The publication data currently available has been vetted by Vanderbilt faculty, staff, administrators and trainees. The data itself is retrieved directly from NCBI's PubMed and is automatically updated on a weekly basis to ensure accuracy and completeness.
If you have any questions or comments, please contact us.
Endocrine and exocrine pancreas tissues are both derived from the posterior foregut endoderm, however, the interdependence of these two cell types during their formation is not well understood. In this study, we generated mutant mice, in which the exocrine tissue is hypoplastic, in order to reveal a possible requirement for exocrine pancreas tissue in endocrine development and/or function. Since previous studies showed an indispensable role for Pdx1 in pancreas organogenesis, we used Elastase-Cre-mediated recombination to inactivate Pdx1 in the pancreatic exocrine lineage during embryonic stages. Along with exocrine defects, including impaired acinar cell maturation, the mutant mice exhibited substantial endocrine defects, including disturbed tip/trunk patterning of the developing ductal structure, a reduced number of Ngn3-expressing endocrine precursors, and ultimately fewer β cells. Notably, postnatal expansion of the endocrine cell content was extremely poor, and the mutant mice exhibited impaired glucose homeostasis. These findings suggest the existence of an unknown but essential factor(s) in the adjacent exocrine tissue that regulates proper formation of endocrine precursors and the expansion and function of endocrine tissues during embryonic and postnatal stages.
BACKGROUND - Administration of ALL-TRANS retinoic acid (ATRA) to adult Sprague-Dawley rats with emphysema induced by porcine pancreatic elastase (PPE) reversed the emphysema perhaps by inducing new alveolar formation.
OBJECTIVE - A study was conducted to determine whether ATRA can induce new alveolar septa and reverse the airspace enlargement caused in adult mice by PPE treatment.
METHODS - 48 FVB mice were divided into 6 groups. Three groups received 15 microg of PPE in 0.1 ml of 0.9% saline and 3 groups received 0.1 ml of saline, intratracheally. Starting at day 22, the mice received 12 daily intraperitoneal injections of cottonseed oil, with or without ATRA (12.5 microg or 50 microg). The mice were killed for study 1 day after the last injection.
RESULTS - Measurements of plasma and lung tissue ATRA levels showed statistically significant elevated levels after the 50-microg but not after the 12.5-microg doses of ATRA. In situ hybridization studies of elastin and alpha(1)(I) collagen mRNA expression in pulmonary parenchyma as well as in airways and blood vessels showed no effect of ATRA. Airspace size was determined by the mean linear intercept (Lm) method. The Lm of the groups receiving PPE and ATRA (46.2 +/- 4.1 microm, mean +/- SD) was not significantly different from the group receiving PPE and oil (47.8 +/- 6.0 microm). The Lm for groups receiving saline and ATRA (40.6 +/- 2.5 microm) were not significantly different from the group receiving saline and oil (41.0 +/- 2.7 microm). Comparison of the fixed lung volume data and calculated internal surface area also showed no differences between the control and ATRA-treated groups.
CONCLUSION - ATRA treatment does not affect airspace size or expression of elastin or alpha(1)(I) collagen mRNA in adult FVB mice with PPE-induced emphysema.
Copyright 2003 S. Karger AG, Basel
The homeodomain protein PDX-1 is critical for pancreas development and is a key regulator of insulin gene expression. PDX-1 nullizygosity and haploinsufficiency in mice and humans results in pancreatic agenesis and diabetes, respectively. At embryonic day (e) 10.5, PDX-1 is expressed in all pluripotential gut-derived epithelial cells destined to differentiate into the exocrine and endocrine pancreas. At e15, PDX-1 expression is downregulated in exocrine cells, but remains high in endocrine cells. The aim of this study was to determine whether targeted overexpression of PDX-1 to the exocrine compartment of the developing pancreas at e15 would allow for respecification of the exocrine cells. Transgenic (TG) mice were generated in which PDX-1 was expressed in the exocrine pancreas using the exocrine-specific elastase-1 promoter. These mice exhibited a marked dysmorphogenesis of the exocrine pancreas, manifested by increased rates of replication and apoptosis in acinar cells and a progressive fatty infiltration of the exocrine pancreas with age. Interestingly, the TG mice exhibited improved glucose tolerance, but absolute beta-cell mass was not increased. These findings indicate that downregulation of PDX-1 is required for the proper maintenance of the exocrine cell phenotype and that upregulation of PDX-1 in acinar cells affects beta-cell function. The mechanisms underlying these observations remain to be elucidated.
HOX proteins and some orphan homeodomain proteins form complexes with either PBX or MEIS subclasses of homeodomain proteins. This interaction can increase the binding specificity and transcriptional effectiveness of the HOX partner. Here we show that specific members of both PBX and MEIS subclasses form a multimeric complex with the pancreatic homeodomain protein PDX1 and switch the nature of its transcriptional activity. The two activities of PDX1 are exhibited through the 10-bp B element of the transcriptional enhancer of the pancreatic elastase I gene (ELA1). In pancreatic acinar cells the activity of the B element requires other elements of the ELA1 enhancer; in beta-cells the B element can activate a promoter in the absence of other enhancer elements. In acinar cell lines the activity is mediated by a complex comprising PDX1, PBX1b, and MRG1 (MEIS2). In contrast, beta-cell lines are devoid of PBX1b and MRG1, so that a trimeric complex does not form, and the beta-cell-type activity is mediated by PDX1 without PBX1b and MRG1. The presence of specific nuclear isoforms of PBX and MEIS is precisely regulated in a cell-type-specific manner. The beta-cell-type activity can be detected in acinar cells if the B element is altered to retain binding of PDX1 but prevent binding of the PDX1-PBX1b-MRG1 complex. These observations suggest that association with PBX and MEIS partners controls the nature of the transcriptional activity of the organ-specific PDX1 transcription factor in exocrine versus endocrine cells.
Seminiferous tubule basement membrane (STBM) plays an important role in spermatogenesis. In the present study, the composition and structural organization of type IV collagen of bovine STBM was investigated. STBM was found to be composed of all six alpha-chains of type IV collagen based upon immunocytochemical and biochemical analysis. The content of alpha3(IV) chain (40%) and the alpha4(IV) chain (18%) was substantially higher than in any other basement membrane collagen. The supramolecular structure of the six alpha(IV) chains was investigated using pseudolysin (EC 22.214.171.124) digestion to excise triple-helical molecules, subsequent collagenase digestion to produce NC1 hexamers and antibody affinity chromatography to resolve populations of NC1 hexamers. The hexamers, which reflect specific arrangements of alpha(IV) chains, were characterized for their alpha(IV) chain composition using high performance liquid chromatography, two-dimensional electrophoresis, and immunoblotting with alpha(IV) chain-specific antibodies. Three major hexamer populations were found that represent the classical network of the alpha1(IV) and alpha2(IV) chains and two novel networks, one composed of the alpha1(IV)-alpha6(IV) chains and the other composed of the alpha3(IV)-alpha6(IV) chains. The results establish a structural linkage between the alpha3(IV) and alpha5(IV) chains, suggesting a molecular basis for the conundrum in which mutations in the gene encoding the alpha5(IV) chain cause defective assembly of the alpha3(IV) chain in the glomerular basement membrane of patients with Alport syndrome.
Normal glomerular capillaries filter plasma through a basement membrane (GBM) rich in alpha3(IV), alpha4(IV), and alpha5(IV) chains of type IV collagen. We now show that these latter isoforms are absent biochemically from the glomeruli in patients with X-linked Alport syndrome (XAS). Their GBM instead retain a fetal distribution of alpha1(IV) and alpha2(IV) isoforms because they fail to developmentally switch their alpha-chain use. The anomalous persistence of these fetal isoforms of type IV collagen in the GBM in XAS also confers an unexpected increase in susceptibility to proteolytic attack by collagenases and cathepsins. The incorporation of cysteine-rich alpha3(IV), alpha4(IV), and alpha5(IV) chains into specialized basement membranes like the GBM may have normally evolved to protectively enhance their resistance to proteolytic degradation at the site of glomerular filtration. The relative absence of these potentially protective collagen IV isoforms in GBM from XAS may explain the progressive basement membrane splitting and increased damage as these kidneys deteriorate.
Neutrophils have been implicated as important cellular mediators of the pulmonary dysfunction observed following endotoxemia in chronically instrumented awake sheep. Several areas of research suggest that neutrophil-derived proteases may be mediators of this dysfunction. We hypothesized that neutrophil elastase inhibitors would attenuate the effects of endotoxemia in sheep. To test this hypothesis, we studied the effects of two putative neutrophil elastase inhibitors, SC-37698 and SC-39026 (Searle, Skokie, IL), on endotoxin-induced lung dysfunction in awake sheep. Sheep were given intravenous neutrophil elastase inhibitor alone (20 mg/kg/h for 6 h), intravenous endotoxin (E. coli endotoxin, 0.5 microgram/kg over 20 min) 1 h after beginning the 6-h infusion of elastase inhibitor, or endotoxin 1 h after beginning a 6-h infusion of elastase inhibitor vehicle. SC-37698 attenuated the increase in lung lymph flow and lung lymph protein clearance, the alterations in lung mechanics, and the fall in white blood count. Qualitatively similar effects were seen with SC-39026. These data suggest the need for further research examining the role of protease-antiprotease interactions and the potential utility of neutrophil elastase inhibitors in acute lung injury like that observed in the adult respiratory distress syndrome (ARDS) in the human.
To determine the chain composition of type IV collagen of bovine thoracic aorta, we analyzed collagenase-solubilized carboxyl-terminal noncollagenous (NC1)-domains by high-pressure liquid chromatography, two-dimensional electrophoresis, immunoblotting and enzyme-linked immunoassay. In addition to the classical alpha 1- and alpha 2-chains, we found small amounts of the recently discovered alpha 3-, alpha 4- and alpha 5-chains. The alpha 3- and alpha 4-chains were, collectively, 7-13% of the total, and the alpha 5-chain was present in a low amount. Seventy-nine percent of the NC1-domains were dimerized. Immunolocalization studies on sections of aorta showed that the alpha 3- and alpha 5-chains were present, along with alpha 1- and alpha 2-chains, in the subendothelium and media. In capillaries of the media, the alpha 3-chain was found at relatively high levels and was co-localized with alpha 1- and alpha 2-chains. Digestion of aorta with Pseudomonas aeruginosa elastase yielded soluble multimolecular assemblies of type IV collagen. Electron microscopy results provided a direct demonstration of the supramolecular structure, in which the collagen molecules were tetramerized at the amino-terminal end and dimerized at the carboxyl-terminal end.
The myeloperoxidase (MPO) and neutrophil elastase genes are expressed specifically in immature myeloid cells. The integrity of a polyomavirus enhancer core sequence, 5'-AACCACA-3', is critical to the activity of the murine MPO proximal enhancer. This element binds two species, myeloid nuclear factors 1 alpha and 1 beta (MyNF1 alpha and -beta), present in 32D cl3 myeloid cell nuclear extracts. The levels of the MyNF1s increase during early 32D cl3 cell granulocytic differentiation. Both MyNF1 alpha and -beta supershift with an antiserum raised by using a peptide derived from the N terminus of polyomavirus enhancer-binding protein 2/core-binding factor (PEBP2/CBF) alpha subunit. The specific peptide inhibits these supershifts. In vitro-translated PEBP2/CBF DNA-binding domain binds the murine MPO PEBP2/CBF site. An alternate PEBP2/CBF consensus site, 5'-GACCGCA-3', but not a simian virus 40 enhancer core sequence, 5'-TTCCACA-3', binds the MyNF1s in vitro and activates a minimal murine MPO-thymidine kinase promoter in vivo. The murine neutrophil elastase gene 100-bp 5'-flanking sequences contain several functional elements, including potential binding sites for PU.1, C/EBP, c-Myb, and PEBP2/CBF. The functional element 5'-GGCCACA-3' located at positions -66 to 72 differs from the PEBP2/CBF consensus (5'-PuACCPuCA-3') only by an A-to-G transition at position 2. This DNA element binds MyNF1 alpha and -beta weakly. The N terminis of two PEBP2/CBF alpha subunit family members, PEBP2 alpha A and PEBP2 alpha B (murine AML1), are nearly identical, and 32D c13 cl3 cells contain both corresponding mRNAs. Since t(8;21), t(3;21), and inv(16), associated with myeloid leukemias, disrupt subunits of PEBP2/CBF, we speculate that the resulting oncoproteins, AML1-ETO, AML1-EAP, AML1-Evi1, and CBF beta-MYH11, inhibit early myeloid differentiation.