Mitochondrial electron transport chain is essential for acute inflammatory stress responses in mouse fibroblasts

Fibroblasts are linked to stress responses in a broad number of diseases. Here, we used immortalized mouse embryonic fibroblasts (iMEFs) to elucidate their signaling behavior in response to proinflammatory lipopolysaccharides (LPS) and angiotensin II (Ang-II). To test for the role of the mitochondrial electron transport chain (ETC), iMEFs were cultured in glucose- and galactose-containing media promoting glycolysis and mitochondrial oxidative phosphorylation, respectively. In addition, we used alternative oxidase (AOX), a ubiquinol oxidoreductase that serves as a naturally evolved rescue mechanism in case of ETC disruption. We found that within 24 h of treatment, LPS upregulated a number of proinflammatory genes, namely Tlr4, Il6, Tgfb1, Nlrp3, Casp1, and Il1b; largely, the effect was more pronounced in galactose-containing media and attenuated by AOX. The increase in transcripts resulted partly in elevated cytokine secretion. Twenty-four hours of Ang-II treatment also induced these genes, albeit to a lesser degree and less sensitive to AOX. Cellular oxygen consumption rates (OCRs) were higher in galactose media but remained unaffected by either stimulus. Our results suggest that fibroblasts undergo a similar proinflammatory phenotypic shift in response to different stressors. This response is shaped by ETC activity, which, surprisingly, is not reflected in altered OCRs.