VDAC regulates AAC-mediated apoptosis and cytochrome c release in yeast

The small yeast GTPase Rho5 requires specific mitochondrial outer membrane proteins for translocation under oxidative stress and interacts with the VDAC Por1

Yeast Rho5 is a small GTPase which mediates the response to nutrient and oxidative stress, and triggers mitophagy and apoptosis. We here studied the rapid translocation of a GFP-tagged Rho5 to mitochondria under such stress conditions by live-cell fluorescence microscopy in the background of strains lacking different mitochondrial outer membrane proteins (MOMP). Fun14, Msp1 and Alo1 were found to be required for efficient recruitment of the GTPase, whereas translocation of Dck1 and Lmo1, the subunits of its dimeric GDP/GTP exchange factor (GEF), remained unaffected. An influence of the voltage-dependent anion channel (VDAC) Por1 on the association of GFP-Rho5 with mitochondria under oxidative stress conditions appeared to be strain-dependent. However, epistasis analyses and bimolecular fluorescence complementation (BiFC) studies indicate a genetic and physical interaction. All four strains lacking a single MOMP were investigated for their effect on mitophagy.

Exposure to Ozone Downregulates Bcl-2 and Increases Executing Caspases-3 and -8 in the Hippocampus, Frontal Cortex, and Cerebellum of Rats

Introduction Ozone (O3) is one of the most prevalent atmospheric pollutants, arising from a photochemical reaction between volatile organic compounds (VOC), nitrogen oxides (NOx), and sunlight. O3 triggers oxidative stress, resulting in lipid oxidation, inflammation, alterations in metabolic and cellular signaling, and potentially initiating cell death in vulnerable brain regions. Inflammation and oxidative stress are recognized for their ability to induce cell death, primarily through the apoptosis pathway, involving various proteins that participate in this process via two pathways: intrinsic and extrinsic. Objective This study aims to identify the expression of pro-apoptotic proteins and Bcl-2 in the frontal cortex, cerebellum, and hippocampus of rats exposed to O3 acutely. Methods Two groups of 20 Wistar rodents (250-300 g) were established. The control group (n=10) was exposed to unrestricted polluted air for 12 hours, while the experimental group (n=10) was exposed to 1 ppm of O3. After exposure, the animals were sacrificed for immunofluorescence and Western blot analysis. Using a t-test, the arbitrary units of pro-apoptotic proteins and Bcl-2 were compared between the two groups. Results Significant increases in caspase-8 and caspase-3 activation were found in the O3-exposed group compared to the control group, specifically in the frontal cortex, cerebellum, and hippocampus. Additionally, notable changes in Bcl-2 expression were observed in these brain regions. The TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay further indicated significant differences in immunopositivity between the groups in the same areas. However, intrinsic apoptotic proteins such as Bax, VDAC1, and cytochrome-c did not show significant differences between the groups within these structures. Western blot analyses aligned with the immunofluorescence results, showing statistically significant concentrations of caspase-8 in the cerebellum, caspase-3 in the hippocampus, and Bcl-2 in the frontal cortex in the O3 exposed group. Conversely, proteins like Bax, cytochrome-c, and VDAC1 did not exhibit significant differences in all analyzed structures. Conclusions This study demonstrates that acute exposure to 1 ppm of ozone can trigger neuronal apoptosis in the frontal cortex, hippocampus, and cerebellum of rats, primarily through the activation of the extrinsic apoptosis pathway via caspase-8 and caspase-3. Additionally, it causes a reduction in Bcl-2 expression, an essential antiapoptotic protein. Despite not observing the activation of intrinsic pathway proteins like BAX, VDAC, or cytochrome-c, the study suggests that chronic O3 exposure might promote cell death by activating this pathway, requiring further long-term research.

A dynamic actin cytoskeleton is required to prevent constitutive VDAC-dependent MAPK signalling and aberrant lipid homeostasis

The dynamic nature of the actin cytoskeleton is required to coordinate many cellular processes, and a loss of its plasticity has been linked to accelerated cell aging and attenuation of adaptive response mechanisms. Cofilin is an actin-binding protein that controls actin dynamics and has been linked to mitochondrial signaling pathways that control drug resistance and cell death. Here we show that cofilin-driven chronic depolarization of the actin cytoskeleton activates cell wall integrity mitogen-activated protein kinase (MAPK) signalling and disrupts lipid homeostasis in a voltage-dependent anion channel (VDAC)-dependent manner. Expression of the cof1-5 mutation, which reduces the dynamic nature of actin, triggers loss of cell wall integrity, vacuole fragmentation, disruption of lipid homeostasis, lipid droplet (LD) accumulation, and the promotion of cell death. The integrity of the actin cytoskeleton is therefore essential to maintain the fidelity of MAPK signaling, lipid homeostasis, and cell health in S. cerevisiae.

Ca2+/Calmodulin-Dependent Protein Kinase II Disrupts the Voltage Dependency of the Voltage-Dependent Anion Channel on the Lipid Bilayer Membrane

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a key enzyme that plays a significant role in intracellular signaling and the modulation of mitochondrial membrane properties. It is known that the voltage-dependent anion channel (VDAC) is one of the most abundant outer mitochondrial membrane (OMM) proteins acting as a significant passageway and regulatory site for various enzymes, proteins, ions, and metabolites. Considering this, we hypothesize that VDAC could be one of the targets for CaMKII enzymatic activity. Our in vitro experiments indicate that VDAC can be phosphorylated by the CaMKII enzyme. Moreover, the bilayer electrophysiology experimental data indicate that CaMKII significantly reduces VDAC's single-channel conductivity; its open probability remains high at all the applied potentials between +60 and -60 mV, and the voltage dependency was lost, which suggests that CaMKII disrupted the VDAC's single-channel activities. Hence, we can infer that VDAC interacts with CaMKII and thus acts as a vital target for its activity. Furthermore, our findings suggest that CaMKII could play a significant role during the transport of ions and metabolites across the outer mitochondrial membrane (OMM) through VDAC and thus regulate apoptotic events.

Pro-Apoptotic and Anti-Invasive Properties Underscore the Tumor-Suppressing Impact of Myoglobin on a Subset of Human Breast Cancer Cells

The expression of myoglobin (MB), well known as the oxygen storage and transport protein of myocytes, is a novel hallmark of the luminal subtype in breast cancer patients and correlates with better prognosis. The mechanisms by which MB impacts mammary tumorigenesis are hitherto unclear. We aimed to unravel this role by using CRISPR/Cas9 technology to generate MB-deficient clones of MCF7 and SKBR3 breast cancer cell lines and subsequently characterize them by transcriptomics plus molecular and functional analyses. As main findings, loss of MB at normoxia upregulated the expression of cell cyclins and increased cell survival, while it prevented apoptosis in MCF7 cells. Additionally, MB-deficient cells were less sensitive to doxorubicin but not ionizing radiation. Under hypoxia, the loss of MB enhanced the partial epithelial to mesenchymal transition, thus, augmenting the migratory and invasive behavior of cells. Notably, in human invasive mammary ductal carcinoma tissues, MB and apoptotic marker levels were positively correlated. In addition, MB protein expression in invasive ductal carcinomas was associated with a positive prognostic value, independent of the known tumor suppressor p53. In conclusion, we provide multiple lines of evidence that endogenous MB in cancer cells by itself exerts novel tumor-suppressive roles through which it can reduce cancer malignancy.

Contribution of non-selective membrane channels and receptors in epilepsy

Overcoming refractory epilepsy's resistance to the combination of antiepileptic drugs (AED), mitigating side effects, and preventing sudden unexpected death in epilepsy are critical goals for therapy of this disorder. Current therapeutic strategies are based primarily on neurocentric mechanisms, overlooking the participation of astrocytes and microglia in the pathophysiology of epilepsy. This review is focused on a set of non-selective membrane channels (permeable to ions and small molecules), including channels and ionotropic receptors of neurons, astrocytes, and microglia, such as: the hemichannels formed by Cx43 and Panx1; the purinergic P2X7 receptors; the transient receptor potential vanilloid (TRPV1 and TRPV4) channels; calcium homeostasis modulators (CALHMs); transient receptor potential canonical (TRPC) channels; transient receptor potential melastatin (TRPM) channels; voltage-dependent anion channels (VDACs) and volume-regulated anion channels (VRACs), which all have in common being activated by epileptic activity and the capacity to exacerbate seizure intensity. Specifically, we highlight evidence for the activation of these channels/receptors during epilepsy including neuroinflammation and oxidative stress, discuss signaling pathways and feedback mechanisms, and propose the functions of each of them in acute and chronic epilepsy. Studying the role of these non-selective membrane channels in epilepsy and identifying appropriate blockers for one or more of them could provide complementary therapies to better alleviate the disease.

Development of an automated yeast-based spectrophotometric method for toxicity screening: Application to ionic liquids, GUMBOS, and deep eutectic solvents

Saccharomyces cerevisiae has been used as a eukaryotic model organism for studying the toxic effects of various compounds. In this context, an automated spectrophotometric method based on the enzymatic reduction of methylene blue dye to a colorless product by living yeast cells was implemented in a sequential injection analysis system. Loss of yeast viability/impaired metabolic activity was monitored by an increase in optical density at 664 nm. To prove the usefulness of this approach, the toxicity of ILs (ionic liquids), GUMBOS (group of uniform materials based on organic salts), and DESs (deep eutectic solvents) was examined. Differences obtained between IC₅₀ values confirmed the impact of structural elements on each compounds' toxicity. While DESs appeared to be less toxic than ILs, GUMBOS were found to be among the most toxic compounds to yeast cells and thus can be viewed as promising antimicrobial candidates. The automated methodology showed satisfactory repeatability and reproducibility (RSD < 9%), which is in good agreement with Green Chemistry principles. In fact, the method required consumption of only 40 μL of reagents and produced less than 2 mL of effluents per cycle. Thus, the developed assay can be used as an alternative tool for toxicity screening.

Regulation of Cell Death Induced by Acetic Acid in Yeasts

Acetic acid has long been considered a molecule of great interest in the yeast research field. It is mostly recognized as a by-product of alcoholic fermentation or as a product of the metabolism of acetic and lactic acid bacteria, as well as of lignocellulosic biomass pretreatment. High acetic acid levels are commonly associated with arrested fermentations or with utilization as vinegar in the food industry. Due to its obvious interest to industrial processes, research on the mechanisms underlying the impact of acetic acid in yeast cells has been increasing. In the past twenty years, a plethora of studies have addressed the intricate cascade of molecular events involved in cell death induced by acetic acid, which is now considered a model in the yeast regulated cell death field. As such, understanding how acetic acid modulates cellular functions brought about important knowledge on modulable targets not only in biotechnology but also in biomedicine. Here, we performed a comprehensive literature review to compile information from published studies performed with lethal concentrations of acetic acid, which shed light on regulated cell death mechanisms. We present an historical retrospective of research on this topic, first providing an overview of the cell death process induced by acetic acid, including functional and structural alterations, followed by an in-depth description of its pharmacological and genetic regulation. As the mechanistic understanding of regulated cell death is crucial both to design improved biomedical strategies and to develop more robust and resilient yeast strains for industrial applications, acetic acid-induced cell death remains a fruitful and open field of study.

Deletion of Voltage-Dependent Anion Channel 1 knocks mitochondria down triggering metabolic rewiring in yeast

The Voltage-Dependent Anion-selective Channel (VDAC) is the pore-forming protein of mitochondrial outer membrane, allowing metabolites and ions exchanges. In Saccharomyces cerevisiae, inactivation of POR1, encoding VDAC1, produces defective growth in the presence of non-fermentable carbon source. Here, we characterized the whole-genome expression pattern of a VDAC1-null strain (Δpor1) by microarray analysis, discovering that the expression of mitochondrial genes was completely abolished, as consequence of the dramatic reduction of mtDNA. To overcome organelle dysfunction, Δpor1 cells do not activate the rescue signaling retrograde response, as ρ0 cells, and rather carry out complete metabolic rewiring. The TCA cycle works in a "branched" fashion, shunting intermediates towards mitochondrial pyruvate generation via malic enzyme, and the glycolysis-derived pyruvate is pushed towards cytosolic utilization by PDH bypass rather than the canonical mitochondrial uptake. Overall, Δpor1 cells enhance phospholipid biosynthesis, accumulate lipid droplets, increase vacuoles and cell size, overproduce and excrete inositol. Such unexpected re-arrangement of whole metabolism suggests a regulatory role of VDAC1 in cell bioenergetics.

Regulation of the mitochondrial permeability transition pore and its effects on aging

Aging is an evolutionarily conserved process and is tightly connected to mitochondria. To uncover the aging molecular mechanisms related to mitochondria, different organisms have been extensively used as model systems. Among these, the budding yeast Saccharomyces cerevisiae has been reported multiple times as a model of choice when studying cellular aging. In particular, yeast provides a quick and trustworthy system to identify shared aging genes and pathway patterns. In this viewpoint on aging and mitochondria, I will focus on the mitochondrial permeability transition pore (mPTP), which has been reported and proposed as a main player in cellular aging. I will make several parallelisms with yeast to highlight how this unicellular organism can be used as a guidance system to understand conserved cellular and molecular events in multicellular organisms such as humans. Overall, a thread connecting the preservation of mitochondrial functionality with the activity of the mPTP emerges in the regulation of cell survival and cell death, which in turn could potentially affect aging and aging-related diseases.

Transcriptional and epigenetic control of regulated cell death in yeast

Unicellular organisms like yeast can undergo controlled demise in a manner that is partly reminiscent of mammalian cell death. This is true at the levels of both mechanistic and functional conservation. Yeast offers the combination of unparalleled genetic amenability and a comparatively simple biology to understand both the regulation and evolution of cell death. In this minireview, we address the capacity of the nucleus as a regulatory hub during yeast regulated cell death (RCD), which is becoming an increasingly central question in yeast RCD research. In particular, we explore and critically discuss the available data on stressors and signals that specifically impinge on the nucleus. Moreover, we also analyze the current knowledge on nuclear factors as well as on transcriptional control and epigenetic events that orchestrate yeast RCD. Altogether we conclude that the functional significance of the nucleus for yeast RCD in undisputable, but that further exploration beyond correlative work is necessary to disentangle the role of nuclear events in the regulatory network.

First Proteomic Approach to Identify Cell Death Biomarkers in Wine Yeasts during Sparkling Wine Production

Apoptosis and later autolysis are biological processes which take place in Saccharomyces cerevisiae during industrial fermentation processes, which involve costly and time-consuming aging periods. Therefore, the identification of potential cell death biomarkers can contribute to the creation of a long-term strategy in order to improve and accelerate the winemaking process. Here, we performed a proteomic analysis based on the detection of possible apoptosis and autolysis protein biomarkers in two industrial yeast strains commonly used in post-fermentative processes (sparkling wine secondary fermentation and biological aging) under typical sparkling wine elaboration conditions. Pressure had a negatively effect on viability for flor yeast, whereas the sparkling wine strain seems to be more adapted to these conditions. Flor yeast strain experienced an increase in content of apoptosis-related proteins, glucanases and vacuolar proteases at the first month of aging. Significant correlations between viability and apoptosis proteins were established in both yeast strains. Multivariate analysis based on the proteome of each process allowed to distinguish among samples and strains. The proteomic profile obtained in this study could provide useful information on the selection of wine strains and yeast behavior during sparkling wine elaboration. Additionally, the use of flor yeasts for sparkling wine improvement and elaboration is proposed.

Saccharomyces cerevisiae mitochondrial Por1/yVDAC1 (voltage-dependent anion channel 1) interacts physically with the MBOAT O-acyltransferase Gup1/HHATL in the control of cell wall integrity and programmed cell death

Gup1 is the yeast counterpart of the high eukaryotes HHATL. This and the close homologue Gup2/HHAT regulate the Hedgehog morphogenic, developmental pathway. In yeasts, a similar paracrine pathway is not known though the Δgup1 mutant is associated with morphology and proliferation/death processes. As a first step toward identifying the actual molecular/enzymatic function of Gup1, this work identified by co-immunoprecipitation the yeast mitochondria membrane VDAC1/Por1 as a physical partner of Gup1. Gup1 locates in the ER and the plasma membrane. It was now confirmed to further locate, as Por1, in the mitochondrial sub-cellular fraction. The yeast Por1-Gup1 association was found important for (i) the sensitivity to cell wall perturbing agents and high temperature, (ii) the differentiation into structured colonies, (iii) the size achieved by multicellular aggregates/mats and (iv) acetic-acid-induced Programmed Cell Death. Moreover, the absence of Gup1 increased the levels of POR1 mRNA, while decreasing the amounts of intracellular Por1, which was concomitantly previously known to be secreted by the mutant but not by wt. Additionally, Por1 patchy distribution in the mitochondrial membrane was evened. Results suggest that Por1 and Gup1 collaborate in the control of colony morphology and mat development, but more importantly of cellular integrity and death.

Activation of prolyl hydroxylase-2 for stabilization of mitochondrial stress along with simultaneous downregulation of HIF-1α/FASN in ER + breast cancer subtype

The present study was undertaken to inquest the chemical activation of prolyl hydroxylase-2 for the curtailment of hypoxia-inducible factor-1α and fatty acid synthase. It was well documented that hypoxia-inducible factor-1α and fatty acid synthase were overexpressed in mammary gland carcinomas. After screening a battery of compounds, BBAP-2 was retrieved as a potential prolyl hydroxylase-2 activator and validates its activity using ER + MCF-7 cell line and n-methyl-n-nitrosourea-induced rat in vivo model, respectively. BBAP-2 was palpable for the morphological characteristics of apoptosis along with changes in the mitochondrial intergrity as visualized by acridine orange/ethidium bromide and JC-1 staining against ER + MCF-7 cells. BBAP-2 also arrest the cell cycle of ER + MCF-7 cells at G2/M phase. Afterward, BBAP-2 has scrutinized against n-methyl-n-nitrosourea-induced mammary gland carcinoma in albino Wistar rats. BBAP-2 restored the morphological architecture when screened through carmine staining, haematoxylin and eosin staining, and scanning electron microscopy. BBAP-2 also delineated the markers of oxidative stress favourably. The immunoblotting and mRNA expression analysis validated that BBAP-2 has a potentialty activate the prolyl hydroxylase-2 with sequential downregulating effect on hypoxia-inducible factor-1α and its downstream checkpoint. BBAP-2 also fostered apoptosis through mitochondrial-mediated death pathway. The present study elaborates the chemical activation of prolyl hydroxylase-2 by which the increased expression of HIF-1α and FASN can be reduced in mammary gland carcinoma.

Patulin Induces Autophagy-Dependent Apoptosis through Lysosomal-Mitochondrial Axis and Impaired Mitophagy in HepG2 Cells

Patulin (PAT) is a compound produced by fungi including those of the Aspergillus, Penicillium, and Byssochlamys species. PAT has been linked with negative outcomes in certain microorganisms and animal species, but how it causes hepatotoxicity is poorly understood. In this study, we determined that, by treating HepG2 cells using PAT, these cells could be induced to rapidly undergo autophagy, and this was followed within 12 h of treatment by lysosomal membrane permeabilization (LMP) and cathepsin B release. We were able to block these outcomes if cells were treated with 3-methyladenine (3MA), an inhibitor of autophagy, prior to PAT treatment. Moreover, PAT-induced collapse of mitochondrial membrane potential (ΔΨm) depended both on cathepsin B and autophagy. 3MA was further able to reduce the induction of apoptosis in response to PAT, suggesting that autophagy is a driving mechanism for this apoptotic induction. Inhibiting cathepsin B using CA-074 Me further reduced PAT-induced collapses of ΔΨm, mitochondiral cytochrome c release, and apoptosis. We also found that extended treatment of HepG2 cells using PAT over a period of 24 h led to the impairment of mitophagy such that morphologically swollen mitochondria accumulated within cells, and PINK1 failed to colocalize with LC3. Together these data reveal that PAT treatment can promote the induction of apoptosis in HepG2 cells in a manner dependent upon autophagy that progresses via the lysosomal-mitochondrial axis. This study thereby affords new insights into the mechanisms by which PAT drives hepatotoxicity.

Contacts in Death: The Role of the ER-Mitochondria Axis in Acetic Acid-Induced Apoptosis in Yeast

Endoplasmic reticulum-mitochondria contact sites have been a subject of increasing scientific interest since the discovery that these structures are disrupted in several pathologies. Due to the emerging data that correlate endoplasmic reticulum-mitochondria contact sites function with known events of the apoptotic program, we aimed to dissect this interplay using our well-established model of acetic acid-induced apoptosis in Saccharomyces cerevisiae. Until recently, the only known tethering complex between ER and mitochondria in this organism was the ER-mitochondria encounter structure (ERMES). Following our results from a screening designed to identify genes whose deletion rendered cells with an altered sensitivity to acetic acid, we hypothesized that the ERMES complex could be involved in cell death mediated by this stressor. Herein we demonstrate that single ablation of the ERMES components Mdm10p, Mdm12p and Mdm34p increases the resistance of S. cerevisiae to acetic acid-induced apoptosis, which is associated with a prominent delay in the appearance of several apoptotic markers. Moreover, abrogation of Mdm10p or Mdm34p abolished cytochrome c release from mitochondria. Since these two proteins are embedded in the mitochondrial outer membrane, we propose that the ERMES complex plays a part in cytochrome c release, a key event of the apoptotic cascade. In all, these findings will aid in targeted therapies for diseases where apoptosis is disrupted, as well as assist in the development of acetic acid-resistant strains for industrial processes.

Guidelines and recommendations on yeast cell death nomenclature

Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cel-lular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the defi-nition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differ-ential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death rou-tines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the au-thors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the pro-gress of this vibrant field of research.