RANKL/RANK is required for cytokine-induced beta cell death; osteoprotegerin, a RANKL inhibitor, reverses rodent type 1 diabetes

Treatment for type 1 diabetes (T1D) requires stimulation of functional β cell regeneration and survival under stress. Previously, we showed that inhibition of the RANKL/RANK [receptor activator of nuclear factor kappa Β (NF-κB) ligand] pathway, by osteoprotegerin and the anti-osteoporotic drug denosumab, induces rodent and human β cell proliferation. We demonstrate that the RANK pathway mediates cytokine-induced rodent and human β cell death through RANK-TRAF6 interaction and induction of NF-κB activation. Osteoprotegerin and denosumab protected β cells against this cytotoxicity. In human immune cells, osteoprotegerin and denosumab reduce proinflammatory cytokines in activated T-cells by inhibiting RANKL-induced activation of monocytes. In vivo, osteoprotegerin reversed recent-onset T1D in nonobese diabetic/Ltj mice, reduced insulitis, improved glucose homeostasis, and increased plasma insulin, β cell proliferation, and mass in these mice. Serum from T1D subjects induced human β cell death and dysfunction, but not α cell death. Osteoprotegerin and denosumab reduced T1D serum-induced β cell cytotoxicity and dysfunction. Inhibiting RANKL/RANK could have therapeutic potential.

Mapping and targeted viral activation of pancreatic nerves in mice reveal their roles in the regulation of glucose metabolism

A lack of comprehensive mapping of ganglionic inputs into the pancreas and of technology for the modulation of the activity of specific pancreatic nerves has hindered the study of how they regulate metabolic processes. Here we show that the pancreas-innervating neurons in sympathetic, parasympathetic and sensory ganglia can be mapped in detail by using tissue clearing and retrograde tracing (the tracing of neural connections from the synapse to the cell body), and that genetic payloads can be delivered via intrapancreatic injection to target sites in efferent pancreatic nerves in live mice through optimized adeno-associated viruses and neural-tissue-specific promoters. We also show that, in male mice, the targeted activation of parasympathetic cholinergic intrapancreatic ganglia and neurons doubled plasma-insulin levels and improved glucose tolerance, and that tolerance was impaired by stimulating pancreas-projecting sympathetic neurons. The ability to map the peripheral ganglia innervating the pancreas and to deliver transgenes to specific pancreas-projecting neurons will facilitate the examination of ganglionic inputs and the study of the roles of pancreatic efferent innervation in glucose metabolism.

LGR4, a G Protein-Coupled Receptor With a Systemic Role: From Development to Metabolic Regulation

Leucine-rich repeat-containing G protein-coupled receptor 4 (LGR4/GPR48), a member of the GPCR (G protein-coupled receptors) superfamily, subfamily B, is a common intestinal crypt stem cell marker. It binds R-spondins/Norrin as classical ligands and plays a crucial role in Wnt signaling potentiation. Interaction between LGR4 and R-spondins initiates many Wnt-driven developmental processes, e.g., kidney, eye, or reproductive tract formation, as well as intestinal crypt (Paneth) stem cell pool maintenance. Besides the well-described role of LGR4 in development, several novel functions of this receptor have recently been discovered. In this context, LGR4 was indicated to participate in TGFβ and NFκB signaling regulation in hematopoietic precursors and intestinal cells, respectively, and found to be a new, alternative receptor for RANKL (Receptor Activator of NF kappa B Ligand) in bone cells. LGR4 inhibits the process of osteoclast differentiation, by antagonizing the interaction between RANK (Receptor Activator of NF kappa B) and its ligand-RANKL. It is also known to trigger anti-inflammatory responses in different tissues (liver, intestine, cardiac cells, and skin), serve as a sensor of the circadian clock in the liver, regulate adipogenesis and energy expenditure in adipose tissue and skeletal muscles, respectively. The extracellular domain of LGR4 (LGR4-ECD) has emerged as a potential new therapeutic for osteoporosis and cancer. LGR4 integrates different signaling pathways and regulates various cellular processes vital for maintaining whole-body homeostasis. Yet, the role of LGR4 in many cell types (e.g. pancreatic beta cells) and diseases (e.g., diabetes) remains to be elucidated. Considering the broad spectrum of LGR4 actions, this review aims to discuss both canonical and novel roles of LGR4, with emphasis on emerging research directions focused on this receptor.

LGR4 and Its Extracellular Domain as Novel Regulators of ß-Cell Survival and Proliferation

Our lab has shown that RANK (Receptor activator of the NF-κB) by interacting with its ligand, RANKL, inhibits ß-cell proliferation and survival; which can be reversed by Osteoprotegerin (OPG). Recently, the G protein-coupled receptor LGR4 (leucine-rich repeat-containing G protein-coupled receptor 4), which binds R-spondin (RSPO), was identified as a novel receptor for RANKL in osteoclast precursor cells. Thus, RANKL can bind two distinct receptors, RANK and LGR4 in osteoclasts, leading to opposite effects on osteoclastogenesis. LGR4 is expressed in rodent and human ß-cells, but the role of this receptor in ß-cells remains unknown. We postulated that LGR4 through its interaction with RANKL is involved in regulating ß-cell survival and proliferation. Our data indicate expression of specific LGR4 family members, Lgr4, Rank, Rankl, is modulated by stressors, such as cytokines, ER stress, diabetes and aging, in INS1 cells, rodent and human islets. Knocking down Lgr4 in INS1 cells or rodent islets has no significant effect on ß-cell proliferation but is detrimental for ß-cell survival in basal and cytokine-stimulated conditions. We also propose that the soluble extracellular domain of LGR4 (LGR4-ECD), which binds to its ligands (RSPO/RANKL), holds therapeutic potential like OPG, by inhibiting the interaction between RANKL/RANK. At 200ng/ml LGR4-ECD significantly enhances young adult (8-12-week-old) and aged (1.y.o.) rodent ß-cell proliferation, as well as human ß-cell proliferation, in islets from not only control subjects (45±17 y.o.), but also with Type 2 diabetes (48±7 y.o.). Additionally, LGR4-ECD significantly promotes mouse and human ß-cell survival against cytokine-induced cell death. Future studies will determine the physiological role of LGR4 and the therapeutic potential of LGR4-ECD on the beta cell in vivo in basal conditions and in the setting of diabetes.

Acknowledgements: Funding: JDRF postdoctoral fellowship # 3-PDF-2020-936-A-N to JF; Human Islets: IIDP

Lactogens Reduce Endoplasmic Reticulum Stress-Induced Rodent and Human β-Cell Death and Diabetes Incidence in Akita Mice

Diabetes occurs due to a loss of functional β-cells, resulting from β-cell death and dysfunction. Lactogens protect rodent and human β-cells in vitro and in vivo against triggers of β-cell cytotoxicity relevant to diabetes, many of which converge onto a common pathway of endoplasmic reticulum (ER) stress. However, whether lactogens modulate the ER stress pathway is unknown. This study examines whether lactogens can protect β-cells against ER stress and mitigate diabetes incidence in Akita (Ak) mice, a rodent model of ER stress-induced diabetes, akin to neonatal diabetes in humans. We show that lactogens protect INS-1 cells, primary rodent and human β-cells in vitro against two distinct ER stressors, tunicamycin and thapsigargin, through activation of the JAK2/STAT5 pathway. Lactogens mitigate expression of proapoptotic molecules in the ER stress pathway that are induced by chronic ER stress in INS-1 cells and rodent islets. Transgenic expression of placental lactogen in β-cells of Ak mice drastically reduces the severe hyperglycemia, diabetes incidence, hypoinsulinemia, β-cell death, and loss of β-cell mass observed in Ak littermates. These are the first studies in any cell type demonstrating that lactogens modulate the ER stress pathway, causing enhanced β-cell survival and reduced diabetes incidence in the face of chronic ER stress.

PKCζ Is Essential for Pancreatic β-Cell Replication During Insulin Resistance by Regulating mTOR and Cyclin-D2

Adaptive β-cell replication occurs in response to increased metabolic demand during insulin resistance. The intracellular mediators of this compensatory response are poorly defined and their identification could provide significant targets for β-cell regeneration therapies. Here we show that glucose and insulin in vitro and insulin resistance in vivo activate protein kinase C ζ (PKCζ) in pancreatic islets and β-cells. PKCζ is required for glucose- and glucokinase activator-induced proliferation of rodent and human β-cells in vitro. Furthermore, either kinase-dead PKCζ expression (KD-PKCζ) or disruption of PKCζ in mouse β-cells blocks compensatory β-cell replication when acute hyperglycemia/hyperinsulinemia is induced. Importantly, KD-PKCζ inhibits insulin resistance-mediated mammalian target of rapamycin (mTOR) activation and cyclin-D2 upregulation independent of Akt activation. In summary, PKCζ activation is key for early compensatory β-cell replication in insulin resistance by regulating the downstream signals mTOR and cyclin-D2. This suggests that alterations in PKCζ expression or activity might contribute to inadequate β-cell mass expansion and β-cell failure leading to type 2 diabetes.

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.

Osteoprotegerin and Denosumab Stimulate Human Beta Cell Proliferation through Inhibition of the Receptor Activator of NF-κB Ligand Pathway

Diabetes results from a reduction of pancreatic β-cells. Stimulating replication could normalize β-cell mass. However, adult human β-cells are recalcitrant to proliferation. We identified osteoprotegerin, a bone-related decoy receptor, as a β-cell mitogen. Osteoprotegerin was induced by and required for lactogen-mediated rodent β-cell replication. Osteoprotegerin enhanced β-cell proliferation in young, aged, and diabetic mice. This resulted in increased β-cell mass in young mice and significantly delayed hyperglycemia in diabetic mice. Osteoprotegerin stimulated replication of adult human β-cells, without causing dedifferentiation. Mechanistically, osteoprotegerin induced human and rodent β-cell replication by modulating CREB and GSK3 pathways, through binding Receptor Activator of NF-κB (RANK) Ligand (RANKL), a brake in β-cell proliferation. Denosumab, an FDA-approved osteoporosis drug, and RANKL-specific antibody induced human β-cell proliferation in vitro, and in vivo, in humanized mice. Thus, osteoprotegerin and Denosumab prevent RANKL/RANK interaction to stimulate β-cell replication, highlighting the potential for repurposing an osteoporosis drug to treat diabetes.

Human β-cell proliferation and intracellular signaling: part 3

This is the third in a series of Perspectives on intracellular signaling pathways coupled to proliferation in pancreatic β-cells. We contrast the large knowledge base in rodent β-cells with the more limited human database. With the increasing incidence of type 1 diabetes and the recognition that type 2 diabetes is also due in part to a deficiency of functioning β-cells, there is great urgency to identify therapeutic approaches to expand human β-cell numbers. Therapeutic approaches might include stem cell differentiation, transdifferentiation, or expansion of cadaver islets or residual endogenous β-cells. In these Perspectives, we focus on β-cell proliferation. Past Perspectives reviewed fundamental cell cycle regulation and its upstream regulation by insulin/IGF signaling via phosphatidylinositol-3 kinase/mammalian target of rapamycin signaling, glucose, glycogen synthase kinase-3 and liver kinase B1, protein kinase Cζ, calcium-calcineurin-nuclear factor of activated T cells, epidermal growth factor/platelet-derived growth factor family members, Wnt/β-catenin, leptin, and estrogen and progesterone. Here, we emphasize Janus kinase/signal transducers and activators of transcription, Ras/Raf/extracellular signal-related kinase, cadherins and integrins, G-protein-coupled receptors, and transforming growth factor β signaling. We hope these three Perspectives will serve to introduce these pathways to new researchers and will encourage additional investigators to focus on understanding how to harness key intracellular signaling pathways for therapeutic human β-cell regeneration for diabetes.

Diabetes mellitus--advances and challenges in human β-cell proliferation

The treatment of diabetes mellitus represents one of the greatest medical challenges of our era. Diabetes results from a deficiency or functional impairment of insulin-producing β cells, alone or in combination with insulin resistance. It logically follows that the replacement or regeneration of β cells should reverse the progression of diabetes and, indeed, this seems to be the case in humans and rodents. This concept has prompted attempts in many laboratories to create new human β cells using stem-cell strategies to transdifferentiate or reprogramme non-β cells into β cells or to discover small molecules or other compounds that can induce proliferation of human β cells. This latter approach has shown promise, but has also proven particularly challenging to implement. In this Review, we discuss the physiology of normal human β-cell replication, the molecular mechanisms that regulate the cell cycle in human β cells, the upstream intracellular signalling pathways that connect them to cell surface receptors on β cells, the epigenetic mechanisms that control human β-cell proliferation and unbiased approaches for discovering novel molecules that can drive human β-cell proliferation. Finally, we discuss the potential and challenges of implementing strategies that replace or regenerate β cells.

Hepatocyte growth factor/c-Met signaling is required for β-cell regeneration

Hepatocyte growth factor (HGF) is a mitogen required for β-cell replication during pregnancy. To determine whether HGF/c-Met signaling is required for β-cell regeneration, we characterized mice with pancreatic deletion of the HGF receptor, c-Met (PancMet KO mice), in two models of reduced β-cell mass and regeneration: multiple low-dose streptozotocin (MLDS) and partial pancreatectomy (Ppx). We also analyzed whether HGF administration could accelerate β-cell regeneration in wild-type (WT) mice after Ppx. Mouse islets obtained 7 days post-Ppx displayed significantly increased c-Met, suggesting a potential role for HGF/c-Met in β-cell proliferation in situations of reduced β-cell mass. Indeed, adult PancMet KO mice displayed markedly reduced β-cell replication compared with WT mice 7 days post-Ppx. Similarly, β-cell proliferation was decreased in PancMet KO mice in the MLDS mouse model. The decrease in β-cell proliferation post-Ppx correlated with a striking decrease in D-cyclin levels. Importantly, PancMet KO mice showed significantly diminished β-cell mass, decreased glucose tolerance, and impaired insulin secretion compared with WT mice 28 days post-Ppx. Conversely, HGF administration in WT Ppx mice further accelerated β-cell regeneration. These results indicate that HGF/c-Met signaling is critical for β-cell proliferation in situations of diminished β-cell mass and suggest that activation of this pathway can enhance β-cell regeneration.

ChREBP mediates glucose-stimulated pancreatic β-cell proliferation

Glucose stimulates rodent and human β-cell replication, but the intracellular signaling mechanisms are poorly understood. Carbohydrate response element-binding protein (ChREBP) is a lipogenic glucose-sensing transcription factor with unknown functions in pancreatic β-cells. We tested the hypothesis that ChREBP is required for glucose-stimulated β-cell proliferation. The relative expression of ChREBP was determined in liver and β-cells using quantitative RT-PCR (qRT-PCR), immunoblotting, and immunohistochemistry. Loss- and gain-of-function studies were performed using small interfering RNA and genetic deletion of ChREBP and adenoviral overexpression of ChREBP in rodent and human β-cells. Proliferation was measured by 5-bromo-2'-deoxyuridine incorporation, [(3)H]thymidine incorporation, and fluorescence-activated cell sorter analysis. In addition, the expression of cell cycle regulatory genes was measured by qRT-PCR and immunoblotting. ChREBP expression was comparable with liver in mouse pancreata and in rat and human islets. Depletion of ChREBP decreased glucose-stimulated proliferation in β-cells isolated from ChREBP(-/-) mice, in INS-1-derived 832/13 cells, and in primary rat and human β-cells. Furthermore, depletion of ChREBP decreased the glucose-stimulated expression of cell cycle accelerators. Overexpression of ChREBP amplified glucose-stimulated proliferation in rat and human β-cells, with concomitant increases in cyclin gene expression. In conclusion, ChREBP mediates glucose-stimulated proliferation in pancreatic β-cells.

Lactogens protect rodent and human beta cells against glucolipotoxicity-induced cell death through Janus kinase-2 (JAK2)/signal transducer and activator of transcription-5 (STAT5) signalling

AIMS/HYPOTHESIS

A leading cause of type 2 diabetes is a reduction in functional beta cell mass partly due to increased beta cell death, triggered by stressors such as glucolipotoxicity (GLT). This study evaluates the hypothesis that lactogens can protect beta cells against GLT and examines the mechanism behind the pro-survival effect.

METHODS

The effect of exogenous treatment or endogenous expression of lactogens on GLT-induced beta cell death was examined in INS-1 cells, and in rodent and human islets. The mechanism behind the pro-survival effect of lactogens was determined using an inhibitor, siRNAs, a dominant negative (DN) mutant, and Cre-lox-mediated gene deletion analysis.

RESULTS

Lactogens significantly protect INS-1 and primary rodent beta cells against GLT-induced cell death. The pro-survival effect of lactogens in rodent beta cells is mediated through activation of the Janus kinase-2 (JAK2)/signal transducer and activator of transcription-5 (STAT5) signalling pathway. Lactogen-induced increase in the anti-apoptotic B cell lymphoma-extra large (BCLXL) protein is required to mediate its pro-survival effects in both INS-1 cells and primary rodent beta cells. Most importantly, lactogens significantly protect human beta cells against GLT-induced cell death, and their pro-survival effect is also mediated through the JAK2/STAT5 pathway.

CONCLUSIONS/INTERPRETATION

These studies, together with previous work, clearly demonstrate the pro-survival nature of lactogens and identify the JAK2/STAT5 pathway as an important mediator of this effect in both rodent and human beta cells. Future studies will determine the effectiveness of this peptide in vivo in the pathophysiology of type 2 diabetes.

Loss of HGF/c-Met signaling in pancreatic β-cells leads to incomplete maternal β-cell adaptation and gestational diabetes mellitus

Hepatocyte growth factor (HGF) is a mitogen and insulinotropic agent for the β-cell. However, whether HGF/c-Met has a role in maternal β-cell adaptation during pregnancy is unknown. To address this issue, we characterized glucose and β-cell homeostasis in pregnant mice lacking c-Met in the pancreas (PancMet KO mice). Circulating HGF and islet c-Met and HGF expression were increased in pregnant mice. Importantly, PancMet KO mice displayed decreased β-cell replication and increased β-cell apoptosis at gestational day (GD)15. The decreased β-cell replication was associated with reductions in islet prolactin receptor levels, STAT5 nuclear localization and forkhead box M1 mRNA, and upregulation of p27. Furthermore, PancMet KO mouse β-cells were more sensitive to dexamethasone-induced cytotoxicity, whereas HGF protected human β-cells against dexamethasone in vitro. These detrimental alterations in β-cell proliferation and death led to incomplete maternal β-cell mass expansion in PancMet KO mice at GD19 and early postpartum periods. The decreased β-cell mass was accompanied by increased blood glucose, decreased plasma insulin, and impaired glucose tolerance. PancMet KO mouse islets failed to upregulate GLUT2 and pancreatic duodenal homeobox-1 mRNA, insulin content, and glucose-stimulated insulin secretion during gestation. These studies indicate that HGF/c-Met signaling is essential for maternal β-cell adaptation during pregnancy and that its absence/attenuation leads to gestational diabetes mellitus.

Systemic and acute administration of parathyroid hormone-related peptide(1-36) stimulates endogenous beta cell proliferation while preserving function in adult mice

AIMS/HYPOTHESIS

A major focus in the treatment of diabetes is to identify factors that stimulate endogenous beta cell growth while preserving function. The first 36 amino acids of parathyroid hormone-related protein (PTHrP) are sufficient to enhance proliferation and function in rodent and human beta cells in vitro. This study examined whether acute and systemic administration of the amino-terminal PTHrP(1-36) peptide can achieve similar effects in rodent beta cells in vivo.

METHODS

Adult male mice were injected with 40, 80 or 160 μg of PTHrP(1-36) per kg body weight or with vehicle for 25 days. Glucose and beta cell homeostasis, as well as expression of differentiation markers and cell cycle genes were analysed.

RESULTS

All three doses of PTHrP(1-36) significantly enhanced beta cell proliferation in vivo at day 25, with 160 μg/kg PTHrP(1-36) increasing proliferation as early as day 5. Importantly, the two higher doses of PTHrP(1-36) caused a significant 30% expansion of beta cell mass, with a short-term improvement in glucose tolerance. PTHrP(1-36) did not cause hypercalcaemia, or change islet number, beta cell size, beta cell death or expression of differentiation markers. Analysis of islet G1/S cell cycle proteins revealed that chronic overabundance of PTHrP(1-139) in the beta cell significantly increased the cell cycle activator cyclin D2 and decreased levels of cyclin-dependent kinase 4 inhibitor (p16( Ink4a ) [Ink4a also known as Cdkn2a]), but acute treatment with PTHrP(1-36) did not.

CONCLUSIONS/INTERPRETATION

Acute and systemic administration of PTHrP(1-36) increases rodent beta cell proliferation and mass without negatively affecting function or survival. These findings highlight the future potential therapeutic effectiveness of this peptide under diabetes-related pathophysiological conditions.

Activation of protein kinase C-ζ in pancreatic β-cells in vivo improves glucose tolerance and induces β-cell expansion via mTOR activation

OBJECTIVE

PKC-ζ activation is a key signaling event for growth factor-induced β-cell replication in vitro. However, the effect of direct PKC-ζ activation in the β-cell in vivo is unknown. In this study, we examined the effects of PKC-ζ activation in β-cell expansion and function in vivo in mice and the mechanisms associated with these effects.

RESEARCH DESIGN AND METHODS

We characterized glucose homeostasis and β-cell phenotype of transgenic (TG) mice with constitutive activation of PKC-ζ in the β-cell. We also analyzed the expression and regulation of signaling pathways, G1/S cell cycle molecules, and β-cell functional markers in TG and wild-type mouse islets.

RESULTS

TG mice displayed increased plasma insulin, improved glucose tolerance, and enhanced insulin secretion with concomitant upregulation of islet insulin and glucokinase expression. In addition, TG mice displayed increased β-cell proliferation, size, and mass compared with wild-type littermates. The increase in β-cell proliferation was associated with upregulation of cyclins D1, D2, D3, and A and downregulation of p21. Phosphorylation of D-cyclins, known to initiate their rapid degradation, was reduced in TG mouse islets. Phosphorylation/inactivation of GSK-3β and phosphorylation/activation of mTOR, critical regulators of D-cyclin expression and β-cell proliferation, were enhanced in TG mouse islets, without changes in Akt phosphorylation status. Rapamycin treatment in vivo eliminated the increases in β-cell proliferation, size, and mass; the upregulation of cyclins Ds and A in TG mice; and the improvement in glucose tolerance-identifying mTOR as a novel downstream mediator of PKC-ζ-induced β-cell replication and expansion in vivo. CONCLUSIONS PKC:-ζ, through mTOR activation, modifies the expression pattern of β-cell cycle molecules leading to increased β-cell replication and mass with a concomitant enhancement in β-cell function. Approaches to enhance PKC-ζ activity may be of value as a therapeutic strategy for the treatment of diabetes.

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.

Parathyroid hormone-related protein enhances human ß-cell proliferation and function with associated induction of cyclin-dependent kinase 2 and cyclin E expression

OBJECTIVE

Inducing human β-cell growth while enhancing function is a major goal in the treatment of diabetes. Parathyroid hormone-related protein (PTHrP) enhances rodent β-cell growth and function through the parathyroid hormone-1 receptor (PTH1R). Based on this, we hypothesized that PTH1R is expressed in human β-cells and that PTHrP has the potential to enhance human β-cell proliferation and/or function.

RESEARCH DESIGN AND METHODS

PTH1R expression, β-cell proliferation, glucose-stimulated insulin secretion (GSIS), and expression of differentiation and cell-cycle genes were analyzed in human islets transduced with adenoviral PTHrP constructs or treated with PTHrP peptides. The effect of overexpression of late G1/S cell cycle molecules was also assessed on human β-cell proliferation.

RESULTS

We found that human β-cells express PTH1R. More importantly, overexpression of PTHrP causes a significant approximately threefold increase in human β-cell proliferation. Furthermore, the amino terminus PTHrP(1-36) peptide is sufficient to increase replication as well as expression of the late G1/S cell-cycle proteins cyclin E and cyclin-dependent kinase 2 (cdk2) in human islets. Notably, PTHrP(1-36) also enhances GSIS. Finally, overexpression of cyclin E alone, but not cdk2, augments human β-cell proliferation, and when both molecules are expressed simultaneously there is a further marked synergistic increase in replication.

CONCLUSIONS

PTHrP(1-36) peptide enhances human β-cell proliferation as well as function, with associated upregulation of two specific cell-cycle activators that together can induce human β-cell proliferation several fold. The future therapeutic potential of PTHrP(1-36) for the treatment of diabetes is especially relevant given the complementary therapeutic efficacy of PTHrP(1-36) in postmenopausal osteoporosis.

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.

Gestational diabetes mellitus resulting from impaired beta-cell compensation in the absence of FoxM1, a novel downstream effector of placental lactogen

OBJECTIVE

The objectives of the study were to determine whether the cell cycle transcription factor, FoxM1, is required for glucose homeostasis and beta-cell mass expansion in maternal islets during pregnancy and whether FoxM1 is essential for placental lactogen (PL)-induced beta-cell proliferation.

RESEARCH DESIGN AND METHODS

beta-Cell mass, beta-cell proliferation, and glucose homeostasis were assessed in virgin, pregnant, and postpartum mice with a pancreas-wide Foxm1 deletion (FoxM1(Deltapanc)). Wild-type islets were cultured with or without PL and examined for Foxm1 induction. Transgenic mice overexpressing PL in beta-cells were bred with FoxM1(Deltapanc) mice, and beta-cell proliferation was examined.

RESULTS

Foxm1 was upregulated in maternal islets during pregnancy. In contrast to controls, beta-cell proliferation did not increase in pregnant FoxM1(Deltapanc) females. Mutant islets showed increased Menin and nuclear p27. FoxM1(Deltapanc) females developed gestational diabetes mellitus as pregnancy progressed. After parturition, euglycemia was restored in FoxM1(Deltapanc) females, but islet size was significantly reduced. Strikingly, beta-cell mass was normal in postpartum FoxM1(Deltapanc) pancreata due to a combination of increased beta-cell size and islet neogenesis. Evidence for neogenesis included increased number of endocrine clusters, increased proportion of smaller islets, and increased neurogenin 3 or insulin expression in cells adjacent to ducts. PL induced Foxm1 expression in cultured islets, and FoxM1 was essential for PL-mediated increases in beta-cell proliferation in vivo.

CONCLUSIONS

FoxM1 is essential for beta-cell compensation during pregnancy. In the absence of increased beta-cell proliferation, neogenesis is induced in postpartum FoxM1(Deltapanc) pancreata. Our results suggest that FoxM1 functions downstream of PL to mediate its effects on beta-cell proliferation.

The retinoblastoma protein and its homolog p130 regulate the G1/S transition in pancreatic beta-cells

OBJECTIVE

The retinoblastoma protein family (pRb, p130, p107) plays a central role in the regulation of cell cycle progression. Surprisingly, loss of pRb in the beta-cell has no discernible effect on cell cycle control. Therefore, we explored the effects of individual loss of either p130 or p107 in addition to the simultaneous loss of both pRb/p130 on the beta-cell.

RESEARCH DESIGN AND METHODS

Adult mice deficient in either p130 or p107 or both pRb/p130 were examined for effects on beta-cell replication, function, and survival. The Cre-Lox system was also used to inactivate pRb in wild-type and p130-deficient beta-cells in vitro.

RESULTS

In vivo loss of either p107 or p130 did not affect beta-cell replication or function. Combined pRb/p130 loss, however, resulted in dramatically accelerated proliferation as well as apoptotic cell death. Pancreas and beta-cell mass were significantly reduced in double mutants. Despite this, overall glucose tolerance was normal, except for mild postprandial hyperglycemia. Ex vivo, acute deletion of pRb in p130-deficient beta-cells also caused a striking increase in proliferation. The combined deletion of pRb/p130 upregulated islet expression of E2F2 but not E2F1.

CONCLUSIONS

These studies define an essential role for the pocket proteins in controlling the G(1)/S transition in beta-cells. When deficient in both pRb and p130, beta-cells undergo unrestrained cell cycle reentry and activation of apoptosis. These studies underscore the central role of the pRb pathway in controlling beta-cell turnover and provide new cellular targets for beta-cell regeneration.

Protein kinase C-zeta activation markedly enhances beta-cell proliferation: an essential role in growth factor mediated beta-cell mitogenesis

OBJECTIVE

Diabetes results from a deficiency of functional beta-cells. Previous studies have identified hepatocyte growth factor (HGF) and parathyroid hormone-related protein (PTHrP) as two potent beta-cell mitogens. The objective of this study is to determine 1) whether HGF and PTHrP have additive/synergistic effects on beta-cell growth and proliferation; 2) the signaling pathways through which these growth factors mediate beta-cell mitogenesis; and 3) whether activation of this/these signaling pathway(s) enhances human beta-cell replication.

RESEARCH DESIGN AND METHODS

We generated and phenotypically analyzed doubly transgenic mice overexpressing PTHrP and HGF in the beta-cell. INS-1 and primary mouse and human islet cells were used to identify mitogenic signaling pathways activated by HGF and/or PTHrP.

RESULTS

Combined overexpression of HGF and PTHrP in the beta-cell of doubly transgenic mice did not result in additive/synergistic effects on beta-cell growth and proliferation, suggesting potential cross-talk between signaling pathways activated by both growth factors. Examination of these signaling pathways in INS-1 cells revealed atypical protein kinase C (PKC) as a novel intracellular target activated by both HGF and PTHrP in beta-cells. Knockdown of PKC zeta, but not PKC iota/lambda, expression using specific small-interfering RNAs blocked growth factor-induced INS-1 cell proliferation. Furthermore, adenovirus-mediated delivery of kinase-dead PKC zeta completely inhibited beta-cell proliferation in primary islet cells overexpressing PTHrP and/or HGF. Finally, adenovirus-mediated delivery of constitutively active PKC zeta in mouse and human primary islet cells significantly enhanced beta-cell proliferation.

CONCLUSIONS

PKC zeta is essential for PTHrP- and HGF-induced beta-cell proliferation. PKC zeta activation could be useful in therapeutic strategies for expanding beta-cell mass in vitro and in vivo.

Lactogens promote beta cell survival through JAK2/STAT5 activation and Bcl-XL upregulation

One of the goals in the treatment for diabetes is to enhance pancreatic beta cell function, proliferation, and survival. This study explores the role of lactogenic hormones, prolactin (PRL) and placental lactogen (PL), in beta cell survival. We have previously shown that transgenic mice expressing mouse placental lactogen-1 (mPL1) in beta cells under the rat insulin II promoter (RIP) are resistant to the diabetogenic and cytotoxic effects of streptozotocin (STZ) in vivo. The current study demonstrates that lactogens protect rat insulinoma (INS-1) cells and primary mouse beta cells against two distinct beta cell death inducers, STZ and dexamethasone (DEX), in vitro. Further, we identify the mechanism through which lactogens protect beta cells against DEX-induced death. The signaling pathway mediating this protective effect is the janus-activated-kinase-2/signal transducer and activator of transcription-5 (JAK2/STAT5) pathway. This is demonstrated in INS-1 cells and primary mouse beta cells using three separate approaches, pharmacological inhibitors, JAK2-specific siRNAs and a dominant-negative STAT5 mutant. Furthermore, lactogens specifically and significantly increase the anti-apoptotic protein Bcl-XL in insulinoma cells and mouse islets. Bcl-XL-specific siRNA significantly inhibits lactogen-mediated protection against DEX-induced beta cell death. We believe this is the first direct demonstration of lactogens mediating their protective effect through the JAK2/STAT5 pathway in the beta cell and through Bcl-XL in any cell type.

Tissue-specific deletion of the retinoblastoma protein in the pancreatic beta-cell has limited effects on beta-cell replication, mass, and function

Animal studies show that G(1/S) regulatory molecules (D-cyclins, cdk-4, p18, p21, p27) are critical for normal regulation of beta-cell proliferation, mass, and function. The retinoblastoma protein, pRb, is positioned at the very end of a cascade of these regulatory proteins and is considered the final checkpoint molecule that maintains beta-cell cycle arrest. Logically, removal of pRb from the beta-cell should result in unrestrained beta-cell replication, increased beta-cell mass, and insulin-mediated hypoglycemia. Because global loss of both pRb alleles is embryonic lethal, this hypothesis has not been tested in beta-cells. We developed two types of conditional knockout (CKO) mice in which both alleles of the pRb gene were inactivated specifically in beta-cells. Surprisingly, although the pRb gene was efficiently recombined in beta-cells of both CKO models, changes in beta-cell mass, beta-cell replication rates, insulin concentrations, and blood glucose levels were limited or absent. Other pRb family members, p107 and p130, were not substantially upregulated. In contrast to dogma, the pRb protein is not essential to maintain cell cycle arrest in the pancreatic beta-cell. This may reflect fundamental inaccuracies in models of beta-cell cycle control or complementation for pRb by undefined proteins.

Growth factors and beta cell replication

Recent studies have demonstrated that human islet allograft transplantation can be a successful therapeutic option in the treatment of patients with Type I diabetes. However, this impressive recent advance is accompanied by a very important constraint. There is a critical paucity of pancreatic islets or pancreatic beta cells for islet transplantation to become a large-scale therapeutic option in patients with diabetes. This has prompted many laboratories around the world to invigorate their efforts in finding ways for increasing the availability of beta cells or beta cell surrogates that potentially could be transplanted into patients with diabetes. The number of studies analyzing the mechanisms that govern beta cell proliferation and growth in physiological and pathological conditions has increased exponentially during the last decade. These studies exploring the role of growth factors, intracellular signaling molecules and cell cycle regulators constitute the substrate for future strategies aimed at expanding human beta cells in vitro and/or in vivo after transplantation. In this review, we describe the current knowledge on the effects of several beta cell growth factors that have been shown to increase beta cell proliferation and expand beta cell mass in vitro and/or in vivo and that they could be potentially deployed in an effort to increase the number of patients transplanted with islets. Furthermore, we also analyze in this review recent studies deciphering the relevance of these specific islet growth factors as physiological and pathophysiological regulators of beta cell proliferation and islet growth.

Targeted inactivation of hepatocyte growth factor receptor c-met in beta-cells leads to defective insulin secretion and GLUT-2 downregulation without alteration of beta-cell mass

Overexpression of hepatocyte growth factor (HGF) in the beta-cell of transgenic mice enhances beta-cell proliferation, survival, and function. In the current studies, we have used conditional ablation of the c-met gene to uncover the physiological role of HGF in beta-cell growth and function. Mice in which c-met is inactivated in the beta-cell (MetCKO mice) display normal body weight, blood glucose, and plasma insulin compared with control littermates. In contrast, MetCKO mice displayed significantly diminished glucose tolerance and reduced plasma insulin after a glucose challenge in vivo. This impaired glucose tolerance in MetCKO mice was not caused by insulin resistance because sensitivity to exogenous insulin was similar in both groups. Importantly, in vitro glucose-stimulated insulin secretion in MetCKO islets was decreased by approximately 50% at high glucose concentrations compared with control islets. Furthermore, whereas insulin and glucokinase expression in MetCKO islets were normal, GLUT-2 expression was decreased by approximately 50%. These changes in beta-cell function in MetCKO mice were not accompanied by changes in total beta-cell mass, islet morphology, islet cell composition, and beta-cell proliferation. Interestingly, however, MetCKO mice display an increased number of small islets, mainly single and doublet beta-cells. We conclude that HGF/c-met signaling in the beta-cell is not essential for beta-cell growth, but it is essential for normal glucose-dependent insulin secretion.

Characterization of mice doubly transgenic for parathyroid hormone-related protein and murine placental lactogen: a novel role for placental lactogen in pancreatic beta-cell survival

Transgenic overexpression of either parathyroid hormone-related peptide (PTHrP) or mouse placental lactogen type 1 (mPL1) in pancreatic beta-cells, using the rat insulin II promoter (RIP), results in islet hyperplasia either through prolonged beta-cell survival or through increased beta-cell proliferation and hypertrophy, respectively. For determining whether the two proteins might exert complementary, additive, or synergistic effects on islet mass and function when simultaneously overexpressed in beta-cells in vivo, RIP-PTHrP and RIP-mPL1 mice were crossed to generate mice doubly transgenic for PTHrP and mPL1. These double-transgenic mice displayed marked islet hyperplasia (threefold), hypoglycemia, increased beta-cell proliferation (threefold), and resistance to the diabetogenic and cytotoxic effects of streptozotocin compared with their normal siblings. Although the phenotype of the double-transgenic mice was neither additive nor synergistic relative to their single-transgenic counterparts, it was indeed complementary, yielding the maximal salutary phenotypic features of both individual transgenes. Finally, mPL1, for the first time, was shown to exert a protective effect on the survival of beta-cells, placing it among the few proteins that can improve function and proliferation and prolong the survival of beta-cells. Placental lactogen 1 is an attractive target for future therapeutic strategies in diabetes.

Hepatocyte growth factor gene therapy for islet transplantation

Recent clinical studies have documented that human islet transplantation has the potential to replace pancreatic endocrine function in patients with type 1 diabetes. These studies have also highlighted an enormous shortage of human islets that impedes the use of islet transplantation in clinical practice on a larger scale. To address this problem, one potential approach is to use islet growth factors to increase beta cell replication, to improve beta cell function and to enhance beta cell survival. In that context, transgenic mice overexpressing hepatocyte growth factor (HGF) in the pancreatic beta cell display increased beta cell proliferation, function and survival. More importantly, HGF-overexpressing transgenic mouse islets markedly improve transplant performance in severe combined immunodeficiency (SCID) mice and reduce the number of islets required for successful islet transplantation. Recently, adenoviral-mediated gene transfer of HGF into normal rodent islets has confirmed the beneficial effects of HGF in improving islet transplant outcomes in two marginal mass islet transplant models in rodents: islet transplant under the kidney capsule in SCID mice; and portal islet allograft transplantation in rats treated with the Edmonton immunosuppressive regimen. These studies suggest that ex vivo HGF gene therapy has the potential to reduce the number of human islets required for successful islet transplantation.

Adenovirus-mediated hepatocyte growth factor expression in mouse islets improves pancreatic islet transplant performance and reduces beta cell death

Hepatocyte growth factor (HGF) increases beta cell proliferation and function in rat insulin promoter (RIP)-targeted transgenic mice. RIP-HGF mouse islets also function superiorly to normal islets in a transplant setting. Here, we aimed to determine whether viral gene transfer of the HGF gene into mouse islets ex vivo could enhance the performance of normal islets in a streptozotocin-diabetic severe combined immunodeficient mouse marginal islet mass model in which 300 uninfected or adenovirus (Adv) LacZ-transduced islet equivalents were insufficient to correct hyperglycemia. In dramatic contrast, 300 AdvHGF-transduced islet equivalents promptly (day 1) and significantly (p < 0.01) decreased random non-fasting blood glucose levels, from 351 +/- 20 mg/dl to an average of 191 +/- 7 mg/dl over 8 weeks. At day 1 post-transplant, beta cell death was significantly (p < 0.05) decreased, and the total insulin content was significantly (p < 0.05) increased in AdvHGF-transduced islets containing grafts. This anti-beta cell death action of HGF was independently confirmed in RIP-HGF mice and in INS-1 cells, both treated with streptozotocin. Activation of the phosphatidylinositol 3-kinase/Akt intracellular-signaling pathway appeared to be involved in this beta cell protective effect of HGF in vitro. In summary, adenoviral delivery of HGF to murine islets ex vivo improves islet transplant survival and blood glucose control in a subcapsular renal graft model in immuno-incompetent diabetic mice.

Overexpression of parathyroid hormone-related protein inhibits pancreatic beta-cell death in vivo and in vitro

Pancreatic beta-cell survival is critical in the setting of diabetes as well as in islet transplantation. Transgenic mice overexpressing parathyroid hormone-related protein (PTHrP) targeted to beta-cells using the rat insulin II promoter (RIP) display hyperinsulinemia, hypoglycemia, and islet hyperplasia, without a concomitant increase in beta-cell proliferation rate or enlargement of individual beta-cell size. Thus, the mechanism for increased beta-cell mass is unknown. In this study, we demonstrated that beta-cells of transgenic mice are resistant to the cytotoxic effects of streptozotocin (STZ) in vivo, as documented by a sixfold reduction in the rate of STZ-induced beta-cell death in RIP-PTHrP mice relative to their normal siblings. The reduced cell death in transgenic mice is due neither to their increased islet mass nor to a decrease in their sensing of STZ, but rather results from PTHrP-induced resistance to beta-cell death. This is also demonstrated in vitro by markedly reduced cell death rates observed in beta-cells of transgenic mice compared with normal mice when cultured in the absence of serum and glucose or in the presence of STZ. Finally, we demonstrated that NH(2)-terminal PTHrP inhibits beta-cell death. These findings support the concept that PTHrP overexpression increases islet mass in transgenic mice through inhibition of beta-cell death.

Transgenic overexpression of hepatocyte growth factor in the beta-cell markedly improves islet function and islet transplant outcomes in mice

Recent advances in human islet transplantation have highlighted the need for expanding the pool of beta-cells available for transplantation. We have developed three transgenic models in which growth factors (hepatocyte growth factor [HGF], placental lactogen, or parathyroid hormone-related protein) have been targeted to the beta-cell using rat insulin promoter (RIP). Each displays an increase in islet size and islet number, and each displays insulin-mediated hypoglycemia. Of these three models, the RIP-HGF mouse displays the least impressive phenotype under basal conditions. In this study, we show that this mild basal phenotype is misleading and that RIP-HGF mice have a unique and salutary phenotype. Compared with normal islets, RIP-HGF islets contain more insulin per beta-cell (50 +/- 5 vs. 78 +/- 9 ng/islet equivalent [IE] in normal vs. RIP-HGF islets, P < 0.025), secrete more insulin in response to glucose in vivo (0.66 +/- 0.06 vs. 0.91 +/- 0.10 ng/ml in normal vs. RIP-HGF mice, P < 0.05) and in vitro (at 22.2 mmol/l glucose: 640 +/- 120.1 vs. 1,615 +/- 196.9 pg. microg protein(-1). 30 min(-1) in normal vs. RIP-HGF islets, P < 0.01), have two- to threefold higher GLUT2 and glucokinase steady-state mRNA levels, take up and metabolize glucose more effectively, and most importantly, function at least twice as effectively after transplantation. These findings indicate that HGF has surprisingly positive effects on beta-cell mitogenesis, glucose sensing, beta-cell markers of differentiation, and transplant survival. It appears to have a unique and unanticipated effective profile as an islet mass- and function-enhancing agent in vivo.

Using beta-cell growth factors to enhance human pancreatic Islet transplantation

This is a particularly exciting time in the field of pancreatic islet growth, development, and survival. The recent publication of a study demonstrating that human pancreatic islet transplantation is both technically and immunologically feasible has highlighted the need for large supplies of pancreatic islets or pancreatic beta cells for larger-scale islet transplantation in patients with diabetes. This, together with a rapid expansion in the past several years of the understanding of mechanisms of islet growth, development, and survival, has accelerated and invigorated efforts to therapeutically harness the cellular mechanisms responsible for pancreatic beta-cell proliferation, survival, and development and to take advantage of this new knowledge to enhance the availability, survival, and function of pancreatic beta cells in human islet transplantation for diabetes mellitus. Here, we briefly review the confluence of events that have provided optimism and energy to the islet transplant field, and we focus on peptide growth factors that eventually may be deployed in the effort to augment islet mass and function in patients with diabetes.

Targeted expression of placental lactogen in the beta cells of transgenic mice results in beta cell proliferation, islet mass augmentation, and hypoglycemia

The factors that regulate pancreatic beta cell proliferation are not well defined. In order to explore the role of murine placental lactogen (PL)-I (mPL-I) in islet mass regulation in vivo, we developed transgenic mice in which mPL-I is targeted to the beta cell using the rat insulin II promoter. Rat insulin II-mPL-I mice displayed both fasting and postprandial hypoglycemia (71 and 105 mg/dl, respectively) as compared with normal mice (92 and 129 mg/dl; p < 0.00005 for both). Plasma insulin concentrations were inappropriately elevated, and insulin content in the pancreas was increased 2-fold. Glucose-stimulated insulin secretion by perifused islets was indistinguishable from controls at 7.5, 15, and 20 mm glucose. Beta cell proliferation rates were twice normal (p = 0. 0005). This hyperplasia, together with a 20% increase in beta cell size, resulted in a 2-fold increase in islet mass (p = 0.0005) and a 1.45-fold increase in islet number (p = 0.0012). In mice, murine PL-I is a potent islet mitogen, is capable of increasing islet mass, and is associated with hypoglycemia over the long term. It can be targeted to the beta cell using standard gene targeting techniques. Potential exists for beta cell engineering using this strategy.

Hepatocyte growth factor overexpression in the islet of transgenic mice increases beta cell proliferation, enhances islet mass, and induces mild hypoglycemia

Hepatocyte growth factor (HGF) is produced in pancreatic mesenchyme-derived cells and in islet cells. In vitro, HGF increases the insulin content and proliferation of islets. To study the role of HGF in the islet in vivo, we have developed three lines of transgenic mice overexpressing mHGF using the rat insulin II promoter (RIP). Each RIP-HGF transgenic line displays clear expression of HGF mRNA and protein in the islet. RIP-mHGF mice are relatively hypoglycemic in post-prandial and fasting states compared with their normal littermates. They display inappropriate insulin production, striking overexpression of insulin mRNA in the islet, and a 2-fold increase in the insulin content in islet extracts. Importantly, beta cell replication rates in vivo are two to three times higher in RIP-HGF mice. This increase in proliferation results in a 2-3-fold increase in islet mass. Moreover, the islet number per pancreatic area was also increased by approximately 50%. Finally, RIP-mHGF mice show a dramatically attenuated response to the diabetogenic effects of streptozotocin. We conclude that the overexpression of HGF in the islet increases beta cell proliferation, islet number, beta cell mass, and total insulin production in vivo. These combined effects result in mild hypoglycemia and resistance to the diabetogenic effects of streptozotocin.

Studies on microencapsulation of 5-fluorouracil with poly(ortho ester) polymers

Microencapsulation of 5-fluorouracil was successfully accomplished with poly(ortho ester) polymers by the emulsification-solvent evaporation method. While actual drug loading increased with increasing drug load (5-15% w/w), the entrapment efficiency remained essentially unaffected, under a given set of experimental conditions. Incorporation of sorbitan sesquioleate enhanced entrapment efficiency, decreased the volume-surface mean diameter of the poly(ortho ester) microspheres and provided controlled release of 5-fluorouracil. The volume of the aqueous phase was more important than the concentration of polyvinyl alcohol in it. The entrapment efficiency improved from 13 to 33% when the volume of the aqueous phase was increased from 20 to 80 ml. The volume of organic phase (methylene chloride) and the concentration of polymer in it played an important role. The use of smaller volumes of more concentrated polymer solution enhanced actual drug loading, entrapment efficiency and produced larger microspheres. The release studies conducted in 0.01 M phosphate buffer at 37+/-1.0 degrees C demonstrated that the release of 5-FU from the microspheres prepared with sorbitan sequioleate was nearly independent of the initial drug load with a mean zero-order rate constant of 0.0063% per hour. The data suggested that drug release was largely a diffusional process with contributions from dissolution and polymer degradation.

Parathyroid hormone-related protein in the pancreatic islet and the cardiovascular system

Parathyroid hormone-related protein was discovered as the causative agent responsible for the common paraneoplastic syndrome, humoral hypercalcemia of malignancy. It is now clear that the PTHrP gene is expressed in virtually every cell and tissue in the body at some point in development or adult life and that the peptide is critical for normal life. Two of the tissues that produce PTHrP are the insulin-producing beta cells of the pancreatic islet and the vascular smooth muscle cells of the arterial wall. In this review, the physiologic roles of PTHrP in the islet and in the arterial wall are explored. PTHrP is a classical neuroendocrine prohormone that undergoes extensive post-translational processing to yield a family of daughter peptides that are the mature secretory forms of the peptide. In addition to its ability to act as a traditional endocrine, paracrine, or autocrine factor, PTHrP appears to be able to act as an "intracrine" factor as well, directly entering the nucleus after translation and stimulating proliferation, apoptosis, and perhaps other cellular responses as well. The cell biology underlying this phenomenon is also explored herein.

Progressive pancreatic islet hyperplasia in the islet-targeted, parathyroid hormone-related protein-overexpressing mouse

PTH-related protein (PTHrP) is a paracrine/autocrine factor produced in most cell types in the body. Its functions include the regulation of cell cycle, of differentiation, of apoptosis, and of developmental events. One of the cells which produces PTHrP is the pancreatic beta cell. We have previously described a transgenic mouse model of targeted overexpression of PTHrP in the beta cell, the RIP-PTHrP mouse. These studies showed that PTHrP overexpression markedly increased islet mass and insulin secretion and resulted in hypoglycemia. Those studies were limited to RIP-PTHrP mice of 8-12 weeks of age. In the current report, we demonstrate that PTHrP overexpression induces a progressive increase in islet mass over the life of the RIP-PTHrP mouse, and that, in contrast to some other models of targeted PTHrP overexpression, the phenotype is not developmental, but occurs postnatally. The marked increase in islet mass is not associated with a measurable increase in beta cell replication rates. A further slowing in the normally low islet apoptosis rate could not be demonstrated in the RIP-PTHrP islet. Thus, the marked increase in islet mass in the RIP-PTHrP mouse is unexplained in mechanistic terms. Finally, RIP-PTHrP mice are resistant to the diabetogenic effects of streptozotocin. The mechanisms responsible for the increase in islet mass in the RIP-PTHrP mouse likely lie in either very subtle changes in islet turnover or in early steps in islet differentiation and development. The ability of PTHrP to increase islet mass and function, as well as its ability to attenuate the diabetogenic effects of streptozotocin, indicate that further study of PTHrP on islet development and function are important and may lead to therapeutic strategies in diabetes mellitus.

Transfection and overexpression of the calcium binding protein calbindin-D28k results in a stimulatory effect on insulin synthesis in a rat beta cell line (RIN 1046-38)

Calbindin-D28k, a calcium binding protein that is thought to act as a facilitator of calcium diffusion in intestine and kidney, is known to be regulated by vitamin D in these tissues. Calbindin-D28k is also present in pancreatic beta cells, but its function in these cells is not known. To determine a role for calbindin-D28k in the beta cell, rat calbindin-D28k was overexpressed in the pancreatic beta cell line RIN 1046-38 by transfection of calbindin in expression vector, and changes in insulin mRNA were examined. Five transfected RIN cell clones were found to overexpress calbindin 6- to 35-fold as determined by radioimmunoassay. Northern blot analysis revealed increases in abundance in calbindin mRNA (>20-fold for most clones). Overexpressed calbindin was functional because it was capable of buffering calcium in response to a rapid calcium influx induced by 1 and 5 microM calcium ionophore. In cells transfected with calbindin, there was a marked increase in the expression of insulin mRNA (>20-fold for most clones compared with vector transfected cells). Besides an increase in insulin mRNA, calbindin overexpression was also associated with an increase in insulin content and release (a 5.8-fold increase in insulin release was noted for clone C10, and a 54-fold increase was noted for clone C2). To begin to address the mechanism whereby overexpression of calbindin results in increased insulin gene expression, calbindin-overexpressing clones were transiently transfected with plasmids incorporating various regions of the rat insulin I (rInsI) promoter linked to the chloramphenicol acetyltransferase coding sequence. Transient transfection with reporter plasmids bearing the regulatory sequences of the rInsI promoter (-345/+1) or five copies of the Far-FLAT minienhancer (-247/-198) from the rInsI promoter suggests that increased insulin mRNA in calbindin transfected cells is due, at least in part, to enhanced insulin gene transcription. These studies provide the first direct evidence (to our knowledge) for a role for calbindin in beta cell function.

Structural and physiologic characterization of the mid-region secretory species of parathyroid hormone-related protein

Parathyroid hormone-related protein (PTHrP) is initially translated as a preprohormone which is posttranslationally processed to yield a family of mature secretory forms. Most attention has focused on the amino-terminal portion of the molecule which is homologous to parathyroid hormone. It is clear, however, that a mid-region species of PTHrP is posttranslationally cleaved from the highly conserved mid-region of PTHrP, and that the amino terminus of this peptide is Ala38. The purposes of the current study were three: 1) to confirm that Arg37 immediately preceding Ala38 serves as a posttranslational processing site in the PTHrP precursor, 2) to determine the carboxyl terminus of the mid-region secretory species of PTHrP, and 3) to synthesize this authentic mid-region secretory form of PTHrP and determine whether it is biologically active. The results indicate that: 1) Arg37 is indeed a processing site in the PTHrP precursor; 2) three distinct mid-region PTHrP species are generated by posttranslational processing, PTHrP(38-94)amide, PTHrP(38-95), and most likely, PTHrP(38-101); and 3) synthetic mid-region PTHrP(38-94)amide is active in four different biological systems. These studies confirm the finding that PTHrP is a prohormone. More importantly, they define a novel, biologically active highly conserved mid-region secretory form of PTHrP.

Overexpression of parathyroid hormone-related protein in the pancreatic islets of transgenic mice causes islet hyperplasia, hyperinsulinemia, and hypoglycemia

Parathyroid hormone-related protein (PTHrP) is produced by the pancreatic islet. It also has receptors on islet cells, suggesting that it may serve a paracrine or autocrine role within the islet. We have developed transgenic mice, which overexpress PTHrP in the islet through the use of the rat insulin II promoter (RIP). Glucose homeostasis in these mice is markedly abnormal; RIP-PTHrP mice are hypoglycemic in the postprandial and fasting states and display inappropriate hyperinsulinemia. At the end of a 24-hour fast, blood glucose values are 49 mg/dl in RIP-PTHrP mice, as compared to 77 mg/dl in normal littermates; insulin concentrations at this time are 6.3 and 3.9 ng/ml, respectively. Islet perifusion studies failed to demonstrate abnormalities in insulin secretion. In contrast, quantitative islet histomorphometry demonstrates that the total islet number and total islet mass are 2-fold higher in RIP-PTHrP mice than in their normal littermates. PTHrP very likely plays a normal physiologic role within the pancreatic islet. This role is most likely paracrine or autocrine. PTHrP appears to regulate insulin secretion either directly or indirectly, through developmental or growth effects on islet mass. PTHrP may have a role as an agent that enhances islet mass and/or enhances insulin secretion.

Defining the roles of parathyroid hormone-related protein in normal physiology

Parathyroid hormone-related protein (PTHrP) was discovered as a result of a search for the circulating factor secreted by cancers which causes the common paraneoplastic syndrome humoral hypercalcemia of malignancy. Since the identification of the peptide in 1982 and the cloning of the cDNA in 1987, it has become clear that PTHrP is a prohormone that is posttranslationally cleaved by prohormone convertases to yield a complex family of peptides, each of which is believed to have its own receptor. It is also clear that the PTHrP gene is expressed not only in cancers but also in the vast majority of normal tissues during adult and/or fetal life. In contrast to the situation in humoral hypercalcemia of malignancy in which PTHrP plays the role of a classical "endocrine" hormone, under normal circumstances PTHrP plays predominantly paracrine and/or autocrine roles. These apparent physiological functions are also complex and appear to include 1) regulation of smooth muscle (vascular, intestinal, uterine, bladder) tone, 2) regulation of transepithelial (renal, placental, oviduct, mammary gland) calcium transport, and 3) regulation of tissue and organ development, differentiation, and proliferation. In this review, the discovery of PTHrP, the structure of its gene and its cDNAs, and the posttranslational processing of the initial translation products are briefly reviewed. Attention is then focused on a detailed organ system-oriented review of the normal physiological functions of PTHrP.

Further evidence for a novel receptor for amino-terminal parathyroid hormone-related protein on keratinocytes and squamous carcinoma cell lines

PTH and PTH-related peptides (PTHrPs) interact with a common PTH/PTHrP receptor (type I), which is expressed in many tissues, including bone and kidney. Amino-terminal PTH and PTHrPs also recognize receptors in several nonclassical PTH target tissues, and in some of these, the signaling mechanisms differ qualitatively from those of the classical type I receptor. In normal keratinocytes and squamous carcinoma cell lines, PTH and PTHrP stimulate a rise in intracellular calcium, but not cAMP, suggesting the existence of an alternate, type II PTH/PTHrP receptor. SqCC/Y1 squamous carcinoma cells stably expressing the type I receptor displayed sensitive intracellular cAMP responses to PTHrP and PTH, indicating that these cells express functional GS proteins and that the type I receptor is capable of signaling through adenylyl cyclase in this cell line. Therefore, the endogenous type II receptor in SqCC/Y1 cells differs from the cloned type I receptor. We next examined whether messenger RNA (mRNA) from keratinocytes and squamous cell lines could hybridize to a human type I PTH/PTHrP receptor complementary DNA [1.9 kilobases (kb)]. No type I receptor mRNA (2.3 kb) was detected in polyadenylated RNA from any of the squamous cell lines. However, squamous cell lines did express several mRNA transcripts that hybridized with the type I receptor probe, yet were smaller (1 and 1.5 kb) or larger (3.5-5 kb) than the cloned receptor mRNA. The predominant mRNA in two squamous carcinoma cell lines and normal keratinocytes was a 1-kb transcript. Northern analysis with five different region-specific probes that span the entire coding region of the human type I receptor was used to map homologous regions within each of the transcripts. Several of the transcripts identified in squamous lines are also present in polyadenylated RNA from SaOS-2 human bone cells, but a unique 1-kb transcript hybridizing to probe 2 (nucleotides 490-870) was observed only in squamous cells. The smaller 1- and 1.5-kb transcripts did not hybridize to probes corresponding to the extreme 5'- and 3'-coding regions of the type I receptor complementary DNA. Ribonuclease protection analysis employing riboprobes that correspond to the five region-specific DNA probes revealed strong RNA signals of the expected size in SaOS-2 cells, but no hybridization with squamous cell RNA. Several smaller, but minor, bands that were unique to squamous cells were observed with riboprobe 2 only, suggesting partial homology of this region with the type I receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Region-specific methylation of the parathyroid hormone-related peptide gene determines its expression in human renal carcinoma cell lines

Tumor production of a parathyroid hormone-related peptide (PTHrP) is a common cause of the syndrome of humoral hypercalcemia of malignancy, which is frequently associated with renal cell carcinomas. Why certain renal cell carcinomas produce PTHrP while others do not is unknown. Using a system of 12 human renal carcinoma cell lines which either do (n = 6) or do not (n = 6) produce PTHrP, we found that the expression of the PTHrP gene in these cell lines is controlled at the transcriptional level. Transfection studies failed to demonstrate variation in PTHrP promoter activity in these cell lines sufficient to account for the differential PTHrP expression, implicating a cis-acting mechanism. Transcription of the PTHrP gene in these cell lines was found to correlate with the methylation state of specific CpG dinucleotides located within the promoter region but outside a CpG island. The functional importance of this mechanism of control was confirmed by the ability of the demethylating agent, 5-azacytidine, to induce PTHrP mRNA expression in previously nonexpressing cell lines.

Effects of oleic acid/propylene glycol on rat abdominal stratum corneum: lipid extraction and appearance of propylene glycol in the dermis measured by Fourier transform infrared/attenuated total reflectance (FT-IR/ATR) spectroscopy

Fourie transform infrared/attenuated total reflection analysis demonstrated that the absorbance intensity of C = O stretching bands, which reflect the amounts of lipids in the stratum corneum, decreased with an increase in the duration of skin treatment with 0.15 M oleic acid/propylene glycol (PG) system, suggesting that the oleic acid/PG system induced the lipid extraction, which was followed by a reorganization of the stratum corneum structures. The spectral peaks which originated from the PG molecule were detected in dermal tissues after 30 min of treatment of the stratum corneum with the same system. This observation suggested that the reorganization of the lipid domains due to the lipid extraction by the oleic acid/PG system helped the PG molecules enter the dermal tissues. It was also suggested that an effective volume within the stratum corneum for solutes and/or solvents which could penetrate through the inter-, and/or intracellular routes could be altered in conjunction with the structural changes of the lipids.

Identification and characterization of a GC-rich promoter of the human parathyroid hormone-related peptide gene

The human PTH-related peptide (PTHrP) gene comprises eight exons spanning more than 15 kilobases of genomic DNA. The gene has a highly complex controlling region, which contains four alternatively spliced, noncoding exons and at least two putative promoters, one 5' of exon 1A (up-stream TATA element) and the other 5' of exon 2 (down-stream TATA element). To define important cis regulatory sequences of this gene, a functional dissection of PTHrP 5'-flanking DNA was initiated, using chimeric PTHrP-chloramphenicol acetyltransferase (CAT) constructs. This analysis was carried out in PTHrP-negative human renal carcinoma cells, so that RNA derived from transfected DNA could be studied without interference from endogenous PTHrP sequences. Of the initial series of constructs prepared, the most active was a 1.1-kilobase BamHI-HindIII PTHrP-CAT plasmid containing 350 basepairs of DNA 5' of exon 1C and extending into exon 3. Analysis of transfection products by RNase protection and primer extension revealed that this region contains a previously unrecognized promoter of the gene. This element is located immediately 5' of exon 1C, is active in transfected cells when cloned in isolation up-stream of the CAT gene, and appears to be functional in a number of cell lines and tissues on the basis of primer extension analysis. Unlike the other two PTHrP gene promoters, this element is GC rich and does not possess canonical TATA or CAAT sequences. The human PTHrP gene is one of a handful of genes that appear to use both TATA and GC-rich promoter elements.

Transdermal delivery of isoproterenol HCl: an investigation of stability, solubility, partition coefficient, and vehicle effects

Effects of solubility, partition coefficient, and selected adjuvants (propylene glycol and Azone) on percutaneous penetration of isoproterenol HCl have been investigated using human cadaver skin. Isoproterenol was found to be stable (less than 1% decomposition) for 24 hr at 22 +/- 0.5 degrees C in the pH range 1 to 7 in the following solvents: water, normal saline, propylene glycol and a series of propylene glycol-water mixtures (10, 20, 40, and 60%; v/v); however, decomposition was significant beyond pH 8. In normal saline, the rate of decomposition increased significantly with an increase in temperature to 37 degrees C. The solubility of isoproterenol HCl decreased and its skin/vehicle partition coefficient increased with increasing proportions of propylene glycol in the vehicle, while the product of the solubility and partition coefficient appeared to plateau at 20% propylene glycol in water. Optimal penetration enhancing effects of Azone were seen when incorporated at a concentration of 1% (v/v) in the 20% (v/v) propylene glycol-water blend and, more significantly, when skin was pretreated with pure Azone for 60 min prior to application of the drug formulation.

In vitro release of salicylic acid from lanolin alcohols-ethylcellulose films

Lanolin alcohols-ethylcellulose films were investigated as a potential drug delivery system for the controlled release of salicylic acid. The effects of changes in film composition, drug concentration, drug solubility, and stirrer speed on the in vitro release of salicylic acid have been examined. The drug release has been found to obey a diffusion-controlled matrix model and square root of time release profile both in the suspension and solution cases.