Hyaluronan rafts on airway epithelial cells [Glycobiology and Extracellular Matrices]

November 24th, 2015 by Abbadi, A., Lauer, M., Swaidani, S., Wang, A., Hascall, V.

Many cells, including murine airway epithelial cells, respond to a variety of inflammatory stimuli by synthesizing leukocyte-adhesive hyaluronan cables that remain attached to their cell surfaces. This study shows that air-liquid interface cultures of murine airway epithelial cells (AECs) also actively synthesize and release a majority of their HA onto their ciliated apical surfaces to form a heavy chain-hyaluronan (HC-HA) matrix in the absence of inflammatory stimuli. These matrices do not resemble the rope-like HA cables, but occur in distinct sheets or rafts, that can capture and embed leukocytes from cell suspensions. The HC-HA modification involves the transfer of heavy chains from the inter-α-inhibitor (IαI) proteoglycan, which has 2 heavy chains (HC1 and HC2) on its chondroitin sulfate (CS) chain. The transesterification transfer of HCs from CS to HA is mediated by tumor-necrosis-factor-induced-gene 6 (TSG-6), which is upregulated in inflammatory reactions. Because the AEC cultures do not have TSG-6 nor serum, the source of IαI, assays for HCs and TSG-6 were done. The results show that AECs synthesize TSG-6 and their own heavy chain donor (pre-IαI) with a single heavy chain 3 (HC3), which are also constitutively expressed by human renal proximal tubular epithelial cells. These leukocyte adhesive HC3-HA structures were also found in the bronchoalveolar lavage (BAL) of naιve mice, and were observed on their apical ciliated surfaces. Thus, these leukocyte-adhesive HA rafts are now identified as HC3-HA complexes that could be part of a host defense mechanism filling some important gaps in our current understanding of murine airway epithelial biology and secretions.