Betacellulin-delta4, a novel differentiation factor for pancreatic beta-cells, ameliorates glucose intolerance in streptozotocin-treated rats

Searching for Biomarkers in Proliferative Diabetic Retinopathy: Amphiregulin and Progranulin

Objective

Diabetic retinopathy is a common diabetic microvascular problem. Its diagnosis and classification are based on visible changes in clinical fundus examination. However, the discovery of possible vitreous biomarkers in patients with proliferative and nonproliferative diabetic retinopathy may guide both the differentiation and degree of retinopathy. Biomarkers that will be accepted can be also a treatment target. Amphiregulin (AREG) promotes proliferative and regenerative activity and repairs most cell types by binding and activating epidermal growth factor receptors. Progranulin (PGRN) has complex functions in many physiological and pathological processes. Thus, this study aimed to report vitreous AREG and PGRN levels in patients with diabetes and proliferative retinopathy and compare the results with those without diabetes.

Methods

Thirty-three eyes of 33 patients with proliferative diabetic retinopathy and 31 eyes of 31 patients without diabetes were included in this study. Vitreous humor samples were collected from all patients at the time of pars plana vitrectomy surgery immediately before the surgical procedure. Vitreous AREG and PGRN values were determined by the ELISA method.

Results

The mean AREG and PGRN values were similar in the groups (p=0.427, p=0.459, respectively).

Conclusions

The results demonstrated that vitreous AREG and PGRN levels have no significant relationship with proliferative diabetic retinopathy.

Inhibition of EGF signaling protects the diabetic retina from insulin-induced vascular leakage

Diabetes mellitus is a disease with considerable morbidity and mortality worldwide. Breakdown of the blood-retinal barrier and leakage from the retinal vasculature leads to diabetic macular edema, an important cause of vision loss in patients with diabetes. Although epidemiologic studies and randomized clinical trials suggest that glycemic control plays a major role in the development of vascular complications of diabetes, insulin therapies for control of glucose metabolism cannot prevent long-term retinal complications. The phenomenon of temporary paradoxical worsening of diabetic macular edema after insulin treatment has been observed in a number of studies. In prospective studies on non-insulin-dependent (type 2) diabetes mellitus patients, a change in treatment from oral drugs to insulin was often associated with a significant increased risk of retinopathy progression and visual impairment. Although insulin therapies are critical for regulation of the metabolic disease, their role in the retina is controversial. In this study with diabetic mice, insulin treatment resulted in increased vascular leakage apparently mediated by betacellulin and signaling via the epidermal growth factor (EGF) receptor. In addition, treatment with EGF receptor inhibitors reduced retinal vascular leakage in diabetic mice on insulin. These findings provide unique insight into the role of insulin signaling in mediating retinal effects in diabetes and open new avenues for therapeutics to treat the retinal complications of diabetes mellitus.

Involvement of the parasympathetic nervous system in the initiation of regeneration of pancreatic β-cells

The mechanism that initiates regeneration of pancreatic β-cells is not clear at present. The vagal nerve is implicated in the regulation of gastrointestinal functions, glucose metabolism and proliferation of pancreatic β-cells under physiological conditions. To elucidate the triggering mechanism of the regeneration of pancreatic β-cells, we examined the involvement of the vagal nerve. To this end, we employed a rat pancreatic duct ligation (DL) model, in which profound β-cell neogenesis and β-cell proliferation were observed within a week. We administered atropine to block the vagal nerve. Administration of atropine inhibited proliferation of β-cells in both islets and islet-like cell clusters (ICC), without affecting ductal cell proliferation in the ligated pancreas. The numbers of PDX-1 and MafB-positive cells in or attaching to the ducts were significantly reduced by atropine. MafB/glucagon and MafB/insulin double-positive cells were also decreased by atropine. Finally, atropine reduced the number of MafA-positive ductal cells, all of which were positive for insulin, by 50% on day 5. These results strongly suggest that the vagal nerve is involved in β-cell proliferation, induction of endocrine progenitors and neogenesis of α- and β-cells.

Alkaloid conophylline in combination with betacellulin-δ4 promotes the differentiation of fetal porcine pancreatic duct stem cells

AIM: To investigate the impact of alkaloid conophylline (CnP) in combination with betacellulin-δ4 (BTCδ4) on the differentiation of porcine fetal pancreatic duct stem cells in vitro.

METHODS: For inducing cell differentiation, porcine fetal pancreatic duct stem cells were cultured in Medium 199 (M199) with CnP and BTCδ4, alone or in combination. Then cell viability was assessed by the trypan blue dye exclusion assay. Enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry were used to measure the content of insulin released by islet-like cell clusters (ICCs). The expression of PDX-1, Neuro D/Beta2 and insulin mRNAs was detected by reverse transcription-polymerase chain reaction (RT-PCR). Insulin release in response to glucose was assessed by glucose load test.

RESULTS: Conophylline at concentrations below 0.1 g/L showed no marked toxicity toward the ICCs. Either CnP or BTCδ4 weakly enhanced the content of insulin, while CnP in combination with BTCδ4 synergistically increased cellular insulin content. The expression of PDX-1, insulin and Neuro D/Beta2 mRNAs could be detected in untreated ICCs. After treatment with CnP in combination with BTCδ4, the ICCs exhibited a prompt response to 25.0 mmol/L glucose by increasing insulin secretion.

CONCLUSION: CnP in combination with BTCδ4 potentiated the differentiation of porcine pancreatic duct stem cells in cluster cultures towards β-cells.

Serum HER-2 concentration is associated with insulin resistance and decreases after weight loss

Background

HER2/neu is a member of the epidermal growth factor receptor family easily detectable in the serum of cancer patients. We aimed to evaluate circulating HER-2 concentrations in association with insulin resistance in healthy and obese subjects.

Methods

Insulin sensitivity (minimal model) and serum HER-2 concentrations were evaluated in a cross sectional study in men (cohort 1, n = 167) and longitudinally after weight loss in obese subjects (cohort 2, n = 30).

Results

Serum HER-2 concentrations were positively associated with BMI and waist circumference (both r = 0.18, p = 0.02), post-load glucose (r = 0.28, p = 0.001) and fasting triglycerides (r = 0.26, p = 0.001); and negatively associated with insulin sensitivity (r = -0.29, p = 0.002, n = 109). Subjects with type 2 diabetes showed significantly increased soluble serum HER-2 concentrations. In different multivariate regression models, fasting triglycerides emerged as the factor that independently contributed to 10-11% of serum HER-2 variance.

Serum HER-2 concentrations correlated significantly with fasting triglycerides and insulin sensitivity index in subjects from cohort 2. Weight loss led to a significant decrease of serum HER-2 concentrations. The change in serum HER-2 concentrations were significantly associated with the change in percent body fat and fasting triglycerides in young (below the median age of the cohort) subjects.

Conclusions

Serum HER-2 concentrations might be implicated in the pathophysiology of insulin resistance and associated comorbidities.

Administration of conophylline and betacellulin-delta4 increases the beta-cell mass in neonatal streptozotocin-treated rats

The present study was conducted to examine the effect of administration of conophylline (CnP) and betacellulindelta4 (BTCdelta4) on the beta-cell mass in neonatal streptozotocin-treated rats (neonatal STZ rats). STZ (100 microg/g) was injected into neonatal rats, and then CnP (2 microg/g) and/or BTCdelta4 (200 pmol/g) were administered to neonatal STZ rats for 1 week. The plasma glucose concentration was monitored, and an intraperitoneal glucose tolerance test (ipGTT) was performed on day 8 and at 8 weeks after the STZ injection. In neonatal STZ rats treated with control solution (S group), the plasma glucose concentration increased for several days after the STZ injection, returned to nearly normal levels, and then increased gradually after six weeks of age. Eight weeks after the STZ-injection, the plasma glucose concentration was increased significantly compared to that of normal rats. The glucose response to ipGTT was significantly reduced in neonatal STZ rats treated with CnP (CnP group), BTCdelta4 (delta4 group) and CnP+BTCdelta4 (CnP+delta4 group). The beta-cell mass and the insulin content of the pancreas were significantly increased in the CnP group and delta4 group. The effect of CnP+delta4 was greater than that of CnP alone or BTCdelta4 alone. CnP+BTCdelta4 significantly increased the number of PDX-1-positive ductal cells and the number of insulin/BrdU double-positive ductal cells. These results indicate the efficacy of CnP and BTCdelta4 in increasing the beta-cells mass of neonatal STZ-treated rats.

EGF receptor in pancreatic beta-cell mass regulation

Pancreatic islet development is impaired in mice lacking EGFRs (epidermal growth factor receptors). Even partial tissue-specific attenuation of EGFR signalling in the islets leads to markedly reduced beta-cell proliferation and development of diabetes during the first weeks after birth. Out of the many EGFR ligands, betacellulin has been specifically associated with positive effects on beta-cell growth, through both increased proliferation and neogenesis. EGFR action is also necessary for the beta-cell mitogenic activity of the gut hormone GLP-1 (glucagon-like peptide 1). Finally, in vitro models demonstrate a central role for EGFR in transdifferentiation of pancreatic acinar and ductal cells into endocrine islet cells. EGFR thus plays an essential role in beta-cell mass regulation, but its mechanisms of action remain poorly understood.

A simple method to induce differentiation of murine bone marrow mesenchymal cells to insulin-producing cells using conophylline and betacellulin-delta4

The present study was conducted to establish a method to induce differentiation of bone marrow (MB)-derived mesenchymal cells into insulin-producing cells. When mouse BM-derived mesenchymal cells were cultured for 60 days in medium containing 10% fetal calf serum and 25 mM glucose, they expressed insulin. Addition of activin A and betacellulin (BTC) accelerated differentiation, and immunoreactive insulin was detected 14 days after the treatment. Insulin-containing secretory granules were observed in differentiated cells by electron microscopy. Treatment of BM-derived mesenchymal cells with conophylline (CnP) and BTC-delta4 further accelerated differentiation, and mRNA for insulin was detected 5 to 7 days after the treatment. Mesencymal cells treated with CnP and BTC-delta4 responded to a high concentration of glucose and secreted mature insulin. When these cells were transplanted into streptozotocin-treated mice, they markedly reduced the plasma glucose concentration, and the effect continued for at least 4 weeks. These results indicate an efficacy of the combination of CnP and BTC-delta4 in inducing differentiation of BM-derived mesenchymal cells into insulin-producing cells.

A betacellulin mutant promotes differentiation of pancreatic acinar AR42J cells into insulin-producing cells with low affinity of binding to ErbB1

Betacellulin (BTC) is one of the members of the epidermal growth factor (EGF) ligand family of ErbB receptor tyrosine kinases. It is a differentiation factor as well as a potent mitogen. BTC promotes the differentiation of pancreatic acinar-derived AR42J cells into insulin-producing cells. It independently and preferentially binds to two type I tyrosine kinase receptors, the EGF receptor (ErbB1) and ErbB4. However, the physiochemical characteristics of BTC that are responsible for its preferential binding to these two receptors have not been fully defined. In this study, to investigate the essential amino acid residues of BTC for binding to the two receptors, we introduced point mutations into the EGF domain of BTC employing error-prone PCR. The receptor binding abilities of 190 mutants expressed in Escherichia coli were assessed by enzyme immunoassay. Replacement of the glutamic acid residue at position 88 with a lysine residue in BTC was found to produce a significant loss of affinity for binding to ErbB1, while the affinity of binding to ErbB4 was unchanged. In addition, the mutant of BTC-E/88/K showed less growth-promoting activity on BALB/c 3T3 cells compared with that of the wild-type BTC protein. Interestingly, the BTC mutant protein promoted differentiation of pancreatic acinar AR42J cells at a high frequency into insulin-producing cells compared with AR42J cells that were treated with wild-type BTC protein. These results indicate the possibility of designing BTC mutants, which have an activity of inducing differentiation only, without facilitating growth promotion.

Conophylline and betacellulin-delta4: an effective combination of differentiation factors for pancreatic beta cells

Conophylline and betacellulin-delta4 reproduce differentiation-inducing activity of activin A and betacellulin, respectively. We examined the effect of conophylline and betacellulin-delta4 on beta cell differentiation. In AR42J cells, conophylline and betacellulin-delta4 converted them into insulin-producing cells. Cells treated with conophylline and betacellulin-delta4 continued to grow after differentiation. Thus, cell number and insulin content were much greater compared to cells treated with activin A and betacellulin. Furthermore, cells treated with conophylline and betacellulin-delta4 secreted insulin in response to glucose. Likewise, conophylline and betacellulin-delta4 converted pancreatic ductal cells into insulin-producing cells. Insulin content, cell number and glucose-evoked insulin secretion were significantly greater than those in cells treated with activin A and betacellulin. Transplantation of pseudoislets prepared using ductal cells treated with conophylline and betacellulin-delta4 was able to reduce effectively the plasma glucose concentration in streptozotocin-treated nude mice. Conophylline and betacellulin-delta4 are effective in inducing differentiation of beta cells from progenitors.

Neogenesis and proliferation of beta-cells induced by human betacellulin gene transduction via retrograde pancreatic duct injection of an adenovirus vector

Betacellulin (BTC) has been shown to have a role in the differentiation and proliferation of beta-cells both in vitro and in vivo. We administered a human betacellulin (hBTC) adenovirus vector to male ICR mice via retrograde pancreatic duct injection. As a control, we administered a beta-galactosidase adenovirus vector. In the mice, hBTC protein was mainly overexpressed by pancreatic duct cells. On immunohistochemical analysis, we observed features of beta-cell neogenesis as newly formed insulin-positive cells in the duct cell lining or islet-like cell clusters (ICCs) closely associated with the ducts. The BrdU labeling index of beta-cells was also increased by the betacellulin vector compared with that of control mice. These results indicate that hBTC gene transduction into adult pancreatic duct cells promoted beta-cell differentiation (mainly from duct cells) and proliferation of pre-existing beta-cells, resulting in an increase of the beta-cell mass that improved glucose tolerance in diabetic mice.

Association of a polymorphism in the betacellulin gene with type 1 diabetes mellitus in two populations

Betacellulin, a member of the epidermal growth factor family, is expressed in fetal and adult pancreas. In vitro and in vivo studies suggest a role for betacellulin in islet neogenesis and regeneration. Therefore, a mutation in the betacellulin gene might lead to fewer beta cells. With reduced beta cell reserve, beta cells may not be able to compensate for an autoimmune attack, and in turn, susceptibility to type 1 diabetes mellitus (T1DM) would increase. Previous mutational analysis identified seven polymorphisms in the betacellulin gene [5' UT (-233G>C, -226A>G), exon 1 (TGC19GGC, Cys7Gly), exon 2 (CTC130TTC, Leu44Phe), exon 4 (TTG370ATG, Leu124Met), intron 2 (-31T>C), and intron 4 (-4C>T)]. An association study of these variants with T1DM was first carried out in 100 Caucasian subjects with T1DM and 282 Caucasian subjects without diabetes recruited at the University of Maryland. The frequency of the intron 4 T-4 allele was significantly higher among nondiabetic controls than that among diabetic cases (0.29 vs 0.21, p=0.04). Allele frequencies for the other polymorphisms did not differ significantly between cases and controls. The intron 4 T-4 association was then replicated by transmission disequilibrium testing in a separate population of Caucasian parent/offspring with T1DM trios (n=168 trios, 113 informative) recruited at the Medical College of Wisconsin (p=0.024). An interaction of the intron 4 T-4 allele and human leukocyte antigen (HLA) was also detected with undertransmission of the T allele in those T1DM subjects with susceptible HLA types as compared to those T1DM subjects without susceptible HLA types (p=0.018). RNA studies of the intron T-4 variant showed similar RNA levels for intron 4 T-4 and intron 4 C-4 alleles. Additionally, there was no evidence for an effect of this variant on exon-intron splicing. We conclude that the intron 4 T-4 allele in the betacellulin gene is associated with lower risk of T1DM and may interact with HLA. Further studies will be necessary to establish the significance of this association.

Long-term in vitro growth of human insulin-secreting insulinoma cells

OBJECTIVE

Long-term in vitro maintenance of human insulin-secreting insulinoma cells.

METHODS

(1) Cell culture of ex vivo-derived insulinoma cell suspensions from 8 individual human donors, using various cell culture medium supplementations; (2) determination of insulin synthesis and secretion using immunocytochemistry and insulin and pro-insulin radioimmunoassays; (3) nestin-immunostaining of long-term in vitro grown insulinoma cell suspensions, and (4) phase-contrast light microscopy for analyzing the in vitro growth characteristics of the insulinoma cells.

RESULTS

(1) Parallel persistence of in vitro insulinoma cell proliferation as well as insulin-synthesizing and -secreting capacity depended on both the co-culture of insulinoma cells with human fibroblasts and the supplementation of the cell culture medium with tissue culture supernatant derived from the rodent pituitary adenoma cell line GH-3; (2) immunostaining for insulin and secretagogin confirmed the neuroendocrine origin of the insulinoma cells grown in vitro; (3) insulin secretion capability persisted up to an observation period of 25 weeks; (4) insulin secretion rates after 6 weeks of in vitro growth ranged from 3.5 to 83.3 muU/ml/h/60,000 cells plated, and (5) after long-term in vitro growth of insulinoma-derived cell suspensions with persistent insulin-secreting capacity, nestin staining was observed predominantly in co-cultured fibroblasts.

CONCLUSION

Our data describe for the first time the long-term in vitro culture of insulin-secreting human insulinomas and highlight the importance of beta-cell trophic factors for insulinoma cell growth.