Brain structure and synaptic protein expression alterations after antidepressant treatment in a Wistar-Kyoto rat model of depression

The impact of long-term isolation on anxiety, depressive-like and social behavior in aging Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) male rats

Aging is a complex process associated with multimorbidity. Hypertension, one of widespread states, is among main causes of age-related alterations in behavior, emotionality and sociability. We studied the effects of long-term isolated housing on anxiety, depressive-like and social behavior as well as changes in the adrenocortical and sympathetic systems in the aging normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Ten-month-old male rats of both strains were subjected to 90-day isolated or group housing. Surprisingly, social isolation induced only mild effect on anxiety without influencing other affective-related behaviors. No effects of isolated housing on sociability or social novelty preferences were revealed. Despite the adrenal gland hypertrophy in the SHRs, corticosterone levels remained stable within the period of isolation but the expression of nuclear glucocorticoid receptor (Nr3c1) mRNA in the adrenals was lower in the SHR as compared to WKY rats. Pre-existing hypertension, associated with SHR genotype, did not significantly contribute to the effects of social isolation. The data suggest that the aged WKY and SHR rats are relatively resilient to chronic social stress associated with isolated housing.

Ubiquitin ligase RFWD2 promotes dendritic spine and synapse formation by activating the ERK/PEA3/c-Jun pathway in rat cerebral cortical neurons

The regulation of protein degradation through the ubiquitin-proteasome system is essential for normal brain development, axon growth, synaptic growth and plasticity. The E3 ubiquitin ligase RFWD2 plays a key role in the onset and development of neurological diseases, including the pathogenesis of Alzheimer's disease (AD), but the mechanisms controlling the homeostasis of neuronal synaptic proteins are still poorly understood. Here, we showed that the expression level of RFWD2 gradually decreased with the age of the rats and was negatively correlated with the development of cerebral cortical neurons and dendrites in vivo. RFWD2 was shown to localize to presynaptic terminals and some postsynaptic sides of both excitatory synapses and inhibitory synapses via colocalization with neuronal synaptic proteins (SYN, PSD95, Vglut1 and GAD67). Overexpression of RFWD2 promoted dendrite development and dendritic spine formation and markedly decreased the expression of synaptophysin and PSD95 by reducing the expression of ETV1, ETV4, ETV5 and c-JUN in vitro. Furthermore, the whole-cell membrane slice clamp results showed that RFWD2 overexpression resulted in greater membrane capacitance in neuronal cells, inadequate cell repolarization, and a longer time course for neurons to emit action potentials with decreased excitability. RFWD2 regulates dendritic development and plasticity, dendritic spine formation and synaptic function in rat cerebral cortex neurons by activating the ERK/PEA3/c-Jun pathway via a posttranslational regulatory mechanism and can be used as an efficient treatment target for neurological diseases.

Proteomic characterization of the medial prefrontal cortex in chronic restraint stress mice

Depression is a prominent contributor to global disability. A growing body of data suggests that depression is associated with the pathophysiology of the medial prefrontal cortex (mPFC), but the underlying mechanisms remain poorly understood. Mice were subjected to chronic restraint stress (CRS) for 3 weeks to create depression models during this investigation. Protein tandem mass tag (TMT) quantification and LC-MS/MS analysis were conducted to examine proteome patterns. Afterwards, to further explore the enrichment of differential proteins and the signaling pathways involved, we annotated these differentially expressed proteins. We confirmed that CRS mice developed depression-like and anxiety-like behaviors. Among the 8081 measured proteins, a total of 15 proteins were found to be differentially expressed. These proteins exhibited functional enrichment in a variety of biological functions, and among these pathways, alterations in synaptic function and autophagy are noteworthy. In addition, we identified a differentially expressed protein called Wnt2b and found that CRS may disrupt synaptic plasticity by affecting the activation of the Wnt2b/β-catenin pathway. Our findings showed depression-like behaviors in the CRS mouse model and molecular alterations in the mPFC, which may help explain the pathogenesis of depression and identify novel antidepressant medication targets. SIGNIFICANCE: Depression is a prevalent and frequent chronic mental illness and is now a significant contributor to global disability. In this study, we used chronic restraint stress to establish a mouse model of depression, and differentially expressed proteins in the medial prefrontal cortex of depressed model mice were detected by TMT proteomics. Our study verified the presence of altered synaptic function and excessive autophagy in the mPFC of CRS-induced mice from a proteomic perspective. Furthermore, we demonstrated that CRS may disrupt synaptic plasticity by affecting the activation of the Wnt2b/β-catenin pathway, which may be a key link in the pathogenesis of depression and may provide new insights for identifying new antidepressant drug targets.

Ameliorated Effects of Fucoidan on Dextran Sulfate Sodium-Induced Ulcerative Colitis and Accompanying Anxiety and Depressive Behaviors in Aged C57BL/6 Mice

Fucoidan has shown better effects on the improvement of acute ulcerative colitis (UC). However, the specific mechanisms by which fucoidan improves UC-related behavioral disorders in aged mice, especially its effect on the gut-brain axis, remain to be further explored. C57BL/6 male mice aged 8 months were gavaged with 400 or 100 mg/kg bw day fucoidan for five consecutive weeks, with UC being induced by ad libitum to dextran sulfate sodium (DSS) solution in the fifth week. The results showed that fucoidan ameliorated UC and accompanying anxiety- and depressive-like behaviors with downregulated expressions of (NOD)-like receptor family and pyrin domain-containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC), cysteine aspartate-specific protease-1 (Caspase-1) and interlekin-1β (IL-1β), and elevated mRNA levels of brain-derived neurotrophic factor (Bdnf) and postsynaptic-density protein 95 (Psd-95) in cortex and hippocampus. Furthermore, fucoidan improved the permeability of intestinal barrier and blood-brain barrier and restored the abnormal structure of the gut microbiota with a significantly decreased ratio of Firmicutes to Bacteroidota (F/B) and obviously increased abundance of Akkermansia. As a diet-derived bioactive ingredient, fucoidan might be a better alternative for the prevention of UC and accompanying anxiety- and depressive-like behaviors.

Rosmarinic acid alleviate CORT-induced depressive-like behavior by promoting neurogenesis and regulating BDNF/TrkB/PI3K signaling axis

Rosmarinic acid (RA), a natural phenolic acid compound with a variety of bioactive properties. However, the antidepressant activity and mechanism of RA remain unclear. The aim of this study is to investigate the effects and potential mechanisms of RA on chronic CORT injection induced depression-like behavior in mice. Male C57BL/6 J mice were intraperitoneally injected with CORT (10 mg/kg) and were orally given RA daily (10 or 20 mg/kg) for 21 consecutive days. In vitro, the HT22 cells were exposed to CORT (200 μM) with RA (12.5, 25 or 50 μM) and LY294002 (a PI3K inhibitor) or ANA-12 (a TrkB inhibitor) treatment. The depression-like behavior and various neurobiological changes in the mice and cell injury and levels of target proteins in vitro were subsequently assessed. Here, RA treatment decreased the expression of p-GR/GR, HSP90, FKBP51, SGK-1 in mice hippocampi. Besides, RA increased the average optical density of Nissl bodies and number of dendritic spines in CA3 region, and enhanced Brdu and DCX expression and synaptic transduction in DG region, as well as up-regulated both the BDNF/TrkB/CREB and PI3K/Akt/mTOR signaling. Moreover, RA reduced structural damage and apoptosis in HT22 cells, increased the differentiation and maturation of them. More importantly, LY294002, but not ANA-12, reversed the effect of RA on GR nuclear translocation. Taken together, RA exerted antidepressant activities by modulating the hippocampal glucocorticoid signaling and hippocampal neurogenesis, which related to the BDNF/TrkB/PI3K signaling axis regulating GR nuclear translocation, provide evidence for the application of RA as a candidate for depression.

Sleep deprivation alleviates depression-like behaviors in mice via inhibiting immune and inflammatory pathways and improving neuroplasticity

BACKGROUND

Sleep deprivation (SD) has been suggested to have a rapid antidepressant effect. There is substantial evidence that neuroinflammation and neuroplasticity play critical roles in the pathophysiology and treatment of depression. Here, we investigated the mechanisms of SD to alleviate depression-like behaviors of mice, and the role of neuroinflammation and neuroplasticity in it.

METHODS

Adult male C57BL/6 J mice were subjected to chronic restraint stress (CRS) for 6 weeks, and 6 h of SD were administrated. Behavioral tests were performed to measure depression-like behaviors. RNA-sequencing and bioinformatic analysis were performed in the anterior cingulate cortex (ACC). The differentially expressed genes were confirmed by quantitative real-time polymerase chain reaction (RT-qPCR). Neuroinflammation and neuroplasticity were measured by western blotting and immunofluorescence staining.

RESULTS

Behavioral tests demonstrated that SD swiftly attenuated the depression-like behaviors induced by CRS. RNA-sequencing identified the upregulated immune and inflammatory pathways after CRS exposure were downregulated by SD. Furthermore, SD reversed the levels of immune and inflammation-related mRNA, pro-inflammatory factors and microglia activation in ACC. Additionally, the impaired neuroplasticity elicited by CRS in the prefrontal cortex (PFC) and ACC were improved by SD.

LIMITATIONS

More in-depth studies are required to determine the role of different SD protocols in depressive symptoms and their underlying mechanisms.

CONCLUSIONS

Our study revealed the rapid antidepressant effect of SD on CRS mice through the reduction of the neuroinflammatory response in ACC and the improvement of neuroplasticity in PFC and ACC, providing a theoretical basis for the clinical application of SD as a rapid antidepressant treatment.

Evidence on differential role for alpha 1 and alpha 2 subtypes of AP-2 adaptin in the Central Nervous System

Two subtypes of alpha (α)subunits , α1and α2, belonging to AP-2 complex have been described in the central nervous system (CNS). The specific role of each subtype is still unclear. In this study, we evaluated the expression and interaction with cell membranes of both subtypes in the postnatal developing cerebral cortex and cerebellum in two rat strains that display distinct developmental features. We observed that α2 displays higher variations than α1 during development, and at lesser extent in the rats with delayed rate of development. Additionally, by in vitro binding assays we evaluated the interaction of α subunits with bovine brain membranes. Both subtypes displayed clear differences in their performance, maximum binding of α1 was higher and α2 reached it faster than α1. In addition, both subtypes displayed different binding to membranes when bivalent cations or nucleotides were added. We conclude that both subtypes interact differently with membranes and that they may play different roles in clathrin-mediated endocytosis in the CNS.

The Wistar Kyoto Rat: A Model of Depression Traits

There is an ongoing debate about the value of animal research in psychiatry with valid lines of reasoning stating the limits of individual animal models compared to human psychiatric illnesses. Human depression is not a homogenous disorder; therefore, one cannot expect a single animal model to reflect depression heterogeneity. This limited review presents arguments that the Wistar Kyoto (WKY) rats show intrinsic depression traits. The phenotypes of WKY do not completely mirror those of human depression but clearly indicate characteristics that are common with it. WKYs present despair- like behavior, passive coping with stress, comorbid anxiety, and enhanced drug use compared to other routinely used inbred or outbred strains of rats. The commonly used tests identifying these phenotypes reflect exploratory, escape-oriented, and withdrawal-like behaviors. The WKYs consistently choose withdrawal or avoidance in novel environments and freezing behaviors in response to a challenge in these tests. The physiological response to a stressful environment is exaggerated in WKYs. Selective breeding generated two WKY substrains that are nearly isogenic but show clear behavioral differences, including that of depression-like behavior. WKY and its substrains may share characteristics of subgroups of depressed individuals with social withdrawal, low energy, weight loss, sleep disturbances, and specific cognitive dysfunction. The genomes of the WKY and WKY substrains contain variations that impact the function of many genes identified in recent human genetic studies of depression. Thus, these strains of rats share characteristics of human depression at both phenotypic and genetic levels, making them a model of depression traits.