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Abstract
In diabetes research, bioluminescence imaging (BLI) has been applied in studies of β-cell impairment, development, and islet transplantation. To develop a mouse model that enables noninvasive imaging of β cells, we generated a bacterial artificial chromosome (BAC) transgenic mouse in which a mouse 200-kbp genomic fragment comprising the insulin I gene drives luciferase expression (Ins1-luc BAC transgenic mouse). BLI of mice was performed using the IVIS Spectrum system after intraperitoneal injection of luciferin, and the bioluminescence signal from the pancreatic region analyzed. When compared with MIP-Luc-VU mice [FVB/N-Tg(Ins1-luc)VUPwrs/J] expressing luciferase under the control of the 9.2-kbp mouse insulin I promoter (MIP), the bioluminescence emission from Ins1-luc BAC transgenic mice was enhanced approximately 4-fold. Streptozotocin-treated Ins1-luc BAC transgenic mice developed severe diabetes concomitant with a sharp decline in the BLI signal intensity in the pancreas. Conversely, mice fed a high-fat diet for 8 weeks showed an increase in the signal, reflecting a decrease or increase in the β-cell mass. Although the bioluminescence intensity of the islets correlated well with the number of isolated islets in vitro, the intensity obtained from a living mouse in vivo did not necessarily reflect an absolute quantification of the β-cell mass under pathological conditions. On the other hand, adenovirus-mediated gene transduction of β-cell-related transcription factors in Ins1-luc BAC transgenic mice generated luminescence from the hepatic region for more than 1 week. These results demonstrate that BLI in Ins1-luc BAC transgenic mice provides a noninvasive method of imaging islet β cells and extrapancreatic activity of the insulin gene in the liver under normal and pathological conditions.
Highlights
In type I diabetes, autoimmune reaction to b cells leads to destruction of insulin-producing cells, and in type II diabetes, cumulative cell damage evoked by various stresses induces b-cell dysfunction, eventually resulting in insufficient insulin supply and a reduction in b-cell mass [1,2]
On bioluminescence imaging (BLI) screening of the 8 F0 transgenic mice, 4 mice did not emit any BLI signal, 2 mice exhibited an ectopic bioluminescence signal, and the remaining 2 mice exhibited considerable signal intensities emanating from the pancreatic region
Luciferase activity was detected in the pancreatic extracts (3.562.46104 relative light units (RLU)/mg protein; n = 3), but not in the other tissue extracts including those from the thymus and pituitary glands, indicating that the reporter gene was expressed only in the pancreas (Figure 1C)
Summary
In type I diabetes, autoimmune reaction to b cells leads to destruction of insulin-producing cells, and in type II diabetes, cumulative cell damage evoked by various stresses induces b-cell dysfunction, eventually resulting in insufficient insulin supply and a reduction in b-cell mass [1,2]. Various modalities such as positron emission tomography (PET), single photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI) have been shown to be useful means for quantification of native and transplanted b-cell mass [4]. In contrast to other modalities, bioluminescence imaging (BLI) provides quantifiable data with high throughput and inherently low background; it is difficult to use current BLI technology for in situ quantification of human b cells because the light emission quickly diminishes as it propagates through tissues [5]. An increasing number of studies have proposed successful quantification of b-cell mass using. BLI has been applied in animal studies on b-cell development, islet transplantation, and b-cell function [4,8,9,10,11]
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