NogoA-expressing astrocytes limit peripheral macrophage infiltration after ischemic brain injury in primates

Reactive astrocytes play critical roles after brain injury, but their precise function is not well defined, particularly in humans and nonhuman primates (NHPs). Here, we utilized single nuclei transcriptomics to characterize astrocytes after ischemic stroke in the primary visual cortex (V1) of the marmoset monkey. We observed nearly complete segregation between stroke and control astrocyte clusters. Screening the top 30 differentially expressed genes to identify candidates that might limit stroke recovery, we discovered that RTN4A/ NogoA, a neurite-outgrowth inhibitory protein previously associated specifically with oligodendrocytes but not astrocytes, was expressed in a majority of reactive astrocytes. Robust NogoA upregulation on reactive astrocytes following stroke was confirmed in both the marmoset and human brain, whereas rodents exhibited only a marginal change in NogoA expression following stroke. Further, in vivo and in vitro studies determined that NogoA mediated an anti-inflammatory response which likely contributes to limiting deeper infiltration of peripheral macrophages into the surviving parenchyma during the subacute post-stroke period. These findings are directly relevant to the development of NogoA-targeting therapies designed for clinical use shortly after ischemic stroke. In addition, our data have uncovered the complexity of astrocyte responses in primates, which highlights the importance of preclinical model selection for discovery research designed to identify novel therapeutics for brain injury. Overall design: Adult marmosets (n=3) received unilateral injections of endothelin-1 (ET-1) to the primary visual cortex (V1), with grey matter tissues encompassing all cortical layers of operculum collected 7 days later. Non-lesioned adult marmoset (n=3) V1 was used as control.