22(R)-hydroxycholesterol induces HuR-dependent MAP kinase phosphatase-1 expression via mGluR5-mediated Ca(2+)/PKCα signaling

ELAV/Hu RNA-binding protein family: key regulators in neurological disorders, cancer, and other diseases

The ELAV/Hu family represents a crucial group of RNA-binding proteins predominantly expressed in neurons, playing significant roles in mRNA transcription and translation. These proteins bind to AU-rich elements in transcripts to regulate the expression of cytokines, growth factors, and the development and maintenance of neurons. Elav-like RNA-binding proteins exhibit remarkable molecular weight conservation across different species, highlighting their evolutionary conservation. Although these proteins are widely expressed in the nervous system and other cell types, variations in the DNA sequences of the four Elav proteins contribute to their distinct roles in neurological disorders, cancer, and other Diseases . Elavl1, a ubiquitously expressed family member, is integral to processes such as cell growth, ageing, tumorigenesis, and inflammatory diseases. Elavl2, primarily expressed in the nervous and reproductive systems, is critical for central nervous system and retinal development; its dysregulation has been implicated in neurodevelopmental disorders such as autism. Both Elavl3 and Elavl4 are restricted to the nervous system and are involved in neuronal differentiation and excitability. Elavl3 is essential for cerebellar function and has been associated with epilepsy, while Elavl4 is linked to neurodegenerative diseases, including Parkinson's and Alzheimer's diseases. This paper provides a comprehensive review of the ELAV/Hu family's role in nervous system development, neurological disorders, cancer, and other diseases.

Red nucleus mGluR1 and mGluR5 facilitate the development of neuropathic pain through stimulating the expressions of TNF-α and IL-1β

Our previous study has identified that glutamate in the red nucleus (RN) facilitates the development of neuropathic pain through metabotropic glutamate receptors (mGluR). Here, we further explored the actions and possible molecular mechanisms of red nucleus mGluR Ⅰ (mGluR1 and mGluR5) in the development of neuropathic pain induced by spared nerve injury (SNI). Our data indicated that both mGluR1 and mGluR5 were constitutively expressed in the RN of normal rats. Two weeks after SNI, the expressions of mGluR1 and mGluR5 were significantly boosted in the RN contralateral to the nerve injury. Administration of mGluR1 antagonist LY367385 or mGluR5 antagonist MTEP to the RN contralateral to the nerve injury at 2 weeks post-SNI significantly ameliorated SNI-induced neuropathic pain. However, unilateral administration of mGluRⅠ agonist DHPG to the RN of normal rats provoked a significant mechanical allodynia, this effect could be blocked by LY367385 or MTEP. Further studies indicated that the expressions of TNF-α and IL-1β in the RN were also elevated at 2 weeks post-SNI. Administration of mGluR1 antagonist LY367385 or mGluR5 antagonist MTEP to the RN at 2 weeks post-SNI significantly inhibited the elevations of TNF-α and IL-1β. However, administration of mGluR Ⅰ agonist DHPG to the RN of normal rats significantly enhanced the expressions of TNF-α and IL-1β, these effects were blocked by LY367385 or MTEP. These results suggest that activation of red nucleus mGluR1 and mGluR5 facilitate the development of neuropathic pain by stimulating the expressions of TNF-α and IL-1β. mGluR Ⅰ maybe potential targets for drug development and clinical treatment of neuropathic pain.

Efficient production of 22(R)-hydroxycholesterol via combination optimization of Saccharomyces cerevisiae

22(R)-hydroxycholesterol (22(R)-HCHO) is a crucial precursor of steroids biosynthesis with various biological functions. However, the production of 22(R)-HCHO is expensive and unsustainable due to chemical synthesis and extraction from plants or animals. This study aimed to construct a microbial cell factory to efficiently produce 22(R)-HCHO through systems metabolic engineering. First, we tested 7-dehydrocholesterol reductase (Dhcr7s) and cholesterol C22-hydroxylases from different sources in Saccharomyces cerevisiae, and the titer of 22(R)-HCHO reached 128.30 mg L-1 in the engineered strain expressing Dhcr7 from Columba livia (ClDhcr7) and cholesterol 22-hydroxylase from Veratrum californicum (VcCyp90b27). Subsequently, the 22(R)-HCHO titer was significantly increased to 427.78 mg L-1 by optimizing the critical genes involved in 22(R)-HCHO biosynthesis. Furthermore, hybrid diploids were constructed to balance cell growth and 22(R)-HCHO production and to improve stress tolerance. Finally, the engineered strain produced 2.03 g L-1 of 22(R)-HCHO in a 5-L fermenter, representing the highest 22(R)-HCHO titer reported to date in engineered microbial cell factories. The results of this study provide a foundation for further applications of 22(R)-HCHO in various industrially valuable steroids.

Blockade of mGluR5 in astrocytes derived from human iPSCs modulates astrocytic function and increases phagocytosis

TNF-α is essential for induction and maintenance of inflammatory responses and its dysregulation is associated with susceptibility to various pathogens that infect the central nervous system. Activation of both microglia and astrocytes leads to TNF-α production, which in turn triggers further activation of these cells. Astrocytes have been implicated in the pathophysiology of a wide range of neurodegenerative diseases with either harmful or protective roles, as these cells are capable of secreting several inflammatory factors and also promote synapse elimination and remodeling. These responses are possible because they sense their surroundings via several receptors, including the metabotropic glutamate receptor 5 (mGluR5). Under neuroinflammatory conditions, mGluR5 activation in astrocytes can be neuroprotective or have the opposite effect. In the current study, we investigated the role of mGluR5 in hiPSC-derived astrocytes subjected to pro-inflammatory stimulation by recombinant TNF-α (rTNF-α). Our results show that mGluR5 blockade by CTEP decreases the secreted levels of pro-inflammatory cytokines (IL-6 and IL-8) following short rTNF-α stimulation, although this effect subsides with time. Additionally, CTEP enhances synaptoneurosome phagocytosis by astrocytes in both non-stimulated and rTNF-α-stimulated conditions, indicating that mGluR5 blockade alone is enough to drive synaptic material engulfment. Finally, mGluR5 antagonism as well as rTNF-α stimulation augment the expression of the reactivity marker SERPINA3 and reduces the expression of synaptogenic molecules. Altogether, these data suggest a complex role for mGluR5 in human astrocytes, since its blockade may have beneficial and detrimental effects under inflammatory conditions.

25-Hydroxycholesterol suppress IFN-γ-induced inflammation in microglia by disrupting lipid raft formation and caveolin-mediated signaling endosomes

Acute microglial activation plays an important role in neuroprotection. However, dysregulated, prolonged microgliosis exacerbates neurodegeneration through excessive release of pro-inflammatory cytokines and cytotoxic factors. Interferon-gamma (IFN-γ), an inflammatory cytokine, exacerbates the detrimental microglial response. Although various anti-inflammatory drugs have been evaluated as interventions for microglia-mediated neuroinflammation, no anti-inflammatories are in clinical use for microgliosis. The present study evaluated the anti-inflammatory mechanisms of oxysterols, blood brain barrier (BBB) penetrable bioactive lipids, revealing that this intervention suppresses neuroinflammation by disrupting membrane lipid raft formation and caveolae-mediated endosomal IFN-γ signaling. We find that 25-hydroxycholesterol (25-HC) rapidly repressed IFN-γ receptor trafficking to lipid rafts in microglia by disrupting raft formation, thereby suppressing microglial inflammatory response. IFN-γ treatment upregulated expression of Cav-1, a major component of caveolae, and IFN-γ signaling was sustained through Cav-1+ signaling endosomes. 25-HC repressed IFN-γ induction of Cav-1 expression in microglia, and subsequently suppressed the chronic inflammatory response. Taken together, these findings demonstrated that 25-HC effectively regulate the inflammatory status of microglia by mediating the formation of rafts and caveolae-dependent signaling endosomes. Given the important roles of IFN-γ and microglia in the pathology of neurodegenerative brain diseases, a novel anti-inflammatory mechanism of 25-HC that is not receptor-dependent, but rather is related to the regulation of membrane rafts and caveolae, suggests a new therapeutic target for inflammatory neurodegenerations.

Phosphoregulation on mitochondria: Integration of cell and organelle responses

Mitochondria are highly integrated organelles that are crucial to cell adaptation and mitigating adverse physiology. Recent studies demonstrate that fundamental signal transduction pathways incorporate mitochondrial substrates into their biological programs. Reversible phosphorylation is emerging as a useful mechanism to modulate mitochondrial function in accordance with cellular changes. Critical serine/threonine protein kinases, such as the c-Jun N-terminal kinase (JNK), protein kinase A (PKA), PTEN-induced kinase-1 (PINK1), and AMP-dependent protein kinase (AMPK), readily translocate to the outer mitochondrial membrane (OMM), the interface of mitochondria-cell communication. OMM protein kinases phosphorylate diverse mitochondrial substrates that have discrete effects on organelle dynamics, protein import, respiratory complex activity, antioxidant capacity, and apoptosis. OMM phosphorylation events can be tempered through the actions of local protein phosphatases, such as mitogen-activated protein kinase phosphatase-1 (MKP-1) and protein phosphatase 2A (PP2A), to regulate the extent and duration of signaling. The central mediators of OMM signal transduction are the scaffold proteins because the relative abundance of these accessory proteins determines the magnitude and duration of a signaling event on the mitochondrial surface, which dictates the biological outcome of a local signal transduction pathway. The concentrations of scaffold proteins, such as A-kinase anchoring proteins (AKAPs) and Sab (or SH3 binding protein 5-SH3BP5), have been shown to influence neuronal survival and vulnerability, respectively, in models of Parkinson's disease (PD), highlighting the importance of OMM signaling to health and disease. Despite recent progress, much remains to be discovered concerning the mechanisms of OMM signaling. Nonetheless, enhancing beneficial OMM signaling events and inhibiting detrimental protein-protein interactions on the mitochondrial surface may represent highly selective approaches to restore mitochondrial health and homeostasis and mitigate organelle dysfunction in conditions such as PD.

Oxysterols and nuclear receptors

Oxysterols are derivatives of cholesterol and an important regulator of cholesterol metabolism, in part due to their role as ligands for nuclear receptors, such as the liver X receptors. Oxysterols are also known to be ligands for the RAR-related orphan receptors, involved in normal T cell differentiation. However, increasing evidence supports a role for oxysterols in the progression of several diseases. Here, we review recent developments in oxysterol research, highlighting the biological functions that oxysterols exert through their target nuclear receptors: the liver X receptors, estrogen receptors, RAR-related orphan receptors and the glucocorticoid receptor. We also bring the regulation of the immune system into the context of interaction between oxysterols and nuclear receptors, discussing the effect of such interaction on the pro-inflammatory function of macrophages and the development of T cells. Finally, we examine the impact that oxysterols have on various disease models, including cancer, Alzheimer's disease and atherosclerosis, stressing the role of nuclear receptors if previously identified. This review underscores the need to consider the multifaceted roles of oxysterols in terms of multiple receptor engagements and selective modulation of these receptors.

25-hydroxycholesterol down-regulates oxysterol binding protein like 2 (OSBPL2) via the p53/SREBF2/NFYA signaling pathway

Oxysterol Binding Protein Like 2 (OSBPL2) is a lipid-binding protein implicated in various cellular processes. Previous studies have shown that depression of OSBPL2 significantly increases the level of cellular 25-hydroxycholesterol (25-OHC) which regulates the expression of lipid-metabolism-related genes. However, whether 25-OHC can regulate the expression of OSBPL2 remains unanswered. This study aimed to explore the molecular mechanism of 25-OHC regulating the expression of OSBPL2. Using dual-luciferase reporter assay, we found a decrease of nuclear transcription factor Y subunit alpha (NFYA) bound with OSBPL2 promoter when HeLa cells were treated with 25-OHC. Furthermore, transcriptome sequencing and RNA interference results revealed that the p53/sterol regulatory element binding transcription factor 2 (SREBF2) signaling pathway was involved in the NFYA-dependent transcription of OSBPL2 induced by 25-OHC. Based on these results, we concluded that pleomorphic adenoma gene 1 (PLAG1) and NFYA participated in the basal transcription of OSBPL2 and that 25-OHC decreased the transcription of OSBPL2 via the p53/SREBF2/NFYA signaling pathway. 25-OHC will accumulate over time in OSBPL2 knockdown cells. These results may provide a new insight into the deafness caused by OSBPL2 mutation.

Analyses of gene expression profiles in the rat dorsal horn of the spinal cord using RNA sequencing in chronic constriction injury rats

Background

Neuropathic pain is caused by damage to the nervous system, resulting in aberrant pain, which is associated with gene expression changes in the sensory pathway. However, the molecular mechanisms are not fully understood.

Methods

Wistar rats were employed for the establishment of the chronic constriction injury (CCI) models. Using the Illumina HiSeq 4000 platform, we examined differentially expressed genes (DEGs) in the rat dorsal horn by RNA sequencing (RNA-seq) between CCI and control groups. Then, enrichment analyses were performed for these DEGs using Gene Ontology (GO) function, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, Hierarchical Cluster, and protein-protein interaction (PPI) network.

Results

A total of 63 DEGs were found significantly changed with 56 upregulated (e.g., Cxcl13, C1qc, Fcgr3a) and 7 downregulated (e.g., Dusp1) at 14 days after CCI. Quantitative reverse-transcribed PCR (qRT-PCR) verified changes in 13 randomly selected DEGs. GO and KEGG biological pathway analyses showed that the upregulated DEGs were mostly enriched in immune response-related biological processes, as well as 14 immune- and inflammation-related pathways. The downregulated DEGs were enriched in inactivation of mitogen-activated protein kinase (MAPK) activity. PPI network analysis showed that Cd68, C1qc, C1qa, Laptm5, and Fcgr3a were crucial nodes with high connectivity degrees. Most of these genes which have previously been linked to immune and inflammation-related pathways have not been reported in neuropathic pain (e.g., Laptm5, Fcgr3a).

Conclusions

Our results revealed that immune and defense pathways may contribute to the generation of neuropathic pain after CCI. These mRNAs may represent new therapeutic targets for the treatment of neuropathic pain.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1316-0) contains supplementary material, which is available to authorized users.