Identification of mitochondrial hormone receptors in avian muscle cells

The major objective of this study was to assess the expression of mitochondrial hormone receptors for progesterone (PR), estrogen (ER), glucocorticoid (GR), thyroid (TR), and insulin (IR) in avian muscle cells (quail muscle 7, QM7) and in breast muscle of quail and broilers. Visualization of receptor location in QM7 cells was accomplished by immunofluorescence. QM7 cells were stained with Mito Tracker Deep Red CMX, fixed in methanol, immune stained with anti-PR, -GR, -TR, -IR, and -ER primary antibodies overnight at 4°C, and visualized with Alexa Fluor 488-conjugated secondary antibody. After staining the nucleus with 4',6-diamidino-2-phenylindole, images were obtained by immunofluorescence microscopy. Merged images revealed the presence of all 5 hormone receptors on mitochondria in QM7 cells. Western blot analysis identified; (a) the β-isoform of the PR, (b) the α-isoform of GR, (c) the α-receptor of TR, (d) the β-subunit of IR, and (e) the α-isoform of the ER on mitochondria isolated from broiler breast muscle. Similar results were obtained in quail breast muscle mitochondria with the exception that the α-isoform of the GR was not detected. To our knowledge, this is the first report of hormone receptors (PR, TR, GR, IR, and ER) on mitochondria in avian cells. We hypothesize that these receptors could play important roles in regulating mitochondrial function in avian muscle cells.