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

Area of Science:

• Pulmonary biology
• Glycobiology
• Biochemistry

Background:

• The lung epithelial glycocalyx, a carbohydrate layer, has unknown composition and function.
• Previous studies have visualized the lung epithelial glycocalyx but lacked compositional and functional data.

Purpose of the Study:

• To identify the composition of the lung epithelial glycocalyx.
• To investigate the role of lung epithelial glycocalyx components in maintaining lung barrier integrity.
• To explore the mechanisms of glycocalyx shedding during lung injury.

Main Methods:

• Immunofluorescence and mass spectrometry to identify glycocalyx components.
• Enzymatic degradation to assess the function of specific glycans.
• Mass spectrometry and gel electrophoresis to analyze glycans in bronchoalveolar lavage (BAL) fluid.
• Pharmacologic and transgenic approaches to investigate matrix metalloproteinase involvement.
• Analysis of clinical samples from patients with acute respiratory distress syndrome (ARDS).

Main Results:

• Heparan sulfate (HS) and chondroitin sulfate were identified in the lung epithelial glycocalyx.
• Degradation of epithelial HS, but not chondroitin sulfate, increased lung permeability.
• Shedding of HS (≥20 saccharides) into BAL fluid was observed in LPS-induced lung injury.
• Airspace HS levels correlated with alveolar permeability in ARDS patients.
• Matrix metalloproteinases were found to partially mediate HS shedding.

Conclusions:

• Epithelial HS is a crucial component of the lung epithelial barrier.
• Degradation of epithelial HS is sufficient to increase lung permeability.
• Matrix metalloproteinase inhibition partially reduces HS shedding but does not fully restore barrier function in LPS-induced lung injury.
• The clinical relevance of HS shedding in lung injury and ARDS is highlighted.