HMGB1 is upregulated in ASM in asthma and induces ASM contraction via TLR4

Abstract

Introduction: High mobility group box-1 (HMGB1) is released during tissue damage and inflammation, and is involved in inflammatory diseases including asthma. We hypothesised that HMGB1 expression in airway smooth muscle (ASM) of asthmatics is increased and amplifies agonist-induced ASM contraction via receptor for advanced glycosylation end products (RAGE) and/or Toll-like receptor 4 (TLR4). Methods: HMGB1 expression was assessed in bronchial biopsies of asthmatics (n=16) and healthy controls (n=10). HMGB1, RAGE and TLR4 expression in primary ASM cells was measured by flow cytometry. The effect of HMGB1 on bradykinin-induced ASM contraction was assessed in collagen gel-embedded ASM cells in the presence or absence of soluble RAGE, an antagonist of RAGE activation, and the TLR4 antagonist LPS-RS. Results: HMGB1 expression was increased in ASM of asthmatics vs non-asthmatics (546±127 vs 211±36 HMGB1+ve cells/mm 2 ASM; p=0.021). HMGB1 expression was upregulated in primary ASM cells stimulated with pro-inflammatory cytokines (IL-1β, TNFα, and IFNγ, n=14; p Conclusions: HMGB1 upregulation ex vivo in ASM of asthmatics and in vitro following activation suggests that ASM can release HMGB1 in a pro-inflammatory environment or following viral exposure. HMGB1 amplifies ASM agonist-induced contraction via a TLR4-dependent mechanism suggesting HMGB1 may act upon ASM in an autocrine/paracrine manner to enhance airway hyperresponsiveness in asthma.