Postnatal development of numbers and mean sizes of pancreatic islets and beta-cells in healthy mice and GIPR(dn) transgenic diabetic mice

Abstract

The aim of this study was to examine postnatal islet and beta-cell expansion in healthy female control mice and its disturbances in diabetic GIPR(dn) transgenic mice, which exhibit an early reduction of beta-cell mass. Pancreata of female control and GIPR(dn) transgenic mice, aged 10, 45, 90 and 180 days were examined, using state-of-the-art quantitative-stereological methods. Total islet and beta-cell volumes, as well as their absolute numbers increased significantly until 90 days in control mice, and remained stable thereafter. The mean islet volumes of controls also increased slightly but significantly between 10 and 45 days of age, and then remained stable until 180 days. The total volume of isolated beta-cells, an indicator of islet neogenesis, and the number of proliferating (BrdU-positive) islet cells were highest in 10-day-old controls and declined significantly between 10 and 45 days. In GIPR(dn) transgenic mice, the numbers of islets and beta-cells were significantly reduced from 10 days of age onwards vs. controls, and no postnatal expansion of total islet and beta-cell volumes occurred due to a reduction in islet neogenesis whereas early islet-cell proliferation and apoptosis were unchanged as compared to control mice. Insulin secretion in response to pharmacological doses of GIP was preserved in GIPR(dn) transgenic mice, and serum insulin to pancreatic insulin content in response to GLP-1 and arginine was significantly higher in GIPR(dn) transgenic mice vs. controls. We could show that the increase in islet number is mainly responsible for expansion of islet and beta-cell mass in healthy control mice. GIPR(dn) transgenic mice show a disturbed expansion of the endocrine pancreas, due to perturbed islet neogenesis.

Figure 1. Representative islet profiles, sampling of sections, counting Q⁻ islets.

Example of an islet profile of a control (A) and a GIPR^dn transgenic mouse (B) immunohistochemically stained for insulin; (C) Sampling scheme for drawing primary and reference sections; (D) Primary section and (E) reference section for counting Q⁻ islets, one Q⁻ may be counted in the example (arrow in E).

Figure 2. Quantitative-stereological investigations of the endocrine pancreas.

(A) Total islet volume (V_(Islets,Pan), (B) total beta-cell volume (V_{(B-cells,Islets)}, (C) Number of islets (N_{(Islets, Pan)}, (D) mean islet volume (v_(islets), (E) beta-cell number (N_{(B-cells,Islets)}, (F) mean beta-cell volume (v_(B-cells). Open bars: female control mice; filled bars: female GIPR^dn transgenic mice; Data represent means and SEM. * p<0.05 vs. age-matched control; +p<0.05 vs. previous time point.

Figure 3. Islet-cell replication, isolated beta-cells, and islet-cell apoptosis.

(A) number of BrdU positive islet cells per 10⁵ cells (N_(BrdU)), (B) total volume of isolated beta-cells (V_(Neo,Pan), (C) number of apoptotic islet cells per 10⁵ cells (N_(Apoptosis)). Open bars: female control mice; filled bars: female GIPR^dn transgenic mice; Data represent means and SEM. * p<0.05 vs. age-matched control; +p<0.05 vs. previous time point.

Figure 4. In vivo investigations.

(A) Randomly fed (10 days) and fasting blood glucose (45-180 days), and (B) randomly fed (10 days) and postprandial serum insulin levels (45–90 days), (C) insulin tolerance test, (D), and area under glucose curve (AUC) during insulin tolerance test shown in C; co, control; tg, GIPR^dn transgenic; Data represent means and SEM, * p<0.05 vs. age-matched control.

Figure 5. In vivo insulin secretion studies at 10 days of age.

(A) Blood glucose, (B) serum insulin levels, (C) increase of serum insulin levels from basal levels (fold insulin secretion), (D) serum insulin to pancreatic insulin ratio; Open bars: control mice; filled bars: GIPR^dn transgenic mice; Data represent means and SEM. * p<0.05 vs. age-matched control; + p<0.05 vs. basal values.