Date of Award

4-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Biomedical Sciences

Track

Cancer and Developmental Biology

Research Advisor

Mondira Kundu, MD, PhD

Committee

Shannon McKinney-Freeman, PhD Susan A. Miranda, PhD John D. Schuetz, PhD Mitchell J. Weiss, MD, PhD

Keywords

Autophagy, Cell Biology, Hematopoiesis, Mouse Models, Stem Cell, ULK

Abstract

The ability of hematopoietic stem cells to self-renew and differentiate is required for the maintenance of all blood lineages under basal physiologic conditions and in response to inflammatory stress. The degradative capacity of the autophagy-lysosomal system is a determinant of hematopoietic stem cell (HSC) activation status with low autophagy predicting activation of HSCs, and autophagy deficiency causing the spontaneous loss of quiescence and HSC exhaustion. Although an increase in mitochondrial activity has been suggested as the cause of HSC depletion in autophagy-defective models, the contribution of mitophagy to HSC function remains to be elucidated. Here, we capitalized on the observation that HSCs lacking the mammalian Atg1 homologues, ULK1 and ULK2, have a defect in mitophagy but no significant impairment in basal flux through the autophagy pathways to explore the role of mitophagy in HSCs. Despite the comparable increase in mitochondrial content in HSCs lacking Ulk1/2 or Atg7 expression, Ulk1/2-deficiency failed to recapitulate the exhaustion of HSCs and associated multilineage cytopenia caused by the autophagy defect in Atg7-deficient HSCs that show high levels of reactive oxygen species (ROS) and a higher proportion of cycling cells at steady state. Mitophagy-defective HSCs aberrantly accrued ROS only upon HSC activation, sensitizing them to apoptosis, cell cycle delay, and/or differentiation, ultimately resulting in failure of the HSC population to expand appropriately in response to a variety of different inflammatory stimuli. Thus, a defect in mitophagy alone is not sufficient to activate HSCs, but rather disrupts ROS homeostasis upon activation of HSCs, thereby influencing cell fate. Our results highlight distinct contributions of basal autophagy and mitophagy in ROS homeostasis and HSC function.

Declaration of Authorship

Declaration of Authorship is included in the supplemental files.

ORCID

http://orcid.org/0000-0003-1806-2528

DOI

10.21007/etd.cghs.2022.0586

Additional Files
2022-001-Smith-DOA.pdf (181 kB)
Declaration of Authorship
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