Pancreatic beta cell/islet mass and body mass index

Body mass index (BMI) is widely used to define obesity. In studies of pancreatic beta-cell/islet mass, BMI is also a common standard for matching control subjects in comparative studies along with age and sex, based on the existing dogma of their significant positive correlation reported in the literature. We aimed to test the feasibility of BMI and BSA to assess obesity and predict beta-cell/islet mass. We used National Health and Nutrition Examination Survey (NHANES) data that provided dual-energy Xray absorptiometry (DXA)-measured fat mass (percent body fat; %BF), BMI, and BSA for adult subjects (20-75y; 4,879 males and 4,953 females). We then analyzed 152 cases of islet isolation performed at our center for correlation between islet yields and various donor anthropometric indices. From NHANES, over 50% of male subjects and 60% of female subjects with BMI:20.1–28.1 were obese as defined by %BF, indicating a poor correlation between BMI and %BF. BSA was also a poor indicator of %BF, as broad overlap was observed in different BSA ranges. Additionally, BMI and BSA ranges markedly varied between sex and race/ethnicity groups. From islet isolation, BMI and BSA accounted for only a small proportion of variance in islet equivalent (IEQ; r² = 0.09 and 0.11, respectively). BMI and obesity were strongly correlated in cases of high BMI subjects. However, the critical populations were non-obese subjects with BMI ranging from 20.1–28.1, in which a substantial proportion of individuals may carry excess body fat. Correlations between BMI, BSA, pancreas weight and beta-cell/islet mass were low.     

Molecular basis for the regulation of islet beta cell mass in mice: the role of E-cadherin

Aims/hypothesis

In rodents and humans, the rate of beta cell proliferation declines rapidly after birth; formation of the islets of Langerhans begins perinatally and continues after birth. Here, we tested the hypothesis that increasing levels of E-cadherin during islet formation mediate the decline in beta cell proliferation rate by contributing to a reduction of nuclear β-catenin and D-cyclins.

Methods

We examined E-cadherin, nuclear β-catenin, and D-cyclin levels, as well as cell proliferation during in vitro and in vivo formation of islet cell aggregates, using β-TC6 cells and transgenic mice with green fluorescent protein (GFP)-labelled beta cells, respectively. We tested the role of E-cadherin using antisense-mediated reductions of E-cadherin in β-TC6 cells, and mice segregating for a beta cell-specific E-cadherin knockout (Ecad [also known as Cdh1] βKO).

Results

In vitro, pseudo-islets of β-TC6 cells displayed increased E-cadherin but decreased nuclear β-catenin and cyclin D2, and reduced rates of cell proliferation, compared with monolayers. Antisense knockdown of E-cadherin increased cell proliferation and levels of cyclins D1 and D2. After birth, beta cells showed increased levels of E-cadherin, but decreased levels of D-cyclin, whereas islets of Ecad βKO mice showed increased levels of D-cyclins and nuclear β-catenin, as well as increased beta cell proliferation. These islets were significantly larger than those of control mice and displayed reduced levels of connexin 36. These changes correlated with reduced insulin response to ambient glucose, both in vitro and in vivo.

Conclusions/interpretation

The findings support our hypothesis by indicating an important role of E-cadherin in the control of beta cell mass and function.     

Pancreatic deletion of insulin receptor substrate 2 reduces beta and alpha cell mass and impairs glucose homeostasis in mice

Aims/hypothesis Insulin signalling pathways regulate pancreatic beta cell function. Conditional gene targeting using the Cre/loxP system has demonstrated that mice lacking insulin receptor substrate 2 (IRS2) in the beta cell have reduced beta cell mass. However, these studies have been complicated by hypothalamic deletion when the RIPCre (B6.Cg-tg(Ins2-cre)25Mgn/J) transgenic mouse (expressing Cre recombinase under the control of the rat insulin II promoter) is used to delete floxed alleles in insulin-expressing cells. These features have led to marked insulin resistance making the beta cell-autonomous role of IRS2 difficult to determine. To establish the effect of deleting Irs2 only in the pancreas, we generated PIrs2KO mice in which Cre recombinase expression was driven by the promoter of the pancreatic and duodenal homeobox factor 1 (Pdx1, also known as Ipf1) gene. Materials and methods In vivo glucose homeostasis was examined in PIrs2KO mice using glucose tolerance and glucose-stimulated insulin secretion tests. Endocrine cell mass was determined by morphometric analysis. Islet function was examined in static cultures and by performing calcium imaging in Fluo3am-loaded beta cells. Islet gene expression was determined by RT-PCR. Results The PIrs2KO mice displayed glucose intolerance and impaired glucose-stimulated insulin secretion in vivo. Pancreatic insulin and glucagon content and beta and alpha cell mass were reduced. Glucose-stimulated insulin secretion and calcium mobilisation were attenuated in PIrs2KO islets. Expression of the Glut2 gene (also known as Slc2a2) was also reduced in PIrs2KO mice. Conclusions/interpretation These studies suggest that IRS2-dependent signalling in pancreatic islets is required not only for the maintenance of normal beta and alpha cell mass but is also involved in the regulation of insulin secretion. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Correlation between beta cell mass and glycemic control in type 1 diabetic recipients of islet cell graft

Islet grafts can induce insulin independence in type 1 diabetic patients, but their function is variable with only 10% insulin independence after 5 years. We investigated whether cultured grafts with defined beta cell number help standardize metabolic outcome. Nonuremic C-peptide-negative patients received an intraportal graft with 0.5-5.0 x 10(6) beta cells per kilogram of body weight (kg BW) under antithymocyte globulin and mycophenolate mofetil plus tacrolimus. Metabolic outcome at posttransplant (PT) month 2 was used to decide on a second graft under maintenance mycophenolate mofetil/tacrolimus. Graft function was defined by C-peptide >0.5 ng/ml and reduced insulin needs, metabolic control by reductions in HbA(1c), glycemia coefficient of variation, and hypoglycemia. At PT month 2, graft function was present in 16 of 17 recipients of >2 x 10(6) beta cells per kg BW versus 0 of 5 with lower number. The nine patients with C-peptide >1 ng/ml and glycemia coefficient of variation of <25% did not receive a second graft; five of them were insulin-independent until PT month 12. The 12 others received a second implant; it achieved insulin-independence at PT month 12 when the first and second graft contained >2 x 10(6) beta cells per kg BW. Of the 20 recipients of at least one graft with >2 x 10(6) beta cells per kg BW, 17 maintained graft function and metabolic control up to PT month 12. At PT month 12, beta cell function in insulin-independent patients ranged around 25% of age-matched control values. Thus, 1-year metabolic control can be reproducibly achieved and standardized by cultured islet cell grafts with defined beta cell number.     

Conditional islet hypovascularisation does not preclude beta cell expansion during pregnancy in mice

Aims/hypothesis

Endothelial–endocrine cell interactions and vascular endothelial growth factor (VEGF)-A signalling are deemed essential for maternal islet vascularisation, glucose control and beta cell expansion during mouse pregnancy. The aim of this study was to assess whether pregnancy-associated beta cell expansion was affected under conditions of islet hypovascularisation.

Methods

Soluble fms-like tyrosine kinase 1 (sFLT1), a VEGF-A decoy receptor, was conditionally overexpressed in maternal mouse beta cells from 1.5 to 14.5 days post coitum. Islet vascularisation, glycaemic control, beta cell proliferation, individual beta cell size and total beta cell volume were assessed in both pregnant mice and non-pregnant littermates.

Results

Conditional overexpression of sFLT1 in beta cells resulted in islet hypovascularisation and glucose intolerance in both pregnant and non-pregnant mice. In contrast to non-pregnant littermates, glucose intolerance in pregnant mice was transient. sFLT1 overexpression did not affect pregnancy-associated changes in beta cell proliferation, individual beta cell size or total beta cell volume.

Conclusions/interpretation

Reduced intra-islet VEGF-A signalling results in maternal islet hypovascularisation and impaired glycaemic control but does not preclude beta cell expansion during mouse pregnancy.

     

Early onset of neoplasia in the prostate and skin of mice with tissue-specific deletion of Pten

PTEN is a tumor suppressor gene mutated in various advanced human neoplasias, including glioblastomas and prostate, breast, endometrial, and kidney cancers. This tumor suppressor is a lipid phosphatase that negatively regulates cell survival and proliferation mediated by phosphatidylinositol 3-kinase/protein kinase B signaling. Using the Cre-loxP system, we selectively inactivated Pten in murine tissues in which the MMTV-LTR promoter is active, resulting in hyperproliferation and neoplastic changes in Pten-null skin and prostate. These phenotypes had early onset and were completely penetrant. Abnormalities in Pten mutant skin consisted of mild epidermal hyperplasia, whereas prostates from these mice exhibited high-grade prostatic intraepithelial neoplasia (HGPIN) that frequently progressed to focally invasive cancer. These data demonstrate that Pten is an important physiological regulator of growth in the skin and prostate. Further, the early onset of HGPIN in Pten mutant males is unique to this animal model and implicates PTEN mutations in the initiation of prostate cancer. Consistent with high PTEN mutation rates in human prostate tumors, these data indicate that PTEN is a critical tumor suppressor in this organ.     

胆固醇代谢与胰岛β细胞功能

2型糖尿病是以胰岛素抵抗和β细胞功能障碍为主要特征的一类疾病,其中胰岛β细胞的丢失和功能障碍在疾病的发生和发展中起决定性作用.近年来的研究表明,胆固醇代谢与β细胞功能密切相关.正常情况下,胰岛β细胞可以通过其表面表达的一系列受体和转运分子来控制细胞内胆固醇的摄入和流出,使得细胞内胆固醇的含量维持在一个动态平衡.胰岛β细...     

Exendin-4 increases islet amyloid deposition but offsets the resultant beta cell toxicity in human islet amyloid polypeptide transgenic mouse islets

Aims/hypothesis  

In type 2 diabetes, aggregation of islet amyloid polypeptide (IAPP) into amyloid is associated with beta cell loss. As IAPP is co-secreted with insulin, we hypothesised that IAPP secretion is necessary for amyloid formation and that treatments that increase insulin (and IAPP) secretion would thereby increase amyloid formation and toxicity. We also hypothesised that the unique properties of the glucagon-like peptide-1 (GLP-1) receptor agonist exendin-4 to maintain or increase beta cell mass would offset the amyloid-induced toxicity.     

In vivo proliferation of differentiated pancreatic islet beta cells in transgenic mice expressing mutated cyclin-dependent kinase 4

Aims/hypothesis It has previously been hypothesised that highly differentiated endocrine cells do not proliferate or regenerate. However, recent studies have revealed that cyclin-dependent kinase 4 (CDK4) is necessary for the proliferation of pancreatic islet beta cells. The aim of this study was to determine whether activation of CDK4 can potentially be used as a radical treatment for diabetes without malignant transformation.Methods We generated transgenic mice expressing mutant CDK4 under the control of the insulin promoter to examine the effect of activated CDK4 overexpression in the postnatal development of pancreatic islets.Results In the transgenic mice, total CDK4 protein expression was increased by up to 5-fold, with a concomitant increase in CDK4 activity indicated by the detection of phosphorylated Rb protein in pancreatic islets. Histopathologically, many cells tested positive for proliferating cell nuclear antigen, and pancreatic islets displayed hyperplasia due to the extreme proliferation of beta cells containing a large number of insulin granules. Pancreatic islet alpha, delta and PP cells did not increase. Over an 18-month observation period, the transgenic mice did not develop insulinoma. Levels of expression of GLUT1 and c-myc were comparable to those in the littermates of the transgenic mice. GLUT2 expression was identified in the pancreatic islets of transgenic mice. No significant differences in telomerase activities were detected between transgenic mice and their littermates. Transgenic mice were superior to their littermates in terms of glucose tolerance and insulin secretion in response to the intraperitoneal injection of glucose, and hypoglycaemia was not observed.Conclusions/interpretation Activated CDK4 stimulates postnatal pancreatic beta cell proliferation, during which the highly differentiated phenotypes of pancreatic islet beta cells are preserved without malignant transformation.     

细胞内脂肪堆积和β细胞增殖的关系

目的 研究脂肪酸（FA）对β细胞增殖抑制与细胞内的脂肪堆积的关系及相关的葡萄糖（Glu）浓度的影响。方法 培养胰岛β细胞株Ins-1E细胞，用^3H-胸腺嘧啶和^3H-棕榈酸掺入的方法分别研究β细胞增殖及β细胞内脂肪堆积。利用RT-PCR方法测定肉毒碱棕榈酰转移酶1（CPT-1）基因表达。结果 与3．3mmol／L Glu比较，24小时后6．6mmol／L和11mmol／L Glu使细胞增殖增加2．27和3．04倍（P〈0．05）；加入0．4mmol／L棕榈酸后细胞增殖降为1．1和0．86倍（与无棕榈酸相比P〈0．05）。高浓度的Glu使细胞内脂肪堆积增加15％～92％。Triacsin C或Wyl4643能减少13％～54％的脂肪堆积，同时缓解FA对细胞增殖的抑制作用48％～71％。FA刺激CPT-1基因的表达，Glu对其有剂量依赖性的抑制，20mmol／L Glu使CPT-1基因的表达减少50％（P〈0．05）。结论 FA对B细胞增殖的抑制与脂肪在细胞内堆积有关，Glu可能通过抑制FA刺激CPT-1基因的表达，增加FA堆积从而介导FA对细胞增殖的抑制作用。     

Neural crest stem cells increase beta cell proliferation and improve islet function in co-transplanted murine pancreatic islets

Aims/hypothesis  

Long-term graft survival after islet transplantation to patients with type 1 diabetes is insufficient, necessitating the development of new strategies to enhance transplant viability. Here we investigated whether co-transplantation of neural crest stem cells (NCSCs) with islets improves islet survival and function in normoglycaemic and diabetic mice.     

Glucagon-like peptide-1 receptor agonist treatment reduces beta cell mass in normoglycaemic mice

Aims/hypothesis

Incretin-based therapies improve glycaemic control in patients with type 2 diabetes. In animal models of diabetes, glucagon-like peptide-1 receptor agonists (GLP-1RAs) increase beta cell mass. GLP-1RAs are also evaluated in non-diabetic individuals with obesity and cardiovascular disease. However, their effect on beta cell mass in normoglycaemic conditions is not clear. Here, we investigate the effects of the GLP-1RA liraglutide on beta cell mass and function in normoglycaemic mice.

Methods

C57BL/6J mice were treated with the GLP-1RA liraglutide or PBS and fed a control or high-fat diet (HFD) for 1 or 6 weeks. Glucose and insulin tolerance tests were performed after 6 weeks. BrdU was given to label proliferating cells 1 week before the animals were killed. The pancreas was taken for either histology or islet isolation followed by a glucose-induced insulin-secretion test.

Results

Treatment with liraglutide for 6 weeks led to increased insulin sensitivity and attenuation of HFD-induced insulin resistance. A reduction in beta cell mass was observed in liraglutide-treated control and HFD-fed mice at 6 weeks, and was associated with a lower beta cell proliferation rate after 1 week of treatment. A similar reduction in alpha cell mass occurred, resulting in an unchanged alpha to beta cell ratio. In contrast, acinar cell proliferation was increased. Finally, islets isolated from liraglutide-treated control mice had enhanced glucose-induced insulin secretion.

Conclusions/interpretation

Our data show that GLP-1RA treatment in normoglycaemic mice leads to increases in insulin sensitivity and beta cell function that are associated with reduced beta cell mass to maintain normoglycaemia.