Mitochondrial Signaling Pathways Associated with DNA Damage Responses

Mitochondria and MICOS - function and modeling

An extensive review is presented on mitochondrial structure and function, mitochondrial proteins, the outer and inner membranes, cristae, the role of F1FO-ATP synthase, the mitochondrial contact site and cristae organizing system (MICOS), the sorting and assembly machinery morphology and function, and phospholipids, in particular cardiolipin. Aspects of mitochondrial regulation under physiological and pathological conditions are outlined, in particular the role of dysregulated MICOS protein subunit Mic60 in Parkinson's disease, the relations between mitochondrial quality control and proteins, and mitochondria as signaling organelles. A mathematical modeling approach of cristae and MICOS using mechanical beam theory is introduced and outlined. The proposed modeling is based on the premise that an optimization framework can be used for a better understanding of critical mitochondrial function and also to better map certain experiments and clinical interventions.

Fractionated radiation therapy alters energy metabolism and induces cellular quiescence exit in patient-derived orthotopic xenograft models of high-grade glioma

Radiation is one of the standard therapies for pediatric high-grade glioma (pHGG), of which the prognosis remains poor. To gain an in-depth understanding of biological consequences beyond the classic DNA damage, we treated 9 patient-derived orthotopic xenograft (PDOX) models, including one with DNA mismatch repair (MMR) deficiency, with fractionated radiations (2 Gy/day x 5 days). Extension of survival time was noted in 5 PDOX models (P < 0.05) accompanied by γH2AX positivity in >95 % tumor cells in tumor core and >85 % in the invasive foci as well as ∼30 % apoptotic and mitotic catastrophic cell death. The model with DNA MMR (IC-1406HGG) was the most responsive to radiation with a reduction of Ki-67(+) cells. Altered metabolism, including mitochondria number elevation, COX IV activation and reactive oxygen species accumulation, were detected together with the enrichment of CD133+ tumor cells. The latter was caused by the entry of quiescent G0 cells into cell cycle and the activation of self-renewal (SOX2 and BMI1) and epithelial mesenchymal transition (fibronectin) genes. These novel insights about the cellular and molecular mechanisms of fractionated radiation in vivo should support the development of new radio-sensitizing therapies.

An In Vitro Study on the Cytotoxic, Antioxidant, and Antimicrobial Properties of Yamogenin-A Plant Steroidal Saponin and Evaluation of Its Mechanism of Action in Gastric Cancer Cells

Yamogenin is a steroidal saponin occurring in plant species such as Asparagus officinalis, Dioscorea collettii, Trigonella foenum-graecum, and Agave sp. In this study, we evaluated in vitro cytotoxic, antioxidant, and antimicrobial properties of yamogenin. The cytotoxic activity was estimated on human colon cancer HCT116, gastric cancer AGS, squamous carcinoma UM-SCC-6 cells, and human normal fibroblasts with MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. The amount of apoptotic and dead AGS cells after treatment with yamogenin was estimated with flow cytometry. Also, in yamogenin-treated AGS cells we investigated the reactive oxygen species (ROS) production, mitochondrial membrane depolarization, activity level of caspase-8 and -9, and gene expression at mRNA level with flow cytometry, luminometry, and RT-PCR, respectively. The antioxidant properties of yamogenin were assessed with DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) assays. The antimicrobial potential of the compound was estimated on Staphylococcus aureus, Bacillus cereus, Klebsiella pneumoniae, Escherichia coli, Salmonella enterica, Helicobacter pylori, Campylobacter coli, Campylobacter jejuni, Listeria monocytogenes, Lactobacillus paracasei, and Lactobacillus acidophilus bacteria strains. Yamogenin showed the strongest cytotoxic effect on AGS cells (IC50 18.50 ± 1.24 µg/mL) among the tested cell lines. This effect was significantly stronger in combinations of yamogenin with oxaliplatin or capecitabine than for the single compounds. Furthermore, yamogenin induced ROS production, depolarized mitochondrial membrane, and increased the activity level of caspase-8 and -9 in AGS cells. RT-PCR analysis revealed that this sapogenin strongly up-regulated TNFRSF25 expression at the mRNA level. These results indicate that yamogenin induced cell death via the extrinsic and intrinsic way of apoptosis. Antioxidant study showed that yamogenin had moderate in vitro potential (IC50 704.7 ± 5.9 µg/mL in DPPH and 631.09 ± 3.51 µg/mL in ABTS assay) as well as the inhibition of protein denaturation properties (with IC50 1421.92 ± 6.06 µg/mL). Antimicrobial test revealed a weak effect of yamogenin on bacteria strains, the strongest one being against S. aureus (with MIC value of 350 µg/mL). In conclusion, yamogenin may be a potential candidate for the treatment and prevention of gastric cancers.

DAMPs and radiation injury

The heightened risk of ionizing radiation exposure, stemming from radiation accidents and potential acts of terrorism, has spurred growing interests in devising effective countermeasures against radiation injury. High-dose ionizing radiation exposure triggers acute radiation syndrome (ARS), manifesting as hematopoietic, gastrointestinal, and neurovascular ARS. Hematopoietic ARS typically presents with neutropenia and thrombocytopenia, while gastrointestinal ARS results in intestinal mucosal injury, often culminating in lethal sepsis and gastrointestinal bleeding. This deleterious impact can be attributed to radiation-induced DNA damage and oxidative stress, leading to various forms of cell death, such as apoptosis, necrosis and ferroptosis. Damage-associated molecular patterns (DAMPs) are intrinsic molecules released by cells undergoing injury or in the process of dying, either through passive or active pathways. These molecules then interact with pattern recognition receptors, triggering inflammatory responses. Such a cascade of events ultimately results in further tissue and organ damage, contributing to the elevated mortality rate. Notably, infection and sepsis often develop in ARS cases, further increasing the release of DAMPs. Given that lethal sepsis stands as a major contributor to the mortality in ARS, DAMPs hold the potential to function as mediators, exacerbating radiation-induced organ injury and consequently worsening overall survival. This review describes the intricate mechanisms underlying radiation-induced release of DAMPs. Furthermore, it discusses the detrimental effects of DAMPs on the immune system and explores potential DAMP-targeting therapeutic strategies to alleviate radiation-induced injury.

Nuclear DNA damage-triggered ATM-dependent AMPK activation regulates the mitochondrial radiation response

PURPOSE

AMP-activated protein kinase (AMPK) acts as a cellular energy sensor and is essential for controlling mitochondrial homeostasis. Here, we investigated the regulatory mechanisms involved in AMPK activation to elucidate how networks of intracellular signaling pathways respond to stress conditions.

MATERIALS AND METHODS

Inhibitors of ATM, DNA-PK, and AKT were tested in normal TIG-3 and MRC-5 human fibroblasts to determine which upstream kinases are responsible for AMPK activation. SV40 transformed-human ATM-deficient fibroblasts (AT5BIVA) and their ATM-complemented cells (i.e., AT5BIVA/ATMwt) were also used. Protein expression associated with AMPK signaling was examined by immunostaining and/or Western blotting.

RESULTS

Radiation-induced nuclear DNA damage activates ATM-dependent AMPK signaling pathways that regulate mitochondrial quality control. In contrast, hypoxia and glucose starvation caused ATP depletion and activated AMPK via a pathway independent of ATM. DNA-PK and AKT are not involved in AMPK-mediated mitochondrial signaling pathways.

CONCLUSION

Activation of the AMPK signaling pathway differs depending on the stimulus. Radiation activates AMPK through two pathways: depletion of ATP-mediated LKB1 signaling and nuclear DNA damage-induced ATM signaling. Nuclear DNA damage signaling to mitochondria therefore plays a pivotal role in determining the cell fates of irradiated cells.

Quercetin Alleviates Toxicity Induced by High Levels of Copper in Porcine Follicular Granulosa Cells by Scavenging Reactive Oxygen Species and Improving Mitochondrial Function

CuSO4 is the most commonly used feed additive in pig production at present, but long-term ingestion of excessive copper would lead to chronic copper toxicity. High copper could reduce the reproductive efficiency of sows and seriously affect the development of the pig industry. Quercetin (QUE), a powerful antioxidant, reduces toxicity of a number of heavy metals. Porcine granulosa cells (pGCs) are crucial to the fate of follicle development. The present study found that high concentrations of CuSO4 induced ROS production, which resulted in decreased mRNA expression of antioxidant-related genes GPX4, CAT, and SOD2 and increased mRNA expression of SOD1, TRX, and HO-1. The protein expression of antioxidant enzymes SOD2 and HO-1 decreased. Moreover, the concentration of MDA increased, the activity of CAT decreased, and the content of GSH decreased. After high copper treatment, the mitochondrial membrane potential (MMP) was decreased and the morphological structure was changed. However, the combined treatment with Quercetin (QUE) reversed these changes, and the level of cellular oxidative stress decreased. Therefore, we conclude that high copper has oxidative toxicity to pGCs, and QUE could remove the ROS induced by high copper, protect mitochondria from oxidative stress damage, and improve the function of pGCs.