Protective effect of Homer 1a against hydrogen peroxide-induced oxidative stress in PC12 cells

A critical appraisal on the involvement of plant-based extracts as neuroprotective agents (2012-2022): an effort to ease out decision-making process for researchers

The purpose of this review study is to provide a condensed compilation of 164 medicinal plants that have been investigated for their neuroprotective aspects by researchers between the years 2012 and 2022 which also includes a recent update of 2023-2024. After using certain keywords to retrieve the data from SCOPUS, it was manually sorted to eliminate any instances of duplication. The article is streamlined into three major segments. The first segment takes a dig into the current global trend and attempts to decrypt vital information related to plant names, families, plant parts used, and neurological disorders investigated. The second segment of the article makes an attempt to present a comprehensive insight into the various mechanistic pathways through which phytochemicals can intervene to exert neuroprotection. The final segment of the manuscript is a bibliometric appraisal of all researches conducted. The study is based on 256 handpicked articles based on decided inclusion criteria. Illustrative compilation of various pathways citing their activation and deactivation channels are also presented with possible hitting points of various phytochemicals. The present study employed Microsoft Excel 2019 and VOS viewer as data visualisation tools.

Homer signaling pathways as effective therapeutic targets for ischemic and traumatic brain injuries and retinal lesions

Ischemic and traumatic insults to the central nervous system account for most serious acute and fatal brain injuries and are usually characterized by primary and secondary damage. Secondary damage presents the greatest challenge for medical staff; however, there are currently few effective therapeutic targets for secondary damage. Homer proteins are postsynaptic scaffolding proteins that have been implicated in ischemic and traumatic insults to the central nervous system. Homer signaling can exert either positive or negative effects during such insults, depending on the specific subtype of Homer protein. Homer 1b/c couples with other proteins to form postsynaptic densities, which form the basis of synaptic transmission, while Homer1a expression can be induced by harmful external factors. Homer 1c is used as a unique biomarker to reveal alterations in synaptic connectivity before and during the early stages of apoptosis in retinal ganglion cells, mediated or affected by extracellular or intracellular signaling or cytoskeletal processes. This review summarizes the structural features, related signaling pathways, and diverse roles of Homer proteins in physiological and pathological processes. Upregulating Homer1a or downregulating Homer1b/c may play a neuroprotective role in secondary brain injuries. Homer also plays an important role in the formation of photoreceptor synapses. These findings confirm the neuroprotective effects of Homer, and support the future design of therapeutic drug targets or gene therapies for ischemic and traumatic brain injuries and retinal disorders based on Homer proteins.

MicroRNA-137-3p Protects PC12 Cells Against Oxidative Stress by Downregulation of Calpain-2 and nNOS

The imbalance between excess reactive oxygen species (ROS) generation and insufficient antioxidant defenses contribute to a range of neurodegenerative diseases. High ROS levels damage cellular macromolecules such as DNA, proteins and lipids, leading to neuron vulnerability and eventual death. However, the underlying molecular mechanism of the ROS regulation is not fully elucidated. Recently, an increasing number of studies suggest that microRNAs (miRNAs) emerge as the targets in regulating oxidative stress. We recently reported the neuroprotective effect of miR-137-3p for brachial plexus avulsion-induced motoneuron death. The present study is sought to investigate whether miR-137-3p also could protect PC12 cells against hydrogen peroxide (H2O2) induced neurotoxicity. By using cell viability assay, ROS assay, gene and protein expression assay, we found that PC-12 cells exposed to H2O2 exhibited decreased cell viability, increased expression levels of calpain-2 and neuronal nitric oxide synthase (nNOS), whereas a decreased miR-137-3p expression. Importantly, restoring the miR-137-3p levels in H2O2 exposure robustly inhibited the elevated nNOS, calpain-2 and ROS expression levels, which subsequently improved the cell viability. Furthermore, the suppressive effect of miR-137-3p on the elevated ROS level under oxidative stress was considerably blunted when we mutated the binding site of calpain-2 targted by miR-137-3p, suggesting the critical role of calpain-2 involving the neuroprotective effect of miR-137-3p. Collectively, these findings highlight the neuroprotective role of miR-137-3p through down-regulating calpain and NOS activity, suggesting its potential role for combating oxidative stress insults in the neurodegenerative diseases.

Protective Effect of Ferulic Acid against Hydrogen Peroxide Induced Apoptosis in PC12 Cells

Ferulic Acid (FA) is a highly abundant phenolic phytochemical which is present in plant tissues. FA has biological effects on physiological and pathological processes due to its anti-apoptotic and anti-oxidative properties, however, the detailed mechanism(s) of function is poorly understood. We have identified FA as a molecule that inhibits apoptosis induced by hydrogen peroxide (H₂O₂) or actinomycin D (ActD) in rat pheochromocytoma, PC12 cell. We also found that FA reduces H₂O₂-induced reactive oxygen species (ROS) production in PC12 cell, thereby acting as an anti-oxidant. Then, we analyzed FA-mediated signaling responses in rat pheochromocytoma, PC12 cells using antibody arrays for phosphokinase and apoptosis related proteins. This FA signaling pathway in PC12 cells includes inactivation of pro-apoptotic proteins, SMAC/Diablo and Bad. In addition, FA attenuates the cell injury by H₂O₂ through the inhibition of phosphorylation of the extracellular signal-regulated kinase (ERK). Importantly, we find that FA restores expression levels of brain-derived neurotrophic factor (BDNF), a key neuroprotective effector, in H₂O₂-treated PC12 cells. As a possible mechanism, FA increases BDNF by regulating microRNA-10b expression following H₂O₂ stimulation. Taken together, FA has broad biological effects as a neuroprotective modulator to regulate the expression of phosphokinases, apoptosis-related proteins and microRNAs against oxidative stress in PC12 cells.

Chinese medicine Di-Huang-Yi-Zhi protects PC12 cells from H2O2-induced apoptosis by regulating ROS-ASK1-JNK/p38 MAPK signaling

Background

Oxidative stress mediates the nerve injury during the pathogenesis of Alzheimer’s disease (AD). Protecting against oxidative stress damage is an important strategy to prevent and treat AD. Di-Huang-Yi-Zhi (DHYZ) is a Chinese medicine used for the treatment of AD, but its mechanism remains unknown. This study is aimed to investigate the effect of DHYZ on H₂O₂ induced oxidative damage in PC12 cells.

Methods

PC12 cells were treated with H₂O₂ and DHYZ. Cell proliferation was detected by Cell counting kit-8 (CCK-8) assay. Cytotoxicity of H₂O₂ was measured by lactate dehydrogenase (LDH) release assay. Apoptosis were identified by Annexin V-FITC/PI staining. Caspase 3 activity was detected by commercial kit. Mitochondrial membrane potential (MMP) was detected by JC-1 staining. Reactive oxygen species (ROS) was 2′, 7′-Dichlorodihydrofluorescein diacetate (DCFH-DA) staining. Protein expression and phosphorylation was identified by western blot.

Results

The results showed that DHYZ antagonized H₂O₂-mediated cytotoxicity and proliferation inhibition. DHYZ reduced ROS production, stabilize mitochondrial membrane potential, inhibit Caspase-3 activity and apoptosis induced by H₂O₂. In addition, DHYZ inhibited the phosphorylation of ASK1, JNK1/2/3 and p38 MAPK which were up-regulated by H₂O₂.

Conclusions

The present study suggested that DHYZ protected PC12 cells from H₂O₂-induced oxidative stress damage and was related to inhibition of ROS production and ASK1-JNK/p38 MAPK signaling. The present study provides experimental evidence for the application of DHYZ for the management of oxidative stress damage and AD.

Arc silence aggravates traumatic neuronal injury via mGluR1-mediated ER stress and necroptosis

Delayed neuronal death is associated with neurological deficits and mortality after traumatic brain injury (TBI), where post-synaptic density (PSD) proteins are thought to play key roles. The immediate-early gene (IEG) coded protein Arc is a brain-specific PSD protein that controls synaptic plasticity and learning behaviors. In this study, we investigated the expression and biological function of Arc in neuronal death after TBI in an in vitro model mimicked by traumatic neuronal injury (TNI) in cortical neurons. TNI caused a temporal increase of Arc expression at 3 and 6 h. Knockdown of Arc expression using small interfering RNA (Si-Arc-3) promoted TNI-induced cytotoxicity and apoptosis. The results of western blot showed that Si-Arc-3 transfection further enhanced the activation of endoplasmic reticulum (ER) stress-associated factors, including glucose-regulated protein 78 (GRP78), C/EBP homologous protein (CHOP) and caspase-12 after TNI. In addition, knockdown of Arc significantly increased expression of (receptor-interacting protein kinase 1) RIP1 and the number of necroptotic cells, which were apparently prevented by necrostatin-1 (Nec-1). The results of immunostaining and western blot showed that knockdown of Arc activated the metabotropic glutamate receptor 1 (mGluR1) and intracellular Ca²⁺ release in neurons. Mechanistically, the Si-Arc-3-induced activation of ER stress-associated factors, RIP1 expression, apoptosis, and necroptosis were partially reversed by the mGluR1 antagonist AIDA. In summary, our data suggest that silence of Arc expression aggravates neuronal death after TNI by promoting apoptosis and necroptosis. These data support for the first time that Arc may represent a novel candidate for therapies against TBI.

γ-Oryzanol suppresses cell apoptosis by inhibiting reactive oxygen species-mediated mitochondrial signaling pathway in H2O2-stimulated L02 cells

γ-Oryzanol, a mixture of ferulic acid esters of plant sterols and triterpene alcohols existed in rice bran oil, can ameliorate lipid metabolism and enhance antioxidant activity. In this study, we used hydrogen peroxide (H₂O₂)-induced injury in human hepatic L02 cells to investigate the mechanisms involved in the hepatoprotective activity of γ-oryzanol. The injuries produced by H₂O₂ in L02 cells include increased levels of malondialdehyde (MDA) and intracellular reactive oxygen species (ROS), decreased activities of superoxide dismutase (SOD) and catalase (CAT), loss of mitochondrial membrane potential (MMP), increased protein expressions of caspase-9 and caspase-3, and induced apoptosis. Pretreatment with γ-oryzanol enhanced the ROS scavenging activity of endogenous antioxidant enzymes and decreased lipid peroxidation in H₂O₂ treated cells. Moreover, pretreatment with γ-oryzanol inhibited H₂O₂-induced apoptosis by restoring MMP, upregulating the expression ratio of Bcl-2/Bax, and inhibiting the activation of caspase-9 and caspase-3. These findings show that γ-oryzanol can prevent H₂O₂-induced apoptosis by suppressing intracellular accumulation of ROS and impeding ROS-activated mitochondrial apoptotic pathway.

Bone mesenchymal stem cell-conditioned medium attenuates the effect of oxidative stress injury on NSCs by inhibiting the Notch1 signaling pathway

Numerous studies have demonstrated the therapeutic effect of bone mesenchymal stem cells on spinal cord injury (SCI), especially on neural stem cells (NSCs). However, the predominant mechanisms of bone mesenchymal stem cells (BMSCs) are unclear. Recently, some researchers have found that paracrine signaling plays a key role in the therapeutic capacity of BMSCs and emphasized that the protective effect of BMSCs may be due to paracrine factors. In this study, we aimed to investigate the potential mechanisms of BMSCs to protect NSCs. NSCs were identified by immunocytochemistry. The oxidative stress environment was simulated by H₂ O₂ (50, 100, 200 μM) for 2 h. The apoptotic rate of the NSCs was detected via flow cytometry. Lactate dehydrogenase (LDH), malondialdehyde (MDA), and superoxide dismutase (SOD) activity were evaluated via corresponding assay kits. Western blot was used to detect the expressions of Notch1, HES1, caspase-3, cleave caspase-3, Bax, and Bcl-2. We found that H₂ O₂ could significantly induce the apoptosis of NSCs, increase LDH, MDA levels, and decrease SOD activity by activating the Notch1 signaling pathway. DAPT (the specific blocker of Notch1) and BMSC-conditioned medium (BMSC-CM) could significantly prevent the apoptotic effect and oxidative stress injury on NSCs that were treated with H₂ O₂ . We also revealed that BMSC-CM could decrease the expression of Notch1, Hes1, cleave caspase-3, Bax, and increases the expression of Bcl-2 in NSCs, which was induced by H₂ O₂ . These results have revealed that BMSC-CM can neutralize the effect against oxidative stress injury on the apoptosis of NSCs by inhibiting the Notch1 signaling pathway.

Homer1a Attenuates Endoplasmic Reticulum Stress-Induced Mitochondrial Stress After Ischemic Reperfusion Injury by Inhibiting the PERK Pathway

Homer1a is the short form of a scaffold protein that plays a protective role in many forms of stress. However, the role of Homer1a in cerebral ischemia/reperfusion (I/R) injury and its potential mechanism is still unknown. In this study, we found that Homer1a was upregulated by oxygen and glucose deprivation (OGD) and that overexpression of Homer1a alleviated OGD-induced lactate dehydrogenase (LDH) release and cell death in cultured cortical neurons. After OGD treatment, the overexpression of Homer1a preserved mitochondrial function, as evidenced by less cytochrome c release, less reactive oxygen species (ROS) production, less ATP and mitochondrial membrane potential (MMP) loss, less caspase-9 activation, and inhibition of endoplasmic reticulum (ER) stress confirmed by the decreased expression of phosphate-PKR-like ER Kinase (p-PERK)/PERK and phosphate- inositol-requiring enzyme 1 (p-IRE1)/IRE1 and immunofluorescence (IF) staining. In addition, mitochondrial protection of Homer1a was blocked by the ER stress activator Tunicamycin (TM) with a re-escalated ROS level, increasing ATP and MMP loss. Furthermore, Homer1a overexpression-induced mitochondrial stress attenuation was significantly reversed by activating the PERK pathway with TM and p-IRE1 inhibitor 3,5-dibromosalicylaldehyde (DBSA), as evidenced by increased cytochrome c release, increased ATP loss and a higher ROS level. However, activating the IRE1 pathway with TM and p-PERK inhibitor GSK2656157 showed little change in cytochrome c release and exhibited a moderate upgrade of ATP loss and ROS production in neurons. In summary, these findings demonstrated that Homer1a protects against OGD-induced injury by preserving mitochondrial function through inhibiting the PERK pathway. Our finding may reveal a promising target of protecting neurons from cerebral I/R injury.

Oxidative stress and cell cycle arrest induced by short-term exposure to dustfall PM2.5 in A549 cells

It was reported that in vitro short-term exposure to PM_2.5 caused different lung diseases through inflammatory response, immune toxicity, oxidative stress, and genetic mutations. However, the complex molecular biological mechanism for its toxicity had not been fully elucidated. Therefore, the present study investigated the cytotoxicity, oxidative damage, mitochondria damage, apoptosis, and cell cycle arrest of NX and QH PM_2.5 in A549 cells. Further, cell cycle arrest-related gene levels in PM_2.5-induced A549 cells were also detected. Our results suggested that PM_2.5 reduced the cell viability in A549 cells. Simultaneously, excessive ROS decreased MMP levels and damaged mitochondrial membrane integrity and induced mitochondrial oxidative damage through the oxygen-dependent killer route, resulting in mitochondrial damage and cell apoptosis. Besides, the results also showed that PM_2.5 induced A549 cell cycle alteration in G2/M phase after co-culture for 24 h. G2/M phase arrest was induced by upregulation of p53 and p21 and downregulation of CDK1 mRNA expression. In addition, lncRNA Sox2ot might play an important role as the specific oncogenes and it participated in G2/M phase arrest by regulating the expression of EZH₂.

Neuroprotective Effect of CeO2@PAA-LXW7 Against H2O2-Induced Cytotoxicity in NGF-Differentiated PC12 Cells

CeO₂ nanoparticles (nanoceria) have been used in many studies as a powerful free radical scavenger, and LXW7, a small-molecule peptide, can specifically target the integrin αvβ3, whose neuroprotective effects have also been demonstrated. The objective of this study is to observe the neuroprotective effect and potential mechanism of CeO₂@PAA-LXW7, a new compound that couples CeO₂@PAA (nanoceria modified with the functional group of polyacrylic acid) with LXW7 via a series of chemical reactions, in H₂O₂-induced NGF-differentiated PC12 cells. We examined the effects of LXW7, CeO₂@PAA, and CeO₂@PAA-LXW7 on the viability of primary hippocampal neurons and found that there was no significant difference under control conditions, but increased cellular viability was observed in the case of H₂O₂-induced injury. We used H₂O₂-induced NGF-differentiated PC12 cells as the classical injury model to investigate the neuroprotective effect of CeO₂@PAA-LXW7. In this study, LXW7, CeO₂@PAA, and CeO₂@PAA-LXW7 inhibit H₂O₂-induced oxidative stress by reducing the production of reactive oxygen species (ROS) and regulating Bax/Bcl-2, cleaved caspase-3 and mitochondrial cytochrome C (cyto C) in the apoptotic signaling pathways. We found that the levels of phosphorylation of focal adhesion kinase (FAK) and of signal transducer and activator of transcription 3 (STAT3) increased significantly in H₂O₂-induced NGF-differentiated PC12 cells, whereas LXW7, CeO₂@PAA, and CeO₂@PAA-LXW7 suppressed the increase to different degrees. Among the abovementioned changes, the inhibitory effect of CeO₂@PAA-LXW7 on H₂O₂-induced changes, including the increases in the levels of p-FAK and p-STAT3, is more obvious than that of LXW7 or CeO₂@PAA alone. In summary, these results suggest that integrin signaling participates in the regulation of apoptosis via the regulation of ROS and of the apoptosis pathway in H₂O₂-induced NGF-differentiated PC12 cells. LXW7, CeO₂@PAA, and CeO₂@PAA-LXW7 can play neuroprotective roles by counteracting the oxidative stress and apoptosis induced by H₂O₂ in NGF-differentiated PC12 cells. CeO₂@PAA-LXW7 exerting a more powerful synergistic effect via the conjunction of LXW7 and CeO₂@PAA.

Homer1a Attenuates Hydrogen Peroxide-Induced Oxidative Damage in HT-22 Cells through AMPK-Dependent Autophagy

Neuronal oxidative stress is involved in diverse neurological disorders. Homer1a, as an important member of the Homer family and localized at the postsynaptic density, is known to protect cells against oxidative injury. However, the exact neuroprotective mechanism of Homer1a has not been fully elucidated. Here, we found that Homer1a promoted cell viability and reduced H₂O₂-induced LDH release. The overexpression of Homer1a enhanced autophagy after H₂O₂ treatment, which was confirmed by increased expression of LC3II, Beclin-1, and greater autophagosome formation. In addition, we demonstrated that activating autophagy improved cell survival and reduced H₂O₂-induced oxidative stress and mitochondrial damage. Moreover, the autophagy inhibitor 3-MA partially prevented the protective effects of Homer1a against oxidative challenge. We also found that the upregulation of Homer1a after H₂O₂ treatment increased the phosphorylation of AMPK. Furthermore, the AMPK inhibitor compound C inhibited Homer1a-induced autophagy and abolished Homer1a-mediated neuroprotection. All the above data suggests that Homer1a confers protection against H₂O₂-induced oxidative damage via AMPK-dependent autophagy.

Homer1a attenuates glutamate-induced oxidative injury in HT-22 cells through regulation of store-operated calcium entry

Calcium disequilibrium is extensively involved in oxidative stress-induced neuronal injury. Although Homer1a is known to regulate several neuronal calcium pathways, its effects on, or its exact relationship with, oxidative stress-induced neuronal injury has not yet been fully elucidated. We found that Homer1a protected HT-22 cells from glutamate-induced oxidative stress injury by inhibiting final-phase intracellular calcium overload and mitochondrial oxidative stress. In these cells, stromal interactive molecule 1 (STIM1) puncta, but not the protein level, was significantly increased after glutamate treatment. Store-operated calcium entry (SOCE) inhibitors and cells in which a key component of SOCE (STIM1) was knocked out were used as glutamate-induced oxidative stress injury models. Both models demonstrated significant improvement of HT-22 cell survival after glutamate treatment. Additionally, increased Homer1a protein levels significantly inhibited SOCE and decreased the association of STIM1-Orai1 triggered by glutamate. These results suggest that up-regulation of Homer1a can protect HT-22 cells from glutamate-induced oxidative injury by disrupting the STIM1-Oria1 association, and then by inhibiting the SOCE-mediated final-phrase calcium overload. Thus, regulation of Homer1a, either alone or in conjunction with SOCE inhibition, may serve as key therapeutic interventional targets for neurological diseases in which oxidative stress is involved in the etiology or progression of the disease.

Protective Effects of Costunolide against Hydrogen Peroxide-Induced Injury in PC12 Cells

Oxidative stress-mediated cellular injury has been considered as a major cause of neurodegenerative diseases including Alzheimer’s and Parkinson’s diseases. The scavenging of reactive oxygen species (ROS) mediated by antioxidants may be a potential strategy for retarding the diseases’ progression. Costunolide (CS) is a well-known sesquiterpene lactone, used as a popular herbal remedy, which possesses anti-inflammatory and antioxidant activity. This study aimed to investigate the protective role of CS against the cytotoxicity induced by hydrogen peroxide (H₂O₂) and to elucidate potential protective mechanisms in PC12 cells. The results showed that the treatment of PC12 cells with CS prior to H₂O₂ exposure effectively increased the cell viability. Furthermore, it decreased the intracellular ROS, stabilized the mitochondria membrane potential (MMP), and reduced apoptosis-related protein such as caspase 3. In addition, CS treatment attenuated the cell injury by H₂O₂ through the inhibition of phosphorylation of p38 and the extracellular signal-regulated kinase (ERK). These results demonstrated that CS is promising as a potential therapeutic candidate for neurodegenerative diseases resulting from oxidative damage and further research on this topic should be encouraged.

Protective effect of reduced glutathione C60 derivative against hydrogen peroxide-induced apoptosis in HEK 293T cells

Hydrogen peroxide (H2O2) and free radicals cause oxidative stress, which induces cellular injuries, metabolic dysfunction, and even cell death in various clinical abnormalities. Fullerene (C60) is critical for scavenging oxygen free radicals originated from cell metabolism, and reduced glutathione (GSH) is another important endogenous antioxidant. In this study, a novel water-soluble reduced glutathione fullerene derivative (C60-GSH) was successfully synthesized, and its beneficial roles in protecting against H2O2-induced oxidative stress and apoptosis in cultured HEK 293T cells were investigated. Fourier Transform infrared spectroscopy and (1)H nuclear magnetic resonance were used to confirm the chemical structure of C60-GSH. Our results demonstrated that C60-GSH prevented the reactive oxygen species (ROS)-mediated cell damage. Additionally, C60-GSH pretreatment significantly attenuated H2O2-induced superoxide dismutase (SOD) consumption and malondialdehyde (MDA) elevation. Furthermore, C60-GSH inhibited intracellular calcium mobilization, and subsequent cell apoptosis via bcl-2/bax-caspase-3 signaling pathway induced by H2O2 stimulation in HEK 293T cells. Importantly, these protective effects of C60-GSH were superior to those of GSH. In conclusion, these results suggested that C60-GSH has potential to protect against H2O2-induced cell apoptosis by scavenging free radicals and maintaining intracellular calcium homeostasis without evident toxicity.

Chikusetsu saponin IVa confers cardioprotection via SIRT1/ERK1/2 and Homer1a pathway

Hyperglycemia-induced reactive oxygen species (ROS) generation and Ca²⁺ overload contribute to the development of diabetic cardiomyopathy. In this study, we aimed to study the protective effects of Chikusetsu saponin IVa (CHS) from Aralia taibaiensis against hyperglycemia-induced myocardial injuries. Treatment of H9c2 cells with high glucose (HG) for 24 h resulted in a loss of cell viability and increase of ROS, LDH and Ca²⁺ levels, and also induced cell apoptosis, and those changes were all markedly reversed by the administration of CHS. In further studies, CHS dose-dependently increased the expression of Homer1a, ERK1/2 and SIRT1 in both H9c2 cells and rat primary cardiomyocytes. However, transfection of Homer1a-specific siRNA abolished the ability of CHS in controlling the ROS and Ca²⁺ homeostasis. Moreover, specific SIRT1 inhibitors or siRNA significantly suppressed the enhanced phosphorylation of ERK1/2 and expression of Homer1a induced by CHS as well as its cytoprotective effect. CHS induced Homer1a expression was also suppressed by siERK1/2. Additionally, results in diabetic mice also showed that CHS protected myocardium from I/R-introduced apoptosis by activating the SIRT1/ERK1/2/Homer1a pathway. These results demonstrated that CHS protected against hyperglycemia-induced myocardial injury through SIRT1/ERK1/2 and Homer1a pathway in vivo and in vitro.

The carbonic anhydrase inhibitor methazolamide prevents amyloid beta-induced mitochondrial dysfunction and caspase activation protecting neuronal and glial cells in vitro and in the mouse brain

Mitochondrial dysfunction has been recognized as an early event in Alzheimer's disease (AD) pathology, preceding and inducing neurodegeneration and memory loss. The presence of cytochrome c (CytC) released from the mitochondria into the cytoplasm is often detected after acute or chronic neurodegenerative insults, including AD. The carbonic anhydrase inhibitor (CAI) methazolamide (MTZ) was identified among a library of drugs as an inhibitor of CytC release and proved to be neuroprotective in Huntington's disease and stroke models. Here, using neuronal and glial cell cultures, in addition to an acute model of amyloid beta (Aβ) toxicity, which replicates by intra-hippocampal injection the consequences of interstitial and cellular accumulation of Aβ, we analyzed the effects of MTZ on neuronal and glial degeneration induced by the Alzheimer's amyloid. MTZ prevented DNA fragmentation, CytC release and activation of caspase 9 and caspase 3 induced by Aβ in neuronal and glial cells in culture through the inhibition of mitochondrial hydrogen peroxide production. Moreover, intraperitoneal administration of MTZ prevented neurodegeneration induced by intra-hippocampal Aβ injection in the mouse brain and was effective at reducing caspase 3 activation in neurons and microglia in the area surrounding the injection site. Our results, delineating the molecular mechanism of action of MTZ against Aβ-mediated mitochondrial dysfunction and caspase activation, and demonstrating its efficiency in a model of acute amyloid-mediated toxicity, provide the first combined in vitro and in vivo evidence supporting the potential of a new therapy employing FDA-approved CAIs in AD.

Scaffolding protein Homer1a protects against NMDA-induced neuronal injury

Excessive N-methyl-D-aspartate receptor (NMDAR) activation and the resulting activation of neuronal nitric oxide synthase (nNOS) cause neuronal injury. Homer1b/c facilitates NMDAR-PSD95-nNOS complex interactions, and Homer1a is a negative competitor of Homer1b/c. We report that Homer1a was both upregulated by and protected against NMDA-induced neuronal injury in vitro and in vivo. The neuroprotective activity of Homer1a was associated with NMDA-induced Ca²⁺ influx, oxidative stress and the resultant downstream signaling activation. Additionally, we found that Homer1a functionally regulated NMDAR channel properties in neurons, but did not regulate recombinant NR1/NR2B receptors in HEK293 cells. Furthermore, we found that Homer1a detached the physical links among NR2B, PSD95 and nNOS and reduced the membrane distribution of NMDAR. NMDA-induced neuronal injury was more severe in Homer1a homozygous knockout mice (KO, Homer1a^−/−) when compared with NMDA-induced neuronal injury in wild-type mice (WT, Homer1a^+/+). Additionally, Homer1a overexpression in the cortex of Homer1a^−/− mice alleviated NMDA-induced neuronal injury. These findings suggest that Homer1a may be a key neuroprotective endogenous molecule that protects against NMDA-induced neuronal injury by disassembling NR2B-PSD95-nNOS complexes and reducing the membrane distribution of NMDARs.

Upregulation of Homer1a Promoted Retinal Ganglion Cell Survival After Retinal Ischemia and Reperfusion via Interacting with Erk Pathway

Retinal ischemia and reperfusion (I/R) is extensively involved in ocular diseases, causing retinal ganglion cell (RGCs) death resulting in visual impairment and blindness. Homer1a is considered as an endogenous neuroprotective protein in traumatic brain injury. However, the roles of Homer1a in RGCs I/R injury have not been elucidated. The present study investigated the changes in expression and effect of Homer1a in RGCs both in vitro and in vivo after I/R injury using Western blot, TUNEL assay, gene interference and overexpression, and gene knockout procedures. The levels of Homer1a and phosphorylated Erk (p-Erk) increased in RGCs and retinas after I/R injury. Upregulation of Homer1a in RGCs after I/R injury decreased the level of p-Erk, and mitigated RGCs apoptosis. Conversely, downregulation of Homer1a increased the level of p-Erk, and augmented RGCs apoptosis. Furthermore, inhibition of the p-ERK reduced RGCs apoptosis, and increased the expression of Homer 1a after I/R injury. Finally, the retinas of Homer1a KO mice treated with I/R injury had significantly less dendrites and RGCs, compared with Homer1a WT mice. These findings demonstrated that Homer1a may contribute to RGCs survival after I/R injury by interacting with Erk pathway.

Sirt3 protects cortical neurons against oxidative stress via regulating mitochondrial Ca2+ and mitochondrial biogenesis

Oxidative stress is a well-established event in the pathology of several neurobiological diseases. Sirt3 is a nicotinamide adenine nucleotide (NAD+)-dependent protein deacetylase that regulates mitochondrial function and metabolism in response to caloric restriction and stress. This study aims to investigate the role of Sirt3 in H2O2 induced oxidative neuronal injury in primary cultured rat cortical neurons. We found that H2O2 treatment significantly increased the expression of Sirt3 in a time-dependent manner at both mRNA and protein levels. Knockdown of Sirt3 with a specific small interfering RNA (siRNA) exacerbated H2O2-induced neuronal injury, whereas overexpression of Sirt3 by lentivirus transfection inhibited H2O2-induced neuronal damage reduced the generation of reactive oxygen species (ROS), and increased the activities of endogenous antioxidant enzymes. In addition, the intra-mitochondrial Ca2+ overload, but not cytosolic Ca2+ increase after H2O2 treatment, was strongly attenuated after Sirt3 overexpression. Overexpression of Sirt3 also increased the content of mitochondrial DNA (mtDNA) and the expression of mitochondrial biogenesis related transcription factors. All these results suggest that Sirt3 acts as a prosurvival factor playing an essential role to protect cortical neurons under H2O2 induced oxidative stress, possibly through regulating mitochondrial Ca2+ homeostasis and mitochondrial biogenesis.

Down-regulation of Homer1b/c attenuates group I metabotropic glutamate receptors dependent Ca²⁺ signaling through regulating endoplasmic reticulum Ca²⁺ release in PC12 cells

The molecular basis for group I metabotropic glutamate receptors (mGluR1 and 5) coupling to membrane ion channels and intracellular calcium pools is not fully understood. Homer is a family of post synaptic density proteins functionally and physically attached to target proteins at proline-rich sequences. In the present study, we demonstrate that Homer1b/c is constitutively expressed in PC12 cells, whereas Homer1a, the immediate early gene product, can be up-regulated by brain derived neurotrophic factor (BDNF) and glutamate. Knockdown of Homer1b/c using specific target small interfering RNA (siRNA) did not interfere the expression of mGluR1, mGluR5 and their downstream effectors, including inositol-1,4,5-trisphosphate receptors (IP3R), phospholipase C (PLC) and Gq proteins. By analyzing Ca(2+) imaging in PC12 cells, we demonstrated that Homer1b/c is an essential regulator of the Ca(2+) release from the endoplasmic reticulum (ER) induced by the activation of group I mGluRs, IP3R and ryanodine receptors (RyR). Furthermore, the group I mGluRs activation-dependent refilling of the Ca(2+) stores in both resting and depolarizing conditions were strongly attenuated in the absence of Homer1b/c. Together, our results demonstrate that in PC12 cells Homer1b/c is a regulator of group I mGluRs related Ca(2+) homeostasis that is essential for the maintenance of normal Ca(2+) levels in the ER.

Postsynaptic scaffold protein Homer 1a protects against traumatic brain injury via regulating group I metabotropic glutamate receptors

Traumatic brain injury (TBI) produces excessive glutamate, leading to excitotoxicity via the activation of glutamate receptors. Postsynaptic density scaffold proteins have crucial roles in mediating signal transduction from glutamate receptors to their downstream mediators. Therefore, studies on the mechanisms underlying regulation of excitotoxicity by scaffold proteins can uncover new treatments for TBI. Here, we demonstrated that the postsynaptic scaffold protein Homer 1a was neuroprotective against TBI in vitro and in vivo, and this neuroprotection was associated with its effects on group I metabotropic glutamate receptors (mGluRs). Upon further study, we found that Homer 1a mainly affected neuronal injury induced by mGluR1 activation after TBI and also influenced mGluR5 function when its activity was restored. The ability of Homer 1a to disrupt mGluR-ERK signaling contributed to its ability to regulate the functions of mGluR1 and mGluR5 after traumatic injury. Intracellular Ca(2+) and PKC were two important factors involved in the mediation of mGluR-ERK signaling by Homer 1a. These results define Homer 1a as a novel endogenous neuroprotective agent against TBI.

Downregulation of Homer1b/c improves neuronal survival after traumatic neuronal injury

Homer protein, a member of the post-synaptic density protein family, plays an important role in the neuronal synaptic activity and is extensively involved in neurological disorders. The present study investigates the role of Homer1b/c in modulating neuronal survival by using an in vitro traumatic neuronal injury model, which was achieved by using a punch device that consisted of 28 stainless steel blades joined together and produced 28 parallel cuts. Downregulation of Homer1b/c by specific siRNA significantly (p<0.05) alleviated the cytoplasmic calcium levels and neuron lactate dehydrogenase release, and ultimately decreased the apoptotic rate after traumatic neuronal injury compared with non-targeting siRNA control treatment in cultured rat cortical neurons. Moreover, the expression of metabotropic glutamate receptor 1a (mGluR1a) was significantly (p<0.05) reduced in the Homer1b/c siRNA-transfected neurons after injury. Therefore, Homer1b/c not only modulated the mGluR1a-inositol 1,4,5-triphosphate receptors-Ca(2+) signal transduction pathway, but also regulated the expression of mGluR1a in mechanical neuronal injury. These findings indicate that the suppression of Homer1b/c expression potentially protects neurons from glutamate excitotoxicity after injury and might be an effective intervention target in traumatic brain injury.

Notoginsenoside R1-mediated neuroprotection involves estrogen receptor-dependent crosstalk between Akt and ERK1/2 pathways: a novel mechanism of Nrf2/ARE signaling activation

Notoginsenoside R1 (NGR1), a novel phytoestrogen isolated from Panax notoginseng, has antioxidant and anti-apoptotic properties. Oxidative stress plays a pivotal role in neurodegenerative diseases. To mimic oxidative stress in neurons and explore the neuroprotection of NGR1, H₂O₂-induced neurotoxicity in NGF-induced differentiation of PC12 cells was used. In this study, NGR1 preconditioning provided neuroprotective effects via suppressing H₂O₂-induced the intracellular ROS accumulation, the increase in the product of lipid peroxidation (MDA), protein oxidation (protein carbonyl), and DNA fragmentation (8-OHdG), and mitochondrial membrane depolarization as well as caspase-3 activation. Moreover, NGR1 treatment alone potently increased the nuclear translocation of Nrf2, augmented ARE enhancer activity, and upregulated the expression and activity of phase II antioxidant enzymes including HO-1, NQO-1, and γ-GCSc. NGR1 could also increase the ERE activity and activate Akt and ERK1/2 pathways. NGR1-mediated activation of Nrf2/ARE signaling and neuroprotection were abolished by genetic silencing of Nrf2 using siRNA or the pharmacological blockade of estrogen receptors using ICI-182780, and partially inhibited by Akt siRNA or ERK siRNA transfection. In addition, the phosphorylation of ERK1/2 mediated by NGR1 was markedly inhibited in PC12 cells transfected with Akt siRNA. On the contrary, ERK1/2 siRNA transfection hardly had any effect on the phosphorylation of Akt mediated by NGR1. NGR1-mediated activation of Akt and ERK1/2 pathways was blocked by ICI-182780. In conclusion, NGR1 provided neuroprotection via inducing an estrogen receptor-dependent crosstalk between Akt and ERK1/2 pathways, subsequently activating Nrf2/ARE signaling and thereby up-regulating phase II antioxidant enzymes.

Protective effect of Homer 1a on tumor necrosis factor-α with cycloheximide-induced apoptosis is mediated by mitogen-activated protein kinase pathways

Although Homer 1, of the postsynaptic density, regulates apoptosis, the signaling mechanisms are not fully elucidated. In this study, we found that tumor necrosis factor-α (TNF-α)/cycloheximide (CHX) treatment transiently increased Homer 1a (the short variant of Homer 1), but did not affect Homer 1b/c (the long variant of Homer 1). Overexpression of Homer 1a blocked TNF-α/CHX-induced apoptotic cell death, whereas inhibition of Homer 1a induction enhanced the pro-apoptotic effect of TNF-α/CHX treatment. Moreover, brain-derived neurotrophic factor, as a potential activator of endogenous Homer 1a, inhibited apoptotic cell death after TNF-α/CHX treatment through induction of Homer 1a. Since three major mitogen-activated protein kinase (MAPK) pathways have important roles in apoptosis, we examined if Homer 1a is involved in the effects of MAPK pathways on apoptosis. It was shown that inhibition of the ERK1/2 pathway increased the expression and the protective effect of Homer 1a, but inhibition of the p38 pathway produced the opposite effect. Cross-talk among MAPK pathways was also associated with the regulation of Homer 1a during apoptotic cell death. Blocking the p38 pathway increased the activity in the ERK1/2 pathway, while inhibition of ERK1/2 pathway abolished the effect of p38 inhibitor on Homer 1a. Furthermore, Homer 1a reversely affected the activation of MAPK pathways. These findings suggest that Homer 1a plays an important role in the prevention of apoptotic cell death and contributes to distinct regulatory effects of MAPK pathways on apoptotic cell death.

Inhibition of store-operated calcium entry attenuates MPP(+)-induced oxidative stress via preservation of mitochondrial function in PC12 cells: involvement of Homer1a

The process of store-operated calcium entry (SOCE), whereby the release of intracellular Ca²⁺ from endoplasmic reticulum (ER) activates Ca²⁺ influx channels in the plasma membrane, has been demonstrated to impact a diverse range of cell functions. In the present study, we investigated the potential protective effect of SOCE inhibition against 1-methyl-4-phenylpyridinium (MPP⁺) injury by using pharmacological antagonists or specific small interfering RNA (siRNA) in PC12 cells. The results showed that both antagonists (15 μM MRS-1845 and 50 μM ML-9) and stromal interacting molecule-1 (STIM1) targeted siRNA (Si-STIM1) significantly increased cell viability, decreased apoptotic cell death and reduced intracellular reactive oxygen species (ROS) production and lipid peroxidation in MPP⁺ injured PC12 cells. SOCE inhibition also prevented MPP⁺ induced mitochondrial dysfunction and activation of mitochondrial related apoptotic factors, while had no effect on mitochondrial biogenesis. Moreover, inhibition of SOCE by antagonists and siRNA increased the expression levels of Homer1a mRNA and protein, and knockdown of Homer1a expression by specific siRNA partly reversed the protective effects induced by SOCE inhibition in PC12 cells. All these results indicated that SOCE inhibition protected PC12 cells against MPP⁺ insult through upregulation of Homer1a expression, and SOCE might be an ideal target for investigating therapeutic strategy against neuronal injury in PD patients.

Blockade of SOCE protects HT22 cells from hydrogen peroxide-induced apoptosis

Oxidative stress is an established event in the pathology of neurobiological diseases. Previous studies indicated that store-operated Ca(2+) entry (SOCE) has been involved in oxidative stress. The present study was carried out to investigate the effects of SOCE inhibition on neuronal oxidative stress injury induced by hydrogen peroxide (H2O2) in HT22 cells, a murine hippocampal neuronal model. H2O2 insult induced significant intracellular Ca(2+) overload, mitochondrial dysfunction and cell viability decrease. Inhibition of SOCE by pharmacological inhibitor and STIM1 RNAi significantly alleviated intracellular Ca(2+) overload, restored the mitochondrial membrane potential (MMP), decreased cytochrome C release and eventually inhibited H2O2-induced cell apoptosis. These findings suggest that SOCE inhibition exhibited neuroprotection against oxidative stress induced by H2O2 and SOCE might be a useful therapeutic target in neurobiological disorders.

Downregulation of postsynaptic density-95-interacting regulator of spine morphogenesis reduces glutamate-induced excitotoxicity by differentially regulating glutamate receptors in rat cortical neurons

Glutamate-induced excitotoxicity is involved in many neurological diseases. Preso, a novel postsynaptic scaffold protein, mediates excitatory synaptic transmission and various synaptic functions. In this study, we investigated the role of Preso in the regulation of glutamate-induced excitotoxicity in rat cortical neurons. Knockdown of Preso with small interfering RNA improved neuronal viability and attenuated the elevation of lactate dehydrogenase (LDH) release after glutamate treatment. Downregulation of Preso also inhibited an increase in the BAX/Bcl-2 ratio and cleavage of caspase-9 and caspase-3. Although the expression and distribution of metabotropic glutamate receptor (mGluR) 1/5, NR1, NR2A and NR2B were not changed by knockdown of Preso, downregulation of Preso protected neurons from glutamate-induced excitotoxicity by inhibiting mGluR and N-methyl-D-aspartate receptor function. However, downregulation of Preso neither affected the expression of GluR1 and GluR2 nor influenced the function of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor after glutamate treatment. Furthermore, intracellular Ca(2+) was an important downstream effector of Preso in the regulation of excitotoxicity. These results suggest that expression of Preso promotes the induction of excitotoxicity by facilitating different glutamate receptor signaling pathways. Therefore, Preso might be a potential pharmacological target for preventing and treating neurological diseases.

Homer1 knockdown protects dopamine neurons through regulating calcium homeostasis in an in vitro model of Parkinson's disease

Homer1 protein is an important scaffold protein at postsynaptic density and has been demonstrated to play a central role in calcium signaling in the central nervous system. The aim of this study was to investigate the effects of Homer1 knockdown on MPP(+) induced neuronal injury in cultured dopamine (DA) neurons. We found that down-regulating Homer1 expression with specific small interfering RNA (siRNA) significantly suppressed LDH release, reduced Propidium iodide (PI) or Hoechst staining, increased the number of tyrosine hydroxylase (TH) positive cells and DA uptake, and attenuated apoptotic and necrotic cell death after MPP(+) injury. Homer1 knockdown decreased intracellular reactive oxygen species (ROS) generation through inhibition of intracellular calcium overload, but did not affect the endogenous antioxidant enzyme activities. Calcium imaging was used to examine the changes of intracellular Ca(2+) concentration ([Ca(2+)]cyt) and Ca(2+) in endoplasmic reticulum (ER) ([Ca(2+)]ER), and the results showed that Homer1 siRNA transfection attenuated ER Ca(2+) release up to 120min after MPP(+) injury. Furthermore, decrease of [Ca(2+)]cyt induced by Homer1 knockdown in MPP(+) treated neurons was further enhanced by NMDA receptor antagonists MK-801 and AP-5, but not canonical transient receptor potential (TRPC) channel antagonist SKF-96365. l-type calcium antagonist isradipine but not nimodipine further inhibited intracellular calcium overload after MPP(+) insult in Homer1 down-regulated neurons. These results suggest that Homer1 knockdown has protective effects against neuronal injury in in vitro PD model by reducing calcium overload mediated ROS generation, and this protection may be dependent at least in part on the regulatory effects on the function of calcium channels in both plasma membrane and ER.

Negative feedback regulation of Homer 1a on norepinephrine-dependent cardiac hypertrophy

Homers are scaffolding proteins that modulate diverse cell functions being able to assemble signalling complexes. In this study, the presence, sub-cellular distribution and function of Homer 1 was investigated. Homer 1a and Homer 1b/c are constitutively expressed in cardiac muscle of both mouse and rat and in HL-1 cells, a cardiac cell line. As judged by confocal immunofluorescence microscopy, Homer 1a displays sarcomeric and peri-nuclear localization. In cardiomyocytes and cultured HL-1 cells, the hypertrophic agonist norepinephrine (NE) induces α1-adrenergic specific Homer 1a over-expression, with a two-to-three-fold increase within 1h, and no up-regulation of Homer 1b/c, as judged by Western blot and qPCR. In HL-1 cells, plasmid-driven over-expression of Homer 1a partially antagonizes activation of ERK phosphorylation and ANF up-regulation, two well-established, early markers of hypertrophy. At the morphometric level, NE-induced increase of cell size is likewise and partially counteracted by exogenous Homer 1a. Under the same experimental conditions, Homer 1b/c does not have any effect on ANF up-regulation nor on cell hypertrophy. Thus, Homer 1a up-regulation is associated to early stages of cardiac hypertrophy and appears to play a negative feedback regulation on molecular transducers of hypertrophy.

New role of JAK2/STAT3 signaling in endothelial cell oxidative stress injury and protective effect of melatonin

Previous studies have shown that the JAK2/STAT3 signaling pathway plays a regulatory role in cellular oxidative stress injury (OSI). In this study, we explored the role of the JAK2/STAT3 signaling pathway in hydrogen peroxide (H₂O₂)-induced OSI and the protective effect of melatonin against (H₂O₂)-induced injury in human umbilical vein endothelial cells (HUVECs). AG490 (a specific inhibitor of the JAK2/STAT3 signaling pathway) and JAK2 siRNA were used to manipulate JAK2/STAT3 activity, and the results showed that AG490 and JAK2 siRNA inhibited OSI and the levels of p-JAK2 and p-STAT3. HUVECs were then subjected to H₂O₂ in the absence or presence of melatonin, the main secretory product of the pineal gland. Melatonin conferred a protective effect against H₂O₂, which was evidenced by improvements in cell viability, adhesive ability and migratory ability, decreases in the apoptotic index and reactive oxygen species (ROS) production and several biochemical parameters in HUVECs. Immunofluorescence and Western blotting showed that H₂O₂ treatment increased the levels of p-JAK2, p-STAT3, Cytochrome c, Bax and Caspase3 and decreased the levels of Bcl2, whereas melatonin treatment partially reversed these effects. We, for the first time, demonstrate that the inhibition of the JAK2/STAT3 signaling pathway results in a protective effect against endothelial OSI. The protective effects of melatonin against OSI, at least partially, depend upon JAK2/STAT3 inhibition.

Curcumin attenuates endothelial cell oxidative stress injury through Notch signaling inhibition

Previous studies have demonstrated that Notch signaling pathway plays a regulatory role in cellular oxidative stress injury (OSI). In this study, our aim was to explore the role of the Notch signaling pathway in hydrogen peroxide (H(2)O(2))-induced OSI and the protective effect of curcumin during (H(2)O(2))-induced injury in human umbilical vein endothelial cells (HUVECs). DAPT, a specific inhibitor of the Notch signaling pathway, and Notch1 siRNA were used to study Notch activity. Further, HUVECs were exposed to H(2)O(2) in the absence or presence of curcumin. DAPT and Notch1 siRNA significantly inhibited OSI and the expression of Notch1 and Hes1. Curcumin conferred a protective effect on the HUVECs against H(2)O(2), which was evidenced by improved cell viability, adhesive ability and migratory ability and a decreased apoptotic index, decreased production of reactive oxygen species (ROS) and a reduction in several biochemical parameters. Immunofluorescence and Western blotting analyses demonstrated that H(2)O(2) treatment upregulated the expression of Notch1, Hes1, Caspase3, Bax and cytochrome c downregulated the expression of Bcl2, and treatment with curcumin reversed these effects. We demonstrated for the first time that the inhibition of Notch signaling pathway imparts a protective effect against endothelial OSI. The protective effects of curcumin against OSI are at least in part dependent on Notch1 inhibition.

Interactions between SIRT1 and MAPK/ERK regulate neuronal apoptosis induced by traumatic brain injury in vitro and in vivo

Traumatic brain injury (TBI) is a serious insult that frequently leads to neurological dysfunction or death. Silent information regulator family protein 1 (SIRT1), as the founding member of nicotinamide adenine dinucleotide (NAD)-dependent deacetylases, has recently been demonstrated to have neuroprotective effect in several models of neurodegenerative diseases. The present study attempts to determine whether SIRT1 has a neuroprotective effect in the model of TBI, and further to investigate the possible regulatory mechanism of neuron death. Thus, we employ transection model in vitro and weight-drop model in vivo to mimic the insults of TBI. The study shows that the expressions of SIRT1, phosphorylation extracellular signal-regulated kinase (p-ERK) and cleaved Caspase-3 are induced after trauma injury in vitro or in vivo. Furthermore, inhibiting SIRT1 by pharmacological inhibitor salermide or SIRT1 siRNA significantly promotes apoptotic neuron death and reduces ERK1/2 activation induced by mechanical injury in vitro and in vivo. Inhibition of ERK1/2 activation with PD98059 or U0126 (two mitogen activated protein kinase kinase inhibitors) in vitro and in vivo significantly attenuates the SIRT1 and cleaved Caspase-3 expression to protect neuron against TBI-induced apoptosis. These results reveal that SIRT1 plays a neuroprotective effect against neuronal apoptosis induced by TBI. The interactions between SIRT1 and MAPK/ERK pathway regulate neuronal apoptosis induced by mechanical trauma injury in vitro and in vivo.