Roles of oxidative stress and the ERK1/2, PTEN and p70S6K signaling pathways in arsenite-induced autophagy

Arsenic-induced disruption of circadian rhythms and glutamine anaplerosis in human urothelial carcinoma

Inorganic arsenic (iAs)-induced urothelial carcinoma (UC) develops into a poor-prognosis malignancy. Arsenic-induced oxidative stress contributes to circadian rhythm disruption altered metabolism. Glutamine anaplerosis is a common metabolic feature of rapidly proliferating malignant cells, in which glutaminase (GLS) is a key enzyme in this process. Therefore, this study intends to determine if arsenic-induced oxidative stress can alter circadian rhythms and promote glutamine anaplerosis. Exonic expression of core circadian molecules (CLOCK, ARNTL, and NR1D1) and GLS in varying grades of UC were assessed using 423 bladder cancer samples from the TCGA Urothelial Bladder Cancer (BLCA) dataset. The levels of circadian proteins and metabolic markers in 44 UC patients from non-black foot disease (BFD) and BFD areas were detected by immunohistochemistry. In vitro and in vivo experiments elucidated the regulatory mechanisms of arsenic-mediated circadian disturbance and metabolic alteration. Public database analysis showed that ARNTL, NR1D1, and GLS exhibited greater expression in more high-grade UC. Strong immunoreactivity for BMAL1, GLS, and low levels of NR1D1 were found in malignant urothelial lesions, especially in arsenic-exposed UC. Arsenic-induced overexpression of BMAL1 and GLS involves activation of NADH: quinone oxidoreductase 1 (NQO1), continuously altering the NADH oscillations to promote glutamate metabolism in SV-HUC-1, T24 and BFTC-905 cells. These phenomenon were also demonstrated in the urothelium of arsenic-exposed animals. The present findings highlight the potential clinical significance of BMAL1 and GLS in UC in the BFD region. Furthermore, these results suggest that arsenic interferes with circadian rhythm and glutamine anaplerosis by NADH oscillatory imbalance in urothelial cells and urothelial cancer cells, predisposing them to malignant development.

Research progress on the regulatory mechanism of cell senescence in arsenic toxicity: a systematic review

As an element with metalloid properties, arsenic is pervasively present in the environment and is recognized as a potent carcinogen. Consequently, the issue of human arsenic exposure has become a significant concern within the global public health sector. Numerous studies have indicated that arsenic induces cellular senescence through various mechanisms, including triggering epigenetic alterations, inducing the senescence-associated secretory phenotype (SASP), promoting telomere shortening, and causing mitochondrial dysfunction. This article collates and summarizes the latest research advancements on the involvement of cellular senescence in arsenic toxicity and explores the mechanisms of arsenic-induced toxicity. This study aims to provide new perspectives and directions for future research on arsenic toxicity and the development of prevention and treatment strategies.

NBR1-mediated autophagic degradation of caspase 8 protects vascular endothelial cells against arsenite-induced apoptotic cell death

Vascular endothelial cells play a critical role in maintaining the health of blood vessels, but dysfunction can lead to cardiovascular diseases. The impact of arsenite exposure on cardiovascular health is a significant concern due to its potential adverse effects. This study aims to explore how NBR1-mediated autophagy in vascular endothelial cells can protect against oxidative stress and apoptosis induced by arsenite. Initially, our observations revealed that arsenite exposure increased oxidative stress and triggered apoptotic cell death in human umbilical vein endothelial cells (HUVECs). However, treatment with the apoptosis inhibitor Z-VAD-FMK notably reduced arsenite-induced apoptosis. Additionally, arsenite activated the autophagy pathway and enhanced autophagic flux in HUVECs. Interestingly, inhibition of autophagy exacerbated arsenite-induced apoptotic cell death. Our findings also demonstrated the importance of autophagy receptor NBR1 in arsenite-induced cytotoxicity, as it facilitated the recruitment of caspase 8 to autophagosomes for degradation. The protective effect of NBR1 against arsenite-induced apoptosis was compromised when autophagy was inhibited using pharmacological inhibitors or through genetic knockdown of essential autophagy genes. Conversely, overexpression of NBR1 facilitated caspase 8 degradation and reduced apoptotic cell death in arsenite-treated HUVECs. In conclusion, our study highlights the vital role of NBR1-mediated autophagic degradation of caspase 8 in safeguarding vascular endothelial cells from arsenite-induced oxidative stress and apoptotic cell death. Targeting this pathway could offer a promising therapeutic approach to mitigate cardiovascular diseases associated with arsenite exposure.

CircRNA_0026344 via miR-21 is involved in cigarette smoke-induced autophagy and apoptosis of alveolar epithelial cells in emphysema

Cigarette smoke (CS), a main source of indoor air pollution, is a primary risk factor for emphysema, and aberrant cellular autophagy is related to the pathogenesis of emphysema. Circular RNAs (circRNAs) affect the expression of mRNAs via acting as microRNA (miRNA) sponges, but their role in emphysema progression is not established. In the present investigation, CS, acting on alveolar epithelial cells, caused higher levels of miR-21, p-ERK, and cleaved-caspase 3 and led to lower levels of circRNA_0026344 and PTEN, which induced autophagy and apoptosis. miR-21 suppressed the expression of PTEN, which was involved in the regulation of autophagy and apoptosis. Further, in alveolar epithelial cells, overexpression of circRNA_0026344 blocked cigarette smoke extract (CSE)-induced autophagy and apoptosis, but this blockage was reversed by upregulation of miR-21 with a mimic. These results demonstrated that, in alveolar epithelial cells, CS decreases circRNA_0026344 levels, which sponge miR-21 to inhibit the miR-21 target, PTEN, which, in turn, activates ERK and thereby promotes autophagy and apoptosis, leading to emphysema. Thus, for emphysema, circRNA_0026344 regulates the PTEN/ERK axis by sponging miR-21, which is associated with the CS-induced autophagy and apoptosis of alveolar epithelial cells. In sum, the present investigation identifies a novel mechanism for CS-induced emphysema and provides information useful for the diagnosis and treatment of CS-induced emphysema.

Caloric restriction induced epigenetic effects on aging

Aging is the subject of many studies, facilitating the discovery of many interventions. Epigenetic influences numerous life processes by regulating gene expression and also plays a crucial role in aging regulation. Increasing data suggests that dietary changes can alter epigenetic marks associated with aging. Caloric restriction (CR)is considered an intervention to regulate aging and prolong life span. At present, CR has made some progress by regulating signaling pathways associated with aging as well as the mechanism of action of intercellular signaling molecules against aging. In this review, we will focus on autophagy and epigenetic modifications to elaborate the molecular mechanisms by which CR delays aging by triggering autophagy, epigenetic modifications, and the interaction between the two in caloric restriction. In order to provide new ideas for the study of the mechanism of aging and delaying aging.

The Dual Role of Oxidative-Stress-Induced Autophagy in Cellular Senescence: Comprehension and Therapeutic Approaches

The contemporary lifestyle of the last decade has undeniably caused a tremendous increase in oxidative-stress-inducing environmental sources. This phenomenon is not only connected with the rise of ROS levels in multiple tissues but is also associated with the induction of senescence in different cell types. Several signaling pathways that are associated with the reduction in ROS levels and the regulation of the cell cycle are being activated, so that the organism can battle deleterious effects. Within this context, autophagy plays a significant role. Through autophagy, cells can maintain their homeostasis, as if it were a self-degradation process, which removes the "wounded" molecules from the cells and uses their materials as a substrate for the creation of new useful cell particles. However, the role of autophagy in senescence has both a "dark" and a "bright" side. This review is an attempt to reveal the mechanistic aspects of this dual role. Nanomedicine can play a significant role, providing materials that are able to act by either preventing ROS generation or controllably inducing it, thus functioning as potential therapeutic agents regulating the activation or inhibition of autophagy.

Risk Compounds, Preclinical Toxicity Evaluation, and Potential Mechanisms of Chinese Materia Medica-Induced Cardiotoxicity

Chinese materia medica (CMM) has been applied for the prevention and treatment of diseases for thousands of years. However, arrhythmia, myocardial ischemia, heart failure, and other cardiac adverse reactions during CMM application were gradually reported. CMM-induced cardiotoxicity has aroused widespread attention. Our review aimed to summarize the risk compounds, preclinical toxicity evaluation, and potential mechanisms of CMM-induced cardiotoxicity. All relevant articles published on the PubMed, Embase, and China National Knowledge Infrastructure (CNKI) databases for the latest twenty years were searched and manually extracted. The risk substances of CMM-induced cardiotoxicity are relatively complex. A single CMM usually contains various risk compounds, and the same risk substance may exist in various CMM. The active and risk substances in CMM may be transformed into each other under different conditions, such as drug dosage, medication methods, and body status. Generally, the risk compounds of CMM-induced cardiotoxicity can be classified into alkaloids, terpenoids, steroids, heavy metals, organic acids, toxic proteins, and peptides. Traditional evaluation methods of chemical drug-induced cardiotoxicity primarily include cardiac function monitoring, endomyocardial biopsy, myocardial zymogram, and biomarker determination. In the preclinical stage, CMM-induced cardiotoxicity should be systematically evaluated at the overall, tissue, cellular, and molecular levels, including cardiac function, histopathology, cytology, myocardial zymogram, and biomarkers. Thanks to the development of systematic biology, the higher specificity and sensitivity of biomarkers, such as genes, proteins, and metabolic small molecules, are gradually applied for evaluating CMM-induced cardiotoxicity. Previous studies on the mechanisms of CMM-induced cardiotoxicity focused on a single drug, monomer or components of CMM. The interaction among ion homeostasis (sodium, potassium, and calcium ions), oxidative damage, mitochondrial injury, apoptosis and autophagy, and metabolic disturbance is involved in CMM-induced cardiotoxicity. Clarification on the risk compounds, preclinical toxicity evaluation, and potential mechanisms of CMM-induced cardiotoxicity must be beneficial to guide new CMM development and post-marketed CMM reevaluation.

A Litopenaeus vannamei p70S6K gene is involved in the antioxidative and apoptosis under low temperature

p70S6K is involved in cellular response, such as tumor metastases, the immune response and tissue repair in vertebrates. The role of p70S6K in these physiological processes in crustaceans remains, however, unknown. In this study, the Lvp70S6K was identified, containing a 5' UTR of 294 bp, an ORF of 1494 bp ad a 3' UTR of 211 bp, encoding 497 amino acids with a theoretical molecular weight of 70 kDa and an estimated isoelectric point of (pI) of 5.16. The multiple alignment found that Lvp70S6K was highly homologous with other invertebrates. Lvp70S6K mRNA was detected in all the tested tissues and the Lvp70S6K expression levels was significantly down-regulated and reached the lowest level (0.44-fold, p < 0.01) at 1.5 h after low temperature stress. The subcellular localization of Lvp70S6K could be detected in cytoplasm. ROS production was significantly up-regulation (1.19-fold, p < 0.01), total hemocyte count (THC) was significantly down-regulation (0.22-fold, p < 0.01), apoptosis rate was markedly increased (1.09-fold, p < 0.01), apoptosis-related genes of LvPDCD4 (1.61-fold, p < 0.01) and LvCyt.C (1.23-fold, p < 0.01) were up-regulated, and anti-apoptotic gene of LvBcl-2 (0.69-fold, p < 0.01), LvIAP1 (0.68-fold, p < 0.01) and LvIAP2 (0.45-fold, p < 0.01) were decreased after low temperature stress in hemolymph of Lvp70S6K-silenced shrimp at 1.5 h. Silencing of LvPTEN significantly increased Lvp70S6K, LvPI3K, LvAKT and LvmTOR expression. In summary, these results indicated that Lvp70S6K play a crucial role in oxidative and apoptosis, which was able to negatively regulate by PTEN.

Long-term arsenite exposure decreases autophagy by increased release of Nrf2 in transformed human keratinocytes

Autophagy dysfunction in arsenite toxicity plays critical roles in cancer development and progression. However, the precise mechanisms of arsenite-induced skin cancer by blocking autophagy remain uncertain. Herein, this study investigated molecular mechanisms of arsenite-induced autophagy dysfunction mediated by nuclear factor erythroid-2 related factor 2 (Nrf2) in human keratinocyte (HaCaT) cells. The effects of long-term arsenite exposure on Nrf2 activation and autophagy were established using a siRNA interference assay and western blots. A specific siRNA of Nrf2 was used to verify that autophagy induced by arsenite can be influenced by Nrf2. Specific inhibitors of PI3K (LY294002) and mTOR (Rapamycin) and siRNA of Nrf2 were employed to verify that upregulation of Nrf2 correlated with activating the PI3K/Akt pathway. Downstream mTOR and Bcl2 were upregulated by Nrf2 signaling, inhibiting autophagy initiation in arsenite-exposed HaCaT cells. In conclusion, our data suggest that long-term exposure to arsenite promotes Nrf2 upregulation via the PI3K/Akt pathway and, along with upregulation of downstream mTOR and Bcl2, contributes to autophagy dysfunction in transformed HaCaT cells. This work provides new insights into the mechanisms underlying arsenite-induced autophagy dysfunction in cancer promotion and malignancy progression.

Arsenite induces testicular oxidative stress in vivo and in vitro leading to ferroptosis

Ferroptosis is a newly identified form of cell death characterized by accumulation of intracellular iron and requirement of lipid peroxidation. However, whether arsenite triggers testicular cell death via ferroptosis remains unclear. In this study, after administrating of adult male mice with 0.5, 5 and 50 mg/L arsenite for six months via drinking water, the results showed that arsenite caused the pathological changes in mouse testis and significantly reduced the number of sperm. Mitochondrial injuries were observed as the major ultrastructural damages induced by arsenite, and these damages were accompanied by the apparent mitochondrial oxidative damage in the testis, manifested by accumulation of iron, production of reactive oxygen species and lipid peroxidation products. We also demonstrated that arsenite significantly activated ferroptosis-related signal pathways in the mouse testis. To further verify the results obtained in the animal model, GC-2spd cells were employed as the in vitro culture system. Consistently, the results revealed arsenite remarkably triggered the ferroptotic cell death in vitro, and inhibition of ferroptosis by ferrostatin-1 could attenuate this adverse effect in cells. These findings together indicate that arsenite can trigger oxidative stress thus leading to testicular cell death by ferroptosis, suggesting that inhibition of ferroptosis would be a potential strategy for treatment of arsenite-related male reproductive toxicity.

PINK1/Parkin-mediated mitophagy is involved in NaAsO2-induced apoptosis of human hepatic cells through activation of ERK signaling

Mitochondrial dysfunction has been demonstrated as one key event in arsenic-induced hepatic cell damage though the exact molecular target remains unknown. Here we examined NaAsO₂-induced mitochondrial damage in the L-02 cell led to mitochondrial depolarization and cytochrome c release, mitophagy, apoptosis in a dose response manner. Mitophagy was measured by analysis of PINK1, Parkin, LC3-II and p62 protein. Apoptosis was assessed by measuring Annexin V. Using the mitophagy inhibitor cyclosporine A (CsA) or ERK inhibitor (PD98059), the balance between mitophagy and apoptosis were further explored. When CsA was used prior to cell exposure to NaAsO₂, it was found that the levels of mitophagy were decreased as expected and apoptosis was increased in response. CsA alone had no effect on the apoptosis rate. When the ERK signaling inhibitor PD98059 was used, there was a similar result that mitophagy was reduced though in contrast with CsA the apoptosis rate was also decreased compared with NaAsO₂ alone. This result, along with the increased levels of ERK measured here in response to NaAsO₂, indicates that ERK activation is a second key molecular response to NaAsO₂ through the activation of both apoptosis and mitophagy. Thus the results with CsA indicate that the likely key biological event in NaAsO₂ toxicity is at the level of the mitochondria leading to cytochrome c release and apoptosis. Mitophagy is increased in response to a secondary effect of NaAsO₂ on ERK signaling that activates both mitophagy and apoptosis. The activation of mitophagy allows the cell to avoid some apoptosis. When ERK signaling is inhibited by PD98059 both the levels of apoptosis and mitophagy are decreased compared with the response produced by NaAsO₂ alone in comparison to the inhibition of mitophagy by CsA that reduced mitophagy but dramatically increased apoptosis in response.

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

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

EGCG regulates CTR1 expression through its pro-oxidative property in non-small-cell lung cancer cells

Copper transporter 1 (CTR1) plays an important role in increasing cisplatin intake. Our previous studies showed that CTR1 expression was upregulated by (-)-epigallocatechin-3-gallate (EGCG), a green tea polyphenol, therefore enhanced cisplatin sensitivity in ovary cancer and non-small-cell lung cancer (NSCLC) cells. In the current study in the non-small-cell lung cancer cells, we uncovered a potential mechanism of EGCG-induced CTR1 through its pro-oxidative property. We found that EGCG increased reactive oxygen species (ROS) generation, while in the presence of ROS scavenger N-acetyl-cysteine (NAC), ROS production was eliminated. Changes of CTR1 expression were consistent with the ROS level. Simultaneously, EGCG downregulated ERK1/2 while upregulated lncRNA nuclear paraspeckle assembly transcript 1 (NEAT1) through ROS to induce CTR1 expression. Besides, in a nude mouse xenografts model, EGCG treatment raised ROS level, expression of CTR1 and NEAT1 in tumor tissue. Also, ERK1/2 and p-ERK1/2 were suppressed as well. Taken together, these results suggested a novel mechanism that EGCG mediated ROS to regulate CTR1 expression through the ERK1/2/NEAT1 signaling pathway, which provided more possibilities for EGCG as a natural agent in adjuvant therapy of lung cancer.

MiR-132 controls pancreatic beta cell proliferation and survival through Pten/Akt/Foxo3 signaling

Objective

MicroRNAs (miRNAs) play an integral role in maintaining beta cell function and identity. Deciphering their targets and precise role, however, remains challenging. In this study, we aimed to identify miRNAs and their downstream targets involved in the regeneration of islet beta cells following partial pancreatectomy in mice.

Methods

RNA from laser capture microdissected (LCM) islets of partially pancreatectomized and sham-operated mice were profiled with microarrays to identify putative miRNAs implicated in beta cell regeneration. Altered expression of the selected miRNAs, including miR-132, was verified by RT-PCR. Potential targets of miR-132 were selected through bioinformatic data mining. Predicted miR-132 targets were validated for their changed RNA, protein expression levels, and signaling upon miR-132 knockdown and/or overexpression in mouse MIN6 and human EndoC-βH1 insulinoma cells. The ability of miR-132 to foster beta cell proliferation in vivo was further assessed in pancreatectomized miR-132^−/− and control mice.

Results

Partial pancreatectomy significantly increased the number of BrdU⁺/insulin⁺ islet cells. Microarray profiling revealed that 14 miRNAs, including miR-132 and -141, were significantly upregulated in the LCM islets of the partially pancreatectomized mice compared to the LCM islets of the control mice. In the same comparison, miR-760 was the only downregulated miRNA. The changed expression of these miRNAs in the islets of the partially pancreatectomized mice was confirmed by RT-PCR only in the case of miR-132 and -141. Based on previous knowledge of its function, we focused our attention on miR-132. Downregulation of miR-132 reduced the proliferation of MIN6 cells while enhancing the levels of pro-apoptotic cleaved caspase-9. The opposite was observed in miR-132 overexpressing MIN6 cells. Microarray profiling, RT-PCR, and immunoblotting of the latter cells demonstrated their downregulated expression of Pten with concomitant increased levels of pro-proliferative factors phospho-Akt and phospho-Creb and inactivation of pro-apoptotic Foxo3a via its phosphorylation. Downregulation of Pten was further confirmed in the LCM islets of pancreatectomized mice compared to the sham-operated mice. Moreover, overexpression of miR-132 correlated with increased proliferation of EndoC-βH1 cells. The regeneration of beta cells following partial pancreatectomy was lower in the miR-132/212^−/− mice than the control littermates.

Conclusions

This study provides compelling evidence about the critical role of miR-132 for the regeneration of mouse islet beta cells through the downregulation of its target Pten. Hence, the miR-132/Pten/Akt/Foxo3 signaling pathway may represent a suitable target to enhance beta cell mass.

•

miR-132 is induced in mouse islets upon partial pancreatectomy.

•

miR-132 promotes regeneration of β-cells in vivo following partial pancreatectomy.

•

miR-132 fosters in vitro proliferation/survival through Pten/Akt/Foxo3 signaling.

•

Downstream targets of miR-132 were identified in pancreatic β-cells.

•

miR-132^−/− mice have impaired β-cell proliferation.

Arsenite exposure suppresses adipogenesis, mitochondrial biogenesis and thermogenesis via autophagy inhibition in brown adipose tissue

Arsenite, a trivalent form of arsenic, is an element that occurs naturally in the environment. Humans are exposed to high dose of arsenite through consuming arsenite-contaminated drinking water and food, and the arsenite can accumulate in the human tissues. Arsenite induces oxidative stress, which is linked to metabolic disorders such as obesity and diabetes. Brown adipocytes dissipating energy as heat have emerging roles for obesity treatment and prevention. Therefore, understanding the pathophysiological role of brown adipocytes can provide effective strategies delineating the link between arsenite exposure and metabolic disorders. Our study revealed that arsenite significantly reduced differentiation of murine brown adipocytes and mitochondrial biogenesis and respiration, leading to attenuated thermogenesis via decreasing UCP1 expression. Oral administration of arsenite in mice resulted in heavy accumulation in brown adipose tissue and suppression of lipogenesis, mitochondrial biogenesis and thermogenesis. Mechanistically, arsenite exposure significantly inhibited autophagy necessary for homeostasis of brown adipose tissue through suppression of Sestrin2 and ULK1. These results clearly confirm the emerging mechanisms underlying the implications of arsenite exposure in metabolic disorders.

Effects of Ischemic Post-Conditioning on the Expressions of LC3-II and Beclin-1 in the Hippocampus of Rats After Cerebral Ischemia and Reperfusion

Objective

To investigate the effects of postconditioning ischemia on the expressions of the hippocampus neuron autophagy-related proteins LC3-II and Beclin-1 in rats following cerebral ischemia reperfusion.

Methods

A total of 128 male Sprague-Dawley rats were randomly divided into 4 groups: control, cerebral ischemia-reperfusion (IR), cerebral ischemia post-conditioning group (IP), and PI3K/Akt inhibitor (LY294002). The rat cerebral ischemia model was established by the improved Pulsinelli four vessel occlusion method. The durations across the platform and escape latent period were recorded using the water maze experiment. The changes in cell morphology and the number of surviving hippocampal neurons were detected by hematoxylin-eosin (HE) staining. The cells with Beclin-1 and LC3-II in the hippocampal region were detected by immunohistochemical staining and Western blotting.

Results

When compared with the IR at 48 and 72 h, the number of platform passes increased and the escape latency time was shortened. Consequently, the HE staining detected positive cells with LC3-II and Beclin-1 increased in number at each time point in immunohistochemistry and the expressions of the LC3-II and Beclin-1 proteins were improved in the IP (P < 0.05).

Conclusions

Cerebral ischemic post-conditioning promoted the expressions of autophagy-related proteins LC3-II and Beclin-1 while relieving the injuries caused by cerebral ischemia reperfusion.

Autophagy regulation and its role in normal and malignant hematopoiesis

Autophagy, the molecular machinery of self-eating, plays a dual role of a tumor promoter and tumor suppressor. This mechanism affects different clinical responses in cancer cells. Autophagy is targeted for treating patients resistant to chemotherapy or radiation. Limited reports investigate the significance of autophagy in cancer therapy, the regulation of hematopoietic and leukemic stem cells and leukemia formation. In the current review, the role of autophagy is discussed in various stages of hematopoiesis including quiescence, self-renewal, and differentiation.

Alpha-lipoic acid alleviated 6-OHDA-induced cell damage by inhibiting AMPK/mTOR mediated autophagy

Oxidative stress and autophagy are involved in the pathogenesis of Parkinson's disease. The relationship between oxidative stress and autophagy is a hot spot of scientific research. Alpha-lipoic acid (ALA) is a natural antioxidant. ALA has been reported to reduce oxidative stress and apoptosis in PD models, but its role in autophagy regulation of PD has been reported very little. In this study, we investigated the protective effects of ALA on 6-OHDA induced neurotoxicity, and explored the potential mechanisms associated with the crosstalk between oxidative stress and autophagy. Our results showed that 6-OHDA induced accumulation of ROS in SH-SY5Y cells, accompanied by excessive autophagy and apoptosis. ALA protected against 6-OHDA induced neuronal death through inhibition of oxidative stress and autophagy. Furthermore, we found that ALA inhibited AMPK phosphorylation while activated mTOR phosphorylation thereby blocking AMPK/mTOR signaling pathway involved autophagy. In conclusion, ALA alleviated 6-OHDA induced cell injury possibly by inhibiting autophagy mediated by AMPK/mTOR pathway.

Toxicant-mediated redox control of proteostasis in neurodegeneration

Disruption in redox signaling and control of cellular processes has emerged as a key player in many pathologies including neurodegeneration. As protein aggregations are a common hallmark of several neuronal pathologies, a firm understanding of the interplay between redox signaling, oxidative and free radical stress, and proteinopathies is required to sort out the complex mechanisms in these diseases. Fortunately, models of toxicant-induced neurodegeneration can be utilized to evaluate and report mechanistic alterations in the proteostasis network (PN). The epidemiological links between environmental toxicants and neurological disease gives further credence into characterizing the toxicant-mediated PN disruptions observed in these conditions. Reviewed here are examples of mechanistic interaction between oxidative or free radical stress and PN alterations. Additionally, investigations into toxicant-mediated PN disruptions, specifically focusing on environmental metals and pesticides, are discussed. Finally, we emphasize the need to distinguish whether the presence of protein aggregations are contributory to phenotypes related to neurodegeneration, or if they are a byproduct of PN deficiencies.

Oxidative Stress and Autophagy

Living in a complex environment, humans are always faced with various external stimuli and internal changes including oxidative stress and tissue damage. To adapt to these stimuli, maintain physiological stability, and ensure survival, cells in the body initiate a series of interactive and regulatory response pathways. For example, increased reactive oxygen species in the body can induce autophagy through a variety of signalling pathways. This section will focus on ROS-mediated regulation of autophagy through PI3K/Akt, AMPK, JNK, ERK, ATG4, and other pathways.

Cmk2 kinase is essential for survival in arsenite by modulating translation together with RACK1 orthologue Cpc2 in Schizosaccharomyces pombe

Different studies have demonstrated multiple effects of arsenite on human physiology. However, there are many open questions concerning the mechanism of response to arsenite. Schizosaccharomyces pombe activates the Sty1 MAPK pathway as a common response to several stress conditions. The specificity of the response is due to the activation of different transcription factors and specific targets such the Cmk2 MAPKAP kinase. We have previously shown that Cmk2 is phosphorylated and activated by the MAPK Sty1 in response to oxidative stress. Here, we report that Cmk2 kinase is specifically necessary to overcome the stress caused by metalloid agents, in particular arsenite. Deletion of cmk2 increases the protein level of various components of the MAPK pathway. Moreover, Cmk2 negatively regulates translation through the Cpc2 kinase: the RACK1 orthologue in fission yeast. RACK1 is a receptor for activated C-kinase. Interestingly, RACK1 is a constituent of the eukaryotic ribosome specifically localized in the head region of the 40 S subunit. Cmk2 controls arsenite response through Cpc2 and it does so through Cpc2 ribosomal function, as observed in genetic analysis using a Cpc2 mutant unable to bind to ribosome. These findings suggest a role for Cmk2 in regulating translation and facilitating adaptation to arsenite stress in the ribosome.

Stress granules counteract senescence by sequestration of PAI-1

Cellular senescence is a physiological response by which an organism halts the proliferation of potentially harmful and damaged cells. However, the accumulation of senescent cells over time can become deleterious leading to diseases and physiological decline. Our data reveal a novel interplay between senescence and the stress response that affects both the progression of senescence and the behavior of senescent cells. We show that constitutive exposure to stress induces the formation of stress granules (SGs) in proliferative and presenescent cells, but not in fully senescent cells. Stress granule assembly alone is sufficient to decrease the number of senescent cells without affecting the expression of bona fide senescence markers. SG‐mediated inhibition of senescence is associated with the recruitment of the plasminogen activator inhibitor‐1 (PAI‐1), a known promoter of senescence, to these entities. PAI‐1 localization to SGs increases the translocation of cyclin D1 to the nucleus, promotes RB phosphorylation, and maintains a proliferative, non‐senescent state. Together, our data indicate that SGs may be targets of intervention to modulate senescence in order to impair or prevent its deleterious effects.

Regulation of autophagy factors by oxidative stress and cardiac enzymes imbalance during arsenic or/and copper induced cardiotoxicity in Gallus gallus

Basal autophagy has an indispensable role in the functioning and maintenance of cardiac geometry under physiological conditions. Recently, increasing evidence has demonstrated that arsenic (As)/copper (Cu) play important roles in the autophagy of the heart. The current study was to evaluate whether oxidative damage by As or/and Cu was correlated with autophagy through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway in the heart of birds. Arsenic trioxide (30mg/kg) or/and cupric sulfate (300mg/kg) were administered in a basal diet to male Hy-line chickens (one-day-old) for 12 weeks. The results showed that heart weight/body weight ratio decreased in the As + Cu group only at 4, 8 and 12 weeks. Moreover, we observed that As or/and Cu decreased high-density lipoprotein cholesterol (HDL-C) concentrations, increased total cholesterol (T-CHO) concentrations and cardiac enzymes activities in the serum. On the other hand, As or/and Cu significantly reduced the activities of total antioxidant (T-AOC), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px)) along with decreased nonenzymic antioxidant (glutathione (GSH)) concentrations and increased malondialdehyde (MDA) concentrations in the heart. Furthermore, As or/and Cu could induce autophagy in the heart of chickens through decreased mRNA levels of TORC1, TORC2, microtubule associated light chains 3-I (LC3-I) and increased PI3K, AKT1, Beclin1, autophagy associated gene 4B (Atg4B), microtubule associated light chains 3-II (LC3-II), autophagy associated gene 5 (Atg5) and Dynein. Meanwhile, ultrastructural examinations showed that As/Cu could result in the appearance of autolygosomes, autophagic vacuoles and double-membrane structures in the heart. In conclusion, As or/and Cu induced cardiac damage and autophagy via elevating cardiac enzymes activities, inducing oxidative stress and activating the PI3K/AKT/mTORC pathway in heart of chickens. Moreover, As and Cu had a possible synergistic relationship in the heart of chickens.

Brain-derived neurotrophic factor: a mediator of inflammation-associated neurogenesis in Alzheimer's disease

In early- or late-onset Alzheimer's disease (AD), inflammation, which is triggered by pathologic conditions, influences the progression of neurodegeneration. Brain-derived neurotrophic factor (BDNF) has emerged as a crucial mediator of neurogenesis, because it exhibits a remarkable activity-dependent regulation of expression, which suggests that it may link inflammation to neurogenesis. Emerging evidence suggests that acute and chronic inflammation in AD differentially modulates neurotrophin functions, which are related to the roles of inflammation in neuroprotection and neurodegeneration. Recent studies also indicate novel mechanisms of BDNF-mediated neuroprotection, including the modulation of autophagy. Numerous research studies have demonstrated reverse parallel alterations between proinflammatory cytokines and BDNF during neurodegeneration; thus, we hypothesize that one mechanism that underlies the negative impact of chronic inflammation on neurogenesis is the reduction of BDNF production and function by proinflammatory cytokines.

Inhibition of miR-128-3p by Tongxinluo Protects Human Cardiomyocytes from Ischemia/reperfusion Injury via Upregulation of p70s6k1/p-p70s6k1

Background and Aims: Tongxinluo (TXL) is a multifunctional traditional Chinese medicine that has been widely used to treat cardiovascular and cerebrovascular diseases. However, no studies have explored whether TXL can protect human cardiomyocytes (HCMs) from ischemia/reperfusion (I/R) injury. Reperfusion Injury Salvage Kinase (RISK) pathway activation was previously demonstrated to protect the hearts against I/R injury and it is generally activated via Akt or (and) Erk 1/2, and their common downstream protein, ribosomal protein S6 kinase (p70s6k). In addition, prior studies proved that TXL treatment of cells promoted secretion of VEGF, which could be stimulated by the increased phosphorylation of one p70s6k subtype, p70s6k1. Consequently, we hypothesized TXL could protect HCMs from I/R injury by activating p70s6k1 and investigated the underlying mechanism.

Methods and Results: HCMs were exposed to hypoxia (18 h) and reoxygenation (2 h) (H/R), with or without TXL pretreatment. H/R reduced mitochondrial membrane potential, increased bax/bcl-2 ratios and cytochrome C levels and induced HCM apoptosis. TXL preconditioning reversed these H/R-induced changes in a dose-dependent manner and was most effective at 400 μg/mL. The anti-apoptotic effect of TXL was abrogated by rapamycin, an inhibitor of p70s6k. However, inhibitors of Erk1/2 (U0126) or Akt (LY294002) failed to inhibit the protective effect of TXL. TXL increased p70s6k1 expression and, thus, enhanced its phosphorylation. Furthermore, transfection of cardiomyocytes with siRNA to p70s6k1 abolished the protective effects of TXL. Among the micro-RNAs (miR-145-5p, miR-128-3p and miR-497-5p) previously reported to target p70s6k1, TXL downregulated miR-128-3p in HCMs during H/R, but had no effects on miR-145-5p and miR-497-5p. An in vivo study confirmed the role of the p70s6k1 pathway in the infarct-sparing effect of TXL, demonstrating that TXL decreased miR-128-3p levels in the rat myocardium during I/R. Transfection of HCMs with a hsa-miR-128-3p mimic eliminated the protective effects of TXL.

Conclusions: The miR-128-3p/p70s6k1 signaling pathway is involved in protection by TXL against HCM apoptosis during H/R. Overexpression of p70s6k1 is, therefore, a potential new strategy for alleviating myocardial reperfusion injury.

Impaired autophagic flux and p62-mediated EMT are involved in arsenite-induced transformation of L-02 cells

Autophagy is a catabolic process essential for preserving cellular homeostasis, and the epithelial-to-mesenchymal transition (EMT) is involved during tissue development and cancer progression. In arsenite-treated human hepatic epithelial (L-02) cells, arsenite reduced the autophagic flux, which caused accumulation of p62, an adaptor and receptor of autophagy. Further, in arsenite-transformed L-02 cells, the levels of E-cadherin were attenuated, but the levels of vimentin, which is expressed in mesenchymal cells, and Snail, a transcription regulator of the EMT, were up-regulated. Thus, after chronic exposure of L-02 cells to arsenite, the impaired autophagic flux induced the accumulation of p62, which up-regulated the expression of Snail, a protein involved in arsenite-induced EMT of these cells. Knockdown of p62 by siRNA reversed the arsenite-induced EMT and decreased the capacities of arsenite-transformed L-02 cells for colony formation and invasion and migration. Therefore, in arsenite-induced transformation of L-02 cells, the accumulation of p62, by impairing autophagic flux, mediates the EMT via Snail. These results provide a previously unknown mechanism underlying arsenic toxicity and carcinogenicity.

Roles of PTEN with DNA Repair in Parkinson's Disease

Oxidative stress is considered to play key roles in aging and pathogenesis of many neurodegenerative diseases such as Parkinson’s disease, which could bring DNA damage by cells. The DNA damage may lead to the cell apoptosis, which could contribute to the degeneration of neuronal tissues. Recent evidence suggests that PTEN (phosphatase and tensin homolog on chromosome 10) may be involved in the pathophysiology of the neurodegenerative disorders. Since PTEN expression appears to be one dominant determinant of the neuronal cell death, PTEN should be a potential molecular target of novel therapeutic strategies against Parkinson’s disease. In addition, defects in DNA damage response and DNA repair are often associated with modulation of hormone signaling pathways. Especially, many observations imply a role for estrogen in a regulation of the DNA repair action. In the present review, we have attempted to summarize the function of DNA repair molecules at a viewpoint of the PTEN signaling pathway and the hormone related functional modulation of cells, providing a broad interpretation on the molecular mechanisms for treatment of Parkinson’s disease. Particular attention will be paid to the mechanisms proposed to explain the health effects of food ingredients against Parkinson’s disease related to reduce oxidative stress for an efficient therapeutic intervention.

MicroRNA-21 activation of ERK signaling via PTEN is involved in arsenite-induced autophagy in human hepatic L-02 cells

Autophagy, an evolutionarily conserved cellular process, has diverse physiological and pathological roles in biological functions. Whether autophagy is induced by arsenite, a well-established human carcinogen, and the molecular mechanisms involved, remain to be established. Further, microRNAs (miRNAs) act as regulators in various cancers, but how miRNAs regulate autophagy remains largely unexplored. We have found that, in human hepatic epithelial (L-02) cells, arsenite increases levels of autophagy-related proteins in a concentration- and time-dependent manner and elevates the number of autophagic vacuoles (AVs). Arsenite also activates the ERK pathway in a dose- and time-dependent manner. In L-02 cells exposed to arsenite, microRNA-21 (miRNA-21) is over-expressed, and its target proteins, PTEN, PDCD4, and Spry1, are decreased. Moreover, inhibition of miR-21 increases levels of PTEN, and reduces levels of Beclin 1 and LC3 II/I, indicating that miR-21 is involved in arsenite-induced autophagy. In addition, ectopic expression of PTEN blocks the effect of miR-21 on the arsenite-induced autophagy and decreases p-ERK levels. Also, ERK promotes the autophagy induced by arsenite. In sum, upon exposure of cells to arsenite, over-expression of miR-21 activates ERK through PTEN, factors that participate in arsenite-induced autophagy. This link, mediated through miRNAs, establishes a mechanism for the development of autophagy that is associated with arsenic toxicity. Such information contributes to an understanding of the liver toxicity caused by arsenite.