Abstract
Aims/hypothesisDynamic processes in pancreatic tissue are difficult to study. We aimed to develop an intravital imaging method to longitudinally examine engraftment, vascularisation, expansion and differentiation in mature islets or embryonic pancreases transplanted under the kidney capsule.MethodsIsolated pancreatic islets from adult mice and murine embryonic day (E)12.5 pancreases containing fluorescent biomarkers were transplanted under the kidney capsule of immunodeficient recipient mice. Human islet cells were dispersed, transduced with a lentivirus expressing a fluorescent label and reaggregated before transplantation. Graft-containing kidneys were positioned subcutaneously and an imaging window was fitted into the skin on top of the kidney. Intravital imaging using multiphoton microscopy was performed for up to 2 weeks. Volumes of fluorescently labelled cells were determined as a measure of development and survival.ResultsTransplanted islets and embryonic pancreases showed good engraftment and remained viable. Engraftment and vascularisation could be longitudinally examined in murine and human islet cells. Murine islet beta cell volume was unchanged over time. Transplanted embryonic pancreases increased to up to 6.1 times of their original volume and beta cell volume increased 90 times during 2 weeks.Conclusions/interpretationThis method allows for repeated intravital imaging of grafts containing various sources of pancreatic tissue transplanted under the kidney capsule. Using fluorescent markers, dynamic information concerning engraftment or differentiation can be visualised and measured.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-016-4049-6) contains peer-reviewed but unedited supplementary material, which is available to authorised users.
Highlights
Islet cell development, dynamic processes involved in islet engraftment and changes in islet composition are difficult processes to study in vivo
Mature pancreatic islets and intact E12.5 embryonic pancreases were isolated from mouse insulin promoter–enhanced green fluorescent protein (MIP-EGFP) (Jackson Laboratory, Bar Harbor, ME, USA, stock no. 006864) and cytomegalovirus– actin–globin promoter red fluorescent protein (CAG-DsRed) (Jackson Laboratory, stock no. 005441) mice
Transplanted islets function normally in mice fitted with an abdominal imaging window Mice recovered quickly after surgery and were fully active after 1 h
Summary
Dynamic processes involved in islet engraftment and changes in islet composition are difficult processes to study in vivo. To obtain longitudinal information in combination with functional data, new imaging methods are required that allow sequential measurements in individual animals. Transplantation of pancreatic islets under the kidney capsule is considered the gold standard for the in vivo evaluation of graft insulin secretory capacity and survival in mice [1]. Isolated islets derived from humans and different animal species can be used for transplantation at this site [2]. There is good vascularisation of the transplanted islets, allowing the rapid release and action of insulin. Nephrectomy of the graftcontaining kidney followed by determination of blood glucose values validates graft function [3]. By transplanting a cell pellet that remains compact after transplantation, grafts can be retrieved and histologically analysed
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