GDM-associated insulin deficiency hinders the dissociation of SERT from ERp44 and down-regulates placental 5-HT uptake

Multiorgan Regulation Mechanisms and Nutritional Intervention Strategies in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) affects millions of pregnant women worldwide and leads to both short- and long-term complications for mothers and their fetuses. Managing GDM through diet, physical activity, and medical interventions can significantly reduce these risks. Studies have identified the individual and combined roles of organs regulated by placental hormones, cytokines, and gut microbiota as key pathways contributing to impaired glucose homeostasis. In this context, placental hormones mediate the crosstalk among the placenta, pancreas, and adipose tissue, stimulating endocrine pancreas adaptation and adipose tissue expansion. However, insufficient maternal physiological adaptations, such as dysregulated adipocytokines, adipokines, and oxidative stress in the pancreas, can create an environment conducive to the onset of GDM. Furthermore, gut dysbiosis implies potential mechanisms of gut-host interaction associated with the occurrence of GDM, with short-chain fatty acids possibly serving as crucial targets. Nutritional therapy is recognized as the first-line approach for managing GDM, encompassing dietary guidance and supplementation with micro- and macronutrients as well as bioactive components. Importantly, combined interventions involving multiple nutrients, such as probiotics and prebiotics with vitamins or minerals, may exert stronger beneficial effects on the prevention and treatment of GDM and its complications. This review paper discusses the regulatory role of multiorgans in GDM and the implementation of nutritional therapy for its prevention and management, along with associated complications.

Investigating the Role of Skin Autofluorescence in Gestational Diabetes Mellitus: A Systematic Review

Gestational diabetes mellitus (GDM) is a pregnancy-specific condition that can cause serious complications for both the mother and the fetus. Preventing these complications requires optimum glycemic control. Skin autofluorescence (SAF) is a non-invasive and innovative method that evaluates the levels of advanced glycation end products, markers of hyperglycemia, that could aid in the optimum management of GDM-complicated pregnancies. This systematic review aims to assess SAF's potential utility in the prediction of short-term and long-term outcomes in GDM. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology, with the protocol identifier CRD42024559012, we used "(skin autofluorescence OR SAF) AND (gestational diabetes mellitus OR GDM)" as a search criterion on the PubMed, Scopus, and Web of Science databases. After a rigorous selection process, we included five articles, which evaluated SAF values and GDM, SAF and pregnancies complicated by diabetes mellitus, and SAF and macrosomia. GDM diagnosis varies due to the different approaches among the major guidelines, leading to variations in interpretation and diagnostic thresholds. Across studies, this variability contributes to inconsistent SAF values. As a standardized and objective marker, SAF could provide a uniform criterion, improving GDM management. Further research is needed to validate its clinical utility.

The Continued Mismeasurement of Plasma Serotonin: A Systematic Review

Studies reporting on the analysis of free plasma (platelet-poor plasma, PPP) serotonin (5-hydroxytryptamine, 5-HT) in plasma obtained from healthy humans have been systematically reviewed. The review covered the period from 2010 to July 2024 and is a follow-up of a similar review published in 2011 which found that nearly all published reported of PPP 5-HT were clearly and markedly erroneously high. This problem has persisted unabated with nearly all retrieved 47 reports from the past 14 years also apparently being erroneously high. Possible causes and consequences of the problem are discussed along with potential approaches to improving the analysis and reporting of plasma 5-HT. Most of the errors appear to arise from pre-analytical problems that occur during the preparation of PPP due to residual platelets and/or due to the release of platelet 5-HT. The large number of fields interested in plasma 5-HT and the disparate publication venues appear to have contributed to a general lack of awareness of the difficulties with analyzing plasma 5-HT. The reporting of erroneous plasma 5-HT values has led to unsupported conclusions about possible alterations in plasma 5-HT and about the role of plasma 5-HT across a wide range of biomedical research areas.

Gestational diabetes mellitus and development of intergenerational non-alcoholic fatty liver disease (NAFLD) after delivery: a systematic review and meta-analysis

Background

It is known that gestational diabetes mellitus (GDM)-complicated pregnancies could affect maternal cardiometabolic health after delivery, resulting in hepatic dysfunction and a heightened risk of developing non-alcoholic fatty liver disease (NAFLD). Hence, this study aims to summarise existing literature on the impact of GDM on NAFLD in mothers and investigate the intergenerational impact on NAFLD in offspring.

Methods

Using 4 databases (PubMed, Embase, Web of Science and Scopus) between January 1980 and December 2023, randomized controlled trials and observational studies that assessed the effect of maternal GDM on intergenerational liver outcomes were extracted and analysed using random-effects meta-analysis to investigate the effect of GDM on NAFLD in mothers and offspring. Pooled odds ratio (OR) was calculated using hazards ratio (HR), relative risk (RR), or OR reported from each study, with corresponding 95% confidence intervals (CI), and statistical heterogeneity was assessed with the Cochran Q-test and I2 statistic, with two-sided p values. The study protocol was pre-registered on PROSPERO (CRD42023392428).

Findings

Twenty studies pertaining to mothers and offspring met the inclusion criteria and 12 papers were included further for meta-analysis on intergenerational NAFLD development. Compared with mothers without a history of GDM, mothers with a history of GDM had a 50% increased risk of developing NAFLD (OR 1.50; 95% CI: 1.21-1.87, over a follow-up period of 16 months-25 years. Similarly, compared with offspring born to non-GDM-complicated pregnancies, offspring born to GDM-complicated pregnancies displayed an approximately two-fold elevated risk of NAFLD development (2.14; 1.57-2.92), over a follow-up period of 1-17.8 years.

Interpretation

This systematic review and meta-analysis suggests that both mothers and offspring from GDM-complicated pregnancies exhibit a greater risk to develop NAFLD. These findings underline the importance of early monitoring of liver function and prompt intervention of NAFLD in both generations from GDM-complicated pregnancies.

Funding

No funding was available for this research.

Serotonin Transporter-dependent Histone Serotonylation in Placenta Contributes to the Neurodevelopmental Transcriptome

Brain development requires appropriate regulation of serotonin (5-HT) signaling from distinct tissue sources across embryogenesis. At the maternal-fetal interface, the placenta is thought to be an important contributor of offspring brain 5-HT and is critical to overall fetal health. Yet, how placental 5-HT is acquired, and the mechanisms through which 5-HT influences placental functions, are not well understood. Recently, our group identified a novel epigenetic role for 5-HT, in which 5-HT can be added to histone proteins to regulate transcription, a process called H3 serotonylation. Here, we show that H3 serotonylation undergoes dynamic regulation during placental development, corresponding to gene expression changes that are known to influence key metabolic processes. Using transgenic mice, we demonstrate that placental H3 serotonylation is dependent on 5-HT uptake by the serotonin transporter (SERT/SLC6A4). SERT deletion robustly reduces enrichment of H3 serotonylation across the placental genome, and disrupts neurodevelopmental gene networks in early embryonic brain tissues. Thus, these findings suggest a novel role for H3 serotonylation in coordinating placental transcription at the intersection of maternal physiology and offspring brain development.

Serotonin transporter-dependent histone serotonylation in placenta contributes to the neurodevelopmental transcriptome

Brain development requires appropriate regulation of serotonin (5-HT) signaling from distinct tissue sources across embryogenesis. At the maternal-fetal interface, the placenta is thought to be an important contributor of offspring brain 5-HT and is critical to overall fetal health. Yet, how placental 5-HT is acquired, and the mechanisms through which 5-HT influences placental functions, are not well understood. Recently, our group identified a novel epigenetic role for 5-HT, in which 5-HT can be added to histone proteins to regulate transcription, a process called H3 serotonylation. Here, we show that H3 serotonylation undergoes dynamic regulation during placental development, corresponding to gene expression changes that are known to influence key metabolic processes. Using transgenic mice, we demonstrate that placental H3 serotonylation largely depends on 5-HT uptake by the serotonin transporter (SERT/SLC6A4). SERT deletion robustly reduces enrichment of H3 serotonylation across the placental genome, and disrupts neurodevelopmental gene networks in early embryonic brain tissues. Thus, these findings suggest a novel role for H3 serotonylation in coordinating placental transcription at the intersection of maternal physiology and offspring brain development.

Glucose, Insulin and Oxygen Modulate Expression of Serotonin-Regulating Genes in Human First-Trimester Trophoblast Cell Line ACH-3P

Serotonin signaling plays an important role in regulating development and functions of the placenta. We hypothesized that metabolic disturbances associated with maternal obesity and/or gestational diabetes mellitus (GDM) affect placental serotonin homeostasis. Therefore, we examined the effects of high glucose (25 mM) and insulin (10 nM)-two hallmarks of maternal obesity and GDM-on mRNA expression of key regulators of serotonin homeostasis, including serotonin transporter (SERT), tryptophan hydroxylase 1 (TPH1), and monoamine oxidase A (MAOA), in the first-trimester trophoblast cell line ACH-3P, focusing on oxygen levels characteristic of early human placental development. Glucose downregulated expression of SERT and MAOA independently of oxygen level and upregulated expression of TPH1 at 6.5% oxygen but not at 2.5% oxygen. Compared to 6.5% oxygen, 2.5% oxygen upregulated SERT and downregulated TPH1 expression, with no effect on MAOA expression. Insulin upregulated SERT only at 2.5% oxygen but had no effect on TPH1 and MAOA expression. These results suggest that maternal metabolic alterations in early pregnancy may be a driving force for changes in placental serotonin homeostasis.

The nature of the binding between insulin receptor and serotonin transporter in placenta (review)

The interplay between the insulin receptor (IR) and serotonin transporter (SERT) allows reciprocal regulation of each other's physiological roles to ensure appropriate responses to specific environmental and developmental signals. The studies reported herein provided substantial evidence of how insulin signaling influences the modification and trafficking of SERT to the plasma membrane via enabling its association with specific endoplasmic reticulum (ER) proteins. While insulin signaling is important for the modifications of SERT proteins, the fact that phosphorylation of IR was significantly down-regulated in the placenta of SERT knock out (KO) mice suggests that SERT also regulates IR. Further suggestive of SERT functional regulation of IR, SERT-KO mice developed obesity and glucose intolerance with symptoms similar to those of type 2 diabetes. The picture emerging from those studies proposes that the interplay between IR and SERT maintains conditions supportive of IR phosphorylation and regulates insulin signaling in placenta which ultimately enables the trafficking of SERT to the plasma membrane. IR-SERT association thus appears to play a protective metabolic role in placenta and is impaired under diabetic conditions. This review focuses on recent findings describing the functional and physical associations between IR and SERT in placental cells, and the dysregulation of this process in diabetes.

Serotonin system in the human placenta - the knowns and unknowns

The biogenic monoamine serotonin (5-hydroxytryptamine, 5-HT) is a chemical messenger widely distributed in the brain and various other organs. Its homeostasis is maintained by the coordinated activity of a variety of proteins, including enzymes of serotonin metabolism, transmembrane transporters of serotonin, and serotonin receptors. The serotonin system has been identified also in the placenta in rodent models as a key component of placental physiology. However, serotonin pathways in the human placenta are far from well understood. Their alterations may have long-lasting consequences for the fetus that can manifest later in life. In this review, we summarize information on the location of the components of the serotonin system in the human placenta, their regulation, function, and alterations in pathological pregnancies. We highlight current controversies and discuss important topics for future research.

Research progress of placental vascular pathophysiological changes in pregnancy-induced hypertension and gestational diabetes mellitus

The placenta is a vital organ for fetal development, providing the fetus with nutrients, oxygen, and other important factors. Placenta is rich in blood vessels. Abnormal placental vascular function and blood circulation may lead to insufficient blood supply to the fetus in the uterus, leading to serious consequences such as pregnancy complications, fetal distress and even stillbirth. Pregnancy-induced hypertension (PIH) and gestational diabetes mellitus (GDM) are common complications of pregnancy. Recent studies report that pregnancy complications are often accompanied by changes in placental vascular structure and function. What are the physiological characteristics of human placental blood vessels? What are the pathological changes in the state of PIH and GDM? What are the relationships between these pathological changes and the occurrence of these pregnancy complications? Answers to these questions not only increase the understanding of placental vascular characteristics, but also provide important information for revealing the pathological mechanism of PIH and GDM. This article will summarize the research on the pathological changes of placental blood vessels in PIH and GDM, hoping to further unravel the physiological and pathological characteristics of placental blood vessels in the state of PIH and GDM, provide information for guiding clinical treatment for PIH and GDM.

Identification of the Active Compound of Liu Wei Di Huang Wan for Treatment of Gestational Diabetes Mellitus via Network Pharmacology and Molecular Docking

Liu Wei Di Huang Wan (LWDHW) is a well-known Chinese herbal compound, which has been prescribed for the treatment of gestational diabetes mellitus (GDM). We sought to clarify the potential therapeutic effects of LWDHW against GDM. Differentially expressed genes (DEGs) in GDM were firstly identified from the Gene Expression Omnibus (GEO) database. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed to reveal the biological functions of the DEGs. Subsequently, the LWDHW-compound-target network was constructed based on public databases to identify the relationship between the active components in LWDHW and the corresponding targets. Furthermore, gene functional analysis and protein-protein interaction (PPI) network construction were applied to investigate the function of potential targets and to evaluate hub genes. Finally, molecular docking was used to verify the binding activities between active ingredients and hub targets. Thirteen active components and 39 corresponding therapeutic target genes were obtained via network pharmacology analysis. The enrichment analysis demonstrated that the anti-GDM effect of LWDHW included oxidoreductase activity, involvement in renal system process, and regulation of blood pressure, which may be achieved through regulation of serotonergic synapses, vascular smooth muscle contraction, and neuroactive ligand-receptor interaction pathways. Additionally, molecular docking revealed that the main active component, Mu Dan Pi, exhibited the best affinity for proteins encoded by hub genes. This study applied network pharmacology analysis and molecular docking to display the multicomponent and multitarget characteristics of LWDHW in the treatment of GDM. Our findings provide novel insights into the pathogenesis of GDM and the therapeutic mechanisms of LWDHW against GDM.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

Differential Serotonin Uptake Mechanisms at the Human Maternal-Fetal Interface

Serotonin (5-HT) plays an extensive role during pregnancy in regulating both the placental physiology and embryonic/fetal development. The uptake of 5-HT into cells is central to the control of local concentrations of 5-HT near its molecular targets. Here, we investigated the mechanisms of 5-HT uptake into human primary placental cells and cord blood platelets, all isolated immediately after birth. Trophoblasts and cord blood platelets showed 5-HT uptake with similar Michaelis constant (Km) values (~0.6 μM), typical of the high-affinity serotonin transporter (SERT). The uptake of 5-HT into trophoblasts was efficiently inhibited by various SERT-targeting drugs. In contrast, the uptake of 5-HT into feto-placental endothelial cells was not inhibited by a SERT blocker and showed a Km value (~782 μM) in the low-affinity range. Consistent with this, SERT mRNAs were abundant in term trophoblasts but sparse in feto-placental endothelial cells, whereas the opposite was found for the low-affinity plasma membrane monoamine transporter (PMAT) mRNAs. Organic cation transporter (OCT) 1, 2, and 3 mRNAs were absent or sparse in both cell types. In summary, the results demonstrate, for the first time, the presence of functional 5-HT uptake systems in feto-placental endothelial cells and fetal platelets, cells that are in direct contact with fetal blood plasma. The data also highlight the sensitivity to various psychotropic drugs of 5-HT transport into trophoblasts facing the maternal blood. The multiple, high-, and low-affinity systems present for the cellular uptake of 5-HT underscore the importance of 5-HT homeostasis at the maternal-fetal interface.

The placenta-brain-axis

All mammalian species depend on the placenta, a transient organ, for exchange of gases, nutrients, and waste between the mother and conceptus. Besides serving as a conduit for such exchanges, the placenta produces hormones and other factors that influence maternal physiology and fetal development. To meet all of these adaptations, the placenta has evolved to become the most structurally diverse organ within all mammalian taxa. However, commonalities exist as to how placental responses promote survival against in utero threats and can alter the trajectory of fetal development, in particular the brain. Increasing evidence suggests that reactions of the  placenta to various in utero stressors may lead to long-standing health outcomes, otherwise considered developmental origin of health and disease effects. Besides transferring nutrients and gases, the placenta produces neurotransmitters, including serotonin, dopamine, norepinephrine/epinephrine, that may circulate and influence brain development. Neurobehavioral disorders, such as autism spectrum disorders, likely trace their origins back to placental disturbances. This intimate relationship between the placenta and brain has led to coinage of the term, the placenta-brain-axis. This axis will be the focus herein, including how conceptus sex might influence it, and technologies employed to parse out the effects of placental-specific transcript expression changes on later neurobehavioral disorders. Ultimately, the placenta might provide a historical record of in utero threats the fetus confronted and a roadmap to understand how placenta responses to such encounters impacts the placental-brain-axis. Improved early diagnostic and preventative approaches may thereby be designed to mitigate such placental disruptions.

The regulatory network of lncRNA DLX6-AS1/miR-149-5p/ERP44 is possibly related to the progression of preeclampsia

BACKGROUND

Long noncoding RNA DLX6 antisense RNA 1 (DLX6-AS1) has been reported to be involved in various human diseases, however, its potential role in the pathogenesis of preeclampsia (PE) has not been fully explored.

METHODS

The levels of DLX6-AS1, microRNA-149-5p (miR-149-5p) and endoplasmic reticulum protein 44 (ERP44) were measured by quantitative real-time polymerase chain reaction (qRT-PCR). Some clinicopathological parameters of PE were statistically analyzed. The cell proliferation, invasion and angiogenesis were assessed by methylthiazolyldiphenyl-tetrazolium bromide (MTT), transwell and tube formation assays, respectively. Levels of all protein were detected by western blot. The target relationship was predicted by StarBase v2.0 and confirmed by dual-luciferase reporter assay.

RESULTS

Higher levels of DLX6-AS1 and ERP44, lower level of miR-149-5p were observed in PE placenta tissues. Compared with PE group with low DLX6-AS1 expression, the systolic blood pressure, diastolic blood pressure and proteinuria levels in the group with high DLX6-AS1 expression were higher, and the infant body weight level was lower. The role of miR-149-5p on these clinicopathological parameters of PE patients was opposite to that of DLX6-AS1, while ERP44 had the same effect as DLX6-AS1. Besides, DLX6-AS1 directly targeted miR-149-5p and miR-149-5p targeted ERP44. The inhibitory impact of DLX6-AS1 overexpression or ERP44 overexpression on proliferation and invasion of trophoblast cells as well as angiogenesis of HUVEC cells was reversed by up-regulating miR-149-5p. We also found that DLX6-AS1 could enhance ERP44 expression by sponging miR-149-5p.

CONCLUSION

DLX6-AS1 inhibited proliferation and invasion of trophoblast cells, and suppressed angiogenesis of HUVEC cells by miR-149-5p/ERP44 pathway.

Epigenetic Profiles Reveal That ADCYAP1 Serves as Key Molecule in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) refers to the condition which shows abnormal glucose metabolism that occurs during pregnancy, while normal glucose metabolism before pregnancy. In the present study, a novel analytical procedure was used to explore the key molecule of gestational diabetes mellitus. First, the weighted pathway model was carried out subsequently to eliminate the gene-overlapping effects among pathways. Second, we assessed the enriched pathways by a combination of Fisher's t-test and the Mann–Whitney U test. We carried out the functional principal component analysis by estimating F values of genes to identify the hub genes in the enriched pathways. Results showed that a total of 4 differential pathways were enriched. The key pathway was considered as the insulin secretion pathway. F values of each gene in the key pathway were calculated. Three hub molecules were identified as hub differentially methylated genes, namely, CAMK2B, ADCYAP1, and KCNN2. In addition, by further comparing the gene expression data in a validation cohort, one key molecule was obtained, ADCYAP1. Therefore, ADCYAP1 may serve as a potential target for the treatment of GDM.

Serotonin-estrogen interactions: What can we learn from pregnancy?

We have reviewed the scientific literature related to four diseases in which to serotonin (5-HT) is involved in the etiology, herein named 5-HT-linked diseases, and whose prevalence is influenced by estrogenic status: depression, migraine, irritable bowel syndrome and eating disorders. These diseases all have in common a sex-dimorphic prevalence, with women more frequently affected than men. The co-occurrence between these 5-HT-linked diseases suggests that they have common physiopathological mechanisms. In most 5-HT-linked diseases (except for anorexia nervosa and irritable bowel syndrome), a decrease in the serotonergic tone is observed and estrogens are thought to contribute to the improvement of symptoms by stimulating the serotonergic system. Human pregnancy is characterized by a unique 5-HT and estrogen synthesis by the placenta. Pregnancy-specific disorders, such as hyperemesis gravidarum, gestational diabetes mellitus and pre-eclampsia, are associated with a hyperserotonergic state and decreased estrogen levels. Fetal programming of 5-HT-linked diseases is a complex phenomenon that involves notably fetal-sex differences, which suggest the implication of sex steroids. From a mechanistic point of view, we hypothesize that estrogens regulate the serotonergic system, resulting in a protective effect against 5-HT-linked diseases, but that, in turn, 5-HT affects estrogen synthesis in an attempt to retrieve homeostasis. These two processes (5-HT and estrogen biosynthesis) are crucial for successful pregnancy outcomes, and thus, a disruption of this 5-HT-estrogen relationship may explain pregnancy-specific pathologies or pregnancy complications associated with 5-HT-linked diseases.

RETRACTED: Placental serotonin systems in pregnancy metabolic complications associated with maternal obesity and gestational diabetes mellitus

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). The publication was retracted by request of the authors following an investigation by Monash University performed following its Procedures for Investigating Code Breaches and in accordance with the Australian Code for the Responsible Conduct of Research. The University concluded on the balance of probability that a significant part of the text in the paper was included without knowledge, without consent and without correct attribution of the original author who, at the time, was a student at the University. The results discussed in the review article are still scientifically valid. ☆ This article is part of a Special Issue entitled: Membrane Transporters and Receptors in Pregnancy Metabolic Complications edited by Luis Sobrevia.

Post-translational modifications of serotonin transporter

The serotonin transporter (SERT) is an oligomeric glycoprotein with two sialic acid residues on each of two complex oligosaccharide molecules. Studies using in vivo and in vitro model systems demonstrated that diverse post-translational modifications, including phosphorylation, glycosylation, serotonylation, and disulfide bond formation, all favorably influences SERT conformation and allows the transporter to function most efficiently. This review discusses the post-translational modifications and their importance on the structure, maturation, and serotonin (5-HT) uptake ability of SERT. Finally, we discuss how these modifications are altered in diabetes mellitus and subsequently impairs the 5-HT uptake ability of SERT.

Association with serotonin transporter enables the phosphorylation of insulin receptor in placenta

Upon binding to insulin, the β-subunit of insulin receptor (IR) is phosphorylated and instantly activates intracellular signaling. A defect in this process causes the development of several metabolic disorders including non-insulin-dependent diabetes, such as type 2 and gestational diabetes mellitus (GDM). Under diabetic conditions the phosphorylation of IR in placenta, but not in platelets, is impaired. Interestingly the cellular distribution of the serotonin transporter (SERT), which utilizes the insulin signaling for posttranslational modification, shows tissue-type-dependent variation: SERT function is impaired in GDM-associated placenta, but not in platelets. In order to understand the correlation between IR, SERT and their tissue-type-dependent features, we tested an association between SERT and IR and whether this association affects the phosphorylation of IR. Using various approaches, we demonstrated a physical association between the Carboxyl terminal of SERT and the β-subunit of IR. This association was found on the plasma membrane of the placenta and the platelets. Next, the contribution of the SERT-IR association to the phosphorylation of IR was analyzed in heterologous and endogenous expression systems following insulin-treatment. The in vivo impact of SERT-IR association on the phosphorylation of IR was explored in placenta and platelets of SERT gene knockout (KO) mice. The IR phosphorylation was significantly downregulated only in the placenta, but not in platelets of SERT-KO mice. These findings are supported by time course experiments, which demonstrate that the phosphorylation of IR occurs vis-a-vis IR-SERT association, and at least one of the IR binding domains is identified as the carboxyl-terminus of SERT. These findings suggest an important role for IR-SERT association in maintaining the phosphorylation of IR and regulating the insulin signaling in placenta.

Pathway of Maternal Serotonin to the Human Embryo and Fetus

Serotonin [5-hydroxytryptamine (5-HT)] is essential to intrauterine development, but its source is debated. We used immunocytochemistry to gauge 5-HT, its biosynthetic enzyme tryptophan hydroxylase 1 (TPH1); an importer (serotonin transporter, 5-HTT/SERT/SLC6A); other transporters [P-glycoprotein 1 (P-gp/ABCB1), OCT3/SLC22A3, and gap junction connexin-43]; and the 5-HT degradative enzyme monoamine oxidase A (MAOA) in sections of placentas. In humans, 5-HT was faintly stained only in first-trimester trophoblasts, whereas TPH1 was not seen at any stage. SERT was expressed in syncytiotrophoblasts and, more strongly, in cytotrophoblasts. MAOA was prominent in syncytiotrophoblasts, OCT3 and gap junctions were stained in cytotrophoblasts, and P-gp was present at the apical surfaces of both epithelia. 5-HT added to cultured placental explants accumulated in the trophoblast epithelium and reached the villus core vessels. Trophoblast uptake was blocked by the SERT inhibitor escitalopram. Inhibition of gap junctions with heptanol prevented the accumulation of 5-HT in cytotrophoblasts, whereas blocking OCT3 with decynium-22 and P-gp with mitotane led to its accumulation in cytotrophoblasts. Reducing 5-HT destruction by inhibiting MAOA with clorgyline increased the accumulation of 5-HT throughout the villus. In the mouse fetus, intravascular platelets stained prominently for 5-HT at day 13.5, whereas the placenta and yolk sac endoderm were both negative. TPH1 was not detected, but SERT was prominent in these mouse tissues. We conclude that serotonin is conveyed from the maternal blood stream through syncytiotrophoblasts, cytotrophoblasts and the villus core to the fetus through a physiological pathway that involves at least SERT, gap junctions, P-gp, OCT3, and MAOA.

Polysaccharide IV from Lycium barbarum L. Improves Lipid Profiles of Gestational Diabetes Mellitus of Pregnancy by Upregulating ABCA1 and Downregulating Sterol Regulatory Element-Binding Transcription 1 via miR-33

Lycium barbarum L. (LBL) has beneficial effects on gestational diabetes mellitus (GDM) but the related mechanism remains unclear. Polysaccharides of LBL (LBLP) are the main bioactive components of LBL. miR-33, ATP-binding cassette transporter A1 (ABCA1) and sterol regulatory element-binding transcription 1 (SREBF1) affect lipid profiles, which are associated with GDM risk. LBLP may exert protective against GDM by affecting these molecules. Four LBLP fractions: LBLP-I, LBLP-II, LBLP-III, and LBLP-IV were isolated from LBL and further purified by using DEAE-Sephadex column. The effects of purified each fraction on pancreatic beta cells were comparatively evaluated. A total of 158 GDM patients were recruited and randomly divided into LBL group (LG) and placebo group (CG). miR-33 levels, lipid profiles, insulin resistance and secretory functions were measured. The association between serum miR-33 levels and lipid profiles were evaluated by using Spearman's rank-order correlation test. After 4-week therapy, LBL reduced miR-33 level, insulin resistance and increased insulin secretion of GDM patients. LBL increased the levels of ABCA1, high-density lipoprotein cholesterol (HDL-C) and reduced miR-33, SREBF1, low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), triglyceride (TG), and malondialdehyde. Homeostatic model assessment of β-cell function and insulin resistance was lower in LG than in CG, whereas homeostatic model assessment of β-cell function and insulin secretory function was higher in LG than in CG. There was a strong positive association between miR-33 level and TG, or TC and or LDL-C, and a strong negative association between miR-33 level and HDL-C. The levels of miR-33 had negative relation with ABCA1 and positive relation with SREBF1. ABCA1 has negative relation with TG, TC, and LDL-C and positive relation with HDL-C. Inversely, SREBF1 had positive relation with TG, TC, and LDL-C and negative relation with HDL-C. The main bioactive compound LBLP-IV of LBL increased insulin secretion of beta cells and the levels of ABCA1, and reduced miR-33 levels and SREBF1 in beta cells. However, LBLP-IV could not change the levels of these molecules anymore when miR-33 was overexpressed or silenced. LBLP-IV had the similar effects with LBL on beta cells while other components had no such effects. Thus, LBLP-IV from LBL improves lipid profiles by upregulating ABCA1 and downregulating SREBF1 via miR-33.

Combined Metabolomic Analysis of Plasma and Urine Reveals AHBA, Tryptophan and Serotonin Metabolism as Potential Risk Factors in Gestational Diabetes Mellitus (GDM)

Gestational diabetes mellitus during pregnancy has severe implications for the health of the mother and the fetus. Therefore, early prediction and an understanding of the physiology are an important part of prenatal care. Metabolite profiling is a long established method for the analysis and prediction of metabolic diseases. Here, we applied untargeted and targeted metabolomic protocols to analyze plasma and urine samples of pregnant women with and without GDM. Univariate and multivariate statistical analyses of metabolomic profiles revealed markers such as 2-hydroxybutanoic acid (AHBA), 3-hydroxybutanoic acid (BHBA), amino acids valine and alanine, the glucose-alanine-cycle, but also plant-derived compounds like sitosterin as different between control and GDM patients. PLS-DA and VIP analysis revealed tryptophan as a strong variable separating control and GDM. As tryptophan is biotransformed to serotonin we hypothesized whether serotonin metabolism might also be altered in GDM. To test this hypothesis we applied a method for the analysis of serotonin, metabolic intermediates and dopamine in urine by stable isotope dilution direct infusion electrospray ionization mass spectrometry (SID-MS). Indeed, serotonin and related metabolites differ significantly between control and GDM patients confirming the involvement of serotonin metabolism in GDM. Clustered correlation coefficient visualization of metabolite correlation networks revealed the different metabolic signatures between control and GDM patients. Eventually, the combination of selected blood plasma and urine sample metabolites improved the AUC prediction accuracy to 0.99. The detected GDM candidate biomarkers and the related systemic metabolic signatures are discussed in their pathophysiological context. Further studies with larger cohorts are necessary to underpin these observations.

What is precise pathophysiology in development of hypertension in pregnancy? Precision medicine requires precise physiology and pathophysiology

It is widely accepted that placental ischemia is central in the evolution of hypertension in pregnancy. Many studies and reviews have targeted placental ischemia to explain mechanisms for initiating pregnancy hypertension. The placenta is rich in blood vessels, which are the basis for developing placental ischemia. However, is the physiology of placental vessels the same as that of nonplacental vessels? What is the pathophysiology of placental vessels in development of pregnancy hypertension? This review aims to provide a comprehensive summary of special features of placental vascular regulations and the pathophysiological changes linked to preeclamptic conditions. Interestingly, some popular theories or accepted concepts could be based on our limited knowledge and evidence regarding placental vascular physiology, pharmacology and pathophysiology. New views raised could offer interesting ideas for future investigation of mechanisms as well as targets for pregnancy hypertension.

Sex-Specific Neurodevelopmental Programming by Placental Insulin Receptors on Stress Reactivity and Sensorimotor Gating

BACKGROUND

Diabetes, obesity, and overweight are prevalent pregnancy complications that predispose offspring to neurodevelopmental disorders, including autism, attention-deficit/hyperactivity disorder, and schizophrenia. Although male individuals are three to four times more likely than female individuals to develop these disorders, the mechanisms driving the sex specificity of disease vulnerability remain unclear. Because defective placental insulin receptor (InsR) signaling is a hallmark of pregnancy metabolic dysfunction, we hypothesized that it may be an important contributor and novel mechanistic link to sex-specific neurodevelopmental changes underlying disease risk.

METHODS

We used Cre/loxP transgenic mice to conditionally target InsRs in fetally derived placental trophoblasts. Adult offspring were evaluated for effects of placental trophoblast-specific InsR deficiency on stress sensitivity, cognitive function, sensorimotor gating, and prefrontal cortical transcriptional reprogramming. To evaluate molecular mechanisms driving sex-specific outcomes, we assessed genome-wide expression profiles in the placenta and fetal brain.

RESULTS

Male, but not female, mice with placental trophoblast-specific InsR deficiency showed a significantly increased hypothalamic-pituitary-adrenal axis stress response and impaired sensorimotor gating, phenotypic effects that were associated with dysregulated nucleotide metabolic processes in the male prefrontal cortex. Within the placenta, InsR deficiency elicited changes in gene expression, predominantly in male mice, reflecting potential shifts in vasculature, amino acid transport, serotonin homeostasis, and mitochondrial function. These placental disruptions were associated with altered gene expression profiles in the male fetal brain and suggested delayed cortical development.

CONCLUSIONS

Together, these data demonstrate the novel role of placental InsRs in sex-specific neurodevelopment and reveal a potential mechanism for neurodevelopmental disorder risk in pregnancies complicated by maternal metabolic disorders, including diabetes and obesity.

Epigenetic adaptation of the placental serotonin transporter gene (SLC6A4) to gestational diabetes mellitus

We tested the hypothesis that gestational diabetes mellitus (GDM) alters the DNA methylation pattern of the fetal serotonin transporter gene (SLC6A4), and examined the functional relevance of DNA methylation for regulation of the SLC6A4 expression in the human placenta. The study included 50 mother-infant pairs. Eighteen mothers were diagnosed with GDM and 32 had normal glucose tolerance (NGT). All neonates were of normal birth weight and born at term by planned Cesarean section. DNA and RNA were isolated from samples of tissue collected from the fetal side of the placenta immediately after delivery. DNA methylation was quantified at 7 CpG sites within the SLC6A4 distal promoter region using PCR amplification of bisulfite treated DNA and subsequent DNA sequencing. SLC6A4 mRNA levels were measured by reverse transcription—quantitative PCR (RT-qPCR). Functional SLC6A4 polymorphisms (5HTTLPR, STin2, rs25531) were genotyped using standard PCR-based procedures. Average DNA methylation across the 7 analyzed loci was decreased in the GDM as compared to the NGT group (by 27.1%, p = 0.037) and negatively correlated, before and after adjustment for potential confounder/s, with maternal plasma glucose levels at the 24th to 28th week of gestation (p<0.05). Placental SLC6A4 mRNA levels were inversely correlated with average DNA methylation (p = 0.010) while no statistically significant association was found with the SLC6A4 genotypes (p>0.05). The results suggest that DNA methylation of the fetal SLC6A4 gene is sensitive to the maternal metabolic state in pregnancy. They also indicate a predominant role of epigenetic over genetic mechanisms in the regulation of SLC6A4 expression in the human placenta. Longitudinal studies in larger cohorts are needed to verify these results and determine to which degree placental SLC6A4 changes may contribute to long-term outcomes of infants exposed to GDM.

Prevalence of Intervillous Thrombi Is Increased in Placentas from Pregnancies Complicated by Diabetes

Intervillous thrombus (IVT) is a placental pathology of unclear cause. One possible cause is that IVT protects against fetomaternal transfusion due to trophoblastic disruption. A role for hyperglycemia in trophoblast apoptosis has been suggested. We sought to determine whether placentas from pregnancies complicated by diabetes had an increased incidence of IVT. Medical records of 206 patients with type 1 diabetes (n = 39), type 2 diabetes (n = 37), and gestational diabetes (GDM, n = 130) at the Massachusetts General Hospital were identified. Placental pathology reports were reviewed to determine prevalence of IVT. Gestational and maternal age-matched controls were selected from the pathology archives consisting of placentas examined only for the indication of group B streptococcus screen positivity; controls were confirmed euglycemic and reviewed for IVT. Fisher exact test was used for statistical analysis. An increased incidence of IVT was present in all diabetics (type 1, type 2, and GDM; 32 of 206; 15.5%; P = 0.04) and GDM exclusively (22 of 130; 16.9%; P = 0.03) versus controls (7 of 99; 7.1%). IVT were also increased in patients with type 1 diabetes (4 of 39; 10.3%) and type 2 diabetes (6 of 37; 16.2%) compared to controls (7 of 99; 7.1%), but the results did not attain statistical significance (P = 0.73 and 0.19, respectively). The incidence of IVT was increased in the placentas of patients with diabetes as a group (type 1, type 2, and GDM), and in patients with GDM in particular. This is the first report of an association between diabetes and an increased incidence of placental IVT.

Serotonin transporter protects the placental cells against apoptosis in caspase 3-independent pathway

Serotonin (5-HT) and its specific transporter, SERT play important roles in pregnancy. Using placentas dissected from 18d gestational SERT-knock out (KO), peripheral 5-HT (TPH1)-KO, and wild-type (WT) mice, we explored the role of 5-HT and SERT in placental functions in detail. An abnormal thick band of fibrosis and necrosis under the giant cell layer in SERT-KO placentas appeared only moderately in TPH1-KO and minimally present in WT placentas. The majority of the changes were located at the junctional zone of the placentas in SERT. The etiology of these findings was tested with TUNEL assays. The placentas from SERT-KO and TPH1-KO showed 49- and 8-fold increase in TUNEL-positive cells without a concurrent change in the DNA repair or cell proliferation compared to WT placentas. While the proliferation rate in the embryos of TPH1-KO mice was 16-fold lower than the rate in gestational age matched embryos of WT or SERT-KO mice. These findings highlight an important role of continuous 5-HT signaling on trophoblast cell viability. SERT may contribute to protecting trophoblast cells against cell death via terminating the 5-HT signaling which changes cell death ratio in trophoblast as well as proliferation rate in embryos. However, the cell death in SERT-KO placentas is in caspase 3-independent pathway.

Developmental origins of NAFLD: a womb with a clue

Changes in the maternal environment leading to an altered intrauterine milieu can result in subtle insults to the fetus, promoting increased lifetime disease risk and/or disease acceleration in childhood and later in life. Particularly worrisome is that the prevalence of NAFLD is rapidly increasing among children and adults, and is being diagnosed at increasingly younger ages, pointing towards an early-life origin. A wealth of evidence, in humans and non-human primates, suggests that maternal nutrition affects the placenta and fetal tissues, leading to persistent changes in hepatic metabolism, mitochondrial function, the intestinal microbiota, liver macrophage activation and susceptibility to NASH postnatally. Deleterious exposures in utero include fetal hypoxia, increased nutrient supply, inflammation and altered gut microbiota that might produce metabolic clues, including fatty acids, metabolites, endotoxins, bile acids and cytokines, which prime the infant liver for NAFLD in a persistent manner and increase susceptibility to NASH. Mechanistic links to early disease pathways might involve shifts in lipid metabolism, mitochondrial dysfunction, pioneering gut microorganisms, macrophage programming and epigenetic changes that alter the liver microenvironment, favouring liver injury. In this Review, we discuss how maternal, fetal, neonatal and infant exposures provide developmental clues and mechanisms to help explain NAFLD acceleration and increased disease prevalence. Mechanisms identified in clinical and preclinical models suggest important opportunities for prevention and intervention that could slow down the growing epidemic of NAFLD in the next generation.

Impact of Maternal Serotonin Transporter Genotype on Placental Serotonin, Fetal Forebrain Serotonin, and Neurodevelopment

Biomarker, neuroimaging, and genetic findings implicate the serotonin transporter (SERT) in autism spectrum disorder (ASD). Previously, we found that adult male mice expressing the autism-associated SERT Ala56 variant have altered central serotonin (5-HT) system function, as well as elevated peripheral blood 5-HT levels. Early in gestation, before midbrain 5-HT projections have reached the cortex, peripheral sources supply 5-HT to the forebrain, suggesting that altered maternal or placenta 5-HT system function could impact the developing embryo. We therefore used different combinations of maternal and embryo SERT Ala56 genotypes to examine effects on blood, placenta and embryo serotonin levels and neurodevelopment at embryonic day E14.5, when peripheral sources of 5-HT predominate, and E18.5, when midbrain 5-HT projections have reached the forebrain. Maternal SERT Ala56 genotype was associated with decreased placenta and embryonic forebrain 5-HT levels at E14.5. Low 5-HT in the placenta persisted, but forebrain levels normalized by E18.5. Maternal SERT Ala56 genotype effects on forebrain 5-HT levels were accompanied by a broadening of 5-HT-sensitive thalamocortical axon projections. In contrast, no effect of embryo genotype was seen in concepti from heterozygous dams. Blood 5-HT levels were dynamic across pregnancy and were increased in SERT Ala56 dams at E14.5. Placenta RNA sequencing data at E14.5 indicated substantial impact of maternal SERT Ala56 genotype, with alterations in immune and metabolic-related pathways. Collectively, these findings indicate that maternal SERT function impacts offspring placental 5-HT levels, forebrain 5-HT levels, and neurodevelopment.

The 'Developmental Origins' Hypothesis: relevance to the obstetrician and gynecologist

The recognition of 'fetal origins of adult disease' has placed new responsibilities on the obstetrician, as antenatal care is no longer simply about ensuring good perinatal outcomes, but also needs to plan for optimal long-term health for mother and baby. Recently, it has become clear that the intrauterine environment has a broad and long-lasting impact, influencing fetal and childhood growth and development as well as future cardiovascular health, non-communicable disease risk and fertility. This article looks specifically at the importance of the developmental origins of ovarian reserve and ageing, the role of the placenta and maternal nutrition before and during pregnancy. It also reviews recent insights in developmental medicine of relevance to the obstetrician, and outlines emerging evidence supporting a proactive clinical approach to optimizing periconceptional as well as antenatal care aimed to protect newborns against long-term disease susceptibility.

Discrepancy in Insulin Regulation between Gestational Diabetes Mellitus (GDM) Platelets and Placenta

Earlier findings have identified the requirement of insulin signaling on maturation and the translocation of serotonin (5-HT) transporter, SERT to the plasma membrane of the trophoblast in placenta. Because of the defect on insulin receptor (IR) in the trophoblast of the gestational diabetes mellitus (GDM)-associated placenta, SERT is found entrapped in the cytoplasm of the GDM-trophoblast. SERT is encoded by the same gene expressed in trophoblast and platelets. Additionally, alteration in plasma 5-HT levels and the 5-HT uptake rates are associated with the aggregation rates of platelets. Therefore, here, we investigated a novel hypothesis that GDM-associated defects in platelet IR should change their 5-HT uptake rates, and this should be a leading factor for thrombosis in GDM maternal blood. The maternal blood and the placentas were obtained at the time of cesarean section from the GDM and non-diabetic subjects (n = 6 for each group), and the platelets and trophoblasts were isolated to determine the IR activity, surface level of SERT, and their 5-HT uptake rates.Interestingly, no significant differences were evident in IR tyrosine phosphorylation or the downstream elements, AKT and S6K in platelets and their aggregation rates in both groups. Furthermore, insulin stimulation up-regulated 5-HT uptake rates of GDM-platelets as it does in the control group. However, the phosphorylation of IR and the downstream elements were significantly lower in GDM-trophoblast and showed no response to the insulin stimulation while they showed 4-fold increase to insulin stimulation in control group. Similarly, the 5-HT uptake rates of GDM-trophoblast and the SERT expression on their surface were severalfold lower compared with control subjects. IR is expressed in all tissues, but it is not known if diabetes affects IR in all tissues equally. Here, for the first time, our findings with clinical samples show that in GDM-associated defect on IR is tissue type-dependent. While IR is impaired in GDM-placenta, it is unaffected in GDM-platelet.

The Placenta as a Mediator of Stress Effects on Neurodevelopmental Reprogramming

Adversity experienced during gestation is a predictor of lifetime neuropsychiatric disease susceptibility. Specifically, maternal stress during pregnancy predisposes offspring to sex-biased neurodevelopmental disorders, including schizophrenia, attention deficit/hyperactivity disorder, and autism spectrum disorders. Animal models have demonstrated disease-relevant endophenotypes in prenatally stressed offspring and have provided unique insight into potential programmatic mechanisms. The placenta has a critical role in the deleterious and sex-specific effects of maternal stress and other fetal exposures on the developing brain. Stress-induced perturbations of the maternal milieu are conveyed to the embryo via the placenta, the maternal-fetal intermediary responsible for maintaining intrauterine homeostasis. Disruption of vital placental functions can have a significant impact on fetal development, including the brain, outcomes that are largely sex-specific. Here we review the novel involvement of the placenta in the transmission of the maternal adverse environment and effects on the developing brain.