[Show abstract][Hide abstract] ABSTRACT: β-Cells that express an imaging reporter have provided powerful tools for studying β-cell development, islet transplantation, and β-cell autoimmunity. To further expedite diabetes research, we generated transgenic C57BL/6 "MIP-TF" mice that have a mouse insulin promoter (MIP) driving the expression of a trifusion (TF) protein of three imaging reporters (luciferase/enhanced green fluorescent protein/HSV1-sr39 thymidine kinase) in their β-cells. This should enable the noninvasive imaging of β-cells by charge-coupled device (CCD) and micro-positron emission tomography (PET), as well as the identification of β-cells at the cellular level by fluorescent microscopy.
MIP-TF mouse β-cells were multimodality imaged in models of type 1 and type 2 diabetes.
MIP-TF mouse β-cells were readily identified in pancreatic tissue sections using fluorescent microscopy. We show that MIP-TF β-cells can be noninvasively imaged using microPET. There was a correlation between CCD and microPET signals from the pancreas region of individual mice. After low-dose streptozotocin administration to induce type 1 diabetes, we observed a progressive reduction in bioluminescence from the pancreas region before the appearance of hyperglycemia. Although there have been reports of hyperglycemia inducing proinsulin expression in extrapancreatic tissues, we did not observe bioluminescent signals from extrapancreatic tissues of diabetic MIP-TF mice. Because MIP-TF mouse β-cells express a viral thymidine kinase, ganciclovir treatment induced hyperglycemia, providing a new experimental model of type 1 diabetes. Mice fed a high-fat diet to model early type 2 diabetes displayed a progressive increase in their pancreatic bioluminescent signals, which were positively correlated with area under the curve-intraperitoneal glucose tolerance test (AUC-IPGTT).
MIP-TF mice provide a new tool for monitoring β-cells from the single cell level to noninvasive assessments of β-cells in models of type 1 diabetes and type 2 diabetes.
[Show abstract][Hide abstract] ABSTRACT: Islet transplantation offers a potential therapy to restore glucose homeostasis in type 1 diabetes patients. However, islet transplantation is not routinely successful because most islet recipients gradually lose graft function. Furthermore, serological markers of islet function are insensitive to islet loss until the latter stages of islet graft rejection. A noninvasive method of monitoring islet grafts would aid in the assessment of islet graft survival and the evaluation of interventions designed to prolong graft survival. Here, we show that recombinant adenovirus can engineer isolated islets to express a positron-emission tomography (PET) reporter gene and that these islets can be repeatedly imaged by using microPET after transplantation into mice. The magnitude of signal from engineered islets implanted into the axillary cavity was directly related to the implanted islet mass. PET signals attenuated over the following weeks because of the transient nature of adenovirus-mediated gene expression. Because the liver is the preferred site for islet implantation in humans, we also tested whether islets could be imaged after transfusion into the mouse liver. Control studies revealed that both intrahepatic islet transplantation and hyperglycemia altered the biodistribution kinetics of the PET probe systemically. Although transplanted islets were dispersed throughout the liver, clear signals from the liver region of mice receiving PET reporter-expressing islets were detectable for several weeks. Viral transduction, PET reporter expression, and repeated microPET imaging had no apparent deleterious effects on islet function after implantation. These studies lay a foundation for noninvasive quantitative assessments of islet graft survival using PET.
Full-text · Article · Aug 2006 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Islet transplantation offers a potential therapy to restore glucose homeostasis in type 1 diabetes patients. A method to image transplanted islets noninvasively and repeatedly would greatly assist studies of islet transplantation. Using recombinant adenovirus, we show that isolated rodent and human islets can be genetically engineered to express luciferase and then imaged after implantation into NOD-scid mice using a cooled charge-coupled device. The magnitude of the signal was dependent on the islet dose. Adenovirus-directed luciferase expression, however, rapidly attenuated. We next tested lentivirus vectors that should direct the long-term expression of reporter genes in transduced islets. Transplanted lentivirus-transduced islets restored euglycemia long term in streptozotocin-treated NOD-scid mice. The signal from implanted lentivirus-transduced islets was related directly to the implanted islet mass, and the signal did not attenuate over the observation period. Viral transduction, luciferase expression, and repeated imaging had no apparent long-term deleterious effects on islet function after implantation. These data demonstrate that the introduction of reporter genes into an isolated tissue allows the long-term monitoring of its survival following implantation. Such imaging technologies may allow earlier detection of graft rejection and the adjustment of therapies to prolong graft survival posttransplantation.