The clock gene Bmal1 inhibits macrophage motility, phagocytosis, and impairs defense against pneumonia

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 117; no. 3; pp. 1543 - 1551
• Main Authors: Kitchen, Gareth B., Cunningham, Peter S., Poolman, Toryn M., Iqbal, Mudassar, Maidstone, Robert, Baxter, Matthew, Bagnall, James, Begley, Nicola, Saer, Ben, Hussell, Tracy, Matthews, Laura C., Dockrell, David H., Durrington, Hannah J., Gibbs, Julie E., Blaikley, John F., Loudon, Andrew S., Ray, David W.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 21-01-2020
• Subjects: Actin; Actins - metabolism; Animals; ARNTL Transcription Factors - antagonists & inhibitors; ARNTL Transcription Factors - genetics; Bacteria; Bacterial diseases; Binding sites; Biological clocks; Biological Sciences; Blood circulation; BMAL1 protein; Cell morphology; Cell Movement - drug effects; Circadian Clocks - genetics; Circadian Clocks - physiology; Circadian rhythms; Clock gene; Clonal deletion; Cytology; Cytoskeleton; Disease Models, Animal; Disease Resistance - genetics; Female; Gene expression; Genes; In vivo methods and tests; Ingestion; Macrophages; Macrophages - drug effects; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphology; Motility; Phagocytes; Phagocytosis; Phagocytosis - drug effects; Phenotypes; Pneumonia; Pneumonia, Pneumococcal - metabolism; rhoA GTP-Binding Protein - metabolism; RhoA protein; Streptococcus pneumoniae - pathogenicity; Time of use; Weight loss; Weight reduction; actin cytoskeleton; phagocytosis; circadian; RhoA; Streptococcus pneumoniae
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1915932117

The circadian clock regulates many aspects of immunity. Bacterial infections are affected by time of day, but the mechanisms involved remain undefined. Here we show that loss of the core clock protein BMAL1 in macrophages confers protection against pneumococcal pneumonia. Infected mice show both reduced weight loss and lower bacterial burden in circulating blood. In vivo studies of macrophage phagocytosis reveal increased bacterial ingestion following Bmal1 deletion, which was also seen in vitro. BMAL1−/− macrophages exhibited marked differences in actin cytoskeletal organization, a phosphoproteome enriched for cytoskeletal changes, with reduced phosphocofilin and increased active RhoA. Further analysis of the BMAL1−/− macrophages identified altered cell morphology and increased motility. Mechanistically, BMAL1 regulated a network of cell movement genes, 148 of which were within 100 kb of high-confidence BMAL1 binding sites. Links to RhoA function were identified, with 29 genes impacting RhoA expression or activation. RhoA inhibition restored the phagocytic phenotype to that seen in control macrophages. In summary, we identify a surprising gain of antibacterial function due to loss of BMAL1 in macrophages, associated with a RhoA-dependent cytoskeletal change, an increase in cell motility, and gain of phagocytic function.