Figure 1.

Absence of PEC recruitment in aging mice. (A) Timeline of the experiment. Mice were killed after 1.5, 3, 6, 12, and 18 months as indicated by the arrows (1.5–12 months, n=5; 18 months, n=3). Dox, doxycycline. (B–D) Representative histologic images of X-gal/eosin-stained kidney sections at different time points. At all time points, X-gal staining persisted in PECs (arrowheads). β-Gal–positive cells were rarely observed within the glomerular tuft and almost always localized to the vascular pole (arrows with tails). These cells are transitional cells, which are directly labeled by the PEC-rtTA mouse.¹² Within the tubules, scattered tubular cells were labeled (arrows). (E) Statistical analysis of β-gal–positive cells in 100 glomerular cross-sections of X-gal–stained frozen sections in aging PEC-rtTA/LC1/R26R mice shows no significant changes over time. Glom., glomeruli. (F and G) Periodic acid–Schiff (PAS)-stained kidney of an 18-month-old PEC-rtTA mouse shows (F, arrow) protein casts, (G, arrow) mesangial expansion/sclerosis, and (G, arrowhead) a thickened irregular GBM. (H) Mesangial expansion and sclerosis were confirmed by transmission electron microscopy (arrow). In addition, the GBM was thickened with spikes/humps (arrowheads) and covered by podocytes with filopodial protrusions (open arrow).