Stress granules plug and stabilize damaged endolysosomal membranes.

Endomembrane damage represents a form of stress that is detrimental for eukaryotic cells1,2. To cope with this threat, cells possess mechanisms that repair the damage and restore cellular homeostasis3-7. Endomembrane damage also results in organelle instability and the mechanisms by which cells stabilize damaged endomembranes to enable membrane repair remains unknown. Here, by combining in vitro and in cellulo studies with computational modelling we uncover a biological function for stress granules whereby these biomolecular condensates form rapidly at endomembrane damage sites and act as a plug that stabilizes the ruptured membrane. Functionally, we demonstrate that stress granule formation and membrane stabilization enable efficient repair of damaged endolysosomes, through both ESCRT (endosomal sorting complex required for transport)-dependent and independent mechanisms. We also show that blocking stress granule formation in human macrophages creates a permissive environment for Mycobacterium tuberculosis, a human pathogen that exploits endomembrane damage to survive within the host.

Correlative light electron ion microscopy reveals in vivo localisation of bedaquiline in Mycobacterium tuberculosis-infected lungs.

Correlative light, electron, and ion microscopy (CLEIM) offers huge potential to track the intracellular fate of antibiotics, with organelle-level resolution. However, a correlative approach that enables subcellular antibiotic visualisation in pathogen-infected tissue is lacking. Here, we developed correlative light, electron, and ion microscopy in tissue (CLEIMiT) and used it to identify the cell type-specific accumulation of an antibiotic in lung lesions of mice infected with Mycobacterium tuberculosis. Using CLEIMiT, we found that the anti-tuberculosis (TB) drug bedaquiline (BDQ) is localised not only in foamy macrophages in the lungs during infection but also accumulate in polymorphonuclear (PMN) cells.

LRRK2 is a negative regulator of Mycobacterium tuberculosis phagosome maturation in macrophages.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) are associated with Parkinson's disease, chronic inflammation and mycobacterial infections. Although there is evidence supporting the idea that LRRK2 has an immune function, the cellular function of this kinase is still largely unknown. By using genetic, pharmacological and proteomics approaches, we show that LRRK2 kinase activity negatively regulates phagosome maturation via the recruitment of the Class III phosphatidylinositol-3 kinase complex and Rubicon to the phagosome in macrophages. Moreover, inhibition of LRRK2 kinase activity in mouse and human macrophages enhanced Mycobacterium tuberculosis phagosome maturation and mycobacterial control independently of autophagy. In vivo, LRRK2 deficiency in mice resulted in a significant decrease in M. tuberculosis burdens early during the infection. Collectively, our findings provide a molecular mechanism explaining genetic evidence linking LRRK2 to mycobacterial diseases and establish an LRRK2-dependent cellular pathway that controls M. tuberculosis replication by regulating phagosome maturation.

An essential bifunctional enzyme in Mycobacterium tuberculosis for itaconate dissimilation and leucine catabolism.

Mycobacterium tuberculosis (Mtb) is the etiological agent of tuberculosis. One-fourth of the global population is estimated to be infected with Mtb, accounting for ∼1.3 million deaths in 2017. As part of the immune response to Mtb infection, macrophages produce metabolites with the purpose of inhibiting or killing the bacterial cell. Itaconate is an abundant host metabolite thought to be both an antimicrobial agent and a modulator of the host inflammatory response. However, the exact mode of action of itaconate remains unclear. Here, we show that Mtb has an itaconate dissimilation pathway and that the last enzyme in this pathway, Rv2498c, also participates in l-leucine catabolism. Our results from phylogenetic analysis, in vitro enzymatic assays, X-ray crystallography, and in vivo Mtb experiments, identified Mtb Rv2498c as a bifunctional ß-hydroxyacyl-CoA lyase and that deletion of the rv2498c gene from the Mtb genome resulted in attenuation in a mouse infection model. Altogether, this report describes an itaconate resistance mechanism in Mtb and an l-leucine catabolic pathway that proceeds via an unprecedented (R)-3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) stereospecific route in nature.

Cmr is a redox-responsive regulator of DosR that contributes to M. tuberculosis virulence.

Mycobacterium tuberculosis (MTb) is the causative agent of pulmonary tuberculosis (TB). MTb colonizes the human lung, often entering a non-replicating state before progressing to life-threatening active infections. Transcriptional reprogramming is essential for TB pathogenesis. In vitro, Cmr (a member of the CRP/FNR super-family of transcription regulators) bound at a single DNA site to act as a dual regulator of cmr transcription and an activator of the divergent rv1676 gene. Transcriptional profiling and DNA-binding assays suggested that Cmr directly represses dosR expression. The DosR regulon is thought to be involved in establishing latent tuberculosis infections in response to hypoxia and nitric oxide. Accordingly, DNA-binding by Cmr was severely impaired by nitrosation. A cmr mutant was better able to survive a nitrosative stress challenge but was attenuated in a mouse aerosol infection model. The complemented mutant exhibited a ∼2-fold increase in cmr expression, which led to increased sensitivity to nitrosative stress. This, and the inability to restore wild-type behaviour in the infection model, suggests that precise regulation of the cmr locus, which is associated with Region of Difference 150 in hypervirulent Beijing strains of Mtb, is important for TB pathogenesis.

Why Finding a Treatment for Alopecia Areata Is Important: A Multifaceted Perspective.

Alopecia areata is an autoimmune disease that alters one's appearance. Some define it as a cosmetic disease despite evidence that substantial psychosocial burden is associated with it. As a physician, support group leader, consultant for the National Alopecia Areata Foundation, and patient, I discuss the evidence behind the psychosocial impact of alopecia areata and the importance of comprehensive treatment.

Report of the proceedings of a UK skin safety advisory group.

Moisture-associated skin damage, especially incontinence-associated dermatitis, continues to present significant health challenges and requires multidisciplinary input to provide effective prevention and treatment. In the absence of mandatory reporting such damage is under- or wrongfully reported, resulting in a lack of accurate data on prevalence and costs of associated care. In March this year, a multidisciplinary team of experts met in the UK to seek to determine measures to improve patient skin care. They aimed to identify activities to increase awareness and education, collect data, and improve prevention and treatment regimes. This article describes that discussion and the conclusions made by the group, such as the key actions required to effect policy changes.

Developing eLearning for pressure ulcer prevention and management.

The impact of pressure ulcers is psychologically, physically and clinically challenging for both patients and NHS staff. NHS Greater Glasgow and Clyde (NHS GGC), in line with the Scottish Best Practice Statement for the Prevention and Management of Pressure Ulcers ( Quality Improvement Scotland, 2009 ), and the NHS Health Improvement Scotland (2011) Preventing Pressure Ulcers Change Package, launched an awareness campaign throughout the organisation in April 2012 and has more recently adopted a 'zero-tolerance' approach to pressure damage. The tissue viability service in NHS GGC recognised that in order to achieve this aim, education of front-line staff is essential. An educational framework for pressure ulcer prevention was developed for all levels of healthcare staff involved in the delivery of patient care. As a means to support the framework, an initiative to develop web-based eLearning modules has been taken forward. This has resulted in the creation of an accessible, cost-effective, stimulating, relevant, and evidence-based education programme designed around the educational needs of all healthcare staff. In conjunction with the organisation's 'top ten tools' for pressure ulcer prevention and management, the modular online education programme addresses the aims of quality improvement and zero tolerance by supporting the provision of safe and effective person-centered care.

OX40 ligand fusion protein delivered simultaneously with the BCG vaccine provides superior protection against murine Mycobacterium tuberculosis infection.

Mycobacterium tuberculosis infection claims approximately 2 million lives per year, and improved efficacy of the BCG vaccine remains a World Health Organization priority. Successful vaccination against M. tuberculosis requires the induction and maintenance of T cells. Targeting molecules that promote T-cell survival may therefore provide an alternative strategy to classic adjuvants. We show that the interaction between T-cell-expressed OX40 and OX40L on antigen-presenting cells is critical for effective immunity to BCG. However, because OX40L is lost rapidly from antigen-presenting cells following BCG vaccination, maintenance of OX40-expressing vaccine-activated T cells may not be optimal. Delivering an OX40L:Ig fusion protein simultaneously with BCG provided superior immunity to intravenous and aerosol M. tuberculosis challenge even 6 months after vaccination, an effect that depends on natural killer 1.1(+) cells. Attenuated vaccines may therefore lack sufficient innate stimulation to maintain vaccine-specific T cells, which can be replaced by reagents binding inducible T-cell costimulators.

Important role for Mycobacterium tuberculosis UvrD1 in pathogenesis and persistence apart from its function in nucleotide excision repair.

Mycobacterium tuberculosis survives and replicates in macrophages, where it is exposed to reactive oxygen and nitrogen species that damage DNA. In this study, we investigated the roles of UvrA and UvrD1, thought to be parts of the nucleotide excision repair pathway of M. tuberculosis. Strains in which uvrD1 was inactivated either alone or in conjunction with uvrA were constructed. Inactivation of uvrD1 resulted in a small colony phenotype, although growth in liquid culture was not significantly affected. The sensitivity of the mutant strains to UV irradiation and to mitomycin C highlighted the importance of the targeted genes for nucleotide excision repair. The mutant strains all exhibited heightened susceptibility to representatives of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI). The uvrD1 and the uvrA uvrD1 mutants showed decreased intracellular multiplication following infection of macrophages. Most importantly, the uvrA uvrD1 mutant was markedly attenuated following infection of mice by either the aerosol or the intravenous route.

Forkhead-associated (FHA) domain containing ABC transporter Rv1747 is positively regulated by Ser/Thr phosphorylation in Mycobacterium tuberculosis.

One major signaling method employed by Mycobacterium tuberculosis, the causative agent of tuberculosis, is through reversible phosphorylation of proteins mediated by protein kinases and phosphatases. This study concerns one of these enzymes, the serine/threonine protein kinase PknF, that is encoded in an operon with Rv1747, an ABC transporter that is necessary for growth of M. tuberculosis in vivo and contains two forkhead-associated (FHA) domains. FHA domains are phosphopeptide recognition motifs that specifically recognize phosphothreonine-containing epitopes. Experiments to determine how PknF regulates the function of Rv1747 demonstrated that phosphorylation occurs on two specific threonine residues, Thr-150 and Thr-208. To determine the in vivo consequences of phosphorylation, infection experiments were performed in bone marrow-derived macrophages and in mice using threonine-to-alanine mutants of Rv1747 that prevent specific phosphorylation and revealed that phosphorylation positively modulates Rv1747 function in vivo. The role of the FHA domains in this regulation was further demonstrated by isothermal titration calorimetry, using peptides containing both phosphothreonine residues. FHA-1 domain mutation resulted in attenuation in macrophages highlighting the critical role of this domain in Rv1747 function. A mutant deleted for pknF did not, however, have a growth phenotype in an infection, suggesting that other kinases can fulfill its role when it is absent. This study provides the first information on the molecular mechanism(s) regulating Rv1747 through PknF-dependent phosphorylation but also indicates that phosphorylation activates Rv1747, which may have important consequences in regulating growth of M. tuberculosis.

Lysosomal damage drives mitochondrial proteome remodelling and reprograms macrophage immunometabolism.

Transient lysosomal damage after infection with cytosolic pathogens or silica crystals uptake results in protease leakage. Whether limited leakage of lysosomal contents into the cytosol affects the function of cytoplasmic organelles is unknown. Here, we show that sterile and non-sterile lysosomal damage triggers a cell death independent proteolytic remodelling of the mitochondrial proteome in macrophages. Mitochondrial metabolic reprogramming required leakage of lysosomal cathepsins and was independent of mitophagy, mitoproteases and proteasome degradation. In an in vivo mouse model of endomembrane damage, live lung macrophages that internalised crystals displayed impaired mitochondrial function. Single-cell RNA-sequencing revealed that lysosomal damage skewed metabolic and immune responses in alveolar macrophages subsets with increased lysosomal content. Functionally, drug modulation of macrophage metabolism impacted host responses to Mycobacterium tuberculosis infection in an endomembrane damage dependent way. This work uncovers an inter-organelle communication pathway, providing a general mechanism by which macrophages undergo mitochondrial metabolic reprograming after endomembrane damage.

The Mycobacterium tuberculosis sRNA F6 Modifies Expression of Essential Chaperonins, GroEL2 and GroES.

Almost 140 years after the identification of Mycobacterium tuberculosis as the etiological agent of tuberculosis, important aspects of its biology remain poorly described. Little is known about the role of posttranscriptional control of gene expression and RNA biology, including the role of most of the small RNAs (sRNAs) identified to date. We have carried out a detailed investigation of the M. tuberculosis sRNA F6 and shown it to be dependent on SigF for expression and significantly induced in starvation conditions in vitro and in a mouse model of infection. Further exploration of F6 using an in vitro starvation model of infection indicates that F6 affects the expression of the essential chaperonins GroEL2 and GroES. Our results point toward a role for F6 during periods of low metabolic activity typically associated with long-term survival of M. tuberculosis in human granulomas. IMPORTANCE Control of gene expression via small regulatory RNAs (sRNAs) is poorly understood in one of the most successful pathogens, Mycobacterium tuberculosis. Here, we present an in-depth characterization of the sRNA F6, including its expression in different infection models and the differential gene expression observed upon deletion of the sRNA. Our results demonstrate that deletion of F6 leads to dysregulation of the two essential chaperonins GroEL2 and GroES and, moreover, indicate a role for F6 in the long-term survival and persistence of M. tuberculosis in the human host.

Comparative fitness analysis of D-cycloserine resistant mutants reveals both fitness-neutral and high-fitness cost genotypes.

Drug resistant infections represent one of the most challenging medical problems of our time. D-cycloserine is an antibiotic used for six decades without significant appearance and dissemination of antibiotic resistant strains, making it an ideal model compound to understand what drives resistance evasion. We therefore investigated why Mycobacterium tuberculosis fails to become resistant to D-cycloserine. To address this question, we employed a combination of bacterial genetics, genomics, biochemistry and fitness analysis in vitro, in macrophages and in mice. Altogether, our results suggest that the ultra-low rate of emergence of D-cycloserine resistance mutations is the dominant biological factor delaying the appearance of clinical resistance to this antibiotic. Furthermore, we also identified potential compensatory mechanisms able to minimize the severe fitness costs of primary D-cycloserine resistance conferring mutations.

A Rab20-Dependent Membrane Trafficking Pathway Controls M. tuberculosis Replication by Regulating Phagosome Spaciousness and Integrity.

The intracellular pathogen Mycobacterium tuberculosis (Mtb) lives within phagosomes and also disrupts these organelles to access the cytosol. The host pathways and mechanisms that contribute to maintaining Mtb phagosome integrity have not been investigated. Here, we examined the spatiotemporal dynamics of Mtb-containing phagosomes and identified an interferon-gamma-stimulated and Rab20-dependent membrane trafficking pathway in macrophages that maintains Mtb in spacious proteolytic phagolysosomes. This pathway functions to promote endosomal membrane influx in infected macrophages, and is required to preserve Mtb phagosome integrity and control Mtb replication. Rab20 is specifically and significantly upregulated in the sputum of human patients with active tuberculosis. Altogether, we uncover an immune-regulated cellular pathway of defense that promotes maintenance of Mtb within intact membrane-bound compartments for efficient elimination.

Potential correlates of BCG induced protection against tuberculosis detected in a mouse aerosol model using gene expression profiling.

Tuberculosis (TB) is responsible for more than 2 million deaths per year with the incidence of new cases rising throughout the world. Mycobacterium bovis bacillus Calmette Guerin (BCG) is currently the only available licensed vaccine against M. tuberculosis. Despite the variable protective efficacy in different populations it affords some protection, particularly against childhood and disseminated forms of the disease. BCG remains the gold standard for assessing other prospective TB vaccines, yet there is a lack of information on the mechanisms of BCG protection and consequently there are no definitive correlates of protection for this vaccine. In order to further studies in this area we assessed lung RNA homogenates from naïve, BCG vaccinated and aerosol challenged mice. We found increased IFN-gamma levels in lungs of aerosol challenged mice previously vaccinated with BCG and a number of transcripts regulated by IFN-gamma were also increased in the lungs of these animals. These transcripts represent a cluster of IFN-gamma related transcripts that may assist in determining if BCG and maybe other potential vaccines will elicit protection against M. tuberculosis.

The proneurotrophin receptor sortilin is required for Mycobacterium tuberculosis control by macrophages.

Sorting of luminal and membrane proteins into phagosomes is critical for the immune function of this organelle. However, little is known about the mechanisms that contribute to the spatiotemporal regulation of this process. Here, we investigated the role of the proneurotrophin receptor sortilin during phagosome maturation and mycobacterial killing. We show that this receptor is acquired by mycobacteria-containing phagosomes via interactions with the adaptor proteins AP-1 and GGAs. Interestingly, the phagosomal association of sortilin is critical for the delivery of acid sphingomyelinase (ASMase) and required for efficient phagosome maturation. Macrophages from Sort1(-/-) mice are less efficient in restricting the growth of Mycobacterium bovis BCG and M. tuberculosis. In vivo, Sort1(-/-) mice showed a substantial increase in cellular infiltration of neutrophils in their lungs and higher bacterial burden after infection with M. tuberculosis. Altogether, sortilin defines a pathway required for optimal intracellular mycobacteria control and lung inflammation in vivo.

A phase I study of pegylated liposomal doxorubicin hydrochloride (Caelyx) in combination with cyclophosphamide and vincristine as second-line treatment of patients with small-cell lung cancer.

The purpose of this study was to determine the recommended phase II dose of liposomal doxorubicin (Caelyx ; Doxil in the United States) in combination with cyclophosphamide and vincristine for previously treated patients with good performance status with relapsed or refractory small-cell lung cancer. Twenty-one eligible patients were enrolled between November 1999 and September 2001 and received liposomal doxorubicin 25-40 mg/m2, cyclophosphamide 750-1000 mg/m2, and vincristine 1.2 mg/m2 intravenously (I.V.) every 21 days. At doses of liposomal doxorubicin 40 mg/m2, cyclophosphamide 750 mg/m2, and vincristine 1.2 mg/m2 I.V., 1 of 6 patients had dose-limiting neutropenia and fever in cycle 2 and 2 of 6 developed grade 3 hand-foot syndrome during cycle 3. Therefore, the recommended phase II doses are liposomal doxorubicin 35 mg/m2, cyclophosphamide 750 mg/m2, and vincristine 1.2 mg/m2 I.V. every 21 days. Antitumor activity was seen at all dose levels. This combination is well tolerated and has evidence of antitumor activity. A phase II evaluation is ongoing.