Prenatal stress affects insulin-like growth factor-1 (IGF-1) level and IGF-1 receptor phosphorylation in the brain of adult rats

Stress in pregnancy - Implications for fetal BDNF in amniotic fluid at birth

Introduction

At the maternal-fetal interface in pregnancy, stress during pregnancy can lead to an increased vulnerability to later psychopathology of the fetus. Potential mediators of this association have scarcely been studied and may include early alterations of fetal brain-derived neurotrophic factor (BDNF). Amniotic fluid is of particular interest for effects on fetal endocrine alterations, as the assessment in amniotic fluid allows for measurements over a time integral. This study hypothesized that maternal psychometrics, socioeconomic status and glucocorticoids are related to BDNF levels in amniotic fluid at birth. The association of fetal BDNF with newborn anthropometrics was tested.

Methods

Women near term who underwent elective cesarean section and their newborns were investigated (n = 37). Maternal psychometrics, socioeconomic status and glucocorticoids (the sum of cortisol and cortisone) in amniotic fluid at birth were analyzed for an association with fetal BDNF in amniotic fluid at birth. Newborn anthropometrics were assessed by length, weight, head circumference and gestational age at birth.

Results

In bivariate analysis, maternal psychometrics and socioeconomic status were not related to fetal BDNF in amniotic fluid at birth. The sum of cortisol and cortisone related to increased fetal BDNF in amniotic fluid at birth (r = 0.745, p < 0.001). BDNF in amniotic fluid was associated negatively with fetal birth weight per gestational age (r = -0.519, p < 0.001), length per gestational age (r = -0.374, p = 0.023), head circumference per gestational age (r = -0.508, p = 0.001), but not with gestational age at birth. In multiple regression analysis, the sum of cortisol and cortisone (p < 0.001) and birth weight per gestational age (p = 0.012) related to higher fetal BDNF levels in amniotic fluid at birth (R2 = 0.740, p < 0.001) when controlling for fetal sex and maternal age. Head circumference per gestational age predicted fetal BDNF with borderline significance (p = 0.058) when controlling for confounders.

Conclusion

Glucocorticoids in amniotic fluid were positively associated with high fetal BDNF at birth, which may be an adaptive fetal response. Maternal psychological variables and socioeconomic status did not link to fetal BDNF. Birth weight and head circumference per gestational age were inversely associated with fetal BDNF at birth, which may represent a compensatory upregulation of BDNF in fetuses with low anthropometrics. Longitudinal studies are needed to assess the role of stress during pregnancy on later offspring development. The analysis of additional fetal growth factors and inflammation upon maternal stress in further biomaterials such as the placenta is warranted, to understand mechanistic alterations of how maternal stress links to fetal development and an increased vulnerability for psychopathology.

Prenatal stress aggravates age-dependent cognitive decline, insulin signaling dysfunction, and the pro-inflammatory response in the APPNL-F/NL-F mouse model of Alzheimer's disease

Accumulating evidence indicates that early adverse life experiences may be involved in the pathogenesis of Alzheimer's disease (AD). Prenatal stress (PS) can affect brain maturation and neuroimmune and metabolic interactions, leading to age-dependent cognitive deficits in offspring. However, a multi-faceted cause-and-effect impact of PS on the development of cognitive deficits in the process of physiological ageing and in the APP^NL-F/NL-F mouse model of Alzheimer's disease has not yet been evaluated. We have identified age-dependent cognitive learning and memory deficits using male C57BL/6 J (wild type, WT) and the knock-in APP^NL-F/NL-F (KI) aged 12, 15, and 18 months. An increase in the Aβ42/Aβ40 ratio and mouse ApoE levels in the hippocampus and frontal cortex preceded the onset of cognitive deficits in the KI mice. Moreover, dysfunction in insulin signaling, including increased IRS-1 serine phosphorylation in both brain areas and the tyrosine phosphorylation deficit in the frontal cortex, suggested age-dependent insulin/IGF-1 resistance. Resistance was reflected by disturbances in mTOR or ERK1/2 kinase phosphorylation and excessive pro-inflammatory (TNF-α, IL-6, and IL-23) status in the KI mice. Importantly, our study has provided insights into the higher vulnerability to PS-induced exacerbation of age-dependent cognitive deficits and biochemical dysfunction in KI mice than in WT animals. We anticipate our study will lead to future investigation of a multi-faceted cause-and-effect relationship between stress during neurodevelopment and the onset of AD pathology, distinguishing it from changes in the course of dementia during normal ageing.

Short-Term Irisin Treatment Enhanced Neurotrophin Expression Differently in the Hippocampus and the Prefrontal Cortex of Young Mice

As a result of physical exercise, muscle releases multiple exerkines, such as "irisin", which is thought to induce pro-cognitive and antidepressant effects. We recently demonstrated in young healthy mice the mitigation of depressive behaviors induced by consecutive 5 day irisin administration. To understand which molecular mechanisms might be involved in such effect, we here studied, in a group of mice previously submitted to a behavioral test of depression, the gene expression of neurotrophins and cytokines in the hippocampus and prefrontal cortex (PFC), two brain areas frequently investigated in the depression pathogenesis. We found significantly increased mRNA levels of nerve growth factor (NGF) and fibroblast growth factor 2 (FGF-2) in the hippocampus and brain-derived growth factor (BDNF) in the PFC. We did not detect a difference in the mRNA levels of interleukin 6 (IL-6) and IL-1β in both brain regions. Except for BDNF in the PFC, two-way ANOVA analysis did not reveal sex differences in the expression of the tested genes. Overall, our data evidenced a site-specific cerebral modulation of neurotrophins induced by irisin treatment in the hippocampus and the PFC, contributing to the search for new antidepressant treatments targeted at single depressive events with short-term protocols.

Identification of the molecular mechanism of insulin-like growth factor-1 (IGF-1): a promising therapeutic target for neurodegenerative diseases associated with metabolic syndrome

Neurodegenerative disorders are accompanied by neuronal degeneration and glial dysfunction, resulting in cognitive, psychomotor, and behavioral impairment. Multiple factors including genetic, environmental, metabolic, and oxidant overload contribute to disease progression. Recent evidences suggest that metabolic syndrome is linked to various neurodegenerative diseases. Metabolic syndrome (MetS) is known to be accompanied by symptoms such as hyperglycemia, abdominal obesity, hypertriglyceridemia, and hypertension. Despite advances in knowledge about the pathogenesis of neurodegenerative disorders, effective treatments to combat neurodegenerative disorders caused by MetS have not been developed to date. Insulin growth factor-1 (IGF-1) deficiency has been associated with MetS-related pathologies both in-vivo and in-vitro. IGF-1 is essential for embryonic and adult neurogenesis, neuronal plasticity, neurotropism, angiogenesis, metabolic function, and protein clearance in the brain. Here, we review the evidence for the potential therapeutic effects of IGF-1 in the neurodegeneration related to metabolic syndrome. We elucidate how IGF-1 may be involved in molecular signaling defects that occurs in MetS-related neurodegenerative disorders and highlight the importance of IGF-1 as a potential therapeutic target in MetS-related neurological diseases.

Sex differences in the vulnerability of the hippocampus to prenatal stress

Distressing events during pregnancy that engage activity of the body's endocrine stress response have been linked with later life cognitive deficits in offspring and associated with developmental changes in cognitive-controlling neural regions. Interestingly, prenatal stress (PS)-induced alterations have shown some sex specificity. Here, we review the literature of animal studies examining sex-specific effect of physical PS on the function and structure of the hippocampus as hippocampal impairments likely underlie PS-associated deficits in learning and memory. Furthermore, the connectivity between the hypothalamic-pituitary-adrenal (HPA) axis and the hippocampus as well as the heavy presence of glucocorticoid receptors (GRs) in the hippocampus suggests this structure plays an important role in modulation of activity within stress circuitry in a sex-specific pattern. We hope that better understanding of sex-specific, PS-related hippocampal impairment will assist in uncovering the molecular mechanisms behind sex-based risk factors in PS populations across development, and perhaps contribute to greater precision in management of cognitive disturbances in this vulnerable population.

Antidepressant-like effects of trophic factor receptor signaling

A significant body of research has demonstrated that antidepressants regulate neurotrophic factors and that neurotrophins themselves are capable of independently producing antidepressant-like effects. While brain derived neurotrophic factor (BDNF) remains the best studied molecule in this context, there are several structurally diverse trophic factors that have shown comparable behavioral effects, including basic fibroblast growth factor (FGF-2), insulin-like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF). In this review we discuss the structural and biochemical signaling aspects of these neurotrophic factors with antidepressant activity. We also include a discussion on a cytokine molecule erythropoietin (EPO), widely known and prescribed as a hormone to treat anemia but has recently been shown to function as a neurotrophic factor in the central nervous system (CNS).

Prenatal psychological or metabolic stress increases the risk for psychiatric disorders: the "funnel effect" model

Adverse stressful experiences in utero can redirect fetal brain development, ultimately leading to increased risk for psychiatric disorders. Obesity during pregnancy can have similar effects as maternal stress, affecting mental health in the offspring. In order to explain how similar outcomes may originate from different prenatal conditions, we propose a "funnel effect" model whereby maternal psychological or metabolic stress triggers the same evolutionarily conserved response pathways, increasing vulnerability for psychopathology. In this context, the placenta, which is the main mother-fetus interface, appears to facilitate such convergence, re-directing "stress" signals to the fetus. Characterizing converging pathways activated by different adverse environmental conditions is fundamental to assess the emergence of risk signatures of major psychiatric disorders, which might enable preventive measures in risk populations, and open up new diagnostics, and potentially therapeutic approaches for disease prevention and health promotion already during pregnancy.

Does Sertraline Affect Hypothalamic Food Intake Peptides in the Rat Experimental Model of Chronic Mild Stress-Induced Depression?

Depression is a chronic, recurrent and life-threatening disease affecting approximately 15% of the world population. Depression is responsible for neuropathologies like decreased neurogenesis and increased dendritic atrophy. Antidepressant treatments increase hippocampal neurogenesis and neurotrophic factor expression. Based on this information, it was aimed to investigate effect of sertraline on depression in rats with chronic mild stress (CMS) model and to determine how it affects cell proliferation and hypothalamic peptide levels in hypothalamus. 56 adult male Wistar albino; control, depression(D), depression + sertraline, sertraline were divided into groups. Various stressors were applied to D for 30 days. Open field test (OFT) and forced swimming test (FST) were conducted to check whether the animals were depressed. On the 16th day osmotic minipump was placed subcutaneously and sertraline (10 mg/kg/day) was administered for 15 days. Behavior tests were done. Hypothalamic peptide gene expression levels were analyzed by quantitative RT-PCR. Statistical evaluations were made using ANOVA. It caused a decrease in the percentage of movement in the D and control groups in the OFT, an increase in the immobility time in the D group in the FST, and an increase in the swimming behavior in the DS group. Animals did not show any anxiological behavior based on the elevated plus maze test results. CMS caused a decrease in GLUT2 and NPY gene expression in the hypothalamus of animals, an increase in POMC and FGFR2, and an increase in IGFIR and GLUT2 gene expression in the DS group. Sertraline has been shown to ameliorate the effects of CMS-induced depression. Sertraline is thought to have a positive regulatory effect on both the formation of neural precursor cells and the survival of newly formed neurons in the hypothalamus. Newly formed neurons in the hypothalamus express food intake-related NPY, POMC, GLUT2 neurons, and thus hypothalamic tanycytes may play a key role in the control of energy metabolism.

Associations between major psychiatric disorder polygenic risk scores and blood-based markers in UK biobank

Major depressive disorder (MDD), schizophrenia (SCZ), and bipolar disorder (BD) have both shared and discrete genetic risk factors, and are associated with peripheral abnormalities. The relationships between such genetic architectures and blood-based markers are, however, unclear. We investigated relationships between polygenic risk scores (PRS) for these disorders and peripheral markers in the UK Biobank cohort. We calculated polygenic risk scores for n = 367,329 (MDD PRS), n = 366,465 (SCZ PRS), and n = 366,383 (BD PRS) UK Biobank cohort subjects. We then examined associations between disorder PRS and 58 inflammatory/immune, hematological, bone, cardiovascular, hormone, liver, renal and diabetes-associated blood markers using two generalized linear regression models: 'minimally adjusted' controlling for variables such as age and sex, and 'fully adjusted' including additional lifestyle covariates: BMI, alcohol and smoking status, and medication intake. There were 38/58 MDD PRS, 32/58 SCZ PRS, and 20/58 BD PRS-blood marker associations detected for our minimally adjusted model. Of these, 13/38 (MDD PRS), 14/32 (SCZ PRS), and 10/20 (BD PRS) associations remained significant after controlling for lifestyle factors. Many were disorder-specific, with 8/13 unique MDD PRS associations identified. Several disorder-specific associations for MDD and SCZ were immune-related, with mostly positive and negative associations identified for MDD and SCZ PRS respectively. This study suggests that MDD, SCZ and BD have both shared and distinct peripheral markers associated with disorder-specific genetic risk. The results also implicate inflammatory dysfunction in MDD and SCZ, albeit with differences in patterns between the two conditions, and enrich our understanding of potential underlying pathophysiological mechanisms in major psychiatric disorders.

Telomeres: the role of shortening and senescence in major depressive disorder and its therapeutic implications

Major depressive disorder (MDD) is one of the most prevalent and debilitating psychiatric disorders, with a large number of patients not showing an effective therapeutic response to available treatments. Several biopsychosocial factors, such as stress in childhood and throughout life, and factors related to biological aging, may increase the susceptibility to MDD development. Included in critical biological processes related to aging and underlying biological mechanisms associated with MDD is the shortening of telomeres and changes in telomerase activity. This comprehensive review discusses studies that assessed the length of telomeres or telomerase activity and function in peripheral blood cells and brain tissues of MDD individuals. Also, results from in vitro protocols and animal models of stress and depressive-like behaviors were included. We also expand our discussion to include the role of telomere biology as it relates to other relevant biological mechanisms, such as the hypothalamic-pituitary-adrenal (HPA) axis, oxidative stress, inflammation, genetics, and epigenetic changes. In the text and the discussion, conflicting results in the literature were observed, especially considering the size of telomeres in the central nervous system, on which there are different protocols with divergent results in the literature. Finally, the context of this review is considering cell signaling, transcription factors, and neurotransmission, which are involved in MDD and can be underlying to senescence, telomere shortening, and telomerase functions.

Chronic Piromelatine Treatment Alleviates Anxiety, Depressive Responses and Abnormal Hypothalamic-Pituitary-Adrenal Axis Activity in Prenatally Stressed Male and Female Rats

The prenatal stress (PNS) model in rodents can induce different abnormal responses that replicate the pathophysiology of depression. We applied this model to evaluate the efficacy of piromelatine (Pir), a novel melatonin analog developed for the treatment of insomnia, in male and female offspring. Adult PNS rats from both sexes showed comparable disturbance associated with high levels of anxiety and depressive responses. Both males and females with PNS demonstrated impaired feedback inhibition of the hypothalamic-pituitary-adrenal (HPA) axis compared to the intact offspring and increased glucocorticoid receptors in the hippocampus. However, opposite to female offspring, the male PNS rats showed an increased expression of mineralocorticoid receptors in the hippocampus. Piromelatine (20 mg/kg, i.p., for 21 days injected from postnatal day 60) attenuated the high anxiety level tested in the open field, elevated plus-maze and light-dark test, and depressive-like behavior in the sucrose preference and the forced swimming tests in a sex-specific manner. The drug reversed to control level stress-induced increase of plasma corticosterone 120 min later in both sexes. Piromelatine also corrected to control level the PNS-induced alterations of corticosteroid receptors only in male offspring. Our findings suggest that the piromelatine treatment exerts beneficial effects on impaired behavioral responses and dysregulated HPA axis in both sexes, while it corrects the PNS-induced changes in the hippocampal corticosteroid receptors only in male offspring.

Childhood trauma and insulin-like growth factors in amniotic fluid: An exploratory analysis of 79 women

BACKGROUND

Perinatal stress has adverse effects on fetal outcome, yet the effect of early maternal trauma on fetal outcome has scarcely been studied. We investigated effects of maternal childhood trauma and current environment on important regulators of prenatal growth, fetal insulin-like growth factor (IGF)-1 and IGF-2 in amniotic fluid and assessed the impact of IGFs on newborn anthropometrics.

METHODS

79 pregnant women in their second trimester who underwent amniocentesis (15.9 ± 0.9 weeks of gestational age) and their newborns at birth were analyzed. Maternal childhood trauma was assessed using the childhood trauma questionnaire (CTQ) and current environment was operationalized by assessing maternal psychosocial, physical health and endocrine measurements in amniotic fluid.

RESULTS

In this exploratory analysis of 79 pregnant women, maternal childhood trauma, defined as reporting at least low scores on any of the CTQ subscales, negatively correlated with fetal IGF-1 (M_ln = 3.48 vs. 2.98; p = 0.012) and IGF-2 (Mdn_ln = 4.99 vs. 4.70; p = 0.002). Trauma severity, defined as the overall trauma score, negatively correlated with fetal IGF-2 (r = -0.24; p = 0.037). From trauma subscales, maternal sexual abuse correlated with fetal IGF-1 (r = -0.32; p = 0.006) and IGF-2 (r = -0.39; p = 0.001). Maternal BMI negatively correlated with fetal IGF-1 (r = -0.26; p = 0.023) and IGF-2 (r = -0.29; p = 0.011). Newborn anthropometrics were operationalized by length, weight, sex, gestational age, length/gestational age and weight/gestational age at birth. Fetal weight at birth associated with a trend with fetal IGF-1 when controlling for BMI. Maternal hypothalamus-pituitary-adrenal axis activity and maternal exercise did not contribute significantly to predicting fetal IGFs. Maternal childhood trauma (β = -0.27; p = 0.011) and BMI (β = -0.24; p = 0.026) remained significantly associated with fetal IGF-1. Maternal childhood trauma (β = -0.32; p = 0.003), maternal BMI (β = -0.30; p = 0.005) and maternal sexual abuse (β = -0.22; p = 0.049) remained significantly associated with fetal IGF-2 and with a trend with fetal IGF-1 (β = -0.21; p = 0.076) when excluding women with gestational diabetes.

CONCLUSION

Maternal childhood trauma and BMI associate negatively with fetal IGF-1 and IGF-2 in amniotic fluid. Controlling for maternal BMI, fetal weight at birth remains associated with a trend with fetal IGF-1. The presented data suggests that childhood trauma can affect endocrine measurements of the developing next generation, providing a mechanism by which adverse maternal life events are transmitted to the next generation.

Role of Polyinosinic:Polycytidylic Acid-Induced Maternal Immune Activation and Subsequent Immune Challenge in the Behaviour and Microglial Cell Trajectory in Adult Offspring: A Study of the Neurodevelopmental Model of Schizophrenia

Multiple lines of evidence support the pathogenic role of maternal immune activation (MIA) in the occurrence of the schizophrenia-like disturbances in offspring. While in the brain the homeostatic role of neuron-microglia protein systems is well documented, the participation of the CX3CL1-CX3CR1 and CD200-CD200R dyads in the adverse impact of MIA often goes under-recognized. Therefore, in the present study, we examined the effect of MIA induced by polyinosinic:polycytidylic acid (Poly I:C) on the CX3CL1-CX3CR1 and CD200-CD200R axes, microglial trajectory (MhcII, Cd40, iNos, Il-1β, Tnf-α, Il-6, Arg1, Igf-1, Tgf-β and Il-4), and schizophrenia-like behaviour in adult male offspring of Sprague-Dawley rats. Additionally, according to the “two-hit” hypothesis of schizophrenia, we evaluated the influence of acute challenge with Poly I:C in adult prenatally MIA-exposed animals on the above parameters. In the present study, MIA evoked by Poly I:C injection in the late period of gestation led to the appearance of schizophrenia-like disturbances in adult offspring. Our results revealed the deficits manifested as a diminished number of aggressive interactions, presence of depressive-like episodes, and increase of exploratory activity, as well as a dichotomy in the sensorimotor gating in the prepulse inhibition (PPI) test expressed as two behavioural phenotypes (MIA_PPI-low and MIA_PPI-high). Furthermore, in the offspring rats subjected to a prenatal challenge (i.e., MIA) we noticed the lack of modulation of behavioural changes after the additional acute immune stimulus (Poly I:C) in adulthood. The important finding reported in this article is that MIA affects the expression and levels of the neuron-microglia proteins in the frontal cortex and hippocampus of adult offspring. We found that the changes in the CX3CL1-CX3CR1 axis could affect microglial trajectory, including decreased hippocampal mRNA level of MhcII and elevated cortical expression of Igf-1 in the MIA_PPI-high animals and/or could cause the up-regulation of an inflammatory response (Il-6, Tnf-α, iNos) after the “second hit” in both examined brain regions and, at least in part, might differentiate behavioural disturbances in adult offspring. Consequently, the future effort to identify the biological background of these interactions in the Poly I:C-induced MIA model in Sprague-Dawley rats is desirable to unequivocally clarify this issue.

Insulin-like growth factor 1 of wild vertebrates in a life-history context

Broad variation in intra- and interspecific life-history traits is largely shaped by resource limitation and the ensuing allocation trade-offs that animals are forced to make. Insulin-like growth factor 1 (IGF-1), a growth-hormone-dependent peptide, may be a key player in the regulation of allocation processes. In laboratory animals, the effects of IGF-1 on growth- and development (positive), reproduction (positive), and longevity (negative) are well established. We here review the evidence on these effects in wild vertebrates, where animals are more likely to face resource limitation and other challenges. We point out the similarities and dissimilarities in patterns of IGF-1 functions obtained in these two different study settings and discuss the knowledge we need to develop a comprehensive picture of the role of IGF-1 in mediating life-history variation of wild vertebrates.

Maternal Immune Activation Sensitizes Male Offspring Rats to Lipopolysaccharide-Induced Microglial Deficits Involving the Dysfunction of CD200-CD200R and CX3CL1-CX3CR1 Systems

Early life challenges resulting from maternal immune activation (MIA) may exert persistent effects on the offspring, including the development of psychiatric disorders, such as schizophrenia. Recent evidence has suggested that the adverse effects of MIA may be mediated by neuron-microglia crosstalk, particularly CX3CL1-CX3CR1 and CD200-CD200R dyads. Therefore, the present study assessed the behavioural parameters resembling schizophrenia-like symptoms in the adult male offspring of Sprague-Dawley rats that were exposed to MIA and to an additional acute lipopolysaccharide (LPS) challenge in adulthood, according to the "two-hit" hypothesis of schizophrenia. Simultaneously, we aimed to clarify the role of the CX3CL1-CX3CR1 and CD200-CD200R axes and microglial reactivity in the brains of adult offspring subjected to MIA and the "second hit" wit LPS. In the present study, MIA generated a range of behavioural changes in the adult male offspring, including increased exploratory activity and anxiety-like behaviours. The most intriguing finding was observed in the prepulse inhibition (PPI) test, where the deficit in the sensorimotor gating was age-dependent and present only in part of the rats. We were able to distinguish the occurrence of two groups: responsive and non-responsive (without the deficit). Concurrently, based on the results of the biochemical studies, MIA disrupted mainly the CD200-CD200R system, while the changes of the CX3CL1-CX3CR1 axis were less evident in the frontal cortex of adult non-responsive offspring. MIA markedly affected the immune regulators of the CD200-CD200R pathway as we observed an increase in cortical IL-6 release in the responsive group and IL-4 in the non-responsive offspring. Importantly, the "second hit" generated disturbances at the behavioural and biochemical levels mostly in the non-responsive adult animals. Those offspring were characterized both by disturbed PPI and "priming" microglia. Altogether, the exposure to MIA altered the immunomodulatory mechanisms, including the CD200-CD200R axis, in the brain and sensitized animals to subsequent immunological challenges, leading to the manifestation of schizophrenia-like alterations.

The effect of insulin-like growth factor 1 on the recovery of facial nerve function in a guinea pig model of facial palsy

The efficacy of insulin-like growth factor 1 (IGF-1) in the treatment of peripheral facial nerve palsy was investigated using an animal model. The facial nerve within the temporal bone was exposed and compressed by clamping. The animals were treated with either IGF-1 or saline which was topically administered by a gelatin-based sustained-release hydrogel via an intratemporal route. The recovery from facial nerve palsy was evaluated at 8 weeks postoperatively based on eyelid closure, complete recovery rate, electroneurography and number of axons found on the facial nerve. IGF-1 treatment resulted in significant improvement in the changes of the degree of eyelid closure over the total time period and complete recovery rate. A separate study showed that IGF-1 receptor mRNA was expressed in facial nerves up to 14 days after the nerve-clamping procedure. IGF-1 was thus found to be effective in the treatment of peripheral facial nerve palsy when topically applied using a sustained-release gelatin-based hydrogel via an intratemporal route.

Ozone increases plasma kynurenine-tryptophan ratio and impacts hippocampal serotonin receptor and neurotrophic factor expression: Role of stress hormones

Air pollution is associated with adverse impacts on the brain, including cognitive decline and increased incidence of dementia, depression and anxiety; however, underlying mechanisms remain unclear. We have shown that both ozone and particulate matter activate the hypothalamic-pituitary-adrenal (HPA) axis, increasing plasma glucocorticoids and altering mRNA profiles in multiple tissues including the brain. HPA axis dysregulation has been associated with central nervous system impacts, including key effects in the hippocampus; accordingly, we hypothesized that pollutant-dependent increases in glucocorticoid levels impact biological pathways relevant to brain health. Fischer-344 rats were treated with metyrapone (0 or 50 mg/kg), a glucocorticoid synthesis inhibitor, and exposed to ozone (0 or 0.8 ppm) for 4 h (n = 5/group) to investigate the role of glucocorticoids in ozone-dependent effects on tryptophan metabolism and expression of serotonin receptors and neurotrophic factors. Ozone increased plasma levels of the tryptophan metabolite kynurenine (~2-fold) and decreased tryptophan levels (~1.2 fold). Hippocampal expression of serotonin receptors exhibited differential regulation following exposure, and expression of key neurotrophic factors (brain-derived neurotrophic factor, vascular endothelial growth factor A, insulin-like growth factor-1, tyrosine kinase receptor B, b-cell lymphoma 2) was decreased. Some, but not all effects were abrogated by metyrapone treatment, suggesting both glucocorticoid-dependent and -independent regulation. Exposure to exogenous corticosterone (10 mg/kg) followed by clean air reproduced the ozone effects that were blocked with metyrapone, confirming the specificity of effects to glucocorticoids. These results indicate that ozone can modify pathways relevant to brain health and establish a role for the HPA axis in mediating these effects.

Impact of Brain Insulin Signaling on Dopamine Function, Food Intake, Reward, and Emotional Behavior

PURPOSE OF REVIEW

Dietary obesity is primarily attributed to an imbalance between food intake and energy expenditure. Adherence to lifestyle interventions reducing weight is typically low. As a result, obesity becomes a chronic state with increased co-morbidities such as insulin resistance and diabetes. We review the effects of brain insulin action and dopaminergic signal transmission on food intake, reward, and mood as well as potential modulations of these systems to counteract the obesity epidemic.

RECENT FINDINGS

Central insulin and dopamine action are interlinked and impact on food intake, reward, and mood. Brain insulin resistance causes hyperphagia, anxiety, and depressive-like behavior and compromises the dopaminergic system. Such effects can induce reduced compliance to medical treatment. Insulin receptor sensitization and dopamine receptor agonists show attenuation of obesity and improvement of mental health in rodents and humans. Modulating brain insulin and dopamine signaling in obese patients can potentially improve therapeutic outcomes.

Variants in the Upstream Region of the Insulin Receptor Substrate-1 Gene Is Associated with Major Depressive Disorder in the Han Chinese Population

INTRODUCTION

Major depressive disorder (MDD) is one of the most prevalent and disabling mental disorders, although its underlying genetic mechanism remains unknown. Insulin receptor substrate-1 (IRS-1) is one of the critical downstream molecules in the insulin resistance signaling pathway, linking depression and diabetes. Therefore, we hypothesized that IRS-1 would be a susceptible gene for MDD, and we aimed to examine the genetic association between IRS-1 and MDD.

METHODS

This case-control study included 583 patients with MDD and 564 controls, and the genotypic and allelic distributions of the IRS-1 gene's four single nucleotide polymorphisms (SNPs) were detected by TaqMan SNP genotyping technology. Of the 583 patients, 191 underwent a further detailed interview about symptom severity and family history of mental illness. The chi-square or t test was used to analyze the data, and analyses were performed using SPSS19.0 software.

RESULTS

A haplotype in the 5'-upstream region of IRS-1 consisting of rs13411764 and rs3820926 was a risk factor of MDD. Patients with a family history of mental illness were more likely to have a GG genotype in rs13411764 and a G-T haplotype containing rs13411714-rs3820926.

DISCUSSION

The findings imply that the haplotype consisting of rs13411764 and rs3820926 in the upstream of IRS-1 is a risk factor for MDD. This haplotype could affect IRS-1 expression levels, and it is mostly inherited from parents. Thus, the presence of variants in the upstream region of IRS-1 is a risk factor of MDD, and this study could serve as a convincing reference for further studies.

Role of Chronic Administration of Antidepressant Drugs in the Prenatal Stress-Evoked Inflammatory Response in the Brain of Adult Offspring Rats: Involvement of the NLRP3 Inflammasome-Related Pathway

Evidence indicates that adverse experiences in early life may be a factor for immune disturbances leading to the depression in adulthood. Recently, a pivotal role in the pathogenesis of depression has been assigned to the activation of the brain Nod-like receptor pyrin-containing 3 (NLRP3) inflammasome. We investigated the impact of chronic treatment with antidepressant drugs on the behavioral disturbances and the levels of proinflammatory factors in the hippocampus and frontal cortex of adult male rats after prenatal stress exposure. Next, we explored the involvement of the NLRP3 inflammasome-related pathways in the mechanism of antidepressant action. Our study confirmed that chronic antidepressant treatment attenuated depression-like disturbances and exerted an anxiolytic action. All antidepressants diminished the prenatal stress-induced increase in IL-1β in both brain areas, while IL-18 only in the hippocampus. Moreover, tianeptine administration diminished the increase in CCR2 levels in both brain areas, while in the hippocampus, tianeptine, along with venlafaxine CCL2 and iNOS levels. Next, we observed that in the hippocampus, tianeptine and fluoxetine suppressed upregulation of TLR4. Furthermore, venlafaxine suppressed NFкB p65-subunit phosphorylation, while fluoxetine enhanced the IкB level. Importantly, in the hippocampus, all antidepressants normalized evoked by stress changes in caspase-1 level, while tianeptine and venlafaxine also affect the levels of ASC and NLRP3 subunits. Our results provide new evidence that chronic administration of antidepressants exerts anti-inflammatory effects more pronounced in the hippocampus, through suppression of the NLRP3 inflammasome activation. These effects are accompanied by an improvement in the behavioral dysfunctions evoked by prenatal stress.

The insulin-like growth factor-1 system in the adult mammalian brain and its implications in central maternal adaptation

Our knowledge on the bioavailability and actions of insulin-like growth factor-1 (IGF-1) has markedly expanded in recent years as novel mechanisms were discovered on IGF binding proteins (IGFBPs) and their ability to release IGF-1. The new discoveries allowed a better understanding of the endogenous physiological actions of IGF-1 and also its applicability in therapeutics. The focus of the present review is to summarize novel findings on the neuronal, neuroendocrine and neuroplastic actions of IGF-1 in the adult brain. As most of the new regulatory mechanisms were described in the periphery, their implications on brain IGF system will also be covered. In addition, novel findings on the effects of IGF-1 on lactation and maternal behavior are described. Based on the enormous neuroplastic changes related to the peripartum period, IGF-1 has great but largely unexplored potential in maternal adaptation of the brain, which is highlighted in the present review.

Inflammation in the hippocampus affects IGF1 receptor signaling and contributes to neurological sequelae in rheumatoid arthritis

Aberrant insulin-like growth factor 1 receptor (IGF1R)/insulin receptor signaling in brain has recently been linked to neurodegeneration in diabetes mellitus and in Alzheimer’s disease. In this study, we demonstrate that functional disability and pain in patients with rheumatoid arthritis (RA) and in experimental RA are associated with hippocampal inflammation and inhibition of IGF1R/insulin receptor substrate 1 (IRS1) signal, reproducing an IGF1/insulin-resistant state. This restricts formation of new neurons in the hippocampus, reduces hippocampal volume, and predisposes RA patients to develop neurological symptoms. Improving IRS1 function through down-regulation of IGF1R disinhibits neurogenesis and can potentially ameliorate neurological symptoms. This opens perspectives for drugs that revert IGF1/insulin resistance as an essential complement to the antirheumatic and antiinflammatory arsenal.

Rheumatoid arthritis (RA) is an inflammatory joint disease with a neurological component including depression, cognitive deficits, and pain, which substantially affect patients’ quality of daily life. Insulin-like growth factor 1 receptor (IGF1R) signaling is one of the factors in RA pathogenesis as well as a known regulator of adult neurogenesis. The purpose of this study was to investigate the association between IGF1R signaling and the neurological symptoms in RA. In experimental RA, we demonstrated that arthritis induced enrichment of IBA1⁺ microglia in the hippocampus. This coincided with inhibitory phosphorylation of insulin receptor substrate 1 (IRS1) and up-regulation of IGF1R in the pyramidal cell layer of the cornus ammoni and in the dentate gyrus, reproducing the molecular features of the IGF1/insulin resistance. The aberrant IGF1R signaling was associated with reduced hippocampal neurogenesis, smaller hippocampus, and increased immobility of RA mice. Inhibition of IGF1R in experimental RA led to a reduction of IRS1 inhibition and partial improvement of neurogenesis. Evaluation of physical functioning and brain imaging in RA patients revealed that enhanced functional disability is linked with smaller hippocampus volume and aberrant IGF1R/IRS1 signaling. These results point to abnormal IGF1R signaling in the brain as a mediator of neurological sequelae in RA and provide support for the potentially reversible nature of hippocampal changes.

Changes of Cerebral and/or Peripheral Adenosine A₁ Receptor and IGF-I Concentrations under Extended Sleep Duration in Rats

Extended sleep improves sustained attention and reduces sleep pressure in humans. Downregulation of adenosine A₁ receptor (A₁R) and modulation of the neurotrophic factor insulin growth factor-1 (IGF-I) in brain structures controlling attentional capacities could be involved. In the frontal cortex and hippocampus of rats, we measured adenosine A₁R and IGF-I protein concentrations after photoperiod-induced sleep extension. Two groups of twelve rats were adapted over 14 days to a habitual (CON) 12:12 light-dark (LD) schedule and an extended (EXT) 16:8 LD schedule. IGF-I content was also measured in plasma, liver, and skeletal muscle. In EXT, compared to CON rats, A₁R content in the frontal cortex was significantly lower (p < 0.05), while IGF-I content was higher (p < 0.001), and no significant change was observed in the hippocampus. IGF-I content in plasma and muscle was higher (p < 0.001 and p < 0.01), while it was lower in liver (p < 0.001). The absolute weight and weight gain were higher in EXT rats (p < 0.01). These data suggest that 14 days under a 16:8 LD photoperiod respectively down- and upregulated cortical A₁R and IGF-I levels. This photoperiod induced an anabolic profile with increased weight gain and circulating and muscular IGF-I levels. An extension of sleep duration might favor cerebral and peripheral anabolism, which may help attentional and physical capacities.

Evaluation of the effectiveness of chronic antidepressant drug treatments in the hippocampal mitochondria - A proteomic study in an animal model of depression

Several lines of evidence indicate that adverse experience in early life may be a triggering factor for disturbances in the brain mitochondrial proteins and lead to the development of depression in adulthood. On the other hand, little is known about the impact of chronic administration of various antidepressant drugs on the brain mitochondria, as a target for the pharmacotherapy of depression. The purpose of our study was to compare the impact of chronic treatment with two antidepressant drugs with different mechanisms of action, a tricyclic antidepressant (TCA), imipramine, and an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class, fluoxetine, on the mitochondria-enriched subproteome profile in the hippocampus of 3-month-old male rats following a prenatal stress procedure (an animal model of depression). We clearly confirmed that chronic imipramine and fluoxetine administration not only normalized depression-like disturbances evoked by the prenatal stress procedure but also modulated the mitochondria-enriched subproteome profile in the hippocampus of adult offspring rats. In line with this, two-dimensional electrophoresis coupled with mass spectrometry showed a statistically significant down-regulation of 14-3-3 and cytochrome bc1 proteins and an up-regulation of COP9 signalosome expression after chronic imipramine treatment in the hippocampus of prenatally stressed offspring. Fluoxetine administration strongly up-regulated the expression of cathepsin D, one of the key proteins involved in the prevention of the development of neurodegenerative processes. Furthermore, this antidepressant treatment enhanced expression of proteins engaged in the improvement of learning and memory processes (STMN1, Dnm-1) as well as in mitochondrial biogenesis and defense against oxidative stress (DJ-1). These findings provide new evidence that chronic administration of antidepressants exerts a varied impact on the mitochondria-enriched subproteome in the hippocampus of adult rats following a prenatal stress procedure. In particular, the effect of fluoxetine requires additional experiments to elucidate the possible beneficial biological consequences underlying the effects mediated by this antidepressant.

Regulation of insulin receptor phosphorylation in the brains of prenatally stressed rats: New insight into the benefits of antidepressant drug treatment

A growing body of evidence supports the involvement of disturbances in the brain insulin pathway in the pathogenesis of depression. On the other hand, data concerning the impact of antidepressant drug therapy on brain insulin signaling remain scare and insufficient. We determinated the influence of chronic treatment with antidepressant drugs (imipramine, fluoxetine and tianeptine) on the insulin signaling pathway of the brain of adult prenatally stressed rats. 3-month-old prenatally stressed and control rats were treated for 21 days with imipramine, fluoxetine or tianeptine (10mg/kg/day i.p.).The impact of chronic antidepressant administration was examined in forced swim test. In the frontal cortex and hippocampus, the mRNA and protein expression of insulin, insulin receptor, insulin receptor substrates (IRS-1,IRS-2) and adaptor proteins (Shc1, Grb2) before and after drugs administration were measured.Rats exposed prenatally to stressful stimuli displayed depressive-like disturbances, which were attenuated by antidepressant drug administration. We did not reveal the impact of prenatal stress or antidepressant treatment on insulin and the insulin receptor expression in the examined structures. We revealed that diminished insulin receptor phosphorylation evoked by the prenatal stress procedure was attenuated by drugs treatment. We demonstrated that the favorable effect of antidepressans on insulin receptor phosphorylation in the frontal cortex was mainly related with the normalization of serine312 and tyrosine IRS-1 phosphorylation, while in the hippocampus, it was related with the adaptor proteins Shc1/Grb2. It can be suggested that the behavioral effectiveness of antidepressant drug therapy may be related with the beneficial impact of antidepressant on insulin receptor phosphorylation pathways.

Insulin-like growth factor-1: a possible marker for emotional and cognitive disturbances, and treatment effectiveness in major depressive disorder

Depression and cognitive dysfunction share a common neuropathological platform. Abnormal neural plasticity in the frontolimbic circuits has been linked to changes in the expression of neurotrophic factors, including IGF-1. These changes may result in clinical abnormalities observed over the course of major depressive disorder (MDD), including cognitive dysfunction. The present review aimed to summarize evidence regarding abnormalities of peripheral IGF-1 in MDD patients and assess a marker and predictive role of the neurotrophin for emotional and cognitive disturbances, and treatment effectiveness. A literature search of the PubMed database was conducted for studies, in which peripheral IGF-1 levels were evaluated. Our analysis revealed four main findings: (1) IGF-1 levels in MDD patients mismatch across the studies, which may arise from various factors, e.g., age, gender, the course of the disease, presence of cognitive impairment, ongoing therapy, or general health conditions; (2) the initial peripheral IGF-1 levels may predict the occurrence of depression in future; (3) peripheral IGF-1 levels may reflect cognitive dysfunction, although the data is limited; (4) it is difficult to evaluate the influence of treatment on IGF-1 levels as there is discrepancy of this growth factor among the studies at baseline, although most of them showed a decrease in IGF-1 levels after treatment.

The effect of chronic tianeptine administration on the brain mitochondria: direct links with an animal model of depression

A growing body of evidence has focused on the impact of mitochondrial disturbances in the development of depression, but little data exist regarding the effects of chronic administration of antidepressant drugs on the brain's mitochondrial protein profile. The aim of this study was to investigate the impact of chronic treatment with an atypical antidepressant drug-tianeptine-on the mitochondria-enriched subproteome profile in the hippocampus and the frontal cortex of 3-month-old male rats following a prenatal stress procedure. Rats that were exposed to a prenatal stress procedure displayed depressive- and anxiety-like disturbances based on the elevated plus-maze and Porsolt tests. Moreover, two-dimensional electrophoresis coupled with mass spectrometry showed structure-dependent mitoproteome changes in brains of prenatally stressed rats after chronic tianeptine administration. A component of 2-oxoglutarate and succinate flavoprotein subunit dehydrogenases, isocitrate subunit alpha, was upregulated in the hippocampus. In the frontal cortex, there was a striking increase in the expression of glutamate dehydrogenase and cytochrome bc1 complex subunit 2. These findings suggest that mitochondria are underappreciated targets for therapeutic interventions, and mitochondrial function may be crucial for the effective treatment of stress-related diseases.

The protective effects of insulin-like growth factor-1 on neurochemical phenotypes of dorsal root ganglion neurons with BDE-209-induced neurotoxicity in vitro

Polybrominated diphenyl ethers (PBDEs) exist extensively in the environment as contaminants, in which 2,2',3,3',4,4',5,5',6,6'-decabrominated diphenyl ether (BDE-209) is the most abundant PBDE found in human samples. BDE-209 has been shown to cause neurotoxicity of primary sensory neurons with few effective therapeutic options available. Here, cultured dorsal root ganglion (DRG) neurons were used to determine the therapeutic effects of insulin-like growth factor-1 (IGF-1) on BDE-209-induced neurotoxicity. The results showed that IGF-1 promoted neurite outgrowth and cell viability of DRG neurons with BDE-209-induced neurotoxicity. IGF-1 inhibited oxidative stress and apoptotic cell death caused by BDE-209 exposure. IGF-1 could reverse the decrease in growth-associated protein-43 (GAP-43) and calcitonin gene-related peptide (CGRP), but not neurofilament-200 (NF-200), expression resulting from BDE-209 exposure. The effects of IGF-1 could be blocked by the extracellular signal-regulated protein kinase (ERK1/2) inhibitor PD98059 and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, either alone or in combination. IGF-1 may play an important role in neuroprotective effects on DRG neurons with BDE-209-induced neurotoxicity through inhibiting oxidative stress and apoptosis and regulating GAP-43 and CGRP expression of DRG neurons. Both ERK1/2 and PI3K/Akt signaling pathways were involved in the effects of IGF-1. Thus, IGF-1 might be one of the therapeutic agents on BDE-209-induced neurotoxicity.

Beneficial impact of intracerebroventricular fractalkine administration on behavioral and biochemical changes induced by prenatal stress in adult rats: Possible role of NLRP3 inflammasome pathway

Several lines of evidence indicate that adverse experience in early life may be a triggering factor for pathological inflammatory processes and lead to the development of depression. Fractalkine (CX3CL1), a chemokine, plays an important role not only in the migration, differentiation and proliferation of neuronal and glial cells but also in the regulation of neuronal-microglial signaling and the production of pro-inflammatory factors. In the present study, we examined the impact of a prenatal stress procedure on the expression of fractalkine in the hippocampus and frontal cortex of young and adult male rats. Furthermore, we measured the age-dependent effect of stress during pregnancy on the expression of pro-inflammatory factors IL-1β, IL-18, TNF-α, IL-6, and CCL2 in both brain structures. Next, to illustrate the link between fractalkine signaling and the behavioral and biochemical changes induced by prenatal stress, adult prenatally stressed offspring were injected intracerebroventricularly (icv) with exogenous fractalkine. We reported that prenatal stress leads to long-lasting deficits in fractalkine signaling and enhanced inflammatory activation. The study demonstrates that icv administration of fractalkine attenuates the behavioural changes evoked by prenatal stress procedure in adult animals. Moreover, fractalkine administration, exhibits anti-inflammatory action, mainly in the frontal cortex of adult prenatally stressed rats. The effect of fractalkine is related to inhibition of NLRP3 inflammasome. However, its action on the other members of NOD-like receptor family (NLR) cannot be excluded. These findings provide new in vivo evidence that the behavioral and inflammatory disturbances observed in adult prenatally stressed rats may be related to long-lasting malfunctions in fractalkine signaling.

Fractalkine Attenuates Microglial Cell Activation Induced by Prenatal Stress

The potential contribution of inflammation to the development of neuropsychiatric diseases has recently received substantial attention. In the brain, the main immune cells are the microglia. As they are the main source of inflammatory factors, it is plausible that the regulation of their activation may be a potential therapeutic target. Fractalkine (CX3CL1) and its receptor CX3CR1 play a crucial role in the control of the biological activity of the microglia. In the present study, using microglial cultures we investigated whether fractalkine is able to reverse changes in microglia caused by a prenatal stress procedure. Our study found that the microglia do not express fractalkine. Prenatal stress decreases the expression of the fractalkine receptor, which in turn is enhanced by the administration of exogenous fractalkine. Moreover, treatment with fractalkine diminishes the prenatal stress-induced overproduction of proinflammatory factors such as IL-1β, IL-18, IL-6, TNF-α, CCL2, or NO in the microglial cells derived from prenatally stressed newborns. In conclusion, the present results revealed that the pathological activation of microglia in prenatally stressed newborns may be attenuated by fractalkine administration. Therefore, understanding of the role of the CX3CL1-CX3CR1 system may help to elucidate the mechanisms underlying the neuron-microglia interaction and its role in pathological conditions in the brain.

Chronic mild stress influences nerve growth factor through a matrix metalloproteinase-dependent mechanism

Stress is generally a beneficial experience that motivates an organism to action to overcome the stressful challenge. In particular situations, when stress becomes chronic might be harmful and devastating. The hypothalamus is a critical coordinator of stress and the metabolic response; therefore, disruptions in this structure may be a significant cause of the hormonal and metabolic disturbances observed in depression. Chronic stress induces adverse changes in the morphology of neural cells that are often associated with a deficiency of neurotrophic factors (NTFs); additionally, many studies indicate that insufficient NTF synthesis may participate in the pathogenesis of depression. The aim of the present study was to determine the expression of the nerve growth factor (NGF) in the hypothalamus of male rats subjected to chronic mild stress (CMS) or to prenatal stress (PS) and to PS in combination with an acute stress event (AS). It has been found that chronic mild stress, but not prenatal stress, acute stress or a combination of PS with AS, decreased the concentration of the mature form of NGF (m-NGF) in the rat hypothalamus. A discrepancy between an increase in the Ngf mRNA and a decrease in the m-NGF levels suggested that chronic mild stress inhibited NGF maturation or enhanced the degradation of this factor. We have shown that NGF degradation in the hypothalamus of rats subjected to chronic mild stress is matrix metalloproteinase-dependent and related to an increase in the active forms of some metalloproteinases (MMP), including MMP2, MMP3, MMP9 and MMP13, while the NGF maturation process does not seem to be changed. We suggested that activated MMP2 and MMP9 potently cleave the mature but not the pro- form of NGF into biologically inactive products, which is the reason for m-NGF decomposition. In turn, the enhanced expression of Ngf in the hypothalamus of these rats is an attempt to overcome the reduced levels of m-NGF. Additionally, the decreased level of m-NGF together with the increased level of pro-NGF can decrease TrkA-mediated neuronal survival signalling and enhance the action of pro-NGF on the p75(NTR) receptor, respectively, to evoke pro-apoptotic signalling. This hypothesis is supported by elevated levels of the caspase-3 mRNA in the hypothalamus of rats subjected to chronic mild stress.

The Beneficial Impact of Antidepressant Drugs on Prenatal Stress-Evoked Malfunction of the Insulin-Like Growth Factor-1 (IGF-1) Protein Family in the Olfactory Bulbs of Adult Rats

Insulin-like growth factor-1 (IGF-1) promotes the growth, differentiation, and survival of both neurons and glial cells, and it is believed to exert antidepressant-like activity. Thus, disturbances in the IGF-1 system could be responsible for the course of depression. To date, there have been no papers showing the impact of chronic antidepressant treatment on the IGF-1 network in the olfactory bulb (OB) in an animal model of depression. Prenatal stress was used as model of depression. Twenty-four 3-month-old male offspring of control and stressed mothers were subjected to behavioral testing (forced swim test). The mRNA expression of IGF-1 and IGF-1 receptor (IGF-1R) and the protein level of IGF-1 and its phosphorylation, as well as the concentrations of IGF-binding proteins (IGFBP-2, -4, -3, and -6), were measured in OBs before and after chronic imipramine, fluoxetine, or tianeptine administration. Adult rats exposed prenatally to stressful stimuli displayed not only depression-like behavior but also decreased IGF-1 expression, dysregulation in the IGFBP network, and diminished mRNA expression, as well as IGF-1R phosphorylation, in the OB. The administration of antidepressants normalized most of the changes in the IGF-1 system of the OB evoked by prenatal stress. These results suggested a beneficial effect of chronic antidepressant drug treatment in the alleviation of IGF-1 family malfunction in OBs in an animal model of depression.

Maternal stress predicts altered biogenesis and the profile of mitochondrial proteins in the frontal cortex and hippocampus of adult offspring rats

Currently, much attention is focused on the influence of mitochondrial disturbances at the onset of depression. The goal of this study was to investigate the impact of prenatal stress (an animal model of depression) on the mitochondrial biogenesis proteins and mitoproteome profile in the frontal cortex and hippocampus of adult 3-month-old male rats following a prenatal stress procedure. Our results show that rats that were exposed to prenatal stress stimuli displayed depression-like behaviors based on the sucrose preference and elevated plus maze tests. It has been found that the level of the PGC-1α protein was reduced in the frontal cortex and hippocampus of the adult offspring after the prenatal stress procedure. Moreover, in the frontal cortex, the level of the pro-apoptotic protein Bax was up-regulated. Two-dimensional electrophoresis coupled with mass spectrometry showed the statistically significant down-regulation of the mitochondrial ribosomal protein L12 (Mrpl12) and mitochondrial NADH dehydrogenase [ubiquinone] flavoprotein 2 (NDUFV2) as well as the up-regulation of the Tubulin Polymerization Promoting Proteins (Tppp/p25) in the frontal cortex. In contrast, in the hippocampus, the mitochondrial pyruvate dehydrogenase E1 component subunit beta, the voltage-dependent anion-selective channel protein 2 (VDAC2), and the GTP-binding nuclear protein RAN (RAN) were down-regulated and the expression of phosphatidylethanolamine-binding protein 1 (PEBP-1) was enhanced. These findings provide new evidence that stress during pregnancy may lead not only to behavioral deficits, but also to disturbances in the brain mitoproteome profile in adult rat offspring.

Prenatal stress is a vulnerability factor for altered morphology and biological activity of microglia cells

Several lines of evidence suggest that the dysregulation of the immune system is an important factor in the development of depression. Microglia are the resident macrophages of the central nervous system and a key player in innate immunity of the brain. We hypothesized that prenatal stress (an animal model of depression) as a priming factor could affect microglial cells and might lead to depressive-like disturbances in adult male rat offspring. We investigated the behavioral changes (sucrose preference test, Porsolt test), the expression of C1q and CD40 mRNA and the level of microglia (Iba1 positive) in 3-month-old control and prenatally stressed male offspring rats. In addition, we characterized the morphological and biochemical parameters of potentially harmful (NO, iNOS, IL-1β, IL-18, IL-6, TNF-α, CCL2, CXCL12, CCR2, CXCR4) and beneficial (insulin-like growth factor-1 (IGF-1), brain derived neurotrophic factor (BDNF)) phenotypes in cultures of microglia obtained from the cortices of 1–2 days old control and prenatally stressed pups. The adult prenatally stressed rats showed behavioral (anhedonic- and depression-like) disturbances, enhanced expression of microglial activation markers and an increased number of Iba1-immunopositive cells in the hippocampus and frontal cortex. The morphology of glia was altered in cultures from prenatally stressed rats, as demonstrated by immunofluorescence microscopy. Moreover, in these cultures, we observed enhanced expression of CD40 and MHC II and release of pro-inflammatory cytokines, including IL-1β, IL-18, TNF-α and IL-6. Prenatal stress significantly up-regulated levels of the chemokines CCL2, CXCL12 and altered expression of their receptors, CCR2 and CXCR4 while IGF-1 production was suppressed in cultures of microglia from prenatally stressed rats. Our results suggest that prenatal stress may lead to excessive microglia activation and contribute to the behavioral changes observed in depression in adulthood.

Prenatal stress enhances excitatory synaptic transmission and impairs long-term potentiation in the frontal cortex of adult offspring rats

The effects of prenatal stress procedure were investigated in 3 months old male rats. Prenatally stressed rats showed depressive-like behavior in the forced swim test, including increased immobility, decreased mobility and decreased climbing. In ex vivo frontal cortex slices originating from prenatally stressed animals, the amplitude of extracellular field potentials (FPs) recorded in cortical layer II/III was larger, and the mean amplitude ratio of pharmacologically-isolated NMDA to the AMPA/kainate component of the field potential—smaller than in control preparations. Prenatal stress also resulted in a reduced magnitude of long-term potentiation (LTP). These effects were accompanied by an increase in the mean frequency, but not the mean amplitude, of spontaneous excitatory postsynaptic currents (sEPSCs) in layer II/III pyramidal neurons. These data demonstrate that stress during pregnancy may lead not only to behavioral disturbances, but also impairs the glutamatergic transmission and long-term synaptic plasticity in the frontal cortex of the adult offspring.

Dicholine succinate, the neuronal insulin sensitizer, normalizes behavior, REM sleep, hippocampal pGSK3 beta and mRNAs of NMDA receptor subunits in mouse models of depression

Central insulin receptor-mediated signaling is attracting the growing attention of researchers because of rapidly accumulating evidence implicating it in the mechanisms of plasticity, stress response, and neuropsychiatric disorders including depression. Dicholine succinate (DS), a mitochondrial complex II substrate, was shown to enhance insulin-receptor mediated signaling in neurons and is regarded as a sensitizer of the neuronal insulin receptor. Compounds enhancing neuronal insulin receptor-mediated transmission exert an antidepressant-like effect in several pre-clinical paradigms of depression; similarly, such properties for DS were found with a stress-induced anhedonia model. Here, we additionally studied the effects of DS on several variables which were ameliorated by other insulin receptor sensitizers in mice. Pre-treatment with DS of chronically stressed C57BL6 mice rescued normal contextual fear conditioning, hippocampal gene expression of NMDA receptor subunit NR2A, the NR2A/NR2B ratio and increased REM sleep rebound after acute predation. In 18-month-old C57BL6 mice, a model of elderly depression, DS restored normal sucrose preference and activated the expression of neural plasticity factors in the hippocampus as shown by Illumina microarray. Finally, young naïve DS-treated C57BL6 mice had reduced depressive- and anxiety-like behaviors and, similarly to imipramine-treated mice, preserved hippocampal levels of the phosphorylated (inactive) form of GSK3 beta that was lowered by forced swimming in pharmacologically naïve animals. Thus, DS can ameliorate behavioral and molecular outcomes under a variety of stress- and depression-related conditions. This further highlights neuronal insulin signaling as a new factor of pathogenesis and a potential pharmacotherapy of affective pathologies.