Genetic factors of importance for beta-cell proliferation

Metabolic syndrome predicts long-term mortality in subjects without established diabetes mellitus in asymptomatic Korean population: A propensity score matching analysis from the Korea Initiatives on Coronary Artery Calcification (KOICA) registry

Despite the different features of diabetes mellitus (DM) in Asian populations compared with Western populations, the impact of metabolic syndrome (MetS) on long-term mortality according to DM status has not yet been elucidated in the Asian population.After performing 1:1 propensity score matching (PSM) using clinical variables including age, gender, smoking, and individual MetS components between DM and non-DM subjects from the data of the Korea Initiatives on Coronary Artery Calcification registry, mortality was evaluated according to DM and MetS in 14,956 asymptomatic Korean subjects.The mean follow-up duration was 53.1 months (interquartile range: 33-80). The overall prevalence of MetS was 60%. DM subjects had higher mortality compared with non-DM subjects (1.2% vs 0.7%, respectively; P = 0.001); the cumulative mortality by Kaplan-Meier analysis was higher in DM subjects than in non-DM subjects (log-rank P = 0.001). DM increased the risk of mortality in PSM participants (hazard ratio [HR] 1.74; P = 0.001). In non-DM subjects, MetS (HR 2.32) and one of its components, central obesity (HR 1.97), were associated with an increased risk of mortality (both P < 0.05). In contrast, there was no significant difference in the risk of mortality according to MetS or its components in DM subjects. After adjusting for confounding risk factors, it was shown that MetS independently increased the risk of mortality in non-DM subjects.Compared with non-DM subjects, DM subjects have an increased risk of long-term mortality among PSM participants. MetS appears to have an independent impact on mortality in subjects without established DM among the asymptomatic Korean population. Our results may not be applicable to the whole subjects with MetS because the PSM using MetS components was performed between subjects with and without DM which was very high risk for adverse clinical events.

Comparison of 2-year mortality according to obesity in stabilized patients with type 2 diabetes mellitus after acute myocardial infarction: results from the DIAMOND prospective cohort registry

Background

After acute myocardial infarction (AMI), the replicated phenomenon of obesity paradox, i.e., obesity appearing to be associated with increased survival, has not been evaluated in stabilized (i.e., without clinical events within 1 month post AMI) Asian patients with diabetes mellitus (DM).

Methods

Among 1192 patients in the DIabetic Acute Myocardial InfarctiON Disease (DIAMOND) Korean multicenter registry between April 2010 and June 2012, 2-year cardiac and all-cause death were compared according to obesity (body mass index ≥25 kg/m²) in 1125 stabilized DM patients.

Results

Compared with non-obese DM patients (62 % of AMI patients), obese DM patients had: higher incidence of dyslipidemia (31 vs. 24 %, P < 0.01); lower incidence of chronic kidney disease (26 vs. 33 %) (P < 0.01); higher left ventricular ejection fraction after AMI (53 ± 11 vs. 50 ± 12 %, P < 0.001); and lower 2-year cardiac and all-cause death occurrence (0.7 vs. 3.6 % and 1.9 vs. 5.2 %, both P < 0.01) and cumulative incidence in Kaplan–Meier analysis (P < 0.005, respectively). Likewise, both univariate and multivariate Cox hazard regression analyses adjusted for the respective confounders showed that obesity was associated with decreased risk of both cardiac [HR, 0.18 (95 % CI 0.06–0.60), P = 0.005; and 0.24 (0.07–0.78), P = 0.018, respectively] and all-cause death [0.34 (0.16–0.73), P = 0.005; and 0.44 (0.20–0.95), P = 0.038].

Conclusions

In a Korean population of stabilized DM patients after AMI, non-obese patients appear to have higher cardiac and all-cause mortality compared with obese patients after adjusting for confounding factors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-015-0305-1) contains supplementary material, which is available to authorized users.

Differential association between metabolic syndrome and coronary artery disease evaluated with cardiac computed tomography according to the presence of diabetes in a symptomatic Korean population

BACKGROUND

Metabolic syndrome (MetS) is associated with increased risks of diabetes and coronary artery disease (CAD). Despite the controversial inclusion of established diabetes in MetS, the association between MetS and CAD according to diabetes status has not been elucidated in the Asian population.

METHODS

We evaluated the association between MetS and CAD using the parameters including any plaque, obstructive plaque, and coronary artery calcium score (CACS) >100 according to diabetes status in 2,869 symptomatic Korean subjects who underwent cardiac computed tomographic angiography.

RESULTS

The prevalence of MetS was significantly higher in the diabetic subjects than in the non-diabetic subjects (69% vs. 34%, P <0.001). The incidence of any plaque (64% vs. 43%, P <0.001), obstructive plaque (26% vs. 13%, P = 0.006), and CACS >100 (23% vs. 12%, P = 0.012) was significantly higher in diabetic subjects than in non-diabetic subjects. Among the MetS components, decreased high-density lipoprotein level was significantly associated with any plaque (odds ratio [OR] 1.35), obstructive plaque (OR 1.55), and CACS >100 (OR 1.57) in the non-diabetic subjects (P <0.01, respectively). However, none of the MetS components were associated with all the parameters in the diabetic subjects. Multivariate regression analysis revealed that MetS and the number of MetS components (MetSN) were independently associated with any plaque (MetS: OR 1.55, P <0.001; MetSN: OR 1.22, P <0.001), obstructive plaque (MetS: OR 1.52, P = 0.003; MetSN: OR 1.25, P <0.001), and CACS >100 (MetS: OR 1.46, P = 0.015; MetSN: OR 1.21, P = 0.004) only in the non-diabetic subjects, respectively.

CONCLUSIONS

MetS was independently associated with the presence and severity of CAD only in the non-diabetic subjects among the symptomatic Korean population.

Differential association between obesity and coronary artery disease according to the presence of diabetes in a Korean population

BACKGROUND

Coronary artery disease (CAD) is a major cardiovascular complication in diabetic patients. Despite the significant association between obesity and diabetes, the majority of the diabetic subjects are not obese in an Asian population. This study evaluated the association between obesity and coronary artery disease (CAD) according to the diabetes status in a Korean population.

METHODS

The association between obesity and CAD using the parameters of any plaque, obstructive plaque, and coronary artery calcium score (CACS) >100 according to the presence of diabetes was evaluated in 7,234 Korean adults who underwent multi-detector computed tomography for general health evaluations. Obesity was defined as a body mass index (BMI) ≥25 kg/m(2).

RESULTS

The prevalence of obesity was significantly higher in diabetic subjects than in non-diabetic subjects, but the majority of the diabetic subjects were non-obese (48% vs. 37%, p <0.001). The incidence of any plaque (58% vs. 29%), obstructive plaque (20% vs. 6%), and CACS >100 (20% vs. 6%) were significantly higher in diabetic patients than in non-diabetic subjects (p <0.001, respectively). Incidence of any plaque (33% vs. 26%, p <0.001), obstructive plaque (7% vs. 6%, p = 0.014), and CACS >100 (8% vs. 6%, p = 0.002) was significantly higher in non-diabetic subjects with obesity than in those without obesity, but the incidence of all coronary parameters was not different in diabetic subjects according to the obesity status. After adjusting for confounding risk factors including age, gender, hypertension, dyslipidemia, current smoking, and mild renal dysfunction, obesity was independently associated with increased risks of any plaque (OR 1.14) and CACS >100 (OR 1.31) only in non-diabetic subjects (p <0.05, respectively). Multiple logistic regression models revealed that diabetes was independently associated with all coronary parameters.

CONCLUSION

Despite a significantly higher prevalence of obesity in diabetic subjects than in non-diabetic subjects, obesity is associated with the presence of any plaque and severe coronary calcification only in subjects without established diabetes among Korean population.

Hyperglycemia and hyperinsulinemia have additive effects on activation and proliferation of pancreatic stellate cells: possible explanation of islet-specific fibrosis in type 2 diabetes mellitus

Pancreatic islet fibrosis observed in Type 2 diabetes is one of the major factors leading to progressive beta-cell loss and dysfunction. Despite its importance, the mechanism of islet-restricted fibrogenesis associated with pancreatic stellate cell (PSC) activation and proliferation remains to be defined. Therefore, we studied whether the islet-specific environment represented by hyperglycemia and hyperinsulinemia had additive effects on the activation and proliferation of cultured rat PSCs. Cells were stimulated to activate and proliferate with glucose and insulin, either individually or concomitantly. Both stimuli promoted PSC proliferation and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation independently, but an additive effect was also demonstrated. Blockade of ERK signaling by the mitogen-activated protein kinase kinase (MEK) inhibitor, U0126, suppressed both glucose- and insulin-induced ERK 1/2 phosphorylation and PSC proliferation. Glucose and insulin-induced ERK 1/2 phosphorylation also stimulated connective tissue growth factor gene expression. Thus, hyperglycemia and hyperinsulinemia are two crucial mitogenic factors that activate and proliferate PSCs, and the presence of both states will amplify this response.

Selective beta-cell loss and alpha-cell expansion in patients with type 2 diabetes mellitus in Korea

In the presence of obesity, beta-cell mass needs to be increased to compensate for the accompanying demands and maintain euglycemia. However, in Korea, the majority of type 2 diabetic patients are nonobese. We determined the absolute masses, relative volumes, and ratio of alpha- and beta-cell in the pancreas and islets in normal and diabetic Korean subjects to correlate these findings with the clinical characteristics. Whole pancreases procured from organ donors were divided into 24 parts (control 1, n = 9). Tissue was also obtained by surgical resection after 35 partial pancreatectomies: in 25 diabetic patients, 10 age- and body mass index (BMI)-matched patients of benign or malignant pancreatic tumor without diabetes mellitus (DM) (control 2). Morphometric quantifications were performed. In control 1, the relative volume of beta-cells was 2.1 +/- 0.9%, and the total beta-cell mass was 1.3 +/- 0.3 g. The relative volume of beta-cells was found to be variable (control 1, 2.1 +/- 0.9%; control 2, 1.9 +/- 0.7%; DM, 1.4 +/- 1.0%; P < 0.05 DM vs. control 1 and 2) and showed good correlation with BMI (control 1, r(2) = 0.64; DM, r(2) = 0.55; all subjects, r(2) = 0.38; P < 0.05). Notably, in type 2 diabetic patients, the ratio of alpha-cell area to beta-cell area in the islet was higher than in control 1 and 2 (0.81 +/- 0.4 vs. 0.29 +/- 0.2, 0.20 +/- 0.1, P < 0.05). Additionally, significant alpha-cell expansion and a decreased beta-cell fraction were predominantly observed in larger islets (islet area, >6415 micro m(2); P < 0.05) in control 1 and diabetic patients. The relative volume of beta-cell was found to be correlated with BMI in diabetic patients and normal organ donors. Moreover, decreased beta-cell but increased alpha-cell proportion in the islets suggests for a selective beta-cell loss in the pathogenesis of Korean type 2 diabetes.

Activation of serum response factor in the depolarization induction of Egr-1 transcription in pancreatic islet beta-cells

The results of the current studies define the major elements whereby glucose metabolism in islet beta-cells leads to transcriptional activation of an early response gene in insulinoma cell lines and in rat islets. Glucose stimulation (2-20 mm) resulted in a 4-fold increase in Egr-1 mRNA at 30 min, as did the depolarizing agents KCl and tolbutamide. This response was inhibited by diazoxide and EGTA, indicating that beta-cell depolarization and Ca(2+) influx, respectively, are essential. Pharmacological inhibition of the Egr-1 induction by H89 (48%) and calmidazolium (35%), but not by mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1 and 2 or phosphatidylinositol 3-kinase inhibitors, implied that protein kinase A and Ca(2+)/calmodulin pathways are involved. Deletion mapping of the Egr-1 promoter revealed that the proximal -198 base pairs containing two serum response elements (SREs) and one cAMP-response element retained the depolarization response. Depolarization resulted in phosphorylation of cAMP-response element-binding protein, yet partial inhibition by a dominant negative cAMP-response element-binding protein, along with a robust response of a cAMP-response element-mutated Egr-1 promoter suggested the presence of a second Ca(2+)-responsive element. Depolarization activation of 5XSRE-LUC and serum response factor (SRF)-GAL4 constructs, along with activation of SRF-GAL4 by co-transfection with constitutively active calmodulin kinase IV and protein kinase A, and binding of Ser(103)-phosphorylated SRF in nuclear extracts, indicated that the SRE.SRF complexes contribute to the Ca(2+)-mediated transcriptional regulation of Egr-1. The results of the current experiments demonstrate for the first time SRE-dependent transcription and the role of SRF, a transcription factor known to be a major component of growth responses, in glucose-mediated transcriptional regulation in insulinoma cells.

Signaling through the p38 and p42/44 mitogen-activated families of protein kinases in pancreatic beta-cell proliferation

The present study has focused on the role of the 42- and 44-kDa mitogen-activated protein kinases (p42/44 MAPKs) and the 38-kDa mitogen-activated protein kinase (p38 MAPK) in the proliferation of the pancreatic beta-cell line MIN6. MIN6 beta-cell proliferation was assessed by measuring 5-bromo-2'-deoxyuridine (BrdU) incorporation into cellular DNA. Inhibition of both the p42/44 MAPK pathway using the MEK inhibitor PD098059 (PD) and the p38 MAPK pathway using the p38 inhibitor SB203580 (SB) caused a marked, concentration-dependent reduction in the BrdU immunostaining observed in the presence of 15% FCS when assessed using fluorescence immunocytochemistry. These data provide direct evidence of a role for p42/44 MAPKs in the mitogenic response of MIN6 beta-cells to FCS. Furthermore, these data also suggest a novel role for the p38 MAPK pathway in MIN6 beta-cell proliferation.

Initiation of increased pancreatic islet growth in young normoglycemic mice (Umeå +/?)

Pancreatic islets from obese hyperglycemic mice are large and contain a high proportion of normally functioning beta-cells. We have previously shown that young obese mice have an elevated beta-cell proliferation rate at 3 weeks of age. We now wanted to investigate possible factors involved in the initiation of islet growth, including blood glucose, C peptide, glucagon-like peptide-1, vasoactive intestinal polypeptide, and L-5-hydroxytryptophan. We found that the increased beta-cell proliferation on day 20 precedes the rise in blood glucose by 2 days. The islet cell proliferation, measured as the 5-bromo-2'-deoxyuridine labeling index, in 20-day-old lean mice, was enhanced in a dose-dependent manner when glucagon-like peptide-1 or C peptide was injected s.c. for 2 days. L-5-Hydroxytryptophan inhibited the proliferation. C Peptide also increased the islet cell labeling index during islet culture. We conclude that in addition to the effect of glucose, islet proliferation can be triggered by other factors involved in the physiological regulation of increased insulin release. Stimulation of islet proliferation may be related to the actual release of insulin, and C peptide may function as a mediator of such responses.

Insulin-like growth factor I (IGF-I)-stimulated pancreatic beta-cell growth is glucose-dependent. Synergistic activation of insulin receptor substrate-mediated signal transduction pathways by glucose and IGF-I in INS-1 cells

Nutrients and certain growth factors stimulate pancreatic beta-cell mitogenesis, however, the appropriate mitogenic signal transduction pathways have not been defined. In the glucose-sensitive pancreatic beta-cell line, INS-1, it was found that glucose (6-18 mM) independently increased INS-1 cell proliferation (>20-fold at 15 mM glucose). Insulin-like growth factor I (IGF-I)-induced INS-1 cell proliferation was glucose-dependent only in the physiologically relevant concentration range (6-18 mM glucose). The combination of IGF-I and glucose was synergistic, increasing INS-1 cell proliferation >50-fold at 15 mM glucose + 10 nM IGF-I. Glucose metabolism and phosphatidylinositol 3'-kinase (PI 3'-kinase) activation were necessary for both glucose and IGF-I-stimulated INS-1 cell proliferation. IGF-I and 15 mM glucose increased tyrosine phosphorylation mediated recruitment of Grb2/mSOS and PI 3'-kinase to IRS-2 and pp60. Glucose and IGF-I also induced Shc association with Grb2/mSOS. Glucose (3-18 mM) and IGF-I, independently of glucose, activated mitogen-activated protein kinase but this did not correlate with IGF-I-induced beta-cell proliferation. In contrast, p70(S6K) was activated with increasing glucose concentration (between 6 and 18 mM), and potentiated by IGF-I in the same glucose concentration range which correlated with INS-1 cell proliferation rate. Thus, glucose and IGF-I-induced beta-cell proliferation were mediated via a signaling mechanism that was facilitated by mitogen-activated protein kinase but dependent on IRS-mediated induction of PI 3'-kinase activity and downstream activation of p70(S6K). The glucose dependence of IGF-I mediated INS-1 cell proliferation emphasizes beta-cell signaling mechanisms are rather unique in being tightly linked to glycolytic metabolic flux.

Effects of vascular endothelial growth factor on pancreatic duct cell replication and the insulin production of fetal islet-like cell clusters in vitro

We have previously shown that the tyrosine kinase receptor Flk-1 and its ligand, vascular endothelial growth factor (VEGF), may play a role in the development of fetal rat islet-like structures in vitro, possibly by stimulating the maturation of endocrine precursor cells in the pancreatic ductal epithelium. In order to further assess this, adult rat pancreatic ducts and fetal porcine islet-like cell clusters (ICC) were cultured in the presence of VEGF. In ducts, VEGF stimulated the mitogenesis in the epithelium. Culture of ICC in the presence of VEGF significantly enhanced their insulin content, but decreased the insulin accumulation to the culture medium. Glucose-stimulated acute insulin release was not affected by VEGF. Northern blot analysis after partial pancreatectomy in adult rats revealed induction of VEGF mRNA 3 days after the operation. Immunohistochemistry of fetal rat pancreas showed staining mainly in the islets of Langerhans. We conclude that VEGF directly stimulates the replication of the ductal epithelium, a possible prerequisite for beta-cell formation. This could require local production of VEGF, which may alter in response to physiological demands.

Effects of transforming growth factor beta, tumor necrosis factor alpha and interferon gamma on pancreatic islet beta-cell responsiveness to transforming growth factor alpha

The insulin-producing pancreatic islet beta-cell, characterized by low proliferative potential, is normally not responsive to the polypeptide epidermal growth factor (EGF) or its homolog transforming growth factor alpha (TGF-alpha). Since EGF receptors in other tissues can be up-regulated by other growth factors and by cytokines, we have in this paper investigated whether such a beta-cell responsiveness to TGF-alpha, or EGF, can be conferred by co-culture with interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha) or transforming growth factor beta (TGF-beta) in various combinations. To this end, fetal rat pancreatic islets enriched in beta-cells were isolated and cultured for 3 days with or without 200 pM or 20 nM TGF-alpha. It was found that neither of these TGF-alpha concentrations affected beta-cell mitogenesis, insulin content or insulin secretion. However, IFN-gamma (1000 U/ml) evoked a modest stimulation of beta-cell replication, while suppressing insulin secretion and leaving the islet insulin content unaltered. TNF-alpha (1000 U/ml), on the other hand, affected none of these parameters either alone or in any combination with TGF-alpha or IFN-gamma. However, when TNF-alpha or IFN-gamma, either alone or in combination, were combined with the cytokine interleukin-1 beta, this resulted in islet disintegration, whereas the latter cytokine alone did not exert any gross necrotic changes evident by light microscopy. TGF-beta (500 pM) stimulated insulin secretion but did not influence islet insulin content or beta-cell mitogenesis either alone or in combination with TGF-alpha (200 pM or 20 nM). In no instance could any mitogenic or secretory response to low or high concentrations of TGF-alpha be conferred by IFN-gamma. TNF-alpha or TGF-beta whether used alone or in combinations. Hence, responsiveness to TGF-alpha or EGF in the beta-cell obviously cannot be achieved by any of these peptides.

Development of insulin secretory function in young obese hyperglycemic mice (Umeå ob/ob)

The obese-hyperglycemic syndrome is well characterized in adult mice. However, little is known about islet morphology and function at an early age when obese mice islets start to proliferate. We have now studied islet morphology and functional development in obese-hyperglycemic mice (Umeå ob/ob) and their lean littermates at ages < or = 38 days. The weight of obese mice began to increase more than that of the lean littermates at days 8 to 12. At day 18, clinical diagnosis of the ob/ob syndrome could be made with 100% certainty. Islets from obese mice started to show enhanced growth rate during week 4, coinciding with the time of onset of hyperglycemia. 3H-thymidine labeling index is enhanced in ob/ob mice from day 22. Insulin secretion in islets from mice aged 18 to 21 days was the same in obese and lean mice from the same litter. At days 30 to 33, second-phase release and islet insulin content were decreased in islets from obese animals, but were restored after an overnight fast. It is likely that the hyperglycemia rather than increased insulin demand triggers increased beta-cell growth.

Regulation of insulinoma cell proliferation and insulin accumulation by peptides and second messengers

The regulation of clonal rat insulinoma (RINm5F) cell proliferation and hormone accumulation was investigated with the aim of identifying putative compounds capable of inducing differentiation, i.e. decreased growth and increased insulin accumulation, by the tumor cells. In particular, interest was focused on the role of a number of peptides as well as pharmacological probes modulating various signal transduction systems and which have been shown to regulate normal beta-cell proliferation and insulin accumulation. Growth hormone stimulated insulin accumulation and inhibited DNA synthesis, whereas galanin and insulin-like growth factor I caused a moderate suppression of insulin accumulation but did not affect proliferation, while epidermal growth factor, transforming growth factor beta, platelet-derived growth factor, acidic and basic fibroblast growth factor, bradykinin and somatostatin were virtually inactive on all parameters tested. Exogenous prostaglandins E2 and F1 alpha were inactive, while the cycloxygenase inhibitor indomethacin slightly suppressed insulin accumulation. The cytokine IL-1 beta caused a significant decrease in both beta-cell mitogenesis and insulin accumulation, effects that were mediated through nitric oxide generation. The vitamin A derivative retinyl acetate slightly inhibited serum-stimulated DNA synthesis, but did not affect insulin accumulation. The vitamin E alpha-tocopherol significantly enhanced insulin release but did not affect mitogenesis. By contrast, gamma-tocopherol was inactive on both these parameters. The alpha-adrenergic agonist clonidine evoked a slight inhibition of serum-stimulated DNA synthesis, without influencing insulin accumulation, whereas phenylephrine did not affect any of these parameters. Carbamylcholine increased insulin accumulation, but not cell proliferation, whereas the adenylyl cyclase activator forskolin suppressed mitogenesis but did not affect insulin accumulation. Inhibition of protein kinase C with staurosporine or prolonged treatment with phorbol ester suppressed DNA synthesis, as did the tyrosine kinase inhibitor genistein. Stimulating Ca2+ influx by closing ATP-dependent K+ channels with glibenclamide enhanced DNA synthesis, while opening of these channels with diazoxide suppressed cell growth. Conversely, preventing Ca2+ influx by the Ca2+ channel antagonist D-600, chelating intracellular Ca2+ by fura-2 AM or inhibiting the Ca2+/calmodulin-dependent protein kinase by calmidazol resulted in a decreased DNA synthesis. On the other hand, uncontrolled influx or mobilization of Ca2+ by ionomycin or thapsigargin resulted in an arrested DNA synthesis. The present paper shows that RINm5F insulinoma cell proliferation and insulin accumulation can be modulated by various peptidergic and pharmacological agents regulating certain signal transduction pathways. However, mitogenesis in the insulinoma cells seemingly is controlled in a vastly different manner in comparison to that in normal beta-cells. The most spectacular finding in this screening study, i.e. that growth hormone, contrarily to its effect on normal beta-cells, suppresses insulinoma cell growth, merits further elucidation of the underlying mechanisms. Possibly the hormone might become of utility in a clinical setting in the treatment of patients with insulin-producing tumors.

Beta-cell proliferation in normal and streptozotocin-treated newborn rats: site, dynamics and capacity

Regeneration of neonatal beta cells after streptozotocin (STZ)-induced destruction may be due to either replication from pre-existing intra-islet beta cells or extra-islet precursor cells. To further investigate this issue, beta-cell growth was analysed in normal and streptozotocin-treated newborn rats (100 micrograms/g body weight) at several time points during the first 20 days of life. Beta cells were identified by insulin immunostaining, non-isotopic in situ hybridization for rat preproinsulin mRNA, and electron microscopy. Their proliferative activity was recorded by bromodeoxyuridine-pulse labelling. Beta-cell size and total volume were determined by computerized morphometry. In normal rats, there was a threefold increase in total beta-cell volume during the first 5 days of life, with no further expansion till day 20. The bromodeoxyuridine labelling index of the intra-islet beta cells was smaller than that of the extra-islet beta cells (2-3% vs 15-20%). Comparison of the cell birth rate, calculated from the beta-cell labelling index, with the observed increase in beta-cell volume suggested that in normal neonatal rats proliferation of the intra-islet beta-cell population could account for only 10% of the observed expansion. Administration of streptozotocin at birth resulted in more than 90% reduction of the total beta-cell volume at day 2 which then increased to 39% of the normal value by day 20. During this period of partial regeneration, which restored normoglycaemia, the labelling index of intra-islet beta cells was higher than in normal rats (9% vs 2%, p < 0.001), whereas no change was seen in the extra-islet beta-cell labelling index.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of protein tyrosine kinases in islet cells: possible role of the Flk-1 receptor for beta-cell maturation from duct cells

To elucidate the expression of genes of importance for beta-cell replication and the production of insulin, single-stranded cDNAs from different preparations of insulin producing cells were used as template for the polymerase chain reaction (PCR) using primers specific for protein tyrosine kinases (PTKs). In RINm5F cells, as well as in fetal rat islets, the receptor PTK fetal liver kinase-1 (Flk-1) was expressed among other receptor and cytoplasmic tyrosine kinases. To elucidate the putative effects of stimulation of the Flk-1 receptor, fetal rat islet-like structures were cultured in the presence of the ligand for this receptor, vascular endothelial growth factor (VEGF). VEGF was found to stimulate both the insulin content/islet DNA ratio and the accumulation of insulin in the culture medium without affecting the rates of beta-cell replication. To investigate the localization of expression of the Flk-1 receptor in the pancreas, serial sections of fetal pancreata were immunostained for Flk-1 and insulin. Expression of Flk-1 was detected in endothelial-like cells and cells lining pancreatic ducts. The latter are considered to contain precursor cells for the endocrine pancreas. In conclusion, specific protein tyrosine kinases are expressed in islet cells, and are presumably participating in the regulation of islet function. Specifically, the receptor PTK Flk-1 may play a role of beta-cell maturation from pancreatic duct cells.