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Published on: April 3, 2017
Macrophage LRP1 (Low-Density Lipoprotein Receptor-Related Protein 1) Is Required for the Effect of CD47 Blockade on
Paul A Mueller1, Yoko Kojima2, Katherine T Huynh1
1Center for Preventive Cardiology, Knight Cardiovascular Institute, Oregon Health & Science University, Portland (P.A.M., K.T.H., R.A.M., H.T., N.P., S.F.).
Objective:
Antibody blockade of the "do not eat me" signal CD47 (cluster of differentiation 47) enhances efferocytosis and reduces lesion size and necrotic core formation in murine atherosclerosis. TNF (Tumor necrosis factor)-α expression directly enhances CD47 expression, and elevated TNF-α is observed in the absence of the proefferocytosis receptor LRP1 (low-density lipoprotein receptor-related protein 1), a regulator of atherogenesis and inflammation. Thus, we tested the hypothesis that CD47 blockade requires the presence of macrophage LRP1 to enhance efferocytosis, temper TNF-α-dependent inflammation, and limit atherosclerosis. Approach and Results: Mice lacking systemic apoE (apoE-/-), alone or in combination with the loss of macrophage LRP1 (double knockout), were fed a Western-type diet for 12 weeks while receiving anti-CD47 antibody (anti-CD47) or IgG every other day. In apoE-/- mice, treatment with anti-CD47 reduced lesion size by 25.4%, decreased necrotic core area by 34.5%, and decreased the ratio of free:macrophage-associated apoptotic bodies by 47.6% compared with IgG controls (P<0.05), confirming previous reports. Double knockout mice treated with anti-CD47 showed no differences in lesion size, necrotic core area, or the ratio of free:macrophage-associated apoptotic bodies compared with IgG controls. In vitro efferocytosis was 30% higher when apoE-/- phagocytes were incubated with anti-CD47 compared with IgG controls (P<0.05); however, anti-CD47 had no effect on efferocytosis in double knockout phagocytes. Analyses of mRNA and protein showed increased CD47 expression in anti-inflammatory IL (interleukin)-4 treated LRP1-/- macrophages compared with wild type, but no differences were observed in inflammatory lipopolysaccharide-treated macrophages.
Conclusions:
The proefferocytosis receptor LRP1 in macrophages is necessary for anti-CD47 blockade to enhance efferocytosis, limit atherogenesis, and decrease necrotic core formation in the apoE-/- model of atherosclerosis.
Insights
Blockading the CD47 "do not eat me" signal enhances efferocytosis in atherosclerosis models. However, this effect requires macrophage LRP1 to reduce inflammation and lesion size.
Area of Science:
- Immunology
- Cardiovascular Research
- Cell Biology
Background:
- CD47 (cluster of differentiation 47) blockade enhances efferocytosis and reduces atherosclerosis in mouse models.
- Tumor necrosis factor-α (TNF-α) upregulates CD47 expression.
- Low-density lipoprotein receptor-related protein 1 (LRP1) is a regulator of atherogenesis and inflammation, and its absence is linked to elevated TNF-α.
Purpose of the Study:
- To test if CD47 blockade requires macrophage LRP1 to enhance efferocytosis, reduce TNF-α-dependent inflammation, and limit atherosclerosis.
Main Methods:
- Mice lacking apoE (apoE-/-), with or without macrophage LRP1, were treated with anti-CD47 antibody or IgG.
- Atherosclerosis progression was assessed by lesion size and necrotic core formation.
- In vitro efferocytosis assays were performed using phagocytes from these mice.
- mRNA and protein analyses were conducted on macrophages.
Main Results:
- In apoE-/- mice, anti-CD47 treatment reduced lesion size, necrotic core area, and increased efferocytosis.
- In mice lacking macrophage LRP1, anti-CD47 treatment had no significant effect on atherosclerosis or efferocytosis.
- In vitro, anti-CD47 enhanced efferocytosis in apoE-/- phagocytes but not in those lacking LRP1.
- CD47 expression was increased in LRP1-/- macrophages treated with IL-4, but not LPS.
Conclusions:
- Macrophage LRP1 is essential for the therapeutic effects of CD47 blockade in atherosclerosis.
- CD47 blockade's ability to enhance efferocytosis and reduce atherosclerosis is dependent on the presence of LRP1.
