Role of insulin, adenosine, and adipokine receptors in the foetoplacental vascular dysfunction in gestational diabetes mellitus

Regulation of placental amino acid transport in health and disease

Abnormal fetal growth, i.e., intrauterine growth restriction (IUGR) or fetal growth restriction (FGR) and fetal overgrowth, is associated with increased perinatal morbidity and mortality and is strongly linked to the development of metabolic and cardiovascular disease in childhood and later in life. Emerging evidence suggests that changes in placental amino acid transport may contribute to abnormal fetal growth. This review is focused on amino acid transport in the human placenta, however, relevant animal models will be discussed to add mechanistic insights. At least 25 distinct amino acid transporters with different characteristics and substrate preferences have been identified in the human placenta. Of these, System A, transporting neutral nonessential amino acids, and System L, mediating the transport of essential amino acids, have been studied in some detail. Importantly, decreased placental Systems A and L transporter activity is strongly associated with IUGR and increased placental activity of these two amino acid transporters has been linked to fetal overgrowth in human pregnancy. An array of factors in the maternal circulation, including insulin, IGF-1, and adiponectin, and placental signaling pathways such as mTOR, have been identified as key regulators of placental Systems A and L. Studies using trophoblast-specific gene targeting in mice have provided compelling evidence that changes in placental Systems A and L are mechanistically linked to altered fetal growth. It is possible that targeting specific placental amino acid transporters or their upstream regulators represents a novel intervention to alleviate the short- and long-term consequences of abnormal fetal growth in the future.

Pathomechanisms of Prenatally Programmed Adult Diseases

Based on epidemiological observations Barker et al. put forward the hypothesis/concept that an adverse intrauterine environment (involving an insufficient nutrient supply, chronic hypoxia, stress, and toxic substances) is an important risk factor for the development of chronic diseases later in life. The fetus responds to the unfavorable environment with adaptive reactions, which ensure survival in the short run, but at the expense of initiating pathological processes leading to adult diseases. In this review, the major mechanisms (including telomere dysfunction, epigenetic modifications, and cardiovascular-renal-endocrine-metabolic reactions) will be outlined, with a particular emphasis on the role of oxidative stress in the fetal origin of adult diseases.

Chemerin-Induced Down-Regulation of Placenta-Derived Exosomal miR-140-3p and miR-574-3p Promotes Umbilical Vein Endothelial Cells Proliferation, Migration, and Tube Formation in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) leads to poor pregnancy outcomes and fetoplacental endothelial dysfunction; however, the underlying mechanisms remain unknown. This study aimed to investigate the effect of placenta-derived exosomal miRNAs on fetoplacental endothelial dysfunction in GDM, as well as to further explore the role of chemerin to this end. Placenta-derived exosomal miR-140-3p and miR-574-3p expression (next-generation sequencing, quantitative real-time PCR), its interactions with cell function (Cell Counting Kit-8, Transwell, tube formation assay), chemerin interactions (Western blotting), and placental inflammation (immunofluorescence staining, enzyme-linked immunosorbent assay) were investigated. Placenta-derived exosomal miR-140-3p and miR-574-3p were downregulated in GDM. Additionally, miR-140-3p and miR-574-3p inhibited the proliferation, migration, and tube formation ability of umbilical vein endothelial cells by targeting vascular endothelial growth factor. Interestingly, miR-140-3p and miR-574-3p expression levels were negatively correlated with chemerin, which induced placental inflammation through the recruitment of macrophage cells and release of IL-18 and IL-1β. These findings indicate that chemerin reduces placenta-derived exosomal miR-140-3p and miR-574-3p levels by inducing placental inflammation, thereby promoting the proliferation, migration, and tube formation of umbilical vein endothelial cells in GDM, providing a novel perspective on the underlying pathogenesis and therapeutic targets for GDM and its offspring complications.

Research progress on N6-methyladenosine in the human placenta

OBJECTIVES

N6-methyladenosine (m6A) is one of the most common epigenetic modifications of eukaryotic RNA. Under the jointly reversible regulation of related enzymes, m6A regulates many aspects of RNA, such as translation, stability and degradation. The aim of this study is to investigate the role of m6A in placenta-related diseases.

METHODS

Data were compiled from 2018 to 2021 citations in PubMed and Google Scholar using the keywords: placenta AND N6-methyladenosine. Seven studies were included.

RESULTS

In this study, we introduced some conventional methods to detect m6A modification at the whole RNA, region (peak) and single base levels. We also summarized the current studies of m6A modification in the placenta and briefly describe m6A in placental-related diseases, including recurrent miscarriage (RM), preeclampsia (PE) and gestational diabetes mellitus (GDM).

CONCLUSIONS

Although the relevant reports are still in the preliminary stage and some results are inconsistent, studies on methylation m6A modification have contributed new ideas for the research of reproductive diseases, providing a new basis for the diagnosis, treatment, prognosis and monitoring of related diseases.

Increased Fetal Cardiovascular Disease Risk: Potential Synergy Between Gestational Diabetes Mellitus and Maternal Hypercholesterolemia

Cardiovascular diseases (CVD) remain a major cause of death worldwide. Evidence suggests that the risk for CVD can increase at the fetal stages due to maternal metabolic diseases, such as gestational diabetes mellitus (GDM) and maternal supraphysiological hypercholesterolemia (MSPH). GDM is a hyperglycemic, inflammatory, and insulin-resistant state that increases plasma levels of free fatty acids and triglycerides, impairs endothelial vascular tone regulation, and due to the increased nutrient transport, exposes the fetus to the altered metabolic conditions of the mother. MSPH involves increased levels of cholesterol (mainly as low-density lipoprotein cholesterol) which also causes endothelial dysfunction and alters nutrient transport to the fetus. Despite that an association has already been established between MSPH and increased CVD risk, however, little is known about the cellular processes underlying this relationship. Our knowledge is further obscured when the simultaneous presentation of MSPH and GDM takes place. In this context, GDM and MSPH may substantially increase fetal CVD risk due to synergistic impairment of placental nutrient transport and endothelial dysfunction. More studies on the separate and/or cumulative role of both processes are warranted to suggest specific treatment options.

The implications of the purinergic signaling throughout pregnancy

Purinergic signaling is a necessary mechanism to trigger or even amplify cell communication. Its ligands, notably adenosine triphosphate (ATP) and adenosine, modulate specific membrane-bound receptors in virtually all human cells. Regardless of the stage of the pregnancy, cellular communication between maternal, placental, and fetal cells is the paramount mechanism to sustain its optimal status. In this review, we describe the crucial role of purinergic signaling on the regulation of the maternal-fetal trophic exchanges, immune control, and endocrine exchanges throughout pregnancy. The nature of the modulation of both ATP and adenosine on the embryo-maternal interface, going through placental invasion until birth delivery depends on the general maternal-fetal health state and consequently on the selective activation of their specific receptors. In addition, an increasing number of studies have been demonstrating the pivotal role of ATP and adenosine in modulating deleterious effects of suboptimal conditions of pregnancy. Here, we discuss the role of purinergic signaling on the balance that coordinates the embryo-maternal exchanges and a promising therapeutic venue in the context of pregnancy disorders.

Effect of type 2 diabetes mellitus on placental expression and activity of nutrient transporters and their association with birth weight and neonatal adiposity

AIMS

Infants born to women with Type 2 Diabetes Mellitus (T2DM) are at risk of being born large for gestational age due to excess fetal fat accretion. Placental nutrient transport determines fetal nutrient availability, impacting fetal growth. The aims of the study were to evaluate the effect of T2DM on placental insulin signaling, placental nutrient transporters and neonatal adiposity.

METHODS

Placentas were collected from BMI-matched normoglycemic controls (NGT, n = 9) and T2DM (n = 9) women. Syncytiotrophoblast microvillous (MVM) and basal (BM) plasma membranes were isolated. Expression of glucose (GLUT1, -4), fatty acid (FATP2, -4, -6, FAT/CD36), amino acid (SNAT1, -2, -4, LAT1, -2) transporters, insulin signaling, and System A transporter activity was determined. Neonatal fat mass (%) was measured in a subset of neonates born to T2DM women.

RESULTS

GLUT1 protein expression was increased (p = 0.001) and GLUT4 decreased (p = 0.006) in BM from T2DM. MVM FATP6 expression was increased (p = 0.02) and correlated with birth weight in both T2DM and NGT groups (r = 0.65, p = 0.02). BM FATP6 expression was increased (p = 0.01) in T2DM. In MVM of T2DM placentas, SNAT1 expression was increased (p = 0.05) and correlated with birth weight (r = 0.84, p = 0.004); SNAT2 was increased (p = 0.01), however System A transporter activity was not different between groups. MVM LAT1 expression was increased (p = 0.01) in T2DM and correlated with birth weight (r = 0.59, p = 0.04) and neonatal fat mass (r = 0.76, p = 0.06).

CONCLUSION

In pregnancies complicated by T2DM placental protein expression of transporters for glucose, amino acids and fatty acids is increased, which may contribute to increased fetal growth and neonatal adiposity.

m6A mRNA methylation regulates the development of gestational diabetes mellitus in Han Chinese women

N6-methyladenosine (m6A) is the most prevalent mRNA modification in mammals. However, m6A modification profiling and its potential role in gestational diabetes mellitus (GDM) have not yet been investigated. In this work, we performed comprehensive m6A analysis in placental tissues from GDM and control patients to elucidate the role of m6A in GDM. An m6A RNA profile identified that m6A levels were strongly decreased in 3'-untranslated regions (UTRs) and coding sequences (CDSs) near stop codons in GDM placenta samples. Among the many methylated mRNAs, MazF-qPCR verified that the m6A levels of the BAMBI 3'-UTR and CDS were significantly decreased in GDM. BAMBI mRNA and protein expression was significantly decreased in GDM, suggesting that m6A plays a key role in regulating gene expression. In addition, it was verified that the m6A levels of GDM related genes (INSR and IRS1) were significantly reduced in GDM. Taken together, our data suggest that down-regulation of m6A both in the 3'-UTR and CDS near stop codons of placental mRNAs is involved in GDM development in Han Chinese women.

Alteration of purinergic signaling in diabetes: Focus on vascular function

Diabetes is an important risk factor for the development of cardiovascular disease including atherosclerosis and ischemic heart disease. Vascular complications including macro- and micro-vascular dysfunction are the leading causes of morbidity and mortality in diabetes. Disease mechanisms at present are unclear and no ideal therapies are available, which urgently calls for the identification of novel therapeutic targets/agents. An altered nucleotide- and nucleoside-mediated purinergic signaling has been implicated to cause diabetes-associated vascular dysfunction in major organs. Alteration of both purinergic P1 and P2 receptor sensitivity rather than the changes in receptor expression accounts for vascular dysfunction in diabetes. Activation of P2X₇ receptors plays a crucial role in diabetes-induced retinal microvascular dysfunction. Recent findings have revealed that both ecto-nucleotidase CD39, a key enzyme hydrolyzing ATP, and CD73, an enzyme regulating adenosine turnover, are involved in the renal vascular injury in diabetes. Interestingly, erythrocyte dysfunction in diabetes by decreasing ATP release in response to physiological stimuli may serve as an important trigger to induce vascular dysfunction. Nucleot(s)ide-mediated purinergic activation also exerts long-term actions including inflammatory and atherogenic effects in hyperglycemic and diabetic conditions. This review highlights the current knowledge regarding the altered nucleot(s)ide-mediated purinergic signaling as an important disease mechanism for the diabetes-associated vascular complications. Better understanding the role of key receptor-mediated signaling in diabetes will provide more insights into their potential as targets for the treatment.

Association between Aldose Reductase Gene C(-106)T Polymorphism and Diabetic Retinopathy: A Systematic Review and Meta-Analysis

Controversial results regarding the associations between aldose reductase (AR) genetic polymorphisms and diabetic retinopathy (DR) have been reported for many years. The present meta-analysis was performed to clarify the effects of the AR gene C(-106)T polymorphism on DR risk. The PubMed, Web of Sciences, Cochrane library, EMBASE, Chinese National Knowledge Infrastructure, and Wan Fang databases were extensively searched in Chinese to select relevant studies with an updated date of April 25, 2018. The Newcastle-Ottawa Scale (NOS) was applied to assess quality. The random-effects model was applied to calculate the pooled OR and 95% CI. This meta-analysis identified 23 studies with an average score of 7.52 for NOS analysis, including 4,313 DR cases and 5,128 diabetes mellitus (DM) control cases. In the overall analysis, a significant association between the AR gene C(-106)T polymorphism and DR susceptibility was found. In subgroups stratified by DM type and ethnicity, significantly increased risks for DR were found in DM type 1, East Asian populations, and Middle Eastern populations. Compared with DR control cases, the following associations were found: T vs. C: OR 0.91, 95% CI 0.85-0.97, I2 = 72.9%; CT + TT vs. CC: OR 0.75, 95% CI 0.68-0.81, I2 = 86.7%; and CT vs. CC: OR 0.86, 95% CI 0.78-0.94, I2 = 70.5%. The results of this meta-analysis showed a significant association between the AR gene C(-106)T polymorphism and susceptibility to DR in DM patients. DM patients with allele T and CT+TT genotype of the AR gene may have a lower risk of DR.

Omentin-1 in diabetes mellitus: A systematic review and meta-analysis

OBJECTIVE

Previous studies found inconsistent results on the relationship between diabetes mellitus and concentrations of omentin-1. This study performed a systematic review and meta-analysis to summarize previous findings on this relationship.

METHODS

Studies related to this outcome were obtained using a systematic search in the electronic databases of Cochrane Library, PubMed, Embase, SCOPUS, Google Scholar, gray literature and Web of Science in September 2019. The random effects model was used to measure the strength of the association between diabetes mellitus and concentrations of omentin-1, using standardized mean difference.

RESULTS

Forty-two eligible studies were included in the final meta-analysis. There was no significant difference in omentin-1 concentration between patients with type 1 diabetes mellitus and the controls. On the other hand, lower concentration levels of omentin-1 were observed in patients with gestational diabetes mellitus (standardized mean difference:-0.44, 95% confidence interval:-0.76; -0.12, p = 0.007), or type 2 diabetes mellitus (standardized mean difference: -1.74, 95% confidence interval: -2.31; -1.16, p< 0.001) than in the controls.

CONCLUSION

Decreased omentin-1 concentrations may be an important indicator for gestational diabetes mellitus and type 2 diabetes mellitus. More studies are needed to validate this hypothesis and evaluate the role of omentin-1 concentrations in type 1 diabetes mellitus.

Neonates from women with pregestational maternal obesity show reduced umbilical vein endothelial response to insulin

OBJECTIVE

Pregestational maternal obesity (PGMO) associates with foetoplacental vascular endothelial dysfunction and higher risk for insulin resistance in the neonate. We characterised the PGMO consequences on the insulin response of the human foetoplacental vasculature.

METHODS

Umbilical veins were from pregnancies where the mother was with PGMO (body mass index 30-42.3 kg/m², n = 33) or normal pregestational weight (PGMN) (body mass index 19.5-24.4 kg/m², n = 21) with total gestational weight gain within the physiological range. Umbilical vein ring segments were mounted in a myograph for isometric force measurements. Primary cultures of human umbilical vein endothelial cells were used in passage 3. Vessel rings and cells were exposed to 1 nmol/L insulin (20 min) in the absence or presence of 100 μmol/L N^G-nitro-l-arginine methyl ester (inhibitor of nitric oxide synthase, NOS).

RESULTS

Vessel rings from PGMO showed reduced nitric oxide synthase-activity dependent dilation to insulin or calcitonin-gene related peptide compared with PGMN. PGMO associated with higher inhibitor phosphorylation of the insulin receptor substrate 1 (IRS-1) and lower activator phosphorylation of protein kinase B/Akt (Akt). Cells from PGMO also showed lower nitric oxide level and reduced activator serine¹¹⁷⁷ but increased inhibitor threonine⁴⁹⁵ phosphorylation of endothelial nitric oxide synthase (eNOS) and saturable transport of l-arginine. HUVECs from PGMO were not responsive to insulin.

CONCLUSION

The lack of response to insulin by the foetoplacental endothelium may result from reduced IRS-1/Akt/eNOS signalling in PGMO. These findings may result in higher risk of insulin resistance in neonates to PGMO pregnancies.