Sub-lethal signals in the mitochondrial apoptosis apparatus: pernicious by-product or physiological event?

Zn2+ protects H9C2 cardiomyocytes by alleviating MAMs-associated apoptosis and calcium signaling dysregulation

PURPOSE

This study aims to investigate whether zinc ion (Zn2+) alleviates myocardial ischemia-reperfusion injury (MIRI) through the MAM-associated signaling pathway and to explore its impact on ERS and calcium overload.

METHODS

H9C2 cells were cultured in a DMEM supplemented with 10 % fetal bovine serum and 1 % antibiotic solution. A MIRI model was established through simulated ischemia and reoxygenation with Zn2+ treatment in a complete medium. Cells were then treated with the MCU inhibitor ruthenium red (RR), the MCU activator spermine (SP), and siRNAs targeting Bap31, MCU, VDAC1, and FUNDC1. Cell viability was assessed using MTT and CCK-8 assays. Lactate dehydrogenase (LDH) levels were measured with a commercial kit. Western blot was performed to detect protein expression levels. Cell apoptosis, intracellular zinc, calcium levels, mitochondrial membrane potential, and protein fluorescence changes were observed using laser scanning confocal microscopy.

RESULTS

Compared to the control group, cell viability was significantly reduced in the I/R group, accompanied by increased expression of apoptosis and calcium overload-related proteins increased cell injury, apoptosis, calcium overload, and a decrease in mitochondrial membrane potential. Zn2+ treatment reversed the detrimental effects of I/R in the I/R + Zn2+ group. When Bap31, VDAC1, FUNDC1, or MCU were silenced using siRNA, the protective effect of Zn2+ was further enhanced (P < 0.05).

CONCLUSIONS

Ischemia-reperfusion (I/R) leads to cardiomyocyte injury and apoptosis. Zn2+ downregulates the expression of key apoptotic proteins through the Bap31/Fis1 pathway and regulates MCU activity through the IP3R1-GRP75-VDAC1 and IP3R2/FUNDC1 pathways to alleviate calcium overload and ultimately protect cardiomyocytes after I/R.

Cuproptosis-Inducing Functional Nanocomposites for Enhanced and Synergistic Cancer Radiotherapy

Radiotherapy is crucial in local cancer management and needs advancements. Tumor cells elevate intracellular copper levels to promote growth and resist radiation; thus, targeted copper delivery to mitochondria could enhance radiotherapy by inducing cuproptosis in tumor cells. In this study, we engineered a multifunctional nanoliposome complex, termed Lipo-Ele@CuO2, which encapsulates both copper peroxide (CuO2) and the copper chelator elesclomol, which can delivery Cu ions to the mitochondria. The Lipo-Ele@CuO2 complex induces mitochondria-mediated cuproptosis in tumor cells and synergistically enhances the efficacy of radiotherapy. CuO2 acts as a copper donor and exhibits inherent sensitivity to acidic environments. Additionally, it depletes intracellular glutathione, thereby sensitizing cells to cuproptosis. Leveraging its pH-responsive properties in the acidic tumor microenvironment, the Lipo-Ele@CuO2 facilitate the controlled release of elesclomol, efficiently delivering copper ions to mitochondria at tumor sites. The combined in vitro and in vivo studies demonstrate that Lipo-Ele@CuO2-based therapy significantly improves antitumor efficacy and exhibits excellent safety profiles, effectively inducing cuproptosis in tumor cells and boosting the effectiveness of radiotherapy. Furthermore, metabolomic and transcriptomic analyses reveal that this combination therapy precipitates significant alterations in tumor energy metabolism, notably repressing genes related to iron-sulfur cluster assembly and glycolysis, thereby confirming the induction of cuproptosis. This therapeutic strategy provides a viable approach for addressing clinical radiotherapy resistance and demonstrates significant translational potential.

Caspase 3 and caspase 7 promote cytoprotective autophagy and the DNA damage response during non-lethal stress conditions in human breast cancer cells

Cell stress adaptation plays a key role in normal development and in various diseases including cancer. Caspases are activated in response to cell stress, and growing evidence supports their function in non-apoptotic cellular processes. A role for effector caspases in promoting stress-induced cytoprotective autophagy was demonstrated in Drosophila, but has not been explored in the context of human cells. We found a functionally conserved role for effector caspase 3 (CASP3) and caspase 7 (CASP7) in promoting starvation or proteasome inhibition-induced cytoprotective autophagy in human breast cancer cells. The loss of CASP3 and CASP7 resulted in an increase in PARP1 cleavage, reduction in LC3B and ATG7 transcript levels, and a reduction in H2AX phosphorylation, consistent with a block in autophagy and DNA damage-induced stress response pathways. Surprisingly, in non-lethal cell stress conditions, CASP7 underwent non-canonical processing at two calpain cleavage sites flanking a PARP1 exosite, resulting in stable CASP7-p29/p30 fragments. Expression of CASP7-p29/p30 fragment(s) could rescue H2AX phosphorylation in the CASP3 and CASP7 double knockout background. Strikingly, yet consistent with these phenotypes, the loss of CASP3 and CASP7 exhibited synthetic lethality with BRCA1 loss. These findings support a role for human caspases in stress adaptation through PARP1 modulation and reveal new therapeutic avenues for investigation.

Aging and physiological barriers: mechanisms of barrier integrity changes and implications for age-related diseases

The phenomenon of compartmentalization is one of the key traits of life. Biological membranes and histohematic barriers protect the internal environment of the cell and organism from endogenous and exogenous impacts. It is known that the integrity of these barriers decreases with age due to the loss of homeostasis, including age-related gene expression profile changes and the abnormal folding/assembly, crosslinking, and cleavage of barrier-forming macromolecules in addition to morphological changes in cells and tissues. The critical molecular and cellular mechanisms involved in physiological barrier integrity maintenance and aging-associated changes in their functioning are reviewed on different levels: molecular, organelle, cellular, tissue (histohematic, epithelial, and endothelial barriers), and organ one (skin). Biogerontology, which studies physiological barriers in the aspect of age, is still in its infancy; data are being accumulated, but there is no talk of the synthesis of complex theories yet. This paper mainly presents the mechanisms that will become targets of anti-aging therapy only in the future, possibly: pharmacological, cellular, and gene therapies, including potential geroprotectors, hormetins, senomorphic drugs, and senolytics.

Complex regulation of mitochondrial signaling by human adenovirus minor capsid protein VI

The controlled release of mitochondrial content into the cytosol has emerged as one of the key steps in mitochondrial signaling. In particular, the release of mitochondrial DNA (mtDNA) into the cytosol has been shown to activate interferon beta (IFN-β) gene expression to execute the innate immune response. In this report, we show that human adenovirus type 5 (HAdV-C5) infection induces the release of mtDNA into the cytosol. The release of mtDNA is mediated by the viral minor capsid protein VI (pVI), which localizes to mitochondria. The presence of the mitochondrial membrane proteins Bak and Bax are needed for the mtDNA release, whereas the viral E1B-19K protein blocked pVI-mediated mtDNA release. Surprisingly, the pVI-mediated mtDNA release did not increase but inhibited the IFN-β gene expression. Notably, the pVI expression caused mitochondrial leakage of the HSP60 protein. The latter prevented specific phosphorylation of the interferon regulatory factor 3 (IRF3) needed for IFN-β gene expression. Overall, we assign a new mitochondria and IFN-β signaling-modulating function to the HAdV-C5 minor capsid protein VI.

IMPORTANCE

Human adenoviruses (HAdVs) are common pathogens causing various self-limiting diseases, including conjunctivitis and the common cold. HAdVs need to interfere with multiple cellular signaling pathways during the infection to gain control over the host cell. In this study, we identified human adenovirus type 5 (HAdV-C5) minor capsid protein VI as a factor modulating mitochondrial membrane integrity and mitochondrial signaling. We show that pVI-altered mitochondrial signaling impedes the cell's innate immune response, which may benefit HAdV growth. Overall, our study provides new detailed insights into the HAdV-mitochondria interactions and signaling. This knowledge is helpful when developing new anti-viral treatments against pathogenic HAdV infections and improving HAdV-based therapeutics.

The regulation of the apoptotic pore-An immunological tightrope walk

Apoptotic pore formation in mitochondria is the pivotal point for cell death during mitochondrial apoptosis. It is regulated by BCL-2 family proteins in response to various cellular stress triggers and mediates mitochondrial outer membrane permeabilization (MOMP). This allows the release of mitochondrial contents into the cytosol, which triggers rapid cell death and clearance through the activation of caspases. However, under conditions of low caspase activity, the mitochondrial contents released into the cytosol through apoptotic pores serve as inflammatory signals and activate various inflammatory responses. In this chapter, we discuss how the formation of the apoptotic pore is regulated by BCL-2 proteins as well as other cellular or mitochondrial proteins and membrane lipids. Moreover, we highlight the importance of sublethal MOMP in the regulation of mitochondrial-activated inflammation and discuss its physiological consequences in the context of pathogen infection and disease and how it can potentially be exploited therapeutically, for example to improve cancer treatment.

Mcl-1 mediates intrinsic resistance to RAF inhibitors in mutant BRAF papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is the most frequent form of thyroid cancer. PTC commonly presents with mutations of the serine/threonine kinase BRAF (BRAFV600E), which drive ERK1/2 pathway activation to support growth and suppress apoptosis. PTC patients often undergo surgical resection; however, since the average age of PTC patients is under 50, adverse effects associated with prolonged maintenance therapy following total thyroidectomy are a concern. The development of mutant-selective BRAF inhibitors (BRAFi), like vemurafenib, has been efficacious in patients with metastatic melanoma, but the response rate is low for mutant BRAF PTC patients. Here, we assay the therapeutic response of BRAFi in a panel of human PTC cell lines and freshly biopsied patient samples. We observed heterogeneous responses to BRAFi, and multi-omic comparisons between susceptible and resistant mutant BRAF PTC revealed overrepresented stress response pathways and the absence of compensatory RTK activation - features that may underpin innate resistance. Importantly, resistant cell lines and patient samples had increased hallmarks of failed apoptosis; a cellular state defined by sublethal caspase activation and DNA damage. Further analysis suggests that the failed apoptotic phenotypes may have features of "minority mitochondrial outer membrane permeabilization (MOMP)" - a stress-related response characterized by fragmented and porous mitochondria known to contribute to cancer aggressiveness. We found that cells presenting with minority MOMP-like phenotypes are dependent on the apoptotic regulator, Mcl-1, as treatment with the Mcl-1 inhibitor, AZD5991, potently induced cell death in resistant cells. Furthermore, PI3K/AKT inhibitors sensitized resistant cells to BRAFi; an effect that was at least in part associated with reduced Mcl-1 levels. Together, these data implicate minority MOMP as a mechanism associated with intrinsic drug resistance and underscore the benefits of targeting Mcl-1 in mutant BRAF PTC.

TRAIL-induced apoptosis and proteasomal activity - Mechanisms, signalling and interplay

Programmed cell death, in particular apoptosis, is essential during development and tissue homeostasis, and also is the primary strategy to induce cancer cell death by cytotoxic therapies. Precision therapeutics targeting TRAIL death receptors are being evaluated as novel anti-cancer agents, while in parallel highly specific proteasome inhibitors have gained approval as drugs. TRAIL-dependent signalling and proteasomal control of cellular proteostasis are intricate processes, and their interplay can be exploited to enhance therapeutic killing of cancer cells in combination therapies. This review provides detailed insights into the complex signalling of TRAIL-induced pathways and the activities of the proteasome. It explores their core mechanisms of action, pharmaceutical druggability, and describes how their interplay can be strategically leveraged to enhance cell death responses in cancer cells. Offering this comprehensive and timely overview will allow to navigate the complexity of the processes governing cell death mechanisms in TRAIL- and proteasome inhibitor-based treatment conditions.

Venetoclax Combined with Intensive Chemotherapy: A New Hope for Refractory and/or Relapsed Acute Myeloid Leukemia?

Background. Primary resistance of acute myeloid leukemia (AML) to the conventional 3 + 7 intensive chemotherapy and relapses after first-line chemotherapy are two highly challenging clinical scenarios. In these cases, when allogeneic stem cell transplantation is feasible, patients are usually retreated with other chemotherapeutic regimens, as transplantation is still considered, nowadays, the only curative option. Methods. We discuss the mechanisms behind resistance to chemotherapy and offer a comprehensive review on current treatments of refractory/relapsed AML with a focus on novel approaches incorporating the BCL-2 inhibitor venetoclax. Results. Alas, complete remission rates after salvage chemotherapy remain relatively low, between 30 and 60% at best. More recently, the BCL-2 inhibitor venetoclax was combined either with hypomethylating agents or chemotherapy in refractory/relapsed patients. In particular, its combination with chemotherapy offered promising results by achieving higher rates of remission and bridging a substantial number of patients to transplantation. Conclusions. Venetoclax-based approaches might become, in the near future, the new standard of care for refractory/relapsed AML.

Expanding roles of BCL-2 proteins in apoptosis execution and beyond

The proteins of the BCL-2 family are known as key regulators of apoptosis, with interactions between family members determining permeabilisation of the mitochondrial outer membrane (MOM) and subsequent cell death. However, the exact mechanism through which they form the apoptotic pore responsible for MOM permeabilisation (MOMP), the structure and specific components of this pore, and what roles BCL-2 proteins play outside of directly regulating MOMP are incompletely understood. Owing to the link between apoptosis dysregulation and disease, the BCL-2 proteins are important targets for drug development. With the development and clinical use of drugs targeting BCL-2 proteins showing success in multiple haematological malignancies, enhancing the efficacy of these drugs, or indeed developing novel drugs targeting BCL-2 proteins is of great interest to treat cancer patients who have developed resistance or who suffer other disease types. Here, we review our current understanding of the molecular mechanism of MOMP, with a particular focus on recently discovered roles of BCL-2 proteins in apoptosis and beyond, and discuss what implications these functions might have in both healthy tissues and disease.

Mechanisms of BCL-2 family proteins in mitochondrial apoptosis

The proteins of the BCL-2 family are key regulators of mitochondrial apoptosis, acting as either promoters or inhibitors of cell death. The functional interplay and balance between the opposing BCL-2 family members control permeabilization of the outer mitochondrial membrane, leading to the release of activators of the caspase cascade into the cytosol and ultimately resulting in cell death. Despite considerable research, our knowledge about the mechanisms of the BCL-2 family of proteins remains insufficient, which complicates cell fate predictions and does not allow us to fully exploit these proteins as targets for drug discovery. Detailed understanding of the formation and molecular architecture of the apoptotic pore in the outer mitochondrial membrane remains a holy grail in the field, but new studies allow us to begin constructing a structural model of its arrangement. Recent literature has also revealed unexpected activities for several BCL-2 family members that challenge established concepts of how they regulate mitochondrial permeabilization. In this Review, we revisit the most important advances in the field and integrate them into a new structure-function-based classification of the BCL-2 family members that intends to provide a comprehensive model for BCL-2 action in apoptosis. We close this Review by discussing the potential of drugging the BCL-2 family in diseases characterized by aberrant apoptosis.

Informing the Cannabis Conjecture: From Life's Beginnings to Mitochondria, Membranes and the Electrome-A Review

Before the late 1980s, ideas around how the lipophilic phytocannabinoids might be working involved membranes and bioenergetics as these disciplines were "in vogue". However, as interest in genetics and pharmacology grew, interest in mitochondria (and membranes) waned. The discovery of the cognate receptor for tetrahydrocannabinol (THC) led to the classification of the endocannabinoid system (ECS) and the conjecture that phytocannabinoids might be "working" through this system. However, the how and the "why" they might be beneficial, especially for compounds like CBD, remains unclear. Given the centrality of membranes and mitochondria in complex organisms, and their evolutionary heritage from the beginnings of life, revisiting phytocannabinoid action in this light could be enlightening. For example, life can be described as a self-organising and replicating far from equilibrium dissipating system, which is defined by the movement of charge across a membrane. Hence the building evidence, at least in animals, that THC and CBD modulate mitochondrial function could be highly informative. In this paper, we offer a unique perspective to the question, why and how do compounds like CBD potentially work as medicines in so many different conditions? The answer, we suggest, is that they can modulate membrane fluidity in a number of ways and thus dissipation and engender homeostasis, particularly under stress. To understand this, we need to embrace origins of life theories, the role of mitochondria in plants and explanations of disease and ageing from an adaptive thermodynamic perspective, as well as quantum mechanics.

ATX-LPA-Dependent Nuclear Translocation of Endonuclease G in Respiratory Epithelial Cells: A New Mode Action for DNA Damage Induced by Crystalline Silica Particles

Crystalline silica particles (CSi) are an established human carcinogen, but it is not clear how these particles cause necessary mutations. A well-established scenario includes inflammation caused by retained particles in the bronchioles, activated macrophages, and reactive oxygen species (ROS) that cause DNA damage. In previous studies, we showed that CSi in contact with the plasma membrane of human bronchial epithelium induced double strand breaks within minutes. A signaling pathway implicating the ATX-LPA axis, Rac1, NLRP3, and mitochondrial depolarization upstream of DSB formation was delineated. In this paper, we provide in vitro and in vivo evidence that this signaling pathway triggers endonuclease G (EndoG) translocation from the mitochondria to the nucleus. The DNA damage is documented as γH2AX and p53BP1 nuclear foci, strand breaks in the Comet assay, and as micronuclei. In addition, the DNA damage is induced by low doses of CSi that do not induce apoptosis. By inhibiting the ATX-LPA axis or by EndoG knockdown, we prevent EndoG translocation and DSB formation. Our data indicate that CSi in low doses induces DSBs by sub-apoptotic activation of EndoG, adding CSi to a list of carcinogens that may induce mutations via sub-apoptotic and "minority MOMP" effects. This is the first report linking the ATX-LPA axis to this type of carcinogenic effect.

The roles of ERIANIN in tumor and innate immunity and its' perspectives in immunotherapy

Traditional Chinese medicine has been used in China for thousands of years. In 2022, the 14th Five-Year Plan for the Development of Traditional Chinese Medicine was released, aiming to enhance traditional Chinese medicine health services and improve policies and systems for high-quality traditional Chinese medicinal development by 2025. ERIANIN, the main component of the traditional Chinese medicine Dendrobium, plays an important role in anti-inflammatory, antiviral, antitumor, antiangiogenic, and other pharmacological effects. ERIANIN has broad-spectrum antitumor effects, and its tumor-suppressive effects have been confirmed in the study of various diseases, such as precancerous lesions of the stomach, gastric cancer, liver cancer, lung cancer, prostate cancer, bladder cancer, breast cancer, cervical cancer, osteosarcoma, colorectal cancer, leukaemia, nasopharyngeal cancer and melanoma through the multiple signaling pathways. Thus, the aim of this review was to systematically summarise the research on ERIANIN with the aim of serving as a reference for future research on this compound and briefly discuss some future perspectives development of ERIANIN in combined immunotherapy.