Fractional re-distribution among cell motility states during ageing

Ageing in humans is associated with a decreased capacity to regulate cell physiology. Cellular properties, such as cell morphology and cell mechanics, encode ageing information and as a result can be used as robust ageing biomarkers. Using a panel of dermal fibroblasts derived from healthy donors spanning a wide age range, we observe an age-related reduction in average cell motility, which we show is not due to the decreased motility of all cells, but results from fractional re-distribution among motility states. By taking advantage of the single-cell nature of our motility data, we show that cells can be classified based on spatial and activity patterns that define age-dependent motility states. These findings highlight an important feature of ageing cells shown by the decrease in the heterogeneity of cell movement in older adults, that potentially offer new mechanistic insights into the ageing process and avenues for novel biomarker development. ### Competing Interest Statement The authors have declared no competing interest. * MSD6 : Mean-squared displacements at time lag equal to 6 minutes MSD60 : Mean-squared displacement at time lag equal to 60 minutes Pp : Persistence time along the primary axis of migration Pnp : Persistence time along the secondary axis of migration PRW : Persistence random walk APRW : Anisotropic persistence random walk Mean-squared displacement (MSD) : the average displacement of a cell per unit time lag ( dt ), which is a multiple of the time step. The MSD is a common measure of random movements of cells. Autocorrelation function of velocity (ACF) : is a measure of the correlation in cell velocities per unit time lag ( dt ). Higher values of the ACF typically indicate that cells are more persistent in their movement. Angular velocity magnitude : is a measure of the magnitude of average cell velocities evaluated at different orientations after re-alignment along the primary axis of migration. This reveals the degree of anisotropy of cell velocities. If the velocity profile is isotropic (circular), as is typical in cases of persistent random walks, the average magnitude of the velocity is equally likely in all directions. However, if the velocity is anisotropic, as seen for cells from young donors, the average velocity along the primary axis is significantly higher that along other axes of movements. Spatial clusters (Pn) : Motility clusters defined based on the eight motility parameters defined using the APRW model Activity clusters (ACn) : Motility clusters defined by the 1D displacement profiles of single cells that define the temporal motility patterns Shannon entropy (S) : A surrogate measurement of cellular heterogeneity based on the number of states and the abundances of cells within each state SP6 : Average speed computed at a 6-min time lag ![Formula][1] SP60 : Average speed computed at a 60-min time lag ![Formula][2] Dp : Diffusivity along the primary axis of migration (motility coefficient) ![Formula][3] Dnp : Diffusivity along the secondary axis of migration (motility coefficient) ![Formula][4] Dtot : Total diffusivity, equal to the sum of diffusivities along the primary and secondary axes of migration ![Formula][5] Psi (ϕ) : Anisotropy (spatial persistence), equal to the ratio of the diffusivities in the primary and secondary axes of migration ![Formula][6] Trains : length of time steps within the normalized activity profile per cells having a value greater than or equal to one standard deviation above the baseline. Lags : length of time steps within the normalized activity profile per cells having a value less than one standard deviation above the baseline. [1]: /embed/graphic-13.gif [2]: /embed/graphic-14.gif [3]: /embed/graphic-15.gif [4]: /embed/graphic-16.gif [5]: /embed/graphic-17.gif [6]: /embed/graphic-18.gif