Understanding the role of ATM in neutrophil development and activity

Neutrophils are the most abundant white blood cell and the first line of defence against pathogens. Their development is characterised by the compaction and lobulation of their nuclei. They have a wide variety of mechanisms to clear out pathogens and defects in their development or activity result in severe immunodeficiency. To better understand neutrophil function, we analysed ataxia-telangiectasia (A-T), a genetic recessive disease caused by mutations in ataxia telangiectasia mutated (ATM) gene. A-T patients suffer from increased susceptibility to bacterial infections and malignancies. ATM is involved in chromatin double strand break repair and has been shown to be necessary for the development of B- and T-cells. However, little is known about the role of ATM in neutrophil biology. Based on the immunodeficiency observed in A-T patients, we hypothesised ATM might regulate neutrophil development and/or function. We established a CRISPR/Cas9 ATM knockout (ATM-/-) and inducible ATM shRNA knockdown cell line, which we differentiated into a neutrophil-like cell. We tested the antimicrobial capacity of the cell line as well as primary neutrophils treated with an ATM inhibitor and found a decreased ability to kill Staphyloccocus aureus in both systems. To understand the mechanism behind this phenotype, we compared differentiation from precursors as well as different antimicrobial responses in both WT and ATM-/- cells. We found increased expression of CD11b and decreased expression of C-type lectin receptors, indicating developmental disturbances as well as reduced production of reactive oxygen species (ROS) and NETs. Increased CD11b surface marker expression was confirmed in neutrophils from A-T patients. These differences were related to dysregulated transcription and nuclear organisation in ATM deficient cells, implicating ATM in neutrophil chromatin regulation. In conclusion, we identified ATM as a regulator of neutrophil development and antimicrobial activity, and a potential therapeutic target in immunodeficiency or inflammatory disease.