Fig. 3.

SR model provides an explanation for the change in senescent cell levels after parabiosis. a The SR model, parameterized according to Karin et al. [25], was simulated before and after parabiosis, using Eq. 3. After isochronic parabiosis, there is a slight decrease in senescent cells in both young (YY, dashed green line) and old (OO, solid green line) parabionts, compared with baseline (dashed gray line). On the other hand, there is a large decrease in senescent cells in old heterochronic parabionts (OY, solid purple line), and a slight increase in the young heterochronic parabionts (YO, dashed purple line). The changes occur on the timescale of a few weeks due to senescent cell turnover. b After 2 months of parabiosis, there is a clear order of senescent cell abundance YY < YO < OY < OO, similar to the effect shown in Fig. 2. Model parameters are provided in the “Materials and methods” section