Phosphatidylinositol 3-kinase redistribution is associated with skeletal muscle insulin resistance in gestational diabetes mellitus

Effects of Gestational Diabetes Mellitus and Selenium Deficiency on the Offspring Growth and Blood Glucose Mechanisms of C57BL/6J Mice

This study aimed to explore the effects and mechanisms of maternal gestational diabetes mellitus (GDM) and selenium (Se) deficiency on the growth and glucose metabolism of offspring. Female C57BL/6J mice were divided into four groups as follows: a control group, a GDM group, a Se deficiency group, and a GDM with Se deficiency group. GDM animal models were established via S961. Pregnant mice fed their offspring until weaning. Then, offspring continued to be fed with a basic diet until adulthood. Body weight and fasting blood glucose were measured weekly. Se content, oxidative stress indicators, and the protein expression of the PI3K/Akt signaling pathway were detected. GDM increased susceptibility to obesity in lactating offspring, with gender differences observed in adult offspring. The effect of Se deficiency on SOD activity only appeared in female offspring during adulthood but was shown in male offspring during weaning though it disappeared during adulthood. GDM and Se deficiency increased the risk of abnormal glucose metabolism in female offspring from weaning to adulthood but gradually decreased in male offspring. The influence on the expression of PI3K/Akt signaling pathway-related proteins showed the same trend. GDM and Se deficiency affected the growth and glucose metabolism of offspring through oxidative stress and PI3K/Akt signaling pathway-related proteins, and gender differences existed.

Mechanisms by which smoothelin-like protein 1 reverses insulin resistance in myotubules and mice

Insulin resistance (InR) is manifested in skeletal muscle by decreased insulin-stimulated glucose uptake due to impaired insulin signaling and multiple post-receptor intracellular defects. Chronic glucose-induced insulin resistance leads to the activation of Ser/Thr kinases and elevated phosphorylation of insulin receptor substrate 1 (IRS1) on Ser residues. Phosphorylation of IRS1 triggers the dissociation of IRS1 and its downstream effector, phosphatidylinositol 3-kinase. In the present study, we provide evidence for the insulin-sensitizing role of smoothelin-like protein 1 (SMTNL1) that is a ligand-dependent co-regulator of steroid receptors, predominantly the progesterone receptor. SMTNL1 was transiently overexpressed in insulin-resistant C2C12 myotubes. A proteome profiler array revealed that mTOR and Ser/Thr kinases were SMTNL1-dependent signaling pathways. In the presence of progesterone, overexpression was coupled to decreased Ser phosphorylation of IRS1 at Ser307, Ser318, and Ser612 residues. SMTNL1 also induced the expression and activity of the p85 subunit of PI3K. SMTNL1 regulated the expression of PKCε, which phosphorylates IRS1 at Ser318 residue. SMTNL1 also regulated ERK1/2 and JNK, which phosphorylate IRS1 at Ser612 and Ser307, respectively. Real-time metabolic measurements of oxygen consumption rate and extracellular acidification rate revealed that SMTNL1 improved glycolysis and promoted the utilization of alternative carbon fuels. SMTNL1 also rescued the mitochondrial respiration defect induced by chronic insulin exposure. Collectively, SMTNL1 plays a crucial role in maintaining the physiological ratio of Tyr/Ser IRS1 phosphorylation and attenuates the insulin-signaling cascade that contributes to impaired glucose disposal, which makes it a potential therapeutic target for improving InR.

The association between serum selenium level and gestational diabetes mellitus: A systematic review and meta-analysis

BACKGROUND

The relationship between serum selenium level and gestational diabetes mellitus (GDM) is controversial. The purpose is to update and summarize previous studies to understand the relationship in more detail.

METHODS

PubMed, The Cochrane Library, EMBASE, Web of science, CNKI, WANFANG DATA and Cqvip were searched for studies published up to 3 September 2021. The random-effects model was used to measure the combined estimation. The overall effect was reported in a standard mean difference (SMD) and 95% confidence interval (95% CI). All data were analysed by Review Manager 5.4.

RESULTS

Twenty-seven studies involving 1588 patients with GDM and 2450 healthy pregnant women contributed to this meta-analysis. Selenium level was significantly lower in women with GDM than those without GDM (SMD = -1.29; 95% CI: -1.60 to -0.97, p < 0.00001). Subgroup analyses showed that such trend was consistent within the non-European population (Asia: SMD = -1.44; 95% CI: -1.79 to -1.08, p < 0.00001; Africa: SMD = -2.62; 95% CI: -4.50 to -0.74, p = 0.006) and in the second and third trimesters (the second trimester: SMD = -1.41; 95% CI: -1.82 to -0.99, p < 0.00001; the third trimester: SMD = -1.54; 95% CI: -2.09 to -0.98, p < 0.00001), but not within the European population (SMD = -0.47; 95% CI: -1.09 to 0.16, p = 0.14) or in the first trimester (SMD = -0.52; 95% CI: -1.13 to 0.10, p = 0.10).

CONCLUSIONS

This meta-analysis showed that the serum selenium level of patients with GDM was lower than that in healthy pregnant women, especially within the non-European population and in the second and third trimesters.

An insight into major signaling pathways and protein-protein interaction networks involved in the pathogenesis of gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is associated with the increase of glucose in the blood rather than being absorbed by the cells. A better understanding of the signaling pathways is necessary to understand the pathophysiology of GDM. This study provides details about a series of signaling pathways and protein-protein interactions involved in the pathogenesis of GDM and their evaluations in GDM development. Protein-protein interactions were found between proteins of several signaling pathways that suggest interlink between these signaling pathways. Protein-protein interactions were generated with high confidence interaction scores based on textmining, co-occurrence, coexpression, neighborhood, gene fusion, experiments and databases. The dysregulation of signaling pathways may also contribute to the increased risk of complications associated with GDM in the mother and child. Further, studies on signaling pathways involved in the pathogenesis of GDM would help in the development of an effective intervention to prevent GDM along with the identification of key targets for effective therapies in the future. This article is protected by copyright. All rights reserved.

Ulk1, Not Ulk2, Is Required for Exercise Training-Induced Improvement of Insulin Response in Skeletal Muscle

Unc51 like autophagy activating kinase 1 (Ulk1), the primary autophagy regulator, has been linked to metabolic adaptation in skeletal muscle to exercise training. Here we compared the roles of Ulk1 and homologous Ulk2 in skeletal muscle insulin action following exercise training to gain more mechanistic insights. Inducible, skeletal muscle-specific Ulk1 knock-out (Ulk1-iMKO) mice and global Ulk2 knock-out (Ulk2^–/–) mice were subjected to voluntary wheel running for 6 weeks followed by assessment of exercise capacity, glucose tolerance, and insulin signaling in skeletal muscle after a bolus injection of insulin. Both Ulk1-iMKO and Ulk2^–/– mice had improved endurance exercise capacity post-exercise. Ulk1-iMKO did not improve glucose clearance during glucose tolerance test, while Ulk2^–/– had only marginal improvement. However, exercise training-induced improvement of insulin action in skeletal muscle, indicated by Akt-S473 phosphorylation, was only impaired in Ulk1-iMKO. These data suggest that Ulk1, but not Ulk2, is required for exercise training-induced improvement of insulin action in skeletal muscle, implicating crosstalk between catabolic and anabolic signaling as integral to metabolic adaptation to energetic stress.

Placenta-Derived Osteoprotegerin Is Required for Glucose Homeostasis in Gestational Diabetes Mellitus

Osteoprotegerin (OPG) is involved in various biological processes, including bone remodeling, vascular calcification and pancreatic β-cell function. Although some clinical studies have shown an increase in serum OPG level during pregnancy, the role of OPG in gestational diabetes mellitus (GDM) is largely unknown. Therefore, we explored the effect of OPG in metabolic homeostasis during pregnancy. We initially evaluated serum OPG levels using ELISA and western blotting techniques on samples from GDM patients. We also assessed OPG expression levels in maternal mice. We then used blastocysts transduced with lentiviruses capable of trophoblast-specific transgene expression to establish placenta-specific OPG knockdown or overexpression mouse models for functional and mechanistic investigation after embryo transplantation. We found that OPG expression was positively associated with GDM in clinical samples, and OPG levels were significantly increased in GDM patient sera and term placenta. Serum OPG was significantly increased in maternal compared to non-pregnant mice, and expression levels of OPG were the highest in placenta compared with other organs, including bone, liver and pancreas. OPG was also significantly increased in pregnant mice fed a high-fat diet (HFD). Placenta-specific OPG knockdown induced glucose intolerance, decreased β-cell proliferation and decreased serum insulin levels, whereas placenta-specific OPG overexpression promoted glucose tolerance and enhanced β-cell proliferation, which increased serum insulin production and decreased fetal weight in HFD-feeding pregnant mice. Placenta-derived OPG (pl-OPG) regulated glucose homeostasis during pregnancy via enhancement of β-cell proliferation, which suggests a potential therapeutic application of OPG for GDM.

Are Cape Peninsula baboons raiding their way to obesity and type II diabetes? - a comparative study

Researchers, managers and conservationists in the Cape Peninsula, South Africa, have reported cases of individual baboons (Papio ursinus) appearing overweight, lethargic and having poor teeth. Despite an intensive baboon management programme, there are certain individual baboons and troops that continue to raid human food sources. These food sources often are high in processed carbohydrates and saturated fats. As this diet is highly associated with obesity, insulin resistance and type II diabetes, the present study aimed to establish if these baboons may be at risk of developing insulin resistance. Post mortem muscle samples from 17 Cape Peninsula and 7 control adult male baboons were rapidly frozen in liquid nitrogen and analysed for insulin receptor substrate-1 (IRS-1), glucose transporter 4 (GLUT4), oxidative and glycolytic markers of metabolism (citrate synthase, 3-hydroxyacyl-CoA-dehydrogenase, lactate dehydrogenase and creatine kinase activities), and muscle fibre morphology. The sampled Peninsula baboons were heavier (33 ± 2 vs. 29 ± 2 kg, P < 0.05) and had a higher frequency of poor teeth compared to control baboons. Muscle fibre type, fibre size, GLUT4 content, oxidative and glycolytic metabolism were not different between the two groups. However, IRS-1 content, a marker of insulin sensitivity, was significantly lower (by 43%, P < 0.001) in the Peninsula baboons compared to the controls. This study provides the first indirect evidence that some Peninsula baboons with a history of raiding human food sources, may be at risk of developing insulin resistance in the wild, with long term implications for population health.

Exploring the causes and consequences of maternal metabolic maladaptations during pregnancy: Lessons from animal models

Pregnancy is a remarkable physiological state, during which the metabolic system of the mother adapts to ensure that nutrients are made available for transfer to the fetus for growth and development. Adaptations of maternal metabolism during pregnancy are influenced by the metabolic and nutritional status of the mother and the production of endocrine factors by the placenta that exert metabolic effects. Insufficient or inappropriate adaptations in maternal metabolism during pregnancy may lead to pregnancy complications with important short- and long-term effects for both the health of the child and mother. This is very evident in gestational diabetes, which is marked by greater glucose intolerance and insulin resistance above that expected of a normal pregnancy. Gestational diabetes is associated with increased fetal weight and/or increased adiposity, higher instrumented delivery rates and greater risks for both mother and child of developing type 2 diabetes in the long-term. However, despite the negative health impacts of such metabolic imbalances during pregnancy, the precise mechanisms responsible for orchestrating these changes remain largely unknown. The present review describes the dynamic pregnancy-specific changes that occur in the metabolic system of the mother during pregnancy. It also discusses findings using surgical, pharmacological, genetic and dietary methods in experimental animals that highlight the role of pathways in maternal tissues that lead to metabolic dysfunction, with a particular focus on gestational diabetes. Finally, it summarises the work largely employing gene targeting and hormone administration in rodents that have illuminated the involvement of placental endocrine function in driving maternal metabolic adaptations. While current animal models may not fully replicate what is observed in humans, these have been instrumental in showing that there is a dynamic interplay between changes in maternal metabolic physiology and the placental production of endocrine factors that govern the availability of nutrients to the growing fetus. However, more work is required to specifically identify the placenta-driven changes in maternal metabolic physiology that ensure the appropriate level of insulin production and action during pregnancy. In doing so, these studies may pave the way to understanding the development of pregnancy complications like gestational diabetes, as well as further our understanding of type-2 diabetes and the control of metabolic physiology more broadly.

Impact of GPR1 signaling on maternal high-fat feeding and placenta metabolism in mice

Chemerin and G protein-coupled receptor 1 (GPR1) are increased in serum and placenta in mice during pregnancy. Interestingly, we observed increased serum chemerin levels and decreased GPR1 expression in placenta of high-fat-diet-fed mice compared with chow-fed mice at gestational day 18. GPR1 protein and gene levels were significantly decreased in gestational diabetes mellitus (GDM) patient placentas. Therefore, we hypothesized that chemerin/GPR1 signaling might participate in the pathogenic mechanism of GDM. We investigated the role of GPR1 in carbohydrate homeostasis during pregnancy using pregnant mice transfected with small interfering RNA for GPR1 or a negative control. GPR1 knockdown exacerbated glucose intolerance, disrupted lipid metabolism, and decreased β-cell proliferation and insulin levels. Glucose transport protein-3 and fatty acid binding protein-4 were downregulated with reducing GPR1 in vivo and in vitro via phosphorylated AKT pathway. Taken together, our findings first demonstrate the expression of GPR1, the characterization of its direct biological effects in humans and mice, as well as the molecular mechanism that indicates the role of GPR1 signaling in maternal metabolism during pregnancy, suggesting a novel feedback mechanism to regulate glucose balance during pregnancy, and GPR1 could be a potential target for the detection and therapy of GDM.

The relationship between urotensin II and insulin resistance in women with gestational diabetes mellitus

AIM

Urotensin II (UII), a pluripotent vasoactive peptide, plays a crucial role in development of insulin resistance. Gestational diabetes mellitus (GDM) is a metabolic disorder associated with insulin resistance. The aims of the current study were to compare UII levels in women with or without GDM and to investigate the relationship between UII and insulin resistance in women with GDM.

METHODS

A total of 84 women were recruited in this case-control study (42 women with GDM and 42 age- and body mass index (BMI)-matched pregnant women without GDM as controls). GDM was diagnosed by a 2-h 75-g oral glucose tolerance test over a period of 24-28 gestational weeks. Circulating UII levels were assessed via the ELISA method. The metabolic parameters of the recruited women were also determined.

RESULTS

The circulating levels of UII in women with GDM were higher than in controls (11.56 ± 4.13 vs. 7.62 ± 3.45 ng/ml, P < 0.001). UII showed a positive correlation with insulin resistance marker (HOMA-IR), fasting blood glucose, and BMI. Moreover, according to the results of multiple linear regression analyses, UII was independently related to HOMA-IR. Additionally, the binary logistic analysis revealed that the women with the highest tertile of UII levels showed increased risk for GDM by comparison with those women with the lowest tertile of UII levels.

CONCLUSION

Elevated UII levels are associated with insulin resistance in women with GDM.

A Western-style obesogenic diet alters maternal metabolic physiology with consequences for fetal nutrient acquisition in mice

KEY POINTS

In the Western world, obesogenic diets containing high fat and high sugar (HFHS) are commonly consumed during pregnancy, although their effects on the metabolism of the mother, in relation to feto-placental glucose utilization and growth, are unknown. In the present study, the consumption of an obesogenic HFHS diet compromised maternal glucose tolerance and insulin sensitivity in late pregnancy in association with dysregulated lipid and glucose handling by the dam. These maternal metabolic changes induced by HFHS feeding were related to altered feto-placental glucose metabolism and growth. A HFHS diet during pregnancy therefore causes maternal metabolic dysfunction with consequences for maternal nutrient allocation for fetal growth. These findings have implications for the health of women and their infants, who consume obesogenic diets during pregnancy.

ABSTRACT

In the Western world, obesogenic diets containing high fat and high sugar (HFHS) are commonly consumed during pregnancy. However, the impacts of a HFHS diet during pregnancy on maternal insulin sensitivity and signalling in relation to feto-placental growth and glucose utilization are unknown. The present study examined the effects of a HFHS diet during mouse pregnancy on maternal glucose tolerance and insulin resistance, as well as, on feto-placental glucose metabolism. Female mice were fed a control or HFHS diet from day (D) 1 of pregnancy (term = D20.5). At D16 or D19, dams were assessed for body composition, metabolite and hormone concentrations, tissue abundance of growth and metabolic signalling pathways, glucose tolerance and utilization and insulin sensitivity. HFHS feeding perturbed maternal insulin sensitivity in late pregnancy; hepatic insulin sensitivity was higher, whereas sensitivity of the skeletal muscle and white adipose tissue was lower in HFHS than control dams. These changes were accompanied by increased adiposity and reduced glucose production and glucose tolerance of HFHS dams. The HFHS diet also disturbed the hormone and metabolite milieu and altered expression of growth and metabolic signalling pathways in maternal tissues. Furthermore, HFHS feeding was associated with impaired feto-placental glucose metabolism and growth. A HFHS diet during pregnancy therefore causes maternal metabolic dysfunction with consequences for maternal nutrient allocation for fetal growth. These findings have implications for the health of women and their infants, who consume HFHS diets during pregnancy.

Absence of a gestational diabetes phenotype in the LepRdb/+ mouse is independent of control strain, diet, misty allele, or parity

Treatment options for gestational diabetes (GDM) are limited. In order to better understand mechanisms and improve treatments, appropriate animal models of GDM are crucial. Heterozygous db mice (db/+) present with glucose intolerance, insulin resistance, and increased weight gain during, but not prior to, pregnancy. This makes them an ideal model for GDM. However, several recent studies have reported an absence of GDM phenotype in their colony. We investigated several hypotheses for why the phenotype may be absent, with the aim of re-establishing it and preventing further resources being wasted on an ineffective model. Experiments were carried out across two laboratories in two countries (New Zealand and China), and were designed to assess type of control strain, diet, presence of the misty allele, and parity as potential contributors to the lost phenotype. While hyperleptinemia and pre-pregnancy weight gain were present in all db/+mice across the four studies, we found no consistent evidence of glucose intolerance or insulin resistance during pregnancy. In conclusion, we were unable to acquire the GDM phenotype in any of our experiments, and we recommend researchers do not use the db/+ mouse as a model of GDM unless they are certain the phenotype remains in their colony.

Resveratrol ameliorates the chemical and microbial induction of inflammation and insulin resistance in human placenta, adipose tissue and skeletal muscle

Gestational diabetes mellitus (GDM), which complicates up to 20% of all pregnancies, is associated with low-grade maternal inflammation and peripheral insulin resistance. Sterile inflammation and infection are key mediators of this inflammation and peripheral insulin resistance. Resveratrol, a stilbene-type phytophenol, has been implicated to exert beneficial properties including potent anti-inflammatory and antidiabetic effects in non-pregnant humans and experimental animal models of GDM. However, studies showing the effects of resveratrol on inflammation and insulin resistance associated with GDM in human tissues have been limited. In this study, human placenta, adipose (omental and subcutaneous) tissue and skeletal muscle were stimulated with pro-inflammatory cytokines TNF-α and IL-1β, the bacterial product lipopolysaccharide (LPS) and the synthetic viral dsRNA analogue polyinosinic:polycytidylic acid (poly(I:C)) to induce a GDM-like model. Treatment with resveratrol significantly reduced the expression and secretion of pro-inflammatory cytokines IL-6, IL-1α, IL-1β and pro-inflammatory chemokines IL-8 and MCP-1 in human placenta and omental and subcutaneous adipose tissue. Resveratrol also significantly restored the defects in the insulin signalling pathway and glucose uptake induced by TNF-α, LPS and poly(I:C). Collectively, these findings suggest that resveratrol reduces inflammation and insulin resistance induced by chemical and microbial products. Resveratrol may be a useful preventative therapeutic for pregnancies complicated by inflammation and insulin resistance, like GDM.

Positive Correlation between Enhanced Expression of TLR4/MyD88/NF-κB with Insulin Resistance in Placentae of Gestational Diabetes Mellitus

Insulin resistance (IR) is a critical factor of the pathophysiology of Gestational diabetes mellitus (GDM). Studies on key organs involved in IR, such as livers and adipose tissues, showed that Toll-like receptor 4 (TLR4) can regulate insulin sensitivity. As a maternal-fetal interface with multi-functions, placentae could contribute to the development of IR for GDM. Thus, we investigated the expressions of TLR4/Myeloid Differentiation factor 88 (MyD88)/Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-kB) in term placentae from 33 GDM women and 36 healthy pregnant women with normal glucose tolerance, evaluated local and systemic IR and furthermore identified the association between placental TLR4 and IR. TLR4 protein was expressed in various cells of term placenta, particularly in syncytiotrophoblast of villi. Compared with normal pregnancy, the expression of TLR4/MyD88/NF-kB pathway increased in the placenta of GDM (p<0.05), and these differences were more pronounced in the maternal section of the placenta and the syncytiotrophoblast of villi. In addition, more severe IR was observed in the placenta of GDM patients than the control group, evidenced with higher pIRS-1(ser312) (p<0.001) and lower IRS-1 (p<0.05) as well as pAkt proteins (p<0.01). The expression of TLR4 in placentae is positively correlated with local IR (pIRS-1: r = 0.76, p <0.001 and pAkt: r = -0.47, p <0.001) and maternal fasting (r = 0.42, p <0.01), one-hour (r = 0.52, p <0.01) and two-hour glucose (r = 0.54, p <0.01) at OGTT. We found an that enhanced expression of the TLR4-MyD88-NF-kB pathway occurs in GDM placentae, which positively correlates with heightened local IR in placentae and higher maternal hyperglycemia. The TLR4/MyD88/NF-kB pathway may play a potential role in the development of IR in placentae of GDM.

Endoplasmic reticulum stress regulates inflammation and insulin resistance in skeletal muscle from pregnant women

Sterile inflammation and infection are key mediators of inflammation and peripheral insulin resistance associated with gestational diabetes mellitus (GDM). Studies have shown endoplasmic reticulum (ER) stress to induce inflammation and insulin resistance associated with obesity and type 2 diabetes, however is paucity of studies investigating the effects of ER stress in skeletal muscle on inflammation and insulin resistance associated with GDM. ER stress proteins IRE1α, GRP78 and XBP-1s were upregulated in skeletal muscle of obese pregnant women, whereas IRE1α was increased in GDM women. Suppression of ER stress, using ER stress inhibitor tauroursodeoxycholic acid (TUDCA) or siRNA knockdown of IRE1α and GRP78, significantly downregulated LPS-, poly(I:C)- or IL-1β-induced production of IL-6, IL-8, IL-1β and MCP-1. Furthermore, LPS-, poly(I:C)- or TNF-α-induced insulin resistance was improved following suppression of ER stress, by increasing insulin-stimulated phosphorylation of IR-β, IRS-1, GLUT-4 expression and glucose uptake. In summary, our inducible obesity and GDM-like models suggests that the development of GDM may be involved in activating ER stress-induced inflammation and insulin resistance in human skeletal muscle.

Proximity to Delivery Alters Insulin Sensitivity and Glucose Metabolism in Pregnant Mice

In late pregnancy, maternal insulin resistance occurs to support fetal growth, but little is known about insulin-glucose dynamics close to delivery. This study measured insulin sensitivity in mice in late pregnancy at day 16 (D16) and near term at D19. Nonpregnant (NP) and pregnant mice were assessed for metabolite and hormone concentrations, body composition by DEXA, tissue insulin signaling protein abundance by Western blotting, glucose tolerance and utilization, and insulin sensitivity using acute insulin administration and hyperinsulinemic-euglycemic clamps with [(3)H]glucose infusion. Whole-body insulin resistance occurred in D16 pregnant dams in association with basal hyperinsulinemia, insulin-resistant endogenous glucose production, and downregulation of several proteins in hepatic and skeletal muscle insulin signaling pathways relative to NP and D19 values. Insulin resistance was less pronounced at D19, with restoration of NP insulin concentrations, improved hepatic insulin sensitivity, and increased abundance of hepatic insulin signaling proteins. At D16, insulin resistance at whole-body, tissue, and molecular levels will favor fetal glucose acquisition, while improved D19 hepatic insulin sensitivity will conserve glucose for maternal use in anticipation of lactation. Tissue sensitivity to insulin, therefore, alters differentially with proximity to delivery in pregnant mice, with implications for human and other species.

Pregnancy and Smoothelin-like Protein 1 (SMTNL1) Deletion Promote the Switching of Skeletal Muscle to a Glycolytic Phenotype in Human and Mice

Pregnancy promotes physiological adaptations throughout the body, mediated by the female sex hormones progesterone and estrogen. Changes in the metabolic properties of skeletal muscle enable the female body to cope with the physiological challenges of pregnancy and may also be linked to the development of insulin resistance. We conducted global microarray, proteomic, and metabolic analyses to study the role of the progesterone receptor and its transcriptional regulator, smoothelin-like protein 1 (SMTNL1) in the adaptation of skeletal muscle to pregnancy. We demonstrate that pregnancy promotes fiber-type changes from an oxidative to glycolytic isoform in skeletal muscle. This phenomenon is regulated through an interaction between SMTNL1 and progesterone receptor, which alters the expression of contractile and metabolic proteins. smtnl1(-/-) mice are metabolically less efficient and show impaired glucose tolerance. Pregnancy antagonizes these effects by inducing metabolic activity and increasing glucose tolerance. Our results suggest that SMTNL1 has a role in mediating the actions of steroid hormones to promote fiber switching in skeletal muscle during pregnancy. Our findings also bear on the management of gestational diabetes that develops as a complication of pregnancy in ~4% of women.

Double stranded viral RNA induces inflammation and insulin resistance in skeletal muscle from pregnant women in vitro

OBJECTIVE

Maternal peripheral insulin resistance and increased inflammation are two features of pregnancies complicated by pre-existing maternal obesity and gestational diabetes mellitus (GDM). There is now increasing evidence that activation of Toll-like receptor (TLR) signalling pathways by viral products may play a role in the pathophysiology of diabetes. Thus, the aim of this study was to assess the effect of the TLR3 ligand and viral dsRNA analogue polyinosinic polycytidilic acid (poly(I:C)) on inflammation and the insulin signalling pathway in skeletal muscle from pregnant women.

MATERIALS/METHODS

Human skeletal muscle tissue explants were performed to determine the effect of poly(I:C) on the expression and secretion of markers of inflammation, and the insulin signalling pathway and glucose uptake.

RESULTS

Poly(I:C) significantly increased the expression of a number of inflammatory markers in skeletal muscle from pregnant women. Specifically, there was an increase in the expression and/or secretion of the pro-inflammatory cytokines TNF-α, and IL-6 and the pro-inflammatory chemokines IL-8 and MCP-1. These effect of poly(I:C) appear to mediated via a number of signalling molecules including the pro-inflammatory transcription factor NF-κB, and the serine threonine kinases GSK3 and AMPKα. Additionally, poly(I:C) decreased insulin stimulated GLUT-4 expression and glucose uptake in skeletal muscle from pregnant women.

CONCLUSIONS

The in vitro data presented in this study suggests that viral infection may contribute to the pathophysiology of pregnancies complicated by pre-existing maternal obesity and/or GDM. It should be noted that the in vitro studies cannot be directly used to infer the same outcomes in the intact subject.

The risk of placental abruption and placenta previa in pregnant women with chronic hepatitis B viral infection: a systematic review and meta-analysis

INTRODUCTION

Several epidemiological studies have found a positive association between chronic hepatitis B virus (CHB) infection and the risk of placental abruption and placenta previa, but various studies have reported conflicting findings. The objective was to systematically review the literature to determine a possible association between CHB infection and these two placental complications.

METHODS

We conducted a computerized search in electronic database through March 1, 2014, supplemented with a manual search of reference lists, to identify original published research on placental abruption and placenta previa rates in women with CHB infection. Data were independently extracted, and relative risks were calculated. The meta-analysis was performed using Stata version 10.0 software.

RESULTS

Five studies involving 9088 placenta previa cases were identified. No significant association between CHB infection and placenta previa was identified (OR = 0.98, 95% CI = 0.60-1.62). Five studies involving 15571 placental abruption cases were identified. No significant association between CHB infection and placental abruption was identified (OR = 1.42, 95% CI, 0.93-2.15).

DISCUSSION

The immune response against the virus represents a key factor in determining infection outcomes. No observation of significant increased risk of the placental complications could be partially explained by the complex immune response during CHB infection.

CONCLUSIONS

Our meta-analysis found no evidence of significant associations between CHB infection and increased risk of placental abruption as well as placenta previa. Further well-designed studies were warranted to assess any potential association between CHB infection and increased risk of placental abruption as well as placenta previa.

Phosphatidylinositol 3-kinase (PI3K) activity bound to insulin-like growth factor-I (IGF-I) receptor, which is continuously sustained by IGF-I stimulation, is required for IGF-I-induced cell proliferation

Continuous stimulation of cells with insulin-like growth factors (IGFs) in G(1) phase is a well established requirement for IGF-induced cell proliferation; however, the molecular components of this prolonged signaling pathway that is essential for cell cycle progression from G(1) to S phase are unclear. IGF-I activates IGF-I receptor (IGF-IR) tyrosine kinase, followed by phosphorylation of substrates such as insulin receptor substrates (IRS) leading to binding of signaling molecules containing SH2 domains, including phosphatidylinositol 3-kinase (PI3K) to IRS and activation of the downstream signaling pathways. In this study, we found prolonged (>9 h) association of PI3K with IGF-IR induced by IGF-I stimulation. PI3K activity was present in this complex in thyrocytes and fibroblasts, although tyrosine phosphorylation of IRS was not yet evident after 9 h of IGF-I stimulation. IGF-I withdrawal in mid-G(1) phase impaired the association of PI3K with IGF-IR and suppressed DNA synthesis the same as when PI3K inhibitor was added. Furthermore, we demonstrated that Tyr(1316)-X-X-Met of IGF-IR functioned as a PI3K binding sequence when this tyrosine is phosphorylated. We then analyzed IGF signaling and proliferation of IGF-IR(-/-) fibroblasts expressing exogenous mutant IGF-IR in which Tyr(1316) was substituted with Phe (Y1316F). In these cells, IGF-I stimulation induced tyrosine phosphorylation of IGF-IR and IRS-1/2, but mutated IGF-IR failed to bind PI3K and to induce maximal phosphorylation of GSK3β and cell proliferation in response to IGF-I. Based on these results, we concluded that PI3K activity bound to IGF-IR, which is continuously sustained by IGF-I stimulation, is required for IGF-I-induced cell proliferation.

Chronically increased S6K1 is associated with impaired IRS1 signaling in skeletal muscle of GDM women with impaired glucose tolerance postpartum

CONTEXT

The rapidly increasing prevalence of gestational diabetes mellitus (GDM) globally places a growing population at risk for developing type 2 diabetes mellitus (T2DM), particularly those with persistent impaired glucose tolerance (IGT) postpartum.

OBJECTIVE

We sought to 1) identify dynamic insulin signaling abnormalities in vivo in a prospective, longitudinal study of GDM women compared to weight-matched pregnant controls both antepartum and postpartum; and 2) determine abnormalities that might distinguish GDM women who normalize their glucose tolerance postpartum from those with persistent IGT.

DESIGN

Skeletal muscle biopsies were obtained before and after a 75-g glucose load in nine overweight to obese GDM women and 10 weight-matched pregnant controls antepartum and postpartum. Postpartum biopsies were collected in five weight-matched GDM women with IGT (GDM/IGT).

RESULTS

GDM women had decreased skeletal muscle insulin-stimulated insulin receptor and insulin receptor substrate 1 (IRS1) tyrosine activation and reduced IRS1, concomitant with increased basal IRS1 serine phosphorylation and basal p70 S6-kinase (S6K1) activation, which resolved postpartum. However, GDM/IGT subjects had a persistent impairment in IRS1 activation and increased S6K1 phosphorylation compared to GDM subjects with normal glucose tolerance.

CONCLUSIONS

This study reveals that women with GDM demonstrate impaired IRS1 signaling associated with increased S6K1 activation in skeletal muscle in vivo. This defect is maintained postpartum in GDM/IGT subjects, despite similar body weights and cytokine levels. Given that GDM women with persistent IGT are at a high risk of developing T2DM, understanding how the nutrient-sensitive mammalian target of rapamycin/S6K1 pathway is chronically activated in GDM may lead to important therapies that could prevent the progression to T2DM.

High-saturated-fat diet induces gestational diabetes and placental vasculopathy in C57BL/6 mice

Gestational diabetes mellitus (GDM) is a commonly encountered disorder of mid to late pregnancy that is characterized by hyperglycemia, hyperinsulinemia, and impaired glucose tolerance. Gestational diabetes mellitus is thought to be multifactorial in origin and derives from both genetic and environmental factors. However, the mechanisms underlying GDM are incompletely understood; and current GDM animal models do not appear to closely mimic the clinical situation in humans. The present study used environmental exposure to high-saturated-fat diet (HFD) in an effort to develop a GDM mouse model that closely simulates metabolic abnormalities seen in human GDM. This model was then used to determine the contributions of HFD-induced placental oxidative stress (OS) and vascular dysregulation, which are observed in GDM patients and are believed to contribute to the pathogenesis of the disease. Pathologic manifestations of the disease were quantified by evaluating the extent of placental lipid peroxidation and by determining protective effects of dietary antioxidant quercetin supplementation to reduce HFD-associated placental OS. In this study, female C57BL/6 mice were fed HFD for 1 month before conception and throughout gestation to mimic chronic maternal fast food consumption. Maternal body weight increased from gestation day (GD) 0 to GD19 by 41% with HFD, as compared with 23% in control dams; HFD dams also developed insulin resistance (66% increase in plasma insulin and 27% increase in plasma glucose levels by GD10) as compared with control dams. Placentas from HFD GD19 dams demonstrated loss of trophoblasts and OS-mediated labyrinthine endothelial cellular damage, the latter of which was prevented with quercetin supplementation. Our findings suggest that prenatal HFD alters glucose metabolism and elevates placental OS, which are believed to collectively relate to improper formation of the conceptus and impaired birth outcome.

Scoparia dulcis (SDF7) endowed with glucose uptake properties on L6 myotubes compared insulin

AIM OF THE STUDY

Insulin stimulates glucose uptake and promotes the translocation of glucose transporter 4 (Glut 4) to the plasma membrane on L6 myotubes. The aim of this study is to investigate affect of Scoparia dulcis Linn water extracts on glucose uptake activity and the Glut 4 translocation components (i.e., IRS-1, PI 3-kinase, PKB/Akt2, PKC and TC 10) in L6 myotubes compared to insulin.

MATERIALS AND METHODS

Extract from TLC fraction-7 (SDF7) was used in this study. The L6 myotubes were treated by various concentrations of SDF7 (1 to 50 microg/ml) and insulin (1 to 100 nM). The glucose uptake activities of L6 myotubes were evaluated using 2-Deoxy-D-glucose uptake assay in with or without fatty acid-induced medium. The Glut 4 translocation components in SDF7-treated L6 myotubes were detected using immunoblotting and quantified by densitometry compared to insulin. Plasma membrane lawn assay and glycogen colorimetry assay were carried out in SDF7- and insulin-treated L6 myotubes in this study.

RESULTS

Here, our data clearly shows that SDF7 possesses glucose uptake properties on L6 myotubes that are dose-dependent, time-dependent and plasma membrane Glut 4 expression-dependent. SDF7 successfully stimulates glucose uptake activity as potent as insulin at a maximum concentration of 50 microg/ml at 480 min on L6 myotubes. Furthermore, SDF7 stimulates increased Glut 4 expression and translocation to plasma membranes at equivalent times. Even in the insulin resistance stage (free fatty acids-induced), SDF7-treated L6 myotubes were found to be more capable at glucose transport than insulin treatment.

CONCLUSIONS

Thus, we suggested that Scoparia dulcis has the potential to be categorized as a hypoglycemic medicinal plant based on its good glucose transport properties.

Multiple abnormalities of myocardial insulin signaling in a porcine model of diet-induced obesity

Heightened cardiovascular risk among patients with systemic insulin resistance is not fully explained by the extent of atherosclerosis. It is unknown whether myocardial insulin resistance accompanies systemic insulin resistance and contributes to increased cardiovascular risk. This study utilized a porcine model of diet-induced obesity to determine if myocardial insulin resistance develops in parallel with systemic insulin resistance and investigated potential mechanisms for such changes. Micropigs (n = 16) were assigned to control (low fat, no added sugars) or intervention (25% wt/wt coconut oil and 20% high-fructose corn syrup) diet for 7 mo. Intervention diet resulted in obesity, hypertension, and dyslipidemia. Systemic insulin resistance was manifest by elevated fasting glucose and insulin, abnormal response to intravenous glucose tolerance testing, and blunted skeletal muscle phosphatidylinositol-3-kinase (PI 3-kinase) activation and protein kinase B (Akt) phosphorylation in response to insulin. In myocardium, insulin-stimulated glucose uptake, PI 3-kinase activation, and Akt phosphorylation were also blunted in the intervention diet group. These findings were explained by increased myocardial content of p85alpha (regulatory subunit of PI 3-kinase), diminished association of PI 3-kinase with insulin receptor substrate (IRS)-1 in response to insulin, and increased serine-307 phosphorylation of IRS-1. Thus, in a porcine model of diet-induced obesity that recapitulates many characteristics of insulin-resistant patients, myocardial insulin resistance develops along with systemic insulin resistance and is associated with multiple abnormalities of insulin signaling.

Effects of water extract and crude polysaccharides from Liriope spicata var. prolifera on InsR/IRS-1/PI3K pathway and glucose metabolism in mice

AIM OF THE STUDY

The present study was designed to investigate the effects of water extract (WE) and crude polysaccharides (CPs) from the tuberous root of Liriope spicata var. prolifer on the InsR/IRS-1/PI3K pathway and glucose metabolism in type 2 diabetic mice.

MATERIALS AND METHODS

WE and CPs were administered orally at different doses (200 and 100mg/kg body weight) to streptozotocin (STZ)-induced type 2 diabetic male BABL/c mice, respectively. After 4 weeks of administration, immunohistochemistry and western blot were applied to detect the expression levels of insulin receptor-alpha (InsR-alpha), insulin receptor substrate-1 (IRS-1) and phosphatidylinositol 3-kinase (PI3K) in renal tissues of mice. Moreover, the hepatic glycogen content, glucokinase (GK) and glucose-6-phosphatase (G6Pase) activities were measured to investigate the effect of WE and CPs on glucose metabolism.

RESULTS

Compared with diabetic control, greater immunostaining for InsR-alpha, IRS-1 and PI3K was present in the tubulointerstitial regions of WE and CPS groups in renal tissues and the expression levels of these three signal molecules from WE and CPs groups were significantly increased; the glycogen content and GK activity from WE and CPs groups in liver were significantly increased, yet the G6Pase activity was significantly lower.

CONCLUSIONS

It is demonstrated that WE and CPs can ameliorate insulin signaling transduction and glucose metabolism, as a result, lessen IR and hyperglycemia eventually. So, this study has provided more powerful evidences for Liriope spicata var. prolifer to be a potential hypoglycemic agent and insulin sensitizer.

17beta-estradiol treatment is unable to reproduce p85 alpha redistribution associated with gestational insulin resistance in rats

Maternal metabolic adaptations are essential to ensure proper fetal development. According to changes in insulin sensitivity, pregnancy can be divided into two periods: early pregnancy, characterized by an increase in maternal insulin sensitivity, and late pregnancy, in which there is a significant increase in insulin resistance. The aims of the present work were two-fold: firstly, the molecular mechanisms associated with the development of pregnancy-related insulin resistance in peripheral tissues, mainly retroperitoneal adipose tissue and skeletal muscle, were studied in pregnant rats at 6, 11, and 16 days gestation. Secondly, the role of 17beta-estradiol in this process was elucidated in an animal model consisting of ovariectomized rats treated with 17beta-estradiol to mimic plasma gestational levels. The results support the conclusion that retroperitoneal adipose tissue plays a pivotal role in the decrease in insulin sensitivity during pregnancy, through a mechanism that involves p85 alpha redistribution to the insulin receptor and impairment of Glut4 translocation to the plasma membrane. Treatment with 17beta-estradiol did not reproduce the molecular adaptations that occur during pregnancy, suggesting that other hormonal factors presents in gestation but absent in our experimental model are responsible for p85 alpha redistribution to the insulin receptor.

Down-regulation of growth signaling pathways linked to a reduced cotyledonary vascularity in placentomes of over-nourished, obese pregnant ewes

Both protein kinase B (Akt) and extracellular signal-regulated kinase 1/2 (ERK1/2) are down-stream components of the insulin/insulin like growth factor-1 (IGF-1) signaling pathway. AMP-activated protein kinase (AMPK) is known to sensitize cells to insulin/IGF-1 signaling. The objective of this study was to assess the activity of AMPK and its role in the observed down-regulation of insulin/IGF-1 signaling in cotyledonary (COT) arteries supplying the placental component of the ewe placentome. Nonpregnant ewes were randomly assigned to a control (C, 100% of NRC recommendations) or obesogenic (OB, 150% of NRC) diet from 60 days before conception until necropsy on day 75 of gestation (n=5/group) or until lambing (n=5/group). At necropsy on day 75 of gestation, the smallest terminal arteries that entered the COT tissues (0.5-1.0 mm in diameter) were collected for analyses. Fetal weights were approximately 20% greater (P<0.05) on OB than C ewes, but birth weights of lambs were similar across dietary groups. Fetal plasma concentrations of glucose, insulin and IGF-1 were higher (P<0.05) in the blood of fetuses from OB than C ewes. Total AMPK and phosphorylated AMPK at Thr 172 (the active form) were reduced (P<0.05) by 19.7+/-8.4% and 25.9+/-7.7%, respectively in the COT arterial tissues of OB ewes. Total acetyl-CoA carboxylase (ACC), a down-stream target of AMPK, and its phosphorylated form were also reduced (P<0.05) by 32.9+/-9.2% and 45.4+/-14.6%, respectively. The phosphorylation of IRS-1 at Ser 789, a site phosphorylated by AMPK, was 24.5+/-9.0% lower (P<0.05) in COT arteries of OB than C ewes. No alteration in total insulin receptor, total IGF-1 receptor or their phosphorylated forms was observed, down-stream insulin signaling was down-regulated in COT arteries of OB ewes, which may have resulted in the observed decrease in COT vascular development in OB ewes.

Increased endothelial nitric-oxide synthase expression reduces hypertension and hyperinsulinemia in fructose-treated rats

Endothelial dysfunction and decreased production of nitric oxide (NO) by endothelial NO synthase (eNOS) are implicated in the pathogenesis of hypertension and insulin resistance. Because the potential influence of increased eNOS expression/activity on these parameters is unclear, the present study examined the effects of eNOS gene therapy on insulin resistance and blood pressure alterations in a fructose-induced hypertension model in rats. As predicted, 2 weeks of fructose consumption in the drinking water resulted in elevated systolic blood pressure and insulin resistance. These and other physiologic alterations were reversed within 2 weeks after a single intravenous injection of a vector containing the human eNOS cDNA (pcDNA3.1-eNOS), whereas injection of an empty vector (pcDNA3.1) was without effect. In support of the beneficial effects of pcDNA3.1-eNOS treatment being because of enhanced eNOS expression and activity, increased eNOS protein levels were documented in aorta, liver, kidney, and heart of fructose-treated rats injected with pcDNA3.1-eNOS, and corresponding elevations in nitrite/nitrate and cGMP concentrations were observed in urine. Furthermore, pcDNA3.1-eNOS treatment prevented fructose-induced decreases in expression levels of insulin receptor substrate-1, the p110 catalytic subunit of phosphatidylinositol 3-kinase, phosphorylated Akt, and phosphorylated AMP-activated protein kinases in liver, aorta, and skeletal muscle. The results of this study cumulatively indicate that gene therapy with human eNOS decreased fructose-induced hypertension and insulin resistance in rats and suggest potential signaling pathways that mediate these effects. These data highlight the potential utility of eNOS gene therapy in the treatment of hypertension and insulin resistance.

AMP-activated protein kinase signalling pathways are down regulated and skeletal muscle development impaired in fetuses of obese, over-nourished sheep

Maternal obesity and over-nutrition give rise to both obstetric problems and neonatal morbidity. The objective of this study was to evaluate effects of maternal obesity and over-nutrition on signalling of the AMP-activated protein kinase (AMPK) pathway in fetal skeletal muscle in an obese pregnant sheep model. Non-pregnant ewes were assigned to a control group (Con, fed 100% of NRC nutrient recommendations, n = 7) or obesogenic group (OB, fed 150% of National Research Council (NRC) recommendations, n = 7) diet from 60 days before to 75 days after conception (term 150 days) when fetal semitendinosus skeletal muscle (St) was sampled. OB mothers developed severe obesity accompanied by higher maternal and fetal plasma glucose and insulin levels. In fetal St, activity of phosphoinositide-3 kinase (PI3K) associated with insulin receptor substrate-1 (IRS-1) was attenuated (P < 0.05), in agreement with the increased phophorylation of IRS-1 at serine 1011. Phosphorylation of AMP-activated protein kinase (AMPK) at Thr 172, acetyl-CoA carboxylase at Ser 79, tuberous sclerosis 2 at Thr 1462 and eukaryotic translation initiation factor 4E-binding protein 1 at Thr 37/46 were reduced in OB compared to Con fetal St. No difference in energy status (AMP/ATP ratio) was observed. The expression of protein phosphatase 2C was increased in OB compared to Con fetal St. Plasma tumour necrosis factor alpha (TNFalpha) was increased in OB fetuses indicating an increased inflammatory state. Expression of peroxisome proliferator-activated receptor gamma (PPARgamma) was higher in OB St, indicating enhanced adipogenesis. The glutathione: glutathione disulphide ratio was also lower, showing increased oxidative stress in OB fetal St. In summary, we have demonstrated decreased signalling of the AMPK system in skeletal muscle of fetuses of OB mothers, which may play a role in altered muscle development and development of insulin resistance in the offspring.

Increased skeletal muscle tumor necrosis factor-alpha and impaired insulin signaling persist in obese women with gestational diabetes mellitus 1 year postpartum

OBJECTIVE

Women with gestational diabetes mellitus (GDM) demonstrate chronic and progressive insulin resistance and a markedly increased risk of converting to type 2 diabetes after pregnancy. However, the cellular mechanisms underlying this insulin resistance are unknown.

RESEARCH DESIGN AND METHODS

We investigated the progression of insulin resistance in nine obese women with GDM during late pregnancy (30-36 weeks) and 1 year postpartum. Skeletal muscle biopsies were obtained at each visit, and insulin resistance was determined by the hyperinsulinemic-euglycemic clamp technique.

RESULTS

Insulin resistance was not significantly improved in GDM women (4.1 +/- 0.4 vs. 5.8 +/- 1.1 10(-2) mg x kg FFM x min(-1)/microU x ml(-1)). Subjects did not experience significant weight loss postpartum. Body weight, fat mass, fasting glucose, and plasma tumor necrosis factor (TNF)-alpha remained higher 1 year postpartum than seen in previously studied normal glucose-tolerant women. Skeletal muscle TNF-alpha mRNA was elevated five- to sixfold in GDM women and remained higher 1 year postpartum. While levels of insulin receptor (IR), IR substrate (IRS)-1, and p85 alpha improved postpartum, insulin-stimulated IR tyrosine phosphorylation and receptor tyrosine kinase activity did not significantly improve postpartum in GDM. The levels of (312)Ser-IRS-1 also did not improve postpartum and correlated with TNF-alpha mRNA (r(2) = 0.19, P < 0.03), consistent with a state of subclinical inflammation and chronic skeletal muscle insulin resistance.

CONCLUSIONS

These results suggest the mechanisms underlying chronic insulin resistance in GDM women may be driven by increased inflammation that impinges on the IR and IRS-1 signaling cascade in skeletal muscle. These findings have important implications for the health of GDM women during subsequent pregnancies and their risk for progression to type 2 diabetes.

Hepatic and muscle insulin action during late pregnancy in the dog

We evaluated the effects of physiologic increases in insulin on hepatic and peripheral glucose metabolism in nonpregnant (NP) and pregnant (P; 3rd trimester) conscious dogs (n = 9 each) using tracer and arteriovenous difference techniques during a hyperinsulinemic euglycemic clamp. Insulin was initially (-150 to 0 min) infused intraportally at a basal rate. During 0-120 min (Low Insulin), the rate was increased by 0.2 mU x kg(-1) x min(-1), and from 120 to 240 min (High Insulin) insulin was infused at 1.5 mU x kg(-1) x min(-1). Insulin concentrations were significantly higher in NP than P during all periods. Matched subsets (n = 5 NP and 6 P) were identified. In the subsets, insulin was 7 +/- 1, 9 +/- 1, and 28 +/- 3 microU/ml (basal, Low Insulin, and High Insulin, respectively) in NP, and 5 +/- 1, 7 +/- 1, and 27 +/- 3 microU/ml in P. Net hepatic glucose output was suppressed similarly in both subsets (> or =50% with Low Insulin, 100% with High Insulin), as was endogenous glucose rate of appearance. During High Insulin, NP dogs required more glucose (10.8 +/- 1.5 vs. 6.2 +/- 1.0 mg x kg(-1) x min(-1), P < 0.05), and hindlimb (primarily skeletal muscle) glucose uptake tended to be greater in NP than P (18.6 +/- 2.5 mg/min vs. 13.6 +/- 2.0 mg/min, P = 0.06). The normal canine liver remains insulin sensitive during late pregnancy. Differing insulin concentrations in pregnant and nonpregnant women and excessive insulin infusion rates may explain previous findings of hepatic insulin resistance in healthy pregnant women.

Association of insulin receptor substrate-1 G972R variant with baseline characteristics of the patients with gestational diabetes mellitus

OBJECTIVE

Insulin receptor substrate-1 (IRS-1) expression and tyrosine phosphorylation is decreased during pregnancy. Pregnancy may be a suitable condition to detect any abnormalities related to IRS-1 polymorphisms. Therefore, we aimed to investigate the prevalence and metabolic impacts of IRS-1 G972R polymorphism in patients with gestational diabetes mellitus (GDM).

STUDY DESIGN

Anthropometric and metabolic variables of 62 women who were diagnosed as having GDM according to 100 g oral glucose tolerance test were compared on the basis of IRS-1 polymorphism by univariate analysis of covariance.

RESULTS

Patients with IRS-1 G972R were more obese at the beginning of pregnancy, had higher serum fasting insulin and glucose levels. Weight gain during pregnancy and insulin and glucose levels after glucose ingestion was comparable between groups.

CONCLUSION

IRS-1 G972R was associated with the baseline characteristics of the patients with GDM, and might be related to insulin resistance that is seen in obese patients with GDM.

The impact of maternal HBsAg carrier status on pregnancy outcomes: a case-control study

BACKGROUND/AIMS

To examine the impact of maternal HBsAg carrier status on pregnancy outcomes.

METHODS

Two hundred and fifty-three carriers of hepatitis B surface antigen (HBsAg) with singleton pregnancy, were retrospectively compared with 253 controls matched for age and parity and year of delivery.

RESULTS

On univariable analysis, HBsAg carriers had higher incidences of threatened preterm labour at <37 weeks (11.9% vs. 6.3%, P=0.030), preterm birth at <34 weeks (4.7% vs. 1.2%, P=0.033), gestational diabetes mellitus (19.0% vs. 11.1%, P=0.012) and antepartum haemorrhage (11.5% vs. 5.5%, P=0.026). Their infants had lower Apgar scores at the 1st (8.47+/-1.67 vs. 8.87+/-1.07, P=0.001) and 5th minute (9.56+/-1.29 vs. 9.80+/-0.54, P=0.007), and increased incidence of intraventricular haemorrhage (4.7% vs. 0.8%, P=0.007). On multivariable analysis, the association between HBsAg carrier state with antepartum haemorrhage, gestational diabetes mellitus and threatened preterm labour were confirmed.

CONCLUSIONS

HBsAg carriers have increased risk of gestational diabetes mellitus, antepartum haemorrhage, and threatened preterm labour. This may be related to the chronic inflammatory state in these subjects. The role of chronic HBV infection in pregnancy complications has to be further elucidated.

PKA-dependent and PKA-independent pathways for cAMP-regulated exocytosis

Stimulus-secretion coupling is an essential process in secretory cells in which regulated exocytosis occurs, including neuronal, neuroendocrine, endocrine, and exocrine cells. While an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) is the principal signal, other intracellular signals also are important in regulated exocytosis. In particular, the cAMP signaling system is well known to regulate and modulate exocytosis in a variety of secretory cells. Until recently, it was generally thought that the effects of cAMP in regulated exocytosis are mediated by activation of cAMP-dependent protein kinase (PKA), a major cAMP target, followed by phosphorylation of the relevant proteins. Although the involvement of PKA-independent mechanisms has been suggested in cAMP-regulated exocytosis by pharmacological approaches, the molecular mechanisms are unknown. Newly discovered cAMP-GEF/Epac, which belongs to the cAMP-binding protein family, exhibits guanine nucleotide exchange factor activities and exerts diverse effects on cellular functions including hormone/transmitter secretion, cell adhesion, and intracellular Ca(2+) mobilization. cAMP-GEF/Epac mediates the PKA-independent effects on cAMP-regulated exocytosis. Thus cAMP regulates and modulates exocytosis by coordinating both PKA-dependent and PKA-independent mechanisms. Localization of cAMP within intracellular compartments (cAMP compartmentation or compartmentalization) may be a key mechanism underlying the distinct effects of cAMP in different domains of the cell.

In vivo insulin signaling through PI3-kinase is impaired in skeletal muscle of adult rat offspring exposed to ethanol in utero

It is now known that prenatal ethanol (EtOH) exposure is associated with impaired glucose tolerance and insulin resistance in rat offspring, but the underlying mechanism(s) is not known. To test the hypothesis that in vivo insulin signaling through phosphatidylinositol 3 (PI3)-kinase is reduced in skeletal muscle of adult rat offspring exposed to EtOH in utero, we gave insulin intravenously to these rats and probed steps in the PI3-kinase insulin signaling pathway. After insulin treatment, EtOH-exposed rats had decreased tyrosine phosphorylation of the insulin receptor β-subunit and of insulin receptor substrate-1 (IRS-1), as well as reduced IRS-1-associated PI3-kinase in the gastrocnemius muscle compared with control rats. There was no significant difference in basal or insulin-stimulated Akt activity between EtOH-exposed rats and controls. Insulin-stimulated PKC isoform ζ phosphorylation and membrane association were reduced in EtOH-exposed rats compared with controls. Muscle insulin binding and peptide contents of insulin receptor, IRS-1, p85 subunit of PI3-kinase, Akt/PKB, and atypical PKC isoform ζ were not different between EtOH-exposed rats and controls. Thus insulin resistance in rat offspring exposed to EtOH in utero may be explained, at least in part, by impaired insulin signaling through the PI3-kinase pathway in skeletal muscle.

Early signaling interactions between the insulin and leptin pathways in bovine myogenic cells

Cross-talk between hormone signaling pathways provides mechanisms to facilitate flexibility in the cellular response to extracellular conditions. One function of insulin is to signal high extracellular glucose, while leptin may signal the abundance of extracellular lipid, both energy sources being readily utilized by muscle. The present study reports early signaling events in the insulin and leptin cascades in primary bovine myogenic cells (BMC). BMC were treated with insulin, or leptin for 1, 10, 30 and 120 min, or pretreated with leptin for 10 min followed by insulin for 1, 10, 30 and 120 min. BMC were insulin resistant, showing a significant inhibition of IRS-1 association with the insulin receptor (IR) following insulin stimulation, a corresponding increase in PI 3-kinase association with the IR, and a slow and modest increase in GLUT4 recruitment to the plasma membrane. Pretreatment of BMC for 10 min leptin, followed by insulin time-course, caused IRS-1 recruitment to be unresponsive, but evoked a rapid, phasic response of PI 3-kinase recruitment to the IR and abrogated the response of GLUT4 translocation to the plasma membrane evoked by insulin alone. The lack of insulin response was independent of IR abundance or affinity. JAK-2 association with the ObR and JAK-2 tyrosine phosphorylation were responsive to all three treatments. Insulin alone down-regulated the leptin signaling pathway, JAK-2 association with ObR decreased at all time-points, and JAK-2 phosphorylation decreased similarly. Leptin alone also appeared to down-regulate JAK-2 association with the ObR, but stimulated the down-regulated pathway to signal, JAK-2 tyrosine phosphorylation being increased at later time-points. Pretreatment with leptin followed by insulin time-course showed marked up-regulation of the early leptin signaling pathway, JAK-2 association with the ObR being increased by insulin while JAK-2 tyrosine phosphorylation was also increased. The contrasting responses of BMC to insulin alone, leptin alone and the sequential leptin-insulin treatment may point to the ability of these cells to respond to energy substrate availability, as bovine muscle has evolved to utilize lipids and fatty acids in response to a metabolism which provides only limited glucose. This cross-talk between insulin and leptin signaling pathways points to a better understanding of the mechanisms driving energy substrate utilization in ruminant muscle and may provide a useful model for greater understanding of the molecular mechanisms underlying the development of insulin resistance and Type 2 diabetes in man.

Gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is defined as glucose intolerance of various degrees that is first detected during pregnancy. GDM is detected through the screening of pregnant women for clinical risk factors and, among at-risk women, testing for abnormal glucose tolerance that is usually, but not invariably, mild and asymptomatic. GDM appears to result from the same broad spectrum of physiological and genetic abnormalities that characterize diabetes outside of pregnancy. Indeed, women with GDM are at high risk for having or developing diabetes when they are not pregnant. Thus, GDM provides a unique opportunity to study the early pathogenesis of diabetes and to develop interventions to prevent the disease.

Therapeutic Actions of an Insulin Receptor Activator and a Novel Peroxisome Proliferator-Activated Receptor γ Agonist in the Spontaneously Hypertensive Obese Rat Model of Metabolic Syndrome X

Insulin resistance clusters with hyperlipidemia, impaired glucose tolerance, and hypertension as metabolic syndrome X. We tested a low molecular weight insulin receptor activator, demethylasterriquinone B-1 (DMAQ-B1), and a novel indole peroxisome proliferator-activated receptor gamma agonist, 2-(2-(4-phenoxy-2-propylphenoxy)ethyl)indole-5-acetic acid (PPEIA), in spontaneously hypertensive obese rats (SHROB), a genetic model of syndrome X. Agents were given orally for 19 days. SHROB showed fasting normoglycemia but impaired glucose tolerance after an oral load, as shown by increased glucose area under the curve (AUC) [20,700 mg x min/ml versus 8100 in lean spontaneously hypertensive rats (SHR)]. Insulin resistance was indicated by 20-fold excess fasting insulin and increased insulin AUC (6300 ng x min/ml versus 990 in SHR). DMAQ-B1 did not affect glucose tolerance (glucose AUC = 21,300) but reduced fasting insulin 2-fold and insulin AUC (insulin AUC = 4300). PPEIA normalized glucose tolerance (glucose AUC = 9100) and reduced insulin AUC (to 3180) without affecting fasting insulin. PPEIA also increased food intake, fat mass, and body weight gain (81 +/- 12 versus 45 +/- 8 g in untreated controls), whereas DMAQ-B1 had no effect on body weight but reduced subscapular fat mass. PPEIA but not DMAQ-B1 reduced blood pressure. In skeletal muscle, insulin-stimulated phosphorylation of the insulin receptor and insulin receptor substrate protein 1-associated phosphatidylinositol 3-kinase activity were decreased by 40 to 55% in SHROB relative to lean SHR. PPEIA, but not DMAQ-B1, enhanced both insulin actions. SHROB also showed severe hypertriglyceridemia (355 +/- 42 mg/dl versus 65 +/- 3 in SHR) attenuated by both agents (DMAQ-B1, 228 +/- 18; PPEIA, 79 +/- 3). Both these novel antidiabetic agents attenuate insulin resistance and hypertriglyceridemia associated with metabolic syndrome but via distinct mechanisms.

Insulin Receptor Substrate 2 Plays Diverse Cell-specific Roles in the Regulation of Glucose Transport

The insulin receptor substrate 2 (IRS-2) protein is one of the major insulin-signaling substrates. In the present study, we investigated the role of IRS-2 in skin epidermal keratinocytes and dermal fibroblasts. Although skin is not a classical insulin target tissue, we have previously demonstrated that insulin, via the insulin receptor, is essential for normal skin cell physiology. To identify the role of IRS-2 in skin cells, we studied cells isolated from IRS-2 knock-out (KO) mice. Whereas proliferation and differentiation were not affected in the IRS-2 KO cells, a striking effect was observed on glucose transport. In IRS-2 KO keratinocytes, the lack of IRS-2 resulted in a dramatic increase in basal and insulin-stimulated glucose transport. The increase in glucose transport was associated with an increase in total phosphatidylinositol (PI) 3-kinase and Akt activation. In contrast, fibroblasts lacking IRS-2 exhibited a significant decrease in basal and insulin-induced glucose transport. We identified the point of divergence, leading to these differences between keratinocytes and fibroblasts, at the IRS-PI 3-kinase association step. In epidermal keratinocytes, PI 3-kinase is associated with and activated by only the IRS-1 protein. On the other hand, in dermal fibroblasts, PI 3-kinase is exclusively associated with and activated by the IRS-2 protein. These observations suggest that IRS-2 functions as a negative or positive regulator of glucose transport in a cell-specific manner. Our results also show that IRS-2 function depends on its cell-specific association with PI 3-kinase.

Gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is defined as glucose intolerance of various degrees that is first detected during pregnancy. GDM is detected through the screening of pregnant women for clinical risk factors and, among at-risk women, testing for abnormal glucose tolerance that is usually, but not invariably, mild and asymptomatic. GDM appears to result from the same broad spectrum of physiological and genetic abnormalities that characterize diabetes outside of pregnancy. Indeed, women with GDM are at high risk for having or developing diabetes when they are not pregnant. Thus, GDM provides a unique opportunity to study the early pathogenesis of diabetes and to develop interventions to prevent the disease.

Decreased contraction-stimulated glucose transport in isolated epitrochlearis muscles of pregnant rats

Late pregnancy is characterized by insulin resistance for glucose transport in skeletal muscle. The main purpose of this study was to investigate the effect of late pregnancy on contraction-stimulated glucose transport in isolated rat skeletal muscle after in vitro electrical stimulation. Isolated epitrochlearis muscles of 19-day pregnant and aged-matched nonpregnant control rats were studied. One muscle from each rat was stimulated to contract, and the contralateral muscle served as a resting control. Tension developed during contractile activity, 3-O-methylglucose (3-MG) transport rate, and glycogen concentration were determined. Epitrochlearis muscles from other rats were used to measure insulin-stimulated 3-MG transport. There was no detectable difference between the nonpregnant and pregnant groups for contractile performance (peak tension, total tension, or fatigue). Pregnancy was not associated with significant changes in muscle glycogen concentration (resting or after contractile activity) or the contraction-stimulated decrement in glycogen concentration. For muscles from pregnant vs. nonpregnant groups, there was a 22% reduction (P < or = 0.05) in contraction-stimulated glucose transport, a 28% decrease (P < or = 0.05) in insulin-stimulated glucose transport, and unchanged basal glucose transport. In conclusion, isolated epitrochlearis muscles from pregnant vs. nonpregnant rats had a relative decrement in contraction-stimulated glucose transport that was similar to the relative decline in insulin-stimulated glucose transport. The decrement in contraction-stimulated glucose transport was not attributable to pregnancy-related changes in tension development or glycogen levels. The similar relative decline in insulin- and contraction-stimulated glucose transport raises the possibility that pregnancy impairs a distal process that is common to mechanisms whereby each stimulus activates glucose transport.

Sending the signal: molecular mechanisms regulating glucose uptake

The molecular signaling mechanisms by which insulin leads to increased glucose transport and metabolism and gene expression are not completely elucidated. We have characterized the nature of insulin signaling defects in skeletal muscle from Type 2 diabetic patients. Insulin receptor substrate (IRS-1) phosphorylation, phosphatidylinositol (PI) 3-kinase activity, and glucose transport activity are impaired as a consequence of functional defects, whereas insulin receptor tyrosine phosphorylation, mitogen-activated protein kinase (MAPK) phosphorylation, and glycogen synthase activity are normal. Using biotinylated photoaffinity labeling, we have shown that reduced cell surface GLUT4 levels can explain glucose transport defects in skeletal muscle from Type 2 diabetic patients under insulin-stimulated conditions. Current work is focused on mechanisms behind insulin-dependent and insulin-independent regulation of glucose uptake. We have recently determined the independent effects of insulin and hypoxia/AICAR exposure on glucose transport and cell surface GLUT4 content in skeletal muscle from nondiabetic and Type 2 diabetic subjects. Hypoxia and AICAR increase glucose transport via an insulin-independent mechanism involving activation of 5'-AMP-activated kinase (AMPK). AMPK signaling is intact, because 5-aminoimidazole-4-carboxamide 1-beta-D-ribonucleoside (AICAR) increased AMPK and acetyl-CoA carboxylase (ACC) phosphorylation to a similar extent in Type 2 diabetic and nondiabetic subjects. However, AICAR responses on glucose uptake were impaired. Our studies highlight important AMPK-dependent and independent pathways in the regulation of GLUT4 and glucose transport activity in insulin resistant skeletal muscle. Understanding signaling mechanisms to downstream metabolic responses may provide valuable clues to a future therapy for Type 2 diabetes.

Interaction of the retinal insulin receptor beta-subunit with the p85 subunit of phosphoinositide 3-kinase

Recently, we have shown that phosphoinositide 3-kinase (PI3K) in retina is regulated in vivo through light activation of the insulin receptor beta-subunit. In this study, we have cloned the 41 kDa cytoplasmic region of the retinal insulin receptor (IRbeta) and used the two-hybrid assay of protein-protein interaction in the yeast Saccharomyces cerevisiae to demonstrate the interaction between the p85 subunit of PI3K and the cytoplasmic region of IRbeta. Under conditions where IRbeta autophosphorylates, substitution of Y1322F and M1325P in IRbeta resulted in the abolition of p85 binding to the IRbeta, confirming that the p85 subunit of PI3K binds to Y1322. The binding site for p85 on IRbeta was also confirmed in the yeast three-hybrid system. Using the C-terminal region of IRbeta (amino acids 1293-1343 encompassing the YHTM motif) as bait and supplying an exogenous tyrosine kinase gene to yeast cells, we determined that the IRbeta-pYTHM motif interacts with p85. We also used retinal organ cultures to demonstrate insulin activation of the insulin receptor and subsequent binding of p85, measured through GST pull-down assays with p85 fusion proteins. Further, the Y960F mutant insulin receptor, which does not bind IRS-1, is capable of bringing down PI3K activity from retina lysates. On the other hand, in response to insulin, IRS-2 is able to interact with the p85 subunit of PI3K in the retina. These results suggest that multiple signaling pathways could regulate the PI3K activity and subsequent activation of Akt in the retina.

Early insulin signaling cascade in a model of oxidative skeletal muscle: mouse Sol8 cell line

Cell models provide important tools to investigate the mechanisms modulating the insulin-signaling cascade. Insulin interaction and subsequent signaling of cells is complex and regulated at multiple levels: receptor abundance, binding dynamics, phosphorylation/dephosphorylation of tyrosine and serine/threonine residues, and subsequent interactions of key intracellular messengers. We report early insulin signaling events in the mouse Sol8 myogenic cell line. Sol8 cells responded to insulin by increasing total IRS-1, p85 PI3-kinase and tyrosine phosphorylated IRS-1 (pY-IRS-1) at 10 min (P<0.05), but not at 1 min of insulin stimulation. The dose-response relationships at 10-min insulin (10 to 300 nM) stimulation showed that IRS-1 and pY-IRS-1 responded to 100 and 300 nM insulin, and the p85 PI3-kinase response peaked at 30 nM insulin. PI3-kinase appeared to be present in high abundance and, in response to insulin, recruitment to the insulin receptor tyrosine kinase (IR) of IRS-1 and PI3-kinase was observed. The increase in IRS-1 detected in IR immunoprecipitates was twofold, while the corresponding increase in PI3-kinase was threefold, suggesting direct recruitment of PI3-kinase to the IR. PI3-kinase detected in IRS-1 immunoprecipitates in response to insulin increased 1.7-fold. An ultimate target of this pathway, GLUT4 recruitment to the PM, was delayed (30 min), the increase in GLUT4 being of similar magnitude (1.6-fold) to the early signaling events. Saturation binding analysis indicated that IR in the plasma membrane was not down-regulated in response to insulin. The present study suggests that early signaling events in the insulin cascade are invoked in Sol8 myogenic cells and that this cell line provides a useful model to study insulin signaling.

Human placental growth hormone increases expression of the p85 regulatory unit of phosphatidylinositol 3-kinase and triggers severe insulin resistance in skeletal muscle

The insulin resistance of normal pregnancy is necessary to divert fuels to the fetus to meet fetal growth demands and is mediated by placental hormones. We recently demonstrated that human placental GH (hPGH) can trigger severe insulin resistance in transgenic (TG) mice. In this study we sought to elucidate the cellular mechanisms by which hPGH interferes with insulin signaling in muscle in TG mice. Insulin-stimulated GLUT-4 translocation to the plasma membrane (PM) was reduced in the TG compared with wild-type (WT) mice (P = 0.05). Insulin receptor (IR) levels were modestly reduced by 19% (P < 0.01) in TG mice, but there were no changes in phosphorylation of IR or IR substrate-1 (IRS-1) between WT and TG mice. A singular finding was a highly significant increase in the p85 alpha regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase; P < 0.001), yet a reduced ability of insulin to stimulate IRS-1-associated PI 3-kinase activity (P < 0.05). Although the levels of the p110 catalytic subunit protein of PI 3-kinase and IRS-1 were unchanged in the TG mice, insulin's ability to stimulate p110 association with IRS-1 was markedly reduced (P < 0.0001). We demonstrate a unique mechanism of insulin resistance and suggest that hPGH may contribute to the insulin resistance of normal pregnancy by increasing the expression of the p85 alpha monomer, which competes in a dominant negative fashion with the p85-p110 heterodimer for binding to IRS-1 protein.

Aberrant p38 mitogen-activated protein kinase signalling in skeletal muscle from Type 2 diabetic patients

AIMS/HYPOTHESIS

p38 mitogen activated protein kinase (MAPK) is generally thought to facilitate signal transduction to genomic, rather than metabolic responses. However, recent evidence implicates a role for p38 MAPK in the regulation of glucose transport; a site of insulin resistance in Type 2 diabetes. Thus we determined p38 MAPK protein expression and phosphorylation in skeletal muscle from Type 2 diabetic patients and non-diabetic subjects.

METHODS

In vitro effects of insulin (120 nmol/l) or AICAR (1 mmol/l) on p38 MAPK expression and phosphorylation were determined in skeletal muscle from non-diabetic (n=6) and Type 2 diabetic (n=9) subjects.

RESULTS

p38 MAPK protein expression was similar between Type 2 diabetic patients and non-diabetic subjects. Insulin exposure increased p38 MAPK phosphorylation in non-diabetic, but not in Type 2 diabetic patients. In contrast, basal phosphorylation of p38 MAPK was increased in skeletal muscle from Type 2 diabetic patients.

CONCLUSION/INTERPRETATION

Insulin increases p38 MAPK phosphorylation in skeletal muscle from non-diabetic subjects, but not in Type 2 diabetic patients. However, basal p38 MAPK phosphorylation is increased in skeletal muscle from Type 2 diabetic patients. Thus, aberrant p38 MAPK signalling might contribute to the pathogenesis of insulin resistance.

Insulin signalling and resistance in patients with chronic heart failure

We investigated whether insulin resistance in patients with chronic heart failure (CHF) is associated with impaired insulin signalling in skeletal muscle and whether exercise training would lead to an improvement in insulin signalling, concomitant with enhanced insulin action. Fourteen men with CHF due to idiopathic dilated cardiomyopathy, with mild-to-moderate limitation of physical activity and a left-ventricular ejection fraction of less than 45 %, were studied before and after either a 5 month exercise training programme (n = 7) or standard care (n = 7). Seven healthy men participated as controls. Whole-body insulin-stimulated glucose uptake was determined by the euglycaemic hyperinsulinaemic clamp technique and skeletal muscle biopsy samples were obtained before and after the insulin infusion for insulin signalling measurements. Insulin-stimulated glucose uptake was 20 % lower in CHF patients versus healthy subjects. Physiological hyperinsulinaemia increased tyrosine phosphorylation of insulin receptor substrate (IRS)-1 by approximately 2.5-fold, IRS-1-associated phosphatidylinositol 3-kinase (PI-3-kinase) activity by approximately 2-fold and Akt (protein kinase B) phosphorylation by approximately 3-fold, with similar responses between healthy subjects and CHF patients. Insulin-mediated glucose uptake was not altered in patients after standard care, whereas exercise training elicited a 25 % increase in glucose uptake. Neither standard care nor exercise training altered insulin-stimulated tyrosine phosphorylation of IRS-1, IRS-1-associated PI-3-kinase activity or Akt phosphorylation. In conclusion, the CHF patients demonstrated impaired insulin-stimulated glucose uptake, despite normal signal transduction in skeletal muscle at the level of IRS-1, PI-3-kinase and Akt. Of clinical relevance is the finding that exercise training improves glucose uptake. However, these changes in insulin action after exercise training appear to be independent of enhanced insulin signalling at the level of IRS-1, PI-3-kinase or Akt.