Induction of the Cpx Envelope Stress Pathway Contributes to Escherichia coli Tolerance to Antimicrobial Peptides

Antimicrobial peptides produced by multicellular organisms as part of their innate system of defense against microorganisms are currently considered potential alternatives to conventional antibiotics in case of infection by multiresistant bacteria. However, while the mode of action of antimicrobial peptides is relatively well described, resistance mechanisms potentially induced or selected by these peptides are still poorly understood. In this work, we studied the mechanisms of action and resistance potentially induced by ApoEdpL-W, a new antimicrobial peptide derived from human apolipoprotein E. Investigation of the genetic response of Escherichia coli upon exposure to sublethal concentrations of ApoEdpL-W revealed that this antimicrobial peptide triggers activation of RcsCDB, CpxAR, and σ^E envelope stress pathways. This genetic response is not restricted to ApoEdpL-W, since several other antimicrobial peptides, including polymyxin B, melittin, LL-37, and modified S₄ dermaseptin, also activate several E. coli envelope stress pathways. Finally, we demonstrate that induction of the CpxAR two-component system directly contributes to E. coli tolerance toward ApoEdpL-W, polymyxin B, and melittin. These results therefore show that E. coli senses and responds to different antimicrobial peptides by activation of the CpxAR pathway. While this study further extends the understanding of the array of peptide-induced stress signaling systems, it also provides insight into the contribution of Cpx envelope stress pathway to E. coli tolerance to antimicrobial peptides.     

Survivorship in Wild Frogs Infected with Chytridiomycosis

Chytridiomycosis is an emerging infectious disease that has been implicated as the causative agent of many recent amphibian population declines and extinctions that have taken place in relatively pristine locations worldwide. While there exists a growing body of literature regarding the effect of the fungus on experimentally infected frogs, few studies have examined the effect of the fungus on apparently healthy wild frogs from nondeclining, infected populations. We examined the temporal pattern of chytrid infection in individually marked Stony Creek Frogs (Litoria wilcoxii) at a lowland site in southeast Queensland, Australia. We provide the first evidence that wild frogs are capable of both acquiring chytridiomycosis as adults, and also of clearing their infections entirely. Changes in disease status in individual frogs largely tracked changing climatic conditions, with infections tending to appear in cooler months and disappearing in warmer months. Though 27.2% of the adult frogs we sampled were infected at some point in the study, we found no evidence that chytridiomycosis was negatively affecting adult survivorship, suggesting either: (1) chytrid-induced mortality in this population is generally restricted to metamorphs and juveniles; (2) this population was not exposed to conditions which favored lethal disease outbreaks; or (3) this population has evolved sufficient resistance to the disease to persist relatively unaffected.     

Temporal changes in dietary fats: role of n-6 polyunsaturated fatty acids in excessive adipose tissue development and relationship to obesity

The importance of a high fat intake in the increasing prevalence of childhood and adult obesity remains controversial. Moreover, qualitative changes (i.e. the fatty acid composition of fats) have been largely disregarded. Herein is reviewed the role of polyunsaturated fatty acids (PUFAs) of the n-6 series in promoting adipogenesis in vitro and favouring adipose tissue development in rodents during the gestation/suckling period. Epidemiological data from infant studies as well as the assessment of the fatty acid composition of mature breast milk and infant formulas over the last decades in the Western industrialized world are revisited and appear consistent with animal data. Changes over decades in the intake of n-6 and n-3 PUFAs, with a striking increase in the linoleic acid/alpha-linolenic ratio, are observed. In adults, using a consumption model based upon production data, similar changes in the PUFA content of ingested lipids have been found for France, and are associated with an increase of fat consumption over the last 40 years. These profound quantitative and qualitative alterations can be traced in the food chain and shown to be due to changes in human dietary habits as well as in the feeding pattern of breeding stock. If prevention of obesity is a key issue for future generations, agricultural and food industry policies should be thoroughly reevaluated.     

Infection-Mediated Priming of Phagocytes Protects against Lethal Secondary Aspergillus fumigatus Challenge

Phagocytes restrict the germination of Aspergillus fumigatus conidia and prevent the establishment of invasive pulmonary aspergillosis in immunecompetent mice. Here we report that immunecompetent mice recovering from a primary A. fumigatus challenge are protected against a secondary lethal challenge. Using RAGγc knock-out mice we show that this protection is independent of T, B and NK cells. In protected mice, lung phagocytes are recruited more rapidly and are more efficient in conidial phagocytosis and killing. Protection was also associated with an enhanced expression of CXCR2 and Dectin-1 on bone marrow phagocytes. We also show that protective lung cytokine and chemokine responses are induced more rapidly and with enhanced dynamics in protected mice. Our findings support the hypothesis that following a first encounter with a non-lethal dose of A. fumigatus conidia, the innate immune system is primed and can mediate protection against a secondary lethal infection.     

The Parkinson’s disease kinase LRRK2 autophosphorylates its GTPase domain at multiple sites

Mutations in leucine-rich repeat kinase 2 (LRRK2) are a common cause of inherited Parkinson’s disease (PD). The protein is large and complex, but pathogenic mutations cluster in a region containing GTPase and kinase domains. LRRK2 can autophosphorylate in vitro within a dimer pair, although the significance of this reaction is unclear. Here, we mapped the sites of autophosphorylation within LRRK2 and found several potential phosphorylation sites within the GTPase domain. Using mass spectrometry, we found that Thr1343 is phosphorylated and, using kinase dead versions of LRRK2, show that this is an autophosphorylation site. However, we also find evidence for additional sites in the GTPase domain and in other regions of the protein suggesting that there may be multiple autophosphorylation sites within LRRK2. These data suggest that the kinase and GTPase activities of LRRK2 may exhibit complex autoregulatory interdependence.