Generation And Analysis Of Murine Models Of Pancreatic Regeneration

Pancreatic regeneration is an attractive phenomenon especially to the expection of finding an alternative to cure diabetes. However, the mechanism is still largely unknown. In this study, we investigated pancreas regeneration in three murine models, including partial pancreatectomy (Ppx), streptozotocin,(STZ) injection, and partial duct ligation (PDL). The result showed that tubular complexes (TC), a typical structure in newly regenerated pancreas, could be easily identified in PDL models. In addition, the number of insulin positive cells increased in normal pancreatic duct as well as in the TC structures. New lobes with the characteristic of TC structures could also be found in 90% Ppx mice. However, due to extensive injury, the death rate in this model was usually very high. The TC structure was rarely found in the 50% and 70% Ppx mice or STZ models. Moreover, besides the islet numbers, the transcript levels of PDX-1, Ngn3, Ki67 and pro-insulin were not increased as compared to the controls. Therefore, PDL was a better model to study pancreas regeneration as compared to Ppx and STZ. In order to study the mechanism underlying pancreas regeneration, we established a technique for pancreatic duct labeling by retrograde injection of adenovirus carrying an EGFP expression cassette. The result showed that about 15% pancreatic ductal and acinar cells were labeled with EGFP in 12-day or two-month old mice 1.5 days after the operation. However, islets with EGFP positive cells in the middle appeared only in 12-day old mice. Furthermore, the number of EGFP labeled islets increased remarkably as the operation time extended from 3 days to 7 days. At the same time, the percentage of 5-bromo-2-deoxyuridine (BrdU) labeled cells was significantly higher in EGFP positive islets as compared to that in EGFP negative ones, indicating EGFP positive islets were newly generated from the duct with elevated mitotic activity. This hypothesis was further supported by the following observations: EGFP positive islets expressed more Ki67 transcripts and possessed longer telomeres than the controls. Finally,when ductal labeling was carried out in 90% Ppx mice, the preliminary data suggested that no new islets were generated from the duct.Therefore,the mechanism for islet regeneration was different from islet development in the embryo. We postulated that insulin positive cells underwent apoptosis eventually, and that regenerated islet beta cells were derived from pancreatic progenitor cells within pre-existing islets.