Microglial STAT1-sufficiency is required for resistance to toxoplasmic encephalitis

Abstract

Toxoplasma gondii is a ubiquitous intracellular protozoan parasite that establishes a life-long chronic infection largely restricted to the central nervous system (CNS). Constant immune pressure, notably IFN-γ-STAT1 signaling, is required for preventing fatal pathology during T. gondii infection. Here, we report that abrogation of STAT1 signaling in microglia, the resident immune cells of the CNS, is sufficient to induce a loss of parasite control in the CNS and susceptibility to toxoplasmic encephalitis during the early stages of chronic infection. Using a microglia-specific genetic labeling and targeting system that discriminates microglia from blood-derived myeloid cells that infiltrate the brain during infection, we find that, contrary to previous in vitro reports, microglia do not express inducible nitric-oxide synthase (iNOS) during T. gondii infection in vivo. Instead, transcriptomic analyses of microglia reveal that STAT1 regulates both (i) a transcriptional shift from homeostatic to “disease-associated microglia” (DAM) phenotype conserved across several neuroinflammatory models, including T. gondii infection, and (ii) the expression of anti-parasitic cytosolic molecules that are required for eliminating T. gondii in a cell-intrinsic manner. Further, genetic deletion of Stat1 from microglia during T. gondii challenge leads to fatal pathology despite largely equivalent or enhanced immune effector functions displayed by brain-infiltrating immune populations. Finally, we show that microglial STAT1-deficiency results in the overrepresentation of the highly replicative, lytic tachyzoite form of T. gondii, relative to its quiescent, semi-dormant bradyzoite form typical of chronic CNS infection. Our data suggest an overall protective role of CNS-resident microglia against T. gondii infection, illuminating (i) general mechanisms of CNS-specific immunity to infection (ii) and a clear role for IFN-STAT1 signaling in regulating a microglial activation phenotype observed across diverse neuroinflammatory disease states.

Microglia Depletion Reduces Human Neuronal APOE4-Driven Pathologies in a Chimeric Alzheimer’s Disease Model

“…These data imply that cluster 4 may represent a microglia subpopulation responding specifically to transplanted human neurons expressing APOE, especially APOE4. Examining the DEGs in this cluster more closely revealed significant upregulation of MHC-II antigen presentation genes ( Cd74, H2-Ab1, Tap1 ) 64,65 and genes involved in chemokine/interferon response signaling ( Stat1, Irf1, B2m, Ccl5, Ccl12 ) 66–68 (Figure 7H). Each of these gene subsets serves as distinct markers for MHC-II expressing (MHC-II) microglia and interferon-responsive (IFN-R) microglia, two activated microglia subpopulations previously described in AD mouse models 64 .…”

Chronic IL-1-induced DNA double-strand break response in hippocampal neurons drives cognitive deficits

“…Cultured cells were washed in PBS and scraped into RIPA buffer according to 11 . Briefly, lysates were sonicated for 10 min at 4°C and spun in a refrigerated microcentrifuge at maximal speed for 10 min.…”

“…Studies of T. gondii experimental infection in the mouse, one of the parasite’s natural hosts, have indicated that the parasite burden in the brain, the level of neuroinflammation, and the extent of neurological symptoms vary with the combination of parasite strain and mouse genetic background, most likely since these processes are influenced by the efficiency of parasite immune control in the brain. Several (neuro)immune cells contribute to T. gondii immune surveillance in the CNS, including microglia 11 , astrocytes 12,13 , monocytes 14 , and CD8+ T lymphocytes, which play a central role 15,16 . C57BL/6 mice are known to be naturally susceptible to develop encephalitis upon infection by type II T. gondii.…”

Microglia at the scene of the crime: what their transcriptomics reveal about brain health

“…Innate immune signaling via interferon γ (IFNγ)-STAT1 is vital for controlling this parasite within the murine CNS. Microglial-specific deletion of STAT1 leads to a profound increase in mortality and a 300-fold increase in parasite levels in the brain [27 ▪▪ ]. These STAT1-deficient microglia displayed a loss of transcriptional signatures characteristic of microglial activation, failing to downregulate both homeostatic genes including C-X3-C Chemokine receptor 1 (CX3CR1), Fcrls and transforming growth factor beta 1 and upregulation of genes characteristic of a disease-associated microglia (DAM) signature, including integrin subunit alpha X, Axl, cytochrome B-245 beta chain and glycoprotein nonmetastatic melanoma protein B.…”