G9a and Sirtuin6 epigenetically modulate host cholesterol accumulation to facilitate mycobacterial survival

Influence of cell bioenergetics on host-pathogen interaction in the lung

Pulmonary diseases, arising from infections caused by bacteria, fungi, and viruses, or stemming from underlying genetic factors are one of the leading causes of mortality in humans, accounting for millions of deaths every year. At the onset of pulmonary diseases, crucial roles are played by phagocytic immune cells, particularly tissue-resident macrophages, in regulating the immune response at the mucosal barrier. Recent strides have illuminated the pivotal role of host bioenergetics modulated by metabolites derived from both pathogens and hosts in influencing the pathophysiology of major organs. Their influence extends to processes such as the infiltration of immune cells, activation of macrophages, and the polarization phenomenon. Furthermore, host-derived metabolites, such as itaconate, contribute to the promotion of anti-inflammatory responses, thereby preventing immunopathology and facilitating the preservation of mucosal niches to thrive for the long-term. This review explores recent advancements in the field of immunometabolism, with a particular emphasis on the intricacies of disease progression in pulmonary infections caused by bacteria such as P. aeruginosa, M. tuberculosis and S. aureus and fungi like C. albicans.

Sirtuins as modulators of infection outcomes in the battle of host-pathogen dynamics

Sirtuins's central role in governing metabolic processes has been known for decades. However, over the past two decades, sirtuin functions have been linked to immune regulation and immunity. Sirtuins are NAD+ dependent protein deacylases involved in the regulation of several important biological processes ranging from energy homeostasis, metabolism, aging, apoptosis, autophagy, immunity, adipocyte, and muscle differentiation. Here, in this review, we discuss the role of sirtuins in several infectious diseases including viral, bacterial, and protozoan infections with detailed emphasis on bacterial-host interactions. We have aimed to explore both host and bacterial sirtuin functions contributing to the infection progression, host responses and their influence on the everlasting host-pathogen tug-of-war. In order to manipulate host pathways, pathogens such as intracellular bacteria have evolved parallelly and harbor bacterial sirtuins. The recent discoveries of bacterial sirtuins influencing the host-pathogen interaction outcomes pave the way for the discovery of potential therapeutic targets.

Increased autophagy activity regulated by LC3B gene promoter DNA methylation is associated with progression to active pulmonary tuberculosis disease

BACKGROUND

This study aims to explore the role of autophagy-associated genes (ATG) and their epigenetic markers in the progression of mycobacterium tuberculosis (M. tb) infection, and to test the effects of de-methylation agents on macrophage functions against TB.

METHODS

ATG expressions and their gene promoter DNA methylation levels of blood immune cells were measured in 60 patients with active pulmonary TB disease, 31 subjects with latent TB infection (LTBI), and 15 non-infected healthy subjects (NIHS). An in vitro monocytic THP-1 cell culture model under M. tb-specific antigen stimuli was applied.

RESULTS

LC3B protein expression of blood M1/M2a monocyte, ATG5 protein expression of M2a, and mean DNA methylation levels of the LC3B gene promoter region of peripheral blood mononuclear cells were all increased in active TB patients versus either LTBI or NIHS group. The LC3B methylation levels were negatively correlated with its protein expressions. The discrimination of active TB disease from LTBI or NIHS was optimally captured by prediction scores, which combined LC3B (+) percentage of blood M1/M2a monocyte, LC3B gene promoter DNA methylation level, male gender, and body mass index. LC3B and ATG5 expressions of both blood M2a and neutrophil were decreased after 6-month anti-TB therapy, but hypermethylated LC3B gene promoter persisted. In vitro 5-Aza-2'-deoxycytidine treatment improved bactericidal, apoptosis and phagocytosis functions through augmenting autophagy flux via mechanisms other than demethylation of the LC3B gene promoter in THP-1 cells.

CONCLUSIONS

Increased LC3B expression and LC3B gene promoter hypermethylation may serve as biomarkers for progression of M. tb infection, while use of de-methylation agent may be a potential approach to host-directed immunotherapy in active TB disease.

Enhanced autophagy and cholesterol efflux in mouse mesenchymal stem cells infected with H37Rv compared to H37Ra

Autophagy, metabolism, and associated signaling pathways play critical roles in bacterial survival within mammalian cells and influence the immunopathogenesis of infections. Mesenchymal stem cells (MSCs) are important host cells during Mycobacterium tuberculosis (Mtb) infection, yet how autophagy, metabolism, and related pathways are modulated in MSCs infected with the virulent H37Rv or the attenuated H37Ra strain of Mtb remains poorly understood. In this study, we utilized RNA-Seq screening, qRT-PCR, and Western Blotting to investigate the differences in these processes between H37Rv and H37Ra infections. Our results show that, at early time points (no more than 24h), infection with H37Rv significantly increased the expression of TlLR2, Prkaa2, and Prkaa2 phosphorylation in MSCs compared with H37Ra infection. Further analysis revealed that H37Rv infection induced a stronger autophagic response (evidenced by increased Atg9b and LC3II/LC3I) through the TLR2-AMP-AMPK pathway than H37Ra infection. Despite these differences in autophagy, there was no statistically significant difference in bacillary loads, suggesting that, in addition to autophagy, other factors such as apoptosis and immune-inflammatory responses may also regulate Mtb growth in MSCs. Additionally, the metabolic analysis showed that H37Rv infection led to increased expression of SLC2A3, PFKFB3, HK1, and ABCA1 in MSCs compared to H37Ra infection. These findings confirm that, during the early stages of infection, H37Rv induces enhanced autophagy, glucose metabolism, and cholesterol efflux through a more active TLR2-AMP-AMPK pathway than H37Ra. Therefore, MSCs may represent a novel target for the prevention and treatment of tuberculosis.

The impact of Mycobacterium tuberculosis on the macrophage cholesterol metabolism pathway

Mycobacterium tuberculosis (Mtb) is an intracellular pathogen capable of adapting and surviving within macrophages, utilizing host nutrients for its growth and replication. Cholesterol is the main carbon source during the infection process of Mtb. Cholesterol metabolism in macrophages is tightly associated with cell functions such as phagocytosis of pathogens, antigen presentation, inflammatory responses, and tissue repair. Research has shown that Mtb infection increases the uptake of low-density lipoprotein (LDL) and cholesterol by macrophages, and enhances de novo cholesterol synthesis in macrophages. Excessive cholesterol is converted into cholesterol esters, while the degradation of cholesterol esters in macrophages is inhibited by Mtb. Furthermore, Mtb infection suppresses the expression of ATP-binding cassette (ABC) transporters in macrophages, impeding cholesterol efflux. These alterations result in the massive accumulation of cholesterol in macrophages, promoting the formation of lipid droplets and foam cells, which ultimately facilitates the persistent survival of Mtb and the progression of tuberculosis (TB), including granuloma formation, tissue cavitation, and systemic dissemination. Mtb infection may also promote the conversion of cholesterol into oxidized cholesterol within macrophages, with the oxidized cholesterol exhibiting anti-Mtb activity. Recent drug development has discovered that reducing cholesterol levels in macrophages can inhibit the invasion of Mtb into macrophages and increase the permeability of anti-tuberculosis drugs. The development of drugs targeting cholesterol metabolic pathways in macrophages, as well as the modification of existing drugs, holds promise for the development of more efficient anti-tuberculosis medications.

Bigger problems from smaller colonies: emergence of antibiotic-tolerant small colony variants of Mycobacterium avium complex in MAC-pulmonary disease patients

BACKGROUND

Mycobacterium avium complex (MAC) is a group of slow-growing mycobacteria that includes Mycobacterium avium and Mycobacterium intracellulare. MAC pulmonary disease (MAC-PD) poses a threat to immunocompromised individuals and those with structural pulmonary diseases worldwide. The standard treatment regimen for MAC-PD includes a macrolide in combination with rifampicin and ethambutol. However, the treatment failure and disease recurrence rates after successful treatment remain high.

RESULTS

In the present study, we investigated the unique characteristics of small colony variants (SCVs) isolated from patients with MAC-PD. Furthermore, revertant (RVT) phenotype, emerged from the SCVs after prolonged incubation on 7H10 agar. We observed that SCVs exhibited slower growth rates than wild-type (WT) strains but had higher minimum inhibitory concentrations (MICs) against multiple antibiotics. However, some antibiotics showed low MICs for the WT, SCVs, and RVT phenotypes. Additionally, the genotypes were identical among SCVs, WT, and RVT. Based on the MIC data, we conducted time-kill kinetic experiments using various antibiotic combinations. The response to antibiotics varied among the phenotypes, with RVT being the most susceptible, WT showing intermediate susceptibility, and SCVs displaying the lowest susceptibility.

CONCLUSIONS

In conclusion, the emergence of the SCVs phenotype represents a survival strategy adopted by MAC to adapt to hostile environments and persist during infection within the host. Additionally, combining the current drugs in the treatment regimen with additional drugs that promote the conversion of SCVs to RVT may offer a promising strategy to improve the clinical outcomes of patients with refractory MAC-PD.