Year of Publication

2021

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Biology

First Advisor

Dr. Ashley W. Seifert

Abstract

Mammalian system consists of stress-sensing molecules that regulates their cellular response against damage, injury and oncogenic stress. During vertebrate regeneration, cells responding to injury re-enter the cell cycle and proliferate to form new tissue. Cell cycle re-entry or arrest is at least partly regulated by cellular senescence which negatively impacts the proliferative pool of cells during regeneration. What remains unclear is whether cells in regenerating systems possess an increased propensity to proliferate and are refractory to signals that induce senescence. My thesis work has focused on how fibroblasts from the ear pinna differentially regulate healing in highly regenerative mammals (e.g., Acomys and Oryctolagus) and mammals that heal by scarring (e.g., Mus and Rattus). Fibroblasts are important because they tend to proliferate and migrate to heal injured tissue. Hydrogen peroxide (H2O2) exposure significantly decreased cell proliferation and activated senescent pathways in cells from mice and rats whereas cells from spiny mice and rabbits were highly resistant to this H2O2 exposure. We found increased intracellular H2O2 was detoxified more efficiently in cells from regenerating specie by higher GPx activity and this in turn helped to maintain mitochondrial stability. Importantly, pretreatment with N-acetylcysteine (NAC) protected Mus and Rattus cells from ROS-induced cellular senescence. Collectively, our research shows that intrinsic cellular differences in stress-sensing mechanisms partially explain inter-specific variation in regenerative ability. My first manuscript summarizing first part of my dissertation research was published in one of the top biology journals, Nature Communications in 2019.

In the second part of my thesis, we tested how injury-induced oxidative stress (ROS) regulates cell proliferation during regeneration of the ear pinna in spiny mice compared to scarring in lab mice. It was previously shown that ROS is required for regeneration in two different vertebrate regeneration models (zebrafish and Xenopus). However, it remains unknown whether this type of ROS generation is required for regeneration in Acomys and if so, how this signaling regulates the regeneration response. Our data suggested that initial ROS burst act as a signaling center to help in cell proliferation during regeneration in Acomys whereas the imbalanced ROS burst leads to cell cycle arrest during scarring in Mus. The third part of my thesis is focused on how mitochondrial phenotype can impact the tissue healing process. Till date, we found that Acomys fibroblasts have rounded morphology, lower mitochondrial mass and rely on glycolysis for their energy needs whereas Mus fibroblasts have elongated morphology, higher mitochondrial mass and they mostly fulfil their energy demand via oxidative phosphorylation.

This work will uncover the differential injury responses of regenerating or scarring animals and the extent to which the injury response relies on mitochondrial bioenergetics. I believe we have opened up a new frontier in regeneration science with the potential to have a significant impact on our society.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.189

Funding Information

Department of Biology, Teaching Assistantship (Fall 2016, Spring 2017, Fall 2017, Spring 2018, Fall 2018, Fall 2019, Spring 2020, Spring 2021)

Research Assistantship (Summer 2017, Summer 2018, Summer 2019, Summer 2020)

Department of Biology, Merit fellowship (1 semester-Spring 2019)

College of Arts and Sciences, Dean's competitive fellowship (1 semester-Fall 2020)

Available for download on Sunday, May 29, 2022

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