Epithelial Heparan Sulfate Contributes to Alveolar Barrier Function and Is Shed during Lung Injury

Abstract

The lung epithelial glycocalyx is a carbohydrate-enriched layer lining the pulmonary epithelial surface. Although epithelial glycocalyx visualization has been reported, its composition and function remain unknown. Using immunofluorescence and mass spectrometry, we identified heparan sulfate (HS) and chondroitin sulfate within the lung epithelial glycocalyx. In vivo selective enzymatic degradation of epithelial HS, but not chondroitin sulfate, increased lung permeability. Using mass spectrometry and gel electrophoresis approaches to determine the fate of epithelial HS during lung injury, we detected shedding of 20 saccharide-long or greater HS into BAL fluid in intratracheal LPS-treated mice. Furthermore, airspace HS in clinical samples from patients with acute respiratory distress syndrome correlated with indices of alveolar permeability, reflecting the clinical relevance of these findings. The length of HS shed during intratracheal LPS-induced injury (≥20 saccharides) suggests cleavage of the proteoglycan anchoring HS to the epithelial surface, rather than cleavage of HS itself. We used pharmacologic and transgenic animal approaches to determine that matrix metalloproteinases partially mediate HS shedding during intratracheal LPS-induced lung injury. Although there was a trend toward decreased alveolar permeability after treatment with the matrix metalloproteinase inhibitor, doxycycline, this did not reach statistical significance. These studies suggest that epithelial HS contributes to the lung epithelial barrier and its degradation is sufficient to increase lung permeability. The partial reduction of HS shedding achieved with doxycycline is not sufficient to rescue epithelial barrier function during intratracheal LPS-induced lung injury; however, whether complete attenuation of HS shedding is sufficient to rescue epithelial barrier function remains unknown.

Intravenous fluid resuscitation is associated with septic endothelial glycocalyx degradation

“…This highly sensitive approach, previously developed [29] and validated [30] by our group, is capable of detecting circulating heparan sulfate of all sulfation types, contrasting the limitation of antibody-based assays to only a few sulfation patterns. We have previously demonstrated that this LC-MS/MS MRM approach to measuring circulating heparan sulfate is highly sensitive to both septic and non-septic glycocalyx degradation [31] and is an early predictor of glycocalyx degradation-associated organ injury [28].…”

More Than Just a Barrier: The Immune Functions of the Airway Epithelium in Asthma Pathogenesis

“…Although the glycocalyx appears to be static on the architectural level, it may not be invariant in terms of its molecular composition. It was shown that lipopolysaccharide exposure could lead to heparan sulfate shedding from the airway epithelium thereby causing increased lung permeability (52). Allergen exposure of experimental animals resulted in different glycosylation patterns of the glycocalyx (75), which may result in a deviant presentation of viral and bacterial receptors on the cell surface.…”

Reduced-flow ex vivo lung perfusion to rehabilitate lungs donated after circulatory death

“…23−26 A key component of the vascular endothelium is the glycocalyx, a polyanionic layer on the luminal side of endothelial cells comprised of membrane bound proteoglycans, glycosaminoglycans, and glycoproteins that together regulate endothelial permeability, mediate interactions with circulating cells, and facilitate mechanotransduction. 27,28 Hyaluronan, a component of the endothelial glycocalyx, has been shown to be especially important in preventing the accumulation of tissue edema and is vital for appropriate mechanotransduction and shear-induced nitric oxide synthesis for vascular regulation. 29−31 In the setting of EVLP, endothelial function is known to be important for graft outcomes, and other glycocalyx breakdown components have been examined as markers of organ quality during EVLP.…”