miR-138 Reduces the Dysfunction of T Follicular Helper Cells in Osteosarcoma via the PI3K/Akt/mTOR Pathway by Targeting PDK1

Objective. To study the effect of miR-138 on the function of osteosarcoma (OS) T follicular helper cells (Tfh cells) and its mechanism. Methods. Peripheral blood mononuclear cells (PBMCs) were isolated from patients with osteosarcoma (OS group) and healthy volunteers (control group). CD4+CXCR5+ Tfh cells and CD9+ B cells were sorted by flow cytometry. qRT-PCR was used to detect the expression of miR-138 and PDK1 in the peripheral blood and CD4+CXCR5+ Tfh cells. Flow cytometry was employed to detect the proportion of CD4+CXCR5+ Tfh cells in CD4+ T cells, the level of CD40L in CD4+CXCR5+ Tfh cells, and the expression of CD27 and CD38 in B cells. Western blot was used to determine the protein expression of PDK1, PI3K, p-Akt, Akt, p-mTOR, and mTOR. In addition, dual-luciferase reporter assay was performed to verify the relationship between miR-138 and PDK1. ELISA method was used to determine the levels of IgM, IgG, IL-10, and IL-21. Results. Compared with that of the control group, the expression of miR-138 in PBMC and CD4+CXCR5+ Tfh cells of the OS group was lower; overexpression of miR-138 could promote the maturation of Tfh cells and immature B cells. The results of the dual-luciferase report experiment showed that miR-138 can target and negatively regulate PDK1, and PDK1 can reverse the effect of miR-138 on the function of Tfh cells and immature B cells. Conclusion. miR-138 inhibits the PI3K/Akt/mTOR pathway by targeting and negatively regulating PDK1 to alleviate the dysfunction of T follicular helper cells in OS.