The basic helix-loop-helix transcription factor Neurog3 (Neurogenin3 or Ngn3) actively drives endodermal progenitor cells towards endocrine islet cell differentiation during embryogenesis. Here, we manipulate Neurog3 expression levels in endocrine progenitor cells without altering its expression pattern using heterozygosity and a hypomorph. Lowered Neurog3 gene dosage in the developing pancreatic epithelium reduces the overall production of endocrine islet cells without significantly affecting the proportions of various islet cell types that do form. A reduced Neurog3 production level in the endocrine-directed pancreatic progenitor population activates the expression of Neurog3 in an increased number of epithelial progenitors. Yet a significant number of these Neurog3+ cells detected in heterozygous and hypomorphic pancreata, possibly those that express low levels of Neurog3, move on to adopt pancreatic ductal or acinar fates. These data directly demonstrate that achieving high levels of Neurog3 expression is a critical step for endocrine commitment from multipotent pancreatic progenitors. These findings also suggest that a high level of Neurog3 expression could mediate lateral inhibition or other unknown feedback mechanisms to regulate the number of cells that initiate Neurog3 transcription and protein production. The control of Neurog3+ cell number and the Neurog3 threshold-dependent endocrine differentiation mechanism combine to select a specific proportion of pancreatic progenitor cells to adopt the islet cell fate.

The prototypic second messenger cyclic AMP (cAMP) is essential for controlling cellular metabolism, including glucose and lipid homeostasis. In mammals, the majority of cAMP functions are mediated by cAMP-dependent protein kinase (PKA) and exchange proteins directly activated by cAMP (Epacs). To explore the physiological functions of Epac1, we generated Epac1 knockout mice. Here we report that Epac1 null mutants have reduced white adipose tissue and reduced plasma leptin levels but display heightened leptin sensitivity. Epac1-deficient mice are more resistant to high-fat diet-induced obesity, hyperleptinemia, and glucose intolerance. Furthermore, pharmacological inhibition of Epac by use of an Epac-specific inhibitor reduces plasma leptin levels in vivo and enhances leptin signaling in organotypic hypothalamic slices. Taken together, our results demonstrate that Epac1 plays an important role in regulating adiposity and energy balance. Obesity is a grave health problem, as it is closely related to the leading causes of morbidity and mortality, such as cardiovascular diseases, type 2 diabetes, hypertension, depression, and cancer (1). Over the last 2 decades, obesity has reached epidemic proportions in the United States: more than 35% of adults in the United States are obese, and more than two-thirds are overweight (2). Furthermore, 500 million people worldwide are obese, representing approximately 12% of the adult population on earth (3). Chronic excessive food/energy intake, mediated by leptin resistance, is a major factor contributing to obesity. To date, few effective treatment options are available for obesity (4). Therefore, a better understanding of the underlying molecular mechanisms of obesity development and effective, safe therapeutic interventions are urgently needed. Cyclic AMP (cAMP)-mediated signaling pathways are important for maintaining metabolic homeostasis and have been implicated in regulating leptin production and secretion (5-7). In mammals, the majority of cAMP functions are mediated by cAMP-dependent protein kinase (PKA) and exchange proteins directly activated by cAMP (Epacs) (8-10). A recent study revealed that activation of Epacs by an Epac-selective cAMP analog, 8-CPT-2=-O-Me-cAMP (11), interferes with leptin signaling in the hypothalamus, suggesting that Epacs may contribute to the pathophysiology of leptin resistance and represent a novel pharmacological target for treatment of obesity (12). To investigate the functional significance of Epac1 in leptin-mediated energy balance in vivo, we generated global loss-of-function mutants for Epac1. Analysis of these animals indicated resistance to high-fat diet (HFD)-induced obesity, heightened leptin signaling in the arcuate nucleus (AN), and improved glucose tolerance. These findings reveal an important role of Epac1 in metabolism and suggest that Epac1 may represent a novel therapeutic target for obesity. MATERIALS AND METHODS Mice.To construct an Epac1 targeting vector, two loxP sites were inserted into introns 2 and 5. A 3.8-kb upstream ...

Endoplasmic reticulum (ER)-associated aminopeptidase (ERAP)1 has been implicated in the final proteolytic processing of peptides presented by major histocompatibility complex (MHC) class I molecules. To evaluate the in vivo role of ERAP1, we have generated ERAP1-deficient mice. Cell surface expression of the class Ia molecules H-2Kb and H-2Db and of the class Ib molecule Qa-2 was significantly reduced in these animals. Although cells from mutant animals exhibited reduced capacity to present several self- and foreign antigens to Kb-, Db-, or Qa-1b–restricted CD8+ cytotoxic T cells, presentation of some antigens was unaffected or significantly enhanced. Consistent with these findings, mice generated defective CD8+ T cell responses against class I–presented antigens. These findings reveal an important in vivo role of ER-associated peptidase activity in tailoring peptides for presentation by MHC class Ia and class Ib molecules.

Activating mutations in the Kras gene are commonly found in some but not all epithelial cancers. In order to understand the susceptibility of different epithelial tissues to Kras-induced tumorigenesis, we introduced one of the most common Kras mutations, KrasG12D, broadly in epithelial tissues. We used a mouse model in which the G12D mutation is placed in the endogenous Kras locus controlled by inducible, Cre-mediated recombination in tissues expressing cytokeratin 19 including the oral cavity, GI tract, lungs, and ducts of the liver, kidney, and the pancreas. Introduction of the KrasG12D mutation in adult mouse tissues led to neoplastic changes in some but not all of these tissues. Notably, many hyperplasias, metaplasias and adenomas were observed in the oral cavity, stomach, colon and lungs, suggesting that exposure to products of the outside environment promotes KrasG12D-initiated tumorigenesis. However, environmental exposure did not consistently correlate with tumor formation, such as in the small intestine, suggesting that there are also intrinsic differences in susceptibility to Kras activation. The pancreas developed small numbers of mucinous metaplasias with characteristics of early stage pancreatic intraepithelial neoplasms (PanINs), supporting the hypothesis that pancreatic ducts have the potential to give rise pancreatic cancer.

The Bone Morphogenetic Protein antagonist Gremlin 2 (Grem2) is required for atrial differentiation and establishment of cardiac rhythm during embryonic development. A human Grem2 variant has been associated with familial atrial fibrillation, suggesting that abnormal Grem2 activity causes arrhythmias. However, it is not known how Grem2 integrates into signaling pathways to direct atrial cardiomyocyte differentiation. Here, we demonstrate that Grem2 expression is induced concurrently with the emergence of cardiovascular progenitor cells during differentiation of mouse embryonic (ES) stem cells. Grem2 exposure enhances the cardiogenic potential of ES cells by ~20–120 fold, preferentially inducing genes expressed in atrial myocytes such as Myl7, Nppa and Sarcolipin. We show that Grem2 acts upstream to upregulate pro-atrial transcriptional factors CoupTFII and Hey1 and downregulate atrial fate repressors Irx4 and Hey2. The molecular phenotype of Grem2-induced atrial cardiomyocytes was further supported by induction of ion channels encoded by Kcnj3, Kcnj5, and Cacna1D genes and establishment of atrial-like action potentials shown by electrophysiological recordings. We show that promotion of atrial-like cardiomyocyte is specific to the Gremlin subfamily of BMP antagonists. Grem2 pro-atrial differentiation activity is conveyed by non-canonical BMP signaling through phosphorylation of JNK and can be reversed by specific JNK inhibitors, but not by dorsomorphin, an inhibitor of canonical BMP signaling. Taken together, our data provide novel mechanistic insights into atrial cardiomyocyte differentiation from pluripotent stem cells and will assist the development of future approaches to study and treat arrhythmias.

Hepatic ischemia/reperfusion (I/R) is a major challenge for liver surgery and specific severe conditions of chronic liver disease. Current surgical and pharmacological strategies are limited to improve liver function after hepatic I/R injury. Thus, an in-depth understanding of the liver I/R mechanism is pivotal to develop new therapeutic methods. The cellular repressor of E1A-stimulated genes (CREG), a key regulator of cellular proliferation, exerts protective roles in cardiovascular diseases and participates in lipid accumulation and inflammatory response in the liver. However, the role of CREG in hepatic I/R remains largely unknown. A genetic engineering technique was employed to explore the function of CREG in hepatic I/R injury. Hepatocyte-specific Creg knockout (Creg ) and transgenic (HTG) mice were generated and subjected to hepatic I/R injury, as were the controls. CREG in hepatocytes prevented against liver I/R injury by suppressing cell death and inflammation. In vitro studies were performed using primary hepatocytes isolated from Creg that were challenged by hypoxia/reoxygenation insult. These cells exhibited more cell death and inflammatory cytokines production similar to observations in vivo. Moreover, further molecular experiments showed that CREG suppressed MAPK signaling by inhibiting TAK1 phosphorylation. Inhibiting TAK1 by 5Z-7-ox or mutating the TAK1-binding domain of CREG abolished the protective role of CREG, indicating that CREG binding to TAK1 was required for prevention against hepatic I/R injury. Conclusion These data demonstrated that CREG prevents hepatocytes from liver I/R injury. The CREG-TAK1 interaction inhibited the phosphorylation of TAK1 and the activation of MAPK signaling, which protected against cell death and inflammation during hepatic I/R injury. This article is protected by copyright. All rights reserved.

Although the specificity of AFB + WLB is lower than WLB alone, AFB + WLB seems to significantly improve the sensitivity to detect intraepithelial neoplasia. However, this advantage over WLB alone seems much less in detecting invasive lung cancer.

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