Etudes des propriétés rhéologiques, d’hydratations et osmotiques du mucus pulmonaire

Kawthar SHAALAN

Project description

In some lung diseases, patients suffer from bronchial obstruction caused or favored by an overproduction and/or by an alteration of the mechanical properties of mucus. These abnormalities alter the ability of the ciliated epithelium of the airways to eliminate the mucus produced (this is called "mucociliary clearance"). Correlations are observed between the rheological properties of pulmonary mucus and bronchial obstruction: generally, mucus is more elastic than mucus from a healthy subject and has an abnormally high yield stress. Several therapeutic strategies targeting the consequences of mucus abnormalities (bronchial obstruction and exacerbations) exist or are under development in obstructive bronchial diseases, but the understanding of the mode of action of these therapies on mucus remains very incomplete.
 
The viscoelastic properties of pulmonary mucus depend strongly on its composition, at least on the dry matter. Indeed, pulmonary mucus is a gel, constituted of 98% water in the healthy state, a proportion which can fall to 90% in pathological conditions. Its elastic properties come mainly from mucins secreted by epithelial cells, which form a three-dimensional network. Like other viscoelastic gels, it is expected that the elasticity of the gel will increase with the density of this network. Hydration itself is not the only parameter modifying these rheological and structural properties: the ionic strength, but especially the presence of calcium ions, as well as the pH can also play an important role. Finally, the production and transport of mucus in the bronchial tract remain dynamic processes: mucins are produced continuously, and compositional and thermal exchanges occur between the mucus layer, the air and the epithelium. The capacity and dynamics with which mucus can be hydrated is currently very poorly known, as well as, more generally, its dynamic response to osmotic stresses.
 
The main objective of this thesis is to quantify these dynamic aspects: how, and with what spatio-temporal dynamics, can mucus rehydrate or on the contrary dry out? How do these compositional variations (mucins, calcium ions, pH, …) continuously influence its rheological and structural properties? The strategy envisaged will consist in quantifying at the microscopic scale the local rheological properties of mucus, and to follow their evolution in space and time, following osmotic stresses (contact with dry or humid air, hot or cold, water, buffer solutions, mucin solutions, etc…). We will also study the potential coupling between mechanical and osmotic stresses: under a sufficient mechanical stress, mucus flows and we seek to characterize and understand how this affects the transport and transfer properties of solutes.

To do this, we will use passive and/or active microrheology techniques, available in the laboratory, consisting respectively in following by confocal microscopy the rapid movement of tracers, or in imposing a displacement on them by an optical tweezers. Osmotic stresses will be generated by microfluidic devices that we will specifically develop and that will allow a temporal control of the stress. We will use different types of mucus samples: lung mucus mimetic substitutes, mucus produced by reconstituted epithelia, but also eventually samples taken during endoscopy from patients suffering from bronchial obstruction. This last type of sample will be tested in close collaboration with the medical follow-up of these patients, which will allow to test the action of different treatments. 

Supervisors

Hugues Bodiguel

Bruno Degano