Maternal immune activation alters fetal brain development through interleukin-6

Abstract

Schizophrenia and autism are thought to result from the interaction between a susceptibility genotype and environmental risk factors. The offspring of women who experience infection while pregnant have an increased risk for these disorders. Maternal immune activation (MIA) in pregnant rodents produces offspring with abnormalities in behavior, histology, and gene expression that are reminiscent of schizophrenia and autism, making MIA a useful model of the disorders. However, the mechanism by which MIA causes long-term behavioral deficits in the offspring is unknown. Here we show that the cytokine interleukin-6 (IL-6) is critical for mediating the behavioral and transcriptional changes in the offspring. A single maternal injection of IL-6 on day 12.5 of mouse pregnancy causes prepulse inhibition (PPI) and latent inhibition (LI) deficits in the adult offspring. Moreover, coadministration of an anti-IL-6 antibody in the poly(I:C) model of MIA prevents the PPI, LI, and exploratory and social deficits caused by poly(I:C) and normalizes the associated changes in gene expression in the brains of adult offspring. Finally, MIA in IL-6 knock-out mice does not result in several of the behavioral changes seen in the offspring of wild-type mice after MIA. The identification of IL-6 as a key intermediary should aid in the molecular dissection of the pathways whereby MIA alters fetal brain development, which can shed new light on the pathophysiological mechanisms that predispose to schizophrenia and autism.

Figure 1.

The offspring of mice given injections of recombinant IL-6 exhibit abnormal behaviors. a, Offspring of mice given injections of IL-6 but not IFNγ have a PPI deficit at a prepulse intensity of 85 dB (F_(2,79) = 4.369; p < 0.05). *p < 0.05 versus control. b, PE offspring of control mice show normal LI compared with NPE animals, as do PE offspring of IFNγ-injected mothers. Offspring of IL-6-injected mothers, in contrast, do not demonstrate significant LI (F_(3,103) = 10.22; p < 0.0001). *p < 0.05 versus NPE; **p < 0.001 versus NPE.

Figure 2.

Abnormal behavior in MIA offspring is prevented by maternal treatment with anti-IL-6 antibody. a, Offspring of mice treated with poly(I:C) lack LI. Coinjection of anti-IL-6 with poly(I:C) restores significant LI, whereas coinjection of anti-IFNγ does not (F_(4,132) = 7.566; p < 0.0001). **p < 0.001 versus NPE; *p < 0.01 versus NPE. b, Compared with controls, the offspring of mice treated with poly(I:C) show a PPI deficit at a prepulse level of 85 dB. Coinjection with anti-IL-6 prevents this deficit. The PPI of offspring of mice given coinjections of poly(I:C) and anti-IFNγ or anti-IL-1β are not significantly different from control or poly(I:C) (F_(4,270) = 4.195; p < 0.005). *p < 0.001 versus control; ^#p < 0.05 versus poly(I:C). c, d, In the open-field test, offspring of mice treated with poly(I:C) make fewer entries than controls into the center (c) and travel less total distance (d). Offspring of mice given coinjections of anti-IL-6 enter the center as often as control mice [F_(3,123) = 3.703; p < 0.05; *p < 0.05 vs control; ^#p < 0.05 vs poly(I:C)] and move a similar total distance [F_(3,123) = 6.666; p < 0.0005; *p < 0.01 vs control; ^#p < 0.001 vs poly(I:C)]. Offspring of mice given coinjections of poly(I:C) and anti-IFNγ are not significantly different from controls or poly(I:C). e, Tracks recorded during the open-field session demonstrate increased thigmotaxis in offspring of poly(I:C)-treated mice compared with offspring of mice given coinjections of an IL-6 antibody. f, In the social interaction test, control mice show a strong preference for the social chamber [defined as (percentage of time in social chamber) − (percentage of time in opposite chamber)], whereas the offspring of poly(I:C)-treated mice show no such preference. Again, the deficit is corrected by maternal administration of IL-6 antibody (F_(3,50) = 4.244; p < 0.01). *p < 0.05 versus control; ^#p < 0.05 versus poly(I:C).

Figure 3.

Unsupervised clustering of microarray data show anti-IL-6 treatment rescues transcriptome changes in MIA offspring. Sixty-one genes show significant (p < 0.01) expression differences between the adult offspring of poly(I:C)-treated and saline-injected mice. Two-dimensional, unsupervised clustering of these genes (x-axis genes, y-axis samples) reveals control (Sal; blue bars), poly(I:C) (pIC; red bars), and poly(I:C) plus anti-IL-6 (pIC+aIL6; purple bars) animals cluster according to treatment, with only one pIC+aIL6 outlier. Significantly, the pIC+aIL6 animals cluster with saline-injected controls, rather than with pIC offspring. Each column represents expression values from a single animal. Genes are annotated by Affymetrix probe set/Unigene identifiers. Color intensity represents the magnitude of the gene expression change compared with the overall average intensity (green, decreased; red, increased; black, unchanged).