Compromised autophagy allows Burkholderia cenocepacia persistence in macrophages derived from cystic fibrosis patients
Final Report Abstract
Burkholderia cenocepacia causes severe infections in patients with pulmonary diseases like cystic fibrosis (CF) triggering destructive lung inflammation and sepsis with often lethal outcome. Since B. cenocepacia harbors an intrinsic resistance to most existing antibiotics, it is very difficult to eradicate from colonized lung tissue and significantly increases mortality after lung transplantation. Therefore, it is crucial to reduce the need for antimicrobial therapy by identifying novel targets to develop new treatment strategies in CF. Autophagy, an intracellular catabolic process leading to the breakdown of damaged proteins or organelles, and the elimination of intracellular pathogens, successfully restricts B. cenocepacia in healthy macrophages. Caspase-11-dependent regulation of actin dynamics via cofilin positively regulates autophagosome formation and trafficking in murine macrophages in response to B. cenocepacia resulting in efficient fusion of the B. cenocepacia-containing phagosome with lysosomes. The absence of caspase-11 causes an accumulation of the small GTPase Rab7 and reduced colocalization of B. cenocepacia with the autophagy marker LC3 as well as acidic compartments accompanied by increased bacterial replication in vitro and in vivo. Similar to caspase-11-/- macrophages, cystic fibrosis macrophages harboring the most common F508del mutation within the cystic fibrosis transmembrane conductance regulator (CFTR) gene, are permissive to B. cenocepacia infection due to defective autophagy. Major autophagy molecules such as Atg5 and Atg7 are sequestered within mutant CFTR protein aggregates thereby making them unavailable for autophagosome formation. As a result, CF macrophages exhibit diminished autophagic activity in response to starvation or B. cenocepacia infection. Additionally, inherently increased expression of the microRNA cluster Mir17~92 further impairs autophagy by targeting autophagy-related genes. In accordance with these findings, pharmacological intervention aimed to correct weak autophagy in CF promotes clearance of intracellular B. cenocepacia. Furthermore, reducing the expression of Mir17~92 cluster members restores autophagic activity and improves CFTR function. Notably, in CF sputum samples Mir17~92 cluster expression correlates with pulmonary exacerbation, thus making it a promising candidate to be used as biomarker in CF. Overall, restoration of functional autophagy represents a potential therapeutic strategy to prevent and eliminate antibiotic-resistant infections in CF.
Publications
- 2015. Caspase-11 and caspase-1 differentially modulate actin polymerization via RhoA and Slingshot proteins to promote bacterial clearance. Sci Rep. 5:18479
Caution K, MA Gavrilin, M Tazi, A Kanneganti, D Layman, S Hoque, K Krause and AO Amer
(See online at https://doi.org/10.1038/srep18479) - An intricate link between autophagy, microRNAs and cystic fibrosis. Annual North American Cystic Fibrosis Conference (NACFC), 2015, Phoenix AZ, USA
Mia F. Tazi, Duaa A. Dakhlallah, Kyle Caution, Kathrin Krause, Amr Ahmed, Hany Khalil, Ian Davis, Clay Marsh, Larry S. Schlesinger, Estelle Cormet-Boyaka and Amal O. Amer
- 2016. Caspase Exploitation by Legionella pneumophila. Front Microbiol. 7:515
Krause K and AO Amer
(See online at https://doi.org/10.3389/fmicb.2016.00515) - 2016. Elevated Mirc1/Mir17-92 cluster expression negatively regulates autophagy and CFTR (cystic fibrosis transmembrane conductance regulator) function in CF macrophages. Autophagy. 12(11):2026-2037
Tazi MF, DA Dakhlallah, K Caution, MM Gerber, SW Chang, H Khalil, BT Kopp, AE Ahmed, K Krause, I Davis, C Marsh, AE Lovett-Racke, LS Schlesinger, E Cormet- Boyaka and AO Amer
(See online at https://doi.org/10.1080/15548627.2016.1217370) - Caspase-11 contributes to Burkholderia cenocepacia clearance in mice. CMIB Symposium, 2016, Columbus OH, USA
Kathrin Krause, Kyle Caution, Daniel Layman and Amal O. Amer
