Author ORCID Identifier

0000-0002-3593-5901

Date of Graduation

12-2020

Document Type

Dissertation (PhD)

Program Affiliation

Cancer Biology

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Jian Hu

Committee Member

Andrew Bean

Committee Member

Jichao Chen

Committee Member

Junjie Chen

Committee Member

George T. Eisenhoffer

Committee Member

Sheng Zhang

Committee Member

Yong Zhou

Abstract

Cells obtain cholesterol in two ways, de novo biosynthesis and uptake from circulation. While most tissues utilize both sources, eye lens and brain depend extensively on cholesterol biosynthesis due to the limited supply from circulation. Lens cell membrane consists of highest portion of cholesterol. Brain is the most cholesterol-rich organ, which accounts for 23% of total cholesterol. Genetic mutations of cholesterol biosynthesis enzymes in humans and animal models present cataracts and hypomyelinating disorders linked to neurological impairment. Yet, it remains unclear how gene expression of cholesterol biosynthesis is regulated in lens and brain. Therefore, studying cholesterol biosynthesis in both tissues could potentially provide insights into a tissue-specific gene regulation of cholesterol biosynthesis. We found Quaking (Qki) is a novel transcriptional activator of cholesterol biosynthesis. Using transcriptomic profiling, we found cholesterol biosynthesis was the most downregulated pathway in Qki-depleted lens and brain. Indeed, mRNA and protein levels of cholesterol biosynthesis genes were reduced in Qki-depleted lens cells and oligodendrocytes. Consistently, total cholesterol level was also decreased upon Qki depletion in both tissues. Qki-depleted mice displayed progressive accumulation of protein aggregates, eventually leading to cataracts, which was greatly attenuated by supplying sterol to the eye. In addition, Qki depletion in brain significantly impaired myelin formation, leading to motor deficits, namely ataxia. Mechanistically, we demonstrated that Qki enhanced cholesterol biosynthesis by recruiting Srebp2 and Pol II in the promoter regions of cholesterol biosynthesis genes. Supporting its function as a transcription co-activator, we found that Qki directly interacted with single-stranded DNA. Together, we propose that Qki-Srebp2–mediated cholesterol biosynthesis is essential for maintaining high demand for cholesterol in lens cells and oligodendrocytes. Our finding potentially provides tissue-specific mechanisms to modulate cholesterol biosynthesis to prevent cataracts and various neurological diseases.

Keywords

Cholesterol, Eye lens, Cataract, Myelin, Oligodendrocyte, Qki, Srebp2, Cholesterol biosynthesis, Protein aggregation

Available for download on Saturday, December 18, 2021

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