Differential Effects of Ischemia and Inflammation on Plasma-Derived Extracellular Vesicle Characteristics and Function in a Mouse Model

Extracellular vesicles (EVs) have long been understood to be important mediators of cell-to-cell communication and may lead to the molecular aftermath and exacerbation of brain injuries such as stroke. This study explored how the source of the EVs influenced their characteristics and the effect these differences had on naïve brain tissue. EVs were isolated from mice post-stroke in the acute or chronic stages of recovery in animals with and without reperfusion (transient and permanent middle cerebral artery occlusion) and from a model of systemic inflammation (i.p. lipopolysaccharide). The data show that neither stroke nor inflammation significantly increases EV numbers compared to sham or naïve animals. Post-stroke EVs exhibited a panel of different platelet and inflammatory markers when compared to EVs derived from a model of inflammation, reflecting differences between stroke and systemic immune activation. When injected into the brain, both stroke-derived and inflammation-derived EVs induced pro-inflammatory cytokine gene expression (IL-1β and CXCL1), suggesting a potential role in neuroinflammation. However, no clear group-level differences in microglial or astrocytic reactivity were detected at the level of regional histological assessment, despite consistent increases in ICAM-1 reactivity. The findings here underscore the complexity of EVs' roles in pathophysiology and highlight the need for improved EV isolation methods. With further longitudinal studies, we may be able to more accurately determine how the context of the injury (reperfusion vs. no reperfusion vs. inflammation) might contribute to the EV populations and their function. Understanding more about EVs in different contexts will improve our ability to use EVs as biomarkers but also our capacity to interfere with EV biology as a novel therapeutic approach.