A complex gene program initiates brain changes in response to cocaine


Date:
July 9, 2020
Source:
University of Alabama at Birmingham
Summary:
Researchers used single-nucleus RNA sequencing to compare
transcriptional responses to acute cocaine in 16 unique cell
populations from the brain nucleus accumbens. The atlas is part
of a major study that used multiple cutting-edge technologies to
describe a dopamine-induced gene expression signature that regulates
the brain's response to cocaine. The study shows neurobiological
processes that control drug-related adaptations and reveals
new information about how transcriptional mechanisms regulate
activity-dependent processes within the central nervous system.



FULL STORY ==========================================================================
The lab of Jeremy Day, Ph.D., at the University of Alabama at
Birmingham, has used single-nucleus RNA sequencing approaches to compare transcriptional responses to acute cocaine in 16 unique cell populations
from a portion of the brain called the nucleus accumbens, or NAc. This molecular atlas is "a previously unachieved level of cellular resolution
for cocaine-mediated gene regulation in this region," said Day, an
associate professor in the UAB Department of Neurobiology.


==========================================================================
The atlas was just the beginning of a major study, published in the
journal Science Advances, that used multiple cutting-edge technologies
to describe a dopamine-induced gene expression signature that regulates
the brain's response to cocaine.

"These results mark a substantial advance in our understanding of
the neurobiological processes that control drug-related adaptations,"
Day said.

"They also reveal new information about how transcriptional mechanisms
regulate activity-dependent processes within the central nervous system."
The approaches used in this study, Day says, may also help dissect the
role of similar gene programs that mediate other types of behavior,
memory formation or neuropsychiatric disorders.

The NAc is deeply involved in drug addiction, and detailed understanding
of how drugs alter its neural circuitry to initiate addictive behavior
can suggest new therapeutic interventions. The NAc is a central integrator
of the brain's reward circuit, and all addictive drugs acutely raise the
level of the neurotransmitter dopamine in the NAc. Dopamine signaling
during repeated drug use leads to widespread changes in gene expression, initiating alterations in neural synaptic circuitry and changes in
behavior associated with drug addiction.

Previous studies of changes in NAc gene expression were only able to look
at bulk tissue -- a mix of many different cell types. When the Day lab
looked at single cell changes by RNA-sequencing 15,631 individual rat
NAc nuclei, they found a surprise. Only a small fraction of neurons in
the NAc were transcriptionally responsive to cocaine administration --
mainly a specific subcluster of medium spiny neurons that express the
Drd1 dopamine receptor.



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The researchers next comprehensively defined the core gene structure
that is activated when dopamine is added to a striatal neuron
culture system. Similar to the responses in the rat NAc after cocaine administration, transcriptional activation predominantly occurred in Drd1-receptor-medium spiny neurons. Day and colleagues identified a core
set of around 100 genes altered by dopamine, which also correlated with
key genes activated in the NAc of rats given cocaine.

It has been hypothesized that gene expression programs in the brain
work in concert to produce downstream effects on neuronal function
and behavior.

However, until recently researchers have lacked a way to test key gene expression programs, which requires inducing multiple genes at the
same time.

Day and colleagues engineered a multiplexed CRISPR guide-RNA array to
target 16 of the top candidate genes altered by dopamine. When paired
with a neuron- optimized CRISPR/dead-Cas9 activation system, they were
able to simultaneously upregulate the 16 genes in neuronal cultures
or in the NAc of live rats. They then explored the transcriptional, physiological and behavioral consequences.

In primary neuronal culture, induction of this gene signature produced
large- scale transcriptional changes that were enriched for genes
involved in synaptic plasticity, neuronal morphogenesis and ion channel function. This program also significantly increased neuron burst firing frequency. In live rats, induction of the gene signature produced
sensitization to repeated cocaine administration. These changes seen
in the neuronal culture and live rats are similar to the neuronal and behavioral changes initiated by drugs of abuse.

Day says his group's study is the first proof-of-principle evidence that
CRISPR activation can be used for simultaneous and selective regulation
of a gene expression signature in vivo.

"Critically," Day said, "these results represent the first
demonstration -- to our knowledge -- of multiplexed gene regulation in
any neuropsychiatric model, providing a roadmap for future studies to investigate the relationship between altered gene programs and neuronal
disease states.

"While the present work provides insight into how cellular diversity contributes to transcriptional responses after an initial cocaine
experience," Day said, "repeated exposure to drugs of abuse promotes neurophysiological adaptations that are thought to drive compulsive drug-seeking long after cessation of use. Hence, it will be critical for
future studies to expand on this work by examining the transcriptional consequence of repeated or self- administered drug use at the single-cell level, as well as understanding how these changes are maintained within different cell populations over longer periods of time and as a result
of volitional drug experience."

========================================================================== Story Source: Materials provided by
University_of_Alabama_at_Birmingham. Original written by Jeff
Hansen. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Katherine E. Savell, Jennifer J. Tuscher, Morgan E. Zipperly,
Corey G.

Duke, Robert A. Phillips, Allison J. Bauman, Saakshi Thukral,
Faraz A.

Sultan, Nicholas A. Goska, Lara Ianov, Jeremy J. Day. A
dopamine-induced gene expression signature regulates neuronal
function and cocaine response. Science Advances, 2020; 6 (26):
eaba4221 DOI: 10.1126/ sciadv.aba4221 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200709172848.htm

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