Background and purpose: The infiltration of tumor-associated macrophage (TAM) is closely related to tumor progression

but the mechanism of its action is not yet clear. Therefore

we explored the effects of miR-99a on macrophage polarization and its putative effects on the cell proliferation and invasion of endometrial cancer cells. Methods: We detected the expression of CD68 in endometrial cancer tissues and analyzed its relationship with the clinicopathological parameters of patients. The supernatants of human endometrial cancer cells HEC-1B and RL95-2 were used to induce human monocyte U937 to differentiate into M2-type macrophages

namely TAMs. The synthetic miR-99a mimic fragment was transfected into induced TAM. After transfection

real-time fluorescence quantitative polymerase chain reaction (RTFQ-PCR) and flow cytometry were used to explore the expression of macrophage-associated factors CD68

CD163 and CD206

and enzyme-linked immunosorbent assay (ELISA) were used to measure the secretions of IL-12

IL-4 and IL-10 upon induction. TAMs overexpressing miR-99a were co-cultured with endometrial cancer cells. Cell counting kit-8 (CCK-8) and Matrigel invasion assay were used to detect its effects on the cell proliferation and invasion of endometrial cancer and putative mechanisms. Results: The high expression of CD68 indicating the TAM infiltration were positively related with tumor myometrial invasion and new angiogenesis. The supernatant of cancer cells successfully induced monocytes U937 differentiating into M2-type TAM. Overexpression of miR-99a in TAM decreased the expression of M2-type macrophage markers

CD68 and CD163

compared with the control group (P0.01)

while the expression of CD206 showed no significant difference (P0.05). The secretion of IL-12 increased (P0.01)

while the secretions of IL-4 and IL-10 decreased (P0.01)

suggesting that macrophages were polarized towards M1 type. Moreover

transfection with miR-99a in TAMs attenuated proliferation (P0.01) and invasion (P0.05) of endometrial cancer cells. Lastly

the expressions of mTOR and its downstream genes were down-regulated. Conclusion: The high expression of CD68 indicating the TAM infiltration is positively related with tumor myometrial invasion and new angiogenesis of endometrial cancer. Overexpression of miR-99a can reverse the polarization of monocytes to M2 phenotype

and thus inhibits the cell growth and invasion of endometrial cancer cells

probably through suppressing the signal pathway of mTOR.