Glutamine promotes the proliferation of epithelial cells via mTOR/S6 pathway in oral lichen planus.

BACKGROUND
Although abnormal cell proliferation and apoptosis are associated with the pathogenesis of OLP, the exactly mechanism of which is not yet known. It has been reported that glutamine (Gln) can promote cell proliferation and inhibit apoptosis of various tumor cells. This study aims to evaluate the effect of Gln metabolism on the balance of proliferation and apoptosis in epithelial cells of OLP.


METHODS
30 Human OLP specimens and 11 normal controls were stained by immunohistochemistry (IHC) to detect the levels of proliferation and Gln metabolism related proteins. Then, the critical role of Gln in cell proliferation and apoptosis was determined by Gln deprivation or treatment with glutaminase inhibitor (CB-839) to intervene Gln metabolism in human gingival epithelial cells (HGECs). Cell proliferation was detected using CCK8, p-mTOR and p-S6 proteins were detected using Western Blot, cell apoptosis and cell cycle were detected using flow cytometry, and cell stress was detected using immunofluorescence.


RESULTS
Compared with normal controls, OLP specimens showed higher levels of Ki-67 and Gln metabolism-related proteins, including Gln transporter (ASCT2), glutaminase (GLS), and pathway proteins (p-mTOR and p-S6). In vitro, Gln promoted cell proliferation and simultaneously upregulated the activity of mTOR/S6 pathway. Moreover, rapamycin, an mTOR pathway inhibitor, could effectively block the Gln-induced cell proliferation. MHY1485, an mTOR pathway agonist, could effectively reverse the decline of cell proliferation under Gln deprivation. In addition, inhibiting Gln metabolism caused the accumulation of intracellular ROS and induced cell apoptosis. However, N-acetylcysteine (NAC) reversed this state and then decreased cell apoptosis by eliminating intracellular ROS.


CONCLUSION
Gln metabolism is essential to maintain the balance of proliferation and apoptosis in oral epithelial cells, and inhibition of Gln metabolism may have a beneficial effect on OLP treatment.