Role of insulin receptor substrate-1 serine 307 phosphorylation and adiponectin in adipose tissue insulin resistance in late pregnancy

A cross-ancestry genome-wide meta-analysis, fine-mapping, and gene prioritization approach to characterize the genetic architecture of adiponectin

Previous genome-wide association studies (GWASs) for adiponectin, a complex trait linked to type 2 diabetes and obesity, identified >20 associated loci. However, most loci were identified in populations of European ancestry, and many of the target genes underlying the associations remain unknown. We conducted a cross-ancestry adiponectin GWAS meta-analysis in ≤46,434 individuals from the Metabolic Syndrome in Men (METSIM) cohort and the ADIPOGen and AGEN consortiums. We combined study-specific association summary statistics using a fixed-effects, inverse variance-weighted approach. We identified 22 loci associated with adiponectin (p < 5×10-8), including 15 known and seven previously unreported loci. Among individuals of European ancestry, Genome-wide Complex Traits Analysis joint conditional analysis (GCTA-COJO) identified 14 additional distinct signals at the ADIPOQ, CDH13, HCAR1, and ZNF664 loci. Leveraging the cross-ancestry data, FINEMAP + SuSiE identified 45 causal variants (PP > 0.9), which also exhibited potential pleiotropy for cardiometabolic traits. To prioritize target genes at associated loci, we propose a combinatorial likelihood scoring formalism (Gene Priority Score [GPScore]) based on measures derived from 11 gene prioritization strategies and the physical distance to the transcription start site. With GPScore, we prioritize the 30 most probable target genes underlying the adiponectin-associated variants in the cross-ancestry analysis, including well-known causal genes (e.g., ADIPOQ, CDH13) and additional genes (e.g., CSF1, RGS17). Functional association networks revealed complex interactions of prioritized genes, their functionally connected genes, and their underlying pathways centered around insulin and adiponectin signaling, indicating an essential role in regulating energy balance in the body, inflammation, coagulation, fibrinolysis, insulin resistance, and diabetes. Overall, our analyses identify and characterize adiponectin association signals and inform experimental interrogation of target genes for adiponectin.

Phosphorylation Codes in IRS-1 and IRS-2 Are Associated with the Activation/Inhibition of Insulin Canonical Signaling Pathways

Insulin receptor substrates 1 and 2 (IRS-1 and IRS-2) are signaling adaptor proteins that participate in canonical pathways, where insulin cascade activation occurs, as well as in non-canonical pathways, in which phosphorylation of substrates is carried out by a diverse array of receptors including integrins, cytokines, steroid hormones, and others. IRS proteins are subject to a spectrum of post-translational modifications essential for their activation, encompassing phosphorylation events in distinct tyrosine, serine, and threonine residues. Tyrosine residue phosphorylation is intricately linked to the activation of the insulin receptor cascade and its interaction with SH2 domains within a spectrum of proteins, including PI3K. Conversely, serine residue phosphorylation assumes a different function, serving to attenuate the effects of insulin. In this review, we have identified over 50 serine residues within IRS-1 that have been reported to undergo phosphorylation orchestrated by a spectrum of kinases, thereby engendering the activation or inhibition of different signaling pathways. Furthermore, we delineate the phosphorylation of over 10 distinct tyrosine residues at IRS-1 or IRS-2 in response to insulin, a process essential for signal transduction and the subsequent activation of PI3K.

The Role of Adiponectin during Pregnancy and Gestational Diabetes

Pregnancy involves a range of metabolic adaptations to supply adequate energy for fetal growth and development. Gestational diabetes (GDM) is defined as hyperglycemia with first onset during pregnancy. GDM is a recognized risk factor for both pregnancy complications and long-term maternal and offspring risk of cardiometabolic disease development. While pregnancy changes maternal metabolism, GDM can be viewed as a maladaptation by maternal systems to pregnancy, which may include mechanisms such as insufficient insulin secretion, dysregulated hepatic glucose output, mitochondrial dysfunction and lipotoxicity. Adiponectin is an adipose-tissue-derived adipokine that circulates in the body and regulates a diverse range of physiologic mechanisms including energy metabolism and insulin sensitivity. In pregnant women, circulating adiponectin levels decrease correspondingly with insulin sensitivity, and adiponectin levels are low in GDM. In this review, we summarize the current state of knowledge about metabolic adaptations to pregnancy and the role of adiponectin in these processes, with a focus on GDM. Recent studies from rodent model systems have clarified that adiponectin deficiency during pregnancy contributes to GDM development. The upregulation of adiponectin alleviates hyperglycemia in pregnant mice, although much remains to be understood for adiponectin to be utilized clinically for GDM.

Obesity and pregnancy, the perfect metabolic storm

Pregnancy is a physiological stress that requires dynamic, regulated changes affecting maternal and fetal adiposity. Excessive accumulation of dysfunctional adipose tissue defined by metabolic and molecular alterations cause severe health consequences for mother and fetus. When subjected to sustained overnutrition, the cellular and lipid composition of the adipose tissue changes predisposing to insulin resistance, diabetes, and other metabolic disorders compromising the outcome of the pregnancy. Moreover, excessive maternal weight gain, usually in the context of obesity, predisposes to an increased flux of nutrients from mother to fetus throughout the placenta. The fetus of an obese mother will accumulate more adiposity and may increase the risk of future metabolic disorder later in life. Thus, further understanding of the interaction between maternal metabolism, epigenetic regulation of the adipose tissue, and their transgenerational transfer are required to mitigate the adverse health outcomes for the mother and the fetus associated with maternal obesity.

Apolipoprotein A-I Protects Against Pregnancy-Induced Insulin Resistance in Rats

Objective- Insulin resistance and inflammation in pregnancy are risk factors for gestational diabetes mellitus. Increased plasma HDL (high-density lipoprotein) and apo (apolipoprotein) A-I levels have been reported to improve glucose metabolism and inhibit inflammation in animals and humans. This study asks whether increasing plasma apoA-I levels improves insulin sensitivity and reduces inflammation in insulin-resistant pregnant rats. Approach and Results- Insulin-resistant pregnant rats received intravenous infusions of lipid-free apoA-I (8 mg/kg) or saline on days 6, 9, 12, 15, and 18 of pregnancy. The rats were then subjected to a euglycemic-hyperinsulinemic clamp. Glucose uptake was increased in white and brown adipose tissue by 57±13% and 32±10%, respectively ( P<0.05 for both), and in quadriceps and gastrocnemius muscle by 35±9.7% and 47±14%, respectively ( P<0.05 for both), in the apoA-I-treated pregnant rats relative to saline-infused pregnant rats. The pregnant rats that were treated with apoA-I also had reduced plasma TNF-α (tumor necrosis factor-α) levels by 57±8.4%, plasma IL (interleukin)-6 levels by 67±9.5%, and adipose tissue macrophage content by 54±8.2% ( P<0.05 for all) relative to the saline-treated pregnant rats. Conclusions- These studies establish that apoA-I protects against pregnancy-induced insulin resistance in rats by increasing insulin sensitivity in adipose tissue and skeletal muscle and inhibiting inflammation. This identifies apoA-I as a potential target for preventing pregnancy-induced insulin resistance and reducing the incidence of gestational diabetes mellitus.

Connecting Metainflammation and Neuroinflammation Through the PTN-MK-RPTPβ/ζ Axis: Relevance in Therapeutic Development

Inflammation is a common factor of pathologies such as obesity, type 2 diabetes or neurodegenerative diseases. Chronic inflammation is considered part of the pathogenic mechanisms of different disorders associated with aging. Interestingly, peripheral inflammation and the associated metabolic alterations not only facilitate insulin resistance and diabetes but also neurodegenerative disorders. Therefore, the identification of novel pathways, common to the development of these diseases, which modulate the immune response and signaling is key. It will provide highly relevant information to advance our knowledge of the multifactorial process of aging, and to establish new biomarkers and/or therapeutic targets to counteract the underlying chronic inflammatory processes. One novel pathway that regulates peripheral and central immune responses is triggered by the cytokines pleiotrophin (PTN) and midkine (MK), which bind its receptor, Receptor Protein Tyrosine Phosphatase (RPTP) β/ζ, and inactivate its phosphatase activity. In this review, we compile a growing body of knowledge suggesting that PTN and MK modulate the immune response and/or inflammation in different pathologies characterized by peripheral inflammation associated with insulin resistance, such as aging, and in central disorders characterized by overt neuroinflammation, such as neurodegenerative diseases and endotoxemia. Evidence strongly suggests that regulation of the PTN and MK signaling pathways may provide new therapeutic opportunities particularly in those neurological disorders characterized by increased PTN and/or MK cerebral levels and neuroinflammation. Importantly, we discuss existing therapeutics, and others being developed, that modulate these signaling pathways, and their potential use in pathologies characterized by overt neuroinflammation.

Geographic diversity in genotype frequencies and meta-analysis of the association between rs1801282 polymorphisms and gestational diabetes mellitus

AIMS

To derive a better understanding of the association between peroxisome proliferator-activated receptor gamma (PPAR-γ) rs1801282 polymorphisms and gestational diabetes mellitus (GDM) in general and in racial and ethnic subgroups and to illustrate geographic distribution of the protective of G allele of rs1801282 in women with and without GDM.

METHODS

ProQuest, PubMed, Medline, Web of Science, and Wanfang Data were systematically searched. Case-control studies on association between rs1801282 polymorphisms and GDM were selected. Comprehensive Meta-Analysis 2.0 statistical software was used to determine the relationship between GDM and rs1801282 polymorphism. Race/ethnicity-based and country-based stratified analysis was conducted.

RESULTS

Sixteen studies involving 3129 cases and 7168 controls were included. Significant associations were observed between rs1801282 polymorphisms and GDM under the dominant, heterozygote, and allele models. The G allele of rs1801282 polymorphism was associated with a reduced risk of GDM in Asian, especially Chinese, populations. Data revealed significant geographic diversity in frequency of the protective G allele in women with and without GDM.

CONCLUSIONS

The rs1801282 polymorphism may not be associated with genetic susceptibility to GDM in whites. The G allele of rs1801282 polymorphism was associated with reduced risk of GDM in Asians, especially Chinese, but not South Koreans.

PPARs and Metabolic Disorders Associated with Challenged Adipose Tissue Plasticity

Peroxisome proliferator-activated receptors (PPARs) are members of a family of nuclear hormone receptors that exert their transcriptional control on genes harboring PPAR-responsive regulatory elements (PPRE) in partnership with retinoid X receptors (RXR). The activation of PPARs coordinated by specific coactivators/repressors regulate networks of genes controlling diverse homeostatic processes involving inflammation, adipogenesis, lipid metabolism, glucose homeostasis, and insulin resistance. Defects in PPARs have been linked to lipodystrophy, obesity, and insulin resistance as a result of the impairment of adipose tissue expandability and functionality. PPARs can act as lipid sensors, and when optimally activated, can rewire many of the metabolic pathways typically disrupted in obesity leading to an improvement of metabolic homeostasis. PPARs also contribute to the homeostasis of adipose tissue under challenging physiological circumstances, such as pregnancy and aging. Given their potential pathogenic role and their therapeutic potential, the benefits of PPARs activation should not only be considered relevant in the context of energy balance-associated pathologies and insulin resistance but also as potential relevant targets in the context of diabetic pregnancy and changes in body composition and metabolic stress associated with aging. Here, we review the rationale for the optimization of PPAR activation under these conditions.

Body condition score prior to parturition is associated with plasma and adipose tissue biomarkers of lipid metabolism and inflammation in Holstein cows

Background

Previous research has revealed a strong inflammatory response within adipose (AT) tissue during the transition into lactation. Whether this effect is a result of oxidative stress induced by lipolysis and fatty acid oxidation associated with differences in prepartum body condition score remains to be determined. The objectives of this study were to investigate systemic biomarkers of energy balance and inflammation and the expression of lipid metabolism- and inflammation-related genes in AT during the transition period in dairy cows.

Results

Twenty multiparous Holstein cows were retrospectively divided by body condition score (BCS) prior to parturition into two groups (10 cows/group): BCS ≤ 3.25 (LoBCS) and BCS ≥ 3.75 (HiBCS). Subcutaneous adipose tissue was biopsied from the tail-head region at d − 10, 7 and 20 relative to parturition. Plasma was used to evaluate biomarkers of energy balance (EBAL) [free fatty acids (NEFA), glycerol, insulin] and inflammation [IL-1β, haptoglobin, myeloperoxidase, and reactive oxygen metabolites (ROM)]. Although insulin concentration was not affected by BCS, NEFA was overall greater and glycerol lower in HiBCS cows. Greater activity of myeloperoxidase in plasma coincided with increased haptoglobin and IL-1β postpartum in LoBCS cows. Among genes related with oxidative stress, the expression of the cytosolic antioxidant enzyme SOD1 was greater in LoBCS compared to HiBCS. Cows in LoBCS compared with HiBCS had greater overall expression of ABDH5 and ATGL along with ADIPOQ, indicating enhanced basal lipolysis and secretion of adiponectin. Expression of CPT1A, ACADVL, and ACOX1 was greater overall in HiBCS than LoBCS indicating enhanced NEFA oxidation. Although the temporal increase in plasma NEFA regardless of BCS coincided with the profile of CPT1A, the gradual decrease in genes related with re-esterification of NEFA (PCK1) and glycerol efflux (AQP7) coupled with an increase in glycerol kinase (GK) suggested some stimulation of NEFA utilization within adipose tissue. This idea is supported in part by the gradual decrease in insulin regardless of BCS. Although expression of the inflammation-related gene toll-like receptor 4 (TLR4) was greater in HiBCS versus LoBCS cows at −10 d, expression of TLR9 was greater in HiBCS versus LoBCS at 20 d. These profiles did not seem to be associated with concentrations of pro-inflammatory biomarkers or ROM.

Conclusions

Overall, data indicated that cows with BCS 3.25 or lower before calving experienced greater alterations in systemic inflammation and basal lipolysis without excessive increases in NEFA plasma concentrations. Despite the greater plasma NEFA around parturition, cows with BCS 3.75 or higher seemed to have a more active system for catabolism of NEFA and utilization of glycerol within adipose tissue. A linkage between those pathways and risk of disorders postpartum remains to be determined.

Electronic supplementary material

The online version of this article (10.1186/s40104-017-0221-1) contains supplementary material, which is available to authorized users.

Loss of Anticontractile Effect of Perivascular Adipose Tissue on Pregnant Rats: A Potential Role of Tumor Necrosis Factor-α

The present investigation examined the effect of pregnancy on the anticontractile effect of perivascular adipose tissue (PVAT) on the rat. Ring segments of the aorta, with and without PVAT, were set up in organ baths for isometric tension recording. In both groups, concentration-response curves to 5-hydroxytryptamine (5-HT) were displaced to the right with a reduction of the maximum response in aorta segments with PVAT. The anticontractile effect of PVAT was attenuated on segments from pregnant rats. 4-Aminopyridine (4-AP), an inhibitor of voltage-gated potassium (Kv) channels, enhanced 5-HT-induced contractions of aorta segments from pregnant and nonpregnant rats only when PVAT was attached. There was no difference in the effect of 4-aminopyridine on 5-HT-induced contractions of aorta segments with PVAT from pregnant and nonpregnant rats. There was also no significant difference in the expression of Kv7.4 channels in aorta segments (with PVAT) between pregnant and nonpregnant rats. Tumor necrosis factor-α (TNF-α) was detected in PVAT from pregnant and nonpregnant rats. The level of TNF-α was significantly greater in PVAT from pregnant rats. Treatment of pregnant rats with pentoxyphyline significantly reduced the level of TNF-α in the PVAT and restored the anticontractile effect of PVAT on aorta segments from pregnant rats. Finally, TNF-α (10 ng/mL) potentiated 5-HT-induced contractions of PVAT-containing pregnant rat aorta. These results would suggest that the loss of anticontractile effect of PVAT in pregnant rat aorta could be due to enhanced production of TNF-α in the PVAT in these rats.

Peroxisome proliferator activated receptor gamma 2 modulates late pregnancy homeostatic metabolic adaptations

Pregnancy requires the adaptation of maternal energy metabolism including expansion and functional modifications of adipose tissue. Insulin resistance (IR), predominantly during late gestation, is a physiological metabolic adaptation that serves to support the metabolic demands of fetal growth. The molecular mechanisms underlying these adaptations are not fully understood and may contribute to gestational diabetes mellitus. Peroxisome proliferator-activated receptor gamma (PPARγ) controls adipogenesis, glucose and lipid metabolism and insulin sensitivity. The PPARγ2 isoform is mainly expressed in adipocytes and is thus likely to contribute to adipose tissue adaptation during late pregnancy. In the present study, we investigated the contribution of PPARγ2 to the metabolic adaptations occurring during the late phase of pregnancy in the context of IR. Using a model of late pregnancy in PPARγ2 knockout (KO) mice, we found that deletion of PPARγ2 exacerbated IR in association with lower serum adiponectin levels, increased body weight and enhanced lipid accumulation in liver. Lack of PPARγ2 provoked changes in the distribution of fat mass and preferentially prevented the expansion of the perigonadal depot while at the same time exacerbating inflammation. PPARγ2KO pregnant mice presented adipose tissue depot-dependent decreased expression of genes involved in lipid metabolism. Collectively, these data indicate that PPARγ2 is essential to promote healthy adipose tissue expansion and immune and metabolic functionality during pregnancy, contributing to the physiological adaptations that lead gestation to term.

Maternal cardiac metabolism in pregnancy

Pregnancy causes dramatic physiological changes in the expectant mother. The placenta, mostly foetal in origin, invades maternal uterine tissue early in pregnancy and unleashes a barrage of hormones and other factors. This foetal 'invasion' profoundly reprogrammes maternal physiology, affecting nearly every organ, including the heart and its metabolism. We briefly review here maternal systemic metabolic changes during pregnancy and cardiac metabolism in general. We then discuss changes in cardiac haemodynamic during pregnancy and review what is known about maternal cardiac metabolism during pregnancy. Lastly, we discuss cardiac diseases during pregnancy, including peripartum cardiomyopathy, and the potential contribution of aberrant cardiac metabolism to disease aetiology.

Fructose during pregnancy affects maternal and fetal leptin signaling

Fructose intake from added sugars correlates with the epidemic rise in obesity, metabolic syndrome and cardiovascular diseases. Fructose intake also causes features of metabolic syndrome in laboratory animals. Therefore, we have investigated whether fructose modifies lipidemia in pregnant rats and produces changes in their fetuses. Thus, fructose administration (10% wt/vol.) in the drinking water of rats throughout gestation leads to maternal hypertriglyceridemia. This change was not observed in glucose-fed rats, although both carbohydrates produced similar changes in liver triglycerides and in the expression of transcription factors and enzymes involved in lipogenesis. After fasting overnight, mothers fed with carbohydrates were found to be hyperleptinemic. However, after a bolus of glucose, leptinemia in fructose-fed mothers showed no response, whereas it increased in parallel in glucose-fed and control mothers. Fetuses from fructose-fed mothers showed hypotriglyceridemia and a higher hepatic triglyceride content than fetuses from control or glucose-fed mothers. A higher expression of genes related to lipogenesis and a lower expression of fatty acid catabolism genes were also found in fetuses from fructose-fed mothers. Moreover, although hyperleptinemic, these fetuses exhibited increased tyrosine phosphorylation of the signal transducer and activator of transcription-3 (STAT-3) protein, without a parallel increase in the serine phosphorylation of STAT-3 nor in the suppressor of cytokine signaling-3 protein levels whose expression is regulated by leptin through STAT-3 activation. Thus, fructose intake during gestation provoked a diminished maternal leptin response to fasting and refeeding and an impairment in the transduction of the leptin signal in the fetuses, which could be responsible for their hepatic steatosis.

Pioglitazone therapy in mouse offspring exposed to maternal obesity

OBJECTIVE

Pioglitazone (PIO), an antidiabetic drug of the thiazolidinedione family, improves glucose and lipid metabolism in muscle, adipose, and liver tissues via peroxisome proliferator-activated receptor gamma activation. We hypothesize that PIO therapy will improve the metabolic status of offspring exposed to maternal obesity in a mouse model developmentally programmed for metabolic syndrome.

STUDY DESIGN

CD-1 female mice were fed a high-fat diet for 3 months prior to breeding and throughout pregnancy and lactation. The pups were weaned to a standard-fat diet. Offspring were randomly assigned to receive 40 mg/kg of PIO in 0.5% of methyl cellulose or 0.5% methyl cellulose by daily oral gavage for 2 weeks. The pre- and posttreatment total body weights of the pups were recorded. Visceral and subcutaneous adipose tissue were evaluated using microcomputed tomography. Serum analytes were measured. After treatment, minimally invasive microendoscopic fluorescence confocal imaging and intraperitoneal glucose tolerance tests were performed. The data were analyzed using appropriate statistical tests (significance, P < .05).

RESULTS

PIO therapy resulted in lower total body weight and lower visceral adipose tissue gain and increased subcutaneous adipose tissue. PIO significantly lowered triglycerides, insulin levels, and homeostasis model assessment of insulin resistance in males and fasting glucose in females. There was a trend toward larger adipocyte size.

CONCLUSION

Short-term PIO therapy in the offspring of obese mothers attenuates metabolic changes associated with the developmental programming of metabolic syndrome. These novel data suggest a potential role for drugs that activate peroxisome proliferator-activated receptor gamma receptors to prevent metabolic syndrome in the adult offspring at risk to develop metabolic alterations.

Peroxisome proliferator-activated receptorα agonists differentially regulate inhibitor of DNA binding expression in rodents and human cells

Inhibitor of DNA binding (Id2) is a helix-loop-helix (HLH) transcription factor that participates in cell differentiation and proliferation. Id2 has been linked to the development of cardiovascular diseases since thiazolidinediones, antidiabetic agents and peroxisome proliferator-activated receptor (PPAR) gamma agonists, have been reported to diminish Id2 expression in human cells. We hypothesized that PPARα activators may also alter Id2 expression. Fenofibrate diminished hepatic Id2 expression in both late pregnant and unmated rats. In 24 hour fasted rats, Id2 expression was decreased under conditions known to activate PPARα. In order to determine whether the fibrate effects were mediated by PPARα, wild-type mice and PPARα-null mice were treated with Wy-14,643 (WY). WY reduced Id2 expression in wild-type mice without an effect in PPARα-null mice. In contrast, fenofibrate induced Id2 expression after 24 hours of treatment in human hepatocarcinoma cells (HepG2). MK-886, a PPARα antagonist, did not block fenofibrate-induced activation of Id2 expression, suggesting a PPARα-independent effect was involved. These findings confirm that Id2 is a gene responsive to PPARα agonists. Like other genes (apolipoprotein A-I, apolipoprotein A-V), the opposite directional transcriptional effect in rodents and a human cell line further emphasizes that PPARα agonists have different effects in rodents and humans.

ROS constitute a convergence nexus in the development of IGF1 resistance and impaired wound healing in a rat model of type 2 diabetes

An indolent non-healing wound and insulin and/or insulin-like growth factor (IGF1) resistance are cardinal features of diabetes, inflammation and hypercortisolemia. Little is known about why these phenomena occur in so many contexts. Do the various triggers that induce insulin and/or IGF1 resistance and retard wound healing act through a common mechanism? Cultured dermal fibroblasts from rats and full-thickness excisional wounds were used as models to test the premise that reactive oxygen species (ROS) play a causal role in the development of IGF1 resistance and impaired wound healing under different but pathophysiologically relevant clinical settings, including diabetes, dexamethasone-induced hypercortisolemia and TNFα-induced inflammation. In normal fibroblasts, IGF1 initiated a strong degree of phosphorylation of insulin receptor substrate 1 (IRS1) (Tyr612) and Akt (Ser473), concomitantly with increased PI3K activity. This phenomenon seemed to be attenuated in fibroblasts that had phenotypic features of diabetes, inflammation or hypercortisolemia. Notably, these cells also exhibited an increase in the activity of the ROS–phospho-JNK (p-JNK)–p-IRS1 (Ser307) axis. The above-mentioned defects were reflected functionally by attenuation in IGF1-dependent stimulation of key fibroblast functions, including collagen synthesis and cell proliferation, migration and contraction. The effects of IGF1 on glucose disposal and cutaneous wound healing were also impaired in diabetic or hypercortisolemic rats. The ROS suppressors EUK-134 and α-lipoic acid, or small interfering RNA (siRNA)-mediated silencing of JNK expression, restored IGF1 sensitivity both in vitro and in vivo, and also ameliorated the impairment in IGF1-mediated wound responses during diabetes, inflammation and hypercortisolemia. Our data advance the notion that ROS constitute a convergence nexus for the development of IGF1 resistance and impaired wound healing under different but pathophysiologically relevant clinical settings, with a proof of concept for the beneficial effect of ROS suppressors.

Implication of low level inflammation in the insulin resistance of adipose tissue at late pregnancy

Insulin resistance is a characteristic of late pregnancy, and adipose tissue is one of the tissues that most actively contributes to the reduced maternal insulin sensitivity. There is evidence that pregnancy is a condition of moderate inflammation, although the physiological role of this low-grade inflammation remains unclear. The present study was designed to validate whether low-grade inflammation plays a role in the development of insulin resistance in adipose tissue during late pregnancy. To this end, we analyzed proinflammatory adipokines and kinases in lumbar adipose tissue of nonpregnant and late pregnant rats at d 18 and 20 of gestation. We found that circulating and tissue levels of adipokines, such as IL-1β, plasminogen activator inhibitor-1, and TNF-α, were increased at late pregnancy, which correlated with insulin resistance. The observed increase in adipokines coincided with an enhanced activation of p38 MAPK in adipose tissue. Treatment of pregnant rats with the p38 MAPK inhibitor SB 202190 increased insulin-stimulated tyrosine phosphorylation of the insulin receptor (IR) and IR substrate-1 in adipose tissue, which was paralleled by a reduction of IR substrate-1 serine phosphorylation and an enhancement of the metabolic actions of insulin. These results indicate that activation of p38 MAPK in adipose tissue contributes to adipose tissue insulin resistance at late pregnancy. Furthermore, the results of the present study support the hypothesis that physiological low-grade inflammation in the maternal organism is relevant to the development of pregnancy-associated insulin resistance.

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.

Adverse adipose phenotype and hyperinsulinemia in gravid mice deficient in placental growth factor

Pregnancy-induced metabolic changes are regulated by signals from an expanded adipose organ. Placental growth factor (PlGF), acting through vascular endothelial growth factor receptor-1, may be among those signals. There is a steep rise in circulating PlGF during normal pregnancy, which is repressed in gravidas who develop preeclampsia. PlGF-deficiency in mice impairs adipose vascularization and development. Here we studied young-adult PlGF-deficient (PlGF(-/-)) and wild-type mice on a high-fat diet in the nongravid state and at embryonic day (E) 13.5 or E18.5 of gestation. Litter size and weight were normal, but E18.5 placentas were smaller in PlGF(-/-) pregnancies. PlGF(-/-) mice showed altered intraadipose dynamics, with the following: 1) less blood vessels and fewer brown, uncoupling protein (UCP)-1-positive, adipocytes in white sc and perigonadal fat compartments and 2) white adipocyte hypertrophy. The mRNA expression of beta(3)-adrenergic receptors, peroxisome proliferator-activated receptor-gamma coactivator-1alpha, and UCP-1 was decreased accordingly. Moreover, PlGF(-/-) mice showed hyperinsulinemia. Pregnancy-associated changes were largely comparable in PlGF(-/-) and wild-type dams. They included expanded sc fat compartments and adipocyte hypertrophy, whereas adipose expression of key angiogenesis/adipogenesis (vascular endothelial growth factor receptor-1, peroxisome proliferator-activated receptor-gamma(2)) and thermogenesis (beta(3)-adrenergic receptors, peroxisome proliferator-activated receptor-gamma coactivator-1alpha, and UCP-1) genes was down-regulated; circulating insulin levels gradually increased during pregnancy. In conclusion, reduced adipose vascularization in PlGF(-/-) mice impairs adaptive thermogenesis in favor of energy storage, thereby promoting insulin resistance and hyperinsulinemia. Pregnancy adds to these changes by PlGF-independent mechanisms. Disturbed intraadipose dynamics is a novel mechanism to explain metabolic changes in late pregnancy in general and preeclamptic pregnancy in particular.

AdipoR1 mediates the anorexigenic and insulin/leptin-like actions of adiponectin in the hypothalamus

Adiponectin exerts an insulin-sensitizing effect, improving insulin action in peripheral tissues and restraining insulin resistance. Here, we explore the hypothesis that adiponectin can reproduce some of the actions of insulin/leptin in the hypothalamus. The presence of AdipoR1 and AdipoR2 was mapped to the arcuate and lateral hypothalamic nuclei. Icv adiponectin reduced food intake, which was accompanied by activation/engagement of IRS1/2, ERK, Akt, FOXO1, JAK2 and STAT3. All these actions were dependent on AdipoR1, since inhibition of this receptor, and not of AdipoR2, completely reversed the effects described above. Thus, adiponectin acts in the hypothalamus, activating elements of the canonical insulin and leptin signaling pathways and promoting reduction of food intake.