Differences in the post-stroke innate immune response between young and old

Aging is associated to progressive changes impairing fundamental cellular and tissue functions, and the relationships amongst them through the vascular and immune systems. Aging factors are key to understanding the pathophysiology of stroke since they increase its risk and worsen its functional outcome. Most currently recognised hallmarks of aging are also involved in the cerebral responses to stroke. Notably, age-associated chronic low-grade inflammation is related to innate immune responses highlighted by induction of type-I interferon. The interferon program is prominent in microglia where it interrelates cell damage, danger signals, and phagocytosis with immunometabolic disturbances and inflammation. Microglia engulfment of damaged myelin and cell debris may overwhelm the cellular capacity for waste removal inducing intracellular lipid accumulation. Acute inflammation and interferon-stimulated gene expression are also typical features of acute stroke, where danger signal recognition by microglia trigger immunometabolic alterations underscored by lipid droplet biogenesis. Aging reduces the capacity to control these responses causing increased and persistent inflammation, metabolic dysregulation, and impaired cellular waste disposal. In turn, chronic peripheral inflammation during aging induces immunosenescence further worsening stroke-induced immunodepression, thus increasing the risk of post-stroke infection. Aging also alters gut microbiota composition inducing dysbiosis. These changes are enhanced by age-related diseases, such as atherosclerosis and type-II diabetes, that further promote vascular aging, predispose to stroke, and exacerbate brain inflammation after stroke. Current advances in aging research suggest that some age-associated alterations may be reversed. Future work will unravel whether such evolving anti-aging research may enable designing strategies to improve stroke outcome in the elderly.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Study supported by grant PID2020-113202RB-I00 funded by Ministerio de Ciencia e Innovación (MCIN)/Agencia Estatal de Investigación (AEI), Gobierno de España/ 10.13039/501100011033 and “European Regional Development Fund (ERDF). A way of making Europe”. The Interdisciplinary Thematic Platform PTI-NEURO-AGING+ of the Spanish National Research Council (CSIC) provided support for this work, and funded MG. MAR had a predoctoral fellowship (PRE2018-085737) funded by MCIN/AEI/ 10.13039/501100011033 and by “European Social Fund (ESF) Investing in your future”. DB acknowledges the funding provided by the Fundação para a Ciência e a Tecnologia (FCT-Portugal-PTDC/MED-IMU/0870/2020)