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The effect of ageing on β-cell regeneration under hyperglycemia has not been defined and may best be addressed using a unique islet-transplantation model.Streptozotocin-induced diabetic FVB/NJ mice were rendered normoglycemic with a therapeutic mass of syngeneic islets implanted in the epididymal fat pad, followed by a subrenal capsular implantation of a subtherapeutic mass of 25 islets from young (3 months) or old (24 months) mice. Three weeks after the second transplant, the islet containing fat pad was removed to reintroduce hyperglycemia. Bromodeoxyuridine (BrdU) was provided to mice continuously in drinking water. Islet grafts under the kidney capsule were harvested at different time points and examined for markers of β-cell regeneration by immunohistochemistry.After a 7-day labeling, BrdU was detected in 54.2% or 53.0% β cells of the young or old islet grafts, respectively, under hyperglycemia when compared with 3.3% in grafts under normoglycemia. Ki67-positive β cells were enhanced from a baseline level of 0.5% to 5.2% (young islets) or 4.0% (old islets) on day 7 of hyperglycemia, then decreased to 2.4% on day 21, at which time point an accumulative 75.3% or 66.8% BrdU-positive β cells was detected in the young or old grafts, respectively. No statistic difference in the percent BrdU- or Ki67-positive β cells was detected between the young and aged grafts at any time point studied.These data reveal that islet β cells from aged mice can replicate in response to hyperglycemia after transplantation at a capacity and frequencies not significantly different than that of the young adult ones.