Mycobacterium tuberculosis-infected alveolar epithelial cells modulate dendritic cell function through the HIF-1α-NOS2 axis

Roles of HIF-1α signaling in Mycobacterium tuberculosis infection: New targets for anti-TB therapeutics?

Tuberculosis (TB), a deadly infectious disease induced by Mycobacterium tuberculosis (Mtb), continues to be a global public health issue that kill millions of patents every year. Despite significant efforts have been paid to identify effective TB treatments, the emergence of drug-resistant strains of the disease and the presence of comorbidities in TB patients urges us to explore the detailed mechanisms involved in TB immunity and develop more effective innovative anti-TB strategies. HIF-1α, a protein involved in regulating cellular immune responses during TB infection, has been highlighted as a promising target for the development of novel strategies for TB treatment due to its critical roles in anti-TB host immunity. This review provides a summary of current research progress on the roles of HIF-1α in TB infection, highlighting its importance in regulating the host immune response upon Mtb infection and summarizing the influences and mechanisms of HIF-1α on anti-TB immunological responses of host cells. This review also discusses the various challenges associated with developing HIF-1α as a target for anti-TB therapies, including ensuring specificity and avoiding off-target effects on normal cell function, determining the regulation and expression of HIF-1α in TB patients, and developing drugs that can inhibit HIF-1α. More deep understanding of the molecular mechanisms involved in HIF-1α signaling, its impact on TB host status, and systematic animal testing and clinical trials may benefit the optimization of HIF-1α as a novel therapeutic target for TB.

Lung type 3 innate lymphoid cells respond early following Mycobacterium tuberculosis infection

Tuberculosis is the leading cause of death due to an infectious disease worldwide. Innate lymphoid type 3 cells (ILC3s) mediate early protection during Mycobacterium tuberculosis (Mtb) infection. However, the early signaling mechanisms that govern ILC3 activation or recruitment within the lung during Mtb infection are unclear. scRNA-seq analysis of Mtb-infected mouse lung innate lymphoid cells (ILCs) has revealed the presence of different clusters of ILC populations, suggesting heterogeneity. Using mouse models, we show that during Mtb infection, interleukin-1 receptor (IL-1R) signaling on epithelial cells drives ILC3 expansion and regulates ILC3 accumulation in the lung. Furthermore, our data revealed that C-X-C motif chemokine receptor 5 (CXCR5) signaling plays a crucial role in ILC3 recruitment from periphery during Mtb infection. Our study thus establishes the early responses that drive ILC3 accumulation during Mtb infection and points to ILC3s as a potential vaccine target.

IMPORTANCE

Tuberculosis is a leading cause of death due to a single infectious agent accounting for 1.6 million deaths each year. In our study, we determined the role of type 3 innate lymphoid cells in early immune events necessary for achieving protection during Mtb infection. Our study reveals distinct clusters of ILC2, ILC3, and ILC3/ILC1-like cells in Mtb infection. Moreover, our study reveal that IL-1R signaling on lung type 2 epithelial cells plays a key role in lung ILC3 accumulation during Mtb infection. CXCR5 on ILC3s is involved in ILC3 homing from periphery during Mtb infection. Thus, our study provides novel insights into the early immune mechanisms governed by innate lymphoid cells that can be targeted for potential vaccine-induced protection.

NOS2/miR-493-5p Signaling Regulates in the LPS-Induced Inflammatory Response in the RAW264.7 Cells

Tuberculosis (TB) is a fatal infectious disease; however, the molecular mechanisms underlying the pathogenicity of TB remain elusive. The present study aims to identify potential biomarkers associated with Mycobacterium tuberculosis (M.tb) infection by using integrated bioinformatics and in vitro validation studies. GSE50050, GSE78706, and GSE108844 data from the gene expression omnibus (GEO) database were downloaded to identify differentially expressed genes (DEGs). The functions of DEGs were further subjected to gene ontology (GO) and KEGG pathway analysis. The hub genes from the DEGs were determined based on the protein-protein interaction (PPI) network analysis. Finally, the hub genes were experimentally validated using the in vitro functional studies. A total of 26 common DEGs were identified among GSE50050, GSE78706, and GSE108844. The functional enrichment analysis showed that the common DEGs were associated with cytokines response and TB pathways. The PPI network analysis identified nine hub genes. Further in vitro studies showed that nitric oxide synthase 2 (NOS2) was up-regulated in RAW264.7 cells upon lipopolysaccharides (LPS) stimulation, which was accompanied by increased inflammatory cytokines release. Furthermore, NOS2 was found to be a target of miR-493-5p, which was confirmed by luciferase reporter assay. NOS2 was repressed by miR-493-5p overexpression and was up-regulated after miR-493-5p inhibition in RAW264.7 cells. The rescue experiments showed that LPS-induced increase in the inflammatory cytokines of the RAW264.7 cells was significantly attenuated by NOS2 knockdown and miR-493-5p overexpression. Collectively, our results for the first time demonstrated that NOS2/miR-493-5p signaling pathway may potentially involve in the inflammatory response during bacterial infection such as M. tb infection.

Pathological and protective roles of dendritic cells in Mycobacterium tuberculosis infection: Interaction between host immune responses and pathogen evasion

Dendritic cells (DCs) are principal defense components that play multifactorial roles in translating innate immune responses to adaptive immunity in Mycobacterium tuberculosis (Mtb) infections. The heterogeneous nature of DC subsets follows their altered functions by interacting with other immune cells, Mtb, and its products, enhancing host defense mechanisms or facilitating pathogen evasion. Thus, a better understanding of the immune responses initiated, promoted, and amplified or inhibited by DCs in Mtb infection is an essential step in developing anti-tuberculosis (TB) control measures, such as host-directed adjunctive therapy and anti-TB vaccines. This review summarizes the recent advances in salient DC subsets, including their phenotypic classification, cytokine profiles, functional alterations according to disease stages and environments, and consequent TB outcomes. A comprehensive overview of the role of DCs from various perspectives enables a deeper understanding of TB pathogenesis and could be useful in developing DC-based vaccines and immunotherapies.

MicroRNA-20b carried by mesenchymal stem cell-derived extracellular vesicles protects alveolar epithelial type II cells from Mycobacterium tuberculosis infection in vitro

Mesenchymal stem cells (MSCs) have been largely used for their immunomodulatory and regenerative properties in the treatment of immune-based disorders and bacterial infections. This study explores the function of MSC-derived extracellular vesicles (MSC-EVs) in alveolar epithelial type II cells (AECII) against Mycobacterium tuberculosis (MTB) infection. EVs were extracted from the acquired MSCs. AECII-like MLE-15 and A549 cells were treated with MSC-EVs and then subjected to MTB infection. MSC-EVs treatment significantly prevented the increase in bacterial load, and it prevented the production of proinflammatory cytokines in cells induced by MTB infection. MicroRNA-20b (miR-20b) was upregulated in cells after MSC-EVs treatment. Artificial inhibition of miR-20b blocked the protective effects of MSC-EVs against MTB infection. A Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis was performed to analyze the key molecules involved in the immune regulation in cells mediated by miR-20b. miR-20b directly targeted nuclear factor of activated T cells 5 (NFAT5) and inactivated the Toll-Like Receptor (TLR) signaling pathway by reducing the formation of TLR2-TLR4 dimer after MTB infection. In conclusion, this study suggests that MSC-EVs carry miR-20b to inhibit NFAT5 and inactivate the TLR signaling pathway, thus mediating innate immune response and preventing AECII from MTB infection-induced damage.

Estradiol inhibits autophagy of Mycobacterium tuberculosis‑infected 16HBE cells and controls the proliferation of intracellular Mycobacterium tuberculosis

Tracheobronchial tuberculosis (TBTB) is most common in young, middle-aged females. Despite adequate anti-tuberculosis therapy, >90% of patients develop tracheobronchial stenosis, which has a high rate of resulting in disability. The present study aimed to explore the effect of estradiol on the development of TBTB. Estrogen receptor (ER) expression in granulomatous tissue was assessed via immunofluorescence. In order to determine whether estrogen affected the proliferation of intracellular Mycobacterium tuberculosis (Mtb), 16HBE cells were infected with Mtb in vitro, followed by estradiol treatment. Intracellular Mtb was quantified via colony counting. The effect of estradiol on autophagy of infected 16HBE cells was determined via western blotting and transmission electron microscopy. Necrosis assays of infected 16HBE cells were analyzed using propidium iodide staining and assessing lactate dehydrogenase (LDH) release. To determine how estradiol affects autophagy, infected 16HBE cells were treated with ER-specific and non-specific modulators. Reactive oxygen species (ROS) levels were analyzed via flow cytometry. Additionally, the protein expression levels of autophagy-associated proteins were determined via western blotting. Mtb could enter human lobar bronchial goblet cells and ciliated cells in patients with TBTB. The results also demonstrated that ERα was expressed in granulomatous tissue from patients with TBTB. Administration of 10⁻⁶ M estradiol reduced the number of intracellular Mtb colony-forming units in vitro in the 16HBE human bronchial epithelial cell line at day 3 after infection. Furthermore, cells treated with estradiol and infected with Mtb released less LDH at 72 h and exhibited reduced necrosis levels at 24 h compared with the untreated cells. In addition, autophagy of infected 16HBE cells was inhibited by estradiol. Estradiol and the specific ERα agonist had similar effects on autophagy in infected 16HBE cells. Additionally, treatment with the ERα antagonist abolished the inhibition of autophagy by estradiol in infected 16BHE cells. Compared with the untreated infected 16HBE cells, the ROS levels in the infected 16HBE cells treated with estradiol and the ERα agonist significantly decreased. The levels of phosphorylated (p)-mTOR and p-AKT notably increased in estradiol- and ERα agonist-treated infected 16HBE cells. In summary, estradiol may serve a key role in the development of TBTB through binding to ERα.

Nicotine associates to intracellular Mycobacterium tuberculosis inducing genes related with resistance to antimicrobial peptides

Tobacco consumption is related to an increased risk to develop tuberculosis. Antimicrobial peptides are essential molecules in the response to Mycobacterium tuberculosis (Mtb) because of their direct antimicrobial activity. The aim of this study was to demonstrate that nicotine enters into Mtb infected epithelial cells and associates with the mycobacteria inducing genes related to antimicrobial peptides resistance. Epithelial cells were infected with virulent Mtb, afterwards cells were stimulated with nicotine. The internalization of nicotine was followed using electron and confocal microscopy. The lysX expression was evaluated isolating mycobacterial RNA and submitted to RT-PCR analysis. Our results indicated that nicotine promotes Mtb growth in a dose-dependent manner in infected cells. We also reported that nicotine induces lysX expression. In conclusion, nicotine associates to intracellular mycobacteria promoting intracellular survival.

ceRNA regulatory network of FIH inhibitor as a radioprotector for gastrointestinal toxicity by activating the HIF-1 pathway

Given the relentless renewal ability of intestinal crypt-base stem cells, small intestine in the gastrointestinal (GI) tract is more vulnerable to radiation-induced disruption. Through promoting epithelial integrity and reducing intracellular reactive oxygen species (ROS) levels, hypoxia-inducible factors (HIFs) have been proved to exhibit radioprotective effects in the GI tract. Therefore, enhancing stability or transcriptional activity of HIFs might be a therapeutic strategy for developing radioprotectors. Factor inhibiting HIF (FIH or HIF-1AN) can hamper transcriptional capacity of HIF-1α via interacting with Asn803 in its C-terminal domain. Previously, we discovered promoting HIF-1α transcriptional activity in vitro by FIH inhibitor-N-oxalyl-D-phenylalanine (NOFD) exerts radioprotection on cells. However, the radioprotective effect of FIH inhibitor on the GI tract and its competing endogenous RNA (ceRNA) regulatory network from the FIH/HIF axis has never been addressed. Here we verified radioprotection of NOFD for the GI tract by an animal model and performed whole-transcriptome analysis to fully elucidate the radioprotective mechanism from the FIH/HIF axis against GI syndrome. We identified two novel circular RNAs (circRNAs) (circRNA_2909 and circRNA_0323) and two long non-coding RNAs (lncRNAs) (NONMMUT140549.1 and NONMMUT148249.1) that promote expression of HIF1A and NOS2 in the HIF-1 pathway by sponging microRNAs (miRNAs), especially mmu-miR-92a-1-5p. The de-repression of HIF-1α transcriptional capacity by inhibiting FIH proteomic activity suggests a new therapeutic strategy in alleviating radiation-induced GI syndrome.