Contribution of postnatally formed small beta cell aggregates to functional beta cell mass in adult rat pancreas

Abstract

Aims/hypothesis Neogenesis of beta cells and their clustering to small aggregates is a key process in prenatal development of beta cell mass. We investigated the contribution of postnatally formed small aggregates to functional beta cell mass in adult rats. Methods Conditions were defined for (1) counting total beta cell number in pancreases with relative error of <10% and (2) determining their distribution over aggregates of different size and over functionally different subpopulations. Results Pancreases of 10-week-old male Wistar rats contained 2.8±0.2×10 6 beta cells, of which >90% was generated postnatally, involving: (1) neo-formation of 30,000 aggregates with diameter <50 μm including single cells; and (2) growth of 5,500 aggregates to larger sizes, accounting for 90% of the increase in cell number, with number of growing aggregates in the tail 50% greater than elsewhere. At 10 weeks, 86% of aggregates were <50 μm; compared with aggregates >200 μm, their beta cells exhibited a higher basal insulin content that was also resistant to glibenclamide-induced degranulation. The pool of Ki67-positive beta cells was sixfold larger than at birth and distributed over all aggregate sizes. Conclusions/interpretation We describe a method for in situ counting of beta cell numbers and subpopulations with low relative error. In adult rats, >90% of beta cells and beta cell aggregates are formed after birth. Aggregates <50 μm are more than 100-fold more abundant than aggregates >200 μm, which are selected for isolated islet studies. Their topographic and functional properties contribute to the functional heterogeneity of the beta cell population; their growth to larger aggregates with characteristic beta cell functions may serve future metabolic needs.

Islet Neogenesis: A Possible Pathway for Beta-Cell Replenishment

“…In another study, donor pancreata had little or no Ki67 + insulin-positive cells, but grafts of isolated islets from such donors had 0.22 ± 0.03% Ki67 + insulinpositive cells after 4 week transplantation in immunocompromised normoglycemic mice; this level was also found in frozen human pancreas obtained at surgery [70]. An important concept recently emphasized by Chintinne et al in rodents is that, in the adult, the large β-cell population can provide a significant pool of proliferating β-cells even though the proliferation frequency (% Ki67 + cells) is lower than in neonates [8].…”

“…After extensive counting of total β-cells at day 2-3 and 10 weeks, Chintinne et al concluded that about 30,000 β-cell clusters of less than 50 mm diameter formed during this time in male Wistar rats [8]; this represented a 14-fold increase in the number of small aggregates of insulin-positive cells. Similarly, Peng et al showed that the islet number in mice increased from about 50/pancreas at 1 week to about 900 at 2 months after which it was stable, suggesting that impressive neogenesis occurred after birth, but became undetectable by 2 months [9].…”

Functional characteristics of neonatal rat β cells with distinct markers

“…1C and D). The fraction of all endogenous b cells that could be isolated and studied further in vitro was similar in neonates and 10-week-old rats and amounted to G10% of total b cell number contained in the whole pancreas (Chintinne et al 2010). Electron microscopy indicated a 32% higher crosssectional surface of 10-week-old than neonatal b cells (P!0.005, Supplementary Table 1, see section on supplementary data given at the end of this article).…”

Pancreatic hyperplasia after gastric bypass surgery in a GK rat model of non-obese type 2 diabetes

“…In relation to total sections, 1.9% to 2.5% of each pancreas was analyzed. A minimal sample size equal to 1.22% of the total is sufficient to achieve measurement error !10% (Chintinne et al 2010). Sections were examined using a confocal microscope (A1; Nikon, Tokyo, Japan) connected to a computer with NIS elements software (Nikon).…”