Introduction: Transplantation of neonatal pig islets is a potential treatment for type 1 diabetes. As we acquire further our knowledge on the immune response to pig islet xenografts, our current knowledge on the fundamental biology of pig islets has been limited. In neonatal pigs, islet cells are scattered throughout the pancreas as single or clusters of few cells while in the adult pig pancreas, islet cells are composed of more cells in clusters bound by a membrane. Cadherins are glycoproteins that are thought to maintain and control cell to cell interactions by mediating aggregation of endocrine cells, and this is required for the typical cell organization of islets. In this study, we delved on elucidating the mechanism of how pig islets develop after birth by determining the expression and contribution of epithelial (E)- and vascular endothelial (VE)-cadherins to the post-natal development of pig islets after transplantation.
Materials and Methods: Islets from 1, 3, 7, and 10 days old pigs were isolated and transplanted under the kidney capsule of streptozotocin-induced diabetic immune-deficient B6 rag-/- mice. Blood glucose levels (BGL) of these mice were monitored weekly and the mice were euthanized at various time points post-transplantation (ptx). The kidneys with islet xenograft were procured and processed for immunohistochemistry using antibodies to islet precursor cells (CK7), endocrine hormones (insulin, glucagon), neurons (PGP9.5), and the cadherins, to determine the amount of these molecules in the samples.
Results: At 1, 30, and 50 days ptx all mice remained diabetic although as time progressed their BGL slowly decreased. At >100 days ptx, most mice achieved normoglycemia and were able to lower their BGL during a glucose tolerance test. Insulin and glucagon-positive cells were observed to be randomly scattered within the grafts at earlier time points ptx, however at 50 days ptx these cells formed clusters.VE-cadherin as well as CK7-positive cells were less present at later time points ptx. E-cadherin was observed to be present in the same area where endocrine cells were located at 50 days ptx. PGP9.5-positive cells were also found where endocrine cells were located at this time point and there appears to be a comparable amount of PGP9.5 staining to that of the endocrine cells. Discussion: As islet cells form clusters, an increased number of endocrine cells and a decreased expression of VE-cadherin and CK7 were observed, indicating that these molecules contribute to the formation of islets at earlier time points of post-natal development. E-cadherin and PGP9.5 were present with endocrine cells suggesting their role in the maintenance of cell to cell contact and innervation, respectively.
Conclusions: Our data indicate that E- and VE-cadherins may play a role in the development of pig islets and may be important in the maintenance of islet structure and function but this needs to be confirmed in future studies.