Legionella pneumophilamultiplication is enhanced by chronic AMPK signalling in mitochondrially diseased Dictyostelium cells

Abstract

SUMMARYHuman patients with mitochondrial diseases are more susceptible to bacterial infections, particularly of the respiratory tract. To investigate the susceptibility of mitochondrially diseased cells to an intracellular bacterial respiratory pathogen, we exploited the advantages of Dictyostelium discoideum as an established model for mitochondrial disease and for Legionella pneumophila pathogenesis. Legionella infection of macrophages involves recruitment of mitochondria to the Legionella-containing phagosome. We confirm here that this also occurs in Dictyostelium and investigate the effect of mitochondrial dysfunction on host cell susceptibility to Legionella. In mitochondrially diseased Dictyostelium strains, the pathogen was taken up at normal rates, but it grew faster and reached counts that were twofold higher than in the wild-type host. We reported previously that other mitochondrial disease phenotypes for Dictyostelium are the result of the activity of an energy-sensing cellular alarm protein, AMP-activated protein kinase (AMPK). Here, we show that the increased ability of mitochondrially diseased cells to support Legionella proliferation is suppressed by antisense-inhibiting expression of the catalytic AMPKα subunit. Conversely, mitochondrial dysfunction is phenocopied, and intracellular Legionella growth is enhanced, by overexpressing an active form of AMPKα in otherwise normal cells. These results indicate that AMPK signalling in response to mitochondrial dysfunction enhances Legionella proliferation in host cells.

Listeria monocytogenes transiently alters mitochondrial dynamics during infection

“…Mitochondria (stained with anti-cytochrome c) showed strongly inhibited fragmentation in the absence of calcium, whereas blocking potassium efflux by incubation in 135 mM KCl did not prevent LLO-induced mitochondrial fragmentation. agreement with this notion, mitochondrial dysfunction has been linked to increased susceptibility to bacterial infection (51,52). Our work shows that mitochondrial dynamics plays a role in infection with the human pathogen L. monocytogenes.…”

Phosphoinositides differentially regulate bacterial uptake and Nramp1-induced resistance toLegionellainfection inDictyostelium

“…Both in Dictyostelium and macrophages Legionella forms a replicative vacuole that avoids fusion with lysosomes, recruits mitochondria and acquires proteins of the endoplasmic reticulum and other trafficking routes (Derre and Isberg, 2004;Fajardo et al, 2004;Francione et al, 2009;Kagan and Roy, 2002;Lu and Clarke, 2005;Robinson and Roy, 2006;Swanson and Isberg, 1995). To investigate whether the stimulatory effect of PI3K inactivation on Legionella intracellular growth could be mediated by alterations in LCV fusion with vesicles of the endolysosomal pathway, we assayed the effects of LY294002 on recruitment to the LCV of calnexin, V-H In A, the two-sample two-tailed t-test assuming unequal variance or the non parametric Kruskal-Wallis test gave a value of *P<0.05 for HM1295, whereas for HM1284 a one-tailed t-test of the null hypothesis (which stated that the infection level was not significantly higher in the null mutant) was *P0.04.…”

Autophagy in Dictyostelium: Genes and pathways, cell death and infection

“…188 Second, while studying the causes of increased susceptibility of patients with mitochondrial diseases to Legionella infection, Paul Fisher's group highlighted the profound impact of an upregulation of the energy-sensing protein kinase AMPK. 189 Upregulation of AMPK is a primary response to the impaired energy production in such diseases, but the resulting dysfunction on the containment of Legionella infection was a relative surprise. Overexpression of AMPK in wild-type Dictyostelium phenocopied the situation in mutant cells, identifying AMPK as a dominant regulator of intracellular immunity to Legionella, 189 possibly via the TOR-autophagy or p38ERK-MAPK cascade pathways.…”

“…189 Upregulation of AMPK is a primary response to the impaired energy production in such diseases, but the resulting dysfunction on the containment of Legionella infection was a relative surprise. Overexpression of AMPK in wild-type Dictyostelium phenocopied the situation in mutant cells, identifying AMPK as a dominant regulator of intracellular immunity to Legionella, 189 possibly via the TOR-autophagy or p38ERK-MAPK cascade pathways. More work is required to answer these exciting developments, but another study might point in that direction.…”