Investigating the bidirectional relationship between circadian rhythms and cannabinoid use

PROJECT SUMMARY/ABSTRACT Cannabis use is on an upward trajectory due to recent decriminalization and legalization. This increased use is associated with numerous health and behavioral effects, including risk for developing cannabis use disorder (CUD). Despite the growing use of cannabis and cannabis-derived products as sleep aids due to their ability to

promote sleep, evidence suggests that chronic cannabis use paradoxically leads to disrupted sleep and circadian rhythms. Moreover, sleep disturbances such as insomnia are a hallmark feature of cannabis withdrawal and increase risk of relapse and continued use. However, very little is known about the molecular and cellular

mechanisms underlying the bidirectional relationship between circadian rhythms and cannabis use. The effects of cannabinoids on sleep may be driven, in part, through their interaction with the core molecular clock, which consists of a series of transcriptional-translational feedback loops that control circadian-dependent (near 24

hour) gene expression. Notably, the endocannabinoid and circadian systems are tightly linked, with endocannabinoids showing diurnal rhythms in expression in the periphery and brain, including the nucleus accumbens (NAc). Moreover, cannabinoids directly impact the molecular clock and influence peripheral and

behavioral rhythms. However, the effects of cannabinoids on molecular rhythms in the brain and differences between cell types differentially implicated in cannabis use have not been investigated. Measures of molecular rhythms in human postmortem brain are challenging since each brain represents a single circadian timepoint.

However, an innovative analysis uses “time of death” (TOD) to fit subjects on a 24-hr ‘clock’, making it possible to reconstruct molecular rhythm patterns in the human brain. Using this approach, we and others have demonstrated robust molecular rhythms of the human brain transcriptome, with altered rhythms in psychiatric

and substance use disorders. The central hypothesis of this R01 proposal is that there are bidirectional relationships between molecular rhythms and cannabinoid use, with cannabinoids disrupting cell type-specific molecular rhythms in the NAc, and these disruptions contributing to escalating cannabinoid use. To test this

hypothesis, we will use a rat model to determine how cannabinoid self-administration affects cell type-specific molecular rhythms in the NAc, as well as EEG-based measures of sleep/wake rhythms and sleep architecture (Aim 1). We will then determine whether cell type-specific molecular rhythm disruption in the NAc is sufficient to

cause changes in self-administration (Aim 2). Lastly, we will perform translational studies to determine how molecular rhythms are altered in distinct cell types of the NAc using single nucleus RNA sequencing (snRNA- seq) in subjects with CUD (Aim 3). Together, these studies will be the first to examine molecular rhythms in the

human brain of subjects with CUD and explore the mechanistic interactions of rhythm alterations and cannabinoid use. A better understanding of these interactions will not only provide insights into the neurobiology of cannabis use, but also the identification of novel therapeutic targets and treatment strategies for CUD.