Altered granulopoiesis aggravates stroke in the elderly [bulk RNA-seq]

Ischemic stroke is one of the leading causes of disability and mortality worldwide, recognizing aging as a prominent risk factor and determinant of dismal outcome. Aging is known to lead to overall frailty due to multifactorial changes, but pathogenic mechanisms underlying poor outcome remain unclear. Here we show that deterioration in elderly stroke is preceded by neutrophil accumulation and clogging in the ischemic brain microcirculation leading to a worse no-reflow phenomenon. With high-dimensional single-cell profiling over time of the brain's, blood's, and bone marrow's immune response, we could delineate after stroke four main neutrophil clusters in the blood whose quantitative and temporal dynamic of release is deranged in the bone marrow of the old. In the elderly, stroke triggers an early surge in the blood of the CD62Llo neutrophil subset characterized by a signature of bone marrow proximity, senescence, and oxidative stress. Functionally, transfer of this neutrophil subset displaying prominent thrombogenic features in young stroke mice leads to increased clogging of the ischemic brain microcirculation, worse no-reflow and outcome. Interrogating the blood leukocyte landscape of a large human stroke cohort with extensive single-cell proteome analyses, we confirmed that older stroke patients display a similar precocious accumulation of blood CD62Llo neutrophil subset, worse reperfusion and outcome. Our results demonstrate how age-related alterations in the process of neutrophil differentiation and release from the bone marrow have a relevant pathogenic role in the major cerebrovascular disorder affecting the world population, that unleash emergency granulopoiesis. 16 samples of circulating CD62L low neutrophils collected from young and aged mice in basal conditions and 24h after MCAo