Maternal Glucose Supplementation in a Murine Model of Chorioamnionitis Alleviates Dysregulation of Autophagy in Fetal Brain

Placental Macrophages Demonstrate Sex-Specific Response to Intrauterine Inflammation and May Serve as a Marker of Perinatal Neuroinflammation

Preterm birth (PTB) is considered to be one of the most frequent causes of neonatal death. Prompt and effective measures to predict adverse fetal outcome following PTB are urgently needed. Placenta macrophages are a critical immune cell population during pregnancy, phenotypically divided into M1 and M2 subsets. An established mouse model of intrauterine inflammation (IUI) was applied. Placenta (labyrinth) and corresponding fetal brain were harvested within 24 hours post injection (hpi). Flow cytometry, Western blot, real-time qPCR, and regular histology were utilized to examine the cytokines, macrophage polarization, and sex-specificity. Placental exposure to LPS led to significantly reduced labyrinth thickness compared to PBS-exposed controls as early as 3 hpi, accompanied by apoptosis and necrosis. Pro-inflammatory M1 markers, Il-1β, and iNOS, and anti-inflammatory M2 marker Il-10 increased significantly in placentas exposed to IUI. Analysis of flow cytometry revealed that fetal macrophages (Hofbauer cell, HBCs) were mostly M1-like and that maternal inter-labyrinth macrophages (MIM) were M2-like in their features in IUI. Male fetuses displayed significantly decreased M2-like features in HBCs at 3 and 6 hpi, while female fetuses showed significant increase in M2-like features in MIM at 3 and 6 hpi. Furthermore, there was a significant correlation between the frequency of HBCs and corresponding microglial marker expression at 3 and 6 hpi. Placental macrophages demonstrated sex-specific features in response to IUI. Specifically, HBCs may be a potential biomarker for fetal brain injury at preterm birth.

Fetal Neuroprotective Strategies: Therapeutic Agents and Their Underlying Synaptic Pathways

Synaptic signaling is integral for proper brain function. During fetal development, exposure to inflammation or mild hypoxic-ischemic insult may lead to synaptic changes and neurological damage that impairs future brain function. Preterm neonates are most susceptible to these deleterious outcomes. Evaluating clinically used and novel fetal neuroprotective measures is essential for expanding treatment options to mitigate the short and long-term consequences of fetal brain injury. Magnesium sulfate is a clinical fetal neuroprotective agent utilized in cases of imminent preterm birth. By blocking N-methyl-D-aspartate receptors, magnesium sulfate reduces glutamatergic signaling, which alters calcium influx, leading to a decrease in excitotoxicity. Emerging evidence suggests that melatonin and N-acetyl-L-cysteine (NAC) may also serve as novel putative fetal neuroprotective candidates. Melatonin has important anti-inflammatory and antioxidant properties and is a known mediator of synaptic plasticity and neuronal generation. While NAC acts as an antioxidant and a precursor to glutathione, it also modulates the glutamate system. Glutamate excitotoxicity and dysregulation can induce perinatal preterm brain injury through damage to maturing oligodendrocytes and neurons. The improved drug efficacy and delivery of the dendrimer-bound NAC conjugate provides an opportunity for enhanced pharmacological intervention. Here, we review recent literature on the synaptic pathways underlying these therapeutic strategies, discuss the current gaps in knowledge, and propose future directions for the field of fetal neuroprotective agents.

Deficiency of the oxidative stress-responsive kinase p70S6K1 restores autophagy and ameliorates neural tube defects in diabetic embryopathy

BACKGROUND

Autophagy is highly active in neuroepithelial cells of the developing neuroepithelium, and impairment of autophagy leads to neural tube defects. In this study, we have found that maternal diabetes suppresses autophagy that leads to neural tube defects and consequent cellular imbalance in the endoplasmic reticulum where critical events occur, leading to the induction of diabetic embryopathy. Because the mammalian target of rapamycin pathway suppresses autophagy, we hypothesized that 70 kDa ribosomal protein S6 kinase 1 (p70S6K1), a major downstream effector of mammalian target of rapamycin, mediates the inhibitory effect of maternal diabetes on autophagy in the developing neuroepithelium.

OBJECTIVE

We investigated whether p70S6K1 mediates the inhibitory effect of maternal diabetes on autophagy during neurulation. We also examined whether p70S6K1 deficiency restores autophagy and therefore relieves endoplasmic reticulum stress and inhibits maternal diabetes-induced apoptosis, which leads to reduction in neural tube defect incidence in diabetic embryopathy.

STUDY DESIGN

Female p70S6K1 heterogeneous knockout (p70S6K1+/-) mice were bred with male p70S6K1 heterogeneous knockout (p70S6K1+/-) mice to generate wild-type (WT), p70S6K1+/- and p70S6K1 knockout (p70S6K1-/-) embryos. Embryos at embryonic day 8.5 were harvested for the assessment of indices of autophagy, endoplasmic reticulum stress, and apoptosis. Neural tube defect incidence in embryos was determined at embryonic day 10.5. For in vitro studies, small interfering RNA knockdown of p70S6K1 in C17.2 mouse neural stem cells was used to determine the effect of p70S6K1 deficiency on autophagy impairment and endoplasmic reticulum stress under high glucose conditions.

RESULTS

Knockout of the Rps6kb1 gene, which encodes for p70S6K1, ameliorated maternal diabetes-induced NTDs and restored autophagosome formation in neuroepithelial cells suppressed by maternal diabetes. Maternal diabetes-suppressed conversion of LC3-I (microtubule-associated protein 1A/1B-light chain 3) to LC3-II, an index of autophagic activity, in neurulation stage embryos was abrogated in the absence of p70S6K1. p70S6K1 knockdown in neural stem cells also restored autophagosome formation and the conversion of LC3-I to LC3-II. The activation of the major unfolded protein response, indicated by phosphorylation of inositol-requiring enzyme 1 alpha, and protein kinase R-like endoplasmic reticulum kinase, and eukaryotic translation initiation factor 2α, and the increase of the endoplasmic reticulum stress marker, C/EBP homologous protein, were induced by maternal diabetes in vivo and high glucose in vitro. Unfolded protein response and endoplasmic reticulum stress induced by maternal diabetes or high glucose were reduced by Rps6kb1 deletion or p70S6K1 knockdown, respectively. Rps6kb1 knockout blocked maternal diabetes-induced caspase cleavage and neuroepithelial cell apoptosis. The superoxide dismutase mimetic Tempol abolished high glucose-induced p70S6K1 activation.

CONCLUSION

The study revealed the critical involvement of p70S6K1 in the pathogenesis of diabetic embryopathy.

Maternal inflammation leads to different mTORC1 activity varied by anatomic locations in mouse placenta†

Maternal inflammation (MI) is associated with many adverse perinatal outcomes. The placenta plays a vital role in mediating maternal-fetal resource allocation. Studies have shown that MI contributes to placental dysfunction, which then leads to adverse birth outcomes and high health risks throughout childhood. Placental mammalian target of rapamycin complex 1 (mTORC1) signaling pathway links maternal nutrient availability to fetal growth; however, the impact of MI on mTORC1 signaling in the placenta remains unclear. In this study, we sought to explore the changes of mTORC1 signaling in the mouse placenta at late gestation by using two models of MI employing lipopolysaccharide (LPS) and interleukin-1β (IL-1β) to mimic acute (aMI) and sub-chronic (cMI) inflammatory states, respectively. We determined placental mTORC1 activity by measuring the activity of mTORC1 downstream molecules, including S6k, 4Ebp1, and rpS6. In the aMI model, we found that mTORC1 activity was significantly decreased in the placental decidual and junctional zone at 2 and 6 h after LPS surgery, respectively; however, mTORC1 activity was significantly increased in the placental labyrinth zone at 2, 6, and 24 h after LPS treatment, respectively. In the cMI model, we observed that mTORC1 activity was increased only in the placental labyrinth zone after consecutive IL-1β exposure. Our study reveals that different parts of the mouse placenta react differently to MI, leading to variable mTORC1 activity throughout the placenta. This suggests that different downstream molecules of mTORC1 from different parts of the mouse placenta may be used in clinical research to monitor the fetal well-being during MI.

The effect of intrauterine inflammation on mTOR signaling in mouse fetal brain

Fetuses exposed to an inflammatory environment are predisposed to long-term adverse neurological outcomes. However, the mechanism by which intrauterine inflammation (IUI) is responsible for abnormal fetal brain development is not fully understood. The mechanistic target of rapamycin (mTOR) signaling pathway is closely associated with fetal brain development. We hypothesized that mTOR signaling might be involved in fetal brain injury and malformation when fetuses are exposed to the IUI environment. A well-established IUI model was utilized by intrauterine injection of lipopolysaccharide (LPS) to explore the effect of IUI on mTOR signaling in mouse fetal brains. We found that microglia activation in LPS fetal brains was increased, as demonstrated by elevated Iba-1 protein level and immunofluorescence density. LPS fetal brains also showed reduced neuronal cell counts, decreased cell proliferation demonstrated by low Ki67-positive density, and elevated neuron apoptosis evidenced by high expression of cleaved Caspase 3. Furthermore, we found that mTOR signaling in LPS fetal brains was elevated at 2 hr after LPS treatment, declined at 6 hr and showed overall inhibition at 24 hr. In summary, our study revealed that LPS-induced IUI leads to increased activation of microglia cells, neuronal damage, and dynamic alterations in mTOR signaling in the mouse fetal brain. Our findings indicate that abnormal changes in mTOR signaling may underlie the development of future neurological complications in offspring exposed to prenatal IUI.

IL-1 receptor antagonist therapy mitigates placental dysfunction and perinatal injury following Zika virus infection

Zika virus (ZIKV) infection during pregnancy causes significant adverse sequelae in the developing fetus, and results in long-term structural and neurologic defects. Most preventive and therapeutic efforts have focused on the development of vaccines, antivirals, and antibodies. The placental immunologic response to ZIKV, however, has been largely overlooked as a target for therapeutic intervention. The placental inflammatory response, specifically IL-1β secretion and signaling, is induced by ZIKV infection and represents an environmental factor that is known to increase the risk of perinatal developmental abnormalities. We show in a mouse model that maternally administrated IL-1 receptor antagonist (IRA; Kineret, or anakinra), following ZIKV exposure, can preserve placental function (by improving trophoblast invasion and placental vasculature), increase fetal viability, and reduce neurobehavioral deficits in the offspring. We further demonstrate that while ZIKV RNA is highly detectable in placentas, it is not correlated with fetal viability. Beyond its effects in the placenta, we show that IL-1 blockade may also directly decrease fetal neuroinflammation by mitigating fetal microglial activation in a dose-dependent manner. Our studies distinguish the role of placental inflammation during ZIKV-infected pregnancies, and demonstrate that maternal IRA may attenuate fetal neuroinflammation and improve perinatal outcomes.

Dynamic glucose enhanced MRI of the placenta in a mouse model of intrauterine inflammation

INTRODUCTION

We investigated the feasibility of dynamic glucose enhanced (DGE) MRI in accessing placental function in a mouse model of intrauterine inflammatory injury (IUI). DGE uses the glucose chemical exchange saturation transfer (glucoCEST) effect to reflect infused d-glucose.

METHODS

IUI was induced in pregnant CD1 mice by intrauterine injection of lipopolysaccharide (LPS) on embryonic day 17. In vivo MRI was performed on an 11.7 T scanner at 6 h s after injury, and glucoCEST effect was measured using an on-resonance variable delay multi-pulse (onVDMP) technique. onVDMP acquisition was repeated over a period of 25 min, and d-glucose was infused 5 min after the start. The time-resolved glucoCEST signals were characterized using the normalized signal difference (ΔS_N) between onVDMP-labeled and nonlabeled images.

RESULTS

ΔS_N in the PBS-exposed placentae (n = 6) showed an initial drop between 1 and 3 min after infusion, followed by a positive peak between 5 and 20 min, the time period expected to be associated with the process of glucose uptake and transport. In the LPS-exposed placentae (n = 10), the positive peak was reduced or even absent, and the corresponding area-under-the-curve (AUC) was significantly lower than that in the controls. Particularly, the AUC maps suggested prominent group differences in the fetal side of the placenta. We also found that glucose transporter 1 in the LPS-exposed placentae did not respond to maternal glucose challenge.

DISCUSSION

DGE-MRI is useful for evaluating placental functions related to glucose utilization. The technique uses a non-toxic biodegradable agent (d-glucose) and thus has a potential for rapid translation to human studies of placental disorders.

Journey to the Center of the Fetal Brain: Environmental Exposures and Autophagy

Fetal brain development is known to be affected by adverse environmental exposures during pregnancy, including infection, inflammation, hypoxia, alcohol, starvation, and toxins. These exposures are thought to alter autophagy activity in the fetal brain, leading to adverse perinatal outcomes, such as cognitive and sensorimotor deficits. This review introduces the physiologic autophagy pathways in the fetal brain. Next, methods to detect and monitor fetal brain autophagy activity are outlined. An additional discussion explores possible mechanisms by which environmental exposures during pregnancy alter fetal brain autophagy activity. In the final section, a correlation of fetal autophagy activity with the observed postnatal phenotype is attempted. Our main purpose is to provide the current understanding or a lack thereof mechanisms on autophagy, underlying the fetal brain injury exposed to environmental insults.