Chronic Binge Alcohol Exposure During Pregnancy Alters mTOR System in Rat Fetal Hippocampus

In Vivo Administration of Phosphatidic Acid, a Direct Alcohol Target Rescues Fetal Growth Restriction and Maternal Uterine Artery Dysfunction in Rat FASD Model

Fetal growth restriction is a hallmark of Fetal Alcohol Syndrome (FAS) and is accompanied by maternal uterine circulatory maladaptation. FAS is the most severe form of Fetal Alcohol Spectrum Disorder (FASD), a term for the range of conditions that can develop in a fetus when their pregnant mother consumes alcohol. Alcohol exerts specific direct effects on lipids that control fundamental developmental processes. We previously demonstrated that direct in vitro application of phosphatidic acid (PA, the simplest phospholipid and a direct target of alcohol exposure) to excised uterine arteries from alcohol-exposed rats improved vascular function, but it is unknown if PA can rescue end organ phenotypes in our FASD animal model. Pregnant Sprague-Dawley rats (n = 40 total dams) were gavaged daily from gestational day (GD) 5 to GD 19 with alcohol or maltose dextrin, with and without PA supplementation, for a total of four unique groups. To translate and assess the beneficial effects of PA, we hypothesized that in vivo administration of PA concomitant with chronic binge alcohol would reverse uterine artery dysfunction and fetal growth deficits in our FASD model. Mean fetal weights and placental efficiency were significantly lower in the binge alcohol group compared with those in the control (p < 0.05). However, these differences between the alcohol and the control groups were completely abolished by auxiliary in vivo PA administration with alcohol, indicating a reversal of the classic FAS growth restriction phenotype. Acetylcholine (ACh)-induced uterine artery relaxation was significantly impaired in the uterine arteries of chronic in vivo binge alcohol-administered rats compared to the controls (p < 0.05). Supplementation of PA in vivo throughout pregnancy reversed the alcohol-induced vasodilatory deficit; no differences were detected following in vivo PA administration between the pair-fed control and PA alcohol groups. Maximal ACh-induced vasodilation was significantly lower in the alcohol group compared to all the other treatments, including control, control PA, and alcohol PA groups (p < 0.05). When analyzing excitatory vasodilatory p1177-eNOS, alcohol-induced downregulation of p1177-eNOS was completely reversed following in vivo PA supplementation. In summary, these novel data utilize a specific alcohol target pathway (PA) to demonstrate a lipid-based preventive strategy and provide critical insights important for the development of translatable interventions.

Alcohol Dependence Modulates Amygdalar mTORC2 and PKCε Expression in a Rodent Model

Multiple alcohol use disorder (AUD)-related behavioral alterations are governed by protein kinase C epsilon (PKCε), particularly in the amygdala. Protein kinase C (PKC) is readily phosphorylated at Ser729 before activation by the mTORC2 protein complex. In keeping with this, the current study was conducted to assess the variations in mTORC2 and PKCε during different ethanol exposure stages. The following groups of rats were employed: control, acute, chronic, ethanol withdrawal (EW), and EW + ethanol (EtOH). Ethanol-containing and non-ethanol-containing modified liquid diets (MLDs) were administered for 27 days. On day 28, either saline or ethanol (2.5 g/kg, 20% v/v) was intraperitoneally administered, followed by bilateral amygdala extraction. PKCε mRNA levels were noticeably increased in the amygdala of the EW + EtOH and EW groups. Following chronic ethanol consumption, the stress-activated map kinase-interacting protein 1 (Sin1) gene expression was markedly decreased. In the EW, EW + EtOH, and chronic ethanol groups, there was a profound increase in the protein expression of mTOR, Sin1, PKCε, and phosphorylated PKCε (Ser729). The PKCε gene and protein expressions showed a statistically significant moderate association, according to a correlation analysis. Our results suggest that an elevated PKCε protein expression in the amygdala during EW and EW + EtOH occurred at the transcriptional level. However, an elevation in the PKCε protein expression, but not its mRNA, after chronic ethanol intake warrants further investigation to fully understand the signaling pathways during different episodes of AUD.

A multi-organ analysis of the role of mTOR in fetal alcohol spectrum disorders

Alcohol exposure during gestation can lead to fetal alcohol spectrum disorders (FASD), an array of cognitive and physical developmental impairments. Over the past two and a half decades, Mammalian Target of Rapamycin (mTOR) has emerged at the nexus of many fields of study, and has recently been implicated in FASD etiology. mTOR plays an integral role in modulating anabolic and catabolic activities, including protein synthesis and autophagy. These processes are vital for proper development and can have long lasting effects following alcohol exposure, such as impaired hippocampal and synapse formation, reduced brain size, as well as cognitive, behavioral, and memory impairments. We highlight recent advances in the field of FASD, primarily with regard to animal model discoveries and discuss the interaction between alcohol and mTOR in the context of various tissues, including brain, placenta, bone, and muscle, with respect to developmental alcohol exposure paradigms. The current review focuses on novel FASD research within the context of the mTOR signaling and sheds light on mechanistic etiologies at various biological levels including molecular, cellular, and functional, across multiple stages of development and illuminates the dichotomy between the different mTOR complexes and their unique signaling roles.

Antidepressant-like effect of CP-101,606: Evidence of mTOR pathway activation

BACKGROUND

As a non-competitive N-methyl d-aspartate receptor antagonist, ketamine exerts rapid-onset and long-lasting antidepressant effects on depression, but some side effects limit its use. To identify a safer compound that may provide similar antidepressant effects, here we investigated whether CP-101,606, a selective NR2B receptor inhibitor, provides similar antidepressant effects and explored its underlying mechanisms.

METHODS

To mimic depressive-like behavior, mice were subjected to chronic unpredictable mild stress (CUMS) for 21 days. Mice were treated with CP-101,606 at 10, 20, and 40 mg/kg doses for 7, 14, and 21 days, respectively, followed by a sucrose preference test (SPT), tail suspension test (TST), and forced swimming test (FST). Western blot analysis was performed on several targets (mTOR, p-mTOR, p70S6K, p-p70S6K, PSD-95, and GluA1), along with immunohistochemistry (GluA1) and immunofluorescence (p-mTOR) assays, using hippocampal tissue.

RESULTS

CP-101,606 at 20 and 40 mg/kg doses for 7 and 14 days and fluoxetine 10 mg/kg and CP-101606 20 mg/kg for 21 days ameliorated depression-like behaviors in the SPT, TST, and FST. The effects of CP-101,606 were associated with a reversal of the CUMS-induced decrease in mTOR (Ser2448) and p70S6K (Thr389) phosphorylation and increasing PSD95 and GluA1 synthesis in the hippocampus.

CONCLUSIONS

Our results demonstrate that CP-101,606 produces antidepressant effects in CUMS mice, which may be mediated by mTOR signaling cascade upregulation. Our findings suggest the possible utility of CP-101,606 as a treatment for depression.

Dose-related shifts in proteome and function of extracellular vesicles secreted by fetal neural stem cells following chronic alcohol exposure

Accumulating evidence indicates that extracellular vesicles (EVs) mediate endocrine functions and also pathogenic effects of neurodevelopmental perturbagens like ethanol. We performed mass-spectrometry on EVs secreted by fetal murine cerebral cortical neural stem cells (NSCs), cultured ex-vivo as sex-specific neurosphere cultures, to identify overrepresented proteins and signaling pathways in EVs relative to parental NSCs in controls, and following exposure of parental NSCs to a dose range of ethanol. EV proteomes differ substantially from parental NSCs, and though EVs sequester proteins across sub-cellular compartments, they are enriched for distinct morphogenetic signals including the planar cell polarity pathway. Ethanol exposure favored selective protein sequestration in EVs and depletion in parental NSCs, and also resulted in dose-independent overrepresentation of cell-cycle and DNA replication pathways in EVs as well as dose-dependent overrepresentation of rRNA processing and mTor stress pathways. Transfer of untreated EVs to naïve cells resulted in decreased oxidative metabolism and S-phase, while EVs derived from ethanol-treated NSCs exhibited diminished effect. Collectively, these data show that NSCs secrete EVs with a distinct proteome that may have a general growth-inhibitory effect on recipient cells. Moreover, while ethanol results in selective transfer of proteins from NSCs to EVs, the efficacy of these exposure-derived EVs is diminished.

Binge-like Prenatal Ethanol Exposure Causes Impaired Cellular Differentiation in the Embryonic Forebrain and Synaptic and Behavioral Defects in Adult Mice

An embryo’s in-utero exposure to ethanol due to a mother’s alcohol drinking results in a range of deficits in the child that are collectively termed fetal alcohol spectrum disorders (FASDs). Prenatal ethanol exposure is one of the leading causes of preventable intellectual disability. Its neurobehavioral underpinnings warrant systematic research. We investigated the immediate effects on embryos of acute prenatal ethanol exposure during gestational days (GDs) and the influence of such exposure on persistent neurobehavioral deficits in adult offspring. We administered pregnant C57BL/6J mice with ethanol (1.75 g/kg) (GDE) or saline (GDS) intraperitoneally (i.p.) at 0 h and again at 2 h intervals on GD 8 and GD 12. Subsequently, we assessed apoptosis, differentiation, and signaling events in embryo forebrains (E13.5; GD13.5). Long-lasting effects of GDE were evaluated via a behavioral test battery. We also determined the long-term potentiation and synaptic plasticity-related protein expression in adult hippocampal tissue. GDE caused apoptosis, inhibited differentiation, and reduced pERK and pCREB signaling and the expression of transcription factors Pax6 and Lhx2. GDE caused persistent spatial and social investigation memory deficits compared with saline controls, regardless of sex. Interestingly, GDE adult mice exhibited enhanced repetitive and anxiety-like behavior, irrespective of sex. GDE reduced synaptic plasticity-related protein expression and caused hippocampal synaptic plasticity (LTP and LTD) deficits in adult offspring. These findings demonstrate that binge-like ethanol exposure at the GD8 and GD12 developmental stages causes defects in pERK–pCREB signaling and reduces the expression of Pax6 and Lhx2, leading to impaired cellular differentiation during the embryonic stage. In the adult stage, binge-like ethanol exposure caused persistent synaptic and behavioral abnormalities in adult mice. Furthermore, the findings suggest that combining ethanol exposure at two sensitive stages (GD8 and GD12) causes deficits in synaptic plasticity-associated proteins (Arc, Egr1, Fgf1, GluR1, and GluN1), leading to persistent FASD-like neurobehavioral deficits in mice.

Morphological alteration in rat hippocampal neuronal dendrites following chronic binge prenatal alcohol exposure

Prenatal alcohol exposure (PAE) may result in Fetal Alcohol Spectrum Disorders (FASD). The hippocampus has been recognized as a vulnerable target to alcohol-induced developmental damage. However, the effect of prenatal exposure to alcohol on dendritic morphological adaptations throughout the hippocampal fields in the developing brain still remains largely unknown in the context of FASD. We hypothesized that chronic binge alcohol exposure during pregnancy alters dendrite arborization throughout the developing rat hippocampus. Pregnant Sprague-Dawley rats were assigned to either a pair-fed control (PF-Cont) or a binge alcohol (Alcohol) treatment group. Alcohol dams were acclimatized via a once-daily orogastric gavage of 4.5 g/kg alcohol from gestational day (GD) 5-10 and progressed to 6 g/kg alcohol from GD 11-21. Pair-fed dams similarly received isocaloric maltose dextrin. After parturition, all dams received an ad libitum diet and nursed their offspring until postnatal day (PND) 10 when the pup brains were collected for morphological analysis. PAE increased dendritic arborization and complexities of CA1, CA2/3, and DG neurons in the PND 10 rat hippocampus. The number of primary dendrites, total dendritic length, and number of dendritic branches were significantly increased following PAE, and Sholl analysis revealed significantly more intersections of the dendritic processes in PND 10 offspring following PAE compared with those in the PF-Cont group. We conclude that chronic binge PAE significantly alters hippocampal dendritic morphology in the developing hippocampus. We conjecture that this morphological alteration in postnatal rat hippocampal dendrites following chronic binge prenatal alcohol exposure may play a critical role in FASD neurobiological phenotypes.

Rapamycin Improves Spatial Learning Deficits, Vulnerability to Alcohol Addiction and Altered Expression of the GluN2B Subunit of the NMDA Receptor in Adult Rats Exposed to Ethanol during the Neonatal Period

Ethanol exposure during pregnancy alters the mammalian target of rapamycin (mTOR) signaling pathway in the fetal brain. Hence, in adult rats exposed to ethanol during the neonatal period, we investigated the influence of rapamycin, an mTOR Complex 1 (mTORC1) inhibitor, on deficits in spatial memory and reversal learning in the Barnes maze task, as well as the ethanol-induced rewarding effects (1.0 or 1.5 g/kg) using the conditioning place preference (CPP) paradigm. Rapamycin (3 and 10 mg/kg) was given before intragastric ethanol (5 g/kg/day) administration at postnatal day (PND)4–9 (an equivalent to the third trimester of human pregnancy). Spatial memory/reversal learning and rewarding ethanol effect were evaluated in adult (PND60–70) rats. Additionally, the impact of rapamycin pre-treatment on the expression of the GluN2B subunit of NMDA receptor in the brain was assessed in adult rats. Our results show that neonatal ethanol exposure induced deficits in spatial memory and reversal learning in adulthood, but the reversal learning outcome may have been due to spatial learning impairments rather than cognitive flexibility impairments. Furthermore, in adulthood the ethanol treated rats were also more sensitive to the rewarding effect of ethanol than the control group. Rapamycin prevented the neonatal effect of ethanol and normalized the GluN2B down-regulation in the hippocampus and the prefrontal cortex, as well as normalized this subunit’s up-regulation in the striatum of adult rats. Our results suggest that rapamycin and related drugs may hold promise as a preventive therapy for fetal alcohol spectrum disorders.

Rapamycin Improves Recognition Memory and Normalizes Amino-Acids and Amines Levels in the Hippocampal Dentate Gyrus in Adult Rats Exposed to Ethanol during the Neonatal Period

The mammalian target of rapamycin (mTOR), a serine/ threonine kinase, is implicated in synaptic plasticity by controlling protein synthesis. Research suggests that ethanol exposure during pregnancy alters the mTOR signaling pathway in the fetal hippocampus. Thus, we investigated the influence of pre-treatment with rapamycin, an mTORC1 inhibitor, on the development of recognition memory deficits in adult rats that were neonatally exposed to ethanol. In the study, male and female rat pups received ethanol (5 g/kg/day) by intragastric intubation at postanatal day (PND 4-9), an equivalent to the third trimester of human pregnancy. Rapamycin (3 and 10 mg/kg) was given intraperitoneally before every ethanol administration. Short- and long-term recognition memory was assessed in the novel object recognition (NOR) task in adult (PND 59/60) rats. Locomotor activity and anxiety-like behavior were also evaluated to exclude the influence of such behavior on the outcome of the memory task. Moreover, the effects of rapamycin pre-treatment during neonatal ethanol exposure on the content of amino-acids and amines essential for the proper development of cognitive function in the dentate gyrus (DG) of the hippocampus was evaluated using proton magnetic resonance spectroscopy (1H MRS) in male adult (PND 60) rats. Our results show the deleterious effect of ethanol given to neonatal rats on long-term recognition memory in adults. The effect was more pronounced in male rather than female rats. Rapamycin reversed this ethanol-induced memory impairment and normalized the levels of amino acids and amines in the DG. This suggests the involvement of mTORC1 in the deleterious effect of ethanol on the developing brain.