Effects of interleukin-6 on neuronal development in an in vitro maternal immune activation model

Abstract

Autism is a complex neurodevelopmental disorder. While genetic and environmental factors play key roles in the pathogenesis, epidemiological evidence strongly suggests that maternal infection during pregnancy may contribute to an increased risk of the disorder for the offspring. It is believed that the imbalance of pro-inflammatory cytokines, such as interleukin-6 (IL-6), disrupt prenatal or early postnatal brain development, and subsequently lead to behavioural changes in the child. To better understand how IL-6 modulates neurodevelopment, primary cortical cultures were prepared from wild-type fetal mice at 15-16 days gestation. On day 7 in vitro, cultures were treated with IL-6 for 24 hours (0pg/mL to 2000pg/mL). Cell viability and survival were assessed by MTT and LDH assays, respectively. The expressions of inducible nitric oxide synthase (iNOS), neuronal nitric oxide synthase (nNOS), and phospho-tau were examined by Western blot. Compared to the control group, cortical cultures exposed to 10pg/mL IL-6 did not show any difference in survival. However, cell viability started to decrease at 100pg/mL, and at the concentrations of 1000 pg/mL and 2000 pg/mL, 50% reduction in viability was noted (P<0.01 vs. control). Likewise, IL-6 challenge at 100pg/mL and 1000pg/mL significantly increased the release of LDH (P<0.01 vs. control). The expression of iNOS was significantly increased at 100pg/mL and 1000pg/mL (P<0.01 vs. control). Interestingly, nNOS and phospho-tau expressions showed opposite biphasic responses with increasing IL-6 doses (P<0.01 vs. control). These preliminary data suggest that the rise in IL-6 during pregnancy may disrupt fetal neuronal development by increasing the iNOS-mediated production of nitric oxide (NO), decreasing nNOS-mediated NO release, and interfering with microtubule assembly. Further experiments to confirm these findings and explore the underlying mechanisms are in progress.