Microglial heterogeneity after subarachnoid haemorrhage

single-cell transcriptomics, subarachnoid haemorrhage A specific type of haemorrhagic stroke called aneurysmal subarachnoid haemorrhage (SAH) affects people of working age and is more costly than other types of strokes.After SAH, people may look outwardly normal but experience a range of neurocognitive deficits 1 that affect their quality of life and ability to return to full productive work.SAH is caused by rupture of an aneurysm, which is a bulging structural abnormality of the wall of a cerebral artery in the subarachnoid space, on the brain surface.This results in an injection of blood into the subarachnoid space under arterial pressure with a number of pathological consequences, which may in turn affect clinical outcome.Immediate effects include mechanical injury and ischaemia (since increased intracranial pressure reduces cerebral perfusion within the rigid confines of the skull).Delayed effects include inflammation, the toxic effects of blood-derived products such as haemoglobin, vasospasm and hydrocephalus.Microglia are the brain's resident tissue macrophages, constituting circa 10% of the total cellular population. 2 They are derived from the yolk-sac and self-renew, 2 so are developmentally and functionally distinct from two other types of myeloid-lineage cells in the intracranial compartment, which are replenished continuously from the bloodstream: (1) CD163-positive perivascular, meningeal and choroid plexus macrophages and (2) monocytes in the cerebrospinal fluid -both of these two populations