Gonadal sex and chromosome complement influence the gut microbiome in a mouse model of allergic airway inflammation.

Evidence abounds that gut microbiome components are associated with sex disparities in the immune system. However, it remains unclear whether the observed sex disparity in asthma incidence is associated with sex-dependent differences in immune-modulating gut microbiota, and/or its influence on allergic airway inflammatory processes. Using a mouse model of house dust mite (HDM)-induced allergic inflammation and the four core genotypes (FCG) model, we have previously reported sex differences in lung inflammatory phenotypes. Here, we investigated associations of gut microbiomes to these phenotypes by challenging FCG mice (XXM, XXF, XYM, XYF, n=7/group) withHDM (25 µg) or PBS intranasally for 5 weeks and collecting fecal samples. We extracted fecal DNA and analyzed the 16S microbiome via Targeted Metagenomic Sequencing. We compared alpha and beta diversity across genotypes and assessed the Firmicutes/Bacteroidetes ratio (F/B). When comparing baseline and after exposure for the FCG, we found that the gut F/B was only increased in the XXM genotype. We also found that alpha diversity was significantly increased in all FCG mice upon HDM challenge, with the highest increase in the XXF, and the lowest in the XXM genotypes. Similarly, beta diversity of the microbial community was also affected by challenge in a gonad- and chromosome-dependent manner. In summary, our results indicated that HDM treatment, gonads, and sex chromosomes significantly influence the gut microbial community composition. We concluded that allergic lung inflammation may be affected by the gut microbiome in a sex-dependent manner involving both hormonal and genetic influences.

Transcriptomics analysis of allergen-induced inflammatory gene expression in the Four-Core Genotype mouse model.

Sex differences in allergic inflammation have been reported, but the mechanisms underlying these differences remain unknown. Contributions of both sex hormones and sex-related genes to these mechanisms have been previously suggested in clinical and animal studies. Here, Four-Core Genotypes (FCG) mouse model was used to study the inflammatory response to house dust mite (HDM) challenge and identify differentially expressed genes (DEGs) and regulatory pathways in lung tissue. Briefly, adult mice (8-10 wk old) of the FCG (XXM, XXF, XYM, XYF) were challenged intranasally with 25 µg of HDM or vehicle (PBS-control group) 5 days/wk for 5 wk (n = 3/10 group). At 72 h after the last exposure, we analyzed the eosinophils and neutrophils in the bronchoalveolar lavage (BAL) of FCG mice. We extracted lung tissue and determined DEGs using Templated Oligo-Sequencing (TempO-Seq). DEG analysis was performed using the DESeq2 package and gene enrichment analysis was done using Ingenuity Pathway Analysis. A total of 2,863 DEGs were identified in the FCG. Results revealed increased eosinophilia and neutrophilia in the HDM-treated group with the most significantly expressed genes in XYF phenotype and a predominant effect of female hormones vs. chromosomes. Regardless of the sex hormones, mice with female chromosomes had more downregulated genes in the HDM group but this was reversed in the control group. Interestingly, genes associated with inflammatory responses were overrepresented in the XXM and XYF genotypes treated with HDM. Sex hormones and chromosomes contribute to inflammatory responses to HDM challenge, with female hormones exerting a predominant effect mediated by inflammatory DEGs.NEW & NOTEWORTHY Gene expression profiling helps to provide deep insight into the global view of disease-related mechanisms and responses to therapy. Using the Four-Core Genotype mouse model, our findings revealed the influence of sex hormones and sex chromosomes in the gene expression of lungs exposed to an aeroallergen (House Dust Mite) and identified sex-specific pathways to better understand sex disparities associated with allergic airway inflammation.

Lung proinflammatory microRNA and cytokine expression in a mouse model of allergic inflammation: role of sex chromosome complement and gonadal hormones.

Epigenetic alterations such as dysregulation of miRNAs have been reported to play important roles in interactions between genetic and environmental factors. In this study, we tested the hypothesis that induction of lung inflammation by inhaled allergens triggers a sex-specific miRNA regulation that is dependent on chromosome complement and hormonal milieu. We challenged the four core genotypes (FCGs) model through intranasal sensitization with a house dust mite (HDM) solution (or PBS as a control) for 5 wk. The FCG model allows four combinations of gonads and sex chromosomes: 1) XX mice with ovaries (XXF), 2) XY mice with testes (XYM), 3) XX mice with testes (XXM), and 4) XY mice with ovaries (XYF). Following the challenge (n = 5-7/group), we assessed the expression of 84 inflammatory miRNAs in lung tissue using a PCR array and cytokine levels in bronchoalveolar lavage fluid (BAL) by a multiplex protein assay (n = 4-7 animals/group). Our results showed higher levels of the chemokine KC (an Il-8 homolog) and IL-7 in BAL from XYF mice challenged with HDM. In addition, IL-17A was significantly higher in BAL from both XXF and XYF mice. A three-way interaction among treatment, gonads, and sex chromosome revealed 60 of 64 miRNAs that differed in expression depending on genotype; XXF, XXM, XYF, and XYM mice had 45, 32, 4, and 52 differentially expressed miRNAs, respectively. Regulatory networks of miRNAs identified in this study were implicated in pathways associated with asthma. Female gonadal hormonal effects may alter miRNA expression and contribute to the higher susceptibility of females to asthma.NEW & NOTEWORTHY miRNAs play important roles in regulating gene and environmental interactions. However, their role in mediating sex differences in allergic responses and lung diseases has not been elucidated. Our study used a targeted omics approach to characterize the contributions of gonadal hormones and chromosomal components to lung responses to an allergen challenge. Our results point to the influence of sex hormones in miRNA expression and proinflammatory markers in allergic airway inflammation.

Sex Differences in Airway Remodeling and Inflammation: Clinical and Biological Factors.

Asthma is characterized by an increase in the contraction and inflammation of airway muscles, resulting in airflow obstruction. The prevalence of asthma is lower in females than in males until the start of puberty, and higher in adult women than men. This sex disparity and switch at the onset of puberty has been an object of debate among many researchers. Hence, in this review, we have summarized these observations to pinpoint areas needing more research work and to provide better sex-specific diagnosis and management of asthma. While some researchers have attributed it to the anatomical and physiological differences in the male and female respiratory systems, the influences of hormonal interplay after puberty have also been stressed. Other hormones such as leptin have been linked to the sex differences in asthma in both obese and non-obese patients. Recently, many scientists have also demonstrated the influence of the sex-specific genomic framework as a key player, and others have linked it to environmental, social lifestyle, and occupational exposures. The majority of studies concluded that adult men are less susceptible to developing asthma than women and that women display more severe forms of the disease. Therefore, the understanding of the roles played by sex- and gender-specific factors, and the biological mechanisms involved will help develop novel and more accurate diagnostic and therapeutic plans for sex-specific asthma management.