All-trans retinoic acid ameliorates glycemic control in diabetic mice via modulating pancreatic islet production of vascular endothelial growth factor-A.

Patients with type 1 diabetes mellitus are associated with impairment in vitamin A metabolism. This study evaluated whether treatment with retinoic acid, the biologically active metabolite of vitamin A, can ameliorate diabetes. All-trans retinoic acid (atRA) was used to treat streptozotocin (STZ)-induced diabetic mice which revealed atRA administration ameliorated blood glucose levels of diabetic mice. This hyperglycemic amelioration was accompanied by an increase in the amount of ß cells co-expressed Pdx1 and insulin and by restoration of the vascular laminin expression. The atRA-induced production of vascular endothelial growth factor-A from the pancreatic islets was possibly the key factor that mediated the restoration of islet vascularity and recovery of ß-cell mass. Furthermore, the combination of islet transplantation and atRA administration significantly rescued hyperglycemia in diabetic mice. These findings suggest that vitamin A derivatives can potentially be used as a supplementary treatment to improve diabetes management and glycemic control.

Differentiation of pancreatic acinar cells to hepatocytes requires an intermediate cell type.

BACKGROUND & AIMS: The appearance of hepatic foci in pancreas has been well-documented in animal experiments and in patients with pancreatic cancer. We previously demonstrated that transdifferentiation of pancreatic exocrine cells to hepatocytes required members of the CCAAT enhancer binding protein family. Although the molecular basis of hepatic transdifferentiation is understood, the early cellular events remain to be defined. METHODS: Dexamethasone and oncostatin M were used to induce transdifferentiation of primary cultures of mouse acinar cells and exocrine cell lines into hepatocytes. Fluorescent-activated cell sorting was used to identify intermediate cell types and side-population characteristics. Cre-loxP-based lineage tracing was used to investigate whether acinar cells contribute directly to hepatocytes via intermediates that express adenosine triphosphate-binding cassette subfamily G member 2 (ABCG2). RESULTS: Lineage tracing studies showed that hepatocytes were derived directly from pancreatic cells via ABCG2-expressing intermediates. Exposure of cells to insulin increased Akt phosphorylation, ABCG2 expression, and hepatic transdifferentiation. Inhibition of the phosphoinositide 3-kinase pathway, through addition of LY294002 or overexpression of a dominant-negative form of Akt, was sufficient to prevent transdifferentiation. When ABCG2-expressing cells were incubated with glucagon-like-peptide 1 or epidermal growth factor, the intermediate cells could differentiate into insulin-producing beta-like cells. CONCLUSIONS: The phosphoinositide 3-kinase pathway is important in the transdifferentiation of acinar cells to hepatocytes and those hepatocytes arise from acinar cells via ABCG2-expressing intermediates. Furthermore, ABCG2-expressing cells are multipotent and able to differentiate into hepatocytes and insulin-producing beta cells.

Selection, enrichment, and maintenance of self-renewal liver stem/progenitor cells utilizing polypeptide polyelectrolyte multilayer films.

Recent progress has led to the identification of liver stem/progenitor cells as suitable sources for generating transplantable liver cells. However, the great variability in methods utilized to isolate liver stem/progenitor cells is a considerable challenge for clinical applications. The polyelectrolyte-multilayer technique can constitute a useful method for selective cell adhesion. Whether enrichment of liver stem/progenitor cells can be achieved utilizing polypeptide polyelectrolyte-multilayer films was investigated in current work. Fetal liver cells isolated from E13.5 mouse embryos were seeded on the poly-l-glutamic acid/poly-l-lysine alternating films, and we revealed that fetal liver stem/progenitor cells were selected and formed colonies. These undifferentiated colonies were maintained on the films composed of four alternating layers, with the topmost poly-l-glutamic acid layer judged by the constitutive expression of stem-cell markers such as Dlk-1, CD49f, and CD133 and self-renew marker-beta-catenin. Our work has demonstrated that highly tunable polyelectrolyte-multilayer films were suitable for selective enrichment of liver stem/progenitor cells in vitro.

Maternal vitamin A deficiency during pregnancy affects vascularized islet development.

Vitamin A deficiency is known to affect 20 million pregnant women worldwide. However, the prenatal effects of maternal vitamin A deficiency on pancreas development have not been clearly determined. The present study examined how maternal vitamin A deficiency affects fetal islet development. Vitamin A-deficient mice were generated by feeding female mice with a chemically defined diet lacking vitamin A prior to mating as well as during pregnancy. We found that maternal vitamin A deficiency during pregnancy affected fetal pancreas development. Although the exocrine differentiation appeared normal, development of islet tissue was impaired. In the pancreas of neonatal mice, only a few endocrine cell clusters were formed, and these cell clusters lacked capillary endothelial cells. To further determine how vitamin A metabolites, such as retinoic acid, regulate vascularized islet development, ex vivo culture of embryonic pancreas either in the presence of 4-diethylaminobenzaldehyde (DEAB; an inhibitor of retinaldehyde dehydrogenase), all-trans retinoic acid (atRA) or retinoic acid receptor agonist (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthylenyl)-1-propenyl] benzoic acid (TTNPB) was carried out. We found that the addition of DEAB blocked vascularization and suppressed ß-cell differentiation. Conversely, atRA or TTNPB promoted ß-cell differentiation accompanied by enhanced expression of vascular basement component, laminin. We further demonstrated that atRA regulated vascularization via upregulating vascular endothelial growth factor-A (VEGF-A) secretion in embryonic pancreas and treatment with VEGF-A was able to partially rescue vascularization and ß-cell differentiation in DEAB-treated embryonic pancreas cultures. The findings explain why maternal vitamin A deficiency affects fetal islet development and support an essential role of retinoid signaling in regulating vascularized islet development.

Butyrate reduced lipopolysaccharide-mediated macrophage migration by suppression of Src enhancement and focal adhesion kinase activity.

Macrophage motility is vital in innate immunity. Lipopolysaccharide (LPS)-mediated macrophage migration requires the enhancement of Src expression and enzymatic activity, which can be regulated by inducible nitric oxide synthase (iNOS). As a major short-chain fatty acid with histone deacetylase (HDAC) inhibitor activity, butyrate exerts anti-inflammatory effect by regulating the expression of cytokines. However, the influence of butyrate on macrophage movement was vague. In this study, we observed that butyrate inhibited migration of both RAW264.7 and rat peritoneal macrophages elicited by LPS. Unlike its myeloid relatives (i.e. Lyn, Fgr and Hck) whose expression was almost unaltered in the presence or absence of butyrate in LPS-treated macrophages, LPS-mediated Src induction was greatly suppressed by butyrate and that could be attributable to reduced level of the src transcript. Similar phenomenon was also detected in LPS-treated macrophages exposed to another HDAC inhibitor, trichostatin A (TSA). Consistent with the indispensability of iNOS in promoting macrophage mobilization via Src up-regulation and the activation of both Src and FAK, we did observe concomitant decrement of iNOS, Src and the suppressed activity of Src and FAK in butyrate- or TSA-pretreated macrophages following LPS exposure. These results imply that by virtue of reduction of Src, butyrate could effectively hamper LPS-triggered macrophage locomotion.