Time-series investigation of fused vesicles in microvessel endothelial cells with atomic force microscopy

Vesicles or caveolae within endothelial cells, fusing together to form vacuolar organelles, are implicated in macromolecular transport and cellular element transmigration across the blood-brain barrier (BBB) during inflammation and ischemia. Vacuolar organelles have been described by transmission electron microscopy and immunofluorescence, but the details of their dynamics have not been well addressed yet. Herein, by using tapping mode atomic force microscopy (AFM), we observed the time-series changes of fused vesicles within the serum-free cultured rat cerebral microvessel endothelial cells. The fused vesicles were certainly proved by fluorescent staining of Fm4-64 combining simultaneous AFM imaging, as well as the field emission scanning electron microscopy technique. And energy dispersive spectrum results additionally implied that there may be specific structure and compositions around the vesicle region. These results indicate that increased vesicles in BBB may contribute to the formation of fused vesicles and a higher probability to construct the trans-endothelial channel across endothelium layer. Furthermore, the AFM application may open up a new approach to investigate the details of transcellular process by fused vesicles.