Mitochondrial Electron Transport Chain Research Articles

Innovative formulations for the ocular delivery of coenzyme Q10.

Coenzyme Q10 (CoQ10) is a lipophilic antioxidant agent that plays a crucial role in the mitochondrial electron transport chain. The neuroprotective role of CoQ10, countering mitochondrial dysfunction and oxidative stress, suggests its potential as an adjuvant for ocular neurodegenerative diseases linked to retinal cell loss. However, despite its promising properties, ocular barriers pose challenges for effective delivery. Therefore, the present work aimed to identify new ocular delivery strategies to improve the therapeutic potential of CoQ10 by increasing its ocular bioavailability at the posterior segment and supporting its controlled release. Polymeric micelles of D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) were selected as carriers for the loading of CoQ10, increasing its solubility and promoting its penetration through ocular tissues. After their characterization by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS), loaded micelles were applied to porcine sclera and choroid to confirm their ex vivo retention and permeation capacity. To ensure a controlled release, they were then loaded into a crosslinked polymer film, which was characterized in terms of mechanical properties, swelling degree and release profiles of TPGS and CoQ10. The biocompatibility of this platform was tested by the HET-CAM assay, and ex vivo studies confirmed its ocular potential.

Mitochondrial pathways of copper neurotoxicity: focus on mitochondrial dynamics and mitophagy

Copper (Cu) is essential for brain development and function, yet its overload induces neuronal damage and contributes to neurodegeneration and other neurological disorders. Multiple studies demonstrated that Cu neurotoxicity is associated with mitochondrial dysfunction, routinely assessed by reduction of mitochondrial membrane potential. Nonetheless, the role of alterations of mitochondrial dynamics in brain mitochondrial dysfunction induced by Cu exposure is still debatable. Therefore, the objective of the present narrative review was to discuss the role of mitochondrial dysfunction in Cu-induced neurotoxicity with special emphasis on its influence on brain mitochondrial fusion and fission, as well as mitochondrial clearance by mitophagy. Existing data demonstrate that, in addition to mitochondrial electron transport chain inhibition, membrane damage, and mitochondrial reactive oxygen species (ROS) overproduction, Cu overexposure inhibits mitochondrial fusion by down-regulation of Opa1, Mfn1, and Mfn2 expression, while promoting mitochondrial fission through up-regulation of Drp1. It has been also demonstrated that Cu exposure induces PINK1/Parkin-dependent mitophagy in brain cells, that is considered a compensatory response to Cu-induced mitochondrial dysfunction. However, long-term high-dose Cu exposure impairs mitophagy, resulting in accumulation of dysfunctional mitochondria. Cu-induced inhibition of mitochondrial biogenesis due to down-regulation of PGC-1α further aggravates mitochondrial dysfunction in brain. Studies from non-brain cells corroborate these findings, also offering additional evidence that dysregulation of mitochondrial dynamics and mitophagy may be involved in Cu-induced damage in brain. Finally, Cu exposure induces cuproptosis in brain cells due mitochondrial proteotoxic stress, that may also contribute to neuronal damage and pathogenesis of certain brain diseases. Based on these findings, it is assumed that development of mitoprotective agents, specifically targeting mechanisms of mitochondrial quality control, would be useful for prevention of neurotoxic effects of Cu overload.

Riboflavin kinase binds and activates inducible nitric oxide synthase to reprogram macrophage polarization

Riboflavin kinase (RFK) is essential in riboflavin metabolism, converting riboflavin to flavin mononucleotide (FMN), which is further processed to flavin adenine dinucleotide (FAD). While RFK enhances macrophage phagocytosis of Listeria monocytogenes, its role in macrophage polarization is not well understood. Our study reveals that RFK deficiency impairs M(IFN-γ) and promotes M(IL-4) polarization, both in vitro and in vivo. Mechanistically, RFK interacts with inducible nitric oxide (NO) synthase (iNOS), which requires FMN and FAD as cofactors for activation, leading to increased NO production that alters energy metabolism by inhibiting the tricarboxylic acid cycle and mitochondrial electron transport chain. Exogenous FAD reverses the metabolic and polarization changes caused by RFK deficiency. Furthermore, bone marrow adoptive transfer from high-riboflavin-fed mice into wild-type tumor-bearing mice reprograms tumor-associated macrophage polarization and inhibits tumor growth. These results suggest that targeting RFK-iNOS or modulating riboflavin metabolism could be potential therapies for macrophage-related immune diseases.

Chitosan/siRNA nanoparticles targeting PARP-1 attenuate Neuroinflammation and apoptosis in hyperglycemia-induced oxidative stress in Neuro2a cells

Hyperglycemia induces an excessive production of superoxide by the mitochondria's electron-transport chain triggers several pathways of injury contributing to the development of diabetic complications. This increase in oxidative and nitrosative stress triggers the activation of PARP-1, a nuclear enzyme, through mechanisms such as DNA damage. siRNA-chitosan nanoparticles were formed based on electrostatic interaction, their particle size, zeta potential, STEM, and cellular uptake were characterized. Neuro2a cells were treated with low glucose (LG) and high glucose (HG) for 24 and 48 h. Neuro2a cells were pre-treated with negative siRNA, naked siRNA, siRNA-Lipofectamine™300, and ChNPs-5. qRT-PCR was used to analyze the expression of regulatory, inflammatory, and apoptotic biomarkers. The siRNA-chitosan complex at the weight ratio 1:3000 were approximately uniform spheres with particle size 150.5 nm and a positive zeta potential of about +41.5 mV. The uptake of FITC-labeled nanoparticles into Neuro2a cells was visualized using fluorescence microscopy with no significant cytotoxicity compared to the control cells. High glucose stimulation of Neuro2a cells increased PARP1 expression, and with siRNA-ChNP (1:3000) treatment, significant inhibition of PARP1 expression is observed that consequently reversed the expression of regulatory genes like SIRT1, FOXO1, FOXO3, and p53. PARP-1 inhibition reduced HG-induced inflammatory response, including NF-kB, IL6, IL1β, TNFα, iNOS, and TGF-β expression, and HG-induced apoptosis response, such as Cas-3, Cas-9, BAK, BAX, and AIF expression. This study highlights the crucial role of siRNA delivery via ChNPs and PARP-1 inhibition in hyperglycemia-induced oxidative stress in Neuro2a cells and PARP-1 inhibition may be a feasible strategy for the treatment of hyperglycemia-induced oxidative stress.

Species differences in glycerol-3-phosphate metabolism reveals trade-offs between metabolic adaptations and cell proliferation

The temperate climate-adapted brown hare (Lepus europaeus) and the cold-adapted mountain hare (Lepus timidus) are closely related and interfertile species. However, their skin fibroblasts display distinct gene expression profiles related to fundamental cellular processes. This indicates important metabolic divergence between the two species. Through targeted metabolomics and metabolite tracing, we identified species-specific variations in glycerol 3-phosphate (G3P) metabolism. G3P is a key metabolite of the G3P shuttle, which transfers reducing equivalents from cytosolic NADH to the mitochondrial electron transport chain (ETC), consequently regulating glycolysis, lipid metabolism, and mitochondrial bioenergetics. Alterations in G3P metabolism have been implicated in multiple human pathologies including cancer and diabetes. We observed that mountain hare mitochondria exhibit elevated G3P shuttle activity, alongside increased membrane potential and decreased mitochondrial temperature. Silencing mitochondrial G3P dehydrogenase (GPD2), which couples the conversion of G3P to the ETC, uncovered its species-specific role in controlling mitochondrial membrane potential and highlighted its involvement in skin fibroblast thermogenesis. Unexpectedly, GPD2 silencing enhanced wound healing and cell proliferation rates in a species-specific manner. Our study underscores the pivotal role of the G3P shuttle in mediating physiological, bioenergetic, and metabolic divergence between these hare species.

Sphingosine kinase 2 (SphK2) depletion alters redox metabolism and enhances inflammation in a diet-induced MASH mouse model

Background: Sphingosine-1 phosphate (S1P) is a bioactive lipid molecule that modulates inflammation and hepatic lipid metabolism in MASLD, which affects 1 in 3 people and increases the risk of liver fibrosis and hepatic cancer. S1P can be generated by 2 isoforms of sphingosine kinase (SphK). SphK1 is well-studied in metabolic diseases. In contrast, SphK2 function is not well characterized. Both sphingolipid and redox metabolism dysregulation contribute to MASLD pathologic progression. While SphK2 localizes to both the nucleus and mitochondria, its specific role in early MASH is not well defined. Methods: This study examined SphK2 depletion effects on hepatic redox metabolism, mitochondrial function, and inflammation in a 16-week western diet plus sugar water (WDSW)-induced mouse model of early MASH. Results: WDSW-SphK2 −/− mice exhibit increased hepatic lipid accumulation and hepatic redox dysregulation. In addition, mitochondria-localized cholesterol and S1P precursors were increased. We traced SphK2 −/− -mediated mitochondrial electron transport chain impairment to respiratory complex-IV and found that decreased mitochondrial redox metabolism coincided with increased oxidase gene expression and oxylipin production. Consistent with this relationship, we observed pronounced increases in hepatic inflammatory gene expression, prostaglandin accumulation, and innate immune homing in WDSW-SphK2 −/− mice compared to WDSW-wild-type mice. Conclusions: These studies suggest SphK2-derived S1P maintains hepatic redox metabolism and describe the potential consequences of SphK2 depletion on proinflammatory gene expression, lipid mediator production, and immune infiltration in MASH progression.

Bioorthogonal Activation of Deep Red Photoredox Catalysis Inducing Pyroptosis.

The revolutionary impact of photoredox catalytic processes has ignited novel avenues for exploration, empowering us to delve into nature in unprecedented ways and to pioneer innovative biotechnologies for therapy and diagnosis. However, integrating artificial photoredox catalysis into living systems presents significant challenges, primarily due to concerns over low targetability, low compatibility with complex biological environments, and the safety risks associated with photocatalyst toxicity. To address these challenges, herein, we present a novel bioorthogonally activatable photoredox catalysis approach. In this approach, potent photocatalyst selection via atom replacement of the rhodamine core yielded the bioorthogonally activatable photocatalyst (PC-Tz). The introduction of 1,2,4,5-tetrazine quenched its photocatalytic properties, which were restored upon an intracellular inverse electron-demand Diels-Alder (iEDDA) reaction with trans-cyclooctene (TCO) localized in mitochondria. This reaction led to remarkable photocatalytic oxidation of nicotinamide adenine dinucleotide (NADH), effectively manipulating the mitochondrial electron transport chain (ETC) under hypoxic conditions in cancer cells. Additionally, photocatalytic pyroptotic cell death was observed through a caspase-3/gasdermin E (GSDME) pathway, achieving notable antitumor efficacy and adenosine triphosphate (ATP) reduction in tumor cells. To the best of our knowledge, this represents the first example of bioorthogonally activatable photoredox catalysis, opening new avenues for chemists to spatiotemporally control activity in specific cell organelles without disrupting other native biological processes.

The first proteomics analysis of tonsils in patients with periodic fever, aphthous stomatitis, pharyngitis, and adenitis syndrome (PFAPA).

Periodic fever, aphthous stomatitis, pharyngitis, and adenitis (PFAPA) syndrome is a recurrent fever syndrome. The exact etiopathogenesis of PFAPA syndrome remains unknown. Biological fluids or tissues may provide disease-specific biomarkers that may help clinicians to find new pathogenic pathways. Tonsil tissues of seven patients with PFAPA were collected during the tonsillectomy. Seven patients who underwent tonsillectomy for reasons other than chronic tonsillitis were enrolled as a control group. The nHPLC LC-MS/MS system was used for protein identification and label-free quantification. Bioinformatics analysis was carried out using the UniProt accession numbers of the identified proteins. Proteomics analysis revealed to identity of proteins of which at least 23 were up and 57 were downregulated. Bioinformatics analysis of differentially regulated proteins by STRING indicated that protein folding and clearance machinery were interrupted in PFAPA patients compared to the controls. The affected pathways underlined the importance of the mitochondrial electron transport chain and ATP biosynthesis process. Although it is not clear that changes in tonsil protein expression whether directly related to pathogenesis or simply result of chronic inflammation, the identification of tonsil biomarkers for PFAPA may provide clinicians an opportunity to understand disease pathogenesis or develop new molecular targets for treatments. Proteomics analyses of tonsils revealed the identity of 80 proteins of which at least 23 were up and 57 were downregulated. Bioinformatics analysis underlined the importance of mitochondrial ETC and regulation of ATP biosynthetic process. This is the first study evaluating the proteomics of the tonsils of PFAPA patients. The identification of tonsil biomarkers for PFAPA may provide clinicians an opportunity to understand disease pathogenesis or develop new molecular targets for treatments.

Disease registries and rare disorders: The virtuous example of mitochondrial medicine

Primary mitochondrial disorders (PMDs) are an extraordinarily complex group of rare disorders caused by impairment of the mitochondrial electron transport chain, or respiratory chain. Studying genotype-phenotype relationships in PMDs is a complex task. The clinical variability is large even in individuals with the same genotype, and the statistical power is low in single-center studies because of their rarity. To better define the clinical phenotypes associated with PMDs, in the last 15 years a significant multicenter effort has led to nation-wide studies on large cohorts of patients. Many national registries of mitochondrial patients have been developed in recent years, and now there is a strong effort towards international (and even global) registries. This review will revise the notable advances obtained with such studies in recent years, and will discuss the actual developments and future perspectives.

Arginyltransferase1 drives a mitochondria-dependent program to induce cell death.

Cell death regulation is essential for stress adaptation and/or signal response. Past studies have shown that eukaryotic cell death is mediated by an evolutionarily conserved enzyme, arginyltransferase1 (Ate1). The downregulation of Ate1, as seen in many types of cancer, prominently increases cellular tolerance to a variety of stressing conditions. Conversely, in yeast and mammalian cells, Ate1 is elevated under acute oxidative stress conditions and this change appears to be essential for triggering cell death. However, studies of Ate1 were conventionally focused on its function in inducing protein degradation via the N-end rule pathway in the cytosol, leading to an incomplete understanding of the role of Ate1 in cell death. Our recent investigation shows that Ate1 dually exists in the cytosol and mitochondria, the latter of which has an established role in cell death initiation. Here, by using budding yeast as a model organism, we found that mitochondrial translocation of Ate1 is promoted by the presence of oxidative stressors and is essential for inducing cell death with characteristics of apoptosis. Also, we found that Ate1-induced cell death is dependent on the formation of the mitochondrial permeability pore and at least partly dependent on the action of mitochondria-contained factors including the apoptosis-inducing factor, but is not directly dependent on mitochondrial electron transport chain activity or its derived reactive oxygen species (ROS). Furthermore, our evidence suggests that, contrary to widespread assumptions, the cytosolic protein degradation pathways including ubiquitin-proteasome, autophagy, or endoplasmic reticulum (ER) stress response has little or negligible impacts on Ate1-induced cell death. We conclude that Ate1 controls the mitochondria-dependent cell death pathway.

Skeletal muscle hypertrophy and enhanced mitochondrial bioenergetics following electrical stimulation exercises in spinal cord injury: a randomized clinical trial.

We examined the combined effects of neuromuscular electrical stimulation-resistance training (NMES-RT) and functional electrical stimulation-lower extremity cycling (FES-LEC) compared to passive movement training (PMT) and FES-LEC on mitochondrial electron transport chain (ETC) complexes and citrate synthase (CS) in adults with SCI. Thirty-two participants with chronic SCI were randomized to 24weeks of NMES-RT + FES [n = 16 (14 males and 2 females) with an age range of 20-54years old] or PMT + FES [n = 16 (12 males and 4 females) with an age range of 21-61years old]. The NMES-RT + FES group underwent 12weeks of surface NMES-RT using ankle weights followed by an additional 12weeks of FES-LEC. The PMT + FES performed 12weeks of passive leg extension movements followed by an additional 12weeks of FES-LEC. Using repeated measures design, muscle biopsies of the vastus lateralis were performed at baseline (BL), post-intervention 1 (P1) and post-intervention 2 (P2). Spectrophotometer was used to measure ETC complexes (I-III) and CS using aliquots of the homogenized muscle tissue. Magnetic resonance imaging was used to measure skeletal muscle CSAs. A time effect was noted on CS (P = 0.001) with an interaction between both groups (P = 0.01). 46% of the participants per group had zero activities of CI without any changes following both interventions. A time effect was noted in CII (P = 0.023) following both interventions. Finally, NMES-RT + FES increased CIII at P1 compared to BL (P = 0.023) without additional changes in P2 or following PMT + FES intervention. Skeletal muscle hypertrophy may potentially enhance mitochondrial bioenergetics after SCI. NMES-RT is likely to enhance the activities of complex III in sedentary persons with SCI. Clinical trials # NCT02660073.

Auto-Deactivation of BODIPY-Derived Type I Photosensitizer Post Photodynamic Therapy under Hypoxia.

The long-lasting activity of photosensitizers during photodynamic therapy (PDT) causes excessive damage and arouses great concerns about biosafety. Herein, we synthesized a pyridinium-decorated diiodo-BODIPY compound (PyBDP) and investigated its photosensitizing activity under hypoxic condition in the presence of NADH that is abundant in the mitochondria of hypoxic tumors. The unique property of PyBDP lies in the redox environment-dependent photo-response. At green light exposure, PyBDP is converted into a colorless inactive form by interacting with NADH in a two-step one-electron transfer process. Interestingly, the NADH-dependent hydrogenation of PyBDP is affected by the presence of cytochrome c (Cyt cox) that is an important component of mitochondrial electron transport chain (Mito-ETC), unless Cyt cox is exhausted. Active radical species is produced during the photocatalytic reaction, which adds the understanding of PyBDP-induced photodamage. Therefore, we applied the strategy of auto-deactivation PDT using a BODIPY photosensitizer by tethering triphenylphosphonium to PyBDP. After PDT effect in a type I pathway, the photosensitizer underwent almost entire auto-deactivation in hypoxic HeLa cells. This work paves a way for the development of reductive PDT with enhanced safety and efficacy in fighting hypoxic tumors independent on reactive oxygen species (ROS).

Phosphorylation of cytochrome c at tyrosine 48 finely regulates its binding to the histone chaperone SET/TAF-Iβ in the nucleus.

Post-translational modifications (PTMs) of proteins are ubiquitous processes present in all life kingdoms, involved in the regulation of protein stability, subcellular location and activity. In this context, cytochrome c (Cc) is an excellent case study to analyze the structural and functional changes induced by PTMS as Cc is a small, moonlighting protein playing different roles in different cell compartments at different cell-cycle stages. Cc is actually a key component of the mitochondrial electron transport chain (ETC) under homeostatic conditions but is translocated to the cytoplasm and even the nucleus under apoptotic conditions and/or DNA damage. Phosphorylation does specifically alter the Cc redox activity in the mitochondria and the Cc non-redox interaction with apoptosis-related targets in the cytoplasm. However, little is known on how phosphorylation alters the interaction of Cc with histone chaperones in the nucleus. Here, we report the effect of Cc Tyr48 phosphorylation by examining the protein interaction with SET/TAF-Iβ in the nuclear compartment using a combination of molecular dynamics simulations, biophysical and structural approaches such as isothermal titration calorimetry (ITC) and nuclear magnetic resonance (NMR) and in cell proximity ligation assays. From these experiments, we infer that Tyr48 phosphorylation allows a fine-tuning of the Cc-mediated inhibition of SET/TAF-Iβ histone chaperone activity in vitro. Our findings likewise reveal that phosphorylation impacts the nuclear, stress-responsive functions of Cc, and provide an experimental framework to explore novel aspects of Cc post-translational regulation in the nucleus.

Aging, ROS, and cellular senescence: a trilogy in the progression of liver fibrosis.

Ageing is an inevitable and multifaceted biological process that impacts a wide range of cellular and molecular mechanisms, leading to the development of various diseases, such as liver fibrosis. Liver fibrosis progresses to cirrhosis, which is an advanced form due to high amounts of extracellular matrix and restoration of normal liver structure with failure to repair damaged tissue and cells, marking the end of liver function and total liver failure, ultimately death. The most important factors are reactive oxygen species (ROS) and cellular senescence. Oxidative stress is defined as an impairment by ROS, which are by-products of the mitochondrial electron transport chain and other key molecular pathways that induce cell damage and can activate cellular senescence pathways. Cellular senescence is characterized by pro-inflammatory cytokines, growth factors, and proteases secreted by senescent cells, collectively known as the senescence-associated secretory phenotype (SASP). The presence of senescent cells, which disrupt tissue architecture and function and increase senescent cell production in liver tissues, contributes to fibrogenesis. Hepatic stellate cells (HSCs) are activated in response to chronic liver injury, oxidative stress, and senescence signals that drive excessive production and deposition of extracellular matrix. This review article aims to provide a comprehensive overview of the pathogenic role of ROS and cellular senescence in the aging liver and their contribution to fibrosis.

Lipophilic bisphosphonates reduced cyst burden and ameliorated hyperactivity of mice chronically infected with Toxoplasma gondii.

The current treatments for toxoplasmosis are only active against fast-growing tachyzoites, present in acute infections, with little effect on slow-growing bradyzoites within tissue cysts, present in latent chronic infections. The mitochondrion of Toxoplasma gondii is essential for its survival, and one of the major anti-parasitic drugs, atovaquone, inhibits the mitochondrial electron transport chain at the coenzyme Q:cytochrome c oxidoreductase site. Coenzyme Q (also known as ubiquinone [UQ]) consists of a quinone head and a lipophilic, isoprenoid tail that anchors UQ to membranes. The synthesis of the isoprenoid unit is essential for cell growth and is inhibited by lipophilic bisphosphonates, which inhibit the parasite growth. In this work, we investigated the effect of lipophilic bisphosphonates on the chronic stages of T. gondii. We discovered that three lipophilic bisphosphonates (BPH-1218, BPH-1236, and BPH-1238), effective for the acute infection, were also effective in controlling the development of chronic stages. We showed effectiveness by testing them against in vitro cysts and in vivo derived tissue cysts and, most importantly, these compounds reduced the cyst burden in the brains of chronically infected mice. We monitored the activity of infected mice non-invasively and continuously with a novel device termed the CageDot. A decrease in activity accompanied the acute phase, but mice recovered to normal activity and showed signs of hyperactivity when the chronic infection was established. Moreover, treatment with atovaquone or BPH-1218 ameliorated the hyperactivity observed during the chronic infection.IMPORTANCETreatment for toxoplasmosis is challenged by a lack of effective drugs to eradicate the chronic stages. Most of the drugs currently used are poorly distributed to the central nervous system, and they trigger allergic reactions in a large number of patients. There is a compelling need for safe and effective treatments for toxoplasmosis. Bisphosphonates (BPs) are analogs of inorganic pyrophosphate and are used for the treatment of bone disorders. BPs target the isoprenoid pathway and are effective against several experimental parasitic infections. Some lipophilic BPs can specifically inhibit the mitochondrial activity of Toxoplasma gondii by interfering with the mechanism by which ubiquinone is inserted into the inner mitochondrial membrane. In this work, we present the effect of three lipophilic BPs against T. gondii chronic stages. We also present a new strategy for the monitoring of animal activity during disease and treatment that is non-invasive and continuous.

Abstract 4117594: Fetal Synthetic Glucocorticoid (sGC) Exposure Results in Later Life Cardiac Dysfunction and Ventricular Remodeling in Male Baboon Offspring

The “theory of developmental origins of health and disease” posits that stress in critical developmental periods will program life-course health and may affect cardiovascular (CV) health. Mothers at risk for premature delivery receive synthetic glucocorticoids (sGC) to enhance fetal lung maturation and manage fetal respiratory distress, but sGC exposure is linked to long-term CV dysfunction in offspring. Four groups of male baboons were studied: sGC exposed in utero at middle age (sGC-MA, 13.8±0.2Y), older sGC exposed in utero (sGC-O, 17.1±0.4Y), middle age unexposed (CTR-MA, 13.5±0.6Y), and older, unexposed baboons (CTR-O, 17.4±0.4Y). Gated, breath-hold, cine cardiac magnetic resonance imaging was performed at 3 Tesla (Siemens TIM Trio) to assess left ventricular (LV) function and myocardial strain, analyzed using cvi42® software. Mitochondrial electron transport chain (ETC) complex activity was analyzed using LV tissue from sGC-O and CTR-O euthanized baboons. Protein quantification was used to measure mitochondrial function and RNA-seq assessed differential gene expression and gene ontology (GO) enrichment. Unpaired t-tests were used. Data are reported as mean ± SD. Stroke volume and ejection fraction were similar in the elderly groups (4 sGC-O, 8 CTR-O). However, higher end-systolic and end-diastolic sphericity indexes (SI) and shorter LV axis lengths indicated remodeling. Also, global longitudinal and radial strains were reduced (both p<0.04) in sGC-O vs. CTR-O. Reduced LV cardiac output (p=0.005) was found in 5 sGC-MA animals vs 4 sGC-O animals, but not in 5 CTR-MA vs 8 CTR-O. In sGC-MA vs sGC-O, but not CTR-MA vs CTR-O, significant increases in SI (p=0.001), radial strain (p=0.02), and longitudinal (p=0.03) strain were found, but LV axis length (p=0.03) was reduced. LV mitochondrial analysis in 4 sGC-O vs 4 CTR-O myocardial samples revealed 33.5% less ETC activity (p=0.002) and 19.8% less complex I expression (p=0.048) in sGC. LV RNA-seq identified 63 upregulated and 20 downregulated genes in the sGC-O samples. GO pathway enrichment included changes in heart contraction, wounding responses, and leukocyte regulation pathways. These findings indicate that fetal sGC exposure developmentally programs offspring with LV remodeling and long-term cardiac and gene expression changes in male baboons, the closest available experimental nonhuman primate species to man. Future studies on females will probe sexual dimorphism in developmental programming.

Mitochondrial AOX1a and an H2O2 feed-forward signalling loop regulate flooding tolerance in rice.

Flooding is a widespread natural disaster that causes tremendous yield losses of global food production. Rice is the only cereal capable of growing in aquatic environments. Direct seeding by which seedlings grow underwater is an important cultivation method for reducing rice production cost. Hypoxic germination tolerance and root growth in waterlogged soil are key traits for rice adaptability to flooded environments. Alternative oxidase (AOX) is a non-ATP-producing terminal oxidase in the plant mitochondrial electron transport chain, but its role in hypoxia tolerance had been unclear. We have discovered that AOX1a is necessary and sufficient to promote germination/coleoptile elongation and root development in rice under flooding/hypoxia. Hypoxia enhances endogenous H2O2 accumulation, and H2O2 in turn activates an ensemble of regulatory genes including AOX1a to facilitate the conversion of deleterious reactive oxygen species to H2O2 in rice under hypoxia. We show that AOX1a and H2O2 act interdependently to coordinate three key downstream events, that is, glycolysis/fermentation for minimal ATP production, root aerenchyma development and lateral root emergence under hypoxia. Moreover, we reveal that ectopic AOX1a expression promotes vigorous root and plant growth, and increases grain yield under regular irrigation conditions. Our discoveries provide new insights into a unique sensor-second messenger pair in which AOX1a acts as the sensor perceiving low oxygen tension, while H2O2 accumulation serves as the second messenger triggering downstream root development in rice against hypoxia stress. This work also reveals AOX1a genetic manipulation and H2O2 pretreatment as potential targets for improving flooding tolerance in rice and other crops.

Abstract 4123630: MRPL44 Plays an Important Role in Cardiac Hypertrophy and Function

Background: Mitochondrial ribosomal large subunit 44 (MRPL44) knockout mice were embryonic lethal, for which mutations are known to cause mitochondrial infantile cardiomyopathy and hypertrophic cardiomyopathy. However, it remains unknown how MRPL44 contributes to cardiac function and hypertrophy. Aims: Our aim is to investigate the effect of MRPL44 haploinsufficiency in mice. Methods: MRPL44 haploinsufficient (MRPL44 +/- ) mice were generated. Mineralocorticoid receptor-associated hypertension mice were induced in MRPL44 +/- and wild-type (WT, MRPL44 +/+ ) mice with subcutaneous infusion of aldosterone(Aldo) and 8% NaCl food for 4 weeks after uninephrectomy. Systolic blood pressure was measured by tail cuffs every week. WB, qPCR, cardiac echo, and histological examinations were performed. RNA sequencing analysis, electron microscopy examinations and mitochondrial activity assay were performed to find differences between MRPL44 +/- and MRPL44 +/+ mice. Results: MRPL44 haploinsufficient mice spontaneously developed left ventricular hypertrophy. Heart rate, blood pressure, and cardiac systolic function were normal in MRPL44 haploinsufficient mice. MRPL44 was decreased about to 70% in MRPL44 haploinsufficient mice and mitochondrial arrangement were impaired in electron microscopic analysis. After Aldo treatment, blood pressure elevation were similar, however, MRPL44 haploinsufficient mice developed left ventricular systolic dysfunction and dilation compared with MRPL44 +/+ mice. WB showed mitochondrial electron transport chain protein complex IV expression was significantly decreased. Furthermore, mitochondrial activity assay showed MRPL44 haploinsufficient mice had a significant reduction in complex IV activity, whereas complex I and II activity were similar to MRPL44 +/+ mice. RNA sequencing analysis showed the significant changes in the expression of ribosomal subunits coded by nucleus in addition to mitochondrial ribosomal subunits. These results indicate MRPL44 plays an important role in the cardiac function of mitochondrial electron transport chain protein complexes via the expression of ribosomal protein subunits coded by both nucleus and mitochondria. Conclusion: MRPL44 haploinsufficient mice spontaneously develop left ventricular hypertrophy and shows systolic dysfunction after aldosterone treatment accompanied with oxidative phosphorylation enzyme dysfunction.

Inhibition of VDAC1 oligomerization blocks cysteine deprivation-induced ferroptosis via mitochondrial ROS suppression

Ferroptosis, a regulated form of cell death dependent on reactive oxygen species (ROS), is characterized by iron accumulation and lethal lipid peroxidation. Mitochondria serve as the primary source of ROS and thus play a crucial role in ferroptosis initiation and execution. This study highlights the role of mitochondrial ROS and the significance of voltage-dependent anion channel 1 (VDAC1) oligomerization in ferroptosis induced by cysteine deprivation or ferroptosis-inducer RSL3. Our results demonstrate that the mitochondria-targeted antioxidants MitoQ and MitoT effectively block ferroptosis induction and that dysfunction of complex III of the mitochondrial electron transport chain contributes to ferroptosis induction. Pharmacological inhibitors that target VDAC1 oligomerization have emerged as potent suppressors of ferroptosis that reduce mitochondrial ROS production. These findings underscore the critical involvement of mitochondrial ROS production via complex III of the electron transport chain and the essential role of VDAC1 oligomerization in ferroptosis induced by cysteine deprivation or RSL3. This study deepens our understanding of the intricate molecular networks governing ferroptosis and provides insights into the development of novel therapeutic strategies targeting dysregulated cell death pathways.

TAp73 regulates mitochondrial dynamics and multiciliated cell homeostasis through an OPA1 axis

Dysregulated mitochondrial fusion and fission has been implicated in the pathogenesis of numerous diseases. We have identified a novel function of the p53 family protein TAp73 in regulating mitochondrial dynamics. TAp73 regulates the expression of Optic Atrophy 1 (OPA1), a protein responsible for controlling mitochondrial fusion, cristae biogenesis and electron transport chain function. Disruption of this axis results in a fragmented mitochondrial network and an impaired capacity for energy production via oxidative phosphorylation. Owing to the role of OPA1 in modulating cytochrome c release, TAp73−/− cells display an increased sensitivity to apoptotic cell death, e.g., via BH3-mimetics. We additionally show that the TAp73/OPA1 axis has functional relevance in the upper airway, where TAp73 expression is essential for multiciliated cell differentiation and function. Consistently, ciliated epithelial cells of Trp73−/− (global p73 knock-out) mice display decreased expression of OPA1 and perturbations of the mitochondrial network, which may drive multiciliated cell loss. In support of this, Trp73 and OPA1 gene expression is decreased in chronic obstructive pulmonary disease (COPD) patients, a disease characterised by alterations in mitochondrial dynamics. We therefore highlight a potential mechanism involving the loss of p73 in COPD pathogenesis. Our findings also add to the growing body of evidence for growth-promoting roles of TAp73 isoforms.