Abstract
Exposure to pollutants, such as ozone, exacerbates airway inflammation and hyperresponsiveness (AHR). TNF-stimulated gene 6 (TSG-6) is required to transfer inter-α-inhibitor heavy chains (HC) to hyaluronan (HA), facilitating HA receptor binding. TSG-6 is necessary for AHR in allergic asthma, because it facilitates the development of a pathological HA-HC matrix. However, the role of TSG-6 in acute airway inflammation is not well understood. Here, we hypothesized that TSG-6 is essential for the development of HA- and ozone-induced AHR. TSG-6-/- and TSG-6+/+ mice were exposed to ozone or short-fragment HA (sHA), and AHR was assayed via flexiVent. The AHR response to sHA was evaluated in the isolated tracheal ring assay in tracheal rings from TSG-6-/- or TSG-6+/+, with or without the addition of exogenous TSG-6, and with or without inhibitors of Rho-associated, coiled-coil-containing protein kinase (ROCK), ERK, or PI3K. Smooth-muscle cells from mouse tracheas were assayed in vitro for signaling pathways. We found that TSG-6 deficiency protects against AHR after ozone (in vivo) or sHA (in vitro and in vivo) exposure. Moreover, TSG-6-/- tracheal ring non-responsiveness to sHA was reversed by exogenous TSG-6 addition. sHA rapidly activated RhoA, ERK, and Akt in airway smooth-muscle cells, but only in the presence of TSG-6. Inhibition of ROCK, ERK, or PI3K/Akt blocked sHA/TSG-6-mediated AHR. In conclusion, TSG-6 is necessary for AHR in response to ozone or sHA, in part because it facilitates rapid formation of HA-HC complexes. The sHA/TSG-6 effect is mediated by RhoA, ERK, and PI3K/Akt signaling.
Highlights
This work was supported partly through funds from the Division of Intramural Research, NIEHS, National Institutes of Health, by Grants P01HL107147
Post-ozone cytokines were not statistically different between TNF-stimulated gene 6 (TSG-6) – deficient and –sufficient mice. These results suggest that TSG-6 is necessary for cell influx, but not for cellular activation after ozone exposure
Quantification of the gels using ImageJ showed an absence of heavy chain (HC)–HA deposition regardless of ozone or air exposure in TSG-6 – deficient mice, whereas there was a significant increase in sufficient mice (Fig. 2C). These results suggest that TSG-6 mediates HA–HC complex formation within 24 h after ozone exposure
Summary
We first analyzed cellular and humoral inflammation 24 h after mouse exposure to ozone. Post-ozone cytokines were not statistically different between TSG-6 – deficient and –sufficient mice In aggregate, these results suggest that TSG-6 is necessary for cell influx, but not for cellular activation after ozone exposure. Inhibition of the RhoA pathway using ROCK inhibitor Y27632 ameliorated the TSG-6 –induced contractility in sHA exposure (Fig. 6B) These results suggest that the TSG6 –mediated HA–HC complexes induce AHR through the RhoA pathway. We again used the model of sHA-induced hyperresponsiveness in the tracheal ring assay and replicated the rescue of hyperresponsiveness by the addition of exogenous TSG-6 to deficient tracheal rings as our baseline observation We found that both PD98059 (ERK inhibitor) and LY27632 (PI3K/Akt inhibitor), given for 30 min, ameliorated the TSG-6 rescue effects (Fig. 8). These results suggest that ERK and Akt are necessary for the HA–HC–TSG-6 –induced airway hyperresponsiveness
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
