106 ADAPTIVE β-CELL EXPANSION IN PREGNANT MICE WITHOUT FETUSES

Abstract

Diabetes, an increasingly prevalent metabolic disorder, which is estimated to affect over 300 million people by 2025 (Zimmet et al. 2001 Nature), commonly results from β-cell function failure. In normal physiological conditions, β-cell turnover occurs slowly throughout the lifetime of the adult mammal. During pregnancy, β cells could increase their replication rate through reducing menin expression and then cause islets hyperplasia to match the physiological demands (Karnik et al. 2007 Science). However, whether the fetuses have an influence on the β-cell replication and islets hyperplasia during pregnancy is still unknown. The objective of the present study was to test whether pregnancy without fetuses could also decrease the expression of menin, and then cause an increase in the β-cell replication rate and islets hyperplasia. First, we generated pregnant mice with tetraploid blastocysts (PT mice), which can implant and generate placentas similar to the normal diploid blastocysts, but cannot develop into fetuses. Pancreases from at least 3 mice per group were embedded in optimum cutting temperature compound (OCT) and sectioned at 8-μm intervals. The sections were stained with hematoxylin and eosin (HE), and then the morphological structures of islets were observed under a microscope. The results showed that the islets mass of PT mice had obvious hyperplasia compared with wild-type controls (WT). Second, we isolated the islets of PT mice, and analysed the Men1, p18, and p27 gene expression in PT mice islets using RT-PCR. We found that the expression of Men1, p27, and p18 in PT mice islets was significantly lower compared with WT controls (P < 0.05). Finally, insulin immunofluorescence was performed to evaluate the insulin expression level of β cells in the islets both from PT mice and the WT group. The evaluation of total fluorescence intensity in islets was performed. The average value from the control group islets was set to 1 and used for comparison to the fluorescence intensity of PT mice islets. The results showed that there was no significant difference between PT mice and WT groups at the insulin level of β cells. Taken together, these results demonstrate that under the conditions of pregnancy without fetuses, maternal pancreatic islets can also cause islets mass hyperplasia through reducing menin expression, but not increase the insulin level per β cell to match the dynamic physiological demands. Therefore, it's possible to treat type-2 diabetes by imitating the pregnant physiological condition without fetuses.

This work was supported by grants from the National Natural Science Foundation (No. 31271591) and the National Basic Research Program (No. 2009CB941001 and No. 2011CBA01003) in China.