TrkB-dependent regulation of molecular signaling across septal cell types

Abstract

The lateral septum (LS), a GABAergic structure located in the basal forebrain, is implicated in social behavior, learning and memory. We previously demonstrated that expression of tropomyosin kinase receptor B (TrkB) in LS neurons is required for social novelty recognition. To better understand molecular mechanisms by which TrkB signaling controls behavior, we locally knocked down TrkB in LS and used bulk RNA-sequencing to identify changes in gene expression downstream of TrkB. TrkB knockdown induces upregulation of genes associated with inflammation and immune responses, and downregulation of genes associated with synaptic signaling and plasticity. Next, we generated one of the first atlases of molecular profiles for LS cell types using single nucleus RNA-sequencing (snRNA-seq). We identified markers for the septum broadly, and the LS specifically, as well as for all neuronal cell types. We then investigated whether the differentially expressed genes (DEGs) induced by TrkB knockdown map to specific LS cell types. Enrichment testing identified that downregulated DEGs are broadly expressed across neuronal clusters. Enrichment analyses of these DEGs demonstrated that downregulated genes are uniquely expressed in the LS, and associated with either synaptic plasticity or neurodevelopmental disorders. Upregulated genes are enriched in LS microglia, associated with immune response and inflammation, and linked to both neurodegenerative disease and neuropsychiatric disorders. In addition, many of these genes are implicated in regulating social behaviors. In summary, the findings implicate TrkB signaling in the LS as a critical regulator of gene networks associated with psychiatric disorders that display social deficits, including schizophrenia and autism, and with neurodegenerative diseases, including Alzheimer's.

Transcriptomic characterization of human lateral septum neurons reveals conserved and divergent marker genes across species

“…This analysis found that TRPC4 was highly conserved, confirming the findings from smFISH studies in both human (Fig. S1) and mouse [13]. FREM2 was identified as a human-specific LS marker gene and validated via smFISH results (Fig.…”

“…Nuclei from each donors9 tissue samples were extracted as previously described [13]. Nuclei EZ Lysis Buffer (MilliporeSigna, Cat #NUC101) was chilled on wet ice then added to each 20mL PCR tube containing frozen tissue.…”

“…Human fMRI studies and clinical case reports demonstrated LS involvement in social cognitive processes such as moral sentiments [1–3], social attachment [4], and sexual behaviors [5], while functional studies in rodents demonstrated that molecularly-defined subpopulations of LS neurons critically regulate social behaviors [63–11] and mediate stress-induced social deficits [12]. To more comprehensively characterize the molecular diversity of these LS cell types, recent single nucleus RNA-sequencing (snRNA-seq) studies in mice identified dozens of unique neuronal subtypes that are both transcriptionally and spatially distinct [13–16]. However, no studies to date have investigated the molecular and transcriptional heterogeneity of the human LS.…”

“…We identified 22 transcriptionally distinct cell clusters with 4 neuronal subtypes originating from the LS. These neuronal clusters exhibited high expression of transient receptor potential cation channel subfamily C member 4 ( TRPC4) , which has also been identified as an LS marker in mouse snRNA-seq studies [13], suggesting potential conservation of transcriptional markers across species. Cross-species analysis confirmed TRPC4 as a transcriptional marker of the LS in humans and mice, and identified FRAS1 related extracellular matrix 2 ( FREM2 ) as a human-specific marker.…”

Septo-hypothalamic regulation of binge-like alcohol consumption by the nociceptin system

“…The LS is a GABAergic basal forebrain structure comprised of dorsal (dLS), intermediate (iLS), and ventral (vLS) subdivisions along the dorsal-ventral (DV) gradient, and spans roughly 4 mM along the anterior-posterior (AP) gradient in mice 38–40 . Because nociceptin and NOP expression has not been rigorously canvased within the LS, we used in situ hybridization to quantify VGAT , Pnoc, and Oprl1 mRNA in NOP fl/fl mice ( Fig.…”