Committee Advisor

Calvin Vary

Second Committee Member

Douglas Sawyer

Third Committee Member

Gregory Cox

Additional Committee Members

Christine Lary

Katherine Motyl

Abstract

Myocardial infarction (MI) is one of the leading causes of heart failure (HF). To date, no treatments are available that effectively reverse HF following MI, which can result in irreversible cell damage and decreased heart function. Recently, studies have shown that the stem/progenitor cell secretome is a significant contributor to myocardial angiogenesis and functional recovery following MI. However, the molecular mechanisms by which the secretome contributes to repair remain largely unknown. Activin receptor-like kinase-1 (ALK1)/bone morphogenetic protein-9/10 (BMP9/10) signaling plays an important role in vascular repair pathways including cell differentiation, proliferation, and angiogenesis. Due to the prominent role of BMP9/ALK1 signaling in vascular development and homeostasis, we hypothesized that BMP9/ALK1 signaling is required for cardiac progenitor cell secretome-mediated angiogenesis.

Our lab has isolated mesenchymal cells with progenitor capabilities from the left ventricular epicardium of patients undergoing coronary artery bypass graft (CABG) surgery, which we have termed ‘human highly proliferative progenitor cells’ (hHiPCs). We have shown that hHiPCs can differentiate toward endothelial cells (ECs) and harbor intrinsic progenitor-like properties of the cardiac niche, making them an interesting and potential novel therapeutic target. Our data provide a comprehensive and novel molecular characterization of hHiPCs and identify hHiPCs as a potential therapeutically beneficial cell population following MI treatment in mice. Using unbiased proteomic analysis, we identified BMP9/ALK1 signaling as a mediator of angiogenesis in hHiPC that regulates many downstream secreted proteins, including SOST, ISLR, and IGFBP3. We utilized shRNA, Fc-ligand trapping, and small molecule inhibitor approaches to validate these downstream targets in vitro. The secretome (i.e., conditioned media) isolated from BMP9 treated hHiPCs improved angiogenesis in the tube formation assay in hHiPCs and primary retinal endothelial cells. We utilized recombinant protein stimulation of hHiPCs and identified SOST and ISLR as potential regulators of endothelial cell morphogenesis in vitro. Together, these data support therapeutic benefit of hHiPCs and provide novel molecular pathways involved in the pro-angiogenic secretome of patient-derived cells. Understanding these myocardial cell responses in the context of the cell secretome offers new avenues for investigating these proteins in both basic myocardial biology and for the potential treatment of HF.

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