The resounding success of a new immunosuppressive regimen known as the Edmonton protocol demonstrates that islet cell transplantation is becoming a therapeutic reality for diabetes. However, under the Edmonton protocol, a single donor does not provide enough islets to attain the insulin independence of a transplant recipient. This limitation is mainly caused by islet apoptosis triggered during isolation. In this study, we describe a highly efficient system of transiently transferring antiapoptotic proteins into pancreatic islets, thus opening an exciting new therapeutic opportunity to improve the viability of transplantable islets. We fused ␤-galactosidase to the 11-amino acid residues that constitute the protein transduction domain (PTD) of the HIV/TAT protein and transduced pancreatic islets ex vivo with this fusion protein in a dose-dependent manner with >80% efficiency. We observed that transduction of the anti-apoptotic proteins Bcl-X L and PEA-15 fused to TAT/PTD prevented apoptosis induced by tumor necrosis factor-␣ in a pancreatic ␤-cell line, indicating that TAT/PTD anti-apoptotic proteins retained their biological activity. Finally, we demonstrated that TAT-fusion proteins did not affect the insulin secretion capability of islets, as determined by glucose static incubation and by reversion of hyperglycemia in diabetic immunodeficient mice.

Our study indicates that cold ischemia stimulates inflammatory pathways (chemokine (c-c)ligand-3, phosphorylation of c-jun N-terminal Kinase and mitogen-activated protein kinase-p38, and eukaryotic translation elongation factor-1-alpha-1) and decreases repair/cytoprotective pathways (IL-10, vascular endothelial growth factor, and Clade-B), all of which may negatively affect the quality and mass of islets obtained from a donor pancreas.

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Stem cell technologies hold great potential for the treatment of type 1 diabetes, provided that functional transplantable ␤-cells can be selectively generated in an efficient manner. Such a process should recapitulate, at least to a certain extent, the embryonic development of ␤-cells in vitro. However, progress at identifying the transcription factors involved in ␤-cell development has not been accompanied by a parallel success at unraveling the pattern of their instructive extracellular signals.Here we present proof of principle of a novel approach to circumvent this problem, based on the use of the HIV/TAT protein transduction domain. Neurogenin 3 (ngn3), a factor whose expression is essential for pancreatic endocrine differentiation, was fused to the TAT domain. Administration of TAT/ngn3 to cultured pancreatic explants results in efficient uptake, nuclear translocation, and stimulation of downstream reporter and endogenous genes. Consistent with the predicted activity of the protein, e9.5 and e13.5 mouse pancreatic explants cultured in the presence of TAT/ngn3 show an increased level of endocrine differentiation compared with control samples. Our results raise the possibility of sequentially specifying stem/progenitor cells toward the ␤-cell lineage, by using the appropriate sequence and combination of TAT-fused transcription factors. Diabetes 54:720 -726, 2005 I slet transplantation has proven successful for the treatment of type 1 diabetes (1,2), but the shortage of donor pancreata has hindered the widespread clinical implementation of this therapy. Therefore, it is essential to find additional sources of islets. Human embryonic stem cells may present one promising alternative for the in vitro generation of islet cells. For this prospect to be realistic, however, we need to identify the appropriate conditions that will favor differentiation of islet cell types. Ideally, such conditions should reproduce as accurately as possible the sequence of events that results in islet formation during embryogenesis. Although little is known about the first of such events (endodermal specification), subsequent steps in pancreatic development have been associated with the timed expression of key transcriptional factors, such as insulin promoter factor-1 (Ipf1)/pancreatic and duodenal homeobox factor-1 (pdx1), Ptf1a, neurogenin 3 (ngn3), Pax4, Pax6, and Isl1 (3-8). During murine pancreatic development, endocrine differentiation occurs through a lateral inhibition process, mediated by Notch signaling. Cells in which Notch is activated by the ligands delta or serrate express high levels of HES-1, which in turn represses the proendocrine gene ngn3. However, in ligand-expressing cells, HES-1 expression is not upregulated, thus allowing robust ngn3 expression and differentiation toward the endocrine lineage (5-8).ngn3 encodes a class B basic helix-loop-helix factor, which has been shown by loss-of-function studies to be required for the development of the four endocrine cell lineages of the pancreas (5). The pro-endocrine rol...

BackgroundThe MAPK/ERK1/2 serine kinases are primary mediators of the Ras mitogenic signaling pathway. Phosphorylation by MEK activates MAPK/ERK in the cytoplasm, and phospho-ERK is thought to enter the nucleus readily to modulate transcription.Principal FindingsHere, however, we observe that in primary cultures of breast and ovarian epithelial cells, phosphorylation and activation of ERK1/2 are disassociated from nuclear translocalization and transcription of downstream targets, such as c-Fos, suggesting that nuclear translocation is limited in primary cells. Accordingly, in import assays in vitro, primary cells showed a lower import activity for ERK1/2 than cancer cells, in which activated MAPK readily translocated into the nucleus and activated c-Fos expression. Primary cells express lower levels of nuclear pore complex proteins and the nuclear transport factors, importin B1 and importin 7, which may explain the limiting ERK1/2 import found in primary cells. Additionally, reduction in expression of nucleoporin 153 by siRNA targeting reduced ERK1/2 nuclear activity in cancer cells.ConclusionERK1/2 activation is dissociated from nuclear entry, which is a rate limiting step in primary cells and in vivo, and the restriction of nuclear entry is disrupted in transformed cells by the increased expression of nuclear pores and/or nuclear transport factors.

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Ischemic preconditioning (IPC) confers tissue resistance to subsequent ischemia in several organs. The protective effects are obtained by applying short periods of warm ischemia followed by reperfusion prior to extended ischemic insults to the organs. In the present study, we evaluated whether IPC can reduce pancreatic tissue injury following cold ischemic preservation. Rat pancreata were exposed to IPC (10 min of warm ischemia followed by 10 min of reperfusion) prior to ~18 h of cold preservation before assessment of organ injury or islet isolation. Pancreas IPC improved islet yields (964 ± 336 vs. 711 ± 204 IEQ/pancreas; p = 0.004) and lowered islet loss after culture (33 ± 10% vs. 51 ± 14%; p = 0.0005). Islet potency in vivo was well preserved with diabetes reversal and improved glucose clearance. Pancreas IPC reduced levels of NADPH-dependent oxidase, a source of reactive oxygen species, in pancreas homogenates versus controls (78.4 ± 45.9 vs. 216.2 ± 53.8 RLU/μg; p = 0.002). Microarray genomic analysis of pancreata revealed upregulation of 81 genes and downregulation of 454 genes (greater than twofold change) when comparing IPC-treated glands to controls, respectively, and showing a decrease in markers of apoptosis and oxidative stress. Collectively, our study demonstrates beneficial effects of IPC of the pancreas prior to cold organ preservation and provides evidence of the key role of IPC-mediated modulation of oxidative stress pathways. The use of IPC of the pancreas may contribute to increasing the quality of donor pancreas for transplantation and to improving organ utilization.