LEW.1WR1 Rats Have Decreased Normalized Beta Cell Area

Abstract

Obesity in humans can lead to metabolic problems such as glucose intolerance and insulin resistance, which may result from pancreatic islet dysregulation and reduced insulin sensitivity in the liver. Increased fat10 expression is associated with adiposity, insulin resistance, and inflammation that increases with age as well as type 1 diabetes. The effect of increased fat10 expression on beta cell physiology, however, is not well understood. LEW.1WR1 (1WR1) rats possess a defect in the fat10 promoter which leads to sustained expression of diubiquitin. We suggested previously that fat10 may play a role in increased glucose intolerance, insulin sensitivity, age‐related fat deposition, and changes in beta cell size and density in 1WR1 rats. In that study, we identified through semiquantitative analysis that the 1WR1 rats seemed to have fewer islets compared to the LEW/SsNHsd (SsNHsd) rats. The purpose of this project was to compare normalized beta cell area from these rodents and analyze this data to confirm that the perceived changes in islet number corresponded to differences in beta cell area. We hypothesized that, since the 1WR1 rats had a lower islet number, they would also have lower normalized beta cell area, dysregulated insulin signaling, and an altered cell cycle. Seven week old 1WR1 and SsNHsd rats were given a control diet for 12 weeks. Once the animals were sacrificed, the pancreases were harvested, fixed in formalin, and sent to Histowiz (New York, NY) for immunohistochemical staining against insulin. These stained slides were obtained digitally and opened in ImageJ, which was used to measure beta cell and pancreas area. Comparing these showed that the 1WR1 rats indeed have a lower average normalized beta cell area than SsNHsd rats on a moderate sucrose diet. Using qRT‐PCR, we determined the islets of 1WR1 rats had 3 fold increased insulin and glucagon gene expression. Yet, the β‐cell area (22.05+/‐6.408 vs. 2.276 +/‐1.284mm2; p=0.0016; n=3,4) was significantly reduced in 1WR1 rats. Islet Plin5 expression was upregulated in 1WR1 rats (5.388+/‐0.3806 F.C.; p<0.0001; n=3,3) indicating increased lipid droplet production, while Cyclin D (0.5726+/‐0.08797 F.C.; p=0.0035; n=3,2) was downregulated indicating decreased cell cycle proliferation. These results indicate that the islets of the 1WR1 rats were insensitive to insulin signaling, which may have been caused by increased lipid droplets and a decrease in compensatory islet area. This experiment increases our understanding of the characteristics of the pancreas of LEW.1WR1 rats, which may help us better understand the impact of unregulated fat10 expression on beta cell physiology.