Fatty acid oxidation of alternatively activated macrophages prevents foam cell formation, but Mycobacterium tuberculosis counteracts this process via HIF-1α activation

Abstract

The ability of Mycobacterium tuberculosis (Mtb) to persist inside host cells relies on metabolic adaptation, like the accumulation of lipid bodies (LBs) in the so-called foamy macrophages (FM), which are favorable to Mtb. The activation state of macrophages is tightly associated to different metabolic pathways, such as lipid metabolism, but whether differentiation towards FM differs between the macrophage activation profiles remains unclear. Here, we aimed to elucidate whether distinct macrophage activation states exposed to a tuberculosis-associated microenvironment or directly infected with Mtb can form FM. We showed that the triggering of signal transducer and activator of transcription 6 (STAT6) in interleukin (IL)-4-activated human macrophages (M(IL-4)) prevents FM formation induced by pleural effusion from patients with tuberculosis. In these cells, LBs are disrupted by lipolysis, and the released fatty acids enter the β-oxidation (FAO) pathway fueling the generation of ATP in mitochondria. Accordingly, murine alveolar macrophages, which exhibit a predominant FAO metabolism, are less prone to become FM than bone marrow derived-macrophages. Interestingly, direct infection of M(IL-4) macrophages with Mtb results in the establishment of aerobic glycolytic pathway and FM formation, which could be prevented by FAO activation or inhibition of the hypoxia-inducible factor 1-alpha (HIF-1α)-induced glycolytic pathway. In conclusion, our results demonstrate that Mtb has a remarkable capacity to induce FM formation through the rewiring of metabolic pathways in human macrophages, including the STAT6-driven alternatively activated program. This study provides key insights into macrophage metabolism and pathogen subversion strategies.

Rickettsia conorii survival in THP ‐1 macrophages involves host lipid droplet alterations and active rickettsial protein production

“…Orlistat is an FDA-approved drug that targets the active domain of a multitude of lipases that are specific for hydrolysis of triglycerides predominantly found within LDs but does not significantly affect the function of phospholipases. Orlistat has been used previously to define host LD: intracellular pathogen interactions (Genoula et al, 2020;Tongluan et al, 2017) and is currently being investigated for use as an alternative host-directed antiviral treatment (Ammer et al, 2015;Esser et al, 2018;Hitakarun et al, 2020). Additionally, the concentration of Orlistat used herein was previously shown to have minimal "off-target" effects and allowed THP-1 macrophages to remain viable (Figure S2a) (Hack, Yanovaki, & Calis, 2000;Xiong, Lin, Huang, & Rikihisa, 2019).…”

“…Intriguingly, at early stages of R. conorii infection of THP-1 macrophages, there is an increase in average LD per host cell with a decrease in the average size of the LDs. This phenotype could be due in part by an infection-induced stimulation of both anabolic and catabolic lipid processes as seen in infections of host cells by other intracellular pathogens, including M. tuberculosis, C. pneumoniae and dengue virus (Barisch & Soldati, 2017;Chandra et al, 2020;Daniel, Maamar, Deb, Sirakova, & Kolattukudy, 2011;Genoula et al, 2020;Jordan & Randall, 2017;Walenna et al, 2018). Similarly, Coxiella burnetii infection induced an increase in LDs compared to uninfected controls, while requiring lipid catabolism to regulate LD homeostasis necessary for efficient infection (Mulye, Zapata, & Gilk, 2018).…”

“…A key requirement for FAO is the initial conversion of lipids to acylcarnitine esters by carnitine palmitoyltransferase 1a (CPTIa) that can then be transported across the mitochondrial membrane for catabolism (Lodish et al, 2000). To define the role host FAO has on initiation of LD alterations during infection the CPTIa inhibitor, Etomoxir, was used at a concentration previously utilised to elucidate the role of FAO during infection with various intracellular pathogens (Chandra et al, 2020;Eisele et al, 2013;Genoula et al, 2020;Jordan & Randall, 2017). In addition, the dose of Etomoxir was used at a concentration that allowed THP-1 macrophages to remain viable (Figure S2b) and has been shown to exhibit minimal "off-target" effects in macrophages (Divakaruni et al, 2018).…”

“…To further describe the negative effects a PPARɣ signalling for lipid accumulation may have during R. conorii infection of THP-1 macrophages, a foam cell-like phenotype was induced by addition of oleic acid-albumin. The development and contribution of foam cell development to pathogen intracellular survival have been well characterised for pathogens such as M. tuberculosis and C. pneumoniae (Cheng et al, 2014;Genoula et al, 2020;Mei et al, 2009;Reza et al, 2009). Similarly, oleic acid-albumin was used at a concentration of 400 μM as carried out previously during M. tuberculosis infection (Agarwal et al, 2020).…”

Host-Derived Lipids from Tuberculous Pleurisy Impair Macrophage Microbicidal-Associated Metabolic Activity

“…To address this issue, we used the tuberculous pleural effusion (TB-PE) as a physiologically relevant fluid reflecting the microenvironment found in a human respiratory cavity that is impacted by Mtb infection (Genoula et al, 2018(Genoula et al, , 2020Lastrucci et al, 2015). The pleural effusion (PE) is an excess of fluid recovered from pleural space characterized by a high protein content and specific leukocytes (Vorster et al, 2015).…”