Mitochondrial Electron Transport Chain Research Articles

A myzozoan-specific protein is an essential membrane-anchoring component of the succinate dehydrogenase complex in Toxoplasma parasites.

Succinate dehydrogenase (SDH) is a protein complex that functions in the tricarboxylic acid cycle and the electron transport chain of mitochondria. In most eukaryotes, SDH is highly conserved and comprises the following four subunits: SdhA and SdhB form the catalytic core of the complex, while SdhC and SdhD anchor the complex in the membrane. Toxoplasma gondii is an apicomplexan parasite that infects one-third of humans worldwide. The genome of T. gondii encodes homologues of the catalytic subunits SdhA and SdhB, although the physiological role of the SDH complex in the parasite and the identity of the membrane-anchoring subunits are poorly understood. Here, we show that the SDH complex contributes to optimal proliferation and O2 consumption in the disease-causing tachyzoite stage of the T. gondii life cycle. We characterize a small membrane-bound subunit of the SDH complex called mitochondrial protein ookinete developmental defect (MPODD), which is conserved among myzozoans, a phylogenetic grouping that incorporates apicomplexan parasites and their closest free-living relatives. We demonstrate that TgMPODD is essential for SDH activity and plays a key role in attaching the TgSdhA and TgSdhB proteins to the membrane anchor of the complex. Our findings highlight a unique and important feature of mitochondrial energy metabolism in apicomplexan parasites and their relatives.

Biogenesis of cytochromes c and c 1 in the electron transport chain of malaria parasites.

Plasmodium malaria parasites retain an essential mitochondrional electron transport chain (ETC) that is critical for growth within humans and mosquitoes and a key antimalarial drug target. ETC function requires cytochromes c and c 1 that are unusual among heme proteins due to their covalent binding to heme via conserved CXXCH sequence motifs. Heme attachment to these proteins in most eukaryotes requires the mitochondrial enzyme holocytochrome c synthase (HCCS) that binds heme and the apo cytochrome to facilitate biogenesis of the mature cytochrome c or c 1. Although humans encode a single bifunctional HCCS that attaches heme to both proteins, Plasmodium parasites are like yeast and encode two separate HCCS homologs thought to be specific for heme attachment to cyt c (HCCS) or cyt c 1 (HCC1S). To test the function and specificity of P. falciparum HCCS and HCC1S, we used CRISPR/Cas9 to tag both genes for conditional expression. HCC1S knockdown selectively impaired cyt c 1 biogenesis and caused lethal ETC dysfunction that was not reversed by over-expression of HCCS. Knockdown of HCCS caused a more modest growth defect but strongly sensitized parasites to mitochondrial depolarization by proguanil, revealing key defects in ETC function. These results and prior heterologous studies in E. coli of cyt c hemylation by P. falciparum HCCS and HCC1S strongly suggest that both homologs are essential for mitochondrial ETC function and have distinct specificities for biogenesis of cyt c and c 1, respectively, in parasites. This study lays a foundation to develop novel strategies to selectively block ETC function in malaria parasites.

RNA: De-silencing to the rescue

The fate of transcribed RNA dictates cellular function. A new study finds that mutations in specific RNA processing machinery genes result in de-silencing of a transcript encoding a subunit of the mitochondrial electron transport chain and rescue of a mitochondrial respiratory complex I defect.

Heat stress upregulates arachidonic acid to trigger autophagy in sertoli cells via dysfunctional mitochondrial respiratory chain function

As a key factor in determining testis size and sperm number, sertoli cells (SCs) play a crucial role in male infertility. Heat stress (HS) reduces SCs counts, negatively impacting nutrient transport and supply to germ cells, and leading to spermatogenesis failure in humans and animals. However, how HS affects the number of SCs remains unclear. We hypothesized that changes in SC metabolism contribute to the adverse effects of HS. In this study, we first observed an upregulation of arachidonic acid (AA), an unsaturated fatty acid after HS exposure by LC-MS/MS metabolome detection. By increasing ROS levels, expression of KEAP1 and NRF2 proteins as well as LC3 and LAMP2, 100 µM AA induced autophagy in SCs by activating oxidative stress (OS). We observed adverse effects of AA on mitochondria under HS with a decrease of mitochondrial number and an increase of mitochondrial membrane potential (MMP). We also found that AA alternated the oxygen transport and absorption function of mitochondria by increasing glycolysis flux and decreasing oxygen consumption rate as well as the expression of mitochondrial electron transport chain (ETC) proteins Complex I, II, V. However, pretreatment with 5 mM NAC (ROS inhibitor) and 2 µM Rotenone (mitochondrial ETC inhibitor) reversed the autophagy induced by AA. In summary, AA modulates autophagy in SCs during HS by disrupting mitochondrial ETC function, inferring that the release of AA is a switch-like response, and providing insight into the underlying mechanism of high temperatures causing male infertility.

Ly6Chi Monocytes Are Metabolically Reprogrammed in the Blood during Inflammatory Stimulation and Require Intact OxPhos for Chemotaxis and Monocyte to Macrophage Differentiation.

Acute inflammation is a rapid and dynamic process involving the recruitment and activation of multiple cell types in a coordinated and precise manner. Here, we investigate the origin and transcriptional reprogramming of monocytes using a model of acute inflammation, zymosan-induced peritonitis. Monocyte trafficking and adoptive transfer experiments confirmed that monocytes undergo rapid phenotypic change as they exit the blood and give rise to monocyte-derived macrophages that persist during the resolution of inflammation. Single-cell transcriptomics revealed significant heterogeneity within the surface marker-defined CD11b+Ly6G-Ly6Chi monocyte populations within the blood and at the site of inflammation. We show that two major transcriptional reprogramming events occur during the initial six hours of Ly6Chi monocyte mobilisation, one in the blood priming monocytes for migration and a second at the site of inflammation. Pathway analysis revealed an important role for oxidative phosphorylation (OxPhos) during both these reprogramming events. Experimentally, we demonstrate that OxPhos via the intact mitochondrial electron transport chain is essential for murine and human monocyte chemotaxis. Moreover, OxPhos is needed for monocyte-to-macrophage differentiation and macrophage M(IL-4) polarisation. These new findings from transcriptional profiling open up the possibility that shifting monocyte metabolic capacity towards OxPhos could facilitate enhanced macrophage M2-like polarisation to aid inflammation resolution and tissue repair.

#245 Deficiency of GADD45α expression mediated tubulointerstitial injury in diabetic nephropathy

Abstract Background and Aims The tubulointerstitial injury plays crucial roles in the development of diabetic nephropathy (DN). Recently, some studies have reported that disorder of mitochondrial fatty acid β-oxidation in proximal tubules is involved in tubulointerstitial injury of DN. The growth arrest and DNA damage-inducible gene 45 (GADD45) family proteins, especially, GADD45α, plays a crucial role in various cellular processes, such as mitochondrial biogenesis and lipid metabolism. Recent studies have demonstrated that GADD45α facilitates gene activation by inducing DNA demethylation. Therefore, this study aimed to investigate the role of GADD45α in tubulointerstitial injury of DN and its underlying mechanisms. Methods Bioinformatics and machine learning techniques were employed to identify differentially expressed genes between healthy individuals and DN patients. Experiments were conducted by using high glucose-treated HK-2 cells and streptozotocin (STZ)-induced mice. Lentivirus carrying the GADD45α gene was used to induce GADD45α overexpression in HK-2 cells. Adeno-Associated Virus vectors carrying LoxP-flanked GADD45α were intravenously injected into γGT-Cre transgenic mice expressing Cre recombinase in renal proximal tubular cells, specifically leading to GADD45α overexpression in proximal tubules. Results Through bioinformatics and machine learning techniques, GADD45α was identified and found to exhibit a strong association with tubulointerstitial injury in DN. Further analysis revealed that the expression of GADD45α was decreased in the kidneys of DN patients, diabetic mice, and high glucose-treated HK-2 cells. Notably, GADD45α overexpression ameliorated kidney damage and mitochondrial injury, leading to improved fatty acid β-oxidation, restored ATP production, and reduced ROS production. Transcriptomics analyses further demonstrated that GADD45α overexpression enhanced the expression of genes related to mitochondrial biogenesis, dynamics, and electron transport chain, with six transmembrane epithelial antigen of prostate 4 (STEAP4) being a key protein in this process. Knocking down STEAP4 using siRNA in HK-2 cells exacerbated the damage induced by high glucose. In addition, our further results indicated that high glucose increased methylation of the STEAP4 promoter, while GADD45α overexpression decreased methylation and increased STEAP4 expression. Conclusions Deficiency of GADD45α expression mediated tubulointerstitial injury in DN, which was mainly through the decreased STEAP4 expression by demethylating CpG motifs in the STEAP4 promoter region, thereby resulting in reduced fatty acid oxidation, energy synthesis, and increased ROS production, and finally accelerated tubular injuries. These findings suggested that targeting the GADD45α-STEAP4 pathway could be a potential therapeutic strategy for DN.

Electron-transferring flavoprotein and its dehydrogenase contributed to growth development and virulence in Beauveria bassiana

Electron-transferring flavoprotein (Etf) and its dehydrogenase (Etfdh) are integral components of the electron transport chain in mitochondria. In this study, we characterize two putative etf genes (Bbetfa and Bbetfb) and their dehydrogenase gene Bbetfdh in the entomopathogenic fungus Beauveria bassiana. Individual deletion of these genes caused a significant reduction in vegetative growth, conidiation, and delayed conidial germination. Lack of these genes also led to abnormal metabolism of fatty acid and increasing lipid body accumulation. Furthermore, the virulence of Bbetfs and Bbetfdh deletion mutants was severely impaired due to decreasing infection structure formation. Additionally, all deletion strains showed reduced ATP synthesis compared to the wild-type strain. Taken together, Bbetfa and Bbetfb, along with Bbetfdh, play principal roles in fungal vegetative growth, conidiation, conidial germination, and pathogenicity of B. bassiana due to their essential functions in fatty acid metabolism.

SOURCES OF SUPEROXIDE ANION RADICAL IN SMALL INTESTINE TISSUES IN RATS SUBJECTED TO SURGICAL TRAUMA SIMULATED UNDER EXPERIMENTAL MODEL OF POSTTRAUMATIC STRESS DISORDER

The sources of superoxide anion radical (.О ) in the tissues of the small intestine in rats subjected to surgical trauma simulated under an experimental model of posttraumatic stress disorder (PTSD) were investigated. The study involved 42 white Wistar rats weighing 210-230 g, divided into 6 groups: group 1 comprised intact animals, group 2 included animals with the PTSD induced through single-prolonged stress (SPS), group 3 consisted of rats subjected to a sham surgical operation, group 4 comprised animals undergoing laparotomy, group 5 involved rats undergoing a sham surgical operation following SPS, and group 6 included animals undergoing laparotomy under modeled SPS. The rate of .О generation in the small intestine homogenate was measured spectrophotometrically using the nitroblue tetrazolium test. The .О production by NADPH-dependent (microsomal and NO synthase) electron transport chains (ETC), NADH-dependent (mitochondrial) ETC and leukocyte NADPH oxidase was assessed. The findings obtained have demonstrated that experimental SPS modeling leads to an increase in oxidative stress in the small intestine tissues of rats. This is manifested by an increase in the rate of .О formation with the participation of microsomes, mitochondria and leukocyte NADPH oxidase. On the 7th day after laparotomy under the experimental PTSD model, the .О production in the tissues of the small intestine by different sources (microsomes, mitochondria and leukocyte NADPH oxidase) exceeds their values obtained after a single laparotomy or after performing a sham operation under single long-term stress.

RNAi screens identify HES4 as a regulator of redox balance supporting pyrimidine synthesis and tumor growth.

NADH/NAD+ redox balance is pivotal for cellular metabolism. Systematic identification of NAD(H) redox regulators, although currently lacking, would help uncover unknown effectors critically implicated in the coordination of growth metabolism. In this study, we performed a genome-scale RNA interference (RNAi) screen to globally survey the genes involved in redox modulation and identified the HES family bHLH transcription factor HES4 as a negative regulator of NADH/NAD+ ratio. Functionally, HES4 is shown to be crucial for maintaining mitochondrial electron transport chain (ETC) activity and pyrimidine synthesis. More specifically, HES4 directly represses transcription of SLC44A2 and SDS, thereby inhibiting mitochondrial choline oxidation and cytosolic serine deamination, respectively, which, in turn, ensures coenzyme Q reduction capacity for DHODH-mediated UMP synthesis and serine-derived dTMP production. Accordingly, inhibition of choline oxidation preserves mitochondrial serine catabolism and ETC-coupled redox balance. Furthermore, HES4 protein stability is enhanced under EGFR activation, and increased HES4 levels facilitate EGFR-driven tumor growth and predict poor prognosis of lung adenocarcinoma. These findings illustrate an unidentified mechanism, underlying pyrimidine biosynthesis in the intersection between serine and choline catabolism, and underscore the physiological importance of HES4 in tumor metabolism.

RICTOR/mTORC2 downregulation in BRAFV600E melanoma cells promotes resistance to BRAF/MEK inhibition.

The main drawback of BRAF/MEK inhibitors (BRAF/MEKi)-based targeted therapy in the management of BRAF-mutated cutaneous metastatic melanoma (MM) is the development of therapeutic resistance. We aimed to assess in this context the role of mTORC2, a signaling complex defined by the presence of the essential RICTOR subunit, regarded as an oncogenic driver in several tumor types, including MM. After analyzing The Cancer Genome Atlas MM patients' database to explore both overall survival and molecular signatures as a function of intra-tumor RICTOR levels, we investigated the effects of RICTOR downregulation in BRAFV600E MM cell lines on their response to BRAF/MEKi. We performed proteomic screening to identify proteins modulated by changes in RICTOR expression, and Seahorse analysis to evaluate the effects of RICTOR depletion on mitochondrial respiration. The combination of BRAFi with drugs targeting proteins and processes emerged in the proteomic screening was carried out on RICTOR-deficient cells in vitro and in a xenograft setting in vivo. Low RICTOR levels in BRAF-mutated MM correlate with a worse clinical outcome. Gene Set Enrichment Analysis of low-RICTOR tumors display gene signatures suggestive of activation of the mitochondrial Electron Transport Chain (ETC) energy production. RICTOR-deficient BRAFV600E cells are intrinsically tolerant to BRAF/MEKi and anticipate the onset of resistance to BRAFi upon prolonged drug exposure. Moreover, in drug-naïve cells we observed a decline in RICTOR expression shortly after BRAFi exposure. In RICTOR-depleted cells, both mitochondrial respiration and expression of nicotinamide phosphoribosyltransferase (NAMPT) are enhanced, and their pharmacological inhibition restores sensitivity to BRAFi. Our work unveils an unforeseen tumor-suppressing role for mTORC2 in the early adaptation phase of BRAFV600E melanoma cells to targeted therapy and identifies the NAMPT-ETC axis as a potential therapeutic vulnerability of low RICTOR tumors. Importantly, our findings indicate that the evaluation of intra-tumor RICTOR levels has a prognostic value in metastatic melanoma and may help to guide therapeutic strategies in a personalized manner.

Insights into the Mechanism of Catalytic Activity of Plasmodium Parasite Malate-Quinone Oxidoreductase.

Plasmodium malate-quinone oxidoreductase (MQO) is a membrane flavoprotein catalyzing the oxidation of malate to oxaloacetate and the reduction of quinone to quinol. Recently, using a yeast expression system, we demonstrated that MQO, expressed in place of mitochondrial malate dehydrogenase (MDH), contributes to the TCA cycle and the electron transport chain in mitochondria, making MQO attractive as a promising drug target in Plasmodium malaria parasites, which lack mitochondrial MDH. However, there is little information on the structure of MQO and its catalytic mechanism, information that will be required to develop novel drugs. Here, we investigated the catalytic site of P. falciparum MQO (PfMQO) using our yeast expression system. We generated a model structure for PfMQO with the AI tool AlphaFold and used protein footprinting by acetylation with acetic anhydride to analyze the surface topology of the model, confirming the computational prediction to be reasonably accurate. Moreover, a putative catalytic site, which includes a possible flavin-binding site, was identified by this combination of protein footprinting and structural prediction model. This active site was analyzed by site-directed mutagenesis. By measuring enzyme activity and protein expression levels in the PfMQO mutants, we showed that several residues at the active site are essential for enzyme function. In addition, a single substitution mutation near the catalytic site resulted in enhanced sensitivity to ferulenol, an inhibitor of PfMQO that competes with malate for binding to the enzyme. This strongly supports the notion that the substrate binds to the proposed catalytic site. Then, the location of the catalytic site was demonstrated by structural comparison with a homologous enzyme. Finally, we used our results to propose a mechanism for the catalytic activity of MQO by reference to the mechanism of action of structurally or functionally homologous enzymes.

Examining the Effects of Nutrient Supplementation on Metabolic Pathways via Mitochondrial Ferredoxin in Aging Ovaries.

As women age, oocytes are susceptible to a myriad of dysfunctions, including mitochondrial dysfunction, impaired DNA repair mechanisms, epigenetic alterations, and metabolic disturbances, culminating in reduced fertility rates among older individuals. Ferredoxin (FDX) represents a highly conserved iron-sulfur (Fe-S) protein essential for electron transport across multiple metabolic pathways. Mammalian mitochondria house two distinct ferredoxins, FDX1 and FDX2, which share structural similarities and yet perform unique functions. In our investigation into the regulatory mechanisms governing ovarian aging, we employed a comprehensive multi-omics analysis approach, integrating spatial transcriptomics, single-cell RNA sequencing, human ovarian pathology, and clinical biopsy data. Previous studies have highlighted intricate interactions involving excessive lipid peroxide accumulation, redox-induced metal ion buildup, and alterations in cellular energy metabolism observed in aging cells. Through a multi-omics analysis, we observed a notable decline in the expression of the critical gene FDX1 as ovarian age progressed. This observation prompted speculation regarding FDX1's potential as a promising biomarker for ovarian aging. Following this, we initiated a clinical trial involving 70 patients with aging ovaries. These patients were administered oral nutritional supplements consisting of DHEA, ubiquinol CoQ10, and Cleo-20 T3 for a period of two months to evaluate alterations in energy metabolism regulated by FDX1. Our results demonstrated a significant elevation in FDX1 levels among participants receiving nutritional supplementation. We hypothesize that these nutrients potentiate mitochondrial tricarboxylic acid cycle (TCA) activity or electron transport chain (ETC) efficiency, thereby augmenting FDX1 expression, an essential electron carrier in metabolic pathways, while concurrently mitigating lipid peroxide accumulation and cellular apoptosis. In summary, our findings underscore the potential of nutritional intervention to enhance in vitro fertilization outcomes in senescent cells by bolstering electron transport proteins, thus optimizing energy metabolism and improving oocyte quality in aging women.

Understanding coenzyme Q.

Coenzyme Q (CoQ), also known as ubiquinone, comprises a benzoquinone head group and a long isoprenoid side chain. It is thus extremely hydrophobic and resides in membranes. It is best known for its complex function as an electron transporter in the mitochondrial electron transport chain (ETC) but is also required for several other crucial cellular processes. In fact, CoQ appears to be central to the entire redox balance of the cell. Remarkably, its structure and therefore its properties have not changed from bacteria to vertebrates. In metazoans, it is synthesized in all cells and is found in most, and maybe all, biological membranes. CoQ is also known as a nutritional supplement, mostly because of its involvement with antioxidant defenses. However, whether there is any health benefit from oral consumption of CoQ is not well established. Here we review the function of CoQ as a redox-active molecule in the ETC and other enzymatic systems, its role as a prooxidant in reactive oxygen species generation, and its separate involvement in antioxidant mechanisms. We also review CoQ biosynthesis, which is particularly complex because of its extreme hydrophobicity, as well as the biological consequences of primary and secondary CoQ deficiency, including in human patients. Primary CoQ deficiency is a rare inborn condition due to mutation in CoQ biosynthetic genes. Secondary CoQ deficiency is much more common, as it accompanies a variety of pathological conditions, including mitochondrial disorders as well as aging. In this context, we discuss the importance, but also the great difficulty, of alleviating CoQ deficiency by CoQ supplementation.

Mitochondrial dysfunction in brain tissues and Extracellular Vesicles Fragile X-associated tremor/ataxia syndrome.

Mitochondrial impairments have been implicated in the pathogenesis of Fragile X-associated tremor/ataxia syndrome (FXTAS) based on analysis of mitochondria in peripheral tissues and cultured cells. We sought to assess whether mitochondrial abnormalities present in postmortem brain tissues of patients with FXTAS are also present in plasma neuron-derived extracellular vesicles (NDEVs) from living carriers of fragile X messenger ribonucleoprotein1 (FMR1) gene premutations at an early asymptomatic stage of the disease continuum. We utilized postmortem frozen cerebellar and frontal cortex samples from a cohort of eight patients with FXTAS and nine controls and measured the quantity and activity of the mitochondrial proteins complex IV and complex V. In addition, we evaluated the same measures in isolated plasma NDEVs by selective immunoaffinity capture targeting L1CAM from a separate cohort of eight FMR1 premutation carriers and four age-matched controls. Lower complex IV and V quantity and activity were observed in the cerebellum of FXTAS patients compared to controls, without any differences in total mitochondrial content. No patient-control differences were observed in the frontal cortex. In NDEVs, FMR1 premutation carriers compared to controls had lower activity of Complex IV and Complex V, but higher Complex V quantity. Quantitative and functional abnormalities in mitochondrial electron transport chain complexes IV and V seen in the cerebellum of patients with FXTAS are also manifest in plasma NDEVs of FMR1 premutation carriers. Plasma NDEVs may provide further insights into mitochondrial pathologies in this syndrome and could potentially lead to the development of biomarkers for predicting symptomatic FXTAS among premutation carriers and disease monitoring.

Isolation of Mitochondria for Mitochondrial Supercomplex Analysis from Small Tissue and Cell Culture Samples.

Over the last decades, the evidence accumulated about the existence of respiratory supercomplexes (SCs) has changed our understanding of the mitochondrial electron transport chain organization, giving rise to the proposal of the "plasticity model." This model postulates the coexistence of different proportions of SCs and complexes depending on the tissue or the cellular metabolic status. The dynamic nature of the assembly in SCs would allow cells to optimize the use of available fuels and the efficiency of electron transfer, minimizing reactive oxygen species generation and favoring the ability of cells to adapt to environmental changes. More recently, abnormalities in SC assembly have been reported in different diseases such as neurodegenerative disorders (Alzheimer's and Parkinson's disease), Barth Syndrome, Leigh syndrome, or cancer. The role of SC assembly alterations in disease progression still needs to be confirmed. Nevertheless, the availability of enough amounts of samples to determine the SC assembly status is often a challenge. This happens with biopsy or tissue samples that are small or have to be divided for multiple analyses, with cell cultures that have slow growth or come from microfluidic devices, with some primary cultures or rare cells, or when the effect of particular costly treatments has to be analyzed (with nanoparticles, very expensive compounds, etc.). In these cases, an efficient and easy-to-apply method is required. This paper presents a method adapted to obtain enriched mitochondrial fractions from small amounts of cells or tissues to analyze the structure and function of mitochondrial SCs by native electrophoresis followed by in-gel activity assays or western blot.

A novel inhibitor of the mitochondrial respiratory complex I with uncoupling properties exerts potent antitumor activity

Cancer cells are highly dependent on bioenergetic processes to support their growth and survival. Disruption of metabolic pathways, particularly by targeting the mitochondrial electron transport chain complexes (ETC-I to V) has become an attractive therapeutic strategy. As a result, the search for clinically effective new respiratory chain inhibitors with minimized adverse effects is a major goal. Here, we characterize a new OXPHOS inhibitor compound called MS-L6, which behaves as an inhibitor of ETC-I, combining inhibition of NADH oxidation and uncoupling effect. MS-L6 is effective on both intact and sub-mitochondrial particles, indicating that its efficacy does not depend on its accumulation within the mitochondria. MS-L6 reduces ATP synthesis and induces a metabolic shift with increased glucose consumption and lactate production in cancer cell lines. MS-L6 either dose-dependently inhibits cell proliferation or induces cell death in a variety of cancer cell lines, including B-cell and T-cell lymphomas as well as pediatric sarcoma. Ectopic expression of Saccharomyces cerevisiae NADH dehydrogenase (NDI-1) partially restores the viability of B-lymphoma cells treated with MS-L6, demonstrating that the inhibition of NADH oxidation is functionally linked to its cytotoxic effect. Furthermore, MS-L6 administration induces robust inhibition of lymphoma tumor growth in two murine xenograft models without toxicity. Thus, our data present MS-L6 as an inhibitor of OXPHOS, with a dual mechanism of action on the respiratory chain and with potent antitumor properties in preclinical models, positioning it as the pioneering member of a promising drug class to be evaluated for cancer therapy.MS-L6 exerts dual mitochondrial effects: ETC-I inhibition and uncoupling of OXPHOS. In cancer cells, MS-L6 inhibited ETC-I at least 5 times more than in isolated rat hepatocytes. These mitochondrial effects lead to energy collapse in cancer cells, resulting in proliferation arrest and cell death. In contrast, hepatocytes which completely and rapidly inactivated this molecule, restored their energy status and survived exposure to MS-L6 without apparent toxicity.

The differential effects of acute and prolonged L-NAME exposure on A23187-induced NO-dependent dilation in human arterioles

The Ca2+ ionophore A23187 induces endothelium-dependent and non-receptor-mediated vasodilation in human adipose arterioles (HAA). Preliminary data from our group suggest that while A23187 dilation mainly depends on NO as a vasodilator factor in healthy HAAs, there is a component of non-NO and likely hydrogen peroxide (H2O2)-mediated dilation, especially in arterioles from patients with coronary artery disease (CAD). The mechanisms underlying the release of two different vasodilator factors remain largely unclear. There is evidence that NO-mediated S-nitrosylation inhibits the catalytic activity of mitochondrial electron transport chain (ETC) complexes or other reactive oxygen species (ROS)-producing enzymes such as NADPH oxidases (NOX). The objective of this study was to compare the effects of acute (30 minutes) and prolonged (90 minutes) nitric oxide (NO) synthase inhibitor nitro-L-arginine methyl ester (L-NAME) exposure on A23187 dilation to elucidate whether prolonged incubation with L-NAME results in transition from NO-dependent to H2O2-dependent vasodilation in HAAs. HAAs (~150 μm ID), isolated from fat tissues obtained from subjects with and without CAD, were cannulated and pressurized at 60 mmHg for videomicroscopic measurement of vessel diameters. In non-CAD HAAs constricted with endothelin-1, A23187 (10−11 to 10−7 M) elicited concentration-dependent dilation (maximal dilation at 10−7 M: 68±5%, n=5), and this dilation was largely abolished after acute exposure to L-NAME (maximal dilation at 10−7 M: 21±7%, n=5). Prolonged L-NAME incubation restored A23187-dependent dilation (maximal dilation at 10−7 M: 74±2%, n=5), which was subsequently inhibited by hydrogen peroxide scavenger catalase (500 U/ml; maximal dilation at 10−7 M: 14±4%, n=5). HAAs obtained from CAD patients, responded to A23187 in a similar dose-dependent fashion (maximal dilation at 10−7 M: 68±3%, n=5), and this dilation was not affected by acute L-NAME exposure (maximal dilation at 10−7 M: 65±3%, n=5), but was reduced by catalase (maximal dilation at 10−7 M: 31±6%, n=6). To further determine the role of mitochondria-derived ROS in A23187-induced dilation, we treated arterioles with ETC inhibitor rotenone (1 mM). In non-CAD HAAs not pretreated with L-NAME, rotenone had no effect on A23187-induced dilation (maximal dilation at 10−7 M: 68±6%, n=5). In the presence of rotenone, however, prolonged L-NAME incubation no longer restored A23187-dependent dilation (maximal dilation at 10−7 M: 20±3%, n=5). Together, these data provide the first evidence that in healthy HAAs, prolonged L-NAME exposure changes the mechanism of vasodilation from NO to H2O2-mediated CAD-like vasodilation in response to A23187. In addition, the signaling process likely involves mitochondrial ROS. To elucidate the precise mechanisms underlying this process, future studies will be required to evaluate whether in healthy vasculature, basal NO inhibits mitochondrial ETC or other proteins such as NOXs through NO-mediated protein modification, which can be reversed by prolonged L-NAME incubation thereby promoting a switch from NO to H2O2 -mediated dilation. This work was supported by the National Heart, Lung, and Blood Institute [R01HL096647]. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Cyclin-dependent kinase 12 deficiency reprogrammes cellular metabolism to alleviate ferroptosis potential and promote the progression of castration-resistant prostate cancer.

Cyclin-dependent kinase 12 (CDK12)-deficient prostate cancer defines a subtype of castration-resistant prostate cancer (CRPC) with a poor prognosis. Current therapy, including PARP inhibitors, shows minimal treatment efficacy for this subtype of CRPC, and the underlying mechanism remains elusive. Based on bioinformatics analysis, we evaluated the relationship between CDK12 deficiency and prostate cancer patient's prognosis and treatment resistance. Furthermore, we used CRISPR-Cas9 technology and mass spectrometry-based metabolomic profiling to reveal the metabolic characteristics of CDK12-deficient CRPC. To elucidate the specific mechanisms of CDK12 deficiency-mediated CRPC metabolic reprogramming, we utilized cell RNA-seq profiling and other molecular biology techniques, including cellular reactive oxygen species probes, mitochondrial function assays, ChIP-qPCR and RNA stability analyses, to clarify the role of CDK12 in regulating mitochondrial function and its contribution to ferroptosis. Finally, through in vitro drug sensitivity testing and in vivo experiments in mice, we identified the therapeutic effects of the electron transport chain (ETC) inhibitor IACS-010759 on CDK12-deficient CRPC. CDK12-deficient prostate cancers reprogramme cellular energy metabolism to support their aggressive progression. In particular, CDK12 deficiency enhanced the mitochondrial respiratory chain for electronic transfer and ATP synthesis to create a ferroptosis potential in CRPC cells. However, CDK12 deficiency downregulated ACSL4 expression, which counteracts the lipid oxidation stress, leading to the escape of CRPC cells from ferroptosis. Furthermore, targeting the ETC substantially inhibited the proliferation of CDK12-deficient CRPC cells in vitro and in vivo, suggesting a potential new target for the therapy of CDK12-deficient prostate cancer. Our findings show that energy and lipid metabolism in CDK12-deficient CRPC work together to drive CRPC progression and provide a metabolic insight into the worse prognosis of CDK12-deficient prostate cancer patients. CDK12 deficiency promotes castration-resistant prostate cancer (CRPC) progression by reprogramming cellular metabolism. CDK12 deficiency in CRPC leads to a more active mitochondrial electron transport chain (ETC), ensuring efficient cell energy supply. CDK12 phosphorylates RNA Pol II to ensure the transcription of ACSL4 to regulate ferroptosis. Mitochondrial ETC inhibitors exhibit better selectivity for CDK12-deficient CRPC cells, offering a promising new therapeutic approach for this subtype of CRPC patients.

Increasing HCCS function in vivo mediates restoring heme integrity, limiting superoxide overproduction, and conferring reconditioning mitochondrial function in the acute postischemic heart

Background: A serious consequence of acute myocardial ischemia-reperfusion injury (I/R) is heme impairment which causes mitochondrial dysfunction, which contributes to cell death. Such acute I/R-induced mitochondrial dysfunction is characterized by impaired respiration and overproducing superoxide. The cascading ROS propagates heme damage in the array of mitochondrial electron transport chain, adding insult to myocardial injury. Mitochondrial holocytochrome c synthetase (HCCS) catalyzes attaching heme to apocytochrome c or apocytochrome c1 by forming thioether bonds. We reasoned that overexpression of HCCS would ameliorate I/R injury by stabilization of heme moieties in key mitochondrial enzymes. Methods: A mouse model with overexpression of HCCS in the myocytes (HCCS-tg) was generated and echocardiography was used to evaluate cardiac function. The HCCS-tg mouse was subjected to 30-min of coronary ligation and 24-h of reperfusion. Mitochondria were isolated from the myocardium of the risk region and assessed by OCR. The profile of heme from the cardiac mitochondria was assessed by differential UV/VIS spectral analysis. EPR spin-trapping and ubiquinol (Q2H2)-mediated cytochrome c reduction were used to assay superoxide generation by CxI (complex I) and CxIII (complex III) in mitochondria. Results: We detected gaining HCCS function in vivo (one-fold increase) marginally increases the fractional shortening of the mouse heart. There is no significant difference in heart rate and LVIDs/LVIDd between wild type control and HCCS-tg. Increasing function of HCCS in the myocytes further enhances mitochondrial function of HCCS-tg via increasing state-3 OCR, decreasing state-4 OCR, and alleviating superoxide generation by CxI (NADH-linked) and CxIII (Q2H2-linked). Increased HCCS function significantly decreases the infarct size assessed by IF/AAR and IF/LV when the mouse hearts were subjected to acute I/R injury. Overexpressing HCCS in myocytes further protected the heme integrity and the associated activity of electron transport chain in the mitochondria from acute I/R injury. Acute I/R also mediates downregulation of Cox10 and Cox15 required for mitochondrial a-type heme (heme a) biosynthesis and integrity of Cx4 (complex IV) activity, while increasing HCCS function in vivo preserves the integrity of heme a and protects the levels of Cox10, Cox15, and Cx4 activity after acute I/R injury. Conclusion: Acute I/R mediates mitochondrial heme impairment and associated mitochondrial dysfunction via impairing HCCS function and the thioether bonds of c-type heme, whereas overexpression of HCCS in the myocytes mediates protecting integrity of heme from I/R injury, limiting overproducing superoxide, and conferring reconditioning mitochondrial function in the post-ischemic heart. None. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The interplay between electron transport chain function and iron regulatory factors influences melanin formation in Cryptococcus neoformans.

Mitochondrial functions are critical for the ability of the fungal pathogen Cryptococcus neoformans to cause disease. However, mechanistic connections between key functions such as the mitochondrial electron transport chain (ETC) and virulence factor elaboration have yet to be thoroughly characterized. Here, we observed that inhibition of ETC complex III suppressed melanin formation, a major virulence factor. This inhibition was partially overcome by defects in Cir1 or HapX, two transcription factors that regulate iron acquisition and use. In this regard, loss of Cir1 derepresses the expression of laccase genes as a potential mechanism to restore melanin, while HapX may condition melanin formation by controlling oxidative stress. We hypothesize that ETC dysfunction alters redox homeostasis to influence melanin formation. Consistent with this idea, inhibition of growth by hydrogen peroxide was exacerbated in the presence of the melanin substrate L-DOPA. In addition, loss of the mitochondrial chaperone Mrj1, which influences the activity of ETC complex III and reduces ROS accumulation, also partially overcame antimycin A inhibition of melanin. The phenotypic impact of mitochondrial dysfunction was consistent with RNA-Seq analyses of WT cells treated with antimycin A or L-DOPA, or cells lacking Cir1 that revealed influences on transcripts encoding mitochondrial functions (e.g., ETC components and proteins for Fe-S cluster assembly). Overall, these findings reveal mitochondria-nuclear communication via ROS and iron regulators to control virulence factor production in C. neoformans.IMPORTANCEThere is a growing appreciation of the importance of mitochondrial functions and iron homeostasis in the ability of fungal pathogens to sense the vertebrate host environment and cause disease. Many mitochondrial functions such as heme and iron-sulfur cluster biosynthesis, and the electron transport chain (ETC), are dependent on iron. Connections between factors that regulate iron homeostasis and mitochondrial activities are known in model yeasts and are emerging for fungal pathogens. In this study, we identified connections between iron regulatory transcription factors (e.g., Cir1 and HapX) and the activity of complex III of the ETC that influence the formation of melanin, a key virulence factor in the pathogenic fungus Cryptococcus neoformans. This fungus causes meningoencephalitis in immunocompromised people and is a major threat to the HIV/AIDS population. Thus, understanding how mitochondrial functions influence virulence may support new therapeutic approaches to combat diseases caused by C. neoformans and other fungi.