Mdivi-1 Protects Epileptic Hippocampal Neurons from Apoptosis via Inhibiting Oxidative Stress and Endoplasmic Reticulum Stress in Vitro

PDCD4 silencing alleviates KA‑induced neurotoxicity of HT22 cells by inhibiting endoplasmic reticulum stress via blocking the MAPK/NF‑κB signaling pathway

Human programmed cell death 4 (PDCD4) has been reported to participate in multiple neurological diseases. However, the role of PDCD4 in epilepsy, as well as its underlying mechanism, remains unclear. To induce excitotoxicity, 100 µM kainic acid (KA) was applied for the stimulation of HT22 cells for 12 h. Initially, the mRNA and protein expression levels of PDCD4 were evaluated using reverse transcription-quantitative PCR and western blotting. A lactate dehydrogenase assay was performed to detect cell injury. Cell apoptosis was assessed using flow cytometry and western blotting was performed to determine the expression levels of apoptosis-related proteins. Oxidative stress was detected using dichlorodihydrofluorescein diacetate staining, and malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) assay kits. Furthermore, the expression levels of MAPK/NF-κB signaling-related proteins and endoplasmic reticulum (ER) stress-related proteins C/EBP homologous protein, glucose-regulated protein 78, activating transcription factor 4 and phosphorylated-eukaryotic initiation factor-2α were assessed by western blotting. It was revealed that PDCD4 expression was markedly elevated in KA-induced HT22 cells, whereas PDCD4 silencing alleviated KA-induced neurotoxicity of HT22 cells by alleviating cell injury and inhibiting apoptosis. In addition, PDCD4 silencing reduced the levels of reactive oxygen species and MDA, but elevated those of SOD and GSH-Px. PDCD4 silencing also suppressed ER stress by blocking the MAPK/NF-κB signaling pathway. By contrast, the MAPK agonist phorbol myristate acetate reversed the effects of PDCD4 silencing on KA-induced neurotoxicity and oxidative stress in HT22 cells. In conclusion, PDCD4 silencing alleviated KA-induced neurotoxicity and oxidative stress in HT22 cells by suppressing ER stress through the inhibition of the MAPK/NF-κB signaling pathway, which may provide novel insights into the treatment of epilepsy.

Combination of Zearalenone and Deoxynivalenol Induces Apoptosis by Mitochondrial Pathway in Piglet Sertoli Cells: Role of Endoplasmic Reticulum Stress

Zearalenone (ZEA) and deoxynivalenol (DON) are widely found in various feeds, which harms livestock's reproductive health. Both mitochondria and endoplasmic reticulum (ER) can regulate cell apoptosis. This study aimed to explore the regulatory mechanism of endoplasmic reticulum stress (ERS) on ZEA- combined with DON-induced mitochondrial pathway apoptosis in piglet Sertoli cells (SCs). The results showed that ZEA + DON damaged the ultrastructure of the cells, induced apoptosis, decreased mitochondrial membrane potential, promoted the expression of cytochrome c (CytC), and decreased the cell survival rate. Furthermore, ZEA + DON increased the relative mRNA and protein expression of Bid, Caspase-3, Drp1, and P53, while that of Bcl-2 and Mfn2 declined. ZEA + DON was added after pretreatment with 4-phenylbutyric acid (4-PBA). The results showed that 4-PBA could alleviate the toxicity of ZEA + DON toward SCs. Compared with the ZEA + DON group, 4-PBA improved the cell survival rate, decreased the apoptosis rate, inhibited CytC expression, and increased mitochondrial membrane potential, and the damage to the cell ultrastructure was alleviated. Moreover, after pretreatment with 4-PBA, the relative mRNA and protein expression of Bid, Caspase-3, Drp1, and P53 were downregulated, while the relative mRNA and protein expression of Bcl-2 and Mfn2 were upregulated. It can be concluded that ERS plays an important part in the apoptosis of SCs co-infected with ZEA-DON through the mitochondrial apoptosis pathway, and intervention in this process can provide a new way to alleviate the reproductive toxicity of mycotoxins.

Age-related cataract: GSTP1 ubiquitination and degradation by Parkin inhibits its anti-apoptosis in lens epithelial cells

PURPOSE

Oxidative stress-induced apoptosis of lens epithelial cells (LECs) contributes to the pathogenesis of age-related cataract (ARC). The purpose of this research is to underlie the potential mechanism of E3 ligase Parkin and its oxidative stress-associated substrate in cataractogenesis.

METHODS

The central anterior capsules were obtained from patients with ARC, Emory mice, and corresponding controls. SRA01/04 cells were exposed to H₂O₂ combined with cycloheximide (a translational inhibitor), MG-132 (a proteasome inhibitor), chloroquine (an autophagy inhibitor), Mdivi-1 (a mitochondrial division inhibitor), respectively. Co-immunoprecipitation was employed to detect protein-protein interactions and ubiquitin-tagged protein products. Levels of proteins and mRNA were evaluated by western blotting and quantitative RT-PCR assays.

RESULTS

Glutathione-S-transferase P1 (GSTP1) was identified as a novel Parkin substrate. Compared with corresponding controls, GSTP1 was significantly decreased in the anterior lens capsules obtained from human cataracts and Emory mice. Similarly, GSTP1 was declined in H₂O₂-stimulated SRA01/04 cells. Ectopic expression of GSTP1 mitigated H₂O₂-induced apoptosis, whereas silencing GSTP1 aggregated apoptosis. In addition, H₂O₂ stimulation and Parkin overexpression could promote the degradation of GSTP1 through the ubiquitin-proteasome system, autophagy-lysosome pathway, and mitophagy. After co-transfection with Parkin, the non-ubiquitinatable GSTP1 mutant maintained its anti-apoptotic function, while wildtype GSTP1 failed. Mechanistically, GSTP1 might promote mitochondrial fusion through upregulating Mitofusins 1/2 (MFN1/2).

CONCLUSION

Oxidative stress induces LECs apoptosis via Parkin-regulated degradation of GSTP1, which may provide potential targets for ARC therapy.

Inhibition of Mitochondrial Fission Alleviates Zearalenone-Induced Mitochondria-Associated Endoplasmic Reticulum Membrane Dysfunction in Piglet Sertoli Cells

This study aimed to investigate the effects of zearalenone (ZEA) on piglet Sertoli cell (SC)-mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) based on mitochondrial fission, and to explore the molecular mechanism of ZEA-induced cell damage. After the SCs were exposed to the ZEA, the cell viability decreased, the Ca2+ levels increased, and the MAM showed structural damage. Moreover, glucose-regulated protein 75 (Grp75) and mitochondrial Rho-GTPase 1 (Miro1) were upregulated at the mRNA and protein levels. However, phosphofurin acidic cluster protein 2 (PACS2), mitofusin2 (Mfn2), voltage-dependent anion channel 1 (VDAC1), and inositol 1,4,5-trisphosphate receptor (IP3R) were downregulated at the mRNA and protein levels. A pretreatment with mitochondrial division inhibitor 1 (Mdivi-1) decreased the ZEA-induced cytotoxicity toward the SCs. In the ZEA + Mdivi-1 group, the cell viability increased, the Ca2+ levels decreased, the MAM damage was repaired, and the expression levels of Grp75 and Miro1 decreased, while those of PACS2, Mfn2, VDAC1, and IP3R increased compared with those in the ZEA-only group. Thus, ZEA causes MAM dysfunction in piglet SCs through mitochondrial fission, and mitochondria can regulate the ER via MAM.

Anti-Seizure and Neuronal Protective Effects of Irisin in Kainic Acid-Induced Chronic Epilepsy Model with Spontaneous Seizures

An increased level of reactive oxygen species is a key factor in neuronal apoptosis and epileptic seizures. Irisin reportedly attenuates the apoptosis and injury induced by oxidative stress. Therefore, we evaluated the effects of exogenous irisin in a kainic acid (KA)-induced chronic spontaneous epilepsy rat model. The results indicated that exogenous irisin significantly attenuated the KA-induced neuronal injury, learning and memory defects, and seizures. Irisin treatment also increased the levels of brain-derived neurotrophic factor (BDNF) and uncoupling protein 2 (UCP2), which were initially reduced following KA administration. Furthermore, the specific inhibitor of UCP2 (genipin) was administered to evaluate the possible protective mechanism of irisin. The reduced apoptosis, neurodegeneration, and spontaneous seizures in rats treated with irisin were significantly reversed by genipin administration. Our findings indicated that neuronal injury in KA-induced chronic epilepsy might be related to reduced levels of BDNF and UCP2. Moreover, our results confirmed the inhibition of neuronal injury and epileptic seizures by exogenous irisin. The protective effects of irisin may be mediated through the BDNF-mediated UCP2 level. Our results thus highlight irisin as a valuable therapeutic strategy against neuronal injury and epileptic seizures.

Cdk5 Promotes Mitochondrial Fission via Drp1 Phosphorylation at S616 in Chronic Ethanol Exposure-Induced Cognitive Impairment

Excessive alcohol consumption can lead to alterations in brain structure and function, even causing irreversible learning and memory disorders. The hippocampus is one of the most sensitive areas to alcohol neurotoxicity in the brain. Accumulating evidence indicates that mitochondrial dysfunction contributes to alcohol neurotoxicity. However, little is known about the underlying molecular mechanisms. In this study, we found that chronic exposure to ethanol caused abnormal mitochondrial fission/fusion and morphology by activating the mitochondrial fission protein dynamin-related protein 1 (Drp1) and upregulating Drp1 receptors, such as fission protein 1 (Fis1), mitochondrial dynamics protein of 49 kDa (Mid49), and mitochondrial fission factor (Mff), combined with decreasing optic atrophy 1 (Opa1) and mitochondrial fusion protein mitofusin 1 (Mfn1) levels. In addition, mitochondrial division inhibitor 1 (mdivi-1) abrogated ethanol-induced mitochondrial dysfunction and improved hippocampal synapses and cognitive function in ethanol-exposed mice. Chronic ethanol exposure also resulted in cyclin-dependent kinase 5 (Cdk5) overactivation, as shown by the increase in the levels of Cdk5 and its activator P25 in the hippocampus. Furthermore, a Cdk5/P25 inhibitor (roscovitine) or Cdk5 knockdown using small interfering RNA (LVi-Cdk5) exerted neuroprotection by inhibiting abnormal mitochondrial fission through Drp1 phosphorylation at Ser616 and mitochondrial translocation after chronic ethanol exposure. Taken together, the present study demonstrated that inhibition of aberrant Cdk5 activation attenuates hippocampal neuron injury and cognitive deficits induced by chronic exposure to ethanol through Drp1-mediated mitochondrial fission and mitochondrial dysfunction. Interfering with this pathway might serve as a potential therapeutic approach to prevent ethanol-induced neurotoxicity in the brain.

Effects of GABAB receptor positive allosteric modulator BHF177 and IRS-1 on apoptosis of hippocampal neurons in rats with refractory epilepsy via the PI3K/Akt pathway

The present study was conducted to determine the effects of the γ-aminobutyric acid B (GABA_B ) receptor positive allosteric modulator BHF177 on refractory epilepsy (RE). An RE rat model was initially established via treatment with lithium-pilocarpine. The RE rats were then treated with BHF177 or the GABA_B receptor antagonist CGP46381, followed by recording of their seizure rate and assessment of their spatial learning in the Morris water maze test. Treatment of BHF177 reduced the seizure intensity, whereas this effect was revered upoj treatment with CGP46381. Immunohistochemistry revealed that BHF177 treatment diminished P-glycoprotein (P-gp) expression in the hippocampal tissues of RE rats. Next, we found that BHF177 activated GABA_B receptor, resulting in upregulated expression of insulin receptor substrate 1 (IRS-1) and PI3K, as well as antiapoptotic factors (Bcl-2 and mTOR), along with suppression of the apoptosis factors Bax and cleaved caspase-3 in the hippocampal tissues. Further, activation of GABA_B receptors by BHF177 alleviated the inflammatory response in hippocampal tissues of RE rats, as evidenced by reduced VCAM-1, ICAM-1, and tumor necrosis factor-α levels. Next, we treated primary cultured rat hippocampal neurons with BHF177 and the IRS-1 selective inhibitor NT157. BHF177 inhibited hippocampal apoptosis in rat hippocampal neurons by regulating the IRS-1/PI3K/Akt axis through crosstalk between GABA_B and insulin-like growth factor-1 receptors. Collectively, our findings indicate that the BHF177 inhibited neuron apoptosis, thus protecting against RE through the IRS-1/PI3K/Akt axis, which may present a new therapeutic channel for RE.

The Aerial Parts of Bupleurum Chinense DC. Aromatic Oil Attenuate Kainic Acid-Induced Epilepsy-Like Behavior and Its Potential Mechanisms

The aerial parts of Bupleurum Chinense DC. aromatic oil (BAO) were a well-known Chinese herbal medicine plant extract used to treat epilepsy. This study aimed to explore the therapeutic effect of BAO on kainic acid- (KA-) induced epileptic rats and the possible mechanism of its antiepileptic effect. The composition and content of BAO were analyzed by GC-MS, and BAO was administered orally to alleviate the epileptic behavior induced by KA brain injection. The behavior of epileptic rats was determined by Racine grading criteria. And hematoxylin-eosin staining (HE), Nissl staining, immunohistochemistry, Elisa, Western blot, and other methods were used to study the antiepileptic mechanism of BAO, and the possible mechanism was verified by the epileptic cell model of hippocampal neurons induced by the low-Mg2+ extracellular fluid. BAO was mainly composed of terpenoids and aliphatic compounds. And BAO could improve KA-induced epilepsy-like behavior, neuroinflammation, and neurotransmitter abnormalities in the hippocampus. Furthermore, BAO could regulate the expression of GABA, NMDAR1, Notch1, and MAP2 to improve the symptoms of epilepsy. These results were also validated at the cellular level. These results indicated that BAO could alleviate the epilepsy-like behavior through the action of the Notch/NMDAR/GABA pathway.

Methyl-CpG-Binding Domain Protein 3 Promotes Seizures by Recruiting Methyltransferase DNMT1 to Enhance TREM2 Methylation

Epilepsy represents a hazardous neurological disorder, underpinned by a pathophysiological process that is yet to be fully understood. Here, we aimed to elucidate the effect of methyl-CpG-binding domain protein 3 (MBD3) on hippocampal neuronal damage in epileptic mice by targeting the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway. The expression of MBD3 was determined by Western blot in a hippocampal neuronal culture (HNC) epileptic model established using the low Mg2+ECF culture method. The interaction between MBD3 and DNA methyltransferase 1 (DNMT1) was determined via co-immunoprecipitation and mass spectrometry analysis. Bisulfite modification and sequencing was performed to evaluate the degree of methylation of triggering receptor expressed on myeloid cells 2 (TREM2). The viability and apoptosis of hippocampal neurons were detected by CCK-8 and TUNEL assays, respectively. Finally, the effect of MBD3 was verified in vivo. MBD3 was highly expressed in the HNC model of epilepsy, with its interaction with DNMT1 found to promote the hypermethylation of TREM2 at site cg25748868. Additionally, decreased TREM2 and inhibited PI3K/Akt pathway was observed in the HNC epileptic model. Simultaneous inhibition of MBD3 and DNMT1 decreased the methylation level at cg25748868, up-regulated TREM2 expression, and activated the PI3K/Akt pathway, thereby arresting neuronal damage. Inhibition of MBD3 reduced the level of epileptic seizures, down-regulated cg25748868 methylation, activated TREM2-mediated signaling pathways, and alleviated hippocampal neuronal damage in the acute seizure mouse models. The present study unveiled that MBD3 and DNMT1 synergistically enhanced hypermethylation of cg25748868 in TREM2, and promoted the onset of epilepsy via inhibition of the PI3K/Akt pathway.

miR-485 inhibits histone deacetylase HDAC5, HIF1α and PFKFB3 expression to alleviate epilepsy in cellular and rodent models

We investigated the role of microRNA (miR)-485 and its downstream signaling molecules on mediating epilepsy in cellular and rat models. We established a cellular epilepsy model by exposing hippocampal neurons to magnesium and a rat model by treating ICR mice with lithium chloride (127 mg/kg) and pilocarpine (30 mg/kg). We confirmed that miR-485 could bind and inhibit histone deacetylase 5 (HDAC5) and then measured expression of miR-485 and in mice and cells. Cells were transfected with overexpression or knockdown of miR-485, HDAC5, hypoxia-inducible factor-1alpha (HIF1α), or 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 enzyme (PFKFB3) to verify their roles in apoptosis, oxidative stress, and inflammation in epileptic hippocampal neurons. Binding relationship between miR-485, HDAC5, HIF1α, and PFKFB3 was verified. Oxidative stress and inflammation marker levels in epilepsy model mice were assessed. miR-485 was downregulated and HDAC5 was upregulated in cell and animal model of epilepsy. Seizure, neuronal apoptosis, oxidative stress (increased SOD and GSH-Px expression and decreased MDA and 8-OHdG expression) and inflammation (reduced IL-1β, TNF-α, and IL-6 expression) were reduced by miR-485 in epileptic cells. HIF1α and PFKFB3 expression was reduced by HDAC5 knockdown in cells, which was recapitulated in vivo. Thus, miR-485 alleviates neuronal damage and epilepsy by inhibiting HDAC5, HIF1α, and PFKFB3.

Differential ROS-Mediated Phosphorylation of Drp1 in Mitochondrial Fragmentation Induced by Distinct Cell Death Conditions in Cerebellar Granule Neurons

Reactive oxygen species (ROS) production has been associated with neuronal death. ROS are also involved in mitochondrial fission, which is mediated by Dynamin-related protein 1 (Drp1). The regulation of mitochondrial fragmentation mediated by Drp1 and its relationship to mitochondrial ROS (mtROS) in neuronal death have not been completely clarified. The aim of this study is to evaluate the role of mtROS in cell death and their involvement in the activation of Drp1 and mitochondrial fission in a model of cell death of cultured cerebellar granule neurons (CGN). Neuronal death of CGN induced by potassium deprivation (K5) and staurosporine (ST) triggers mitochondrial ROS production and mitochondrial fragmentation. K5 condition evoked an increase of Drp1 phosphorylation at Ser616, but ST treatment led to a decrease of Drp1 phosphorylation. Moreover, the death of CGN induced by both K5 and ST was markedly reduced in the presence of MitoTEMPO; however, mitochondrial morphology was not recovered. Here, we show that the mitochondria are the initial source of ROS involved in the neuronal death of CGN and that mitochondrial fragmentation is a common event in cell death; however, this process is not mediated by Drp1 phosphorylation at Ser616.

Dynamic-related protein 1 inhibitor eases epileptic seizures and can regulate equilibrative nucleoside transporter 1 expression

Background

Dynamic-related protein 1 (Drp1) is a key protein involved in the regulation of mitochondrial fission, and it could affect the dynamic balance of mitochondria and appears to be protective against neuronal injury in epileptic seizures. Equilibrative nucleoside transporter 1 (ENT1) is expressed and functional in the mitochondrial membrane that equilibrates adenosine concentration across membranes. Whether Drp1 participates in the pathogenesis of epileptic seizures via regulating function of ENT1 remains unclear.

Methods

In the present study, we used pilocarpine to induce status epilepticus (SE) in rats, and we used mitochondrial division inhibitor 1 (Mdivi-1), a selective inhibitor to Drp1, to suppress mitochondrial fission in pilocarpine-induced SE model. Mdivi-1administered by intraperitoneal injection before SE induction, and the latency to firstepileptic seizure and the number of epileptic seizures was thereafter observed. The distribution of Drp1 was detected by immunofluorescence, and the expression patterns of Drp1 and ENT1 were detected by Western blot. Furthermore, the mitochondrial ultrastructure of neurons in the hippocampal CA1 region was observed by transmission electron microscopy.

Results

We found that Drp1 was expressed mainly in neurons and Drp1 expression was significantly upregulated in the hippocampal and temporal neocortex tissues at 6 h and 24 h after induction of SE. Mitochondrial fission inhibitor 1 attenuated epileptic seizures after induction of SE, reduced mitochondrial damage and ENT1 expression.

Conclusions

These data indicate that Drp1 is upregulated in hippocampus and temporal neocortex after pilocarpine-induced SE and the inhibition of Drp1 may lead to potential therapeutic target for SE by regulating ENT1 after pilocarpine-induced SE.

IL-33 Alleviated Brain Damage via Anti-apoptosis, Endoplasmic Reticulum Stress, and Inflammation After Epilepsy

Interleukin (IL)-33 belongs to a novel chromatin-associated cytokine newly recognized by the IL-1 family, and its specific receptor is the orphan IL-1 receptor (ST2). Cumulative evidence suggests that IL-33 plays a crucial effect on the pathological changes and pathogenesis of central nervous system (CNS) diseases and injuries, such as recurrent neonatal seizures (RNS). However, the specific roles of IL-33 and its related molecular mechanisms in RNS remain confused. In the present study, we investigated the protein expression changes and co-localized cell types of IL-33 or ST2, as well as the effect of IL-33 on RNS-induced neurobehavioral defects, weight loss, and apoptosis. Moreover, an inhibitor of IL-33, anti-IL-33 was performed to further exploited underlying mechanisms. We found that administration of IL-33 up-regulated the expression levels of IL-33 and ST2, and increased the number of its co-localization with Olig-2-positive oligodendrocytes and NeuN-positive neurons at 72 h post-RNS. Noteworthily, RNS-induced neurobehavioral deficits, bodyweight loss, and spatial learning and memory impairment, as well as cell apoptosis, were reversed by IL-33 pretreatment. Additionally, the increase in IL-1β and TNF-α levels, up-regulation of ER stress, as well as a decrease in anti-apoptotic protein Bcl-2 and an increase in pro-apoptotic protein CC-3 induced by RNS are prevented by administration of IL-33. Moreover, IL-33 in combination with Anti-IL-33 significantly inverted the effects of IL-33 or Anti-IL-33 alone on apoptosis, ER stress, and inflammation. Collectively, these data suggest that IL-33 attenuates RNS-induced neurobehavioral disorders, bodyweight loss, and spatial learning and memory deficits, at least in part through mechanisms involved in inhibition of apoptosis, ER stress, and neuro-inflammation.

The roles of ER stress in epilepsy: Molecular mechanisms and therapeutic implications

Epilepsies are a diverse group of neurological disorders, which are characterized by spontaneous recurrent seizures. Although a wide range of pathogenic mechanisms such as alterations in ion channels, inflammation and neuronal loss have been reported to be implicated in the epileptogenesis, the underlying pathogenesis of epilepsy remains unclear currently. Endoplasmic reticulum (ER) stress is regarded as a condition that unfolded or misfolded proteins accumulate in the ER lumen. Excessive or prolonged ER stress causes the activation of the unfolded protein response (UPR) to buffer ER stress and restore ER homeostasis. Increasing evidence has indicated dysregulated ER stress during epileptogenesis, which may participate in various pathological processes associated with epilepsy. In this present review, we summarized recent advances in the involvement of ER stress in the pathogenesis of epilepsy. Additionally, the antiepileptic and neuroprotective effects of interventions targeting ER stress were also discussed.

Mdivi-1 attenuates lipopolysaccharide-induced acute lung injury by inhibiting MAPKs, oxidative stress and apoptosis

Sepsis is among the most devastating events in intensive care units. As a complication of sepsis, acute lung injury (ALI) is common and highly associated with poor outcome. The present study demonstrated that abnormal mitochondrial dynamics play a pivotal role in lipopolysaccharide (LPS)-induced ALI. Inhibiting the mitochondrial fission with the specific inhibitor-1 (Mdivi-1) ameliorated ALI as assessed by hematoxylin and eosin (H&E) staining and wet/dry ratio. Furthermore, Mdivi-1 reduced mitogen-activated protein kinases (MAPKs) activation, oxidative stress and apoptosis in the lungs. Plasma pro-inflammation cytokines were also reduced significantly in Mdivi-1-treated mice. In vitro study revealed that Mdivi-1 protected the macrophages from LPS-induced MAPKs activation, oxidative stress and cell apoptosis. Mdivi-1 also inhibited the release of pro-inflammatory cytokines. Morphological analysis showed that Mdivi-1 rescued the macrophages from LPS-induced mitochondrial fragmentation. Moreover, LPS treatment induced significant phosphorylation of Drp1 at Ser616, dephosphorylation at Ser637 and translocation of Drp1 from the cytoplasm to mitochondria, while Mdivi-1 inhibited those effects. Thus, modification of fission to rebuild mitochondrial homeostasis may offer an innovative opportunity for developing therapeutic strategies against ALI.

Novel Positive Allosteric Modulators of Glutamate Transport Have Neuroprotective Properties in an in Vitro Excitotoxic Model

Dysfunction of excitatory amino acid transporters (EAATs) has been implicated in the pathogenesis of various neurological disorders, such as stroke, brain trauma, epilepsy, and several neurodegenerative disorders. EAAT2 is the main transporter subtype responsible for glutamate clearance in the brain, and plays a key role in regulating neurotransmission and preventing excitotoxicity. Therefore, compounds that increase the activity of EAAT2 have therapeutic potential for neuroprotection. In previous studies, we used virtual screening approaches to identify novel positive allosteric modulators (PAMs) of EAAT2. These compounds were shown to selectively increase the activity of EAAT2 and increase V_max of transport, without changing substrate affinity. In this work, our major effort was to investigate whether increasing the activity of EAAT2 by allosteric modulation would translate to neuroprotection in in vitro primary culture models of excitotoxicity. To investigate potential neuroprotective effects of one EAAT2 PAM, GT949, we subjected cultures to acute and prolonged excitotoxic insults by exogenous application of glutamate, or oxidative stress by application of hydrogen peroxide. GT949 administration did not result in neuroprotection in the oxidative stress model, likely due to damage of the glutamate transporters. However, GT949 displayed neuroprotective properties after acute and prolonged glutamate-mediated excitotoxicity. We propose that this compound prevents excess glutamate signaling by increasing the rate of glutamate clearance by EAAT2, thereby preventing excitotoxic damage and cell death. This novel class of compounds is therefore an innovative approach for neuroprotection with potential for translation in in vivo animal models of excitotoxicity.

Synergistic Protective Effects of Mitochondrial Division Inhibitor 1 and Mitochondria-Targeted Small Peptide SS31 in Alzheimer's Disease

The purpose of our study was to determine the synergistic protective effects of mitochondria-targeted antioxidant SS31 and mitochondria division inhibitor 1 (Mdivi1) in Alzheimer's disease (AD). Using biochemical methods, we assessed mitochondrial function by measuring the levels of hydrogen peroxide, lipid peroxidation, cytochrome c oxidase activity, mitochondrial ATP, and GTPase Drp1 enzymatic activity in mutant AβPP cells. Using biochemical methods, we also measured cell survival and apoptotic cell death. Amyloid-β (Aβ) levels were measured using sandwich ELISA, and using real-time quantitative RT-PCR, we assessed mtDNA (mtDNA) copy number in relation to nuclear DNA (nDNA) in all groups of cells. We found significantly reduced levels of Aβ40 and Aβ42 in mutant AβPP cells treated with SS31, Mdivi1, and SS31+Mdivi1, and the reduction of Aβ42 levels were much higher in SS31+Mdivi1 treated cells than individual treatments of SS31 and Mdivi1. The levels of mtDNA copy number and cell survival were significantly increased in SS31, Mdivi1, and SS31+Mdivi1 treated mutant AβPP cells; however, the increased levels of mtDNA copy number and cell survival were much higher in SS31+Mdivi1 treated cells than individual treatments of SS31 and Mdivi1. Mitochondrial dysfunction is significantly reduced in SS31, Mdivi1, and SS31+Mdivi1 treated mutant AβPP cells; however, the reduction is much higher in cells treated with both SS31+Mdvi1. Similarly, GTPase Drp1 activity is reduced in all treatments, but reduced much higher in SS31+Mdivi1 treated cells. These observations strongly suggest that combined treatment of SS31+Mdivi1 is effective than individual treatments of SS31 and Mdivi1. Therefore, we propose that combined treatment of SS31+Mdivi1 is a better therapeutic strategy for AD. Ours is the first study to investigate combined treatment of mitochondria-targeted antioxidant SS31 and mitochondrial division inhibitor 1 in AD neurons.

Mdivi-1 Protects CD4+ T Cells against Apoptosis via Balancing Mitochondrial Fusion-Fission and Preventing the Induction of Endoplasmic Reticulum Stress in Sepsis

Apoptosis of CD4⁺ T cells plays a central role in the progression of sepsis because it is associated with subsequent immunosuppression and the lack of specific treatment. Thus, developing therapeutic strategies to attenuate the apoptosis of CD4⁺ T cells in sepsis is critical. Several studies have demonstrated that Mdivi-1, which is a selective inhibitor of the dynamin-related protein 1 (Drp1), attenuates apoptosis of myocardial cells and neurons during various pathologic states. The present study revealed the impact of Mdivi-1 on the apoptosis of CD4⁺ T cells in sepsis and the potential underlying mechanisms. We used lipopolysaccharide (LPS) stimulation and cecal ligation and puncture (CLP) surgery as sepsis models in vitro and in vivo, respectively. Our results showed that Mdivi-1 attenuated the apoptosis of CD4⁺ T cells both in vitro and in vivo. The potential mechanism underlying the protective effect of Mdivi-1 involved Mdivi-1 reestablishing mitochondrial fusion-fission balance in sepsis, as reflected by the expression of the mitofusin 2 (MFN2) and optic atrophy 1 (OPA1) , Drp1 translocation, and mitochondrial morphology, as observed by electron microscopy. Moreover, Mdivi-1 treatment reduced reactive oxygen species (ROS) production and prevented the induction of endoplasmic reticulum stress (ERS) and associated apoptosis. After using tunicamycin to activate ER stress, the protective effect of Mdivi-1 on CD4⁺ T cells was reversed. Our results suggested that Mdivi-1 ameliorated apoptosis in CD4⁺ T cells by reestablishing mitochondrial fusion-fission balance and preventing the induction of endoplasmic reticulum stress in experimental sepsis.

The vicious circle between mitochondrial oxidative stress and dynamic abnormality mediates triethylene glycol dimethacrylate-induced preodontoblast apoptosis

Oxidative stress (OS) plays crucial roles in triethylene glycol dimethacrylate (TEGDMA, a major component in dental resin)-induced apoptosis of dental pulp cells. Mitochondria are important target organelles for regulating the balance of OS, meanwhile, imbalance of the mitochondrial dynamic associated with mitochondrial dysfunction is one major molecular mechanism for oxidative damages. However, whether these mitochondrial dependent pathways were involved in the apoptosis of dental pulp cells induced by TDGDMA remains unclarified. We demonstrated that TEGDMA decreased viability and induced apoptosis of mouse preodontoblasts (mDPC6T cell line) in a time- and dose-dependent manner. Furthermore, TEGDMA elevated the mitochondrial OS status and induced mitochondrial dysfunction, as reflected by the significant decrease of mitochondrial membrane potential, ATP production, the activity of Complex III and citrate synthase. In this process, we detected a dramatically impaired mitochondrial dynamic that was reflected by significantly enhanced mitochondrial fragmentation. Consistently, we also found a significant enhancement of the key upstream regulators for mitochondrial fission, such as short form of optic atrophy 1, dynamic related protein 1 oligomer and Fission 1. The respective inhibition of mitochondrial OS or mitochondrial fission could mutually attenuate each other, thereby significantly preventing both mitochondrial dysfunction and cell apoptosis. In conclusion, TEGDMA-induced preodontoblasts apoptosis was mediated by the vicious circle between mitochondrial OS and dynamic abnormality, which represented a new target to prevent TEGDMA-induced dental pulp cells apoptosis.

Up-Regulation of Trem2 Inhibits Hippocampal Neuronal Apoptosis and Alleviates Oxidative Stress in Epilepsy via the PI3K/Akt Pathway in Mice

Epilepsy is a chronic and severe neurological disorder that has negative effects on the autonomous activities of patients. Functionally, Trem2 (triggering receptor expressed on myeloid cells-2) is an immunoglobulin receptor that affects neurological and psychiatric genetic diseases. Based on this rationale, we aimed to assess the potential role of Trem2 integration with the PI3K/Akt pathway in epilepsy. We used microarray-based gene expression profiling to identify epilepsy-related differentially-expressed genes. In a mouse hippocampal neuron model of epilepsy, neurons were treated with low-Mg²⁺ extracellular fluid, and the protein and mRNA expression of Trem2 were determined. Using a gain-of-function approach with Trem2, neuronal apoptosis and its related factors were assessed by flow cytometry, RT-qPCR, and Western blot analysis. In a pilocarpine-induced epileptic mouse model, the malondialdehyde (MDA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) content and superoxide dismutase (SOD) and glutathione-peroxidase (GSH-Px) activity in the hippocampus were determined, and the protein expression of Trem2 was measured. In addition, the regulatory effect of Trem2 on the PI3K/Akt pathway was analyzed by inhibiting this pathway in both the cell and mouse models of epilepsy. Trem2 was found to occupy a core position and was correlated with epilepsy. Trem2 was decreased in the hippocampus of epileptic mice and epileptic hippocampal neurons. Of crucial importance, overexpression of Trem2 activated the PI3K/Akt pathway to inhibit neuronal apoptosis. Moreover, activation of the PI3K/Akt pathway through over-expression of Trem2 alleviated oxidative stress, as shown by the increased expression of SOD and GSH-Px and the decreased expression of MDA and 8-OHdG. The current study defines the potential role of Trem2 in inhibiting the development of epilepsy, indicating that Trem2 up-regulation alleviates hippocampal neuronal injury and oxidative stress, and inhibits neuronal apoptosis in epilepsy by activating the PI3K/Akt pathway.

Overexpressed HspB6 Underlines a Novel Inhibitory Role in Kainic Acid-Induced Epileptic Seizure in Rats by Activating the cAMP-PKA Pathway

Epilepsy is a commonly occurring neurological disease that has a large impact on the patient's daily life. Phosphorylation of heat shock protein B6 (HspB6) has been reported to protect the central nervous system. In this investigation, we explored whether HspB6 played a positive effect on epilepsy with the involvement of the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) pathway. The epileptic seizure was induced in rats by intraperitoneal injection of kainic acid (KA). The extent of HspB6 phosphorylation and expressions of HspB6, PKA, and inflammatory factors TNF-α, IL-1β, and IL-6 were quantified along with neuronal apoptosis. To further understand the regulatory mechanism of the HspB6 in the hippocampus, we altered the expression and the extent of HspB6 phosphorylation to see whether the cAMP-PKA pathway was inactivated or not in hippocampal neurons of rats post KA. Results showed that HspB6 was poorly expressed, resulting in the inactivation of the cAMP-PKA pathway in rats post KA, as well as an aggravated inflammatory response and hippocampal neuronal apoptosis. HspB6 overexpression and the cAMP-PKA pathway activation decreased the expression of inflammatory factors and inhibited hippocampal neuronal apoptosis. Additionally, HspB6 phosphorylation further augments the inhibitory effects of HspB6 on the inflammatory response and hippocampal neuronal apoptosis. The cAMP-PKA pathway activation was found to result in increased HspB6 phosphorylation. HspB6 decreased apoptosis signal-regulating kinase 1 (ASK1) expression to inhibit inflammatory response and hippocampal neuronal apoptosis. Collectively, our findings demonstrate that activation of the cAMP-PKA pathway induces overexpression and partial phosphorylation of HspB6 lead to the inhibition of ASK1 expression. This in turn protects rats against epilepsy and provides a potential approach to prevent the onset of epileptic seizure in a clinical setting.

Influence of mTOR signaling pathway on ketamine-induced injuries in the hippocampal neurons of rats

OBJECTIVE

To explore the influences of mammalian target of rapamycin (mTOR) signaling pathway on ketamine-induced apoptosis, oxidative stress and Ca²⁺ concentration in the hippocampal neurons of rats.

METHODS

The primary hippocampal neurons isolated from fetal Sprague Dawley rats were treated with ketamine (0, 50, 100 and 500 μM) for 4 days to observe its effect on mTOR signaling pathway and apoptosis of rat hippocampal neurons. Then, the hippocampal neurons were divided into C (Control), R (Rapamycin, an inhibitor of mTOR signaling pathway), K (Ketamine) and R + K (Rapamycin + Ketamine) groups to detect the apoptosis, reactive oxygen species (ROS) production, and Ca²⁺ concentration via the terminal transferase uridyl nick end labelling (TUNEL) assay, dichloro-dihydro-fluorescein diacetate (DCFH-DA) method and Fluo-3 acetoxymethyl ester (Fluo-3AM) staining, respectively. The expressions of mTOR signaling pathway and apoptosis-related proteins in hippocampal neurons were examined by qRT-PCR and Western blot.

RESULTS

Ketamine could dose-dependently promote the apoptosis of rat hippocampal neurons with upregulation of p-mTOR and its downstream regulators (p-4E-BP-1 and p-p70S6K). However, ketamine-induced apoptosis in hippocampal neurons was reversed significantly by the administration of rapamycin, as evident by the decrease in expressions of pro-apoptotic proteins (Bax and cleaved Caspase-3) and the increase in anti-apoptotic protein (Bcl-2). Meanwhile, the ROS generation and Ca²⁺ concentration was inhibited accompanied with reduced malonildialdehyde levels but elevated superoxide and glutathione peroxidase activities.

CONCLUSION

Inhibition of mTOR signaling pathway protected rat hippocampal neurons from ketamine-induced injuries via reducing apoptosis, oxidative stress, as well as Ca²⁺ concentration.

ABBREVIATIONS

mTOR: mammalian target of rapamycin; SD: Sprague-Dawley; SPF: Specific-pathogen free; ROS: reactive oxygen species; TUNEL: terminal transferase uridyl nick end labelling; DCFH-DA: Dichloro-dihydro-fluorescein diacetate; Fluo-3A: Fluo-3 acetoxymethyl ester; NMDAR: non-competitive N-methyl-D-aspartame glutamate receptor; 4E-BP1: 4E binding protein 1; p70S6K: p70 S6 Kinase; PCR: Polymerase chain reaction; MDA: malonildialdehyde; GSH-PX: glutathione peroxidase; ANOVA: One-way Analysis of Variance.

Mitochondrial Division Inhibitor 1 (mdivi-1) Protects Neurons against Excitotoxicity through the Modulation of Mitochondrial Function and Intracellular Ca2+ Signaling

Excessive dynamin related protein 1 (Drp1)-triggered mitochondrial fission contributes to apoptosis under pathological conditions and therefore it has emerged as a promising therapeutic target. Mitochondrial division inhibitor 1 (mdivi-1) inhibits Drp1-dependent mitochondrial fission and is neuroprotective in several models of brain ischemia and neurodegeneration. However, mdivi-1 also modulates mitochondrial function and oxidative stress independently of Drp1, and consequently the mechanisms through which it protects against neuronal injury are more complex than previously foreseen. In this study, we have analyzed the effects of mdivi-1 on mitochondrial dynamics, Ca²⁺ signaling, mitochondrial bioenergetics and cell viability during neuronal excitotoxicity in vitro. Time-lapse fluorescence microscopy revealed that mdivi-1 blocked NMDA-induced mitochondrial fission but not that triggered by sustained AMPA receptor activation, showing that mdivi-1 inhibits excitotoxic mitochondrial fragmentation in a source specific manner. Similarly, mdivi-1 strongly reduced NMDA-triggered necrotic-like neuronal death and, to a lesser extent, AMPA-induced toxicity. Interestingly, neuroprotection provided by mdivi-1 against NMDA, but not AMPA, correlated with a reduction in cytosolic Ca²⁺ ([Ca²⁺]_cyt) overload and calpain activation indicating additional cytoprotective mechanisms. Indeed, mdivi-1 depolarized mitochondrial membrane and depleted ER Ca²⁺ content, leading to attenuation of mitochondrial [Ca²⁺] increase and enhancement of the integrated stress response (ISR) during NMDA receptor activation. Finally, lentiviral knockdown of Drp1 did not rescue NMDA-induced mitochondrial fission and toxicity, indicating that neuroprotective activity of mdivi-1 is Drp1-independent. Together, these results suggest that mdivi-1 induces a Drp1-independent protective phenotype that prevents predominantly NMDA receptor-mediated excitotoxicity through the modulation of mitochondrial function and intracellular Ca²⁺ signaling.

Mitochondrial division inhibitor 1 protects cortical neurons from excitotoxicity: a mechanistic pathway

Mitochondrial division inhibitor 1 (Mdivi-1) is a selective cell-permeable inhibitor of dynamin-related protein-1 (Drp1) and mitochondrial division. To investigate the effect of Mdivi-1 on cells treated with glutamate, cerebral cortex neurons isolated from neonatal rats were treated with 10 mM glutamate for 24 hours. Normal cultured cells and dimethyl sulfoxide-cultured cells were considered as controls. Apoptotic cells were detected by flow cytometry. Changes in mitochondrial morphology were examined by electron microscopy. Drp1, Bax, and caspase-3 expression was evaluated by western blot assays and immunocytochemistry. Mitochondrial membrane potential was detected using the JC-1 probe. Twenty-four hours after 10 mM glutamate treatment, Drp1, Bax and caspase-3 expression was upregulated, Drp1 and Bax were translocated to mitochondria, mitochondrial membrane potential was decreased and the rate of apoptosis was increased. These effects were inhibited by treatment with 50 μM Mdivi-1 for 2 hours. This finding indicates that Mdivi-1 is a candidate neuroprotective drug that can potentially mitigate against neuronal injury caused by glutamate-induced excitotoxicity.

Mdivi-1 Protects Human W8B2+ Cardiac Stem Cells from Oxidative Stress and Simulated Ischemia-Reperfusion Injury

Cardiac stem cell (CSC) therapy is a promising approach to treat ischemic heart disease. However, the poor survival of transplanted stem cells in the ischemic myocardium has been a major impediment in achieving an effective cell-based therapy against myocardial infarction. Inhibiting mitochondrial fission has been shown to promote survival of several cell types. However, the role of mitochondrial morphology in survival of human CSC remains unknown. In this study, we investigated whether mitochondrial division inhibitor-1 (Mdivi-1), an inhibitor of mitochondrial fission protein dynamin-related protein-1 (Drp1), can improve survival of a novel population of human W8B2⁺ CSCs in hydrogen peroxide (H₂O₂)-induced oxidative stress and simulated ischemia-reperfusion injury models. Mdivi-1 significantly reduced H₂O₂-induced cell death in a dose-dependent manner. This cytoprotective effect was accompanied by an increased proportion of cells with tubular mitochondria, but independent of mitochondrial membrane potential recovery and reduction of mitochondrial superoxide production. In simulated ischemia-reperfusion injury model, Mdivi-1 given as a pretreatment or throughout ischemia-reperfusion injury significantly reduced cell death. However, the cytoprotective effect of Mdivi-1 was not observed when given at reperfusion. Moreover, the cytoprotective effect of Mdivi-1 in the simulated ischemia-reperfusion injury model was not accompanied by changes in mitochondrial morphology, mitochondrial membrane potential, or mitochondrial reactive oxygen species production. Mdivi-1 also did not affect mitochondrial bioenergetics of intact W8B2⁺ CSCs. Taken together, these experiments demonstrated that Mdivi-1 treatment of human W8B2⁺ CSCs enhances their survival and can be employed to improve therapeutic efficacy of CSCs for ischemic heart disease.

Mdivi-1 Protects Adult Rat Hippocampal Neural Stem Cells against Palmitate-Induced Oxidative Stress and Apoptosis

Palmitate concentrations in type 2 diabetic patients are higher than in healthy subjects. The prolonged elevation of plasma palmitate levels induces oxidative stress and mitochondrial dysfunction in neuronal cells. In this study, we examined the role of mdivi-1, a selective inhibitor of mitochondrial fission protein dynamin-regulated protein 1 (Drp1), on the survival of cultured hippocampal neural stem cells (NSCs) exposed to high palmitate. Treatment of hippocampal NSCs with mdivi-1 attenuated palmitate-induced increase in cell death and apoptosis. Palmitate exposure significantly increased Drp1 protein levels, which were prevented by pretreatment of cells with mdivi-1. We found that cytosolic Drp1 was translocated to the mitochondria when cells were exposed to palmitate. In contrast, palmitate-induced translocation of Drp1 was inhibited by mdivi-1 treatment. We also investigated mdivi-1 regulation of apoptosis at the mitochondrial level. Mdivi-1 rescued cells from palmitate-induced lipotoxicity by suppressing intracellular and mitochondrial reactive oxygen species production and stabilizing mitochondrial transmembrane potential. Mdivi-1-treated cells showed an increased Bcl-2/Bax ratio, prevention of cytochrome c release, and inhibition of caspase-3 activation. Our data suggest that mdivi-1 protects hippocampal NSCs against lipotoxicity-associated oxidative stress by preserving mitochondrial integrity and inhibiting mitochondrial apoptotic cascades.

Attenuation of Aβ toxicity by promotion of mitochondrial fusion in neuroblastoma cells by liquiritigenin

Mitochondrial dynamics control mitochondrial morphology and function, and aberrations in these are associated with various neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. To identify novel regulators of mitochondrial dynamics, we screened a phytochemical library and identified liquiritigenin as a potent inducer of mitochondrial fusion. Treatment with liquiritigenin induced an elongated mitochondrial morphology in SK-N-MC cells. In addition, liquiritigenin rescued mitochondrial fragmentation induced by knockout of mitochondrial fusion mediators such as Mfn1, Mfn2, and Opa1. Furthermore, we found that treatment with liquiritigenin notably inhibited mitochondrial fragmentation and cytotoxicity induced by Aβ in SK-N-MC cells.

Mitochondrial fission - a drug target for cytoprotection or cytodestruction?

Mitochondria are morphologically dynamic organelles constantly undergoing processes of fission and fusion that maintain integrity and bioenergetics of the organelle: these processes are vital for cell survival. Disruption in the balance of mitochondrial fusion and fission is thought to play a role in several pathological conditions including ischemic heart disease. Proteins involved in regulating the processes of mitochondrial fusion and fission are therefore potential targets for pharmacological therapies. Mdivi‐1 is a small molecule inhibitor of the mitochondrial fission protein Drp1. Inhibiting mitochondrial fission with Mdivi‐1 has proven cytoprotective benefits in several cell types involved in a wide array of cardiovascular injury models. On the other hand, Mdivi‐1 can also exert antiproliferative and cytotoxic effects, particularly in hyperproliferative cells. In this review, we discuss these divergent effects of Mdivi‐1 on cell survival, as well as the potential and limitations of Mdivi‐1 as a therapeutic agent.