Sangsuwan Rapeepat, Thuamsang Bhasirie, Pacifici Noah, Allen Riley, Han Hyunsoo, Miakicheva Svetlana, Lewis Jamal S
Department of Biomedical Engineering, University of California, Davis, 1 Shields Avenue, Davis, CA 95616 USA.
Cell Mol Bioeng. 2020 Sep 21;13(5):541-557. doi: 10.1007/s12195-020-00652-x. eCollection 2020 Oct.
Lactate secreted by tumors is not just a byproduct, but rather an active modulator of immune cells. There are few studies aimed at investigating the true effect of lactate, which is normally confounded by pH. Such a knowledge gap needs to be addressed. Herein, we studied the immunomodulatory effects of lactate on dendritic cells (DCs) and macrophages (MΦs).
Bone marrow-derived innate immune cells were treated with 50 mM sodium lactate (sLA) and incubated for 2 days or 5 days at 37 °C. Controls included media, lipopolysaccharide (LPS), MCT inhibitors (α-cyano-4-hydroxycinnamic acid and AR-C15585). Flow cytometric analysis of immune phenotypes were performed by incubating cells with specific marker antibodies and viability dye. Differential expression analyses were conducted on R using limma-voom and adjusted p-values were generated using the Bejamini-Hochberg Procedure.
Lactate exposure attenuated DC maturation through the downregulation of CD80 and MHCII expression under LPS stimulation. For MΦs, lactate exposure resulted in M2 polarization as evidenced by the reduction of M1 markers (CD38 and iNOS), and the increase in expression of CD163 and Arg1. We also revealed the role of monocarboxylate transporters (MCTs) in mediating lactate effect in MΦs. MCT4 inhibition significantly boosted lactate M2 polarization, while blocking of MCT1/2 failed to reverse the immunosuppressive effect of lactate, correlating with the result of gene expression that lactate increased MCT4 expression, but downregulated the expression of MCT1/2.
This research provides valuable insight on the influence of metabolic products on tumor immunity and will help to identify novel metabolic targets for augmenting cancer immunotherapies.
肿瘤分泌的乳酸不仅仅是一种副产品，更是免疫细胞的活性调节剂。旨在研究乳酸真正作用的研究较少，其作用通常会受到pH值的干扰。这种知识空白需要得到填补。在此，我们研究了乳酸对树突状细胞（DCs）和巨噬细胞（MΦs）的免疫调节作用。
用50 mM乳酸钠（sLA）处理骨髓来源的天然免疫细胞，并在37°C下孵育2天或5天。对照组包括培养基、脂多糖（LPS）、MCT抑制剂（α-氰基-4-羟基肉桂酸和AR-C15585）。通过用特异性标记抗体和活力染料孵育细胞，对免疫表型进行流式细胞术分析。使用limma-voom在R上进行差异表达分析，并使用Benjamini-Hochberg程序生成校正后的p值。
在LPS刺激下，乳酸暴露通过下调CD80和MHCII表达减弱了DC的成熟。对于MΦs，乳酸暴露导致M2极化，表现为M1标记物（CD38和iNOS）减少，以及CD163和Arg1表达增加。我们还揭示了单羧酸转运蛋白（MCTs）在介导乳酸对MΦs作用中的作用。抑制MCT4显著增强了乳酸诱导的M2极化，而阻断MCT1/2未能逆转乳酸的免疫抑制作用，这与基因表达结果相关，即乳酸增加了MCT4的表达，但下调了MCT1/2的表达。
本研究为代谢产物对肿瘤免疫的影响提供了有价值的见解，并将有助于确定增强癌症免疫治疗的新代谢靶点。
