The role of Siglec-5 and Siglec-14 in macrophage polarization

• Main Authors: Yu-Chang Ku, 顧育彰
• Other Authors: Yung-Chi Chang
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/bd3khh

碩士 === 國立臺灣大學 === 微生物學研究所 === 107 === Macrophages are highly plastic immune cells which can be further polarized into M1 or M2 macrophages in response to their surrounding microenvironment, and they play a critical role in maintaining the physiological homeostasis of the body. Siglec-5 and Siglec-14 are paired receptors primarily expresssing on macrophages and have the same sequence of amino acid in their first two N-terminal domains which are critical for ligand binding. However, Siglec-5 delivers inhibitory signals through its intracellular ITIM motif while Siglec-14 transduces activating signaling through the coupled ITAM-containing adaptor, DAP12, upon ligand engagement. In addition, sialylated glycoproteins derived from tumor cells have been shown to target various Siglec receptors to modulate macrophage polarizing into tumor-associated macrophages (TAMs) which can generate an immunosuppressive and pro-tumoral environment to assist cancer progression. In this study, we aim to investigate the role of Siglec-5 and Siglec-14 in macrophage polarization in response to different environmental cues. We first tried to establish a THP-1 macrophage polarization system driven by LPS/IFN-γ and IL-4/IL-13 stimulation, and a successful polarizing stimulation was proved by examing the expression of classical markers often used to classify the M1 and M2 population. Next, expression of M2/TAM markers of the THP-1 macrophages cultured with the tumor conditional medium were studied to explore the impact of the paired Siglec receptors, Siglec-5 and Siglec-14, in TAM programming. Comparable expression of M1 macrophage markers were observed in the Siglec-5/THP-1 and Siglec-14/THP-1 cells upon LPS/IFN-γ treatment, suggesting that exogenous expression of Siglec-5 and Siglec-14 on THP-1 cells did not affect M1 macrophage polarization. Notably, increased expression of M2-specific markers, CCL18, CCL22, IL-1RA, CD36 and CD204, as well as transcriptional factor involved in M2 polarization, PPAR-γ and LXR-α, were detected in Siglec-14-expressing THP-1 cells upon IL-4/IL-13 treatment. Moreover, we found that conditional mediums (CMs) derived from all the tested colorectal cancer cells (SW480, SW620 and HT29) successfully induce THP-1 macrophage differentiating into TAMs, while CM derived from lung cnacer cells (CL1-0 and CL1-5) and breast cancer cells (BT549) failed to achieve the same effects in our experimental condition. Importantly, Siglec-5 and Siglec-14 differentially regulated the TAM-related markers expression of the THP-1 macrophages stimulated with colon cancer CMs. Siglec-14/THP-1 cells expressed more CCL18, CCL22, IL-1RA, CD36, CD204 and IDO, while Siglec-5/THP-1 cells generated more IL-10 and MMP-9. Siglec-14 may induce the activation of STAT3 and the transcription of LXR-α to facilitate TAM formation upon colon cancer CM treatment. In conclusion, our results demonstrate that Siglec-5 and Siglec-14 can modulate the polarization of macrophages in response to IL-4/IL-13 and colon cancer CM, but further studies are required to elucidate the involved mechanisms.