Bacteria fight back against Toll-like receptors

The curious case of SARM1: Dr. Jekyll and Mr. Hyde in cell death and immunity?

Sterile alpha and toll/interleukin-1 receptor motif-containing protein 1 (SARM1) was first identified as a novel ortholog of Drosophila protein CG7915 and was subsequently placed as the fifth member of the human TIR-containing adaptor protein. SARM1 holds a unique position in this family where, unlike other members, it downregulates NFκB activity in response to immunogenic stimulation, interacts with another member of the family, TRIF, to negatively regulate its function, and it also mediates cell death responses. Over the past decade, SARM1 has emerged as one of the primary mediators of programmed axonal degeneration and this robust regulation of axonal degeneration-especially in models of peripheral neuropathy and traumatic injury-makes it an attractive target for therapeutic intervention. The TIR domain of SARM1 possesses an intrinsic NADase activity resulting in cellular energy deficits within the axons, a striking deviation from its other family members of human TLR adaptors. Interestingly, the TIR NADase activity, as seen in SARM1, is also observed in several prokaryotic TIR-containing proteins where they are involved in immune evasion once within the host. Although the immune function of SARM1 is yet to be conclusively discerned, this closeness in function with the prokaryotic TIR-domain containing proteins, places it at an interesting juncture of evolution raising questions about its origin and function in cell death and immunity. In this review, we discuss how a conserved immune adaptor protein like SARM1 switches to a pro-neurodegenerative function and the evolutionarily significance of the process.

A minor structure modification serendipitously leads to a highly carbapenemase-specific fluorogenic probe

Reported herein is a fluorogenic probe for the detection of carbapenemase activity. This reagent features carbapenem as an enzyme recognition motif and a carbon-carbon double bond between carbapenem and the fluorophore, exhibiting high specificity to all carbapenemases, including metallo carbapenemases and serine carbapenemases, over other β-lactamases.

Molecular analysis of a novel Toll/interleukin-1 receptor (TIR)-domain containing virulence protein of Y. pseudotuberculosis among Far East scarlet-like fever serotype I strains

Pathogenicity of Yersinia pseudotuberculosis is determined by an arsenal of virulence factors. Particularly, the Yersinia outer proteins (Yops) and the Type III secretion system (T3SS) encoded on the pYV virulence plasmid are required for Yersinia pathogenicity. A specific group of Y. pseudotuberculosis, responsible for the clinical syndrome described as Far East scarlet-like fever (FESLF), is known to have an altered virulence gene cluster. Far East strains cause unique clinical symptoms for which the pYV virulence plasmid plays apparently a rather secondary role. Here, we characterize a previously unknown protein of Y. pseudotuberculosis serotype I strains (TcpYI) which can be found particularly among the FESLF strain group. The TcpYI protein shares considerable sequence homology to members of the Toll/IL-1 receptor family. Bacterial TIR domain containing proteins (Tcps) interact with the innate immune system by TIR-TIR interactions and subvert host defenses via individual, multifaceted mechanisms. In terms of virulence, it appears that the TcpYI protein of Y. pseudotuberculosis displays its own virulence phenotype compared to the previously characterized bacterial Tcps. Our results clearly demonstrate that TcpYI increases the intracellular survival of the respective strains in vitro. Furthermore, we show here that the intracellular survival benefit of the wild-type strain correlates with an increase in tcpYI gene expression inside murine macrophages. In support of this, we found that TcpYI enhances the survival inside the spleens of mice in a mouse model of peritonitis. Our results may point toward involvement of the TcpYI protein in inhibition of phagocytosis, particularly in distinct Y. pseudotuberculosis strains of the FESLF strain group where the pYV virulence plasmid is absent.

Treating acute cystitis with biodegradable micelle-encapsulated quercetin

Intravesical application of an anti-inflammatory drug is an efficient strategy for acute cystitis therapy. Quercetin (QU) is a potent anti-inflammatory agent; however, its poor water solubility restricts its clinical application. In an attempt to improve water solubility of QU, biodegradable monomethoxy poly(ethylene glycol)-poly(ɛ-caprolactone) (MPEG-PCL) micelles were used to encapsulate QU by self-assembly methods, creating QU/MPEG-PCL micelles. These QU/MPEG-PCL micelles with DL of 7% had a mean particle size of <34 nm, and could release QU for an extended period in vitro. The in vivo study indicated that intravesical application of MPEG-PCL micelles did not induce any toxicity to the bladder, and could efficiently deliver cargo to the bladder. Moreover, the therapeutic efficiency of intravesical administration of QU/MPEG-PCL micelles on acute cystitis was evaluated in vivo. Results indicated that QU/MPEG-PCL micelle treatment efficiently reduced the edema and inflammatory cell infiltration of the bladder in an Escherichia coli-induced acute cystitis model. These data suggested that MPEG-PCL micelle was a candidate intravesical drug carrier, and QU/MPEG-PCL micelles may have potential application in acute cystitis therapy.

Analysis of membrane antigens on neutrophils from patients with sepsis

The aim of the present study was to assess changes of cell membrane antigens on neutrophils in septic patients. Expression levels of neutrophil membrane antigens were measured employing a FACS calibur flow cytometer with several fluorescence-labeled monoclonal antibodies. Expression levels of the CD14 antigen were higher in patients with sepsis than in healthy individuals. In particular, the expression levels of CD14 increased in patients complicated by septic shock. Expression levels of TLR-4 were higher in patients with sepsis or septic shock than in healthy individuals. Expression levels of CD11b and CD16 were lower in patients with sepsis or septic shock than in healthy individuals and were even lower in those complicated by septic shock. Expression levels of neutrophil membrane antigens in patients with sepsis markedly changed in the acute phase. However, these levels tended to return to those of healthy individuals in the convalescing phase. Analyses of the surface antigens on neutrophils strongly involved in biological defense or tissue injury are informative for understanding the pathology of sepsis and for conducting therapy targeting neutrophils in the future.

Molecular mimicry in innate immunity: crystal structure of a bacterial TIR domain

Macrophages detect pathogen infection via the activation of their plasma membrane-bound Toll-like receptor proteins (TLRs). The heterotypic interaction between the Toll/interleukin-1 receptor (TIR) domains of TLRs and adaptor proteins, like Myeloid differentiation primary response gene 88 (MyD88), is the first intracellular step in the signaling pathway of the mammalian innate immune response. The hetero-oligomerization of the TIRs of the receptor and adaptor brings about the activation of the transcription factor NF-kappaB, which regulates the synthesis of pro-inflammatory cytokines. Here, we report the first crystal structure of a bacterial TIR domain solved at 2.5 A resolution. The three-dimensional fold of Paracoccus denitrificans TIR is identical to that observed for the TIR of human TLRs and MyD88 proteins. The structure shows a unique dimerization interface involving the DD-loop and EE-loop residues, whereas leaving the BB-loop highly exposed. Peptide amide hydrogen-deuterium exchange mass spectrometry also reveals that the same region is used for dimerization in solution and in the context of the full-length protein. These results, together with a functional interaction between P. denitrificans TIR and MyD88 visualized in a co-immunoprecipitation assay, further substantiate the model that bacterial TIR proteins adopt structural mimicry of the host active receptor TIR domains to interfere with the signaling of TLRs and their adaptors to decrease the inflammatory response.