TNF-α reduces Cell Proliferation-related microRNAs in Extracellular Vesicles Released from Parotid Cells

The oral mucosa is constantly exposed to abrasions caused by various stimuli such as bites from teeth, punctures, and burns. Despite the high risk of infection due to the presence of numerous bacteria in the oral cavity, progression to a serious disease is rare. Saliva is considered to contribute because of its multiple functions, including antibacterial activity and mucosal protection. Furthermore, exosomes, which are components of the saliva, have garnered attention in recent years. Exosomes are a type of extracellular vesicle(EV) containing microRNAs(miRNAs) and proteins, and thought to reflect the state of cells. However, their mechanisms of action and functions remain unclear. In this study, based on the hypothesis that EVs influence the oral mucosal healing process, we isolated EVs from cultured salivary gland cells. Purification of the EVs was confirmed using electron microscopy. We confirmed that tumor necrosis factor-α(TNF-α) stimulation did not affect cell proliferation or the protein composition of the released exosomes. However, next-generation sequencing analysis detected differential miRNA expression. Five highly expressed miRNAs were selected from among those whose expression levels decreased to less than half after TNF-α stimulation. A database study indicated that all five miRNAs are involved in cell proliferation. The most highly expressed miRNAs are involved in wound healing and osteoblast differentiation induction. These miRNAs possibly play a role in maintaining a healthy oral environment, suggesting a novel function of saliva mediated by EVs.