Autophagy role in environmental pollutants exposure

Cadmium toxicity and autophagy: a review

Cadmium (Cd) is an important environmental pollutant that poses a threat to human health and represents a critical component of air pollutants, food sources, and cigarette smoke. Cd is a known carcinogen and has toxic effects on the environment and various organs in humans. Heavy metals within an organism are difficult to biodegrade, and those that enter the respiratory tract are difficult to remove. Autophagy is a key mechanism for counteracting extracellular (microorganisms and foreign bodies) or intracellular (damaged organelles and proteins that cannot be degraded by the proteasome) stress and represents a self-protective mechanism for eukaryotes against heavy metal toxicity. Autophagy maintains cellular homeostasis by isolating and gathering information about foreign chemicals associated with other molecular events. However, autophagy may trigger cell death under certain pathological conditions, including cancer. Autophagy dysfunction is one of the main mechanisms underlying Cd-induced cytotoxicity. In this review, the toxic effects of Cd-induced autophagy on different human organ systems were evaluated, with a focus on hepatotoxicity, nephrotoxicity, respiratory toxicity, and neurotoxicity. This review also highlighted the classical molecular pathways of Cd-induced autophagy, including the ROS-dependent signaling pathways, endoplasmic reticulum (ER) stress pathway, Mammalian target of rapamycin (mTOR) pathway, Beclin-1 and Bcl-2 family, and recently identified molecules associated with Cd. Moreover, research directions for Cd toxicity regarding autophagic function were proposed. This review presents the latest theories to comprehensively reveal autophagy behavior in response to Cd toxicity and proposes novel potential autophagy-targeted prevention and treatment strategies for Cd toxicity and Cd-associated diseases in humans.

Research progress on the role of autophagy in the development of varicocele

Varicocele (VC) is a common cause of infertility in men. Pathophysiological changes caused by VC, such as testicular hypoxia, high temperatures, oxidative stress, abnormal reproductive hormones, and Cd accumulation, can induce autophagy, thus affecting the reproductive function in patients with this condition. Autophagy regulators can be classified as activators or inhibitors. Autophagy activators upregulate autophagy, reduce the damage to the testis and epididymis, inhibit spermatogenic cell apoptosis, and protect fertility. In contrast, autophagy inhibitors block autophagy and aggravate the damage to the reproductive functions. Therefore, elucidating the role of autophagy in the occurrence, development, and regulation of VC may provide additional therapeutic options for men with infertility and VC. In this review, we briefly describe the progress made in autophagy research in the context of VC.

Real-Time Autophagic Flux Measurements in Live Cells Using a Novel Fluorescent Marker DAPRed

Autophagy is a conserved homeostatic mechanism involved in cellular homeostasis and many disease processes. Although it was first described in yeast cells undergoing starvation, we have learned over the years that autophagy gets activated in many stress conditions and during development and aging in mammalian cells. Understanding the fundamental mechanisms underlying autophagy effects can bring us closer to better insights into the pathogenesis of many disease conditions (e.g., cardiac muscle necrosis, Alzheimer's disease, and chronic lung injury). Due to the complex and dynamic nature of the autophagic processes, many different techniques (e.g., western blotting, fluorescent labeling, and genetic modifications of key autophagy proteins) have been developed to delineate autophagy effects. Although these methods are valid, they are not well suited for the assessment of time-dependent autophagy kinetics. Here, we describe a novel approach: the use of DAPRed for autophagic flux measurement via live cell imaging, utilizing A549 cells, that can visualize and quantify autophagic flux in real time in single live cells. This approach is relatively straightforward in comparison to other experimental procedures and should be applicable to any in vitro cell/tissue models. Key features • Allows real-time qualitative imaging of autophagic flux at single-cell level. • Primary cells and cell lines can also be utilized with this technique. • Use of confocal microscopy allows visualization of autophagy without disturbing cellular functions.

BDE-47-mediated cytotoxicity via autophagy blockade in 3D HepaRG spheroids cultured in alginate microcapsules

Polybrominated Diphenyl Ethers (PBDEs) are a major class of brominated flame retardants, and their widespread use has led them to be considered contaminants with emerging concern. PBDEs have been detected in the indoor air, house dust, food, and all environmental compartments. The congener BDE-47 (2,2',4,4'-tetrabromodiphenyl ether) is the most prevalent, and hepatotoxicity, neurotoxicity, immunological changes, endocrine disruption, and genotoxic potential have been related to its exposure. Although the BDE-47 molecular toxicity pathway is directly related to intrinsic apoptotic cell death, the role of autophagy in BDE-47 toxicity remains unclear. In this context, three-dimensional cell culture has emerged as a good strategy for the replacement of animals in toxicological testing. Here, we used HepaRG spheroids cultured in alginate microcapsules to investigate the role of autophagy in BDE-47-mediated hepatotoxicity. We developed mature and functional HepaRG spheroids by culturing them in alginate microcapsules. Histological analysis revealed that HepaRG spheroids formed an extracellular matrix and stored glycogen. No apoptotic and/or necrotic cores were observed. BDE-47 showed concentration- and time-dependent cytotoxicity in HepaRG spheroids. In the early exposure period, BDE-47 initially disrupted mitochondrial activity and increased the formation of acid compartments that promoted the increase in autophagic activity; however, this autophagy was blocked, and long-term exposure to BDE-47 promoted efficient apoptotic cell death through autophagy blockade, as evidenced by an increased number of fragmented/condensed nuclei. Therefore, for the first time, we demonstrated BDE-47 toxicity and its cell pathway induces cell death using a three-dimensional liver cell culture, the HepaRG cell line.

Ferritinophagy Mediated by Oxidative Stress-Driven Mitochondrial Damage Is Involved in the Polystyrene Nanoparticles-Induced Ferroptosis of Lung Injury

Nanoplastics are a common type of contaminant in the air. However, no investigations have focused on the toxic mechanism of lung injury induced by nanoplastic exposure. In the present study, polystyrene nanoplastics (PS-NPs) caused ferroptosis in lung epithelial cells, which could be alleviated by ferrostatin-1, deferoxamine, and N-acetylcysteine. Further investigation found that PS-NPs disturbed mitochondrial structure and function and triggered autophagy. Mechanistically, oxidative stress-derived mitochondrial damage contributed to ferroptosis, and autophagy-dependent ferritinophagy was a pivotal intermediate link, resulting in ferritin degradation and iron ion release. Furthermore, inhibition of ferroptosis using ferrostatin-1 alleviated pulmonary and systemic toxicity to reverse the mouse lung injury induced by PS-NPs inhalation. Most importantly, the lung-on-a-chip was further used to clarify the role of ferroptosis in the PS-NPs-induced lung injury by visualizing the ferroptosis, oxidative stress, and alveolar-capillary barrier dysfunction at the organ level. In summary, our study indicated that ferroptosis was an important mechanism for nanoplastics-induced lung injury through different lung cells, mouse inhalation models, and three-dimensional-based lung-on-a-chip, providing an insightful reference for pulmonary toxicity assessment of nanoplastics.

Effects of true-to-life PET nanoplastics using primary human nasal epithelial cells

Since inhalation is a relevant exposure route, studies using appropriate micro/nanoplastic (MNPLs) models, representative targeted cells, and relevant biomarkers of effect are required. We have used lab-made polyethylene terephthalate (PET)NPLs obtained from PET plastic water bottles. Human primary nasal epithelial cells (HNEpCs) were used as a model of the first barrier of the respiratory system. Cell internalization and intracellular reactive oxygen species (iROS) induction, as well as the effects on mitochondria functionality and in the modulation of the autophagy pathway, were evaluated. The data indicated significant cellular uptake and increased levels of iROS. Furthermore, a loss of mitochondrial membrane potential was observed in the exposed cells. Regarding the effects on the autophagy pathway, PETNPLs exposure significantly increases LC3-II protein expression levels. PETNPLs exposure also induced significant increases in the expression of p62. This is the first study showing that true-to-life PETNPLs can alter the autophagy pathway in HNEpCs.

The Emerging Role of Autophagy as a Target of Environmental Pollutants: An Update on Mechanisms

Autophagy is an evolutionarily conserved cellular system crucial for cellular homeostasis that protects cells from a broad range of internal and extracellular stresses. Autophagy decreases metabolic load and toxicity by removing damaged cellular components. Environmental contaminants, particularly industrial substances, can influence autophagic flux by enhancing it as a protective response, preventing it, or converting its protective function into a pro-cell death mechanism. Environmental toxic materials are also notorious for their tendency to bioaccumulate and induce pathophysiological vulnerability. Many environmental pollutants have been found to influence stress which increases autophagy. Increasing autophagy was recently shown to improve stress resistance and reduce genetic damage. Moreover, suppressing autophagy or depleting its resources either increases or decreases toxicity, depending on the circumstances. The essential process of selective autophagy is utilized by mammalian cells in order to eliminate particulate matter, nanoparticles, toxic metals, and smoke exposure without inflicting damage on cytosolic components. Moreover, cigarette smoke and aging are the chief causes of chronic obstructive pulmonary disease (COPD)-emphysema; however, the disease's molecular mechanism is poorly known. Therefore, understanding the impacts of environmental exposure via autophagy offers new approaches for risk assessment, protection, and preventative actions which will counter the harmful effects of environmental contaminants on human and animal health.

Hazard Assessment of Polystyrene Nanoplastics in Primary Human Nasal Epithelial Cells, Focusing on the Autophagic Effects

The human health risks posed by micro/nanoplastics (MNPLs), as emerging pollutants of environmental/health concern, need to be urgently addressed as part of a needed hazard assessment. The routes of MNPL exposure in humans could mainly come from oral, inhalation, or dermal means. Among them, inhalation exposure to MNPLs is the least studied area, even though their widespread presence in the air is dramatically increasing. In this context, this study focused on the potential hazard of polystyrene nanoplastics (PSNPLs with sizes 50 and 500 nm) in human primary nasal epithelial cells (HNEpCs), with the first line of cells acting as a physical and immune barrier in the respiratory system. Primarily, cellular internalization was evaluated by utilizing laboratory-labeled fluorescence PSNPLs with iDye, a commercial, pink-colored dye, using confocal microscopy, and found PSNPLs to be significantly internalized by HNEpCs. After, various cellular effects, such as the induction of intracellular reactive oxygen species (iROS), the loss of mitochondrial membrane potential (MMP), and the modulation of the autophagy pathway in the form of the accumulation of autophagosomes (LC3-II) and p62 markers (a ubiquitin involved in the clearance of cell debris), were evaluated after cell exposure. The data demonstrated significant increases in iROS, a decrease in MMP, as well as a greater accumulation of LC3-II and p62 in the presence of PSNPLs. Notably, the autophagic effects did indicate the implications of PSNPLs in defective or insufficient autophagy. This is the first study showing the autophagy pathway as a possible target for PSNPL-induced adverse effects in HNEpCs. When taken together, this study proved the cellular effects of PSNPLs in HNEpCs and adds value to the existing studies as a part of the respiratory risk assessment of MNPLs.

Maternal Exposure to Acephate Caused Nephrotoxicity in Adult Offspring Rats Mediated by Excessive Autophagy Activation, Oxidative Stress Induction, and Altered Epithelial Sodium Channel and Na+/K+-ATPase Gene Expression

This study examined how maternal exposure to acephate-an organophosphate-based insecticide-affected the renal development in rat offspring during adulthood. Virgin female Wistar rats were randomly allocated to three groups: group 1 (control) received sterile water; groups 2 and 3 were intragastrically exposed to low (14 mg/kg) and high (28 mg/kg) doses of acephate from day 6 of pregnancy until delivery, respectively. Further, the offspring of the adult female rats were euthanized in postnatal week 8. Compared with the controls, the adult rat offspring with exposure to low and high doses of acephate exhibited elevated plasma creatinine and blood urea nitrogen levels. Additionally, immunofluorescence analysis revealed the upregulation of autophagic marker genes (Beclin-1 and LC-3) in the acephate-treated rat offspring, thereby suggesting the induction of an autophagic mechanism. Notably, the increased malondialdehyde level, decreased glutathione level, and decreased superoxide dismutase and catalase activities confirmed the ability of acephate to induce oxidative stress and apoptosis in the kidneys of the rat offspring. This may explain the renal histopathological injury detected using hematoxylin and eosin staining. Furthermore, a reverse transcription polymerase chain reaction revealed that the mRNA expression levels of the Na⁺/K⁺-ATPase and the epithelial sodium channel (ENaC) genes were significantly higher in the kidney of female offspring than that of controls owing to acephate toxicity. However, there was no significant effect of acephate on the expression of NHE3 in the treatment group compared with the control group. Overall, the present findings suggest that oxidative stress caused by prenatal exposure to acephate causes nephrotoxicity and histopathological alterations in adult rat offspring, likely by actions on renal ENaC and Na⁺/K⁺-ATPase genes as well as the autophagic markers Beclin-1 and LC-3.

Heterozygous disruption of beclin 1 alleviates neurotoxicity induced by sub-chronic exposure of arsenite in mice

Arsenite is a well-documented neurotoxicant that widely exists in the environment. However, the detailed mechanisms of arsenite neurotoxicity are not fully clarified. Autophagy has been reported to be involved in many neurological problems induced by arsenite. Since beclin 1 is an essential mediator of autophagy, we herein used both adult wild-type (beclin 1^+/+) and heterozygous disruption of beclin 1 (beclin 1^+/-) mice for chronic administration of 50 mg/L arsenite via drinking water for 3 months. Our results demonstrated that exposure of arsenite caused the working memory deficit, anxiety-like behavior and motor coordination disorder in beclin 1^+/+ mice, accompanied with pathological changes in morphology and electrophysiology in the cortical tissues. This treatment of arsenite significantly reduced the number of neuronal cells and induced microglia activation and synaptic transmission disorders in the wild-type mice as compared with vehicle controls. Intriguingly, by using beclin 1^+/- mice, we found that heterozygous disruption of beclin 1 profoundly attenuated these neurotoxic effects induced by arsenite, mainly manifested by improvements in the neurobehavioral impairments, abnormal electrophysiologic alterations as well as dysregulation of synaptic transmission. These findings together indicate that regulation of autophagy via beclin 1 would be a potential strategy for treatment against arsenite neurotoxicity.

Triphenyl phosphate (TPP) promotes hepatocyte toxicity via induction of endoplasmic reticulum stress and inhibition of autophagy flux

Triphenyl phosphate (TPP), a commonly used organophosphate flame retardant, is frequently found in environmental and biota samples, indicating widespread human exposure. Recent studies have shown that TPP causes hepatotoxicity, but the underlying cellular mechanisms are not fully elucidated. Here, by using normal hepatocyte AML12 cells as a model, we showed that TPP induced apoptotic cell death. RNA sequencing analyses revealed that differentially expressed genes induced by TPP were related to endoplasmic reticulum (ER) stress and autophagy. Immunostaining and western blot results further confirmed that TPP activated ER stress. Interestingly, though TPP increased LC3-II, a canonical marker for autophagy, TPP inhibited autophagy flux rather than induced autophagy. Interestingly, TPP-induced ER stress facilitated autophagy flux inhibition and apoptosis. Furthermore, inhibition of autophagy aggravated, and activation of autophagy attenuated apoptosis induced by TPP. Collectively, these results uncovered that ER stress and autophagy flux inhibition were responsible for TPP-induced apoptosis in mouse hepatocytes. Thus, our foundlings provided novel insight into the potential mechanisms of TPP-induced hepatocyte toxicity.

Bisphenol S exposure induces cytotoxicity in mouse Leydig cells

Bisphenol S (BPS), an increasingly used alternative to bisphenol A, has been linked to testosterone deficiency and male reproductive dysfunction in laboratory animals. This study aimed to examine the cytotoxicity of BPS exposure to Leydig cells and to investigate its possible mechanisms. After treatment with BPS (100, 200 and 400 μM) for 48 h in vitro, TM3 mouse Leydig cells exhibited a dose-dependent decrease in the viability. Furthermore, BPS challenge triggered oxidative stress manifested by compromised activities of superoxide dismutase and catalase with exaggerated formation of reactive oxygen species. Especially, BPS exposure resulted in augmented mitochondrial permeability transition pore opening, dissipated mitochondrial membrane potential and reduced ATP generation, along with an altered energy metabolism. Moreover, BPS stimulation enhanced BAX expression and caspase-3 activity and inhibited BCL-2 expression. In addition, BPS-treated TM3 cells showed an accumulation of autophagic vacuoles, together with increased Beclin1 and P62 expression and elevated LC3B-II/LC3B-I ratio. These results demonstrated that in vitro exposure to BPS exerted cytotoxicity to TM3 Leydig cells through inducing oxidative stress, mitochondrial impairment, autophagic disturbance and apoptosis.

Ethylbenzene exposure disrupts ovarian function in Wistar rats via altering folliculogenesis and steroidogenesis-related markers and activating autophagy and apoptosis

Ethylbenzene is a hydrocarbon that is extensively used in both industry and in the home and has been reported as toxic to various tissues. Nevertheless, its effect on ovarian function remains unclear. For this purpose, we assessed ovarian tissue morphology, evaluated protein and gene expression related to folliculogenesis and steroidogenesis, and investigated the involvement of both apoptosis and autophagy processes in this effect. Female Wistar albinos rats were treated with 2000, 4000 and 8000 ppm doses of ethylbenzene by inhalation for 30 min daily for one month. Ovaries were then removed and proceeded for histopathological and molecular analyses. We found that ethylbenzene affected folliculogenesis by decreasing the number of growing follicles and increasing the number of abnormal follicles, leading to faster female reproductive aging. Interestingly, it disrupted female reproductive hormone balance, including progesterone, estradiol, testosterone and IGF-1 plasma levels. The latter protein, along with GDF-9, significantly decreased in all ethylbenzene-treated groups, leading to the disruption of follicular cell proliferation and development. TUNEL assay study showed that ethylbenzene exposure significantly increased the number of apoptotic cells. The mRNA levels of genes involved in granulosa cell proliferation and differentiation, such as INSL3, CCND2 and ACTB, were significantly decreased. In addition, LC3 protein expression increased, and its encoding gene was upregulated, suggesting that ethylbenzene treatment induced autophagy. In summary, ethylbenzene exposure caused structural and functional disorders of the ovary by disrupting the normal growth of follicles, altering reproductive hormone balance, inhibiting the expression of key reproductive proteins and triggering autophagy as well as apoptosis.

Toluene Can Disrupt Rat Ovarian Follicullogenesis and Steroidogenesis and Induce Both Autophagy and Apoptosis

Toluene has been shown to be highly toxic to humans and animals and can cause damage to various tissues. However, studies reporting its effects on ovarian function are still limited. In this study, we investigated the in vivo effect of toluene using female Wistar rats. We found that toluene exposure decreased ovarian weight and affected ovarian structure by increasing the number of abnormally growing follicles. Moreover, it significantly increased progesterone and testosterone levels. We also showed that toluene exposure decreased GDF-9 protein and its encoding gene. In addition, it inhibited the expression of most of the genes involved in granulosa cell proliferation and differentiation, such as Insl3, ccnd2 and actb. The TUNEL assay showed that apoptosis occurred at the middle and high doses only (4000 and 8000 ppm, respectively), whereas no effect was observed at the low dose (2000 ppm). Interestingly, we showed that toluene exposure induced autophagy as LC3 protein and its encoding gene significantly increased for all doses of treatment. These results may suggest that the activation of autophagy at a low dose of exposure was to protect ovarian cells against death by inhibiting apoptosis, whereas its activation at high doses of exposure triggered apoptosis leading to cell death.

Silver Nanoparticles Induced Oxidative Stress and Mitochondrial Injuries Mediated Autophagy in HC11 Cells Through Akt/AMPK/mTOR Pathway

Silver nanoparticles (AgNPs) are widely used in industrial products, and they have good antibacterial properties, with potential for prevention and treatment of cow mastitis. However, concerns exist about the cytotoxicity of AgNPs. Thus, we have studied the role of autophagy in AgNP-induced cytotoxicity in mouse HC11 mammary epithelium cells. We found that AgNPs injured HC11 cells, with release of lactate dehydrogenase (LDH). AgNPs also induced autophagy in HC11 cells, which was associated with oxidative stress, as indicated by increased reactive oxygen species (ROS) and increased expression of hemoxygenase-1(HO-1) and Nrf2. Mitochondria were altered by AgNPs: mitochondrial membrane potential (MMP) was decreased and the expression of PINK1 and Parkin was increased. AgNPs also increased the expression of p-AMPK and decreased the expression of p-Akt and p-mTOR. The addition of 3-methyl adenine inhibited autophagy and enhanced the cytotoxicity of AgNPs, indicating that autophagy is protective against AgNP-induced cell death. In summary, AgNPs induced protective autophagy in HC11 cells via the Akt/AMPK/mTOR pathway, associated with cellular oxidative stress and mitochondrial alterations. Our research confirms that AgNPs may damage the breast tissue in clinical applications and should be used with caution. Further research is necessary to clarify whether the damage caused by AgNPs will affect the lactation function of the mammary glands and possible residues in milk.