On Top of the Alveolar Epithelium: Surfactant and the Glycocalyx
Open Access
- 27 April 2020
- journal article
- review article
- Published by MDPI AG in International Journal of Molecular Sciences
- Vol. 21 (9), 3075
- https://doi.org/10.3390/ijms21093075
Abstract
Gas exchange in the lung takes place via the air-blood barrier in the septal walls of alveoli. The tissue elements that oxygen molecules have to cross are the alveolar epithelium, the interstitium and the capillary endothelium. The epithelium that lines the alveolar surface is covered by a thin and continuous liquid lining layer. Pulmonary surfactant acts at this air-liquid interface. By virtue of its biophysical and immunomodulatory functions, surfactant keeps alveoli open, dry and clean. What needs to be added to this picture is the glycocalyx of the alveolar epithelium. Here, we briefly review what is known about this glycocalyx and how it can be visualized using electron microscopy. The application of colloidal thorium dioxide as a staining agent reveals differences in the staining pattern between type I and type II alveolar epithelial cells and shows close associations of the glycocalyx with intraalveolar surfactant subtypes such as tubular myelin. These morphological findings indicate that specific spatial interactions between components of the surfactant system and those of the alveolar epithelial glycocalyx exist which may contribute to the maintenance of alveolar homeostasis, in particular to alveolar micromechanics, to the functional integrity of the air-blood barrier, to the regulation of the thickness and viscosity of the alveolar lining layer, and to the defence against inhaled pathogens. Exploring the alveolar epithelial glycocalyx in conjunction with the surfactant system opens novel physiological perspectives of potential clinical relevance for future research.Keywords
Funding Information
- Deutsche Forschungsgemeinschaft (OC23/7-3, 8-1, 9-3, 10-1; SFB 587/TP B18; SFB-TR84/TP C06, C09; INST 192/504-1, 193/57-1; REBIRTH Cluster of Excellence)
This publication has 79 references indexed in Scilit:
- Imaging the Endothelial Glycocalyx In Vitro by Rapid Freezing/Freeze Substitution Transmission Electron MicroscopyArteriosclerosis, Thrombosis, and Vascular Biology, 2011
- A Disintegrin and Metalloproteinase 17 (ADAM17) Mediates Inflammation-induced Shedding of Syndecan-1 and -4 by Lung Epithelial CellsOnline Journal of Public Health Informatics, 2010
- The Closer we Look the more we See? Quantitative Microscopic Analysis of the Pulmonary Surfactant SystemCellular Physiology and Biochemistry, 2010
- The endothelial glycocalyx: composition, functions, and visualizationPflügers Archiv - European Journal of Physiology, 2007
- Visualization and quantitative analysis of nanoparticles in the respiratory tract by transmission electron microscopyParticle and Fibre Toxicology, 2007
- The Role of Hyaluronan in the Pulmonary AlveolusJournal of Theoretical Biology, 2001
- The Pulmonary Collectins and Surfactant MetabolismAnnual Review of Physiology, 2001
- Improvements in demonstration of lining layer of lung alveoli by electron microscopyRespiration Physiology, 1969
- Electron microscopic demonstration of an extracellular duplex lining layer of alveoliRespiration Physiology, 1968
- Structure of the Alveolar Lining Film of the LungsNature, 1964