Maternal Circulating Transthyretin Level Is Longitudinally Associated With Increased Risk of Gestational Diabetes Mellitus: It Is Not Just an Indicator of Nutritional Status

Associations of maternal serum transthyretin concentration with pregnancy and birth outcomes

OBJECTIVE

This study aims to explore the association of maternal serum transthyretin (TTR) concentrations with adverse pregnancy and birth outcomes, as well as the variations in TTR concentrations across different gestational weeks in relation to these outcomes.

METHODS

This retrospective cohort study included 6,584 women who delivered at The Second Affiliated Hospital of Wenzhou Medical University between January 1, 2022 and January 30, 2024. Logistic regression and Restricted cubic spline (RCS) models were applied to evaluate the association between TTR levels and the risk of complications, based on TTR quartile analyses. Locally estimated scatter plot smoothing (LOESS) curves were performed to provide a graphical representation of the relationship between TTR levels and gestational weeks.

RESULTS

Significant negative correlations were observed between maternal TTR levels and the risk of gestational diabetes mellitus (GDM), preeclampsia (PE), liver disease, anemia during pregnancy, and preterm delivery (all P < 0.001). The RCS models revealed a non-linear relationship between TTR levels and maternal comorbidities, including anemia (adjusted OR 0.992 [95% CI 0.990-0.994]; P = 0.017), liver disease (adjusted OR 0.991 [95% CI 0.988-0.994]; P < 0.001), hypothyroidism (adjusted OR 0.999 [95% CI 0.996-1.001]; P = 0.023) and preterm delivery (adjusted OR 0.986 [95% CI 0.983-0.989]; P < 0.001). The LOESS curves indicated a declining trend in TTR concentrations during the third trimester of pregnancy.

CONCLUSION

Maternal TTR concentrations showed an inverse linear association with the incidence of GDM and PE. Moreover, complex non-linear relationships were identified with TTR levels and comorbidities such as liver disease, anemia, hypothyroidism during pregnancy, and preterm delivery.

Proteomic analysis of plasma total exosomes and placenta-derived exosomes in patients with gestational diabetes mellitus in the first and second trimesters

Gestational diabetes mellitus (GDM) is the first spontaneous hyperglycemia during pregnancy. Early diagnosis and intervention are important for the management of the disease. This study compared and analyzed the proteins of total plasma exosomes (T-EXO) and placental-derived exosomes (PLAP-EXO) in pregnant women who subsequently developed GDM (12-16 weeks), GDM patients (24-28 weeks) and their corresponding controls to investigate the pathogenesis and biomarkers of GDM associated with exosomes. The exosomal proteins were extracted and studied by proteomics approach, then bioinformatics analysis was applied to the differentially expressed proteins (DEPs) between the groups. At 12-16 and 24-28 weeks of gestation, 36 and 21 DEPs were identified in T-EXO, while 34 and 20 DEPs were identified in PLAP-EXO between GDM and controls, respectively. These proteins are mainly involved in complement pathways, immunity, inflammation, coagulation and other pathways, most of them have been previously reported as blood or exosomal proteins associated with GDM. The findings suggest that the development of GDM is a progressive process and that early changes promote the development of the disease. Maternal and placental factors play a key role in the pathogenesis of GDM. These proteins especially Hub proteins have the potential to become predictive and diagnostic biomarkers for GDM.

Exploring the Physiological Role of Transthyretin in Glucose Metabolism in the Liver

Transthyretin (TTR), a 55 kDa evolutionarily conserved protein, presents altered levels in several conditions, including malnutrition, inflammation, diabetes, and Alzheimer’s Disease. It has been shown that TTR is involved in several functions, such as insulin release from pancreatic β-cells, recovery of blood glucose and glucagon levels of the islets of Langerhans, food intake, and body weight. Here, the role of TTR in hepatic glucose metabolism was explored by studying the levels of glucose in mice with different TTR genetic backgrounds, namely with two copies of the TTR gene, TTR+/+; with only one copy, TTR+/−; and without TTR, TTR−/−. Results showed that TTR haploinsufficiency (TTR+/−) leads to higher glucose in both plasma and in primary hepatocyte culture media and lower expression of the influx glucose transporters, GLUT1, GLUT3, and GLUT4. Further, we showed that TTR haploinsufficiency decreases pyruvate kinase M type (PKM) levels in mice livers, by qRT-PCR, but it does not affect the hepatic production of the studied metabolites, as determined by 1H NMR. Finally, we demonstrated that TTR increases mitochondrial density in HepG2 cells and that TTR insufficiency triggers a higher degree of oxidative phosphorylation in the liver. Altogether, these results indicate that TTR contributes to the homeostasis of glucose by regulating the levels of glucose transporters and PKM enzyme and by protecting against mitochondrial oxidative stress.

Transthyretin contributes to insulin resistance and diminishes exercise-induced insulin sensitivity in obese mice by inhibiting AMPK activity in skeletal muscle

Exercise improves obesity-induced insulin resistance and metabolic disorders via mechanisms that remain unclear. Here, we show that the levels of the hepatokine transthyretin (TTR) in circulation are elevated in insulin-resistant individuals including high-fat diet (HFD)-induced obese mice, db/db mice, and patients with metabolic syndrome. Liver Ttr mRNA and circulating TTR levels were reduced in mice by treadmill training, as was the TTR levels in quadriceps femoris muscle; however, AMP-activated protein kinase (AMPK) signaling activity was enhanced. Transgenic overexpression of TTR or injection of purified TTR triggered insulin resistance in mice fed on regular chow (RC). Furthermore, TTR overexpression reduced the beneficial effects of exercise on insulin sensitivity in HFD-fed mice. TTR was internalized by muscle cells via the membrane receptor Grp78 and the internalization into the quadriceps femoris was reduced by treadmill training. The TTR/Grp78 combination in C2C12 cells was increased, whereas the AMPK activity of C2C12 cells was decreased as the TTR concentration rose. In addition, Grp78 silencing prevented the TTR internalization and reversed its inhibitory effect on AMPK activity in C2C12 cells. Our study suggests that elevated circulating TTR may contribute to insulin resistance and counteract the exercise-induced insulin sensitivity improvement; the TTR suppression might be an adaptive response to exercise through enhancing AMPK activity in skeletal muscles.NEW & NOTEWORTHY Exercise improves obesity-induced insulin resistance via mechanisms that remain unclear. The novel findings of the study are that circulating TTR (a hepatokine) level is decreased by exercise, and the elevated circulating TTR, as was the elevated transthyretin internalization mediated by Grp78, counteracts the exercise-induced insulin sensitivity by downregulating AMPK activity in skeletal muscle of obese mice. These data suggest that TTR suppression might be an adaptive response to exercise through the crosstalk between liver and muscle.

Association between transthyretin concentrations and gestational diabetes mellitus in Chinese women

BACKGROUND

Transthyretin (TTR) is considered to be associated with insulin resistance in humans. This study aimed to investigate TTR level in gestational diabetes mellitus (GDM) and its association with glucose metabolism.

METHODS

Fifty pregnant women with GDM and 47 pregnant women with normal glucose tolerance matched for body mass index and age were enrolled in this study. Their blood samples were collected to detect TTR, retinol-binding protein 4 (RBP4), and their association with glucose and lipid metabolism.

RESULTS

Serum TTR levels in the GDM group were significantly higher than those in the control group (median, 93.44 [interquartile range, 73.81, 117.79] μg/ml vs. 80.83 [74.19, 89.38] μg/ml; P = 0.006). GDM subjects had a lower RBP4/TTR ratio than the control subjects (median, 517.57 [interquartile range, 348.38, 685.27] vs. 602.56 [460.28, 730.62]; P = 0.02). The serum TTR concentrations were positively associated with neonatal weight (r = 0.223, P = 0.028), homeostatic model assessment of insulin resistance (r = 0.246, P = 0.015), and fasting blood glucose (FBG) (r = 0.363, P < 0.001). In stepwise multivariate linear regression analysis, FBG (standardized beta = 0.27, P = 0.004) and neonatal weight (standardized beta = 0.345, P < 0.001) were independent predictors of serum TTR concentrations. Additionally, FBG (standardized beta = - 0.306, P = 0.002) and triglyceride (TG) (beta = 0.219, P = 0.025) were independently associated with RBP4/TTR ratio.

CONCLUSIONS

Serum TTR concentrations were significantly higher in women with GDM than that in women without GDM, suggesting that elevated TTR level may play a role in the pathogenesis of GDM. Meanwhile, TTR was positively and independently associated with FBG and neonatal weight, while FBG and TG were independent predictors of RBP4/TTR ratio. Moreover, serum TTR levels and RBP4/TTR ratio were considered valuable markers of insulin resistance and GDM.

Undiscovered Roles for Transthyretin: From a Transporter Protein to a New Therapeutic Target for Alzheimer's Disease

Transthyretin (TTR), an homotetrameric protein mainly synthesized by the liver and the choroid plexus, and secreted into the blood and the cerebrospinal fluid, respectively, has been specially acknowledged for its functions as a transporter protein of thyroxine and retinol (the latter through binding to the retinol-binding protein), in these fluids. Still, this protein has managed to stay in the spotlight as it has been assigned new and varied functions. In this review, we cover knowledge on novel TTR functions and the cellular pathways involved, spanning from neuroprotection to vascular events, while emphasizing its involvement in Alzheimer’s disease (AD). We describe details of TTR as an amyloid binding protein and discuss its interaction with the amyloid Aβ peptides, and the proposed mechanisms underlying TTR neuroprotection in AD. We also present the importance of translating advances in the knowledge of the TTR neuroprotective role into drug discovery strategies focused on TTR as a new target in AD therapeutics.

Early maternal circulating alkaline phosphatase with subsequent gestational diabetes mellitus and glucose regulation: a prospective cohort study in China

PURPOSE

Emerging clinical evidence has implied that alkaline phosphatase (ALP) may contribute to gestational diabetes mellitus (GDM). However, there were no studies to reveal the independent and prospective associations between ALP and GDM. Our aim was to explore the independent and prospective associations between early maternal ALP level and GDM risk and glucose regulation.

METHODS

In a prospective cohort study with 2073 singleton mothers at four maternity units in China, maternal serum ALP levels were measured before 20 gestational weeks. Using logistic regression, we analyzed the relationship between maternal ALP level and risk of GDM. We further explored the relationships of ALP level to fasting blood glucose (FBG), 1-h and 2-h post-load blood glucose (1-h, 2-h PBG) with multiple linear regression. Finally, we analyzed the association between maternal ALP level and isolated impaired fasting glucose (i-IFG) and isolated impaired glucose tolerance (i-IGT) risk.

RESULTS

The maximum value of maternal ALP level was 90 U/L, within the normal range. After adjustment for confounding factors, the odds ratio (ORs) of GDM increased linearly with ALP level (p for overall association = 0.002, p for nonlinear association = 0.799), with the OR comparing the highest versus lowest quartile of 2.47 (95% CI 1.47, 4.15). Moreover, each additional of 10 U/L ALP level was associated with a 2% higher FBG (p = 0.043) and a 12% higher 1-h PBG (p = 0.004). Higher ALP level also increased the risk of i-IFG (OR 3.73, 95% CI 1.17-11.86) and i-IGT (OR 2.03, 95% CI 1.07-3.84).

CONCLUSIONS

Even within the upper limit of normal, higher early maternal ALP level could increase the risk of GDM. Moreover, both FBG and PBG were increased with early maternal ALP.