Diverse Cell Death Mechanisms Are Simultaneously Activated in Macrophages Infected by Virulent Mycobacterium tuberculosis

Abstract

Macrophages are necessary to eliminate pathogens. However, some pathogens have developed mechanisms to avoid the immune response. One of them is modulating the cell death mechanism to favor pathogen survival. In this study, we evaluated if virulent Mycobacterium tuberculosis (M. tb) can simultaneously activate more than one cell death mechanism. We infected human monocyte-derived macrophages (MDM) in vitro with avirulent (H37Ra) and virulent (H37Rv) strains, and then we measured molecules involved in apoptosis, necroptosis, and pyroptosis. Our data showed that H37Rv infection increased the BCL-2 transcript and protein, decreased the BAX transcript, and increased phosphorylated BCL-2 at the protein level. Moreover, H37Rv infection increased the expression of the molecules involved in the necroptotic pathway, such as ASK1, p-38, RIPK1, RIPK3, and caspase-8, while H37Ra increased caspase-8 and decreased RIPK3 at the transcriptional level. In addition, NLRP3 and CASP1 expression was increased at low MOI in both strains, while IL-1β was independent of virulence but dependent on infection MOI, suggesting the activation of pyroptosis. These findings suggest that virulent M. tb inhibits the apoptosis mediated by BCL-2 family molecules but, at the same time, increases the expression of molecules involved in apoptosis, necroptosis, and pyroptosis at the transcriptional and protein levels, probably as a mechanism to avoid the immune response and guarantee its survival.

MicroRNA-144-3p Inhibits Host Lipid Catabolism and Autophagy by Targeting PPARα and ABCA1 During Mycobacterium Tuberculosis Infection

“…In laboratory studies of TB pathophysiology, reference strains of Mtb, virulent strain H37Rv and avirulent strain H37Ra, are widely used. , In this study, we established an H37Ra infection model and demonstrated how the bacterium modifies host immunity and lipid metabolism via miR-144-3p. Although H37Ra and H37Rv have a strong genetic link and perform substantially comparable roles, , the virulence of Mtb may result in different immune escape responses to the host. , Given the regulatory mechanism described here, it remains to be determined whether the involvement of miR-144-3p during H37Ra infection can be applied to H37Rv or animal experiments to generate greater physiological significance.…”

“…Although H37Ra and H37Rv have a strong genetic link and perform substantially comparable roles, 43,44 the virulence of Mtb may result in different immune escape responses to the host. 45,46 Given the regulatory mechanism described here, it remains to be determined whether the involvement of miR-144-3p during H37Ra infection can be applied to H37Rv or animal experiments to generate greater physiological significance.…”

Mycobacterium tuberculosis-macrophage interaction: Molecular updates

“…Mtb successfully manipulates host immune responses by simultaneously activating more than one cell death mechanisms (aforementioned cell killing pathways). In vitro, human monocytederived macrophages (MDM)-infected virulent Mtb inhibits the apoptosis mediated by BCL-2 family molecules but, at the same time, increases the expression of molecules involved in apoptosis (BCL-2, BAX , and phosphorylated BCL-2), necroptosis (ASK1, p-38, RIPK1, RIPK3, and CASP8), and pyroptosis (NLRP3, CASP1, and IL-1b secretion) at the transcriptional and protein levels (Ramon-Luing et al, 2022). During the selective elimination of invading pathogens (xenophagy), autophagic receptor proteins (SQSTM1/p62, CALCOCO2/NDP52, and optineurin) are required, and Mtb co-opts ubiquitin effectors such as PtpA (Deretic et al, 2013;Wang et al, 2015;Chai et al, 2020).…”

Host‐pathogen dialogues in different cell death modes during Mycobacterium tuberculosis infection

“…Although our understanding of the impact of Mtb factors on host cell death has significantly expanded, 13,14 the molecular mechanisms that regulate the different modes of death and the impact on the outcome of infection remain unclear. This review highlights recent advances in apoptosis, autophagy, pyroptosis, ferroptosis, and necrosis during Mtb infection and discusses how Mtb regulate different death modes for immune escape.…”