Graduation Year

2023

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Medical Sciences

Major Professor

Paula C. Bickford, Ph.D.

Committee Member

Kevin Nash, Ph.D.

Committee Member

Stanley Stevens, Jr., Ph.D.

Committee Member

Thomas Taylor-Clark, Ph.D.

Keywords

Python, GOplot, microglia, mTORC2, neuroinflammation, proteomics

Abstract

Age-related disease is a growing concern as the global geriatric population increases. Neurodegenerative diseases scale unfavorably in prevalence with aging and inflict disastrous consequences to human health and well-being. These disorders are challenging to investigate because they arise from complex molecular origins. The neuroimmune system is a common factor among these diseases and microglia play an important role in maintaining homeostasis in the central nervous system. Aging progressively impairs microglia by decreasing their ability to adapt and respond to noxious environmental stimuli or injury. Microglial dysfunction aggravates neurodegenerative pathology when microglia are unable to regulate neuroinflammation effectively. We investigated aging microglial dysfunction by using mass spectrometry-based proteomics and bioinformatic analysis. In our first set of experiments, we isolated microglia from young and aged rats, identified differentially expressed proteins between the two age groups, and determined functional enrichment among canonical microglial signaling cascades in our AGING comparison. Aged microglia possessed an elevated pro-inflammatory phenotype characterized by metabolic irregularity. We then examined how polyphenol supplementation modified dysfunctional signaling in aging microglia. We fed aged rats a 30-day polyphenol diet and evaluated changes in their microglial proteomes relative to their age-matched counterparts fed a control diet. Polyphenol supplementation mitigated activation in neuroinflammatory pathways and reversed aberrant trends we observed in aging microglia. In our second set of experiments, we modeled aging dysfunction in microglia by disrupting the nutrient-sensing mTORC2 pathway in vivo. We generated mice expressing both Cre-recombinase under the Cx3cr1 promoter and loxP sites flanking exon 11 of the RICTOR gene. Tamoxifen treatment induced microglial-specific RICTOR depletion. We then identified differentially expressed proteins in male and female RICTOR-KO microglia and performed bioinformatics. We confirmed that RICTOR-deficient microglia expressed a pro-inflammatory phenotype that paralleled trends we observed in aging microglia. Disrupting mTORC2 signaling activated inflammatory canonical pathways and evoked metabolic dysfunction in male and female microglia. Our experimental results highlight the potential molecular underpinnings of aging in microglia.

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