Single nuclei transcriptomics in human and non-human primate striatum in opioid use disorder

In brain, the striatum is a heterogenous region involved in reward and goal-directed behaviors. Striatal dysfunction is linked to psychiatric disorders, including opioid use disorder (OUD). Striatal subregions are divided based on neuroanatomy, each with unique roles in OUD. In OUD, the dorsal striatum is involved in altered reward processing, formation of habits, and development of negative affect during withdrawal. Using single nuclei RNA-sequencing, we identified both canonical (e.g., dopamine receptor subtype) and less abundant cell populations (e.g., interneurons) in human dorsal striatum. Pathways related to neurodegeneration, interferon response, and DNA damage were significantly enriched in striatal neurons of individuals with OUD. DNA damage markers were also elevated in striatal neurons of opioid-exposed rhesus macaques. Sex-specific molecular differences in glial cell subtypes associated with chronic stress were found in OUD, particularly female individuals. Together, we describe different cell types in human dorsal striatum and identify cell type-specific alterations in OUD.

Selective Neuronal Knockout of STAT3 Function Inhibits Epilepsy Progression, Improves Cognition, and Restores Dysregulated Gene Networks in a Temporal Lobe Epilepsy Model

OBJECTIVE

Temporal lobe epilepsy (TLE) is a progressive disorder mediated by pathological changes in molecular cascades and hippocampal neural circuit remodeling that results in spontaneous seizures and cognitive dysfunction. Targeting these cascades may provide disease-modifying treatments for TLE patients. Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) inhibitors have emerged as potential disease-modifying therapies; a more detailed understanding of JAK/STAT participation in epileptogenic responses is required, however, to increase the therapeutic efficacy and reduce adverse effects associated with global inhibition.

METHODS

We developed a mouse line in which tamoxifen treatment conditionally abolishes STAT3 signaling from forebrain excitatory neurons (nSTAT3KO). Seizure frequency (continuous in vivo electroencephalography) and memory (contextual fear conditioning and motor learning) were analyzed in wild-type and nSTAT3KO mice after intrahippocampal kainate (IHKA) injection as a model of TLE. Hippocampal RNA was obtained 24 h after IHKA and subjected to deep sequencing.

RESULTS

Selective STAT3 knock-out in excitatory neurons reduced seizure progression and hippocampal memory deficits without reducing the extent of cell death or mossy fiber sprouting induced by IHKA injection. Gene expression was rescued in major networks associated with response to brain injury, neuronal plasticity, and learning and memory. We also provide the first evidence that neuronal STAT3 may directly influence brain inflammation.

INTERPRETATION

Inhibiting neuronal STAT3 signaling improved outcomes in an animal model of TLE, prevented progression of seizures and cognitive co-morbidities while rescuing pathogenic changes in gene expression of major networks associated with epileptogenesis. Specifically targeting neuronal STAT3 may be an effective disease-modifying strategy for TLE. ANN NEUROL 2023;94:106-122.

Abstinence from Escalation of Cocaine Intake Changes the microRNA Landscape in the Cortico-Accumbal Pathway

Cocaine administration alters the microRNA (miRNA) landscape in the cortico-accumbal pathway. These changes in miRNA can play a major role in the posttranscriptional regulation of gene expression during withdrawal. This study aimed to investigate the changes in microRNA expression in the cortico-accumbal pathway during acute withdrawal and protracted abstinence following escalated cocaine intake. Small RNA sequencing (sRNA-seq) was used to profile miRNA transcriptomic changes in the cortico-accumbal pathway [infralimbic- and prelimbic-prefrontal cortex (IL and PL) and nucleus accumbens (NAc)] of rats with extended access to cocaine self-administration followed by an 18-h withdrawal or a 4-week abstinence. An 18-h withdrawal led to differential expression (fold-change > 1.5 and p < 0.05) of 21 miRNAs in the IL, 18 miRNAs in the PL, and two miRNAs in the NAc. The mRNAs potentially targeted by these miRNAs were enriched in the following pathways: gap junctions, neurotrophin signaling, MAPK signaling, and cocaine addiction. Moreover, a 4-week abstinence led to differential expression (fold-change > 1.5 and p < 0.05) of 23 miRNAs in the IL, seven in the PL, and five miRNAs in the NAc. The mRNAs potentially targeted by these miRNAs were enriched in pathways including gap junctions, cocaine addiction, MAPK signaling, glutamatergic synapse, morphine addiction, and amphetamine addiction. Additionally, the expression levels of several miRNAs differentially expressed in either the IL or the NAc were significantly correlated with addiction behaviors. Our findings highlight the impact of acute and protracted abstinence from escalated cocaine intake on miRNA expression in the cortico-accumbal pathway, a key circuit in addiction, and suggest developing novel biomarkers and therapeutic approaches to prevent relapse by targeting abstinence-associated miRNAs and their regulated mRNAs.

Regulation of Inhibitory Signaling at the Receptor and Cellular Level; Advances in Our Understanding of GABAergic Neurotransmission and the Mechanisms by Which It Is Disrupted in Epilepsy

Inhibitory signaling in the brain organizes the neural circuits that orchestrate how living creatures interact with the world around them and how they build representations of objects and ideas. Without tight control at multiple points of cellular engagement, the brain’s inhibitory systems would run down and the ability to extract meaningful information from excitatory events would be lost leaving behind a system vulnerable to seizures and to cognitive decline. In this review, we will cover many of the salient features that have emerged regarding the dynamic regulation of inhibitory signaling seen through the lens of cell biology with an emphasis on the major building blocks, the ligand-gated ion channel receptors that are the first transduction point when the neurotransmitter GABA is released into the synapse. Epilepsy association will be used to indicate importance of key proteins and their pathways to brain function and to introduce novel areas for therapeutic intervention.

Data from single nuclei RNA-sequencing reveals a prodromal gene network response in excitatory neurons of a humanized rat Alzheimer's disease model

BACKGROUND

Despite significant investment into treatments for AD, little progress has been made in bringing new therapeutics to market. Recent failure of monoclonal antibodies targeting Ab plaques to slow disease progression in phase 3 clinical trials, suggests now more than ever it is imperative to identify early disease signatures before symptom onset whose modification may alter disease trajectory. Our collaborating lab recently identified early dysfunction in the transgenic tri-synaptic hippocampal circuit using in vivo recordings during awake immobility in the TgF344-AD rat model (doi: 10.1101/2021.05.10.443512). This dysfunction emerges between 6-9 months, prior to when TgF344-AD rat shows overt pathology (including Ab plaques, frank neuronal loss, and endogenous tau pathology) at 16 and 26 mo, but not at 6 mo (Towne, 2013).

METHODS

The molecular basis of this trisynpatic circuit dysfunction was explored using 10x Genomics' v3 gene expression assay to perform snRNA-seq on freshly dissected hippocampi from 6 mo male and female littermate pairs of Tg and Wt rats (n=16). ∼2000 cells/subject were collected, and cDNA libraries were sequenced (NovaSeq 600) to a depth of ∼120k reads/nuclei. Cell Ranger Pipeline demultiplexed and aligned reads to rat pre-mRNA reference and generated gene count matrices. A final dataset of 33,079 high quality nuclei were clustered (Louvain graph-based), and cell-type specific marke used to determine identity. Identity was collapsed into broad neuronal and glial cell types for differential gene expression (DEG) across genotype (Hurdle Model).

RESULTS

DEGs revealed profound alterations between genotype in cell types important in the trisynaptic circuit, including dentate granule cells (DGCs), and excitatory neurons (ExcNs). (FDR cutoff=0.05, 1111 (DGCs) and 1070 (ExcN's) DEGs between genotypes). Pathway enrichment revealed dysregulation relevant to memory function: including decreased synaptogenesis, neurite branching, proliferation, and microtubule and cytoskeleton dynamics. DEG's were enriched for neurological signs including epilepsy, seizures, hyperactivity, and dementia.

CONCLUSION

Prior to development of overt pathology or memory deficits, TgF344-AD rats display transcriptomic alterations in their excitatory neurons, suggestive of impaired ability to form new connections and susceptibility to aberrant, hyperactivity. Electrophysiological detection, followed by intervention targeting these early alterations in gene expression may prevent progression of disease to a symptomatic stage.