Replenished microglia partially rescue schizophrenia-related stress response.

Background: Microglia play an important role in the maintenance of brain and behavioral homeostasis. The protective effect of microglial replenishment was reported in neurological diseases, but whether microglial therapy would benefit psychiatric disorders such as schizophrenia has been unclear. As schizophrenia is a stress-vulnerable disorder and psychosocial stress promotes inflammation and microglial activation, we aim to understand how microglial replenishment works in stress-associated schizophrenia. Methods: We used a CSF1R-mediated pharmacological approach to study repopulated microglia (repMg) in a cohort of mice (n = 10/group) undergoing chronic unpredictable stress (CUS). We further studied a cohort of first-episode schizophrenia (FES, n = 74) patients who had higher perceived stress scores (PSS) than healthy controls (HCs, n = 68). Results: Reborn microglia attenuated CUS-induced learned hopelessness and social withdrawal but not anxiety in mice. Compared to control, CUS- or repMg-induced differentially expressed genes (DEGs) in the prefrontal cortex regulated nervous system development and axonal guidance. CUS also caused microglial hyper-ramification and increased engulfment of synaptophysin and vesicular glutamate transporter-2 by microglia and astrocytes, which were recovered in CUS + repMg (all p < 0.05). Moreover, FES patients had smaller hippocampal fimbria than HCs (p < 1e-7), which were negatively associated with PSS (r = -0.397, p = 0.003). Blood DEGs involved in immune system development were also associated with PSS and the right fimbria more prominently in FES patients than HCs (Zr, p < 0.0001). The KCNQ1 was a partial mediator between PSS and fimbria size (ß = -0.442, 95% CI: -1.326 ~ -0.087). Conclusion: Microglial replenishment may potentially benefit psychiatric disorders such as schizophrenia.

Glial receptor PLXNB2 regulates schizophrenia-related stress perception via the amygdala.

Stress is a trigger for the development of psychiatric disorders. However, how stress trait differs in schizophrenia patients is still unclear. Stress also induces and exacerbates immune activation in psychiatric disorders. Plexins (Plxn) and its ligands semaphorins (Sema) are important cellular receptors with plural functions in both the brain and the immune system. Recently, the role of Plxn/Sema in regulation of neuroinflammation was also noticed. Here, when investigating immune mechanisms underlying stress susceptibility in schizophrenia, we discovered the role of Plxnb2 in stress response. Patients of first-episode schizophrenia (FES) with high stress (FES-hs, n=51) and low stress (FES-ls, n=50) perception and healthy controls (HCs) (n=49) were first recruited for neuroimaging and blood bulk RNA sequencing (RNA-seq). A mouse model of chronic unpredictable stress (CUS) and intra-amygdaloid functional blocking of Plxnb2 were further explored to depict target gene functions. Compared to HCs, FES-hs patients had bigger caudate and thalamus (FDR=0.02&0.001, respectively) whereas FES-ls patients had smaller amygdala (FDR=0.002). Blood RNA-seq showed differentially expressed PLXNB2 and its ligands among patient groups and HCs (FDR<0.05~0.01). Amygdaloid size and PLXNB2 level were both negatively correlated with stress perception (p<0.01&0.05, respectively), which fully mediated the amygdaloid positive association with PLXNB2 expression (ß=0.9318, 95% CI: 0.058~1.886) in FES-hs patients. In mice, Plxnb2 was enriched in astrocytes and microglia and CUS reduced its expression in astrocytes (p<0.05). Inhibition of amygdaloid Plxnb2 by its functional blocking monoclonal antibody (mAb)-102 induced mice anxiety (p<0.05), amygdaloid enlargement (p<0.05), and microglial ramification (p<0.001) compared to saline. These data suggest that PLXNB2 regulates amygdala-dependent stress responses.

Monocytic Subsets Impact Cerebral Cortex and Cognition: Differences Between Healthy Subjects and Patients With First-Episode Schizophrenia.

Monocytes are a highly heterogeneous population subcategorized into classical, intermediate and nonclassical subsets. How monocytes and their subsets may shape brain structures and functions in schizophrenia remains unclear. The primary goal of this cross-sectional study was to investigate monocytic subsets and their specific signature genes in regulation of cerebral cortical thickness and cognitive functions in first-episode schizophrenia (FES) patients. Whole-blood RNA sequencing of 128 FES patients and 111 healthy controls (HCs) were conducted and monocyte-specific differentially expressed genes were further analyzed. The MATRICS Consensus Cognitive Battery (MCCB) test, cortical neuroimaging and flow cytometric staining of peripheral blood monocytic subsets were performed among the participants. Significant changes in expressions of 54 monocytic signature genes were found in patients, especially for intermediate and nonclassical monocytic subsets with the most outstanding alterations being downregulated S100 Calcium Binding Protein A (S100A) and upregulated Interferon Induced Transmembrane Protein (IFITM) family members, respectively. Meanwhile, percentage of blood nonclassical monocytes was decreased in patients. Cortical thicknesses and MCCB performance were expectantly reduced and weaker intra-relationships among monocytic signature genes and cortices, respectively, were noted in patients compared to HCs. Monocytic genes were negatively associated with both cortical thicknesses and cognition in HCs, which was interestingly weakened or even reversed in patients, with nonclassical monocytic genes showing the greatest statistical significance. This study reveals that while monocytes may have negative effects on brain structure and cognition, the ameliorated phenomenon observed in schizophrenia may reflect an (mal)adaptive change of monocytes at early stage of the disorder.

Enhanced Anxiety and Olfactory Microglial Activation in Early-Stage Familial Alzheimer's Disease Mouse Model.

Anxiety is a known comorbidity and risk factor for conversion to neuroinflammation-mediated dementia in patients with Alzheimer's disease (AD). Here, we investigated if anxiety occurred as an early endophenotype of mutant familial AD (5 × FAD) male mice and the underlying neuroinflammatory mechanisms. We observed that compared to wildtype (WT) littermates, 5 × FAD mice showed enhanced anxiety at as early as 2 months old (mo). Interestingly, these 5 × FAD male mice had concomitantly increased mRNA levels of pro-inflammatory cytokines such as interleukin 1 beta (Il1b) and tumor necrosis factor (Tnf) in the olfactory bulb (OB) but not the frontal cortex (FC). Increased expression of Tnf in the OB was significantly correlated with the anxious behavior in the FAD but not WT mice. Furthermore, we found more prominent microglial activation and morphological changes in the OB of 2 mo 5 × FAD mice, while only microglial ramification was seen in the FC. To understand if neuroinflammatory changes in the FC could occur at a later stage, we studied 5~6 mo male mice and found that Il1b, interleukin 18 (Il18), and Tnf were upregulated in the FC at this older age. Furthermore, we observed that numbers of microglia and macrophage as well as microglial synaptic pruning, as indicated by phagocytosis of presynaptic component of vesicular glutamate transporter-2, were increased in the OB but not the FC of 5~6 mo 5 × FAD mice. Our findings demonstrated the OB as a more sensitive brain region than the cerebral cortex for microglia-mediated neuroinflammation in association with anxiety in FAD mice and supported the notion that the OB can be an early-stage biomarker in AD.

[Noradrenaline modulates the spontaneous firing activities of Purkinje cells via α2-adrenergic receptor in mouse cerebellar cortex].

Cerebellar Purkinje cells (PCs) exhibit two types of discharge activities: simple spike (SS) and complex spike (CS). Previous studies found that noradrenaline (NA) can inhibit CS and bidirectionally regulate SS, but the enhancement of NA on SS is overwhelmed by the strong inhibition of excitatory molecular layer interneurons. However, the mechanism underlying the effect of NA on SS discharge frequency is not clear. Therefore, in the present study, we examined the mechanism underlying the increasing effect of NA on SS firing of PC in mouse cerebellar cortex in vivo and in cerebellar slice by cell-attached and whole-cell recording technique and pharmacological methods. GABAA receptor was blocked by 100 µmol/L picrotoxin in the whole process. In vivo results showed that NA significantly reduced the number of spikelets of spontaneous CS and enhanced the discharge frequency of SS, but did not affect the discharge frequency of CS. In vitro experiments showed that NA reduced the number of CS spikelets and after hyperpolarization potential (AHP) induced by electrical stimulation, and increased the discharge frequency of SS. NA also reduced the amplitude of excitatory postsynaptic current (EPSC) of parallel fiber (PF)-PC and significantly increased the paired-pulse ratio (PPR). Application of yohimbine, an antagonist of α2-adrenergic receptor (AR), completely eliminated the enhancing effect of NA on SS. The α2-AR agonist, UK14304, also increased the frequency of SS. The ß-AR blocker, propranolol, did not affect the effects of NA on PC. These results suggest that in the absence of GABAA receptors, NA could attenuate the synaptic transmission of climbing fiber (CF)-PC via activating α2-AR, inhibit CS activity and reduce AHP, thus enhancing the SS discharge frequency of PC. This result suggests that NA neurons of locus coeruleus can finely regulate PC signal output by regulating CF-PC synaptic transmission.

Differences of Microglia in the Brain and the Spinal Cord.

Microglia were previously regarded as a homogenous myeloid cell lineage in the mammalian central nervous system (CNS). However, accumulating evidences show that microglia in the brain and SC are quite different in development, cellular phenotypes and biological functions. Although this is a very interesting phenomenon, the underlying mechanisms and its significance for neurological diseases in association with behavioral and cognitive changes are still unclear. How microglia differ between these two regions and whether such diversity may contribute to CNS development and functions as well as neurological diseases will be discussed in this Perspective.

Propofol Inhibits Cerebellar Parallel Fiber-Purkinje Cell Synaptic Transmission via Activation of Presynaptic GABAB Receptors in vitro in Mice.

Propofol is a widely used intravenous sedative-hypnotic agent, which causes rapid and reliable loss of consciousness via activation of γ -aminobutyric acid A (GABAA) receptors. We previously found that propofol inhibited cerebellar Purkinje cells (PC) activity via both GABAA and glycine receptors in vivo in mice. We here examined the effect of propofol on the cerebellar parallel fiber (PF)-PC synaptic transmission in mouse cerebellar slices by whole-cell recording technique and pharmacological methods. We found that following blockade of GABAA and glycine receptors activity, propofol reversely decreased the amplitude of PF-PC excitatory postsynaptic currents (PF-PC EPSCs), and significantly increased paired-pulse ratio (PPR). The propofol-induced decrease in amplitude of PF-PC EPSCs was concentration-dependent. The half-inhibitory concentration (IC50) of propofol for inhibiting PF-PC EPSCs was 4.7 µM. Notably, the propofol-induced changes in amplitude and PPR of PF-PC EPSCs were abolished by GABAB receptor antagonist, saclofen (10 µM), but not blocked by N-methyl-D-aspartate receptor (NMDA) receptor antagonist, D-APV (50 µM). Application of the GABAB receptor agonist baclofen induced a decrease in amplitude and an increase in PPR of PF-PC EPSCs, as well masked the propofol-induced changes in PF-PC EPSCs. Moreover, the propofol-induced changes in amplitude and PPR of PF-PC EPSCs were abolished by a specific protein kinase A (PKA) inhibitor, KT5720. These results indicate that application of propofol facilitates presynaptic GABAB receptors, resulting in a depression of PF-PC synaptic transmission via PKA signaling pathway in mouse cerebellar cortex. The results suggest that the interaction with GABAB receptors may contribute to the general anesthetic action of propofol.

Comparative Analysis of the Rats' Gut Microbiota Composition in Animals with Different Ginsenosides Metabolizing Activity.

Following oral intake of Panax ginseng, major ginsenosides are metabolized to deglycosylated ginsenosides by gut microbiota before absorption into the blood. As the composition of gut microbiota varies between individuals, metabolic activities are significantly different. We selected 6 rats with low efficiency metabolism (LEM) and 6 rats with high efficiency metabolism (HEM) from 60 rats following oral administration of Panax ginseng extract, and analyzed their gut microbiota composition using Illumina HiSeq sequencing of the 16S rRNA gene. The components of gut microbiota between the LEM and HEM groups were significantly different. Between the 2 groups, S24-7, Alcaligenaceae, and Erysipelotrichaceae occupied most OTUs of the HEM group, which was notably higher than the LEM group. Furthermore, we isolated Bifidobacterium animalis GM1 that could convert the ginsenoside Rb1 to Rd. The result implies that these specific intestinal bacteria may dominate the metabolism of Panax ginseng.