Absence de protéine intégrine ß1 : conséquence sur les réponses mécaniques et physico-chimiques du cartilage articulaire

Consequence of the absence of protein ß1 integrin in mechanical and physicochemical responses for hyaline cartilage
Livia CUERU¹, Carole BOUGAULT², Ana-Maria TRUNFIO-SFARGHIU¹, Frédéric MALLEIN-GERIN², Yves BERTHIER^1
1UMR 5259, INSA de Lyon, Université de Lyon, CNRS, INSERM - Lyon

²FRE 3310, UCBL, Université de Lyon, CNRS – Lyon
Livia [e-mail]- 06.71.24.52.01
Context Cartilage mechanical properties are essential for the proper joints function (dissipation of mechanical stress) and for the nutrition of the tissue (diffusion of molecules through an avascular matrix). These properties are given by the molecular composition, especially by the network of collagen fibers, that provide tensile strength and by the proteoglycans gel, which is responsible for the compression resistance. These molecular components are synthesized by cartilage cells (chondrocytes) thanks to a strong mechanical interaction between cell and extracellular matrix (mechanotransduction). This work aims to study the role of a protein like ß1 integrin, which establish a physical link between the cell and the extracellular matrix. We try to determine if the absence of this β1 integrin alters the biomechanical and physicochemical properties of cartilage.
Methods We studied mouse cartilage isolated from mutant embryos lacking 1 integrins, comparing with mouse cartilage isolated from normal embryos with β1 integrins (wild-WT).

Mechanical properties: the apparent elastic modulus was obtained from rheometric tests after 5 compression / relaxation cycles.

Physico-chemical properties: the diffusion coefficient of water in mutant/ wild cartilage was calculated by fluorescence recovery after photobleaching technique (FRAP).
Results For Itgβ1-lacking cartilage (mutant) the apparent elastic modulus was found 1.6-fold higher than for wild type cartilage (WT). Also a decrease of the diffusion coefficient in the mutant cartilage compared to wild cartilage was observed. This difference is more important at the cellular level (about 14 fold higher for the wild type compared to mutant type) that at the matrix level (about 1.25 fold higher for the wild type compared to mutant type). Therefore, we concluded that the absence of β1-integrin affects the mechanical and physico-chemical properties, by increasing cartilage rigidity and decreasing its permeability. Unexpectedly, no alteration was observed in extracellular matrix composition, neither in proteoglycan deposition, nor in type II collagen network. However, mutant cells showed abnormal rounded shape within the tissue.

Atomic Force Microscopy and micropipette experiments are planned in order to understand if the origins of these differences are due to:

-changes in the mechanical properties of the cell

-cell membrane/cytoskeleton interactions.