Early life stress from allergic dermatitis causes depressive-like behaviors in adolescent male mice through neuroinflammatory priming

Apoptosis-induced decline in hippocampal microglia mediates the development of depression-like behaviors in adult mice triggered by unpredictable stress during adolescence

Depression triggered by harmful stress during adolescence is a common problem that can affect mental health. To date, the mechanisms underlying this type of depression remain unclear. One mechanism for the promotion of depression by chronic stress in adulthood is the loss of hippocampal microglia. Since deleterious stress in adolescence also activates microglia, we investigated the dynamic changes of microglia in the hippocampus in mice exposed to chronic unpredictable stress (CUS) in adolescence. Our results showed that 12 days of CUS stimulation in adolescence induced typical depression-like behaviors in adult mice, which were accompanied by a significant decrease and dystrophy of microglia in the dentate gyrus of the hippocampus. Further analysis showed that this decrease in microglia was mediated by the initial response of microglia to unpredictable stress in the dentate gyrus of the hippocampus and their subsequent apoptosis. Blocking the initial response of microglia to unpredictable stress by pretreatment with minocycline was able to prevent apoptosis and microglial decline as well as the development of depression-like behaviors in adult mice induced by adolescent CUS. Moreover, administration of lipopolysaccharide (LPS) or macrophage-colony stimulatory factor (M-CSF), two drugs that reversed microglia decline in the dentate gyrus, ameliorated the depression-like behaviors induced by CUS stimulation in adolescence. These findings reveal a novel mechanism for the development of depression-like behaviors in animals triggered by deleterious stress in adolescence and suggest that reversing microglial decline in the hippocampus may be a hopeful strategy for the treatment of depression triggered by deleterious stress in adolescence.

New Insights into the Pivotal Role of the Amygdala in Inflammation-Related Depression and Anxiety Disorder

Depression and anxiety disorders are the two most prevalent psychiatric diseases that affect hundreds of millions of individuals worldwide. Understanding the etiology and related mechanisms is of great importance and might yield new therapeutic strategies to treat these diseases effectively. During the past decades, a growing number of studies have pointed out the importance of the stress-induced inflammatory response in the amygdala, a kernel region for processing emotional stimuli, as a potentially critical contributor to the pathophysiology of depression and anxiety disorders. In this review, we first summarized the recent progress from both animal and human studies toward understanding the causal link between stress-induced inflammation and depression and anxiety disorders, with particular emphasis on findings showing the effect of inflammation on the functional changes in neurons in the amygdala, at levels ranging from molecular signaling, cellular function, synaptic plasticity, and the neural circuit to behavior, as well as their contributions to the pathology of inflammation-related depression and anxiety disorders. Finally, we concluded by discussing some of the difficulties surrounding the current research and propose some issues worth future study in this field.

Astilbin ameliorates depressive-like behavior caused by postnatal immune activation through Menin-regulated astrocyte inflammation

Postnatal immune activation (PIA) can affect normal brain development and increase the risk of behavioral abnormalities in later life, including depressive-like behavior. Therefore, there is an urgent need to find safe and effective clinical medications for PIA. Recently, the protective effect of astilbin (ASB) in nervous system diseases has attracted much attention. However, the effect of ASB on neurodevelopmental diseases remains unclear. In this study, we used a lipopolysaccharide (LPS)-induced PIA mouse model and found that ASB specifically improved PIA-induced depressive-like behavior but not anxiety-like behavior in adult mice. Astrocytes play an essential role in regulating neuroinflammation, and are the most abundant cell type in the brain. In the PIA model, we found that ASB selectively inhibited astrocyte activation but not microglial activation in the cortex and hippocampus. Moreover, our results showed that ASB specifically upregulated the expression of menin protein in astrocytes and blocked the entry of P65 protein into the nucleus, thus inhibiting the secretion of IL-1β and TNF-α by astrocytes. Taken together, ASB reduced the occurrence of astrocyte-mediated neuroinflammation by targeting menin, thereby attenuating the PIA-induced depressive-like behavior. Our results reveal that ASB may be an attractive antidepressant drug and exert an antidepressant effect in PIA. In terms of drug selection, ASB may be a specific drug for patients with depressive symptoms.

Folic Acid Attenuates Glial Activation in Neonatal Mice and Improves Adult Mood Disorders Through Epigenetic Regulation

Growing evidence indicates that postnatal immune activation (PIA) can adversely increase the lifetime risk for several neuropsychiatric disorders, including anxiety and depression, which involve the activation of glial cells and early neural developmental events. Several glia-targeted agents are required to protect neonates. Folic acid (FA), a clinical medication used during pregnancy, has been reported to have neuroprotective properties. However, the effects and mechanisms of FA in PIA-induced neonatal encephalitis and mood disorders remain unclear. Here, we investigated the roles of FA in a mouse model of PIA, and found that FA treatment improved depressive- and anxiety-like behaviors in adults, accompanied by a decrease in the number of activated microglia and astrocytes, as well as a reduction in the inflammatory response in the cortex and hippocampus of neonatal mice. Furthermore, we offer new evidence describing the functional differences in FA between microglia and astrocytes. Our data show that epigenetic regulation plays an essential role in FA-treated glial cells following PIA stimulation. In astrocytes, FA promoted the expression of IL-10 by decreasing the level of EZH2-mediated H3K27me3 at its promoter, whereas FA promoted the expression of IL-13 by reducing the promoter binding of H3K9me3 mediated by KDM4A in microglia. Importantly, FA specifically regulated the expression level of BDNF in astrocytes through H3K27me3. Overall, our data supported that FA may be an effective treatment for reducing mood disorders induced by PIA, and we also demonstrated significant functional differences in FA between the two cell types following PIA stimulation.

Biological, Psychological, and Social Determinants of Depression: A Review of Recent Literature

Depression is one of the leading causes of disability, and, if left unmanaged, it can increase the risk for suicide. The evidence base on the determinants of depression is fragmented, which makes the interpretation of the results across studies difficult. The objective of this study is to conduct a thorough synthesis of the literature assessing the biological, psychological, and social determinants of depression in order to piece together the puzzle of the key factors that are related to this condition. Titles and abstracts published between 2017 and 2020 were identified in PubMed, as well as Medline, Scopus, and PsycInfo. Key words relating to biological, social, and psychological determinants as well as depression were applied to the databases, and the screening and data charting of the documents took place. We included 470 documents in this literature review. The findings showed that there are a plethora of risk and protective factors (relating to biological, psychological, and social determinants) that are related to depression; these determinants are interlinked and influence depression outcomes through a web of causation. In this paper, we describe and present the vast, fragmented, and complex literature related to this topic. This review may be used to guide practice, public health efforts, policy, and research related to mental health and, specifically, depression.