Pioglitazone, a PPARγ agonist rescues depression associated with obesity using chronic unpredictable mild stress model in experimental mice

Visceral adipose tissue-derived extracellular vesicles promote stress susceptibility in obese mice via miR-140-5p

Obesity increases the risk of depression. Evidence shows that peripheral inflammation, glycemic dysregulation, and hyperactivity within the hypothalamic-pituitary-adrenal axis are implicated in both obesity and depression. In this study we investigated the impact of visceral adipose tissue (VAT), a crucial characteristic of obesity, on stress susceptibility in obese mice. Age-matched mice were fed with chow diet (CD) or high-fat diet (HFD), respectively, for 12 weeks. CD mice were deprived of VAT and received transplantation of VAT from HFD mice (TransHFD) or CD mice (TransCD). Extracellular vesicles (EVs) were prepared from VAT of CD or HFD mice, and intravenously injected (100 μg, 4 times in 2 weeks) in naïve mice or injected into hippocampus (5 μg, 4 times in 2 weeks) through implanted bilateral cannula. Depression-like behaviors were assessed 14 days after transplantation. We showed that HFD mice exhibited significantly higher body weight gain and impaired insulin and glucose tolerance, accompanied by increased stress susceptibility. Transplantation of VAT or VAT-derived EVs from HFD mice caused synaptic damage and promoted stress susceptibility in recipient mice. Through inhibiting miRNA biogenesis in the VAT and miRNA sequencing analysis, we demonstrated that miR-140-5p was significantly upregulated in both VAT-EVs and hippocampus of HFD mice. Overexpression of hippocampal miR-140-5p in naïve mice not only facilitated acute stress-induced depression-like behaviors, but also decreased hippocampal CREB-BDNF signaling cascade and synaptic plasticity. Conversely, knockdown of miR-140-5p in the VAT, VAT-EVs or hippocampus of HFD mice protected against acute stress, reducing stress susceptibility that were mediated via CREB-BDNF pathway. In summary, VAT-EVs or the cargo miRNAs in obese mice promote synaptic damage and stress susceptibility, providing potential therapeutic targets for metabolism-related affective disorders.

Pioglitazone attenuates behavioral and electrophysiological dysfunctions induced by two-hit model of schizophrenia in adult rodent offspring

Maternal infection and stress exposure, especially during childhood and adolescence, have been implicated as risk factors for schizophrenia. Both insults induce an exacerbated inflammatory response, which could mediate disturbance of neurodevelopmental processes and, ultimately, malfunctioning of neural systems observed in this disorder. Thus, anti-inflammatory drugs, such as PPARγ agonists, may potentially be used to prevent the development of schizophrenia. Microglia culture was prepared from the offspring of saline or poly(I:C)-injected mice. The cells were pretreated with pioglitazone and then, stimulated by LPS. Proinflammatory mediators and phagocytic activity were measured. Also, pregnant rats were injected with saline or poly(I:C) on GD17. The offspring were subjected to footshock during adolescence and subsequently injected with pioglitazone or vehicle. At adulthood, behavior and dopaminergic activity were evaluated. Pioglitazone reduced proinflammatory mediators induced by poly(I:C) microglia stimulated by LPS without affecting their decreased phagocytic activity. The PPARγ agonist also prevented the emergence of social and cognitive impairments, as well as attenuated the increased number of spontaneously active dopamine neurons in the VTA, observed in both males and females from poly(I:C) and stress group. Therefore, pioglitazone could potentially prevent the emergence of the schizophrenia-like alterations induced by the two-hit model via reduction of microglial activation.

Key role of PPAR-γ-mediated suppression of the NFκB signaling pathway in rutin's antidepressant effect

BACKGROUND

Depression is a chronic and recurrent disorder with an unknown etiology. Efficacious antidepressant treatments with minimal side effects are urgently needed. Neuroinflammation may contribute to depression, as anti-inflammatory drugs have been shown to alleviate depressive symptoms in clinical practice. Rutin, a naturally occurring flavonoid derived from plants, is abundant in many antidepressant herbs, including Hemerocallis citrina Baroni. Historical Chinese medical texts, including the renowned Compendium of Materia Medica, document H. citrina Baroni as possessing antidepressant properties. Rutin, one of its primary active constituents, is recognized for its anti-inflammatory effects. Despite this, little is known about its specific target and mechanism.

METHODS

In the present study, molecular docking, and surface plasmon resonance imaging (SPRi) analysis were used to identify the special targets of rutin. Meanwhile, the potential antidepressant effects were evaluated in the chronic social defeat stress (CSDS) paradigm, an animal model of depression. Then, Western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), Co-immunoprecipitation (Co-IP) as well as antagonists of PPAR-γ were utilized to investigate the mechanism underlying the antidepressant effect of rutin.

RESULTS

Both molecular docking and SPRi analysis showed high docking scores and interactions between rutin and PPAR-γ. In vivo, rutin promoted the nuclear translocation of PPAR-γ in the hippocampus of mice, inhibited NFκB-mediated inflammatory pathways, and subsequently reduced the expression of pro-inflammatory factors (e.g., iNOS, IL-6), aligning with an antidepressant effect. However, this therapeutic effect was attenuated by GW9662, a specific antagonist of PPAR-γ.

CONCLUSION

As a result of activating PPAR-γ and inhibiting NFκB pathway activation, rutin reduces neuroinflammation and exhibits an antidepressant effect. These findings shed light on the antidepressant mechanism of rutin and could be valuable for the development of new antidepressants.

Targeting Toll-like Receptor 4/Nuclear Factor-κB and Nrf2/Heme Oxygenase-1 Crosstalk via Trimetazidine Alleviates Lipopolysaccharide-Induced Depressive-like Behaviors in Mice

Depression is a global psychiatric illness that imposes a substantial economic burden. Unfortunately, traditional antidepressants induce many side effects which limit patient compliance thus, exploring alternative therapies with fewer adverse effects became urgent. This study aimed to investigate the effect of trimetazidine (TMZ); a well-known anti-ischemic drug in lipopolysaccharide (LPS) mouse model of depression focusing on its ability to regulate toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) as well as nuclear factor erythroid 2 related factor 2 (Nrf2)/ heme oxygenase-1 (HO-1) signaling pathways. Male Swiss albino mice were injected with LPS (500 µg/kg, i.p) every other day alone or parallel with oral doses of either escitalopram (Esc) (10 mg/kg/day) or TMZ (20 mg/kg/day) for 14 days. Treatment with TMZ attenuated LPS-induced animals' despair with reduced immobility time inforced swimming test. TMZ also diminished LPS- induced neuro-inflammation via inhibition of TLR4/NF-κB pathway contrary to Nrf2/HO-1 cascade activation with consequent increase in reduced glutathione (GSH) and HO-1 levels whereas the pro-inflammatory cytokines; tumor necrosis factor-α (TNF-α) and interleukin (IL)-1β were evidently reduced. Besides, TMZ replenished brain serotonin levels via serotonin transporter (SERT) inhibition. Thus, TMZ hindered LPS-induced neuro-inflammation, oxidative stress, serotonin deficiency besides its anti-apoptotic effect which was reflected by decreased caspase-3 level. Neuroprotective effects of TMZ were confirmed by the histological photomicrographs which showed prominent neuronal survival. Here we showed that TMZ is an affluent nominee for depression management via targeting TLR4/NF-κB and Nrf2/HO-1 pathways. Future research addressing TMZ-antidepressant activity in humans is mandatory to enroll it as a novel therapeutic strategy for depression.

SIRT1/PARP-1/NLRP3 cascade as a potential target for niacin neuroprotective effect in lipopolysaccharide-induced depressive-like behavior in mice

Depression is a serious mood disorder characterized by monoamines deficiency, oxidative stress, neuroinflammation, and cell death. Niacin (vitamin B3 or nicotinic acid, NA), a chief mediator of neuronal development and survival in the central nervous system, exerts neuroprotective effects in several experimental models.

AIMS

This study aimed to investigate the effect of NA in lipopolysaccharide (LPS) mouse model of depression exploring its ability to regulate sirtuin1/poly (ADP-ribose) polymerase-1 (PARP-1)/nod-likereceptor protein 3 (NLRP3) signaling.

MAIN METHODS

Mice were injected with LPS (500 µg/kg, i.p) every other day alone or concurrently with oral doses of either NA (40 mg/kg/day) or escitalopram (10 mg/kg/day) for 14 days.

KEY FINDINGS

Administration of NA resulted in significant attenuation of animals' despair reflected by decreased immobility time in forced swimming test. Moreover, NA induced monoamines upsurge in addition to sirtuin1 activation with subsequent down regulation of PARP-1 in the hippocampus. Further, it diminished nuclear factor-κB (NF-κB) levels and inhibited NLRP3 inflammasome with consequent reduction of caspase-1, interleukin-1β and tumor necrosis factor-α levels, thus mitigating LPS-induced neuroinflammation. NA also reduced tumor suppressor protein (p53) while elevating brain-derived neurotrophic factor levels. LPS-induced decline in neuronal survival was reversed by NA administration with an obvious increase in the number of intact cells recorded in the histopathological micrographs.

SIGNIFICANCE

Accordingly, NA is deemed as a prosperous candidate for depression management via targeting SIRT1/PARP-1 pathway.

Selective aryl hydrocarbon receptor modulators can act as antidepressants in obese female mice

BACKGROUND

Obese females are more likely to suffer from depression and are also more likely to be resistant to current medications. This study examined the potential antidepressant-like effects of 1,4-dihydroxy-2-napthoic acid (DHNA), a selective aryl hydrocarbon receptor modulator (SAhRM), in obese female mice.

METHODS

Obesity was established by feeding C57BL/6N female mice a high fat diet (HFD) for 9-10 weeks. Subsequently, mice were subjected to unpredictable chronic mild stress (UCMS) or remained unstressed. Daily administration of vehicle or 20 mg/kg DHNA began three weeks prior or on the third week of UCMS. Mice were examined for depression-like behaviors (sucrose preference, forced swim test (FST), splash and tape groom tests), anxiety (open-field test, light/dark test, novelty-induced hypophagia), and cognition (object location recognition, novel object recognition, Morris water maze).

RESULTS

UCMS did not alter, and DHNA slightly increased, weight gain in HFD-fed females. HFD decreased sucrose preference, increased FST immobility time, but did not alter splash and tape tests' grooming time. UCMS did not have additional effects on sucrose preference. UCMS further increased FST immobility time and decreased splash and tape tests' grooming time; these effects were prevented and reversed by DHNA treatment. HFD did not affect behaviors in the cognitive tests. UCMS impaired spatial learning; this effect was not prevented nor reversed by DHNA.

CONCLUSIONS

DHNA protected against UCMS-induced depression-like behaviors in HFD-fed female mice. DHNA neither improved nor worsened UCMS-induced impairment of spatial learning. Our findings indicate that DHNA has high potential to act as an antidepressant in obese females.

Microglial Inflammatory-Metabolic Pathways and Their Potential Therapeutic Implication in Major Depressive Disorder

Increasing evidence supports the notion that neuroinflammation plays a critical role in the etiology of major depressive disorder (MDD), at least in a subset of patients. By virtue of their capacity to transform into reactive states in response to inflammatory insults, microglia, the brain's resident immune cells, play a pivotal role in the induction of neuroinflammation. Experimental studies have demonstrated the ability of microglia to recognize pathogens or damaged cells, leading to the activation of a cytotoxic response that exacerbates damage to brain cells. However, microglia display a wide range of responses to injury and may also promote resolution stages of inflammation and tissue regeneration. MDD has been associated with chronic priming of microglia. Recent studies suggest that altered microglial morphology and function, caused either by intense inflammatory activation or by senescence, may contribute to depression and associated impairments in neuroplasticity. In this context, modifying microglia phenotype by tuning inflammatory pathways might have important translational relevance to harness neuroinflammation in MDD. Interestingly, it was recently shown that different microglial phenotypes are associated with distinct metabolic pathways and analysis of the underlying molecular mechanisms points to an instrumental role for energy metabolism in shaping microglial functions. Here, we review various canonical pro-inflammatory, anti-inflammatory and metabolic pathways in microglia that may provide new therapeutic opportunities to control neuroinflammation in brain disorders, with a strong focus on MDD.

Effect of parthenolide, an NLRP3 inflammasome inhibitor, on insulin resistance in high-fat diet-obese mice

The activation of Nod-like receptor proteins (NLRP3) containing the pyrin domain inflammasome is a hallmark of the pathogenesis of metabolic disorders. Inhibition of the NLRP3 inflammasome by phytoconstituents has been attempted as a strategy to mitigate these disorders. Therefore, the present study aimed to evaluate the efficacy of an NLRP3 inflammasome inhibitor, parthenolide (PN; 5 mg/kg i.p.) against inflammation and insulin resistance in high-fat diet (HFD) - obese mice. Treatment with PN and pioglitazone (PIO; 30 mg/kg p.o.) attenuated lipopolysaccharide (LPS; 1 ng/ml) - induced elevation of tumor necrosis factor-α and interleukin-1β in mouse peritoneal macrophages in a dose-dependent manner. Sixty days of PN and PIO treatment marginally reduced obesity-induced insulin resistance in HFD-obese mice. PN treatment also decreased blood glucose from 14th to 60th day, supporting the hypothesis of simultaneous attenuation of inflammation and insulin resistance in obese mice. Thus, PN treatment was also evident with significant improvement in glucose tolerance and peripheral insulin resistance validated through the respective tolerance tests. Therefore, the present study suggests that PN, an NLRP3 inflammasome inhibitor, could be a possible therapeutic agent for attenuating obesity-induced insulin resistance.

Effects of High-fat Diet and Chronic Mild Stress on Depression-like Behaviors and Levels of Inflammatory Cytokines in the Hippocampus and Prefrontal Cortex of Rats

Obesity and depression tend to co-occur, and obese patients with chronic low-grade inflammation have a higher risk of developing depression. However, mechanisms explaining these connections have not been fully elucidated. Here, an animal model of comorbid obesity and depression induced by high-fat diet (HFD) combined with chronic unpredictable mild stress (CUMS) was used, and sucrose preference, open field, elevated plus maze and Morris water maze tests were used to detected depression-and anxiety-like behaviors and spatial memory. The levels of inflammatory cytokines and NF-κB and microglial activation in the hippocampus and prefrontal cortex were examined in the study. Our results revealed that the comorbidity group exhibited the most severe depression-like behavior. Obesity but unstressed rats had the highest serum lipid levels among groups. The HFD and CUMS alone and combination of them increased levels of IL-1β, IL-6 and TNF-α in the hippocampus and prefrontal cortex, which was significantly related to depression-like behaviors. Further, NF-κB protein and mRNA levels and microglial activation in the hippocampus and prefrontal cortex significantly increased in stressed, obese and comorbid groups, with animals in comorbid group having the highest NF-κB mRNA levels in the hippocampus and level of NF-κB proteins in the prefrontal cortex, and the highest microglial activation in both brain areas. The study concluded that HFD and CUMS alone and combination induce depression-like symptoms, abnormal serum lipid levels, microglial activation and increased inflammatory cytokines in the brain, effects that are possibly mediated by TLR4-NF-κB signaling.

Incident Major Depressive Disorder Predicted by Three Measures of Insulin Resistance: A Dutch Cohort Study

OBJECTIVE

Major depressive disorder is the leading cause of disability worldwide. Yet, there remain significant challenges in predicting new cases of major depression and devising strategies to prevent the disorder. An important first step in this process is identifying risk factors for the incidence of major depression. There is accumulating biological evidence linking insulin resistance, another highly prevalent condition, and depressive disorders. The objectives of this study were to examine whether three surrogate measures of insulin resistance (high triglyceride-HDL [high-density lipoprotein] ratio; prediabetes, as indicated by fasting plasma glucose level; and high central adiposity, as measured by waist circumference) at the time of study enrollment were associated with an increased rate of incident major depressive disorder over a 9-year follow-up period and to assess whether the new onset of these surrogate measures during the first 2 years after study enrollment was predictive of incident major depressive disorder during the subsequent follow-up period.

METHODS

The Netherlands Study of Depression and Anxiety (NESDA) is a multisite longitudinal study of the course and consequences of depressive and anxiety disorders in adults. The study population comprised 601 NESDA participants (18-65 years old) without a lifetime history of depression or anxiety disorders. The study's outcome was incident major depressive disorder, defined using DSM-IV criteria. Exposure measures included triglyceride-HDL ratio, fasting plasma glucose level, and waist circumference.

RESULTS

Fourteen percent of the sample developed major depressive disorder during follow-up. Cox proportional hazards models indicated that higher triglyceride-HDL ratio was positively associated with an increased risk for incident major depression (hazard ratio=1.89, 95% CI=1.15, 3.11), as were higher fasting plasma glucose levels (hazard ratio=1.37, 95% CI=1.05, 1.77) and higher waist circumference (hazard ratio=1.11 95% CI=1.01, 1.21). The development of prediabetes in the 2-year period after study enrollment was positively associated with incident major depressive disorder (hazard ratio=2.66, 95% CI=1.13, 6.27). The development of high triglyceride-HDL ratio and high central adiposity (cut-point ≥100 cm) in the same period was not associated with incident major depression.

CONCLUSIONS

Three surrogate measures of insulin resistance positively predicted incident major depressive disorder in a 9-year follow-up period among adults with no history of depression or anxiety disorder. In addition, the development of prediabetes between enrollment and the 2-year study visit was positively associated with incident major depressive disorder. These findings may have utility for evaluating the risk for the development of major depression among patients with insulin resistance or metabolic pathology.

Depression-like behavior associated with E/I imbalance of mPFC and amygdala without TRPC channels in mice of knockout IL-10 from microglia

Depression has a growing impact on public health. Accumulating evidence supports an association between depression and increased immune system activity. IL-10 is a key cytokine that inhibits excessive inflammatory responses and is related to the anti-inflammatory and protective functions of the central nervous system (CNS). Cx3cr1^CreERIL-10^-/- mice were used in our study. We aimed to identify the role of IL-10 in microglia in depression and anxiety-like behavior. We performed a series of behavioral tests on the mice; the Cx3cr1^CreERIL-10^-/- male mice showed depression- and anxiety-like behavior compared with the littermates. The expression of transient receptor potential canonical 5 (TRPC5) decreased in both the medial prefrontal cortex (mPFC) and amygdala regions. The cytokines IL-1β and IL-6 increased, and IL-10 was decreased by western blotting. The knockout mice showed different trends in the effects of synaptic proteins. In the mPFC, IL-10 knockout induced a decrease in NR2B and synaptophysin; in the amygdala region, there was a significant increase in NR2B and PSD95. IL-10 knockout from microglia induced a decrease in GAD67 and parvalbumin (Pv) in the mPFC, but not in the amygdala. Our results showed enhanced depression and anxiety-like behavior in the Cx3cr1^CreER IL-10^-/- mice, which could be related to an imbalance in local excitatory and inhibitory transmission, as well as neuroinflammation in the mPFC and amygdala. This imbalance was associated with increased local inflammation. Although many studies have demonstrated the role of TRPC channels in emotional responses, our study showed that TRPC was not involved in this process in Cx3cr1^CreERIL-10^-/- mice.

Pioglitazone Enhances β-Arrestin2 Signaling and Ameliorates Insulin Resistance in Classical Insulin Target Tissues

INTRODUCTION

Pioglitazone is a thiazolidinedione oral antidiabetic agent. This study aimed to investigate the effects of pioglitazone as insulin sensitizer on β-arrestin2 signaling in classical insulin target tissues.

METHODS

Experiments involved three groups of mice; the first one involved mice fed standard chow diet for 16 weeks; the second one involved mice fed high-fructose, high-fat diet (HFrHFD) for 16 weeks; and the third one involved mice fed HFrHFD for 16 weeks and received pioglitazone (30 mg/kg/day, orally) in the last four weeks of feeding HFrHFD.

RESULTS

The results showed significant improvement in the insulin sensitivity of pioglitazone-treated mice as manifested by significant reduction in the insulin resistance index. This improvement in insulin sensitivity was associated with significant increases in the β-arrestin2 levels in the adipose tissue, liver, and skeletal muscle. Moreover, pioglitazone significantly increased β-arrestin2 signaling in all the examined tissues as estimated from significant increases in phosphatidylinositol 4,5 bisphosphate and phosphorylation of Akt at serine 473 and significant decrease in diacylglycerol level.

CONCLUSION

To the best of our knowledge, our work reports a new mechanism of action for pioglitazone through which it can enhance the insulin sensitivity. Pioglitazone increases β-arrestin2 signaling in the adipose tissue, liver, and skeletal muscle of HFrHFD-fed mice.

The involvement of ADAR1 in antidepressant action by regulating BDNF via miR-432

Brain-derived neurotrophic factor (BDNF) is a biomarker of depression. Recent studies have found adenosine deaminase acting on RNA1 (ADAR1) is a novel target being sensitive to stress at epigenetic level. The epigenetic regulation mechanism of stress-related depression is still unclear so far. To explore the potential regulating mechanism of ADAR1 on BDNF, over and low expression of ADAR1 in PC12 and SH-SY5Y cell lines are prepared. In the meanwhile, chronic unpredictable stress (CUS) mice are treated with ADAR1 inducer (interferon-γ, IFN-γ). ADAR1 regulates BDNF expression, which is proven by that over and low expressions of ADAR1 increase and decrease BDNF mRNA and protein respectively in vitro. Additionally, ADAR1 inducer alleviates the depressive-like behavior of CUS mice by recovering the decreased BDNF protein in brain and serum. Moreover, over and low expressions of ADAR1 reduce and enhance microRNA-432 (miR-432) expression respectively in vitro. Furtherly, over and low miR-432 expressions lead to decreased and increased BDNF and ADAR1 mRNA, protein and immunoreactivity respectively in vitro. The above results demonstrate that ADAR1 is involved in antidepressant action by regulating BDNF via miR-432. Those novel findings can provide a new idea for the study of epigenetic regulation mechanism, early diagnosis, and effective treatment of stress-related depression.

Antidepressant activity of anti-hyperglycemic agents in experimental models: A review

BACKGROUND AND AIMS

Diabetes Mellitus (DM) and depression occur comorbidly and share some pathophysiological mechanisms. The course of depression in patients with the two conditions is severe. Treatment of depression in diabetic patients requires special attention because most of psychopharmacological agents can worsen glycemic control. This article aims to review studies evaluating the antidepressant effect of anti-hyperglycemic agents from preclinical perspective.

METHODS

A literature search was performed with PubMed and Google Scholar using relevant keywords (antidiabetic; diabetes; depression; antidepressant; animals) to extract relevant studies evaluating the antidepressant activity of anti-hyperglycemic agents in experimental models.

RESULTS

Several studies have reported that some traditional anti-hyperglycemic agents reduce depression-like behavior in the absence or presence of diabetes. These drugs include insulin, glyburide, metformin, pioglitazone, vildagliptin, liraglutide, and exenatide. The antidepressant activity of anti-hyperglycemic agents may be mediated by reducing the blood glucose level, ameliorating the central oxidative stress and inflammation, and regulating the hypothalamic-pituitary-adrenal axis (HPAA).

CONCLUSIONS

Drugs which have both antidiabetic and antidepressant activities can provide better treatment strategy for patients with diabetes-associated depression. However, further research studies are still required in human subjects.

The neuroprotective effect of curcumin against Cd-induced neurotoxicity and hippocampal neurogenesis promotion through CREB-BDNF signaling pathway

Heavy metal neurotoxicity is one of the major challenges in today's era due to the large scale and widespread mechanisation of the production. However, the causative factors responsible for neurotoxicity are neither known nor do we have the availability of therapeutic approaches to deal with it. One of the major causative agents of neurotoxicity is a non-essential transition heavy metal, Cadmium (Cd), that reaches the central nervous system (CNS) through the nasal mucosa and olfactory pathway causing adverse structural and functional effects. In this study, we explored the neuroprotective efficacy of plant derived Curcumin which is reported to have pleiotropic biological activity including anti-oxidant, anti-inflammatory, anti-apoptotic, anti-carcinogenic and anti-angiogenic effects. Four different concentrations of curcumin (20, 40, 80 and 160 mg/kg of the body weight) were used to assess the behavioural, biochemical, hippocampal proteins (BDNF, CREB, DCX and Synapsin II) and histological changes in Swiss Albino mice that were pre-treated with Cd (2.5 mg/kg). The findings showed that Cd exposure led to the behavioural impairment through oxidative stress, reduction of hippocampal neurogenesis associated proteins, and degeneration of CA3 and cortical neurons. However, treatment of different curcumin concentrations had effectively restored the behavioural changes in Cd-exposed mice through regulation of oxidative stress and up-regulation of hippocampal proteins in a dose-dependent manner. Significantly, a dose of 160 mg/kg body weight was found to be glaringly effective. From this study, we infer that curcumin reverses the adverse effects of neurotoxicity induced by Cd and promotes neurogenesis.

PPARγ-mediated microglial activation phenotype is involved in depressive-like behaviors and neuroinflammation in stressed C57BL/6J and ob/ob mice

BACKGROUND

There is an increased risk for obese patients with chronic low-grade inflammation to develop depression. Stress induces microglial activation and neuroinflammation that play crucial roles in the pathogenesis of depression. Peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear transcription factor, regulates microglial polarization and neuroinflammation. Our study aimed to investigate the role of PPARγ in the development of depressive symptoms and neuroinflammation induced by chronic unpredictable mild stress (CUMS) in wild-type/C57BL/6J (wt) and leptin-deficient (ob/ob) mice.

METHODS

CUMS was used to build a depression model with wt and ob/ob mice. Depressive-like behaviors were evaluated by sucrose preference test, open field test, tail suspension test, and Morris water maze test. Cytokines, the activated microglial state, and nuclear factor-κB (NF-κB) and PPARγ expression in the prefrontal cortex (PFC) and hippocampus (HIP) were examined by enzyme-linked immunosorbent assay (ELISA), immunofluorescence, and western blotting. Additionally, pioglitazone, an agonist of PPARγ, was used as a treatment intervention.

RESULTS

After CUMS, ob/ob mice exhibited severe behavioral disorders and spatial memory impairment, and higher levels of pro-inflammatory cytokines, M1/M2 ratios, and NF-κB activation, as well as lower levels of anti-inflammatory cytokines and PPARγ expression in the PFC and HIP compared to wt mice. Administration of pioglitazone relieved these alterations in wt and ob/ob mice.

CONCLUSIONS

CUMS was able to induce severe depressive-like behaviors, neuroinflammation, and reduced expression of PPARγ in ob/ob mice as compared to wt mice. This suggests that PPARγ mediates the microglial activation phenotype, which might be related to the susceptibility of stressed ob/ob mice to develop depressive disorder.

Potential role of insulin on the pathogenesis of depression

The regulation of insulin on depression and depression-like behaviour has been widely reported. Insulin and activation of its receptor can promote learning and memory, affect the hypothalamic-pituitary-adrenal axis (HPA) balance, regulate the secretion of neurotrophic factors and neurotransmitters, interact with gastrointestinal microbiome, exert neuroprotective effects and have an impact on depression. However, the role of insulin on depression remains largely unclear. Therefore, in this review, we summarized the potential role of insulin on depression. It may provide new insight for clarifying role of insulin on the pathogenesis of depression.

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.

Stress-Induced Epigenetic Changes in Hippocampal Mkp-1 Promote Persistent Depressive Behaviors

Chronic stress induces persistent depressive behaviors. Stress-induced transcriptional alteration over the homeostatic range in stress hormone-sensitive brain regions is believed to underlie long-lasting depressive behaviors. However, the detailed mechanisms by which chronic stress causes those adaptive changes are not clearly understood. In the present study, we investigated whether epigenetic changes regulate stress-induced depressive behaviors. We found that chronic stress in mice downregulates the epigenetic factors HDAC2 and SUV39H1 in the hippocampus. A series of follow-up analyses including ChIP assay and siRNA-mediated functional analyses reveal that glucocorticoids released by stress cumulatively increase Mkp-1 expression in the hippocampus, and increased Mkp-1 then debilitates p-CREB and PPARγ, which in turn suppress the epigenetic factors HDAC2 and SUV39H1. Furthermore, HDAC2 and SUV39H1 normally suppress the transcription of the Mkp-1, and therefore the reduced expression of HDAC2 and SUV39H1 increases Mkp-1 expression. Accordingly, repeated stress progressively strengthens a vicious cycle of the Mkp-1 signaling cascade that facilitates depressive behaviors. These results suggest that the hippocampal stress adaptation system comprising HDAC2/SUV39H1-regulated Mkp-1 signaling network determines the vulnerability to chronic stress and the maintenance of depressive behaviors.

Identification of genes and pathways related to atherosclerosis comorbidity and depressive behavior via RNA-seq and bioinformation analysis in ApoE-/- mice

Background

Depression is an independent risk factor for atherosclerosis (AS), which can increase the risk of death and disability from AS. However, the mechanism of AS comorbidity with depression is complex.

Methods

ApoE^-/- and C57BL/6J mice were fed with a high-fat diet (model group, N=12 ♂) and a normal diet (control group, N=12 ♂). During the 15-week experimental period, the following tests were performed: coat color score, body weight, and sucrose preference tests (every 2 weeks); open-field test (1^st, 7^th, and 15^th weeks); and light/dark and tail suspension tests (15^th week). Oil Red O and hematoxylin and eosin (HE) stainings were used to assess the area of atherosclerotic status. The levels of triglyceride and total and low-density lipoprotein cholesterol in the serum and secretion of pro-inflammatory cytokines were determined using the enzyme-linked immunosorbent assay. The differentially expressed genes (DEGs) in the hippocampus and prefrontal cortex were screened by RNA-sequencing (RNA-seq) and analyzed using the Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations.

Results

Our findings showed that compared with C57 mice in the control group, ApoE^-/- mice in the model group gradually developed depression-like behavioral changes with elevated blood lipid concentrations, serum inflammatory factor levels, and atherosclerotic plaque formation in the thoracic aorta. Consequently, in the RNA-seq and bioinformatics analysis, the high expression of inflammatory chemokine genes was found in the hippocampus and prefrontal cortex area. The regulation of movement, feeding, and reproduction of the gene expression decreased.

Conclusions

These results indicate that when ApoE^-/- mice were fed a high-fat diet for 15 weeks, depression-like behavioral changes occurred with the formation of atherosclerotic lesions. The RNA-seq, combined with bioinformatics analysis, showed that this AS comorbidity with depressive behavior was associated with the high expression of inflammation-related genes and pathways in the hippocampus and prefrontal cortex.

Social Defeat Modulates T Helper Cell Percentages in Stress Susceptible and Resilient Mice

Altered adaptive immunity involving T lymphocytes has been found in depressed patients and in stress-induced depression-like behavior in animal models. Peripheral T cells play important roles in homeostasis and function of the central nervous system and thus modulate behavior. However, the T cell phenotype and function associated with susceptibility and resilience to depression remain largely unknown. Here, we characterized splenic T cells in susceptible and resilient mice after 10 days of social defeat stress (SDS). We found equally decreased T cell frequencies and comparably altered expression levels of genes associated with T helper (Th) cell function in resilient and susceptible mice. Interleukin (IL)-17 producing CD4⁺ and CD8⁺ T cell numbers in the spleen were significantly increased in susceptible mice. These animals further exhibited significantly reduced numbers of regulatory T cells (T_reg) and decreased gene expression levels of TGF-β. Mice with enhanced Th17 differentiation induced by conditional deletion of PPARγ in CD4⁺ cells (CD4-PPARγ^KO), an inhibitor of Th17 development, were equally susceptible to SDS when compared to CD4-PPARγ^WT controls. These data indicate that enhanced Th17 differentiation alone does not alter stress vulnerability. Thus, SDS promotes Th17 cell and suppresses T_reg cell differentiation predominantly in susceptible mice with yet unknown effects in immune responses after stress exposure.

Interaction Between AGTR1 and PPARγ Gene Polymorphisms on the Risk of Nonalcoholic Fatty Liver Disease

AIMS

Nonalcoholic fatty liver disease (NAFLD) is an important public health issue worldwide. Several recent studies have reported that peroxisome proliferator-activated receptor-γ (PPARγ) and angiotensin II type 1 receptor (AGTR1) variants are associated with NAFLD occurrence, but the results have been inconsistent. The aim of this study was to analyze the interactions between PPARγ and AGTR1 polymorphisms and their associations with NAFLD in Chinese adults.

METHODS

Seven single nucleotide polymorphisms (SNPs) of the PPARγ gene and 5 SNPs of the AGTR1 gene were selected and genotyped in 1591 unrelated Chinese adults. The SNPAssoc package of R was used to examine the relationships between the selected SNPs and NAFLD.

RESULTS

After adjusting the covariance, the results from the overdominant model showed that participants carrying the T/C genotype of rs2638360 in AGTR1 have a decreased risk of NAFLD compared with those with T/T-C/C genotypes (odds ratio: 0.70, 95% confidence interval: 0.49-1.00). However, our results showed that none of the selected PPARγ variants were significantly associated with the risk of NAFLD after applying a false discovery rate correction. Among the 12 selected SNPs from PPARγ and AGTR1, model-based multifactor dimensionality reduction (MB-MDR) analyses for gene-gene interactions revealed that all the models were significantly associated with the increased risk of NAFLD (p < 0.05) except the 2-, 10-, 11-, and 12-locus models. Further, among the 10 SNPs negatively associated with NAFLD, the four-locus model (rs13431696 and rs3856806 in PPARγ, and rs5182, rs1492100 in ATGR1) and the five-locus model (rs9817428, rs1175543, rs13433696, and rs2920502 in PPARγ, and rs1492100 in ATGR1) were closely related with NAFLD susceptibility (p = 0.019 and p = 0.048, respectively).

CONCLUSION

Our present study suggests that interactions among multiple AGTR1 and PPARγ polymorphisms are associated with the risk of NAFLD in the Chinese population.

Morus alba L. Diminishes visceral adiposity, insulin resistance, behavioral alterations via regulation of gene expression of leptin, resistin and adiponectin in rats fed a high-cholesterol diet

Ethanolic extract of leaves of Morus alba L. (M. alba), known as white mulberry, was orally administered (100 mg/kg b.wt) for 8 weeks to female Wistar rats that were fed a high-cholesterol diet (HCD), to investigate the potential of M. alba leaves in attenuation of obesity, dyslipidemia, insulin resistance, and deficits in mood, cognitive as well as motor activity that are linked to the adipokines secretions of visceral adipose tissue. Results showed that M. alba diminished body weight gain, hypercholesterolemia, hypertriglyceridemia, atherogenic (AI) & coronary artery indices (CRI), and ameliorated glucose level and insulin resistance index in rats on HCD, compared with untreated HCD rats. Moreover, M. alba administration significantly decreased serum leptin and resistin contents as well as their mRNA expression in visceral adipose tissue, but significantly increased serum adiponectin level, and its mRNA expression in visceral adipose tissue in rats fed on HCD, compared to those in untreated HCD group. Regarding behavioral alterations, M. alba attenuated motor deficit, declined memory, depression and anxiety-like behavior, as well in rats on HCD, compared to that noticed in untreated HCD rats. The current data showed that serum leptin and resistin showed a positive correlation with and body weight gain, triglycerides (TG), AI as well as CRI, but showed a negative correlation with exploration, declined memory, depression- and anxiety-like behavior. Conversely, serum adiponectin showed a negative correlation with and body weight gain, TG, AI as well as CRI, but showed a positive correlation with locomotor activity, exploration, declined memory, and depression- and anxiety-like behavior. In conclusion, M. alba leaves supplementation could attenuate adiposity, insulin resistance behavioral deficits via down-regulation of regulation of gene expression of leptin, resistin, but up-regulation of adiponectin gene expression in the visceral adipose tissue of rats fed a high-cholesterol diet.

Interplay Between the Gut-Brain Axis, Obesity and Cognitive Function

Obesity continues to be one of the major public health problems due to its high prevalence and co-morbidities. Common co-morbidities not only include cardiometabolic disorders but also mood and cognitive disorders. Obese subjects often show deficits in memory, learning and executive functions compared to normal weight subjects. Epidemiological studies also indicate that obesity is associated with a higher risk of developing depression and anxiety, and vice versa. These associations between pathologies that presumably have different etiologies suggest shared pathological mechanisms. Gut microbiota is a mediating factor between the environmental pressures (e.g., diet, lifestyle) and host physiology, and its alteration could partly explain the cross-link between those pathologies. Westernized dietary patterns are known to be a major cause of the obesity epidemic, which also promotes a dysbiotic drift in the gut microbiota; this, in turn, seems to contribute to obesity-related complications. Experimental studies in animal models and, to a lesser extent, in humans suggest that the obesity-associated microbiota may contribute to the endocrine, neurochemical and inflammatory alterations underlying obesity and its comorbidities. These include dysregulation of the HPA-axis with overproduction of glucocorticoids, alterations in levels of neuroactive metabolites (e.g., neurotransmitters, short-chain fatty acids) and activation of a pro-inflammatory milieu that can cause neuro-inflammation. This review updates current knowledge about the role and mode of action of the gut microbiota in the cross-link between energy metabolism, mood and cognitive function.

Insulin resistance, an unmasked culprit in depressive disorders: Promises for interventions

Depressive disorders constitute a set of debilitating diseases with psychological, societal, economic and humanitarian consequences for millions of people worldwide. Scientists are beginning to understand the reciprocal communication between the brain and the rest of the body in the etiology of these diseases. In particular, scientists have noted a connection between depressive disorders, which are primarily seen as brain-based, and, insulin resistance (IR), a modifiable metabolic inflammatory state that is typically seen as peripheral. We highlight evidence showing how treating IR, with drugs or behavioral interventions, may ameliorate or possibly prevent, depressive disorders and their long-term consequences at various stages of the life course. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Puerarin ameliorated the behavioral deficits induced by chronic stress in rats

The present study aimed to investigate the mechanisms underlying the antidepressant-like effects of puerarin via the chronic unpredictable stress (CUS) procedure in rats. Similar to Sertraline (Ser), Chronic treatment of puerarin (60 and 120 mg/kg, i.g) elicited the antidepressant-like effects by reversing the decreased sucrose preference in sucrose preference test (SPT), by blocking the increased latency to feed in novelty-suppressed feeding test (NSFT) and the increased immobility time in forced swimming test (FST) without affecting locomotor activity. However, acute puerarin treatment did not ameliorate the antidepressant- and anxiolytic- like effects in FST and NSFT, respectively. In addition, enzyme linked immunosorbent assay (ELISA) and high performance liquid chromatography-electrochemical detection (HPLC-ECD) showed that chronic treatment of puerarin (60 and 120 mg/kg, i.g) reversed the decreased levels of progesterone, allopregnanolone, serotonin (5-HT) and 5-Hydroxyindoleacetic acid (5-HIAA) in prefrontal cortex and hippocampus of post-CUS rats. Furthermore, puerarin (60 and 120 mg/kg, i.g) blocked the increased corticotropin releasing hormone (CRH), corticosterone (Cort) and adrenocorticotropic hormone (ACTH). Collectively, repeated administration of puerarin alleviated the behavioral deficits induced by chronic stress which was associated with the biosynthesis of neurosteroids, normalization of serotonergic system and preventing HPA axis dysfunction.

Optimized animal model to mimic the reality of stress-induced depression in the clinic

BACKGROUND

Animal models are useful tools for verifying the relationship between stress and depression; however, an operational criterion for excluding the resilient animals from the analysis has not been established yet, which hinders the model's ability to more accurately mimic the scenario in humans.

METHODS

To induce depression-like symptoms, rats received maternal deprivation (MD) during PND1-14, and/or chronic unpredictable stress (CUS) exposure. The latent profile analysis (LPA) was used to determine latent subgroups in treatment naive adult rats. The percentile method was used to distinguish sensitive and non-sensitive behaviors in rats.

RESULTS

The sucrose preference rate of treatment naive adult rats was fit using a Beta distribution, while immobility time was fit using a Gamma distribution. Indexes of behavioral tests revealed the 4-class model as the best fit for treatment naive adult rats. The incidence of stress-resilience in MD rats was significantly higher than that in CUS rats and MD + CUS rats. There was a significantly higher incidence of stress-resilience in CUS rats compared with MD + CUS rats. Recovery rate of anhedonia-like and sub anhedonia-like behaviors in CUS rats was significantly higher than that in MD and MD + CUS rats. There was a significantly higher recovery rate of anhedonia-like behaviors in MD rats compared to MD + CUS rats.

CONCLUSIONS

The percentile method is suitable for setting up an operational cutoff to classify depression-like, sub depression-like, and resilient behaviors in rats exposed to MD and CUS.