TGFβ signaling mediates microglial resilience to spatiotemporally restricted myelin degeneration.

Microglia survey and regulate central nervous system myelination during embryonic development and adult homeostasis. However, whether microglia-myelin interactions are spatiotemporally regulated remains unexplored. Here, by examining spinal cord white matter tracts in mice, we determined that myelin degeneration was particularly prominent in the dorsal column (DC) during normal aging. This was accompanied by molecular and functional changes in DC microglia as well as an upregulation of transforming growth factor beta (TGF)β signaling. Disrupting TGFβ signaling in microglia led to unrestrained microglial responses and myelin loss in the DC, accompanied by neurological deficits exacerbated with aging. Single-nucleus RNA-sequencing analyses revealed the emergence of a TGFβ signaling-sensitive microglial subset and a disease-associated oligodendrocyte subset, both of which were spatially restricted to the DC. We further discovered that microglia rely on a TGFβ autocrine mechanism to prevent damage of myelin in the DC. These findings demonstrate that TGFβ signaling is crucial for maintaining microglial resilience to myelin degeneration in the DC during aging. This highlights a previously unresolved checkpoint mechanism of TGFβ signaling with regional specificity and spatially restricted microglia-oligodendrocyte interactions.