Autophagy plays a positive role in zinc-induced apoptosis in intestinal porcine epithelial cells

Contribution of zinc accumulation to ischemic brain injury and its mechanisms about oxidative stress, inflammation, and autophagy: an update

Ischemic stroke is a leading cause of death and disability worldwide, and presently, there is no effective neuroprotective therapy. Zinc is an essential trace element that plays important physiological roles in the central nervous system. Free zinc concentration is tightly regulated by zinc-related proteins in the brain under normal conditions. Disruption of zinc homeostasis, however, has been found to play an important role in the mechanism of brain injury following ischemic stroke. A large of free zinc releases from storage sites after cerebral ischemia, which affects the functions and survival of nerve cells, including neurons, astrocytes, and microglia, resulting in cell death. Ischemia-triggered intracellular zinc accumulation also disrupts the function of blood-brain barrier via increasing its permeability, impairing endothelial cell function, and altering tight junction levels. Oxidative stress and neuroinflammation have been reported to be as major pathological mechanisms in cerebral ischemia/reperfusion injury. Studies have showed that the accumulation of intracellular free zinc could impair mitochondrial function to result in oxidative stress, and form a positive feedback loop between zinc accumulation and reactive oxygen species production, which leads to a series of harmful reactions. Meanwhile, elevated intracellular zinc leads to neuroinflammation. Recent studies also showed that autophagy is one of the important mechanisms of zinc toxicity after ischemic injury. Interrupting the accumulation of zinc will reduce cerebral ischemia injury and improve neurological outcomes. This review summarizes the role of zinc toxicity in cellular and tissue damage following cerebral ischemia, focusing on the mechanisms about oxidative stress, inflammation, and autophagy.

CXCR3 Inhibition Blocks the NF-κB Signaling Pathway by Elevating Autophagy to Ameliorate Lipopolysaccharide-Induced Intestinal Dysfunction in Mice

Autophagy is a cellular catabolic process in the evolutionarily conservative turnover of intracellular substances in eukaryotes, which is involved in both immune homeostasis and injury repairment. CXCR3 is an interferon-induced chemokine receptor that participates in immune regulation and inflammatory responses. However, CXCR3 regulating intestine injury via autophagy along with the precise underlying mechanism have yet to be elucidated. In the current study, we employed an LPS-induced inflammatory mouse model and confirmed that CXCR3 knockout significantly attenuates intestinal mucosal structural damage and increases tight junction protein expression. CXCR3 knockout alleviated the LPS-induced increase in the expression of inflammatory factors including TNF-α, IL-6, p-65, and JNK-1 and enhanced autophagy by elevating LC3II, ATG12, and PINK1/Parkin expression. Mechanistically, the function of CXCR3 regarding autophagy and immunity was investigated in IPEC-J2 cells. CXCR3 inhibition by AMG487 enhanced autophagy and reduced the inflammatory response, as well as blocked the NF-κB signaling pathway and elevated the expression of the tight junction protein marker Claudin-1. Correspondingly, these effects were abolished by autophagy inhibition with the selective blocker, 3-MA. Moreover, the immunofluorescence assay results further demonstrated that CXCR3 inhibition-mediated autophagy blocked p65 nuclear translocation, and the majority of Claudin-1 was located at the tight junctions. In conclusion, CXCR3 inhibition reversed LPS-induced intestinal barrier damage and alleviated the NF-κB signaling pathway via enhancing autophagy. These data provided a theoretical basis for elucidating the immunoregulatory mechanism by targeting CXCR3 to prevent intestinal dysfunction.

Zinc Deficiency Induces Autophagy in HT-22 Mouse Hippocampal Neuronal Cell Line

Zinc is a trace metal vital for various functions in nerve cells, although the effect of zinc deficiency on neuronal autophagy remains unclear. This study aimed to elucidate whether zinc deficiency induced by treatment with N, N, N′, N′-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a zinc chelator, affects and alters autophagy activity. In cell viability assays, TPEN showed cytotoxicity in HT-22 cells. TPEN treatment also increased LC3-II levels and the ratio of LC3-II to LC3-I. Western blot analysis showed that phospho-AMP-activated protein kinase levels and the ratio of phospho-AMP-activated protein kinase to total AMP-activated protein kinase increased. Protein levels of the mammalian target of rapamycin and sirtuin 1 decreased following TPEN treatment. When TPEN-treated HT-22 cells were cotreated with autophagy inhibitors, 3-methyladenine (1 mM), or bafilomycin A1 (3 nM), the TPEN-induced decrease in cell viability was exacerbated. Cotreatment with chloroquine (10 μM) partially restored cell viability. The study showed that zinc deficiency induces autophagy and may be cytoprotective in neurons. We expect our results to add a new perspective to our understanding of the neuronal pathology related to zinc deficiency.

Zinc in Cognitive Impairment and Aging

Zinc, an essential micronutrient for life, was first discovered in 1869 and later found to be indispensable for the normal development of plants and for the normal growth of rats and birds. Zinc plays an important role in many physiological and pathological processes in normal mammalian brain development, especially in the development of the central nervous system. Zinc deficiency can lead to neurodegenerative diseases, mental abnormalities, sleep disorders, tumors, vascular diseases, and other pathological conditions, which can cause cognitive impairment and premature aging. This study aimed to review the important effects of zinc and zinc-associated proteins in cognitive impairment and aging, to reveal its molecular mechanism, and to highlight potential interventions for zinc-associated aging and cognitive impairments.

Anti-tumour activity of zinc ionophore pyrithione in human ovarian cancer cells through inhibition of proliferation and migration and promotion of lysosome-mitochondrial apoptosis

Zinc pyrithione (ZPT) is widely used as an antimicrobial. Zinc is a necessary trace element of the human whose homeostasis associated with several cancers. However, the anticancer effect of increased Zinc in ovarian cancer is still unclear. This study focussed on the anti-tumour effects of ZPT combined with Zinc in SKOV3 and SKOV3/DDP cells. The cell viability, apoptosis, migration, and invasion assays were detected by CCK-8, flow cytometry, wound healing and transwell assay, respectively. The distribution of Zinc in cells was monitored by staining of Zinc fluorescent dye and lysosome tracker. The changes in lysosomal membrane stability were reflected by acridine orange fluorescence and cathepsin D reposition. Expression of the proteins about invasion and apoptosis was evaluated by western blot. The results indicated that ZPT combined with Zinc could notably reduce cell viability, inhibit migration and invasion in SKOV3 and SKOV3/DDP cells. Besides, ZPT performed as a Zinc carrier targeted lysosomes, caused the increase of its membrane permeability and the release of cathepsin D accompanied by mitochondrial apoptosis in SKOV3/DDP cells. In conclusion, our work suggests that ZPT combined with Zinc could inhibit proliferation, migration, invasion, and promote apoptosis by trigger the lysosome-mitochondrial apoptosis pathway in ovarian carcinoma.

Effects of nonylphenol induced oxidative stress on apoptosis and autophagy in rat ovarian granulosa cells

Nonylphenol (NP) is a kind of environmental endocrine disruptors which is generally recognized to cause female reproductive toxicity, but its basic mechanism has not been fully elucidated. In this study, granulosa cells (GCs) were treated with 0-70 μM NP for 24 h, the cell viability of GCs was reduced significantly, as well as increased cell apoptosis with G2/M arrest. Furthermore, NP significantly induced autophagy and the production of reactive oxygen species (ROS). However, these phenomenons were inhibited by blocking the production of ROS with N-Acetyl-l-cysteine (NAC) administration. Intriguingly, the inhibition of autophagy with 3-Methyladenine (3-MA) could enhance the apoptosis induced by NP. Moreover, the down regulating of p-Akt/Akt, p-mTOR/mTOR and subsequent up-regulation of p-AMPK/AMPK induced by NP can be rescued by pretreatment of NAC. Our findings suggested that NP promotes rat ovarian GCs apoptosis and autophagy simultaneously, which may involve the activation of ROS-dependent Akt/AMPK/mTOR pathway. Whatever, the activation of autophagy is likely to develop a protective mechanism to improve the apoptosis of rat ovarian GCs induced by NP.

Interplay Between Autophagy and Zinc

Autophagy is a conserved catabolic process that plays an important role in cellular homeostasis. The study of the interplay between autophagy and zinc has gained interest over the last years. Multiple studies have indicated that zinc stimulates autophagy and is critical for basal and induced autophagy in mammalian cells. Conversely, autophagy is induced by zinc starvation in yeast. There are no studies analyzing the role of zinc in either Microautophagy or Chaperone-Mediated-Autophagy. The mechanisms by which zinc modulates autophagy are still poorly understood. Studies examining loss of function of genes involved in cellular zinc homeostasis have provided novel insights into the role of zinc in autophagy. Autophagy may help cells adapt to changes in zinc availability in medium by controlling zinc mobilization, recycling, and secretion. Zinc is a key player in toxic and protective autophagy.

Repression of deoxynivalenol-triggered cytotoxicity and apoptosis by mannan/β-glucans from yeast cell wall: Involvement of autophagy and PI3K-AKT-mTOR signaling pathway

Deoxynivalenol (DON) is the most common trichothecene distributed in food and feed. So far, much work has focused on investigating the cytotoxicity of DON, while there is few researches aimed at intervening in the toxic impacts on humans and livestock posed by DON. The objective of this study is to investigate the underlying mechanism of biomacromolecules mannan/β-glucans from yeast cell wall (BYCW) for their potency to impede the cytotoxicity and apoptosis caused by DON with porcine jejunum epithelial cell lines (IPEC-J2) used as a cell injury model. We analyzed the cell morphology, cell activity, oxidative stress, fluorescence intensity and expressions of proteins relevant to autophagy, apoptosis and PI3K-AKT-mTOR signaling pathway by using inverted microscopy, MTS, reactive oxygen species (ROS), glutathione (GSH) and malondialdehyde (MDA) assay, Annexin V-FITC / propidium iodide (PI) double staining and Western blot assay. The consequent data demonstrated that in the presence of BYCW, the cell morphology and activity were relatively ameliorated and that the oxidation damage was attenuated with DON-induced autophagy concomitantly decreased, which, furthermore, was found involved in the positive regulation on PI3K-AKT-mTOR signaling pathway by BYCW. In a word, BYCW possess an ability to repress the cytotoxicity and apoptosis induced by DON through the inhibition of autophagy via activating PI3K-AKT-mTOR signaling pathway.

Zinc and Autophagy in Age-Related Macular Degeneration

Zinc supplementation is reported to slow down the progression of age-related macular degeneration (AMD), but there is no general consensus on the beneficiary effect on zinc in AMD. As zinc can stimulate autophagy that is declined in AMD, it is rational to assume that it can slow down its progression. As melanosomes are the main reservoir of zinc in the retina, zinc may decrease the number of lipofuscin granules that are substrates for autophagy. The triad zinc–autophagy–AMD could explain some controversies associated with population studies on zinc supplementation in AMD as the effect of zinc on AMD may be modulated by genetic background. This aspect was not determined in many studies regarding zinc in AMD. Zinc deficiency induces several events associated with AMD pathogenesis, including increased oxidative stress, lipid peroxidation and the resulting lipofuscinogenesis. The latter requires autophagy, which is impaired. This is a vicious cycle-like reaction that may contribute to AMD progression. Promising results with zinc deficiency and supplementation in AMD patients and animal models, as well as emerging evidence of the importance of autophagy in AMD, are the rationale for future research on the role of autophagy in the role of zinc supplementation in AMD.

Inhibition of cell migration and induction of apoptosis by a novel class II histone deacetylase inhibitor, MCC2344

Epigenetic modifiers provide a new target for the development of anti-cancer drugs. The eraser histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase that targets various non-histone proteins such as transcription factors, nuclear receptors, cytoskeletal proteins, DNA repair proteins, and molecular chaperones. Therefore, it became an attractive target for cancer treatment. In this study, virtual screening was applied to the MicroCombiChem database with 1162 drug-like compounds to identify new HDAC6 inhibitors. Five compounds were tested in silico and in vitro as HDAC6 inhibitors. Both analyses revealed 1-cyclohexene-1-carboxamide, 2-hydroxy-4,4-dimethyl-N-1-naphthalenyl-6-oxo- (MCC2344) as the best HDAC6 inhibitor among the five ligands. The binding affinity of MCC2344 to HDAC6 was further confirmed by microscale thermophoresis. Additionally, the anti-cancer activity of MCC2344 was tested in several tumor cell lines. Leukemia cells were the most sensitive cells towards MCC2344, particularly the P-glycoprotein-overexpressing multidrug-resistant cell line CEM/ADR5000 exhibited remarkable collateral sensitivity towards MCC2344. Transcriptome analysis using microarray hybridization was performed for investigating downstream mechanisms of action of MCC2344 in leukemia cells. MCC2344 affected microtubule dynamics and suppressed cell migration in the wound healing assay as well as in a spheroid model by hyper-acetylation of tubulin and HSP-90. MCC2344 induced cell death in CEM/ADR5000 cells by activation of PARP, caspase-3, and p21 in addition to the downregulation of p62. MCC2344 significantly inhibited tumor growth in vivo in zebrafish larvae without mortality until 20 pM. We propose MCC2344 as a novel HDAC6 inhibitor for cancer treatment.

Deoxynivalenol-Induced Cytotoxicity and Apoptosis in IPEC-J2 Cells Through the Activation of Autophagy by Inhibiting PI3K-AKT-mTOR Signaling Pathway

With the purpose to explore the relationship between deoxynivalenol (DON)-induced apoptosis and autophagy and provide mechanistic explanations for the toxic effects of DON on IPEC-J2 cells, we determined the cell viability, cell morphology, apoptosis, and autophagy by using autophagy inhibitor 3-methyladenine (3-MA), PI3K pathway inhibitor LY294002, and activator 740Y-P. It turned out that 3-MA was able to attenuate the reduction of cell viability induced by DON. Moreover, 3-MA was capable of upregulating the expression of DON-induced autophagic protein p62 and downregulating the expressions of DON-induced autophagic protein LC3-II and apoptotic protein Bax, suggesting that autophagy is a driving mechanism for this apoptotic induction. The results of Annexin V-FITC/PI double staining indicated that DON could induce apoptosis by inhibiting the PI3K-AKT-mTOR signaling pathway. Subsequently, it was further confirmed by Western blot analysis that DON significantly decreased expressions of P-AKT/AKT, p-mTOR/mTOR, and autophagic protein p62, and increased expression of autophagy-related protein LC3-II, suggesting that DON triggered autophagy by inhibiting the PI3K-AKT-mTOR signaling pathway. To conclude, these data reveal that DON may induce cytotoxicity and apoptosis through the activation of autophagy by suppressing the PI3K-AKT-mTOR signaling pathway. This study provides new insights into the mechanisms by which DON incurs cytotoxic effects.

Protective effects of mannan/β-glucans from yeast cell wall on the deoxyniyalenol-induced oxidative stress and autophagy in IPEC-J2 cells

The aim of this study was to investigate the effects of biomacromolecules mannan/β-glucans from yeast cell wall (BYCW) to alleviate Deoxynivalenol(DON)-induced injury. Considering that DON has strong oxidizing effect and stimulates autophagy and apoptosis, we examined the effects of BYCW on consequent oxidative stress damage indicators, cells autophagy and apoptosis induced by DON using the porcine jejunum epithelial cell lines (IPEC-J2) as a cell culture model. The results showed that application of BYCW could reverse the decrease of cell viability by DON significantly, and suppress the levels of tumor necrosis factor-α (TNF-α) and interleukin-8 and -6 (IL-8 and IL-6), except IL-1β. Further experiments revealed that BYCW treatment counteracted the DON-induced down-regulation of intracellular glutathione (GSH) and up-regulation of reactive oxygen species (ROS) and malondialdehyde (MDA). Through western blot analysis, we observed that BYCW treatment was able to down-regulate the expression of autophagy protein LC3-II and up-regulate the expression of P62 protein against DON, which suggested that autophagy induced by DON may be suppressed. Altogether, these results indicated a potential ability of supplementation of BYCW to improve cell growth and metabolism as well as the preventive properties of BYCW against the DON-induced cell damage by activating antioxidant system.

Rapid Communication: Porcine CRTC3 gene clone, expression pattern, and its regulatory role in intestinal epithelial cells

In the current study, we aimed to clone the full-length cDNA of porcine CRTC3 (pCRTC3) gene and examine its expression pattern and function in intestinal epithelial cells. The full-length cDNA sequence of pCRTC3 was 2,173 bp (GenBank accession no. MF964215), with a 1,860-bp open reading frame encoding a 620-AA protein. Comparison of the deduced AA sequence with different species including human, mouse, rat, Papio, cattle, and rabbit showed 89% to 91.9% similarity. The pCRTC3 was highly expressed in small intestine and spleen, to a lesser degree in lung, liver, and adipose tissue, and was expressed at a low but detectable level in skeletal muscle, kidney, and heart. In addition, high protein levels of pCRTC3 were found in IPEC-J2 cells, in which pCRTC3 was mainly localized in cytoplasm. Furthermore, we demonstrated that knockdown of pCRTC3 significantly decreased the expression of the porcine tight junction-related genes including zonula occludens-1 (ZO-1), ZO-2, occludin, and claudin-1 by 57.88% (P < 0.01), 40.19% (P < 0.01), 51.59% (P < 0.01), and 35.70% (P < 0.05), respectively. Taken together, we first cloned the full-length sequence of pCRTC3 and revealed the tissue-specific expression pattern, localization, and function of pCRTC3 in regulating the expression of intestinal tight junction-related genes. This study could provide some useful information for understanding the function of CRTC3 in pigs.

Effects of Quercetin on Proliferation and H₂O₂-Induced Apoptosis of Intestinal Porcine Enterocyte Cells

Weanling stress and toxicosis, which are harmful to the health of pigs' intestines, are associated with oxidative stress. Quercetin (Que) is a polyphenolic compound that shows good anti-cancer, anti-inflammation and anti-oxidation effects. This study aimed to elaborate whether or not Que promotes IPEC-J2 (intestinal porcine enterocyte cells) proliferation and protects IPEC-J2 from oxidative damage. Thus, we examined the effects of Que on proliferation and H₂O₂-induced apoptosis in IPEC-J2. The results showed that Que increased IPEC-J2 viabililty, propelled cells from G1 phase into S phase and down-regulated gene levels of P27 and P21, respectively. Besides, H₂O₂-induced cell damage was alleviated by Que after different exposure times, and Que depressed apoptosis rate, reactive oxygen species (ROS) level and percentage of G1 phase cells and elevated the percentage of cells in G2 phase and S phase and mitochondrial membrane potential (Δψm) after IPEC-J2 exposure to H₂O₂. Meanwhile, Que reduced the value of Bax/Bcl-2 in H₂O₂ exposed cells. In low-degree oxidative damage cells, lipid peroxidation product malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were increased. In turn, Que could reverse the change of MDA content and SOD activity in low-degree damage cells. Nevertheless, catalase (CAT) activity was not changed in IPEC-J2 incubated with Que under low-degree damage conditions. Interestingly, relative expressive levels of the proteins claudin-1 and occludin were not altered under low-degree damage conditions, but Que could improve claudin-1 and occludin levels, slightly. This research indicates that Que can be greatly beneficial for intestinal porcine enterocyte cell proliferation and it protects intestinal porcine enterocyte cells from oxidation-induced apoptosis, and could be used as a potential feed additive for porcine intestinal health against pathogenic factor-induced oxidative damages and apoptosis.

Overview and Comparison of Intestinal Organotypic Models, Intestinal Cells, and Intestinal Explants Used for Toxicity Studies

The intestine is a complex organ formed of different types of cell distributed in different layers of tissue. To minimize animal experiments, for decades, researchers have been trying to develop in vitro/ex vivo systems able to mimic the cellular diversity naturally found in the gut. Such models not only help our understanding of the gut physiology but also of intestinal toxicity. This review describes the different systems used to evaluate the effects of drugs/contaminants on intestinal functions and compares their advantages and limitations. The comparison showed that the organotypic model is the best available model to perform intestinal toxicity studies, including on human tissues.