Maternal Allergic Asthma Induces Prenatal Neuroinflammation

Abstract

Autism spectrum disorder (ASD) is a class of neurodevelopmental disorders characterized by impaired social interactions and communication skills and repetitive or stereotyped behaviors. Rates of ASD diagnosis continue to rise, with current estimates at 1 in 44 children in the US (Maenner 2021). Epidemiological studies have suggested a link between maternal allergic asthma and an increased likelihood of having a child diagnosed with ASD. However, a lack of robust laboratory models prevents mechanistic research from being carried out. We developed a novel mouse model of maternal asthma-allergy (MAA) and previously reported that offspring from these mothers exhibit behavioral deficits compared to controls. In addition, it was shown that epigenetic regulation of gene expression in microglia was altered in these offspring, including several autism candidate genes. To further elucidate if there is neuroinflammation in the fetus following MAA, we investigated how allergic asthma impacts the maternal environment and inflammatory markers in the placenta and fetal brain during gestation. Female C57Bl/6 mice were primed with ovalbumin (OVA) prior to allergic asthma induction during pregnancy by administering aerosolized ovalbumin or PBS control to pregnant dams at gestational days (GD)9.5, 12.5, and 17.5. Four hours after the final induction, placenta and fetal brains were collected and measured for changes in cytokines using a Luminex bead-based multiplex assay. Placental MAA tissue showed a decrease in interleukin (IL)-17 in male and female offspring. There was a sex-dependent decrease in female monocyte chemoattractant protein 1 (MCP-1). In male placentas, IL-4, C-X-C motif chemokine 10 (CXCL10)-also known as interferon γ-induced protein 10 kDa (IP-10)-and chemokine (C-C motif) ligand 5 (RANTES) were decreased. In fetal brains, elevated inflammatory cytokines were found in MAA offspring when compared to controls. Specifically, interferon-gamma (IFN-γ), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 1α (IL-1α), IL-6, and tumor necrosis factor α (TNFα) were elevated in both males and females. In contrast, a decrease in the cytokine IL-9 was also observed. There were slight sex differences after OVA exposures. Male fetal brains showed elevated levels of macrophage inflammatory protein-2 (MIP-2), whereas female brains showed increased keratinocytes-derived chemokine (KC). In addition, IL-1𝛽 and IP-10 in male fetal brains were decreased. Together, these data indicate that repeated exposure to allergic asthma during pregnancy alters cytokine expression in the fetal environment in a sex-dependent way, resulting in homeostatic and neuroinflammatory alterations in the fetal brain.

Keywords: ADHD; allergy; asthma; autism spectrum disorder; cytokines; fetal brain; mouse model; neurodevelopment; neuroinflammation; placenta; pregnancy; schizophrenia.

Figure 3

Cytokine concentrations in the fetal brain (whole-brain homogenates) taken at GD17.5 following final maternal asthma challenge. Concentrations of cytokines from male and female offspring of OVA- and PBS-exposed dams were assessed using a multiplex bead-based immunoassay. The concentrations of (A) GM-CSF, (B) IFN𝛾, (C) IL-1𝛼, (D) IL-6, (E) IL-9, (F) TNF𝛼, (G) IL-1𝛽, (H) IP-10, (I) MIP-2, and (J) KC are represented as pg/mL after being normalized to total protein content. Statistical significance determined by multilevel mixed-effects modeling.

Figure 1

Cytokine concentrations in maternal sera of dams exposed to PBS and OVA taken at GD17.5. Serum was collected prior to fetal offspring and placenta collections. Cytokine levels were assessed using a multiplex bead-based immunoassay. (A) IL-4, (B) IL-5, (C) IL-13, (D) IL-6, (E) IL-12 (p40), (F) IL-17, and (G) MIP-1α are represented as pg/mL after being normalized to total protein content. Statistical significance determined by Mann–Whitney U test. PBS dams n = 8, OVA dams n = 10.

Figure 2

Cytokine concentrations in the placenta taken from dams exposed to PBS and OVA at GD 17.5 after final allergic asthma challenge. Cytokine levels were assessed using a multiplex bead-based immunoassay. The concentrations of (A) IL-17, (B) MCP-1, (C) IL-4, (D) IP-10, and (E) RANTES are represented as pg/mL after being normalized to total protein content. Statistical significance was determined by Mann–Whitney U test.