Optimal Dynamics for Quality Control in Spatially Distributed Mitochondrial Networks
Figure 9
Maintenance of mitochondrial health requires a discrete health parameter.
(A) The average steady-state health of the mitochondrial population can be maintained above the autophagy threshold when the number of HUs per mitochondrion is small, but falls off rapidly to zero due to loss of mitochondria via autophagy as the total number of HUs increases toward a continuum health variable. When the rate of fusion is nonzero, cells can tolerate less discreteness in the health parameter (more HUs) due to the additional stochasticity introduced by fission and by sequestering mitochondria from autophagy while fused. (B) Histograms of the healths of mitochondria in simulations conducted with different maximum HU values and fusion rates (points labeled in (A)) show that the overall health depends on the distribution of mitochondria and this overall distribution is similar for a given average steady-state health as long as the fusion rate is nonzero.