The effect of prenatal Mycobacterium tuberculosis infection on offspring neurodevelopment and autistic-like behaviours in a valproic acid mouse model of autism.

Abstract

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by restricted repetitive patterns, communication challenges and lack of social skills. ASD has no distinct biomarkers, with symptoms overlapping with related developmental disorders like Schizophrenia. Maternal immune activation (MIA) is when the maternal immune system is invaded by a pathogen causing an immune response that interferes with the normal fetal brain development process. Mycobacterium tuberculosis (Mtb) infections are common during pregnancy and are known to affect fetal health, often causing spontaneous abortions and low birth weights. Valproic acid (VPA) is an anticonvulsant and mood stabilizer associated with ASD when administered during pregnancy. Gestational VPA exposure of mice on Embryonic day 12.5 (E12.5) induces ASD-traits in offspring, as such, this study employed VPA as a positive control. This study investigated the effects of prenatal exposure to Mycobacterium tuberculosis (Mtb) (singularly and in combination with VPA) on developmental delays and offspring behaviour. Pregnant mice were divided into saline, VPA, Mtb, and VPA+Mtb; treatments were administered on E12.5. Developmental milestones were measured between post-natal day 7 (PND 7) and 28. Offspring were subjected to neurobehavioural studies to test for social interaction and repetitive behaviours on PND 35. Ionised calcium binding molecule 1 (IBA-1) and Glial Fibrillary acid protein (GFAP) expression in the prefrontal cortex (PFC) and cerebellum regions were analysed using immunohistochemistry (IHC). The effect on the BBB’s function was determined using Evans blue dye-albumin extravasation method on PND 35. Additionally, cerebellar tissues were homogenized and processed for molecular analyses of NRXN1, NRXN2, NLGN1, NLGN2 and SHANK3 expression. Changes in expression patterns of NRXNs and NLGNs causes an imbalance in the excitation and inhibition of neurons, a feature associated with ASD. The Mtb treated group had significantly low litter count and high fetal resorption compared to saline treated group. Neuroinflammation was evident in the Mtb offspring at PND 35 as shown by a significant increase in GFAP and IBA-1 expressing astrocytes and microglia in the PFC and cerebellum compared to saline group. The BBB’s integrity was compromised as shown by the increased permeability to EB-dye in the PFC and cerebellum of Mtb, VPA and VPA+Mtb offspring. The Mtb offspring also displayed systemic inflammation and altered ASD-linked behaviours. NRXN1 and NLGN1 were overexpressed in the cerebellum of Mtb-induced MIA offspring compared to saline offspring. Dual exposure to VPA and Mtb restored NRXN1 expression levels, reduced astrocyte and microglia injury in the PFC, rescued social behaviours and restored normal eye-opening patterns in offspring. The study demonstrates impaired fetal development which persists into the post-natal period. The impaired development was accompanied by neuroanatomical changes and behavioural patterns consistent with ASD pathophysiology. These findings might be attributed to Mtb-induced maternal system inflammation in pregnancy that induces fetal inflammation via the placenta and BBB of a developing fetus causing insult in the brain. Immune dysregulation and synaptic defects are hallmarks of ASD. We therefore conclude that prenatal Mtb infection predisposes offspring to a higher risk of neurodevelopmental challenges later in life and dual exposure to VPA and Mtb rescues some of these challenges.