Key roles for the innate immune response to genotoxic stress in neurological disease

Mounting evidence indicates that DNA damage accumulation in the brain centrally contributes to a number of neurodevelopmental, psychiatric, and neurodegenerative disorders. Yet, little is currently known about the specific molecular pathways that the brain relies on to safeguard itself from DNA insults or how altered regulation of these pathways leads to neurological disease. In recent years, a number of new innate immune signaling pathways that respond to genotoxic stress have been identified. While many of these genomic sensors are highly expressed in the central nervous system (CNS), their roles in CNS homeostasis and disease remain poorly understood. In our recent unpublished studies, we have identified a novel DNA damage sensor that centrally contributes to both neurodevelopmental and neurodegenerative disease. Deletion of this genomic sensor in neurodevelopment was found to cause excessive DNA damage accumulation throughout the brain, abnormal CNS maturation, and the development of motor dysfunction, anxiety, and autism-related behaviors. Moreover, engagement of this DNA damage response in the adult brain was found to drive neurodegenerative disease. Interestingly, we observe that DNA damage-induced cytokine responses are not directly responsible for driving neurological disease in our model. In contrast, our findings using genetic knockout mouse strains, indicate that immune-based genomic sensors influence CNS function and health by regulating cell death signaling. Our studies demonstrate that DNA damage surveillance by the innate immune response coordinates the expulsion of genetically compromised cells from the brain and reveal novel roles for immune-based genomic sensors in CNS disease.

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.

Critical roles for microbiota-mediated regulation of Th17 responses in a maternal immune activation model of autism

Recent studies suggest that autism is often associated with altered microbiota composition and gastrointestinal inflammation. This work has led to growing speculation of a potential role for the microbiome in autism spectrum disorder (ASD). However, how microbiota diversity mechanistically influences the development of autistic phenotypes has not been studied in great detail to date. To formally investigate this, we evaluated how environmentally induced changes in gut microbiota landscape influence the incidence and severity of MIA-induced neurodevelopmental disorders. Herein, we report critical roles for prenatal microbiota composition in the development of behavioral abnormalities in a MIA mouse model of autism. Mechanistically, we show that microflora-dependent calibration of the immune response underlies the effects of the microbiome on inflammation-induced ASD-like phenotypes. Specifically, we find that neutralization of IL-17a ameliorates the ability of the microbiome to affect the development of autism-related behaviors. Our results identify the immune system as a link between gut microbiota and the brain in neurodevelopmental disorders, and suggest that targeting the microbiome and maternal immune responses during gestation may offer strategies to limit autism development in at-risk pregnancies.