Gating of Leptin Transport into the Cerebrospinal Fluid at the Choroid Plexus

项目总结

Project Summary The central goal of this proposal is to elucidate how leptin transport into the cerebrospinal fluid (CSF) and brain is gated at the choroid plexus (ChP), how such gating influences the action of leptin on reward- related dopaminergic neurons, and how saturated ChP transport may contribute to leptin resistance in obesity. Regulation of energy expenditure and feeding are crucial to an animal’s ability to survive and maintain physiological homeostasis. Leptin is an endocrine factor secreted by adipocytes that participates in the regulation of food intake and body weight. Acting on receptors in the brain, leptin exerts an overall effect to decrease feeding, increase energy expenditure, and promote a lean phenotype. Leptin must enter the brain to reach its receptors. In obesity, circulating leptin levels are elevated, but the ratio of CSF to serum leptin is reduced, and leptin suppresses food intake when administered centrally but not peripherally. This suggests insufficient transport of leptin into the CSF as a potential contributor to the development of obesity. Preliminary work has implicated transcytosis through the blood-cerebrospinal fluid barrier of the ChP epithelium as a critical pathway of leptin entry into the brain. In fact, local deletion of endocytic receptor low density lipoprotein receptor-related protein 1 (LRP1) in the ChP epithelium impairs feeding suppression by peripheral leptin while keeping intact the decrease in food intake in response to centrally delivered leptin. However, the real time dynamics of this proposed transcytotic transport at the ChP are poorly understood. I propose to apply novel in vivo imaging techniques to study leptin transcytosis through the ChP epithelium as well as its access to and effects on leptin-sensitive dopaminergic circuitry in the ventral tegmental area (VTA) in real time in awake, behaving mice. In Aim 1, I will refine recently developed tools to visualize leptin transcytosis at the ChP in real time (see preliminary data) and quantitatively assess the effects of LRP1 deletion or overexpression on leptin transport from the blood into the CSF. Once it reaches the brain, leptin is known to engage a number of neural circuits. Dopaminergic neurons in the VTA encode the motivational salience of food and are normally inhibited by leptin, leading to reduced motivation for food consumption. In obesity, however, dysregulated VTA dopaminergic activity promotes compulsive eating. In Aim 2, I will extend the imaging toolkit to track the access of leptin to the VTA parenchyma in parallel with recording the activity of individual VTA dopaminergic neurons, and rigorously assess the interplay between leptin transcytosis at the ChP and the VTA dopaminergic responses to palatable food in lean and obese mice. Additionally, I will confirm if LRP1 overexpression in the ChP epithelium could be protective against the development of obesity. These studies will provide novel insights into the pathways and mechanisms of leptin entry into the brain, assess the dynamics and downstream effects of leptin signaling with unprecedented precision, and propose new therapeutic approaches for obesity and other metabolic disorders.