Activated Hepatic Stellate Cells Induce Infiltration and Formation of CD163+ Macrophages via CCL2/CCR2 Pathway

Abstract Background: Growing evidence indicates that activated hepatic stellate cells (aHSCs) play unexpected roles in regulating immune cells’ function during liver fibrosis. Macrophages feature with inducible plasticity according to the circumstances while patrol for potential pathogens. However, studies seldom investigate whether and how the aHSCs regulate the phenotype and function of macrophages during liver fibrosis. Methods: 96 patients with different stages of liver fibrosis were involved in our study. Metavir score system was used to evaluate the degree of fibrosis. The expression of hepatic CCL2 and CD163 were detected by immunohistochemistry, and the relationship among CD163, CCL2, and fibrosis scores were explored. We co-cultured the aHSCs and THP-1-derived M0-type macrophages (M0MФ) to observe whether aHSCs modulate the expression of CD163 on macrophages in vitro. Furthermore, we treated the M0MФ with aHSCs’ supernatant and investigated the production of CCL2 in aHSCs by ELISA and immunofluorescence assay. To explore whether CCL2/CCR2 axis plays a crucial role in macrophage phenotypic changes during liver fibrosis, we used recombinant CCL2 and its specific receptor antagonist. Moreover, we employed LX2 system to confirm our results. Results: We found that hepatic M2 macrophages (CD163+) infiltration increased in different stages of liver fibrosis (F0-1: 34.95±18.12; F2-3: 77.57±32.48; F4: 99.62±40.84, F0-1 vs. F2-3, P<0.001; F2-3 vs. F4, P=0.074). After in vitro co-cultured with aHSCs, the macrophages expressed higher levels of CD163 (29.5±6.1% vs. 2.7±1.1%) as well as CD206 (28.0±4.2% vs. 2.4±1.2%) compared with the control. Then we found aHSC supernatant up-regulated the expression of CD163 (26.1±2.8%) and CD206 (25.8±3.8%) on macrophages independently. We noted aHSCs’ supernatant contained a high level of CCL2, which increased dramatically while TGF-β stimulation. Meanwhile, CCL2 staining score increased with the progress of fibrosis ( N: 23.26±13.85; F1: 4 8.56±19.18; F2: 58.25±16.24; F3: 81.32±18.48; F4: 110.93±24.75). Intriguingly, CCL2 significantly up-regulated the expression of CD163 (27.6±7.0%) and CD206 (26.5±5.1%) on macrophages besides inducing their aggregation. Results were confirmed with LX2 co-culture system. Conclusions: (1) The expression of M2 macrophage marker CD163 increased significantly during the progress of liver fibrosis and associated with fibrosis severity. (2) AHSCs can recruit macrophages and induce their M2 phenotypic transformation through CCL2/CCR2 pathway.