Umbilical cord mesenchymal stromal cells transplantation delays the onset of hyperglycemia in the RIP-B7.1 mouse model of experimental autoimmune diabetes through multiple immunosuppressive and anti-inflammatory responses

Type 1 diabetes mellitus (T1DM) is an autoimmune disorder specifically targeting pancreatic islet beta cells. Despite many efforts focused on identifying new therapies able to counteract this autoimmune attack and/or stimulate beta cells regeneration, TD1M remains without effective clinical treatments providing no clear advantages over the conventional treatment with insulin. We previously postulated that both the inflammatory and immune responses and beta cell survival/regeneration must be simultaneously targeted to blunt the progression of disease. Umbilical cord-derived mesenchymal stromal cells (UC-MSC) exhibit anti-inflammatory, trophic, immunomodulatory and regenerative properties and have shown some beneficial yet controversial effects in clinical trials for T1DM. In order to clarify conflicting results, we herein dissected the cellular and molecular events derived from UC-MSC intraperitoneal administration (i.p.) in the RIP-B7.1 mouse model of experimental autoimmune diabetes. Intraperitoneal (i.p.) transplantation of heterologous mouse UC-MSC delayed the onset of diabetes in RIP-B7.1 mice. Importantly, UC-MSC i. p. transplantation led to a strong peritoneal recruitment of myeloid-derived suppressor cells (MDSC) followed by multiple T-, B- and myeloid cells immunosuppressive responses in peritoneal fluid cells, spleen, pancreatic lymph nodes and the pancreas, which displayed significantly reduced insulitis and pancreatic infiltration of T and B Cells and pro-inflammatory macrophages. Altogether, these results suggest that UC-MSC i. p. transplantation can block or delay the development of hyperglycemia through suppression of inflammation and the immune attack.

Formation of acrylamide at temperatures lower than 100°C: the case of prunes and a model study

Acrylamide concentrations in prune products – baby strained prunes (range = 75–265 μg kg⁻⁻¹), baby apple/prune juice (33–61 μg kg⁻⁻¹), prune juice (186–916 μg kg⁻⁻¹) and prunes (58–332 μg kg⁻⁻¹) – on the Canadian market were determined. The formation of acrylamide in a simulated plum juice was also investigated under ‘drying conditions’ in an open vessel at temperatures <100°C for 24 h and under ‘wet conditions’ in a closed vessel at a temperature of 120°C for 1 h. Acrylamide was produced in a simulated plum juice under ‘drying conditions’ in amounts comparable with those found in prunes and prune juices. Acrylamide was not produced in simulated plum juice under ‘wet conditions’ in a closed vessel at temperature of 120°C for 1 h, but under the same condition an authentic prune juice doubled its acrylamide concentration. Formation of acrylamide in prune products was attributed to the presence of asparagine and sugars in the starting materials.

Migration of bisphenol A from plastic baby bottles, baby bottle liners and reusable polycarbonate drinking bottles

Human exposure to bisphenol A (BPA) has recently received special attention. It has been shown that exposure to BPA may occur through the consumption of beverages or foods that have been in contact with polycarbonate (PC) plastic containers or epoxy resins in food packaging. A BPA migration study was conducted using a variety of plastic containers, including polycarbonate baby bottles, non-PC baby bottles, baby bottle liners, and reusable PC drinking bottles. Water was used to simulate migration into aqueous and acidic foods; 10% ethanol solution to simulate migration to low- and high-alcoholic foods; and 50% ethanol solution to simulate migration to fatty foods. By combining solid-phase extraction, BPA derivatization and analysis by GC-EI/MS/MS, a very low detection limit at the ng l(-1) level was obtained. Migration of BPA at 40 degrees C ranged from 0.11 microg l(-1) in water incubated for 8 h to 2.39 microg l(-1) in 50% ethanol incubated for 240 h. Residual BPA leaching from PC bottles increased with temperature and incubation time. In comparison with the migration observed from PC bottles, non-PC baby bottles and baby bottle liners showed only trace levels of BPA. Tests for leachable lead and cadmium were also conducted on glass baby bottles since these represent a potential alternative to plastic bottles. No detectable lead or cadmium was found to leach from the glass. This study indicated that non-PC plastic baby bottles, baby bottle liners and glass baby bottles might be good alternatives for polycarbonate bottles.

The transcription factor PAX4 acts as a survival gene in INS-1E insulinoma cells

The paired/homeodomain transcription factor Pax4 is essential for islet beta-cell generation during pancreas development and their survival in adulthood. High Pax4 expression was reported in human insulinomas indicating that deregulation of the gene may be associated with tumorigenesis. We report that rat insulinoma INS-1E cells express 25-fold higher Pax4 mRNA levels than rat islets. In contrast to primary beta-cells, activin A but not betacellulin or glucose induced Pax4 mRNA levels indicating dissociation of Pax4 expression from insulinoma cell proliferation. Short hairpin RNA adenoviral constructs targeted to the paired domain or homeodomain (viPax4PD and viPax4HD) were generated. Pax4 mRNA levels were lowered by 73 and 50% in cells expressing either viPax4PD or viPax4HD. Transcript levels of the Pax4 target gene bcl-xl were reduced by 53 and 47%, whereas Pax6 and Pdx1 mRNA levels were unchanged. viPax4PD-infected cells displayed a twofold increase in spontaneous apoptosis and were more susceptible to cytokine-induced cell death. In contrast, proliferation was unaltered. RNA interference-mediated repression of insulin had no adverse effects on either Pax4 or Pdx1 expression as well as on cell replication or apoptosis. These results indicate that Pax4 is redundant for proliferation of insulinoma cells, whereas it is essential for survival through upregulation of the antiapoptotic gene bcl-xl.

Dopamine modulates von Willebrand factor secretion in endothelial cells via D2-D4 receptors

OBJECTIVE

von Willebrand factor (VWF) is acutely released from endothelial cells in response to numerous calcium-raising agents (e.g. thrombin, histamine) and cAMP-raising agents (e.g. epinephrine, adenosine, vasopressin). In contrast, very few inhibitors of endothelial VWF secretion have been described. The neurotransmitter dopamine is a modulator of exocytosis in several endocrine cells, and is possibly involved in the regulation of several endothelial cell functions. We therefore investigated the effect of dopamine on endothelial VWF secretion.

RESULTS

Dopamine, D2/D3- and D4-specific agonists inhibited histamine- but not thrombin-induced VWF secretion. Expression of dopamine D2, D3 and D4 receptors was demonstrated by reverse transcription polymerase chain reaction (RT-PCR) in both human aortic (HAEC) and umbilical vein (HUVEC) endothelial cells. D2-D4 agonists did not inhibit histamine-induced rise in [Ca(2+)](i): they inhibited histamine-induced secretion even in the absence of extracellular calcium. Thus, the dopamine effects are not mediated by [Ca(2+)](i)-dependent signalling. D2/D3- and D4-specific agonists inhibited neither the rise in cAMP nor VWF secretion in response to epinephrine and adenosine, arguing against an effect on cAMP-mediated signalling. D1 and D5 receptors were not detected in HAEC or HUVEC by RT-PCR, and the D1/D5-specific agonist SKF 38 393 failed to modulate VWF secretion, arguing against a role for these receptors in endothelial exocytosis.

CONCLUSIONS

Dopamine inhibits histamine-induced endothelial exocytosis by activating D2-D4 receptor, via a mechanism distinct from [Ca(2+)](i)-or cAMP-mediated signaling. In contrast, D1 and D5 receptors are not functionally expressed in cultured endothelial cells. Dopamine agonists may be useful as inhibitors of endothelial activation in inflammation and cardiovascular disease.

Characterization of two distinct liver progenitor cell subpopulations of hematopoietic and hepatic origins

Despite extensive studies, the hematopoietic versus hepatic origin of liver progenitor oval cells remains controversial. The aim of this study was to determine the origin of such cells after liver injury and to establish an oval cell line. Rat liver injury was induced by subcutaneous insertion of 2-AAF pellets for 7 days with subsequent injection of CCl(4). Livers were removed 9 to 13 days post-CCl(4) treatment. Immunohistochemistry was performed using anti-c-kit, OV6, Thy1, CK19, AFP, vWF and Rab3b. Isolated non-parenchymal cells were grown on mouse embryonic fibroblast, and their gene expression profile was characterized by RT-PCR. We identified a subpopulation of OV6/CK19/Rab3b-expressing cells that was activated in the periportal region of traumatized livers. We also characterized a second subpopulation that expressed the HSCs marker c-kit but not Thy1. Although we successfully isolated both cell types, OV6/CK19/Rab3b(+) cells fail to propagate while c-kit(+)-HSCs appeared to proliferate for up to 7 weeks. Cells formed clusters which expressed c-kit, Thy1 and albumin. Our results indicate that a bona fide oval progenitor cell population resides within the liver and is distinct from c-kit(+)-HSCs. Oval cells require the hepatic niche to proliferate, while cells mobilized from the circulation proliferate and transdifferentiate into hepatocytes without evidence of cell fusion.

Association of childhood type 1 diabetes mellitus with a variant of PAX4: possible link to beta cell regenerative capacity

AIMS/HYPOTHESIS

Loss of pancreatic beta cells is the crucial event in the development of type 1 diabetes. It is the result of an imbalance between autoimmune destruction and insufficient regeneration of islet cells. To study the role of islet cell regeneration in the pathogenesis of type 1 diabetes, we focused on PAX4, a paired homeodomain transcriptional repressor that is involved in islet cell growth.

METHODS

The study included 379 diabetic children and 1,070 controls from two distinct populations, and a cohort of children who had not developed type 1 diabetes, despite the presence of islet cell antibodies. Genomic DNA analysis of PAX4 was carried out via direct sequencing of PCR-amplified fragments and allelic discrimination. We compared the transrepression potential of the PAX4 variants in betaTC3 cells and analysed their influence on beta cell growth.

RESULTS

The type 1 diabetic subjects are different from the normal individuals in terms of the genotype distribution of the A1168C single nucleotide polymorphism in PAX4. The C/C genotype is frequent among type 1 diabetic children (73%) and rare among the control population (32%). Conversely, the A/C genotype is prevalent among control subjects (62%) and antibody-positive children without type 1 diabetes (73.6%), but uncommon among subjects with type 1 diabetes (17.5%). The combination of PAX4A and PAX4C is functionally more active than PAX4C alone (the "diabetic" variant). Beta cells expressing PAX4A and PAX4C efficiently proliferate when stimulated with glucose, whereas cells expressing the PAX4C variant alone do not.

CONCLUSIONS/INTERPRETATION

We have identified a link between beta cell regenerative capacity and susceptibility to type 1 diabetes. This finding could explain the fact that not all of the individuals who develop autoimmunity against beta cells actually contract the disease. The C/C genotype of the A1168C polymorphism in PAX4 can be viewed as a predisposition marker that can help to detect individuals prone to develop type 1 diabetes.

Suppression of Pdx-1 perturbs proinsulin processing, insulin secretion and GLP-1 signalling in INS-1 cells

AIMS/HYPOTHESIS

Mutations in genes encoding HNF-4alpha, HNF-1alpha and IPF-1/Pdx-1 are associated with, respectively, MODY subtypes-1, -3 and -4. Impaired glucose-stimulated insulin secretion is the common primary defect of these monogenic forms of diabetes. A regulatory circuit between these three transcription factors has also been suggested. We aimed to explore how Pdx-1 regulates beta cell function and gene expression patterns.

METHODS

We studied two previously established INS-1 stable cell lines permitting inducible expression of, respectively, Pdx-1 and its dominant-negative mutant. We used HPLC for insulin processing, adenovirally encoded aequorin for cytosolic [Ca2+], and transient transfection of human growth hormone or patch-clamp capacitance recordings to monitor exocytosis.

RESULTS

Induction of DN-Pdx-1 resulted in defective glucose-stimulated and K+-depolarisation-induced insulin secretion in INS-1 cells, while overexpression of Pdx-1 had no effect. We found that DN-Pdx-1 caused down-regulation of fibroblast growth factor receptor 1 (FGFR1), and consequently prohormone convertases (PC-1/3 and -2). As a result, DN-Pdx-1 severely impaired proinsulin processing. In addition, induction of Pdx-1 suppressed the expression of glucagon-like peptide 1 receptor (GLP-1R), which resulted in marked reduction of both basal and GLP-1 agonist exendin-4-stimulated cellular cAMP levels. Induction of DN-Pdx-1 did not affect glucokinase activity, glycolysis, mitochondrial metabolism or ATP generation. The K+-induced cytosolic [Ca2+] rise and Ca2+-evoked exocytosis (membrane capacitance) were not abrogated.

CONCLUSIONS/INTERPRETATION

The severely impaired proinsulin processing combined with decreased GLP-1R expression and cellular cAMP content, rather than metabolic defects or altered exocytosis, may contribute to the beta cell dysfunction induced by Pdx-1 deficiency.

Ectopic expression of the beta-cell specific transcription factor Pdx1 inhibits glucagon gene transcription

AIMS/HYPOTHESIS

The transcription factor Pdx1 is required for the development and differentiation of all pancreatic cells. Beta-cell specific inactivation of Pdx1 in developing or adult mice leads to an increase in glucagon-expressing cells, suggesting that absence of Pdx1could favour glucagon gene expression by a default mechanism.

METHOD

We investigated the inhibitory role of Pdx1 on glucagon gene expression in vitro. The glucagonoma cell line InR1G9 was transduced with a Pdx1-encoding lentiviral vector and insulin and glucagon mRNA levels were analysed by northern blot and real-time PCR. To understand the mechanism by which Pdx1 inhibits glucagon gene expression, we studied its effect on glucagon promoter activity in non-islet cells using transient transfections and gel-shift analysis.

RESULTS

In glucagonoma cells transduced with a Pdx1-encoding lentiviral vector, insulin gene expression was induced while glucagon mRNA levels were reduced by 50 to 60%. In the heterologous cell line BHK-21, Pdx1 inhibited by 60 to 80% the activation of the alpha-cell specific element G1 conferred by Pax-6 and/or Cdx-2/3. Although Pdx1 could bind three AT-rich motifs within G1, two of which are binding sites for Pax-6 and Cdx-2/3, the affinity of Pdx1 for G1 was much lower as compared to Pax-6. In addition, Pdx1 inhibited Pax-6 mediated activation through G3, to which Pdx1 was unable to bind. Moreover, a mutation impairing DNA binding of Pdx1 had no effect on its inhibition on Cdx-2/3. Since Pdx1 interacts directly with Pax-6 and Cdx-2/3 forming heterodimers, we suggest that Pdx1 inhibits glucagon gene transcription through protein to protein interactions with Pax-6 and Cdx-2/3.

CONCLUSION/INTERPRETATION

Cell-specific expression of the glucagon gene can only occur when Pdx1 expression extinguishes from the early alpha cell precursor.

The pancreatic beta-cell-specific transcription factor Pax-4 inhibits glucagon gene expression through Pax-6

AIMS/HYPOTHESIS

The paired-homeobox genes pax-4 and pax-6 are crucial for islet development; whereas the null mutation of pax-6 results in the nearly absence of glucagon-producing alpha cells, pax-4 homozygous mutant mice lack insulin and somatostatin-producing beta and delta cells but contain an increased number of alpha cells suggesting that alpha cells could develop by a default mechanism.

METHODS

To investigate whether beta-cell specific factors act negatively on glucagon gene transcription, we ectopically expressed pax-4 in glucagon producing InR1G9 cells; Pax-4 inhibited basal transcription of the glucagon gene promoter by 60%. To assess the mechanism of this inhibition, we cotransfected the non-islet cell line BHK-21 with Pax-4 and various transcription factors present in alpha cells.

RESULTS

In addition to a general repressor activity on basal glucagon gene promoter activity of 30-50%, a specific 90% inhibition of Pax-6 mediated transactivation was observed. In contrast, Pax-4 had no effect on Cdx-2/3 or HNF3alpha mediated transcriptional activation. Pax-4 showed similar affinity to the Pax-6 binding sites on the glucagon gene promoter compared to Pax-6, but varying with KCl concentrations.

CONCLUSION/INTERPRETATION

Pax-4 impairs glucagon gene transcription specifically through inhibition of Pax-6 mediated transactivation. Transcriptional inhibition seems to be mediated by direct DNA binding competition with Pax-6 and potentially additional mechanisms such as protein-protein interactions and a general repressor activity of Pax-4. Glucagon gene expression in alpha cells could thus result from both the presence of islet cell specific transcription factors and the absence of Pax-4.

Characterization of a novel liver-specific protein/DNA binding site in the human HMG CoA reductase promoter

These studies define a novel binding element (site C) within the human HMG CoA reductase promoter using a combination of in vitro DNase I footprinting and gel mobility shift assays. The factor interacting with site C appears to be restricted to the liver, indicating a possible role for this protein in regulating hepatic expression of the gene. Studies based on competitive gel mobility shift assays and transient co-transfection experiments performed using a reporter construct harbouring the promoter of HMG CoA reductase suggest that the protein binding to site C may belong to the C/EBP family of transcription factors. A factor interacting with this binding element was also identified in human liver nuclear protein extracts.

Hepatic lipase affects both HDL and ApoB-containing lipoprotein levels in the mouse

Transgenic mice were created overproducing a range of human HL (hHL) activities (4-23-fold increase) to further examine the role of hepatic lipase (HL) in lipoprotein metabolism. A 5-fold increase in heparin releasable HL activity was accompanied by moderate (approx. 20%) decreases in plasma total and high density lipoprotein (HDL) cholesterol and phospholipid (PL) but no significant change in triglyceride (TG). A 23-fold increase in HL activity caused a more significant decrease in plasma total and HDL cholesterol, PL and TG (77%, 64%, 60%, and 24% respectively), and a substantial decrease in lipoprotein lipids amongst IDL, LDL and HDL fractions. High levels of HL activity diminished the plasma concentration of apoA-I, A-II and apoE (76%, 48% and 75%, respectively). In contrast, the levels of apoA-IV-containing lipoproteins appear relatively resistant to increased titers of hHL activity. Increased hHL activity was associated with a progressive decrease in the levels and an increase in the density of LpAI and LpB48 particles. The increased rate of disappearance of 125I-labeled human HDL from the plasma of hHL transgenic mice suggests increased clearance of HDL apoproteins in the transgenic mice. The effect of increased HL activity on apoB100-containing lipoproteins was more complex. HL-deficient mice have substantially decreased apoB100-containing low density lipoproteins (LDL) compared to controls. Increased HL activity is associated with a transformation of the lipoprotein density profile from predominantly buoyant (VLDL/IDL) lipoproteins to more dense (LDL) fractions. Increased HL activity from moderate (4-fold) to higher (5-fold) levels decreased the levels of apoB100-containing particles. Thus, at normal to moderately high levels in the mouse, HL promotes the metabolism of both HDL and apoB-containing lipoproteins and thereby acts as a key determinant of plasma levels of both HDL and LDL.