Background DICAM, a dual Ig domain containing adhesion molecule, is involved in cell-cell adhesion through a direct interaction with αVβ3 integrin. In our previous study showing the inhibitory role in osteoclastogenesis, we found a clue that DICAM also has a suppressive role in macrophage differentiation. However, it remains still obscure the role of DICAM in macrophage differentiation and M1/M2 polarization.
Objectives To investigate the role of DICAM in macrophage differentiation and M1/M2 polarization.
Methods To induce differentiation into resting M0 macrophage, THP-1 cells were cultured with 100 nM PMA for 24 h, then rested for 6 days. For M1/M2 polarization, resting M0 THP-1 macrophages were treated with IFN-γ or IL-4 for 24 h. To investigate the role of DICAM during THP-1 macrophage differentiation, THP-1 cells were infected with 50 moi of control LacZ adenovirus or with DICAM adenovirus.
Results The expression of DICAM was increased during PMA-induced THP-1 differentiation, and DICAM was slightly decreased by IFN-γ for M1 polarization and increased by IL-4 for M2 polarization. The overexpresion of DICAM in THP-1 cells suppressed PMA-mediated macrophage differentiation in the number of activated branched macrophage and macrophage marker expression, CD14 and CD68. However, DICAM does not affect the viability and proliferation of PMA-stimulated THP-1 macrophage. Functionally, DICAM attenuated the TNF-α secretion of differentiated THP-1 cells and their phagocytic activity as well. To investigate the molecular mechanisms for DICAM-mediated suppression of macrophage differentiation, we conducted microarray analyses, which revealed that DICAM overexpression significantly suppressed type 1 interferon system. Among interferon regulatory factors (IRFs) family, IRF7 was most significantly reduced by DICAM. DICAM also attenuated Akt activation and increased a nuclear translocation of FoxO3a that is known to be a critical negative regulator of IRF7. Consistently, DICAM also decreased total integrin β3 level and integrin-linked kinase (ILK) phosphorylation, the major adaptor molecule of integrin β3. Based on the fact that type 1 interferon is important in M1 macrophage polarization, we investigated the role of DICAM in M1/M2 polarization of macrophage. Overexpression of DICAM induced downregulation of M1-associated genes such as IL-12b p40, IL12 p19, TNFa, IL-6, and IL-1b but did not affect M2 genes, Arg1 and Fizz1. In addition, DICAM increased IL-10, but decreased TNFa and INF-β.
Conclusions DICAM potently reduces differentiation and function of THP-1 macrophage and skews a THP-1 polarization into M2-like macrophage via suppression of integrin αVβ3-dependent Akt-FoxO3a-IRF7 pathway.
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Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (2011-0007402, 2013-R1A2A2A01069204).
Disclosure of Interest : None declared