Abstract

Following cardiovascular injury, neonatal mammalian hearts are capable of restoring damaged tissue while adult hearts cannot. Adults are hindered by their inability to replenish lost cardiomyocytes resulting in increased scar tissue formation and reduced cardiovascular function. The Hippo pathway and its downstream effector Yap1 have recently been identified as key modulators of cardiac development and regeneration in neonates. We investigated the role of Yap1 in a sheep model of cell-based cardiovascular repair in which regenerative neonatal cardiovascular progenitor cells (CPCs) were introduced following LAD ligation. Yap1 was induced in the infarcted regions of the heart following cell treatment, as shown by PCR and Western Blot analysis. MicroRNA-199a which positively regulates Yap1 expression was also induced in the cardiovascular repair zone of neonatal CPC-treated, infarcted sheep. Given the regenerative nature of neonatal progenitors, we evaluated differences in Yap1 expression between adult and neonatal CPCs. Yap1 transcripts were significantly downregulated in adults compared to neonates highlighting a decline of Yap1 expression with age. In order to identify methods of reintroducing Yap1 expression in adults, we treated adult CPCs with 17-AAG which prevents the phosphorylation/inhibition of Yap1. We observed elevated Yap1 expression and reduced phosphorylation after 72 hours of treatment along with an induction of other downstream targets. Supporting miRNAs related to cell proliferation and repair were also stimulated by 17-AAG. The regulatory role of the Hippo pathway in cardiovascular repair was found to be modifiable upon treatment with this FDA approved drug. We next examined the impact of microgravity on Yap1 expression in adult CPCs. Short-term exposure to microgravity on the International Space Station (ISS) induces transcriptomic changes in adult CPCs that are consistent with enhanced stemness and activation of the cell cycle. Among these changes, we observed elevated expression of Yap1, SOD2, and other downstream markers of the Hippo pathway. Simulated microgravity exposure on Earth yielded similar results in a shorter timeframe. Our findings support the feasibility of inducing Yap1 expression in CPCs derived from older adults and raise the possibility that conditioning adult progenitors prior to cell-based repair may improve outcomes of stem cell-based treatments outside of the neonatal window.

LLU Discipline

Physiology

Department

Physiology

School

School of Medicine

First Advisor

Mary Kearns-Jonker

Second Advisor

Arlin B. Blood

Third Advisor

Johnny Figueroa

Fourth Advisor

Sean Wilson

Fifth Advisor

Abba Zubair

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

2021

Date (Title Page)

6-2021

Language

English

Library of Congress/MESH Subject Headings

Myocardial Infarction; Hippo Signaling Pathway; Microgravity; Cardiovascular Progenitor Cells; Regenerative Medicine

Type

Dissertation

Page Count

xvii, 131 p.

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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