Endothelial progenitor cells (EPCs) are detectable in the blood and bone marrow throughout life. These cells contribute to new blood vessel formation (neovascularization) in physiological states such as wound healing and in pathological states such as tumor angiogenesis. We hypothesized that bone marrow-derived EPCs could play a role in the response to pancreatic islet cell injury. We used a murine model of experimentally induced ␤-cell injury followed by transplantation with genetically marked bone marrow cells. Bone marrow-derived cells were detectable throughout the pancreas after transplantation. Whereas the total number of bone marrow-derived cells in the pancreas decreased over time, the frequency of endothelial cells (of both donor and recipient origin) increased after transplantation in the animals in which ␤-cell injury had been induced. There was no evidence in this model that bone marrowderived cells differentiated into insulin-expressing cells. This study provides evidence that bone marrowderived EPCs are recruited to the pancreas in response to islet injury. EPC-mediated neovascularization of the pancreas could in principle be exploited to facilitate the recovery of non-terminally injured ␤-cells or to improve the survival and/or function of islet allografts. Diabetes 53: [91][92][93][94][95][96][97][98] 2004

There are three types of cell death; apoptosis, necrosis, and autophagy. The possibility that activation of the macroautophagy (autophagy) pathway may increase beta cell death is addressed in this study. Increased autophagy was present in pancreatic islets from Pdx1 ؉/؊ mice with reduced insulin secretion and beta cell mass. Pdx1 expression was reduced in mouse insulinoma 6 (MIN6) cells by delivering small hairpin RNAs using a lentiviral vector. The MIN6 cells died after 7 days of Pdx1 deficiency, and autophagy was evident prior to the onset of cell death. Inhibition of autophagy prolonged cell survival and delayed cell death. Nutrient deprivation increased autophagy in MIN6 cells and mouse and human islets after starvation. Autophagy inhibition partly prevented amino acid starvation-induced MIN6 cell death. The in vivo effects of reduced autophagy were studied by crossing Pdx1 ؉/؊ mice to Normal pancreatic beta cell function is essential for normal glucose tolerance, and abnormal beta cell function leads to glucose intolerance and diabetes. A progressive reduction in beta cell mass has been shown to occur in the evolution of diabetes (1). Thus understanding the mechanisms responsible for the reduction in beta cell mass is important for understanding the pathogenesis of diabetes and in developing novel approaches to prevention and treatment.There are three types of cell death; apoptosis, necrosis, and autophagy (2). Previous studies have focused on apoptosis as the mechanism underlying beta cell death (1, 3-5). The possibility that activation of the macroautophagy (hereafter referred to as autophagy) pathway may increase beta cell death has not been systematically studied. Autophagy is a regulated lysosomal pathway leading to the degradation and recycling of longlived proteins and organelles. During autophagy, cytoplasmic constituents are sequestered into autophagosomes with double membranes and fused to lysosomes (autolysosomes), where degradation occurs. Under certain circumstances such as in response to nutrient deprivation, autophagy may function as a pro-survival pathway by mediating cellular turnover of proteins and organelles (6 -8). On the other hand, an increase in autophagy can cause autophagic cell death distinct from apoptosis (9, 10). It has been suggested that autophagy plays a key role in the turnover of insulin secretory granules and of mitochondria within the beta cell, thereby regulating insulin secretion (11,12). Complete genetic ablation of Atg7 in beta cells resulted in degradation of islets and impaired glucose tolerance, suggesting that "basal autophagy" is important for maintenance of normal islet architecture and function (13,14).The present study was designed to determine whether activation of autophagy can contribute to pancreatic beta cell death that occurs with reduced expression of Pdx1 (pancreas duodenal homeobox 1). We chose to study Pdx1 deficiency because this homeodomain-containing transcription factor is essential for normal pancreatic beta cell function and survival. Complete...

The t(8;21)(q22;q22) translocation, present in 10 -15% of acute myeloid leukemia (AML) cases, generates the AML1͞ETO fusion protein.To study the role of AML1͞ETO in the pathogenesis of AML, we used the Ly6A locus that encodes the well characterized hematopoietic stem cell marker, Sca1, to target expression of AML1͞ETO to the hematopoietic stem cell compartment in mice. Whereas germ-line expression of AML1͞ETO from the AML1 promoter results in embryonic lethality, heterozygous Sca1 ؉/AML1-ETO ires EGFP (abbreviated Sca ؉/AE ) mutant mice are born in Mendelian ratios with no apparent abnormalities in growth or fertility. Hematopoietic cells from Sca ؉/AE mice have markedly extended survival in vitro and increasing myeloid clonogenic progenitor output over time. Sca ؉/AE mice develop a spontaneous myeloproliferative disorder with a latency of 6 months and a penetrance of 82% at 14 months. These results reinforce the notion that the phenotype of murine transgenic models of human leukemia is critically dependent on the cellular compartment targeted by the transgene. This model should provide a useful platform to analyze the effect of AML1͞ETO on hematopoiesis and its potential cooperation with other mutations in the pathogenesis of leukemia.T he t(8;21)(q22;q22) translocation is one of the most commonly detected karyotypic abnormalities in acute myeloid leukemia (AML). This genetic alteration is found in up to 40% of de novo AML cases of the French-American-British M2 subtype, and in 12-15% of AML cases overall (1, 2). In many instances of AML, t(8;21) is the sole cytogenetic abnormality, suggesting that the translocation plays a key role in transformation. The t(8;21) translocation fuses sequences from the AML1 (RUNX1, CBFA2, and PEBP␣) gene on chromosome 21 to the ETO (MTG8) gene on chromosome 8. This translocation results in production of the AML1͞ETO protein, an in-frame fusion of the N terminus of AML1 and virtually the entire ETO protein. AML1 is the DNAbinding subunit of core-binding factor (CBF), a multimeric transcription factor complex that includes CBF␤ and additional transcriptional coactivators. Mice lacking either Aml1 or Cbf␤ fail to develop definitive intraembryonic hematopoiesis and die midgestation (3-6). Mice heterozygous for an AML1͞ETO allele knocked into the Aml1 locus have an identical phenotype, providing genetic evidence that the AML1͞ETO fusion protein acts as a dominant inhibitor of CBF activity (7,8).Although it is clear that CBF plays a critical role in hematopoietic development, several lines of evidence suggest that expression of its dominant inhibitor AML1͞ETO is not sufficient to cause AML. AML1͞ETO expression is frequently detectable in peripheral blood cells from t(8;21) AML patients for years into durable remission (9, 10). Conversely, clonotypic AML1͞ETO sequences were identified in DNA retrospectively extracted from neonatal blood samples from 5 of 10 children with t(8;21) AML, preceding the development of AML by 5-10 years in these cases (11). Several strains of AML1͞ETO-express...

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