Development of phenotypic indexes for the description of morphological injury in breast cancer cell mitochondria

Background: Mitochondriopathy has been recently rekindled as new cancer theory. We report on structural damage of breast-infiltrating ductal carcinoma (IDC) mitochondria characterised by reduced expression levels of the oxidative phosphorylation system (OXPHOS). Methods: Mitochondria from HMC-1 (human mammary carcinoma) and HMEC (human mammary epithelial cell) cultures, traced by Mitotracker, were assayed for OXPHOS expression levels using cryo-immunoelectron microscopy (CIEM) quantitative labelling and fluorescence immunolabelling on unfractionated HMC-1 and HEMC cells. Convolution degeneration was established by transmission electron microscopy (TEM). Twenty different cell sections for both HMC-1 and HEMC cells, including 65 and 72 mitochondria, respectively, were randomly recorded and quantitatively analyzed for the percentage of area occupied by intact cristae to provide a grading of mitochondrial damage (cristae loss index). Results: Depressed expression levels were detected for all HMC-1 OXPHOS complexes by CIEM. Normalized labelling density (HEMC/HMC-1), expressed as colloidal gold particles/mitochondrial area (ρ) provided the following values: 1.77 for the NADH-ubiquinone oxidoreductase complex I NDUFS3; 1.86 for the succinate- dehydrogenase complex II SDH-B protein; 1.63 for the ubiquinol cytochrome c reductase complex III UQCRC2; 4.88 and 1.58 for the cytochrome-oxidase complex IV (CO) subunit I and IV, respectively; 2.70 for the ATP-synthase complex V F1β protein. Fluorescence immunolabelling confirmed CIEM quantitative data. MitoTracker's co-staining showed altered membrane potential and permeability. Injury grading was categorised assigning three levels of morphological damage: i) severe, ii) moderate, iii) slight, corresponding to 0 % (6.2 % and 1.4 % for HMC-1 and HMEC, respectively), 1–50 % (21.5 % and 2.8 % for HMC-1 and HMEC, respectively) and 51–75 % (44.6 % and 15.3 % for HMC-1 and HMEC, respectively) of area occupied by intact cristae (p<0.0001, χ2Test). The entire HMC-1 mitochondrial damage resulted 3.7 times higher than that observed for HMEC cells (72.3HMC-1 %/19.5HMEC %). Conclusions: New phenotypic harm indexes for IDC cell mitochondria might provide new hallmarks in breast cancer cell biology. No significant financial relationships to disclose.