Activation of HCA2 regulates microglial responses to alleviate neurodegeneration in LPS-induced in vivo and in vitro models

Frataxin deficiency shifts metabolism to promote reactive microglia via glucose catabolism

Immunometabolism investigates the intricate relationship between the immune system and cellular metabolism. This study delves into the consequences of mitochondrial frataxin (FXN) depletion, the primary cause of Friedreich's ataxia (FRDA), a debilitating neurodegenerative condition characterized by impaired coordination and muscle control. By using single-cell RNA sequencing, we have identified distinct cellular clusters within the cerebellum of an FRDA mouse model, emphasizing a significant loss in the homeostatic response of microglial cells lacking FXN. Remarkably, these microglia deficient in FXN display heightened reactive responses to inflammatory stimuli. Furthermore, our metabolomic analyses reveal a shift towards glycolysis and itaconate production in these cells. Remarkably, treatment with butyrate counteracts these immunometabolic changes, triggering an antioxidant response via the itaconate-Nrf2-GSH pathways and suppressing the expression of inflammatory genes. Furthermore, we identify Hcar2 (GPR109A) as a mediator involved in restoring the homeostasis of microglia without FXN. Motor function tests conducted on FRDA mice underscore the neuroprotective attributes of butyrate supplementation, enhancing neuromotor performance. In conclusion, our findings elucidate the role of disrupted homeostatic function in cerebellar microglia in the pathogenesis of FRDA. Moreover, they underscore the potential of butyrate to mitigate inflammatory gene expression, correct metabolic imbalances, and improve neuromotor capabilities in FRDA.

Cannabidiol ameliorates PTSD-like symptoms by inhibiting neuroinflammation through its action on CB2 receptors in the brain of male mice

Post-traumatic stress disorder (PTSD) is a debilitating mental health disease related to traumatic experience, and its treatment outcomes are unsatisfactory. Accumulating research has indicated that cannabidiol (CBD) exhibits anti-PTSD effects, however, the underlying mechanism of CBD remains inadequately investigated. Although many studies pertaining to PTSD have primarily focused on aberrations in neuronal functioning, the present study aimed to elucidate the involvement and functionality of microglia/macrophages in PTSD while also investigated the modulatory effects of CBD on neuroinflammation associated with this condition. We constructed a modified single-prolonged stress (SPS) mice PTSD model and verified the PTSD-related behaviors by various behavioral tests (contextual freezing test, elevated plus maze test, tail suspension test and novel object recognition test). We observed a significant upregulation of Iba-1 and alteration of microglial/macrophage morphology within the prefrontal cortex and hippocampus, but not the amygdala, two weeks after the PTSD-related stress, suggesting a persistent neuroinflammatory phenotype in the PTSD-modeled group. CBD (10 mg/kg, i.p.) inhibited all PTSD-related behaviors and reversed the alterations in both microglial/macrophage quantity and morphology when administered prior to behavioral assessments. We further found increased pro-inflammatory factors, decreased PSD95 expression, and impaired synaptic density in the hippocampus of the modeled group, all of which were also restored by CBD treatment. CBD dramatically increased the level of anandamide, one of the endocannabinoids, and cannabinoid type 2 receptors (CB2Rs) transcripts in the hippocampus compared with PTSD-modeled group. Importantly, we discovered the expression of CB2Rs mRNA in Arg-1-positive cells in vivo and found that the behavioral effects of CBD were diminished by CB2Rs antagonist AM630 (1 mg/kg, i.p.) and both the behavioral and molecular effects of CBD were abolished in CB2Rs knockout mice. These findings suggest that CBD would alleviate PTSD-like behaviors in mice by suppressing PTSD-related neuroinflammation and upregulation and activation of CB2Rs may serve as one of the underlying mechanisms for this therapeutic effect. The present study offers innovative experimental evidence supporting the utilization of CBD in PTSD treatment from the perspective of its regulation of neuroinflammation, and paves the way for leveraging the endocannabinoid system to regulate neuroinflammation as a potential therapeutic approach for psychiatric disorders.

Microglial activation in spaceflight and microgravity: potential risk of cognitive dysfunction and poor neural health

Due to the increased crewed spaceflights in recent years, it is vital to understand how the space environment affects human health. A lack of gravitational force is known to risk multiple physiological functions of astronauts, particularly damage to the central nervous system (CNS). As innate immune cells of the CNS, microglia can transition from a quiescent state to a pathological state, releasing pro-inflammatory cytokines that contribute to neuroinflammation. There are reports indicating that microglia can be activated by simulating microgravity or exposure to galactic cosmic rays (GCR). Consequently, microglia may play a role in the development of neuroinflammation during spaceflight. Prolonged spaceflight sessions raise concerns about the chronic activation of microglia, which could give rise to various neurological disorders, posing concealed risks to the neural health of astronauts. This review summarizes the risks associated with neural health owing to microglial activation and explores the stressors that trigger microglial activation in the space environment. These stressors include GCR, microgravity, and exposure to isolation and stress. Of particular focus is the activation of microglia under microgravity conditions, along with the proposal of a potential mechanism.

Orally administered neohesperidin attenuates MPTP-induced neurodegeneration by inhibiting inflammatory responses and regulating intestinal flora in mice

Parkinson's disease (PD), a neurodegenerative disease, is the leading cause of movement disorders. Neuroinflammation plays a critical role in PD pathogenesis. Neohesperidin (Neo), a natural flavonoid extracted from citric fruits exhibits anti-inflammatory effects. However, the effect of Neo on PD progression is unclear. This study aimed to investigate the effects of Neo on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD in mice and its underlying mechanism. Our results indicated that Neo administration ameliorated motor impairment and neural damage in MPTP-injected mice, by inhibiting neuroinflammation and regulating gut microbial imbalance. Additionally, Neo administration reduced colonic inflammation and tissue damage. Mechanistic studies revealed that Neo suppressed the MPTP-induced inflammatory response by inhibiting excessive activation of NF-κB and MAPK pathways. In summary, the present study demonstrated that Neo administration attenuates neurodegeneration in MPTP-injected mice by inhibiting inflammatory responses and regulating the gut microbial composition. This study may provide the scientific basis for the use of Neo in the treatment of PD and other related diseases.

Multi-Omics Profiling Identifies Microglial Annexin A2 as a Key Mediator of NF-κB Pro-inflammatory Signaling in Ischemic Reperfusion Injury

Cerebral stroke is one of the leading causes of mortality and disability worldwide. Restoring the cerebral circulation following a period of occlusion and subsequent tissue oxygenation leads to reperfusion injury. Cerebral ischemic reperfusion (I/R) injury triggers immune and inflammatory responses, apoptosis, neuronal damage, and even death. However, the cellular function and molecular mechanisms underlying cerebral I/R-induced neuronal injury are incompletely understood. By integrating proteomic, phosphoproteomic, and transcriptomic profiling in mouse hippocampi after cerebral I/R, we revealed that the differentially expressed genes and proteins mainly fall into several immune inflammatory response-related pathways. We identified that Annexin 2 (Anxa2) was exclusively upregulated in microglial cells in response to cerebral I/R in vivo and oxygen-glucose deprivation and reoxygenation (OGD/R) in vitro. RNA-seq analysis revealed a critical role of Anxa2 in the expression of inflammation-related genes in microglia via the NF-κB signaling. Mechanistically, microglial Anxa2 is required for nuclear translocation of the p65 subunit of NF-κB and its transcriptional activity upon OGD/R in BV2 microglial cells. Anxa2 knockdown inhibited the OGD/R-induced microglia activation and markedly reduced the expression of pro-inflammatory factors, including TNF-α, IL-1β, and IL-6. Interestingly, conditional medium derived from Anxa2-depleted BV2 cell cultures with OGD/R treatment alleviated neuronal death in vitro. Altogether, our findings revealed that microglia Anxa2 plays a critical role in I/R injury by regulating NF-κB inflammatory responses in a non-cell-autonomous manner, which might be a potential target for the neuroprotection against cerebral I/R injury.

Diosgenin alters LPS-induced macrophage polarization by activating PPARγ/NF-κB signaling pathway

Diosgenin (DG) is a steroidal saponin derived from plants, and it exhibits anti-inflammatory properties. In this study, we employed an in vitro model of P.g.-LPS-stimulated mouse macrophage cell line RAW264.7 to investigate the anti-inflammatory effects and mechanism of DG under the condition of altered polarization of macrophages. The RAW264.7 cells were subjected to pre-treatment with DG with or without P.g.-LPS. In cultured macrophages, DG inhibited P.g.-LPS-induced pro-inflammatory M1 macrophages, and increased anti-inflammatory M2 macrophages. Notably, DG reduced the expression of phosphorylation levels of NF-κB p65 and IκB while increasing the expression of PPARγ. Further studies revealed that PPARγ inhibitor GW9662 or PPARγ siRNA reversed the inhibitory effect of DG on M1 phenotype. Collectively, the anti-inflammatory mechanism of DG is related to altering macrophage polarization by activating PPARγ and inhibiting NF-κB signaling pathways.

Alleviating symptoms of neurodegenerative disorders by astrocyte-specific overexpression of TMEM164 in mice

Neuroinflammatory microglia secrete cytokines to induce neurotoxic reactive astrocytes, which are one of the major causes of neuronal death. However, the intrinsic key regulators underlying neurotoxic reactive astrocytes induction are unknown. Here we show that the transmembrane protein 164 (TMEM164) is an early-response intrinsic factor that regulates neurotoxic astrocyte reactivity. TMEM164 overexpression inhibits the induction of neurotoxic reactive astrocytes, maintains normal astrocytic functions and suppresses neurotoxic reactive astrocyte-mediated neuronal death by decreasing the secretion of neurotoxic saturated lipids. Adeno-associated virus-mediated, astrocyte-specific TMEM164 overexpression in male and female mice prevents the induction of neurotoxic reactive astrocytes, dopaminergic neuronal loss and motor deficits in a Parkinson's disease model. Notably, brain-wide astrocyte-specific TMEM164 overexpression prevents the induction of neurotoxic reactive astrocytes, amyloid β deposition, neurodegeneration and memory decline in the 5XFAD Alzheimer's disease mouse model, suggesting that TMEM164 could serve as a potential therapeutic target for neurodegenerative disorders.