Increased β-cell replication and β-cell mass regeneration in syngeneically transplanted rat islets overexpressing insulin-like growth factor II

The Parasite-Derived Peptide, FhHDM-1, Selectively Modulates miRNA Expression in β-Cells to Prevent Apoptotic Pathways Induced by Proinflammatory Cytokines

We have previously identified a parasite-derived peptide, FhHDM-1, that prevented the progression of diabetes in nonobese diabetic (NOD) mice. Disease prevention was mediated by the activation of the PI3K/Akt pathway to promote β-cell survival and metabolism without inducing proliferation. To determine the molecular mechanisms driving the antidiabetogenic effects of FhHDM-1, miRNA:mRNA interactions and in silico predictions of the gene networks were characterised in β-cells, which were exposed to the proinflammatory cytokines that mediate β-cell destruction in Type 1 diabetes (T1D), in the presence and absence of FhHDM-1. The predicted gene targets of miRNAs differentially regulated by FhHDM-1 mapped to the biological pathways that regulate β-cell biology. Six miRNAs were identified as important nodes in the regulation of PI3K/Akt signaling. Additionally, IGF-2 was identified as a miRNA gene target that mediated the beneficial effects of FhHDM-1 on β-cells. The findings provide a putative mechanism by which FhHDM-1 positively impacts β-cells to permanently prevent diabetes. As β-cell death/dysfunction underlies diabetes development, FhHDM-1 opens new therapeutic avenues.

A gelatin hydrogel nonwoven fabric improves outcomes of subcutaneous islet transplantation

Subcutaneous islet transplantation is a promising treatment for severe diabetes; however, poor engraftment hinders its prevalence. We previously reported that a recombinant peptide (RCP) enhances subcutaneous islet engraftment. However, it is impractical for clinical use because RCP must be removed when transplanting islets. We herein investigated whether a novel bioabsorbable gelatin hydrogel nonwoven fabric (GHNF) could improve subcutaneous islet engraftment. A silicon spacer with or without GHNF was implanted into the subcutaneous space of diabetic mice. Syngeneic islets were transplanted into the pretreated space or intraportally (Ipo group). Blood glucose, intraperitoneal glucose tolerance, immunohistochemistry, CT angiography and gene expression were evaluated. The cure rate and glucose tolerance of the GHNF group were significantly better than in the control and Ipo groups (p < 0.01, p < 0.05, respectively). In the GHNF group, a limited increase of vWF-positive vessels was detected in the islet capsule, whereas laminin (p < 0.05), collagen III and IV were considerably enhanced. TaqMan arrays revealed a significant upregulation of 19 target genes (including insulin-like growth factor-2) in the pretreated space. GHNF markedly improved the subcutaneous islet transplantation outcomes, likely due to ECM compensation and protection of islet function by various growth factors, rather than enhanced neovascularization.

The Roles of the IGF Axis in the Regulation of the Metabolism: Interaction and Difference between Insulin Receptor Signaling and IGF-I Receptor Signaling

It has been well established that insulin-like growth factors (IGFs) mainly mediate long-term actions in cell fates, whereas insulin predominantly exerts its role on metabolic activity. Indeed, insulin mediates multiple anabolic biological activities in glucose and amino acid transport, lipid and protein synthesis, the induction of glycogen, the inhibition of gluconeogenesis, lipolysis, and protein degradation. The interactions and differences between insulin receptor signaling and IGF-I receptor signaling in the metabolism and the cell fates are quite complicated. Because of the overlapping actions of IGF-I singling with insulin signaling, it has been difficult to distinguish the role of both signaling mechanisms on the metabolism. Furthermore, comprehensive information on the IGF-I function in respective tissues remains insufficient. Therefore, we need to clarify the precise roles of IGF-I signaling on the metabolism separate from those of insulin signaling. This review focuses on the metabolic roles of IGFs in the respective tissues, especially in terms of comparison with those of insulin, by overviewing the metabolic phenotypes of tissue-specific IGF-I and insulin receptor knockout mice, as well as those in mice treated with the dual insulin receptor/IGF-I receptor inhibitor OSI-906.

Autocrine IGF2 programmes β-cell plasticity under conditions of increased metabolic demand

When exposed to nutrient excess and insulin resistance, pancreatic β-cells undergo adaptive changes in order to maintain glucose homeostasis. The role that growth control genes, highly expressed in early pancreas development, might exert in programming β-cell plasticity in later life is a poorly studied area. The imprinted Igf2 (insulin-like growth factor 2) gene is highly transcribed during early life and has been identified in recent genome-wide association studies as a type 2 diabetes susceptibility gene in humans. Hence, here we investigate the long-term phenotypic metabolic consequences of conditional Igf2 deletion in pancreatic β-cells (Igf2βKO) in mice. We show that autocrine actions of IGF2 are not critical for β-cell development, or for the early post-natal wave of β-cell remodelling. Additionally, adult Igf2βKO mice maintain glucose homeostasis when fed a chow diet. However, pregnant Igf2βKO females become hyperglycemic and hyperinsulinemic, and their conceptuses exhibit hyperinsulinemia and placentomegalia. Insulin resistance induced by congenital leptin deficiency also renders Igf2βKO females more hyperglycaemic compared to leptin-deficient controls. Upon high-fat diet feeding, Igf2βKO females are less susceptible to develop insulin resistance. Based on these findings, we conclude that in female mice, autocrine actions of β-cell IGF2 during early development determine their adaptive capacity in adult life.

The developmental and experience-dependent expression of IGF-2 in mice visual cortex

The circuitry associated with the visual cortex is particularly sensitive to experiences during the early stages of life, which are collectively known as critical periods. Critical period of ocular dominance plasticity is regulated by both environmental and genetic factors. Previous studies demonstrated that IGF-1 significantly influenced the regulation of visual cortex synaptic plasticity. IGF-2 can reportedly regulate synapse formation, dendritic spine maturation, and memory consolidation in rodents. Association between IGF-2 and the regulation of visual cortex synaptic plasticity remains unclear. Here, we first aimed to elucidate the normal expression patterns of IGF-2 and its laminar expression pattern during the process of visual cortex development in mice. This confirmed that IGF-2 may influence the regulation of ocular dominance plasticity in mice. We further elucidated the role of IGF-2 in the regulation of visual cortex synaptic plasticity by examining the effect of monocular deprivation (MD) on IGF-2 expression in the visual cortex. Interestingly, we observed that MD remarkably reduced IGF-2 expression in the visual cortex. Rodents reared in an enriched environment, with enhanced sensory, motor, and social experiences, were capable of effectively accelerating the development of the visual system and could restore normal visual acuity. Although the enriched environment facilitated the restoration of normal visual acuity in the MD mice, IGF-2 expression levels in the visual cortex remained unchanged. Therefore, we considered the possibility that IGF-2 may have a different role with regard to the modulation of plasticity in the visual cortex of the mice, which we aim to study in the future.

Assessing Islet Transplantation Outcome in Mice

Islet transplantation is a potential treatment for Type 1 diabetes; however, improvements need to be made before it could become clinically widely available. In preclinical studies, the mouse is often used to model islet transplantation, with most studies aiming to improve transplantation outcome by manipulating the islets prior to transplantation or by treating the recipient mouse. Here, we describe the process of islet transplantation in the mouse, including how one can make the mouse diabetic, isolate donor islets, and transplant the islets into two different sites. Finally, we discuss how to assess the outcome of the transplantation in order to determine whether the experimental intervention has been beneficial.

Determining Beta Cell Mass, Apoptosis, Proliferation, and Individual Beta Cell Size in Pancreatic Sections

Pancreatic beta cells have a significant remodeling capacity which plays an essential role in the maintenance of glucose homeostasis. Beta cell apoptosis, replication, size, dedifferentiation, and (neo)generation contribute to the beta cell mass regulation. However, the extent of their respective contribution varies significantly depending on the specific condition, and it is the balance among them that determines the eventual change in beta cell mass. Thus, the study of the pancreatic beta cell mass regulation requires the determination of all these factors. In this chapter, we describe the quantification of beta cell replication based on the incorporation of thymidine analogs into replicated DNA strands and on the expression of Ki67 antigen and phosphorylation of histone H3. Beta cell apoptosis is analyzed by the TUNEL technique, and beta cell mass and cross-sectional area of individual beta cells are determined by computerized image processing methods.

A Model for Human Islet Transplantation to Immunodeficient Streptozotocin-Induced Diabetic Mice

Streptozotocin (STZ) is a cytotoxic glucose analogue that causes beta cell death and is widely used to induce experimental diabetes in rodents. The sensitivity of beta cells to STZ is species-specific and human beta cells are resistant to STZ. In experimental islet transplantation to rodents, STZ-diabetes must be induced before transplantation to avoid destruction of grafted islets by STZ. In human islet transplantation, injection of STZ before transplantation is inconvenient and costly, since human islet availability depends on organ donation and frail STZ-diabetic mice must be kept for unpredictable lapses of time until a human islet preparation is available. Based on the high resistance of human beta cells to STZ, we have tested a new model for STZ-diabetes induction in which STZ is injected after human islet transplantation. Human and mouse islets were transplanted under the kidney capsule of athymic nude mice, and 10–14 days after transplantation mice were intraperitoneally injected with five consecutive daily doses of STZ or vehicle. Beta-cell death increased and beta-cell mass was reduced in mouse islet grafts after STZ injection. In contrast, in human islet grafts beta cell death and mass did not change after STZ injection. Mice transplanted with rodent islets developed hyperglycemia after STZ-injection. Mice transplanted with human islets remained normoglycemic and developed hyperglycemia when the graft was harvested. STZ had no detectable toxic effects on beta cell death, mass and function of human transplanted islets. We provide a new, more convenient and cost-saving model for human islet transplantation to STZ-diabetic recipients in which STZ is injected after islet transplantation.

The Fate of Allogeneic Pancreatic Islets following Intraportal Transplantation: Challenges and Solutions

Pancreatic islet transplantation as a therapeutic option for type 1 diabetes mellitus is gaining widespread attention because this approach can restore physiological insulin secretion, minimize the risk of hypoglycemic unawareness, and reduce the risk of death due to severe hypoglycemia. However, there are many obstacles contributing to the early mass loss of the islets and progressive islet loss in the late stages of clinical islet transplantation, including hypoxia injury, instant blood-mediated inflammatory reactions, inflammatory cytokines, immune rejection, metabolic exhaustion, and immunosuppression-related toxicity that is detrimental to the islet allograft. Here, we discuss the fate of intrahepatic islets infused through the portal vein and propose potential interventions to promote islet allograft survival and improve long-term graft function.

β-cell insulin receptor deficiency during in utero development induces an islet compensatory overgrowth response

The presence of insulin receptor (IR) on β-cells suggests that insulin has an autocrine/paracrine role in the regulation of β-cell function. It has previously been reported that the β-cell specific loss of IR (βIRKO) leads to the development of impaired glycemic regulation and β-cell death in mice. However, temporally controlled βIRKO induced during the distinct transitions of fetal pancreas development has yet to be investigated. We hypothesized that the presence of IR on β-cells during the 2nd transition phase of the fetal murine pancreas is required for maintaining normal islet development.We utilized a mouse insulin 1 promoter driven tamoxifen-inducible Cre-recombinase IR knockout (MIP-βIRKO) mouse model to investigate the loss of β-cell IR during pancreatic development at embryonic day (e) 13, a phase of endocrine proliferation and β-cell fate determination. Fetal pancreata examined at e19-20 showed significantly reduced IR levels in the β-cells of MIP-βIRKO mice. Morphologically, MIP-βIRKO pancreata exhibited significantly enlarged islet size with increased β-cell area and proliferation. MIP-βIRKO pancreata also displayed significantly increased Igf-2 protein level and Akt activity with a reduction in phospho-p53 when compared to control littermates. Islet vascular formation and Vegf-a protein level was significantly increased in MIP-βIRKO pancreata.Our results demonstrate a developmental role for the β-cell IR, whereby its loss leads to an islet compensatory overgrowth, and contributes further information towards elucidating the temporally sensitive signaling during β-cell commitment.

Insulin-like growth factor 2 mitigates depressive behavior in a rat model of chronic stress

Depression is a common psychiatric disorder associated with chronic stress. Insulin-like growth factor 2 (IGF2) is a growth factor that serves important roles in the brain during development and at adulthood. Here, the role of IGF2 expression in the hippocampus was investigated in a rat model of depression. A chronic restraint stress (CRS) model of depression was established in rats, exhibiting depression-like behavior as assessed with the sucrose preference test (SPT) and forced swimming test (FST), and with evaluation of the corticosterone levels. Hippocampal IGF2 levels were significantly lower in rats suffering CRS than in controls, as were levels of pERK1/2 and GluR1. Lentivirus-mediated hippocampal IGF2 overexpression alleviated depressive behavior in restrained rats, elevated the levels of pERK1/2 and GluR1 proteins, but it did not affect the expression of pGSK3β, GluR2, NMDAR1, and NMDAR2A. These results suggest the chronic restraint stress induces depressive behavior, which may be mediated by ERK-dependent IGF2 signaling, pointing to an antidepressant role for this molecular pathway.

Human Serum Versus Human Serum Albumin Supplementation in Human Islet Pretransplantation Culture: In Vitro and In Vivo Assessment

There is conflicting evidence favoring both the use of human serum (HS) and of human serum albumin (HSA) in human islet culture. We evaluated the effects of HS versus HSA supplementation on 1) in vitro β-cell viability and function and 2) in vivo islet graft revascularization, islet viability, β-cell death, and metabolic outcome after transplantation. Islets isolated from 14 cadaveric organ donors were cultured for 3 days in CMRL 1066 medium supplemented with HS or HSA. After 3 days in culture, β-cell apoptosis was lower in HS group (1.41 ± 0.27 vs. 2.38 ± 0.39%, p = 0.029), and the recovery of islets was 77 ± 11% and 54 ± 1% in HS- and HSA-cultured groups, respectively. Glucose-stimulated insulin secretion (GSIS) was higher in HS group (29.4, range 10.4-99.9, vs. 22.3, range 8.7-70.6, p = 0.031). In vivo viability and revascularization was determined in HS- and HSA-cultured islets transplanted into the anterior chamber of the eye of Balb/c mice (n = 14), and β-cell apoptosis in paraffin-embedded mouse eyes. Islet viability and β-cell apoptosis were similar in both groups. Revascularization was observed in one graft (HS group) on day 10 after transplantation. Islet function was determined in streptozotocin (STZ)-diabetic nude mice (n = 33) transplanted with 2,000 IEQs cultured with HS or HSA that showed similar blood glucose levels and percentage of normoglycemic animals over time. In conclusion, human islets cultured in medium supplemented with HS showed higher survival in vitro, as well as islet viability and function. The higher in vitro survival increased the number of islets available for transplantation. However, the beneficial effect on viability and function did not translate into an improved metabolic evolution when a similar number of HSA- and HS-cultured islets was transplanted.

IGF2: an endocrine hormone to improve islet transplant survival

In the week following pancreatic islet transplantation, up to 50% of transplanted islets are lost due to apoptotic cell death triggered by hypoxic and pro-inflammatory cytokine-mediated cell stress. Thus, therapeutic approaches designed to protect islet cells from apoptosis could significantly improve islet transplant success. IGF2 is an anti-apoptotic endocrine protein that inhibits apoptotic cell death through the mitochondrial (intrinsic pathway) or via antagonising activation of pro-inflammatory cytokine signalling (extrinsic pathway), in doing so IGF2 has emerged as a promising therapeutic molecule to improve islet survival in the immediate post-transplant period. The development of novel biomaterials coated with IGF2 is a promising strategy to achieve this. This review examines the mechanisms mediating islet cell apoptosis in the peri- and post-transplant period and aims to identify the utility of IGF2 to promote islet survival and enhance long-term insulin independence rates within the setting of clinical islet transplantation.

Bisphenol A enhances kisspeptin neurons in anteroventral periventricular nucleus of female mice

Bisphenol-A (BPA), an environmental estrogen, adversely affects female reproductive health. However, the underlying mechanisms remain largely unknown. We found that oral administration (p.o.) of BPA (20  μg/kg) to adult female mice at proestrus, but not at estrus or diestrus, significantly increased the levels of plasma E₂, LH and FSH, and Gnrh mRNA within 6  h. The administration of BPA at proestrus, but not at diestrus, could elevate the levels of Kiss1 mRNA and kisspeptin protein in anteroventral periventricular nucleus (AVPV) within 6  h. In contrast, the level of Kiss1 mRNA in arcuate nucleus (ARC) was hardly altered by BPA administration. In addition, at proestrus, a single injection (i.c.v.) of BPA dose-dependently enhanced the AVPV-kisspeptin expression within 6  h, this was sensitive to E₂ depletion by ovariectomy and an estrogen receptor α (ERα) antagonist. Similarly, the injection of BPA (i.c.v.) at proestrus could elevate the levels of plasma E₂, LH, and Gnrh mRNA within 6  h in a dose-dependent manner, which was blocked by antagonists of GPR54 or ERα. Injection of BPA (i.c.v.) at proestrus failed to alter the timing and peak concentration of LH-surge generation. In ovariectomized mice, the application of E₂ induced a dose-dependent increase in the AVPV-Kiss1 mRNA level, indicating 'E₂-induced positive feedback', which was enhanced by BPA injection (i.c.v.). The levels of Erα (Esr1) and Erβ (Esr2) mRNAs in AVPV and ARC did not differ significantly between vehicle-and BPA-treated groups. This study provides in vivo evidence that exposure of adult female mice to a low dose of BPA disrupts the hypothalamic-pituitary-gonadal reproductive endocrine system through enhancing AVPV-kisspeptin expression and release.