Expression and function of the Atypical Chemokine Receptor 2 in endothelial cell biology

Atypical chemokine receptor 2 (ACKR2) is a scavenger receptor able to bind and lead to degradation most CC inflammatory chemokines acting as negative regulator of this system. Several studies reported its implication in tumor and inflammatory pathologies. ACKR2 was found expressed by syncytiotrophoblast cells in placenta and in noninflamed tissue, by endothelial cells in the afferent part of the lymphatic compartment in human skin, gut and lungs. Lower expression of the receptor was found in some leukocytes, such as alveolar macrophages and B lymphocytes. In order to elucidate the expression of ACKR2 in murine tissue and to understand the relevance of the receptor in cancer and inflammation, we generated a TdTomato/Luciferase reporter mouse, by introducing a cassette into the Ackr2 gene locus. Taking advantage of this reporter mouse, we have found a previously uncharacterized expression of ACKR2 in pulmonary vascular endothelial cell that we deeper investigated by flow cytometry. ACKR2 is expressed by ~50% of vascular endothelial cells that present high levels of the endothelial markers CD34, Tie-2, CD102, CD105, Sca-1, Meca-32, and CDH5. The expression of ACKR2 was also confirmed on human pulmonary vascular endothelial cells of healthy people and Non Small Cell Lung Carcinoma (NSCLC) patients. In addition, by RNA-seq analysis we found that ACKR2-deficiency in the lung endothelium alters the expression of genes regulating endothelial cell proliferation, viability, and development, and induces a pro-inflammatory phenotype. Lack of ACKR2 in hematopoietic progenitor cells resulted in increased levels of inflammatory chemokine receptors. Finally, performing preclinical model of melanoma primary tumor and metastasis by an orthotopic or intravenous injection of B16F10 cells, we found that WT and ACKR2-deficient mice display similar primary tumor growth, but ACKR2-deficient mice are protected from lung metastasis. The protection is lost when ACKR2 is missed only in lymphatic endothelial cells in conditional ACKR2 knockout mice. Collectively, these results indicate that ACKR2 is selectively expressed by a subpopulation of lung endothelial cells and that it has an important role in the control of inflammatory responses. The ACKR2 floxed colony we have generated will be 6 useful for future studies on the cellular and molecular role of ACKR2 in endothelial cell functions. Moreover, the specific targeting of ACKR2 in vascular or hematopoietic compartment could hint the possibility in the future to validate ACKR2 as a new target for innovative therapies for lung pathologies against infection and cancer.