[Ecological quality assessment of Xiongan New Area based on remote sensing ecological index]. / 基于遥感生态指数的雄安新区生态质量评估.

The continuous urbanization leads to increasing pressure on the ecological environment. It is a key point to measure regional ecological environment quality objectively, accurately and quickly from multiple directions in ecological research. In this study, the normalized vegetation index (NDVI), wet index (WET), land surface temperature (LST), and normalized difference building-soil index (NDBSI) were extracted from the aspects of greenness, humidity, heat and dryness. The ecological quality of Xiongan New Area between 1995 and 2015 was evaluated by integrating selected indicators to measure the remote sensing ecological index (RSEI) with principal component analysis technology based on ENVI platform. The results showed that the average RSEI of Xiongan New Area was 0.724, 0.710, and 0.682 in 1995, 2004 and 2015, respectively, showing a downward trend. RSEI mainly changed from 4, 5 to 1, 2 and 3 in the study area from 1995 to 2015. Ecological quality improved and deteriorated area accounted for 8.9% and 20.9% of the total area respectively. The ecological quality improved area was mainly located in the east and south of Xiongxian County, because a large area of forests and gardens was highly valued and strictly protected by the local government. The ecological quality deteriorated area was in the periphery of the town and the surrounding area of Baiyangdian due to the sharp decline of the water area of Baiyangdian and the continuous urbanization. The three-year average correlation coefficient between RSEI and each component index was 0.804, which was higher than that between other component indices. Our results showed that RSEI could efficiently integrate the information of each component index and comprehensively and accurately reflect the ecological quality of the study area.

Splice variant-specific stabilization of JNKs by IB1/JIP1.

Islet-Brain 1 (IB1) (also called JNK-interacting protein 1; JIP1) is a scaffold protein that tethers components of the JNK mitogen-activated protein kinase pathway inducing a modulation of the activity and the target specificity of the JNK kinases. Dysfunctions in IB1 have been associated with diseases such as early type II diabetes. To gain more insight in the functions of IB1, its ability to modulate the expression levels of the various JNK proteins was assessed. Each of the three JNK genes gives rise to several splice variants encoding short or long proteins. The expression levels of the short JNK proteins, but not of the long variants, were systematically higher in rat tissues and in transformed cell lines expressing high IB1 levels compared to tissues and cells with no or low IB1 expression. HEK293 cells bearing a tetracycline-inducible IB1 construct showed a specific increase of the short JNK endogenous splice variants in the presence of tetracycline. The augmented expression level of the short JNK splice variants induced by IB1 resulted from an increased stability towards degradation. Modulation of the stability of specific JNK splice variants represents therefore a newly identified mechanism used by IB1 to regulate the JNK MAPK pathway.

Impaired Akt activity down-modulation, caspase-3 activation, and apoptosis in cells expressing a caspase-resistant mutant of RasGAP at position 157.

RasGAP bears two caspase-3 cleavage sites that are used sequentially as caspase activity increases in cells. When caspase-3 is mildly activated, RasGAP is first cleaved at position 455. This leads to the production of an N-terminal fragment, called fragment N, that activates the Ras-PI3K-Akt pathway and that promotes cell survival. At higher caspase activity, RasGAP is further cleaved at position 157 generating two small N-terminal fragments named N1 and N2. We have now determined the contribution of this second cleavage event in the regulation of apoptosis using cells in which the wild-type RasGAP gene has been replaced by a cDNA encoding a RasGAP mutant that cannot be cleaved at position 157. Our results show that cleavage of fragment N at position 157 leads to a marked reduction in Akt activity. This is accompanied by efficient processing of caspase-3 that favors cell death in response to various apoptotic stimuli. In nontumorigenic cells, fragments N1 and N2 do not modulate apoptosis. Therefore, the role of the second caspase-mediated cleavage of RasGAP is to allow the inactivation of the antiapoptotic function of fragment N so that caspases are no longer hampered in their ability to kill cells.

Partial cleavage of RasGAP by caspases is required for cell survival in mild stress conditions.

Tight control of apoptosis is required for proper development and maintenance of homeostasis in multicellular organisms. Cells can protect themselves from potentially lethal stimuli by expressing antiapoptotic factors, such as inhibitors of apoptosis, FLICE (caspase 8)-inhibitory proteins, and members of the Bcl2 family. Here, we describe a mechanism that allows cells to survive once executioner caspases have been activated. This mechanism relies on the partial cleavage of RasGAP by caspase 3 into an amino-terminal fragment called fragment N. Generation of this fragment leads to the activation of the antiapoptotic Akt kinase, preventing further amplification of caspase activity. Partial cleavage of RasGAP is required for cell survival under stress conditions because cells expressing an uncleavable RasGAP mutant cannot activate Akt, cannot prevent amplification of caspase 3 activity, and eventually undergo apoptosis. Executioner caspases therefore control the extent of their own activation by a feedback regulatory mechanism initiated by the partial cleavage of RasGAP that is crucial for cell survival under adverse conditions.

A RasGAP-derived cell permeable peptide potently enhances genotoxin-induced cytotoxicity in tumor cells.

Treatment of many cancers relies on the combined action of several genotoxins, but the detrimental effect of these drugs on normal cells can cause severe side effects. One major challenge in anticancer therapy is therefore to increase the selectivity of current treatments toward cancer cells in order to spare normal cells. We have recently demonstrated that a RasGAP caspase cleavage fragment is able to sensitize HeLa cells towards cisplatin-induced apoptosis. Here, we extend this observation by showing that this fragment also enhances cell death induced by adriamycin and mitoxantrone, two other widely used genotoxins. Furthermore, we have delineated a short sequence within this fragment that still bears the genotoxin-sensitization property. The peptide encoded by this sequence, when fused to the TAT cell permeation sequence, potently sensitized a number of tumors cells, but not normal cells, towards apoptosis induced by cisplatin, adriamycin and mitoxantrone. This sensitization effect was not mediated through modulation of NFkappaB activity or activation of the JNK and p38 MAPK pathways. Our results demonstrate the feasibility in enhancing the efficacy of currently used drugs to selectively kill cancer cells using peptides derived from pro-apoptotic caspase substrate fragments.

Surviving the kiss of death.

Executioner caspases induce the biochemical and cellular changes characteristic of apoptosis. Activation of caspases is therefore regarded as "the kiss of death" resulting in the cell's demise. Recent reports indicate however that in some situations, caspase activation may induce other responses than apoptosis. These findings raise the question of how cells manage to counteract the killing activities of executioner caspases. Experiments performed in our laboratory have unraveled a mechanism that allows cells to survive in the presence of activated executioner caspases. This mechanism is based on the partial cleavage of RasGAP into an N-terminal fragment that activates the Ras-PI3K-Akt survival pathway. This protective pathway may be activated to allow cells to use executioner caspases for other purposes than inducing apoptosis.

Role of mTOR, Bad, and Survivin in RasGAP Fragment N-Mediated Cell Protection.

Partial cleavage of p120 RasGAP by caspase-3 in stressed cells generates an N-terminal fragment, called fragment N, which activates an anti-apoptotic Akt-dependent survival response. Akt regulates several effectors but which of these mediate fragment N-dependent cell protection has not been defined yet. Here we have investigated the role of mTORC1, Bad, and survivin in the capacity of fragment N to protect cells from apoptosis. Neither rapamycin, an inhibitor of mTORC1, nor silencing of raptor, a subunit of the mTORC1 complex, altered the ability of fragment N from inhibiting cisplatin- and Fas ligand-induced death. Cells lacking Bad, despite displaying a stronger resistance to apoptosis, were still protected by fragment N against cisplatin-induced death. Fragment N was also able to protect cells from Fas ligand-induced death in conditions where Bad plays no role in apoptosis regulation. Fragment N expression in cells did neither modulate survivin mRNA nor its protein expression. Moreover, the expression of cytoplasmic survivin, known to exert anti-apoptotic actions in cells, still occurred in UV-B-irradiated epidermis of mouse expressing a caspase-3-resistant RasGAP mutant that cannot produce fragment N. Additionally, survivin function in cell cycle progression was not affected by fragment N. These results indicate that, taken individually, mTOR, Bad, or Survivin are not required for fragment N to protect cells from cell death. We conclude that downstream targets of Akt other than mTORC1, Bad, or survivin mediate fragment N-induced protection or that several Akt effectors can compensate for each other to induce the pro-survival fragment N-dependent response.

Relationship between physical fitness and energy balance related behaviors of primary school students in Shaanxi Province / 中国学校卫生

Objective@#To explore the relationship between physical fitness and energy balance related behaviors (EBRBs), and their influencing factors among primary school students, so as to provide a scientific basis for the improvement of physical fitness in primary school students.@*Methods@#By using a random sampling method, a total of 1 451 pupils aged 10-12 were selected from 8 regions of Shannxi Province (Fengxiang, Weibin, Danfeng, Shangzhou, Huazhou, Linwei, Gaoling, Weiyang). According to the total score of physical fitness test, pupils were divided into the excellent good physical fitness group and the pass failed group. The students EBRBs and their influencing factors were investigated cross sectionally, and the Mann-Whitney U test and stepwise linear regression analysis were used to explore the relationship between physical fitness and EBRBs.@*Results@#Breakfasts behavior( r = 0.061 ) and physical activity behavior( r =0.105) among primary school students were positively correlated with total physical scores, with the excellent good physical fitness group (757.56, 768.57)were higher than that of the pass failed group(710.93, 705.67) ( Z= -2.41, -2.69, P <0.05). The screen behavior ( r =-0.065) was negatively correlated with the total physical fitness scores, with the excellent good physical fitness group (681.96) was significantly lower than the pass failed group(747.04) ( Z=2.78, P < 0.05 ). There was no statistically significant correlation between the frequency of beverage behavior and the total score of physical fitness ( P >0.05). The excellent good physical fitness group scored(762.22, 761.19, 758.82, 756.00, 761.20, 755.57, 761.52, 759.48, 781.78) higher than the pass failed group(708.70, 709.19, 710.32, 711.67, 709.19, 711.88, 709.04, 710.01, 699.36) including health beliefs, parental norms and parental role models for breakfast behaviors, and preferences, self efficacy, and self regulation for physical activities, as well as self efficacy, parental role models, family rules for screen behavior ( Z=-2.40, -2.78, -2.35, -2.48, -2.52, -2.27, -2.35, -2.22, -3.65, P <0.05).@*Conclusion@#The physical fitness of primary school students is affected by EBRBs. Parents should model positive behaviors in the family, promote the health behavior of primary school students, improve the physical health of primary school students health.

Relationship between physical fitness and energy balance related behaviors of primary school students in Shaanxi Province / 中国学校卫生

Objective@#To explore the relationship between physical fitness and energy balance related behaviors (EBRBs), and their influencing factors among primary school students, so as to provide a scientific basis for the improvement of physical fitness in primary school students.@*Methods@#By using a random sampling method, a total of 1 451 pupils aged 10-12 were selected from 8 regions of Shannxi Province (Fengxiang, Weibin, Danfeng, Shangzhou, Huazhou, Linwei, Gaoling, Weiyang). According to the total score of physical fitness test, pupils were divided into the excellent good physical fitness group and the pass failed group. The students EBRBs and their influencing factors were investigated cross sectionally, and the Mann-Whitney U test and stepwise linear regression analysis were used to explore the relationship between physical fitness and EBRBs.@*Results@#Breakfasts behavior( r = 0.061 ) and physical activity behavior( r =0.105) among primary school students were positively correlated with total physical scores, with the excellent good physical fitness group (757.56, 768.57)were higher than that of the pass failed group(710.93, 705.67) ( Z= -2.41, -2.69, P <0.05). The screen behavior ( r =-0.065) was negatively correlated with the total physical fitness scores, with the excellent good physical fitness group (681.96) was significantly lower than the pass failed group(747.04) ( Z=2.78, P < 0.05 ). There was no statistically significant correlation between the frequency of beverage behavior and the total score of physical fitness ( P >0.05). The excellent good physical fitness group scored(762.22, 761.19, 758.82, 756.00, 761.20, 755.57, 761.52, 759.48, 781.78) higher than the pass failed group(708.70, 709.19, 710.32, 711.67, 709.19, 711.88, 709.04, 710.01, 699.36) including health beliefs, parental norms and parental role models for breakfast behaviors, and preferences, self efficacy, and self regulation for physical activities, as well as self efficacy, parental role models, family rules for screen behavior ( Z=-2.40, -2.78, -2.35, -2.48, -2.52, -2.27, -2.35, -2.22, -3.65, P <0.05).@*Conclusion@#The physical fitness of primary school students is affected by EBRBs. Parents should model positive behaviors in the family, promote the health behavior of primary school students, improve the physical health of primary school students health.

Relationship between physical fitness and energy balance related behaviors of primary school students in Shaanxi Province / 中国学校卫生

Objective@#To explore the relationship between physical fitness and energy balance related behaviors (EBRBs), and their influencing factors among primary school students, so as to provide a scientific basis for the improvement of physical fitness in primary school students.@*Methods@#By using a random sampling method, a total of 1 451 pupils aged 10-12 were selected from 8 regions of Shannxi Province (Fengxiang, Weibin, Danfeng, Shangzhou, Huazhou, Linwei, Gaoling, Weiyang). According to the total score of physical fitness test, pupils were divided into the excellent good physical fitness group and the pass failed group. The students EBRBs and their influencing factors were investigated cross sectionally, and the Mann-Whitney U test and stepwise linear regression analysis were used to explore the relationship between physical fitness and EBRBs.@*Results@#Breakfasts behavior( r = 0.061 ) and physical activity behavior( r =0.105) among primary school students were positively correlated with total physical scores, with the excellent good physical fitness group (757.56, 768.57)were higher than that of the pass failed group(710.93, 705.67) ( Z= -2.41, -2.69, P <0.05). The screen behavior ( r =-0.065) was negatively correlated with the total physical fitness scores, with the excellent good physical fitness group (681.96) was significantly lower than the pass failed group(747.04) ( Z=2.78, P < 0.05 ). There was no statistically significant correlation between the frequency of beverage behavior and the total score of physical fitness ( P >0.05). The excellent good physical fitness group scored(762.22, 761.19, 758.82, 756.00, 761.20, 755.57, 761.52, 759.48, 781.78) higher than the pass failed group(708.70, 709.19, 710.32, 711.67, 709.19, 711.88, 709.04, 710.01, 699.36) including health beliefs, parental norms and parental role models for breakfast behaviors, and preferences, self efficacy, and self regulation for physical activities, as well as self efficacy, parental role models, family rules for screen behavior ( Z=-2.40, -2.78, -2.35, -2.48, -2.52, -2.27, -2.35, -2.22, -3.65, P <0.05).@*Conclusion@#The physical fitness of primary school students is affected by EBRBs. Parents should model positive behaviors in the family, promote the health behavior of primary school students, improve the physical health of primary school students health.

Caspase-3 protects stressed organs against cell death.

The ability to generate appropriate defense responses is crucial for the survival of an organism exposed to pathogenesis-inducing insults. However, the mechanisms that allow tissues and organs to cope with such stresses are poorly understood. Here we show that caspase-3-knockout mice or caspase inhibitor-treated mice were defective in activating the antiapoptotic Akt kinase in response to various chemical and environmental stresses causing sunburns, cardiomyopathy, or colitis. Defective Akt activation in caspase-3-knockout mice was accompanied by increased cell death and impaired survival in some cases. Mice homozygous for a mutation in RasGAP that prevents its cleavage by caspase-3 exhibited a similar defect in Akt activation, leading to increased apoptosis in stressed organs, marked deterioration of their physiological functions, and stronger disease development. Our results provide evidence for the relevance of caspase-3 as a stress intensity sensor that controls cell fate by either initiating a RasGAP cleavage-dependent cell resistance program or a cell suicide response.

RasGAP-derived fragment N increases the resistance of beta cells towards apoptosis in NOD mice and delays the progression from mild to overt diabetes.

The caspase-3-generated RasGAP N-terminal fragment (fragment N) inhibits apoptosis in a Ras-PI3K-Akt-dependent manner. Fragment N protects various cell types, including insulin-secreting cells, against different types of stresses. Whether fragment N exerts a protective role during the development of type 1 diabetes is however not known. Non-obese diabetic (NOD) mice represent a well-known model for spontaneous development of type 1 diabetes that shares similarities with the diseases encountered in humans. To assess the role of fragment N in type 1 diabetes development, a transgene encoding fragment N under the control of the rat insulin promoter (RIP) was back-crossed into the NOD background creating the NOD-RIPN strain. Despite a mosaic expression of fragment N in the beta cell population of NOD-RIPN mice, islets isolated from these mice were more resistant to apoptosis than control NOD islets. Islet lymphocytic infiltration and occurrence of a mild increase in glycemia developed with the same kinetics in both strains. However, the period of time separating the mild increase in glycemia and overt diabetes was significantly longer in NOD-RIPN mice compared to the control NOD mice. There was also a significant decrease in the number of apoptotic beta cells in situ at 16 weeks of age in the NOD-RIPN mice. Fragment N exerts therefore a protective effect on beta cells within the pro-diabetogenic NOD background and this prevents a fast progression from mild to overt diabetes.

Role of the transcriptional factor C/EBPbeta in free fatty acid-elicited beta-cell failure.

Fatty acids can favour the development of Type 2 diabetes by reducing insulin secretion and inducing apoptosis of pancreatic beta-cells. Here, we show that sustained exposure of the beta-cell line MIN6 or of isolated pancreatic islets to the most abundant circulating fatty acid palmitate increases the level of C/EBPbeta, an insulin transcriptional repressor. In contrast, two unsaturated fatty acids, oleate and linoleate were without effect. The induction of C/EBPbeta elicited by palmitate was prevented by inhibiting the ERK1/2 MAP kinase pathway or by reducing mitochondrial fatty acid oxidation with an inhibitor of Carnitine Palmitoyl Transferase-1. Overexpression of C/EBPbeta mimicked the detrimental effects of palmitate and resulted in a drastic reduction in insulin promoter activity, impairment in the capacity to respond to secretory stimuli and an increase in apoptosis. Our data suggest a potential involvement of C/EBPbeta as mediator of the deleterious effects of unsaturated free fatty acids on beta-cell function.

Glucagon-like peptide-1 protects beta-cells against apoptosis by increasing the activity of an IGF-2/IGF-1 receptor autocrine loop.

OBJECTIVE: The gluco-incretin hormones glucagon-like peptide (GLP)-1 and gastric inhibitory peptide (GIP) protect beta-cells against cytokine-induced apoptosis. Their action is initiated by binding to specific receptors that activate the cAMP signaling pathway, but the downstream events are not fully elucidated. Here we searched for mechanisms that may underlie this protective effect. RESEARCH DESIGN AND METHODS: We performed comparative transcriptomic analysis of islets from control and GipR(-/-);Glp-1-R(-/-) mice, which have increased sensitivity to cytokine-induced apoptosis. We found that IGF-1 receptor expression was markedly reduced in the mutant islets. Because the IGF-1 receptor signaling pathway is known for its antiapoptotic effect, we explored the relationship between gluco-incretin action, IGF-1 receptor expression and signaling, and apoptosis. RESULTS: We found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression. We demonstrated that GLP-1-induced Akt phosphorylation required active secretion, indicating the presence of an autocrine activation mechanism; we showed that activation of IGF-1 receptor signaling was dependent on the secretion of IGF-2. We demonstrated, both in MIN6 cell line and primary beta-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1-induced protection against apoptosis. CONCLUSIONS: An IGF-2/IGF-1 receptor autocrine loop operates in beta-cells. GLP-1 increases its activity by augmenting IGF-1 receptor expression and by stimulating secretion; this mechanism is required for GLP-1-induced protection against apoptosis. These findings may lead to novel ways of preventing beta-cell loss in the pathogenesis of diabetes.

Expression of the NH(2)-terminal fragment of RasGAP in pancreatic beta-cells increases their resistance to stresses and protects mice from diabetes.

OBJECTIVE: Our laboratory has previously established in vitro that a caspase-generated RasGAP NH(2)-terminal moiety, called fragment N, potently protects cells, including insulinomas, from apoptotic stress. We aimed to determine whether fragment N can increase the resistance of pancreatic beta-cells in a physiological setting. RESEARCH DESIGN AND METHODS: A mouse line, called rat insulin promoter (RIP)-N, was generated that bears a transgene containing the rat insulin promoter followed by the cDNA-encoding fragment N. The histology, functionality, and resistance to stress of RIP-N islets were then assessed. RESULTS: Pancreatic beta-cells of RIP-N mice express fragment N, activate Akt, and block nuclear factor kappaB activity without affecting islet cell proliferation or the morphology and cellular composition of islets. Intraperitoneal glucose tolerance tests revealed that RIP-N mice control their glycemia similarly as wild-type mice throughout their lifespan. Moreover, islets isolated from RIP-N mice showed normal glucose-induced insulin secretory capacities. They, however, displayed increased resistance to apoptosis induced by a series of stresses including inflammatory cytokines, fatty acids, and hyperglycemia. RIP-N mice were also protected from multiple low-dose streptozotocin-induced diabetes, and this was associated with reduced in vivo beta-cell apoptosis. CONCLUSIONS: Fragment N efficiently increases the overall resistance of beta-cells to noxious stimuli without interfering with the physiological functions of the cells. Fragment N and the pathway it regulates represent, therefore, a potential target for the development of antidiabetes tools.

Involvement of 4E-BP1 in the protection induced by HDLs on pancreatic beta-cells.

High-density lipoproteins (HDLs) protect pancreatic beta-cells against apoptosis. This property might relate to the increased risk to develop diabetes in patients with low HDL blood levels. However, the mechanisms by which HDLs protect beta-cells are poorly characterized. Here we used a transcriptomic approach to identify genes differentially modulated by HDLs in beta-cells subjected to apoptotic stimuli. The transcript encoding 4E-binding protein (4E-BP)1 was up-regulated by serum starvation, and HDLs blocked this increase. 4E-BP1 inhibits cap-dependent translation in its non- or hypophosphorylated state but it loses this ability when hyperphosphorylated. At the protein level, 4E-BP1 was also up-regulated in response to starvation and IL-1beta, and this was blunted by HDLs. Whereas an ectopic increase of 4E-BP1 expression induced beta-cell death, silencing 4E-BP1 increase with short hairpin RNAs inhibited the apoptotic-inducing capacities of starvation. HDLs can therefore protect beta-cells by blocking 4E-BP1 protein expression, but this is not the sole protective mechanism activated by HDLs. Indeed, HDLs blocked apoptosis induced by endoplasmic reticulum stress with no associated decrease in total 4E-BP1 induction. Although, HDLs favored the phosphorylation, and hence the inactivation of 4E-BP1 in these conditions, this appeared not to be required for HDL protection. Our results indicate that HDLs can protect beta-cells through modulation of 4E-BP1 depending on the type of stress stimuli.

Alterations in microRNA expression contribute to fatty acid-induced pancreatic beta-cell dysfunction.

OBJECTIVE: Visceral obesity and elevated plasma free fatty acids are predisposing factors for type 2 diabetes. Chronic exposure to these lipids is detrimental for pancreatic beta-cells, resulting in reduced insulin content, defective insulin secretion, and apoptosis. We investigated the involvement in this phenomenon of microRNAs (miRNAs), a class of noncoding RNAs regulating gene expression by sequence-specific inhibition of mRNA translation. RESEARCH DESIGN AND METHODS: We analyzed miRNA expression in insulin-secreting cell lines or pancreatic islets exposed to palmitate for 3 days and in islets from diabetic db/db mice. We studied the signaling pathways triggering the changes in miRNA expression and determined the impact of the miRNAs affected by palmitate on insulin secretion and apoptosis. RESULTS: Prolonged exposure of the beta-cell line MIN6B1 and pancreatic islets to palmitate causes a time- and dose-dependent increase of miR34a and miR146. Elevated levels of these miRNAs are also observed in islets of diabetic db/db mice. miR34a rise is linked to activation of p53 and results in sensitization to apoptosis and impaired nutrient-induced secretion. The latter effect is associated with inhibition of the expression of vesicle-associated membrane protein 2, a key player in beta-cell exocytosis. Higher miR146 levels do not affect the capacity to release insulin but contribute to increased apoptosis. Treatment with oligonucleotides that block miR34a or miR146 activity partially protects palmitate-treated cells from apoptosis but is insufficient to restore normal secretion. CONCLUSIONS: Our findings suggest that at least part of the detrimental effects of palmitate on beta-cells is caused by alterations in the level of specific miRNAs.

Exendin-4 protects beta-cells from interleukin-1 beta-induced apoptosis by interfering with the c-Jun NH2-terminal kinase pathway.

OBJECTIVE: The pro-inflammatory cytokine interleukin-1 beta (IL-1 beta) generates pancreatic beta-cells apoptosis mainly through activation of the c-Jun NH(2)-terminal kinase (JNK) pathway. This study was designed to investigate whether the long-acting agonist of the hormone glucagon-like peptide 1 (GLP-1) receptor exendin-4 (ex-4), which mediates protective effects against cytokine-induced beta-cell apoptosis, could interfere with the JNK pathway. RESEARCH DESIGN AND METHODS: Isolated human, rat, and mouse islets and the rat insulin-secreting INS-1E cells were incubated with ex-4 in the presence or absence of IL-1 beta. JNK activity was assessed by solid-phase JNK kinase assay and quantification of c-Jun expression. Cell apoptosis was determined by scoring cells displaying pycnotic nuclei. RESULTS: Ex-4 inhibited induction of the JNK pathway elicited by IL-1 beta. This effect was mimicked with the use of cAMP-raising agents isobutylmethylxanthine and forskolin and required activation of the protein kinase A. Inhibition of the JNK pathway by ex-4 or IBMX and forskolin was concomitant with a rise in the levels of islet-brain 1 (IB1), a potent blocker of the stress-induced JNK pathway. In fact, ex-4 as well as IBMX and forskolin induced expression of IB1 at the promoter level through cAMP response element binding transcription factor 1. Suppression of IB1 levels with the use of RNA interference strategy impaired the protective effects of ex-4 against apoptosis induced by IL-1 beta. CONCLUSIONS: The data establish the requirement of IB1 in the protective action of ex-4 against apoptosis elicited by IL-1 beta and highlight the GLP-1 mimetics as new potent inhibitors of the JNK signaling induced by cytokines.

Expression of an uncleavable N-terminal RasGAP fragment in insulin-secreting cells increases their resistance toward apoptotic stimuli without affecting their glucose-induced insulin secretion.

Apoptosis of pancreatic beta cells is implicated in the onset of type 1 and type 2 diabetes. Consequently, strategies aimed at increasing the resistance of beta cells toward apoptosis could be beneficial in the treatment of diabetes. RasGAP, a regulator of Ras and Rho GTPases, is an atypical caspase substrate, since it inhibits, rather than favors, apoptosis when it is partially cleaved by caspase-3 at position 455. The antiapoptotic signal generated by the partial processing of RasGAP is mediated by the N-terminal fragment (fragment N) in a Ras-phosphatidylinositol 3-kinase-Akt-dependent, but NF-kappaB-independent, manner. Further cleavage of fragment N at position 157 abrogates its antiapoptotic properties. Here we demonstrate that an uncleavable form of fragment N activates Akt, represses NF-kappaB activity, and protects the conditionally immortalized pancreatic insulinoma betaTC-tet cell line against various insults, including exposure to genotoxins, trophic support withdrawal, and incubation with inflammatory cytokines. Fragment N also induced Akt activity and protection against cytokine-induced apoptosis in primary pancreatic islet cells. Fragment N did not alter insulin cell content and insulin secretion in response to glucose. These data indicate that fragment N protects beta cells without affecting their function. The pathways regulated by fragment N are therefore promising targets for antidiabetogenic therapy.

The RasGAP N-terminal fragment generated by caspase cleavage protects cells in a Ras/PI3K/Akt-dependent manner that does not rely on NFkappa B activation.

RasGAP, a regulator of Ras GTPase family members, is cleaved at low levels of caspase activity into an N-terminal fragment (fragment N) that generates potent anti-apoptotic signals. At higher levels of caspase activity, fragment N is further cleaved into two fragments that strongly potentiate apoptosis. RasGAP could thus function as a sensor of caspase activity to determine whether a cell should survive or not. Here we show that fragment N protects cells by activating the Ras-PI3K-Akt pathway. Surprisingly, even though nuclear factor kappaB (NFkappaB) can be activated by Akt, it plays no role in the anti-apoptotic functions of fragment N. This indicates that Akt effectors are differentially regulated when fragment N is generated.