Type I Diabetes is an increasingly common autoimmune condition, with over 100,000 cases in Australia. Even with effective insulin replacement therapy, there are still major side-effects of hyperglycaemia including renal failure, nerve dysfunction, blindness and cardiovascular disease. In addition, loss of awareness of hypoglycemic episodes presents a real threat of sudden death in a subset of diabetic patients. Transplantation of islets offers the promise of a return to insulin independence, but in its current form the long-term immune-suppression required to prevent the islet cell rejection is itself nephrotoxic.
Currently there is no islet graft imaging model in which grafts can be studied and imaged in real time. Therefore we have developed a novel method for imaging long-term grafted islets under the kidney capsule of live mice, allowing investigation of cell migration and dynamic cell-to-cell interactions in real time using multiphoton microscopy.
The islet-grafting protocol involves use of the beta-cell toxin, streptozotocin, to render mice diabetic. Donor islet cells are then transplanted under the kidney capsule and serial blood glucose measurements are used to monitor graft function. We have designed and 3D-printed a kidney-supporting intravital imaging platform that allows direct visualization of the mouse kidney and the transplanted islet cells. Islets were harvested from a genetically modified mouse in which all cells express the fluorescent protein tomato. We examined the isolated islets directly before transplantation by confocal and multiphoton microscopy and then imaged the grafted islets one day after transplantation. We also imaged the grafts at >6 months after grafting and could still visualise the transplanted islets and their associated vasculature.
This is a very powerful new tool for direct visualization of the immune-mediated rejection of islet cells in real time, allowing longitudinal studies of islet graft survival and testing of new methods for preventing graft rejection.