Fig. 6: Intracellular heme accumulation induces cytoplasmic vacuolation in human primary endothelial cells

a-f Electron microscopy analysis performed on control a, c, e and FLVCR1a-silenced b, d, f HMECs. a Control HMECs displayed a well-organized ER and normal mitochondria. b FLVCR1a-deficient HMECs showed some swollen ER cisternae (black arrows) and many vacuoles partially containing electron-dense dots (white arrowheads). Some damaged mitochondria (*) were also observed. Interestingly, electron-dense deposits (black arrowheads) were found in the cytosol of some FLVCR1a-deficient HMECs. c Control HMECs treated with ALA 5 mM for 16 h. ALA treatment induced the same morphological changes observed in the absence of FLVCR1a. Intracellular vacuoles (white arrowheads) and swollen mitochondria (*), are shown. d FLVCR1a-silenced HMECs treated with ALA displayed huge intracellular vacuoles (V) and heavily damaged swollen mitochondria (*), indicating a mechanism of paraptotic cell death. e, f HMECs co-treated with ALA and CHX (5 μg/ml) for 16 h, are shown. The inhibition of protein synthesis by CHX strongly reduced the number and size of intracellular vacuoles. Electron-dense dots in FLVCR1a-silenced cells f are indicated by black arrowhead. ER endoplasmic reticulum; G Golgi apparatus; M mitochondrion; N nucleus; V vacuole; CHX Cycloheximide; ALA Aminolevulinic acid