Non-Tuberculous Mycobacteria Infection Changes Macrophage Nitric Oxide Levels and Mitochondrial Bioenergetics: Improvement by mitoTEMPO Open Access

Lin, Channing (Spring 2020)

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Non-tuberculous mycobacteria (NTM) are ubiquitous bacilli that cause lung infections in patients with a weakened immune system or an underlying lung disease such as cystic fibrosis, COPD, or prior tuberculosis. While it is well-established that NTM cause lung disease, there are currently no established treatment regimens, and the host response to NTM infection has not been well-characterized. The production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) by innate immune cells is considered a major defense mechanism against mycobacteria. Nitric oxide (NO), a bactericidal and anti-inflammatory product of inducible nitric oxide synthase (iNOS) in macrophages, plays an essential role in M. tuberculosis (MTb) infection. Therefore, we hypothesized that NTM infection may upregulate iNOS expression, which in turn may contribute to the host response to NTM infection. RAW 264.7 cells, virus- transformed murine macrophages, MH-S alveolar macrophages, and bone marrow-derived macrophages (BMDM) were exposed to NTM, specifically M. avium-intracellulare (MAI) and M. abscessus (MAB), in our studies. NO levels decreased following 4 hours of NTM exposure and remained decreased for 48 hours. NTM infection increased the expression of iNOS (P<0.05). siiNOS2-transfected cells and L-NNA-inhibited cells infected with MAI had greater levels of intracellular MAI compared to control. Disrupted mitochondrial biology and decelerated bioenergetics were observed in MAI infection (P<0.05). Our data are the first to demonstrate that NTM increases NOS2 expression while decreasing NO levels. We hypothesize that ROS reduce NO availability and that mitochondrial antioxidant such as mitoTEMPO can alleviate infections. We found that the increase in ROS levels during MAI infection could be reduced by mitoTEMPO and that mitoTEMPO restores cellular bioenergetics and improves NO levels and bacterial killing. Therefore, antioxidant treatments targeting ROS can be developed as an alternative to conventional antibiotic treatments. 

Table of Contents

CHAPTER 1. Introduction -------------------------------------------- 1                         

           Non-Tuberculous Mycobacteria -------------------------------- 2                               

           Macrophages in NTM Immune Response ---------------------- 4

Nitric Oxide and Reactive Oxygen Species --------------------------- 6 

           Mitochondria -------------------------------------------------- 9                          

Summary and Hypothesis ------------------------------------------- 10                   

CHAPTER 2. Methods ----------------------------------------------- 12                               

CHAPTER 3. Results ------------------------------------------------ 20                                 

CHAPTER 4. Discussion --------------------------------------------- 37                                 

Table and Figures --------------------------------------------------- 43                                

References ---------------------------------------------------------- 44                                              

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