SPATIAL TRANSCRIPTOMICS REVEALS DISTINCT MOLECULAR SIGNATURE OF MOTOR NEURONS AND INTERNEURONS IN CONTROL AND PRE-SYMPTOMATIC STAGES OF AN ALS MOUSE MODEL

Amyotrophic Lateral Sclerosis (ALS) is a rapidly progressive and fatal neurodegenerative disorder impacting motor neurons (MNs) in the brain and spinal cord and resulting in muscle denervation and wasting. Previous work in the lab focused on SOD1^G93A mouse model of ALS, carrying missense mutations in SOD1 gene, and showed that inhibitory inputs (V1 ^En1+ interneurons) in the spinal cord are lost as early as pre-symptomatic stages of the disease and prior onset of MNs degeneration. Here, we present spatial transcriptomics to uncover the molecular signature of V1 ^En1+ interneurons (INs) and MNs. Spinal cord was dissected from WT and SOD1^G93A mice at pre-symptomatic stages of disease (P45, P63 and P84) and processed for spatial transcriptomics using GeoMx Digital Spatial Profiler. At basal state, MNs display enrichment of cytoskeletal dynamics and transport-related targets. INs, on the other end, preferentially express genes involved in RNA splicing, mitochondrial organization and neurotransmission. Across early timepoints of disease, MNs present higher downregulation opposite to the biased upregulation observed in INs. Furthermore, a drastic drop in differential expression changes is observed in INs at P84 hinting at their premature loss. Additionally, increased gliogenesis is uniquely observed in INs as early as P45, possibly indicating a compensatory if not pro-degenerative role. Metabolic, transport and synaptic transmission processes are similarly dysregulated in MNs and INs across disease timepoints. Downregulation of synaptic targets (Snap25, Stxbp1, Unc13a) will be investigated to evaluate a putative role in early loss of connectivity between INs and MNs alongside other relevant targets and pathways.