Endoplasmic reticulum stress and calcium imbalance are involved in cadmium-induced lipid aberrancy in Saccharomyces cerevisiae

Clemastine Reduces post-stroke Neurodegeneration by Alleviating Endoplasmic Reticulum stress-mediated Demyelination and Cognitive Impairment Through PERK/ATF4/CHOP Signaling Pathway

The progressive brain damage following ischemic stroke is primarily due to oxidative stress and activation of inflammatory pathways. Post-stroke neurodegeneration can lead to the loss of neurons and glial cells, including oligodendrocytes, contributing to demyelination. Following ischemic stroke, reperfusion results in increased intracellular calcium, generation of free radicals, and inflammation culminating in accumulation of misfolded proteins in the endoplasmic reticulum (ER) lumen augmenting the ER stress. ER stress has been shown to aggravate post-stroke neurodegeneration by triggering neuronal apoptosis and also contributing towards demyelination of neurons. To address the limitations of current stroke therapies, repurposing of drugs as future adjunctive therapy may be promising. Clemastine, an antihistaminic drug, improves post stroke outcome as evident in the present study. Male Sprague Dawley (SD) rats were treated with clemastine following ischemic stroke. Harvested brain tissues were subjected to different biochemical assays, molecular assays, and histopathological analysis. Clemastine was able to reduce infarct size, alleviate oxidative stress, improve neuronal count, and functional outcomes. Clemastine downregulated genes and proteins responsible for ER stress, apoptosis and demyelination as shown by the western blot and qPCR results. Our study suggests that clemastine may alleviate endoplasmic reticulum stress-mediated demyelination by modulating PERK/ATF4/CHOP axis, and may be used as one of the adjunctive therapies for stroke in future.

Fine particulate matter‑induced cardiac developmental toxicity (Review)

Fine particulate matter (PM2.5) has become an important risk factor threatening human health. Epidemiological and toxicological investigations have revealed that PM2.5 not only leads to cardiovascular dysfunction, but it also gives rise to various adverse health effects on the human body, such as cardiovascular and cerebrovascular diseases, cancers, neurodevelopmental disorders, depression and autism. PM2.5 is able to penetrate both respiratory and placental barriers, thereby resulting in negative effects on fetal development. A large body of epidemiological evidences has suggested that gestational exposure to PM2.5 increases the incidence of congenital diseases in offspring, including congenital heart defects. In addition, animal model studies have revealed that gestational exposure to PM2.5 can disrupt normal heart development in offspring, although the potential molecular mechanisms have yet to be fully elucidated. The aim of the present review was to provide a brief overview of what is currently known regarding the molecular mechanisms underlying cardiac developmental toxicity in offspring induced by gestational exposure to PM2.5.

Astilbin antagonizes developmental cardiotoxicity after cadmium exposure in chicken embryos by inhibiting endoplasmic reticulum stress and maintaining calcium homeostasis

Cadmium (Cd) is a dangerous heavy metal with high toxicity that is known to impair development. Astilbin (ASB) is a protective flavonoid compound. We aimed to explore whether ASB can antagonize the myocardial developmental toxicity of Cd exposure. Cd (2 µg) and/or ASB (0.002 µg) were injected into embryonized eggs that were 1 day old. Histological examinations revealed Cd-induced ventricular dilation, reduced wall thickness, and disrupted myocardial fiber connections, while co-administration of ASB mitigated these effects. Electron microscopy confirmed ASB's ability to counteract Cd-induced myocardial cell myofibril damage. Real-time quantitative PCR (QRT-PCR) and western blot (WB) molecular investigations revealed that Cd increased endoplasmic reticulum stress in myocardial tissue and primary cardiomyocytes, as shown by raised expression of stress-related genes (GRP78, XBP1, GRP94, ATF4, ATF6, IRE1, and CHOP). Moreover, Cd disrupted calcium homeostasis, affecting important genes linked to Ca2+ channels and causing an excess of Ca2+ in the cytoplasm. In addition, we detected genes related to development and differentiation-related genes in myocardial tissue and primary cardiomyocytes. The results showed that the downregulation of transcription factors in the IrxA cluster, Mefs, and Tbxs families after Cd exposure indicated that cardiac transcription was hindered and cardiac markers (TnnT2, TnnC1, Gata4, Gata6, and Nkx2-5) were abnormally expressed. ASB successfully mitigated these disturbances. During the cell cycle, primary cardiomyocytes undergo growth arrest in flow cytometry. These results suggest that the maturation and differentiation of cardiomyocytes are inhibited after Cd exposure, and ASB has an antagonistic effect on Cd. The present study indicated that Cd could trigger developmental cardiotoxicity in chicken embryos and primary cardiomyocytes by endoplasmic reticulum stress and Ca2+ overload, respectively, while ASB has an antagonistic effect.

Heavy Metals in Follicular Fluid Affect the Ultrastructure of the Human Mature Cumulus-Oocyte Complex

It is known that exposure to heavy metal such as lead (Pb) and cadmium (Cd) has several adverse effects, particularly on the human reproductive system. Pb and Cd have been associated with infertility in both men and women. In pregnant women, they have been associated with spontaneous abortion, preterm birth, and impairment of the development of the fetus. Since these heavy metals come from both natural and anthropogenic activities and their harmful effects have been observed even at low levels of exposure, exposure to them remains a public health issue, especially for the reproductive system. Given this, the present study aimed to investigate the potential reproductive effects of Pb and Cd levels in the follicular fluid (FF) of infertile women and non-smokers exposed to heavy metals for professional reasons or as a result of living in rural areas near landfills and waste disposal areas in order to correlate the intrafollicular presence of these metals with possible alterations in the ultrastructure of human cumulus-oocyte complexes (COCs), which are probably responsible for infertility. Blood and FF metals were measured using atomic absorption spectrometry. COCs corresponding to each FF analyzed were subjected to ultrastructural analyses using transmission electron microscopy. We demonstrated for the first time that intrafollicular levels of Pb (0.66 µg/dL-0.85 µg/dL) and Cd (0.26 µg/L-0.41 µg/L) could be associated with morphological alterations of both the oocyte and cumulus cells' (CCs) ultrastructure. Since blood Cd levels (0.54 µg/L-1.87 µg/L) were above the current reference values established by the guidelines of the Agency for Toxic Substances and Disease Registry (ATSDR) and the Environmental Protection Agency (EPA) (0.4 µg/L), whereas blood Pb levels (1.28 µg/dL-3.98 µg/dL) were below the ATSDR reference values (≤5 µg/dL), we believe that these alterations could be due especially to Cd, even if we cannot exclude a possible additional effect of Pb. Our results highlighted that oocytes were affected in maturation and quality, whereas CCs showed scarcely active steroidogenic elements. Regressing CCs, with cytoplasmic alterations, were also numerous. According to Cd's endocrine-disrupting activity, the poor steroidogenic activity of CCs might correlate with delayed oocyte cytoplasmic maturation. So, we conclude that levels of heavy metals in the blood and the FF might negatively affect fertilization, embryo development, and pregnancy, compromising oocyte competence in fertilization both directly and indirectly, impairing CC steroidogenic activity, and inducing CC apoptosis.

CaHMA1 promotes Cd accumulation in pepper fruit

The main planting areas for pepper (Capsicum sp.) are high in cadmium (Cd), which is the most prevalent heavy metal pollutant worldwide. Breeding pepper cultivars with low Cd levels can promote sustainable agricultural production and ensure the safety of pepper products. To identify breeding targets for reducing Cd accumulation in pepper fruits, we performed a genome-wide association study on 186 accessions. Polymorphisms were associated with fruit Cd content in a genomic region containing a homolog of Arabidopsis (Arabidopsis thaliana) Heavy metal-transporting ATPase 1 (HMA1) encoding a P-type ATPase. In two cultivars with contrasting Cd accumulation, transcriptome analysis revealed differentially expressed genes enriched for carbohydrate metabolism and photosynthesis in fruits with high Cd accumulation, and a Cd2+/Zn2+-exporting ATPase gene (HMA). Heterologous expression of CaHMA1 in yeast increases Cd sensitivity. Overexpression of CaHMA1 conferred a severe increase in Cd content in Arabidopsis plants, whereas reduced CaHMA1 expression in pepper fruits decreased Cd content. We propose that CaHMA1 expression may be an important component of the high Cd accumulation in pepper plants.

Impairment of RPN4, a transcription factor, induces ER stress and lipid abnormality in Saccharomyces cerevisiae

Accumulation of misfolded/unfolded proteins in the endoplasmic reticulum (ER) induces ER stress. The transcription factor RPN4 {"Regulatory Particle Non-ATPase"} regulates protein homeostasis by degrading proteins that elude proper folding or assembly via the proteasomal degradation pathway. Here, we studied the lipid alterations exerted by Saccharomyces cerevisiae to mitigate (ER) stress during adaptive responses in rpn4∆ cells. The loss of RPN4-induced ER stress increased phospholipid synthesis, leading to altered membrane structures and accumulation of neutral lipids, causing an increase in lipid droplets (LDs). There was a significant upregulation of genes involved in neutral lipid and membrane lipid synthesis in rpn4∆ cells. Overexpression of RPN4 restored the defects caused by rpn4∆ cells. Thus, our study provides new insight that RPN4 impacts lipid homeostasis.

The acyltransferase Gpc1 is both a target and an effector of the unfolded protein response in Saccharomyces cerevisiae

The unfolded protein response (UPR) is sensitive to proteotoxic and membrane bilayer stress, both of which are sensed by the ER protein Ire1. When activated, Ire1 splices HAC1 mRNA, producing a transcription factor that targets genes involved in proteostasis and lipid metabolism, among others. The major membrane lipid phosphatidylcholine (PC) is subject to phospholipase-mediated deacylation, producing glycerophosphocholine (GPC), followed by reacylation of GPC through the PC deacylation/reacylation pathway (PC-DRP). The reacylation events occur via a two-step process catalyzed first by the GPC acyltransferase Gpc1, followed by acylation of the lyso-PC molecule by Ale1. However, whether Gpc1 is critical for ER bilayer homeostasis is unclear. Using an improved method for C14-choline-GPC radiolabeling, we first show that loss of Gpc1 results in abrogation of PC synthesis through PC-DRP and that Gpc1 colocalizes with the ER. We then probe the role of Gpc1 as both a target and an effector of the UPR. Exposure to the UPR-inducing compounds tunicamycin, DTT, and canavanine results in a Hac1-dependent increase in GPC1 message. Further, cells lacking Gpc1 exhibit increased sensitivity to those proteotoxic stressors. Inositol limitation, known to induce the UPR via bilayer stress, also induces GPC1 expression. Finally, we show that loss of GPC1 induces the UPR. A gpc1Δ mutant displays upregulation of the UPR in strains expressing a mutant form of Ire1 that is unresponsive to unfolded proteins, indicating that bilayer stress is responsible for the observed upregulation. Collectively, our data indicate an important role for Gpc1 in yeast ER bilayer homeostasis.

Cadmium perturbed lipid profile and induced liver dysfunction in mice through phosphatidylcholine remodeling and promoting arachidonic acid synthesis and metabolism

Cadmium ion (Cd²⁺) exposure has been reported to associate with the prevalence of dyslipidemia, and contribute to the initiation and progression of nonalcoholic fatty liver disease (NAFLD). However, Cd²⁺ exposure perturbed specific metabolic pathways and underlying mechanisms are still unclear. In the present study, through lipidomics analyses of differential metabolites in serum between the Cd²⁺-exposed mice and the control group, 179 differential metabolites were identified, among which phosphatidylcholines (PCs) accounted for 49 % metabolites. Moreover, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment assay indicates that PCs participate in the metabolic pathways, including the Arachidonic Acid (AA) metabolism, which also could be potential NAFLD biomarkers. Moreover, in vivo and in vitro results suggested that Cd²⁺ exposure induced PC synthesis and remodeling, and increased AA level by promoting fatty acid desaturase 1 (FADS1) to catalyze synthesis process instead of cytosolic phospholipase A2 (cPLA2) mediated release pathway. Inhibition of FADS1 by T3364366 could reverse Cd-induced AA, prostaglandin E2 (PGE2) and triglyceride (TAG) levels, and it also reduce cisplatin resistance in HepG2 cells. This study provides new evidence of Cd²⁺-induced dyslipidemia and reveals underlying molecular mechanism involved in liver dysfunction of Cd²⁺ exposure.

Endoplasmic Reticulum Stress and the Unfolded Protein Response in Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is an acute cerebrovascular disease characterized by sudden interruption of blood flow in a certain part of the brain, leading to serious disability and death. At present, treatment methods for ischemic stroke are limited to thrombolysis or thrombus removal, but the treatment window is very narrow. However, recovery of cerebral blood circulation further causes cerebral ischemia/reperfusion injury (CIRI). The endoplasmic reticulum (ER) plays an important role in protein secretion, membrane protein folding, transportation, and maintenance of intracellular calcium homeostasis. Endoplasmic reticulum stress (ERS) plays a crucial role in cerebral ischemia pathophysiology. Mild ERS helps improve cell tolerance and restore cell homeostasis; however, excessive or long-term ERS causes apoptotic pathway activation. Specifically, the protein kinase R-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1) pathways are significantly activated following initiation of the unfolded protein response (UPR). CIRI-induced apoptosis leads to nerve cell death, which ultimately aggravates neurological deficits in patients. Therefore, it is necessary and important to comprehensively explore the mechanism of ERS in CIRI to identify methods for preserving brain cells and neuronal function after ischemia.

Impairment of transcription factor Gcr1p binding motif perturbs OPI3 transcription in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, the transcription factor GCR1 plays a vital role in carbohydrate metabolism and in the current study we tried to elucidate its role in lipid metabolism. In silico analysis revealed the upstream activation sequence (UAS) in the promoter region of OPI3 possessed six conserved recognition sequences for Gcr1p and the ChIP assay confirmed the binding of Gcr1p on the OPI3 promoter region. The real-time quantitative polymerase chain reaction and promoter-reporter activity revealed a substantial reduction in OPI3 expression and was supported with decreased phosphatidylcholine (PC) level that is rescued with exogenous choline supplementation in gcr1∆ cells. Simultaneously, there was an increase in triacylglycerol level, accompanied with increased number and size of lipid droplets in gcr1∆ cells. The expression of pT1, pT2 truncations in opi3∆ cells revealed the -1 to -500 bp in the promoter region is essential for the activation of OPI3 transcription. The mutation specifically at UAS_{CT box} (-265) in the OPI3 promoter region displayed a reduction in the PC level and the additional mutation at UAS_INO (-165) further reduced the PC level. Collectively, our data suggest that the GCR1 transcription factor also regulates the OPI3 expression and has an impact on lipid homeostasis.

Molecular Biology of Cadmium Toxicity in Saccharomyces cerevisiae

Cadmium (Cd) is a toxic heavy metal mainly originating from industrial activities and causes environmental pollution. To better understand its toxicity and pollution remediation, we must understand the effects of Cd on living beings. Saccharomyces cerevisiae (budding yeast) is an eukaryotic unicellular model organism. It has provided much scientific knowledge about cellular and molecular biology in addition to its economic benefits. Effects associated with copper and zinc, sulfur and selenium metabolism, calcium (Ca2+) balance/signaling, and structure of phospholipids as a result of exposure to cadmium have been evaluated. In yeast as a result of cadmium stress, "mitogen-activated protein kinase," "high osmolarity glycerol," and "cell wall integrity" pathways have been reported to activate different signaling pathways. In addition, abnormalities and changes in protein structure, ribosomes, cell cycle disruption, and reactive oxygen species (ROS) following cadmium cytotoxicity have also been detailed. Moreover, the key OLE1 gene that encodes for delta-9 FA desaturase in relation to cadmium toxicity has been discussed in more detail. Keeping all these studies in mind, an attempt has been made to evaluate published cellular and molecular toxicity data related to Cd stress, and specifically published on S. cerevisiae.

The Transient Receptor Potential Channel Yvc1 Deletion Recovers the Growth Defect of Calcineurin Mutant Under Endoplasmic Reticulum Stress in Candida albicans

Transient receptor potential (TRP) channel Yvc1 was related with hyphal growth, oxidative stress response, and pathogenicity. Calcineurin subunit Cnb1 was activated immediately in yeasts when exposed to severe stimulation. However, the relationship between Yvc1 and Cnb1-governed calcium ions and endoplasmic reticulum (ER) stress response remains unrevealed. In this study, we found that the mutant cnb1Δ/Δ was sensitive to TN, which was related with the overexpression of membrane calcium ion channels that could increase the cytosol calcium concentration. However, the growth of the cnb1Δ/Δyvc1Δ/Δ mutant was recovered and its cell vitality was better than the cnb1Δ/Δ strain. Meanwhile, the cellular calcium concentration was decreased and its fluctuation was weakened under ER stress in the cnb1Δ/Δyvc1Δ/Δ strain. To verify the regulation role of Yvc1 in the calcium concentration, we found that the addition of CaCl2 led to the worse viability, while the growth state was relieved under the treatment of EGTA in the cnb1Δ/Δ strain. In conclusion, the deletion of YVC1 could reduce the cellular calcium and relieve the ER stress sensitivity of the cnb1Δ/Δ strain. Thereby, our findings shed a novel light on the relationship between the Yvc1-governed cellular calcium concentration and ER stress response in C. albicans.

Study on the interaction mechanism of phospholipid imbalance and endoplasmic reticulum protein secretion imbalance in Aspergillus niger

As the largest membrane organelle, the endoplasmic reticulum (ER) is the main location for protein preliminary processing and phospholipid synthesis. Phospholipid bilayer is the main component of the ER, so it plays an intuitively important role in the steady state of protein synthesis in the ER. Despite of their importance, relationship between phospholipid homeostasis and protein processing in Aspergillus niger remains poorly understood. In this study, phosphatidyl ethanolamine (PE)/phosphatidyl choline (PC) and phosphatidyl acid (PA) metabolic mutants and ER protein processing mutants were established by knockout the key genes in phospholipid synthesis or UPR effector hacA. Based on global transcriptome and lipidome analysis, the relationship between the phospholipids imbalance and ER protein secretory imbalance was revealed as followed: The cells compensate for the damage caused by ER protein secretory deficiency or phospholipid deficiency from enhancing the protein processing and the synthesis of phospholipids at the transcription level, therefore phospholipid deficiency (Δopi3) and continuous activation of UPR (hacAi) have a synergistic effect in promoting protein secretion and phospholipid biosynthesis. At the same time, the metabolic deficiencies of phospholipid homeostasis and the processing deficiencies of ER protein will also cause cells sensitive to oxidative stress, cell wall inhibition and DNA damage.

Role of bisphenol A on calcium influx and its potential toxicity on the testis of Danio rerio

This study investigated the acute in vitro effect of low-concentration bisphenol A (BPA) on calcium (⁴⁵Ca²⁺) influx in zebrafish (Danio rerio) testis and examined whether intracellular Ca²⁺ was involved in the effects of BPA on testicular toxicity. In vitro studies on ⁴⁵Ca²⁺ influx were performed in the testes after incubation with BPA for 30 min. Inhibitors were added 15 min before the addition of ⁴⁵Ca²⁺ and BPA to testes to study the mechanism of action of BPA. The involvement of intracellular calcium from stores on lactate dehydrogenase (LDH) release and on triacylglycerol (TAG) content were carried out after in vitro incubation of testes with BPA for 1 h. Furthermore, gamma-glutamyl transpeptidase (GGT) and aspartate aminotransferase (AST) activities were analyzed in the liver at 1 h after in vitro BPA incubation of D. rerio. Our data show that the acute in vitro treatment of D. rerio testes with BPA at very low concentration activates plasma membrane ionic channels, such as voltage-dependent calcium channels and calcium-dependent chloride channels, and protein kinase C (PKC), which stimulates Ca²⁺ influx. In addition, BPA increased cytosolic Ca²⁺ by activating inositol triphosphate receptor (IP₃R) and inhibiting sarco/endoplasmic reticulum calcium ATPase (SERCA) at the endoplasmic reticulum, contributing to intracellular Ca²⁺ overload. The protein kinases, PKC, MEK 1/2 and PI3K, are involved in the mechanism of action of BPA, which may indicate a crosstalk between the non-genomic initiation effects mediated by PLC/PKC/IP₃R signaling and genomic responses of BPA mediated by the estrogen receptor (ESR). In vitro exposure to a higher concentration of BPA caused cell damage and plasma membrane injury with increased LDH release and TAG content; both effects were dependent on intracellular Ca²⁺ and mediated by IP₃R. Furthermore, BPA potentially induced liver damage, as demonstrated by increased GGT activity. In conclusion, in vitro effect of BPA in a low concentration triggers cytosolic Ca²⁺ overload and activates downstream protein kinases pointing to a crosstalk between its non-genomic and genomic effects of BPA mediated by ESR. Moreover, in vitro exposure to a higher concentration of BPA caused intracellular Ca²⁺-dependent testicular cell damage and plasma membrane injury. This acute toxicity was reinforced by increased testicular LDH release and GGT activity in the liver.

Impairment of MET transcriptional activators, MET4 and MET31 induced lipid accumulation in Saccharomyces cerevisiae

The genes involved in the methionine pathway are closely associated with phospholipid homeostasis in yeast. The impact of the deletion of methionine (MET) transcriptional activators (MET31, MET32 and MET4) in lipid homeostasis is studied. Our lipid profiling data showed that aberrant phospholipid and neutral lipid accumulation occurred in met31∆ and met4∆ strains with low Met. The expression pattern of phospholipid biosynthetic genes such as CHO2, OPI3 and triacylglycerol (TAG) biosynthetic gene, DGA1 were upregulated in met31∆, and met4∆ strains when compared to wild type (WT). The accumulation of triacylglycerol and sterol esters (SE) content supports the concomitant increase in lipid droplets in met31∆ and met4∆ strains. However, excessive supplies of methionine (1 mM) in the cells lacking the MET transcriptional activators MET31 and MET4 ameliorates the abnormal lipogenesis and causes aberrant lipid accumulation. These findings implicate the methionine accessibility plays a pivotal role in lipid metabolism in the yeast model.

Effect of cadmium on essential metals and their impact on lipid metabolism in Saccharomyces cerevisiae

Cadmium (Cd) is a toxic heavy metal that induces irregularity in numerous lipid metabolic pathways. Saccharomyces cerevisiae, a model to study lipid metabolism, has been used to establish the molecular basis of cellular responses to Cd toxicity in relation to essential minerals and lipid homeostasis. Multiple pathways sense these environmental stresses and trigger the mineral imbalances specifically calcium (Ca) and zinc (Zn). This review is aimed to elucidate the role of Cd toxicity in yeast, in three different perspectives: (1) elucidate stress response and its adaptation to Cd, (2) understand the physiological role of a macromolecule such as lipids, and (3) study the stress rescue mechanism. Here, we explored the impact of Cd interference on the essential minerals such as Zn and Ca and their influence on endoplasmic reticulum stress and lipid metabolism. Cd toxicity contributes to lipid droplet synthesis by activating OLE1 that is essential to alleviate lipotoxicity. In this review, we expanded our current findings about the effect of Cd on lipid metabolism of budding yeast.

Celastrol ameliorates Cd-induced neuronal apoptosis by targeting NOX2-derived ROS-dependent PP5-JNK signaling pathway

Celastrol, a plant-derived triterpene, has neuroprotective benefit in the models of neurodegenerative disorders that are characterized by overproduction of reactive oxygen species (ROS). Recently, we have reported that cadmium (Cd) activates c-Jun N-terminal kinase (JNK) pathway leading to neuronal cell death by inducing ROS inactivation of protein phosphatase 5 (PP5), and celastrol prevents Cd-activated JNK pathway against neuronal apoptosis. Therefore, we hypothesized that celastrol could hinder Cd induction of ROS-dependent PP5-JNK signaling pathway from apoptosis in neuronal cells. Here, we show that celastrol attenuated Cd-induced expression of NADPH oxidase 2 (NOX2) and its regulatory proteins (p22^phox , p40^phox , p47^phox , p67^phox , and Rac1), as well as the generation of ROS in PC12 cells and primary neurons. Also, N-acetyl-l-cysteine, a ROS scavenger, potentiated celastrol's inhibition of the events in the cells triggered by Cd, implying neuroprotection by celastrol via blocking Cd-evoked NOX2-derived ROS. Further research revealed that celastrol was involved in the regulation of PP5 inactivation and JNK/c-Jun activation induced by Cd, as celastrol prevented Cd from reducing PP5 expression, and over-expression of wild-type PP5 or dominant negative c-Jun strengthened celastrol's inhibition of Cd-induced phosphorylation of JNK and/or c-Jun, as well as apoptosis in neuronal cells. Of importance, inhibiting NOX2 with apocynin or silencing NOX2 by RNA interference enhanced the inhibitory effects of celastrol on Cd-induced inactivation of PP5, activation of JNK/c-Jun, ROS, and apoptosis in the cells. Furthermore, we noticed that expression of wild-type PP5 or dominant negative c-Jun, or pretreatment with JNK inhibitor SP600125 reinforced celastrol's suppression of Cd-induced NOX2 and its regulatory proteins, and consequential ROS in neuronal cells. These findings indicate that celastrol ameliorates Cd-induced neuronal apoptosis via targeting NOX2-derived ROS-dependent PP5-JNK signaling pathway. Our data highlight a beneficial role of celastrol in the prevention of Cd-induced oxidative stress and neurodegenerative diseases.

Diacylglycerol Kinases Are Widespread in Higher Plants and Display Inducible Gene Expression in Response to Beneficial Elements, Metal, and Metalloid Ions

Diacylglycerol kinases (DGKs) are pivotal signaling enzymes that phosphorylate diacylglycerol (DAG) to yield phosphatidic acid (PA). The biosynthesis of PA from phospholipase D (PLD) and the coupled phospholipase C (PLC)/DGK route is a crucial signaling process in eukaryotic cells. Next to PLD, the PLC/DGK pathway is the second most important generator of PA in response to biotic and abiotic stresses. In eukaryotic cells, DGK, DAG, and PA are implicated in vital processes such as growth, development, and responses to environmental cues. A plethora of DGK isoforms have been identified so far, making this a rather large family of enzymes in plants. Herein we performed a comprehensive phylogenetic analysis of DGK isoforms in model and crop plants in order to gain insight into the evolution of higher plant DGKs. Furthermore, we explored the expression profiling data available in public data bases concerning the regulation of plant DGK genes in response to beneficial elements and other metal and metalloid ions, including silver (Ag), aluminum (Al), arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and sodium (Na). In all plant genomes explored, we were able to find DGK representatives, though in different numbers. The phylogenetic analysis revealed that these enzymes fall into three major clusters, whose distribution depends on the composition of structural domains. The catalytic domain conserves the consensus sequence GXGXXG/A where ATP binds. The expression profiling data demonstrated that DGK genes are rapidly but transiently regulated in response to certain concentrations and time exposures of beneficial elements and other ions in different plant tissues analyzed, suggesting that DGKs may mediate signals triggered by these elements. Though this evidence is conclusive, further signaling cascades that such elements may stimulate during hormesis, involving the phosphoinositide signaling pathway and DGK genes and enzymes, remain to be elucidated.