title: Sensitivity of alveolar macrophages to substrate mechanical and adhesive properties.
abstract: In order to understand the sensitivity of alveolar macrophages (AMs) to substrate properties, we have developed a new model of macrophages cultured on substrates of increasing Young's modulus: (i) a monolayer of alveolar epithelial cells representing the supple (approximately 0.1 kPa) physiological substrate, (ii) polyacrylamide gels with two concentrations of bis-acrylamide representing low and high intermediate stiffness (respectively 40 kPa and 160 kPa) and, (iii) a highly rigid surface of plastic or glass (respectively 3 MPa and 70 MPa), the two latter being or not functionalized with type I-collagen. The macrophage response was studied through their shape (characterized by 3D-reconstructions of F-actin structure) and their cytoskeletal stiffness (estimated by transient twisting of magnetic RGD-coated beads and corrected for actual bead immersion). Macrophage shape dramatically changed from rounded to flattened as substrate stiffness increased from soft ((i) and (ii)) to rigid (iii) substrates, indicating a net sensitivity of alveolar macrophages to substrate stiffness but without generating F-actin stress fibers. Macrophage stiffness was also increased by large substrate stiffness increase but this increase was not due to an increase in internal tension assessed by the negligible effect of a F-actin depolymerizing drug (cytochalasine D) on bead twisting. The mechanical sensitivity of AMs could be partly explained by an idealized numerical model describing how low cell height enhances the substrate-stiffness-dependence of the apparent (measured) AM stiffness. Altogether, these results suggest that macrophages are able to probe their physical environment but the mechanosensitive mechanism behind appears quite different from tissue cells, since it occurs at no significant cell-scale prestress, shape changes through minimal actin remodeling and finally an AMs stiffness not affected by the loss in F-actin integrity.
authors.affiliation: Inserm UMR 651, Fonctions Cellulaires et Moléculaires de l'Appareil Respiratoire et des Vaisseaux, Equipe Biomécanique Cellulaire et Respiratoire et Université Paris XII, Faculté de Médecine, Institut Supérieur des Biosciences de Paris, Créteil, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Féréol
authors.forename: Redouane
authors.initials: R
authors.lastname: Fodil
authors.forename: Béatrice
authors.initials: B
authors.lastname: Labat
authors.forename: Stéphane
authors.initials: S
authors.lastname: Galiacy
authors.forename: Valérie M
authors.initials: VM
authors.lastname: Laurent
authors.forename: Bruno
authors.initials: B
authors.lastname: Louis
authors.forename: Daniel
authors.initials: D
authors.lastname: Isabey
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Planus
mesh_terms: D000178:Acrylamides; D000180:Acrylic Resins; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D018929:Cell Culture Techniques / Q000379:methods*; D018920:Coculture Techniques; D003599:Cytoskeleton / Q000502:physiology* / Q000648:ultrastructure; D004548:Elasticity; D004847:Epithelial Cells / Q000166:cytology; D005260:Female; D005898:Glass; D016676:Macrophages, Alveolar / Q000166:cytology* / Q000648:ultrastructure; D008297:Male; D018613:Microscopy, Confocal / Q000379:methods; D010969:Plastics; D011650:Pulmonary Alveoli / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013314:Stress, Mechanical; D013379:Substrate Specificity
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D010969:Plastics; C016680:polyacrylamide gels