Oligodendrocyte progenitor cell responses to inflammatory demyelination with aging.

Oligodendrocyte progenitor cells (OPCs) have the capacity to self-renew, differentiate into mature myelinating cells, and remyelinate the central nervous system in response to demyelination. Normal aging is associated with a reduction in the functional capacity of OPCs and induces distinct transcriptional signatures even in the absence of an autoimmune inflammatory demyelination insult. To determine how aging impacts the OPC response to an acute inflammatory insult comparable to a demyelinating event in multiple sclerosis (MS), we performed adoptive transfer of young myelin-reactive Th17 T cells into young and aged mice. Spinal cord OPC responses were quantified using lineage tracing and myelin sheath thickness was quantified using transmission electron microscopy. In the subacute phase 9-10 days after adoptive transfer, the density of both young and aged OPCs is enriched in spinal cord lesions compared to non-lesion white matter. After adoptive transfer, the density of aged OPCs is significantly higher than naïve/non-adoptive transfer aged spinal cord. Differentiated oligodendrocytes (OLs) are relatively preserved within lesions of aged and young animals despite an overall reduction in OL density after adoptive transfer. While lineage tracing identified newly formed oligodendrocytes after adoptive transfer in both young and aged lesions, less oligodendrocyte differentiation was observed in aged animals. Despite the reduction of OPC differentiation in aged animals, there was no significant difference in the extent of remyelination observed for young and aged lesions. Aged OPCs rise to the challenge in response to a strong auto-immune attack, suggesting that compensatory strategies allow both young and aged OPCs to survive and remyelinate in the inflammatory environment. Identifying pathways that promote resilience of young and aged OPCs in the face of an inflammatory challenge will facilitate the development of remyelinating therapies for the treatment of people with MS across the full spectrum of human aging.