IL-6 produced by prostate epithelial cells stimulated with <i>Trichomonas vaginalis</i> promotes proliferation of prostate cancer cells by inducing M2 polarization of THP-1-derived macrophages

Trichomonas vaginalis (Tv), a protozoan parasite causing sexually-transmitted disease, has been detected in tissue of prostatitis, benign prostatic hyperplasia (BPH) and prostate cancer (PCa). IL-6, a mediator of chronic inflammation, induces the progression of prostate cancer, and influences the polarization of M2 macrophages, which are the main tumor-associated macrophages. We investigated whether IL-6 produced by human prostate epithelial cells stimulated with Tv induces the M2 polarization of THP-1-derived macrophages, which in turn promotes the progression of PCa. Conditioned medium was prepared from Tv-infected (TCM) and uninfected (CM) prostate epithelial cells (RWPE-1). Thereafter conditioned medium was prepared from macrophages after incubation with CM (M-CM) or TCM (M-TCM). RWPE-1 cells infected with Tv produced IL-6 and chemokines such as CCL2 and CXCL8. When human macrophages were treated with conditioned medium of RWPE-1 cells co-cultured with Tv (TCM), they became polarized to M2-like macrophages as indicated by the production of IL-10 and TGF-β, and the expression of CD36 and arginase-1, which are M2 macrophage markers. Moreover, proliferation of the M2-like macrophages was also increased by TCM. Blockade of IL-6 signaling with IL-6 receptor antibody and JAK inhibitor (Ruxolitinib) inhibited M2 polarization of THP-1-derived macrophages and proliferation of the macrophages. To assess the effect of crosstalk between macrophages and prostate epithelial cells inflamed by Tv infection on the growth of prostate cancer (PCa) cells, PC3, DU145 and LNCaP cells were treated with conditioned medium from THP-1-derived macrophages stimulated with TCM (M-TCM). Proliferation and migration of the PCa cells were significantly increased by the M-TCM. Our findings suggest that IL-6 produced in response to Tv infection of the prostate has an important effect on the tumor microenvironment by promoting progression of PCa cells following induction of M2 macrophage polarization.阴道毛滴虫（Trichomonas vaginalis, Tv）是一种可引发性传播疾病的原生动物寄生虫，目前已在前列腺炎、良性前列腺增生（benign prostatic hyperplasia, BPH）以及前列腺癌（prostate cancer, PCa）的病变组织中被检出。白细胞介素6（IL-6）作为慢性炎症的关键介导因子，不仅可促进前列腺癌进展，还可调控M2型巨噬细胞（M2 macrophages）的极化过程——这类细胞是肿瘤微环境中的主要肿瘤相关巨噬细胞。本研究旨在探究经Tv刺激的人类前列腺上皮细胞所分泌的IL-6，是否会诱导THP-1源性巨噬细胞（THP-1-derived macrophages）发生M2极化，进而推动前列腺癌的恶性进展。实验人员分别从感染Tv的前列腺上皮RWPE-1细胞（TCM组）与未感染Tv的RWPE-1细胞（CM组）中制备条件培养基；随后将巨噬细胞分别与CM、TCM共孵育，进一步制备得到M-CM与M-TCM两种条件培养基。感染Tv的RWPE-1细胞可分泌IL-6及CCL2、CXCL8等趋化因子。当人类巨噬细胞经与Tv共培养的RWPE-1细胞的条件培养基（TCM）处理后，会极化为M2样巨噬细胞，具体表征为IL-10、转化生长因子β（TGF-β）的分泌量上升，以及M2型巨噬细胞标志性分子CD36与精氨酸酶-1（arginase-1）的表达上调。此外，TCM还可显著促进M2样巨噬细胞的增殖。通过IL-6受体抗体与JAK抑制剂芦可替尼（Ruxolitinib）阻断IL-6信号通路后，可有效抑制THP-1源性巨噬细胞的M2极化过程以及巨噬细胞的增殖能力。为明确Tv感染引发炎症的前列腺上皮细胞与巨噬细胞之间的串扰效应对前列腺癌细胞生长的影响，研究人员使用经TCM刺激的THP-1源性巨噬细胞的条件培养基（M-TCM）处理PC3、DU145及LNCaP三种前列腺癌细胞系。结果表明，M-TCM可显著提升前列腺癌细胞的增殖与迁移能力。综上，本研究结果提示：前列腺组织感染Tv后产生的IL-6，可通过诱导M2型巨噬细胞极化，进而促进前列腺癌细胞的恶性进展，最终对肿瘤微环境发挥重要的调控作用。