Heme oxygenase-1 inhibition promotes IFNγ- and NOS2-mediated control of Mycobacterium tuberculosis infection

Abstract

Mycobacterium tuberculosis (Mtb) infection induces pulmonary expression of the heme-degrading enzyme heme oxygenase-1 (HO-1). We have previously shown that pharmacological inhibition of HO-1 activity in experimental tuberculosis results in decreased bacterial loads and unexpectedly that this outcome depends on the presence of T lymphocytes. Here we extend these findings by demonstrating that IFNγ production by T lymphocytes and NOS2 expression underlie this T cell requirement and that HO-1 inhibition potentiates IFNγ-induced NOS2-dependent control of Mtb by macrophages in vitro. Among the products of heme degradation by HO-1 (biliverdin, carbon monoxide and iron), only iron supplementation reverted the HO-1 inhibition-induced enhancement of bacterial control and this reversal was associated with decreased NOS2 expression and NO production. Additionally, we found that HO-1 inhibition results in decreased labile iron levels in Mtb-infected macrophages in vitro and diminished iron accumulation in Mtb-infected lungs in vivo. Together these results suggest that the T lymphocyte dependence of the therapeutic outcome of HO-1 inhibition on Mtb infection reflects the role of the enzyme in generating iron that suppresses T cell-mediated IFNγ/NOS2-dependent bacterial control. In broader terms, our findings highlight the importance of the crosstalk between iron metabolism and adaptive immunity in determining the outcome of infection.

Enhancement of CD4+ T Cell Function as a Strategy for Improving Antibiotic Therapy Efficacy in Tuberculosis: Does It Work?

“…Murine primers used: Actb F: 5’ AGC TGC GTT TTA CAC CCT TT 3’; Actb R: 5’ AAG CCA TGC CAA TGT TGT CT 3’; Il12b F: 5’ AGC ACC AGC TTC TTC ATC AGG 3’; Il12b R: 5’ GCG CTG GAT TCG AAC AAA G 3’. For flow cytometry, lung single cell suspensions were prepared as previously described ( Costa et al., 2020 ). For intracellular cytokine detection, prior to staining cells were incubated for 5 hours at 37°C with 10 µg/ml ESAT-6 1-20 or Ag85B 280-294 in the presence of brefeldin A and monensin during the whole 5h culture period, as previously published ( Sallin et al., 2018 ).…”

Understanding the Reciprocal Interplay Between Antibiotics and Host Immune System: How Can We Improve the Anti-Mycobacterial Activity of Current Drugs to Better Control Tuberculosis?

“…HO-1 exerts anti-inflammatory and cytoprotective effects, although the underlying mechanisms are not fully understood (196). Several studies have investigated the host beneficial or detrimental roles of HO-1 during TB infection (95,99,(192)(193)(194)(195). Andrade et al showed that active TB patients show a negative correlation between plasma levels of HO-1 and MMP-1 (95).…”

“…Further, early secreted antigen ESAT-6-mediated nuclear translocation of transcription factor NRF-2 is required for Mtb-induced HO-1 expression (193). Recently, Costa et al discovered that HO-1 inhibition improves IFN-g-induced NOS2-dependent bacterial killing by murine macrophages (99). Additionally, HO-1 inhibition induced low intracellular non-protein bound iron in Mtb-infected macrophages and reduced iron deposition in the lungs of Mtb-infected mice (99).…”

“…Recently, Costa et al discovered that HO-1 inhibition improves IFN-g-induced NOS2-dependent bacterial killing by murine macrophages (99). Additionally, HO-1 inhibition induced low intracellular non-protein bound iron in Mtb-infected macrophages and reduced iron deposition in the lungs of Mtb-infected mice (99). Taken together, HO-1 expression inhibits T cell-mediated IFN-g-induced NOS2dependent control of Mtb by producing free iron.…”

“…Interestingly, ROS-mediated damage induced by antibiotics could be rescued by N-acetyl-l-cysteine (NAC) without affecting the antibiotic’s killing ability ( 97 ). In addition, an HO-1 inhibitor showed the same effect in the lungs of Mtb-infected mice as anti-TB drugs ( 99 ). Thus, the long-term use of bactericidal anti-TB drugs can induce cell death due to ROS production and mitochondrial dysfunction, while simultaneously, the produced ROS act as antioxidants and interfere with the removal of Mtb.…”