Phosphatidylinositol-(3,4,5)-Trisphosphate Induces Phagocytosis of Nonmotile Pseudomonas aeruginosa

Abstract

Pathogenic bacteria that establish chronic infections in immunocompromised patients frequently undergo adaptation or selection for traits that are advantageous for their growth and survival. Clinical isolates of , a Gram-negative, opportunistic bacterial pathogen, exhibit a temporal transition from a motile to a nonmotile phenotype through loss of flagellar motility during the course of chronic infection. This progressive loss of motility is associated with increased resistance to both antibiotic and immune clearance. We have previously shown that loss of bacterial motility enables to evade phagocytic clearance both and and fails to activate the phosphatidylinositol 3-kinase (PI3K)/Akt-dependent phagocytic pathway. Therefore, we tested the hypothesis that clearance of phagocytosis-resistant bacteria could be induced by exogenously pretreating innate immune cells with the Akt-activating molecule phosphatidylinositol-(3,4,5)-trisphosphate (PIP). Here, we demonstrate that PIP induces the uptake of nonmotile by primary human neutrophils>25-fold, and this effect is phenocopied with the use of murine phagocytes. However, surprisingly, mechanistic studies revealed that the induction of phagocytosis by PIP occurs because polyphosphoinositides promote bacterial binding by the phagocytes rather than bypassing the requirement for PI3K. Moreover, this induction was selective since the uptake of other nonmotile Gram-negative, but not Gram-positive, bacteria can also be induced by PIP Since there is currently no treatment that effectively eradicates chronic infections, these findings provide novel insights into a potential methodology by which to induce clearance of nonmotile pathogenic bacteria and into the endogenous determinants of phagocytic recognition of.

The Salmonella type-3 secretion system-1 and flagellar motility influence the neutrophil respiratory burst

“…Phagocytosis stimulates neutrophil NADPH oxidase assembly [ 66 ], so it is possible that the amotile mutants are able to associate with neutrophils but are not phagocytosed as efficiently, leading to our observed phenotype. Our data taken together with prior work [ 62 , 65 ] suggest an important role for flagellar motility in neutrophil antimicrobial responses. Further work is needed to establish how STm motility influences the neutrophil respiratory burst.…”

“…Flagellar motility of P . aeruginosa directly stimulates neutrophil and macrophage phagocytosis through activation of the PI3K/Akt pathway [ 64 , 65 ]. Phagocytosis stimulates neutrophil NADPH oxidase assembly [ 66 ], so it is possible that the amotile mutants are able to associate with neutrophils but are not phagocytosed as efficiently, leading to our observed phenotype.…”

Host-induced spermidine production in motile Pseudomonas aeruginosa triggers phagocytic uptake

“…It seems that differences in motility, rather than in adherence, impact phagocytic up-take. As previously demonstrated by Demirdjian et al, the defect in the phagocytosis of non-motile variants could be restored by adding PIP 3 to the host cells (Demirdjian et al, 2018). PIP 3 is a membrane-associated phospholipid that acts as a signaling molecule for many cellular processes such as the Akt-pathway (Czech, 2000;Traynor-Kaplan et al, 1988).…”

“…The activation of these pathways may be responsible for the observed enhanced phagocytic uptake of PA14 ( Figure 5A). In fact, PIP3 has been shown previously to induce Akt phosphorylation and to increase phagocytosis of the non-motile P. aeruginosa (Demirdjian et al, 2018). We therefore analyzed the role of the PIP 3 signaling pathway during phagocytosis of flagella mutants by supplementing histone-bound PIP 3 to RAW264.7 cells to complement the missing activation of the signaling cascade.…”

“…The lower phagocytosis rate of these non-motile strains was explained by diminished activation of the phosphatidylinositol-(3,4,5)-triphosphate (PIP 3 ) pathway in host cells (Demirdjian et al, 2018).…”