Date of Award

Summer 6-6-2025

Embargo Period

6-20-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Medicine

Additional Department

Cell and Molecular Biology and Pathobiology

College

College of Graduate Studies

First Advisor

Amy Bradshaw

Abstract

Heart Failure (HF) is a complex clinical syndrome that is defined by an inability of the heart to meet the oxygen demands of the body. Myocardial interstitial fibrosis (MIF), the diffuse overaccumulation of extracellular matrix (ECM) proteins within the cardiac interstitium, contributes to ventricular dysfunction in HF. Mechanical devices designed to alleviate left ventricular deficiencies, termed left ventricular assist devices (LVADs), provide a pump that delivers oxygenated blood to the aorta thereby decreasing hemodynamic load on the ventricle. This end-stage HF therapy alleviates symptomatic burden for HF patients, however, LVAD support does not reduce MIF in the LV, and myocardial recovery is infrequent for patients on LVAD therapy. Currently, no direct antifibrotic therapies for HF are available representing a critically unmet clinical need. To elucidate molecular mechanisms that contribute to persistent MIF in HF myocardium both prior to LVAD implantation (pre-LVAD) or after unloading with an LVAD (post-LVAD, from heart transplant patients), we sought to characterize both ECM and fibroblast phenotype in pre- and post-LVAD myocardium in comparison to control myocardium. Tissue sections from control (no HF), pre-LVAD, and post-LVAD patients were assessed for myocardial fibrillar collagen and basement membrane content that revealed significant increases in both fibrillar ECM and the basement membrane in pre-LVAD versus control myocardium that were sustained in post-LVAD tissues. Increases in ECM contribute to significant increases in tissue stiffness in pre- and post-LVAD samples. Myocardial fibroblast populations were also found to be significantly elevated in pre- and post-LVAD hearts versus control. To determine whether fibroblast phenotype was altered in HF, primary cultures were isolated from each condition and plated on low (2kPa) and high (8kPa) stiffness substrates to mimic physiological myocardial conditions. Whereas control cells were found to respond to changes in substrate stiffness, fibroblasts from pre- and post-LVAD hearts did not suggest a persistently activated phenotype that was non-responsive to changes in environmental stiffness. Bulk RNA and single-cell RNA sequencing analysis revealed uncoupled mechano-sensory molecular pathways that might contribute to sustained ECM production in HF hearts. In conclusion, these results were consistent with the hypothesis that persistent activation of cardiac fibroblasts in pre- and post-LVAD myocardium maintain ECM content in the myocardium despite changes in hemodynamic load. Which contributes to on-going MIF-dependent myocardial stiffness, resulting from uncoupled mechano-sensory pathways, and the refractory nature of recovery for patients on LVAD therapy.

Rights

Copyright is held by the author. All rights reserved.

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