The influence of asthma on neuroinflammation and neurodevelopment: From epidemiology to basic models.

Asthma is a highly heterogeneous inflammatory disease that can have a significant effect on both the respiratory system and central nervous system. Population based studies and animal models have found asthma to be comorbid with a number of neurological conditions, including depression, anxiety, and neurodevelopmental disorders. In addition, maternal asthma during pregnancy has been associated with neurodevelopmental disorders in the offspring, such as autism spectrum disorders and attention deficit hyperactivity disorder. In this article, we review the most current epidemiological studies of asthma that identify links to neurological conditions, both as it relates to individuals that suffer from asthma and the impacts asthma during pregnancy may have on offspring neurodevelopment. We also discuss the relevant animal models investigating these links, address the gaps in knowledge, and explore the potential future directions in this field.

Characterizing the neuroimmune environment of offspring in a novel model of maternal allergic asthma and particulate matter exposure.

Inflammation during pregnancy is associated with an increased risk for neurodevelopmental disorders (NDD). Increased gestational inflammation can be a result of an immune condition/disease, exposure to infection, and/or environmental factors. Epidemiology studies suggest that cases of NDD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with NDD such as autism spectrum disorders (ASD). Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were sensitized for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA to induce allergic asthma or phosphate buffered saline (PBS) for 1 h. Following the 1-h exposure, pregnant females were then exposed to UIS with a size distribution of 55 to 169 nm at an average concentration of 176 ± 45 µg/m3) (SD), or clean air for 4 h, over 8 exposure sessions. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1ß), and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. There was a suppressive effect of the combined MAA plus UIS on the anti-inflammatory cytokine IL-10. Potentially shifting the cytokine balance towards more neuroinflammation. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Characterizing the Neuroimmune Environment of Offspring in a Novel Model of Maternal Allergic Asthma and Particulate Matter Exposure.

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by the presence of decreased social interactions and an increase in stereotyped and repetitive behaviors. Epidemiology studies suggest that cases of ASD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with ASD. Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders including ASD. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were primed for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA or phosphate buffered saline (PBS) for 1 hour. Following the 1-hour exposure, pregnant females were then exposed to UIS or clean air for 4 hours. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1ß), IL-2, IL-13, and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely interferon gamma (IFNγ) and IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Maternal Allergic Asthma Induces Prenatal Neuroinflammation.

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.

Repeated allergic asthma in early versus late pregnancy differentially impacts offspring brain and behavior development.

BACKGROUND: Stress during pregnancy and maternal inflammation are two common prenatal factors that impact offspring development. Asthma is the leading chronic condition complicating pregnancy and a common source of prenatal stress and inflammation. OBJECTIVE: The goal of this study was to characterize the developmental impact of repeated allergic asthma inflammation during pregnancy on offspring behavioral outcomes and brain inflammation. METHODS: Pregnant female C57BL/6 mice were sensitized with ovalbumin (OVA) or PBS vehicle control and then randomly assigned to receive daily aerosol exposures to the same OVA or PBS treatment during early, gestational days (GD) 2-GD9, or late pregnancy, GD10-GD17. Maternal sera were collected after the first and last aerosol induction regimen and measured for concentrations of corticosterone, anti-OVA IgE, and cytokine profiles. Juvenile male and female offspring were assessed for locomotor and social behaviors and later as adults assessed for anxiety-like, and marble burying behaviors using a series of behavioral tasks. Offspring brains were evaluated for region-specific differences in cytokine concentrations. RESULTS: In early gestation, both PBS and OVA-exposed dams had similar serum corticosterone concentration at the start (GD2) and end (GD9) of daily aerosol inductions. Only OVA-exposed dams showed elevations in cytokines that imply a diverse and robust T helper cell-mediated immune response. Male offspring of early OVA-exposed dams showed decreases in open-arm exploration in the elevated plus maze and increased marble burying without concomitant changes in locomotor activity or social interactions. These behavioral deficits in early OVA-exposed male offspring were associated with lower concentrations of G-CSF, IL-4, IL-7, IFNγ, and TNFα in the hypothalamus. In late gestation, both PBS and OVA-exposed dams had increased corticosterone levels at the end of daily aerosol inductions (GD17) compared to at the start of inductions (GD10). Male offspring from both PBS and OVA-exposed dams in late gestation showed similar decreases in open arm exploration on the elevated plus maze compared to OVA male offspring exposed in early gestation. No behavioral differences were present in female offspring across all treatment groups. However, females of dams exposed to OVA during early gestation displayed similar reductions as males in hypothalamic G-CSF, IL-7, IL-4, and IFNγ. DISCUSSION: The inflammatory responses from maternal allergic asthma in early gestation and resulting increases in anxiety-like behavior in males support a link between the timing of prenatal insults and sex-specific developmental outcomes. Moreover, the heightened stress responses in late gestation and concomitant dampened inflammatory response to allergic asthma suggest that interactions between the maternal immune and stress-response systems shape early life fetal programming.