Oral keratinocyte-derived exosomes regulate proliferation of fibroblasts and epithelial cells

Extracellular vesicles (EVs), including exosomes, are small membrane-bound particles released by cells. From a therapeutic point of view, EVs can often convey similar biological function as their parent cell. Grafts originating from oral mucosa have frequently been used in regenerative medicine, and we have previously described the use of oral cell sheets to prevent stricture formation of the esophagus. Further, we recently found that exosomes derived from these cell sheets have pro-regenerative effect on skin wound healing. Here, we have isolated exosomes from conditioned media from oral keratinocyte ("OKEx") and dermal fibroblast ("FEx") cultures. The exosomes were probed for classical EV-markers by western blot (CD9, annexin V and Flotillin-1), FEx were positive for all markers while OKEx were positive only for CD9. Tunable resistive pulse sensing indicated a mean size of around 110 nm and transmission electron microscopy showed a spherical morphology, for both groups. After fluorescent labelling, we studied the uptake of exosomes co-cultured with fibroblasts or keratinocytes. Signal from OKEx could be detected after 90 min, and signal could be detected in all groups after 16 h. Finally we studied the exosomes' modulation of cell proliferation. Both groups suppressed proliferation of healthy keratinocyte and fibroblasts, at some doses to similar levels as dexamethasone (a drug commonly used to prevent stricture formation). In contrast, the exosomes also suppressed the proliferation of the carcinoma cell line TR146, while dexamethasone had no effect. In conclusion, we believe that exosome-signaling might be one of the mode-of-actions of cell sheet-therapy for stricture prevention.