LC3-associated phagocytosis in bone marrow macrophages suppresses acute myeloid leukemia progression through STING activation
Jamie A. Moore, … , Kristian M. Bowles, Stuart A. Rushworth
Jamie A. Moore, … , Kristian M. Bowles, Stuart A. Rushworth
Published January 6, 2022
Citation Information: J Clin Invest. 2022;132(5):e153157. https://doi.org/10.1172/JCI153157.
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Research Article Hematology Oncology

LC3-associated phagocytosis in bone marrow macrophages suppresses acute myeloid leukemia progression through STING activation

Abstract

The bone marrow (BM) microenvironment regulates acute myeloid leukemia (AML) initiation, proliferation, and chemotherapy resistance. Following cancer cell death, a growing body of evidence suggests an important role for remaining apoptotic debris in regulating the immunologic response to and growth of solid tumors. Here, we investigated the role of macrophage LC3–associated phagocytosis (LAP) within the BM microenvironment of AML. Depletion of BM macrophages (BMMs) increased AML growth in vivo. We show that LAP is the predominate method of BMM phagocytosis of dead and dying cells in the AML microenvironment. Targeted inhibition of LAP led to the accumulation of apoptotic cells (ACs) and apoptotic bodies (ABs), resulting in accelerated leukemia growth. Mechanistically, LAP of AML-derived ABs by BMMs resulted in stimulator of IFN genes (STING) pathway activation. We found that AML-derived mitochondrial damage–associated molecular patterns were processed by BMMs via LAP. Moreover, depletion of mitochondrial DNA (mtDNA) in AML-derived ABs showed that it was this mtDNA that was responsible for the induction of STING signaling in BMMs. Phenotypically, we found that STING activation suppressed AML growth through a mechanism related to increased phagocytosis. In summary, we report that macrophage LAP of apoptotic debris in the AML BM microenvironment suppressed tumor growth.

Authors

Jamie A. Moore, Jayna J. Mistry, Charlotte Hellmich, Rebecca H. Horton, Edyta E. Wojtowicz, Aisha Jibril, Matthew Jefferson, Thomas Wileman, Naiara Beraza, Kristian M. Bowles, Stuart A. Rushworth

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Figure 5

AML-derived ABs contain mitochondria that are processed by BMMs.

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AML-derived ABs contain mitochondria that are processed by BMMs. (A) ABs...
(A) ABs were isolated from MN1 and nonmalignant LSK cells and cultured with BMMs from C57/BL6 mice for 24 hours, and RNA was extracted for qPCR analysis. (B) Relative gene expression of Gbp2, Irf7, and Ifit3 in BMMs cultured with MN1 and LSK ABs (n = 5). (C) Representative images of nonmalignant LSK and MN1 cells stained with MitoTracker Green (MTG) or VybrantDil (VD). ABs were isolated and analyzed via image flow cytometry. Scale bar: 7 μm. (D) Percentage of ABs from LSK and MN1 cells that were positive for MitoTracker Green and VybrantDil (n = 5). (E) Representative confocal microscopy images of human AML cells that were transduced with a GFP membrane virus and stained with MitoTracker Red (MTR) and Hoechst. Arrows indicate blebs containing mitochondria. Scale bar: 10 μm. (F) Nonmalignant CD34, MN1, and human AML cells were stained with MitoTracker Red before isolating the ABs and analyzing them via flow cytometry for the percentage of ABs containing MitoTracker Red (mito+) (n = 5). (G) Schematic diagram of the experimental design. Primary AML cells were transduced with rLV.EF1.mCherry-Mito9 lentivirus (mCh-AML) and injected into NSG mice and left for 35 days (n = 3). (H) BM was extracted and BMMs were analyzed by flow cytometry for mCherry fluorescence (MFI). (I) mCh-AML cells were cocultured with BMSCs and BMMs and analyzed by microscopy for mitochondria uptake, as determined by mCherry MFI (n = 25). Scale bar: 10 μm. Data indicate the mean ± SD. *P < 0.05 and **P < 0.01, by Mann-Whitney U test (B, D, and I) and Kruskal-Wallis test (F and H).