Bone Marrow-Derived Macrophage (BMDM ) Infection by Listeria monocytogenes

Inhibition of Rho GEFs attenuates pulmonary fibrosis through suppressing myofibroblast activation and reprogramming profibrotic macrophages

Idiopathic pulmonary fibrosis has a poor prognosis, with existing medications only partially alleviating symptoms, highlighting the urgent need for new therapeutic approaches. The dysregulations of Rho GTPases/ROCK are related with various diseases, including fibrosis. Nevertheless, the development of drugs for pulmonary fibrosis treatment has predominantly concentrated on ROCK inhibitors. Small GTPases have been historically recognized as "undruggable". Here, we explore a novel Rho GEFs inhibitor GL-V9, and find that GL-V9 alleviates bleomycin-induced pulmonary fibrosis in mice by inhibiting myofibroblast activation and reprogramming profibrotic macrophages. Distinct from the mechanisms of the first-line drug Nintedanib, GL-V9 binds to the DH/PH domain of Rho GEFs and block the activation of Rho GTPase signaling. This action subsequently suppresses myofibroblast activation by interfering with Rho GTPase-dependent cytoskeletal reorganization and the activity of MRTF and YAP, and inhibits M2 macrophage polarization by modulating RhoA/STAT3 activity. The discovery of new regulatory mechanisms of GL-V9 suggests that targeting Rho GEFs represents a potent strategy for pulmonary fibrosis treatment.

Trimethylamine N-oxide aggravates human aortic valve interstitial cell inflammation by regulating the macrophages polarization through a N6-methyladenosine-mediated pathway

BACKGROUND

Trimethylamine N-oxide (TMAO) is a gut microbial metabolite that promotes calcified aortic valve disease (CAVD), but the underlying mechanism remains obscure. Herein, we aim to test the hypothesis that TMAO regulated the inflammatory process in aortic valves via N6-methyladenosine (m6A) RNA methylation-mediated macrophage polarization.

METHODS

In vitro, we stimulated macrophages (Phorbol-12-Myristate-13-Acetate-induced THP-1) with TMAO and assessed the expression of methyltransferase-like 3 (Mettl3), IL-1 receptor associated kinase M (IRAK-M) and polarization markers. The interaction between YTH domain family protein 2 (YTHDF2) and IRAK-M mRNA was explored by RNA-IP and RNA decay assay. Functionally, the effects of macrophages on human aortic valve interstitial cells (AVICs) were measured via macrophage adhesion assay and co-culture system. In vivo, the influence of IRAK-M on CAVD development was verified using Irak-m-/- mice.

RESULT

Mettl3 was highly expressed while IRAK-M was decreased in human calcified aortic valves. In vitro, TMAO upregulated the expression of Mettl3, while the expression of IRAK-M, an important negative regulator of the NF-κB pathway, was remarkably decreased in macrophages. TMAO also induced classical macrophage activation (M1 polarization). Mechanistically, IRAK-M was identified as a target of Mettl3-mediated m6A modification, indicating the involvement of m6A methylation in the regulation of NF-κB activation. Moreover, RIP assay revealed the direct interaction between YTHDF2 and IRAK-M mRNA and this process was dependent on Mettl3. TMAO-treated macrophage conditioned medium induced inflammatory responses in human aortic valve interstitial cells (AVICs). In vivo experiments showed that the deletion of IRAK-M significantly accelerated the progression of aortic valve lesion in mice administrated with high-fat and choline diet (HFCD).

CONCLUSION

TMAO induces the expression of Mettl3 in macrophages. Mettl3 promotes M1 polarization of macrophages by inhibiting IRAK-M through a m6A/YTHDF2 pathway. TMAO-treated macrophages aggravate the inflammation of human AVICs.

Staphylococcus aureus induces mitophagy via the HDAC11/IL10 pathway to sustain intracellular survival

BACKGROUND

The immune evasion and prolonged survival of Staphylococcus aureus (S. aureus) within macrophages are key factors contributing to the difficulty in curing osteomyelitis. Although macrophages play a vital role as innate immune cells, the mechanisms by which S. aureus survives within them and suppresses host immune functions remain incompletely understood.

METHODS

This study employed confocal microscopy, flow cytometry, ELISA, and siRNA technology to assess the survival capacity of S. aureus within macrophages and the impact of inflammatory cytokines on its persistence. Proteomics was used to investigate the potential mechanisms and differential proteins involved in S. aureus intracellular survival. Additionally, confocal microscopy, flow cytometry, Mdivi-1 intervention, and Western blot were utilized to validate the role of mitophagy in supporting S. aureus survival. The study further explored how the HDAC11/IL10 axis enhances mitophagy to promote intracellular S. aureus survival by using HDAC11 overexpression, siRNA, and rapamycin intervention combined with confocal microscopy and flow cytometry.

RESULTS

The findings demonstrated that IL10 promotes mitophagy to clear mitochondrial reactive oxygen species (mtROS), thereby enhancing the intracellular survival of S. aureus within macrophages. Additionally, we discovered that the transcriptional repressor of IL10, HDAC11, was significantly downregulated during S. aureus infection. Overexpression of HDAC11 and the use of the autophagy activator rapamycin further validated that the HDAC11/IL10 axis regulates mitophagy via the mTOR pathway, which is essential for supporting S. aureus intracellular survival.

CONCLUSION

This study reveals that S. aureus enhances IL10 production by inhibiting HDAC11, thereby promoting mitophagy and mtROS clearance, which supports its survival within macrophages. These findings offer new insights into the intracellular survival mechanisms of S. aureus and provide potential therapeutic approaches for the clinical management of osteomyelitis.

Persistent Salmonella infections in humans are associated with mutations in the BarA/SirA regulatory pathway

Several bacterial pathogens, including Salmonella enterica, can cause persistent infections in humans by mechanisms that are poorly understood. By comparing genomes of isolates longitudinally collected from 256 prolonged salmonellosis patients, we identified repeated mutations in global regulators, including the barA/sirA two-component regulatory system, across multiple patients and Salmonella serovars. Comparative RNA-seq analysis revealed that distinct mutations in barA/sirA led to diminished expression of Salmonella pathogenicity islands 1 and 4 genes, which are required for Salmonella invasion and enteritis. Moreover, barA/sirA mutants were attenuated in an acute salmonellosis mouse model and induced weaker transcription of host immune responses. In contrast, in a persistent infection mouse model, these mutants exhibited long-term colonization and prolonged shedding. Taken together, these findings suggest that selection of mutations in global virulence regulators facilitates persistent Salmonella infection in humans, by attenuating Salmonella virulence and inducing a weaker host inflammatory response.

The transcriptional regulation of the horizontally acquired iron uptake system, yersiniabactin and its contribution to oxidative stress tolerance and pathogenicity of globally emerging salmonella strains

The bacterial species Salmonella enterica (S. enterica) is a highly diverse pathogen containing more than 2600 distinct serovars, which can infect a wide range of animal and human hosts. Recent global emergence of multidrug resistant strains, from serovars Infantis and Muenchen is associated with acquisition of the epidemic megaplasmid, pESI that augments antimicrobial resistance and pathogenicity. One of the main pESI's virulence factors is the potent iron uptake system, yersiniabactin encoded by fyuA, irp2-irp1-ybtUTE, ybtA, and ybtPQXS gene cluster. Here we show that yersiniabactin, has an underappreciated distribution among different S. enterica serovars and subspecies, integrated in their chromosome or carried by different conjugative plasmids, including pESI. While the genetic organization and the coding sequence of the yersiniabactin genes are generally conserved, a 201-bp insertion sequence upstream to ybtA, was identified in pESI. Despite this insertion, pESI-encoded yersiniabactin is regulated by YbtA and the ancestral Ferric Uptake Regulator (Fur), which binds directly to the ybtA and irp2 promoters. Furthermore, we show that yersiniabactin genes are specifically induced during the mid-late logarithmic growth phase and in response to iron-starvation or hydrogen peroxide. Concurring, yersiniabactin was found to play a previously unknown role in oxidative stress tolerance and to enhance intestinal colonization of S. Infantis in mice. These results indicate that yersiniabactin contributes to Salmonella fitness and pathogenicity in vivo and is likely to play a role in the rapid dissemination of pESI among globally emerging Salmonella lineages.