Dynamic Modelling of Pathways to Cellular Senescence Reveals Strategies for Targeted Interventions
Figure 6
Mitochondrial dysfunction is driven by decreased mitochondrial dynamics.
(A) Sensitivity analysis averaged along the time course for the mitochondrial species in the model by varying the mitochondrial-related kinetic rate constant parameters. Mitochondrial biogenesis was determined by mTORC1 signalling (k33) but not by AMPK (k34). Clearance of old mitochondria (k36) was not as effective as for new mitochondria (k35). This reduced mitochondrial quality control for the old mitochondrial population implicated an increased and sustained global mitochondrial dysfunction. Scale bar represents the normalised positive or negative sensitivity of each species to each rate constant. (B) In silico time courses over 21 days post-irradiation for the two states of mitochondrial mass (new and old) were computed by separately perturbing the previous kinetic rates by different factors f (f = 1 is the control). These perturbations affected the new mitochondria only at early time points (<10 days), whereas the old mitochondria were affected throughout the time course. Consistent with panel A, the perturbation of the parameters k34 and k36 (dotted lines) did not alter the mitochondrial mass readouts and are therefore overlapped. (C) Representative live cell images of mitochondrial networks in young (control) and senescent (sen) MRC5 fibroblasts. Mitochondrial networks were detected in deconvolved 3D confocal images using mitochondrially targeted fluorescent protein. Individual parts of the cell mitochondrial population are identified using colour coding. Whole frame images are shown in the upper panel, and the boxes highlight the areas (18.2 µm2) analysed for fusion and fission events over 30 minutes. Example images from these areas over 140 s are shown below with the detected fusion and fission events highlighted with white and yellow arrows respectively. A timelapse movie containing the full dataset from a control and senescent cell are available in Movie S1. (D) Quantification of observed fusion and fission events in 18.2 µm2 areas from control and senescent cells. Events were recorded every 20 s over 30 minutes for each cell and expressed per minute and relative to the mitochondrial mass in the area observed. Significant decreases were seen for both fusion and fission in senescent cells (Mann-Whitney, p<0.001, n = 6 cells per sample with between 90–180 events recorded).
