PKA- and Ca2+-dependent p38 MAPK/CREB activation protects against manganese-mediated neuronal apoptosis

Signal Transduction Associated with Mn-induced Neurological Dysfunction

Manganese (Mn) is a heavy metal that occurs widely in nature and has a vital physiological role in growth and development. However, excessive exposure to Mn can cause neurological damage, especially cognitive dysfunction, such as learning disability and memory loss. Numerous studies on the mechanisms of Mn-induced nervous system damage found that this metal targets a variety of metabolic pathways, for example, endoplasmic reticulum stress, apoptosis, neuroinflammation, cellular signaling pathway changes, and neurotransmitter metabolism interference. This article reviews the latest research progress on multiple signaling pathways related to Mn-induced neurological dysfunction.

An approach based on a combination of toxicological experiments and in silico predictions to investigate the adverse outcome pathway (AOP) of paraquat neuro-immunotoxicity

Paraquat (PQ) exposure is strongly associated with neurotoxicity. However, research on the neurotoxicity mechanisms of PQ varies in terms of endpoints of toxic assessment, resulting in a great challenge to understand the early neurotoxic effects of PQ. In this study, we developed an adverse outcome pathway (AOP) to investigate PQ-induced neuro-immunotoxicity from an immunological perspective, combining of traditional toxicology methods and computer simulations. In vivo, PQ can microstructurally lead to an early synaptic loss in the brain mice, which is a large degree regarded as a main reason for cognitive impairment to mice behavior. Both in vitro and in vivo demonstrated synapse loss is caused by excessive activation of the complement C1q/C3-CD11b pathway, which mediates microglial phagocytosis dysfunction. Additionally, the interaction between PQ and C1q was validated by molecular simulation docking. Our findings extend the AOP framework related to PQ neurotoxicity from a neuro-immunotoxic perspective, highlighting C1q activation as the initiating event for PQ-induced neuro-immunotoxicity. In addition, downstream complement cascades induce abnormal microglial phagocytosis, resulting in reduced synaptic density and subsequent non-motor dysfunction. These findings deepen our understanding of neurotoxicity and provide a theoretical basis for ecological risk assessment of PQ.

Dexamethasone attenuates neuropathic pain through spinal microglial expression of dynorphin A via the cAMP/PKA/p38 MAPK/CREB signaling pathway

This study aimed to elucidate the opioid mechanisms underlying dexamethasone-induced pain antihypersensitive effects in neuropathic rats. Dexamethasone (subcutaneous and intrathecal) and membrane-impermeable Dex-BSA (intrathecal) administration dose-dependently inhibited mechanical allodynia and thermal hyperalgesia in neuropathic rats. Dexamethasone and Dex-BSA treatments increased expression of dynorphin A in the spinal cords and primary cultured microglia. Dexamethasone specifically enhanced dynorphin A expression in microglia but not astrocytes or neurons. Intrathecal injection of the microglial metabolic inhibitor minocycline blocked dexamethasone-stimulated spinal dynorphin A expression; intrathecal minocycline, the glucocorticoid receptor antagonist Dex-21-mesylate, dynorphin A antiserum, and κ-opioid receptor antagonist GNTI completely blocked dexamethasone-induced mechanical antiallodynia and thermal antihyperalgesia. Additionally, dexamethasone elevated spinal intracellular cAMP levels, leading to enhanced phosphorylation of PKA, p38 MAPK and CREB. The specific adenylate cyclase inhibitor DDA, PKA inhibitor H89, p38 MAPK inhibitor SB203580 and CREB inhibitor KG-501 completely blocked dexamethasone-induced anti-neuropathic pain and increased microglial dynorphin A exprression. In conclusion, this study reveal that dexamethasone mitigateds neuropathic pain through upregulation of dynorphin A in spinal microglia, likely involving the membrane glucocorticoid receptor/cAMP/PKA/p38 MAPK/CREB signaling pathway.

Lycium barbarum polysaccharides attenuate nonylphenol and octylphenol-induced oxidative stress and neurotransmitter disorders in PC-12 cells

Nonylphenol (NP) and octylphenol (OP) are environmental contaminants with potential endocrine disrupting effects. However, there is limited research on the mechanisms and intervention of combined NP and OP exposure-induced neurotoxicity. This study aims to explore the cytotoxicity of combined NP and OP exposure and evaluate the potential of Lycium barbarum polysaccharides (LBP) in mitigating the aforementioned toxicity. In present study, LBP (62.5, 125 and 250 µg/mL) were applied to intervene rat adrenal pheochromocytoma (PC-12) cells treated with combined NP and OP (NP: OP = 4:1, w/w; 1, 2, 4 and 8 µg/mL). The results showed that NP and OP induced oxidative stress, disrupted the 5-hydroxytryptamine (5-HT) and cholinergic systems in PC-12 cells. Additionally, they activated the p38 protein kinase (p38) and suppressed the expression of silent information regulation type 1 (SIRT1), monoamine oxidase A (MAOA), phosphorylated cyclic-AMP response binding protein (p-CREB), brain-derived neurotrophic factor (BDNF) and phosphorylated tropomyosin-related kinase receptor type B (p-TrkB). However, N-acetyl-L-cysteine (NAC) treatment counteracted the changes of signalling molecule p38, SIRT1/MAOA and CREB/BDNF/TrkB pathways-related proteins induced by NP and OP. LBP pretreatment ameliorated combined NP and OP exposure-induced oxidative stress and neurotransmitter imbalances. Furthermore, the application of LBP and administration of a p38 inhibitor both reversed the alterations in the signaling molecule p38, as well as the proteins associated to the SIRT1/MAOA and CREB/BDNF/TrkB pathways. These results implied that LBP may have neuroprotective effects via p38-mediated SIRT1/MAOA and CREB/BDNF/TrkB pathways.

Prenatal diesel exhaust exposure alters hippocampal synaptic plasticity in offspring

Diesel exhaust particles (DEPs) are major air pollutants emitted from automobile engines. Prenatal exposure to DEPs has been linked to neurodevelopmental and neurodegenerative diseases associated with aging. However, the specific mechanism by DEPs impair the hippocampal synaptic plasticity in the offspring remains unclear. Pregnant C57BL/6 mice were administered DEPs solution via the tail vein every other day for a total of 10 injections, then the male offsprings were studied to assess learning and memory by the Morris water maze. Additionally, protein expression in the hippocampus, including CPEB3, NMDAR (NR1, NR2A, NR2B), PKA, SYP, PSD95, and p-CREB was analyzed using Western blotting and immunohistochemistry. The alterations in the histomorphology of the hippocampus were observed in male offspring on postnatal day 7 following prenatal exposure to DEPs. Furthermore, 8-week-old male offspring exposed to DEPs during prenatal development exhibited impairments in the Morris water maze test, indicating deficits in learning and memory. Mechanistically, the findings from our study indicate that exposure to DEPs during pregnancy may alter the expression of CPEB3, SYP, PSD95, NMDAR (NR1, NR2A, and NR2B), PKA, and p-CREB in the hippocampus of both immature and mature male offspring. The results offer evidence for the role of the NMDAR/PKA/CREB and CPEB3 signaling pathway in mediating the learning and memory toxicity of DEPs in male offspring mice. The alterations in signaling pathways may contribute to the observed damage to synaptic structure and transmission function plasticity caused by DEPs. The findings hold potential for informing future safety assessments of DEPs.

Signaling Pathways Involved in Manganese-Induced Neurotoxicity

Manganese (Mn) is an essential trace element, but insufficient or excessive bodily amounts can induce neurotoxicity. Mn can directly increase neuronal insulin and activate insulin-like growth factor (IGF) receptors. As an important cofactor, Mn regulates signaling pathways involved in various enzymes. The IGF signaling pathway plays a protective role in the neurotoxicity of Mn, reducing apoptosis in neurons and motor deficits by regulating its downstream protein kinase B (Akt), mitogen-activated protein kinase (MAPK), and mammalian target of rapamycin (mTOR). In recent years, some new mechanisms related to neuroinflammation have been shown to also play an important role in Mn-induced neurotoxicity. For example, DNA-sensing receptor cyclic GMP-AMP synthase (cCAS) and its downstream signal efficient interferon gene stimulator (STING), NOD-like receptor family pyrin domain containing 3(NLRP3)-pro-caspase1, cleaves to the active form capase1 (CASP1), nuclear factor κB (NF-κB), sirtuin (SIRT), and Janus kinase (JAK) and signal transducers and activators of the transcription (STAT) signaling pathway. Moreover, autophagy, as an important downstream protein degradation pathway, determines the fate of neurons and is regulated by these upstream signals. Interestingly, the role of autophagy in Mn-induced neurotoxicity is bidirectional. This review summarizes the molecular signaling pathways of Mn-induced neurotoxicity, providing insight for further understanding of the mechanisms of Mn.

Neuronal survival factor TAFA2 suppresses apoptosis through binding to ADGRL1 and activating cAMP/PKA/CREB/BCL2 signaling pathway

AIMS

TAFA2, a cytokine specifically expressed in the central nervous system, plays a vital role in neuronal cell survival. TAFA2 deficiency has been correlated to various neurological disorders in mice and humans. However, the underlying mechanism remains elusive, especially its membrane-binding receptor through which TAFA2 functions. This study aimed to identify the specific binding receptor responsible for the anti-apoptotic effects of TAFA2.

MAIN METHOD

Co-immunoprecipitation (Co-IP) and quantitative mass spectrometry-based proteomic analysis were employed to identify potential TAFA2 binding proteins in V5 knockin mouse brain lysates. Subsequent validation involved in vitro and in vivo Co-IP and pull-down using specific antibodies. The functional analysis included evaluating the effects of ADGRL1 knockout, overexpression, and Lectin-like domain (Lec) deletion mutant on TAFA2's anti-apoptotic activity and analyzing the intracellular signaling pathways mediated by TAFA2 through ADGRL1.

KEY FINDINGS

Our study identified ADGRL1 as a potential receptor for TAFA2, which directly binds to TAFA2 through its lectin-like domain. Overexpression ADGRL1, but not ADGRL1ΔLec, induced apoptosis, which could be effectively suppressed by recombinant TAFA2 (rTAFA2). In ADGRL1-/- cells or re-introducing with ADGRL1ΔLec, responses to rTAFA2 in suppressing cell apoptosis were compromised. Increased cAMP, p-PKA, p-CREB, and BCL2 levels were also observed in response to rTAFA2 treatment, with these responses attenuated in ADGRL1-/- or ADGRL1ΔLec-expressing cells.

SIGNIFICANCE

Our results demonstrated that TAFA2 directly binds to the lectin-like domain of ADGRL1, activating cAMP/PKA/CREB/BCL2 signaling pathway, which is crucial in preventing cell death. These results implicate TAFA2 and its receptor ADGRL1 as potential therapeutic targets for neurological disorders.

Manganese-induced apoptosis through the ROS-activated JNK/FOXO3a signaling pathway in CTX cells, a model of rat astrocytes

Manganese (Mn) is an essential trace element that maintains many normal physiological functions. However, multi-system disorders would occur once overexposure to Mn, especially neurotoxicity. Despite evidence demonstrating the critical role of ROS-activated JNK/FOXO3a signaling pathway in neuronal survival, the specific mechanisms by which it contributes to Mn-induced neurotoxicity are still unclear. The objectives of this study was to examine the modulation of the JNK/FOXO3a signaling pathway, which is activated by ROS, in Mn-induced apoptosis, using a rat brain astrocyte cell line (CTX cells). This study found that a dose-dependent decrease in cell viability of CTX cells was observed with 150, 200, 250, 300 μmol/L Mn. The results of apoptosis-related protein assay showed that Mn decreased the expression of anti-apoptotic protein Bcl-2 and enhanced the expression of apoptosis-related proteins like Bax and Cleaved-Caspase3. In addition, treatment with Mn resulted in elevated ROS levels and increased phosphorylation levels of JNK. Conversely, phosphorylation of nuclear transcription factors FOXO3a, which regulates expression of transcription factors including Bim and PUMA, was decreased. Depletion of ROS by N-acetyl-L-cysteine (NAC) and inhibition of the JNK pathway by SP600125 prevented Mn-induced JNK/FOXO3a pathway activation and, more importantly, the level of apoptosis was also significantly reduced. Confirmation of Mn-induced apoptosis in CTX cells through ROS generation and activation of the JNK/FOXO3a signaling pathway was the outcome of this study. These findings offer fresh insights into the neurotoxic mechanisms of Mn and therapeutic targets following Mn exposure.

Preventive treatment with sodium para-aminosalicylic acid inhibits manganese-induced apoptosis and inflammation via the MAPK pathway in rat thalamus

Excessive exposure to manganese (Mn) may lead to neurotoxicity, referred to as manganism. In several studies, sodium para-aminosalicylic acid (PAS-Na) has shown efficacy against Mn-induced neurodegeneration by attenuating the neuroinflammatory response. The present study investigated the effect of Mn on inflammation and apoptosis in the rat thalamus, as well as the underlying mechanism of the PAS-Na protective effect. The study consisted of sub-acute (Mn treatment for 4 weeks) and sub-chronic (Mn and PAS-Na treatment for 8 weeks) experiments. In the sub-chronic experiments, pro-inflammatory cytokines, namely tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and cyclooxygenase 2 (COX-2) were significantly increased in the Mn-exposed group compared to the control II. PAS-Na treatment led to a significant reduction in the Mn-induced neuroinflammation by inhibiting IL-1β and COX-2 mRNA expression and reducing IL-1β secretion and JNK/p38 MAPK pathway activity. Furthermore, immunohistochemical analysis showed that the expression of caspase-3 was significantly increased in both the sub-acute and sub-chronic experimental paradigms concomitant with a significant decrease in B-cell lymphoma 2 (Bcl-2) in the thalamus of Mn-treated rats. PAS-Na also decreased the expression levels of several apoptotic markers downstream of the MAPK pathway, including Bcl-2/Bax and caspase-3, while up-regulating anti-apoptotic Bcl-2 proteins. In conclusion, Mn exposure led to inflammation in the rat thalamus concomitant with apoptosis, which was mediated via the MAPK signaling pathway. PAS-Na treatment antagonized effectively Mn-induced neurotoxicity by inhibiting the MAPK activity in the same brain region.

Aging-suppressor Klotho: Prospects in diagnostics and therapeutics

INTRODUCTION

The protein Klotho (KL) was first discovered in KL-deficient mice, which developed a syndrome similar to premature aging in humans. Since then, KL has been implicated in multiple molecular signaling pathways and diseases. KL has been shown to have anti-aging, healthspan and lifespan extending, cognitive enhancing, anti-oxidative, anti-inflammatory, and anti-tumor properties. KL levels decrease with age and in many diseases. Therefore, it has been of great interest to develop a KL-boosting or restoring drug, or to supplement endogenous Klotho with exogenous Klotho genetic material or recombinant Klotho protein, and to use KL levels in the body as a marker for the efficacy of such drugs and as a biomarker for the diagnosis and management of diseases.

OBJECTIVE

The goal of this study was to provide a comprehensive review of KL levels across age groups in individuals who are healthy or have certain health conditions, using four sources: blood, cerebrospinal fluid, urine, and whole biopsy/necropsy tissue. By doing so, baseline KL levels can be identified across the lifespan, in the absence or presence of disease. In turn, these findings can be used to guide the development of future KL-based therapeutics and biomarkers, which will heavily rely on an individual's baseline KL range to be efficacious.

METHODS

A total of 65 studies were collected primarily using the PubMed database. Research articles that were published up to April 2022 were included. Statistical analysis was conducted using RStudio.

RESULTS

Mean and median blood KL levels in healthy individuals, mean blood KL levels in individuals with renal conditions, and mean blood KL levels in individuals with metabolic or endocrine conditions were shown to decrease with age. Similarly, CSF KL levels in patients with AD also declined compared with age-matched controls.

CONCLUSIONS

The present study confirms the trend that KL levels in blood decrease with age in humans, among those who are healthy, and even further among those with renal and endocrine/metabolic illnesses. Further, by drawing this trend from multiple published works, we were able to provide a general idea of baseline KL ranges, specifically in blood in these populations. These data add to the current knowledge on normal KL levels in the body and how they change with time and in disease, and can potentially support efforts to create KL-based treatments and screening tools to better manage aging, renal, and metabolic/endocrine diseases.

Molecular mechanisms and therapeutic target of NETosis in diseases

Evidence shows that neutrophils can protect the host against pathogens in multiple ways, including the formation and release of neutrophil extracellular traps (NETs). NETs are web‐like structures composed of fibers, DNA, histones, and various neutrophil granule proteins. NETs can capture and kill pathogens, including bacteria, viruses, fungi, and protozoa. The process of NET formation is called NETosis. According to whether they depend on nicotinamide adenine dinucleotide phosphate (NADPH), NETosis can be divided into two categories: “suicidal” NETosis and “vital” NETosis. However, NET components, including neutrophil elastase, myeloperoxidase, and cell‐free DNA, cause a proinflammatory response and potentially severe diseases. Compelling evidence indicates a link between NETs and the pathogenesis of a number of diseases, including sepsis, systemic lupus erythematosus, rheumatoid arthritis, small‐vessel vasculitis, inflammatory bowel disease, cancer, COVID‐19, and others. Therefore, targeting the process and products of NETosis is critical for treating diseases linked with NETosis. Researchers have discovered that several NET inhibitors, such as toll‐like receptor inhibitors and reactive oxygen species scavengers, can prevent uncontrolled NET development. This review summarizes the mechanism of NETosis, the receptors associated with NETosis, the pathology of NETosis‐induced diseases, and NETosis‐targeted therapy.

Intensive stretch-activated CRT-PMCA1 feedback loop promoted apoptosis of myoblasts through Ca2+ overloading

Mechanical stretch exerted pro-apoptotic effect on myoblasts, the mechanism of which is currently unknown. Intracellular Ca²⁺ accumulation has been implicated in stretch-induced apoptosis. calreticulin (CRT) and plasma membrane Ca²⁺ transporting ATPase 1 (PMCA1) are two critical components of Ca²⁺ signaling system participating in intracellular Ca²⁺ homeostasis. In this study, we explored the contribution of CRT and PMCA1 in mediating stretch-induced Ca²⁺ accumulation and apoptosis of myoblasts. Stretching stimuli elevated level of CRT while inhibited activity of PMCA1. Moreover, there were bidirectional regulations between CRT and PMCA1, which formed the positive feedback loop leading to continuous increment of CRT level and repression of PMCA1 activity, in stretched myoblasts. Specifically, increased CRT level inhibited PMCA1 activity via suppressing Calmodulin (CaM), while reduced PMCA1 activity promoted CRT expression through activating p38MAPK pathway. Thus, the CRT-CaM-PMCA1 and PMCA1-p38MAPK-CRT pathways constituted a close cycle comprising CRT, PMCA1, CaM and p38MAPK. Inhibition of both CaM and p38MAPK affected the other three factors in stretched myoblasts. Circulation of the vicious cycle resulted in escalated Ca²⁺ overloading in myoblasts under continuous stretching stimuli. CRT knock-down, PMCA1 overexpression, and p38MAPK inhibition all attenuated the raised intracellular Ca²⁺ level and ameliorated myoblast apoptosis in the stretching environment. Conversely, CRT overexpression, PMCA1 knock-down, and CaM inhibition all aggravated stretch-induced Ca²⁺ overloading and myoblast apoptosis. A positive feedback loop between CRT and PMCA1 was activated in stretched myoblasts, which contributed to intracellular Ca²⁺ accumulation and resultant myoblast apoptosis.

Neurotoxicity and gene expression alterations in zebrafish larvae in response to manganese exposure

Manganese (Mn) is an essential trace element, but excessive exposure can damage mental, cognitive, and motor functions. Although many studies have reported the toxicity of Mn, the underlying mechanism remains unclear. Here, wild-type and/or Tg(NBT:DsRed) zebrafish embryos/larvae were exposed to different dosages of Mn to determine the effects on mortality, malformation, and hatching rates. A video tracking system was used to analyze the locomotor activities of zebrafish larvae. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay and acridine orange staining were performed to monitor cell apoptosis, while dopamine transporter and tyrosine hydroxylase (TH) expression were detected by immunohistochemical staining. Meanwhile, transcriptome sequencing of the head tissues of zebrafish larvae was performed to search for molecular targets of Mn neurotoxicity. The results showed that Mn exposure increased the mortality and malformation rates of zebrafish larvae, and significantly reduced swim distance and velocity. In addition, the proportion of apoptotic dopaminergic neurons increased, while TH expression significantly decreased. The results of transcriptome sequencing showed that a large number of differentially expressed genes associated with apoptosis and DNA damage repair were upregulated, consistent with the above results. Meanwhile, Western blot analysis showed that higher exposure level of Mn could induce activation of MAPK pathway. These data demonstrate that Mn exposure can damage dopaminergic neurons and cause apoptosis, which has detrimental effects on the motor abilities of zebrafish larvae.

Polystyrene microplastics affect learning and memory in mice by inducing oxidative stress and decreasing the level of acetylcholine

Microplastics pollution has become a growing environmental concern, but its potential neurotoxic effects remain unknown. In this study, we determined the effects of exposure to polystyrene microplastics (micro-PS) on learning and memory, and explored the underlying mechanisms. Kunming mice were orally exposed to 0.01, 0.1, 1 mg/d micro-PS or saline for four weeks. Employing the Morris water maze test, we observed that exposure to micro-PS affected the learning and exploration abilities of mice, and impaired their learning and memory functions. After exposure to micro-PS, the nerve cells in the hippocampus became loose and disordered, and the number of Nissl bodies decreased. Increases in the levels of ROS and MDA, and a decrease in levels of glutathione were found in the brain tissue of the mice exposed to micro-PS. Exposure to micro-PS also induced a reduction in the level of acetylcholine, and inhibited the CREB/BDNF pathway. Importantly, after treatment with the antioxidant, Vitamin E, the learning and memory abilities of the mice were restored, and the release of neurotransmitters rebounded. These results show that micro-PS exposure can affect the learning and memory functions through inducing oxidative stress and decreasing the levels of acetylcholine.

Senkyunolide H protects PC12 cells from OGD/R-induced injury via cAMP-PI3K/AKT signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Senkyunolide H (SNH) is a bioactive phthalide isolated from Ligusticum chuanxiong Hort rhizome and was reported to have multiple pharmacological effects.

AIM OF THE STUDY

The study was performed to verify the potency of SNH protecting PC12 cells from oxygen glucose deprivation/reperfusion (OGD/R)-induced injury and to elucidate the underlying mechanisms.

MATERIALS AND METHODS

OGD/R model was established in PC12 cells and the cell viability was measured by MTT assay. The cell morphology was observed using scanning electron microscope (SEM). The potential targets of SNH and related targets of OGD/R were screened, and a merged protein-protein interaction (PPI) network of SNH and OGD/R was constructed based on the network pharmacology analysis. Kyoto Encyclopedia of Genes and Genomes (KEGG) database was used for pathway analysis. Intracellular cAMP level and the protein expression levels were measured to elucidate the underlying mechanisms.

RESULTS

SNH pretreatment protected PC12 cells against OGD/R-induced cell death. SNH also significantly protected the cell protrusion. A merged PPI network was constructed and the shared candidate targets significantly enriched in cAMP signaling pathway. The level of intracellular cAMP and the protein level of p-CREB, p-AKT, p-PDK1 and PKA protein were up-regulated after the treatment of SNH compared with OGD/R modeling.

CONCLUSIONS

The present study indicated that SNH protected PC12 cells from OGD/R-induced injury via cAMP-PI3K/AKT signaling pathway.

Receptor-Mediated NETosis on Neutrophils

Neutrophil extracellular traps (NETs), a web-like structures containing chromatin, have a significant role in assisting the capture and killing of microorganisms by neutrophils during infection. The specific engagement of cell-surface receptors by extracellular signaling molecules activates diverse intracellular signaling cascades and regulates neutrophil effector functions, including phagocytosis, reactive oxygen species release, degranulation, and NET formation. However, overproduction of NETs is closely related to the occurrence of inflammation, autoimmune disorders, non-canonical thrombosis and tumor metastasis. Therefore, it is necessary to understand neutrophil activation signals and the subsequent formation of NETs, as well as the related immune regulation. In this review, we provide an overview of the immunoreceptor-mediated regulation of NETosis. The pathways involved in the release of NETs during infection or stimulation by noninfectious substances are discussed in detail. The mechanisms by which neutrophils undergo NETosis help to refine our views on the roles of NETs in immune protection and autoimmune diseases, providing a theoretical basis for research on the immune regulation of NETs.

The role of manganese dysregulation in neurological disease: emerging evidence

Manganese is an essential trace metal. The dysregulation of manganese seen in a broad spectrum of neurological disorders reflects its importance in brain development and key neurophysiological processes. Historically, the observation of acquired manganism in miners and people who misuse drugs provided early evidence of brain toxicity related to manganese exposure. The identification of inherited manganese transportopathies, which cause neurodevelopmental and neurodegenerative syndromes, further corroborates the neurotoxic potential of this element. Moreover, manganese dyshomoeostasis is also implicated in Parkinson's disease and other neurodegenerative conditions, such as Alzheimer's disease and Huntington's disease. Ongoing and future research will facilitate the development of better targeted therapeutical strategies than are currently available for manganese-associated neurological disorders.

Impact of environmental toxicants on p38- and ERK-MAPK signaling pathways in the central nervous system

There are several candidate signalling pathways that mediate the response of the central nervous system (CNS) cells to environmental toxins. However, much is still to be learned on how these pathways modulate neurotoxicity. The mitogen-activated protein kinases (MAPKs) signalling pathways, which include the extracellular signal-regulated protein kinase (ERK) and the p38-MAPK, are potentially key pathways to regulate CNS responses to environmental toxins. The pathways play leading roles in the transmission of extracellular signals into the cell nucleus, leading to cell differentiation, cell growth, and apoptosis, to name a few. Moreover, exposure to environmental toxins induces p38- and ERK-MAPK activation, which leads to oxidative stress, inflammation, and apoptosis in the CNS. Here, we provide a concise review of the recent evidence demonstrating the role of p38- and ERK-MAPK signaling pathways and their downstream targets in the CNS following exposure to environmental toxicants such as metals, organophosphorus and persistent organic pollutants.

Molecular Targets of Manganese-Induced Neurotoxicity: A Five-Year Update

Understanding of the immediate mechanisms of Mn-induced neurotoxicity is rapidly evolving. We seek to provide a summary of recent findings in the field, with an emphasis to clarify existing gaps and future research directions. We provide, here, a brief review of pertinent discoveries related to Mn-induced neurotoxicity research from the last five years. Significant progress was achieved in understanding the role of Mn transporters, such as SLC39A14, SLC39A8, and SLC30A10, in the regulation of systemic and brain manganese handling. Genetic analysis identified multiple metabolic pathways that could be considered as Mn neurotoxicity targets, including oxidative stress, endoplasmic reticulum stress, apoptosis, neuroinflammation, cell signaling pathways, and interference with neurotransmitter metabolism, to name a few. Recent findings have also demonstrated the impact of Mn exposure on transcriptional regulation of these pathways. There is a significant role of autophagy as a protective mechanism against cytotoxic Mn neurotoxicity, yet also a role for Mn to induce autophagic flux itself and autophagic dysfunction under conditions of decreased Mn bioavailability. This ambivalent role may be at the crossroad of mitochondrial dysfunction, endoplasmic reticulum stress, and apoptosis. Yet very recent evidence suggests Mn can have toxic impacts below the no observed adverse effect of Mn-induced mitochondrial dysfunction. The impact of Mn exposure on supramolecular complexes SNARE and NLRP3 inflammasome greatly contributes to Mn-induced synaptic dysfunction and neuroinflammation, respectively. The aforementioned effects might be at least partially mediated by the impact of Mn on α-synuclein accumulation. In addition to Mn-induced synaptic dysfunction, impaired neurotransmission is shown to be mediated by the effects of Mn on neurotransmitter systems and their complex interplay. Although multiple novel mechanisms have been highlighted, additional studies are required to identify the critical targets of Mn-induced neurotoxicity.

Perturbed MAPK signaling in ASD: Impact of metal neurotoxicity

The mitogen-activated protein kinase (MAPK) pathways are intracellular signaling pathways necessary for regulating various physiological processes, including neurodevelopment. The developing brain is vulnerable to toxic substances, and metals, such as lead, mercury, nickel, manganese, and others, have been proven to induce disturbances in the MAPK signaling pathway. Since a well-regulated MAPK is necessary for normal neurodevelopment, perturbation of the MAPK pathway results in neurodevelopmental disorders, including autism spectrum disorder (ASD). ASD affects brain parts responsible for communication, cognition, social interaction, and other patterned behaviors. Several studies have addressed the role of metals in the etiopathogenesis of ASD. Here, we briefly review the MAPK signaling pathway and its role in neurodevelopment. Furthermore, we highlight the role of metal toxicity in the development of ASD and how perturbed MAPK signaling may result in ASD.

Antagonistic effect of VDR/CREB1 pathway on cadmium-induced apoptosis in porcine spleen

Cadmium (Cd) is a toxic trace element that can enter the environment with industrial waste and accumulate in the body but the health effects of Cd on ternary pigs are still lacking in research. In order to explore the effect of Cd on the apoptosis of pig spleen and its mechanism, this study chose ternary pig as the research object to detect relevant indicators in pig spleen under Cd exposure. The results of this study showed that Cd exposure can induce apoptosis by promoting the absorption of various toxic trace elements in the spleen and inducing oxidative stress. We also found that the mechanism of Cd-induced apoptosis is closely related to the VDR/CREB1 pathway. On the one hand, Cd exposure can activate VDR, and indirectly regulate the CYP family, affecting the normal function of the spleen. On the other hand, VDR and its downstream genes antagonize the toxicity of Cd by maintaining the stability of the mitochondrial-related endoplasmic reticulum membrane structure. Our research will help researchers to further understand the physiological toxicity of Cd.

An insertion/deletion within the CREB1 gene identified using the RNA-sequencing is associated with sheep body morphometric traits

In a previous study, the cyclic AMP response element-binding protein 1 (CREB1) gene, which is likely involved in the regulation of fat metabolism in sheep adipose tissue, was identified using RNA sequencing. CREB1 is a transcription factor that participates in the regulation of cell proliferation, differentiation, and survival as well as energy metabolism. Therefore, based on preliminary studies, this study aimed to reveal the correlation between the insertion/deletion (indel) polymorphism of the CREB1 gene and sheep growth traits. One insertion variation of the ovine CREB1 gene, C3-ins-26 bp, was investigated in 1847 Chinese and Mongolian sheep breeds. The minor allele frequencies in the CREB1 gene varied from 0.021 to 0.938. Further, statistical analyses indicated that the C3-ins-26 bp indel in the CREB1 gene was significantly related to various body measurements (body length, height, and index; chest width, depth, and width index; cannon circumference index; and height at the hip cross) in a Tan sheep population (p < 0.05). Collectively, these findings may provide important insights into marker-assisted selection of sheep.

Positive regulation of the CREB phosphorylation via JNK-dependent pathway prevents antimony-induced neuronal apoptosis in PC12 cell and mice brain

Antimony (Sb) is a potentially toxic chemical element abundantly found in the environment. We previously reported that Sb promoted neuronal deathvia reactive oxygen species-dependent autophagy. Here, we assessed the role of cyclic adenosine monophosphate response element-binding protein (CREB) in Sb-induced neuronal damage. We found that Sb treatment induced CREB phosphorylation and neuronal apoptosis both in vitro and in vivo. Interestingly, inhibition of CREB's transcriptional activity with 666-15 dramatically enhanced apoptosis in PC12 cells by downregulating B-cell lymphoma 2 (Bcl-2). Additionally, Sb activated ERK, JNK, and p38 signaling ; however, only JNK promoted CREB phosphorylation. In conclusion, our findings suggest that CREB phosphorylation by JNK attenuates Sb-induced neuronal apoptosis via Bcl-2 upregulation. These data suggest that JNK-dependent CREB activation prevents neurons from Sb-induced apoptosis and guides the development of novel strategies to prevent Sb-induced neurotoxicity.

Alpha-synuclein is involved in manganese-induced spatial memory and synaptic plasticity impairments via TrkB/Akt/Fyn-mediated phosphorylation of NMDA receptors

Manganese (Mn) overexposure produces long-term cognitive deficits and reduces brain-derived neurotrophic factor (BDNF) in the hippocampus. However, it remains elusive whether Mn-dependent enhanced alpha-synuclein (α-Syn) expression, suggesting a multifaceted mode of neuronal toxicities, accounts for interference with BDNF/TrkB signaling. In this study, we used C57BL/6J WT and α-Syn knockout (KO) mice to establish a model of manganism and found that Mn-induced impairments in spatial memory and synaptic plasticity were related to the α-Syn protein. In addition, consistent with the long-term potentiation (LTP) impairments that were observed, α-Syn KO relieved Mn-induced degradation of PSD95, phosphorylated CaMKIIα, and downregulated SynGAP protein levels. We transfected HT22 cells with lentivirus (LV)-α-Syn shRNA, followed by BDNF and Mn stimulation. In vitro experiments indicated that α-Syn selectively interacted with TrkB receptors and inhibited BDNF/TrkB signaling, leading to phosphorylation and downregulation of GluN2B. The binding of α-Syn to TrkB and Fyn-mediated phosphorylation of GluN2B were negatively regulated by BDNF. Together, these findings indicate that Mn-dependent enhanced α-Syn expression contributes to further exacerbate BDNF protein-level reduction and to inhibit TrkB/Akt/Fyn signaling, thereby disturbing Fyn-mediated phosphorylation of the NMDA receptor GluN2B subunit at tyrosine. In KO α-Syn mice treated with Mn, spatial memory and LTP impairments were less pronounced than in WT mice. However, the same robust neuronal death was observed as a result of Mn-induced neurotoxicity.

Rh-CSF1 Attenuates Oxidative Stress and Neuronal Apoptosis via the CSF1R/PLCG2/PKA/UCP2 Signaling Pathway in a Rat Model of Neonatal HIE

Oxidative stress (OS) and neuronal apoptosis are major pathological processes after hypoxic-ischemic encephalopathy (HIE). Colony stimulating factor 1 (CSF1), binding to CSF1 receptor (CSF1R), has been shown to reduce neuronal loss after hypoxic-ischemia- (HI-) induced brain injury. In the present study, we hypothesized that CSF1 could alleviate OS-induced neuronal degeneration and apoptosis through the CSF1R/PLCG2/PKA/UCP2 signaling pathway in a rat model of HI. A total of 127 ten-day old Sprague Dawley rat pups were used. HI was induced by right common carotid artery ligation with subsequent exposure to hypoxia for 2.5 h. Exogenous recombinant human CSF1 (rh-CSF1) was administered intranasally at 1 h and 24 h after HI. The CSF1R inhibitor, BLZ945, or phospholipase C-gamma 2 (PLCG2) inhibitor, U73122, was injected intraperitoneally at 1 h before HI induction. Brain infarct volume measurement, cliff avoidance test, righting reflex test, double immunofluorescence staining, western blot assessment, 8-OHdG and MitoSOX staining, Fluoro-Jade C staining, and TUNEL staining were used. Our results indicated that the expressions of endogenous CSF1, CSF1R, p-CSF1R, p-PLCG2, p-PKA, and uncoupling protein2 (UCP2) were increased after HI. CSF1 and CSF1R were expressed in neurons and astrocytes. Rh-CSF1 treatment significantly attenuated neurological deficits, infarct volume, OS, neuronal apoptosis, and degeneration at 48 h after HI. Moreover, activation of CSF1R by rh-CSF1 significantly increased the brain tissue expressions of p-PLCG2, p-PKA, UCP2, and Bcl2/Bax ratio, but reduced the expression of cleaved caspase-3. The neuroprotective effects of rh-CSF1 were abolished by BLZ945 or U73122. These results suggested that rh-CSF1 treatment attenuated OS-induced neuronal degeneration and apoptosis after HI, at least in part, through the CSF1R/PLCG2/PKA/UCP2 signaling pathway. Rh-CSF1 may serve as therapeutic strategy against brain damage in patients with HIE.

Protection of the Geum japonicum Thunb. var. chinense extracts against oxygen-glucose deprivation and re-oxygenation induced astrocytes injury via BDNF/PI3K/Akt/CREB pathway

Geum japonicum Tunb. var. chinense (GJ) is a traditional Chinese medicine usually used for the alleviation of dizziness and headache. Previous studies have reported that the GJ extracts could alleviate cerebral I/R injury by reducing apoptosis in vivo. To further elucidate the positive role and underlying mechanism of the GJ extracts in cerebral I/R injury, the current study investigated the effects of the GJ extracts on oxygen-glucose deprivation and re-oxygenation (OGD/R)-induced astrocytes injury in light of BDNF/PI3K/Akt/CREB signaling pathway with seropharmacological method. In the present study, the LC-MS profiling of the GJ extracts, obtain by reflux extraction, led to the identification of three possible active components were 5-desgalloylstachyurin, tellimagrandin II (TG II) and 3,4,5-Trihydroxybenzaldehyde (THBA). Drug-containing serum was collected from rats given different doses of the GJ extracts (0, 1.75 g/kg, 7 g/kg). Data indicated that the GJ extracts could increase the cell viability and decrease apoptosis and the expression of glial fibrillary acidic protein (GFAP) in OGD/R-induced astrocytes. In addition, the detection of apoptosis-related factors showed that the GJ extracts could obviously increase the expression of Bcl-2 and reduce the expression of Bax, Caspase-3 and cleaved-Caspase-3. Furthermore, the GJ extracts markedly increased the expression of BDNF, TrkB, PI3K, p-Akt and p-CREB. All these effects of the GJ extracts could be significantly reversed by LY294002, an inhibitor of PI3K. These data indicated that the GJ extracts could protect astrocytes against OGD/R-induced injury by inhibiting astrocytes reactivity and apoptosis, owing to the activation of the BDNF/PI3K/Akt/CREB pathway. The results support the application of the GJ extracts in the treatment of ischemic stroke and other ischemic encephalopathy.

Vaspin protects mouse mesenchymal stem cells from oxidative stress-induced apoptosis through the MAPK/p38 pathway

The aim of the work was to study the influence of vaspin on oxidative stress-induced apoptosis of mouse mesenchymal stem cells (MSCs). MSCs originated from bone marrow of C57BL/6 mouse were treated with vaspin and/or H₂O₂ in a dose-dependent manner. Cellular viability detected by CCK-8 and cell apoptosis studied by flow cytometry and TUNEL assay were observed in these cells. The protein expressions of PI3K, p-PI3K, Akt, p-Akt, T-ERK1/2, p-ERK1/2, p38, p-p38, JNK, and p-JNK were tested by Western blot. Vaspin had no significant effect on cellular viability, but significantly reduced H₂O₂-induced apoptosis. Western blot assay showed that pretreatment with vaspin promoted the activation of p-p38. Inhibition of p38 by SB203580 suppressed the protective effect of vaspin on oxidative stress-induced apoptosis. Vaspin inhibits oxidative stress-induced apoptosis of MSCs via the activation of MAPK/p38 signaling pathway. These findings indicate that vaspin is prone to osteoporosis protection.