Single Cell Characterization of Epigenetic Mechanisms Underlying Cocaine Craving

Addiction is a chronic, relapsing mental disease that has profound familial and societal impact. The Centers for Disease Control and Prevention (CDC) report that more than half a million Americans died from drug overdoses between 2000 and 2017, and more than 72,000 overdose deaths in 2017 alone – a two-fold increase in a decade. These numbers underline the severity of the epidemic of drug abuse, and the urgency and need of better understanding and treatment of this brain disorder. Relapse to drug use is the major challenge in combating drug addiction – the relapse rate for all substance abuse disorders ranges from 40 to 60%. Relapse is often precipitated by drug craving triggered by environmental cues linked to drug use. In both human and animal models, cue-triggered craving progressively increases after withdrawal, a phenomenon known as “incubation of craving”. Drug-induced neuroremodeling in the brain’s reward and addiction circuitry is suggested to be crucial to this behavior. However, it is largely unknown what molecular mechanisms are responsible for the remodeling, and how they differ in different parts or pathways of the circuitry. Incubation of craving is time-dependent and long-lasting, showing the characteristics of epigenetic regulations that enforce stable and long-term alterations in gene expression. We hypothesize that the DNA methylation, a major epigenetic mark, plays a critical role in incubation of craving, contributing to the regulation of neural plasticity and network remodeling in response to drug consumption and withdrawal. The proposed project aims to test this hypothesis and measure the impact of the incubation of craving on DNA methylation at single cell resolution to identify novel epigenetic markers and molecular mechanisms that drive the incubation of drug craving. In my previous work, I have developed an interdisciplinary approach to examine DNA methylation landscapes in individual neurons (using single cell DNA methylation sequencing) in specifically targeted neural circuitry of interest (using retrograde tracing techniques). In the proposed study, I will apply this strategy to cocaine intravenous self administration (IVSA) mouse model, the most construct-valid animal model for addiction. This study will provide the first single-cell resolution and neural pathway-specific dissection of molecular changes associated with cocaine addiction and withdrawal, and identify candidate molecular markers of drug craving for follow-up functional studies. The results can be directly translated to understanding the relapse to drug use, and will facilitate the development of new therapeutic avenues to combat drug abuse. In addition, the research strategy and technical framework of the study can be applied to study the abuse of other substances such as opioids, which will have profound impact on public health. In summary, this project brings together expertise in single cell genomics, epigenetics, neural circuitry study, and animal models of drug addiction and withdrawal, and will generate high-impact results and provide foundation for future funding applications.

Grant Recipients

Dr. Zhuzhu Zhang

Dr. Zhuzhu Zhang is a postdoctoral research fellow at the Salk Institute for Biological Studies. Before joining Salk Institute, Dr. Zhang received her Ph.D. in Computational Biology and Bioinformatics as well as a M.S. degree in Statistics at University of North Carolina at Chapel Hill in 2014, and a M.S. degree in Developmental Biology at Purdue University in 2008. Dr. Zhang is broadly interested in applying her expertise in both experimental and computational biology to define molecular signatures for the huge diversity of cell types found in the brain and leveraging this information to more clearly understand their functional roles. Specifically, her current work focuses on understanding the molecular property of individual neurons in brain regions and neural circuits that coordinate key brain functions including memory, motivation, and reward, and how these neurons change when the brain functions are disrupted or distorted in neurological diseases such as Alzheimer’s and addiction. Leveraging the state-of-the-art single cell genomic sequencing approaches to examine the molecular properties of individual neurons, and utilizing neuronal tracing methods to probe targeted neural pathways and circuits, Dr. Zhang’s pioneers the study of dissecting the molecular function of single neurons wired in specific neural circuits of interest. Supported by the L.I.F.E. foundation and collaborating with Dr. Amanda Roberts at the Scripps Research Institute, Dr. Zhuzhu Zhang is actively investigating the molecular changes in individual neurons of the reward circuit in addicted brains using the well-established mouse model of addiction and her innovative single cell genomic approaches. The study would further our understanding of the molecular mechanisms underlying addiction, with the long term goal of identifying novel potential molecular targets to facilitate the development of new therapeutic avenues to combat drug abuse.