Intracellular Bacterial Pathogens Trigger the Formation of U Small Nuclear RNA Bodies (U Bodies) through Metabolic Stress Induction.

Invasive bacterial pathogens induce an amino acid starvation (AAS) response in infected host cells that controls host defense in part by promoting autophagy. However, whether AAS has additional significant effects on the host response to intracellular bacteria remains poorly characterized. Here we showed that Shigella, Salmonella, and Listeria interfere with spliceosomal U snRNA maturation in the cytosol. Bacterial infection resulted in the rerouting of U snRNAs and their cytoplasmic escort, the survival motor neuron (SMN) complex, to processing bodies, thus forming U snRNA bodies (U bodies). This process likely contributes to the decline in the cytosolic levels of U snRNAs and of the SMN complex proteins SMN and DDX20 that we observed in infected cells. U body formation was triggered by membrane damage in infected cells and was associated with the induction of metabolic stresses, such as AAS or endoplasmic reticulum stress. Mechanistically, targeting of U snRNAs to U bodies was regulated by translation initiation inhibition and the ATF4/ATF3 pathway, and U bodies rapidly disappeared upon removal of the stress, suggesting that their accumulation represented an adaptive response to metabolic stress. Importantly, this process likely contributed to shape the host response to invasive bacteria because down-regulation of DDX20 expression using short hairpin RNA (shRNA) amplified ATF3- and NF-κB-dependent signaling. Together, these results identify a critical role for metabolic stress and invasive bacterial pathogens in U body formation and suggest that this process contributes to host defense.

Nutrient sensing and metabolic stress pathways in innate immunity.

Cells monitor nutrient availability through several highly conserved pathways that include the mTOR signalling axis regulated by AKT/PI3K, HIF and AMPK, as well as the GCN2/eIF2α integrated stress response pathway that provides cellular adaptation to amino acid starvation. Recent evidence has identified a critical interplay between these nutrient sensing pathways and innate immunity to bacterial pathogens, viruses and parasites. These observations suggest that, in addition to the well-characterized pro-inflammatory signalling mediated by pattern recognition molecules, a metabolic stress programme contributes to shape the global response to pathogens.

Post-transcriptional inhibition of luciferase reporter assays by the Nod-like receptor proteins NLRX1 and NLRC3.

Luciferase reporter assays (LRAs) are widely used to assess the activity of specific signal transduction pathways. Although powerful, rapid and convenient, this technique can also generate artifactual results, as revealed for instance in the case of high throughput screens of inhibitory molecules. Here we demonstrate that the previously reported inhibitory effect of the Nod-like receptor (NLR) protein NLRX1 on NF-κB- and type I interferon-dependent pathways in LRAs was a nonspecific consequence of the overexpression of the NLRX1 leucine-rich repeat (LRR) domain. By comparing luciferase activity and luciferase gene expression using quantitative PCR from the same samples, we showed that NLRX1 inhibited LRAs in a post-transcriptional manner. In agreement, NLRX1 also repressed LRAs if luciferase was expressed under the control of a constitutive promoter, although the degree of inhibition by NLRX1 seemed to correlate with the dynamic inducibility of luciferase reporter constructs. Similarly, we observed that overexpression of another NLR protein, NLRC3, also resulted in artifactual inhibition of LRAs; thus suggesting that the capacity to inhibit LRAs at a post-transcriptional level is not unique to NLRX1. Finally, we demonstrate that host type I interferon response to Sendai virus infection was normal in NLRX1-silenced human HEK293T cells. Our results thus highlight the fact that LRAs are not a reliable technique to assess the inhibitory function of NLRs, and possibly other overexpressed proteins, on signal transduction pathways.

Minimum data set for treatment effectiveness in pyoderma gangrenosum (MIDSTEP): an international protocol of an e-Delphi study to develop a clinical physician-driven treatment effectiveness registry on behalf of the UPGRADE initiative.

Pyoderma gangrenosum (PG) is a rare inflammatory condition with an immense disease burden that remains understudied. With limited approved treatments and low-quality clinical evidence, PG continues to have poor patient outcomes. Unfortunately, improvement in PG treatments and patient care is based on additional research endeavors that can only be developed from existing high-quality data. The following protocol outlines the development of the Minimum Data Set for Treatment Effectiveness in Pyoderma gangrenosum (MIDSTEP), a core set of domains and domain items for the Pyoderma Gangrenosum Treatment Effectiveness (PyGaTE) international registry. The outcomes and benefits are focused on providing real-world data for physicians to improve their clinical decisions on PG treatment and inform clinical trial design, promoting clinical research among the international scientific community. MIDSTEP is a multi-phase project. The first phase will produce a domain item list from a literature review to take into the second phase which would finalize the core data set by an e-Delphi exercise. There will be a single stakeholder group participating together in the e-Delphi consisting of PG experts (healthcare providers, researchers, methodologists, industry representatives, and regulators), ulcerative PG patients, and PG patient advocates. The methodology outlined in the protocol is a systematic method based on several guidelines through COMET and established dermatologic registries and outcome sets with systematic methodologies of their own. The third phase will identify the instruments for the items, the 'when to measure' the items, and the platform for the registry. The last phase is the implementation and continued maintenance of the international registry PyGaTE. By solidifying a consensus on standardized outcomes and collecting information on PG treatment effectiveness in a centralized database, existing treatments can be compared more systematically and analyzed with increased evidence. MIDSTEP and the PyGaTE international registry will have the ambitious goal to generate and disseminate real-world data that can be used by all stakeholders to improve health outcomes for PG patients. Future potential for the outcome of this project includes the development of a gold-standard PG treatment.

Cathelicidin LL-37 Ignites Primed NLRP3 Inflammasomes in Rosacea.

Microbes and commensal mites contribute to the development of inflammation and neurovascular dysregulation in rosacea. Cathelicidin family proteins are epithelial antimicrobial peptides expressed in higher-order mammals. In humans, mature LL-37 is cleaved from its precursor in response to microbial infection, UV light, and injury. In their new article in the Journal of Investigative Dermatology, Yoon et al. expand on existing evidence supporting LL-37 proinflammatory activity in lipopolysaccharide (LPS)- and UV-primed models of rosacea. They show in vitro that LL-37 promotes NLRP3-mediated inflammasome activation through lysosomal destabilization in the presence of LPS and that the injection of LL-37 in vivo leads to skin inflammation that is abrogated by direct NLRP3 inhibition and homozygous knockout in a murine model.

Identifying a Potential Therapeutic Host Target in Cutaneous Leishmaniasis.

Intracellular cutaneous infectious agents can trigger autoreactive immune responses, exacerbating or leading to new acute and chronic systemic illness. Cutaneous leishmaniasis (CL) causes vigorous immunopathologic responses that contribute to mucosal disease and ulceration. In this issue of the Journal of Investigative Dermatology, Novais et al. (2020) expand on their previous work demonstrating that a cytotoxic CD8+ response is associated with therapeutic failure. In this study, they show that inhibition of granzyme B with the Jak1/3 inhibitor, tofacitinib, is associated with decreased severity of cutaneous lesions without the attenuation of T helper type 1 signaling or parasite control. Their findings, including the utility of topical delivery, suggest an attractive role for Jak inhibition alongside antiparasitic agents in the treatment of CL in patients.

A Mother's Touch: Emerging Roles in Development of the Cutaneous Microbiome.

Skin-associated bacteria constitute a large proportion of the human microbiome and influence host immunity. The healthy cutaneous microbiome adopts site-specific composition, weeks to months postpartum. Zhu et al. (2019) expand the scope of pediatric data, tracking infant skin microflora changes by site, through childhood, and establish new associations with delivery mode and maternal microbiome.

Infectious endocarditis and vertebral osteomyelitis caused by Moraxella catarrhalis.

Moraxella catarrhalis frequently colonises the oropharynges of healthy individuals. Disease is usually limited to the oropharynx, upper airways and lower airways in patients with predisposing conditions. The pathogen rarely causes more invasive disease. We present the case of a 65-year-old woman with Crohn's disease on azathioprine, who was diagnosed with native valve M. catarrhalis endocarditis and vertebral osteomyelitis several weeks after an upper respiratory tract infection. She presented to hospital with 5 weeks of worsening malaise, nausea, relapsing fevers, weight loss, acute-on-chronic exacerbation of lower back pain and diffuse myalgia. Transoesophageal echocardiogram showed a 12 mm vegetation on her mitral valve, contrast-enhanced MRI was consistent with L4 osteomyelitis and blood cultures were persistently positive for M. catarrhalis She was initially treated with ceftriaxone 2 g intravenously daily, and although her symptoms initially resolved, she experienced a relapse of osteomyelitis with L3 extension a few weeks after treatment discontinuation.