Phosphatidylinositol 3-kinase signaling to Akt mediates survival in isolated canine islets of Langerhans

Polystyrene nanoplastics with different functional groups and charges have different impacts on type 2 diabetes

BACKGROUND

Increasing attention is being paid to the environmental and health impacts of nanoplastics (NPs) pollution. Exposure to nanoplastics (NPs) with different charges and functional groups may have different adverse effects after ingestion by organisms, yet the potential ramifications on mammalian blood glucose levels, and the risk of diabetes remain unexplored.

RESULTS

Mice were exposed to PS-NPs/COOH/NH2 at a dose of 5 mg/kg/day for nine weeks, either alone or in a T2DM model. The findings demonstrated that exposure to PS-NPs modified by different functional groups caused a notable rise in fasting blood glucose (FBG) levels, glucose intolerance, and insulin resistance in a mouse model of T2DM. Exposure to PS-NPs-NH2 alone can also lead the above effects to a certain degree. PS-NPs exposure could induce glycogen accumulation and hepatocellular edema, as well as injury to the pancreas. Comparing the effect of different functional groups or charges on T2DM, the PS-NPs-NH2 group exhibited the most significant FBG elevation, glycogen accumulation, and insulin resistance. The phosphorylation of AKT and FoxO1 was found to be inhibited by PS-NPs exposure. Treatment with SC79, the selective AKT activator was shown to effectively rescue this process and attenuate T2DM like lesions.

CONCLUSIONS

Exposure to PS-NPs with different functional groups (charges) induced T2DM-like lesions. Amino-modified PS-NPs cause more serious T2DM-like lesions than pristine PS-NPs or carboxyl functionalized PS-NPs. The underlying mechanisms involved the inhibition of P-AKT/P-FoxO1. This study highlights the potential risk of NPs pollution on T2DM, and provides a new perspective for evaluating the impact of plastics aging.

Gamma-Aminobutyric Acid Signaling in Damage Response, Metabolism, and Disease

Gamma-aminobutyric acid (GABA) plays a crucial role in signal transduction and can function as a neurotransmitter. Although many studies have been conducted on GABA in brain biology, the cellular function and physiological relevance of GABA in other metabolic organs remain unclear. Here, we will discuss recent advances in understanding GABA metabolism with a focus on its biosynthesis and cellular functions in other organs. The mechanisms of GABA in liver biology and disease have revealed new ways to link the biosynthesis of GABA to its cellular function. By reviewing what is known about the distinct effects of GABA and GABA-mediated metabolites in physiological pathways, we provide a framework for understanding newly identified targets regulating the damage response, with implications for ameliorating metabolic diseases. With this review, we suggest that further research is necessary to develop GABA's beneficial and toxic effects on metabolic disease progression.

Insulin resistance and the role of gamma-aminobutyric acid

Insulin resistance (IR) is mentioned to be a disorder in insulin ability in insulin-target tissues. Skeletal muscle (SkM) and liver function are more affected by IR than other insulin target cells. SkM is the main site for the consumption of ingested glucose. An effective treatment for IR has two properties: An inhibition of β-cell death and a promotion of β-cell replication. Gamma-aminobutyric acid (GABA) can improve beta-cell mass and function. Multiple studies have shown that GABA decreases IR probably via increase in glucose transporter 4 (GLUT4) gene expression and prevention of gluconeogenesis pathway in the liver. This review focused on the general aspects of IR in skeletal muscle (SkM), liver; the cellular mechanism(s) lead to the development of IR in these organs, and the role of GABA to reduce insulin resistance.

Different combinations of GABA, BMP7, and Activin A induced the in vitro differentiation of rat pancreatic ductal stem cells into insulin-secreting islet-like cell clusters

AIMS

We investigated the in vitro differentiation of adult rat PDESCs into β-like cells through supplementation of different combinations of GABA, BMP7, and Activin A in basic culture media.

MATERIALS AND METHODS

The PDESCs were cultured using different inducement combinations for 28 days and microscopy, dithizone (DTZ) staining, immunohistochemical staining, real-time PCR, and glucose-stimulated insulin secretion (GSIS) assay were used to delineate the differentiation inducement potential of these combinations.

KEY FINDINGS

The results show that after 28 days, the PDESCs were differentiated into ICCs containing insulin-secreting β-like cells in different groups treated with A + B, A + G, B + G, and A + B + G but not in the control group. Upon DTZ staining the cells in ICCs were stained crimson red, demonstrating the presence of β-like cells in ICCs and the immunohistochemistry showed the expression of Pdx1 and insulin in ICCs. Further, on 28 d the expression of Pdx1 and insulin mRNA was high in inducement groups as compared to the control group and β-like cells in ICCs also secreted insulin and C-peptide upon glucose stimulation. Thus, the supplementation of GABA, BMP7, and Activin A in different combinations in basic culture media can induce the in vitro differentiation of PDESCs into ICCs containing β-like cells.

SIGNIFICANCE

The in vitro development of β-like cells is a herald for cell therapy of diabetic patients and our results are a step closer towards finding the cure for diabetes.

Gimmicks of gamma-aminobutyric acid (GABA) in pancreatic β-cell regeneration through transdifferentiation of pancreatic α- to β-cells

In vivo regeneration of lost or dysfunctional islet β cells can fulfill the promise of improved therapy for diabetic patients. To achieve this, many mitogenic factors have been attempted, including gamma-aminobutyric acid (GABA). GABA remarkably affects pancreatic islet cells' (α cells and β cells) function through paracrine and/or autocrine binding to its membrane receptors on these cells. GABA has also been studied for promoting the transformation of α cells to β cells. Nonetheless, the gimmickry of GABA-induced α-cell transformation to β cells has two different perspectives. On the one hand, GABA was found to induce α-cell transformation to β cells in vivo and insulin-secreting β-like cells in vitro. On the other hand, GABA treatment showed that it has no α- to β-cell transformation response. Here, we will summarize the physiological effects of GABA on pancreatic islet β cells with an emphasis on its regenerative effects for transdifferentiation of islet α cells to β cells. We will also critically discuss the controversial results about GABA-mediated transdifferentiation of α cells to β cells.

Nephrin Contributes to Insulin Secretion and Affects Mammalian Target of Rapamycin Signaling Independently of Insulin Receptor

Nephrin belongs to a family of highly conserved proteins with a well characterized function as modulators of cell adhesion and guidance, and nephrin may have a role in metabolic pathways linked to podocyte and pancreatic β-cell survival. However, this role is incompletely characterized. In this study, we developed floxed nephrin mice for pancreatic β-cell-specific deletion of nephrin, which had no effect on islet size and glycemia. Nephrin deficiency, however, resulted in glucose intolerance in vivo and impaired glucose-stimulated insulin release ex vivo Glucose intolerance was also observed in eight patients with nephrin mutations compared with three patients with other genetic forms of nephrotic syndrome or nine healthy controls.In vitro experiments were conducted to investigate if nephrin affects autocrine signaling through insulin receptor A (IRA) and B (IRB), which are both expressed in human podocytes and pancreatic islets. Coimmunoprecipitation of nephrin and IRB but not IRA was observed and required IR phosphorylation. Nephrin per se was sufficient to induce phosphorylation of p70S6K in an phosphatidylinositol 3-kinase-dependent but IR/Src-independent manner, which was not augmented by exogenous insulin. These results suggest a role for nephrin as an independent modulator of podocyte and pancreatic β-cell nutrient sensing in the fasting state and the potential of nephrin as a drug target in diabetes.

Matrine inhibits the growth and induces apoptosis of osteosarcoma cells in vitro by inactivating the Akt pathway

Matrine, a natural product, has been demonstrated to be a promising chemotherapeutic drug for some cancers. Using flow cytometric analysis of the cell cycle and apoptosis, we found that matrine inhibited the proliferation and induced apoptosis in the human osteosarcoma (OS) cell lines MG63, HOS, U2OS, and SAOS2 in vitro in a dose-dependent manner. We therefore assessed the role of the serine/threonine kinase Akt in the regulation of matrine-mediated cell growth inhibition and apoptosis induction in human OS cell lines. After treatment for 48 h, matrine induced G0/G1-stage cell cycle arrest in MG63, U2OS, and SAOS2 cells associated with an increase in the expression of p27(Kip1) and a decrease in the expression of Akt, glycogen synthase kinase 3 (GSK3)-β (Ser9), and cyclin D1. Furthermore, the pro-apoptotic factor Bax was upregulated. Overall, our findings suggest that matrine may be an effective anti-osteosarcoma drug due to its ability to inhibit proliferation and induce apoptosis in OS cells, possibly through the involvement of Akt signaling.

The role of growth factors in intestinal regeneration and repair in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intestinal disease resulting in major neonatal morbidity and mortality. The pathology is poorly understood, and the means of preventing and treating NEC are limited. Several endogenous growth factors have been identified as having important roles in intestinal growth as well as aiding intestinal repair from injury or inflammation. In this review, we will discuss several growth factors as mediators of intestinal regeneration and repair as well as potential therapeutic agents for NEC.

Gene transfer of active Akt1 by an infectivity-enhanced adenovirus impacts β-cell survival and proliferation differentially in vitro and in vivo

Type 1 Diabetes is characterized by an absolute insulin deficiency due to the autoimmune destruction of insulin producing β-cells in the pancreatic islets. Akt1/Protein Kinase B is the direct downstream target of PI3 Kinase activation, and has shown potent anti-apoptotic and proliferation-inducing activities. This study was designed to explore whether gene transfer of constitutively active Akt1 (CA-Akt1) would promote β-cell survival and proliferation, thus be protective against experimental diabetes. In the study, a fiber-modified infectivity-enhanced adenoviral vector, Ad5RGDpK7, was used to deliver rat insulin promoter (RIP)-driven CA-Akt1 into β-cells. Our data showed this vector efficiently delivered CA-Akt1 into freshly isolated pancreatic islets, and promoted islet cell survival and β-cell proliferation in vitro. The therapeutic effect of the vector in vivo was assessed using streptozotocin (STZ)-induced diabetes mice. Two means of vector administration were explored: intravenous and intra-bile ductal injections. While direct vector administration into pancreas via bile-ductal injection resulted in local adverse effect, intravenous injection of the vectors offered therapeutic benefits. Further analysis suggests systemic vector administration caused endogenous Akt expression and activation in islets, which may be responsible, at least in part, for the protective effect of the infectivity-enhanced CA-Akt1 gene delivery vector. Taken together, our data suggest CA-Akt1 is effective in promoting β-cell survival and proliferation in vitro, but direct in vivo use is compromised by the efficacy of transgene delivery into β-cells. Nonetheless, the vector evoked the expression and activation of endogenous Akt in the islets, thus offering beneficial bystander effect against STZ-induced diabetes.

Supplements in human islet culture: human serum albumin is inferior to fetal bovine serum

Culture of human islets before clinical transplantation or distribution for research purposes is standard practice. At the time the Edmonton protocol was introduced, clinical islet manufacturing did not include culture, and human serum albumin (HSA), instead of fetal bovine serum (FBS), was used during other steps of the process to avoid the introduction of xenogeneic material. When culture was subsequently introduced, HSA was also used for medium supplementation instead of FBS, which was typically used for research islet culture. The use of HSA as culture supplement was not evaluated before this implementation. We performed a retrospective analysis of 103 high-purity islet preparations (76 research preparations, all with FBS culture supplementation, and 27 clinical preparations, all with HSA supplementation) for oxygen consumption rate per DNA content (OCR/DNA; a measure of viability) and diabetes reversal rate in diabetic nude mice (a measure of potency). After 2-day culture, research preparations exhibited an average OCR/DNA 51% higher (p < 0.001) and an average diabetes reversal rate 54% higher (p < 0.05) than clinical preparations, despite 87% of the research islet preparations having been derived from research-grade pancreata that are considered of lower quality. In a prospective paired study on islets from eight research preparations, OCR/DNA was, on average, 27% higher with FBS supplementation than that with HSA supplementation (p < 0.05). We conclude that the quality of clinical islet preparations can be improved when culture is performed in media supplemented with serum instead of albumin.

Effects of oxidative stress on intestinal type I insulin-like growth factor receptor expression

INTRODUCTION

Oxidative stress activates multiple signaling transduction pathways, including the phosphatidylinositol 3-kinase (PI3-K), in an injured intestine as occurs in necrotizing enterocolitis (NEC). We have previously shown that hydrogen peroxide (H2O2)-induced PI3-K activation is significantly enhanced with exogenous insulin-like growth factor (IGF)-1 in intestinal epithelial cells. However, the effects of oxidative stress on IGF receptor type I (IGF-IR) activation and expression in the neonatal intestine during NEC are unknown.

MATERIAL AND METHODS

Intestinal sections from neonates undergoing bowel resections (control = 3, NEC = 20) were analyzed for IGF-IR expression. NEC was induced in newborn mouse pups using hypoxia and hyperosmolar feeds, and distal small bowel segments were analyzed for IGF-IR expression (control = 3, NEC = 7). H2O2 was used to induce oxidative stress in rat (RIE-1) and fetal human (FHs74 Int) intestinal epithelial cells. Phosphorylation of IGF-IR, Akt, a downstream effector of PI3-K, and IGF-IR levels were determined by Western blotting. Flow cytometry, immunofluorescence, immunohistochemistry, IGF-IR tyrosine phosphorylation array, cell death enzyme-linked immunosorbent assay, and Western blotting were used to determine the IGF-IR expression.

RESULTS

An increased IGF-IR expression was noted in intestinal sections from NEC as well as murine model of NEC. H2O2 treatment rapidly activated IGF-IR and increased the expression in RIE-1 and FHs74 Int cells. Inhibition of IGF-IR resulted in significant RIE-1 cell apoptosis during oxidative stress. IGF-IR tyrosine phosphorylation array showed the recruitment of several key SH2 domain-containing proteins and oncogenes to the IGF-IR tyrosine kinase domain in H2O2-treated RIE-1 cells.

CONCLUSION

IGF-IR-mediated activation of intracellular signaling may play a critical role during oxidative stress-induced apoptosis in NEC.

Atrial natriuretic peptide promotes pancreatic islet beta-cell growth and Akt/Foxo1a/cyclin D2 signaling

The adult differentiated insulin-secreting pancreatic islet beta-cell experiences slow growth. This study shows that atrial natriuretic peptide (ANP) stimulates cell proliferation and [(3)H]thymidine incorporation in INS-1E glucose-sensitive rat beta-cell line cells and isolated rat islet DNA. In addition, cGMP, the second messenger of natriuretic peptide receptors (NPR) A and B, stimulated islet DNA biosynthesis. The NPR-A receptor was expressed in INS-1E cells and islets. ANP-stimulated INS-1E cell DNA biosynthesis was blocked by preincubation with LY294002 (50 microM), an inhibitor of phosphatidylinositol 3'-kinase (PI3K). An indicator of cell cycle progression, cyclin D2 mRNA was increased by 2- to 3-fold in ANP- or 8-Br-cGMP-treated INS-1E cells and islets, and these responses were inhibited by LY294002. ANP and 8-Br-cGMP stimulated the phosphorylation of Akt and Foxo1a in INS-1E cells and islets, and LY294002 inhibited these responses. In contrast, ANP reduced the levels of phospho-ERK in INS-1E cells. Pancreas duodenum homeobox-1 (PDX-1) is essential for pancreas development, insulin production, and glucose homeostasis, and ANP increased PDX-1 mRNA levels by 2- to 3-fold in INS-1E cells and islets. The levels of glucokinase mRNA in islets and INS-1E cells were also increased in response to ANP. The evidence suggests that pancreatic beta-cell NPR-A stimulation results in activation of a growth-promoting signaling pathway that includes PI3K/Akt/Foxo1a/cyclin D2. These data support the conclusion that the activation of Akt by ANP or 8-Br-cGMP promotes cyclin D2, PDX-1, and glucokinase transcription by phosphorylating and restricting Foxo1a activity.

IGF-1 and pAKT signaling promote hippocampal CA1 neuronal survival following injury to dentate granule cells

Insulin-like growth factor-1 (IGF-1) protects neurons from apoptosis and in vivo offers neuroprotective support to hippocampal CA1 pyramidal neurons following ischemia or seizure. IGF-1 signals through IGF-1 receptors activating phosphytidylinositol 3-kinase (PI3K)/Akt or pMAPK pathways. IGF-1 can be induced with injury and microglia and astrocytes may serve as a source of this neurotrophic factor to promote neuronal survival. An acute systemic injection of trimethyltin (TMT; 2 mg/kg, ip) to mice induces apoptosis of dentate granule neurons within 24 h and a differential response of microglia with ramified microglia present in the CA-1 region. Using this model, we studied the role of IGF-1 in the survival of CA-1 pyramidal neurons under conditions of altered synaptic input due to changes in the dentate gyrus. Within 24 h of injection, IGF-1 mRNA levels were elevated in the hippocampus and IGF-1 protein detected in both astrocytes and microglia. IGF-1 was redistributed within the CA-1 neurons corresponding with an increase in cytoplasmic pAkt, elevated PKBalpha/Akt protein levels, and a decrease in the antagonist, Rho. pMAPK was not detected in CA-1 neurons and ERK2 showed a transient decrease followed by a significant increase, suggesting a lack of recruitment of the pMAPK signaling pathway for neuronal survival. In mice deficient for IGF-1, a similar level of apoptosis was observed in dentate granule neurons as compared to wildtype; however, TMT induced a significant level CA-1 neuronal death, further supporting a role for IGF-1 in the survival of CA-1 neurons.

CXCL10 impairs beta cell function and viability in diabetes through TLR4 signaling

In type 1 and type 2 diabetes (T1/T2DM), beta cell destruction by apoptosis results in decreased beta cell mass and progression of the disease. In this study, we found that the interferon gamma-inducible protein 10 plays an important role in triggering beta cell destruction. Islets isolated from patients with T2DM secreted CXCL10 and contained 33.5-fold more CXCL10 mRNA than islets from control patients. Pancreatic sections from obese nondiabetic individuals and patients with T2DM and T1DM expressed CXCL10 in beta cells. Treatment of human islets with CXCL10 decreased beta cell viability, impaired insulin secretion, and decreased insulin mRNA. CXCL10 induced sustained activation of Akt, JNK, and cleavage of p21-activated protein kinase 2 (PAK-2), switching Akt signals from proliferation to apoptosis. These effects were not mediated by the commonly known CXCL10 receptor CXCR3 but through TLR4. Our data suggest CXCL10 as a binding partner for TLR4 and as a signal toward beta cell failure in diabetes.

Rapamycin inhibits growth factor-induced cell cycle regulation in pancreatic beta cells

A progressive decline in islet function is a major obstacle to success of islet transplantation. The cause of this decline is islet function is unclear, but immunosuppressive agents may contribute. Insulin-like growth factor-I (IGF-I) and betacellulin are important for islet cell survival and/or proliferation. In the present study, we performed studies of IGF-I and betacellulin on progression of islet cells through the cell cycle and the impact of immunosuppressive agents. Treatment of INS-1 cells for 24 hours with 20 ng/mL betacellulin or 50 ng/mL IGF-1 increased cells in S phase by ~2-fold. Treatment of INS-1 cells with IGF-I or betacellulin also increased cyclin D1 expression and nuclear exclusion of the cyclindependent kinase inhibitors p21(Cip1) and p27(Kip1). In INS-1 cells and islets, betacellulin- and IGF-I increased the increase in p70(s6 kinase) phosphorylation stimulated by betacellulin- and IGF-I in INS-1 cells. Rapamycin also inhibited betacellulin- and IGF-I IN IGF-1 cells. Rapamycin also inhibited betacellulin- and IGF-I-induced entry of cells into S phase and 5'-Bromo-2'-deoxyuridine incorporation as well as the effect of betacellulin and IGF-I on cyclin D1 expression and nuclear exclusion of p21(Cip1) and p(27Kip1). Together, these data suggest that the effect of betacellulin and IGF-I on islet cell growth and proliferation is mediated, in part, via signaling through mammalian target of rapamycin. As rapamycin is used to treat islet transplant recipients, these results suggest that rapamycin could have deleterious effects on islet proliferation and function over time.

IGF-I protects human oral buccal mucosal epithelial cells from sodium nitroprusside-induced apoptosis via PI3-kinase

OBJECTIVE

Cancers of the head and neck account for the vast majority of all malignancies of the oral cavity. The insulin-like growth factor (IGF) family of proteins is well documented to have an important role in rescuing cells from apoptosis. While it is known the IGF proteins are present in normal oral epithelial and cancer cells its role is not fully understood. Our aim was to study the ability of IGFs to rescue sodium nitroprusside (SNP)-induced apoptotic normal oral epithelial cells in vitro.

DESIGN

Cultured normal human oral keratinocytes (NOKs) or epithelial cells were used. Apoptosis was induced by SNP then cells were exposed to IGF-I or IGF-II to rescue them. Cell viability was assessed by ELISA (for cell death and caspase 3) and FACS analysis; post receptor effects of IGF-I or IGF-II were assessed by [(3)H] thymidine incorporation. Cell signaling events were measured by western blotting using antibodies against phosphorylated Akt or p42/p44 MAPK, and measuring PI3-K activity by ELISA.

RESULTS

SNP induced apoptosis of NOKs and activated the PI3-K/Akt survival pathway. Exposing cells to IGF proteins prevented their apoptosis. IGF-I and -II caused significant increases in PI3-K, but not MAPK, activity. SNP and LY294002, a PI3-K inhibitor, both caused a significant rise in caspase 3 release from NOKs which was reduced in the presence of IGFs.

CONCLUSIONS

The data establishes the importance of IGF-activated PI3-K in rescuing cells from apoptosis. It lends further evidence to the significance of IGF proteins in the possible development of oral cancer.

Inhibition of c-jun N terminal kinase (JNK) improves functional beta cell mass in human islets and leads to AKT and glycogen synthase kinase-3 (GSK-3) phosphorylation

AIMS/HYPOTHESIS

Activation of c-jun N-terminal kinase (JNK) has been described in islet isolation and engraftment, making JNK a key target in islet transplantation. The objective of this study was to investigate if JNK inhibition with a cell-permeable TAT peptide inhibitor (L-JNKI) protects functional beta cell mass in human islets and affects AKT and its substrates in islet cells.

METHODS

The effect of L-JNKI (10 micromol/l) on islet count, mitochondrial membrane potential, glucose-stimulated insulin release and phosphorylation of both AKT and its substrates, as well as on reversal of diabetes in immunodeficient diabetic Nu/Nu mice was studied.

RESULTS

In vitro, L-JNKI reduced the islet loss in culture and protected from cell death caused by acute cytokine exposure. In vivo, treatment of freshly isolated human islets and diabetic Nu/Nu mice recipients of such islets resulted in improved functional beta cell mass. We showed that L-JNKI activates AKT and downregulates glycogen synthase kinase-3 beta (GSK-3B) in human islets exposed to cytokines, while other AKT substrates were unaffected, suggesting that a specific AKT/GSK-3B regulation by L-JNKI may represent one of its mechanisms of cytoprotection.

CONCLUSIONS/INTERPRETATION

In conclusion, we have demonstrated that targeting JNK in human pancreatic islets results in improved functional beta cell mass and in the regulation of AKT/GSK3B activity.

Autocrine insulin action activates Akt and increases survival of isolated human islets

AIMS/HYPOTHESIS

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway plays a critical role in promoting the survival of pancreatic beta cells. Akt becomes activated in isolated human islets following overnight culture despite significant levels of cell death. The aim of the current study was to identify the cause of the observed increase in Akt phosphorylation in isolated islets. We hypothesised that a factor secreted by the islets in culture was acting in an autocrine manner to activate Akt.

METHODS

In order to identify the stimulus of the PI3K/Akt pathway in culture, we examined the effects of different culture conditions on Akt phosphorylation and islet survival during the immediate post-isolation period.

RESULTS

We demonstrated that islet-conditioned medium induced Akt phosphorylation in freshly isolated human islets, whereas frequent medium replacement decreased Akt phosphorylation. Following overnight culture, islet-conditioned medium contained significantly elevated levels of insulin, indicating that insulin may be responsible for the observed increase in Akt phosphorylation. Indeed, treatment with an anti-insulin antibody or with inhibitors of insulin receptor/IGF receptor 1 kinase activity suppressed Akt phosphorylation, leading to decreased islet survival. In addition, dispersion of islets into single cells also suppressed Akt phosphorylation and induced islet cell death, indicating that islet integrity is also required for maximal Akt phosphorylation.

CONCLUSIONS/INTERPRETATION

Our findings demonstrate that insulin acts in an autocrine manner to activate Akt and mediate the survival of isolated human islets. These findings provide new information on how culturing islets prior to transplantation may be beneficial to their survival by allowing for autocrine activation of the pro-survival Akt pathway.

Tumor necrosis factor-alpha production by human islets leads to postisolation cell death

BACKGROUND

Recent successes in islet transplantation highlight the importance of islet isolation by experienced centers and minimization of cell injury as crucial to the achievement of insulin independence. Islet injury may manifest as cell death by apoptosis, shorter graft survival, and the need for retransplantation. Although an inflammatory cytokine response at the graft site is known to inhibit engraftment, recent evidence indicates that islet cells may contribute to this response.

METHODS

Isolated human islets were cultured for up to one week in serum-free CMRL-1066 with 25 microM of tumor necrosis factor (TNF)alpha inhibitor RDP58. Gene expression was measured by reverse transcriptase polymerase chain reaction, apoptosis and TNFalpha secretion by enzyme-linked immunosorbent assay and enzyme-linked immunospot, and islet function by stimulated insulin secretion.

RESULTS

Isolation induced a twofold increase in TNFalpha expression between days one and three (P<0.05), while TNFalpha secretion peaked at day one. RDP58 reduced TNFalpha secretion by 70.6% (P<0.02), though TNFalpha gene expression was unaffected. RDP58 reduced the frequency of TNFalpha-secreting islets by 64.4% (P<0.05) and reduced apoptotic levels by 26.4% within 24 hr postisolation (P<0.05). The reduction in apoptosis was maintained throughout the week (P<0.01), while apoptosis increased in control cultures. Finally, RDP58-treated islets displayed increased insulin secretion in response to both elevated glucose (1915.0+/-396.6 vs. 825.3+/-261.1 mU/L, P<0.01) and secretagogues (2294.3+/-529.5 vs. 939.8+/-333.7 mU/L, P<0.02).

CONCLUSIONS

These data demonstrate that intraislet cytokine production should be considered as a factor leading to islet cell death postisolation and postengraftment, and strategies aimed at countering islet cytokine production represent a novel target for improving islet viability and function.

IGF-1 protects intestinal epithelial cells from oxidative stress-induced apoptosis

BACKGROUND

Reactive oxygen species (ROS) are involved in the pathogenesis of necrotizing enterocolitis (NEC) in premature infants. We have recently found that activation of multiple cellular signaling transduction pathways occurs during ROS-induced intestinal cell apoptosis; the phosphatidylinositol 3-kinase (PI3-K) pathway plays an anti-apoptotic role during this process. Insulin-like growth factor (IGF)-1 activates PI3-K pathway to promote cell survival; however, the effects of IGF-1 treatment during gut injury are not clearly defined. The purpose of this study was to determine whether IGF-1 protects intestinal cells from ROS-induced apoptosis.

MATERIALS AND METHODS

Rat intestinal epithelial (RIE)-1 cells were treated with either IGF-1 (100 nm), hydrogen peroxide (H2O2; 500 microm), or combination. Western blotting was performed to assess phosphorylation of Akt, a downstream effector of PI3-K. Cell Death Detection ELISA, DCHF, and JC-1 assays were performed to demonstrate protective effects of IGF-1. Wortmannin, an inhibitor of PI3-K, was used to show PI3-K-dependent mechanism of action for IGF-1.

RESULTS

H2O2 treatment resulted in increased intestinal epithelial cell apoptosis with intracellular ROS generation and mitochondrial membrane depolarization; IGF-1 pre-treatment attenuated this response without affecting ROS production. H2O2-induced phosphorylation of Akt was further increased with IGF-1 treatment; wortmannin abolished these effects in RIE-1 cells.

CONCLUSIONS

PI3-K pathway is activated during ROS-induced intestinal epithelial cell injury; IGF-1 exerted an anti-apoptotic effect during this response by PI3-K activation. A better understanding of the exact role of IGF-1-mediated activation of PI3-K may allow us to facilitate the development of novel therapy against NEC.

IGF-I mediated survival pathways in normal and malignant cells

The type-I and -II insulin-like growth factors (IGF-I, II) are now established as survival- or proliferation-factors in many in vitro systems. Of note IGFs provide trophic support for multiple cell types or organ cultures explanted from various species, and delay the onset of programmed cell death (apoptosis) through the mitochondrial (intrinsic pathway) or by antagonizing activation of cytotoxic cytokine signaling (extrinsic pathway). In some instances, IGFs protect against other forms of death such as necrosis or autophagy. The effect of IGFs on cell survival appears to be context specific, being determined both by the cell origin (tissue specific) and the cellular stress that induces loss of cellular viability. In many human cancers, there is a strong association with dysregulated IGF signaling, and this association has been extensively reviewed recently. IGF-regulation is also disrupted in childhood cancers as a consequence of chromosomal translocations. IGFs are implicated also in acute renal failure, traumatic injury to brain tissue, and cardiac disease. This article focuses on the role of IGFs and their cellular signaling pathways that provide survival signals in stressed cells.

Selective deletion of Pten in pancreatic beta cells leads to increased islet mass and resistance to STZ-induced diabetes

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a lipid phosphatase. PTEN inhibits the action of phosphatidylinositol-3-kinase and reduces the levels of phosphatidylinositol triphosphate, a crucial second messenger for cell proliferation and survival, as well as insulin signaling. In this study, we deleted Pten specifically in the insulin producing beta cells during murine pancreatic development. Pten deletion leads to increased cell proliferation and decreased cell death, without significant alteration of beta-cell differentiation. Consequently, the mutant pancreas generates more and larger islets, with a significant increase in total beta-cell mass. PTEN loss also protects animals from developing streptozotocin-induced diabetes. Our data demonstrate that PTEN loss in beta cells is not tumorigenic but beneficial. This suggests that modulating the PTEN-controlled signaling pathway is a potential approach for beta-cell protection and regeneration therapies.

Insulin-like growth factor I interfaces with brain-derived neurotrophic factor-mediated synaptic plasticity to modulate aspects of exercise-induced cognitive function

The ability of exercise to benefit neuronal and cognitive plasticity is well recognized. This study reveals that the effects of exercise on brain neuronal and cognitive plasticity are in part modulated by a central source of insulin-like growth factor-I. Exercise selectively increased insulin-like growth factor-I expression without affecting insulin-like growth factor-II expression in the rat hippocampus. To determine the role that insulin-like growth factor-I holds in mediating exercise-induced neuronal and cognitive enhancement, a specific antibody against the insulin-like growth factor-I receptor was used to block the action of insulin-like growth factor-I in the hippocampus during a 5-day voluntary exercise period. A two-trial-per-day Morris water maze was performed for five consecutive days, succeeded by a probe trial 2 days later. Blocking hippocampal insulin-like growth factor-I receptors did not significantly attenuate the ability of exercise to enhance learning acquisition, but abolished the effect of exercise on augmenting recall. Blocking the insulin-like growth factor-I receptor significantly reversed the exercise-induced increase in the levels of brain-derived neurotrophic factor mRNA and protein and pro-brain-derived neurotrophic factor protein, suggesting that the effects of insulin-like growth factor-I may be partially accomplished by modulating the precursor to the mature brain-derived neurotrophic factor. A molecular analysis revealed that exercise significantly elevated proteins downstream to brain-derived neurotrophic factor activation important for synaptic function, i.e. synapsin I, and signal transduction cascades associated with memory processes, i.e. phosphorylated calcium/calmodulin protein kinase II and phosphorylated mitogen-activated protein kinase II. Blocking the insulin-like growth factor-I receptor abolished these exercise-induced increases. Our results illustrate a possible mechanism by which insulin-like growth factor-I interfaces with the brain-derived neurotrophic factor system to mediate exercise-induced synaptic and cognitive plasticity.

Signaling through interleukin-1 type 1 receptor diminishes Haemophilus somnus lipooligosaccharide-mediated apoptosis of endothelial cells

During sepsis, endothelial cells are both a source and target of pro-inflammatory cytokines (e.g. IL-1alpha, IL-1beta, TNFalpha and others), which may be detrimental to vascular homeostasis. Our laboratory has demonstrated that Haemophilus somnus, a gram-negative pathogen of cattle that causes sepsis and vasculitis, and its lipooligosaccharide (LOS) induce caspases-3, -8 and -9 activation, and apoptosis of endothelial cells in vitro. In this study, we provide evidence that H. somnus LOS increases IL-1alpha and IL-1beta mRNA expression, and caspase-1 activation in endothelial cells. Addition of a caspase-1 inhibitor (YVAD), or incubation in a high extracellular potassium buffer (150 mM), reduced caspase-1 activation and significantly enhanced H. somnus LOS-mediated caspase-3 activation. Likewise, blocking the IL-1 type 1 receptor by addition of IL-receptor antagonist (IL-1ra) significantly enhanced LOS-mediated caspase-3 activation. Conversely, addition of exogenous recombinant bovine IL-1beta (100 ng/mL) to endothelial cells diminished LOS-mediated apoptosis. IL-1beta has been reported previously to protect numerous cell types from apoptosis by activating PI3 kinase/p-Akt signaling pathways. Addition of selective PI3 kinase inhibitors (e.g. wortmannin and LY294002) significantly enhanced LOS-mediated caspase-3 activation. Exposure of endothelial cells to IL-1beta or LOS increased pAkt protein as assessed by western blot. Overall, these results suggest that signaling through the IL-1 type 1 receptor diminishes H. somnus LOS-mediated apoptosis.

Glucagon-like peptide-1 protects beta cells from cytokine-induced apoptosis and necrosis: role of protein kinase B

AIMS/HYPOTHESIS

The gut hormone glucagon-like peptide-1 (GLP-1) decreases beta cell apoptosis in a protein kinase B (PKB)-dependent fashion, and increases islet cell mass and function in vivo. In contrast, cytokines induce beta cell apoptosis, leading to decreased islet mass and type 1 diabetes. In the present study we used rat INS-1E beta cells and primary rat islet cells to examine the potential role of PKB as a mediator of the effect of GLP-1 on cytokine-induced apoptosis.

METHODS

Cell viability was determined by MTT assay, and apoptosis and necrosis by Hoechst 33342-propidium iodide staining. Immunoblot analysis was used to detect changes in protein expression, including active (phosphorylated) and total PKB, phosphorylated and total glycogen synthase kinase-3beta, activated caspase-3 and inducible nitric oxide synthase. Reactive oxygen species were determined by 1,7-dichlorofluorescein (DCF) analysis, and mutant forms of PKB were introduced into cells using adenoviral vectors.

RESULTS

Incubation of INS-1E cells with cytokines (IL-1beta, TNF-alpha and interferon-gamma; 10-50 ng/ml) for 18 h significantly decreased cell viability (by 44%, p<0.001), cell proliferation (by 80%, p<0.001), and activation of PKB (by 67%, p<0.001). Pre-treatment with exendin-4 (10(-7) mol/l), a long-acting GLP-1 receptor agonist, partially protected the cells against cytokine-induced toxicity (p<0.01) in association with a reduction in cytokine-induced inhibition of PKB phosphorylation (p<0.05). Exendin-4 pre-treatment did not change cell proliferation. Cytokine treatment increased apoptosis (by 156%, p<0.05) and necrosis (from undetectable to 2.6% of cells). These increases were both reduced by pre-treatment with exendin-4 (p<0.05-0.01). Furthermore, cytokine-induced apoptosis and necrosis were significantly increased in cells infected with kinase-dead PKB (p<0.05), and the protective effect of exendin-4 on both parameters was fully abolished in these cells. Similar changes were observed in primary islet cells. In parallel with these changes, exendin-4 decreased the cytokine-induced activation of caspase-3 (by 46%, p<0.05), and decreased levels of inducible nitric oxide synthase (by 71%, p<0.05) and reactive oxygen species (by 27%, p<0.05).

CONCLUSIONS/INTERPRETATION

The results of our study indicate that GLP-1 plays a protective role against cytokine-induced apoptosis and necrosis in beta cells through a PKB-dependent signalling pathway.

Cross-talk between phosphatidylinositol 3-kinase/AKT and c-jun NH2-terminal kinase mediates survival of isolated human islets

Therapeutic strategies aimed at the inhibition of specific cell death mechanisms may increase islet yield and improve cell viability and function after routine isolation. The aim of the current study was to explore the possibility of AKT-JNK cross-talk in islets after isolation and the relevance of c-jun NH2-terminal kinases (JNK) suppression on islet survival. After routine isolation, increased AKT activity correlated with suppression of JNK activation, suggesting that they may be related events. Indeed, the increase in AKT activation after isolation correlated with suppression of apoptosis signal-regulating kinase 1 (ASK1), a kinase acting upstream of JNK, by phosphorylation at Ser83. We therefore examined whether modulators of phosphatidylinositol 3-kinase (PI3K)/AKT signaling affected JNK activation. PI3K inhibition led to increased JNK phosphorylation and islet cell death, which could be reversed by the specific JNK inhibitor SP600125. In addition, IGF-I suppressed cytokine-mediated JNK activation in a PI3K-dependent manner. We also demonstrate that inhibition of PI3K rendered islets more susceptible to cytokine-mediated cell death. SP600125 transiently protected islets from cytokine-mediated cell death, suggesting that JNK may not be necessary for cytokine-induced cell death. When administered immediately after isolation, SP600125 improved islet survival and function, even 48 h after removal of SP600125, suggesting that JNK inhibition by SP600125 may be a viable strategy for improving isolated islet survival. Taken together, these results demonstrate that PI3K/AKT suppresses the JNK pathway in islets, and this cross-talk represents an important antiapoptotic consequence of PI3K/AKT activation.

Enriched human pancreatic ductal cultures obtained from selective death of acinar cells express pancreatic and duodenal homeobox gene-1 age-dependently

Adult pancreatic ductal cells are believed to be islet precursors. Our aim was to obtain an enriched human ductal cell population in defined culture conditions, and to characterize these cultures for the presence of pancreatic developmental transcription factors. Non-endocrine adult human pancreatic digest was cultured for 4 days in serum-containing and serum-free media. During this time, analysis was done for phenotypic changes, cell death, and expression of islet and islet precursor markers. Culture in serum-supplemented and serum-free media gave similar recoveries of an enriched ductal population after 4 days. Extensive cell death due to apoptosis and necrosis was also observed over this time period. A donor-age dependent expression of pancreatic and duodenal homeobox gene-1 (PDX-1) in ductal cells was seen at 4 days whereby donors <25 yr expressed significantly more than donors >25 yr. Analysis of gene expression by RT-PCR showed the presence of islet developmental transcription factors neuroD, Nkx6.1, and PDX-1, as well as mature islet hormones. While acinar-ductal transdifferentiation of some cells cannot be ruled out, we provide evidence that the predominant mechanism for the derivation of enriched human ductal cultures in our culture conditions is selective acinar cell death. Furthermore, we have shown that ductal cultures from younger donors exhibit greater plasticity through expression of PDX-1, and may be of greater value in attempts to induce islet neogenesis. The presence, however, of insulin and glucagon mRNA indicates that contaminating endocrine cells remain in these cultures and underscores the need to use caution when assessing differentiation potential.

×Phosphorylation of Bax Ser184 by Akt Regulates Its Activity and Apoptosis in Neutrophils

Although important for apoptosis, the mechanism of Bax regulation is poorly understood. This study demonstrates that phosphorylation of Ser(184) regulates Bax activity. The phosphorylation required phosphatidylinositol 3-kinase/Akt activation and appeared to be mediated by Akt itself. In the serine-phosphorylated form, Bax was detected in the cytoplasm, could not be immunoprecipitated with the activation-specific antibody 6A7, and promoted heterodimerization with Mcl-1, Bcl-x(L), and A1. Apoptotic neutrophils possessed reduced levels of serine-phosphorylated Bax correlating with an increase in activated Bax as well as an increase in the amount of Bax found translocated to the mitochondria. We suggest that Bax is regulated by phosphorylation of Ser(184) in an Akt-dependent manner and that phosphorylation inhibits Bax effects on the mitochondria by maintaining the protein in the cytoplasm, heterodimerized with antiapoptotic Bcl-2 family members.

Mono-unsaturated fatty acids protect against beta-cell apoptosis induced by saturated fatty acids, serum withdrawal or cytokine exposure

Long-chain saturated fatty acids are cytotoxic to pancreatic beta-cells while shorter-chain saturated and long-chain unsaturated molecules are better tolerated. Mono-unsaturated fatty acids are not, however, inert since they inhibit the pro-apoptotic effects of saturated molecules. In the present work we show that the mono-unsaturates palmitoleate (C16:1) or oleate (C18:1) also cause marked inhibition of apoptosis induced by exposure of clonal BRIN-BD11 beta-cells to serum withdrawal or a combination of interleukin-1beta plus interferon-gamma. This response was dose-dependent and not accompanied by changes in NO formation. Taken together, the results suggest that mono-unsaturated fatty acids regulate a distal step common to several apoptotic pathways in pancreatic beta-cells.

Glucagon-like peptide-1 regulates proliferation and apoptosis via activation of protein kinase B in pancreatic INS-1 beta cells

AIMS/HYPOTHESIS

The incretin hormone glucagon-like peptide-1 augments islet cell mass in vivo by increasing proliferation and decreasing apoptosis of the beta cells. However, the signalling pathways that mediate these effects are mostly unknown. Using a clonal rat pancreatic beta cell line (INS-1), we examined the role of protein kinase B in mediating beta-cell growth and survival stimulated by glucagon-like peptide-1.

METHODS

Immunoblot analysis was used to detect active (phospho-) and total protein kinase B. Proliferation was assessed using (3)H-thymidine incorporation, while apoptosis was quantitated using 4'-6-diamidino-2-phenylindole staining and APO percentage apoptosis assay. Kinase-dead and wild-type protein kinase B was introduced into cells using adenoviral vectors.

RESULTS

Glucagon-like peptide-1 rapidly activated protein kinase B in INS-1 cells (by 2.7+/-0.7-fold, p<0.05). This effect was completely abrogated by inhibition, with wortmannin, of the upstream activator of protein kinase B, phosphatidylinositol-3-kinase. Glucagon-like peptide-1 also stimulated INS-1 cell proliferation in a dose-dependent manner (by 1.8+/-0.5-fold at 10(-7) mol/l, p<0.01), and inhibited staurosporine-induced apoptosis (by 69+/-12%, p<0.05). Both of these effects were also prevented by wortmannin treatment. Ablation of protein kinase B by adenovirus-mediated overexpression of the kinase-dead form of protein kinase Balpha prevented protein kinase B phosphorylation and completely abrogated both cellular proliferation ( p<0.05) and protection from drug-induced cellular death ( p<0.01) induced by glucagon-like peptide-1.

CONCLUSIONS/INTERPRETATION

These results identify protein kinase B as an essential mediator linking the glucagon-like peptide-1 signal to the intracellular machinery that modulates beta-cell growth and survival.

Signals for death and differentiation: a two-step mechanism for in vitro transformation of adult islets of Langerhans to duct epithelial structures

Phenotypic change of adult pancreatic islets has been implicated in the development of certain pancreatic cancers and in islet transplant failure. The aim of this study was to characterize intracellular events that mediate changes in adult islet phenotype. Using an in vitro islet-to-duct transformation model, canine islets were induced to undergo phenotypic transformation to duct-like epithelial structures through a two-stage process. Stage one was characterized by widespread islet cell apoptosis associated with the formation of cavitary spaces within the islets. During this stage, c-Jun N-terminal regulated kinase (JNK) and caspase-3 activities were elevated, while extracellular signal-regulated kinase (ERK) and Akt activities were decreased. The second stage of the process was characterized by an inversion in the balance in activity between these signal transduction pathways and by a concomitant decrease in apoptosis. The transformed islets were no longer immunoreactive for islet cell hormones, but expressed the duct epithelial cell marker CK-AE1/AE3. In contrast to islet cells, these duct epithelial cells were highly proliferative. To clarify the role of the identified changes in signal transduction events, we performed additional studies using pharmacological inhibitors of enzyme activity and demonstrated that inhibition of JNK and caspase-3 activity prevented cystic transformation. Our results indicate that the balance in signaling activity between ERK/Akt and JNK/caspase-3 appears to be an important regulator of islet cell death and differentiation.

Cytokine-mediated down-regulation of the transcription factor cAMP-response element-binding protein in pancreatic beta-cells

Cytokines are known to induce apoptosis of pancreatic beta-cells. Impaired expression of the anti-apoptotic gene bcl-2 is one of the mechanisms involved. In this study, we identified a defect involving transcription factor cAMP-response element-binding protein (CREB) in the expression of bcl-2. Exposure of mouse pancreatic beta-cell line, MIN6 cells, to cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma) led to a significant (p < 0.01) decrease in Bcl-2 protein and mRNA levels. Cytokines decreased (56%) the activity of the bcl-2 promoter that contains a cAMP-response element (CRE) site. Similar decreases were seen with a luciferase reporter gene driven by tandem repeats of CRE and a CREB-specific Gal4-luciferase reporter, suggesting a defect at the level of CREB. The active phospho form (serine 133) of CREB diminished significantly (p < 0.01) in cells exposed to cytokines. Examination of signaling pathways upstream of CREB revealed a reduction in the active form of Akt. Cytokine-induced decrease of bcl-2 promoter activity was partially restored when cells were cotransfected with a constitutively active form of Akt. Several end points of cytokine action including decreases in phospho-CREB, phospho-Akt, and BCl-2 levels and activation of caspase-9 were observed in isolated mouse islets. Overexpression of wild-type CREB in MIN6 cells by plasmid transfection and adenoviral infection led to protection against cytokine-induced apoptosis. Adenoviral transfer of dominant-negative forms of CREB, on the other hand, resulted in activation of caspase-9 and exaggeration of cytokine-induced beta-cell apoptosis. Together, these results point to CREB as a novel target for strategies aimed at improving the survival of beta-cells.

Justification for antioxidant preconditioning (or how to protect insulin-mediated actions under oxidative stress)

Insulin resistance is characterized by impaired glucose utilization in the peripheral tissues, accelerated muscle protein degradation, impaired antioxidant defences and extensive cell death. Apparently, both insulin and IGF-1 at physiological concentrations support cell survival by phosphatidylinositol 3 kinase-dependent and independent mechanisms. Postprandial hyperglycemia and hyperinsulinemia are found in insulin resistance, which accompanies the so-called noninsulin dependent diabetes mellitus (diabetes type 2). Evidence also indicates that increased susceptibility of muscle cells and cardiomycoytes to oxidative stress is among the harmful complications of insulin resistance and diabetes. Limited knowledge showing benefits of preconditioning with anti- oxidants (vitamin C, E, a-lipoic acid, N-acetylcysteine) in order to protect insulin action under oxidative stress prompted the author to discuss the theoretical background to this approach. It should be stressed that antioxidant preconditioning is relevant to prevention of both diabetes- and insulin resistance-associated side-effects such as low viability and cell deletion. Furthermore, antioxidant conditioning promises to provide higher efficacy for clinical applications in myoblast transfer therapy and cardiomyoplasty.

Blockade of IRS1 in isolated rat pancreatic islets improves glucose-induced insulin secretion

Several neural, hormonal and biochemical inputs actively participate in the balance of insulin secretion induced by blood glucose fluctuations. The exact role of insulin as an autocrine and paracrine participant in the control of its own secretion remains to be determined, mostly due to insufficient knowledge about the molecular phenomena that govern insulin signaling in pancreatic islets. In the present experiments we demonstrate that higher insulin receptor and insulin receptor substrates-1 and -2 (IRS1 and IRS2) concentrations are predominantly encountered in cells of the periphery of rat pancreatic islets, as compared to centrally located cells, and that partial blockade of IRS1 protein expression by antisense oligonucleotide treatment leads to improved insulin secretion induced by glucose overload, which is accompanied by lower steady-state glucagon secretion and blunted glucose-induced glucagon fall. These data reinforce the inhibitory role of insulin upon its own secretion in isolated, undisrupted pancreatic islets.

Simvastatin induces activation of the serine-threonine protein kinase AKT and increases survival of isolated human pancreatic islets

BACKGROUND

Pancreatic islets are susceptible to myriad insults that occur during islet isolation and transplantation. Studies demonstrated the role of Akt in regulating pancreatic beta-cell growth and survival. Activation of Akt maintains Bad phosphorylation and prevents its binding to mitochondrial targets, decreases caspase-9 activity, and prevents the translocation of forkhead transcription factors (FKHR). Simvastatin activates Akt in mammalian cells; therefore, we investigated the role of simvastatin on human pancreatic islets (HPI) survival.

METHODS

HPI were treated with simvastatin, with and without LY294002, an inhibitor of phosphoinositide 3-kinase. PI viability was examined with ethidium bromide-acridine orange, and apoptosis was examined using a quantitative assay. Akt, Bad, FKHR phosphorylation, and mitochondrial cytochrome release were analyzed by Western blots. Caspase-9 activity was assessed by a fluorometric assay. A limited number of HPI were transplanted after simvastatin treatment in diabetic NOD-SCID mice.

RESULTS

Low levels of Akt phosphorylation (activation) were demonstrated early after islet isolation. Akt activation; increase in islet viability; and decrease in Bad phosphorylation, cytochrome release, caspase-9 activation, and translocation of FKHR were observed after simvastatin treatment, effects reversed by LY294002. Among recipients of islets without simvastatin, none demonstrated reversal of diabetes after the transplant. In contrast, 58% of the recipients given islets treated with simvastatin remained euglycemic 30 days after the transplant.

CONCLUSIONS

Targeting the survival pathway with simvastatin exerts a cytoprotective effect on isolated PI. Activation of the Akt pathway is a potential new therapeutic approach to reduce loss of functional islet mass to bolster success in clinical islet transplantation.

Activation of phosphatidylinositol 3-kinase contributes to insulin-like growth factor I-mediated inhibition of pancreatic beta-cell death

To begin to determine whether IGF-I treatment represents a potential means of enhancing the survival of islet cell grafts after transplantation, the present studies established a model of beta-cell death secondary to loss of trophic support and examined the ability of IGF-I to prevent cell death. The studies were performed using the rat pancreatic beta-cell line, INS-1. Incubating INS-1 cells in RPMI 1640 and 0.25% BSA for 48 h increased cell death, as determined by lactate dehydrogenase release, compared with that of cells maintained in RPMI and 10% fetal calf serum. Addition of 100 ng/ml IGF-I to the serum-free medium decreased lactate dehydrogenase release to a level comparable to that found in cells maintained in fetal calf serum. Similar results were seen using a mouse beta-cell line, MIN6, infected with an adenovirus expressing IGF-I. Examination of IGF-I-stimulated signaling demonstrated that IGF-I increased the phosphorylation of protein kinase B in both cell lines, whereas IGF-I-induced phosphorylation of the MAPKs, ERK1 and -2, was observed only in INS-1 cells. The effect of IGF-I on phosphorylation of substrates of phosphatidylinositol 3-kinase (PI 3-kinase) or protein kinase B was also examined in INS-1 cells. IGF-I increased the phosphorylation of glycogen synthase kinase 3beta, BAD, FKHR, and p70(S6) kinase. Another pathway that has been shown to mediate the protective of IGF-I in some cell types is activation of cAMP response element-binding protein (CREB). IGF-I increased CREB phosphorylation at a concentration as low as 10 ng/ml, and this effect was inhibited by H89, a PKA inhibitor, and PD98059, a MAPK kinase inhibitor. Consistent with the effect of IGF-I on CREB phosphorylation, IGF-I increased the transcriptional activity of CREB, although it had no effect on CREB binding to DNA. Use of inhibitors of the PI 3-kinase (LY 294002) or ERK (PD98059) pathways or CREB phosphorylation (H89) in the cell death assay demonstrated partial abrogation of the protective effect of IGF-I with LY 294002. These data demonstrate that IGF-I protects pancreatic beta-cells from cell death secondary to loss of trophic support and that, although IGF-I activates several signaling pathways that contribute to its protective effect in other cell types, only activation of PI 3-kinase contributes to this effect in beta-cells.

GTP-binding proteins in cell survival and demise: the emerging picture in the pancreatic beta-cell

It is widely believed that guanine nucleotide-binding regulatory proteins (G-proteins) play central roles as "molecular switches" in a variety of cellular processes ranging from signal transduction to protein and vesicle trafficking. To achieve these regulatory functions, G-proteins form complexes with a wide range of effector molecules whose activities are altered upon interaction with the G-protein. These effector molecules can be either soluble or membrane bound, and it is likely that some are localized to secretory granules where they direct the movement, docking, and fusion of granules during exocytosis. The effector molecules regulated by G-proteins are diverse and include phospholipases, protein kinases, protein phosphatases, ion channels, adenylate cyclases, cytoskeletal elements, as well as secretory vesicle and plasma membrane-associated fusion-proteins. The majority of studies performed in the pancreatic beta-cell have focused on the role of G-proteins in the regulation of insulin secretion, whereas very little attention has been focused on their potential involvement in other cellular processes. Such studies have identified and implicated both heterotrimeric (comprising alpha, beta, and gamma subunits) and monomeric (low molecular mass) G-proteins in the regulation of insulin secretion, but intriguing recent evidence has also begun to emerge which favors the view that they may be involved in the maintenance of beta-cell viability. In the present commentary, we will review this evidence and discuss the current understanding of the role of G-proteins in the life and death of the beta-cell.

Activation of SHIP by NADPH oxidase-stimulated Lyn leads to enhanced apoptosis in neutrophils

Neutrophils undergo rapid spontaneous apoptosis. Multiple antiapoptotic stimuli can inhibit this process via activation of the Akt pathway. However, despite no such effect singly, combined anti- and proapoptotic stimuli inhibit Akt activity, leaving the cells susceptible to accelerated apoptosis. The blockade of Akt activation depended on reduced phosphoinositide 3,4,5-trisphosphate levels but not decreased phosphatidylinositol 3-kinase activity, thus implicating the involvement of an inositol phosphatase. Evidence for SHIP involvement was provided by SHIP localization to membrane receptors and subsequent activation along with the observed inability of SHIP -/- neutrophils to exhibit enhanced apoptosis with the stimulus combination. Activation of SHIP was found to depend on Lyn activation, and this, in turn, required NADPH oxidase. Neutrophils from chronic granulomatous disease patients and Lyn -/- mice no longer responded to the combined stimuli. Thus, we propose a role for oxidants and Lyn in SHIP regulation and suggest a novel mechanism for regulating neutrophil apoptosis.

Tumor necrosis factor(alpha) and insulin-like growth factor-I in the brain: is the whole greater than the sum of its parts?

The cytokine tumor necrosis factor(alpha) (TNFalpha) and the hormone insulin-like growth factor-I (IGF-I) have both been shown to regulate inflammatory events in the central nervous system (CNS). This review summarizes the seemingly independent roles of TNFalpha and IGF-I in promoting and inhibiting neurodegenerative diseases. We then offer evidence that the combined effects of IGF-I and TNFalpha on neuronal survival can be vastly different when both receptors are stimulated simultaneously, as is likely to occur in vivo. We propose the framework of a molecular model of hormone-cytokine receptor cross talk in which disparate cell surface receptors share intracellular substrates that regulate neuronal survival.

Inhibition of Na,K-ATPase activates PI3 kinase and inhibits apoptosis in LLC-PK1 cells

In the present study we used LLC-PK1 cells, a porcine renal proximal tubular cell line, to investigate whether PI3 kinase activation was involved in the anti-apoptotic effect of ouabain, a specific inhibitor of Na,K-ATPase. Apoptosis was induced by actinomycin D (Act D, 5 microM) and assessed by appearance of hypodiploid nuclei and DNA fragmentation. Ouabain attenuated Act D-induced apoptotic response in a dose-dependent manner. Incubation in a low K(+) medium (0.1 mM) which is another way to decrease Na,K-ATPase activity also had anti-apoptotic effect. Both ouabain and low K(+) medium increased the PI3 kinase activity in p85 immunoprecipitates. Ouabain, as well as incubation in the low K(+) medium, also increased the phosphorylation of Akt. Inhibition of PI3 kinase by either wortmannin or LY294002 reversed the cytoprotective effect of ouabain. These data together indicate that inhibition of Na,K-ATPase activates PI3 kinase in LLC-PK1 cells which could then exert the cytoprotective effect.