SIRPA-Inhibited, Marrow-Derived Macrophages Engorge, Accumulate, and Differentiate in Antibody-Targeted Regression of Solid Tumors

Abstract

SUMMARY Marrow-derived macrophages are highly phagocytic, but whether they can also traffic into solid tumors and engulf cancer cells is questionable, given the well-known limitations of tumor-associated macrophages (TAMs). Here, SIRPα on macrophages from mouse and human marrow was inhibited to block recognition of its ligand, the “marker of self” CD47 on all other cells. These macrophages were then systemically injected into mice with fluorescent human tumors that had been antibody targeted. Within days, the tumors regressed, and single-cell fluorescence analyses showed that the more the macrophages engulfed, the more they accumulated within regressing tumors. Human-marrow-derived macrophages engorged on the human tumors, while TAMs were minimally phagocytic, even toward CD47-knockdown tumors. Past studies had opsonized tumors in situ with antibody and/or relied on mouse TAMs but had not injected SIRPα-inhibited cells; also, unlike past injections of anti-CD47, blood parameters remained normal and safe. Consistent with tumor-selective engorge-and-accumulate processes in vivo, phagocytosis in vitro inhibited macrophage migration through micropores that mimic features of dense 3D tissue. Accumulation of SIRPα-inhibited macrophages in tumors favored tumor regression for 1–2 weeks, but donor macrophages quickly differentiated toward non-phagocytic, high-SIRPα TAMs. Analyses of macrophages on soft (like marrow) or stiff (like solid tumors) collagenous gels demonstrated a stiffness-driven, retinoic-acid-modulated upregulation of SIRPα and the mechanosensitive nuclear marker lamin-A. Mechanosensitive differentiation was similarly evident in vivo and likely limited the anti-tumor effects, as confirmed by re-initiation of tumor regression by fresh injections of SIRPα-inhibited macrophages. Macrophage motility, phagocytosis, and differentiation in vivo are thus coupled.

Efferocytosis Fuels Requirements of Fatty Acid Oxidation and the Electron Transport Chain to Polarize Macrophages for Tissue Repair

“…In separate experiments, in which we screened transcriptomic responses to efferocytosis, gene ontology enrichment analysis of canonical pathways from our mRNA-seq analysis revealed the most significantly mobilized pathways; these included mitochondrial electron transport ( Figure 2D). Sequencing reads were aligned to murine gene annotation files to distinguish from human sequence (Alvey et al, 2017). Consistent with the metabolomics profile, we also validated that apoptotic cell stimulation of primary macrophages induced expression of genes involved in FAO, the electron transport chain, and oxidative phosphorylation pathways ( Figure 2E).…”

miR‐378a Modulates Macrophage Phagocytosis and Differentiation through Targeting CD47‐SIRPα Axis in Atherosclerosis

“…In the analysis, up‐ or downregulation of genes is represented by red or blue colour, respectively (Figure B). The mRNA associated with macrophage phenotypes ( Mrc1, Emr1 ) and Sirpa‐CD47 axis ( Sirpa, Slamf7, Itgam, Ptpn6 and CD47 ) was labelled on the clustering. Importantly, the expression of Sirpa, Itgam and Ptpn6 (also known as Shp1 ) increased obviously accompanying by decreasing phagocytic phenotype in ApoE −/− mice, compared with WT mice (‐log2 [fold change] >2 and P < 0.01).…”

Nuclear deformation causes DNA damage by increasing replication stress

“…As a result, cells frequently experience severe nuclear deformation and nuclear envelope (NE) rupture during confined migration (Bakhoum et al, 2018;Denais et al, 2016;Elacqua et al, 2018;Irianto et al, 2017a;Pfeifer et al, 2018;Raab et al, 2016;Wolf et al, 2013;Xia et al, 2019). Transient loss of NE integrity allows uncontrolled exchange between the nucleoplasm and cytoplasm, exposes the genomic DNA to cytoplasmic components such as nucleases, and leads to DNA damage (Nader et al, 2020;Alvey et al, 2017;Bakhoum et al, 2018;Cho et al, 2017;Cho et al, 2019;Denais et al, 2016;Elacqua et al, 2018;Hatch, 2018;Irianto et al, 2016;Pfeifer et al, 2018;Raab et al, 2016;Shah et al, 2017). Although cells rapidly repair their NE and continue to survive and migrate (Denais et al, 2016;Elacqua et al, 2018;Raab et al, 2016), the acquired DNA damage can increase genomic instability in these cancer cells (Nader et al, 2020;Alvey et al, 2017;Bakhoum et al, 2018;Irianto et al, 2017a;Pfeifer et al, 2018;Zhang et al, 2015) which could further enhance their metastatic potential and resistance to therapies.…”

“…While it is now well recognized that confined migration can cause DNA damage, the underlying molecular mechanism remains incompletely understood. Recent reports have implicated loss of DNA repair factors during NE rupture or local exclusion of repair factors due to nuclear deformation as possible mechanisms (Alvey et al, 2017;Cho et al, 2019;Irianto et al, 2016;Pfeifer et al, 2018;Xia et al, 2019). Exposure to cytoplasmic DNases such as TREX1 following NE rupture (Nader et al, 2020;Hatch, 2018;Shah et al, 2017) and mislocalization of organelles like mitochondria post NE rupture (Vargas et al, 2012) have also been suggested as cause of DNA damage.…”