Mild Subcortical Stroke Induces Widespread Chronic Reactive Astrogliosis That Is Largely Unaffected by Microglia and Age

Ischemic stroke induces a plethora of pathophysiological changes, including neuroinflammation and chronic cerebrovascular dysfunction. In humans, even small, silent strokes can trigger these pathologies, which can spread to brain regions far beyond the infarct and persist chronically, ultimately worsening prognosis and increasing the risk for vascular dementia and Alzheimer's disease. The cause of this pathology is unknown, but reactive astrocytes and microglia are likely contributors. Here, we describe an optimized short-duration middle cerebral artery occlusion model that produces a clinically relevant small stroke mostly confined to subcortical regions, similar to many silent strokes in humans. We termed this model the mild subcortical infarct (MSCI). We then mapped the spatiotemporal extent of reactive astrocytes and microglia during the sub-acute period (1, 3, and 7 days) following MSCI. We observed that reactive astrogliosis develops more rapidly and spreads more extensively, compared to the reactive microglia response following this small infarct. Microglial depletion resulted in larger infarct sizes but did not prevent reactive astrocytes. Aging mice exposed to MSCI exhibited a comparably strong response of reactive astrocytes and microglia as young mice. Lastly, reactive astrocytes persisted for at least nine months after MSCI. We propose that this mild ischemia model is valuable for examining the chronic effects of subcortical stroke. It may be especially useful for investigating the functional impact of reactive astrogliosis in regions distal from the primary injury site.