Neutrophils play an essential role in Alzheimer's disease (AD) pathology. However, the extent of their heterogeneity remains poorly explored, particularly in the context of developing novel therapies targeting these cells.
We investigate the population structure of neutrophils purified from peripheral blood samples of AD mice. Utilizing single cell RNA sequencing, we comprehensively map neutrophil populations into six distinct clusters and find that the Neu-5 subset is specially enriched in AD mice. This subset exhibits fewer specific granules and a lower mature score. Gene ontology (GO) analysis reveals that genes involved in cytokine-mediated signaling are downregulated in the Neu-5 cluster. Furthermore, we identify the Ccrl2 gene is specifically upregulated in this subgroup, which is confirmed by flow cytometry in AD mice. Finally, immunohistochemical staining indicates that CCRL2 protein is increased in the brains of AD mice.
We identify a unique CCRL2 positive neutrophil cluster, that is specifically enriched in the peripheral blood of AD mice.
© 2024. The Author(s).

CCRL2 belongs to the G protein-coupled receptor family and is one of the three chemerin receptors. It is considered as a non-signaling receptor, presenting chemerin to cells expressing the functional chemerin receptor ChemR23/CMKLR1 and possibly GPR1. In the present work, we investigate the role played by CCRL2 in mouse cancer models. Loss of function of Ccrl2 accelerated the development of papillomas in a chemical model of skin carcinogenesis (DMBA/TPA), whereas the growth of B16 and LLC tumor cell grafts was delayed. Delayed tumor growth was also observed when B16 and LLC cells overexpress CCRL2, while knockout of Ccrl2 in tumor cells reversed the consequences of Ccrl2 knockout in the host. The phenotypes associated with CCRL2 gain or loss of function were largely abrogated by knocking out the chemerin or Cmklr1 genes. Cells harboring CCRL2 could concentrate bioactive chemerin and promote the activation of CMKLR1-expressing cells. A reduction of neoangiogenesis was observed in tumor grafts expressing CCRL2, mimicking the phenotype of chemerin-expressing tumors. This study demonstrates that CCRL2 shares functional similarities with the family of atypical chemokine receptors (ACKRs). Its expression by tumor cells can significantly tune the effects of the chemerin/CMKLR1 system and act as a negative regulator of tumorigenesis.

CCRL2 is a nonsignaling seven-transmembrane domain receptor. CCRL2 binds chemerin, a protein that promotes chemotaxis of leukocytes, including macrophages and natural killer (NK) cells. In addition, CCRL2 controls the inflammatory response in different pathologic settings, such as hypersensitivity, inflammatory arthritis, and experimental autoimmune encephalitis. Here, we investigated the role of CCRL2 in the regulation of lung cancer-related inflammation. The genetic deletion of Ccrl2 promoted tumor progression in urethane-induced and in Kras G12D/+/p53 LoxP lung tumor mouse models. Similarly, a Kras-mutant lung tumor displayed enhanced growth in Ccrl2-deficient mice. This phenotype was associated with a reduced inflammatory infiltrate characterized by the impaired recruitment of several leukocyte populations including NK cells. Bone marrow chimeras showed that CCRL2 expression by the nonhematopoietic cell compartment was responsible for the increased tumor formation observed in Kras-mutant Ccrl2-deficient mice. In human and mouse lungs, CCRL2 was expressed by a fraction of CD31+ endothelial cells, where it could control NK infiltration. Elevated CCRL2 expression in biopsies from human lung adenocarcinoma positively correlated with clinical outcome. These results provide evidence for a crucial role of CCRL2 in shaping an anti-lung tumor immune response.
©2019 American Association for Cancer Research.