Structural, morphological and nanomechanical characterisation of intermediate states in the ageing of erythrocytes.

The study of the mechanical properties of biosystems and the relationship with their biochemical and structural functionality is an increasingly interesting subject of investigation. In recent years, in particular, the use of the atomic force microscopy provides the tools for understanding the molecular basis of the mechanical behaviour of the biosystems. The ageing of erythrocytes [red blood cells (RBCs)] constitutes a particularly interesting subject of study because of its fundamental role in triggering the cell turnover by promoting the removal of malfunctioning RBCs when specific ageing markers appear on their surface. Moreover, it is also interesting to study the role that the variation in the cells mechanical properties plays in the progress of the phenomenon. In this study, the ageing of RBCs, accelerated by depleting the cells of their ATP, has been investigated by two methods. The first is a recently developed nondestructive approach that correlates the roughness of the plasma membrane to the mechanical characteristics and the structural integrity of the cell membrane-skeleton. The second consists in directly measuring the nanomechanical properties by acquiring and analysing force curves on the cell membrane. The application of the two methods allowed to define, for the first time, the general scheme of alterations the cells experience during the ageing. In particular, a progressive decrease of the membrane roughness, correlated to a weakening of the membrane-skeleton support, and a complex pattern of changes in the nanomechanical properties, which drives the morphological variation and the occurrence of the specific ageing markers on the cells, have been revealed.