Role of autophagy in regulating interleukin-10 and the responses to corticosteroids and statins in asthma

Background: Interleukin (IL)-10 is a key anti-inflammatory cytokine that may be reduced in asthma but is enhanced by corticosteroids, especially when combined with a statin, although the mechanisms of these effects are uncertain. Objective: To study the role of autophagy in macrophages in promoting inflammation in asthma through reducing IL-10 secretion and how corticosteroids and statins may reverse this process. Methods: We conducted a randomised double-blind placebo-controlled study in moderate to severe asthmatic patients (n = 44) to investigate the effect of an inhaled corticosteroid (budesonide 400 mu g/day) and the combination of budesonide with an oral statin (simvastatin 10 mg/day) given for 8 weeks on autophagy protein expression in sputum cells by using immunocytochemistry and measurement of IL-10 release. In in vitro experiments, we studied cross-regulation between autophagy and IL-10 release by measuring the expression of autophagy proteins in M2-like macrophages and the effects of budesonide and simvastatin on these mechanisms. Results: In asthmatic patients, inhaled budesonide inhibited airway macrophage autophagy (beclin-1, LC3) as well as autophagic flux (p62), which was enhanced by simvastatin and was correlated with increased sputum IL-10 and reduced IL-4 concentrations. In macrophages in vitro, budesonide and simvastatin inhibited rapamycin-induced autophagy as well as autophagic flux, with reduced expression of beclin-1 and LC3, but enhanced the accumulation of p62 and increased expression of IL-10, which itself further inhibited autophagy in macrophages. With siRNA-mediated silencing, LC3-deficient macrophages also showed a maximal induction of IL-10 transcription. Neutralisation of IL-10 with recombinant specific blocking antibody and silencing IL-10 transcription reversed the inhibitory effects of budesonide and simvastatin on macrophage autophagy. Conclusion and clinical relevance: Inhibition by corticosteroids and a statin of macrophage autophagy enhances IL-10 production, resulting in the control of asthmatic inflammation.