Increased alpha and beta cell mass during mouse pregnancy is not dependent on transdifferentiation

Maternal pancreatic beta-cell mass (BCM) increases during pregnancy to compensate for relative insulin resistance. If BCM expansion is suboptimal, gestational diabetes mellitus can develop. Alpha-cell mass (ACM) also changes during pregnancy, but there is a lack of information about α-cell plasticity in pregnancy and whether α- to β-cell transdifferentiation can occur. To investigate this, we used a mouse model of gestational glucose intolerance induced by feeding low-protein (LP) diet from conception until weaning and compared pregnant female offspring to control diet-fed animals. Control and LP pancreata were collected for immunohistochemical analysis and serum glucagon levels were measured. In order to lineage trace α- to β-cell conversion, we utilized transgenic mice expressing yellow fluorescent protein behind the proglucagon gene promoter (Gcg-Cre/YFP) and collected pancreata for histology at various gestational timepoints. Alpha-cell proliferation increased significantly at gestational day (GD) 9.5 in control pregnancies resulting in an increased ACM at GD18.5, and this was significantly reduced in LP animals. Despite these changes, serum glucagon was higher in LP mice at GD18.5. Pregnant Gcg-Cre/YFP mice showed no increase in the abundance of insulin+YFP+glucagon- cells (phenotypic β-cells). A second population of insulin+YFP+glucagon+ cells was identified which also did not alter during pregnancy. However, there was an altered anatomical distribution within islets with fewer insulin+YFP+glucagon- cells but more insulin+YFP+glucagon+ cells being present in the islet mantle at GD18.5. These findings demonstrate that dynamic changes in ACM occur during normal pregnancy and were altered in glucose-intolerant pregnancies.

Altered pancreas remodeling following glucose intolerance in pregnancy in mice

Gestational diabetes mellitus increases the risk of dysglycemia postpartum, in part, due to pancreatic β-cell dysfunction. However, no histological evidence exists comparing endocrine pancreas after healthy and glucose-intolerant pregnancies. This study sought to address this knowledge gap, in addition to exploring the contribution of an inflammatory environment to changes in endocrine pancreas after parturition. We used a previously established mouse model of gestational glucose intolerance induced by dietary low protein insult from conception until weaning. Pancreas and adipose samples were collected at 7, 30 and 90 days postpartum for histomorphometric and cytokine analyses, respectively. Glucose tolerance tests were performed prior to euthanasia and blood was collected via cardiac puncture. Pregnant female mice born to dams fed a low protein diet previously shown to develop glucose intolerance at late gestation relative to controls continued to be glucose intolerant until 1 month postpartum. However, glucose tolerance normalized by 3 months postpartum. Glucose intolerance at 7 days postpartum was associated with lower beta- and alpha-cell fractional areas and higher adipose levels of pro-inflammatory cytokine, interleukin-6. By 3 months postpartum, a compensatory increase in the number of small islets and a higher insulin to glucagon ratio likely enabled euglycemia to be attained in the previously glucose-intolerant mice. The results show that impairments in endocrine pancreas compensation in hyperglycemic pregnancy persist after parturition and contribute to prolonged glucose intolerance. These impairments may increase the susceptibility to development of future type 2 diabetes.

A mouse model of gestational glucose intolerance through exposure to a low protein diet during fetal and neonatal development

KEY POINTS

Pancreatic β-cell dysfunction is hypothesized to be the significant determinant of gestational diabetes pathogenesis, however pancreatic samples from patients are scarce. This study reports a novel mouse model of gestational glucose intolerance in pregnancy, originating from previous nutrition restriction in utero, in which glucose intolerance was restricted to late gestation as is seen in human gestational diabetes. Glucose intolerance was attributed to reduced β-cell proliferation, leading to impaired gestational β-cell mass expansion in maternal endocrine pancreas, in addition to reduced glucose-stimulated insulin secretion. This model reproduces some of the features of gestational diabetes and is suitable for testing safe therapeutic interventions that increase β-cell mass during pregnancy and prevent or reverse gestational glucose intolerance.

ABSTRACT

Gestational diabetes mellitus (GDM) is an increasingly prevalent form of diabetes that appears during pregnancy. Pathological studies link a failure to adaptively increase maternal pancreatic β-cell mass (BCM) in pregnancy to GDM. Due to the scarcity of pancreatic samples from GDM patients, we sought to develop a novel mouse model for impaired gestational glucose tolerance. Mature female C57Bl/6 mouse offspring (F1) born to dams fed either a control (C) or low-protein (LP) diet during gestation and lactation were randomly allocated into two subsequent study groups: pregnant (CP, LPP) or non-pregnant (CNP, LPNP). Glucose tolerance tests were performed at gestational day (GD) 9, 12 and 18. Subsequently, pancreata were removed for fluorescence immunohistochemistry to assess α-cell mass (ACM), BCM and β-cell proliferation. An additional group of animals was used to measure insulin secretion from isolated islets at GD18. LPP females displayed glucose intolerance compared to CP females at GD18 (P < 0.001). BCM increased threefold at GD18 in CP females. However, LPP females had reduced BCM expansion (P < 0.01) concurrent with reduced β-cell proliferation at GD12 (P < 0.05). LPP females also had reduced ACM expansion at GD18 (P < 0.01). LPP islets had impaired glucose-stimulated insulin secretion in vitro compared to CP islets (P < 0.01). Therefore, impaired glucose tolerance during pregnancy is associated with a failure to adequately adapt BCM, as a result of reduced β-cell proliferation, in addition to lower glucose-stimulated insulin secretion. This model could be used to evaluate novel interventions during pregnancy to increase BCM or function as a strategy to prevent/reverse GDM.

Direct comparison of the abilities of bone marrow mesenchymal versus hematopoietic stem cells to reverse hyperglycemia in diabetic NOD.SCID mice

Both bone marrow-derived hematopoietic stem cells (HSC) and mesenchymal stem cells (MSC) improve glycemic control in diabetic mice, but their kinetics and associated changes in pancreatic morphology have not been directly compared. Our goal was to examine the time course of improvements in glucose tolerance and associated changes in β-cell mass and proliferation following transplantation of equivalent numbers of HSC or MSC from the same bone marrow into diabetic non-obese diabetic severe combined immune deficiency (NOD.SCID) mice. We used transgenic mice with a targeted expression of yellow fluorescent protein (YFP) driven by the Vav1 gene promoter to genetically tag HSC and progeny. HSC were separated from bone marrow by fluorescence-activated cell sorting and MSC following cell culture. Equivalent numbers of isolated HSC or MSC were transplanted directly into the pancreas of NOD.SCID mice previously made diabetic with streptozotocin. Glucose tolerance, serum insulin, β-cell mass and β-cell proliferation were examined up to 28 days following transplant. Transplantation with MSC improved glucose tolerance within 7 days and serum insulin levels increased, but with no increase in β-cell mass. Mice transplanted with HSC showed improved glucose tolerance only after 3 weeks associated with increased β-cell proliferation and mass. We conclude that single injections of either MSC or HSC transiently improved glycemic control in diabetic NOD.SCID mice, but with different time courses. However, only HSC infiltrated the islets and were associated with an expanded β-cell mass. This suggests that MSC and HSC have differing mechanisms of action.

Decrease in Ins+Glut2LO β-cells with advancing age in mouse and human pancreas

The presence and location of resident pancreatic β-cell progenitors is controversial. A subpopulation of insulin-expressing but glucose transporter-2-low (Ins⁺Glut2^LO) cells may represent multipotent pancreatic progenitors in adult mouse and in human islets, and they are enriched in small, extra-islet β-cell clusters (<5 β cells) in mice. Here, we sought to identify and compare the ontogeny of these cells in mouse and human pancreata throughout life. Mouse pancreata were collected at postnatal days 7, 14, 21, 28, and at 3, 6, 12, and 18 months of age, and in the first 28 days after β-cell mass depletion following streptozotocin (STZ) administration. Samples of human pancreas were examined during fetal life (22-30 weeks gestation), infancy (0-1 year), childhood (2-9), adolescence (10-17), and adulthood (18-80). Tissues were analyzed by immunohistochemistry for the expression and location of insulin, GLUT2 and Ki67. The proportion of β cells within clusters relative to that in islets was higher in pancreas of human than of mouse at all ages examined, and decreased significantly at adolescence. In mice, the total number of Ins⁺Glut2^LO cells decreased after 7 days concurrent with the proportion of clusters. These cells were more abundant in clusters than in islets in both species. A positive association existed between the appearance of new β cells after the STZ treatment of young mice, particularly in clusters and smaller islets, and an increased proportional presence of Ins⁺Glut2^LO cells during early β-cell regeneration. These data suggest that Ins⁺Glut2^LO cells are preferentially located within β-cell clusters throughout life in pancreas of mouse and human, and may represent a source of β-cell plasticity.

Insulin-positive, Glut2-low cells present within mouse pancreas exhibit lineage plasticity and are enriched within extra-islet endocrine cell clusters

Regeneration of insulin-producing β-cells from resident pancreas progenitors requires an understanding of both progenitor identity and lineage plasticity. One model suggested that a rare β-cell sub-population within islets demonstrated multi-lineage plasticity. We hypothesized that β-cells from young mice (postnatal day 7, P7) exhibit such plasticity and used a model of islet dedifferentiation toward a ductal epithelial-cell phenotype to test this theory. RIPCre;Z/AP(+/+) mice were used to lineage trace the fate of β-cells during dedifferentiation culture by a human placental alkaline phosphatase (HPAP) reporter. There was a significant loss of HPAP-expressing β-cells in culture, but remaining HPAP(+) cells lost insulin expression while gaining expression of the epithelial duct cell marker cytokeratin-19 (Ck19). Flow cytometry and recovery of β-cell subpopulations from whole pancreas vs. islets suggest that the HPAP(+)Ck19(+) cells had derived from insulin-positive, glucose-transporter-2-low (Ins(+)Glut2(LO)) cells, representing 3.5% of all insulin-expressing cells. The majority of these cells were found outside of islets within clusters of <5 β-cells. These insulin(+)Glut2(LO) cells demonstrated a greater proliferation rate in vivo and in vitro as compared to insulin(+)Glut2(+) cells at P7, were retained into adulthood, and a subset differentiated into endocrine, ductal, and neural lineages, illustrating substantial plasticity. Results were confirmed using RIPCre;ROSA- eYFP mice. Quantitative PCR data indicated these cells possess an immature β-cell phenotype. These Ins(+)Glut2(LO) cells may represent a resident population of cells capable of forming new, functional β-cells, and which may be potentially exploited for regenerative therapies in the future.

11 beta-Hydroxysteroid dehydrogenase 1 activity and gene expression in human adipose stromal cells: effect on aromatase activity

The biological activity of glucocorticoids in target tissues can be influenced by locally produced 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD), the enzyme responsible for the interconversion of cortisol and its inactive metabolite cortisone. In human adipose stromal cells, glucocorticoids are potent stimulators of the conversion of androgens to estrogens (aromatase activity). The present study was designed to determine whether 11 beta-HSD activity was present in human adipose stromal cells, and if changes in the activity of this enzyme could influence aromatase activity. 11 beta-HSD activity was determined by a radiometric conversion assay in breast adipose tissue from six patients. It was found that both dehydrogenase (cortisol to cortisone) and reductase (cortisone to cortisol) activities were present in all six subjects, and the reductase activity was always predominant. Carbenoxolone (CBX), a potent inhibitor of 11 beta-HSD, added to the culture medium at 50 and 200 microM, resulted in 39 +/- 4% and 85 +/- 1% inhibition, respectively, of both reductase and dehydrogenase activity of 11 beta-HSD. To determine whether alterations in 11 beta-HSD could influence aromatase activity, the effect of CBX (200 microM) on cortisol- and cortisone-induced changes in the conversion of androstenedione to estrone was examined. CBX prevented the stimulatory effect of cortisone and minimally potentiated the stimulatory effect of cortisol on aromatase activity, reflecting an inhibition of the local activation of cortisone and the local metabolism of cortisol, respectively. In order to determine whether the product of the 11 beta-HSD 1 gene was responsible for the observed 11 beta-HSD activity, total RNA extracts from these cells were subjected to Northern blot analysis using human 11 beta-HSD 1 cDNA as the probe. A single 1.8 11 beta-HSD 1 transcript was detected, and its abundance was reduced by CBX. No 11 beta-HSD 2 mRNA was detected. The present results demonstrate that the 11 beta-HSD 1 gene is expressed and functional in human breast adipose stromal cells and that changes in 11 beta-HSD 1 activity result in alterations in aromatase activity.

Estrone formation from dehydroepiandrosterone in cultured human breast adipose stromal cells

The metabolism of dehydroepiandrosterone (DHA) and androstenedione (A-dione) was studied in cultured human adipose stromal cells obtained from breast tissue of six premenopausal patients undergoing reduction mammoplasty. Cells were maintained in culture in the presence of 10% fetal bovine serum. Studies were carried out during the proliferative and confluent phases of culture with radiolabelled substrates (2 microCi, 10 nM). During the early phases of replication 7 alpha-hydroxydehydroepiandrosterone (7 alpha-OHDHA) was formed from DHA. As the cells reached confluence, the major metabolite of DHA in cells from all patients was A-dione indicating the presence of 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD). The conversion of DHA to A-dione was variable among patients when cells were confluent with 30-80% of substrate being metabolized to this product. Adipose stromal cells synthesized estrone (E1) from DHA once A-dione formation was established. Under basal conditions E1 was obtained in cells from three of the six patients examined with up to 36% substrate converted to this product. Dexamethasone (Dex 10(-7) M) stimulated E1 formation in cells from all subjects with up to 50% of substrate being converted. Parallel studies comparing the conversion of DHA with A-dione to E1 revealed that as the cells became confluent, E1 formation from both substrates was similar. The pattern of steroid metabolism was also examined in primary culture and in subculture. Passage 1 cells continued to form A-dione as a major metabolite of DHA, and did not revert to the pattern of metabolism found in primary cells during the early stages of replication, when 7 alpha-hydroxylation predominated. Human adipose stromal cells actively metabolize DHA, producing 7 alpha-OHDHA, A-dione and E1 as principal metabolites. Changes in the circulating levels of DHA may directly influence the formation of E1 in peripheral tissues. This source of E1 will be modulated by factors controlling 3 beta-HSD and aromatase activities.

Genetic activity of X chromosomes in pluripotent female teratocarcinoma cells and their differentiated progeny

We have induced teratocarcinomas from female embryos heterozygous for electrophoretic variants of the X-linked gene coding for phosphoglycerate kinase (PGK). An embryonal carcinoma cell line, P10, has been isolated from such a teratocarcinoma. It has a normal female karyotype and cultures contain both PGK isoenzymic forms. Clonal populations derived from P10 also contain both PGK electrophoretic variants. In addition, both X chromosomes in these cells replicate in synchrony with the autosomes during early S phase of the cell cycle. These data indicate that the undifferentiated P10 embryonal carcinoma cells contain two active X chromosomes. When cultured under the appropriate conditions, the P10 cells differentiate to form a variety of tissue types. At least some of these differentiated cells contain an inactive X chromosome as determined by cytogenetic analysis. Apparently X chromosome inactivation accompanies the differentiation of these female embryonal carcinoma cells.