Cysteamine-mediated clearance of antibiotic-resistant pathogens in human cystic fibrosis macrophages.

Chandra L Shrestha,Florentina Albastroiu,Larry S Schlesinger,Shuzhong Zhang,Hannah Rinehardt,Richard Shell,Kaivon D Assani,Benjamin T Kopp,Amal O Amer

doi:10.1371/journal.pone.0186169

Chandra L Shrestha, Florentina Albastroiu + Show 7 more

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https://doi.org/10.1371/journal.pone.0186169

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Abstract

Members of the Burkholderia cepacia complex are virulent, multi-drug resistant pathogens that survive and replicate intracellularly in patients with cystic fibrosis (CF). We have discovered that B. cenocepacia cannot be cleared from CF macrophages due to defective autophagy, causing continued systemic inflammation and infection. Defective autophagy in CF is mediated through constitutive reactive oxygen species (ROS) activation of transglutaminase-2 (TG2), which causes the sequestration (accumulation) of essential autophagy initiating proteins. Cysteamine is a TG2 inhibitor and proteostasis regulator with the potential to restore autophagy. Therefore, we sought to examine the impact of cysteamine on CF macrophage autophagy and bacterial killing. Human peripheral blood monocyte-derived macrophages (MDMs) and alveolar macrophages were isolated from CF and non-CF donors. Macrophages were infected with clinical isolates of relevant CF pathogens. Cysteamine caused direct bacterial growth killing of live B. cenocepacia, B. multivorans, P. aeruginosa and MRSA in the absence of cells. Additionally, B. cenocepacia, B. multivorans, and P. aeruginosa invasion were significantly decreased in CF MDMs treated with cysteamine. Finally, cysteamine decreased TG2, p62, and beclin-1 accumulation in CF, leading to increased Burkholderia uptake into autophagosomes, increased macrophage CFTR expression, and decreased ROS and IL-1β production. Cysteamine has direct anti-bacterial growth killing and improves human CF macrophage autophagy resulting in increased macrophage-mediated bacterial clearance, decreased inflammation, and reduced constitutive ROS production. Thus, cysteamine may be an effective adjunct to antibiotic regimens in CF.

Highlights

Cystic fibrosis (CF) is characterized by chronic sinopulmonary bacterial and fungal infections leading to inflammation, tissue damage, and accelerated loss of lung function [1]
We have discovered that B. cenocepacia cannot be cleared from CF macrophages due to defective autophagy, causing continued systemic inflammation and infection. [2, 9, 14] B. cenocepacia can further suppress autophagy independent of the host [2, 15], but its connection to TG2 is unclear
Due to the broad antimicrobial properties of cysteamine and known gastrointestinal side effects [22], we tested for direct bacterial killing against common enteric pathogens to determine if cysteamine’s impact was specific to CF pathogens or more general in nature

Summary

Introduction

Cystic fibrosis (CF) is characterized by chronic sinopulmonary bacterial and fungal infections leading to inflammation, tissue damage, and accelerated loss of lung function [1]. Deficiencies in innate immune responses combined with extensive bacterial biofilm formation [6, 7] may explain why many chronic bacterial infections in CF are recalcitrant to antibiotic treatment, promoting their persistence in CF airways. One mechanism by which pathogens can subvert host immune responses to increase their survival in CF is through altering macrophage autophagy [2, 8, 9]. Restoration of functional autophagy reduces inflammation [11] and improves bacterial killing in CF [2], but it is unknown how TG2 mediates human macrophage bacterial killing

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