Mycobacterium marinum down-regulates miR-148a in macrophages in an EsxA-dependent manner

miRNA-Mediated Fine Regulation of TLR-Induced M1 Polarization

Macrophage polarization to the M1 spectrum is induced by bacterial cell wall components through stimulation of Toll-like family (TLR) receptors. By orchestrating the expression of relevant mediators of the TLR cascade, as well as associated pathways and feedback loops, macrophage polarization is coordinated to ensure an appropriate immune response. This is central to the successful control of pathogens and the maintenance of health. Macrophage polarization is known to be modulated at both the transcriptional and post-transcriptional levels. In recent years, the miRNA-based post-transcriptional regulation of M1 polarization has received increasing attention from the scientific community. Comparative studies have shown that TLR stimulation alters the miRNA profile of macrophages and that macrophages from the M1 or the M2 spectrum differ in terms of miRNAs expressed. Simultaneously, miRNAs are considered critical post-transcriptional regulators of macrophage polarization. In particular, miRNAs are thought to play a regulatory role in the switch between the early proinflammatory response and the resolution phase. In this review, we will discuss the current state of knowledge on the complex interaction of transcriptional and post-transcriptional regulatory mechanisms that ultimately determine the functionality of macrophages.

Circular RNAs in tuberculosis: From mechanism of action to potential diagnostic biomarker

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tuberculosis), continues to be a major global health concern. Understanding the molecular intricacies of TB pathogenesis is crucial for developing effective diagnostic and therapeutic approaches. Circular RNAs (circRNAs), a class of single-stranded RNA molecules characterized by covalently closed loops, have recently emerged as potential diagnostic biomarkers in various diseases. CircRNAs have been demonstrated to modulate the host's immunological responses against TB, specifically by reducing monocyte apoptosis, augmenting autophagy, and facilitating macrophage polarization. This review comprehensively explores the roles and mechanisms of circRNAs in TB pathogenesis. We also discuss the growing body of evidence supporting their utility as promising diagnostic biomarkers for TB. By bridging the gap between fundamental circRNA biology and TB diagnostics, this review offers insights into the exciting potential of circRNAs in combatting this infectious disease.

Understanding microRNAs in the Context of Infection to Find New Treatments against Human Bacterial Pathogens

The development of RNA-based anti-infectives has gained interest with the successful application of mRNA-based vaccines. Small RNAs are molecules of RNA of <200 nucleotides in length that may control the expression of specific genes. Small RNAs include small interference RNAs (siRNAs), Piwi-interacting RNAs (piRNAs), or microRNAs (miRNAs). Notably, the role of miRNAs on the post-transcriptional regulation of gene expression has been studied in detail in the context of cancer and many other genetic diseases. However, it is also becoming apparent that some human miRNAs possess important antimicrobial roles by silencing host genes essential for the progress of bacterial or viral infections. Therefore, their potential use as novel antimicrobial therapies has gained interest during the last decade. The challenges of the transport and delivery of miRNAs to target cells are important, but recent research with exosomes is overcoming the limitations in RNA-cellular uptake, avoiding their degradation. Therefore, in this review, we have summarised the latest developments in the exosomal delivery of miRNA-based therapies, which may soon be another complementary treatment to pathogen-targeted antibiotics that could help solve the problem caused by multidrug-resistant bacteria.

MicroRNA‑502‑3p promotes Mycobacterium tuberculosis survival in macrophages by modulating the inflammatory response by targeting ROCK1

Tuberculosis (TB) is caused by Mycobacterium tuberculosis (M. tuberculosis) infection and has the highest mortality rate of any single infectious disease worldwide. The aim of the present study was to investigate the function of microRNA (miR)-502-3p in M. tuberculosis-infected macrophages. The Gene Expression Omnibus database was used to analyze miR-502-3p expression in patients with TB and healthy individuals. THP-1 and RAW 264.7 cells were transfected with miR-502-3p mimic, miR-502-3p inhibitor, pcDNA3.1-ROCK1 or their negative controls. The expression levels of miR-502-3p and inflammatory cytokines were evaluated using reverse transcription-quantitative PCR. The colony-forming unit assay was performed to assess the survival of M. tuberculosis in macrophages, and Toll-like receptor (TLR)4/NF-κB signaling pathway-associated protein expression levels were detected by western blotting. The nuclear translocation of NF-κB p65 was detected via immunocytochemistry. TargetScan was used to predict the binding sites between miR-502-3p and ROCK1. The interaction between miR-502-3p and Rho-associated coiled-coil-forming protein kinase 1 (ROCK1) was confirmed using a dual-luciferase reporter assay; ROCK1 was demonstrated to be a direct target gene of miR-502-3p. Results from the present study demonstrated that miR-502-3p expression was significantly increased during M. tuberculosis infection in macrophages. Upregulation of miR-502-3p expression levels significantly enhanced the survival of intracellular M. tuberculosis. IL-6, TNF-α, and IL-1β mRNA expression levels were significantly upregulated during M. tuberculosis infection but were downregulated by miR-502-3p overexpression. Moreover, miR-502-3p mimics transfection significantly downregulated TLR4/NF-κB signaling pathway-associated protein expression and significantly reduced nuclear transcription of NF-κB in M. tuberculosis-infected macrophages. ROCK1 overexpression reversed the miR-502-3p inhibitory effect on cytokine production in M. tuberculosis-infected macrophages. In conclusion, miR-502-3p/ROCK1 may serve an anti-inflammatory role and may improve the survival of M. tuberculosis within macrophages, which may provide a promising therapeutic target for TB.

A Small Protein but with Diverse Roles: A Review of EsxA in Mycobacterium-Host Interaction

As a major effector of the ESX-1 secretion system, EsxA is essential for the virulence of pathogenic mycobacteria, such as Mycobacterium tuberculosis (Mtb) and Mycobacterium marinum (Mm). EsxA possesses an acidic pH-dependent membrane permeabilizing activity and plays an essential role by mediating mycobacterial escape from the phagosome and translocation to the cytosol for intracellular replication. Moreover, EsxA regulates host immune responses as a potent T-cell antigen and a strong immunoregulator. EsxA interacts with multiple cellular proteins and stimulates several signal pathways, such as necrosis, apoptosis, autophagy, and antigen presentation. Interestingly, there is a co-dependency in the expression and secretion of EsxA and other mycobacterial factors, which greatly increases the complexity of dissecting the precise roles of EsxA and other factors in mycobacterium-host interaction. In this review, we summarize the current understandings of the roles and functions of EsxA in mycobacterial infection and discuss the challenges and future directions.

The effects of intradermal M. bovis and M. avium PPD test on immune-related mRNA and miRNA in dermal oedema exudates of water buffaloes (Bubalus bubalis)

Tuberculosis (TB) is a zoonotic disease primarily caused by pathogens belonging to the genus of Mycobacterium. Programs of control and eradication for bovine TB include a screening using single intradermal tuberculin (SIT) test with Mycobacterium bovis (M. bovis)-purified protein derivatives (PPD-B) single or concurrent with Mycobacterium avium (M. avium)-purified protein derivatives (PPD-A). This study aimed to determine the effects of intradermal PPD-B and PPD-A test on immune-related mRNA and microRNAs in dermal oedema exudates of water buffaloes (Bubalus bubalis). The investigation was carried out on RNA extracted from dermal oedema exudates of 36 animals, of which 24 were M. bovis positive (M. bovis+) and 12 M. avium positive (M. avium+). The lymphocyte polarization toward Th1, Th2, TReg, and Th17 lineages was addressed by measuring the abundance of the respective cytokines and transcription factors, namely TBET, STAT4, IFNγ, and IL1β for Th1; STAT5B, and IL4 for Th2; FOXP3 and IL10 for TReg; and RORC, STAT3, and IL17A for Th17. Due to the very low abundance of Th17-related genes, a digital PCR protocol was also applied. The abundance of microRNAs involved in the immune response against PPDs, including miR-122-5p, miR-148a-3p, miR30a, and miR-455-5p, was equally measured. Results showed that IFNγ (fold change = 2.54; p = 0.037) and miR-148a-3p (fold change = 2.54; p = 0.03) were upregulated in M. bovis+ as compared to M. avium+ samples. Our preliminary results supported the pivotal role of IFNγ in the local immune response related to PPD-B and highlighted the differential expression of miR-148a-3p, which downregulates the proinflammatory cytokines and the TLR4-mediated NF-κB activation, providing an anti-inflammation modulator in responses to mycobacterial infection.

The role of non-coding RNA on macrophage modification in tuberculosis infection

Tuberculosis (TB), a serious disease caused by Mycobacterium tuberculosis (Mtb), remains the world's top infectious killer. It is well-established that TB can circumvent the host's immune response for long-term survival. Macrophages serve as the major host cells for TB growth and persistence and their altered functions are critical for the response of the host defense against TB exposure (elimination, latency, reactivation, and bacillary dissemination). Noncoding RNAs are crucial posttranscriptional regulators of macrophage discrimination. Therefore, this review highlights the regulatory mechanism underlying the relationship between noncoding RNAs and macrophages in TB infection, which may facilitate the identification of potential therapeutic targets and effective diagnosis biomarkers for TB disease.

The ESX-1 Virulence Factors Downregulate miR-147-3p in Mycobacterium marinum-Infected Macrophages

As important virulence factors of Mycobacterium tuberculosis, EsxA and EsxB not only play a role in phagosome rupture and M. tuberculosis cytosolic translocation but also function as modulators of host immune responses by modulating numerous microRNAs (miRNAs). Recently, we have found that mycobacterial infection downregulated miR-148a-3p (now termed miR-148) in macrophages in an ESX-1-dependent manner. The upregulation of miR-148 reduced mycobacterial intracellular survival. Here, we investigated miR-147-3p (now termed miR-147), a negative regulator of inflammatory cytokines (e.g., interleukin-6 [IL-6] and IL-10), in mycobacterial infection. We infected murine RAW264.7 macrophages with Mycobacterium marinum, a surrogate model organism for M. tuberculosis, and found that the esxBA-knockout strain (M. marinum ΔesxBA) upregulated miR-147 to a level that was significantly higher than that induced by the M. marinum wild-type (WT) strain or by the M. marinum ΔesxBA complemented strain, M. marinum ΔesxBA/pesxBA, suggesting that the ESX-1 system (potentially EsxBA and/or other codependently secreted factors) is the negative regulator of miR-147. miR-147 was also downregulated by directly incubating the macrophages with the purified recombinant EsxA or EsxB protein or the EsxBA heterodimer, which further confirms the role of the EsxBA proteins in the downregulation of miR-147. The upregulation of miR-147 inhibited the production of IL-6 and IL-10 and significantly reduced M. marinum intracellular survival. Interestingly, inhibitors of either miR-147 or miR-148 reciprocally compromised the effects of the mimics of their counterparts on M. marinum intracellular survival. This suggests that miR-147 and miR-148 share converged downstream pathways in response to mycobacterial infection, which was supported by data indicating that miR-147 upregulation inhibits the Toll-like receptor 4/NF-κB pathway.

Nα-Acetylation of the virulence factor EsxA is required for mycobacterial cytosolic translocation and virulence

The Mycobacterium tuberculosis virulence factor EsxA and its chaperone EsxB are secreted as a heterodimer (EsxA:B) and are crucial for mycobacterial escape from phagosomes and cytosolic translocation. Current findings support the idea that for EsxA to interact with host membranes, EsxA must dissociate from EsxB at low pH. However, the molecular mechanism by which the EsxA:B heterodimer separates is not clear. In the present study, using liposome-leakage and cytotoxicity assays, LC-MS/MS-based proteomics, and CCF-4 FRET analysis, we obtained evidence that the Nα-acetylation of the Thr-2 residue on EsxA, a post-translational modification that is present in mycobacteria but absent in Escherichia coli, is required for the EsxA:B separation. Substitutions at Thr-2 that precluded Nα-acetylation inhibited the heterodimer separation and hence prevented EsxA from interacting with the host membrane, resulting in attenuated mycobacterial cytosolic translocation and virulence. Molecular dynamics simulations revealed that at low pH, the Nα-acetylated Thr-2 makes direct and frequent "bind-and-release" contacts with EsxB, which generates a force that pulls EsxB away from EsxA. In summary, our findings provide evidence that the Nα-acetylation at Thr-2 of EsxA facilitates dissociation of the EsxA:B heterodimer required for EsxA membrane permeabilization and mycobacterial cytosolic translocation and virulence.