Leveraging single- cell RNA sequencing to unravel the impact of aging on stroke recovery mechanisms in mice

Aging compromises the repair and regrowth of brain vasculature and white matter during stroke recovery, but the underlying mechanisms remain elusive. To understand how aging jeopardizes brain tissue repair after stroke, we performed single -cell transcrip-tomic profiling of young adult and aged mouse brains at acute (3 d) and chronic (14 d) stages after ischemic injury, focusing a priori on the expression of angiogenesis-and oligodendrogenesis-related genes. We identified unique subsets of endothelial cells (ECs) and oligodendrocyte (OL) progenitors in proangiogenesis and pro-oligodendrogenesis phenotypic states 3 d after stroke in young mice. However, this early prorepair transcrip-tomic reprogramming was negligible in aged stroke mice, consistent with the impair-ment of angiogenesis and oligodendrogenesis observed during the chronic injury stages after ischemia. In the stroke brain, microglia and macrophages (MG/M(1)) may drive angiogenesis and oligodendrogenesis through a paracrine mechanism. However, this reparative cell-cell cross talk between MG/M(1) and ECs or OLs is impeded in aged brains. In support of these findings, permanent depletion of MG/M(1) via antagonism of the colony-stimulating factor 1 receptor resulted in remarkably poor neurological recovery and loss of poststroke angiogenesis and oligodendrogenesis. Finally, transplan-tation of MG/M(1) from young, but not aged, mouse brains into the cerebral cortices of aged stroke mice partially restored angiogenesis and oligodendrogenesis and rejuvenated sensorimotor function and spatial learning and memory. Together, these data reveal fundamental mechanisms underlying the age-related decay in brain repair and highlight MG/M(1) as effective targets for promoting stroke recovery.SignificanceWe performed single -cell transcriptomics in young versus aged mouse brains to identify mechanisms governing an age-dependent decline in cerebral vasculature and white matter repair/regrowth after stroke. Unique subsets of endothelial cells and oligodendrocyte progenitors emerged 3 days post-stroke in young mice but lost proregenerative features in aged mice. Aging impaired the ability of microglia (MG)/macrophages (M(1)) to boost angiogenesis and oligodendrogenesis through paracrine cell -to -cell cross talk. Permanent depletion of MG/M(1) impeded angiogenesis and oligodendrogenesis and hindered long- term stroke recovery irrespective of age. Transplantation of MG/M(1) from young brains into aged stroke brains partially restored angiogenesis and oligodendrogenesis and rejuvenated neurological functions. These observations reveal molecular and cellular processes that can be targeted to improve stroke recovery in the aged.

Automated summary

We used single-cell transcriptomics to investigate the mechanisms underlying age-related decline in cerebral vasculature and white matter repair/regrowth after stroke in young versus aged mice. Our findings demonstrate that aging impairs the early prorepair transcriptional reprogramming of angiogenesis and oligodendrogenesis in the brain after stroke. Microglia and macrophages play a crucial role in promoting angiogenesis and oligodendrogenesis, but this reparative cell-cell cross talk is hindered in aged brains. Transplantation of microglia and macrophages from young brains into aged stroke brains partially restored angiogenesis and oligodendrogenesis and improved neurological functions. These findings provide insights into potential targets for improving stroke recovery in the aged.