Nicotine Modulates MyD88-Dependent Signaling Pathway in Macrophages during Mycobacterial Infection

Abstract

Recently, we reported that cigarette smoking, and especially nicotine, increases susceptibility to mycobacterial infection and exacerbates inflammation in patients with Crohn’s disease (CD). The macrophagic response to Mycobacterium avium subspecies paratuberculosis (MAP) in CD and Mycobacteria tuberculosis (MTB) continues to be under investigation. The role of toll-like-receptors (TLRs) and cytoplasmic adaptor protein (MyD88) in proinflammatory response during Mycobacterial infection has been suggested. However, the mechanism of how nicotine modulates macrophage response during infection in CD and exacerbates inflammatory response remain unclear. In this study, we elucidated the mechanistic role of nicotine in modulating MyD88-dependent/TLR pathway signaling in a macrophage system during mycobacterial infection. The data demonstrated that MAP infection in THP-1 derived macrophages was mediated through TLR2 and MyD88 leading to increase in IL-8 in expression and production. On the other hand, LPS-representing, Gram-negative bacteria mediated macrophage response through TLR4. Blocking TLR2 and TLR4 with antagonists voided the effect of MAP, and LPS, respectively in macrophages and reversed response with decrease in expression of iNOS, TNF-α and IL-8. Interestingly, nicotine in infected macrophages significantly (1) downregulated TLR2 and TLR4 expression, (2) activated MyD88, (3) increased M1/M2 ratio, and (4) increased expression and secretion of proinflammatory cytokines especially IL-8, as seen in CD smokers. We also discovered that blocking macrophages during MAP infection with MyD88 antagonist significantly decreased response which illustrates the key role for MyD88 during infection. Surprisingly, dual treatment of MAP-infected macrophages with MyD88 antagonist and nicotine absolutely impaired immune response and decreased MAP viability, which clearly validate the inflammatory role of nicotine in macrophages through TLR2/MyD88 pathway during infection. This is the first report to describe the mechanism by which nicotine modulates TLR2/MyDD88 and exacerbates inflammation in CD smokers associated with infection.

Nicotine in Inflammatory Diseases: Anti-Inflammatory and Pro-Inflammatory Effects

“…In TNBS-induced BALB/C mice model of Crohn's disease, nicotine taken twice a day at a total dose of 7.5 mg/kg for 5 days exacerbated colonic inflammation with the appearance of extensive mucosal necrosis in the proximal colon, extensive crypt damage, complete goblet cell depletion, lamina propria destruction, and massive lymphocytic infiltration, which was associated with the inhibition of colonic CD4 T cell nAChRs regulated by IL-12 (40). Nicotine (4 µg/ml) modulated TLR2/ MyD88/IL-8 and exacerbated inflammation in mycobacteria (Mycobacterium avium paratuberculosis)-infected macrophages, providing important insights to understand the effect of nicotine on worsening inflammation symptoms in patients with Crohn's disease (50). Caution should be exercised in nicotine administration due to organ specificity.…”

Can SARS-CoV-2 Virus Use Multiple Receptors to Enter Host Cells?

“…Taken together, TLR1/2 and TLR2/6 heterodimers may represent a therapeutic target of inhibitory pharmaceuticals to prevent excessive inflammation and viral entry. The recent discovery of MMG11 (a TLR2 inhibitor, which shows preference for the TLR1/2 heterodimer [103,104]) and CuCpt22 (a TLR1/2 heterodimer inhibitor in mice [103] and a TLR1/2/6 inhibitor in humans [103,105]) may represent potential COVID-19 therapeutics. Pre-treatment of MMG11 (5 µg/mL) followed by infection with Mycobacterium avium subspecies paratuberculosis in human macrophages, resulted in significantly reduced concentration of pro-inflammatory cytokines IL-8 and TNFα [104].…”

“…The recent discovery of MMG11 (a TLR2 inhibitor, which shows preference for the TLR1/2 heterodimer [103,104]) and CuCpt22 (a TLR1/2 heterodimer inhibitor in mice [103] and a TLR1/2/6 inhibitor in humans [103,105]) may represent potential COVID-19 therapeutics. Pre-treatment of MMG11 (5 µg/mL) followed by infection with Mycobacterium avium subspecies paratuberculosis in human macrophages, resulted in significantly reduced concentration of pro-inflammatory cytokines IL-8 and TNFα [104]. Similar anti-inflammatory abilities have been observed in human primary bronchial epithelial cells pre-treated with CuCpt22 (50 µM), 30 min before challenge with Streptococcus pneumonia strain D39 [105].…”

Nicotine Increases Macrophage Survival through α7nAChR/NF-κB Pathway in Mycobacterium avium paratuberculosis Infection

“…Nicotine also increased NF-ĸB p52 translocation and activation in macrophages in presence or absence of MAP infection ( Table 2 ). This suggests that nicotine activates the antiapoptotic effect of NF-ĸB in MAP-infected macrophages, which may induce several antiapoptotic genes including inhibit caspase-3 activation [ 12 , 26 ]. These results support previous studies that reported that inhibiting NF-ĸB in macrophages leads to increased apoptosis and reduced viability of intracellular MTB [ 24 ].…”