Hepatocyte growth factor enhances engraftment and function of nonhuman primate islets

Inhibition of the prostaglandin D2-GPR44/DP2 axis improves human islet survival and function

AIMS/HYPOTHESIS

Inflammatory signals and increased prostaglandin synthesis play a role during the development of diabetes. The prostaglandin D₂ (PGD₂) receptor, GPR44/DP2, is highly expressed in human islets and activation of the pathway results in impaired insulin secretion. The role of GPR44 activation on islet function and survival rate during chronic hyperglycaemic conditions is not known. In this study, we investigate GPR44 inhibition by using a selective GPR44 antagonist (AZ8154) in human islets both in vitro and in vivo in diabetic mice transplanted with human islets.

METHODS

Human islets were exposed to PGD₂ or proinflammatory cytokines in vitro to investigate the effect of GPR44 inhibition on islet survival rate. In addition, the molecular mechanisms of GPR44 inhibition were investigated in human islets exposed to high concentrations of glucose (HG) and to IL-1β. For the in vivo part of the study, human islets were transplanted under the kidney capsule of immunodeficient diabetic mice and treated with 6, 60 or 100 mg/kg per day of a GPR44 antagonist starting from the transplantation day until day 4 (short-term study) or day 17 (long-term study) post transplantation. IVGTT was performed on mice at day 10 and day 15 post transplantation. After termination of the study, metabolic variables, circulating human proinflammatory cytokines, and hepatocyte growth factor (HGF) were analysed in the grafted human islets.

RESULTS

PGD₂ or proinflammatory cytokines induced apoptosis in human islets whereas GPR44 inhibition reversed this effect. GPR44 inhibition antagonised the reduction in glucose-stimulated insulin secretion induced by HG and IL-1β in human islets. This was accompanied by activation of the Akt-glycogen synthase kinase 3β signalling pathway together with phosphorylation and inactivation of forkhead box O-1and upregulation of pancreatic and duodenal homeobox-1 and HGF. Administration of the GPR44 antagonist for up to 17 days to diabetic mice transplanted with a marginal number of human islets resulted in reduced fasting blood glucose and lower glucose excursions during IVGTT. Improved glucose regulation was supported by increased human C-peptide levels compared with the vehicle group at day 4 and throughout the treatment period. GPR44 inhibition reduced plasma levels of TNF-α and growth-regulated oncogene-α/chemokine (C-X-C motif) ligand 1 and increased the levels of HGF in human islets.

CONCLUSIONS/INTERPRETATION

Inhibition of GPR44 in human islets has the potential to improve islet function and survival rate under inflammatory and hyperglycaemic stress. This may have implications for better survival rate of islets following transplantation.

Synthesis and Biological Validation of a Harmine-Based, Central Nervous System (CNS)-Avoidant, Selective, Human β-Cell Regenerative Dual-Specificity Tyrosine Phosphorylation-Regulated Kinase A (DYRK1A) Inhibitor

Recently, our group identified that harmine is able to induce β-cell proliferation both in vitro and in vivo, mediated via the DYRK1A-NFAT pathway. Since, harmine suffers from a lack of selectivity, both against other kinases and CNS off-targets, we therefore sought to expand structure-activity relationships for harmine's DYRK1A activity, to enhance selectivity for off-targets while retaining human β-cell proliferation activity. We carried out optimization of the 9-N-position of harmine to synthesize 29 harmine-based analogs. Several novel inhibitors showed excellent DYRK1A inhibition and human β-cell proliferation capability. An optimized DYRK1A inhibitor, 2-2c, was identified as a novel, efficacious in vivo lead candidate. 2-2c also demonstrates improved selectivity for kinases and CNS off-targets, as well as in vivo efficacy for β-cell proliferation and regeneration at lower doses than harmine. Collectively, these findings demonstrate that 2-2c is a much improved in vivo lead candidate as compared to harmine for the treatment of diabetes.

Long-term c-Kit overexpression in beta cells compromises their function in ageing mice

AIMS/HYPOTHESIS

c-Kit signalling regulates intracellular pathways that enhance beta cell proliferation, insulin secretion and islet vascularisation in mice up to 28 weeks of age and on short-term high-fat diet. However, long-term c-Kit activation in ageing mouse islets has yet to be examined. This study utilises beta cell-specific c-Kit-overexpressing transgenic (c-KitβTg) ageing mice (~60 weeks) to determine the effect of its activation on beta cell dysfunction and insulin secretion.

METHODS

Wild-type and c-KitβTg mice, aged 60 weeks, were examined using metabolic tests to determine glucose tolerance and insulin secretion. Pancreas histology and proteins in isolated islets were examined to determine the expression of beta cell transcription factors, proliferation and intracellular signalling. To determine the role of insulin receptor signalling in ageing c-KitβTg mice, we generated beta cell-specific inducible insulin receptor knockout in ageing c-KitβTg mice (c-KitβTg;βIRKO mice) and examined the ageing mice for glucose tolerance and islet histology.

RESULTS

Ageing c-KitβTg mice progressively developed glucose intolerance, compared with age-matched wild-type littermates, due to impaired insulin secretion. Increased beta cell mass, proliferation and nuclear forkhead box transcription factor O1 (FOXO1) expression and reduced exocytotic protein levels were detected in ageing c-KitβTg mouse islets. Protein analyses of isolated islets showed increased insulin receptor, phosphorylated IRS-1^Ser612 and cleaved poly(ADP-ribose) polymerase levels in ageing c-KitβTg mice. Ageing c-KitβTg mouse islets treated ex vivo with insulin demonstrated reduced Akt phosphorylation, indicating that prolonged c-Kit induced beta cell insulin insensitivity. Ageing c-KitβTg;βIRKO mice displayed improved glucose tolerance and beta cell function compared with ageing c-KitβTg mice.

CONCLUSIONS/INTERPRETATION

These findings indicate that long-term c-Kit overexpression in beta cells has a negative impact on insulin exocytosis and that temporally dependent regulation of c-Kit-insulin receptor signalling is important for optimal beta cell function.

Increased Expression of Circulating microRNA 101-3p in Type 1 Diabetes Patients: New Insights Into miRNA-Regulated Pathophysiological Pathways for Type 1 Diabetes

MicroRNAs (miRs) are master regulators of post-transcriptional gene expression, and they are often dysregulated in individuals suffering from diabetes. We investigated the roles of miR-101-3p and miR-204-5p, both of which negatively regulate insulin secretion and cell survival and are highly expressed in pancreatic β cells, in the context of type 1 diabetes (T1D) pathogenesis. Using quantitative real time PCR, we evaluated serum levels of miR-101-3p and miR-204-5p in four groups, including recent-onset T1D patients (T1D group; n = 50), individuals with normal glucose levels expressing one islet autoantibody (Ab) (single Ab group; n = 26) or multiple autoantibodies (multiple Ab group; n = 12), and healthy controls (control group; n = 43). An in silico analysis was performed to identify potential target genes of these miRNAs and to delineate enriched pathways. The relative expression of serum miR-101-3p was approximately three times higher in the multiple Ab and T1D groups than that in the single Ab and control groups (p < 0.0001). When considering all groups together, miR-101-3p expression was positively correlated with the level of islet autoantibodies GADA (r = 0.267; p = 0.0027) and IA-2A (r = 0.291; p = 0.001), and the expression of the miRNA was not correlated with levels of ZnT8A (r = 0.125; p = 0.183). miR-101-3p expression did not correlate with HbA1c (r = 0.178; p = 0.052) or glucose levels (r = 0.177; p = 0.051). No significant differences were observed in miR-204-5p expression among the analyzed groups. Computational analysis of the miR-101-3p target gene pathways indicated a potential activation of the HGF/c-Met, Ephrin receptor, and STAT3 signaling pathways. Our study demonstrated that the circulating levels of miR-101-3p are higher in T1D patients and in individuals with normal glucose levels, testing positive for multiple autoantibodies, indicating that miR-101-3p precedes loss of glucose homeostasis. The pathogenic role of miR-101-3p in T1D may involve multiple molecular pathways.

Mesenchymal Stem Cells from Chronic Pancreatitis Patients Show Comparable Potency Compared to Cells from Healthy Donors

Mesenchymal stem cells (MSCs) are proven to be beneficial in islet transplantation, suggesting a potential therapeutic role of them in total pancreatectomy with islet autotransplantation (TP-IAT) for chronic pancreatitis (CP) patients. We investigated whether MSCs derived from CP patients are suitable for use in autologous cell therapy. MSCs from healthy donors (H-MSCs) and CP patients (CP-MSCs) were studied for phenotype, colony formation potential, multilineage differentiation ability, proliferation, senescence, secretory characters, and immunosuppressive functions. The potential protective effect of CP-MSCs was evaluated on hypoxia-induced islet cell death. Cell surface markers were similar between H-MSCs and CP-MSCs, as well as the ability of colony formation, multilineage differentiation, secretion of vascular endothelial growth factor and transforming growth factor (TGF-β), senescence, and inhibition of T cells proliferation in vitro. We found that growth differentiation factor 6 and hepatocyte growth factor (HGF) were significantly downregulated, whereas TGFβ and matrix metalloproteinase-2 were significantly upregulated in CP-MSCs compared with H-MSCs, among 84 MSC-related genes investigated in this study. MSCs from CP patients secreted less HGF, compared with the H-MSCs. A higher interferon-γ-induced indoleamine 2,3-dioxygenase expression was observed in CP-MSCs compared to H-MSCs. Moreover, CP-MSCs prevented hypoxia-induced β cell deaths to a similar extent as H-MSCs. Regardless of moderate difference in gene expression, CP-MSCs possess similar immunomodulatory and prosurvival functions to H-MSCs, and may be suitable for autologous cell therapy in CP patients undergoing TP-IAT. Stem Cells Translational Medicine 2019;8:418-429.

β-Cell Receptor Tyrosine Kinases in Controlling Insulin Secretion and Exocytotic Machinery: c-Kit and Insulin Receptor

Insulin secretion from pancreatic β-cells is initiated through channel-mediated depolarization, cytoskeletal remodeling, and vesicle tethering at the cell membrane, all of which can be regulated through cell surface receptors. Receptor tyrosine kinases (RTKs) promote β-cell development and postnatal signaling to improve β-cell mass and function, yet their activation has also been shown to initiate exocytotic events in β-cells. This review examines the role of RTK signaling in insulin secretion, with a focus on RTKs c-Kit and insulin receptor (IR). Pathways that control insulin release and the potential interplay between c-Kit and IR signaling are discussed, along with clinical implications of RTK therapy on insulin secretion.

The Role of Hepatocyte Growth Factor (HGF) in Insulin Resistance and Diabetes

In obesity, insulin resistance (IR) and diabetes, there are proteins and hormones that may lead to the discovery of promising biomarkers and treatments for these metabolic disorders. For example, these molecules may impair the insulin signaling pathway or provide protection against IR. Thus, identifying proteins that are upregulated in IR states is relevant to the diagnosis and treatment of the associated disorders. It is becoming clear that hepatocyte growth factor (HGF) is an important component of the pathophysiology of IR, with increased levels in most common IR conditions, including obesity. HGF has a role in the metabolic flux of glucose in different insulin sensitive cell types; plays a key role in β-cell homeostasis; and is capable of modulating the inflammatory response. In this review, we discuss how, and to what extent HGF contributes to IR and diabetes pathophysiology, as well as its role in cancer which is more prevalent in obesity and diabetes. Based on the current literature and knowledge, it is clear that HGF plays a central role in these metabolic disorders. Thus, HGF levels could be employed as a biomarker for disease status/progression, and HGF/c-Met signaling pathway modulators could effectively regulate IR and treat diabetes.

Glial cell-line derived neurotrophic factor protects human islets from nutrient deprivation and endoplasmic reticulum stress induced apoptosis

One of the key limitations to successful human islet transplantation is loss of islets due to stress responses pre- and post-transplantation. Nutrient deprivation and ER stress have been identified as important mechanisms leading to apoptosis. Glial Cell-line Derived Neurotrophic Factor (GDNF) has recently been found to promote islet survival after isolation. However, whether GDNF could rescue human islets from nutrient deprivation and ER stress-mediated apoptosis is unknown. Herein, by mimicking those conditions in vitro, we have shown that GDNF significantly improved glucose stimulated insulin secretion, reduced apoptosis and proinsulin:insulin ratio in nutrient deprived human islets. Furthermore, GDNF alleviated thapsigargin-induced ER stress evidenced by reduced expressions of IRE1α and BiP and consequently apoptosis. Importantly, this was associated with an increase in phosphorylation of PI3K/AKT and GSK3B signaling pathway. Transplantation of ER stressed human islets pre-treated with GDNF under kidney capsule of diabetic mice resulted in reduced expressions of IRE1α and BiP in human islet grafts with improved grafts function shown by higher levels of human C-peptide post-transplantation. We suggest that GDNF has protective and anti-apoptotic effects on nutrient deprived and ER stress activated human islets and could play a significant role in rescuing human islets from stress responses.

Early and Late G1/S Cyclins and Cdks Act Complementarily to Enhance Authentic Human β-Cell Proliferation and Expansion

β-Cell regeneration is a key goal of diabetes research. Progression through the cell cycle is associated with retinoblastoma protein (pRb) inactivation via sequential phosphorylation by the "early" cyclins and cyclin-dependent kinases (cdks) (d-cyclins cdk4/6) and the "late" cyclins and cdks (cyclin A/E and cdk1/2). In β-cells, activation of either early or late G1/S cyclins and/or cdks is an efficient approach to induce cycle entry, but it is unknown whether the combined expression of early and late cyclins and cdks might have synergistic or additive effects. Thus, we explored whether a combination of both early and late cyclins and cdks might more effectively drive human β-cell cell cycle entry than either group alone. We also sought to determine whether authentic replication with the expansion of adult human β-cells could be demonstrated. Late cyclins and cdks do not traffic in response to the induction of replication by early cyclins and cdks in human β-cells but are capable of nuclear translocation when overexpressed. Early plus late cyclins and cdks, acting via pRb phosphorylation on distinct residues, complementarily induce greater proliferation in human β-cells than either group alone. Importantly, the combination of early and late cyclins and cdks clearly increased human β-cell numbers in vitro. These findings provide additional insight into human β-cell expansion. They also provide a novel tool for assessing β-cell expansion in vitro.

Hepatocyte growth factor ameliorates hyperglycemia and corrects β-cell mass in IRS2-deficient mice

Insulin resistance, when combined with decreased β-cell mass and relative insufficient insulin secretion, leads to type 2 diabetes. Mice lacking the IRS2 gene (IRS2(-/-) mice) develop diabetes due to uncompensated insulin resistance and β-cell failure. Hepatocyte growth factor (HGF) activates the phosphatidylinositol 3-kinase/Akt signaling pathway in β-cells without recruitment of IRS1 or IRS2 and increases β-cell proliferation, survival, mass, and function when overexpressed in β-cells of transgenic (TG) mice. We therefore hypothesized that HGF may protect against β-cell failure in IRS2 deficiency. For that purpose, we cross-bred TG mice overexpressing HGF in β-cells with IRS2 knockout (KO) mice. Glucose homeostasis analysis revealed significantly reduced hyperglycemia, compensatory hyperinsulinemia, and improved glucose tolerance in TG/KO mice compared with those in KO mice in the context of similar insulin resistance. HGF overexpression also increased glucose-stimulated insulin secretion in IRS2(-/-) islets. To determine whether this glucose homeostasis improvement correlated with alterations in β-cells, we measured β-cell mass, proliferation, and death in these mice. β-Cell proliferation was increased and death was decreased in TG/KO mice compared with those in KO mice. As a result, β-cell mass was significantly increased in TG/KO mice compared with that in KO mice, reaching levels similar to those in wild-type mice. Analysis of the intracellular targets involved in β-cell failure in IRS2 deficiency showed Pdx-1 up-regulation, Akt/FoxO1 phosphorylation, and p27 down-regulation in TG/KO mouse islets. Taken together, these results indicate that HGF can compensate for IRS2 deficiency and subsequent insulin resistance by normalizing β-cell mass and increasing circulating insulin. HGF may be of value as a therapeutic agent against β-cell failure.

A high-throughput chemical screen reveals that harmine-mediated inhibition of DYRK1A increases human pancreatic beta cell replication

Types 1 and 2 diabetes affect some 380 million people worldwide. Both ultimately result from a deficiency of functional pancreatic insulin-producing beta cells. Beta cells proliferate in humans during a brief temporal window beginning around the time of birth, with a peak percentage (∼2%) engaged in the cell cycle in the first year of life. In embryonic life and after early childhood, beta cell replication is barely detectable. Whereas beta cell expansion seems an obvious therapeutic approach to beta cell deficiency, adult human beta cells have proven recalcitrant to such efforts. Hence, there remains an urgent need for antidiabetic therapeutic agents that can induce regeneration and expansion of adult human beta cells in vivo or ex vivo. Here, using a high-throughput small-molecule screen (HTS), we find that analogs of the small molecule harmine function as a new class of human beta cell mitogenic compounds. We also define dual-specificity tyrosine-regulated kinase-1a (DYRK1A) as the likely target of harmine and the nuclear factors of activated T cells (NFAT) family of transcription factors as likely mediators of human beta cell proliferation and differentiation. Using three different mouse and human islet in vivo-based models, we show that harmine is able to induce beta cell proliferation, increase islet mass and improve glycemic control. These observations suggest that harmine analogs may have unique therapeutic promise for human diabetes therapy. Enhancing the potency and beta cell specificity of these compounds are important future challenges.

Relationship between vascular endothelial cells and pancreatic islet development and stem cell differentiation

As the main components of the pancreatic islet niche, endothelial cells participate in many processes of pancreatic development, including pancreatic cell fate decision, endocrine pancreatic cell differentiation and proliferation, and spatial distribution of the pancreas. On different occasions, endothelial cells play disparate roles by cross-talking with islet cells to influence endocrine pancreatic cell differentiation and islet morphology and function. Cytokines such as hepatocyte growth factor and sphingosine-1-phosphate as well as the extracellular matrixes such as laminin and collagen Ⅳ, which are produced and/or secreted by endothelial cells, play important roles in the regulation of islet development and function. Furthermore, endothelial cells are involved in the balance between self-renewal and differentiation of stem cells. Application of endothelial cells to induce the differentiation of stem cells into functional islet cells may be one of the most promising approaches to cell replacement therapy for diabetes.

Islet β-Cell Mass Preservation and Regeneration in Diabetes Mellitus: Four Factors with Potential Therapeutic Interest

Islet β-cell replacement and regeneration are two promising approaches for the treatment of Type 1 Diabetes Mellitus. Indeed, the success of islet transplantation in normalizing blood glucose in diabetic patients has provided the proof of principle that cell replacement can be employed as a safe and efficacious treatment. Nonetheless, shortage of organ donors has hampered expansion of this approach. Alternative sources of insulin-producing cells are mandatory to fill this gap. Although great advances have been achieved in generating surrogate β-cells from stem cells, current protocols have yet to produce functionally mature insulin-secreting cells. Recently, the concept of islet regeneration in which new β-cells are formed from either residual β-cell proliferation or transdifferentiation of other endocrine islet cells has gained much interest as an attractive therapeutic alternative to restore β-cell mass. Complementary approaches to cell replacement and regeneration could aim at enhancing β-cell survival and function. Herein, we discuss the value of Hepatocyte Growth Factor (HGF), Glucose-Dependent Insulinotropic Peptide (GIP), Paired box gene 4 (Pax4) and Liver Receptor Homolog-1 (LRH-1) as key players for β-cell replacement and regeneration therapies. These factors convey β-cell protection and enhanced function as well as facilitating proliferation and transdifferentiation of other pancreatic cell types to β-cells, under stressful conditions.

Enhanced expression of VEGF-A in β cells increases endothelial cell number but impairs islet morphogenesis and β cell proliferation

There is a reciprocal interaction between pancreatic islet cells and vascular endothelial cells (EC) in which EC-derived signals promote islet cell differentiation and islet development while islet cell-derived angiogenic factors promote EC recruitment and extensive islet vascularization. To examine the role of angiogenic factors in the coordinated development of islets and their associated vessels, we used a "tet-on" inducible system (mice expressing rat insulin promoter-reverse tetracycline activator transgene and a tet-operon-angiogenic factor transgene) to increase the β cell production of vascular endothelial growth factor-A (VEGF-A), angiopoietin-1 (Ang1), or angiopoietin-2 (Ang2) during islet cell differentiation and islet development. In VEGF-A overexpressing embryos, ECs began to accumulate around epithelial tubes residing in the central region of the developing pancreas (associated with endocrine cells) as early as embryonic day 12.5 (E12.5) and increased dramatically by E16.5. While α and β cells formed islet cell clusters in control embryos at E16.5, the increased EC population perturbed endocrine cell differentiation and islet cell clustering in VEGF-A overexpressing embryos. With continued overexpression of VEGF-A, α and β cells became scattered, remained adjacent to ductal structures, and never coalesced into islets, resulting in a reduction in β cell proliferation and β cell mass at postnatal day 1. A similar impact on islet morphology was observed when VEGF-A was overexpressed in β cells during the postnatal period. In contrast, increased expression of Ang1 or Ang2 in β cells in developing or adult islets did not alter islet differentiation, development, or morphology, but altered islet EC ultrastructure. These data indicate that (1) increased EC number does not promote, but actually impairs β cell proliferation and islet formation; (2) the level of VEGF-A production by islet endocrine cells is critical for islet vascularization during development and postnatally; (3) angiopoietin-Tie2 signaling in endothelial cells does not have a crucial role in the development or maintenance of islet vascularization.

Combinatorial human progenitor cell transplantation optimizes islet regeneration through secretion of paracrine factors

Transplanted human bone marrow (BM) and umbilical cord blood (UCB) progenitor cells activate islet-regenerative or revascularization programs depending on the progenitor subtypes administered. Using purification of multiple progenitor subtypes based on a conserved stem cell function, high aldehyde dehydrogenase (ALDH) activity (ALDH(hi)), we have recently shown that transplantation of BM-derived ALDH(hi) progenitors improved systemic hyperglycemia and augmented insulin secretion by increasing islet-associated proliferation and vascularization, without increasing islet number. Conversely, transplantation of culture-expanded multipotent-stromal cells (MSCs) derived from BM ALDH(hi) cells augmented total beta cell mass via formation of beta cell clusters associated with the ductal epithelium, without sustained islet vascularization. To identify paracrine effectors produced by islet-regenerative MSCs, culture-expanded BM ALDH(hi) MSCs were transplanted into streptozotocin-treated nonobese diabetic/severe combine immune deficient (SCID) mice and segregated into islet-regenerative versus nonregenerative cohorts based on hyperglycemia reduction, and subsequently compared for differential production of mRNA and secreted proteins. Regenerative MSCs showed increased expression of matrix metalloproteases, epidermal growth factor receptor (EGFR)-activating ligands, and downstream effectors of Wnt signaling. Regenerative MSC supernatant also contained increased levels of pro-angiogenic versus pro-inflammatory cytokines, and augmented the expansion of ductal epithelial but not beta cells in vitro. Conversely, co-culture with UCB ALDH(hi) cells induced beta cell but not ductal epithelial cell proliferation. Sequential transplantation of MSCs followed by UCB ALDH(hi) cells improved hyperglycemia and glucose tolerance by increasing beta cell mass associated with the ductal epithelium and by augmenting intra-islet capillary densities. Thus, combinatorial human progenitor cell transplantation stimulated both islet-regenerative and revascularization programs. Understanding the progenitor-specific pathways that modulate islet-regenerative and revascularization processes may provide new approaches for diabetes therapy.

Partial hepatectomy improves the outcome of intraportal islet transplantation by promoting revascularization

Revascularization of grafts is one of the important key factors for the success of islet transplantation. After partial hepatectomy, many growth factors such as hepatocyte growth factor and vascular endothelial growth factor are increased in the remnant liver. These growth factors have properties that promote angiogenesis. This might be an optimal environment for revascularization of islets transplanted intraportally. To verify this hypothesis, syngeneic islets (330 per recipient) were transplanted into the right hepatic lobes of streptozotocin-induced diabetic Balb/c mice with (hepatectomy group) or without (control group) left liver resection. Blood glucose was monitored for 28 d after transplantation. Glucose tolerance test was performed on post-operative day (POD) 30, and histological assessments were performed on POD 7 and 30 respectively. Analysis revealed that 36.7% of the control and 90.0% of the hepatectomy mice attained normoglycemia during the observation period (*p = 0.0142). Glucose tolerance was improved in the hepatectomy group (Area under the curve of intraperitoneal glucose tolerance tests on POD 30, Control; 47,700 ± 5,890 min*mg/dl, Hepatectomy; 26,000 ± 2,060 min*mg/dl: **p = 0.00314). Revascularization of grafted islets was more pronounced in the hepatectomy group (Vessel number per islet area on POD 7, Control; 3.20 ± 0.463 × 10 (-4) /µm ( 2) , Hepatectomy; 7.08 ± 0.513 × 10 (-4) /µm ( 2) : **p < 0.01). In the present study, partial hepatectomy (30%) improved the outcome of intraportal islet transplantation. Revascularization of islets transplanted into the liver may have been promoted by the induction of liver regeneration.

Regulated and reversible induction of adult human β-cell replication

Induction of proliferation in adult human β-cells is challenging. It can be accomplished by introduction of cell cycle molecules such as cyclin-dependent kinase 6 (cdk6) and cyclin D1, but their continuous overexpression raises oncogenic concerns. We attempted to mimic normal, transient, perinatal human β-cell proliferation by delivering these molecules in a regulated and reversible manner. Adult cadaveric islets were transduced with doxycycline (Dox)-inducible adenoviruses expressing cdk6 or cyclin D1. End points were cdk6/cyclin D1 expression and human β-cell proliferation, survival, and function. Increasing doses of Dox led to marked dose- and time-related increases in cdk6 and cyclin D1, accompanied by a 20-fold increase in β-cell proliferation. Notably, Dox withdrawal resulted in a reversal of both cdk6 and cyclin D1 expression as well as β-cell proliferation. Re-exposure to Dox reinduced both cdk/cyclin expression and proliferation. β-Cell function and survival were not adversely affected. The adenoviral tetracycline (tet)-on system has not been used previously to drive human β-cell proliferation. Human β-cells can be induced to proliferate or arrest in a regulated, reversible manner, temporally and quantitatively mimicking the transient perinatal physiological proliferation that occurs in human β-cells.

Improving islet engraftment by gene therapy

Islet cell transplantation is currently the only feasible long-term treatment option for patients with type 1 diabetes. However, the majority of transplanted islets experience damage and apoptosis during the isolation process, a blood-mediated inflammatory microenvironment in the portal vein upon islet infusion, hypoxia induced by the low oxygenated milieu, and poor-revascularization-mediated lack of nutrients, and impaired hormone modulation in the local transplanted site. Strategies using genetic modification methods through overexpression or silencing of those proteins involved in promoting new formation of blood vessels or inhibition of apoptosis may overcome these hurdles and improve islet engraftment outcomes.

Cotransplantation of mesenchymal stem cells and islet in the treatment of type 1 diabetes mellitus: recent progress

Islet transplantation for type 1 diabetes mellitus (T1DM) is limited by the lack of nutrients and presence of transplantation-associated inflammation. Most patients still need to be given a small dose of exogenous insulin in the following 3-5 years after islet transplantation. Cotransplantation of mesenchymal stem cells (MSCs) and islet holds great promise for the treatment of T1DM, because it can regulate the immune responses and overcome the shortage of trophic molecules. However, cotransplantation-associated tumorigenesis and the potential for metastasis in vivo should be also taken into consideration. In this review, we focus on the immunomodulatory properties, trophic effect and the potential side effects of cotransplantation of MSC and islet in the treatment of T1DM.

In vivo genetic engineering of murine pancreatic beta cells mediated by single-stranded adeno-associated viral vectors of serotypes 6, 8 and 9

AIMS/HYPOTHESIS

The genetic engineering of pancreatic beta cells could be a powerful tool for examining the role of key genes in the cause and treatment of diabetes. Here we performed a comparative study of the ability of single-stranded (ss) adeno-associated viral vectors (AAV) of serotypes 6, 8 and 9 to transduce the pancreas in vivo.

METHODS

AAV6, AAV8 and AAV9 vectors encoding marker genes were delivered to the pancreas via intraductal or systemic administration. Transduced cells were analysed by immunostaining. AAV9 vectors encoding hepatocyte growth factor (HGF) were delivered intraductally to a transgenic mouse model of type 1 diabetes and glycaemia was monitored.

RESULTS

AAV6, AAV8 and AAV9 mediated efficient and long-term transduction of beta cells, with AAV6 and AAV8 showing the highest efficiency. However, alpha cells were poorly transduced. Acinar cells were transduced by the three serotypes tested and ductal cells only by AAV6. In addition, intraductal delivery resulted in higher AAV-mediated transduction of the pancreas than did systemic administration. As proof of concept, intraductal delivery of AAV9 vectors encoding for the beta cell anti-apoptotic and mitogenic HGF preserved beta cell mass, diminished lymphocytic infiltration of the islets and protected mice from autoimmune diabetes.

CONCLUSIONS/INTERPRETATION

Intraductal administration of AAV6, AAV8 and AAV9 is an efficient way to genetically manipulate the pancreas in vivo. This technology may prove useful in the study of islet physiopathology and in assessment of new gene therapy approaches designed to regenerate beta cell mass during diabetes.

Mechanisms in the adaptation of maternal β-cells during pregnancy

Pancreatic β-cell mass adapts to changing insulin demands in the body. One of the most amazing reversible β-cell adaptations occurs during pregnancy and postpartum conditions. During pregnancy, the increase in maternal insulin resistance is compensated by maternal β-cell hyperplasia and hyperfunctionality to maintain normal blood glucose. Although the cellular mechanisms involved in maternal β-cell expansion have been studied in detail in rodents, human studies are very sparse. A summary of these studies in rodents and humans is described below. Since β-cell mass expands during pregnancy, unraveling the endocrine/paracrine/autocrine molecular mechanisms responsible for these effects can be of great importance for predicting and treating gestational diabetes and for finding new cues that induce β-cell regeneration in diabetes. In addition to the well known implication of lactogens during maternal β-cell expansion, additional participants are being discovered such as serotonin and HGF. Transcription factors, such as hepatocyte nuclear factor-4α and the forkhead box protein-M1, and cell cycle regulators, such as menin, p27 and p18, are important intracellular signals responsible for these effects. In this article, we summarize and discuss novel studies uncovering molecular mechanisms involved in the maternal β-cell adaptive expansion during pregnancy.

Disruption of hepatocyte growth factor/c-Met signaling enhances pancreatic beta-cell death and accelerates the onset of diabetes

OBJECTIVE

To determine the role of hepatocyte growth factor (HGF)/c-Met on β-cell survival in diabetogenic conditions in vivo and in response to cytokines in vitro.

RESEARCH DESIGN AND METHODS

We generated pancreas-specific c-Met-null (PancMet KO) mice and characterized their response to diabetes induced by multiple low-dose streptozotocin (MLDS) administration. We also analyzed the effect of HGF/c-Met signaling in vitro on cytokine-induced β-cell death in mouse and human islets, specifically examining the role of nuclear factor (NF)-κB.

RESULTS

Islets exposed in vitro to cytokines or from MLDS-treated mice displayed significantly increased HGF and c-Met levels, suggesting a potential role for HGF/c-Met in β-cell survival against diabetogenic agents. Adult PancMet KO mice displayed normal glucose and β-cell homeostasis, indicating that pancreatic c-Met loss is not detrimental for β-cell growth and function under basal conditions. However, PancMet KO mice were more susceptible to MLDS-induced diabetes. They displayed higher blood glucose levels, marked hypoinsulinemia, and reduced β-cell mass compared with wild-type littermates. PancMet KO mice showed enhanced intraislet infiltration, islet nitric oxide (NO) and chemokine production, and β-cell apoptosis. c-Met-null β-cells were more sensitive to cytokine-induced cell death in vitro, an effect mediated by NF-κB activation and NO production. Conversely, HGF treatment decreased p65/NF-κB activation and fully protected mouse and, more important, human β-cells against cytokines.

CONCLUSIONS

These results show that HGF/c-Met is critical for β-cell survival by attenuating NF-κB signaling and suggest that activation of the HGF/c-Met signaling pathway represents a novel strategy for enhancing β-cell protection.

Deficiency of Atf3, an adaptive-response gene, protects islets and ameliorates inflammation in a syngeneic mouse transplantation model

AIMS/HYPOTHESIS

Islet transplantation is a potential therapeutic option for type 1 diabetes. However, the need for multiple donors per patient and heavy immunosuppression of the recipients limit its use. The goal of this study was to test whether the gene encoding activating transcription factor 3 (ATF3), a stress-inducible pro-apoptotic gene, plays a role in graft rejection in islet transplantation.

METHODS

We compared wild-type (WT) and Atf3 knockout (KO) islets in vitro using stress paradigms relevant to islet transplantation: isolation, inflammation and hypoxia. We also compared the WT and KO islets in vivo using a syngeneic mouse transplantation model.

RESULTS

ATF3 was induced in all three stress paradigms and played a deleterious role in islet survival, as evidenced by the lower viability of WT islets compared with KO islets. ATF3 upregulated various downstream target genes in a stress-dependent manner. These target genes can be classified into two functional groups: (1) apoptosis (Noxa [also known as Pmaip1] and Bnip3), and (2) immunomodulation (Tnfalpha [also known as Tnf], Il-1beta [also known as Il1b], Il-6 [also known as Il6] and Ccl2 [also known as Mcp-1]). In vivo, Atf3 KO islets performed better than WT islets after transplantation, as evidenced by better glucose homeostasis in the recipients and the reduction of the following variables in the KO grafts: caspase 3 activation, macrophage infiltration and expression of the above apoptotic and immunomodulatory genes.

CONCLUSIONS/INTERPRETATION

ATF3 plays a role in islet graft rejection by contributing to islet cell death and inflammatory responses at the graft sites. Silencing the ATF3 gene may provide therapeutic benefits in islet transplantation.

Agonist of growth hormone-releasing hormone as a potential effector for survival and proliferation of pancreatic islets

Therapeutic strategies for transplantation of pancreatic islet cells are urgently needed to expand beta-cell mass by stimulating islet cell proliferation and/or prolonging islet cell survival. Control of the islets by different growth factors provides a potential venue for augmenting beta-cell mass. In the present study, we show the expression of the biologically active splice variant-1 (SV-1) of growth hormone-releasing hormone (GHRH) receptor in rat insulinoma (INS-1) cells as well as in rat and human pancreatic islets. In studies in vitro of INS-1 cells, the GHRH agonist JI-36 caused a significant increase in cell proliferation and a reduction of cell apoptosis. JI-36 increased islet size and glucose-stimulated insulin secretion in isolated rat islets after 48-72 h. At the ultrastructural level, INS-1 cells treated with agonist JI-36 revealed a metabolic active stimulation state with increased cytoplasm. Coincubation with the GHRH antagonist MIA-602 reversed the actions of the agonist JI-36, indicating the specificity of this agonist. In vivo, the function of pancreatic islets was assessed by transplantation of rat islets under the kidney capsule of streptozotocin-induced diabetic non-obese diabetic-severe combined immunodeficiency (NOD-SCID) mice. Islets treated with GHRH agonist JI-36 were able to achieve normoglycemia earlier and more consistently than untreated islets. Furthermore, in contrast to diabetic animals transplanted with untreated islets, insulin response to an i.p. glucose tolerance test (IPGTT) in animals receiving islets treated with agonist Jl-36 was comparable to that of normal healthy mice. In conclusion, our study provides evidence that agonists of GHRH represent a promising pharmacological therapy aimed at promoting islet graft growth and proliferation in diabetic patients.

Regulated expansion of human pancreatic beta-cells

Although pancreatic beta-cell transplantation may serve as a potential cure for diabetes mellitus (DM), limited donor tissue availability poses a major challenge. Thus, there is a great demand to find new sources for pancreatic beta-cells. Here, we present a lentiviral vector-based approach to achieve beta-cell proliferation through the beta-cell-specific activation of the hepatocyte growth factor (HGF)/cmet signaling pathway. The methodology is based on the beta-cell-specific expression of a ligand-inducible, chimeric receptor (F36Vcmet), under transcriptional control of the promoter from the human insulin gene, and its ability to induce HGF/cmet signaling in the presence of a synthetic ligand (AP20187). High transduction efficiency of human pancreatic islets was achieved utilizing this approach with chimeric receptor expression confined to the beta-cell population. In addition, specific proliferation of human pancreatic beta-cells was induced utilizing this approach. Selective, regulated beta-cell expansion may help to provide greater availability of cells for transplantation in patients with DM.

Novel proapoptotic effect of hepatocyte growth factor: synergy with palmitate to cause pancreatic {beta}-cell apoptosis

Increasing evidence suggests that elevation of plasma fatty acids that often accompanies insulin resistance contributes to beta-cell insufficiency in obesity-related type 2 diabetes. Circulating levels of hepatocyte growth factor (HGF) are increased in humans with metabolic syndrome and obesity. HGF is known to protect beta-cells against streptozotocin and during islet engraftment. However, whether HGF is a beta-cell prosurvival factor in situations of excessive lipid supply has not been deciphered. Mice overexpressing HGF in the beta-cell [rat insulin type II promoter (RIP)-HGF transgenic mice] fed with standard chow display improved glucose homeostasis and increased beta-cell mass and proliferation compared with normal littermates. However, after 15 wk of high-fat feeding, glucose homeostasis and beta-cell expansion and proliferation are indistinguishable between normal and transgenic mice. Interestingly, RIP-HGF transgenic mouse beta-cells and normal beta-cells treated with HGF display increased sensitivity to palmitate-mediated apoptosis in vitro. Palmitate completely eliminates Akt and Bad phosphorylation in RIP-HGF transgenic mouse islets. HGF-overexpressing islets also show significantly decreased AMP-activated protein kinase-alpha and acetyl-coenzyme A carboxylase phosphorylation, diminished fatty acid oxidation, increased serine palmitoyltransferase expression, and enhanced ceramide formation compared with normal islets. Importantly, human islets overexpressing HGF also display increased beta-cell apoptosis in the presence of palmitate. Treatment of both mouse and human islet cells with the de novo ceramide synthesis inhibitors myriocin and fumonisin B1 abrogates beta-cell apoptosis induced by HGF and palmitate. Collectively, these studies indicate that HGF can be detrimental for beta-cell survival in an environment with excessive fatty acid supply.

Expansion of beta-cell mass in response to pregnancy

Inadequate beta-cell mass can lead to insulin insufficiency and diabetes. During times of prolonged metabolic demand for insulin, the endocrine pancreas can respond by increasing beta-cell mass, both by increasing cell size and by changing the balance between beta-cell proliferation and apoptosis. In this paper, we review recent advances in our understanding of the mechanisms that control the adaptive expansion of beta-cell mass, focusing on the islet's response to pregnancy, a physiological state of insulin resistance. Functional characterization of factors controlling both beta-cell proliferation and survival might not only lead to the development of successful therapeutic strategies to enhance the response of the beta-cell to increased metabolic loads, but also improve islet transplantation regimens.

Influence of human allogenic bone marrow and cord blood-derived mesenchymal stem cell secreting trophic factors on ATP (adenosine-5'-triphosphate)/ADP (adenosine-5'-diphosphate) ratio and insulin secretory function of isolated human islets from cadaveric donor

Successful islet transplantation (ITx) is not only dependent on the number of islets, but also their quality, including viability, metabolic activity, and function. Islet quality decreases during cultivation after the isolation procedure. To overcome this obstacle, we established the practice of islet and mesenchymal stem cells (MSCs) coculture. This coculture condition improved the ATP (adenosine-5'-triphosphate)/ADP (adenosine-5'-diphosphate) ratio and insulin secretory function in vitro. It is believed that the enhancement of islet quality in islet-MSCs cocultures may be caused by the secretion of active agents by MSCs. Herein we have shown that interleukin-6 (IL-6), vascular endothelial growth factor-A (VEGF-A), hepatocyte growth factor (HGF), and transforming growth factor-beta (TGF-beta) were significantly increased as measured by enzyme-linked immunosorbent assay (ELISA) in MSCs-cultured medium, factors that have been shown to improve the survival, function, and angiogenesis/revascularization of islets. These results indicated that the quality of human islets was enhanced by trophic molecules secreted by MSCs, which influence the intracellular islet ATP content and insulin secretory function.

Survey of the human pancreatic beta-cell G1/S proteome reveals a potential therapeutic role for cdk-6 and cyclin D1 in enhancing human beta-cell replication and function in vivo

OBJECTIVES

To comprehensively inventory the proteins that control the G1/S cell cycle checkpoint in the human islet and compare them with those in the murine islet, to determine whether these might therapeutically enhance human beta-cell replication, to determine whether human beta-cell replication can be demonstrated in an in vivo model, and to enhance human beta-cell function in vivo.

RESEARCH DESIGN AND METHODS

Thirty-four G1/S regulatory proteins were examined in human islets. Effects of adenoviruses expressing cdk-6, cdk-4, and cyclin D1 on proliferation in human beta-cells were studied in both in vitro and in vivo models.

RESULTS

Multiple differences between murine and human islets occur, most strikingly the presence of cdk-6 in human beta-cells versus its low abundance in the murine islet. Cdk-6 and cyclin D1 in vitro led to marked activation of retinoblastoma protein phosphorylation and cell cycle progression with no induction of cell death. Human islets transduced with cdk-6 and cyclin D1 were transplanted into diabetic NOD-SCID mice and markedly outperformed native human islets in vivo, maintaining glucose control for the entire 6 weeks of the study.

CONCLUSIONS

The human G1/S proteome is described for the first time. Human islets are unlike their rodent counterparts in that they contain easily measurable cdk-6. Cdk-6 overexpression, alone or in combination with cyclin D1, strikingly stimulates human beta-cell replication, both in vitro as well as in vivo, without inducing cell death or loss of function. Using this model, human beta-cell replication can be induced and studied in vivo.