Number, shape, and distribution of mitochondria in HEK293/Tau cells by 3D-imaging technique

Tau is the major microtubule-associated protein promoting the assembly and stabilization of microtubule in neuron. Increased tau accumulation was reported in the brain of aging and several tauopathoes including Alzheimer's disease (AD). Abnormal mitochondria were reported decreased and accumulated around the nuclei in the neuron of AD brain by electron microscopy. Tau has been reported located on the outer mitochondrial membrane. Therefore, we observed the number, shape and distribution of mitochondria in HEK293/tau cells by 3D-Imaging technique in present research. We cultured HEK293/tau (overexpressing the longest form of human tau stably) and HEK293/vec (expressing empty plasmid as control) cells, and stained the nuclei and mitochondria by Hoechest and MitoTracker Red (M7512), respectively. Then the cultured cells were put under a laser confocal microscope (LSM710, Zeiss) and 3D-images were collected. Data were analyzed by Imaris Software (Bitplane). We observed the mitochondria in both cultured cells presented rod-like and circle-like. In HEK293/vec cells the average number of mitochondria was 52.05/cell and 62% were rod-like. In HEK293/tau cells the number of mitochondria was decreased 28.43% to 37.25/cell, 64% mitochondria were circle-like. By calculating the distances between each mitochondrion and the nucleus, we found in HEK293/vec cells the distances of 80% mitochondria to nucleus were within 6.25-18.12μm and in HEK293/tau cells the distances of 80% mitochondria to nucleus were within 4.85-9.64μm. The distances to the nucleus of rod-like mitochondria showed no difference with that of circle-like mitochondria. In HEK293/tau cells the mitochondria were decreased, presented circle-like and located near the nucleus. Mitochondria in HEK293/vec and HEK293/tau cells. We cultured HEK293/tau (overexpressing the longest form of human tau stably) and HEK293/vec (expressing empty plas- mid as control) cells, and stained the nuclei and mitochondria by Hoechest and MitoTracker Red (M7512), respectively (A, B, Bar=10μm). Mitochondria in both cultured cells presented rod-like and circle-like (C). The number and percentage of different mitochondria were shown in D and E. Data in D were presented as means± S.D. n=20, ** p<0.01, vs vector cells. Distribution of Mitochondria in HEK293/vec and HEK293/tau cells. 3D-images were collected under a laser confocal microscope (LSM710, Zeiss). By calculating the distances between each mitochondrion and the nucleus, we found in HEK293/vec cells the distances of 80% mitochondria to nucleus were within 6.25-18.12μm (A) and in HEK293/tau cells the distances of 80% mitochondria to nucleus were within 4.85-9.64μm (D). The distances to the nucleus of rod-like mitochondria showed no difference with that of circle-like mitochondria in the same type of cells (B,C,E,F, n=12).