M2-type Macrophage Polarization Research Articles

Cannabinoid receptor 1 mediates M1 type macrophage polarization by G(α)i/o/RhoA/NF-κB p65 signaling pathway in murine liver injury

Abstract Macrophage, as an essential component of innate immunity, has emerged as a key role in liver injury. There are two main subtypes of macrophages in liver, referred to as tissue-resident Kupffer cells and bone marrow (BM)-derived monocyte/macrophages (BMMs). Macrophages are phenotypically heterogeneous and broadly characterized according to their polarization as M1/M2 types. Our previous research had demonstrated that cannabinoid receptor 1 (CB1) mediated infiltration and activation of BMMs in mouse liver injury. Here we investigated the role of CB1 in macrophage polarization. ICR mice were lethally irradiated and received BM transplants from enhanced GFP transgenic mice. Four weeks later, mice of BM reconstruction were subjected to carbon tetrachloride (CCl4)-induced liver injury. Expressions of M1 gene signatures (CD86, iNOS, IL-1b, IL-6, TNFa) in livers or cultured primary BMMs were measured by RT qPCR or Western blot. In the chimeric murine model, we found that amount of M1 type macrophages were increased from 1 to 28 days in CCl4 treatment with a maximal increase at 28 days by flow cytometry. Almost 70% of M1 type macrophages were from BMMs (CD86+EGFP+) and 30% of them were from Kupffer cells (CD86−EGFP+). Meanwhile, the dynamic changes of M1 gene signatures were consistent in injured livers by RT qPCR or Western blot. Blockage of CB1 by administration of its specific antagonist or siRNA in vivo decreased the amount of M1 type of BMMs origin, but showed little effect on that of Kupffer cells. Activation of CB1 by its agonist, ACEA, promoted M1 polarization of BMMs, depending on G(a)i/o/RhoA/NF-κB p65 signaling pathway. In conclusion, these data suggest that CB1 plays a crucial role in regulating M1 polarization of BMMs in liver injury.

Notch signaling regulates M2 type macrophage polarization during the development of proliferative vitreoretinopathy

Macrophages play an important role in the pathogenesis of proliferative vitreoretinopathy (PVR). M2 macrophages can promote tissue remodeling and repair. In this study, CD206 positive M2 type macrophages were found in preretinal fibrous membranes of the mouse model of PVR induced by the intravitreal injection of retinal pigment epithelial (RPE) cells. Notch signaling determines M2 macrophage polarization. The specific inhibition of Notch signaling pathway by the intravitreal injection of γ-secretase inhibitor DAPT attenuated RPE cells-induced PVR formation as demonstrated by the decreased expression of α-SMA, and inhibited M2 type macrophage infiltation as demonstrated by the decreased expression of Arg-1. Notch signaling may modulate PVR formation by regulating M2 type macrophage polarization.

Doxycycline Inhibits Polarization of Macrophages to the Proangiogenic M2-type and Subsequent Neovascularization

Macrophages occur along a continuum of functional states between M1-type polarized macrophages with antiangiogenic and antitumor activity and M2-type polarized macrophages, which have been implicated to promote angiogenesis and tumor growth. Proangiogenic M2-type macrophages promote various pathologic conditions, including choroidal neovascularization in models of neovascular age-related macular degeneration, or certain cancers, such as glioblastoma multiforme. Thus, a potential novel therapeutic approach to target pathological angiogenesis in these conditions would be to inhibit the polarization of macrophages toward the proangiogenic M2-type. However, no pharmacological inhibitors of M2-type macrophage polarization have been identified yet. Here we performed an unbiased pharmacological and small chemical screen to identify drugs that inhibit proangiogenic M2-type macrophage polarization and block pathologic macrophage-driven neovascularization. We identified the well tolerated and commonly used antibiotic doxycycline as a potent inhibitor of M2-type polarization of macrophages. Doxycycline inhibited, in a dose-dependent manner, M2-type polarization of human and bone marrow-derived mouse macrophages without affecting cell viability. Furthermore, doxycycline inhibited M2-type macrophage polarization and subsequent neovascularization in vivo in a laser injury model of choroidal neovascularization. Thus, doxycycline could be used to enhance current antiangiogenic treatment approaches in various conditions that are promoted by proangiogenic M2-type macrophages, including neovascular age-related macular degeneration and certain cancers.

CCL2 and Interleukin-6 Promote Survival of Human CD11b+ Peripheral Blood Mononuclear Cells and Induce M2-type Macrophage Polarization

CCL2 and interleukin (IL)-6 are among the most prevalent cytokines in the tumor microenvironment, with expression generally correlating with tumor progression and metastasis. CCL2 and IL-6 induced expression of each other in CD11b(+) cells isolated from human peripheral blood. It was demonstrated that both cytokines induce up-regulation of the antiapoptotic proteins cFLIP(L) (cellular caspase-8 (FLICE)-like inhibitory protein), Bcl-2, and Bcl-X(L) and inhibit the cleavage of caspase-8 and subsequent activation of the caspase-cascade, thus protecting cells from apoptosis under serum deprivation stress. Furthermore, both cytokines induced hyperactivation of autophagy in these cells. Upon CCL2 or IL-6 stimulation, CD11b(+) cells demonstrated a significant increase in the mannose receptor (CD206) and the CD14(+)/CD206(+) double-positive cells, suggesting a polarization of macrophages toward the CD206(+) M2-type phenotype. Caspase-8 inhibitors mimicked the cytokine-induced up-regulation of autophagy and M2 polarization. Furthermore, E64D and leupeptin, which are able to function as inhibitors of autophagic degradation, reversed the effect of caspase-8 inhibitors in the M2-macrophage polarization, indicating a role of autophagy in this mechanism. Additionally, in patients with advanced castrate-resistant prostate cancer, metastatic lesions exhibited an increased CD14(+)/CD206(+) double-positive cell population compared with normal tissues. Altogether, these findings suggest a role for CCL2 and IL-6 in the survival of myeloid monocytes recruited to the tumor microenvironment and their differentiation toward tumor-promoting M2-type macrophages via inhibition of caspase-8 cleavage and enhanced autophagy.