AIM2 inflammasome surveillance of DNA damage shapes neurodevelopment.

Neurodevelopment is characterized by rapid rates of neural cell proliferation and differentiation followed by massive cell death in which more than half of all recently generated brain cells are pruned back. Large amounts of DNA damage, cellular debris, and by-products of cellular stress are generated during these neurodevelopmental events, all of which can potentially activate immune signalling. How the immune response to this collateral damage influences brain maturation and function remains unknown. Here we show that the AIM2 inflammasome contributes to normal brain development and that disruption of this immune sensor of genotoxic stress leads to behavioural abnormalities. During infection, activation of the AIM2 inflammasome in response to double-stranded DNA damage triggers the production of cytokines as well as a gasdermin-D-mediated form of cell death known as pyroptosis1-4. We observe pronounced AIM2 inflammasome activation in neurodevelopment and find that defects in this sensor of DNA damage result in anxiety-related behaviours in mice. Furthermore, we show that the AIM2 inflammasome contributes to central nervous system (CNS) homeostasis specifically through its regulation of gasdermin-D, and not via its involvement in the production of the cytokines IL-1 and/or IL-18. Consistent with a role for this sensor of genomic stress in the purging of genetically compromised CNS cells, we find that defective AIM2 inflammasome signalling results in decreased neural cell death both in response to DNA damage-inducing agents and during neurodevelopment. Moreover, mutations in AIM2 lead to excessive accumulation of DNA damage in neurons as well as an increase in the number of neurons that incorporate into the adult brain. Our findings identify the inflammasome as a crucial player in establishing a properly formed CNS through its role in the removal of genetically compromised cells.

Cutting Edge: Critical Roles for Microbiota-Mediated Regulation of the Immune System in a Prenatal Immune Activation Model of Autism.

Recent studies suggest that autism is often associated with dysregulated immune responses and altered microbiota composition. This has led to growing speculation about potential roles for hyperactive immune responses and the microbiome in autism. Yet how microbiome-immune cross-talk contributes to neurodevelopmental disorders currently remains poorly understood. In this study, we report critical roles for prenatal microbiota composition in the development of behavioral abnormalities in a murine maternal immune activation (MIA) model of autism that is driven by the viral mimetic polyinosinic-polycytidylic acid. We show that preconception microbiota transplantation can transfer susceptibility to MIA-associated neurodevelopmental disease and that this is associated with modulation of the maternal immune response. Furthermore, we find that ablation of IL-17a signaling provides protection against the development of neurodevelopmental abnormalities in MIA offspring. Our findings suggest that microbiota landscape can influence MIA-induced neurodevelopmental disease pathogenesis and that this occurs as a result of microflora-associated calibration of gestational IL-17a responses.

TAM receptor signaling dictates lesion location and clinical phenotype during experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE), induced by the adoptive transfer of Th17 cells, typically presents with ascending paralysis and inflammatory demyelination of the spinal cord. Brain white matter is relatively spared. Here we show that treatment of Th17 transfer recipients with a highly selective inhibitor to the TAM family of tyrosine kinase receptors results in ataxia associated with a shift of the inflammatory infiltrate to the hindbrain parenchyma. During homeostasis and preclinical EAE, hindbrain microglia express high levels of the TAM receptor Mer. Our data suggest that constitutive TAM receptor signaling in hindbrain microglia confers region-specific protection against Th17 mediated EAE.