Cadmium impairs the survival and proliferation of cultured adult subventricular neural stem cells through activation of the JNK and p38 MAP kinases

Bisphenol-F and Bisphenol-S (BPF and BPS) Impair the Stemness of Neural Stem Cells and Neuronal Fate Decision in the Hippocampus Leading to Cognitive Dysfunctions

Neurogenesis occurs throughout life in the hippocampus of the brain, and many environmental toxicants inhibit neural stem cell (NSC) function and neuronal generation. Bisphenol-A (BPA), an endocrine disrupter used for surface coating of plastic products causes injury in the developing and adult brain; thus, many countries have banned its usage in plastic consumer products. BPA analogs/alternatives such as bisphenol-F (BPF) and bisphenol-S (BPS) may also cause neurotoxicity; however, their effects on neurogenesis are still not known. We studied the effects of BPF and BPS exposure from gestational day 6 to postnatal day 21 on neurogenesis. We found that exposure to non-cytotoxic concentrations of BPF and BPS significantly decreased the number/size of neurospheres, BrdU+ (proliferating NSC marker) and MAP-2+ (neuronal marker) cells and GFAP+ astrocytes in the hippocampus NSC culture, suggesting reduced NSC stemness and self-renewal and neuronal differentiation and increased gliogenesis. These analogs also reduced the number of BrdU/Sox-2+, BrdU/Dcx+, and BrdU/NeuN+ co-labeled cells in the hippocampus of the rat brain, suggesting decreased NSC proliferation and impaired maturation of newborn neurons. BPF and BPS treatment increases BrdU/cleaved caspase-3+ cells and Bax-2 and cleaved caspase protein levels, leading to increased apoptosis in hippocampal NSCs. Transmission electron microscopy studies suggest that BPF and BPS also caused degeneration of neuronal myelin sheath, altered mitochondrial morphology, and reduced number of synapses in the hippocampus leading to altered cognitive functions. These results suggest that BPF and BPS exposure decreased the NSC pool, inhibited neurogenesis, induced apoptosis of NSCs, caused myelin degeneration/synapse degeneration, and impaired learning and memory in rats.

Adult neurogenesis: a real hope or a delusion?

Adult neurogenesis, the process of creating new neurons, involves the coordinated division, migration, and differentiation of neural stem cells. This process is restricted to neurogenic niches located in two distinct areas of the brain: the subgranular zone of the dentate gyrus of the hippocampus and the subventricular zone of the lateral ventricle, where new neurons are generated and then migrate to the olfactory bulb. Neurogenesis has been thought to occur only during the embryonic and early postnatal stages and to decline with age due to a continuous depletion of neural stem cells. Interestingly, recent years have seen tremendous progress in our understanding of adult brain neurogenesis, bridging the knowledge gap between embryonic and adult neurogenesis. Here, we discuss the current status of adult brain neurogenesis in light of what we know about neural stem cells. In this notion, we talk about the importance of intracellular signaling molecules in mobilizing endogenous neural stem cell proliferation. Based on the current understanding, we can declare that these molecules play a role in targeting neurogenesis in the mature brain. However, to achieve this goal, we need to avoid the undesired proliferation of neural stem cells by controlling the necessary checkpoints, which can lead to tumorigenesis and prove to be a curse instead of a blessing or hope.

An ultrasensitive Cd2+ detection biosensor based on DNAzyme and CRISPR/Cas12a coupled with hybridization chain reaction

The detection of cadmium is essential because it poses a significant threat to human health and the environment. Recent advancements in biosensors that detect nonnucleic-acid targets using CRISPR/Cas12a in combination with aptamers or DNAzymes show promising performance. Herein, we integrated DNAzyme, hybridization chain reaction (HCR) and CRISPR/Cas12a into a single biosensor for the first time and realized the ultrasensitive detection of Cd2+. A single phosphorothioate ribonucleobase (rA)-containing oligonucleotide (PS substrate) and a Cd2+-specific DNAzyme (Cdzyme) are used for Cd2+ recognition, releasing short single-stranded DNA. Then, the HCR is triggered by the cleavage products for signal transduction and amplification. Next, the trans-cleavage activity of Cas12a is activated due to the presence of crRNA complementary strands and PAM sites in the HCR products. As a result, FQ-reporters are cleaved, and the fluorescence values can be easily read using a fluorometer, allowing Cd2+ quantification by measuring the fluorescent signal. The Cd2+ detection biosensor is ultrasensitive with a detection limit of 1.25 pM. Moreover, the biosensor shows great stability under different pH and various anion conditions. The proposed sensor was utilized for environmental water sample detection, demonstrating the dependability of the detection system. Considering the high sensitivity and reliable performance of the assay, it could be further used in environmental monitoring. In addition, the design strategy reported in this study could extend the application of CRISPR/Cas12a in heavy metal detection.

A turn-on signal biosensor for cadmium(II) based on DNAzyme and stem-loop qPCR

Cadmium is a heavy metal that is exceedingly hazardous to humans and can enter the body through tainted food or drink, causing severe harm. It is critical to develop a technology for detecting cadmium in food and water that is sensitive and accurate. One such approach, which employs nucleases, is uncommon. A cadmium(II) turn-on biosensor was successfully created in this work using repetitive cleavage of certain specific nucleases for signal conversion and sophisticated stem-loop qPCR (quantitative polymerase chain reaction) for quick signal amplification and output. The method has strong selectivity and sensitivity for precise quantification, with a detection limit of 6 nmol L-1, i.e. 0.948 g L-1, which is far lower than the 5.0 g L-1 set by the United States Environmental Protection Agency, and it also operates well in retail rice samples.

Integrated metabolomic and transcriptomic analysis reveals perturbed glycerophospholipid metabolism in mouse neural stem cells exposed to cadmium

Cadmium (Cd) is a ubiquitous heavy metal with neurotoxicity. Our previous study reported that Cd could inhibit the proliferation of mouse neural stem cells (mNSCs). However, the underlying mechanisms are obscure. In recent years, the rapid growth of multi-omics techniques enables us to explore the cellular responses that occurred after toxicant exposure at the molecular level. In this study, we used a combination of metabolomics and transcriptomics approaches to investigate the effects of exposure to Cd on mNSCs. After treatment with Cd, the metabolites and transcripts in mNSCs changed significantly with 110 differentially expressed metabolites and 2135 differentially expressed genes identified, respectively. The altered metabolites were mainly involved in glycerophospholipid metabolism, arginine and proline metabolism, arginine biosynthesis, glyoxylate and dicarboxylate metabolism. Meanwhile, the transcriptomic data demonstrated perturbed membrane function and signal transduction. Furthermore, integrated analysis of metabolomic and transcriptomic data suggested that glycerophospholipid metabolism might be the major metabolic pathway affected by Cd in mNSCs. More interestingly, the supplementation of lysophosphatidylethanolamine (LPE) attenuated Cd-induced mitochondrial impairment and the inhibition of cell proliferation and differentiation in mNSCs, further supporting our analysis. Overall, the study provides new insights into the mechanisms of Cd-induced neurotoxicity.

Hybrid Nanoparticle/DNAzyme Electrochemical Biosensor for the Detection of Divalent Heavy Metal Ions and Cr3

A hybrid noble nanoparticle/DNAzyme electrochemical biosensor is proposed for the detection of Pb2+, Cd2+, and Cr3+. The sensor takes advantage of a well-studied material that is known for its selective interaction with heavy metal ions (i.e., DNAzymes), which is combined with metallic nanoparticles. The double-helix structure of DNAzymes is known to dissociate into smaller fragments in the presence of specific heavy metal ions; this results in a measurable change in device resistance due to the collapse of conductive inter-nanoparticle DNAzyme bridging. The paper discusses the effect of DNAzyme anchoring groups (i.e., thiol and amino functionalization groups) on device performance and reports on the successful detection of all three target ions in concentrations that are well below their maximum permitted levels in tap water. While the use of DNAzymes for the detection of lead in particular and, to some extent, cadmium has been studied extensively, this is one of the few reports on the successful detection of chromium (III) via a sensor incorporating DNAzymes. The sensor showed great potential for its future integration in autonomous and remote sensing systems due to its low power characteristics, simple and cost-effective fabrication, and easy automation and measurement.

Selenite Ameliorates Cadmium-induced Cytotoxicity Through Downregulation of ROS Levels and Upregulation of Selenoprotein Thioredoxin Reductase 1 in SH-SY5Y Cells

Cadmium (Cd) as a ubiquitous toxic heavy metal in the environment, causes severe hazards to human health, such as cellular stress and organ injury. Selenium (Se) was reported to reduce Cd toxicity and the mechanisms have been intensively studied so far. However, it is not yet crystal clear whether the protective effect of Se against Cd-induced cytotoxicity is related to selenoproteins in nerve cells or not. In this study, we found that Cd inhibited selenoprotein thioredoxin reductase 1 (TrxR1; TXNRD1) and decreased the expression level of TrxR1, resulting in cellular oxidative stress, and Se supplements ameliorated Cd-induced cytotoxicity in SH-SY5Y cells. Mechanistically, the detoxification of Se against Cd is attributed to the increase of the cellular TrxR activity and upregulated TrxR1 protein level, culminating in strengthened antioxidant capacity. Results showed that Se supplements attenuated the ROS production and apoptosis in SH-SY5Y cells, and significantly mitigated Cd-induced SH-SY5Y cell death. This study may be a valuable reference for shedding light on the mechanism of Cd-induced cytotoxicity and the role of TrxR1 in Se-mitigated cytotoxicity of Cd in neuroblast cells, which may be helpful for understanding the therapeutic potential of Cd and Se in treating or preventing neurodegenerative diseases, like Alzheimer's disease (AD) and Parkinson's disease (PD).

Impact of Copper Nanoparticles and Copper Ions on Transcripts Involved in Neural Repair Mechanisms in Rainbow Trout Olfactory Mucosa

Olfactory mucosa is well known for its lifelong ability for regeneration. Regeneration of neurons and regrowth of severed axons are the most common neural repair mechanisms in olfactory mucosa. Nonetheless, exposure to neurotoxic contaminants, such as copper nanoparticles (CuNPs) and copper ions (Cu²⁺), may alter the reparative capacity of olfactory mucosa. Here, using RNA-sequencing, we investigated the molecular basis of neural repair mechanisms that were affected by CuNPs and Cu²⁺ in rainbow trout olfactory mucosa. The transcript profile of olfactory mucosa suggested that regeneration of neurons was inhibited by CuNPs. Exposure to CuNPs reduced the transcript abundances of pro-inflammatory proteins which are required to initiate neuroregeneration. Moreover, the transcript of genes encoding regeneration promoters, including canonical Wnt/β-catenin signaling proteins and developmental transcription factors, were downregulated in the CuNP-treated fish. The mRNA levels of genes regulating axonal regrowth, including the growth-promoting signals secreted from olfactory ensheathing cells, were mainly increased in the CuNP treatment. However, the reduced transcript abundances of a few cell adhesion molecules and neural polarity genes may restrict axonogenesis in the CuNP-exposed olfactory mucosa. In the Cu²⁺-treated olfactory mucosa, both neural repair strategies were initiated at the transcript level. The stimulation of repair mechanisms can lead to the recovery of Cu²⁺-induced olfactory dysfunction. These results indicated CuNPs and Cu²⁺ differentially affected the neural repair mechanism in olfactory mucosa. Exposure to CuNP had greater effects on the expression of genes involved in olfactory repair mechanisms relative to Cu²⁺ and dysregulated the transcripts associated with stem cell proliferation and neural reconstitution.

Kinase inhibit region of SOCS3 attenuates IL6-induced proliferation and astrocytic differentiation of neural stem cells via cross talk between signaling pathways

AIMS

Efficiency of neural stem cells (NSCs) therapy for brain injury is restricted by astrogliosis around the damaged region, in which JAK2/STAT3 signaling plays a key role. The SOCS3 that can directly inhibit JAK/STAT3 pathway. Here, we investigated the effects of a fusion peptide that combined kinase inhibitory region (KIR) of SOCS3 and virus trans-activator of transcription (TAT) on biological behavior of cultured NSCs under inflammatory conditions.

METHODS

NSCs were isolated from embryonic brain of SD rats, TAT-KIR was synthesized, and penetration rate was evaluated by flow cytometry (FACS). CCK8, immunostaining, and FACS were used to detected of TAT-KIR on the proliferation of NSCs. The expressions of GFAP and β tubulin III positive cells induced by IL6 with/without TAT-KIR were examined by immunostaining and Western blotting to observe the NSCs differentiation, and the effect of TAT-KIR on signaling cross talk was observed by Western blotting.

RESULTS

Penetration rate of TAT-KIR into primary cultured NSCs was up to 94%. TAT-KIR did not affect the growth and viability of NSCs. It significantly reduced the NSCs proliferation that enhanced by IL-6 stimulation via blocking the cell cycle progression from the G0/G1 to S phase. In addition, TAT-KIR attenuated astrocytic differentiation and kept high level of neuronal differentiation derived from IL-6-induced NSCs. The fate of NSCs differentiation under inflammatory conditions was affected by TAT-KIR, which was associated with synchronous inhibition of STAT3 and AKT, while promoting JNK expression.

CONCLUSION

TAT-KIR mimetic of SOCS3 could be a promising approach for brain repair via regulating the biological behaviors of exogenous NSCs.

Integrated approaches to mitigate threats from emerging potentially toxic elements: A way forward for sustainable environmental management

Potentially toxic elements (PTEs) such as toxic metal (loid)s and other emerging hazardous contaminants, exist in the environment and poses a serious threat. A large amount of wastewater containing PTEs such as cadmium, chromium, copper, nickel, arsenic, lead, zinc, etc. Release from industries during production process. Besides these, chemical-based fertilizers used in soils during crop production have become one of the crucial sources of PTEs. Various techniques are being employed for the mitigation of PTEs like chemical precipitation, ion exchange, coagulation, activated carbon, adsorption, membrane filtration, and bioremediation. Among these mitigation strategies, biological processes such as bioremediation, phytoremediation etc. Are extensively used, as they are economic have high-efficiency rate and are eco-friendly. This review intends to provide information on PTEs contamination through various sources; along with the toxicity of metal (loid)s with respect to their patterns of transmission and risks in the changing environment. Various remediation methods for the management of these pollutants along with their techno-economic perspective are also summarized in this review.

Cadmium inhibits signal transducer and activator of transcription 6 leading to pancreatic β cell apoptosis

The toxic heavy metal cadmium has been proven to cause pancreatic dysfunction and lead to the development of DM. However, the underlying mechanisms have not been completely elucidated. Here, we investigated the effects of cadmium on the pancreatic β cell line MIN6 and explored the underlying mechanisms. The Cell Counting Kit-8 (CCK8) assay and flow cytometry were used to determine cell viability and apoptosis in MIN6 cells. The expression levels of signal transducer and activator of transcription 6 (STAT6) were assessed by western blotting. We further assessed the effects of cadmium on the function of pancreatic β cells under high glucose levels using enzyme-linked immunosorbent assay (ELISA) and western blotting. Insulin secretion and expression were decreased by cadmium in MIN6 cells. In addition, cadmium suppressed cell viability and promoted apoptosis of MIN6 cells, downregulated insulin secretion and genesis of MIN6 cells under high glucose conditions, while inhibiting STAT6. Furthermore, after treatment with IL-4, the activator of STAT6, the MIN6 cell viability suppression and apoptosis promotion effect caused by cadmium were blocked. In conclusion, cadmium inhibits pancreatic β cell MIN6 growth by regulating the activation of STAT6. Our findings reveal a new mechanism of cadmium toxicity in pancreatic β cells.

Distribution, toxicity, interactive effects, and detection of ochratoxin and deoxynivalenol in food: A review

Mycotoxins are secondary metabolites of fungi that cause severe damage to agricultural products and food in the food supply chain. These detrimental pollutants have been directly linked with poor socioeconomic patterns and human health issues. Among the natural micropollutants, ochratoxin A (OTA) and deoxynivalenol (DON) are widely distributed in food materials. The primary occurrence of these mycotoxins is reported in almost all cereal grains and fresh agro-products. Both mycotoxins have shown harmful effects, such as nephrotoxic, hepatotoxic, and genotoxic effects, in humans due to their complex structural formation during the degradation/acetylation reaction. In addition, improper preharvest, harvest, and postharvest handling tend to lead to the formation of OTA and DON in various food commodities, which allows different harmful fungicides in practice. Therefore, this review provides more insight into the distribution and toxicity of OTA/DON in the food matrix and human health. Furthermore, the interactive effects of OTA/DON with co-contaminated organic and inorganic compounds are discussed. Finally, international regulation and mitigation strategies for detoxication are critically evaluated to meet food safety and good agriculture practices.

Phytoconstituents from ten natural herbs as potent inhibitors of main protease enzyme of SARS-COV-2: In silico study

BACKGROUND

Lack of treatment of novel Coronavirus disease led to the search of specific antivirals that are capable to inhibit the replication of the virus. The plant kingdom has demonstrated to be an important source of new molecules with antiviral potential.

PURPOSE

The present study aims to utilize various computational tools to identify the most eligible drug candidate that have capabilities to halt the replication of SARS-COV-2 virus by inhibiting Main protease (Mpro) enzyme.

METHODS

We have selected plants whose extracts have inhibitory potential against previously discovered coronaviruses. Their phytoconstituents were surveyed and a library of 100 molecules was prepared. Then, computational tools such as molecular docking, ADMET and molecular dynamic simulations were utilized to screen the compounds and evaluate them against Mpro enzyme.

RESULTS

All the phytoconstituents showed good binding affinities towards Mpro enzyme. Among them laurolitsine possesses the highest binding affinity i.e. -294.1533 kcal/mol. On ADMET analysis of best three ligands were simulated for 1.2 ns, then the stable ligand among them was further simulated for 20 ns. Results revealed that no conformational changes were observed in the laurolitsine w.r.t. protein residues and low RMSD value suggested that the Laurolitsine-protein complex was stable for 20 ns.

CONCLUSION

Laurolitsine, an active constituent of roots of Lindera aggregata, was found to be having good ADMET profile and have capabilities to halt the activity of the enzyme. Therefore, this makes laurolitsine a good drug candidate for the treatment of COVID-19.

Development of a DNAzyme-based colorimetric biosensor assay for dual detection of Cd2+ and Hg2

A colorimetric biosensor assay has been developed for Cd²⁺ and Hg²⁺ detection based on Cd²⁺-dependent DNAzyme cleavage and Hg²⁺-binding-induced conformational switching of the G-quadruplex fragment. Two types of multifunctional magnetic beads (Cd-MBs and Hg-MBs) were synthesized by immobilizing two functionalized DNA sequences on magnetic beads via avidin-biotin chemistry. For Cd²⁺ detection, Cd-MBs are used as recognition probes, which are modified with a single phosphorothioate ribonucleobase (rA) substrate (PS substrate) and a Cd²⁺-specific DNAzyme (Cdzyme). In the presence of Cd²⁺, the PS substrate is cleaved by Cdzyme, and single-stranded DNA is released as the signal transduction sequence. After molecular assembly with the other two oligonucleotides, duplex DNA is produced, and it can be recognized and cleaved by FokI endonuclease. Thus, a signal output component consisting of a G-quadruplex fragment is released, which catalyzes the oxidation of ABTS with the addition of hemin and H₂O₂, inducing a remarkably amplified colorimetric signal. To rule out false-positive results and reduce interference signals, Hg-MBs modified with poly-T fragments were used as Hg²⁺ accumulation probes during the course of Cd²⁺ detection. On the other hand, Hg-MBs can perform their second function in Hg²⁺ detection by changing the catalytic activity of the G-quadruplex/hemin DNAzyme. In the presence of Hg²⁺, the G-quadruplex structure in Hg-MBs is disrupted upon Hg²⁺ binding. In the absence of Hg²⁺, an intensified color change can be observed by the naked eye for the formation of intact G-quadruplex/hemin DNAzymes. The biosensor assay exhibits excellent selectivity and high sensitivity. The detection limits for Cd²⁺ and Hg²⁺ are 1.9 nM and 19.5 nM, respectively. Moreover, the constructed sensors were used to detect environmental water samples, and the results indicate that the detection system is reliable and could be further used in environmental monitoring. The design strategy reported in this study could broadly extend the application of metal ion-specific DNAzyme-based biosensors.

Cadmium induced cerebral toxicity via modulating MTF1-MTs regulatory axis

Metal-responsive transcription factor 1 (MTF1) participates in redox homeostasis and heavy metals detoxification via regulating the expression of metal responsive genes. However, the exact role of MTF1 in Cd-induced cerebral toxicity remains unclear. Herein, we explored the mechanism of Cd-elicited cerebral toxicity through modulating MTF1/MTs pathway in chicken cerebrum exposed to different concentrations of Cd (35 mg, 70 mg, and 140 mg/kg CdCl₂) via diet. Notably, cerebral tissues showed varying degrees of microstructural changes under Cd exposure. Cd exposure significantly up-regulated the expression of metal transporters (DMT1, ZIP8, and ZIP10) with concomitant elevated Cd level, as determined by ICP-MS. Cd significantly altered other cerebral biometals concentrations (particularly, Zn, Fe, Se, Cr, Mo, and Pb) and redox balance, resulting in increased cerebral oxidative stress. More importantly, Cd exposure suppressed MTF1 mRNA and nuclear protein levels and its target metal-responsive genes, notably metallothioneins (MT1 and MT2), and Fe and Cu transporter genes (FPN1, ATOX1, and XIAP). Moreover, Cd disrupted the regulation of expression of selenoproteome (particularly, GPxs and SelW), and cerebral Se level. Overall, our data revealed that molecular mechanisms associated with Cd-induced cerebral damage might include over-expression of DMT1, ZIP8 and ZIP10, and suppression of MTF1 and its main target metal-responsive genes as well as several selenoproteins.

Heavy metals and adult neurogenesis

With extensive use in industrial and agriculture applications, overexposure to heavy metals has become a global public health concern. The nervous system is vulnerable to many heavy metals, including cadmium, lead, and mercury. However, the knowledge about the underlying mechanisms of these metals' neurotoxicity is still very limited. Adult neurogenesis is a process of generating functional neurons from adult neural progenitor/stem cells (aNPCs), which plays an important role in cognitive function and olfaction. The studies of adult neurogenesis provide new insights into mechanisms of heavy metal neurotoxicity. This review summarizes the current research about the effects of heavy metals on adult neurogenesis and discusses their importance in understanding the mechanisms of heavy metals neurotoxicity, as well as challenges and future directions.

Cadmium inhibits neural stem/progenitor cells proliferation via MitoROS-dependent AKT/GSK-3β/β-catenin signaling pathway

Cadmium (Cd) is a toxic heavy metal widely found in the environment. Cd is also a potential neurotoxicant, and its exposure is associated with impairment of cognitive function. However, the underlying mechanisms by which Cd induces neurotoxicity are unclear. In this study, we investigated the in vitro effect of Cd on primary murine neural stem/progenitor cells (mNS/PCs) isolated from the subventricular zone. Our results show that Cd exposure leads to mNS/PCs G1/S arrest, promotes cell apoptosis, and inhibits cell proliferation. In addition, Cd increases intracellular and mitochondrial reactive oxygen species (ROS) that activates mitochondrial oxidative stress, decreases ATP production, and increases mitochondrial proton leak and glycolysis rate in a dose-dependent manner. Furthermore, Cd exposure decreases phosphorylation of protein kinase B (AKT) and glycogen synthase kinase-3 beta (GSK3β) in mNS/PCs. In addition, pretreatment mNS/PCs with MitoTEMPO, a mitochondrial-targeted antioxidant, improves mitochondrial morphology and functions and attenuates Cd-induced inhibition of mNS/PCs proliferation. It also effectively reverses Cd-induced changes of phosphorylation of AKT and the expression of β-catenin and its downstream genes. Taken together, our data suggested that AKT/GSK3β/β-catenin signaling pathway is involved in Cd-induced mNS/PCs proliferation inhibition via MitoROS-dependent pattern.

Resveratrol protects MC3T3-E1 cells against cadmium-induced suppression of osteogenic differentiation by modulating the ERK1/2 and JNK pathways

Resveratrol (RES) is a natural polyphenolic compound with a broad range of physiological and pharmacological properties. Previous studies have shown that RES also plays an important role in protecting and promoting early bone metabolism and differentiation. The accumulation of cadmium (Cd), one of the world's most poisonous substances, can inhibit skeletal growth and bone maturation, thus causing osteoporosis. However, whether RES can prevent the Cd-induced inhibition of osteogenic differentiation remains unknown. In this study, we found that RES promoted the early maturity of osteoblastic MC3T3-E1 cells, as demonstrated by the significantly increased mRNA and protein expression of a range of differentiation markers, including alkaline phosphatase (ALP), collagen 1 (COL1), bone morphogenetic protein-2 (BMP-2), and runt-related transcription factor 2 (RUNX2). In contrast, we found that cadmium chloride (CdCl₂) inhibited the viability and osteogenic maturity of MC3T3-E1 cells. We also demonstrated that RES pretreatment for 30 min provided significant protection against Cd-induced apoptosis and attenuated the inhibition of osteogenic differentiation induced by Cd by modulating ERK1/2 and JNK signaling. In conclusion, our results indicate that RES is a potential femoral protectant that not only enhance the viability and early differentiation of osteoblasts, but also protect osteoblasts from cadmium damage.

MAPK, AKT/FoxO3a and mTOR pathways are involved in cadmium regulating the cell cycle, proliferation and apoptosis of chicken follicular granulosa cells

The occurrence of cadmium (Cd) in feed is a major problem in animal health and production. Studies have confirmed that Cd depresses egg production of laying hens, which is closely related to follicular atresia. This study aimed to assess the toxic impacts of Cd on the ovarian tissue, and to examine the mechanism of Cd-induced granulosa cell proliferation and apoptosis. Results from the nitric oxide (NO) and malondialdehyde (MDA) content, total superoxide dismutase (T-SOD), glutathione peroxide (GSH-Px), total nitric oxide synthase (T-NOS) and adenosine triphosphatase (ATPase) activities, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, and hematoxylin-eosin (H & E) staining indicated that excess Cd induced oxidative stress, granulosa cell apoptosis and follicular atresia in the layer ovary. Low-dose Cd exposure (1 μM) induced the granulosa cell proliferation, upregulated the mRNA levels of RSK1 and RHEB, activated FoxO3a, AKT, ERK1/2, mTOR and p70S6K1 phosphorylation, and promoted cell cycle progression from phase G1 to S. However, high-dose Cd exposure (15 μM) induced reactive oxygen species (ROS) generation and cell apoptosis, upregulated the mRNA levels of the inflammatory factors, ASK1, JNK, p38 and TAK1, downregulated the expressions of RSK1 and RHEB genes, and inhibited the phosphorylation of ERK1/2, mTOR and p70S6K1 proteins, and the cell cycle progression. Rapamycin pre-treatment completely blocked the phosphorylation of mTOR and p70S6K1 proteins, and the cell cycle progression induced by 1 μM Cd, and accelerated 15 μM Cd-induced cell apoptosis and cell cycle arrest. The microRNA sequencing result showed that 15 μM Cd induced differential expression of microRNA genes, which may regulate AKT, ERK1/2 and mTOR signaling and cell cycle progression by regulating the activity of G proteins and cell cycle-related proteins. Conclusively, these results indicated that Cd can cause the ovarian damage and follicular atresia, and regulate cell cycle, cell proliferation or apoptosis of granulosa cells through MAPK, AKT/FoxO3a and mTOR pathways in laying hens.

Cadmium triggers oxidative stress and mitochondrial injury mediated apoptosis in human extravillous trophoblast HTR-8/SVneo cells

Cadmium (Cd) is a bioaccumulative heavy metal element with potential placental toxicity during pregnancy. Up to now, however, the precise toxic effects of Cd on human placentae, particularly as they pertain to trophoblast cells remain obscure. We therefore sought to investigate the cytotoxic effects of Cd on human extravillous trophoblast HTR-8/SVneo cells and the mechanisms involved in the processes. Results in this present study showed that CdCl2 treatment significantly suppressed cell viability and induced noticeable oxidative stress in HTR-8/SVneo cells. Further studies showed that CdCl2 treatment caused distortion of mitochondrial structure, reduction of mitochondrial membrane potential (Δψm), DNA damage and G0/G1 phase arrest. Under the same condition, CdCl2 treatment increased Bax/Bcl-2 ratios by up-regulating Bax expression and down-regulating Bcl-2 expression, and activated apoptotic executive molecule caspase-3, which irreversibly induced HTR-8/SVneo cell apoptosis. N-acetyl-l-cysteine (NAC), ROS scavenger, significantly attenuated CdCl2-caused mitochondrial injury, DNA damage, G0/G1 phase arrest and apoptosis. In addition, in vivo assay suggested that CdCl2 induced trophoblast cells apoptosis but not other cells in mice placental tissue. Taken together, these data suggest that Cd selectively triggers oxidative stress and mitochondrial injury mediated apoptosis in trophoblast cells, which might contribute to placentae impairment and placental-related disorders after Cd exposure. These findings may provide new insights to understand adverse effects of Cd on placentae during pregnancy.

Single-cell RNA sequencing of mouse neural stem cell differentiation reveals adverse effects of cadmium on neurogenesis

Cadmium (Cd) is a toxic heavy metal and widely exists in the environment. Extensive studies have revealed that Cd exposure can elicit neurotoxicity and potentially interfere with neurogenesis. However, underlying mechanisms by which Cd exposure affects neurogenesis remain unclear. In this study, we performed single-cell RNA sequencing (scRNA-seq) of the differentiated mixture from neonatal mouse Neural Stem Cells (mNSCs) that were exposed to Cd for 24 h and differentiated for 7 days. Our results showed that Cd exposure led to an increase in the differentiation of NSCs into astrocytes while a decrease into neurons. Besides, Cd induced subtype-specific response and dysregulated cell-to-cell communication. Collectively, our scRNA-seq data suggested that Cd had toxic effects on NSCs differentiation at the single-cell level, which offered insight into the potential molecular mechanism of Cd on neurogenesis. Furthermore, our findings provided a new method for assessing the neurodevelopmental toxicity of environmental pollutants.

Effects of cadmium on osteoblast cell line: Exportin 1 accumulation, p-JNK activation, DNA damage and cell apoptosis

Cadmium is an environmental metal pollutant that has been a focus of research in recent years, which is reported to cause bone disease; however, its skeletal toxicity and the mechanism involved are not yet fully known. Therefore, this study used MC3T3-E1 subclone 14 cells to determine the mechanism of cadmium toxicity on bone. Cadmium chloride (Cd) significantly reduced cell viability in a concentration-dependent manner. Exposure to Cd inhibited osteoblast-related proteins (Runx2, Col-1, STC2) and decreased alkaline phosphatase (ALP) activity. Cd caused Exportin-1 accumulation and induced DNA damage. Cd significantly down-regulated caspase 9 and induced cleaved-PARP, cleaved-caspase 3 protein level. Treatment with JNK inhibitor, SP600125, suppressed cadmium-induced elevation in the ratio of phosphorylation of JNK to JNK. Inhibition of caspase with pan-caspase inhibitor, Z-VAD-FMK, prevented MC3T3-E1 subclone 14 cells from cadmium-induced reduction of Runx2, STC2, caspase 9, and accumulation of cleaved PARP and cleaved caspase 3. Cd-induced cell survival enhanced by SP600125 but rescued by Z-VAD-FMK or KPT-335. These results suggest that cadmium cytotoxicity on bone involved exportin 1 accumulation, phosphorylation of JNK, induction of DNA damage and pro-apoptosis, which was induced by activation of caspase-dependent pathways.

Thyroid Stem Cells But Not Differentiated Thyrocytes Are Sensitive to Slightly Increased Concentrations of Heavy Metals

Thyroid cancer incidence is markedly increased in volcanic areas where residents are biocontaminated by chronic lifelong exposure to slightly increased metals in the environment. Metals can influence the biology of living cells by a variety of mechanisms, depending not only on the dose and length of exposure but also on the type and stage of differentiation of target cells. We explored the effect of five heavy metals (Cu, Hg, Pd, W and Zn) at nanomolar concentrations (the biocontamination level in residents of the volcanic area in Sicily where thyroid cancer is increased) on stimulating the proliferation of undifferentiated (thyrospheres) and differentiated human thyroid cells. Thyrosphere proliferation was significantly increased after exposure to each individual metal and a greater stimulating effect was observed when a mixture of the examined metals was used. No effect was seen in differentiated thyrocytes. For all metals, the dose-response curve followed a biphasic pattern that is typical of hormesis. Thyrosphere growth concerned the size rather than number, except with the metal mixture. An altered morphology was also observed in metal-treated thyrospheres. Metal-induced proliferation was due to activation of the ERK1/2 pathway, as confirmed by growth inhibition when ERK1/2 signaling was blocked. These studies show that stem/precursor thyroid cells are sensitive to small increases in environmental metal concentrations that are harmless for differentiated thyrocytes.

Cypermethrin Impairs Hippocampal Neurogenesis and Cognitive Functions by Altering Neural Fate Decisions in the Rat Brain

Neurogenesis is a developmental process that involves fine-tuned coordination between self-renewal, proliferation, and differentiation of neural stem cells (NSCs) into neurons. However, early-life assault with environmental toxicants interferes with the regular function of genes, proteins, and other molecules that build brain architecture resulting in attenuated neurogenesis. Cypermethrin is a class II synthetic pyrethroid pesticide extensively used in agriculture, veterinary, and residential applications due to its low mammalian toxicity, high bio-efficacy, and enhanced stability. Despite reports on cypermethrin-mediated behavioral and biochemical alterations, till now, no study implicates whether cypermethrin exposure has any effect on neurogenesis. Therefore, the present study was undertaken to comprehend the effects of cypermethrin treatment on embryonic and adult neurogenesis. We found that cypermethrin exposure led to a considerable decrease in the BrdU/Sox-2+, BrdU/Dcx+, and BrdU/NeuN+ co-labeled cells indicating that cypermethrin treatment decreases NSC proliferation and generation of mature and functional neurons. On the contrary, the generation of BrdU/S100β+ glial cells was increased resulting in neurogliogenesis imbalance in the hippocampus. Further, cypermethrin treatment also led to an increased number of BrdU/cleaved caspase-3+ and Fluoro-Jade B+ cells suggesting an induction of apoptosis in NSCs and increased degeneration of neurons in the hippocampus. Overall, these results explicate that cypermethrin exposure not only reduces the NSC pool but also disturbs the neuron-astrocyte ratio and potentiates neurodegeneration in the hippocampus, leading to cognitive dysfunctions in rats.

Inducible and conditional activation of ERK5 MAP kinase rescues mice from cadmium-induced olfactory memory deficits

Cadmium (Cd) is a heavy metal that is one of the most toxic environmental pollutants throughout the world. We previously reported that Cd exposure impairs olfactory memory in mice. However, the underlying mechanisms for its neurotoxicity for olfactory function are not well understood. Since adult Subventricular zone (SVZ) and Olfactory Bulb (OB) neurogenesis contributes to olfaction, olfactory memory defects caused by Cd may be due to inhibition of neurogenesis. In this study, using bromodeoxyuridine (BrdU) labeling and immunohistochemistry, we found that 0.6 mg/L Cd exposure through drinking water impaired adult SVZ/OB neurogenesis in C57BL/6 mice. To determine if the inhibition of olfactory memory by Cd can be reversed by stimulating adult neurogenesis, we utilized the transgenic caMEK5 mouse strain to conditional stimulate of adult neurogenesis by activating the endogenous ERK5 MAP kinase signaling pathway. This was accomplished by conditionally induced expression of active MEK5 (caMEK5) in adult neural stem/progenitor cells. The caMEK5 mice were exposed to 0.6 mg/L Cd for 38 weeks, and tamoxifen was administered to induce caMEK5 expression and stimulate adult SVZ/OB neurogenesis during Cd exposure. Short-term olfactory memory test and sand-digging based, odor-cued olfactory learning and memory test were conducted after Cd and tamoxifen treatments to examine their effects on olfaction. Here we report that Cd exposure impaired short-term olfactory memory and odor-cued associative learning and memory in mice. Furthermore, the Cd-impaired olfactory memory deficits were rescued by the tamoxifen-induction of caMEK5 expression. This suggests that Cd exposure impairs olfactory function by affecting adult SVZ/OB neurogenesis in mice.

Inducible and Conditional Stimulation of Adult Hippocampal Neurogenesis Rescues Cadmium-Induced Impairments of Adult Hippocampal Neurogenesis and Hippocampus-Dependent Memory in Mice

Cadmium (Cd) is a heavy metal and an environmental pollutant. However, the full spectrum of its neurotoxicity and the underlying mechanisms are not completely understood. Our previous studies demonstrated that Cd exposure impairs adult hippocampal neurogenesis and hippocampus-dependent memory in mice. This study aims to determine if these adverse effects of Cd exposure can be mitigated by genetically and conditionally enhancing adult neurogenesis. To address this issue, we utilized the transgenic constitutive active MEK5 (caMEK5) mouse strain we previously developed and characterized. This mouse strain enables us to genetically and conditionally activate adult neurogenesis by administering tamoxifen to induce expression of a caMEK5 in adult neural stem/progenitor cells, which stimulates adult neurogenesis through activation of the endogenous extracellular signal-regulated kinase 5 mitogen-activated protein kinase pathway. The caMEK5 mice were exposed to 0.6 mg/l Cd through drinking water for 38 weeks. Once impairment of memory was confirmed, tamoxifen was administered to induce caMEK5 expression and to activate adult neurogenesis. Behavior tests were conducted at various time points to monitor hippocampus-dependent memory. Upon completion of the behavior tests, brain tissues were collected for cellular studies of adult hippocampal neurogenesis. We report here that Cd impaired hippocampus-dependent spatial memory and contextual fear memory in mice. These deficits were rescued by the tamoxifen induction of caMEK5 expression. Furthermore, Cd inhibition of adult hippocampal neurogenesis was also reversed. This rescue experiment provides strong evidence for a direct link between Cd-induced impairments of adult hippocampal neurogenesis and hippocampus-dependent memory.

Chronic cadmium exposure causes oocyte meiotic arrest by disrupting spindle assembly checkpoint and maturation promoting factor

Cadmium (Cd) is a bioaccumulative heavy metal element with potential toxicity on the female reproductive system, but the exact molecular mechanisms have not yet been clearly defined. In this study, female mice were exposed to 0.5 mg/kg/day of CdCl₂ for 60 consecutive days. We found that chronic Cd exposure significantly decreased the fecundity of female mice by affecting oocyte meiotic progression as indicated by disrupted spindle assembly, chromosome alignment and kinetochore-microtubule attachments, consequently resulting in aneuploid oocytes. Further studies showed that the periodic fluctuations of MPF activity and cyclin B1 expression were disturbed in Cd-exposed oocytes probably by affecting the spindle assembly checkpoint protein Bub3. In addition, Cd exposure induced oxidative stress as indicated by an increased level of reactive oxygen species and apoptosis in oocytes, leading to oocyte quality deterioration. Taken together, these data suggest that Cd exposure causes disrupted molecular events of meiotic progression and deterioration of oocyte quality via oxidative stress, leading to decrease of female fertility.

Cocoa-laden cadmium threatens human health and cacao economy: A critical view

In the recent decades, Cd burden in cocoa-based products threatened global food safety, human health and the future of chocolateries. Increased Cd bioavailability is an acute problem in cacao-based horticulture. Poverty, poor maintenance, unjustified traditional farming, and paucity of knowledge on Cd-binding propensity in cacao discourage the application of risk-mitigation measures. Progressive accumulation of Cd, with a half-life of 10-30 years, in the human body even at ultra-trace levels may lead to serious health complications. If Cd accumulates in the food chain through cocoa products, consequences in children, who are the primary consumers of chocolates, include morbidity and mortality that may result in a significant demographic transition by the year 2050. Developing cacao clones with an innate capability of taking up low Cd levels from soils, and site-specific Cd-cacao research might contribute to limiting the trophic transfer of Cd. This review highlights the possible routes for Cd uptake in cacao plants and discusses the measures to rescue the chocolateries from Cd pollution to promote "healthy" cacao farming. The potential human health risks of chocolate-laden Cd and mitigation strategies to minimize Cd burden in the human body are also presented. The challenges and prospects in Cd-cacao research are discussed as well.

Downregulation of vdac2 inhibits spermatogenesis via JNK and P53 signalling in mice exposed to cadmium

Previous studies have reported the reproductive toxicity of cadmium (Cd); however, the effect of Cd on spermatogenesis and the underlying mechanism remain to be elucidated. In this study, mouse Leydig TM3 cells were treated with CdCl₂ (0, 5, 10 and 50 μM) for 24 h to evaluate cytotoxicity, and C57BL/6 mice were treated intragastrically with 0.4 mL CdCl₂ (0, 0.01, 0.05 and 0.1 g/L) for 2 months to investigate changes in spermatogenesis. The results showed that Cd aggravated apoptosis and proliferation in a dose-dependent manner, concomitant with deteriorated spermatogenesis and testosterone synthesis. For mechanism exploration, RNA-seq was used to profile alterations in gene expression in response to Cd, and the results indicated focus on P53/JNK signalling pathways and membrane proteins. We found that P53/JNK signalling pathways were activated upon Cd treatment, with the Cd-triggered downregulation of the vdac2 gene. P53/JNK pathway blockade ameliorated the Cd-induced inhibition of steroidogenic acute regulatory protein (STAR) expression and testosterone synthesis. Additionally, vdac2 knockdown in TM3 cells contributed to the phosphorylation of JNK/P53 and reduced the testosterone content. Vdac2 overexpression rescued the aforementioned Cd-induced events. Collectively, our study identified an innovative biomarker of Cd exposure in mice. The results demonstrated that vdac2 downregulation inhibits spermatogenesis via the JNK/P53 cascade. This finding may contribute to our understanding of the regulatory mechanism of Cd reproductive toxicity and provide a candidate list for sperm abnormality factors and pathways.

Dexmedetomidine Alleviates Neurogenesis Damage Following Neonatal Midazolam Exposure in Rats through JNK and P38 MAPK Pathways

Midazolam, a widely used anesthetic, inhibits proliferation of neural stem cells (NSCs) and induces neuroapoptosis in neonates. Dexmedetomidine, an effective auxiliary medicine in clinical anesthesia, protects the developing brain against volatile anesthetic-induced neuroapoptosis. Whether dexmedetomidine protects against neurogenesis damage induced by midazolam remains unknown. This study aims to clarify the protective effect of dexmedetomidine on midazolam-induced neurogenesis damage and explore its potential mechanism. Postnatal 7-day-old Sprague-Dawley (SD) rats and cultured NSCs were treated with either normal saline, midazolam, or dexmedetomidine combined with midazolam. The rats were sacrificed at 1, 3, and 7 days after treatment. Cell proliferation was assessed by 5-bromodeoxyurdine (BrdU) incorporation. Cell viability was determined using MTT assay. Cell differentiation and apoptosis were detected by immunofluorescent staining and terminal dUTP nick-end labeling (TUNEL), respectively. The protein levels of p-JNK, p-P38, and cleaved caspase-3 were quantified using Western blotting. Midazolam decreased cell proliferation and increased cell apoptosis in the subventricular zone (SVZ), the subgranular zone (SGZ) of the hippocampus, and cultured NSCs. Moreover, midazolam decreased cell viability and increased the expression of p-JNK and p-P38 in cultured NSCs. Co-treatment with dexmedetomidine attenuated midazolam-induced changes in cell proliferation, viability, apoptosis, and protein expression of p-JNK and p-P38 in cultured NSCs. Midazolam and dexmedetomidine did not affect the differentiation of the cultured NSCs. These results indicate that dexmedetomidine alleviated midazolam-induced neurogenesis damage via JNK and P38 MAPK pathways.

In vitro and in vivo effects of a mycotoxin, deoxynivalenol, and a trace metal, cadmium, alone or in a mixture on the intestinal barrier

Deoxynivalenol (DON), one of the most widespread mycotoxins in Europe, and cadmium (Cd), a widespread environmental pollutant, are common food contaminants. They exert adverse effects on different organs including kidney, liver, and intestine. The intestine is a common target of DON and Cd when they are ingested. Most studies have focused on their individual effects whereas their combined toxicity has rarely been studied. The aim of this study was thus to evaluate their individual and combined effects on the intestinal barrier function in vitro and in vivo. In vitro, Caco-2 cells were treated with increasing concentrations of DON and Cd (1-30 μM). In vivo, Wistar rats were used as controls or exposed to DON contaminated feed (8.2 mg/kg feed), Cd-contaminated water (5 mg/l) or both for four weeks. In Caco-2 cells, DON, Cd and the DON+Cd mixture reduced transepithelial electrical resistance (TEER) and increased paracellular permeability in a dose-dependent manner. Impairment of the barrier function was associated with a decrease in the amount of E-cadherin and occludin after exposure to the two contaminants alone or combined. A decrease in E-cadherin expression was observed in rats exposed to the two contaminants alone or combined, whereas occludin expression only decreased in animals exposed to DON and DON+Cd. Jejunal crypt depth was reduced in rats exposed to DON or Cd, whereas villi height was not affected. In vitro and in vivo results showed that the effects of exposure to combined DON and Cd on the intestinal barrier function in the jejunum of Wistar rats and in the colorectal cancer cell line (Caco-2) was similar to the effects of each individual contaminant. This suggests that regulations for each individual contaminant are sufficiently protective for consumers.

Effects of environmental stressors on stem cells

Environmental toxicants are ubiquitous, and many are known to cause harmful health effects. However, much of what we know or think we know concerning the targets and long-term effects of exposure to environmental stressors is sadly lacking. Toxicant exposure may have health effects that are currently mischaracterized or at least mechanistically incompletely understood. While much of the recent excitement about stem cells (SCs) focuses on their potential as therapeutic agents, they also offer a valuable resource to give us insight into the mechanisms and risks of toxicant effects. Not only as a response to the increasing ethical pressure to reduce animal testing, SC studies allow us valuable insight into the true effects of human exposure to environmental stressors under controlled conditions. We present a review of the history of publications on the effects of environmental stressors on SCs, followed by a consolidation of the literature over the past five years on a subset of key environmental stressors of importance to human health and their effects on both embryonic and tissue SCs. The review will make constructive suggestions as to areas of toxicant research where further studies are needed, as well as making indications of the potential utility for advancing knowledge and directing research on environmental toxicology.

Cadmium exposure in living organisms: A short review

Cadmium (Cd) is a toxic heavy metal that accumulates in living systems. Exposure can occur occupationally or environmentally. Workers within the electroplating, battery production, and pigment industries are at the highest risk for exposure and have been reported to have increased levels of Cd in their blood and urine. Environmental exposure can be the result of anthropogenic activities or smoking. Cd has a long half-life and bio accumulates in plants, invertebrates, and vertebrates. The toxic effects following exposure include growth retardation and organ system toxicity, with kidney and liver toxicity most reported with in higher organisms. At the molecular level, Cd leads to the production of reactive oxygen species, DNA damage, and inhibition of DNA repair. This article gives a brief overview of the correlations between exposure to cadmium occupationally and environmentally and levels measured in blood and urine. It also examines the bioaccumulation of cadmium in aquatic invertebrates and vertebrates indicating that accumulation varies not only by location but also within and between various species.

Cadmium Exposure Impairs Adult Hippocampal Neurogenesis

Cadmium (Cd) is an environmental pollutant of considerable interest throughout the world and potentially a neurotoxicant. Our recent data indicate that Cd exposure induces impairment of hippocampus-dependent learning and memory in mice. However, the underlying mechanisms for this defect are not known. The goal of this study was to determine if Cd inhibits adult neurogenesis and to identify underlying signaling pathways responsible for this impairment. Adult hippocampal neurogenesis is a process in which adult neural progenitor/stem cells (aNPCs) in the subgranular zone (SGZ) of the dentate gyrus (DG) generate functional new neurons in the hippocampus which contributes to hippocampus-dependent learning and memory. However, studies concerning the effects of neurotoxicants on adult hippocampal neurogenesis and the underlying signaling mechanisms are limited. Here, we report that Cd significantly induces apoptosis, inhibits proliferation, and impairs neuronal differentiation in primary cultured aNPCs derived from the SGZ. In addition, the c-jun NH2-terminal kinase (JNK) and p38 mitogen-activated protein (MAP) kinase signaling pathways are activated by Cd and contribute to its toxicity. Furthermore, we exposed 8-week-old male C57BL/6 mice to Cd through drinking water for 13 weeks to assess the effects of Cd on adult hippocampal neurogenesis in vivo. Cd treatment reduced the number of 5-week old adult-born cells in the DG and impaired the differentiation of adult-born hippocampal neurons. These results suggest that Cd exposure impairs adult hippocampal neurogenesis both in vitro and in vivo. This may contribute to Cd-mediated inhibition of hippocampus-dependent learning and memory.

MeHg-induced autophagy via JNK/Vps34 complex pathway promotes autophagosome accumulation and neuronal cell death

Methylmercury (MeHg), an environmental toxin, may specifically cause neurological disorders. Recent studies have reported that autophagy can be induced by metals and be involved in metal cytotoxicity. However, the role of autophagy in MeHg-induced neurotoxicity remains unknown. Here, we demonstrate that MeHg induces mTOR-independent autophagy through JNK/Vps34 complex pathway, which further promotes autophagosome accumulation and neuronal cell death. In addition to cell death, MeHg increased LC3-II expression in a concentration- and time-dependent manner in neuronal cells; furthermore, western blot analysis of LC3-II expression under baf A1-treated condition indicates that MeHg activates autophagy induction. However, we found lysosomal degradative function was impaired by MeHg. Under this condition, MeHg-activated autophagy induction would elicit autophagosome accumulation and cell death. Consistent with this inference, the autophagy inhibitor decreased the MeHg-induced autophagosome accumulation and neuronal cells death, whereas the autophagy inducers further augmented MeHg cytotoxicity. Then, the mechanism of autophagy induction is investigated. We show that MeHg-induced autophagy is mTOR-independent. Vacuolar protein sorting 34 (Vps34) complex is critical for mTOR-independent autophagy. MeHg induced the interaction between Beclin1 and Vps34 to form Vps34 complex. Importantly, knockdown of Vps34 inhibited autophagy induction by MeHg. Furthermore, we found that JNK, but not p38 or ERK, promoted the formation of Vps34 complex and autophagy induction. Finally, inhibition of JNK or downregulation of Vps34 decreased autophagosome accumulation and alleviated MeHg-induced neuronal cell death. The present study implies that inhibiting JNK/Vps34 complex autophagy induction pathway may be a novel therapeutic approach for the treatment of MeHg-induced neurotoxicity.

Involvement of p38 in Age-Related Decline in Adult Neurogenesis via Modulation of Wnt Signaling

Neurogenesis in specific brain regions in adult mammals decreases with age. Progressive reduction in the proliferation of neural stem and progenitor cells (NS/PCs) is a primary cause of this age-associated decline. However, the mechanism responsible for this reduction is poorly understood. We identify p38 MAPK as a key factor in the proliferation of neural progenitor cells (NPCs) in adult neurogenic niches. p38 expression in adult NS/PCs is downregulated during aging. Deletion of p38α in NS/PCs specifically reduces the proliferation of NPCs but not stem cells. Conversely, forced expression of p38α in NS/PCs in the aged mouse subventricular zone (SVZ) restores NPC proliferation and neurogenesis, and prevents age-dependent SVZ atrophy. We also found that p38 is necessary for suppressing the expression of Wnt antagonists DKK1 and SFRP3, which inhibit the proliferation of NPCs. Age-related reduction in p38 thus leads to decreased adult neurogenesis via downregulation of Wnt signaling.

Cadmium Exposure Impairs Cognition and Olfactory Memory in Male C57BL/6 Mice

Cadmium (Cd) is a heavy metal of high interest to the superfund initiative. Recent epidemiology studies have suggested a possible association between Cd exposure and cognitive as well as olfactory impairments in humans. However, studies in animal models are needed to establish a direct causal relationship between Cd exposure and impairments in cognition and olfaction. This study aims to investigate the toxic effect of Cd on cognition and olfactory function in mice. One group of 8-week-old C57BL/6 male mice was exposed to 3 mg/l Cd (in the form of CdCl2) through drinking water for 20 weeks for behavior tests and final blood Cd concentration analysis. The behavior tests were conducted before, during, and after Cd exposure to analyze the effects of Cd on cognition and olfactory function. Upon completion of behavior tests, blood was collected to measure final blood Cd concentration. Two additional groups of mice were similarly exposed to Cd for 5 or 13 weeks for peak blood Cd concentration measurement. The peak blood Cd concentration was 2.125-2.25 μg/l whereas the final blood Cd concentration was 0.18 μg/l. At this exposure level, Cd impaired hippocampus-dependent learning and memory in novel object location test, T-maze test, and contextual fear memory test. It also caused deficits in short-term olfactory memory and odor-cued olfactory learning and memory. Results in this study demonstrate a direct relationship between Cd exposure and cognitive as well as olfactory impairments in an animal model.

Cadmium induces apoptotic program imbalance and cell cycle inhibitor expression in cultured human astrocytes

Cadmium is a highly neurotoxic heavy metal impairing neurogenesis and induces neurodegenerative disorders. Toxic concentrations of cadmium induce astrocytic apoptosis by depleting intracellular glutathione levels, elevating intracellular calcium levels, altering mitochondria membrane potentials, and activating JNK and PI3K/Akt signaling pathways. Cadmium suppresses cell proliferation in kidney epithelial cells, lung fibroblasts, and primary myelocytes; however, cadmium's effects on proteins regulating oxidative stress, apoptosis, and cell proliferation in astrocytes are less known. The present study hypothesized that cadmium alters levels of antioxidant enzymes, apoptotic regulator proteins, and cell cycle inhibitor proteins, resulting in apoptosis and cell cycle arrest. Concentrations ≥20 μM cadmium induced apoptosis and led to intracellular changes including DNA fragmentation, reduced mRNA expression of antioxidant enzymes (i.e., catalase and glutathione S transferase-A4), downregulation of B-cell lymphoma 2 (Bcl-2), and upregulation of Bcl-2-associated X protein (Bax). Moreover, cadmium suppressed astrocytic proliferation by inducing S and G2/M phase cell cycle arrest and promoting p53, p21, and p27 expression. In conclusion, this study provides mechanistic insight into cadmium-induced cytotoxicity of astrocytes and highlights potential targets for prevention of cadmium-induced apoptosis and cell cycle arrest.

Identification of ARNT-regulated BIRC3 as the target factor in cadmium renal toxicity

Cadmium (Cd) is an environmental contaminant that exhibits renal toxicity. The target transcription factors involved in Cd renal toxicity are still unknown. In this study, we demonstrated that Cd decreased the activity of the ARNT transcription factor, and knockdown of ARNT significantly decreased the viability of human proximal tubular HK-2 cells. Microarray analysis in ARNT knockdown cells revealed a decrease in the expression of a number of genes, including a known apoptosis inhibitor, BIRC3, whose gene and protein expression level was also decreased by Cd treatment. Although the BIRC family consists of 8 members, Cd suppressed only BIRC3 gene expression. BIRC3 is known to suppress apoptosis through the inhibition effect on caspase-3. Knockdown of BIRC3 by siRNA as well as Cd treatment increased the level of active caspase-3. Moreover, knockdown of BIRC3 not only triggered cell toxicity and apoptosis but also strengthened Cd toxicity in HK-2 cells. Meanwhile, the activation of caspase-3 by suppression of BIRC3 gene expression was mostly specific to Cd and to proximal tubular cells. These results suggest that Cd induces apoptosis through the inhibition of ARNT-regulated BIRC3 in human proximal tubular cells.