Qadri, Y. | bioRxiv Science

bioRxiv2022

Cellular and Molecular Organization of the Rhesus Macaque Dorsal Horn with a Comparison to Mouse

Key mechanisms underlying chronic pain occur within the neural circuitry of the dorsal horn. Recent genome-wide association studies (GWAS) have identified genetic variants associated with the predisposition to chronic pain. However, most of these variants lie in regulatory non-coding regions that have so far not been linked to spinal cord function. Here, we take a multi-species approach to determine whether chronic pain variants impact regulatory elements of dorsal horn neurons. We first built a more comprehensive single cell atlas; filling gaps by generating a high-quality Rhesus macaque atlas and integrating it with human and mouse. With cellular-resolution spatial transcriptomics, we mapped the laminar distributions of the resulting species-conserved neuron subtypes, uncovering an unexpected organization. Lastly, we generated a mouse single-nucleus open chromatin atlas to partition the heritability of chronic pain traits. From this, we identified strong, selective associations between specific, conserved neuron subtypes and major forms of chronic pain.

neuroscience↗

bioRxiv2017

Transcriptional Profiling of Somatostatin Interneurons in the Spinal Dorsal Horn

The spinal dorsal horn (SDH) is comprised of distinct neuronal populations that process different somatosensory modalities. Somatostatin (SST)-expressing interneurons in the SDH have been implicated specifically in mediating mechanical pain. Identifying the transcriptomic profile of SST neurons could elucidate the unique genetic features of this population and enable selective analgesic targeting. To that end, we combined the Isolation of Nuclei Tagged in Specific Cell Types (INTACT) method and Fluorescence Activated Nuclei Sorting (FANS) to capture tagged SST nuclei in the SDH of adult male mice. Using RNA-sequencing (RNA-seq), we uncovered more than 13,000 genes. Differential gene expression analysis revealed more than 900 genes with at least 2-fold enrichment. In addition to many known dorsal horn genes, we identified and validated several novel transcripts from pharmacologically tractable functional classes: Carbonic Anhydrase 12 (Car12), Phosphodiesterase 11A (Pde11a), Protease-Activated Receptor 3 (F2rl2) and G-protein Coupled Receptor 26 (Gpr26). In situ hybridization of these novel genes revealed differential expression patterns in the SDH, demonstrating the presence of transcriptionally distinct subpopulations within the SST population. Pathway analysis revealed several enriched signaling pathways including cyclic AMP-mediated signaling, Nitric Oxide Synthase signaling, and voltage-gated calcium channels, highlighting the importance of these pathways to SST neuron function. Overall, our findings provide new insights into the gene repertoire of SST dorsal horn neurons and reveal several candidate targets for pharmacological modulation of this pain-mediating population.\n\nSignificance StatementSomatostatin(SST)-expressing interneurons in the spinal dorsal horn (SDH) are required for the perception of mechanical pain. Identifying the distinctive genes expressed by SST neurons could facilitate the development of novel, circuit-targeting analgesics. Thus, we applied cell type-specific RNA-sequencing (RNA-seq) to provide the first transcriptional profile of SST neurons in the SDH. Bioinformatic analysis revealed hundreds of genes enriched in SST neurons, including several previously undescribed genes from druggable classes (Car12, Pde11a, F2rl2 and Gpr26). Taken together, our study unveils a comprehensive transcriptional signature for SST neurons, highlights promising candidate genes for future analgesic development, and establishes a flexible method for transcriptional profiling of any spinal cord cell type.

neuroscience↗