Valproate improves middle cerebral artery occlusion-induced ischemic cerebral disorders in mice and oxygen-glucose deprivation-induced injuries in microglia by modulating RMRP/PI3K/Akt axis

Research progress on mechanisms of ischemic stroke: Regulatory pathways involving Microglia

Microglia, as the intrinsic immune cells in the brain, are activated following ischemic stroke. Activated microglia participate in the pathological processes after stroke through polarization, autophagy, phagocytosis, pyroptosis, ferroptosis, apoptosis, and necrosis, thereby influencing the injury and repair following stroke. It has been established that polarized M1 and M2 microglia exhibit pro-inflammatory and anti-inflammatory effects, respectively. Autophagy and phagocytosis in microglia following ischemia are dynamic processes, where moderate levels promote cell survival, while excessive responses may exacerbate neurofunctional deficits following stroke. Additionally, pyroptosis and ferroptosis in microglia after ischemic stroke contribute to the release of harmful cytokines, further aggravating the damage to brain tissue due to ischemia. This article discusses the different functional states of microglia in ischemic stroke research, highlighting current research trends and gaps, and provides insights and guidance for further study of ischemic stroke.

Gut Microbiota in Ischemic Stroke: Role of Gut Bacteria-Derived Metabolites

Ischemic stroke (IS) remains a leading cause of death and long-term disability globally. Several mechanisms including glutamate excitotoxicity, calcium overload, neuroinflammation, oxidative stress, mitochondrial damage, and apoptosis are known to be involved in the pathogenesis of IS, but the underlying pathophysiology mechanisms of IS are not fully clarified. During the past decade, gut microbiota were recognized as a key regulator to affect the health of the host either directly or via their metabolites. Recent studies indicate that gut bacterial dysbiosis is closely related to hypertension, diabetes, obesity, dyslipidemia, and metabolic syndrome, which are the main risk factors for cardiovascular diseases. Increasing evidence indicates that IS can lead to perturbation in gut microbiota and increased permeability of the gut mucosa, known as "leaky gut," resulting in endotoxemia and bacterial translocation. In turn, gut dysbiosis and impaired intestinal permeability can alter gut bacterial metabolite signaling profile from the gut to the brain. Microbiota-derived products and metabolites, such as short-chain fatty acids (SCFAs), bile acids (BAs), trimethylamine N-oxide (TMAO), lipopolysaccharides (LPS), and phenylacetylglutamine (PAGln) can exert beneficial or detrimental effects on various extraintestinal organs, including the brain, liver, and heart. These metabolites have been increasingly acknowledged as biomarkers and mediators of IS. However, the specific role of the gut bacterial metabolites in the context of stroke remains incompletely understood. In-depth studies on these products and metabolites may provide new insight for the development of novel therapeutics for IS.

Role of Long Non-coding RNA in Nerve Regeneration

Nerve injury can be caused by a variety of factors. It often takes a long time to repair a nerve injury and severe nerve injury is even difficult to heal. Therefore, increasing attention has focused on nerve injury and repair. Long non-coding RNA (lncRNA) is a newly discovered non-coding RNA with a wide range of biological activities. Numerous studies have shown that a variety of lncRNAs undergo changes in expression after nerve injury, indicating that lncRNAs may be involved in various biological processes of nerve repair and regeneration. Herein, we summarize the biological roles of lncRNAs in neurons, glial cells and other cells during nerve injury and regeneration, which will help lncRNAs to be better applied in nerve injury and regeneration in the future.

Transient plasticity response is regulated by histone deacetylase inhibitor in oxygen-glucose deprivation condition

BACKGROUND

The pathological form of synaptic plasticity, ischemic long-term potentiation (iLTP), induced by oxygen and glucose deprivation (OGD), is implicated in the acute phase of stroke with the potentiation of N-methyl-D-aspartate receptor (NMDAR). While there has been widespread attention on the excitatory system, a recent study reported that γ-aminobutyric acid (GABA)ergic system is also involved in iLTP. Valproic acid (VPA), a histone deacetylase inhibitor, protects against ischemic damage. However, whether VPA regulates early phase plasticity in ischemic stroke remains unknown. The present study aims to investigate the potential role and mechanism of VPA in ischemic stroke.

METHODS

A brief exposure of OGD on the hippocampal slices and the induction of photothrombotic ischemia (PTI) were used as ex vivo and in vivo models of ischemic stroke, respectively.

RESULTS

Using extracellular recordings, iLTP was induced in the hippocampal Schaffer collateral pathway following OGD exposure. VPA treatment abolished hippocampal iLTP via GABAA receptor enhancement and extracellular signal-regulated kinase (ERK) phosphorylation. Administration of VPA reduced brain infarct volume and motor dysfunction in mice with PTI. Moreover, VPA protected against ischemic injury by upregulating the GABAergic system and ERK phosphorylation, as well as by reducing of matrix metalloproteinase in a PTI-induced ischemic stroke model.

CONCLUSIONS

Together, this study revealed the protection of VPA in ex vivo OGD-induced pathological form of neuroplasticity and in vivo PTI-induced brain damage and motor dysfunction through rescuing GABAergic deficiency and the pathological hallmarks of ischemia.

Long non-coding RNA lincRNA-erythroid prosurvival (EPS) alleviates cerebral ischemia/reperfusion injury by maintaining high-temperature requirement protein A1 (Htra1) stability through recruiting heterogeneous nuclear ribonucleoprotein L (HNRNPL)

This study aimed at investigating the role and mechanism of lincRNA-EPS (erythroid prosurvival) in cerebral ischemia/reperfusion (CIR) injury. The results showed that the overexpression of lincRNA-EPS was able to reduce the levels of interleukin-6, tumor necrosis factor-alpha and interleukin-1β stimulated in the OGD-treated Neuro-2a (N-2a) cells. The levels of reactive oxygen species and malondialdehyde were enhanced while the superoxide dismutase levels were reduced by oxygen and glucose deprivation (OGD) treatment, in which the lincRNA-EPS overexpression could reverse this effect in the cells. LincRNA-EPS interacted with high-temperature requirement protein A1 (Htra1) and heterogeneous nuclear ribonucleoprotein L (HNRNPL), and their depletion inhibited the Htra1 mRNA stability in N-2a cells. HNRNPL knockdown blocked lincRNA-EPS overexpression-induced Htra1 expression in the cells. The depletion of Htra1 could rescue lincRNA-EPS overexpression-mediated N-2a cell injury, inflammation, and oxidative stress induced by OGD. Functionally, lincRNA-EPS alleviates CIR injury of the middle cerebral artery occlusion/reperfusion mice in vivo. In conclusion, lincRNA-EPS attenuates CIR injury by maintaining Htra1 stability through recruiting HNRNPL.

LncRNA RMRP knockdown promotes proliferation and migration of Schwann cells by mediating the miR-766-5p/CAND1 axis

The proliferation and migration of Schwann cells (SCs) promote nerve regeneration after facial nerve injury. In recent years, the role of long noncoding RNAs (lncRNAs) in regulating SC proliferation and migration has been gradually uncovered. However, there is little evidence on the function of lncRNA RMRP (lnc-RMRP) in SC growth. In the present study, we performed loss-of-function and overexpression assays to explore the function of lnc-RMRP in SCs. The relationships between lnc-RMRP, miR-766-5p and CAND1 (cullin-associated and neddylation-dissociated 1) were analyzed using bioinformatics analysis, luciferase detection, RNA binding protein immunoprecipitation and RNA pulldown methods. CCK-8, EdU, Transwell and wound healing assays were utilized for the detections of cell proliferation and migration. We found that lnc-RMRP silencing enhanced cell proliferation and migration of SCs, while lnc-RMRP overexpression showed the opposite effect. Mechanistically, lnc-RMRP directly bound to and negatively modulated the expression of miR-766-5p. MiR-766-5p knockdown decreased cell viability, proliferation and migration of SCs, and also reversed the effects of lnc-RMRP silencing. In addition, lnc-RMRP positively regulated CAND1 expression by sponging miR-766-5p. Upregulation of CAND1 rescued the function of lnc-RMRP knockdown in regulating SC proliferation and migration. These data suggested that lnc-RMRP played a significant role in SC proliferation and migration, indicating that lnc-RMRP might be a potential therapeutic target for the treatment of facial nerve injury.

Long Non-coding RNAs and Circular RNAs: Insights Into Microglia and Astrocyte Mediated Neurological Diseases

Microglia and astrocytes maintain tissue homeostasis in the nervous system. Both microglia and astrocytes have pro-inflammatory phenotype and anti-inflammatory phenotype. Activated microglia and activated astrocytes can contribute to several neurological diseases. Long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), two groups of non-coding RNAs (ncRNAs), can function as competing endogenous RNAs (ceRNAs) to impair the microRNA (miRNA) inhibition on targeted messenger RNAs (mRNAs). LncRNAs and circRNAs are involved in various neurological disorders. In this review, we summarized that lncRNAs and circRNAs participate in microglia dysfunction, astrocyte dysfunction, neuron damage, and inflammation. Thereby, lncRNAs and circRNAs can positively or negatively regulate neurological diseases, including spinal cord injury (SCI), traumatic brain injury (TBI), ischemia-reperfusion injury (IRI), stroke, neuropathic pain, epilepsy, Parkinson’s disease (PD), multiple sclerosis (MS), and Alzheimer’s disease (AD). Besides, we also found a lncRNA/circRNA-miRNA-mRNA regulatory network in microglia and astrocyte mediated neurological diseases. Through this review, we hope to cast light on the regulatory mechanisms of lncRNAs and circRNAs in microglia and astrocyte mediated neurological diseases and provide new insights for neurological disease treatment.

LncRNA RNA Component of Mitochondrial RNA-Processing Endoribonuclease Promotes AKT-Dependent Breast Cancer Growth and Migration by Trapping MicroRNA-206

The RNA component of mitochondrial RNA-processing endoribonuclease (RMRP) was recently shown to play a role in cancer development. However, the function and mechanism of RMRP during cancer progression remain incompletely understood. Here, we report that RMRP is amplified and highly expressed in various malignant cancers, and the high level of RMRP is significantly associated with their poor prognosis, including breast cancer. Consistent with this, ectopic RMRP promotes proliferation and migration of TP53-mutated breast cancer cells, whereas depletion of RMRP leads to inhibition of their proliferation and migration. RNA-seq analysis reveals AKT as a downstream target of RMRP. Interestingly, RMRP indirectly elevates AKT expression by preventing AKT mRNA from miR-206-mediated targeting via a competitive sequestering mechanism. Remarkably, RMRP endorses breast cancer progression in an AKT-dependent fashion, as knockdown of AKT completely abolishes RMRP-induced cancer cell growth and migration. Altogether, our results unveil a novel role of the RMRP-miR-206-AKT axis in breast cancer development, providing a potential new target for developing an anti-breast cancer therapy.

Cadmium induces the thymus apoptosis of pigs through ROS-dependent PTEN/PI3K/AKT signaling pathway

Cadmium (Cd) is a transition metal that is toxic to living organisms in the environment and endangers living organisms. To explore whether Cd induces apoptosis in pig thymus and its possible mechanism, the role Cd induction of the PTEN/PI3K/Akt pathway in apoptosis of thymus cells was studied in pigs. We found that Cd exposure (the feed is treated with Cd) significantly increased Cd accumulation in the thymus of pigs. The TUNEL assay confirmed the typical apoptotic characteristics of thymus in Cd group. Moreover, in the Cd group, the activities of antioxidant indices decreased significantly, while the levels of oxidative stress indexes increased significantly, and the mRNA levels of GSH, CAT, Gpx1, GST, SOD1, and SOD2 decreased obviously. Moreover, the mRNA and protein levels of PTEN/PI3K/AKT and apoptosis-related genes were detected by qPCR and western blotting. The results show that the expressions of PI3K and AKT decreased, while the expression of PTEN increased, indicating that pathway activated. With the PTEN/PI3K/AKT pathway regulating, Bcl-2 expression decreased. Conversely, the mRNA and protein expression of apoptosis-related genes were up-regulated. In conclusion, accumulation of Cd in the pigs caused oxidative damage to immune tissues. In addition, Cd-induced oxidative stress activates the PTEN/PI3K/AKT pathway, inducing apoptosis in the thymus of pigs.

Construction of lncRNA-Mediated ceRNA Network for Investigating Immune Pathogenesis of Ischemic Stroke

Ischemic stroke (IS) is a common and serious neurological disease. Extensive evidence indicates that activation of the immune system contributes significantly to the development of IS pathology. In recent years, some long non-coding RNAs (lncRNAs), acting as competing endogenous RNAs (ceRNAs), have been reported to affect IS process, especially the immunological response after stroke. However, the roles of lncRNA-mediated ceRNAs in immune pathogenesis of IS are not systemically investigated. In the present study, we generated a global immune-related ceRNA network containing immune-related genes (IRGs), miRNAs, and lncRNAs based on experimentally verified interactions. Further, we excavated an IS immune-related ceRNA (ISIRC) network through mapping significantly differentially expressed IRGs, miRNAs, and lncRNAs of patients with IS into the global network. We analyzed the topological properties of the two networks, respectively, and found that lncRNA NEAT1 and lncRNA KCNQ1OT1 played core roles in aforementioned two immune-related networks. Moreover, the results of functional enrichment analyses revealed that lncRNAs in the ISIRC network were mainly involved in several immune-related biological processes and pathways. Finally, we identified 17 lncRNAs which were highly related to the immune mechanism of IS through performing random walk with restart for the ISIRC network. Importantly, it has been confirmed that NEAT1, KCNQ1OT1, GAS5, and RMRP could regulate immuno-inflammatory response after stroke, such as production of inflammatory factors and activation of the immune cells. Our results suggested that lncRNAs exerted an important role in the immune pathogenesis of IS and provided a new strategy to do research on IS.

Upregulated LINC00319 aggravates neuronal injury induced by oxygen-glucose deprivation via modulating miR-200a-3p

Ischemic stroke is one of the main causes of physical disability and mortality worldwide. Long non-coding RNAs (lncRNAs) are reported to be dysregulated in various biological progressions and serve important roles in pathological processes of cerebral ischemia. However, their biological actions and potential mechanisms in the progression of ischemic stroke remain unknown. The present study aimed to investigate the functions of LINC00319 on ischemic brain injury. It was identified that LINC00319 was significantly upregulated in the Gene Expression Omnibus profile of ischemic stroke. Furthermore, LINC00319 overexpression elevated caspase-3 activity and increased the apoptotic rate of neuronal cells, as well as decreased cell viability and glucose uptake. It was also demonstrated that LINC00319 participated in oxygen-glucose deprivation (OGD)-induced cerebral ischemic injury. LINC00319 could competitively bind with microRNA (miR)-200a-3p and decrease its expression. Moreover, miR-200a-3p could partly offset the negative effects of LINC00319 overexpression on neuronal injury caused by OGD. Collectively, the present results suggested that LINC00319 promoted apoptosis and aggravated neuronal injury induced by OGD by regulating miR-200a-3p, which may be important for ischemic stroke treatment.

Long Non-coding RNA RMRP in the Pathogenesis of Human Disorders

RNA component of mitochondrial RNA processing endoribonuclease (RMRP) is a non-coding transcript firstly acknowledged for its association with the cartilage-hair hypoplasia (CHH) syndrome, a rare autosomal recessive condition. This transcript has been spotted in both nucleus and mitochondria. In addition to its role in the pathogenesis of CHH, RMRP participates in the pathogenesis of cancers. Independent studies in bladder cancer, colon cancer, hepatocellular carcinoma, lung cancer, breast carcinoma and multiple myeloma have confirmed the oncogenic effects of RMRP. Mechanistically, RMRP serves as a sponge for some miRNAs such as miR-206, miR-613, and miR-217. In addition to these miRNAs, expressions of tens of miRNAs have been altered following RMRP silencing, implying the vast extent of RMRP/miRNA network. In the present narrative review, we explain the role of RMRP in the development of cancers and some other non-malignant disorders.

Receptors, Channel Proteins, and Enzymes Involved in Microglia-mediated Neuroinflammation and Treatments by Targeting Microglia in Ischemic Stroke

Stroke is the largest contributor to global neurological disability-adjusted life-years, posing a huge economic and social burden to the world. Though pharmacological recanalization with recombinant tissue plasminogen activator and mechanical thrombectomy have greatly improved the prognosis of patients with ischemic stroke, clinically, there is still no effective treatment for the secondary injury caused by cerebral ischemia. In recent years, more and more evidences show that neuroinflammation plays a pivotal role in the pathogenesis and progression of ischemic cerebral injury. Microglia are brain resident innate immune cells and act the role peripheral macrophages. They play critical roles in mediating neuroinflammation after ischemic stroke. Microglia-mediated neuroinflammation is not an isolated process and has complex relationships with other pathophysiological processes as oxidative/nitrative stress, excitotoxicity, necrosis, apoptosis, pyroptosis, autophagy, and adaptive immune response. Upon activation, microglia differentially express various receptors, channel proteins, and enzymes involved in promoting or inhibiting the inflammatory processes, making them the targets of intervention for ischemic stroke. To inhibit microglia-related neuroinflammation and promote neurological recovery after ischemic stroke, numerous biochemical agents, cellular therapies, and physical methods have been demonstrated to have therapeutic potentials. Though accumulating experimental evidences have demonstrated that targeting microglia is a promising approach in the treatment of ischemic stroke, the clinical progress is slow. Till now, no clinical study could provide convincing evidence that any biochemical or physical therapies could exert neuroprotective effect by specifically targeting microglia following ischemic stroke.