Depression and type 2 diabetes: A causal relationship and mechanistic pathway.

Depression is a mood disorder that may increase risk for the development of insulin resistance (IR) and type 2 diabetes (T2D), and vice versa. However, the mechanistic pathway linking depression and T2D is not fully elucidated. The aim of this narrative review, therefore, was to discuss the possible link between depression and T2D. The coexistence of T2D and depression is twice as great compared to the occurrence of either condition independently. Hyperglycaemia and dyslipidaemia promote the incidence of depression by enhancing inflammation and reducing brain serotonin (5-hydroxytryptamine [5HT]). Dysregulation of insulin signalling in T2D impairs brain 5HT signalling, leading to the development of depression. Furthermore, depression is associated with the development of hyperglycaemia and poor glycaemic control. Psychological stress and depression promote the development of T2D. In conclusion, T2D could be a potential risk factor for the development of depression through the induction of inflammatory reactions and oxidative stress that affect brain neurotransmission. In addition, chronic stress in depression may induce the development of T2D through dysregulation of the hypothalamic-pituitary-adrenal axis and increase circulating cortisol levels, which triggers IR and T2D.

Zinc oxide nanoparticles exacerbate skin epithelial cell damage by upregulating pro-inflammatory cytokines and exosome secretion in M1 macrophages following UVB irradiation-induced skin injury.

BACKGROUND: Zinc oxide nanoparticles (ZnONPs) are common materials used in skin-related cosmetics and sunscreen products due to their whitening and strong UV light absorption properties. Although the protective effects of ZnONPs against UV light in intact skin have been well demonstrated, the effects of using ZnONPs on damaged or sunburned skin are still unclear. In this study, we aimed to reveal the detailed underlying mechanisms related to keratinocytes and macrophages exposed to UVB and ZnONPs. RESULTS: We demonstrated that ZnONPs exacerbated mouse skin damage after UVB exposure, followed by increased transepidermal water loss (TEWL) levels, cell death and epithelial thickness. In addition, ZnONPs could penetrate through the damaged epithelium, gain access to the dermis cells, and lead to severe inflammation by activation of M1 macrophage. Mechanistic studies indicated that co-exposure of keratinocytes to UVB and ZnONPs lysosomal impairment and autophagy dysfunction, which increased cell exosome release. However, these exosomes could be taken up by macrophages, which accelerated M1 macrophage polarization. Furthermore, ZnONPs also induced a lasting inflammatory response in M1 macrophages and affected epithelial cell repair by regulating the autophagy-mediated NLRP3 inflammasome and macrophage exosome secretion. CONCLUSIONS: Our findings propose a new concept for ZnONP-induced skin toxicity mechanisms and the safety issue of ZnONPs application on vulnerable skin. The process involved an interplay of lysosomal impairment, autophagy-mediated NLRP3 inflammasome and macrophage exosome secretion. The current finding is valuable for evaluating the effects of ZnONPs for cosmetics applications.

Multi-locus deletion mutation induced by silver nanoparticles: Role of lysosomal-autophagy dysfunction.

Due to the rapid production growth and a wide range of applications, safety concerns are being raised about the genotoxic properties of silver nanoparticles (AgNPs). In this research, we found AgNPs induced a size-dependent genotoxicity via lysosomal-autophagy dysfunction in human-hamster hybrid (AL) cells. Compared with 25 nm and 75 nm particles, 5 nm AgNPs could accentuate the genotoxic responses, including DNA double-strand breaks (DSBs) and multi-locus deletion mutation, which could be significantly enhanced by autophagy inhibitors 3-methyl adenine (3-MA), Bafilomycin A1 (BFA), and cathepsin inhibitors, respectively. The autophagy dysfunction was closely related to the accumulation of 5 nm AgNPs in the lysosomes and the interruption of lysosome-autophagosome fusion. With lysosomal protective agent 3-O-Methylsphingomyelin (3-O-M) and endocytosis inhibitor wortmannin, the reactivation of lysosomal function and the recovery of autophagy significantly attenuated AgNP-induced genotoxicity. Our data provide clear evidence to illustrate the role of subcellular targets in the genotoxicity of AgNPs in mammalian cells, which laid the basis for better understanding the health risk of AgNPs and their related products.

Silica Nanoparticles Promote Apoptosis in Ovarian Granulosa Cells via Autophagy Dysfunction.

Although silica nanoparticles (SNPs) are generally thought to be biocompatible and safe, the adverse effects of SNPs were also reported in previous studies. SNPs cause follicular atresia via the induction of ovarian granulosa cell apoptosis. However, the mechanisms for this phenomenon are not well understood. This study focuses on exploring the relationship between autophagy and apoptosis induced by SNPs in ovarian granulosa cells. Our results showed that 25.0 mg/kg body weight (b.w.)/intratracheal instillation of 110 nm in diameter spherical Stöber SNPs caused ovarian granulosa cell apoptosis in follicles in vivo. We also found that SNPs mainly internalized into the lumens of the lysosomes in primary cultured ovarian granulosa cells in vitro. SNPs induced cytotoxicity via a decrease in viability and an increase in apoptosis in a dose-dependent manner. SNPs increased BECLIN-1 and LC3-II levels, leading to the activation of autophagy and increased P62 level, resulting in the blockage of autophagic flux. SNPs increased the BAX/BCL-2 ratio and cleaved the caspase-3 level, resulting in the activation of the mitochondrial-mediated caspase-dependent apoptotic signaling pathway. SNPs enlarged the LysoTracker Red-positive compartments, decreased the CTSD level, and increased the acidity of lysosomes, leading to lysosomal impairment. Our results reveal that SNPs cause autophagy dysfunction via lysosomal impairment, resulting in follicular atresia via the enhancement of apoptosis in ovarian granulosa cells.

Synergistic Lysosomal Impairment and ER Stress Activation for Boosted Autophagy Dysfunction Based on Te Double-Headed Nano-Bullets.

To overcome the autophagy compromised mechanism of protective cellular processes by "eating"/"digesting" damaged organelles or potentially toxic materials with autolysosomes in tumor cells, lysosomal impairment can be utilized as a traditional autophagy dysfunction route for tumor therapy; however, this conventional one-way autophagy dysfunction approach is always limited by the therapeutic efficacy. Herein, an innovative pharmacological strategy that can excessively provoke autophagy via endoplasmic reticulum (ER) stress is implemented along with lysosomal impairment to enhance autophagy dysfunction. In this work, the prepared tellurium double-headed nanobullets (TeDNBs) with controllable morphology are modified with human serum albumin (HSA) which facilitates internalization by tumor cells. On the one hand, ER stress can be stimulated by upregulating the phosphorylation eukaryotic translation initiation factor 2 (P-eIF2α) owing to the production of tellurite (TeO32- ) in the specifical hydrogen peroxide-rich tumor environment; thus, autophagy overstimulation occurs. On the other hand, OME can deacidify and impair lysosomes by downregulating lysosomal-associated membrane protein 1 (LAMP1), therefore blocking autolysosome formation. Both in vitro and in vivo results demonstrate that the synthesized TeDNBs-HSA/OME (TeDNBs-HO) exhibit excellent therapeutic efficacy by autophagy dysfunction through ER stress induction and lysosomal damnification. Thus, TeDNBs-HO is verified to be a promising theranostic nanoagent for effective tumor therapy.

Silica nanoparticles induce pulmonary autophagy dysfunction and epithelial-to-mesenchymal transition via p62/NF-κB signaling pathway.

It has been reported that silica nanoparticles (SiNPs) could cause epithelial-to-mesenchymal transition (EMT), but the specific mechanism is still unclear. Thus, the purpose of this study was to investigate the underlying mechanisms of pulmonary EMT after subacute exposure to SiNPs. The results showed intratracheal instillation of SiNPs increased the pulmonary MDA content, while decreased the activity of SOD and GSH-Px in rats. Western blot analysis demonstrated that SiNPs induced autophagy dysfunction via the upregulation of p62. Meanwhile, the inflammation cytokines (TNF-α, IL-18, IL-1ß) were released in rat lung. Immunohistochemistry and western blot assays both showed that SiNPs could regulate the related protein biomarkers of EMT through decreasing E-cadherin and increasing vimentin in a dose-dependent manner. Besides, SiNPs activated the proteins expression involved in p62/NF-κB signaling pathway, whereas the pulmonary EMT induced by SiNPs was significantly dampened after the knock down of p62. In this study, we illustrated that subacute exposure to SiNPs could trigger the autophagy dysfunction and pulmonary inflammation, further lead to EMT via activating the p62/NF-κB signaling pathway. Our findings provide new molecular evidence for SiNPs-induced pulmonary toxicity.

Silica nanoparticles induce lung inflammation in mice via ROS/PARP/TRPM2 signaling-mediated lysosome impairment and autophagy dysfunction.

BACKGROUND: Wide applications of nanoparticles (NPs) have raised increasing concerns about safety to humans. Oxidative stress and inflammation are extensively investigated as mechanisms for NPs-induced toxicity. Autophagy and lysosomal dysfunction are emerging molecular mechanisms. Inhalation is one of the main pathways of exposing humans to NPs, which has been reported to induce severe pulmonary inflammation. However, the underlying mechanisms and, more specifically, the interplays of above-mentioned mechanisms in NPs-induced pulmonary inflammation are still largely obscure. Considered that NPs exposure in modern society is often unavoidable, it is highly desirable to develop effective strategies that could help to prevent nanomaterials-induced pulmonary inflammation. RESULTS: Pulmonary inflammation induced by intratracheal instillation of silica nanoparticles (SiNPs) in C57BL/6 mice was prevented by PJ34, a poly (ADP-ribose) polymerase (PARP) inhibitor. In human lung bronchial epithelial (BEAS-2B) cells, exposure to SiNPs reduced cell viability, and induced ROS generation, impairment in lysosome function and autophagic flux. Inhibition of ROS generation, PARP and TRPM2 channel suppressed SiNPs-induced lysosome impairment and autophagy dysfunction and consequent inflammatory responses. Consistently, SiNPs-induced pulmonary inflammation was prevented in TRPM2 deficient mice. CONCLUSION: The ROS/PARP/TRPM2 signaling is critical in SiNPs-induced pulmonary inflammation, providing novel mechanistic insights into NPs-induced lung injury. Our study identifies TRPM2 channel as a new target for the development of preventive and therapeutic strategies to mitigate nanomaterials-induced lung inflammation.

Elafibranor interrupts adipose dysfunction-mediated gut and liver injury in mice with alcoholic steatohepatitis.

Background: Reversal of alcohol-induced peroxisome proliferator-activated receptor (PPAR) α (PPARα) and PPARδ dysfunction has been reported to decrease the severity of alcoholic steatohepatitis (ASH). Autophagy is essential for cell survival and tissue energy homeostasis. Emerging evidence indicates that alcohol-induced adipose tissue (AT) autophagy dysfunction contributes to injury in the intestine, liver, and AT of ASH. Methods: The effects and mechanisms of dual PPARα/δ agonist elafibranor on autophagy stimulation were investigated using mice with ASH. Results: C57BL/6 mice on ethanol diet showed AT dysfunction, disrupted intestinal barrier, and ASH, which was accompanied by alcohol-mediated decrease in PPARα, PPARδ, and autophagy levels in intestine, liver, and AT. Chronic treatment with elafibranor attenuated AT apoptosis and inflammation by restoration of tissue PPARα, PPARδ, and autophagy levels. In ASH mice, alcohol-induced AT dysfunction along with increased fatty acid (FA) uptake and decreased free FA (FFA) release from AT was inhibited by elafibranor. The improvement of AT autophagy dysfunction by elafibranor alleviated inflammation and apoptosis-mediated intestinal epithelial disruption in ASH mice. Acute elafibranor incubation inhibited ethanol-induced ASH-mice-sera-enhanced autophagy dysfunction, apoptosis, barrier disruption, and intracellular steatosis in Caco-2 cells and primary hepatocytes (PHs). Conclusion: Altogether, these findings demonstrated that the PPARα/δ agonist, elafibranor, decreased the severity of liver injury by restoration of alcohol-suppressed AT autophagy function and by decreasing the release of apoptotic markers, inflammatory cytokines, and FFA, thereby reducing intestinal epithelium disruption and liver inflammation/apoptosis/steatosis in ASH mice. These data suggest that dual PPAR agonists can serve as potential therapeutic agents for the management of ASH.

In Search of a Converging Cellular Mechanism in Nanotoxicology and Nanomedicine in the Treatment of Cancer.

Multiple applications of nanomaterials have raised concern with regard to their toxicity. With increasing research into nanomaterial safety, mechanisms involved in the toxic effects of nanomaterials have begun to emerge. The importance of nanomaterial-induced lysosomal membrane permeabilization through overloading or direct damage of the lysosomal compartment, resulting in the blockade of autophagosome-lysosome fusion and autophagy dysfunction, as well as inflammasome activation were cited as emerging mechanisms of nanomaterial toxicity. It has recently been proposed that these very mechanisms leading to nanomaterial toxicity may be utilized in nanotherapeutics. This review discusses these nanomaterial-induced mechanisms in detail and how it has been exploited in cancer research. This review also addresses certain considerations that need to be kept in mind when using nanomaterials in therapeutics.

Risk factors for fatty pancreas and effects of fatty infiltration on pancreatic cancer.

Objective: This study clarified the risk factors and pathophysiology of pancreatic cancer by examining the factors associated with fatty pancreas. Methods: The degree of fatty pancreas, background factors, and incidence of pancreatic cancer were examined among nonalcoholic fatty liver disease (NAFLD) patients (n = 281) and intraductal papillary mucinous neoplasm (IPMN) patients with a family history of pancreatic cancer (n = 38). The presence of fatty pancreas was confirmed by the pancreatic CT value/splenic CT value ratio (P/S ratio). Immunohistochemical staining was performed on 10 cases with fatty pancreas, confirmed via postoperative pathology. Results: Fatty pancreas occurred in 126 patients (44.8%) in the NAFLD group who were older (p = 0.0002) and more likely to have hypertension (p < 0.0001). The IPMN group had 18 patients (47.4%) with fatty pancreas, included more men than women (p = 0.0056), and was more likely to have patients with hypertension (p = 0.0010). On histological examination, a significant infiltration of adipocytes into the acini from the pancreatic interstitium induced atrophy of the pancreatic parenchyma, and both M1 and M2 macrophages were detected in the area where adipocytes invaded the pancreatic parenchyma. Accumulation of p62 and increased positive staining of NQO1 molecules related to autophagy dysfunction were detected in pancreatic acinar cells in the fatty area, acinar-ductal metaplasia, and pancreatic cancer cells. The rate of p62-positive cell area and that of NQO1-positive cell area were significantly higher in the fatty pancreatic region than those in the control lesion (pancreatic region with few adipocyte infiltration). Furthermore, the rate of p62-positive cell area or that of NQO1-positive cell area showed strong positive correlations with the rate of fatty pancreatic lesion. These results suggest that adipocyte invasion into the pancreatic parenthyme induced macrophage infiltration and autophagy substrate p62 accumulation. High levels of NQO1 expression in the fatty area may be dependent on p62 accumulation. Conclusion: Hypertension was a significant risk factor for fatty pancreas in patients with NAFLD and IPMN. In fatty pancreas, fatty infiltration into the pancreatic parenchyme might induce autophagy dysfunction, resulting in activation of antioxidant proteins NQO1. Thus, patients with fatty pancreas require careful follow-up.

Defective lysosomal acidification: a new prognostic marker and therapeutic target for neurodegenerative diseases.

Lysosomal acidification dysfunction has been implicated as a key driving factor in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Multiple genetic factors have been linked to lysosomal de-acidification through impairing the vacuolar-type ATPase and ion channels on the organelle membrane. Similar lysosomal abnormalities are also present in sporadic forms of neurodegeneration, although the underlying pathogenic mechanisms are unclear and remain to be investigated. Importantly, recent studies have revealed early occurrence of lysosomal acidification impairment before the onset of neurodegeneration and late-stage pathology. However, there is a lack of methods for organelle pH monitoring in vivo and a dearth of lysosome-acidifying therapeutic agents. Here, we summarize and present evidence for the notion of defective lysosomal acidification as an early indicator of neurodegeneration and urge the critical need for technological advancement in developing tools for lysosomal pH monitoring and detection both in vivo and for clinical applications. We further discuss current preclinical pharmacological agents that modulate lysosomal acidification, including small molecules and nanomedicine, and their potential clinical translation into lysosome-targeting therapies. Both timely detection of lysosomal dysfunction and development of therapeutics that restore lysosomal function represent paradigm shifts in targeting neurodegenerative diseases.

Autophagy Dysfunction as a Phenotypic Readout in hiPSC-Derived Neuronal Cell Models of Neurodegenerative Diseases.

Autophagy is an evolutionarily conserved catabolic pathway for the degradation of cytoplasmic constituents in eukaryotic cells. It is the primary disposal route for selective removal of undesirable cellular materials like aggregation-prone proteins and damaged organelles for maintaining cellular homeostasis, and for bulk degradation of intracellular macromolecules and recycling the breakdown products for providing energy homeostasis during starvation. These functions of autophagy are attributed to cellular survival and thus pertinent for human health; however, malfunction of this process is detrimental to the cells, particularly for post-mitotic neurons. Thus, basal autophagy is vital for maintaining neuronal homeostasis, whereas autophagy dysfunction contributes to neurodegeneration. Defective autophagy has been demonstrated in several neurodegenerative diseases wherein pharmacological induction of autophagy is beneficial in many of these disease models. Elucidating the mechanisms underlying defective autophagy is imperative for the development of therapies targeting this process. Disease-affected human neuronal cells can be established from patient-derived human induced pluripotent stem cells (hiPSCs) that provide a clinically relevant platform for studying disease mechanisms and drug discovery. Thus, modeling autophagy dysfunction as a phenotypic readout in patient-derived neurons provides a more direct platform for investigating the mechanisms underlying defective autophagy and evaluating the therapeutic efficacy of autophagy inducers. Toward this, several hiPSC-derived neuronal cell models of neurodegenerative diseases have been employed. In this review, we highlight the key methodologies pertaining to hiPSC maintenance and neuronal differentiation, and studying autophagy at an endogenous level in hiPSC-derived neuronal cells.

Autophagic Dysfunction in Dementia: Scope for Development of Potential Remedies.

Dementia is a diverse category of chronic and progressive disorder, which is commonly associated with a loss of memory, difficulty in judgment, impaired language, cognitive impairment, and various other symptoms that affect a person's daily routine life and social life. Dementia affects about 50 million people around the globe. Dementia exists in varied forms and is associated with various neurodegenerative disorders. Alzheimer's disease is the most common form, which accords for about 60% of thecases. Abnormal agglomeration of proteins in the brain has been linked to the pathogenesis of dementia. Autophagy is a necessary protein clearance mechanism, which is dependent on lysosomes. It is a basic physiological process that performs the crucial function of maintaining protein homeostasis within the cells. The autophagic dysfunction in dementia further complicates the disease by hampering the degradation and removing abnormal pathogenic proteins. In order to understand autophagic dysfunction, it is essential to know the genetics of autophagy as well as the mutations This understanding at the genetic level helps definethe relationship between dementia and autophagic dysfunction for developing the potential remedies for the treatment of dementia.

Oxidative Stress, Inflammation, and Autophagy: Potential Targets of Mesenchymal Stem Cells-Based Therapies in Ischemic Stroke.

Ischemic stroke is a leading cause of death worldwide; currently available treatment approaches for ischemic stroke are to restore blood flow, which reduce disability but are time limited. The interruption of blood flow in ischemic stroke contributes to intricate pathophysiological processes. Oxidative stress and inflammatory activity are two early events in the cascade of cerebral ischemic injury. These two factors are reciprocal causation and directly trigger the development of autophagy. Appropriate autophagy activity contributes to brain recovery by reducing oxidative stress and inflammatory activity, while autophagy dysfunction aggravates cerebral injury. Abundant evidence demonstrates the beneficial impact of mesenchymal stem cells (MSCs) and secretome on cerebral ischemic injury. MSCs reduce oxidative stress through suppressing reactive oxygen species (ROS) and reactive nitrogen species (RNS) generation and transferring healthy mitochondria to damaged cells. Meanwhile, MSCs exert anti-inflammation properties by the production of cytokines and extracellular vesicles, inhibiting proinflammatory cytokines and inflammatory cells activation, suppressing pyroptosis, and alleviating blood-brain barrier leakage. Additionally, MSCs regulation of autophagy imbalances gives rise to neuroprotection against cerebral ischemic injury. Altogether, MSCs have been a promising candidate for the treatment of ischemic stroke due to their pleiotropic effect.

Iron chelator Deferoxamine protects human neuroblastoma cell line SH-SY5Y from 6-Hydroxydopamine-induced apoptosis and autophagy dysfunction.

BACKGROUND: Intracellular iron involves in Fenton's reaction-mediated Hydroxyl radical (OH·) generation by reacting with the neurotoxic agent 6-Hydroxydopamine (6-OHDA) autoxidation derivative Hydrogen Peroxide (H2O2). Several studies have been conducted so far on the neuroprotective activities of the iron chelator Deferoxamine (DFO) but little or no clear evidence about the underlying cellular mechanism is available. METHODS: The present study was conducted on Human neuroblastoma cell line SH-SY5Y in the absence or presence of 6-OHDA or H2O2 and / or DFO. Following incubation, cell viability assay, intracellular reactive oxygen species (ROS) determination, flow cytometric quantification of apoptotic cells followed by nuclear staining, intracellular tracking of transfected fusion construct of microtubule-associated protein 1B-light chain with Green fluorescent protein - Red fluorescent protein (LC3B-GFP-RFP reporters) and immunocytochemistry of intracellular Cathepsin protein by confocal microscopy, were conducted. In addition, western blotting was carried out to detect expressions of apoptotic and autophagy related proteins. RESULTS: This study confirmed the neuroprotective potential of DFO by inhibiting 6-OHDA-mediated cell death and ROS generation. Reduced percentage of apoptotic cells and appearance of altered nuclei architecture followed by a reduced expression of cleaved PARP (Poly-ADP-ribose Polymerase) and cleaved Caspase-3 were observed upon DFO treatment against 6-OHDA, and as well as against H2O2 in SH-SY5Y cell lines. Besides, DFO induced the intracellular autophagolysosome formation (red puncta) rather than autophagosome (yellow puncta) only. Thereafter it was observed that DFO restored the expression of intracellular lysosomal protease Cathepsin and reduced the expression of the LC3-II. CONCLUSION: Taken together, this study clearly demonstrated that the anti-Fenton activity of DFO inhibited apoptosis and caused blockade in ALP or autophagy dysfunction in SH-SY5Y cell lines. These outcomes further suggest that DFO provides neuroprotection by inhibiting apoptosis and inducing the progression of Autophagy- lysosomal pathway (ALP).

Molecular Association of Glia Maturation Factor with the Autophagic Machinery in Rat Dopaminergic Neurons: a Role for Endoplasmic Reticulum Stress and MAPK Activation.

Parkinson's disease (PD) is one of the several neurodegenerative diseases where accumulation of aggregated proteins like α-synuclein occurs. Dysfunction in autophagy leading to this protein build-up and subsequent dopaminergic neurodegeneration may be one of the causes of PD. The mechanisms that impair autophagy remain poorly understood. 1-Methyl-4-phenylpiridium ion (MPP+) is a neurotoxin that induces experimental PD in vitro. Our studies have shown that glia maturation factor (GMF), a brain-localized inflammatory protein, induces dopaminergic neurodegeneration in PD and that suppression of GMF prevents MPP+-induced loss of dopaminergic neurons. In the present study, we demonstrate a molecular action of GMF on the autophagic machinery resulting in dopaminergic neuronal loss and propose GMF-mediated autophagic dysfunction as one of the contributing factors in PD progression. Using dopaminergic N27 neurons, primary neurons from wild type (WT), and GMF-deficient (GMF-KO) mice, we show that GMF and MPP+ enhanced expression of MAPKs increased the mammalian target of rapamycin (mTOR) activation and endoplasmic reticulum stress markers such as phospho-eukaryotic translation initiation factor 2 alpha kinase 3 (p-PERK) and inositol-requiring enzyme 1α (IRE1α). Further, GMF and MPP+ reduced Beclin 1, focal adhesion kinase (FAK) family-interacting protein of 200 kD (FIP200), and autophagy-related proteins (ATGs) 3, 5, 7, 16L, and 12. The combined results demonstrate that GMF affects autophagy through autophagosome formation with significantly reduced lysosomal-associated membrane protein 1/2, and the number of autophagic acidic vesicles. Using primary neurons, we show that MPP+ treatment leads to differential expression and localization of p62/sequestosome and in GMF-KO neurons, there was a marked increase in p62 staining implying autophagy deficiency with very little co-localization of α-synuclein and p62 as compared with WT neurons. Collectively, this study provides a bidirectional role for GMF in executing dopaminergic neuronal death mediated by autophagy that is relevant to PD.

Restoring autophagic flux attenuates cochlear spiral ganglion neuron degeneration by promoting TFEB nuclear translocation via inhibiting MTOR.

Macroautophagy/autophagy dysfunction is associated with many neurodegenerative diseases. TFEB (transcription factor EB), an important molecule that regulates lysosomal and autophagy function, is regarded as a potential target for treating some neurodegenerative diseases. However, the relationship between autophagy dysfunction and spiral ganglion neuron (SGN) degeneration and the role of TFEB in SGN degeneration has not yet been established. Here, we showed that in degenerated SGNs, induced by sensory epithelial cell loss in the cochlea of mice following kanamycin and furosemide administration, the lipofuscin area and oxidative stress level were increased, the nuclear-to-cytoplasmic TFEB ratio was decreased, and the late stage of autophagic flux was impaired. After autophagy dysfunction was partially ameliorated with an MTOR inhibitor, which promoted TFEB translocation into the nucleus from the cytoplasm, we found that the lysosomal deficits were significantly relieved, the oxidative stress level was reduced, and the density of surviving SGNs and auditory nerve fibers was increased. The results in the present study reveal that autophagy dysfunction is an important component of SGN degeneration, and TFEB may be a potential target for attenuating SGN degeneration following sensory epithelial cell loss in the cochlea of mice. Abbreviations: 3-NT: 3-nitrotyrosine; 4-HNE: 4-hydroxynonenal; 8-OHdG: 8-hydroxy-2'-deoxyguanosine; ABR: auditory brainstem response; APP: amyloid beta (A4) precursor protein; CLEAR: coordinated lysosomal expression and regulation; CTSB: cathespin B; CTSD: cathespin D; SAMR1: senescence-accelerated mouse/resistance 1; SAMP8: senescence-accelerated mouse/prone 8; MAPK1/ERK2: mitogen-activated protein kinase 1; MTOR: mechanistic target of rapamycin kinase; SGN: spiral ganglion neuron; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscope; TFEB: transcription factor EB.

Silica nanoparticles induce autophagosome accumulation via activation of the EIF2AK3 and ATF6 UPR pathways in hepatocytes.

Autophagy dysfunction is a potential toxic effect of nanoparticles. Previous studies have indicated that silica nanoparticles (SiNPs) induce macroautophagy/autophagy dysfunction, while the precise mechanisms remain uncertain. Hence, the present study investigated the molecular mechanisms by which SiNPs enhanced autophagosome synthesis, which then contributed to autophagy dysfunction. First, the effects of SiNPs on autophagy and autophagic flux were verified using transmission electron microscopy, laser scanning confocal microscopy, and western blot assays. Then, the activation of endoplasmic reticular (ER) stress was validated to be through the EIF2AK3 and ATF6 UPR pathways but not the ERN1-XBP1 pathway, along with the upregulation of downstream ATF4 and DDIT3. Thereafter, the ER stress inhibitor 4-phenylbutyrate (4-PBA) was used to verify that SiNP-induced autophagy could be influenced by ER stress. Furthermore, specialized lentiviral shRNA were employed to determine that autophagy was induced via specific activation of the EIF2AK3 and ATF6 UPR pathways. Finally, the 2 autophagic genes LC3B and ATG12 were found to be transcriptionally upregulated by downstream ATF4 and DDIT3 in ER stress, which contributed to the SiNP-enhanced autophagosome synthesis. Taken together, these data suggest that SiNPs induced autophagosome accumulation via the activation of the EIF2AK3 and ATF6 UPR pathways in hepatocytes, which offers a new insight into detailed molecular mechanisms underlying SiNP-induced autophagy dysfunction, and specifically how UPR pathways regulate key autophagic genes. This work provides novel evidence for the study of toxic effects and risk assessment of SiNPs.

Silica nanoparticles induce autophagy dysfunction via lysosomal impairment and inhibition of autophagosome degradation in hepatocytes.

Autophagy dysfunction is considered as a potential toxic mechanism of nanomaterials. Silica nanoparticles (SiNPs) can induce autophagy, but the specific mechanism involved remains unclear. Therefore, the aim of this study was to confirm the effects of SiNPs on autophagy dysfunction and explore the possible underlying mechanism. In this article, we reported that cell-internalized SiNPs exhibited dose- and time-dependent cytotoxicity in both L-02 and HepG2 cells. Multiple methods verified that SiNPs induced autophagy even at the noncytotoxic level and blocked the autophagic flux at the high-dose level. Notably, SiNPs impaired the lysosomal function through damaging lysosomal ultrastructures, increasing membrane permeability, and downregulating the expression of lysosomal proteases, cathepsin B, as evidenced by transmission electron microscopy, acridine orange staining, quantitative reverse transcription-polymerase chain reaction, and Western blot assays. Collectively, these data concluded that SiNPs inhibited autophagosome degradation via lysosomal impairment in hepatocytes, resulting in autophagy dysfunction. The current study not only discloses a potential mechanism of autophagy dysfunction induced by SiNPs but also provides novel evidence for the study of toxic effect and safety evaluation of SiNPs.

Are Dopamine Oxidation Metabolites Involved in the Loss of Dopaminergic Neurons in the Nigrostriatal System in Parkinson's Disease?

In 1967, L-dopa was introduced as part of the pharmacological therapy of Parkinson's disease (PD) and, in spite of extensive research, no additional effective drugs have been discovered to treat PD. This brings forward the question: why have no new drugs been developed? We consider that one of the problems preventing the discovery of new drugs is that we still have no information on the pathophysiology of the neurodegeneration of the neuromelanin-containing nigrostriatal dopaminergic neurons. Currently, it is widely accepted that the degeneration of dopaminergic neurons, i.e., in the substantia nigra pars compacta, involves mitochondrial dysfunction, the formation of neurotoxic oligomers of alpha-synuclein, the dysfunction of protein degradation systems, neuroinflammation, and oxidative and endoplasmic reticulum stress. However, the initial trigger of these mechanisms in the nigrostriatal system is still unknown. It has been reported that aminochrome induces the majority of these mechanisms involved in the neurodegeneration process. Aminochrome is formed within the cytoplasm of neuromelanin-containing dopaminergic neurons during the oxidation of dopamine to neuromelanin. The oxidation of dopamine to neuromelanin is a normal and harmless process, because healthy individuals have intact neuromelanin-containing dopaminergic neurons. Interestingly, aminochrome-induced neurotoxicity is prevented by two enzymes: DT-diaphorase and glutathione transferase M2-2, which explains why melanin-containing dopaminergic neurons are intact in healthy human brains.