PINK1/Parkin-mediated mitophagy play a protective role in manganese induced apoptosis in SH-SY5Y cells

Heavy metal-induced disruption of the autophagy-lysosomal pathway: implications for aging and neurodegenerative disorders

Heavy metals such as lead, mercury, cadmium, magnesium, manganese, arsenic, copper pose considerable threats to neuronal health and are increasingly recognized as factors contributing to aging-related neurodegeneration. Exposure to these environmental toxins disrupts cellular homeostasis, resulting in oxidative stress and compromising critical cellular processes, particularly the autophagy-lysosomal pathway. This pathway is vital for preserving cellular integrity by breaking down damaged proteins and organelles; however, toxicity from heavy metals can hinder this function, leading to the buildup of harmful substances, inflammation, and increased neuronal injury. As individuals age, the consequences of neurodegeneration become more significant, raising the likelihood of developing disorders like Alzheimer's and Parkinson's disease. This review explores the intricate relationship between heavy metal exposure, dysfunction of the autophagy-lysosomal pathway, and aging-related neurodegeneration, emphasizing the urgent need for a comprehensive understanding of these mechanisms. The insights gained from this analysis are crucial for creating targeted therapeutic approaches aimed at alleviating the harmful effects of heavy metals on neuronal health and improving cellular resilience in aging populations.

Investigating the interplay between mitophagy and diabetic neuropathy: Uncovering the hidden secrets of the disease pathology

Mitophagy, the cellular process of selectively eliminating damaged mitochondria, plays a crucial role in maintaining metabolic balance and preventing insulin resistance, both key factors in type 2 diabetes mellitus (T2DM) development. When mitophagy malfunctions in diabetic neuropathy, it triggers a cascade of metabolic disruptions, including reduced energy production, increased oxidative stress, and cell death, ultimately leading to various complications. Thus, targeting mitophagy to enhance the process may have emerged as a promising therapeutic strategy for T2DM and its complications. Notably, plant-derived compounds with β-cell protective and mitophagy-stimulating properties offer potential as novel therapeutic agents. This review highlights the intricate mechanisms linking mitophagy dysfunction to T2DM and its complications, particularly neuropathy, elucidating potential therapeutic interventions for this debilitating disease.

Dopaminergic REST/NRSF is protective against manganese-induced neurotoxicity in mice

Chronic exposure to elevated levels of manganese (Mn) may cause a neurological disorder referred to as manganism. The transcription factor REST is dysregulated in several neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. REST upregulated tyrosine hydroxylase and induced protection against Mn toxicity in neuronal cultures. In the present study, we investigated if dopaminergic REST plays a critical role in protecting against Mn-induced toxicity in vivo using dopaminergic REST conditional knockout (REST-cKO) mice and REST loxP mice as wild-type (WT) controls. Restoration of REST in the substantia nigra (SN) with neuronal REST AAV vector infusion was performed to further support the role of REST in Mn toxicity. Mice were exposed to Mn (330 μg, intranasal, daily for 3 weeks), followed by behavioral tests and molecular biology experiments. Results showed that Mn decreased REST mRNA/protein levels in the SN-containing midbrain, as well as locomotor activity and motor coordination in WT mice, which were further decreased in REST-cKO mice. Mn-induced mitochondrial insults, such as impairment of fission/fusion and mitophagy, apoptosis, and oxidative stress, in the midbrain of WT mice were more pronounced in REST-cKO mice. However, REST restoration in the SN of REST-cKO mice attenuated Mn-induced neurotoxicity. REST's molecular target for its protection is unclear, but REST attenuated Mn-induced mitochondrial dysregulation, indicating that it is a primary intracellular target for both Mn and REST. These novel findings suggest that dopaminergic REST in the nigrostriatal pathway is critical in protecting against Mn toxicity, underscoring REST as a potential therapeutic target for treating manganism.

In vitro evaluation of the cytotoxic and genotoxic effects of Al and Mn in ambient concentrations detected in groundwater intended for human consumption

Environmental exposure to metals can induce cytotoxic and genotoxic effects in cells and affect the health of the exposed population. To investigate the effects of aluminum (Al) and manganese (Mn), we evaluated their cytogenotoxicity using peripheral blood mononuclear cells (PBMCs) exposed to these metals at previously quantified concentrations in groundwater intended for human consumption. The cell viability, membrane integrity, nuclear division index (NDI), oxidative stress, cell death, cell cycle, and DNA damage were analyzed in PBMCs exposed to Al (0.2, 0.6, and 0.8 mg/L) and Mn (0.1, 0.3, 1.0, and 1.5 for 48 h. We found that Al induced late apoptosis; decreased cell viability, NDI, membrane integrity; and increased DNA damage. However, no significant alterations in the early apoptosis, cell cycle, and reactive oxygen species levels were observed. In contrast, exposure to Mn altered all evaluated parameters related to cytogenotoxicity. Our data show that even concentrations allowed by the Brazilian legislation for Al and Mn in groundwater intended for human consumption cause cytotoxic and genotoxic effects in PBMCs. Therefore, in view of the results found, a comprehensive approach through in vivo investigations is needed to give robustness and validity to the results obtained, thus broadening the understanding of the impacts of metals on the health of environmentally exposed people.

The multifaceted mechanisms of ellagic acid in the treatment of tumors: State-of-the-art

Ellagic acid (EA) is a kind of polyphenol compound extracted from a variety of herbs, such as paeoniae paeoniae, raspberry, Chebule, walnut kernel, myrrh, loquat leaf, pomegranate bark, quisquite, and fairy herb. It has anti-tumor, anti-oxidation, anti-inflammatory, anti-mutation, anti-bacterial, anti-allergic and multiple pharmacological properties. Studies have shown its anti-tumor effect in gastric cancer, liver cancer, pancreatic cancer, breast cancer, colorectal cancer, lung cancer and other malignant tumors, mainly through inducing tumor cell apoptosis, inhibiting tumor cell proliferation, inhibiting tumor cell metastasis and invasion, inducing autophagy, affecting tumor metabolic reprogramming and other forms of anti-tumor efficacy. Its molecular mechanism is mainly reflected in inhibiting the proliferation of tumor cells through VEGFR-2 signaling pathway, Notch signaling pathway, PKC signaling pathway and COX-2 signaling pathway. PI3K/Akt signaling pathway, JNK (cJun) signaling pathway, mitochondrial pathway, Bcl-2 / Bax signaling pathway, TGF-β/Smad3 signaling pathway induced apoptosis of tumor cells and blocked EMT process and MMP SDF1α/CXCR4 signaling pathway inhibits the metastasis and invasion of tumor cells, induces autophagy and affects tumor metabolic reprogramming to produce anti-tumor effects. At present, the analysis of the anti-tumor mechanism of ellagic acid is slightly lacking, so this study comprehensively searched the literature on the anti-tumor mechanism of ellagic acid in various databases, reviewed the research progress of the anti-tumor effect and mechanism of ellagic acid, in order to provide reference and theoretical basis for the further development and application of ellagic acid.

Biphasic Dose-Response of Mn-Induced Mitochondrial Damage, PINK1/Parkin Expression, and Mitophagy in SK-N-SH Cells

Excessive manganese (Mn) exposure produces neurotoxicity with mitochondrial damage. Mitophagy is a protective mechanism to eliminate damaged mitochondria to protect cells. The aim of this study was to determine the dose-response of Mn-induced mitochondria damage, the expression of mitophagy-mediated protein PINK1/Parkin and mitophagy in dopamine-producing SK-N-SH cells. Cells were exposed to 0, 300, 900, and 1500 μM Mn²⁺ for 24 h, and ROS production, mitochondrial damage and mitophagy were examined. The levels of dopamine were detected by ELISA and neurotoxicity and mitophagy-related proteins (α-synuclein, PINK1, Parkin, Optineurin, and LC3II/I) were detected by western blot. Mn increased intracellular ROS and apoptosis and decreased mitochondrial membrane potential in a concentration-dependent manner. However, at the low dose of 300 μM Mn, autophagosome was increased 11-fold, but at the high dose of 1500 μM, autophagosome was attenuated to 4-fold, together with decreased mitophagy-mediated protein PINK1/Parkin and LC3II/I ratio and increased Optineurin expression, resulting in increased α-synuclein accumulation and decreased dopamine production. Thus, Mn-induced mitophagy exhibited a novel biphasic regulation: at the low dose, mitophagy is activated to eliminate damaged mitochondria, however, at the high dose, cells gradually loss the adaptive machinery, the PINK1/Parkin-mediated mitophagy weakened, resulting in neurotoxicity.

Investigation of Molecular Mechanisms Involved in Sensitivity to the Anti-Cancer Activity of Costunolide in Breast Cancer Cells

Costunolide (CTL), an active compound isolated from Saussurea lappa Clarke and Laurus nobilis L, has been shown to induce apoptosis via reactive oxygen species (ROS) generation in various types of cancer cells. However, details of molecular mechanisms underlying the difference in sensitivity of cancer cells to CTL are still largely unknown. Here, we tested the effect of CTL on the viability of breast cancer cells and found that CTL had a more efficient cytotoxic effect against SK-BR-3 cells than MCF-7 cells. Mechanically, ROS levels were significantly increased upon CTL treatment only in SK-BR-3 cells, which leads to lysosomal membrane permeabilization (LMP) and cathepsin D release, and subsequent activation of the mitochondrial-dependent intrinsic apoptotic pathway by inducing mitochondrial outer membrane permeabilization (MOMP). In contrast, treatment of MCF-7 cells with CTL activated PINK1/Parkin-dependent mitophagy to remove damaged mitochondria, which prevented the elevation of ROS levels, thereby contributing to their reduced sensitivity to CTL. These results suggest that CTL is a potent anti-cancer agent, and its combination with the inhibition of mitophagy could be an effective method for treating breast cancer cells that are less sensitive to CTL.

Mechanisms of manganese-induced neurotoxicity and the pursuit of neurotherapeutic strategies

Chronic exposure to elevated levels of manganese via occupational or environmental settings causes a neurological disorder known as manganism, resembling the symptoms of Parkinson's disease, such as motor deficits and cognitive impairment. Numerous studies have been conducted to characterize manganese's neurotoxicity mechanisms in search of effective therapeutics, including natural and synthetic compounds to treat manganese toxicity. Several potential molecular targets of manganese toxicity at the epigenetic and transcriptional levels have been identified recently, which may contribute to develop more precise and effective gene therapies. This review updates findings on manganese-induced neurotoxicity mechanisms on intracellular insults such as oxidative stress, inflammation, excitotoxicity, and mitophagy, as well as transcriptional dysregulations involving Yin Yang 1, RE1-silencing transcription factor, transcription factor EB, and nuclear factor erythroid 2-related factor 2 that could be targets of manganese neurotoxicity therapies. This review also features intracellular proteins such as PTEN-inducible kinase 1, parkin, sirtuins, leucine-rich repeat kinase 2, and α-synuclein, which are associated with manganese-induced dysregulation of autophagy/mitophagy. In addition, newer therapeutic approaches to treat manganese's neurotoxicity including natural and synthetic compounds modulating excitotoxicity, autophagy, and mitophagy, were reviewed. Taken together, in-depth mechanistic knowledge accompanied by advances in gene and drug delivery strategies will make significant progress in the development of reliable therapeutic interventions against manganese-induced neurotoxicity.

The emerging multifaceted role of PINK1 in cancer biology

For its various important functions in cells, phosphatase and tensin homolog-induced kinase 1 (PINK1) has drawn considerable attention for the role it plays in early-onset Parkinson's disease. In recent years, emerging evidence has supported the hypothesis that PINK1 plays a part in regulating many physiological and pathophysiological processes in cancer cells, including cytoplasmic homeostasis, cell survival, and cell death. According to the findings of these studies, PINK1 can function as a tumor promoter or suppressor, showing a duality that is dependent on the context. In this study we review the mechanistic characters relating to PINK1 based on available published data from peer-reviewed articles, The Cancer Genome Atlas data mining, and cell-based assays. This mini review focuses on some of the interplays between PINK1 and the context and recent developments in the field, including its growing involvement in mitophagy and its nonmitophagy organelles-related function. This review aims to help readers better grasp how PINK1 is functioning in cell physiological and pathophysiological processes, especially in cancer biology.

A Water-Soluble Quercetin Conjugate with Triple Targeting Exerts Neuron-Protective Effect on Cerebral Ischemia by Mitophagy Activation

The existing treatments for ischemic stroke cannot meet the clinical needs so far. Quercetin (QT) is an effective apoptosis inhibitor and antioxidant flavonoid, but its water solubility is poor and has no targeting. In this study, QT is modified with hyaluronic acid (HA) to form a water-soluble conjugate HA-QT, which can specifically bind to CD44 receptors and response to hyaluronidase. Next, a novel delivery system SS31-HA-QT is prepared by further modification with SS31, a polypeptide capable of penetrating the blood-brain barrier (BBB) and indiscriminately targeting mitochondria. Meanwhile, IR780, a near-infrared dye, is conjugated onto HA-QT and SS31-HA-QT to form diagnosis tools to trace HA-QT and SS31-HA-QT. In vitro and in vivo results shows that SS31 can four-fold increase the drug penetration into BBB without any toxicity. The highly expressed CD44 and hyaluronidase in ischemic area ensured the targeted delivery of QT to the ischemic region. Importantly, the mitochondrial targeting of damaged neurons is also achieved by SS31. Further studies confirmed that SS31-HA-QT exerted neuron-protection by activating mitophagy, and its mechanism involved Akt/mTOR related TFEB and HIF-1α activation. Hence, SS31-HA-QT shall be a promising neuroprotective drug due to its high water-solubility, superior triple-targeted neuroprotective ability, low toxicity, and high efficiency.

The mitochondrial RNA granule modulates manganese-dependent cell toxicity

Prolonged manganese exposure causes manganism, a neurodegenerative movement disorder. The identity of adaptive and nonadaptive cellular processes targeted by manganese remains mostly unexplored. Here we study mechanisms engaged by manganese in genetic cellular models known to increase susceptibility to manganese exposure, the plasma membrane manganese efflux transporter SLC30A10 and the mitochondrial Parkinson's gene PARK2. We found that SLC30A10 and PARK2 mutations as well as manganese exposure compromised the mitochondrial RNA granule composition and function, resulting in disruption of mitochondrial transcript processing. These RNA granule defects led to impaired assembly and function of the mitochondrial respiratory chain. Notably, cells that survived a cytotoxic manganese challenge had impaired RNA granule function, thus suggesting that this granule phenotype was adaptive. CRISPR gene editing of subunits of the mitochondrial RNA granule, FASTKD2 or DHX30, as well as pharmacological inhibition of mitochondrial transcription-translation, were protective rather than deleterious for survival of cells acutely exposed to manganese. Similarly, adult Drosophila mutants with defects in the mitochondrial RNA granule component scully were safeguarded from manganese-induced mortality. We conclude that impairment of the mitochondrial RNA granule function is a protective mechanism for acute manganese toxicity.

Manganese induces S-nitrosylation of PINK1 leading to nerve cell damage by repressing PINK1/Parkin-mediated mitophagy

Chronic exposure to excess manganese (Mn) causes neurotoxicity, which is characterized by Parkinson-like symptoms and referred to as manganism. In the last few decades, mitochondrial damage and subsequent energy failure have been reported to be important mechanisms of Mn toxicity, yet how Mn causes mitochondrial damage remains largely unknown. Here, we demonstrated that Mn induced S-nitrosation of phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1), a master regulator in the mitophagy pathway, results in dysregulation of mitophagy and nerve cell injury in the rat striatum. We cultured primary neurons and used 1400 W, a potent and selective inducible nitric oxide synthase (iNOS) inhibitor, as an intervention to verify the precise mechanism of Mn-induced dysregulation of mitophagy. We demonstrated that Mn-induced S-nitrosylation of PINK1 decreased the phosphorylated level of parkin RBR E3 ubiquitin-protein ligase (Parkin), as well as the translocation of Parkin to damaged mitochondria, which led to the accumulation of damaged mitochondria and mitochondrial-mediated apoptosis. Our findings indicated the unusual connection between nitrative stress and mitochondrial dysfunction in Mn-induced neurotoxicity. These data highlight the role of S-nitrosation of PINK1 in Mn-induced dysregulation of mitophagy and provide a reliable target for the development of specific drugs and the early treatment of manganism, which has important theoretical and practical significance.

PTEN-induced kinase 1 enhances the reparative effects of bone marrow mesenchymal stromal cells on mice with renal ischaemia/reperfusion-induced acute kidney injury

Acute kidney injury (AKI) is a common severe acute syndrome caused by multiple factors and is characterized by a rapid decline in renal function during a short period. Bone marrow mesenchymal stromal cells (BMSCs) are effective in treating AKI. However, the mechanism of their beneficial effects remains unclear. PTEN-induced kinase 1 (PINK1) may play an important role in kidney tissue repair. In this study, we explored the effect of PINK1 overexpression on enhancing BMSC-mediated repair of AKI. In this study, ischaemia/reperfusion-induced AKI (IRI-AKI) in mice and a hypoxia-reoxygenation model in cells were established, and the indices were examined by pathology and immunology experiments. After ischaemia/reperfusion, PINK1 overexpression reduced apoptosis in injured kidney tissue cell, decreased T lymphocyte infiltration, increased macrophage infiltration, and alleviated the inflammatory response. PINK1 relieved the stress response of BMSCs and renal tubular epithelial cells (RTECs), reduced apoptosis, altered the release of inflammatory factors, and reduced the proliferation of peripheral blood mononuclear cells (PBMCs). In conclusion, BMSCs and RTECs undergo stress responses in response to hypoxia, inflammation and other conditions, and overexpressing PINK1 in BMSCs could enhance their ability to resist these stress reactions. Furthermore, PINK1 overexpression can regulate the distribution of immune cells and improve the inflammatory response. The regulation of mitochondrial autophagy during IRI-AKI maintains mitochondrial homeostasis and protects renal function. The results of this study provide new strategies and experimental evidence for BMSC-mediated repair of IRI-AKI.

Role of Mitophagy in neurodegenerative Diseases and potential tagarts for Therapy

Mitochondria dysfunction has been defined as one of the hallmarks of aging-related diseases as is characterized by the destroyed integrity, abnormal distribution and size, insufficient ATP supply, increased ROS production, and subsequently damage and oxidize the proteins, lipids and nucleic acid. Mitophagy, an efficient way of removing damaged or defective mitochondria by autophagy, plays a pivotal role in maintaining the mitochondrial quantity and quality control enabling the degradation of unwanted mitochondria, and thus rescues cellular homeostasis in response to stress. Accumulating evidence demonstrates that impaired mitophagy has been associated with many neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) in a variety of patients and disease models with neural death, oxidative stress and disturbed metabolism, either as the cause or consequence. These findings suggest that modulation of mitophagy may be considered as a valid therapeutic strategy in neurodegenerative diseases. In this review, we summarize recent findings on the mechanisms of mitophagy and its role in neurodegenerative diseases, with a particular focus on mitochondrial proteins acting as receptors that mediate mitophagy in these diseases.

[Curcumin alleviates the manganese-induced neurotoxicity by promoting autophagy in rat models of manganism]

OBJECTIVE

To investigate the protective effects of curcumin(CUR) and its mechanism on a rat model of neurotoxicity induced by manganese chloride (MnCl₂), which mimics mangnism.

METHODS

Sixty male SD rats were randomly divided into 5 groups, with 12 rats in each group. Control group received 0.9% saline solution intraperitoneally (ip) plus double distilled water (dd) H₂O intragastrically (ig), MnCl₂ group received 15 mg/kg MnCl₂(Mn²⁺ 6.48 mg/kg) intraperitoneally plus dd H₂O intragastrically, CUR group received 0.9% saline solution intraperitoneally plus 300 mg/kg CUR intragastrically, MnCl₂+ CUR1 group received 15 mg/kg MnCl₂ intraperitoneally plus 100 mg/kg curcumin intragastrically, MnCl₂+ CUR2 group received 15 mg/kg MnCl₂ intraperitoneally plus 300 mg/kg CUR intragastrically, 5 days/week, 4 weeks. Open-field and rotarod tests were used to detect animals' exploratory behavior, anxiety, depression, movement and balance ability. Morris water maze (MWM) experiment was used to detect animals' learning and memory ability. ICP-MS was used to investigate the Mn contents in striata. The rats per group were perfused in situ, their brains striata were removed by brains model and fixed for transmission electron microscope (TEM), histopathological and immunohistochemistry (ICH) analyses. The other 6 rats per group were sacrificed. Their brains striata were removed and protein expression levels of transcription factor EB (TFEB), mammalian target of rapamycin (mTOR), p-mTOR, Beclin, P62, microtubule-associated protein light chain-3 (LC3) were detected by Western blotting. Terminal deoxynucleotidyl transterase-mediated dUTP nick end labeling (TUNEL) staining was used to determine neurocyte apoptosis of rat striatum.

RESULTS

After exposure to MnCl₂ for four weeks, MnCl₂-treated rats showed depressive-like behavior in open-field test, the impairments of movement coordination and balance in rotarod test and the diminishment of spatial learning and memory in MWM (P < 0.05). The striatal TH⁺ neurocyte significantly decreased, eosinophilic cells, aggregative α-Syn level and TUNEL-positive neurocyte significantly increased in the striatum of MnCl₂ group compared with control group (P < 0.05). Chromatin condensation, mitochondria tumefaction and autophagosomes were observed in rat striatal neurocytes of MnCl₂ group by TEM. TFEB nuclear translocation and autophagy occurred in the striatum of MnCl₂ group. Further, the depressive behavior, movement and balance ability, spatial learning and memory ability of MnCl₂+ CUR2 group were significantly improved compared with MnCl₂ group (P < 0.05). TH+ neurocyte significantly increased, the eosinophilic cells, aggregative α-Syn level significantly decreased in the striatum of MnCl₂+ CUR2 group compared with MnCl₂ group. Further, compared with MnCl₂ group, chromatin condensation, mitochondria tumefaction was alleviated and autophagosomes increased, TFEB-nuclear translocation, autophagy was enhanced and TUNEL-positive neurocyte reduced significantly in the striatum of MnCl₂+ CUR2 group (P < 0.05).

CONCLUSION

Curcumin alleviated the MnCl₂-induced neurotoxicity and α-Syn aggregation probably by promoting TFEB nuclear translocation and enhancing autophagy.

Anticancer activity of ruthenium(II) plumbagin complexes with polypyridyl as ancillary ligands via inhibiting energy metabolism and GADD45A-mediated cell cycle arrest

To study the antitumor activity and action mechanism of Ru(II) polypyridyl plumbagin (PLN) complexes, four complexes [Ru(PLN)(DMSO)₂]Cl (Ru1), [Ru(bpy)₂(PLN)](PF₆) (bpy is bipyridine) (Ru2), [Ru(phen)₂(PLN)](PF₆) (phen is 1,10-phenanthroline) (Ru3), and [Ru(DIP)₂(PLN)](PF₆) (DIP is 4,7-diphenyl-1,10-phenanthroline) (Ru4) were obtained and fully characterized. Lipophilicity, cellular uptake and cytotoxicity of these Ru(II) complexes are in the order of: Ru1<Ru2<Ru3<Ru4. The ancillary polypyridyl ligands affected the bioactivity and action mechanisms of these Ru(II) complexes. Ru3 and Ru4 inhibited energy metabolism by severely impairing mitochondrial respiration and glycolysis processes. Moreover, Ru3 and Ru4 induced DNA damage and the increased expression of GADD45A, which led to cell cycle arrest in G0/G1 phase in MGC-803 cells, while the inactivation of GADD45A attenuated these effects; however, Ru3 or Ru4-induced GADD45A did not affect cell apoptosis. Further studies revealed that Ru3 and Ru4 induced ROS-dependent and caspase-dependent apoptotic cell death by mitochondrial dysfunction, and Ru4 displayed higher potency than Ru3. The in vivo results in MGC-803 xenograft nude mice model also confirmed that Ru4 obviously inhibited tumor growth. Ru4 is a promising candidate to be developed as a chemotherapeutic agent.

Excessive manganese alters serum biochemical indices, induces histopathological alterations, and activates apoptosis in liver and cerebrum of Jianzhou Da'er goat (Capra hircus)

The present study aimed to explore the toxic effects of excessive dietary Mn in livers and cerebrums of Jianzhou Da'er goat (Capra hircus). Three-month old goats were assigned into three groups: control group, fed on basal diet; Mn I group, fed on the basal diet mixed with MnCl₂ (2.5 g/kg); Mn II group, fed on the basal diet mixed with MnCl₂ (5 g/kg). Compared with the control group, the activities of serum alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and the concentrations of interferon-γ (IFN-γ) in Mn I and Mn II groups were significantly increased, but the concentrations of IgG in Mn I and Mn II groups were significantly decreased (p < 0.05). The activities of superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), and the concentrations of glutathione (GSH) in Mn I and Mn II groups were significantly decreased, whereas the concentrations of malondialdehyde (MDA) in Mn I and Mn II groups were significantly increased in livers and cerebrums (p < 0.05). Moreover, the hepatocytes necrosed, inflammatory cells infiltrated, chromatin concentrated, mitochondrial cristae reduced in Mn I and Mn II groups. The nerve cells necrosed, blood vessels congested, inflammatory cells infiltrated, mitochondrial electron density and mitochondrial cristae decreased, and vacuolization increased in Mn I and Mn II groups. Furthermore, the mRNA expressions of tumor necrosis factor alpha (TNF-α), tumor necrosis factor receptor type 1 (TNFR1), fas-associated protein via a death domain (FADD), Bcl2-associated X (Bax), cysteinyl aspartate specific proteinase 3, 8, 9 (Caspase-3, 8, 9) in Mn I and Mn II groups were significantly increased (p < 0.05), but the mRNA expressions of B-cell lymphoma-2 (Bcl-2) in Mn I and Mn II groups were significantly decreased (p < 0.05) in livers. The mRNA expressions of Bcl-2, Bax, Caspase-3, 9, 7, 12 in Mn I and Mn II groups were significantly increased (p < 0.05), however, the ratio of Bcl-2/Bax in Mn I and Mn II groups was significantly decreased (p < 0.05) in cerebrums. In summary, our results provided new insights for better understanding the mechanisms of Mn toxicity in Capra hircus.

Manganese Intoxication Recovery and the Expression Changes of Park2/Parkin in Rats

Occupational overexposure to manganese (Mn) produces Parkinson's disease-like manganism. Acute Mn intoxication in rats causes dopaminergic neuron loss, impairment of motor activity and reduction of the expression of Park2/Parkin. The expression of Park2/Parkin is also reduced. Whether these changes are reversible after cessation of Mn exposure is unknown, and is the goal of this investigation. Adult male rats were injected with Mn²⁺ at doses 1 mg/kg and 5 mg/kg in the form of MnCl₂·4H₂O, every other day for one-month to produce acute Mn neurotoxicity. For a half of rats Mn exposure was suspended for recovery for up to 5 months. Mn neurotoxicity was evaluated by the accumulation of Mn in blood and brain, behavioral activities, dopaminergic neuron loss, and the expression of Park2/Parkin in the blood cells and brain. Dose-dependent Mn neurotoxicity in rats was evidenced by Mn accumulation, rotarod impairments, reduction of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra, decreased level of Park2 mRNA in the blood and brain, and decreased Parkin protein in the brain. After cessation of Mn exposure, the amount of Park2 mRNA in the blood started to increase one month after the recovery. After 5-month of recovery, blood and brain Mn returned to normal, rotarod activity recovered, the reduction of TH-positive dopaminergic neurons ameliorated, and the level of Park2 mRNA in the blood and Park2/Parkin in the midbrain and striatum were returned to the normal. Mn neurotoxicity in rats is reversible after cessation of Mn exposure. The level of Park2 mRNA in the blood could be used as a novel biomarker for Mn exposure and recovery.

PINK1/Parkin-Mediated Mitophagy Plays a Protective Role in the Bone Impairment Caused by Aluminum Exposure

The pollution of aluminum (Al) in agricultural production and its wide application in food processing greatly increase the chance of human and animal exposure. Al can accumulate in bone and cause bone diseases by inducing oxidative stress. Mitophagy can maintain normal cell function by degrading damaged mitochondria and scavenging reactive oxygen species. However, the role of mitophagy in the bone impairment caused by Al is unknown. In this study, we demonstrated that PTEN induced putative kinase 1 (PINK1)/ E3 ubiquitin ligase PARK2 (Parkin)-mediated mitophagy was activated in the bone impairment caused by Al in vivo. Then, the Al-induced mitophagy in Parkin-deficient mice and MC3T3-E1 cells were decreased. Meanwhile, Parkin deficiency exacerbated the bone impairment, mitochondrial damage, and oxidative stress under Al exposure, both in vivo and in vitro. In general, the results reveal that Al exposure can activate PINK1/Parkin-mediated mitophagy, and the PINK1/Parkin-mediated mitophagy plays a protective role in the bone impairment caused by Al.

The Role of Mitophagy in Regulating Cell Death

Mitochondria are multifaceted organelles that serve to power critical cellular functions, including act as power generators of the cell, buffer cytosolic calcium overload, production of reactive oxygen species, and modulating cell survival. The structure and the cellular location of mitochondria are critical for their function and depend on highly regulated activities such as mitochondrial quality control (MQC) mechanisms. The MQC is regulated by several sets of processes: mitochondrial biogenesis, mitochondrial fusion and fission, mitophagy, and other mitochondrial proteostasis mechanisms such as mitochondrial unfolded protein response (mtUPR) or mitochondrial-derived vesicles (MDVs). These processes are important for the maintenance of mitochondrial homeostasis, and alterations in the mitochondrial function and signaling are known to contribute to the dysregulation of cell death pathways. Recent studies have uncovered regulatory mechanisms that control the activity of the key components for mitophagy. In this review, we discuss how mitophagy is controlled and how mitophagy impinges on health and disease through regulating cell death.

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.

Mitophagy Induced by Mitochondrial Function Damage in Chicken Kidney Exposed to Cr(VI)

Cr(VI) is a heavy metal environmental pollutant and carcinogen. Excessive Cr(VI) exposure injures kidneys. This study aimed to investigate mitophagy induced by mitochondrial function damage in chicken kidney exposed to Cr(VI). To explore the mechanism involved, we randomly divided 40 one-day-old Hy-line Brown cockerels into four groups, with each group exposed to different concentrations of Cr(VI), i.e., 0, 10, 30 and 50 mg kg-1, which were orally administered daily for 45 days. Excessive Cr(VI) increased tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and chemokine (C-X-C motif) ligand 1(CXCL1) expression and decreased Ca2+-adenosine triphosphatase (Ca2+-ATPase), Mg2+-ATPase and Na+/k+-ATPase activities in chicken kidney. Furthermore, Cr(VI) significantly increased reactive oxygen species (ROS) production and induced mitochondrial membrane potential (MMP) collapse and typical autophagosome formation. With the increase of Cr(VI) concentration, the Parkin translocation, value of LC3-II increased and decreased the content of p62/SQSTM1 and the translocase of outer mitochondrial membrane 20 (TOMM20). In summary, our findings explicated that mitochondrial function damage and mitophagy-related indicators were related to Cr(VI) concentration in chicken kidney.

The Role of Autophagy in Manganese-Induced Neurotoxicity

Manganese (Mn), an essential micronutrient, acts as a cofactor for multiple enzymes. Epidemiological investigations have shown that an excessive level of Mn is an important environmental factor involved in neurotoxicity. Frequent pollution of air and water by Mn is a serious threat to the health of the population. Overexposure to Mn is particularly detrimental to the central nervous system, leading to symptoms similar to several neurological disorders. Many different mechanisms have been implicated in Mn-induced neurotoxicity, including oxidative/nitrosative stress, toxic protein aggregation, endoplasmic reticulum (ER) stress, mitochondrial dysfunction, dysregulation of autophagy, and the apoptotic cascade, which together promote the progressive neurodegeneration of nerve cells. As a compensatory regulatory mechanism, autophagy plays dual roles in various biological activities under pathological stress conditions. Dysregulation of autophagy is involved in the development of neurodegenerative disorders, with recent emerging evidence indicating a strong, complex relationship between autophagy and Mn-induced neurotoxicity. This review discusses the connection between autophagy and Mn-induced neurotoxicity, especially alpha-synuclein oligomerization, ER stress, and aberrated protein S-nitrosylation, which will provide new insights to profoundly explore the precise mechanisms of Mn-induced neurotoxicity.

Mitochondrial DNA Mutation, Diseases, and Nutrient-Regulated Mitophagy

A wide spectrum of human diseases, including cancer, neurodegenerative diseases, and metabolic disorders, have been shown to be associated with mitochondrial dysfunction through multiple molecular mechanisms. Mitochondria are particularly susceptible to nutrient deficiencies, and nutritional intervention is an essential way to maintain mitochondrial homeostasis. Recent advances in genetic manipulation and next-generation sequencing reveal the crucial roles of mitochondrial DNA (mtDNA) in various pathophysiological conditions. Mitophagy, a term coined to describe autophagy that targets dysfunctional mitochondria, has emerged as an important cellular process to maintain mitochondrial homeostasis and has been shown to be regulated by various nutrients and nutritional stresses. Given the high prevalence of mtDNA mutations in humans and their impact on mitochondrial function, it is important to investigate the mechanisms that regulate mtDNA mutation. Here, we discuss mitochondrial genetics and mtDNA mutations and their implications for human diseases. We also examine the role of mitophagy as a therapeutic target, highlighting how nutrients may eliminate mtDNA mutations through mitophagy.

Dysregulation of TFEB contributes to manganese-induced autophagic failure and mitochondrial dysfunction in astrocytes

Epidemiological and clinical studies have long shown that exposure to high levels of heavy metals are associated with increased risks of neurodegenerative diseases. It is widely accepted that autophagic dysfunction is involved in pathogenesis of various neurodegenerative disorders; however, the role of heavy metals in regulation of macroautophagy/autophagy is unclear. Here, we show that manganese (Mn) induces a decline in nuclear localization of TFEB (transcription factor EB), a master regulator of the autophagy-lysosome pathway, leading to autophagic dysfunction in astrocytes of mouse striatum. We further show that Mn exposure suppresses autophagic-lysosomal degradation of mitochondria and induces accumulation of unhealthy mitochondria. Activation of autophagy by rapamycin or TFEB overexpression ameliorates Mn-induced mitochondrial respiratory dysfunction and reactive oxygen species (ROS) generation in astrocytes, suggesting a causal relation between autophagic failure and mitochondrial dysfunction in Mn toxicity. Taken together, our data demonstrate that Mn inhibits TFEB activity, leading to impaired autophagy that is causally related to mitochondrial dysfunction in astrocytes. These findings reveal a previously unappreciated role for Mn in dysregulation of autophagy and identify TFEB as a potential therapeutic target to mitigate Mn toxicity.

ABBREVIATIONS

BECN1: beclin 1; CTSD: cathepsin D; DMEM: Dulbecco's Modified Eagle Medium; GFAP: glial fibrillary acid protein; GFP: green fluorescent protein; HBSS: hanks balanced salt solution; LAMP: lysosomal-associated membrane protein; LDH: lactate dehydrogenase; Lys Inh: lysosomal inhibitors; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAPK: mitogen-activated protein kinase; Mn: manganese; MTOR: mechanistic target of rapamycin kinase; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; PFA: paraformaldehyde; PI: propidium iodide; ROS: reactive oxygen species; s.c.: subcutaneous; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy; TFEB: transcription factor EB.

Inflammatory injury and mitophagy induced by Cr(VI) in chicken liver

Cr(VI) is a widely used chemical. Excessive Cr(VI) exposure not only causes inflammatory damage but also induces mitophagy. This study aimed to demonstrate the effect of Cr(VI) on inflammatory injury and mitophagy in chicken liver. A total of 120 Hyland Brown cockerels (1 day old) were randomly divided into four groups and orally treated with different Cr(VI) doses (10% median lethal dose, 6% median lethal dose, 2% median lethal dose, and 0% median lethal dose) daily for 45 days to explore the underlying mechanism. Results showed that excessive Cr(VI) increased tumor necrosis factor-α, interleukin-6, and heat shock protein but decreased interferon-γ expression and adenosine triphosphate content in chicken liver. Cr(VI) significantly increased reactive oxygen species production, induced mitochondrial membrane potential collapse, and promoted autophagosome formation. Cr(VI) treatment also caused an increase in LC3-II, stimulated Parkin translocation, and inhibited the expression of p62/SQSTM1 and translocase of outer mitochondrial membrane 20. Therefore, excessive Cr(VI) caused inflammatory damage and mitophagy in chicken liver.

Pyrroloquinoline Quinine and LY294002 Changed Cell Cycle and Apoptosis by Regulating PI3K-AKT-GSK3β Pathway in SH-SY5Y Cells

To verify the role of PI3K-AKT-GSK3β pathway during manganese (Mn)-induced cell death, apoptosis, related indicators were investigated. SH-SY5Y cells were directly exposed to different concentrations of MnCl₂. Then, cell viability, apoptosis, necrosis rate, and cell cycle were detected by MTT, FITC Annexin V Apoptosis Detection Kit with PI and PI staining. Then, in two intervention groups, cells were preconditioned with agonist (PQQ) and suppressant (LY294002). The cell viability decreased with a dose-response relationship (p < 0.05), while apoptosis and necrosis increased (p < 0.05). The ratio of G₀/G1 and G₂/M also decreased, but the percentage of S phase increased (p < 0.05). During above process, PI3K-AKT-GSK3β pathway was involved by regulating the expression of PI3K, AKT, p-AKT, and GSK3β (p < 0.05). For further research, cell cycle and apoptosis were detected pretreatment with PQQ and LY294002 before Mn exposure. The result showed cell ability, apoptosis, and necrosis rate changed obviously compared with non-pretreated group (p < 0.05). The variance of G0/G1 and G2/M ratio and percentage of S phase were also different, especially in 2.0 mM (p < 0.05). Mn can cause apoptosis and necrosis, varying cell cycle of SH-SY5Y cells, which could be changed by PQQ and LY294002 by regulating PI3K-AKT-GSK3β pathway.

Enhanced Mitophagy Activity in Prion-Infected Cultured Cells and Prion-Infected Experimental Mice via a Pink1/Parkin-Dependent Mitophagy Pathway

Mitophagy is an important process for removing damaged mitochondria in cells, the dysfunction of which has been directly linked to an increasing number of neurodegenerative disorders. However, the details of mitophagy in prion diseases still need to be deeply explored. In this study, we identified more autophagosomes and large swelling mitochondria structures in the prion-infected cultured cell line SMB-S15 by transmission electron microscopy, accompanying the molecular evidence of activated autophagic flux. Western blots illustrated that the levels of Pink1 and Parkin, particularly in the mitochondrial fraction, were increased in SMB-S15 cells, whereas the levels of mitochondrial membrane proteins TIMM44, TOMM20, and TIMM23 were decreased. The amount of whole polyubiquitinated proteins decreased, but that of phosphor-polyubiquitinated proteins increased in SMB-S15 cells. The level of MFN2 in SMB-S15 cells were down-regulated, but its polyubiquitinated form was up-regulated. Knockdown of the expressions of Pink1 and Parkin by the individual SiRNAs in SMB-S15 cells reduced autophagic activity but did not seem to influence the expressions of TOMM20 and TIMM23. Moreover, we also demonstrated that the brain levels of Pink1 and Parkin in the mice infected with scrapie strains 139A and ME7 were remarkably increased at the terminal stage of the disease by Western blot and immunohistochemical (IHC) assays. Immunofluorescent assays revealed that Pink1 signals widely colocalized with GAFP-, Iba1-, and NeuN-positive cells in the brains of scrapie-infected mice. IHC assays with serial sections of the brain tissues infected with agents 139A and ME7 showed more Pink1- and Parkin-positive cells located at the areas with more PrP^Sc deposit. These results suggest an activated mitophagy in prion-infected cells and prion-infected experimental mice, probably via an enhanced Pink-Parkin pathway.

FUNDC1 regulates receptor-mediated mitophagy independently of the PINK1/Parkin-dependent pathway in rotenone-treated SH-SY5Y cells

Upon mitochondrial stress, PINK1 and Parkin cooperatively mediate a response that removes damaged mitochondria. In addition to the PINK1/Parkin pathway, the FUNDC1, mitophagy receptor regulates mitochondrial clearance. It is not clear whether these systems coordinate to mediate mitophagy in response to stress. Rotenone caused an increase in LC3II expression, and FUNDC1-knocked down cells showed remarkably reduced LC3 expression compared to control cells. In addition, treatment of cells with autophagy flux inhibitor, chloroquine, induced further accumulation of LC3-II, suggesting that mitophagy induced by rotenone is due to involvement of mitochondrial FUNDC1. Rotenone treatment resulted in PINK1 stabilization on the outer mitochondrial membrane and a subsequent increase in recruitment of Parkin from the cytosol to the abnormal mitochondria, as well as physical interaction of PINK1 with Parkin in the mitochondria of rotenone-treated cells. Interestingly, knockdown of FUNDC1 did not alter PINK1/Parkin expression in the mitochondrial fraction of rotenone-treated cells. Our findings indicate that FUNDC1 involves in receptor-mediated mitophagy separately from PINK1/Parkin-dependent mitophagy. Furthermore, inhibiting mitophagy by FUNDC1 or PINK1 knockdown accelerated rotenone-induced cytotoxicity. Taken together, our findings suggest that rotenone can be induced both receptor-mediated and PINK1/Parkin-dependent mitophagy for mitochondrial clearance, and that mitophagy by removing damaged mitochondria, has cytoprotective effects.

Lanthanum chloride impairs spatial learning and memory by inducing [Ca2+]m overload, mitochondrial fission–fusion disorder and excessive mitophagy in hippocampal nerve cells of rats

Lanthanum chloride damages hippocampal nerve cells of rats through inducing [Ca²⁺]_m overload, mitochondrial fission–fusion disorder, and excessive mitophagy.

Pink1-Mediated Chondrocytic Mitophagy Contributes to Cartilage Degeneration in Osteoarthritis

Cartilage loss is a central event in the pathogenesis of osteoarthritis (OA), though other than mechanical loading, the biochemical mechanisms underlying OA pathology remain poorly elucidated. We investigated the role of Pink1-mediated mitophagy in mitochondrial fission, a crucial process in OA pathogenesis. We used a monosodium iodoacetate (MIA)-induced rodent model of OA, which inhibits the activity of articular chondrocytes, leading to disruption of glycolytic energy metabolism and eventual cell death. The OA rat cartilage exhibits significant induction of autophagy-related proteins LC3B and p62, similar to human osteoarthritic cartilage. Moreover, expression of Pink1 and Parkin proteins were also increased in OA. Here, we confirm that Pink1-mediated mitophagy leads to cell death in chondrocytes following MIA treatment, while deficiency in Pink1 expression was associated with decreased cartilage damage and pain behaviors in MIA-induced OA. Finally, we found that autophagy and mitophagy-related genes are highly expressed in human osteoarthritic cartilage. These results indicate that OA is a degenerative condition associated with mitophagy, and suggest that targeting the Pink1 pathway may provide a therapeutic avenue for OA treatment.

Precisely Control Mitochondria with Light to Manipulate Cell Fate Decision

Mitochondrial dysfunction has been implicated in many pathological conditions and diseases. The normal functioning of mitochondria relies on maintaining the inner mitochondrial membrane potential (also known as ΔΨm) that is essential for ATP synthesis, Ca²⁺ homeostasis, redox balance, and regulation of other key signaling pathways such as mitophagy and apoptosis. However, the detailed mechanisms by which ΔΨm regulates cellular function remain incompletely understood, partially because of the difficulty of manipulating ΔΨm with spatiotemporal resolution, reversibility, or cell type specificity. To address this need, we have developed a next generation optogenetic-based technique for controllable mitochondrial depolarization with light. We demonstrate successful targeting of the heterologous channelrhodopsin-2 fusion protein to the inner mitochondrial membrane and formation of functional cationic channels capable of light-induced selective ΔΨm depolarization and mitochondrial autophagy. Importantly, we for the first time, to our knowledge, show that optogenetic-mediated mitochondrial depolarization can be well controlled to differentially influence the fate of cells expressing mitochondrial channelrhodopsin-2; whereas sustained moderate light illumination induces substantial apoptotic cell death, transient mild light illumination elicits cytoprotection via mitochondrial preconditioning. Finally, we show that Parkin overexpression exacerbates, instead of ameliorating, mitochondrial depolarization-mediated cell death in HeLa cells. In summary, we provide evidence that the described mitochondrial-targeted optogenetics may have a broad application for studying the role of mitochondria in regulating cell function and fate decision.

Genetic Disorders of Manganese Metabolism

Purpose of Review

This article provides an overview of the pathogenesis, clinical presentation and treatment of inherited manganese transporter defects.

Recent Findings

Identification of a new group of manganese transportopathies has greatly advanced our understanding of how manganese homeostasis is regulated in vivo. While the manganese efflux transporter SLC30A10 and the uptake transporter SLC39A14 work synergistically to reduce the manganese load, SLC39A8 has an opposing function facilitating manganese uptake into the organism. Bi-allelic mutations in any of these transporter proteins disrupt the manganese equilibrium and lead to neurological disease: Hypermanganesaemia with dystonia 1 (SLC30A10 deficiency) and hypermanganesaemia with dystonia 2 (SLC39A14 deficiency) are characterised by manganese neurotoxicity while SLC39A8 mutations cause a congenital disorder of glycosylation type IIn due to Mn deficiency.

Summary

Inherited manganese transporter defects are an important differential diagnosis of paediatric movement disorders. Manganese blood levels and MRI brain are diagnostic and allow early diagnosis to avoid treatment delay.

Metabolomic Responses to Manganese Dose in SH-SY5Y Human Neuroblastoma Cells

Manganese (Mn)-associated neurotoxicity has been well recognized. However, Mn is also an essential nutrient to maintain physiological function. Our previous study of human neuroblastoma SH-SY5Y cells showed that Mn treatment comparable to physiological and toxicological concentrations in human brain resulted in different mitochondrial responses, yet cellular metabolic responses associated with such different outcomes remain uncharacterized. Herein, SH-SY5Y cells were examined for metabolic responses discriminated by physiological and toxicological levels of Mn using high-resolution metabolomics (HRM). Before performing HRM, we examined Mn dose (from 0 to100 μM) and time effects on cell death. Although we did not observe any immediate cell death after 5 h exposure to any of the Mn concentrations assessed (0-100 μM), cell loss was present after a 24-h recovery period in cultures treated with Mn ≥ 50 μM. Exposure to Mn for 5 h resulted in a wide range of changes in cellular metabolism including amino acids (AA), neurotransmitters, energy, and fatty acids metabolism. Adaptive responses at 10 μM showed increases in neuroprotective AA metabolites (creatine, phosphocreatine, phosphoserine). A 5-h exposure to 100 µM Mn, a time before any cell death occurred, resulted in decreases in energy and fatty acid metabolites (hexose-1,6 bisphosphate, acyl carnitines). The results show that adjustments in AA metabolism occur in response to Mn that does not cause cell death while disruption in energy and fatty acid metabolism occur in response to Mn that results in subsequent cell death. The present study establishes utility for metabolomics analyses to discriminate adaptive and toxic molecular responses in a human in vitro cellular model that could be exploited in evaluation of Mn toxicity.

Anticancer Cyclometalated Iridium(III) Complexes with Planar Ligands: Mitochondrial DNA Damage and Metabolism Disturbance

Emerging studies have shown that mitochondrial DNA (mtDNA) is a potential target for cancer therapy. Herein, six cyclometalated Ir(III) complexes Ir1-Ir6 containing a series of extended planar diimine ligands have been designed and assessed for their efficacy as anticancer agents. Ir1-Ir6 show much higher cytotoxicity than cisplatin and they can effectively localize to mitochondria. Among them, complexes Ir3 and Ir4 with dipyrido[3,2- a:2',3'- c]phenazine (dppz) ligands can bind to DNA tightly in vitro, intercalate to mtDNA in situ, and induce mtDNA damage. Ir3- and Ir4-impaired mitochondria exhibit decline of mitochondrial membrane potential, disability of adenosine triphosphate generation, disruption of mitochondrial energetic and metabolic status, which subsequently cause protective mitophagy, G₀/G₁ phase cell cycle arrest, and apoptosis. In vivo antitumor evaluations also show that Ir4 can inhibit tumor xenograft growth effectively. Overall, our work proves that targeting the mitochondrial genome may present an effective strategy to develop metal-based anticancer agents to overcome cisplatin resistance.

Taurine rescues the arsenic-induced injury in the pancreas of rat offsprings and in the INS-1 cells

Arsenic was an established carcinogen and toxicant, occurring in drinking water and food. Arsenic was increasingly being blamed as a risk factor for diabetes mellitus. Recent studies have found that arsenic could induce the generation of reactive oxygen species (ROS) and mitochondria were the major targets of ROS. Damage mitochondria could be removed by mitophagy and mitophagy played a defensive role against cellular apoptosis. To investigate whether the arsenic could induce the injury in mitochondria, we treated Wistar rat offsprings and INS-1 cells with As2O3 and sodium arsenite, respectively. Our results showed that arsenic induced the generation of ROS in both rat offsprings' pancreas and INS-1 cells. The generation of ROS induced by arsenic could inhibit the expression of PPARγ. PPARγ is a major impact on mitochondrial function. The inhibition of PPARγ induced the reduction of PINK1 signaling and the upregulation of Bax. PINK1 signaling was one of the classical pathways of mitophagy. The inhibition of mitophagy induced the activation of apoptosis both in rat offsprings' pancreas and INS-1 cells. After treated with Rosiglitazone (RGS, PPARγ receptor agonist), PPARγ was rescued, the expression of PINK1 significantly increasing and the apoptosis was restrained. We used Taurine (Tau) as the protective agent both in rat offsprings' pancreas and INS-1 cells, after treated with Tau, the production of ROS was decreased significantly and the downgrade of PPARγ was rescued.

Regulated Necrosis Orchestrates Microglial Cell Death in Manganese-Induced Toxicity

Microglia, the brain resident immune cells, play prominent roles in immune surveillance, tissue repair and neural regeneration. Despite these pro-survival actions, the relevance of these cells in the progression of several neuropathologies has been established. In the context of manganese (Mn) overexposure, it has been proposed that microglial activation contributes to enhance the neurotoxicity. However, the occurrence of a direct cytotoxic effect of Mn on microglial cells remains controversial. In the present work, we investigated the potential vulnerability of immortalized mouse microglial cells (BV-2) toward Mn²⁺, focusing on the signaling pathways involved in cell death. Evidence obtained showed that Mn²⁺ induces a decrease in cell viability which is associated with reactive oxygen species (ROS) generation. In this report we demonstrated, for the first time, that Mn²⁺ triggers regulated necrosis (RN) in BV-2 cells involving two central mechanisms: parthanatos and lysosomal disruption. The occurrence of parthanatos is supported by several cellular and molecular events: (i) DNA damage; (ii) AIF translocation from mitochondria to the nucleus; (iii) mitochondrial membrane permeabilization; and (iv) PARP1-dependent cell death. On the other hand, Mn²⁺ induces lysosomal membrane permeabilization (LMP) and cathepsin D (CatD) release into the cytosol supporting the lysosomal disruption. Pre-incubation with CatB and D inhibitors partially prevented the Mn²⁺-induced cell viability decrease. Altogether these events point to lysosomes as players in the execution of RN. In summary, our results suggest that microglial cells could be direct targets of Mn²⁺ damage. In this scenario, Mn²⁺ triggers cell death involving RN pathways.

High-content analysis for mitophagy response to nanoparticles: A potential sensitive biomarker for nanosafety assessment

Mitophagy, a selective autophagy of mitochondria, clears up damaged mitochondria to maintain cell homeostasis. We performed high-content analysis (HCA) to detect the increase of PINK1, an essential protein controlling mitophagy, in hepatic cells treated with several nanoparticles (NPs). PINK1 immunofluorescence-based HCA was more sensitive than assays and detections for cell viability and mitochondrial functions. Of which, superparamagnetic iron oxide (SPIO)-NPs or graphene oxide-quantum dots (GO-QDs) was selected as representatives for positive or negative inducer of mitophagy. SPIO-NPs, but not GO-QDs, activated PINK1-dependent mitophagy as demonstrated by recruitment of PARKIN to mitochondria and degradation of injured mitochondria. SPIO-NPs caused the loss of mitochondrial membrane potential, decrease in ATP, and increase in mitochondrial reactive oxide species and Ca²⁺. Blocking mitophagy with PARKIN siRNA aggravated the cytotoxicity of SPIO-NPs. Taken together, PINK1 immunofluorescence-based HCA is considered to be an early, sensitive, and reliable approach to evaluate the bioimpacts of NPs.

The Sources of Reactive Oxygen Species and Its Possible Role in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by progressive loss of dopaminergic neurons in the substantia nigra. The precise mechanism underlying pathogenesis of PD is not fully understood, but it has been widely accepted that excessive reactive oxygen species (ROS) are the key mediator of PD pathogenesis. The causative factors of PD such as gene mutation, neuroinflammation, and iron accumulation all could induce ROS generation, and the later would mediate the dopaminergic neuron death by causing oxidation protein, lipids, and other macromolecules in the cells. Obviously, it is of mechanistic and therapeutic significance to understand where ROS are derived and how ROS induce dopaminergic neuron damage. In the present review, we try to summarize and discuss the main source of ROS in PD and the key pathways through which ROS mediate DA neuron death.

Silencing of PINK1 represses cell growth, migration and induces apoptosis of lung cancer cells

PTEN induced putative kinase 1 (PINK1) has been found to be up-regulated, which promotes the proliferation and chemoresistance in lung cancer. Nevertheless, the role and detailed mechnisms of PINK1 in lung cancer have not been fully understood, which need to be further clarified. In this study, the resluts showed that silencing of PINK1 inhibited proliferation and blocked cell cycle of lung cancer cells. Furthermore, the apoptosis rate was enhanced by PINK1 suppression, as evidenced by increased protein levels of Bax, cleaved caspase-3 and cleaved poly (ADP-ribose) polymerase (PARP), and decreased level of Bcl-2. The migration and invasion abilities were also restrained by PINK1 silencing. Silencing of PINK1 also resulted in oxygen species (ROS) overproduction and decreased mitochondrial membrane potential. Finally, suppression of PINK1 repressed the growth of xenograft tumor and induced apoptosis in tumor tissues in vivo. This study might lead to PINK1 kinase as a novel therapeutic target for lung cancer treatment.

Review of in vitro toxicological research of quantum dot and potentially involved mechanisms

Quantum dots (QDs) are one of emerging engineering nanomaterials (NMs) with advantageous properties which can act as candidates for clinical imaging and diagnosis. Nevertheless, toxicological studies have proved that QDs for better or worse pose threats to diverse systems which are attributed to the release of metal ion and specific characteristics of nanoparticles (NPs), hampering the wide use of QDs to biomedical area. It has been postulated that mechanisms of toxicity evoked by QDs have implications in oxidative stress, reactive oxygen species (ROS), inflammation and release of metal ion. Meanwhile, DNA damage and disturbance of subcellular structures would occur during QDs treatment. This review is intended to conclude the cytotoxicity of QDs in multiple systems, as well as the potential mechanisms on the basis of recent literatures. Finally, toxicity-related factors are clarified, among which chirality seems to be a newly proposed influence factor that determines the destiny of cells in response to QDs. However, details of interaction between QDs and cells have not been well elucidated. Given that molecular mechanisms of QDs-induced toxicity are still not clearly elucidated, further research should be required for this meaningful topic.

Putrescine as indicator of manganese neurotoxicity: Dose-response study in human SH-SY5Y cells

Disrupted polyamine metabolism with elevated putrescine is associated with neuronal dysfunction. Manganese (Mn) is an essential nutrient that causes neurotoxicity in excess, but methods to evaluate biochemical responses to high Mn are limited. No information is available on dose-response effects of Mn on putrescine abundance and related polyamine metabolism. The present research was to test the hypothesis that Mn causes putrescine accumulation over a physiologically adequate to toxic concentration range in a neuronal cell line. We used human SH-SY5Y neuroblastoma cells treated with MnCl2 under conditions that resulted in cell death or no cell death after 48 h. Putrescine and other metabolites were analyzed by liquid chromatography-ultra high-resolution mass spectrometry. Putrescine-related pathway changes were identified with metabolome-wide association study (MWAS). Results show that Mn caused a dose-dependent increase in putrescine over a non-toxic to toxic concentration range. MWAS of putrescine showed positive correlations with the polyamine metabolite N8-acetylspermidine, methionine-related precursors, and arginine-associated urea cycle metabolites, while putrescine was negatively correlated with γ-aminobutyric acid (GABA)-related and succinate-related metabolites (P < 0.001, FDR < 0.01). These data suggest that measurement of putrescine and correlated metabolites may be useful to study effects of Mn intake in the high adequate to UL range.

FOXO3 promoted mitophagy via nuclear retention induced by manganese chloride in SH-SY5Y cells

OBJECTIVES

To evaluate the role of FOXO3 during the process of mitophagy induced by manganese chloride (MnCl₂), mitochondrial dysfunction and mitophagy were detected before and after FOXO3 was knocked down in SH-SY5Y cells.

METHOD

Transmission electron microscopy (TEM), flow cytometry, confocal microscopy and a western blot were used to detect mitochondrial ultrastructure and autophagy, Ca²⁺ levels, mitochondrial reactive oxygen species (ROS) and the mitochondrial membrane potential (MMP), autophagosomes and mitophagy marker proteins (p62, LC3-II/LC3-I, Beclin-1, PINK1 and P-parkin), respectively.

RESULTS

After SH-SY5Y cells were exposed to MnCl₂, the levels of cytoplasmic Ca²⁺ and mitochondrial ROS increased but the mitochondrial MMP decreased significantly compared to the control in a dose- and time-dependent manner (p < 0.05), which indicated that MnCl₂ can lead to mitochondrial dysfunction. Under TEM, mitophagy and autolysosomes were observed. The WB results also showed that mitophagy marker proteins including LC3-II/LC3-I, Beclin-1, PINK1 and P-parkin except for p62 increased in a dose- and time-dependent manner, accompanied by FOXO3 nuclear retention, which indicated that MnCl₂ can lead to mitophagy and FOXO3 nuclear translocation may be involved in this process. After FOXO3 was knocked down, the inverse results of mitophagy and the levels of mitochondrial ROS decreasing were observed, which showed that FOXO3 silencing could inhibit mitophagy and mitochondrial dysfunction induced by MnCl₂.

CONCLUSIONS

Our results indicated that Mn could induce mitophagy by enhancing FOXO3 nuclear retention, which might promote mitophagy induced by MnCl₂.

Dysfunction of various organelles provokes multiple cell death after quantum dot exposure

Quantum dots (QDs) are different from the materials with the micrometer scale. Owing to the superiority in fluorescence and optical stability, QDs act as possible diagnostic and therapeutic tools for application in biomedical field. However, potential threats of QDs to human health hamper their wide utilization in life sciences. It has been reported that oxidative stress and inflammation are involved in toxicity caused by QDs. Recently, accumulating research unveiled that disturbance of subcellular structures plays a magnificent role in cytotoxicity of QDs. Diverse organelles would collapse during QD treatment, including DNA damage, endoplasmic reticulum stress, mitochondrial dysfunction and lysosomal rupture. Different forms of cellular end points on the basis of recent research have been concluded. Apart from apoptosis and autophagy, a new form of cell death termed pyroptosis, which is finely orchestrated by inflammasome complex and gasdermin family with secretion of interleukin-1 beta and interleukin-18, was also summarized. Finally, several potential cellular signaling pathways were also listed. Activation of Toll-like receptor-4/myeloid differentiation primary response 88, nuclear factor kappa-light-chain-enhancer of activated B cells and NACHT, LRR and PYD domains-containing protein 3 inflammasome pathways by QD exposure is associated with regulation of cellular processes. With the development of QDs, toxicity evaluation is far behind its development, where specific mechanisms of toxic effects are not clearly defined. Further studies concerned with this promising area are urgently required.

Lead (Pb) induced ATM-dependent mitophagy via PINK1/Parkin pathway

Lead (Pb), a widely distributed environmental pollutant, is known to induce mitochondrial damage as well as autophagy in vitro and in vivo. In this study, we found that Pb could trigger mitophagy in both HEK293 cells and the kidney cortex of male Kunming mice. However, whether ataxia telangiectasis mutated (ATM) which is reported to be linked with PTEN-induced putative kinase 1 (PINK1)/Parkin pathway (a well-characterized mitophagic pathway) participates in the regulation of Pb-induced mitophagy and its exact role remains enigmatic. Our results indicated that Pb activated ATM in vitro and in vivo, and further in vitro studies showed that ATM could co-localize with PINK1 and Parkin in cytosol and interact with PINK1. Knockdown of ATM by siRNA blocked Pb-induced mitophagy even under the circumstance of enhanced accumulation of PINK1 and mitochondrial Parkin. Intriguingly, elevation instead of reduction in phosphorylation level of PINK1 and Parkin was observed in response to ATM knockdown and Pb did not contribute to the further increase of their phosphorylation level, implying that ATM indirectly regulated PINK1/Parkin pathway. These findings reveal a novel mechanism for Pb toxicity and suggest the regulatory importance of ATM in PINK1/Parkin-mediated mitophagy.

PINK1/Parkin-mediated mitophagy was activated against 1,4-Benzoquinone-induced apoptosis in HL-60 cells

Hematotoxicity of benzene is derived mainly from its active metabolite, 1,4-Benzoquinone (1,4-BQ), which induces cell apoptosis and mitochondrial damage. Damaged mitochondria are degraded through a specialized autophagy pathway, called mitophagy, which is driven by PINK1/Parkin signaling. However, whether mitophagy is involved in 1,4-BQ-induced toxicity remains unclear. This study was designed to investigate whether PINK1/Parkin-mediated mitophagy is activated in 1,4-BQ-treated HL-60 cells, and the roles mitophagy plays in 1,4-BQ-induced apoptosis. Our results demonstrated that 1,4-BQ induced autophagy in HL-60 cells, characterized by increased LC3-II/LC3-I ratio and Beclin1 expression, as well as decreased expression of p62. We confirmed the presence of mitophagosomes using electron microscopy, and found that 1,4-BQ-induced autophagy was blocked by pretreatment with the mitophagy inhibitor Cyclosporine A (CsA). In addition, we found that 1,4-BQ induced mitochondrial stress through decreased mitochondrial membrane potential (MMP) and increasedproduction of reactive oxygen species (ROS). We also confirmed that 1,4-BQ-induced mitophagy was mediated by the PINK1/Parkin pathway, illustrated by increased expression of PINK1 and Parkin mRNA and protein. Finally, we examined 1,4-BQ-induced apoptosis with or without CsA, which demonstrated that apoptosis increased after mitophagy inhibition, suggesting that mitophagy has a protective effect in this context. In conclusion, this study demonstrates that the activated PINK1/Parkin-mediated mitophagy exerts a significantly protective effect against 1,4-BQ-induced apoptosis in HL-60 cells.