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

Homer1 Protects against Retinal Ganglion Cell Pyroptosis by Inhibiting Endoplasmic Reticulum Stress-Associated TXNIP/NLRP3 Inflammasome Activation after Middle Cerebral Artery Occlusion-Induced Retinal Ischemia

Retinal ischemia, after cerebral ischemia, is an easily overlooked pathophysiological problem in which inflammation is considered to play an important role. Pyroptosis is a kind of cell death pattern accompanied by inflammation. Homer scaffold protein 1 (Homer1) has anti-inflammation properties and protects against ischemic injury. However, little is known about pyroptosis following middle cerebral artery occlusion (MCAO)-induced retinal ischemia and the regulatory mechanisms involved by Homer1 for the development of pyroptosis. In the present study, retinal ischemic injury was induced in mice by permanent MCAO in vivo, and retinal ganglion cells (RGCs) were subjected to Oxygen and Glucose Deprivation (OGD) to establish an in vitro model. It was shown that TXNIP/NLRP3-mediated pyroptosis was located predominantly in RGCs, which gradually increased after retinal ischemia and peaked at 24 h after retinal ischemia. Interestingly, the RGCs pyroptosis occurred not only in the cell body but also in the axon. Notably, the occurrence of pyroptosis coincided with the change of Homer1 expression in the retina after retinal ischemia and Homer1 also co-localized with RGCs. It was demonstrated that overexpression of Homer1 not only alleviated RGCs pyroptosis and inhibited the release of pro-inflammatory factors but also led to the increase in phosphorylation of AMPK, inhibition of ER stress, and preservation of visual function after retinal ischemia. In conclusion, it was suggested that Homer1 may protect against MCAO-induced retinal ischemia and RGCs pyroptosis by inhibiting endoplasmic reticulum stress-associated TXNIP/NLRP3 inflammasome activation after MCAO-induced retinal ischemia.

Remembering and forgetting in sleep: Selective synaptic plasticity during sleep driven by scaling factors Homer1a and Arc

Sleep is a conserved and essential process that supports learning and memory. Synapses are a major target of sleep function and a locus of sleep need. Evidence in the literature suggests that the need for sleep has a cellular or microcircuit level basis, and that sleep need can accumulate within localized brain regions as a function of waking activity. Activation of sleep promoting kinases and accumulation of synaptic phosphorylation was recently shown to be part of the molecular basis for the localized sleep need. A prominent hypothesis in the field suggests that some benefits of sleep are mediated by a broad but selective weakening, or scaling-down, of synaptic strength during sleep in order to offset increased excitability from synaptic potentiation during wake. The literature also shows that synapses can be strengthened during sleep, raising the question of what molecular mechanisms may allow for selection of synaptic plasticity types during sleep. Here I describe mechanisms of action of the scaling factors Arc and Homer1a in selective plasticity and links with sleep need. Arc and Homer1a are induced in neurons in response to waking neuronal activity and accumulate with time spent awake. I suggest that during sleep, Arc and Homer1a drive broad weakening of synapses through homeostatic scaling-down, but in a manner that is sensitive to the plasticity history of individual synapses, based on patterned phosphorylation of synaptic proteins. Therefore, Arc and Homer1a may offer insights into the intricate links between a cellular basis of sleep need and memory consolidation during sleep.

Redox Regulation of Autophagy in Cancer: Mechanism, Prevention and Therapy

Reactive oxygen species (ROS), products of normal cellular metabolism, play an important role in signal transduction. Autophagy is an intracellular degradation process in response to various stress conditions, such as nutritional deprivation, organelle damage and accumulation of abnormal proteins. ROS and autophagy both exhibit double-edged sword roles in the occurrence and development of cancer. Studies have shown that oxidative stress, as the converging point of these stimuli, is involved in the mechanical regulation of autophagy process. The regulation of ROS on autophagy can be roughly divided into indirect and direct methods. The indirect regulation of autophagy by ROS includes post-transcriptional and transcriptional modulation. ROS-mediated post-transcriptional regulation of autophagy includes the post-translational modifications and protein interactions of AMPK, Beclin 1, PI3K and other molecules, while transcriptional regulation mainly focuses on p62/Keap1/Nrf2 pathway. Notably, ROS can directly oxidize key autophagy proteins, such as ATG4 and p62, leading to the inhibition of autophagy pathway. In this review, we will elaborate the molecular mechanisms of redox regulation of autophagy in cancer, and discuss ROS- and autophagy-based therapeutic strategies for cancer treatment.

Serotonin Type 3 Receptor Is Potentially Involved in Cellular Stress Induced by Hydrogen Peroxide

Depression is a disease with several molecular mechanisms involved, such as problems in the serotonergic pathway. This disease is very complex and prevalent, and thus important to deeply study and aim to overcome high rates of relapse and therapeutic failure. In this study, two cellular lines were used (HT-22 and SH-SY5Y cells) to gain insight about the role of the serotonin type 3 (5-HT3) receptor in cellular stress induced by hydrogen peroxide and/or corticosterone. In research, these compounds are known to mimic the high levels of oxidative stress and dysfunction of the hypothalamus–hypophysis–adrenal axis by the action of glucocorticoids, usually present in depressed individuals. The receptor 5-HT3 is also known to be involved in depression, previously demonstrated in studies that highlight the role of these receptors as promising targets for antidepressant therapy. Indeed, the drugs used in this work (mirtazapine, scopolamine, and lamotrigine) interact with this serotonergic receptor. Thus, by using cell morphology, cell viability (neutral red and MTT), and HPLC assays, this work aimed to understand the role of these drugs in the stress induced by H₂O₂/corticosterone to HT-22 and SH-SY5Y cell lines. We concluded that the antagonism of the 5-HT3 receptor by these drugs may be important in the attenuation of H₂O₂-induced oxidative stress to the cells, but not in the corticosterone-induced stress.

Homer1 promotes the conversion of A1 astrocytes to A2 astrocytes and improves the recovery of transgenic mice after intracerebral hemorrhage

Background

Inflammation induced by intracerebral hemorrhage (ICH) is one of the main causes of the high mortality and poor prognosis of patients with ICH. A1 astrocytes are closely associated with neuroinflammation and neurotoxicity, whereas A2 astrocytes are neuroprotective. Homer scaffolding protein 1 (Homer1) plays a protective role in ischemic encephalopathy and neurodegenerative diseases. However, the role of Homer1 in ICH-induced inflammation and the effect of Homer1 on the phenotypic conversion of astrocytes remain unknown.

Methods

Femoral artery autologous blood from C57BL/6 mice was used to create an ICH model. We use the A1 phenotype marker C3 and A2 phenotype marker S100A10 to detect astrocyte conversion after ICH. Homer1 overexpression/knock-down mice were constructed by adeno-associated virus (AAV) infection to explore the role of Homer1 and its mechanism of action after ICH. Finally, Homer1 protein and selumetinib were injected into in situ hemorrhage sites in the brains of Homer1^flox/flox/Nestin-Cre^+/− mice to study the efficacy of Homer1 in the treatment of ICH by using a mouse cytokine array to explore the potential mechanism.

Results

The expression of Homer1 peaked on the third day after ICH and colocalized with astrocytes. Homer1 promotes A1 phenotypic conversion in astrocytes in vivo and in vitro. Overexpression of Homer1 inhibits the activation of MAPK signaling, whereas Homer1 knock-down increases the expression of pathway-related proteins. The Homer1 protein and selumetinib, a non-ATP competitive MEK1/2 inhibitor, improved the outcome in ICH in Homer1^flox/flox/Nestin-Cre^+/− mice. The efficacy of Homer1 in the treatment of ICH is associated with reduced expression of the inflammatory factor TNFSF10 and increased expression of the anti-inflammatory factors activin A, persephin, and TWEAK.

Conclusions

Homer1 plays an important role in inhibiting inflammation after ICH by suppressing the A1 phenotype conversion in astrocytes. In situ injection of Homer1 protein may be a novel and effective method for the treatment of inflammation after ICH.

AMPK-PINK1/Parkin Mediated Mitophagy Is Necessary for Alleviating Oxidative Stress-Induced Intestinal Epithelial Barrier Damage and Mitochondrial Energy Metabolism Dysfunction in IPEC-J2

The imbalance of redox biology and oxidative stress leads to intestinal barrier injury and mitophagy. However, much uncertainty still exists about the role of mitophagy in oxidative stress and intestinal function. Here, we showed the effects of hydrogen peroxide (H₂O₂)-induced oxidative stress on intestinal epithelial cell oxidation balance, intestinal barrier function and mitochondrial energy metabolism and its underlying mechanism. In this study, we found that H₂O₂-induced oxidative stress activated adenosine monophosphate-activated protein kinase (AMPK) and enhanced mitophagy in intestinal porcine epithelial cells (IPEC-J2). While compound C (AMPK inhibitor) and mdivi-1 (mitophagy inhibitor) significantly reduced the activity of superoxide dismutase (SOD) and increased mitochondrial reactive oxygen species (ROS) levels in H₂O₂ treated cells. Moreover, compound C and mdivi-1 significantly reduced the trans-epithelium electrical resistant (TER) and increased the fluorescein isothiocyanate-dextran (FD4) flux in H₂O₂ treated IPEC-J2. Furthermore, compound C and mdivi-1 significantly reduced the activity of mitochondrial complex II. Seahorse XF96 data showed that compound C + mdivi-1+ H₂O₂ treatment significantly reduced maximum respiratory oxygen consumption and spare respiratory capacity. Additionally, compound C or mdivi-1 treatment reduced the formation of mitochondrial autophagosomes. These results unveiled that AMPK and PINK1/Parkin mediated mitophagy is necessary for alleviating oxidative stress induced intestinal epithelial barrier damage and mitochondrial energy metabolism dysfunction in IPEC-J2.

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.

STING-Mediated Autophagy Is Protective against H2O2-Induced Cell Death

Stimulator of interferon genes (STING)-mediated type-I interferon signaling is a well characterized instigator of the innate immune response following bacterial or viral infections in the periphery. Emerging evidence has recently linked STING to various neuropathological conditions, however, both protective and deleterious effects of the pathway have been reported. Elevated oxidative stress, such as neuroinflammation, is a feature of a number of neuropathologies, therefore, this study investigated the role of the STING pathway in cell death induced by elevated oxidative stress. Here, we report that the H₂O₂-induced activation of the STING pathway is protective against cell death in wildtype (WT) MEFSV40 cells as compared to STING^−/− MEF SV40 cells. This protective effect of STING can be attributed, in part, to an increase in autophagy flux with an increased LC3II/I ratio identified in H₂O₂-treated WT cells as compared to STING^−/− cells. STING^−/− cells also exhibited impaired autophagic flux as indicated by p62, LC3-II and LAMP2 accumulation following H₂O₂ treatment, suggestive of an impairment at the autophagosome-lysosomal fusion step. This indicates a previously unrecognized role for STING in maintaining efficient autophagy flux and protecting against H₂O₂-induced cell death. This finding supports a multifaceted role for the STING pathway in the underlying cellular mechanisms contributing to the pathogenesis of neurological disorders.

Therapeutic prospects of hydroxytyrosol on experimentally induced diabetic testicular damage: potential interplay with AMPK expression

Male reproductive dysfunction represents one of the overlooked consequences of diabetes that still deserve more scientific attention. We designed this study to explore the therapeutic potential of hydroxytyrosol (HT) on diabetic testicular damage and to investigate its relationship with adenosine monophosphate-activated protein kinase (AMPK) expression. In this context, 30 adult male Wistar rats were utilized and subdivided into control, diabetic and HT-treated diabetic groups. Testicular sections were prepared for histopathological examination and immunohistochemical detection of 8-hydroxy-2'-deoxyguanosine, Sertoli cell vimentin, myoid cell α-SMA, androgen receptors and caspase-3. We also assessed oxidative enzymatic and lipid peroxidation biochemical profiles, sperm count, morphology and motility. Real-time PCR of AMPK expression in tissue homogenate was performed. We observed that HT restored testicular histopathological structure and significantly reduced oxidative DNA damage and the apoptotic index. The HT-treated group also exhibited significantly higher Sertoli cell vimentin, myoid cell α-SMA and androgen receptor immune expression than the diabetic group. A rescue of the oxidative enzymatic activity, lipid peroxidation profiles, sperm count, morphology and motility to control levels was also evident in the HT-treated group. Significant upregulation of AMPK mRNA expression in the HT-treated group clarified the role of AMPK as an underlying molecular interface of the ameliorative effects of HT. We concluded that HT exhibited tangible antioxidant and antiapoptotic impacts on the testicular cytomorphological and immunohistochemical effects of experimentally induced diabetes. Furthermore, AMPK has an impactful role in the molecular machinery of these effects.

MAPK Pathway Inhibitors Attenuated Hydrogen Peroxide Induced Damage in Neural Cells

Background

Oxidative stress due to reactive oxygen species plays a central role in pathophysiology of neurodegenerative diseases. Inhibition of mitogen-activated protein kinase (MAPK) cascades attenuates the oxidative induced cell stress and behaves as potential neuroprotection agent.

Materials and Methods

In this study, we evaluate hydrogen peroxide induced neural cell stress and determine how different MAPK inhibitors restore the cell damage.

Results

The results indicated that oxidative stress induced by neural cell damage commonly exists, and MAPK inhibitors partially and selectively attenuated the cell damage by reducing ROS production and cell apoptosis. The cultured neurons are more susceptible to hydrogen peroxide than subculture cells.

Conclusion

We conclude that the essential role of different MAPK inhibitors is to attenuate the hydrogen peroxide induced neuronal cell damage. Those data broaden the implication between individual neural cells and different MAPK inhibitors and give clues for oxidative stress induced neural diseases.

Ubiquitination status does not affect Vps34 degradation

Vps34 (vacuolar protein-sorting 34) plays important role in autophagy and endosomal trafficking. These processes are closely associated protein ubiquitination and degradation. We have hypothesized that Vps34 ubiquitination status would also control its degradation. Here, we report that our results did not support this assumption. In cells transiently transfected with ubiquitin (UB) constructs contained different lysine residues (Ks), Vps34 ubiquitination could occur regardless of the presence of any Ks in UB. However, Vps34 protein levels were not significantly altered in cells transiently transfected with these UB mutants. We further found that Vps34 protein was altered by pharmacological manipulation of E2/E3 activity; yet this effect was not significantly affected by UB overexpression. In vivo experiments revealed that in APP/PS1 mice, an animal model of Alzheimer's disease (AD), although ubiquitination of Vps34 was significantly reduced, Vps34 protein levels remained unchanged. Vps34 indeed was subjected to proteasomal or lysosomal degradation, as prolonged treatment of proteasomal inhibitor MG132 or lysosomal inhibitor chloroquine elevated Vps34 protein levels. We conclude that unlike most of other proteins, Vps34 ubiquitination is not closely associated with its degradation.

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.

Trilobatin Protects Against Oxidative Injury in Neuronal PC12 Cells Through Regulating Mitochondrial ROS Homeostasis Mediated by AMPK/Nrf2/Sirt3 Signaling Pathway

Oxidative stress-induced neuronal cell damage is a crucial factor in the pathogenesis of mitochondria-associated neurological diseases. Therefore, elimination of overproduction of mitochondrial reactive oxygen species (mtROS) may be a potential strategy for prevention and treatment of neurological diseases. In the present study, the neuroprotective effects of trilobatin (TLB), a novel small molecule monomer derived from Lithocarpus polystachyus Rehd, and its underlying mechanisms were investigated in vitro using hydrogen peroxide (H₂O₂)-induced oxidative stress model in a neuron-like PC12 cell. The findings revealed that pre-treatment with TLB dramatically concentration-dependently suppressed H₂O₂-induced PC12 cells damage by enhancing cell viability, repressed reduction of mitochondrial membrane potential (MMP) and decreased mtROS overgeneration, thereby deferring cell apoptosis. Further study demonstrated that TLB not only increased the enzymatic activities of glutathione peroxidase (GPx), isocitrate dehydrogenase 2 (IDH2),superoxide dismutase 2 (SOD2) and deacetylation of SOD2, but also activated silent mating-type information regulation 2 homolog 3 (Sirt3) within the mitochondria and thereby upregulating forkheadboxO3a (FoxO3a), which regulated mitochondrial DNA genes, then led to improving complex I activity and adenosine triphosphate (ATP) synthesis. What’s more, TLB up-regulated p-adenosine monophosphate-activated protein kinase (AMPK) level, the expression of peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α), and ERRα. Intriguingly, TLB failed to mitigate H₂O₂-induced PC12 injury in the presence of the AMPK inhibitor (Compound C), indicating that the beneficial effects of TLB on the regulation of mtROS homeostasis were reliance on AMPK -Sirt3 signaling pathway. Moreover, TLB also facilitated nuclear factor erythroid 2-related factor 2 (Nrf2) and promoted antioxidant gene expression in turn, and knockdown of Nrf2 by siRNA dramatically reduced the neuroprotective effects of TLB. Notably, AMPK inhibitor abolished the activation of Nrf2 and Sirt3, whereas, knockdown of Nrf2 blocked the upregulation of Sirt3, but it did not affect p-AMPK level. In conclusion, our findings demonstrate that TLB protects against oxidative injury in neuronal PC12 cells through regulating mtROS homeostasis in the first time, which is, at least partly, mediated through the AMPK/Nrf2/Sirt3 signaling pathway.