Caspase-independent apoptosis in infected macrophages triggered by sulforaphane via Nrf2/p38 signaling pathways.

TB Deramaudt,A-L Roux,J-L Herrmann,M Bonay,Y Retory,F Lofaso,J Floquet

doi:10.1038/cddiscovery.2015.22

Abstract

Mycobacterium abscessus (Mabs), a non-tuberculous mycobacterium, is an emerging and rapidly growing opportunistic pathogen that is frequently found in patients with cystic fibrosis and in immunosuppressed patients. Its high tolerance to antibiotics is of great concern for public health. In this study, our results showed that human THP-1-derived macrophages infected with M. abscessus presented an increase in ROS production and cell necrosis. In addition, M. abscessus infection triggered activation of the Nuclear factor E2-related factor 2 (Nrf2) signaling pathway, and the induction of HO-1 and NQO1 expression levels. Interestingly, pretreatment of macrophages with sulforaphane (SFN), an activator of the antioxidant key regulator Nrf2, followed by M. abscessus infection significantly decreased mycobacterial burden. We demonstrated that this reduction in mycobacterial growth was due to an activation in cell apoptosis in SFN-pretreated and M. abscessus-infected macrophages. Pretreatment with specific MAPK inhibitors, PD98059, SP600125, and SB203580 to ERK, JNK, and p38 respectively, failed to inhibit induction of Nrf2 expression, suggesting that Nrf2 signaling pathway was upstream of MAPK signaling. Activation of cell apoptosis was caspase 3/7 independent but p38 MAPK dependent. Moreover, p38 MAPK induction was abolished in macrophages transfected with Nrf2 siRNA. In addition, p38 inhibitor abolished Nrf2-dependent apoptosis in infected macrophages. Taken together, our results indicate that modulation of the Nrf2 signaling using Nrf2 activators may help potentiate the actual drug therapies used to treat mycobacterial infection.

Highlights

Mycobacteria included in the group of rapid growing mycobacteria (RGM) are increasingly becoming a public health concern worldwide
We showed that pretreatment of macrophages with an activator of Nrf[2], sulforaphane (SFN), before M. abscessus challenge decreased mycobacterial growth by activating a caspase-independent apoptotic response
Its high resistance to antibiotics greatly limits patient treatment which may account for the likelihood of developing chronic airway infections and increase the risk of fatal outcome

Summary

Introduction

Mycobacteria included in the group of rapid growing mycobacteria (RGM) are increasingly becoming a public health concern worldwide. Mycobacterium abscessus (Mabs), a non-tuberculous mycobacterium of the RGM group, is an opportunistic pathogen. M. abscessus is an emerging pathogen that has been increasingly involved in patients with cystic fibrosis and in immunosuppressed patients,[1,2,3] and more generally in exacerbation of lung infections. Association of M. abscessus with patients suffering from a pre-existing condition and at risk of developing chronic airway infections makes for a poor clinical outcome. The bacterial growth is enhanced in oxidative condition such as the presence of oxygen-free radicals, while its growth is inhibited in the presence of oxidant scavengers such as MnTE-2-PyP and N-acetyl-L-cysteine.[4] MnTE-2-PyP is able to diminish M. abscessus load in infected macrophages by inducing the fusion of mycobacteria-containing phagosomes with lysosomes into phagolysosomes, promoting cell survival.[5]

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Conclusion