Li Ye - US grants

7. Project Summary: The proposal describes a five-year plan for training Dr. Li Ye to achieve his goal to become an independent investigator in the central regulation of metabolism. The training and career development plan includes a compelling research project, training in laboratory techniques and didactic scientific and career development seminars and courses. The applicant has more than a decade of experiences working in both molecular metabolism and systems neurosciences. During his Ph.D., Dr. Ye was trained with Dr. Bruce Spiegelman, a well-recognized leader in the field of obesity and diabetes. His previous findings in metabolic research have been published in many high-impact journals and have been then cited near 4,000 times in the subsequent works of his peers. During the proposed training, Dr. Karl Deisseroth, a leading expert in neurosciences will mentor the applicant?s scientific and career development. Dr. Deisseroth has trained numerous prominent scientists who now hold faculty positions in academic institutions. In addition, an advisory committee with highly regarded expertise in hypothalamic and feeding research (Dr. Luis de Lecea and Dr. Brad Lowell) will provide the applicant scientific advice and career guidance. The overall goal of the project is to study neural mechanisms responsible for coordinating food intake and metabolic demands. The obesity epidemic is putting an enormous burden on the public health systems, by contributing to the increased prevalence of type 2 diabetes, cardiovascular and neurodegenerative diseases. Obesity is a result of energy imbalance, in which energy consumption chronically exceeds the expenditure. There are two types of feeding, one driven by metabolic need and the other by the hedonic aspect of palatable food. The former is mainly regulated by the hypothalamic and hindbrain structures that are responsive to peripheral hormonal signals such as leptin, insulin, and ghrelin. The latter is predominantly controlled by the reward systems including the mesolimbic pathway and dopamine signaling. Preliminary studies suggested these systems converge in the lateral hypothalamus area (LH). Dissecting the circuit, cellular and molecular bases separating these two systems in the LH is key to understanding the central control of energy balance and its dysfunction during obesity, however, differentiating intermingled neural ensembles within a brain region has been difficult. In his early postdoctoral work, the candidate has developed a series of CLARITY and optogenetics-based technologies with sufficient throughput to map brain-wide connectivity as well as with the ability to retain molecular information at the single cell level to distinguish intermingled neuronal populations. Using these tools, the candidate has successfully dissected two anatomically intermingled but functionally distinct ensembles representing opposite valences in the medial prefrontal cortex. These recent advances in systems neuroscience provide us a unique opportunity to dissect and differentiate the LH ensembles recruited by hedonic vs. metabolic feeding. The central hypothesis of this proposal is that hedonic and metabolic feeding recruit distinct ensembles in the LH. Specifically, these two ensembles quantitatively differ in: (1) the inputs they receive from upstream brain regions, (2) neuronal activity during different types of feeding, and (3) causal impact on feeding behaviors. Moreover, the adaptation of these ensembles to chronic high-fat diet is key to the development of hyperphagia. The general approach will be to use systems neuroscience tools to monitor and manipulate neuronal activity in behaving animals (Aim1 and Aim2). The molecular and structural adaption will be measured using ribosome-profiling and high-throughput imaging approaches (Aim3). Together, the proposal study will elucidate neural mechanisms underlying the HFD-induced hyperphagia; in the meantime, provide the candidate with the essential training to start an independent research program focusing on the central regulation of energy homeostasis. The Deisseroth laboratory and Stanford School of Medicine research community provide an ideal setting for training future independent investigators. This project will also bring together leading laboratories of the advisory committee that complement each other?s expertise. These outstanding resources will maximize the potential for the applicant to successfully transition to an independent investigator.

Project Summary Obesity is currently affecting nearly 40% of adults in the U.S. and clearly a major health problem. Energy intake exceeding the homeostatic need is an essential component for the development of obesity. While the hypothalamus plays a key role in regulating energy homeostasis, brain imaging studies in humans consistently found neural activities in the extrahypothalamic region being highly correlated with the consumption of energy-dense food and obesity. The most profound associations are located in reward- or salience-related brain structures. It is therefore imperative to understand how these higher brain regions contribute to the homeostatic regulation of food intake. Our long-term goal is to understand how higher cortical structures exert top-down control of food intake and homeostatic regulation. During the K01 period, enabled by whole-brain CLARITY and lightsheet imaging, we conducted multiple brain-wide screenings to search for extrahypothalamic circuits recruited by fasting. A previously uncharacterized posterior insular cortex to basolateral amygdala projection (pINS-BLA) was unbiasedly identified as one of the most active projections recruited by overnight fasting based on immediate early gene expression. The insular cortex, a key site for integrating internal and external sensory information and encoding valances, is also one of the most prominent brain regions found to be associated with food reward and obesity across numerous human imaging studies. In this proposal, we will test the hypothesis that the activity of this novel pINS-BLA projection encodes top-down hunger signal and therefore positively regulates food intake. We will pursue the following two specific aims: (1) Employ fiber photometry to track and quantify circuit dynamics of the pINS-BLA projection in relation to fasting and re-feeding. (2) Use optogenetics to determine the causal significance of the pINS-BLA projection in food consumption. The studies proposed here will build upon the unique brain-wide screening capacity and the original discovery of an insular cortex to amygdala projection, both achieved during the K01, to unmask a new top-down mechanism of feeding regulation. The completion of this proposal will greatly expand the existing hypothalamic-centered understanding of homeostatic control. This knowledge will provide insight into how higher brain functions are altered during obesity and offer a novel perspective of targeting obesity, both of which will lay the groundwork for our subsequent R01 application.

Abstract Monitoring the metabolic states of internal organs is crucial for maintaining homeostasis and is believed to be primarily mediated by the vague nerve within the autonomic nervous system. The somatosensory nervous system, characterized by clusters of first-order neurons which reside in the dorsal root ganglia (DRG), it is best known for its role in thermosensation, touch perception, pain, and proprioception through the skin and musculature. Emerging evidence suggests DRG neurons also heavily project to internal organs, but their structures and physiological functions remain much less understood due to the lack of tools with adequate specificity and efficacy to target peripheral sensory nerves. With our unique background in both neurotechnology and metabolism, we propose a systemic and focused effort to develop transformative technologies specifically designed for the mammalian peripheral nervous system to enable optical imaging of whole-body sensory network, innervating target-defined molecular profiling, and organ-specific sensory neuromodulation. The goal of this proposal is to leverage these technologies to unravel the structural, molecular and functional basis of the somatosensory circuitry innervating metabolic organs, with which we will test the central hypothesis that internal somatosensory network is critical for maintaining whole-body metabolic homeostasis by sensing organ-specific metabolic states, and this specificity is determined by the unique topological and molecular characteristics of organ-targeting DRG neurons. A striking finding of our preliminary study was the discovery of a morphologically dense, molecularly distinct, yet historically under-appreciated sensory network innervating adipose tissues. We will first test if fat- specific signals are being conveyed by the DRG neurons upon metabolic challenges and whether this transmission is important for maintaining whole-body homeostasis. Ultimately, the knowledge and expertise gained from this initial fat-focused endeavor will serve as a roadmap to expand our interrogation of sensory circuitry to all metabolic organs and will bring potentially revolutionary strategies to treat metabolic disorders. This proposal is an ambitious, potentially transformative, innovative program ideally suited for the New Innovator Award as it breaks traditional field barriers to establish a new frontier of neurobiology: First, the full revelation of the internal somatosensory network could be paradigm-shifting by challenging the conventional division between exteroception and interoception. Second, a major goal of this proposal is to develop the long- awaited circuit tools designed for the peripheral nervous system, which would potentially have a broader impact on the field by providing a universal, adaptive, and powerful strategy to study the peripheral nervous system. Finally, this project uniquely leverages my interdisciplinary expertise in neurotechnology, molecular biology, and metabolism to spearhead the exploration of a new exciting area of neurobiology and physiology.