Author ORCID Identifier

0000-0002-6539-8406

Date of Graduation

5-2022

Document Type

Dissertation (PhD)

Program Affiliation

Neuroscience

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Cobi J. Heijnen, Ph.D.

Committee Member

M. Neal Waxham, Ph.D.

Committee Member

Robert Dantzer, D.V.M., Ph.D.

Committee Member

David Grosshans, M.D.

Committee Member

James Bankson, Ph.D.

Abstract

One in 8 women in the US will be diagnosed with breast cancer. Currently, doxorubicin is one of the most effective chemotherapies for breast cancer. Unfortunately, up to 60% of survivors report long-term chemotherapy-induced cognitive dysfunction (CICD) characterized by deficits in working memory, processing speed, and executive functioning. Currently, no interventions for CICD have been approved by the US Food and Drug Administration. I show here that a 14-day treatment with a blood-brain barrier permeable histone deacetylase 6 (HDAC6) inhibitor successfully reverses long-term CICD following a therapeutic doxorubicin dosing schedule in female mice, as assessed by the puzzle box test and novel object/place recognition test. Long-term CICD was associated with a decreased expression of the postsynaptic protein PSD95, but no decrease in the presynaptic protein synaptophysin, in the hippocampus. I did not detect a significant decrease in mitochondrial function or morphology in brain synaptosomes, myelination in the cingulate cortex using Black Gold II staining, or changes in astrocyte reactivity as assessed by anti-GFAP immunofluorescence staining. Using advanced imaging techniques and single-nucleus RNA sequencing, I demonstrate that doxorubicin-induced changes are associated with decreased microglial ramification and alterations in the microglia transcriptome that suggest a neurodegenerative microglia phenotype closely resembling stage 1 disease-associated microglia (DAMs). HDAC6 inhibition completely reversed these doxorubicin-induced alterations, indicating a restoration of microglial homeostasis. These results suggest that a stage 1 DAM-like microglia phenotype and decreased postsynaptic integrity contribute to long-term CICD. Moreover, HDAC6 inhibition shows promise as an efficacious pharmaceutical intervention to alleviate CICD and improve quality of life of breast cancer survivors.

Keywords

chemotherapy-induced cognitive dysfunction, chemobrain, HDAC6 inhibition, microglia, single-nucleus RNA sequencing, chemofog, snRNA-seq, synaptic integrity, PSD95

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