Toll-like Receptor 7 Is Reduced in Severe Asthma and Linked to an Altered MicroRNA Profile

Abstract

Rationale: Asthma is one of the most common chronic diseases worldwide, and individuals with severe asthma experience recurrent exacerbations. Exacerbations are predominantly viral associated and have been linked to defective airway IFN responses. Ascertaining the molecular mechanisms underlying this deficiency is a major research goal to identify new therapeutic targets.Objectives: We investigated the hypothesis that reduced Toll-like receptor 7 (TLR7)-derived signaling drove the impaired IFN responses to rhinovirus by asthmatic alveolar macrophages (AMs); the molecular mechanisms underlying this deficiency were explored.Methods: AMs were recovered from bronchoalveolar lavage from healthy subjects and patients with severe asthma. Expression of pattern-recognition receptors and microRNAs was evaluated by quantitative polymerase chain reaction and Western blotting. A TLR7-luciferase reporter construct was created to evaluate binding of microRNAs to the 39 untranslated region of TLR7. IFN production was measured by quantitative polymerase chain reaction and ELISA.Measurements and Main Results: The expression of TLR7 was significantly reduced in severe asthma AMs and was associated with reduced rhinovirus and imiquimod-induced IFN responses by these cells compared with healthy AMs. Severe asthma AMs also expressed increased levels of three microRNAs, which we showed were able to directly reduce TLR7 expression. Ex vivo knockdown of these microRNAs restored TLR7 expression with concomitant augmentation of virus-induced IFN production.Conclusions: In severe asthma, TLR7 deficiency drives impaired innate immune responses to virus by AMs. Blocking a group of microRNAs that are up-regulated in these cells can restore antiviral innate responses, providing a novel approach for therapy in asthma.

IFN Deficiency in Asthma Attacks. Is Restoring Toll-like Receptor-7 Expression a New Treatment Approach in Severe Asthma?

“…Rupani and colleagues, as well as showing IFN deficiency in severe asthma as discussed above, have also reported that TLR7 mRNA and protein expression is decreased in BAL-derived macrophages in severe asthma, that TLR7 function in response to imiquimod is also similarly reduced, and that TLR7 mRNA expression correlated inversely with number of exacerbations in the previous year and with Asthma Control Questionnaire score (14). The authors propose that TLR7 deficiency and the associated impaired IFN response to virus drives the vulnerability of subjects with severe asthma to recurrent lower respiratory virus infections.…”

“…In this issue of the Journal, Rupani and colleagues (pp. 26-37) studied 35 adults with severe asthma (a history of recurrent exacerbations and inadequate disease control [median Asthma Control Questionnaire score of 2.9] despite being on step 4/5 of Global Initiative for Asthma management) (14). In the 10 of these 35 subjects in whom IFN induction was compared with healthy control subjects, IFN-a and IFN-b induction in response to rhinovirus infection of bronchoalveolar lavage (BAL)-derived adherent cells (presumed mostly macrophages) was also shown to be profoundly deficient.…”

“…Rupani and colleagues then went on to investigate possible mechanisms of TLR7 deficiency in asthma (14). They investigated expression of 745 microRNAs (miRNAs) in BAL-derived macrophages and identified that 16 were up-regulated in patients with severe asthma (14).…”

“…They investigated expression of 745 microRNAs (miRNAs) in BAL-derived macrophages and identified that 16 were up-regulated in patients with severe asthma (14). Based on in silico analysis, 3 of these 16 (miR-150, miR-152, and miR-375) potentially target TLR7.…”

Mast cells are permissive for rhinovirus replication: potential implications for asthma exacerbations

“…IFNs induce a range of IFN‐stimulated genes (ISGs) via which they mediate their antiviral activities 15. Deficiencies in IFN production have been reported in bronchial epithelial cells and bronchoalveolar lavage macrophages from asthmatic subjects 16, 17, 18; however, this may relate to severity of disease 19, 20.…”