Populations of inflammation driven neuroprotective lipocalin-2 reactive mouse astrocytes resolve following chronic Toxoplasma infection.

Astrocytes are known to provide physical and metabolic support for neurons, control the blood brain barrier, and regulate crucial neurotransmitters. When CNS homeostatic levels are disrupted, such as during injury or infection, astrocytes become reactive. It is unknown if reactive astrocytes are beneficial or detrimental to the system. It has long been known that following Toxoplasma gondii infection, astrocytes upregulate the astrocyte-specific protein GFAP, produce cytokines and chemokines and are able to kill replicating parasites. However, whether all astrocytes undergo these inflammatory transformations and if distinct subsets are involved in these protective processes is unknown. Using previously published flow cytometry phenotyping, we determined there is inflammation-induced astrocyte heterogeneity over the course of Toxoplasma infection, based on astrocytic expression of CD51, CD63, and CD71. Furthermore, we characterized previously undescribed subsets of astrocytes using this technique. Analysis of single cell RNA sequencing revealed a diverse clustering of astrocytes throughout infection, and identified specific inflammatory responsive populations. In addition to immune regulation, a specific set of lipocalin-2 astrocytes expressing transthyretin were found to correlate with neuroprotective functions such as vasculature regulation and angiogenesis. Finally, the use of a novel inducible Lcn2 reporter mouse allowed the characterization and tracking of astrocyte reactivation over time and revealed populations of labeled astrocytes resolve even in the context of ongoing inflammation.