Abstract DP346: From Microstructure to Molecules: Mechanisms of Stem Cell–Driven White Matter Repair After Chronic Stroke

Introduction: Intraparenchymal transplantation of human neural stem cells (hNSCs) has shown safety and evidence of clinical efficacy in early chronic stroke trials, affecting distributed brain networks beyond the graft site. White matter, essential for communication within these networks, is profoundly disrupted after stroke, yet the spatiotemporal effects of transplanted hNSCs on its microstructural and cellular repair remain unknown. Here, we combined longitudinal diffusion MRI (dMRI) with high-resolution spatial transcriptomics to define mechanisms of hNSC-driven white matter repair. Methods: Adult male Sprague Dawley rats were subjected to 30 min of transient middle cerebral artery occlusion (MCAo) followed 1 month later by ipsilesional striatal injection (Tx) of embryonic-derived hNSCs (NR1) or vehicle. Rats underwent MRI (T2w, FLAIR, DWI, DTI) on a 7T Bruker BioSpec and a battery of neurobehavior tests over a 4-month post-stroke period. dMRI was processed via an atlas-registered pipeline for unbiased ROI- and voxel-wise analyses. 10X Genomics Xenium in situ transcriptomics was performed on coronal brain slices at Tx-site at 1 day and 3 months post-Tx. Results: NR1-treated rats exhibited significantly greater functional recovery than vehicle (p < 0.01). Stroke produced bilateral reductions in fractional anisotropy (FA) and quantitative anisotropy (QA) across major white-matter tracts including corpus callosum (CC) that were partially reversed by NR1; early dMRI changes (1–7 days) predicted long-term outcomes. In CC, NR1 accelerated oligodendrocyte lineage maturation and initiation of myelination (Sox10, Olig2, Enpp6, Bcas1, Plp1, Mag) with enrichment of axon ensheathment and lipid biosynthesis at 1 day. By 3 months, the NR1 group exhibited a mature myelin and compaction signatures (Plp1, Mag, Tspan2, Cryab, Klk6), whereas vehicle animals displayed higher chronic stress signaling (inflammasome, ER/UPR, oxidative/mitochondrial) and comparatively weaker structural myelin gene expression. Cell-state profiling indicated persistent glial activation in both groups, with vehicle skewed toward astrocyte/microglial stress and NR1 favoring immunoregulatory microglia and myelin-supportive signaling. Conclusion: NR1 transplantation drives coordinated microstructural recovery and oligodendrocyte-mediated remyelination of white matter after chronic stroke, linking early dMRI signatures to durable pro-myelinating transcriptional programs.