Retinoblastoma tumor suppressor protein in pancreatic progenitors controls α- and β-cell fate

Pancreatic endocrine cells expand rapidly during embryogenesis by neogenesis and proliferation, but during adulthood, islet cells have a very slow turnover. Disruption of murine retinoblastoma tumor suppressor protein (Rb) in mature pancreatic β-cells has a limited effect on cell proliferation. Here we show that deletion of Rb during embryogenesis in islet progenitors leads to an increase in the neurogenin 3-expressing precursor cell population, which persists in the postnatal period and is associated with increased β-cell mass in adults. In contrast, Rb-deficient islet precursors, through repression of the cell fate factor aristaless related homeobox, result in decreased α-cell mass. The opposing effect on survival of Rb-deficient α- and β-cells was a result of opposing effects on p53 in these cell types. As a consequence, loss of Rb in islet precursors led to a reduced α- to β-cell ratio, leading to improved glucose homeostasis and protection against diabetes.     

The physiological significance of β-actin mRNA localization in determining cell polarity and directional motility

beta-actin mRNA is localized near the leading edge in several cell types, where actin polymerization is actively promoting forward protrusion. The localization of the beta-actin mRNA near the leading edge is facilitated by a short sequence in the 3' untranslated region, the "zip code." Localization of the mRNA at this region is important physiologically. Treatment of chicken embryo fibroblasts with antisense oligonucleotides complementary to the localization sequence (zip code) in the 3' untranslated region leads to delocalization of beta-actin mRNA, alteration of cell phenotype, and a decrease in cell motility. To determine the components of this process responsible for the change in cell behavior after beta-actin mRNA delocalization, the Dynamic Image Analysis System was used to quantify movement of cells in the presence of sense and antisense oligonucleotides to the zip code. It was found that net path length and average speed of antisense-treated cells were significantly lower than in sense-treated cells. Total path length and the velocity of protrusion of antisense-treated cells were not affected compared with those of control cells. These results suggest that a decrease in persistence of direction of movement and not in velocity results from treatment of cells with zip code-directed antisense oligonucleotides. To test this, direct analysis of directionality was performed on antisense-treated cells and showed a decrease in directionality (net path/total path) and persistence of movement. Less directional movement of antisense-treated cells correlated with a unpolarized and discontinuous distribution of free barbed ends of actin filaments and of beta-actin protein. These results indicate that delocalization of beta-actin mRNA results in delocalization of nucleation sites and beta-actin protein from the leading edge followed by loss of cell polarity and directional movement.     

Immunohistochemical detection of β-amyloid and β-amyloid precursor protein in the canine brain and non-neuronal epithelial tissues

We examined the immunohistochemical localization of β-amyloid (Aβ) and β-amyloid precursor protein (AβPP) in the neuronal and non-neuronal tissues of 14 aged (over 10 years old) and 4 young (0–4 years old) dogs. Aβ was detected only in the senile plaque in the cerebrum of aged dogs. AβPP was expressed in the neuronal cell body, neuronal fiber, senile plaque and perimalacic tissue independent of age. In addition, epithelial cells in the bronchus, bronchial glands, gastric and intestinal mucosa, intrahepatic bile ducts, and pancreatic ducts and exocrine glands were immunopositive for AβPP. Thus, it is suggested that AβPP may be expressed in the non-neuronal epithelial tissues independent of age and of the presence of senile plaques, and the expression may depend on individual differences or physiological conditions.     

Reactive oxygen species and uncoupling protein 2 in pancreatic β-cell function

Growing evidence indicates that reactive oxygen species (ROS) are not just deleterious by-products of respiratory metabolism in mitochondria, but can be essential elements for many biological responses, including in pancreatic β-cells. ROS can be a 'second-messenger signal' in response to hormone/receptor activation that serves as part of the 'code' to trigger the ultimate biological response, or it can be a 'protective signal' to increase the levels of antioxidant enzymes and small molecules to scavenge ROS, thus restoring cellular redox homeostasis. In pancreatic β-cells evidence is emerging that acute and transient glucose-dependent ROS contributes to normal glucose-stimulated insulin secretion (GSIS). However, chronic and persistent elevation of ROS, resulting from inflammation or excessive metabolic fuels such as glucose and fatty acids, may elevate antioxidant enzymes such that they blunt ROS and redox signalling, thus impairing β-cell function. An interesting mitochondrial protein whose main function appears to be the control of ROS is uncoupling protein 2 (UCP2). Despite continuing investigation of the exact mechanism by which UCP2 is 'activated', it is clear that UCP2 levels and/or activity impact the efficacy of GSIS in pancreatic islets. This review will focus on the paradoxical roles of ROS in pancreatic β-cell function and the regulatory role of UCP2 in ROS signalling and GSIS.     

Migration of mononuclear cells expressing β-actin through the adventitia into media and intima in coronary arteriogenesis and venogenesis in ischemic myocardium

It was previously thought that arteriogenesis and venogenesis are induced not only by proliferation of vessel-resident smooth muscle cells (SMCs) and endothelial cells (ECs) but also by migration of their precursors. However, it is not well understood through what route(s) the precursors migrate into the existing vessels.We examined through what route or routes circulating mononuclear cells expressing β-actin (β-MNCs), which we identified in canine coronary vessels, migrate into coronary vessel walls and cause arteriogenesis and venogenesis at 1, 2, 4 and 8 weeks after induction of myocardial infarction.The following changes were observed: (1) The β-MNCs migrated via coronary microvessels to the interstitial space at one week; (2) β-MNCs traversed the adventitia into the media and settled in parallel with pre-existing smooth muscle cells (SMCs) in arterioles and arteries and lost β-actin and acquired α-smooth muscle actin (α-SMA) to become mature SMCs at 2-4 weeks; (3) at the same time, other β-MNCs migrated across the adventitia and media into the intima and settled in parallel with pre-existing endothelial cells (ECs) and lost β-actin, while acquiring CD(31), to become mature ECs, resulting in arteriogenesis; (4) Similarly, β-MNCs migrated into venular and venous walls and became SMCs or ECs, resulting in venogenesis.β-MNCs in the interstitial space expressed CD(34) but not other major vascular cell markers.β-MNCs, possibly a vascular progenitor, migrate not from the lumen but across the adventitia into the media or intima of coronary vessels and transit to SMCs or ECs, and participate in arteriogenesis and venogenesis in ischemic myocardium.     

Identification of a mammalian glycerol-3-phosphate phosphatase: Role in metabolism and signaling in pancreatic β-cells and hepatocytes

Obesity, and the associated disturbed glycerolipid/fatty acid (GL/FA) cycle, contribute to insulin resistance, islet β-cell failure, and type 2 diabetes. Flux through the GL/FA cycle is regulated by the availability of glycerol-3-phosphate (Gro3P) and fatty acyl-CoA. We describe here a mammalian Gro3P phosphatase (G3PP), which was not known to exist in mammalian cells, that can directly hydrolyze Gro3P to glycerol. We identified that mammalian phosphoglycolate phosphatase, with an uncertain function, acts in fact as a G3PP. We found that G3PP, by controlling Gro3P levels, regulates glycolysis and glucose oxidation, cellular redox and ATP production, gluconeogenesis, glycerolipid synthesis, and fatty acid oxidation in pancreatic islet β-cells and hepatocytes, and that glucose stimulated insulin secretion and the response to metabolic stress, e.g., glucolipotoxicity, in β-cells. In vivo overexpression of G3PP in rat liver lowers body weight gain and hepatic glucose production from glycerol and elevates plasma HDL levels. G3PP is expressed at various levels in different tissues, and its expression varies according to the nutritional state in some tissues. As Gro3P lies at the crossroads of glucose, lipid, and energy metabolism, control of its availability by G3PP adds a key level of metabolic regulation in mammalian cells, and G3PP offers a potential target for type 2 diabetes and cardiometabolic disorders.The glycerolipid/fatty acid (GL/FA) cycle, which is central to energy homeostasis, balances glucose and lipid metabolism (1, 2), and generates metabolic signals (3, 4). This cycle is deregulated in obesity and type 2 diabetes. Under conditions of fuel surfeit with excessive glucose and free fatty acid (FFA) supply, a substantial portion of glucose is used in mammalian cells via formation of glycerol-3-phosphate (Gro3P) and its incorporation into GL via GL/FA cycle (4, 5). The cycle consists of lipogenesis and lipolysis segments and generates intermediates for the synthesis of various types of complex lipids, but also signals that control many biological processes, including insulin secretion and action (3, 6, 7). The proper operation of this cycle possibly protects β-cells and other cell types from glucolipotoxicity and metabolic stress (4, 8, 9).Lipogenesis, i.e., the successive esterification of glycolysis-derived Gro3P with fatty acyl-CoA (FA-CoA), produces triglyceride (TG), which can be stored as lipid droplets (10). Lipolysis of TG is initiated by adipose TG lipase to generate diacylglycerol (DAG), which is hydrolyzed by hormone sensitive lipase to give rise to monoacylglycerol (MAG). MAG hydrolysis by classical MAG lipase or by α/β-hydrolase domain-6 (ABHD6) to glycerol and FFA completes the lipolytic segment of the GL/FA cycle (2, 3).Presently glycerol release from mammalian cells is thought to occur exclusively from the lipolytic segment of the GL/FA cycle, and glycerol production is considered to reflect lipolysis flux. We proposed earlier that, at high glucose concentrations, the release of glycerol by β-cells, which do not express glycerokinase that transforms glycerol to Gro3P (4), is a mechanism of “glucolipodetoxification,” and that this process is dependent on the lipolysis segment of GL/FA cycle (3, 4). Indeed, mammalian cells are not known to harbor a Gro3P phosphatase (G3PP) (11), which could directly generate glycerol from Gro3P. In an earlier study on mass isotopomer distribution analysis of glucose labeling from [¹³C]glycerol in the liver, Gro3P hydrolysis activity was speculated but was not directly demonstrated (12). Thus, the fate of Gro3P in mammalian cells is thought to be its conversion to dihydroxyacetone phosphate (DHAP) or lysophosphatidate, the first intermediate of the lipogenic arm of the cycle. However, many microbes (13–15) and plants (16) harbor a G3PP. We now describe that a previously known phosphoglycolate phosphatase (PGP) (17) with an uncertain function in mammalian cells acts as a specific G3PP and plays a pivotal role in the regulation of glucose and lipid metabolism and signaling, as well as in the response to metabolic stress.     

Protective effects of epoxypukalide on pancreatic β-cells and glucose metabolism in STZ-induced diabetic mice

Diabetes is a consequence of a decrease on functional β-cell mass. We have recently demonstrated that epoxypukalide (Epoxy) is a natural compound with beneficial effects on primary cultures of rat islets. In this study, we extend our previous investigations to test the hypothesis that Epoxy protects β-cells and improves glucose metabolism in STZ-induced diabetic mice.

We used 3-months old male mice that were treated with Epoxy at 200 μg/kg body weight. Glucose intolerance was induced by multiple intraperitoneal low-doses of streptozotocin (STZ) on 5 consecutive days. Glucose homeostasis was evaluated measuring plasma insulin levels and glucose tolerance. Histomorphometry was used to quantify the number of pancreatic β-cells per islet. β-cell proliferation was assessed by BrdU incorporation, and apoptosis by TUNEL staining. Epoxy treatment significantly improved glucose tolerance and plasma insulin levels. These metabolic changes were associated with increased β-cell numbers, as a result of a two-fold increase in β-cell proliferation and a 50% decrease in β-cell death.

Our results demonstrate that Epoxy improves whole-body glucose homeostasis by preventing pancreatic β-cell death due to STZ-induced toxicity in STZ-treated mice.     

Influence of methionine／valine-depleted enteral nutrition on nucleic acid and protein metabolism in tumor-bearing rats

AIM: To investigate the effects of methionine/valine-depleted enteral nutrition (EN) on RNA, DNA and protein metabolism in tumor-bearing (TB) rats.METHODS: Sprague-Dawlley (SD) rats underwent jejunostomy for nutritional support. A suspension of Walker256 carcinosarcoma cells was subcutaneously inoculated.48 TB rats were randomly divided in 4 groups: A, B, C and D. The TB rats had respectively received jejunal feedings supplemented with balanced amino acids, methioninedepleted, balanced amino acids and valine-depleted for 6days before injection of 740 KBq 3H- methionine/valine via jejunum. The 3H incorporation rate of the radioactivity into RNA, DNA and proteins in tumor tissues at 0.5, 1, 2, 4 h postinjection of tracers was assessed with liquid scintillation counter.RESULTS: Incorporation of 3H into proteins in groups B and D was (0.500±0.020) % to (3.670±0.110) % and (0.708±0.019) % to (3.813±0.076) % respectively, lower than in groups A [(0.659±0.055) % to (4.492±0.108) %]and C r(0.805±0.098) % to (4.180±0.018) %]. Incorporation of 3H into RNA, DNA in group B was (0.237±0.075) %and (0.231±0.052) % respectively, lower than in group A (P＜0.01). There was no significant difference in uptake of 3H by RNA and DNA between group C and D (P＞0.05).CONCLUSION: Protein synthesis was inhibited by methionine/valine starvation in TB rats and nucleic acid synthesis was reduced after methionine depletion, thus resulting in suppression of tumor growth.     

G protein receptor kinase 4 polymorphisms: β-Blocker Pharmacogenetics and treatment-related outcomes in Hypertension

G protein-coupled receptor kinases (GRKs) are important regulatory proteins for many G protein-coupled receptors, but little is known about GRK4 pharmacogenetics. We hypothesized that 3 nonsynonymous GRK4 single-nucleotide polymorphisms, R65L (rs2960306), A142V (rs1024323), and A486V (rs1801058), would be associated with blood pressure response to atenolol, but not hydrochlorothiazide, and would be associated with long-term cardiovascular outcomes (all-cause death, nonfatal myocardial infarction, nonfatal stroke) in participants treated with an atenolol-based versus verapamil-SR-based antihypertensive strategy. GRK4 single-nucleotide polymorphisms were genotyped in 768 hypertensive participants from the Pharmacogenomic Evaluation of Antihypertensive Responses (PEAR) trial. In whites and blacks, increasing copies of the variant 65L-142V haplotype were associated with significantly reduced atenolol-induced diastolic blood pressure lowering (-9.1±6.8 versus -6.8±7.1 versus -5.3±6.4 mm Hg in participants with 0, 1, and 2 copies of 65L-142V, respectively; P=0.0088). One thousand four hundred sixty participants with hypertension and coronary artery disease from the INternational VErapamil SR/Trandolapril STudy (INVEST) were genotyped, and variant alleles of all 3 GRK4 single-nucleotide polymorphisms were associated with increased risk for adverse cardiovascular outcomes in an additive fashion, with 486V homozygotes reaching statistical significance (odds ratio, 2.29 [1.48-3.55]; P=0.0002). These effects on adverse cardiovascular outcomes were independent of antihypertensive treatment. These results suggest that the presence of GRK4 variant alleles may be important determinants of blood pressure response to atenolol and risk for adverse cardiovascular events. The associations with GRK4 variant alleles were stronger in patients who were also ADRB1 389R homozygotes, suggesting a potential interaction between these 2 genes.     

Serum β2-microglobulin,sialic acid,and C-reactive protein in systemic lupus erythematosus

Summary Serum ₂-microglobulin (₂m), sialic acid and C-reactive protein (CRP) were studied in 58 patients with systemic lupus erythematosus (SLE) on 186 occasions. Serum ₂m was significantly higher in SLE patients than in control subjects. Increased serum ₂m levels were seen in 68% of the patients with only extrarenal manifestations of SLE, in 75% of the patients with renal manifestations but normal glomerular filtration rate, and in 100% of the patients with renal failure. Serum ₂m levels in 12 SLE patients with associated Sjögren's syndrome were similar to those in patients without that syndrome. Serum sialic acid was also significantly increased in the SLE patients. Sixty-one (33%) of the 186 sera were positive for CRP (5 mg/l). The CRP elevation was not accompanied by recognized intercurrent infection or other superimposed cause of tissue injury and inflammation in 37 instances (61%). Under such conditions CRP was only moderately increased.     

Regulation of angiotensinogen gene expression and protein in neonatal rat cardiac fibroblasts by glucocorticoid and β-adrenergic stimulation

We previously demonstrated the presence of components for a renin-angiotensin system in fibroblasts cultured from neonatal rat ventricles, the regulation of expression of which has not been studied. Since glucocorticoids and β-adrenergic stimuli have been implicated in cardiac hypertrophy, and function as regulators of the circulating renin-angiotensin system, we examined the effects of dexamethasone and isoproterenol on angiotensinogen mRNA levels and protein secretion in cultured neonatal rat cardiac fibroblasts. Treatment of cardiac fibroblasts for 8 h with 10 μmol/l isoproterenol or 100 nmol/l dexamethasone increased angiotensinogen mRNA levels by 246 ± 7% and 1406 ± 207%, respectively. Over 24 h, dexamethasone and isoproterenol increased angiotensinogen secretion by 148 ± 32% and 123 ± 26%, respectively. Angiotensin II, which has been reported to be a positive regulator of angiotensinogen synthesis and secretion in liver, markedly attenuated the effects of dexamethasone and isoproterenol on angiotensinogen mRNA expression and secretion. In the presence of 1 μmol/l angiotensin II, the stimulation in angiotensinogen secretion observed with dexamethasone and isoproterenol was decreased by 62% and 76%, respectively. The negative feedback of angiotensin II on angiotensinogen expression was primarily mediated through the type one angiotensin II (AT₁) receptor (IC₅₀ = 0.30 ± 0.02 nmol/l). In summary, results from this study demonstrate that angiotensinogen mRNA levels and protein secretion in cardiac fibroblasts are positively regulated by glucocorticoid and β-adrenergic stimulation. In addition, angiotensinogen production by cardiac fibroblasts is under negative feedback control of angiotensin II. Received: 28 October 1999, Returned for revision: 24 November 1999, Revision received: 14 January 2000, Accepted: 26 January 2000     

Functional protein expression of multiple sodium channel α- and β-subunit isoforms in neonatal cardiomyocytes

Voltage-gated sodium channels are composed of pore-forming α- and auxiliary β-subunits and are responsible for the rapid depolarization of cardiac action potentials. Recent evidence indicates that neuronal tetrodotoxin (TTX) sensitive sodium channel α-subunits are expressed in the heart in addition to the predominant cardiac TTX-resistant Na_v1.5 sodium channel α-subunit. These TTX-sensitive isoforms are preferentially localized in the transverse tubules of rodents. Since neonatal cardiomyocytes have yet to develop transverse tubules, we determined the complement of sodium channel subunits expressed in these cells. Neonatal rat ventricular cardiomyocytes were stained with antibodies specific for individual isoforms of sodium channel α- and β-subunits. α-actinin, a component of the z-line, was used as an intracellular marker of sarcomere boundaries. TTX-sensitive sodium channel α-subunit isoforms Na_v1.1, Na_v1.2, Na_v1.3, Na_v1.4 and Na_v1.6 were detected in neonatal rat heart but at levels reduced compared to the predominant cardiac α-subunit isoform, Na_v1.5. Each of the β-subunit isoforms (β1-β4) was also expressed in neonatal cardiac cells. In contrast to adult cardiomyocytes, the α-subunits are distributed in punctate clusters across the membrane surface of neonatal cardiomyocytes; no isoform-specific subcellular localization is observed. Voltage clamp recordings in the absence and presence of 20 nM TTX provided functional evidence for the presence of TTX-sensitive sodium current in neonatal ventricular myocardium which represents between 20 and 30% of the current, depending on membrane potential and experimental conditions. Thus, as in the adult heart, a range of sodium channel α-subunits are expressed in neonatal myocytes in addition to the predominant TTX-resistant Na_v1.5 α-subunit and they contribute to the total sodium current.     

Correlation of integrin β3 mRNA and vascular endothelial growth factor protein expression profiles with the clinicopathological features and prognosis of gastric carcinoma

AIM： To investigate integrin β3 mRNA and vascular endothelial growth factor （VEGF） protein expression in gastric carcinoma, and its correlation with microvascular density, growth-pattern, invasion, metastasis and prognosis. METHODS： In situ hybridization（ISH） of integrin β3 mRNA and immunohistochemistry of VEGF and CD34 protein were performed on samples from 118 patients with gastric cancer. RESULTS： The positive rate of integrin β3 mRNA in non-tumor gastric mucosa （20%） was significantly lower than that of the gastric cancer tissue （52.5%, X^2 = 10.20, P 〈 0.01）. In patients of infiltrating type, stage T3-T4, vessel invasion, lymphatic metastasis, hepatic or peritoneal metastasis, the positive expression rates of integrin β3 mRNA were significantly higher than those in patients of expanding type （P 〈 0.01）, stage T1-T2 （P 〈 0.01）, non-vessel invasion （P 〈 0.01）, without lymphatic metastasis （P 〈 0.01）, without hepatic and peritoneal metastasis （P 〈 0.01）, respectively. In patients of infiltrating type, stage T3-T4, vessel invasion, lymphatic metastasis, hepatic or peritoneal metastasis, the positive expression rates of VEGF protein were significantly higher than those in patients of expanding type （P 〈 0.01）, stage T1-T2 （P 〈 0.01）, non-vessel invasion （P 〈 0.01）, without lymphatic metastasis （P 〈 0.01）, without hepatic and peritoneal metastasis （P 〈 0.01）, respectively. In patients of infiltrating type, stage T3-T4, vessel invasion, lymphatic metastasis, hepatic or peritoneal metastasis, the mean MVD were significantly higher than those in patients of expanding type （P 〈 0.01）, stage T1-T2 （P 〈 0.01）, non-vessel invasion （P 〈 0.01）, without lymphatic metastasis （P 〈 0.01）, without hepatic and peritoneal metastasis （P 〈 0.01）, respectively. It was found that the positive expression rate of integrin β3 mRNA was positively related to that of VEGF protein （P 〈 0.01） and MVD （P 〈 0.05）,     

Tumor-associated antigen profiling in breast and ovarian cancer: mRNA,protein or T cell recognition?

Purpose The absence of tumor-associated antigens (TAA) which might elicit an immune response is one reason for the disappointing results of therapeutical vaccines in cancer patients. Moreover, impaired expression of MHC class-I and components involved in antigen processing, such as TAP-1, -2, LMP-2, -7, and MECL-1, may lead to tumor escape from immune recognition. Expression profiling of TAA is one approach towards the design of well-defined and individualized anti-tumor vaccines.Methods Quantitative polymerase chain reaction (qRT-PCR) is the method of choice to characterize immunologically relevant properties of individual tumors. However, the application of qRT-PCR as a surrogate parameter for the expression of TAAs depends upon the assumption that the level of an mRNA species correlates with the cellular level of the protein it encodes. Therefore, we additionally analyzed TAA expression by immunofluorescence and T cell recognition.Results In the present study we were unable to confirm that impaired TAP-1 or -2 (transporter associated with antigen processing) expression characterized at the mRNA level is an appropriate surrogate parameter for down-regulated MHC class-I expression in breast cancer. In addition, we analyzed the expression pattern of TAAs in breast and ovarian cancer cell lines. Besides the well-known over-expression of HER-2/neu, CEA, and MUC-1, multiple antigens of the MAGE-family were frequently co-expressed. We investigated whether detection of TAAs by qRT-PCR correlates with monoclonal antibody staining, and which method could predict T cell recognition. We demonstrated a correlation between tumor cell lysis by HLA-A*0201-restricted, MUC-1-specific CTL and threshold levels of MUC-1-specific mRNA.Conclusion MUC-1 is an example that TAA profiling by RT-PCR and flow cytometry can fail to correlate with each other and are of limited value in the prediction of T cell recognition.This work was supported by Grants from the Deutsche Forschungsgemeinschaft (GU 511/1–1), the Deutsche Krebshilfe (10–1529 Gü I) (to B.G., C.R.), and the AKF-Programm University of Tübingen (to. S.K.).