UCLA

Estrogen deficiency at menopause is associated with a plethora of symptoms with long-lasting effects on quality of life and health span. These symptoms include decreased energy expenditure that is often accompanied by unpredictable and uncomfortable changes in body temperature known as hot flashes. Hormone therapy can improve metabolic profiles after menopause but can also increase the risk for certain cancers. The overarching goal of my dissertation is to uncover the neuronal and molecular targets of estrogen in the hypothalamus that modulate various aspects of thermoregulation and understand the physiologically relevant contexts in which they function. Ultimately, my research may identify therapeutics that mimic the thermal effects of estrogen while circumventing the negative effects of hormone therapy.The ventrolateral subdivision of the ventromedial hypothalamic nucleus (VMHvl) modulates aspects of energy expenditure and comprises heterogenous estrogen-sensitive neuronal populations. However, whether its role in energy expenditure arise from the activity of specific neuronal subpopulations or the genes defining them, remains unknown. We previously found that the p53-regulated and estrogen-responsive gene Reprimo (Rprm) is expressed within the VMHvl, shows higher expression in females than males, and increases body temperature when transiently silenced. While this initial work identified a molecular candidate that may regulate body temperature in a sex-specific manner, outstanding questions remained due to the lack of a mouse model allowing us to probe further into the function of this specific cell type. My dissertation research has aimed to rigorously define the function of the Rprm+ neuronal population in the VMHvl by discriminating the role of the Rprm gene from the actions of Rprm+ neurons. This is an important distinction to make since the function of a gene does not necessarily equate to the function of the cells that express it. For instance, genes can function in cell non-autonomous ways and neurons express many different genes that coordinate function. To address this, we generated a RprmCre-FRT knock-in mouse model that has enabled me to use state-of-the-art viral tools to understand the molecular, cellular, and circuit-level characteristics of this neuronal population. Altogether, this dissertation makes three key contributions to our understanding of the Rprm+ population in the VMHvl. First, I thoroughly characterized the novel RprmCre-FRT mouse line, verifying construct integrity, Cre recombinase activity and function, and gene expression fidelity (Chapter 2). With this model validated, I then took advantage of the Cre-lox system to define the function of Rprm+ neurons, both by manipulating their activity to determine whether this was sufficient to alter thermoregulation, and by using circuit-mapping viral tools to characterize the anatomical circuitry in which these neurons operate (Chapter 3). Finally, I leveraged the RprmCre-FRT mouse model and the Flp-FRT system to permanently ablate Rprm expression via two approaches differing in temporal and spatial scale, assessing its necessity for thermoregulation across different physiological contexts (Chapter 4).