Figure 5. Mitochondrial transfer from human MSCs is followed by fusion inside macrophages.

Human MSCs and human macrophages (1 × 10⁵) were infected separately with Organelle Lights to label human MSC mitochondria (red) and macrophage mitochondria (green). Twenty-four hours following infection, macrophages were harvested and co-incubated with the human MSCs for 2 h. Images were collected using an inverted Nikon TiE fluorescent microscope equipped with a × 60 oil immersion optic and NIS Elements Software. Organelle Lights were excited using a Lumencor diode-pumped light engine and detected using an ORCA-Flash4.0 sCMOS camera. (a,b) DIC images of two separate fields within the same dish. (c) A zoomed image of the outlined section within b (scale bars, 20 μ). The fluorescence-based images for each field appear in the panels below the DIC images, with d–f showing macrophage mitochondria (green); g–i showing human MSC mitochondria (red); and j–l showing the overlay with yellow indicative of colocalization of human MSC and macrophage mitochondria. Not every macrophage was shown to take up human MSC mitochondria (a,d,g, j).