Abstract

Many cells, including murine airway epithelial cells, respond to a variety of inflammatory stimuli by synthesizing leukocyte-adhesive hyaluronan (HA) 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 two heavy chains (HC1 and HC2) on its chondroitin sulfate chain. The transesterification transfer of HCs from chondroitin sulfate to HA is mediated by tumor necrosis factor-induced gene 6 (TSG-6), which is up-regulated 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 of naïve 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.

Highlights

  • Hyaluronan (HA)2 is a linear, non-sulfated glycosaminoglycan that is made of repeating disaccharides composed of D-glucuronic acid and D-N-acetylglucosamine linked by ␤(1,4) and ␤(1,3) glycosidic bonds

  • This study shows that air-liquid interface cultures of murine airway epithelial cells (AECs) 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

  • The results show that AECs synthesize TNF␣-stimulated gene-6 (TSG-6) and their own heavy chain donor with a single heavy chain 3 (HC3), which are constitutively expressed by human renal proximal tubular epithelial cells

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Summary

Hyaluronan Rafts on Airway Epithelial Cells*

This study shows that air-liquid interface cultures of murine airway epithelial cells (AECs) 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. Airway epithelial cells (AECs) form HA cables on their cell surface in response to a variety of inflammatory stimuli [23], we show in this study that they actively release a majority of their leukocyte-adhesive HA structures into the extracellular space from their apical surface These matrices do not resemble the HA cables but occur in distinct sheets, or rafts, of HA that are leukocyteadhesive. A HA raft with HC-HA structure present in respiratory secretions raises a number of important questions regarding the role it has in inflammatory processes

Experimental Procedures
Primer sequence
Results
Discussion

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