Nano- and microscale mechanical properties of erythrocytes in hereditary spherocytosis.

Hereditary spherocytosis (HS), an erythrocyte membranopathy, is a heterogeneous disease, even at the level of the erythrocyte population. The paper aims at studying the mechanical properties (the Young's modulus, median and RMS roughness of friction force maps; fractal dimension, lacunarity and spatial distribution parameters of lateral force maps) of the cell surface layer of the erythrocytes of two different morphologies (discocytes and spherocytes) in HS using atomic force microscopy. The results of spatial-spectral and fractal analysis showed that the mechanical property maps of the HS spherocyte surface were more structurally homogeneous compared to the maps of HS discocytes. HS spherocytes also had a reduced RMS roughness and lacunarity of the mechanical property maps. The Young's modulus and averaged friction forces over the microscale HS spherocyte surface regions were approximately 20% higher than that of HS discocytes. The revealed significant difference at the nano- and microscales in the structural and mechanical properties of main (discoidal and spheroidal) morphological types of HS erythrocytes can potentially cause blood flow disturbance in the vascular system in HS.

Thermo-mechanical properties of the cell surface assessed by atomic force microscopy.

Atomic force microscopy (AFM) in lateral force mode was applied to assess the microscale thermo-mechanical (frictional) properties of the air-dried cell surface in the wide temperature range (288-363K/15-90°C). AFM-investigated cell surface layer can be represented as a biocomposite composed of several layers including the glycocalyx, the membrane and the intercellular layer containing membrane (cortical) cytoskeleton. The cells with two different cytoskeleton structures, erythrocytes and thymocytes, were studied. Above a certain temperature (T(g)), the significant change in friction force with temperature was revealed for the both cell types whereas there was no similar change in their topography parameters. The experimentally determined value T(g) for erythrocyte samples was lower than that for thymocyte ones. Treating living cells with the cross-linking agent, glutaraldehyde, led to the weakening of the temperature dependence of air-dried cell surface frictional properties in the studied temperature range. Addition of oxidizing agent, peroxynitrite, to living cell suspensions changed the temperature dependence of air-dried cell surface frictional properties depending on cell type and peroxynitrite concentration. The obtained data indicate that the study of thermo-mechanical properties of air-dried cells with AFM in lateral force mode provides expanded information on the structural characteristics of the living cell surface layer, and sets the stage for the development of AFM-based method (with using a lateral force mode) for the cell pathology diagnostics.