Paradoxical Upregulation of Macrophage CXCR7 by Myeloid‐specific Gene Editing in Mice

Abstract

ObjectiveWe previously reported that the chemokine receptor CXCR7 is induced during monocyte‐to‐macrophage differentiation in vitro, leading to a switch of SDF‐1 signaling profile and increased macrophage migration/phagocytosis. However, the role of monocyte/macrophage CXCR7 in vivo remains unknown.Methods and ResultsThe CXCR7‐floxed mice (CXCR7‐floxed+/+) were crossed with the LyzM‐Cre mice (LyzM‐Cre+/+) to obtain myeloid‐specific deletion of CXCR7 in vivo. Unlike the systemic knockouts, this new line was viable, fertile, and did not show obvious gross physical or behavioral abnormalities. However, we found significantly higher number of periphery blood monocytes in CXCR7‐floxed+/+/LyzM‐Cre+/+ mice compared with CXCR7‐floxed+/+/LyzM‐Cre−/− mice, indicating a role of CXCR7 in monocytosis. Further study indicated that this phenotype cannot be solely attributed to the disruption of LyzM gene by Cre insertion or the inclusion of floxed sequence to CXCR7 gene. Surprisingly, CXCR7 mRNA and protein expression were dramatically upregulated in CXCR7‐floxed+/+/LyzM‐Cre+/+ mice compared with littermate CXCR7‐floxed+/+/LyzM‐Cre−/− mice, both in bone marrow‐derived macrophages and in peritoneal macrophages, suggesting a potential compensatory mechanism. This is supported by our finding that PCR mapping indicated partial deletion of myeloid CXCR7 gene via the Cre‐LoxP approach and that adenovirus delivery of the Cre gene into CXCR7‐floxed macrophages in vitro mimicked CXCR7 induction in vivo. In addition, in the mouse peritonitis model, injection of thioglycolate led to more macrophage infiltration into the peritoneum in CXCR7‐floxed+/+/LyzM‐Cre+/+ mice.ConclusionsMyeloid‐specific manipulation of CXCR7 gene by using Cre‐LoxP method leads to compensatory upregulation of CXCR7 in monocytes/macrophages, which is associated with increased monocytosis and cell migration in vivo.Support or Funding InformationAHA national SDG award