Weight loss effect of glucagon-like peptide-1 mimetics on obese/overweight adults without diabetes: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) benefit weight maintenance for diabetic patients. We performed a systematic review to evaluate its weight loss effect on obese/overweight patients without diabetes in randomized controlled trials (RCTs).

METHODS

Literature updated to May 5, 2014 from Cochrane Library, MEDLINE, EMBASE and reference lists from relevant articles were identified. RCTs with GLP-1 mimetics treating obese/overweight adults without diabetes for at least 12 weeks were assessed. Studies lacking primary measurements were excluded. Three authors extracted data independently. Either fixed-effect or random-effect models were used to calculate weighted mean differences (WMDs), combined relative risks (RR) and 95% confidence interval (CI) in meta-analyses. Intertrial heterogeneity across studies was examined by I(2) and Q statistics.

RESULTS

A total of 1345 individuals retrieved from eight studies were involved and all included trials were of mild-to-moderate bias risks. Participants in GLP-1RA groups achieved a larger weight loss than those in control groups (-2.85 kg, 95%CI -3.55 to -2.14), and liraglutide may work in a dose-dependent fashion. GLP-1RAs also reduced body mass index (BMI) and waist circumferences (WC) and benefited systolic blood pressure and triglyceride regulation. But GLP-1RAs were associated with increased nausea and vomiting events.

CONCLUSIONS

GLP-1 mimetics induce a weight loss in addition to BMI and WC reduction in obese/overweight adults without diabetes. Further long-term randomized trials and basic studies are required to investigate the mechanisms.

Effects of p-chlorophenoxyisobutyric acid, arabinogalactan, and activated charcoal on microspore embryogenesis in kale

To improve embryogenesis in microspore cultures of kale (Brassica oleracea L. var. acephala DC.), 6-benzylaminopurine (6-BA), naphthaleneacetic acid (NAA), arabinogalactan (AG), p-chlorophenoxyisobutyric acid (PCIB), and activated charcoal (AC) were added to the medium using four varieties of kale. The results showed that the addition of AG (0.1-0.2 g/L), AC (0.1-0.2 g/L) or a combination of 6-BA (0.1-0.2 mg/L) and NAA (0.1-0.2 mg/L) promoted embryo-genesis. Adding 40 μM PCIB or a combination of 40 μM PCIB and 0.2 g/L AC to NLN-13 medium at pH 5.8 effectively enhanced embryogenesis. Treatment with a combination of 40 μM PCIB and 10 mg/L AG gave the highest rate of embryonic induction, especially in genotype "Y007," which showed a twelve-fold increase in yield.

Serum immunoglobulin E level and its impact on the pregnancy outcome associated with fetal growth restriction: a prospective cohort study

We evaluated the relationship between total serum immunoglobulin E (IgE) levels and pregnancy outcome in a prospective cohort study focusing on fetal growth restriction (FGR). Sixty women with FGR and twenty with normal singleton pregnancy were enrolled during their third trimester. Infants were followed up for 6 months. Blood samples were obtained from pregnant women during the third trimester; cord blood samples were also taken. Six months after birth, blood samples were obtained from infants. Demographic and baseline characteristics were compared between groups. Birth weight, length and head circumference of neonates in the FGR group were lower than those in the control group. Total serum IgE level was significantly increased in third-trimester pregnant women with FGR compared with normal group (P < 0.05). However, this trend was not observed in the cord blood at birth or peripheral blood of 6-month-old infants. The prevalence of atopic eczema between the 2 groups was similar. Linear regression analysis revealed that the IgE level in the third trimester was negatively correlated with birth weight (P < 0.05). Higher serum IgE level in the cord blood was significantly associated with an increased risk of being small for gestational age (P < 0.05). In conclusion, IgE levels in the third trimester of pregnancy and cord blood are strongly related to birth outcomes of FGR.

Orthotopic models of pediatric brain tumors in zebrafish

High-throughput screens (HTS) of compound toxicity against cancer cells can identify thousands of potential new drug-leads. But only limited numbers of these compounds can progress to expensive and labor-intensive efficacy studies in mice, creating a 'bottle neck' in the drug development pipeline. Approaches that triage drug-leads for further study are greatly needed. Here we provide an intermediary platform between HTS and mice by adapting mouse models of pediatric brain tumors to grow as orthotopic xenografts in the brains of zebrafish. Freshly isolated mouse ependymoma, glioma and choroid plexus carcinoma cells expressing red fluorescence protein were conditioned to grow at 34 °C. Conditioned tumor cells were then transplanted orthotopically into the brains of zebrafish acclimatized to ambient temperatures of 34 °C. Live in vivo fluorescence imaging identified robust, quantifiable and reproducible brain tumor growth as well as spinal metastasis in zebrafish. All tumor xenografts in zebrafish retained the histological characteristics of the corresponding parent mouse tumor and efficiently recruited fish endothelial cells to form a tumor vasculature. Finally, by treating zebrafish harboring ERBB2-driven gliomas with an appropriate cytotoxic chemotherapy (5-fluorouracil) or tyrosine kinase inhibitor (erlotinib), we show that these models can effectively assess drug efficacy. Our data demonstrate, for the first time, that mouse brain tumors can grow orthotopically in fish and serve as a platform to study drug efficacy. As large cohorts of brain tumor-bearing zebrafish can be generated rapidly and inexpensively, these models may serve as a powerful tool to triage drug-leads from HTS for formal efficacy testing in mice.

Acarbose monotherapy and weight loss in Eastern and Western populations with hyperglycaemia: an ethnicity-specific meta-analysis

OBJECTIVE

To demonstrate if weight loss achieved with acarbose in individuals with hyperglycaemia differs between Eastern and Western populations.

METHODS

Databases and reference lists of clinical trials on acarbose were searched. Eligible studies were randomised controlled trials of acarbose monotherapy in populations with hyperglycaemia of more than 12-week duration that provided data on body weight (BW) or body mass index (BMI).

RESULTS

A total of 34 trials (6082 participants) were included. The effect of acarbose on BW was superior to that of placebo [weighted mean difference (WMD) = -0.52, 95% confidence interval (CI) -0.78 to -0.25], nateglinide (WMD = -1.33, 95% CI -1.51 to -0.75) and metformin (WMD = -0.67, 95% CI -1.14 to -0.20). Compared with placebo, there was a significantly greater weight loss of 0.92 kg (p < 0.05, I(2)  = 88.8%) with acarbose in Eastern populations (WMD = -1.20, 95% CI -1.51 to -0.75) than that in Western populations (WMD = -0.28, 95% CI -0.59 to 0.03). Across all studies, the acarbose group achieved a significantly larger absolute weight loss of (change from baseline) 1.35 kg (p < 0.05, I(2)  = 94.3%) in Eastern populations (WMD = -2.26, 95% CI -2.70 to -1.81) than in Western populations (WMD = -0.91, 95% CI -1.36 to -0.47). Nevertheless, the possible risk of bias in Eastern studies may influence the results.

CONCLUSION

The effect of acarbose on weight loss seems to be more pronounced in Eastern than in Western populations with hyperglycaemia, and is superior to that of placebo, nateglinide and metformin across both ethnicities.

Increased acyl ghrelin but decreased total ghrelin and unacyl ghrelin in Chinese Han people with impaired fasting glucose combined with impaired glucose tolerance

We assessed the plasma acyl ghrelin (AG), unacyl ghrelin (UAG), and total ghrelin (TGhr) levels in Chinese adults with pre-diabetes and newly diagnosed diabetes mellitus (NDDM) after an oral glucose tolerance test (OGTT), and abdominal subcutaneous fat area and visceral fat area (VFA) were measured. Fasting AG level was increased in the impaired fasting glucose (IFG) combined with impaired glucose tolerance (IFG+IGT) and NDDM groups. AG, UAG, and TGhr levels were significantly decreased post-OGTT, and the decrements of 30-min AG, UAG, and TGhr post-OGTT were not significantly different among groups. UAG and TGhr levels did not differ significantly among the normal glucose tolerance (NGT), IFG and NDDM groups, but they decreased obviously in the IFG+IGT and impaired glucose tolerance (IGT) groups. The NDDM group had larger VFA than the NGT, IGT, and IFG+IGT groups, even after adjustment for height, it was still larger than the NGT group. The factors such as dyslipidemia and obesity which are prone to develop insulin resistance (IR) and decrease insulin sensitivity (IS) were negatively correlated with UAG and TGhr, positively with AG/UAG, while no correlations with AG. In terms of evaluating IS and IR, AG/UAG ratio may be superior in AG concentration. Our findings suggest that relative sufficiency of AG, the deficiency of TGhr and UAG are already present in IFG+IGT patients. We speculate that there is UAG resistance in severe hyperglycemia (diabetic state), which could produce elevated TGhr and UAG compared to IFG+IGT group. In the development of T2D, increase of VFA could be the initiating factor, leading elevated AG, reduced UAG, IR, decreased IS, and finally hyperglycemia.

Gene signatures of drug resistance predict patient survival in colorectal cancer

Different combinations of 5-fluorouracil (5-FU), oxaliplatin, irinotecan and other newly developed agents have been used to treat colorectal cancer. Despite the advent of new treatment regimens, the 5-year survival rate for metastatic colorectal cancer remains low (~10%). Knowing the drug sensitivity of a given tumor for a particular agent could significantly impact decision making and treatment planning. Biomarkers are proven to be successful in characterizing patients into different response groups. Using survival prediction analysis, we have identified three independent gene signatures, which are associated with sensitivity of colorectal cancer cells to 5-FU, oxaliplatin or irinotecan. On the basis of the three gene signatures, three score systems were developed to stratify patients from sensitive to resistance. These score systems exhibited robustness in stratify patients in two independent clinical studies. Patients with high scores in all three drugs exhibited the lowest survival.

The MTMR9 rs2293855 polymorphism is associated with glucose tolerance, insulin secretion, insulin sensitivity and increased risk of prediabetes

BACKGROUND

Polymorphism of rs2293855 in gene MTMR9 has been associated with obesity and metabolic syndrome. We aim to study the association of rs2293855 with type 2 diabetes mellitus (T2DM) intermediate phenotypes in a Han Chinese population.

METHODS

The polymorphism was genotyped in 838 Han Chinese individuals using Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS); all participants underwent a 75 g oral glucose tolerance test (OGTT); associations between the polymorphism and glucose tolerance, indices of insulin secretion and indices of insulin sensitivity were analyzed.

RESULTS

The frequency of genotypes and alleles differed significantly between normal glucose tolerance and prediabetes (P=0.043 and P=0.009, respectively). The GG homozygous presented higher fasting plasma glucose (P=0.009), higher 2-hour plasma glucose (P=0.024) and higher glucose area under the curve (AUC, P=0.01). Moreover, the G allele of rs2293855 was associated with glucose intolerance (fasting glucose, P=0.012; glucose AUC, P=0.006; 2-h glucose, P=0.024); it is also associated with decreased indices of insulin sensitivity (fasting insulin, P=0.043; insulin sensitivity index composite, P=0.009; homeostasis model assessment of insulin resistance, HOMA-IR, P=0.008) and decreased indices of insulin secretion (HOMA of beta cell function, HOMA-B, P=0.028; insulinogenic index, P=0.003). In addition, the minor allele G was also associated with increased risk of prediabetes (OR=1.463, 95%CI: 1.066-2.009, P=0.018).

CONCLUSIONS

Polymorphism of rs2293855 in MTMR9 is associated with measures of glucose tolerance, indices of insulin secretion and indices of insulin sensitivity. We also suggest that allele G is likely to increase the risk of prediabetes by influencing both insulin secretion and insulin sensitivity.

Huwe1 as a therapeutic target for neural injury

The ubiquitin-proteasome system (UPS) regulates many cellular processes, including protein stability, cell cycle control, DNA repair, transcription, signal transduction, and protein trafficking. In fact, UPS plays a key role in various stress conditions such as ischemia, glutamate toxicity, Alzheimer's disease, and Parkinson's disease. Huwe1, a homologous to E6-AP carboxy terminus (HECT) domain ubiquitin ligase, is now being regarded as a vital protein involved in neural stem cell differentiation, adult neurogenesis, and the DNA damage response pathway. In response to DNA damage, Huwe1 may have a dual function in arresting DNA replication and in ending checkpoint signaling. The proliferation and differentiation of neural stem cells regulated by Huwe1-mediated Notch signaling could also play an important role in neural protection following neural injury. Considering Huwe1 is required for neural precursor survival and the regulation of the DNA damage response pathway, there is growing evidence and considerable hope that Huwe1 might be a therapeutic target for neural injury.

Systematic review and meta-analysis of robotic surgery compared with conventional laparoscopic and open resections for gastric carcinoma

BACKGROUND

Robot-assisted gastrectomy (RAG) has been developed in the hope of improving surgical quality and overcoming the limitations of conventional laparoscopically assisted gastrectomy (LAG) and open gastrectomy (OG) for gastric cancer. The aim of this study was to determine the extent of evidence in support of these ideals.

METHODS

A systematic review of the three operation types (RAG, LAG and OG) was carried out to evaluate short-term outcomes including duration of operation, retrieved lymph nodes, estimated blood loss, resection margin status, technical postoperative complications and hospital stay.

RESULTS

Nine non-randomized observational clinical studies involving 7200 patients satisfied the eligibility criteria. RAG was associated with longer operating times than LAG and OG (weighted mean difference 61.99 and 65.73 min respectively; P ≤ 0.001). The number of retrieved lymph nodes and the resection margin length in RAG were comparable with those of LAG and OG. Estimated blood loss as significantly less in RAG than in OG (P = 0.002), but not LAG. Mean hospital stay for RAG was similar to that for LAG (P = 0.14). In contrast, hospital stay was significantly shorter, by a mean of 2.18 days, for RAG compared with OG (P < 0.001). Postoperative complications were similar for all three operative approaches.

CONCLUSION

Short-term oncological outcomes of RAG were comparable with those of the other approaches. LAG was a shorter procedure and less expensive than RAG. Future studies involving RAG should focus on minimizing duration of operation and reducing cost.

Nanogap based graphene coated AFM tips with high spatial resolution, conductivity and durability

After one decade of analyzing the intrinsic properties of graphene, interest into the development of graphene-based devices and micro electromechanical systems is increasing. Here, we fabricate graphene-coated atomic force microscope tips by growing the graphene on copper foil and transferring it onto the apex of a commercially available AFM tip. The resulting tip exhibits surprising enhanced resolution in nanoscale electrical measurements. By means of topographic AFM maps and statistical analyses we determine that this superior performance may be related to the presence of a nanogap between the graphene and the tip apex, which reduces the tip radius and tip-sample contact area. In addition, the graphene-coated tips show a low tip-sample interaction, high conductivity and long life times. The novel fabrication-friendly tip could improve the quality and reliability of AFM experiments, while reducing the cost of AFM-based research.

Activation of PPARβ/δ protects pancreatic β cells from palmitate-induced apoptosis by upregulating the expression of GLP-1 receptor

We previously showed that activated peroxisome proliferator-activated receptor (PPAR)β/δ can protect pancreatic β cells against lipotoxic apoptosis. However, the molecular mechanism remained unclear. Glucagon-like peptide-1 receptor (GLP-1R) has been reported to exhibit a protective effect against lipotoxic apoptosis in pancreatic β cells. In the present study, we aimed to investigate the underlying molecular mechanisms that PPARβ/δ activation suppressed apoptosis and improved β cell function impaired by fatty acids, focusing on contribution of GLP-1R. Isolated rat islets and rat insulin-secreting INS-1 cells were treated with the PPARβ/δ agonist GW501516 (GW) in the presence or absence of palmitate (PA) and transfected with siRNA for PPARβ/δ or treated with the PPARβ/δ antagonist GSK0660. Apoptosis was assessed by DNA fragmentation, Hoechst 33342 staining and flow cytometry. GLP-1R expression in INS-1 cells and islets was assayed by immunoblotting, quantitative PCR (qPCR) and immunofluorescence staining. SREBP-1c, Caveolin-1, Akt, Bcl-2, Bcl-xl and caspase-3 expression was measured using immunoblotting and qPCR. Our results showed that PPARβ/δ activation decreased apoptosis in β cells and robustly stimulated GLP-1R expression under lipotoxic conditions. GW enhanced glucose-stimulated insulin secretion (GSIS) impaired by PA through stimulation of GLP-1R expression in β cells. Moreover, SREBP-1c/Caveolin-1 signaling was involved in PPARβ/δ-regulated GLP-1R expression. Finally, GW exerted anti-apoptotic effects via interfering with GLP-1R-dependent Akt/Bcl-2 and Bcl-xl/caspase-3 signaling pathways. Our study suggested that the anti-apoptotic action of GW may involve its transcriptional regulation of GLP-1R, and PPARβ/δ activation may represent a new therapeutic method for protecting pancreatic β cells from lipotoxicity.

Immune tolerance of skin allograft transplantation induced by immature dendritic cells of a third party carrying donor antigens in mice

BACKGROUND

Dendritic cells (DCs) are the most powerful antigen-presenting cells in the body. Immature DCs (imDCs) can induce transplantation tolerance. In this study, using a mouse model of skin transplantation. We explored the antigen uptake by imDCs, changes in phenotype and function after antigen loading, as well as survival of skin grafts.

METHODS

Mononuclear cells from C57BL/6 mice mixed with a tritiated leucine ([(3)H]Leu) antigen supernate were incubated with Kunming mice imDC and mature DCs. We recorded the expressions of surface molecules that were detected using flow cytometry, mixed lymphocyte reactions, mean survival times, and postoperative morphological changes in skin grafts.

RESULTS

After the addition of allogeneic antigen supernate, the counts per minute of imDCs were significantly higher than those of mature DCs. The expression rates of I(A)/I(E) and CD80 significantly increased on the cell surface of imDCs. The counts per minute of imDCs in mixed lymphocyte reactions in the presence of allogeneic antigens was significantly higher than those of controls. Comparing mean survival times with controls, skin grafts were significantly longer in the imDCs groups from donors or from a third party carrying donor antigens.

CONCLUSIONS

ImDCs display a strong antigen uptake, gradually maturing in terms of phenotype and function after loading. Complementary application of cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin blocks the immune response of imDCs. Both imDCs from the third party carrying donor antigens and those from the donor strain can establish antigen-specific immune tolerance to allogeneic skin grafts.

β-Catenin and AKT are promising targets for combination therapy in acute myeloid leukemia

In this study, we confirmed that combining HHT with ACR can result in synergistic cytotoxicity to AML cells in vitro and in vivo. Combining HHT and ACR simultaneously inhibited PI3K/AKT and WNT/β-catenin signaling in AML cells. Significant increases in growth inhibition and apoptosis were induced by an AKT inhibitor when the WNT3A gene of THP-1 cells was silenced. HHT+ACR could synergistically induce the apoptosis of CD34(+)/CD38(-) primary AML cells. These results highlight β-catenin and AKT are promising targets for combination therapy for AML.

Associations of the PTEN -9C>G polymorphism with insulin sensitivity and central obesity in Chinese

BACKGROUND

Phosphatase and tensin homolog on chromosome 10 gene (PTEN) is known as a tumor-suppressor gene. Previous studies demonstrated that PTEN dysfunction affects the function of insulin. However, investigations of PTEN single nucleotide polymorphisms (SNPs) and IR-related disease associations are limited. The aim of the present study was to investigate whether its polymorphism could be involved in the risk of metabolic syndrome (MetS).

METHODS

The genotype frequency of PTEN -9C>G polymorphism was determined by using a Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) method in 530 subjects with MetS and 202 healthy control subjects of the Han Ethnic Chinese population in a case-control analysis.

RESULTS

The PTEN -9C>G polymorphism was not associated with MetS or its hyperglycemia, hypertension and hypertriglyceridemia components. In the control individuals aged <60 years or ≥60 years, the CG genotype individuals had lower insulin sensitivity than CC individuals (P<0.05). In the <60-year-old MetS group and normal glucose tolerance (NGT) subgroup, the CG individuals had lower insulin sensitivity and higher waist circumference (WC) and waist-height-ratio (WHtR) than CC individuals (P<0.05). Multiple linear regression analysis showed that the PTEN polymorphism (P=0.001) contributed independently to 4.2% (adjusted R(2)) of insulin sensitivity variance (estimated by Matsuda ISI), while age (P=0.004), gender (P=0.000) and the PTEN polymorphism (P=0.032) contributed independently to 5.6% (adjusted R(2)) of WHtR variance.

CONCLUSIONS

The CG genotype of PTEN -9C>G polymorphism was not associated with MetS and some of its components as well. However, it may not only decrease insulin sensitivity in the healthy control and MetS in pre-elderly or NGT subjects, but may also increase the risk of central obesity among these MetS individuals.

Performance improvement of GaN-based LEDs with step stage InGaN/GaN strain relief layers in GaN-based blue LEDs

The performance of nitride-based LEDs was improved by inserting dual stage and step stage InGaN/GaN strain relief layer (SRL) between the active layer and n-GaN template. The influences of step stage InGaN/GaN SRL on the structure, electrical and optical characteristics of GaN-based LEDs were investigated. The analysis of strain effect on recombination rate based k·p method indicated 12.5% reduction of strain in InGaN/GaN MQWs by inserting SRL with step stage InGaN/GaN structures. The surface morphology was improved and a smaller blue shift in the electroluminescence (EL) spectral with increasing injection current was observed for LEDs with step stage SRL compared with conventional LEDs. The output power of LEDs operating at 20 mA was about 15.3 mW, increased by more than 108% by using step stage InGaN/GaN SRL, which shows great potential of such InGaN/GaN SRL in modulating InGaN/GaN MQWs optical properties based on its strain relief function.

Blocking p55PIK signaling inhibits proliferation and induces differentiation of leukemia cells

p55PIK, a regulatory subunit of phosphatidylinositol 3-kinases, promotes cell cycle progression by interacting with cell cycle modulators such as retinoblastoma protein (Rb) via its unique amino-terminal 24 amino-acid residue (N24). Overexpression of N24 specifically inhibits these interactions and leads to cell cycle arrest. Herein, we describe the generation of a fusion protein (Tat transactivator protein (TAT)-N24) that contains the protein transduction domain and N24, and examined its effects on the proliferation and differentiation of leukemia cells. TAT-N24 not only blocks cell proliferation but remarkably induces differentiation of leukemia cells in vitro and in vivo. Systemically administered TAT-N24 also significantly decreases growth of leukemia cell tumors in animal models. Furthermore, overexpression of p55PIK in leukemia cells leads to increased proliferation; however, TAT-N24 blocks this effect and concomitantly induces differentiation. There is significant upregulation of p55PIK mRNA and protein expression in leukemia cells from patients. TAT-N24 inhibits cell cycle progression and induces differentiation of bone marrow cells derived from patients with several different types of leukemia. These results show that cell-permeable N24 peptide induces leukemia cell differentiation and suggest that p55PIK may be a novel drug target for the treatment of hematopoetic malignancies.

PPARδ Activation Rescues Pancreatic β-Cell Line INS-1E from Palmitate-Induced Endoplasmic Reticulum Stress through Enhanced Fatty Acid Oxidation

One of the key factors responsible for the development of type 2 diabetes is the loss of functional pancreatic β cells. This occurs due to a chronic exposure to a high fatty acid environment. ER stress is caused by an accumulation of irreversible misfold or unfold protein: these trigger the death of functional pancreatic β cells. PPARδ is an orphan nuclear receptor. It plays a pivotal role in regulating the metabolism of dietary lipids and fats. However, the correlation between PPARδ of fatty acids and ER stress of pancreatic β cells is not quite clear till date. Here, we show that PPARδ attenuates palmitate-induced ER stress of pancreatic β cells. On the other hand, PPARδ agonist inhibits both abnormal changes in ER structure and activation of signaling cascade, which is downstream ER stress. Further, we illustrate that PPARδ attenuates palmitate-induced ER stress by promoting fatty acid oxidation through treatment with etomoxir, an inhibitor of fatty acid oxidation. It dramatically abolishes PPARδ-mediated inhibition of ER stress. Finally, we show that PPARδ could protect pancreatic β cells from palmitate-induced cell death and dysfunction of insulin secretion. Our work elucidates the protective effect of PPARδ on the fatty-acid-induced toxicity of pancreatic β cells.

Activation of PPARδ up-regulates the expression of insulin gene transcription factor MafA and ameliorates glucose-induced insulin secretion impaired by palmitate

PPARδ, a member of the peroxisome proliferator-activated receptor superfamily, plays a key role in the transcriptional regulation of genes involved in cellular lipid and energy metabolism. Therefore, PPARδ may represent a new target for the treatment of obesity, hyperlipidemia, and type 2 diabetes. MafA is a β-cell-specific and glucose-regulated transcriptional activator for insulin gene expression and plays a crucial role in pancreas development, β-cell differentiation as well as maintenance of β-cell function. However, little is known about how PPARδ regulates MafA and ameliorates glucose-stimulated insulin secretion impaired by free fatty acids (FFA). In the present study, we evaluated the basal insulin secretion (BIS), glucose-stimulated insulin secretion (GSIS), and insulin secretion index (ISI) of INS-1E cells that were cultured in media supplemented with or without 0.5 mM palmitate and treated with or without a PPARδ agonist (GW501516) or PPARδ siRNA. The expression of MafA, glucose transportor-2 (GLUT2), and insulin was found to be up-regulated in cells treated with GW501516. Finally, analysis of the level of JNK phosphorylation revealed that activated PPARδ could inhibit the activation of JNK and increase the expression of MafA. Accordingly, the insulin secretion dysfunction in lipotoxic INS-1E cells was improved. Collectively, these results demonstrate that activation of PPARδ improves insulin secretion impaired by palmitate and plays a role in the JNK-MafA-GLUT2 pathway.

An evolutionary test of the isoform switching hypothesis of functional progesterone withdrawal for parturition: humans have a weaker repressive effect of PR-A than mice

BACKGROUND

A decrease in maternal serum progesterone (P4) concentrations precedes the onset of labor in most placental mammals. Humans differ by maintaining high levels of P4 throughout birth. Parturition in humans probably includes mechanisms that undercut the pregnancy sustaining function of P4. One attractive hypothesis is the isoform switching hypothesis (ISH). ISH is supported by in vitro evidence that progesterone receptor isoform A (PR-A) inhibits PR-B and that the PR-A/PR-B ratio increases towards term.

MATERIALS AND METHODS

Here, we test the hypothesis that isoform switching is an adaptation to high levels of P4 at term, predicting that, in humans, PR-A mediated repression of PR-B is stronger than in mouse. We use reporter assays with human and mouse PRs to detect species differences in the repressive effects of PR-A.

RESULTS

We found that human PR-B is less sensitive to repression by human PR-A than mouse PR-B, contrary to our prediction. The difference between human and mouse PR-B sensitivity is most pronounced at PR-A/PR-B ratios typical for the preterm myometrium.

CONCLUSIONS

Our results are inconsistent with the ISH. We speculate that, instead, the lower sensitivity of human PR-B to PR-A may be relevant for the maintenance of pregnancy at high progesterone levels and increasing PR-A concentrations towards term.