Functional neuronal recovery is limited yet critical after stroke. Wallerian axonal degeneration is a necessary pathological hallmark of ischemic stroke. We previously demonstrated that the loss of pro-degenerative protein SARM1 promotes distal axonal survival after stroke and protects stroke-injured cortical neurons. We further demonstrated that the loss of Sarm1 is associated with a transcriptional shift in stroke-injured surviving cortical neurons towards a regenerative phenotype. Here, we propose that the absence of Sarm1 mediates distinct neuronal reprogramming after ischemic injury that confers their regenerative potential. To investigate this approach, we utilized the Sarm1 knockout genetic mouse model of delayed Wallerian degeneration combined with a unique model of subcortical stroke injury that primarily damages axons. We dissected the overlying cortex of the stroke lesion and isolated a single cell suspension to perform 10X single-cell ATAC- and RNA-sequencing. Cluster-based analysis and comparison of gene expression and ontology (GO) terms were used to identify injury- and genotype-specific signatures. We were able to elucidate pronounced clustering and genetic reprogramming of deep-layered cortical neurons, particularly in Layer 5 extratelencephalic-projecting neurons (L5ETs). The activated GO terms in L5ET subpopulations were enriched for pathways involved with neurogenesis, neuron differentiation, and neuron projection development. UMAP projections clearly demonstrated distinct, genotype-specific neuronal clusters, reflecting a transition toward regenerative transcriptional programs in the absence of Sarm1 after stroke injury. Similar differences in gene accessibility were seen by ATAC-seq suggesting that Sarm1 negatively regulates an epigenetic response to stroke. In summary, Sarm1 deletion in the setting of ischemic white matter injury not only prevents distal axonal degeneration but also preserves cortical neurons and drives a shift in neuronal transcriptional states towards intrinsic pro-regenerative programs. These findings highlight Sarm1 as a promising target for therapies aimed at enhancing endogenous neuronal repair mechanisms after stroke.
Toh et al. (Thu,) studied this question.