Mannose Receptor-Dependent Delay in Phagosome Maturation by Mycobacterium avium Glycopeptidolipids

Abstract

The ability of pathogenic mycobacteria to block phagosome-lysosome fusion is critical for its pathogenesis. The molecules expressed by mycobacteria that inhibit phagosome maturation and the mechanism of this inhibition have been extensively studied. Recent work has indicated that mannosylated lipoarabinomannan (ManLAM) isolated from Mycobacterium tuberculosis can function to delay phagosome-lysosome fusion and that this delay requires the interaction of ManLAM with the mannose receptor (MR). However, the molecules expressed by other pathogenic mycobacteria that function to inhibit phagosome maturation have not been well described. In the present study, we show that phagosomes containing silica beads coated with glycopeptidolipids (GPLs), a major surface component of Mycobacterium avium, showed limited acidification and delayed recruitment of late endosomal/lysosomal markers compared to those of phosphatidylcholine-coated beads. The carbohydrate component of the GPLs was required, as beads coated only with the lipopeptide core failed to delay phagosome-lysosome fusion. Moreover, the ability of GPLs to delay phagosome maturation was dependent on the macrophage expression of the MR. Using CHO cells expressing the MR, we confirmed that the GPLs bind this receptor. Finally, human monocyte-derived macrophages knocked down for MR expression showed increased M. avium phagosome-lysosome fusion relative to control cells. Together, the data indicate that GPLs can function to delay phagosome-lysosome fusion and suggest that GPLs, like ManLAM, work through the MR to mediate this activity.Mycobacterium avium, a prominent opportunistic pathogen in AIDS patients and a source of pulmonary infections in non-AIDS patients, is an intracellular pathogen which resides primarily in host macrophages. Like most pathogenic mycobacteria, M. avium resides within a phagosome which fails to mature to a phagolysosome (22). Phagosomes containing viable M. avium retain early endosomal markers such as Rab5 and the transferrin receptor but lack complete luminal acidification and recruitment of late endosomal/lysosomal markers (7,14,27,28). The mechanism by which pathogenic mycobacteria are able to block phagosome-lysosome (P-L) fusion is of great interest, and how Mycobacterium tuberculosis performs this function has been extensively studied (27). Studies from Deretic and colleagues support that live M. tuberculosis blocks the normal calcium rise initiated upon a phagocytic response, the result of which leads to a diminished recruitment of type III phosphatidyl-inositol-3-kinase VPS34 to the phagosome, which limits phosphatidyl-inositol-3-phosphate (PI3P) formation and association of PI3P binding proteins such as early endosomal antigen 1 (EEA1) (8,26). The result is a loss in the tethering and fusion of late endosomes with the mycobacterial phagosome (8, 26).The M. tuberculosis surface-located mannosylated lipoarabinomannan (ManLAM) has been implicated in delaying P-L fusion. Published reports indicate that ManLAM can block the calcium influx re...

Infection with Mycobacterium avium subsp. paratuberculosis Results in Rapid Interleukin-1β Release and Macrophage Transepithelial Migration

“…Phagosome acidification may seem to be a contradiction to M. avium subsp. paratuberculosis' major goal of survival, as it is well documented that pathogenic mycobacteria employ numerous mechanisms to inhibit the acidification process (37,50,52,56). However, a recent report by Koo et al suggests that phagosome acidification may actually serve as an effective survival and dissemination strategy (24).…”

Altered Toll-Like Receptor 9 Signaling in Mycobacterium avium subsp. paratuberculosis-Infected Bovine Monocytes Reveals Potential Therapeutic Targets

“…As M. avium subsp. paratuberculosis is known to impact the trafficking and maturation of intracellular organelles (12,13,14), the ability to respond to CpG stimulation could reflect an inability to take up ODNs in spite of normal, or even increased, expression of TLR9. This potential disconnect between levels of receptor expression and cellular responsiveness was investigated by quantifying uptake of fluorescently labeled ODNs by uninfected and M. avium subsp.…”

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Glycopeptidolipids: Immuno‐modulators in greasy mycobacterial cell envelope

“…GPLs act synergistically with mono-mannosylated lipoarabinomannan of M. avium to inhibit phagosome maturation, analogous to the action of hyper-mannosylated lipoarabinomannan in M. tuberculosis. This delay in phagosome-lysosome fusion has recently been reported to be dependent on reduced signal transduction from macrophage mannose receptors (38). Macrophage generated from human monocytes, knock downed for the expression of mannose receptors, showed diminished phagosome-lysosome fusion.…”