An increase in intracellular p62/NBR1 and persistence of Burkholderia mallei and B. pseudomallei in infected mice linked to autophagy deficiency

Dedicated bacterial esterases reverse lipopolysaccharide ubiquitylation to block immune sensing

Pathogenic bacteria have evolved diverse mechanisms to counteract cell-autonomous immunity, which otherwise guards both immune and non-immune cells from the onset of an infection1,2. The versatile immunity protein Ring finger protein 213 (RNF213)3-6 mediates the non-canonical ester-linked ubiquitylation of lipopolysaccharide (LPS), marking bacteria that sporadically enter the cytosol for destruction by antibacterial autophagy4. However, whether cytosol-adapted pathogens are ubiquitylated on their LPS and whether they escape RNF213-mediated immunity, remains unknown. Here we show that Burkholderia deubiquitylase (DUB), TssM7-9, is a potent esterase that directly reverses the ubiquitylation of LPS. Without TssM, cytosolic Burkholderia became coated in polyubiquitin and autophagy receptors in an RNF213-dependent fashion. Whereas the expression of TssM was sufficient to enable the replication of the non-cytosol adapted pathogen Salmonella, we demonstrate that Burkholderia has evolved a multi-layered defence system to proliferate in the host cell cytosol, including a block in antibacterial autophagy10-12. Structural analysis provided insight into the molecular basis of TssM esterase activity, allowing it to be uncoupled from isopeptidase function. TssM homologs conserved in another Gram-negative pathogen also reversed non-canonical LPS ubiquitylation, establishing esterase activity as a bacterial virulence mechanism to subvert host cell-autonomous immunity.

Salmonella Enteritidis RfbD enhances bacterial colonization and virulence through inhibiting autophagy

Autophagy is a crucial innate immune response that clears pathogens intracellularly. Salmonella enterica serovar Enteritidis (S.E) has emerged as one of the most important food-borne pathogens. Here, we reported that dTDP-4-dehydro-β-ւ-rhamnose reductase (RfbD) was able to enhance bacterial colonization in vivo and in vitro by regulating autophagy. We screened the transposon mutant library of Salmonella Enteritidis strain Z11 by High-Content Analysis System, found that rfbD gene has an effect on autophagy. The Z11ΔrfbD-infected group showed greater expression of LC3-II than the Z11-infected group in HeLa, RAW264.7, and J774A.1 cells. Overall, the survival of Z11ΔrfbD in RAW264.7 cells was reduced after 8 h of infection compared to that of the Z11 wild-type strain. In addition, we observed that inhibition of autophagic flux significantly increased the survival of Z11ΔrfbD in RAW264.7 cells. Mice infection experiments revealed that Z11ΔrfbD virulence was significantly reduced, and bacterial load was reduced in the liver and cecum in mice model, and LC3-II expression was significantly increased. These findings indicate an important role of Salmonella Enteritidis protein as a strategy to suppress autophagy and provides new ideas for manipulating autophagy as a novel strategy to treat infectious diseases.

Effect of PINK1 and Parkin gene silencing on sodium arsenite-induced mitophagy in normal rat liver cells (BRL-3A)

NaAsO₂-induced liver damage leads to autophagy, which plays an important role in cell quality control. Mitophagy plays an important role in hepatocyte damage, and PINK1 and Parkin constitute an important pathway in mitophagy. PINK1 selectively degrades abnormal mitochondria, and Parkin can recognize damaged mitochondria. However, the mechanism underlying the involvement of PINK1/Parkin in NaAsO₂-induced mitophagy is unclear. Transfection plasmids containing dsRNA were used to interfere with the expression of Parkin in the following groups: the empty plasmid group was established by add the empty plasmid only, the PINK1-knockdown (KD) group was established by adding 5 μg of PINK1 dsRNA and then by adding 10 mM NaAsO₂, and the Parkin-KD group was established by adding 5 μg of Parkin dsRNA and then by adding 10 mM NaAsO₂. The expression of PINK1 and Parkin in autophagy was detected by western blotting and immunofluorescence staining. The ultrastructures of autophagosomes and mitochondria were observed by transmission electron microscopy. The successful KD of PINK1 and Parkin aggravated the NaAsO₂-induced damage to mitophagy. The degeneration of mitochondrial vacuoles and the appearance of autophagosomes were detected in the NaAsO₂, NaAsO₂ + PINK1-KD and NaAsO₂ + Parkin-KD groups. NaAsO₂ can induce mitophagy in rat hepatocytes, and the silencing of PINK1 and Parkin can aggravate mitochondrial damage during this process. This study explored the mechanism of NaAsO₂-induced mitophagy in BRL-3A cells after PINK1 and Parkin gene silencing.

Methodological tools to study species of the genus Burkholderia

Bacteria belonging to the Burkholderia genus are extremely versatile and diverse. They can be environmental isolates, opportunistic pathogens in cystic fibrosis, immunocompromised or chronic granulomatous disease patients, or cause disease in healthy people (e.g., Burkholderia pseudomallei) or animals (as in the case of Burkholderia mallei). Since the genus was separated from the Pseudomonas one in the 1990s, the methodological tools to study and characterize these bacteria are evolving fast. Here we reviewed the techniques used in the last few years to update the taxonomy of the genus, to study gene functions and regulations, to deepen the knowledge on the drug resistance which characterizes these bacteria, and to elucidate their mechanisms to establish infections. The availability of these tools significantly impacts the quality of research on Burkholderia and the choice of the most appropriated is fundamental for a precise characterization of the species of interest.

Key points

• Updated techniques to study the genus Burkholderia were reviewed.

• Taxonomy, genomics, assays, and animal models were described.

• A comprehensive overview on recent advances in Burkholderia studies was made.

MicroRNA-146a inhibits autophagy to maintain the intracellular survival of Burkholderia pseudomallei by targeting LIPA

Burkholderia pseudomallei is the etiological agent of melioidosis, which is an emerging infectious disease endemic to many tropical regions. Autophagy is an intrinsic cellular process that degrades cytoplasmic components and plays an important role in protecting the host against pathogens. Like many intracellular pathogens, B. pseudomallei can evade the autophagy-dependent cellular clearance. However, the underlying mechanism remains unclear. In this study, we applied a combination of multiple assays to monitor autophagy processes and found that B. pseudomallei induced an incomplete autophagic flux and eliminate autophagy clearance in macrophages by blocking autophagosome-lysosome fusion. Based on a high-throughput microarray screening, we found that LIPA (lysosomal acid LIPAse A) was downregulated during B. pseudomallei infection. MiR-146a was then identified to be specifically upregulated upon infection with B. pseudomallei and further regulated LIPA expression by interacting with 3'UTR of LIPA. Furthermore, overexpression of miR-146a contributed to the defect of autophagic flux caused by B. pseudomallei and was beneficial for the survival of B. pseudomallei in macrophages. Therefore, our findings suggest that miR-146a inhibits autophagy via posttranscriptional suppression of LIPA expression to maintain B. pseudomallei survival in macrophages.

Exogenous H2S Protects Colon Cells in Ulcerative Colitis by Inhibiting NLRP3 and Activating Autophagy

Hydrogen sulfide (H₂S) has been reported to participate in intestinal mucosal defense and repair. However, the precise regulatory mechanisms of H₂S in ulcerative colitis (UC) remain unclear. We explored the effects of sodium hydrosulfide (NaHS), a donor of H₂S, in dextran sulfate sodium (DSS)-induced colitis in rats. The pathologic features were determined by analyzing the hematoxylin and eosin-stained samples. Interleukin-1β (IL-1β), IL-6, tumor necrosis factor-α (TNF-α), and myeloperoxidase (MPO) levels were determined using ELISA. The presence of cystathionine-γ-lyase (CSE) and light chain 3B (LC3B) were determined using immunohistochemical and immunofluorescence (IF) approaches, respectively. Next, we investigated the effects of NaHS in lipopolysaccharide (LPS)-stimulated human colonic smooth muscle cells (H2940). The level of reactive oxygen species (ROS) was determined using IF. NOD-like receptor 3 (NLRP3) and CSE were detected using western blot and quantitative real-time polymerase chain reaction. Autophagy was determined using western blot, IF, and electron microscopy. NaHS treatment considerably diminished colitis-induced histological injury and proinflammatory cytokine expressions. MPO, CSE, and H₂S were downregulated, whereas LC3B was upregulated after NaHS administration in colitic rats. NaHS remarkably attenuated the levels of ROS, CSE, and NLRP3 in LPS-stimulated cells and enhanced autophagy, as was revealed by increased LC3-II-to-LC3-I ratio, elevated LC3, and decreased p62. Importantly, NaHS promoted autophagosome formation in LPS-treated cells. Exogenous H₂S ameliorates intestinal injury by downregulating inflammation and activation of autophagy, suggesting the potential of NaHS as a therapeutic agent for UC.

An increase in p62/NBR1 levels in melioidosis patients of Sri Lanka exhibit a characteristic of potential host biomarker

Introduction. Melioidosis, caused by Burkholderia pseudomallei, in endemic areas, poses a challenge for treating the diseased populations without accurate diagnosis, and the disease-specific biomarkers linked with the infection have yet to be reported. Due to the invasive nature of the causative agent, Burkholderia pseudomallei, host innate effector mechanisms, including autophagy are known to be activated, resulting in differential expression of cellular proteins and immune markers. Identification of a disease-specific biomarker associated with B. pseudomallei infection will be helpful to facilitate rapid confirmation of melioidosis, which would enable early treatment and therapeutic success.Aim. We aimed to assess the levels of a host autophagy component, p62/NBR1, which function as a cargo-receptor in the process of autophagy activation leading to the degradation of ubiquitin-coated intracellular bacteria in which p62/NBR1 itself is degraded in the clearance of the pathogen. We further probed the extent of intracellular p62/NBR1 degradation and assessed its potential as a melioidosis biomarker.Methodology. We analysed peripheral blood mononuclear cell (PBMC) lysates using an ELISA-based assay for detecting cytosolic autophagy-related proteins p62/NBR1. We measured p62/NBR1 levels in diseased (confirmed B. pseudomallei infection) and non -diseased populations and utilized receiver operating characteristic (ROC) curve and max Youden index analysis for evaluating potential disease biomarker characteristics.Results. Our results revealed a three to fivefold increase in p62/NBR1 levels confirmed melioidosis cases compared to uninfected healthy donors. Comparable to p62/NBR1, levels of cytosolic LC3-I levels also increased, whereas the levels of degraded membrane bound form LC3-II was low, suggesting autophagy deficiency. Proinflammatory serum cytokine response, particularly IL-6, was consistently higher alongside B. pseudomallei infection in comparison to healthy controls.Conclusions. ROC curve and max Youden index analysis suggest that increased p62/NBR1 levels in diseased populations display characteristics of a potential disease biomarker in melioidosis and illustrates that an elevated p62/NBR1 level, in conjunction with B. pseudomallei infection associated with autophagy deficiency.

Nicotine induces apoptosis through exacerbation of blocked alveolar macrophage autophagic degradation in silicosis

Silica dust mainly attacks alveolar macrophages (AMs). The apoptosis of AMs is correlated with the progress of silicosis. Our previous study showed that autophagic degradation was blocked in AMs from silicosis patients. However, the effects of nicotine on AM autophagy and apoptosis in silicosis are unknown. In this study, we collected AMs from twenty male workers exposed to silica and divided them into observer and silicosis patient groups, according to the tuberous pathological changes observed by X-ray. The AMs from both groups were exposed to nicotine. We found increased levels of LC3, p62, and cleaved caspase-3, decreased levels of LAMP2, and damaged lysosomes after nicotine stimulation of the AMs from both groups. We also found that the autophagy inhibitor 3-methyladenine (3MA) inhibited nicotine-induced apoptosis in the AMs. Furthermore, 3MA reversed both the nicotine-induced decrease in Bcl-2 and the increase in Bax in both groups. These results suggest that nicotine may induce apoptosis by blocking AM autophagic degradation in human silicosis.

Laser Scanning Confocal Microscopy Was Used to Validate the Presence of Burkholderia Pseudomallei or B. Mallei in Formalin-Fixed Paraffin Embedded Tissues

Burkholderia pseudomallei and B. mallei are Gram-negative, facultative intracellular bacteria that cause melioidosis and glanders, respectively. Currently, there are no vaccines for these two diseases. Animal models have been developed to evaluate vaccines and therapeutics. Tissues from infected animals, however, must be fixed in formalin and embedded in paraffin (FFPE) before analysis. A brownish staining material in infected tissues that represents the exopolysaccharide of the pathogen was seen by bright field microscopy but not the actual microorganism. Because of these results, FFPE tissue was examined by laser scanning confocal microscopy (LSCM) in an attempt to see the microorganism. Archival FFPE tissues were examined from ten mice, and five nonhuman primates after exposure to B. pseudomallei or B.mallei by LSCM. Additionally, a historical spleen biopsy from a human suspected of exposure to B. mallei was examined. B. pseudomallei was seen in many of the infected tissues from mice. Four out of five nonhuman primates were positive for the pathogen. In the human sample, B. mallei was seen in pyogranulomas in the spleen biopsy. Thus, the presence of the pathogen was validated by LSCM in murine, nonhuman primate, and human FFPE tissues.

An increase in intracellular p62/NBR1 and persistence of Burkholderia mallei and B. pseudomallei in infected mice linked to autophagy deficiency

Introduction

Burkholderia mallei (B. mallei) and Burkholderia pseudomallei (B. pseudomallei), causative agents of glanders and melioidosis, respectively, are invasive intracellular pathogens that actively multiply in phagocytic and non‐phagocytic cells. Activation of cell‐autonomous autophagy mechanism eliminate intracellular pathogens in which p62 a cytosolic cargo protein is selectively degraded, and an accumulation of this marker occurs if autophagy is deficient. Recurrent, relapsed and reinfection of B. pseudomallei in melioidosis patients in endemic area indicative of lack of complete of clearance and persistence of the pathogen. Reasoning that abundance in the levels of p62 may provide an indication of the intracellular infection, we sought to examine whether increase in intracellular p62 and bacterial burden with Burkholderia infection are linked to autophagy deficiency.

Methods

In this study, we investigated cell culture and mouse models of disease to identify an association between autophagy biomarkers (p62/NBR1) accumulation and intracellular persistence of B. mallei and B. pseudomallei.

Results

We demonstrate, that elevated levels of intracellular p62/NBR1 correlated with bacterial persistence, while pre‐treatment with a pharmacological inducer of autophagy, rapamycin, reduced both intracellular p62, and bacterial survival. Our results showed an elevated p62 levels (2‐5 fold) in spleen and liver cells of Burkholderia‐infected BALB/c mice, as well as in spleen cells of Burkholderia‐infected C57BL/6 mice, suggesting that an increase in p62/NBR1 was due to an autophagy deficiency. Similar to p62, cytosolic LC3‐I levels were also elevated, while the characteristic conversion to the autophagosome‐associated membrane bound form LC3‐II was low in spleens of the infected mice further supporting the conclusion that autophagy was deficient.

Conclusion

Taken together, our results suggest that an increase in intracellular p62/NBR1 may be a potential host cell biomarker of B. mallei or B. pseudomallei infections, and identifying autophagy manipulation may potentially aid to therapeutic approach for complete clearance of the pathogen.