The major forms of diabetes are characterized by pancreatic islet ␤-cell dysfunction and decreased ␤-cell numbers, raising hope for cell replacement therapy. Although human islet transplantation is a cell-based therapy under clinical investigation for the treatment of type 1 diabetes, the limited availability of human cadaveric islets for transplantation will preclude its widespread therapeutic application. The result has been an intense focus on the development of alternate sources of ␤ cells, such as through the guided differentiation of stem or precursor cell populations or the transdifferentiation of more plentiful mature cell populations. Realizing the potential for cell-based therapies, however, requires a thorough understanding of pancreas development and ␤-cell formation. Pancreas development is coordinated by a complex interplay of signaling pathways and transcription factors that determine early pancreatic specification as well as the later differentiation of exocrine and endocrine lineages. This review describes the current knowledge of these factors as they relate specifically to the emergence of endocrine ␤ cells from pancreatic endoderm. Current therapeutic efforts to generate insulin-producing ␤-like cells from embryonic stem cells have already capitalized on recent advances in our understanding of the embryonic signals and transcription factors that dictate lineage specification and will most certainly be further enhanced by a continuing emphasis on the identification of novel factors and regulatory relationships.Diabetes is rapidly becoming a global epidemic, with a staggering health, societal, and economic impact. Recent estimates by the American Diabetes Association suggest that the lifetime risk of developing diabetes for Americans born in the year 2000 is one in three. Diabetes results when insulin production by the pancreatic islet ␤ cell is unable to meet the metabolic demand of peripheral tissues such as liver, fat, and muscle.A reduction in ␤-cell function and mass leads to hyperglycemia (elevated blood sugar) in both type 1 and type 2 diabetes. In type 1 diabetes, autoimmune destruction of the ␤ cell itself severely reduces ␤-cell mass, resulting in marked hypoinsulinemia and potentially lifethreatening ketoacidosis. In contrast, during the progression to type 2 diabetes, impaired ␤-cell compensation in the setting of insulin resistance (impaired insulin action) eventually leads to ␤-cell failure and a modest but significant reduction in ␤-cell mass (Maclean and Ogilvie 1955; Butler et al. 2003;Yoon et al. 2003). More recently, autoimmunity has been detected in a subset of patients with type 2 diabetes, which has led to a revision of the classification to include LADA, latent autoimmune diabetes of adulthood, underscoring the continuum between type 1 and type 2 diabetes, and raising questions as to the role of immunity and inflammation in ␤-cell dysfunction and death in type 2 diabetes (Syed et al. 2002; Pozzilli and Buzzetti 2007). Conversely, forms of ketosis prone diabetes due to sev...

It has been suggested that pancreatic acinar cells can serve as progenitors for pancreatic islets, a concept with substantial implications for therapeutic efforts to increase insulin-producing β cell mass in patients with diabetes. We report what we believe to be the first in vivo lineage tracing approach to determine the plasticity potential of pancreatic acinar cells. We developed an acinar cell-specific inducible Cre recombinase transgenic mouse, which, when mated with a reporter strain and pulsed with tamoxifen, resulted in permanent and specific labeling of acinar cells and their progeny. During various time periods of observation and using several models to provoke injury, we failed to observe any chase of the labeled cells into the endocrine compartment, indicating that acinar cells do not normally transdifferentiate into islet β cells in vivo in adult mice. In contrast, we observed a substantial role for replication of preexisting acinar cells in the regeneration of new acinar cells after partial pancreatectomy. These results indicate that mature acinar cells harbor a facultative acinar but not endocrine progenitor capacity.

Abstract-Oxidative stress stimulates both growth and apoptosis in cardiac myocytes in vitro. We investigated whether oxidative stress mediates hypertrophy and apoptosis in cyclically stretched ventricular myocytes. Neonatal rat ventricular myocytes cultured on laminin-coated silastic membranes were stretched cyclically (1 Hz) at low (nominal 5%) and high (nominal 25%) amplitudes for 24 hours. Stretch caused a graded increase in superoxide anion production as assessed by superoxide dismutase (SOD)-inhibitable cytochrome c reduction or electron paramagnetic resonance spectroscopy. The role of reactive oxygen species (ROS) was assessed using the cell-permeable SOD/catalase mimetics Mn(II/III)tetrakis(1-methyl-4-peridyl) (MnTMPyP) and EUK-8. Stretch-induced increases in protein synthesis ( 3 Hleucine incorporation) and cellular protein content were completely inhibited by MnTMPyP (0.05 mmol/L) at both low and high amplitudes of stretch. In contrast, while MnTMPyP inhibited basal atrial natriuretic factor (ANF) mRNA expression, the stretch-induced increase in ANF mRNA expression was not inhibited by MnTMPyP. In contrast to hypertrophy, only high-amplitude stretch increased myocyte apoptosis, as reflected by increased DNA fragmentation on gel electrophoresis and an Ϸ3-fold increase in the number of TUNEL-positive myocytes. Similarly, only high-amplitude stretch increased the expression of bax mRNA. Myocyte apoptosis and bax expression stimulated by high-amplitude stretch were inhibited by MnTMPyP. Both low-and high-amplitude stretch caused rapid phosphorylation of ERK1/2, while high-, but not low-, amplitude stretch caused phosphorylation of JNKs. Activation of both ERK1/2 and JNKs was ROS-dependent. Thus, cyclic strain causes an amplitude-related increase in ROS, associated with differential activation of kinases and induction of hypertrophic and apoptotic phenotypes.

Abstract-Atherosclerosis involves a complex array of factors, including leukocyte adhesion and platelet vasoactive factors. Aspirin, which is used to prevent secondary complications of atherosclerosis, inhibits platelet production of thromboxane (Tx) A 2 . The actions of TxA 2 as well as of other arachidonic acid products, such as prostaglandin (PG) H 2 , PGF 2␣ , hydroxyeicosatetraenoic acids, and isoprostanes, can be effectively antagonized by blocking thromboxane (TP) receptors. The purpose of this study was to determine the role of platelet-derived TxA 2 in atherosclerotic lesion development by comparing the effects of aspirin and the TP receptor antagonist S18886. The effect of 11 weeks of treatment with aspirin (30 mg ⅐ kgon aortic root atherosclerotic lesions, serum levels of intercellular adhesion molecule-1 (ICAM-1), and the TxA 2 metabolite TxB 2 was determined in apolipoprotein E-deficient mice at 21 weeks of age. Both treatments did not affect body or heart weight or serum cholesterol levels. Aspirin, to a greater extent than S18886, significantly decreased serum TxB 2 levels, indicating the greater efficacy of aspirin in preventing platelet synthesis of TxA 2 . S18886, but not aspirin, significantly decreased aortic root lesions as well as serum ICAM-1 levels. S18886 also prevented the increased expression of ICAM-1 in cultured human endothelial cells stimulated by the TP receptor agonist U46619. These results indicate that inhibition of platelet TxA 2 synthesis with aspirin has no significant effect on atherogenesis or adhesion molecule levels. The effects of S18886 suggest that blockade of TP receptors inhibits atherosclerosis by a mechanism independent of platelet-derived TxA 2 , perhaps by preventing the expression of adhesion molecules whose expression is stimulated by eicosanoids other than TxA 2 .

Heterozygous mutations in the gene encoding the pancreatic homeodomain transcription factor pancreatic duodenal homeobox 1 (PDX1) are associated with maturity onset diabetes of the young, type 4 (MODY4) and type 2 diabetes. Pdx1 governs the early embryonic development of the pancreas and the later differentiation of the insulin-producing islet β cells of the endocrine compartment. We derived a Pdx1 hypomorphic allele that reveals a role for Pdx1 in the specification of endocrine progenitors. Mice homozygous for this allele displayed a selective reduction in endocrine lineages associated with decreased numbers of endocrine progenitors and a marked reduction in levels of mRNA encoding the proendocrine transcription factor neurogenin 3 (Ngn3). During development, Pdx1 occupies an evolutionarily conserved enhancer region of Ngn3 and interacts with the transcription factor one cut homeobox 1 (Hnf6) to activate this enhancer. Furthermore, mRNA levels of all 4 members of the transcription factor network that regulates Ngn3 expression, SRY-box containing gene 9 (Sox9), Hnf6, Hnf1b, and forkhead box A2 (Foxa2), were decreased in homozygous mice. Pdx1 also occupied regulatory sequences in Foxa2 and Hnf1b. Thus, Pdx1 contributes to specification of endocrine progenitors both by regulating expression of Ngn3 directly and by participating in a cross-regulatory transcription factor network during early pancreas development. These results provide insights that may be applicable to β cell replacement strategies involving the guided differentiation of ES cells or other progenitor cell types into the β cell lineage, and they suggest a molecular mechanism whereby human PDX1 mutations cause diabetes. IntroductionInsulin deficiency due to reduced pancreatic islet β cell number underlies the progression of both type 1 and type 2 diabetes, prompting efforts to develop β cell replacement therapies. The high hopes for human islet transplantation as such a therapy have been tempered by their limited availability and short-term function after transplantation, resulting in an intense focus on the development of alternate sources of β cells, through the guided differentiation of stem or progenitor cells or the transdifferentiation of more abundant mature cells. Transdifferentiation approaches have focused largely on the expression of a single or a combination of transcription factors that drive β cell development and differentiation and most have relied, at least in part, upon pancreatic duodenal homeobox 1 (Pdx1), a homeodomain transcription factor with critical regulatory roles in early pancreas development and in the mature β cell (1-5). Recent advances in the derivation of insulin-expressing β-like cells from ES cells (6-11) have also been guided by the principles of embryonic pancreas development (reviewed in ref. 12). Clinical translation of these approaches, however, will require improvements in efficiency, fidelity, and stability of generating the β cell phenotype, efforts which will likely be informed by the identification of novel...

Abstract-Oxidant stress is involved in the events that accompany endothelial cell expression of adhesion molecules and leukocyte adherence in many disease states, including atherosclerosis. A recently discovered benzo(b)pyran-4-one derivative, S17834 (10 to 50 mol/L), reduced tumor necrosis factor-stimulated vascular cell adhesion molecule-1 (VCAM) mRNA accumulation and protein expression in human umbilical vein endothelial cells. Intercellular cell adhesion molecule-1 and E-selectin were also inhibited by S17834, but platelet endothelial cell adhesion molecule-1 was not. Adherence of U937 monocytic cells to the endothelial cells as well as to plastic plates coated with soluble VCAM, intercellular cell adhesion molecule-1, P-selectin, and E-selectin was also decreased. Consistent with an antioxidant mechanism of action, S17834 (10 to 50 mol/L) inhibited tumor necrosis factor-stimulated release of superoxide from endothelial cells measured by cytochrome c reduction. S17834 had no effect on superoxide produced by xanthine oxidase, indicating that rather than by acting as a scavenger of superoxide anion, the drug acts by inhibiting the production of free radicals. Indeed, S17834 inhibited NADPH oxidase activity of endothelial cell membranes. The ability to inhibit superoxide anion production appears to be key in the effect of S17834 on superoxide anion production and VCAM expression, because these actions were mimicked by adenovirus-mediated overexpression of superoxide dismutase. Furthermore, these actions may be relevant in vivo, because S17834 reduced aortic superoxide anion levels by 40% and aortic atherosclerotic lesions by 60% in apolipoprotein E-deficient mice. These results indicate that S17834 inhibits adhesion molecule expression and adherence of leukocytes to endothelial cells as well as aortic atherogenesis and that perhaps these effects can be explained by its ability to inhibit endogenous superoxide anion production.

The TP antagonist inhibits inflammation and accelerated atherogenesis caused by diabetes, most likely by counteracting effects on endothelial function and adhesion molecule expression of eicosanoids stimulated by the diabetic milieu.

This report describes a newly identified nonsense mutation in human NEUROG3 that in the homozygous state is associated with neonatal diabetes and malabsorptive diarrhea.