Non-Invasive Bioluminescence Imaging of β-Cell Function in Obese-Hyperglycemic [ob/ob] Mice

Abstract

BackgroundType 2 diabetes results from failure of the β-cells to compensate for increased insulin demand due to abnormal levels of metabolic factors. The ob/ob(lep-/-) mouse has been extensively studied as an animal model of type 2 diabetes. Previous studies have shown a correlation between β-cell function and bioluminescent imaging in lean genetically engineered mice. The ability to noninvasively monitor β-cell function in ob/ob mice could provide new information on β-cell regulation in type 2 diabetes.MethodsTo create the B6 Albino ob/ob MIP-luc mice (ob/ob-luc), the ob/ob mouse was crossed with the CD1 MIP-luc mouse. All mice were backcrossed over multiple generations to ensure the genetic background of the transgenic mice was over 96% similar to the background of the original ob/ob mouse. Animal weight, blood glucose levels, insulin in plasma, and in vivo bioluminescence (BLI) were monitored weekly or biweekly for up to 70 weeks of age. BL imaging was performed using IVIS Spectrum (Perkin Elmer) and calculated by integrating the bioluminescence signal between 5 and 10 min after i.v. injection of D-luciferin. Insulin immunohistochemistry determined islet beta cell count and insulin secretion assay determined islet insulin function.ResultsThere were significant increases in BLI and insulin levels as the ob/ob-luc mice aged while glucose levels gradually decreased. Ob/ob-luc were sacrificed at different time points to determine ex vivo BLI, islet function and total β-cell numbers using a cell counting training algorithm developed for the Vectra image analysis system (Perkin Elmer). The number of β-cells increased as the mice aged and all three ex vivo measurements correlated with BLI.ConclusionsThe ob/ob-luc mice can serve as a model of metabolic stress, similar to human type 2 diabetes using BLI as a surrogate marker for β-cell function.

Intra-islet lesions and lobular variations in β-cell mass expansion in ob/ob mice revealed by 3D imaging of intact pancreas

“…The reason for this discrepancy is unclear. Whereas a normalization of the blood glucose levels have been observed in ob / ob mice between 30–50 weeks of age 7 26 27 our data (of unfasted animals) display a more fluctuating pattern, which is in agreement with previous observations in our and other ob / ob colonies. I.e., blood glucose values can vary considerably between individual ob / ob mice in the unfasted state 7 26 28 29 (see Fig.…”

“…Previous studies have reported a decline in ob / ob BCV between around 30–48 and 50–56 weeks of age 7 25 . In contrast, our quantitative OPT data and the immunohistochemical analyses of β-cell proliferation indicate that the BCV in ob / ob mice is still expanding at the endpoint of our investigation, i.e.…”

“…Differences in the methodologies utilized (stereology and/or ex viv o bioluminescence versus OPT) may further contribute to this discrepancy. Since previous studies assessing BCM dynamics in the ob / ob mice 7 25 did not report the formation of cystic lesions, it is unclear how this circumstance may have affected BCM quantitations in these studies. Notwithstanding the seemingly high variation in blood glucose levels at later stages, our data raises the possibility that physiological factors other than an increased demand for insulin 30 31 may contribute to BCV expansion in the ob / ob mouse.…”

“…One of the most comprehensive stereological assessments of BCM in the ob / ob mice determined that BCM expansion was primarily due to expansion of already existing islets 6 . Another study, using bioluminescence imaging (BLI) to monitor BCM in ob / ob mice in vivo , also incorporated an extensive stereological β-cell quantification of the model 7 . Although these and other studies provided important information on the BCM dynamics of ob / ob mice, they depend on the extrapolation of two-dimensional data (as do all stereological approaches) or, as in the case of BLI, provide only diminutive spatial information.…”

A Deeper Look into Type 1 Diabetes – Imaging Immune Responses during Onset of Disease

“…However, luciferase needs to be transgenically expressed in these cells, and a secondary imaging modality (e.g., visible light camera, X-ray CT, MRI) is required for anatomical information. Bioluminescence has been utilized in the field of diabetes research by inserting the gene encoding luciferase under control by the mouse insulin promoter (MIP) ( 5 ) enabling non-invasive longitudinal quantification of beta cell mass in the mouse ( 6 ). Similarly, bioluminescence imaging can also be used for more detailed functional assessment of beta cell biology, for example, the technique has been used in pancreatic islet transplantation research, for assessing the level of hypoxia in the engraftment process by expressing luciferase under the control of hypoxia response elements ( 7 ).…”