Murine Borrelia arthritis is highly dependent on ASC and caspase-1, but independent of NLRP3

Introduction

The protein platform called the NOD-like-receptor -family member (NLRP)-3 inflammasome needs to be activated to process intracellular caspase-1. Active caspase-1 is able to cleave pro-Interleukin (IL)-1β, resulting in bioactive IL-1β. IL-1β is a potent proinflammatory cytokine, and thought to play a key role in the pathogenesis of Lyme arthritis, a common manifestation of Borrelia burgdorferi infection. The precise pathways through which B. burgdorferi recognition leads to inflammasome activation and processing of IL-1β in Lyme arthritis has not been elucidated. In the present study, we investigated the contribution of several pattern recognition receptors and inflammasome components in a novel murine model of Lyme arthritis.

Methods

Lyme arthritis was elicited by live B. burgdorferi, injected intra-articularly in knee joints of mice. To identify the relevant pathway components, the model was applied to wild-type, NLRP3-/-, ASC-/-, caspase-1-/-, NOD1-/-, NOD2-/-, and RICK-/- mice. As a control, TLR2-/-, Myd88-/- and IL-1R-/- mice were used. Peritoneal macrophages and bone marrow-derived macrophages were used for in vitro cytokine production and inflammasome activation studies. Joint inflammation was analyzed in synovial specimens and whole knee joints. Mann-Whitney U tests were used to detect statistical differences.

Results

We demonstrate that ASC/caspase-1-driven IL-1β is crucial for induction of B. burgdorferi-induced murine Lyme arthritis. In addition, we show that B. burgdorferi-induced murine Lyme arthritis is less dependent on NOD1/NOD2/RICK pathways while the TLR2-MyD88 pathway is crucial.

Conclusions

Murine Lyme arthritis is strongly dependent on IL-1 production, and B. burgdorferi induces inflammasome-mediated caspase-1 activation. Next to that, murine Lyme arthritis is ASC- and caspase-1-dependent, but NLRP3, NOD1, NOD2, and RICK independent. Also, caspase-1 activation by B. burgdorferi is dependent on TLR2 and MyD88. Based on present results indicating that IL-1 is one of the major mediators in Lyme arthritis, there is a rationale to propose that neutralizing IL-1 activity may also have beneficial effects in chronic Lyme arthritis.     

A novel deconvolution method for modeling UDP-N-acetyl-D-glucosamine biosynthetic pathways based on 13C mass isotopologue profiles under non-steady-state conditions

This article is a response to Wang and Luo. See correspondence article http://www.biomedcentral.com/1741-7007/10/30/ [WEBCITE] and the original research article http://www.biomedcentral.com/1741-7007/9/24 [WEBCITE].     

Pseudomonas aeruginosa Type IV pilus expression in Neisseria gonorrhoeae: effects of pilin subunit composition on function and organelle dynamics

Type IV pili (TFP) play central roles in the expression of many phenotypes including motility, multicellular behavior, sensitivity to bacteriophages, natural genetic transformation, and adherence. In Neisseria gonorrhoeae, these properties require ancillary proteins that act in conjunction with TFP expression and influence organelle dynamics. Here, the intrinsic contributions of the pilin protein itself to TFP dynamics and associated phenotypes were examined by expressing the Pseudomonas aeruginosa PilA(PAK) pilin subunit in N. gonorrhoeae. We show here that, although PilA(PAK) pilin can be readily assembled into TFP in this background, steady-state levels of purifiable fibers are dramatically reduced relative those of endogenous pili. This defect is due to aberrant TFP dynamics as it is suppressed in the absence of the PilT pilus retraction ATPase. Functionally, PilA(PAK) pilin complements gonococcal adherence for human epithelial cells but only in a pilT background, and this property remains dependent on the coexpression of both the PilC adhesin and the PilV pilin-like protein. Since P. aeruginosa pilin only moderately supports neisserial sequence-specific transformation despite its assembly proficiency, these results together suggest that PilA(PAK) pilin functions suboptimally in this environment. This appears to be due to diminished compatibility with resident proteins essential for TFP function and dynamics. Despite this, PilA(PAK) pili support retractile force generation in this background equivalent to that reported for endogenous pili. Furthermore, PilA(PAK) pili are both necessary and sufficient for bacteriophage PO4 binding, although the strain remains phage resistant. Together, these findings have significant implications for TFP biology in both N. gonorrhoeae and P. aeruginosa.     

The [FeFe] hydrogenase of Nyctotherus ovalis has a chimeric origin

Background

The hydrogenosomes of the anaerobic ciliate Nyctotherus ovalis show how mitochondria can evolve into hydrogenosomes because they possess a mitochondrial genome and parts of an electron-transport chain on the one hand, and a hydrogenase on the other hand. The hydrogenase permits direct reoxidation of NADH because it consists of a [FeFe] hydrogenase module that is fused to two modules, which are homologous to the 24 kDa and the 51 kDa subunits of a mitochondrial complex I.

Results

The [FeFe] hydrogenase belongs to a clade of hydrogenases that are different from well-known eukaryotic hydrogenases. The 24 kDa and the 51 kDa modules are most closely related to homologous modules that function in bacterial [NiFe] hydrogenases. Paralogous, mitochondrial 24 kDa and 51 kDa modules function in the mitochondrial complex I in N. ovalis. The different hydrogenase modules have been fused to form a polyprotein that is targeted into the hydrogenosome.

Conclusion

The hydrogenase and their associated modules have most likely been acquired by independent lateral gene transfer from different sources. This scenario for a concerted lateral gene transfer is in agreement with the evolution of the hydrogenosome from a genuine ciliate mitochondrion by evolutionary tinkering.