Sensitivity of mitochondrial DNA depleted ρ0 cells to H2O2 depends on the plasma membrane status

Circular RNA expression profile of H2O2 induced ferroptosis model of human coronary artery endothelial cells

Background and aims

Coronary artery disease (CAD) is among the most common type of cardiovascular diseases. The role of circular RNAs (circRNAs) and ferroptosis in CAD remains largely unexplored. The aim of this study was to evaluate the circRNAs expression profile in ferroptosis of human coronary artery endothelial cells (HCAECs).

Methods

The ferroptosis induced by H₂O₂-stimulated oxidative stress in HCAECs and the role of Ferrostatin-1 (Fer-1) was assessed by the levels of CCK8, oxidized and reduced glutathione (GSSH and GSH), ferrous irons, lactate dehydrogenase (LDH), malondialdehyde (MDA), lipid reactive oxygen species (Lipid ROS), PTGS2 and GPX4. The expression profile of circRNAs was characterized by RNA sequencing.

Results

LDH, MDA, Lipid ROS, ferrous ions, GSSH and PTGS2 were significantly increased, CCK8, GSH and GPX4 were significantly decreased in H₂O₂ induced cell damage. Moreover, Fer-1 increased CCK8, GSH and GPX4 levels and decreased LDH, MDA, Lipid ROS, GSSH and PTGS2 levels, which alleviated H₂O₂ induced cell damage. The circRNA-miRNA-mRNA network and circRNA-protein interactions network were constructed based on differentially expressed circRNAs. In total, 17 downregulated and 18 upregulated circRNAs were identified in H₂O₂ treated HCAECs by RNA sequencing. Parental genes of circRNAs were analyzed by KEGG and GO, detecting pathways related to ferroptosis. 10 differentially expressed circRNAs were verified by qRT-PCR.

Conclusions

These results provide new sight to the character of circRNAs in the progress of HCAECs ferroptosis and contribute a significant data for further investigating the potential mechanisms of CAD.

Oxytocin ameliorates KCC2 decrease induced by oral bacteria-derived LPS that affect rat primary cultured cells and PC-12 cells

Inflammation, especially neuroinflammation, which is caused by stress, leads to central nervous system (CNS) dysfunction. Because lipopolysaccharides (LPSs) cause neuroinflammation, we investigated the effect of LPSs to CNS. In PC-12 cells, LPSs derived from oral bacteria reduced the expression of KCC2, a Cl^- transporter. LPS derived from P. gingivalis (P. g) administered to rat primary cultured cells also reduced the KCC2 expression. However, LPSs derived from E. coli did not reduce the KCC2 expression. LPS treatment activated TLR4, IL-1β, and REST gene expressions, which led to KCC2 inactivation in PC-12 cells. The mechanism of KCC2 has been shown to play an important role in brain maturation, function (such as the GABA switch), and behavioral problems, we investigated the GABA function. We found that the GABA function was changed from inhibitory to excitatory by the LPS derived from P. g treatment. We demonstrated that the GSK3β also involved in the KCC2 reduction by LPS treatment. We show that oxytocin rescued the reduction in KCC2 expression caused by LPSs by inhibiting GSK3β signaling but vasopressin could not. Considered together, our results indicate that the LPSs from oral bacteria but not the LPS from E. coli increase the risk for brain disorders and oxytocin might be a candidate to overcome the abnormal behavior caused by brain disorders such as psychiatric disorders.

Decreased mitochondrial membrane potential is an indicator of radioresistant cancer cells

AIMS

To overcome radioresistant cancer cells, clinically relevant radioresistant (CRR) cells were established. To maintain their radioresistance, CRR cells were exposed 2 Gy/day of X-rays daily (maintenance irradiation: MI). To understand whether the radioresistance induced by X-rays was reversible or irreversible, the difference between CRR cells and those without MI for a year (CRR-NoIR cells) was investigated by the mitochondrial function as an index.

MAIN METHODS

Radiation sensitivity was determined by modified high density survival assay. Mitochondrial membrane potential (Δψm) was determined by 5,5',6,6'-tetrachloro-1,1', tetraethylbenzimidazolocarbo-cyanine iodide (JC-1) staining. Rapid Glucose-Galactose assay was performed to determine the shift in their energy metabolism from aerobic glycolysis to oxidative phosphorylation in CRR cells. Involvement of prohibitin-1 (PHB1) in Δψm was evaluated by knockdown of PHB1 gene followed by real-time PCR.

KEY FINDINGS

CRR cells that exhibited resistant to 2 Gy/day X-ray lost their radioresistance after more than one year of culture without MI for a year. In addition, CRR cells lost their radioresistance when the mitochondria were activated by galactose. Furthermore, Δψm were increased and PHB1 expression was down-regulated, in the process of losing their radioresistance.

SIGNIFICANCE

Our finding reveled that tune regulation of mitochondrial function is implicated in radioresistance phenotype of cancer cells. Moreover, as our findings indicate, though further studies are required to clarify the precise mechanisms underlying cancer cell radioresistance, radioresistant cells induced by irradiation and cancer stem cells that are originally radioresistant should be considered separately, the radioresistance of CRR cells is reversible.

Mitochondrial Dysfunction in Diseases, Longevity, and Treatment Resistance: Tuning Mitochondria Function as a Therapeutic Strategy

Mitochondria are very important intracellular organelles because they have various functions. They produce ATP, are involved in cell signaling and cell death, and are a major source of reactive oxygen species (ROS). Mitochondria have their own DNA (mtDNA) and mutation of mtDNA or change the mtDNA copy numbers leads to disease, cancer chemo/radioresistance and aging including longevity. In this review, we discuss the mtDNA mutation, mitochondrial disease, longevity, and importance of mitochondrial dysfunction in cancer first. In the later part, we particularly focus on the role in cancer resistance and the mitochondrial condition such as mtDNA copy number, mitochondrial membrane potential, ROS levels, and ATP production. We suggest a therapeutic strategy employing mitochondrial transplantation (mtTP) for treatment-resistant cancer.

MiR-7-5p Is Involved in Ferroptosis Signaling and Radioresistance Thru the Generation of ROS in Radioresistant HeLa and SAS Cell Lines

In cancer therapy, radioresistance or chemoresistance cells are major problems. We established clinically relevant radioresistant (CRR) cells that can survive over 30 days after 2 Gy/day X-ray exposures. These cells also show resistance to anticancer agents and hydrogen peroxide (H₂O₂). We have previously demonstrated that all the CRR cells examined had up-regulated miR-7-5p and after miR-7-5p knockdown, they lost radioresistance. However, the mechanism of losing radioresistance remains to be elucidated. Therefore, we investigated the role of miR-7-5p in radioresistance by knockdown of miR-7-5p using CRR cells. As a result, knockdown of miR-7-5p increased reactive oxygen species (ROS), mitochondrial membrane potential, and intracellular Fe²⁺ amount. Furthermore, miR-7-5p knockdown results in the down-regulation of the iron storage gene expression such as ferritin, up-regulation of the ferroptosis marker ALOX12 gene expression, and increases of Liperfluo amount. H₂O₂ treatment after ALOX12 overexpression led to the enhancement of intracellular H₂O₂ amount and lipid peroxidation. By contrast, miR-7-5p knockdown seemed not to be involved in COX-2 and glycolysis signaling but affected the morphology of CRR cells. These results indicate that miR-7-5p control radioresistance via ROS generation that leads to ferroptosis.

Effect of mtDNA depletion from C6 glioma cells and characteristics of the generated C6ρ0 cells

Malignant tumors of the central nervous system (CNS) are among the types of cancer with the poorest prognosis and glioma is the commonest primary CNS tumor. A mitochondrial DNA (mtDNA)-depleted cell line C6ρ0 was generated from C6 glioma cells after long-term exposure to ethidium bromide and 2′,3′-dideoxycytidine in order to determine the effect of mtDNA damage on cell proliferation and pathological changes in glioma cells. Single cell clones were isolated and identified after 42 days of incubation. Repopulated cybrids were formed when the clonal C6ρ0 cells were fused with rat platelets and no difference was observed in their growth in a selective medium without uridine and pyruvate compared with the growth of the parent C6 cells. Disruption of mtDNA resulted in changes in mitochondrial morphology, decreased cell proliferation, reduced intracellular reactive oxygen species and intracellular ATP, along with decreased mtDNA and mitochondrial membrane potential in C6ρ0 cells compared with the C6 cells. Taken together, C6ρ0 cells without mtDNA were established for the first time and their characteristics were compared with parent cells. This C6ρ0 cell line could be used to explore the contribution of mitochondrial dysfunction and mtDNA mutations in the pathogenesis of glioma.

Mitochondrial dysfunction promotes aquaporin expression that controls hydrogen peroxide permeability and ferroptosis

Most anti-cancer agents and radiotherapy exert their therapeutic effects via the production of free radicals. Ferroptosis is a recently described cell death process that is accompanied by iron-dependent lipid peroxidation. Hydrogen peroxide (H₂O₂) has been reported to induce cell death. However, it remains controversial whether H₂O₂-induced cell death is ferroptosis. In the present study, we aimed to elucidate the involvement of mitochondria in H₂O₂-induced ferroptosis and examined the molecules that regulate ferroptosis. We found that one mechanism underlying H₂O₂-induced cell death is ferroptosis, which occurs soon after H₂O₂ treatment (within 3 h after H₂O₂ treatment). We also investigated the involvement of mitochondria in H₂O₂-induced ferroptosis using mitochondrial DNA-depleted ρ⁰ cells because ρ⁰ cells produce more lipid peroxidation, hydroxyl radicals (^•OH), and are more sensitive to H₂O₂ treatment. We found that ρ⁰ cells contain high Fe²⁺ levels that lead to ^•OH production by H₂O₂. Further, we observed that aquaporin (AQP) 3, 5, and 8 bind nicotinamide-adenine dinucleotide phosphate oxidase 2 and regulate the permeability of extracellular H₂O₂, thereby contributing to ferroptosis. Additionally, the role of mitochondria in ferroptosis was investigated using mitochondrial transfer in ρ⁰ cells. When mitochondria were transferred into ρ⁰ cells, the cells exhibited no sensitivity to H₂O₂-induced cytotoxicity because of decreased Fe²⁺ levels. Moreover, mitochondrial transfer upregulated the mitochondrial quality control protein prohibitin 2 (PHB2), which contributes to reduced AQP expression. Our findings also revealed the involvement of AQP and PHB2 in ferroptosis. Our results indicate that H₂O₂ treatment enhances AQP expression, Fe²⁺ level, and lipid peroxidation, and decrease mitochondrial function by downregulating PHB2, and thus, is a promising modality for effective cancer treatment.

Lipid peroxidation increases hydrogen peroxide permeability leading to cell death in cancer cell lines that lack mtDNA

4-Hydroxynonenal (HNE) is an important product of plasma membrane lipid peroxidation, which is a cause of cell and tissue injury. Mitochondrial DNA (mtDNA)-depleted ρ⁰ cells were established using human cervical cancer and oral squamous cell carcinoma cell lines. We investigated the effect of reactive oxygen species in ρ⁰ cells, especially the mechanism of hydrogen peroxide (H₂ O₂ )-mediated cell death. These cell were subjected to high oxidative stress and, compared with their parental cells, showed greater sensitivity to H₂ O₂ and high lipid peroxidation. Upregulation of HNE in the plasma membrane was observed prior to the increase in intracellular H₂ O₂ . The amount of oxidized lipid present changed H₂ O₂ permeability and administration of oxidized lipid led to further cell death after treatment with H₂ O₂ . Expression levels of lipoxygenase ALOX genes (ie ALOX5, ALOX12, and ALOX15) were upregulated in ρ⁰ cells, as were expression levels of ALOX12 and ALOX15 proteins. ALOX5 protein was mainly distributed in the nucleus, while ALOX12 and ALOX15 proteins were distributed in the nucleus and the cytoplasm. Although expression of COX2 gene was upregulated, its protein expression did not increase. ALOX (especially ALOX15) may be involved in the sensitivity of cancer cells to treatment. These data offer promise for the development of novel anticancer agents by altering the oxidation state of the plasma membrane. Our results showed that lipid peroxidation status is important for H₂ O₂ sensitivity and that ALOX15 is involved in lipid peroxidation status.

Clinically relevant radioresistant cells exhibit resistance to H2O2 by decreasing internal H2O2 and lipid peroxidation

Radiation therapy is one of the choices to treat malignant tumors. In radiation therapy, existence of radiation-resistant cell is a major problem to overcome. We established clinically relevant radioresistant cells that had been obtained by exposing to 2 Gy/day X-rays for more than 30 days. These cells are resistant to 2 Gy/day X-ray exposure and anticancer agents. However, the underlying resistance mechanism remains unclear. We investigated the resistance of clinically relevant radioresistant cells to hydrogen peroxide (H₂O₂), confirming a degree of resistance. Neither catalase enzyme activity nor aquaporins appeared to be involved in H₂O₂ resistance. Mitochondrial DNA copy number, adenosine triphosphate (ATP) concentration, and plasma membrane potential were decreased. The timing of H₂O₂ intake was delayed and lipid peroxidation was decreased. Sensitivity of clinically relevant radioresistant cells to H₂O₂ was enhanced by 1-palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphocholine administration. These results suggest that the membrane status is a major factor conferring H₂O₂ resistance in clinically relevant radioresistant cells, and we should further investigate how membrane status could be used to enhance the therapeutic effect on cancer.

Data on the aquaporin gene expression differences among ρ0, clinically relevant radioresistant, and the parental cells of human cervical cancer and human tongue squamous cell carcinoma

We present data about mitochondrial DNA (mtDNA) copy number and aquaporin (AQP) gene expression in clinically radioresistant (CRR), ρ⁰, and their parental cells from human cervical cancer and human tongue squamous cell carcinoma. In both ρ⁰ and CRR cells, the mtDNA copy number was lower than for the parental strain. In addition, the obtained data suggest an association between the gene expression levels of AQP (1, 3, 8, and 9) and the difference in hydrogen peroxide (H₂O₂) sensitivity between ρ⁰ and CRR cells. Here, the composition of cell culture medium differs between CRR and ρ⁰ cells. To compare the gene expression of AQPs between ρ⁰ and CRR cells, therefore, we showed the data as the ratio to that in their parental cells.