Date of Graduation
8-2024
Document Type
Dissertation (PhD)
Program Affiliation
Neuroscience
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Kristin Eckel-Mahan
Committee Member
Qingchun Tong
Committee Member
Jiaqian Wu
Committee Member
John O'Brien
Committee Member
Zheng Chen
Abstract
Circadian rhythms are internal biological rhythms that drive oscillations in physiology and metabolism. Maintained at the level of individual cells throughout the body, the circadian clock is necessary for driving tissue-specific temporal programs of energy balance. Though loss of the circadian transcription factor, BMAL1, in the paraventricular nucleus (PVN) of the hypothalamus has revealed its importance in driving rhythms in energy intake and metabolism, its transcriptional functions across time and in individual cell types in the PVN are not well understood. In this study, we show that loss of BMAL1 in the PVN not only results in arrhythmicity in processes that control energy balance, but it disrupts peripheral clock regulation of gene expression. Using BMAL1 chromatin immunoprecipitation followed by sequencing and single nuclei RNA sequencing (snRNA-seq), we analyzed the genomic and transcriptional regulation by BMAL1 across time and in PVN cell types. Our study reveals not only rhythmic binding at specific loci by BMAL1, but that loss of BMAL1 results in robust changes in both levels of expression and rhythmicity of its targets, including oxytocin, the secretion of which is altered in PVN BMAL1-deficient mice. This study also reveals time- and cell-type-specific regulation by BMAL1, which may be important in driving rhythms that maintain energy balance. While glutamatergic neurons undergo widespread changes in gene expression over the diurnal cycle, astrocytes and oligodendrocytes also show pronounced, diurnal changes in gene expression. Finally, restoring the circulating oxytocin (OXT) peak in BMAL1-PVN KO mice rescues dampened activity, suggesting that BMAL1-mediated regulation of OXT is important for rhythmic behaviors. Collectively, our findings show diurnal gene regulation in neuronal and non-neuronal cells of the PVN, which are likely both important in BMAL1-driven and organism-wide rhythms in metabolism.
Keywords
Circadian clock, BMAL1, Hypothalamus, Paraventricular nucleus of the hypothalmus, metabolism, diurnal, snRNAseq, ChIPseq, Oxytocin