Mycobacterium marinum phthiocerol dimycocerosates enhance macrophage phagosomal permeabilization and membrane damage

Abstract

Phthiocerol dimycocerosates (PDIMs) are a class of mycobacterial lipids that promote virulence in Mycobacterium tuberculosis and Mycobacterium marinum. It has recently been shown that PDIMs work in concert with the M. tuberculosis Type VII secretion system ESX-1 to permeabilize the phagosomal membranes of infected macrophages. As the zebrafish-M. marinum model of infection has revealed the critical role of PDIM at the host-pathogen interface, we set to determine if PDIMs contributed to phagosomal permeabilization in M. marinum. Using an ΔmmpL7 mutant defective in PDIM transport, we find the PDIM-ESX-1 interaction to be conserved in an M. marinum macrophage infection model. However, we find PDIM and ESX-1 mutants differ in their degree of defect, with the PDIM mutant retaining more membrane damaging activity. Using an in vitro hemolysis assay-a common surrogate for cytolytic activity, we find that PDIM and ESX-1 differ in their contributions: the ESX-1 mutant loses hemolytic activity while PDIM retains it. Our observations confirm the involvement of PDIMs in phagosomal permeabilization in M. marinum infection and suggest that PDIM enhances the membrane disrupting activity of pathogenic mycobacteria and indicates that the role they play in damaging phagosomal and red blood cell membranes may differ.

Post-translational knockdown and post-secretional modification of EsxA determine contribution of EsxA membrane permeabilizing activity for mycobacterial intracellular survival

“…Second, it is probably that EsxA is not sufficient for mycobacterial phagosome rupture and cytosolic translocation solely, other factors may also contribute to this process. It has been reported that EsxA works with phthiocerol dimycocerosates (PDIM) to mediate phagosome rupture [ 74 , 75 ], and PDIM alone could maintain certain level of hemolysis with Mm [ 76 ]. Also, deletion of other ESX-1 substrates would impact mycobacteria phagosome escape ability [ 17 , 38 ].…”

Conserved and specialized functions of Type VII secretion systems in non-tuberculous mycobacteria

“…The combined action of PDIM and ESX-1 in phagosomal membrane disruption was confirmed in Mma [83]. Indeed, a mutant defective in MmpL7, the transporter of PDIM, demonstrated decreased phagosomal permeabilization similarly to the ESX-1 deletion mutant [83] (). Moreover, the MmpL7 mutant retains haemolytic activity, suggesting a different mechanism of membrane damage in red blood cells [83].…”

“…Indeed, a mutant defective in MmpL7, the transporter of PDIM, demonstrated decreased phagosomal permeabilization similarly to the ESX-1 deletion mutant [83] (). Moreover, the MmpL7 mutant retains haemolytic activity, suggesting a different mechanism of membrane damage in red blood cells [83]. Mma haemolysis appears to imply another ESX-1 substrate; notably a pe mutant ( MMAR_2894 ) encoding a PE protein secreted by ESX-1, displays a red blood cell lysis defect while maintaining cytolysis activity in macrophages [84].…”

“…For instance, EsxA membrane permeabilization is potentiated by the phthiocerol dimicerosate (PDIM), which are cell-surface associated lipids capable of disrupting the biochemical properties of host membranes [81, 82]. The combined action of PDIM and ESX-1 in phagosomal membrane disruption was confirmed in Mma [83]. Indeed, a mutant defective in MmpL7, the transporter of PDIM, demonstrated decreased phagosomal permeabilization similarly to the ESX-1 deletion mutant [83] ().…”

Genetics in the Host‐Mycobacterium ulcerans interaction

“…36 Accordingly, phthiocerol dimycocerosates (PDIMs) from M. tuberculosis and M marinum were shown to mask underlying pathogen-associated molecular patterns (PAMPs), allowing evasion from Toll-like receptor (TLR) signaling pathways and contributing to phagosome evasion in conjoint with ESAT-6 secretion systems (ESX) -1. [37][38][39][40][41] Other experimental studies with M. tuberculosis show that PDIM molecules can be transferred to the membranes of macrophages and promote biophysical changes that influence cellular processes such as phagocytosis. 42 Phenolic glycolipids (PGLs) further contribute to the virulence of mycobacteria by hijacking the recruitment of more permissive macrophages to the site of infection via the CCL2-CCR2 (C-C motif chemokine receptor 2) axis, impairing phagolysosome maturation and avoiding triggering the production of proinflammatory mediators by the host immune cells.…”