Multi-tissue transcriptomic and serum metabolomic assessment reveals systemic implications of acute ozone-induced stress response in male Wistar Kyoto rats

Air pollutant exposures have been linked to systemic disease; however, the underlying mechanisms between responses of the target tissue and systemic effects are poorly understood. A prototypic inducer of stress, ozone causes respiratory and systemic multiorgan effects through activation of a neuroendocrine stress response. The goal of this study was to assess transcriptomic signatures of multiple tissues and serum metabolomics to understand how neuroendocrine and adrenalderived stress hormones contribute to multiorgan health outcomes. Male Wistar Kyoto rats (12–13 weeks old) were exposed to filtered air or 0.8 ppm ozone for 4-hours, and blood/tissues were collected immediately post-exposure. Each tissue had distinct expression profiles at baseline. Ozone changed 1,640 genes in lung, 274 in hypothalamus, 2,516 in adrenals, 1,333 in liver, 1,242 in adipose, and 5,102 in muscle (adjusted p-value<0.1, absolute fold-change>50%). Serum metabolomic analysis identified 863 metabolites, of which 447 were significantly altered in ozone-exposed rats (adjusted p-value<0.1, absolute fold change>20%). A total of 6 genes were differentially expressed in all 6 tissues. Glucocorticoid signaling, hypoxia, and GPCR signaling were commonly changed, but ozone induced tissue-specific changes in oxidative stress, immune processes, and metabolic pathways. Genes upregulated by TNF-mediated NFkB signaling were differentially expressed in all ozone-exposed tissues, but those defining inflammatory response were tissue-specific. Upstream predictor analysis identified common mediators of effects including glucocorticoids, although the specific genes responsible for these predictors varied by tissue. Metabolomic analysis showed major changes in lipids, amino acids, and metabolites linked to the gut microbiome, concordant with transcriptional changes identified through pathway analysis within liver, muscle, and adipose tissues. The distribution of receptors and transcriptional mechanisms underlying the ozone-induced stress response are tissue-specific and involve induction of unique gene networks and metabolic phenotypes, but the shared initiating triggers converge into shared pathway-level responses. This multi-tissue transcriptomic analysis, combined with circulating metabolomic assessment, allows characterization of the systemic inhaled pollutant-induced stress response.

Impact/Purpose

Often, toxicological studies focus on limited endpoints and prioritize the assessment of a single tissue or organ system. The data presented here demonstrate that the transcriptomic response to an acute ozone stressor is widespread across all organ systems, is incredibly tissue-specific, and that assessment of only a single tissue is likely to overlook critical endpoints. Further, analysis of circulating metabolomic data identified changes that were corroborated with transcriptional changes in metabolically active organs and identified additional changes that were not directly captured by transcriptional changes. The ozone-induced transcriptional changes reflected the involvement of common mediators of transcriptional response among many tissues, such as hypoxia, GPCR signaling, and glucocorticoid signaling. However, these changes were associated with tissue-specific alterations in gene networks. This pattern of changes suggests that an inhaled pollutant-induced stress response has organ-specific mechanisms for their transcriptional activities resulting in the activation/suppression of different sets of genes allowing a coherent homeostatic regulation tailored to the specific stress condition. By analyzing multi-tissue transcriptome and integrating with the circulating metabolome, we are better able to understand the dynamicity of this response and envision how inhaled pollutants could be contributing to diseases of distant organs. The homeostatic stress response, mediating both neural and peripheral signals, could be impaired in individuals with neuropsychiatric and/or chronic diseases, thereby exacerbating these ailments when individuals are exposed to air pollutants.

Citation

Jackson, T., J. House, A. Henriquez, M. Schladweiler, K. Jackson, A. Astriab Fisher, S. Snow, D. Alewel, A. Motsinger-Reif, AND U. Kodavanti. Multi-tissue transcriptomic and serum metabolomic assessment reveals systemic implications of acute ozone-induced stress response in male Wistar Kyoto rats. Plenum Press, New York, NY, 19:81, (2023). [DOI: 10.1007/s11306-023-02043-5]

DOI: Multi-tissue transcriptomic and serum metabolomic assessment reveals systemic implications of acute ozone-induced stress response in male Wistar Kyoto rats