Adaptive beta-cell proliferation is severely restricted with advanced age

Abstract

Objective: Regeneration of the insulin-secreting beta-cells is a fundamental research goal that could benefit patients with either type 1 or type 2 diabetes. beta-Cell proliferation can be acutely stimulated by a variety of stimuli in young rodents. However, it is unknown whether this adaptive beta-cell regeneration capacity is retained into old age.

Research design and methods: We assessed adaptive beta-cell proliferation capacity in adult mice across a wide range of ages with a variety of stimuli: partial pancreatectomy, low-dose administration of the beta-cell toxin streptozotocin, and exendin-4, a glucagon-like peptide 1 (GLP-1) agonist. beta-Cell proliferation was measured by administration of 5-bromo-2'-deoxyuridine (BrdU) in the drinking water.

Results: Basal beta-cell proliferation was severely decreased with advanced age. Partial pancreatectomy greatly stimulated beta-cell proliferation in young mice but failed to increase beta-cell replication in old mice. Streptozotocin stimulated beta-cell replication in young mice but had little effect in old mice. Moreover, administration of GLP-1 agonist exendin-4 stimulated beta-cell proliferation in young but not in old mice. Surprisingly, adaptive beta-cell proliferation capacity was minimal after 12 months of age, which is early middle age for the adult mouse life span.

Conclusions: Adaptive beta-cell proliferation is severely restricted with advanced age in mice, whether stimulated by partial pancreatectomy, low-dose streptozotocin, or exendin-4. Thus, beta-cells in middle-aged mice appear to be largely postmitotic. Young rodents may not faithfully model the regenerative capacity of beta-cells in mature adult mice.

FIG. 1.

Partial pancreatectomy (PP)–induced β-cell replication in mice at 2, 8, 12, 14, and 19 months of age. BrdU was administered for 2 weeks after the procedure before the mice were killed. Representative pancreatic β-cell histology of pancreas sections immunostained with antibodies against insulin (red) and BrdU (green) and counterstained with DAPI (blue) and photographed with a 40× objective. White arrows indicate insulin and BrdU copositive cells; yellow arrows denote BrdU-labeled non–insulin-containing cells within the islet. Scale bars: 100 μm in full image and 20 μm within inset. (A high-quality digital representation of this figure is available in the online issue.)

FIG. 2.

Low-dose streptozotocin (Stz) and exendin-4 induced β-cell replication in mice at 2 and 14–15 months of age. BrdU was administered for 2 weeks before the mice were killed. A: Low-dose streptozotocin. B: Exendin-4. Representative pancreatic β-cell histology of pancreas sections immunostained with antibodies against insulin (red) and BrdU (green) and counterstained with DAPI (blue) and photographed with a 40× objective. White arrows indicate insulin and BrdU copositive cells; yellow arrows denote BrdU-labeled non–insulin-containing cells within the islet. Scale bars: 100 μm in full image and 20 μm within inset. (A high-quality digital representation of this figure is available in the online issue.)

FIG. 3.

Quantitative analysis of β-cell regeneration following partial pancreatectomy, low-dose streptozotocin, or exendin-4 as a function of age in mice. Results are expressed as BrdU-positive β-cells (% total per day) and represent means ± SEM (n = 4–6 animals per group). *P < 0.05; **P < 0.01; ***P < 0.001 sham vs. partial pancreatectomy at various ages. P <0.05 shams at 2 months vs. shams at 12 months, 14 months, or 19 months.

FIG. 4.

Taconic cohort. Partial pancreatectomy (PP) induced β-cell replication in mice at 2 and 19 months of age. BrdU was administered for 2 weeks after the procedure before the mice were killed. A: Representative pancreatic β-cell histology of pancreas sections immunostained with antibodies against insulin (red) and BrdU (green) and counterstained with DAPI (blue) and photographed with a 40× objective. White arrows indicate insulin and BrdU copositive cells; yellow arrows denote BrdU-labeled non–insulin-containing cells within the islet. Scale bars: 100 μm in full image and 20 μm within inset. B: Quantitative analysis of β-cell regeneration following partial pancreatectomy as a function of age in mice. Results are expressed as percent BrdU-positive β-cells per day and represent means ± SEM (n = 4–6 animals per group). **P < 0.01 sham vs. partial pancreatectomy at 2 months. P <0.05 shams at 2 months vs. shams at 19 months. (A high-quality digital representation of this figure is available in the online issue.)

FIG. 5.

Low-dose-BrdU is not toxic to proliferating β-cells. BrdU was continuously administered in the drinking water for 2 weeks to a cohort of mice aged 1 month that were then compared with untreated control mice. A: Representative pancreatic β-cell histology of pancreas sections immunostained with antibodies against insulin (yellow), Ki67 (red), and BrdU (green) and counterstained with DAPI (blue) and photographed with a 40× objective. White arrows indicate insulin and BrdU copositive cells; red arrows denote insulin and Ki67 copositive cells. Scale bars: 100 μm in full image and 20 μm within inset. B: Quantitative analysis of β-cell proliferation as measured by Ki67 incorporation. Continuous BrdU treatment does not slow β-cell proliferation. Results are expressed as percent Ki67-positive β-cells and represent means ± SEM (n = 5 animals per group). (A high-quality digital representation of this figure is available in the online issue.)