Mitochondrial Dynamics Mediated by DRP1 and MFN2 Contributes to Cisplatin Chemoresistance in Human Ovarian Cancer SKOV3 cells

Targeted inhibition of branched-chain amino acid metabolism drives apoptosis of glioblastoma by facilitating ubiquitin degradation of Mfn2 and oxidative stress

Glioblastoma is one of the most challenging malignancies with high aggressiveness and invasiveness and its development and progression of glioblastoma highly depends on branched-chain amino acid (BCAA) metabolism. The study aimed to investigate effects of inhibition of BCAA metabolism with cytosolic branched-chain amino acid transaminase (BCATc) Inhibitor 2 on glioblastoma, elucidate its underlying mechanisms, and explore therapeutic potential of targeting BCAA metabolism. The expression of BCATc was upregulated in glioblastoma and BCATc Inhibitor 2 precipitated apoptosis both in vivo and in vitro with the activation of Bax/Bcl2/Caspase-3/Caspase-9 axis. In addition, BCATc Inhibitor 2 promoted K63-linkage ubiquitination of mitofusin 2 (Mfn2), which subsequently caused lysosomal degradation of Mfn2, and then oxidative stress, mitochondrial fission and loss of mitochondrial membrane potential. Furthermore, BCATc Inhibitor 2 treatment resulted in metabolic reprogramming, and significant inhibition of expression of ATP5A, UQCRC2, SDHB and COX II, indicative of suppressed oxidative phosphorylation. Moreover, Mfn2 overexpression or scavenging mitochondria-originated reactive oxygen species (ROS) with mito-TEMPO ameliorated BCATc Inhibitor 2-induced oxidative stress, mitochondrial membrane potential disruption and mitochondrial fission, and abrogated the inhibitory effect of BCATc Inhibitor 2 on glioblastoma cells through PI3K/AKT/mTOR signaling. All of these findings indicate suppression of BCAA metabolism promotes glioblastoma cell apoptosis via disruption of Mfn2-mediated mitochondrial dynamics and inhibition of PI3K/AKT/mTOR pathway, and suggest that BCAA metabolism can be targeted for developing therapeutic agents to treat glioblastoma.

p32/OPA1 axis-mediated mitochondrial dynamics contributes to cisplatin resistance in non-small cell lung cancer

Cisplatin resistance is a major obstacle in the treatment of non-small cell lung cancer (NSCLC). p32 and OPA1 are the key regulators of mitochondrial morphology and function. This study aims to investigate the role of the p32/OPA1 axis in cisplatin resistance in NSCLC and its underlying mechanism. The levels of p32 protein and mitochondrial fusion protein OPA1 are higher in cisplatin-resistant A549/DDP cells than in cisplatin-sensitive A549 cells, which facilitates mitochondrial fusion in A549/DDP cells. In addition, the expression of p32 and OPA1 protein is also upregulated in A549 cells during the development of cisplatin resistance. Moreover, p32 knockdown effectively downregulates the expression of OPA1, stimulates mitochondrial fission, decreases ATP generation and sensitizes A549/DDP cells to cisplatin-induced apoptosis. Furthermore, metformin significantly downregulates the expressions of p32 and OPA1 and induces mitochondrial fission and a decrease in ATP level in A549/DDP cells. The co-administration of metformin and cisplatin shows a significantly greater decrease in A549/DDP cell viability than cisplatin treatment alone. Moreover, D-erythro-Sphingosine, a potent p32 kinase activator, counteracts the metformin-induced downregulation of OPA1 and mitochondrial fission in A549/DDP cells. Taken together, these findings indicate that p32/OPA1 axis-mediated mitochondrial dynamics contributes to the acquired cisplatin resistance in NSCLC and that metformin resensitizes NSCLC to cisplatin, suggesting that targeting p32 and mitochondrial dynamics is an effective strategy for the prevention of cisplatin resistance.

Alternative splice variants of the mitochondrial fission protein DNM1L/Drp1 regulate mitochondrial dynamics and tumor progression in ovarian cancer

Aberrant mitochondrial fission/fusion dynamics have been reported in cancer cells. While post translational modifications are known regulators of the mitochondrial fission/fusion machinery, we show that alternative splice variants of the fission protein Drp1 (DNM1L) have specific and unique roles in cancer, adding to the complexity of mitochondrial fission/fusion regulation in tumor cells. Ovarian cancer specimens express an alternative splice transcript variant of Drp1 lacking exon 16 of the variable domain, and high expression of this splice variant relative to other transcripts is associated with poor patient outcome. Unlike the full-length variant, expression of Drp1 lacking exon 16 leads to decreased association of Drp1 to mitochondrial fission sites, more fused mitochondrial networks, enhanced respiration, and TCA cycle metabolites, and is associated with a more metastatic phenotype in vitro and in vivo. These pro-tumorigenic effects can also be inhibited by specific siRNA-mediated inhibition of the endogenously expressed transcript lacking exon 16. Moreover, lack of exon 16 abrogates mitochondrial fission in response to pro-apoptotic stimuli and leads to decreased sensitivity to chemotherapeutics. These data emphasize the significance of the pathophysiological consequences of Drp1 alternative splicing and divergent functions of Drp1 splice variants, and strongly warrant consideration of Drp1 splicing in future studies.

FGD5-AS1/miR-5590-3p/PINK1 induces Lenvatinib resistance in hepatocellular carcinoma

BACKGROUND

Lenvatinib is a common systemic treatment for advanced hepatocellular carcinoma (HCC), the resistance to which presents a great challenge. However, the mechanism of lenvatinib resistance in HCC remains unclear. Therefore, elucidating the underlying and key regulatory molecular mechanisms of lenvatinib resistance is urgently needed.

METHODS

Bioinformatic enrichment analysis was used to investigate the gene associated with lenvatinib resistance. RT-PCR, Western blot, immunohistochemistry, and luciferase assays were used to explore the mechanisms of lenvatinib resistance. The effects of the FGD5-AS1/miR-5590-3p/PINK1 axis on lenvatinib resistance were evaluated by colony formation assay, cell viability, apoptosis, mitochondrial homeostasis, and morphology analyses.

RESULTS

Higher expression of PINK1 was observed in lenvatinib-resistant cells and tissues. PINK1 could be activated by increased FGD5-AS1 expression, thereby maintaining the mitochondrial structure and function and promoting the antioxidative stress response. FGD5-AS1/miR-5590-3p showed competitive regulation of PINK1, which affected lenvatinib sensitivity through regulation of mitochondrial structure and antioxidative stress.

CONCLUSIONS

PINK1 was identified as a key gene leading to lenvatinib resistance by maintaining the mitochondrial structure and function. The FGD5-AS1/miR-5590-3p/PINK1 axis may be a promising strategy to overcome lenvatinib resistance in treatment-negative patients.

Mitochondrial dynamics in health and disease: mechanisms and potential targets

Mitochondria are organelles that are able to adjust and respond to different stressors and metabolic needs within a cell, showcasing their plasticity and dynamic nature. These abilities allow them to effectively coordinate various cellular functions. Mitochondrial dynamics refers to the changing process of fission, fusion, mitophagy and transport, which is crucial for optimal function in signal transduction and metabolism. An imbalance in mitochondrial dynamics can disrupt mitochondrial function, leading to abnormal cellular fate, and a range of diseases, including neurodegenerative disorders, metabolic diseases, cardiovascular diseases and cancers. Herein, we review the mechanism of mitochondrial dynamics, and its impacts on cellular function. We also delve into the changes that occur in mitochondrial dynamics during health and disease, and offer novel perspectives on how to target the modulation of mitochondrial dynamics.

The ELK3-DRP1 axis determines the chemosensitivity of triple-negative breast cancer cells to CDDP by regulating mitochondrial dynamics

Triple-negative breast cancer (TNBC) is the most lethal form of breast cancer. TNBC patients have higher rates of metastasis and restricted therapy options. Although chemotherapy is the conventional treatment for TNBC, the frequent occurrence of chemoresistance significantly lowers the efficacy of treatment. Here, we demonstrated that ELK3, an oncogenic transcriptional repressor that is highly expressed in TNBC, determined the chemosensitivity of two representative TNBC cell lines (MDA-MB231 and Hs578T) to cisplatin (CDDP) by regulating mitochondrial dynamics. We observed that the knockdown of ELK3 in MDA-MB231 and Hs578T rendered these cell lines more susceptible to the effects of CDDP. We further demonstrated that the chemosensitivity of TNBC cells was caused by the CDDP-mediated acceleration of mitochondrial fission, excessive mitochondrial reactive oxygen species production, and subsequent DNA damage. In addition, we identified DNM1L, a gene encoding the dynamin-related protein 1 (a major regulator of mitochondrial fission), as a direct downstream target of ELK3. Based on these results, we propose that the suppression of ELK3 expression could be used as a potential therapeutic strategy for overcoming the chemoresistance or inducing the chemosensitivity of TNBC.

Construction and validation of a novel cuproptosis-mitochondrion prognostic model related with tumor immunity in osteosarcoma

BACKGROUND

The purpose of this study was to develop a new prognostic model for osteosarcoma based on cuproptosis-mitochondrion genes.

MATERIALS AND METHODS

The data of osteosarcoma were obtained from TARGET database. By using Cox regression and LASSO regression analysis, a novel risk score was constructed based on cuproptosis-mitochondrion genes. Kaplan-Meier, ROC curve and independent prognostic analyses were performed to validate the risk score in GSE21257 dataset. Then, a predictive nomogram was constructed and further validated by calibration plot, C-index and ROC curve. Based on the risk score, all patients were divided into high-risk and low-risk group. GO and KEGG enrichment, immune correlation and drug sensitivity analyses were performed between groups. Real-time quantitative PCR verified the expression of cuproptosis-mitochondrion prognostic model genes in osteosarcoma. And we explored the function of FDX1 in osteosarcoma by western blotting, CCK8, colony formation assay, wound healing assay and transwell assays.

RESULTS

A total of six cuproptosis-mitochondrion genes (FDX1, COX11, MFN2, TOMM20, NDUFB9 and ATP6V1E1) were identified. A novel risk score and associated prognostic nomogram were constructed with high clinical application value. Strong differences in function enrichment and tumor immune microenvironment were shown between groups. Besides, the correlation of cuproptosis-mitochondrion genes and drug sensitivity were revealed to search for potential therapeutic target. The expression of FDX1, COX11, MFN2, TOMM20 and NDUFB9 at mRNA level was elevated in osteosarcoma cells compared with normal osteoblast hFOB1.19. The mRNA expression level of ATP6V1E1 was decreased in osteosarcoma. Compared with hFOB1.19, western blotting revealed that the expression of FDX1 was significantly elevated in osteosarcoma cells. Functional experiments indicated that FDX1 mainly promoted the migration of osteosarcoma rather than proliferation.

CONCLUSIONS

We developed a novel prognostic model of osteosarcoma based on cuproptosis-mitochondrion genes, which provided great guidance in survival prediction and individualized treatment decision making for patients with osteosarcoma.

The Role of mTORC1 Pathway and Autophagy in Resistance to Platinum-Based Chemotherapeutics

Cisplatin (cis-diamminedichloroplatinum I) is a platinum-based drug, the mainstay of anticancer treatment for numerous solid tumors. Since its approval by the FDA in 1978, the drug has continued to be used for the treatment of half of epithelial cancers. However, resistance to cisplatin represents a major obstacle during anticancer therapy. Here, we review recent findings on how the mTORC1 pathway and autophagy can influence cisplatin sensitivity and resistance and how these data can be applicable for the development of new therapeutic strategies.

Pseudolaric acid B triggers cell apoptosis by activating AMPK/JNK/DRP1/mitochondrial fission pathway in hepatocellular carcinoma

Pseudolaric acid B (PAB), a natural product isolated from the root bark of Pseudolarix kaempferi, has been reported to exert inhibitory effects in various cancers. However, the underlying mechanisms remain largely unclear. In the present study, we investigated the mechanism through which PAB exert its anticancer effects in hepatocellular carcinoma (HCC). PAB inhibited the viability of and induced apoptosis in Hepa1-6 cells in a dose-dependent manner. It disrupted mitochondrial membrane potential (MMP) and impaired ATP production. Furthermore, PAB induced phosphorylation of DRP1 at Ser616 and mitochondrial fission. Blocking DRP1 phosphorylation by Mdivi-1 inhibited mitochondrial fission and PAB-induced apoptosis. Moreover, c-Jun N-terminal kinase (JNK) was activated by PAB, and blocking JNK activity using SP600125 inhibited PAB-induced mitochondrial fission and cell apoptosis. Furthermore, PAB activated AMP-activated protein kinase (AMPK), and inhibiting AMPK by compound C attenuated PAB-stimulated JNK activation and blocked DRP1-dependent mitochondrial fission and apoptosis. Our in vivo data confirmed that PAB inhibited tumor growth and induced apoptosis in an HCC syngeneic mouse model by inducing the AMPK/JNK/DRP1/mitochondrial fission signaling pathway. Furthermore, a combination of PAB and sorafenib showed a synergistic effect in inhibiting tumor growth in vivo. Taken together, our findings highlight a potential therapeutic strategy for HCC.

Ovarian Cancer: A Landscape of Mitochondria with Emphasis on Mitochondrial Dynamics

Ovarian cancer (OC) represents the main cause of death from gynecological malignancies in western countries. Altered cellular and mitochondrial metabolism are considered hallmarks in cancer disease. Several mitochondrial aspects have been found altered in OC, such as the oxidative phosphorylation system, oxidative stress and mitochondrial dynamics. Mitochondrial dynamics includes cristae remodeling, fusion, and fission processes forming a dynamic mitochondrial network. Alteration of mitochondrial dynamics is associated with metabolic change in tumour development and, in particular, the mitochondrial shaping proteins appear also to be responsible for the chemosensitivity and/or chemoresistance in OC. In this review a focus on the mitochondrial dynamics in OC cells is presented.

[ALDH2 attenuates LPS-induced increase of brain microvascular endothelial cell permeability by promoting fusion and inhibiting fission of the mitochondria]

OBJECTIVE

To investigate the effect of aldehyde dehydrogenase 2 (ALDH2) on lipopolysaccharide (LPS)- induced damage of mouse brain microvascular endothelial barrier and explore the role of mitochondrial fusion and fission in maintaining the integrity of endothelial barrier.

METHODS

Mouse brain microvascular endothelial cells were treated with 1 μg/ mL LPS for 24 h with or without pretreatment with 20 μmol/mL Alda-1 (a ALDH2 agonist) for 1 h. The changes in cell viability were assessed using cell counting Kit-8 (CCK8) assay, and the cell permeability was evaluated using transendothelial cell resistance (TEER) and FITC-Dextran assay. The level of oxidative stress in the cells was assessed by detecting the levels of malondialdehyde (MDA) and superoxide dismutase (SOD), and the content of reactive oxygen species (ROS) was detected using a superoxide anion fluorescent probe (DHE). Western blotting was performed to detect the expressions of ALDH2, tight junction proteins ZO-1 and occludin, and mitochondrial fusion- and division-related proteins Mfn2, OPA1, Drp1 and Fis1.

RESULTS

Compared with the untreated cells, the cells treated with LPS showed significantly decreased TEER, increased FITC-dextran leakage, MDA content and ROS production, decreased SOD activity expressions of ALDH2, ZO-1, occludin, Mfn2 and OPA1, and increased expressions of Drp1 and Fis1 (P < 0.05). Pretreatment with Alda-1 prior to LPS exposure strongly suppressed the increase of endothelial cell membrane permeability, reduced ROS production, increased the expressions of ALDH2, ZO-1, occludin, OPA1 and Mfn2, and lowered the expressions of Drp1 and Fis1 (P < 0.05).

CONCLUSION

ALDH2 can alleviate LPS-induced damage of brain microvascular endothelial cell barrier by inhibiting the mitochondrial ROS production and promoting mitochondrial fusion and inhibiting mitochondrial fission.

Protective Effect and Mechanism of Melatonin on Cisplatin-Induced Ovarian Damage in Mice

Chemotherapeutics' development has enhanced the survival rate of cancer patients; however, adverse effects of chemotherapeutics on ovarian functions cause fertility loss in female cancer patients. Cisplatin (CP), an important chemotherapeutic drug for treating solid tumors, has adversely affected ovarian function. Melatonin (MT) has been shown to have beneficial effects on ovarian function owing to its antioxidative function. In this research, an animal model was established to explore the effect of MT on CP-induced ovarian damage. Immunohistochemical analysis and Western blot were also used to explore its mechanism. This study reported that MT protects mouse ovaries from CP-induced damage. Specifically, MT significantly prevented CP-induced ovarian reserve decline by maintaining AMH and BMP15 levels. We also found that MT ameliorated CP-induced cell cycle disorders by up-regulating CDC2 expression, and inhibited CP-induced ovarian inflammation by decreasing IL-1β and IL-18 levels. Moreover, MT protected the ovary from CP-induced mitochondrial damage, as reflected by restoring mitochondria-related protein expression. Furthermore, CP caused ovarian apoptosis, as indicated by up-regulated BAX expression. MT was also shown to activate the MAPK pathway. Our results showed that MT could ameliorate ovarian damage induced by CP, implying that MT may be a viable alternative to preserve female fertility during CP chemotherapy.

Metformin-induced AMPK activation promotes cisplatin resistance through PINK1/Parkin dependent mitophagy in gastric cancer

Gastric cancer (GC) is one of the most common tumors worldwide, and cisplatin is a standard chemotherapeutic reagent for GC treatment. However, chemoresistance is an inherent challenge which limits its application and effectiveness in clinic. This study aims to investigate the mechanism of metformin-induced cisplatin resistance in GC. Intriguingly, the upregulation of mitophagy markers, mitochondrial fission, autophagy and mitophagosome were observed in SGC-7901/DDP cells compared to those in the SGC-7901 cells. Treatment with metformin significantly increased mitochondrial fission and mitophagy in both AGS and SGC-7901 cells, resulting in decreased ATP production, which unexpectedly protected GC cells against the cytotoxicity of cisplatin. In contrast, application of Chloroquine and 3-methyladenine, two inhibitors of autophagy, significantly alleviated the protective effect of metformin on SGC-7901 and AGS cells against cytotoxicity of cisplatin. Moreover, metformin also stimulated the phosphorylation of AMPK (Thr172) and increased the expression of mitophagy markers including Parkin and PINK1 in the AMPK signaling-dependent manner. Consistently, the cell viability and cell apoptosis assay showed that metformin-induced cisplatin resistance was prevented by knockdown of AMPKα1. Taken together, all data in this study indicate that metformin induced AMPK activation and PINK1/Parkin dependent mitophagy, which may contribute to the progression of cisplatin resistance in GC.

Curcumin protects retinal neuronal cells against oxidative stress-induced damage by regulating mitochondrial dynamics

Oxidative stress plays a crucial role in the damage of retinal neuronal cells. Curcumin, the phytocompound, has anti-inflammatory and antioxidative properties. It was shown that curcumin exerted a beneficial effect on retinal neuronal cell survival. However, the role of mitochondrial dynamics in curcumin-mediated protective effect on retinal neuronal cells remains to be elucidated. Here, H₂O₂ was used to mimic the oxidative stress in retinal neuronal R28 cells. Drp1 and Mfn2 are key regulators of mitochondrial fission and fusion. 100 μM of H₂O₂ significantly increased the cleavage of caspase-3 and Drp1 expression, but downregulated the expression of Mfn2. Pretreatment with 5 μM curcumin effectively alleviated H₂O₂-induced alterations in the expression of Drp1 and Mfn2 and mitochondrial fission in R28 cells. In addition, curcumin and Drp1 knockdown prevented H₂O₂-induced intracellular ROS increment and mitochondrial membrane potential disruption. On the contrary, knockdown of Mfn2 diminished curcumin-mediated protection against ROS increment and mitochondrial membrane potential disruption after H₂O₂. Moreover, curcumin protected R28 cells against H₂O₂-induced PINK1 expression, mitophagy, caspase-3 cleavage and apoptosis. Knockdown of Mfn2 significantly alleviated the protective effect of curcumin on R28 cells after H₂O₂. Taken together, our data indicate that curcumin protects against oxidative stress-induced injury in retinal neuronal cells by promoting mitochondrial fusion.

Comprehensive analysis of MFN2 as a prognostic biomarker associated with immune cell infiltration in renal clear cell carcinoma

BACKGROUND

Treatment of advanced kidney renal clear cell carcinoma (KIRC) remains challenging in clinic. The functional role and prognostic significance of MFN2 in KIRC are still unclear.

METHODS

In this study, we first performed a bioinformatic analysis to determine the expression level and prognostic value of MFN2 in KIRC using The Cancer Genome Atlas (TCGA) dataset, and then validated the MFN2 mRNA expression in our cohort of clinical tissue samples and cell lines of KIRC via RT-qPCR. Cox regression model was used to identify the independent prognostic factors. A nomogram was constructed to predict the prognosis of KIRC patients. Gene set enrichment analysis (GSEA) was performed to predict the involved functional pathways of MFN2 co-expressed genes. The association between MFN2 expression level and immune cell infiltration was assessed using the TIMER and the TIDISB databases. In addition, cell proliferation and migration abilities of two KIRC cell lines with MFN2 overexpression were evaluated by MTS and wound healing assays, respectively.

RESULTS

Downregulation of MFN2 was observed in KIRC tissues and cell lines compared to the normal controls. Kaplan-Meier curve analysis indicated an inferior survival outcomes in KIRC patients with lower MFN2 expression, uncovering the tumor-suppressive role of MFN2 in KIRC. Cox regression results showed that higher MFN2 expression was one of the independent protective factors in KIRC. Besides, function predictive analysis revealed that MFN2 co-expressed genes were enriched in the biological processes of energy metabolism and autophagy. Moreover, MFN2 expression was observed to be significantly associated with immune cell infiltration and a variety of markers of tumor infiltrating immune cells (TIICs) including multiple immune checkpoints in KIRC tissues. Finally, MFN2 overexpression significantly inhibited cell proliferation and migration abilities of two KIRC cell lines examined.

CONCLUSION

Generally, our data suggested that MFN2 may serve as a potential prognostic biomarker and therapeutic target in KIRC.