Mycobacterium marinumphthiocerol dimycocerosates enhance macrophage phagosomal permeabilization and membrane damage

Abstract

17 18 Phthiocerol dimycocerosates (PDIMs) are a class of mycobacterial lipids that 19 promote virulence in Mycobacterium tuberculosis and Mycobacterium marinum. It 20 has recently been shown that PDIMs work in concert with the M. tuberculosis Type 21 VII secretion system ESX-1 to permeabilize the phagosomal membranes of infected 22 macrophages. As the zebrafish-M. marinum model of infection has revealed the 23 critical role of PDIM at the host-pathogen interface, we set to determine if PDIMs 24 contributed to phagosomal permeabilization in M. marinum. Using an ΔmmpL725 mutant defective in PDIM transport, we find the PDIM-ESX-1 interaction to be 26 conserved in an M. marinum macrophage infection model. However, we find PDIM 27 and ESX-1 mutants differ in their degree of defect, with the PDIM mutant retaining 28 more membrane damaging activity. Using an in vitro hemolysis assay-a common 29 surrogate for cytolytic activity, we find that PDIM and ESX-1 differ in their 30 contributions: the ESX-1 mutant loses hemolytic activity while PDIM retains it. Our 31 observations confirm the involvement of PDIMs in phagosomal permeabilization in 32 M. marinum infection and suggest that PDIM enhances the membrane disrupting 33 activity of pathogenic mycobacteria and indicates that the role they play in damaging 34 phagosomal and red blood cell membranes may differ.

Spreading of a mycobacterial cell-surface lipid into host epithelial membranes promotes infectivity

“…PDIM has been suggested to interact with the protein substrates of the type VII secretion system ESX-1, including EsxA ( Barczak et al, 2017 ). PDIM and EsxA are both required for cytosolic escape from phagolysosomes ( Osman et al, 2020 ; Quigley et al, 2017 ; van der Wel et al, 2007 ), where PDIM is suggested to enhance the pore-forming activity of EsxA through its ability to infiltrate macrophage membranes ( Augenstreich et al, 2017 ). Thus, we hypothesized that PDIM’s localization may be dependent on EsxA’s pore forming ability.…”

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] (Fig. 3a).…”

“…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] (Fig.…”

Genetics in the Host‐Mycobacterium ulcerans interaction

“…Immunization of mice with dewaxed whole‐cell M. ulcerans antigens, but not formalin‐fixed bacilli, caused an increase in M. ulcerans ‐specific IgG titers, suggesting that these lipidic structures concealed antigens from the host immune system 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 37‐41 . 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 .…”