The complexity of biological cells requires the use of multiple proteins and pathways to maintain a level of homeostasis in changing environments. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that binds to numerous aromatic environmental pollutants, including 2,3,7,8-tetrachlorodibenzo-Ϲ-dioxin (TCDD). The AHR regulates the expression of a battery of genes, most notably drug metabolizing enzymes. While environmental sensing has long been the most studied activity of AHR, there has always been the assumption that AHR could have another function mediated by an endogenous ligand(s). Proposed endogenous ligands of the AHR include cholesterol-related, heme-related, and tryptophanrelated molecules. Growing evidence for AHR to be partially localized to mitochondria leads to the hypothesis that AHR could have an impact on this organelle's activity. Interestingly, another mitochondrial protein, translocator protein (TSPO) is associated with many of the putative AHR endogenous ligands. Due to the shared mitochondrial localization and ligands, the goal of this research was to determine if AHR and TSPO exhibited signaling crosstalk. Transmission electron microscopy was employed to visualize mito-AHR at a high magnification to confirm the suborganellar location. CRISPR technology was used to knock out AHR and TSPO individually in mouse cell lines; BV-2 (microglia), Hepa1c1c7 (liver), and MLE-12 (lung). The influence of AHR and TSPO was studied by treating MLE-12 cells with an AHR ligand (TCDD), TSPO ligand (PK 11195), or both and then collecting the RNA for comparison. RNA-sequencing demonstrated that loss of either AHR or TSPO altered the expression of nuclear-encoded mitochondrial genes including Micu2, which is a component of mitochondrial calcium transport. AHR and TSPO both also influenced the expression of mitochondrial-encoded genes for the electron transport system.℗
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