Abstract
BackgroundAirway inflammation is a hallmark of asthma. Alterations in extracellular matrix (ECM) hyaluronan (HA) content have been shown to modulate the recruitment and retention of inflammatory cells. Bronchial epithelial cells (BECs) regulate the activity of human lung fibroblasts (HLFs); however, their contribution in regulating HLF production of HA in asthma is unknown. In this study, we tested the hypothesis that BECs from asthmatic children promote the generation of a pro-inflammatory, HA-enriched ECM by HLFs, which promotes the retention of leukocytes.MethodsBECs were obtained from well-characterized asthmatic and healthy children ages 6–18 years. HLFs were co-cultured with BECs for 96 h and samples were harvested for analysis of gene expression, synthesis and accumulation of HA, and subjected to a leukocyte adhesion assay with U937 monocytes.ResultsWe observed increased expression of HA synthases HAS2 and HAS3 in HLFs co-cultured with asthmatic BECs. Furthermore, we demonstrated greater total accumulation and increased synthesis of HA by HLFs co-cultured with asthmatic BECs compared to healthy BEC/HLF co-cultures. ECM generated by HLFs co-cultured with asthmatic BECs displayed increased HA-dependent adhesion of leukocytes in a separate in vitro binding assay.ConclusionsOur findings demonstrate that BEC regulation of HA production by HLFs is altered in asthma, which may in turn promote the establishment of a more leukocyte-permissive ECM promoting airway inflammation in this disease.
Highlights
Airway inflammation is a hallmark of asthma
HA is synthesized as a large polymer, high molecular weight HA (HMW-HA, > 250 kDa); it can be degraded into low molecular weight HA (LMW-HA) fragments through the activity of hyaluronidases (Hyals), principally Hyal1 and Hyal2, or reactive oxygen species leading to HA turnover [11, 12]
In the present study, we have demonstrated in an ex vivo model system that human lung fibroblasts (HLFs) co-cultured with primary human bronchial epithelial cells (BECs) obtained from asthmatic children produce an extracellular matrix (ECM) that is enriched with HA compared to HLFs that are co-cultured with BECs obtained from healthy children
Summary
Airway inflammation is a hallmark of asthma. Alterations in extracellular matrix (ECM) hyaluronan (HA) content have been shown to modulate the recruitment and retention of inflammatory cells. Bronchial epithelial cells (BECs) regulate the activity of human lung fibroblasts (HLFs); their contribution in regulating HLF production of HA in asthma is unknown. We tested the hypothesis that BECs from asthmatic children promote the generation of a pro-inflammatory, HA-enriched ECM by HLFs, which promotes the retention of leukocytes. Increased HA levels in airway secretions have been reported in several additional studies and correlate with degree of asthma severity and airway inflammation in humans [16,17,18,19,20] as well as airway inflammation in animal models [3, 4, 21]. In addition to making the ECM more permissible to inflammatory cell infiltration by influencing the viscoelastic properties of the ECM [22], HA can be modified by the binding of various hyaladherins such as the proteoglycan versican (VCAN) or covalently through the activity of tumor necrosis factor stimulated gene 6 (TSG-6), which may increase its avidity for binding and retaining leukocytes [23]
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