Involvement of autophagy in tri-ortho-cresyl phosphate- induced delayed neuropathy in hens

A Tau-Driven Adverse Outcome Pathway Blueprint Toward Memory Loss in Sporadic (Late-Onset) Alzheimer's Disease with Plausible Molecular Initiating Event Plug-Ins for Environmental Neurotoxicants

The worldwide prevalence of sporadic (late-onset) Alzheimer's disease (sAD) is dramatically increasing. Aging and genetics are important risk factors, but systemic and environmental factors contribute to this risk in a still poorly understood way. Within the frame of BioMed21, the Adverse Outcome Pathway (AOP) concept for toxicology was recommended as a tool for enhancing human disease research and accelerating translation of data into human applications. Its potential to capture biological knowledge and to increase mechanistic understanding about human diseases has been substantiated since. In pursuit of the tau-cascade hypothesis, a tau-driven AOP blueprint toward the adverse outcome of memory loss is proposed. Sequences of key events and plausible key event relationships, triggered by the bidirectional relationship between brain cholesterol and glucose dysmetabolism, and contributing to memory loss are captured. To portray how environmental factors may contribute to sAD progression, information on chemicals and drugs, that experimentally or epidemiologically associate with the risk of AD and mechanistically link to sAD progression, are mapped on this AOP. The evidence suggests that chemicals may accelerate disease progression by plugging into sAD relevant processes. The proposed AOP is a simplified framework of key events and plausible key event relationships representing one specific aspect of sAD pathology, and an attempt to portray chemical interference. Other sAD-related AOPs (e.g., Aβ-driven AOP) and a better understanding of the impact of aging and genetic polymorphism are needed to further expand our mechanistic understanding of early AD pathology and the potential impact of environmental and systemic risk factors.

Atg7 Knockout Alleviated the Axonal Injury of Neuro-2a Cells Induced by Tri-Ortho-Cresyl Phosphate

Autophagy is believed to be essential for the maintenance of axonal homeostasis in neurons. However, whether autophagy is causally related to the axon degeneration in organophosphorus-induced delayed neuropathy (OPIDN) still remains unclear. This research was designed to investigate the role of autophagy in axon degeneration following tri-ortho-cresyl phosphate (TOCP) in an in vitro model. Differentiated wild-type and Atg7-/- neuro-2a (N2a) cells were treated with TOCP for 24 h. Axonal degeneration in N2a cells was quantitatively analyzed; the key molecules responsible for axon degeneration and its upstream signaling pathway were determined by Western blotting and real-time PCR. The results found that Atg7-/- cells exhibited a higher resistance to TOCP insult than wild-type cells. Further study revealed that TOCP caused a significant decrease in pro-survival factors NMNATs and SCG10 and a significant increase in pro-degenerative factor SARM1 in both cells. Notably, Atg7-/- cells presented a higher level of pro-survival factors and a lower level of pro-degenerative factors than wild-type cells in the same setting of TOCP administration. Moreover, DLK-MAPK pathway was activated following TOCP. Altogether, our results suggest that autophagy is able to affect TOCP-induced axonal injury via regulating the balance between pro-survival and pro-degenerative factors, providing a promising avenue for the potential therapy for OPIDN patients.

Decrease of an intracellular organic osmolyte contributes to the cytotoxicity of organophosphate in neuroblastoma cells in vitro

Organophosphorus compounds (OP) causes prominent delayed neuropathy in vivo and cytotoxicity to neuronal cells in vitro. The primary target protein of OP's neurotoxicity is neuropathy target esterase (NTE), which can convert phosphatidylcholine (PC) to glycerophosphocholine (GPC). Recent studies reveal that autophagic cell death is important for the initiation and progression of OP-induced neurotoxicity both in vivo and in vitro. However, the mechanism of how OP induces autophagic cell death is unknown. Here it is found that GPC is an important organic osmolyte in the neuroblastoma cells, and treatment with tri-o-cresyl phosphate (TOCP), a representative OP, leads to the decrease of GPC and imbalance of extracellular and intracellular osmolality. Knockdown of GPC metabolizing enzyme glycerophosphodiester phosphodiesterase domain containing 5 (GDPD5) reverses TOCP-induced autophagic cell death, which further supports the notion that the reduced GPC level leads to the autophagic cell death. Furthermore, it is found that autophagic cell death is due to the induction of reactive oxygen species (ROS) and mitochondrial damage by imbalance of osmolality with TOCP treatment. In summary, this study reveals that TOCP treatment decreases GPC level and intracellular osmolality, which induces ROS and mitochondrial damage and leads to the cell death and neurite degradation by autophagy. This study lays the foundation for further investigations on the potential therapeutic approaches for OP neurotoxicity or NTE mutation-related neurological diseases.

Hyperactivity and Seizure Induced by Tricresyl Phosphate Are Isomer Specific and Not Linked to Phenyl Valerate-Neuropathy Target Esterase Activity Inhibition in Zebrafish

Environmental exposure to tricresyl phosphate (TCP) may lead to severe neurotoxic effects, including organophosphate (OP)-induced delayed neuropathy. TCP has three symmetric isomers, distinguished by the methyl group position on the aromatic ring system. One of these isomers, tri-ortho-cresyl phosphate (ToCP), has been reported for years as a neuropathic OP, targeting neuropathic target esterase (NTE/PNPLA6), but its mode of toxic action had not been fully elucidated. Zebrafish eleuthero-embryo and larva were used to characterize the differential action of the TCP isomers. The symmetric isomers inhibited phenyl valerate (PV)-NTE enzymatic activity in vivo with different IC50, while no effect was observed on acetylcholinesterase activity. Moreover, the locomotor behavior was also affected by tri-para-cresyl phosphate and tri-meta-cresyl phosphate, only ToCP exposure led to locomotor hyperactivity lasting several hours, associated with defects in the postural control system and an impaired phototactic response, as revealed by the visual motor response test. The electric field pulse motor response test demonstrated that a seizure-like, multiple C-bend-spaghetti phenotype may be significantly induced by ToCP only, independently of any inhibition of PV-NTE activity. Eleuthero-embryos exposed to picrotoxin, a known gamma-aminobutyric acid type-A receptor inhibitor, exhibited similar adverse outcomes to ToCP exposure. Thus, our results demonstrated that the TCP mode of toxic action was isomer specific and not initially related to modulation of PV-NTE activity. Furthermore, it was suggested that the molecular events involved were linked to an impairment of the balance between excitation and inhibition in neuronal circuits.

In Vitro Immunotoxicity of Organophosphate Flame Retardants in Human THP-1-Derived Macrophages

Scarce attention has been paid to the immunotoxicity of organophosphate flame retardants (PFRs), which poses a challenge to the systematic assessment of their health risks. In this study, a battery of in vitro immunotoxicity screening assays, including adhesion, phagocytosis, and 48 cytokine/chemokine production, was measured after exposing THP-1-derived macrophages to six selected common PFRs (TPHP, TDCPP, TNBP, TOCP, TCEP, and TBOEP) at a noncytotoxic concentration (≤50 μM). Our results showed that TPHP and TBOEP partially attenuated the adhesion and phagocytosis of the THP-1 mφs and that TDCPP caused a functional loss of phagocytosis, implying the potential immunosuppression. In contrast, TNBP and TOCP may cause an immunostimulation by significantly promoting cell adhesion and enhancing phagocytic efficiency. Additionally, the results from a cytokine/chemokine secretion analysis revealed the proinflammatory properties of TDCPP, TPHP, and TBOEP. TOCP was thought to disrupt the inflammatory balance by inhibiting both proinflammatory and antiinflammatory cytokines. TCEP showed no effect on adhesion or phagocytosis and little modulation of cytokine release at this experimental concentration. Overall, this study supports that PFRs can be immunotoxic to macrophages in different ways and provides evidence for developing more sensitive in vitro immunotoxicity bioassay methods.

Melatonin Protects Neural Stem Cells Against Tri-Ortho-Cresyl Phosphate-Induced Autophagy

Tri-ortho-cresyl phosphate (TOCP) is an extensively used organophosphate in industry. It has been proven to lead to toxicity in different organ systems, especially in the nervous system. Neural stem cells (NSCs) play important roles in both embryonic and adult nervous systems. However, whether TOCP induces cytotoxicity in embryonic NSCs remains unclear. In this study, mouse NSCs were exposed to different concentrations of TOCP for 24 h. The results showed that TOCP led to impaired proliferation of NSCs and induced the autophagy of NSCs by increasing the generation of intracellular reactive oxygen species (ROS) and decreasing the phosphorylation of extracellular regulated protein kinase (ERK1/2). Melatonin has been reported to exert neuroprotective effects via various mechanisms. Therefore, we further investigate whether melatonin has potential protective effects against TOCP-induced cytotoxicity on NSCs. Our data showed that melatonin pretreatment attenuated TOCP-induced autophagy by suppressing oxidative stress and restoring ERK1/2 phosphorylation consistently. Taken together, the results indicated that TOCP induced the autophagy in mouse NSCs, and melatonin may effectively protect NSCs against TOCP-induced autophagy.

Prenatal Exposure to Benzophenone-3 Impairs Autophagy, Disrupts RXRs/PPARγ Signaling, and Alters Epigenetic and Post-Translational Statuses in Brain Neurons

The UV absorber benzophenone-3 (BP-3) is the most extensively used chemical substance in various personal care products. Despite that BP-3 exposure is widespread, knowledge about the impact of BP-3 on the brain development is negligible. The present study aimed to explore the mechanisms of prenatal exposure to BP-3 in neuronal cells, with particular emphasis on autophagy and nuclear receptors signaling as well as the epigenetic and post-translational modifications occurring in response to BP-3. To observe the impact of prenatal exposure to BP-3, we administered BP-3 to pregnant mice, and next, we isolated brain tissue from pretreated embryos for primary cell neocortical culture. Our study revealed that prenatal exposure to BP-3 (used in environmentally relevant doses) impairs autophagy in terms of BECLIN-1, MAP1LC3B, autophagosomes, and autophagy-related factors; disrupts the levels of retinoid X receptors (RXRs) and peroxisome proliferator-activated receptor gamma (PPARγ); alters epigenetic status (i.e., attenuates HDAC and sirtuin activities); inhibits post-translational modifications in terms of global sumoylation; and dysregulates expression of neurogenesis- and neurotransmitter-related genes as well as miRNAs involved in pathologies of the nervous system. Our study also showed that BP-3 has good permeability through the BBB. We strongly suggest that BP-3-evoked effects may substantiate a fetal basis of the adult onset of neurological diseases, particularly schizophrenia and Alzheimer’s disease.

A protective role of autophagy in TDCIPP-induced developmental neurotoxicity in zebrafish larvae

Tris (1, 3-dichloro-2-propyl) phosphate (TDCIPP), an extensively used organophosphorus flame retardant, is frequently detected in various environmental media and biota, and has been demonstrated as neurotoxic. Autophagy has been proposed as a protective mechanism against toxicant-induced neurotoxicity. The purpose of the present study was to investigate the effect of TDCIPP exposure on autophagy, and its role in TDCIPP-induced developmental neurotoxicity. Zebrafish embryos (2-120 h post-fertilization [hpf]) were exposed to TDCIPP (0, 5, 50 and 500 μg/l) and a model neurotoxic chemical, chlorpyrifos (CPF, 100 μg/l). The developmental endpoints, locomotive behavior, cholinesterase activities, gene and protein expression related to neurodevelopment and autophagy were measured in the larvae. Our results demonstrate that exposure to TDCIPP (500 μg/l) and CPF causes developmental toxicity, including reduced hatching and survival rates and increased malformation rate (e.g., spinal curvature), as well as altered locomotor behavior. The expression of selected neurodevelopmental gene and protein markers (e.g., mbp, syn2a, and α1-tubulin) was significantly down-regulated in CPF and TDCIPP exposed zebrafish larvae. Treatment with CPF significantly inhibits AChE and BChE, while TDCIPP (0-500 μg/l) exerts no effects on these enzymes. Furthermore, the conversion of microtubule-associated protein I (LC3 I) to LC3 II was significantly increased in TDCIPP exposed zebrafish larvae. In addition, exposure to TDCIPP also activates transcription of several critical genes in autophagy (e.g. Becn1, atg3, atg5, map1lc3b and sqstm1). To further investigate the role of autophagy in TDCIPP induced developmental neurotoxicity, an autophagy inducer (rapamycin, Rapa, 1 nM) and inhibitor (chloroquine, CQ, 1 μM) were used. The results demonstrate that the hatching rate, survival rate, and the expression of mbp and а1-tubulin proteins were all significantly increased in larvae treated with TDCIPP (500 μg/l) and Rapa compared to TDCIPP alone. In contrast, co-treatment with the autophagy inhibitor CQ results in exacerbated neurodevelopmental toxicity. Taken together, our results confirm that exposure to TDCIPP induces autophagy, which plays a protective role in TDCIPP-induced developmental neurotoxicity in zebrafish embryos and larvae.

Role of autophagy in environmental neurotoxicity

Human exposure to neurotoxic pollutants (e.g. metals, pesticides and other chemicals) is recognized as a key risk factor in the pathogenesis of neurodegenerative disorders. Emerging evidence indicates that an alteration in autophagic pathways may be correlated with the onset of the neurotoxicity resulting from chronic exposure to these pollutants. In fact, autophagy is a natural process that permits to preserving cell homeostasis, through the seizure and degradation of the cytosolic damaged elements. However, when an excessive level of intracellular damage is reached, the autophagic process may also induce cell death. A correct modulation of specific stages of autophagy is important to maintain the correct balance in the organism. In this review, we highlight the critical role that autophagy plays in neurotoxicity induced by the most common classes of environmental contaminants. The understanding of this mechanism may be helpful to discover a potential therapeutic strategy to reduce side effects induced by these compounds.

Overexpression of let-7a increases neurotoxicity in a PC12 cell model of Alzheimer's disease via regulating autophagy

Increased deposition of β-amyloid (Aβ) protein is one of the typical characteristics of Alzheimer's disease (AD). Recent evidence has demonstrated that the microRNA let-7 family, which is highly expressed in the central nervous system, participates in the regulation of pathologic processes of AD. In the present study, the effect of let-7a overexpression on Aβ1-40-induced neurotoxicity was evaluated in PC12 and SK-N-SH cells. The results indicated that overexpression of let-7a enhanced the neurotoxicity induced by Aβ1-40 in PC12 and SK-N-SH cells. In addition, the apoptosis induced by Aβ1-40 in PC12 and SK-N-SH cells was increased by let-7a overexpression. Furthermore, Aβ1-40 treatment increased the protein levels of microtubule-associated protein 1A/1B-light chain 3 (LC3) and beclin-1 and increased the LC3 II/I ratio. The mRNA expression levels of beclin-1, autophagy protein 5 (Atg-5) and Atg-7 were also increased by Aβ1-40 treatment in PC12 cells. Let-7a overexpression further upregulated the above autophagy-related markers. Furthermore, the protein level of p62 was increased by Aβ1-40 treatment, and this was further enhanced by let-7a overexpression. Finally, the present results demonstrated that the phosphoinositide-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway was involved in the autophagy regulation by let-7a. In conclusion, the present study demonstrates that the neurotoxicity induced by Aβ1-40 is augmented by let-7a overexpression via regulation of autophagy, and the PI3K/Akt/mTOR signaling pathway also serves a function in this process.

TRPA1 channel mediates organophosphate-induced delayed neuropathy

The organophosphate-induced delayed neuropathy (OPIDN), often leads to paresthesias, ataxia and paralysis, occurs in the late-stage of acute poisoning or after repeated exposures to organophosphate (OP) insecticides or nerve agents, and may contribute to the Gulf War Syndrome. The acute phase of OP poisoning is often attributed to acetylcholinesterase inhibition. However, the underlying mechanism for the delayed neuropathy remains unknown and no treatment is available. Here we demonstrate that TRPA1 channel (Transient receptor potential cation channel, member A1) mediates OPIDN. A variety of OPs, exemplified by malathion, activates TRPA1 but not other neuronal TRP channels. Malathion increases the intracellular calcium levels and upregulates the excitability of mouse dorsal root ganglion neurons in vitro. Mice with repeated exposures to malathion also develop local tissue nerve injuries and pain-related behaviors, which resembles OPIDN. Both the neuropathological changes and the nocifensive behaviors can be attenuated by treatment of TRPA1 antagonist HC030031 or abolished by knockout of Trpa1 gene. In the classic hens OPIDN model, malathion causes nerve injuries and ataxia to a similar level as the positive inducer tri-ortho-cresyl phosphate (TOCP), which also activates TRPA1 channel. Treatment with HC030031 reduces the damages caused by malathion or tri-ortho-cresyl phosphate. Duloxetine and Ketotifen, two commercially available drugs exhibiting TRPA1 inhibitory activity, show neuroprotective effects against OPIDN and might be used in emergency situations. The current study suggests TRPA1 is the major mediator of OPIDN and targeting TRPA1 is an effective way for the treatment of OPIDN.

Autophagy in Tri-o-cresyl Phosphate-Induced Delayed Neurotoxicity

The widely used organophosphorus compound tri-o-cresyl phosphate (TOCP) elicits delayed neurotoxicity characterized by progressive axonal degeneration in the spinal cord and peripheral nerves. However, the precise mechanisms of TOCP-induced delayed neurotoxicity are not clear. Because autophagy has been linked to the pathogenesis of neurodegenerative diseases, we aimed to characterize autophagy in the progression of TOCP-induced delayed neurotoxicity. In vivo experiments using the adult hen animal model showed that autophagy in spinal cord axons and in sciatic nerves was markedly induced at the early preclinical stage of TOCP-induced delayed neurotoxicity; it was decreased as the delayed neurotoxicity progressed to the overt neuropathy stage. In cultured human neuroblastoma SH-SY5Y cells, TOCP reduced cell growth, and induced prominent autophagy. The autophagy inhibitor 3-methyladenine could attenuate TOCP-induced cytotoxicity, indicating that the autophagy is accountable for TOCP-induced neurotoxicity. In addition, we found that TOCP-induced Parkin translocation to mitochondria in SH-SY5Y cells, suggesting that autophagy may function to degrade mitochondria after TOCP exposure. These results suggest that autophagy may play an important role in the initiation and progression of axonal damage during TOCP-induced neurotoxicity.

Tris(pentafluoroethyl)trifluorophosphate-basd ionic liquids as advantageous solid-phase micro-extraction coatings for the extraction of organophosphate esters in environmental waters

Ionic liquids (ILs) containing the tris(pentafluoroethyl)trifluorophosphate [FAP] anion and various cations have great potential in sample preparation because of their excellent hydrophobicity, thermostability and low hydrolysity. In the present study, a [FAP]-based IL, 1-hexyl-3-methylimidazolium tris (pentafluoroethyl) trifluoro phosphate ([HMIM][FAP]), was used as coatings of solid-phase microextraction (SPME) for extracting organophosphate esters (OPEs) from environmental water samples. This SPME fiber was fabricated by coating a stainless steel wire substrate with [HMIM][FAP] via a simple direct dip-coating approach, and the extraction was conducted by the direct immersion solid phase microextraction. Coupling to gas chromatography mass spectrometry (GC-MS), the developed SPME method exhibited excellent selectivity and sensitivity towards the extraction of 11 OPEs from aqueous samples. Satisfactory linearity (R(2)≥0.99) of the calibration curves was obtained over the range of 0.05-50.0ngmL(-1) with the limits of detection (LODs, S/N=3) and limits of quantification (LOQs, S/N=10) ranged from 0.13-7.40ngL(-1) and 0.50-24.0ngL(-1), respectively. The proposed SPME method showed excellent extraction efficiency to OPEs with enrichment factors in the range of 168-2603, and acceptable reproducibility with relative standard deviations (RSDs) ≤15% for single fiber (n=7) and ≤16% for fiber-to-fiber (n=3×3) at a concentration level of 0.5ngmL(-1), respectively. The prepared IL-based fiber was successfully applied to determine eleven common used OPEs in tap water, influent and effluent of sewage treatment plant, with results are comparable to those determined by the reference (UPLC-MS/MS), and spiked recoveries in the range of 84.0-108%, 82.1-123% and 82.8-100%, respectively.

Reduction of autophagy markers mediated protective effects of JNK inhibitor and bucladesine on memory deficit induced by Aβ in rats

Autophagy, the process of self-degradation of cellular components, has an important role in neurodegenerative diseases, such as Alzheimer's disease. In this study, we investigated the effects of SP600125 as c-Jun N-terminal kinase (JNK) inhibitor and bucladesine as a cyclic adenosine 3',5'-monophosphate (cAMP) analog on spatial memory and expression of autophagic factors in Aβ-injected rats. Male Wistar rats were used. Rats were randomly allocated into five groups as following: amyloid beta (Aβ)-only group, Aβ + SP600125 (30 μg/1 μ/side, n = 7) and/or bucladesine (100 μM/1 μl/side, n = 7), and the normal control (vehicle only) group. The treatments were administered bilaterally to the CA1 sub-region of the hippocampus stereotaxically. Spatial reference memory was performed using Morris Water Maze 21 days later. The expression of authophagy markers (beclin1, Atg7, Atg12, and LC3 II/LC3 I) in the hippocampus was evaluated using western blotting. Compared to the vehicle group, Aβ administration reduced spatial reference learning (P < 0.001) and memory (P < 0.01) and upregulated the expression of beclin1, Atg7, Atg12, and LC3 II/I (P < 0.0001). Compare to Aβ-only group, the administration of SP600125 and/or bucladesine improved spatial reference learning (P < 0.001) and memory (P < 0.01). Compared to the Aβ-only group, the treatment with SP600125 and/or bucladesine also reduced beclin1, Atg7, Atg12, and LC3 II/I (P < 0.0001) which was similar to amount of normal rats. In summary, it seems that the improvement of spatial memory by SP600125 and/or bucladesine in Aβ-injected rats is in relation with normalizing of autophagy to the physiologic level, possibly through neuroprotection and/or neuroplasticity.

Involvement of oxidative stress in tri-ortho-cresyl phosphate-induced liver injury in male mice

Tri-ortho-cresyl phosphate (TOCP) has been widely used as plasticizers, plastic softeners, and flame retardants in industry and reported to have delayed neurotoxicity and reproductive toxicology in animals. However, it remains to be elusive whether TOCP induces liver injury. In this study, male mice were orally administered different concentrations of TOCP (100, 200, or 400 mg/kg/day) for 28 days. Histological examination showed that TOCP led to serious hepatocellular injury. In addition, administration of TOCP induced a marked elevation in the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in mice. The content of malondialdehyde (MDA) was increased significantly in the liver after the mice were treated with TOCP; while there was a dramatic decrease in the content of glutathione (GSH) and the activities of antioxidative enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX). TOCP inhibited viability of mouse liver cancer Hepa 1-6 cells in a dose-dependent manner. Meanwhile, TOCP significantly increased MDA content and inhibited GSH content and the activities of SOD and GSH-PX in the cells, respectively. Oxidative stress dramatically inhibited viability of Hepa 1-6 cells; while inhibition of oxidative stress by N-acetyl-l-cysteine could rescue the cell viability inhibited by TOCP to a certain extent. In summary, oxidative stress might be involved in TOCP-induced hepatocellular injury in male mice.

Apelin-13 Prevents the Delayed Neuropathy Induced by Tri-ortho-cresyl Phosphate Through Regulation the Autophagy Flux in Hens

Organophosphate-induced delayed neuropathy (OPIDN) is pathologically characterized by the swollen axon containing aggregations of microtubules, neurofilaments, smooth endoplasmic reticulum and multivesicular vesicles. At present, the exact mechanism of OPIDN is unclear and the effective therapeutic methods is not available to counter this syndrome. Recent studies had shown that the autophagy was involved in OPIDN. The adipocytokine Apelin is a peptide, Apelin and its receptor are abundantly expressed in the nervous system. Recent researches illuminated that Apelin was neuroprotective factor and Apelin could regulate the autophagy in vivo and vitro model. So we investigated the effect of Apelin-13 on the OPIDN induced by Tri-ortho-cresyl phosphate (TOCP) in hens and explored the role of autophagy in Apelin-13 preventing OPIDN. Adult Roman hens were given a single dose of 750 mg/kg TOCP by gavage for 21 days to induce OPIDN, and neural dysfunction were detected, and the formation of autophagosomes in spinal cord neurons was observed by transmission electron microscopy, and the molecular markers of autophagy microtubule-associated protein light chain-3 (LC3) and the autophagy substrates p62/SQSTM1 were determined by Western blot analysis. The results demonstrated that the obvious neurological dysfunction such as hindlimb paralysis and paralysis of gait was present, the number of autophagosomes in the neurons of spinal cords was significantly increased, the level of LC3-II and p62 expressions and the ratio of LC3-II/LC3-I in spinal cords and sciatic nerve were significantly increased in the OPIDN model group compared with the control group. Compared with the OPIDN model group, the neurological dysfunction of tens was obviously reduced, the clinical signs scores was significantly decreased, the number of autophagosomes in the neurons of hen spinal cords was significantly decreased, the level of LC3-II and p62 expressions and the ratio of LC3-II/LC3-I in spinal cords and sciatic nerve were significantly decreased in Apelin-13 treatment group. Our results suggested that Apelin-13 prevented against the OPIDN induced by TOCP in hens, which the mechanism might be associated with regulation autophagy flux by Apelin-13.

Tri-ortho-cresyl phosphate induces autophagy of rat spermatogonial stem cells

Tri-ortho-cresyl phosphate (TOCP) has been widely used as plasticizers, plastic softeners, and flame retardants in industry and reported to have a deleterious effect on the male reproductive system in animals besides delayed neurotoxicity. Our preliminary results found that TOCP could disrupt the seminiferous epithelium in the testis and inhibit spermatogenesis, but the precise mechanism is yet to be elucidated. This study shows that TOCP inhibited viability of rat spermatogonial stem cells in a dose-dependent manner. TOCP could not lead to cell cycle arrest in the cells; the mRNA levels of p21, p27, p53, and cyclin D1 in the cells were also not affected by TOCP. Meanwhile, TOCP did not induce apoptosis of rat spermatogonial stem cells. After treatment with TOCP, however, both LC3-II and the ratio of LC3-II/LC3-I were markedly increased; autophagy proteins ATG5 and beclin 1 were also increased after treatment with TOCP, indicating that TOCP could induce autophagy in the cells. Ultrastructural observation under the transmission electron microscopy indicated that autophagic vesicles in the cytoplasm containing extensively degraded organelles such as mitochondria and endoplasmic reticulum increased significantly after the cells were treated with TOCP. In summary, we have shown that TOCP can inhibit viability of rat spermatogonial stem cells and induce autophagy of the cells, without affecting cell cycle and apoptosis.