YME1L controls the accumulation of respiratory chain subunits and is required for apoptotic resistance, cristae morphogenesis, and cell proliferation

Role of Yme1 in mitochondrial protein homeostasis: from regulation of protein import, OXPHOS function to lipid synthesis and mitochondrial dynamics

Mitochondria are essential organelles of eukaryotic cells and thus mitochondrial proteome is under constant quality control and remodelling. Yme1 is a multi-functional protein and subunit of the homo-hexametric complex i-AAA proteinase. Yme1 plays vital roles in the regulation of mitochondrial protein homeostasis and mitochondrial plasticity, ranging from substrate degradation to the regulation of protein functions involved in mitochondrial protein biosynthesis, energy production, mitochondrial dynamics, and lipid biosynthesis and signalling. In this mini review, we focus on discussing the current understanding of the roles of Yme1 in mitochondrial protein import via TIM22 and TIM23 pathways, oxidative phosphorylation complex function, as well as mitochondrial lipid biosynthesis and signalling, as well as a brief discussion of the role of Yme1 in modulating mitochondrial dynamics.

Expression and functional implications of YME1L in nasopharyngeal carcinoma

Mitochondria play a crucial role in the progression of nasopharyngeal carcinoma (NPC). YME1L, a member of the AAA ATPase family, is a key regulator of mitochondrial function and has been implicated in various cellular processes and diseases. This study investigates the expression and functional significance of YME1L in NPC. YME1L exhibits significant upregulation in NPC tissues from patients and across various primary human NPC cells, while its expression remains relatively low in adjacent normal tissues and primary nasal epithelial cells. Employing genetic silencing through the shRNA strategy or knockout (KO) via the CRISPR-sgRNA method, we demonstrated that YME1L depletion disrupted mitochondrial function, leading to mitochondrial depolarization, reactive oxygen species (ROS) generation, lipid peroxidation, and ATP reduction within primary NPC cells. Additionally, YME1L silencing or KO substantially impeded cell viability, proliferation, cell cycle progression, and migratory capabilities, concomitant with an augmentation of Caspase-apoptosis activation in primary NPC cells. Conversely, ectopic YME1L expression conferred pro-tumorigenic attributes, enhancing ATP production and bolstering NPC cell proliferation and migration. Moreover, our findings illuminate the pivotal role of YME1L in Akt-mTOR activation within NPC cells, with Akt-S6K phosphorylation exhibiting a significant decline upon YME1L depletion but enhancement upon YME1L overexpression. In YME1L-silenced primary NPC cells, the introduction of a constitutively-active Akt1 mutant (caAkt1, at S473D) restored Akt-S6K phosphorylation, effectively ameliorating the inhibitory effects imposed by YME1L shRNA. In vivo studies revealed that intratumoral administration of YME1L-shRNA-expressing adeno-associated virus (AAV) curtailed subcutaneous NPC xenograft growth in nude mice. Furthermore, YME1L downregulation, concurrent with mitochondrial dysfunction and ATP reduction, oxidative injury, Akt-mTOR inactivation, and apoptosis induction were evident within YME1L-silenced NPC xenograft tissues. Collectively, these findings shed light on the notable pro-tumorigenic role by overexpressed YME1L in NPC, with a plausible mechanism involving the promotion of Akt-mTOR activation.

Targeting the mitochondrial protein YME1L to inhibit osteosarcoma cell growth in vitro and in vivo

Exploring novel diagnostic and therapeutic biomarkers is extremely important for osteosarcoma. YME1 Like 1 ATPase (YME1L), locating in the mitochondrial inner membrane, is key in regulating mitochondrial plasticity and metabolic activity. Its expression and potential functions in osteosarcoma are studied in the present study. We show that YME1L mRNA and protein expression is significantly elevated in osteosarcoma tissues derived from different human patients. Moreover, its expression is upregulated in various primary and immortalized osteosarcoma cells. The Cancer Genome Atlas database results revealed that YME1L overexpression was correlated with poor overall survival and poor disease-specific survival in sarcoma patients. In primary and immortalized osteosarcoma cells, silencing of YME1L through lentiviral shRNA robustly inhibited cell viability, proliferation, and migration. Moreover, cell cycle arrest and apoptosis were detected in YME1L-silenced osteosarcoma cells. YME1L silencing impaired mitochondrial functions in osteosarcoma cells, causing mitochondrial depolarization, oxidative injury, lipid peroxidation and DNA damage as well as mitochondrial respiratory chain complex I activity inhibition and ATP depletion. Contrarily, forced YME1L overexpression exerted pro-cancerous activity and strengthened primary osteosarcoma cell proliferation and migration. YME1L is important for Akt-S6K activation in osteosarcoma cells. Phosphorylation of Akt and S6K was inhibited after YME1L silencing in primary osteosarcoma cells, but was strengthened with YME1L overexpression. Restoring Akt-mTOR activation by S473D constitutively active Akt1 mitigated YME1L shRNA-induced anti-osteosarcoma cell activity. Lastly, intratumoral injection of YME1L shRNA adeno-associated virus inhibited subcutaneous osteosarcoma xenograft growth in nude mice. YME1L depletion, mitochondrial dysfunction, oxidative injury, Akt-S6K inactivation, and apoptosis were detected in YME1L shRNA-treated osteosarcoma xenografts. Together, overexpressed YME1L promotes osteosarcoma cell growth, possibly by maintaining mitochondrial function and Akt-mTOR activation.

Wnt/β-catenin Pathway Aggravates Renal Fibrosis by Activating PUM2 Transcription to Repress YME1L-mediated Mitochondrial Homeostasis

Chronic kidney disease (CKD) affects more than 10% of people worldwide and is a leading cause of death. However, the pathogenesis of CKD remains elusive. The oxidative stress and mitochondrial membrane potential were detected using Enzyme-linked immunosorbent assay and JC-1 assay. Co-immunoprecipitation, dual-luciferase assay, chromatin IP, RNA IP and RNA pull-down were used to validate the interactions among genes. Exploiting a H2O2-induced fibrosis model in vitro, PUM2 expression was upregulated in Human kidney 2 cell (HK-2) cells, along with reduced cell viability, enhanced oxidative stress, impaired mitochondrial potential, and upregulated expressions of fibrosis-associated proteins. While PUM2 knockdown reversed the H2O2-induced injury in HK-2 cells. Mechanically, Wnt/β-catenin pathway activated PUM2 transcription via TCF4. It was further identified that Wnt/β-catenin pathway inhibited YME1L expression through PUM2-mediated destabilizing of its mRNA. PUM2 aggravated H2O2-induced oxidative stress, mitochondrial dysfunction, and renal fibrosis in HK-2 cell via suppressing YME1L expression. Our study revealed that Wnt/β-catenin aggravated renal fibrosis by activating PUM2 transcription to repress YME1L-mediated mitochondrial homeostasis, providing novel insights and potential therapeutic targets for the treatment of kidney fibrosis.

YME1L-mediated mitophagy protects renal tubular cells against cellular senescence under diabetic conditions

BACKGROUND

The senescence of renal tubular epithelial cells (RTECs) is crucial in the progression of diabetic kidney disease (DKD). Accumulating evidence suggests a close association between insufficient mitophagy and RTEC senescence. Yeast mitochondrial escape 1-like 1 (YME1L), an inner mitochondrial membrane metalloprotease, maintains mitochondrial integrity. Its functions in DKD remain unclear. Here, we investigated whether YME1L can prevent the progression of DKD by regulating mitophagy and cellular senescence.

METHODS

We analyzed YME1L expression in renal tubules of DKD patients and mice, explored transcriptomic changes associated with YME1L overexpression in RTECs, and assessed its impact on RTEC senescence and renal dysfunction using an HFD/STZ-induced DKD mouse model. Tubule-specific overexpression of YME1L was achieved through the use of recombinant adeno-associated virus 2/9 (rAAV 2/9). We conducted both in vivo and in vitro experiments to evaluate the effects of YME1L overexpression on mitophagy and mitochondrial function. Furthermore, we performed LC-MS/MS analysis to identify potential protein interactions involving YME1L and elucidate the underlying mechanisms.

RESULTS

Our findings revealed a significant decrease in YME1L expression in the renal tubules of DKD patients and mice. However, tubule-specific overexpression of YME1L significantly alleviated RTEC senescence and renal dysfunction in the HFD/STZ-induced DKD mouse model. Moreover, YME1L overexpression exhibited positive effects on enhancing mitophagy and improving mitochondrial function both in vivo and in vitro. Mechanistically, our LC-MS/MS analysis uncovered a crucial mitophagy receptor, BCL2-like 13 (BCL2L13), as an interacting partner of YME1L. Furthermore, YME1L was found to promote the phosphorylation of BCL2L13, highlighting its role in regulating mitophagy.

CONCLUSIONS

This study provides compelling evidence that YME1L plays a critical role in protecting RTECs from cellular senescence and impeding the progression of DKD. Overexpression of YME1L demonstrated significant therapeutic potential by ameliorating both RTEC senescence and renal dysfunction in the DKD mice. Moreover, our findings indicate that YME1L enhances mitophagy and improves mitochondrial function, potentially through its interaction with BCL2L13 and subsequent phosphorylation. These novel insights into the protective mechanisms of YME1L offer a promising strategy for developing therapies targeting DKD.

Mitochondrial AAA+ proteases

Mitochondria are multifunctional organelles that play a central role in a wide range of life-sustaining tasks in eukaryotic cells, including adenosine triphosphate (ATP) production, calcium storage and coenzyme generation pathways such as iron-sulfur cluster biosynthesis. The wide range of mitochondrial functions is carried out by a diverse array of proteins comprising approximately 1500 proteins or polypeptides. Degradation of these proteins is mainly performed by four AAA+ proteases localized in mitochondria. These AAA+ proteases play a quality control role in degrading damaged or misfolded proteins and perform various other functions. This chapter describes previously identified roles for these AAA+ proteases that are localized in the mitochondria of animal cells.

Maternal hepatic adaptations during obese pregnancy encompass lobe-specific mitochondrial alterations and oxidative stress

Maternal obesity (MO) is rising worldwide, affecting half of all gestations, constituting a possible risk-factor for some pregnancy-associated liver diseases (PALD) and hepatic diseases. PALD occur in approximately 3% of pregnancies and are characterized by maternal hepatic oxidative stress (OS) and mitochondrial dysfunction. Maternal hepatic disease increases maternal and fetal morbidity and mortality. Understanding the role of MO on liver function and pathophysiology could be crucial for better understanding the altered pathways leading to PALD and liver disease, possibly paving the way to prevention and adequate management of disease. We investigated specific hepatic metabolic alterations in mitochondria and oxidative stress during MO at late-gestation. Maternal hepatic tissue was collected at 90% gestation in Control and MO ewes (fed 150% of recommended nutrition starting 60 days before conception). Maternal hepatic redox state, mitochondrial respiratory chain (MRC), and OS markers were investigated. MO decreased MRC complex-II activity and its subunits SDHA and SDHB protein expression, increased complex-I and complex-IV activities despite reduced complex-IV subunit mtCO1 protein expression, and increased ATP synthase ATP5A subunit. Hepatic MO-metabolic remodeling was characterized by decreased adenine nucleotide translocator 1 and 2 (ANT-1/2) and voltage-dependent anion channel (VDAC) protein expression and protein kinase A (PKA) activity (P<0.01), and augmented NAD+/NADH ratio due to reduced NADH levels (P<0.01). MO showed an altered redox state with increased OS, increased lipid peroxidation (P<0.01), decreased GSH/GSSG ratio (P=0.005), increased superoxide dismutase (P=0.03) and decreased catalase (P=0.03) antioxidant enzymatic activities, lower catalase, glutathione peroxidase (GPX)-4 and glutathione reductase protein expression (P<0.05), and increased GPX-1 abundance (P=0.03). MO-related hepatic changes were more evident in the right lobe, corroborated by the integrative data analysis. Hepatic tissue from obese pregnant ewes showed alterations in the redox state, consistent with OS and MRC and metabolism remodeling. These are hallmarks of PALD and hepatic disease, supporting MO as a risk-factor and highlighting OS and mitochondrial dysfunction as mechanisms responsible for liver disease predisposition.

Whole-Blood and Peripheral Mononuclear Cell Transcriptional Response to Prolonged Altitude Exposure in Well-Trained Runners

BACKGROUND

Recombinant human erythropoietin (rHuEpo) abuse by athletes threatens the integrity of sport. Due to the overlap in physiological response to rHuEpo and altitude exposure, it remains difficult to differentiate changes in hematological variables caused by rHuEpo or altitude, and therefore, other molecular methods to enhance anti-doping should be explored.

OBJECTIVE

To identify the hematological and transcriptomic response to prolonged altitude exposure typical of practices used by elite athletes.

DESIGN

Longitudinal study.

SETTING

University of Cape Town and Altitude Training Centre in Ethiopia.

PARTICIPANTS AND INTERVENTION

Fourteen well-trained athletes sojourned to an altitude training camp in Sululta, Ethiopia (∼2400-2500 m above sea level) for 27 days. Blood samples were taken before arrival, 24 hours, and 9, 16, and 24 days after arrival at altitude in addition to 24 hours and 6, 13, and 27 days upon return to sea level.

MAIN OUTCOME MEASURES

Blood samples were analyzed for hemoglobin concentration, hematocrit, and reticulocyte percentage. The transcriptomic response in whole blood and peripheral blood mononuclear cells (PBMC) were analyzed using gene expression microarrays.

RESULTS

A unique set of 29 and 10 genes were identified to be commonly expressed at every altitude time point in whole blood and PBMC, respectively. There were no genes identified upon return to sea level in whole blood, and only one gene within PBMC.

CONCLUSIONS

The current study has identified a series of unique genes that can now be integrated with genes previously validated for rHuEpo abuse, thereby enabling the differentiation of rHuEpo from altitude exposure.

A two-step mitochondrial import pathway couples the disulfide relay with matrix complex I biogenesis

Mitochondria critically rely on protein import and its tight regulation. Here, we found that the complex I assembly factor NDUFAF8 follows a two-step import pathway linking IMS and matrix import systems. A weak targeting sequence drives TIM23-dependent NDUFAF8 matrix import, and en route, allows exposure to the IMS disulfide relay, which oxidizes NDUFAF8. Import is closely surveyed by proteases: YME1L prevents accumulation of excess NDUFAF8 in the IMS, while CLPP degrades reduced NDUFAF8 in the matrix. Therefore, NDUFAF8 can only fulfil its function in complex I biogenesis if both oxidation in the IMS and subsequent matrix import work efficiently. We propose that the two-step import pathway for NDUFAF8 allows integration of the activity of matrix complex I biogenesis pathways with the activity of the mitochondrial disulfide relay system in the IMS. Such coordination might not be limited to NDUFAF8 as we identified further proteins that can follow such a two-step import pathway.

Molecular Determinants of Mitochondrial Shape and Function and Their Role in Glaucoma

Significance: Cells depend on well-functioning mitochondria for essential processes such as energy production, redox signaling, coordination of metabolic pathways, and cofactor biosynthesis. Mitochondrial dysfunction, metabolic decline, and protein stress have been implicated in the etiology of multiple late-onset diseases, including various ataxias, diabetes, sarcopenia, neuromuscular disorders, and neurodegenerative diseases such as parkinsonism, amyotrophic lateral sclerosis, and glaucoma. Recent Advances: New evidence supports that increased energy metabolism protects neuron function during aging. Key energy metabolic enzymes, however, are susceptible to oxidative damage making it imperative that the mitochondrial proteome is protected. More than 40 different enzymes have been identified as important factors for guarding mitochondrial health and maintaining a dynamic pool of mitochondria. Critical Issues: Understanding shared mechanisms of age-related disorders of neurodegenerative diseases such as glaucoma, Alzheimer's disease, and Parkinson's disease is important for developing new therapies. Functional mitochondrial shape and dynamics rely on complex interactions between mitochondrial proteases and membrane proteins. Identifying the sequence of molecular events that lead to mitochondrial dysfunction and metabolic stress is a major challenge. Future Directions: A critical need exists for new strategies that reduce mitochondrial protein stress and promote mitochondrial dynamics in age-related neurological disorders. Discovering how mitochondria-associated degradation is related to proteostatic mechanisms in mitochondrial compartments may reveal new opportunities for therapeutic interventions. Also, little is known about how protein and membrane contacts in the inner and outer mitochondrial membrane are regulated, even though they are pivotal for mitochondrial architecture. Future work will need to delineate the molecular details of these processes.

The mitochondrial protein YME1 Like 1 is important for non-small cell lung cancer cell growth

The expression and biological function of the mitochondrial inner membrane protease YME1L (YME1 Like 1 ATPase) in NSCLC are tested here. Bioinformatical analyses and results from local human tissues show that YME1L expression is elevated in NSCLC tissues. YME1L upregulation was observed in primary and immortalized NSCLC cells. In NSCLC cells, shRNA-mediated silence of YME1L or dCas9/sgRNA-induced knockout (KO) of YME1L robustly suppressed cell growth and migration, and provoking apoptosis. YME1L shRNA/KO resulted in mitochondrial dysfunctions in NSCLC cells, leading to mitochondrial depolarization, ROS accumulation and ATP depletion. Conversely, ectopic YME1L overexpression augmented NSCLC cell proliferation and motility. Akt-S6K1 phosphorylation was reduced after YME1L shRNA/KO in primary NSCLC cells, but augmented after YME1L overexpression. Importantly, YME1L KO-caused anti-NSCLC cell activity was attenuated by a constitutively-activate Akt1 (S473D) construct. In vivo, subcutaneous NSCLC xenograft growth was remarkably slowed following intratumoral YME1L shRNA AAV injection in nude mice. YME1L knockdown, Akt-mTOR inactivation and ATP reduction were detected in YME1L-silenced NSCLC xenografts. Taken together, overexpressed YME1L in NSCLC exerts pro-tumorigenic function.

Mitochondrial signalling and homeostasis: from cell biology to neurological disease

Efforts to understand how mitochondrial dysfunction contributes to neurodegeneration have primarily focussed on the role of mitochondria in neuronal energy metabolism. However, progress in understanding the etiological nature of emerging mitochondrial functions has yielded new ideas about the mitochondrial basis of neurological disease. Studies aimed at deciphering how mitochondria signal through interorganellar contacts, vesicular trafficking, and metabolic transmission have revealed that mitochondrial regulation of immunometabolism, cell death, organelle dynamics, and neuroimmune interplay are critical determinants of neural health. Moreover, the homeostatic mechanisms that exist to protect mitochondrial health through turnover via nanoscale proteostasis and lysosomal degradation have become integrated within mitochondrial signalling pathways to support metabolic plasticity and stress responses in the nervous system. This review highlights how these distinct mitochondrial pathways converge to influence neurological health and contribute to disease pathology.

Functional crosstalk between the TIM22 complex and YME1 machinery maintains mitochondrial proteostasis and integrity

TIM22 pathway cargos are essential for sustaining mitochondrial homeostasis as an excess of these proteins leads to proteostatic stress and cell death. Yme1 is an inner membrane metalloprotease that regulates protein quality control with chaperone-like and proteolytic activities. Although the mitochondrial translocase and protease machinery are critical for organelle health, their functional association remains unexplored. The present study unravels a novel genetic connection between the TIM22 complex and YME1 machinery in Saccharomyces cerevisiae that is required for maintaining mitochondrial health. Our genetic analyses indicate that impairment in the TIM22 complex rescues the respiratory growth defects of cells without Yme1. Furthermore, Yme1 is essential for the stability of the TIM22 complex and regulates the proteostasis of TIM22 pathway substrates. Moreover, impairment in the TIM22 complex suppressed the mitochondrial structural and functional defects of Yme1-devoid cells. In summary, excessive levels of TIM22 pathway substrates could be one of the reasons for respiratory growth defects of cells lacking Yme1, and compromising the TIM22 complex can compensate for the imbalance in mitochondrial proteostasis caused by the loss of Yme1.

Respiratory Complex I dysfunction in cancer: from a maze of cellular adaptive responses to potential therapeutic strategies

Mitochondria act as key organelles in cellular bioenergetics and biosynthetic processes producing signals that regulate different molecular networks for proliferation and cell death. This ability is also preserved in pathologic contexts such as tumorigenesis, during which bioenergetic changes and metabolic reprogramming confer flexibility favoring cancer cell survival in a hostile microenvironment. Although different studies epitomize mitochondrial dysfunction as a protumorigenic hit, genetic ablation or pharmacological inhibition of respiratory complex I causing a severe impairment is associated with a low-proliferative phenotype. In this scenario, it must be considered that despite the initial delay in growth, cancer cells may become able to resume proliferation exploiting molecular mechanisms to overcome growth arrest. Here, we highlight the current knowledge on molecular responses activated by complex I-defective cancer cells to bypass physiological control systems and to re-adapt their fitness during microenvironment changes. Such adaptive mechanisms could reveal possible novel molecular players in synthetic lethality with complex I impairment, thus providing new synergistic strategies for mitochondrial-based anticancer therapy.

Sirt3 mitigates LPS-induced mitochondrial damage in renal tubular epithelial cells by deacetylating YME1L1

Acute kidney injury (AKI) is often secondary to sepsis. Increasing evidence suggests that mitochondrial dysfunction contributes to the pathological process of AKI. In this study, we aimed to examine the regulatory roles of Sirt3 in Lipopolysaccharide (LPS)-induced mitochondrial damage in renal tubular epithelial cells (TECs). Sirt3 knockout mice were intraperitoneally injected with LPS, and cultured TECs were stimulated with LPS to evaluate the effects of Sirt3 on mitochondrial structure and function in TECs. Electron microscopy was used to assess mitochondrial morphology. Immunofluorescence staining was performed to detect protein expression and examine mitochondrial morphology. Western blotting was used to quantify protein expression. We observed that LPS increased apoptosis, induced disturbances in mitochondrial function and dynamics, and downregulated Sirt3 expression in a sepsis-induced AKI mouse model and human proximal tubular (HK-2) cells in vitro. Sirt3 deficiency further exacerbated LPS-induced renal pathological damage, apoptosis and disturbances in mitochondrial function and dynamics. On the contrary, Sirt3 overexpression in HK-2 cells alleviated these lesions. Functional studies revealed that Sirt3 overexpression alleviated LPS-induced mitochondrial damage and apoptosis in TECs by promoting OPA1-mediated mitochondrial fusion through the deacetylation of i-AAA protease (YME1L1), an upstream regulatory molecule of OPA1. Our study has identified Sirt3 as a vital factor that protects against LPS-induced mitochondrial damage and apoptosis in TECs via the YME1L1-OPA1 signaling pathway.

Understanding the Role of Yeast Yme1 in Mitochondrial Function Using Biochemical and Proteomics Analyses

Mitochondrial i-AAA proteinase Yme1 is a multifunctional protein that plays important roles in maintaining mitochondrial protein homeostasis and regulating biogenesis and function of mitochondrial proteins. However, due to the complex interplay of mitochondria and the multifunctional nature of Yme1, how Yme1 affects mitochondrial function and protein homeostasis is still poorly understood. In this study, we investigated how YME1 deletion affects yeast Saccharomyces cerevisiae growth, chronological life span, mitochondrial protein homeostasis and function, with a focus on the mitochondrial oxidative phosphorylation (OXPHOS) complexes. Our results show that whilst the YME1 deleted cells grow poorly under respiratory conditions, they grow similar to wild-type yeast under fermentative conditions. However, the chronological life span is impaired, indicating that Yme1 plays a key role in longevity. Using highly enriched mitochondrial extract and proteomic analysis, we show that the abundances of many mitochondrial proteins are altered by YME1 deletion. Several components of the respiratory chain complexes II, III, IV and V were significantly decreased, suggesting that Yme1 plays an important role in maintaining the level and function of complexes II-V. This result was confirmed using blue native-PAGE and in-solution-based enzyme activity assays. Taken together, this study shows that Yme1 plays an important role in the chronological life span and mitochondrial protein homeostasis and has deciphered its function in maintaining the activity of mitochondrial OXPHOS complexes.

TIMM44 is a potential therapeutic target of human glioma

TIMM44 (translocase of inner mitochondrial membrane 44) is essential for the maintenance of mitochondrial functions. Bioinformatics studies and results from the local high-grade glioma tissues showed that TIMM44 mRNA and protein levels are elevated in glioma, correlating with poor overall survival. Mitochondrial TIMM44 upregulation was also detected in patient-derived primary glioma cells and immortalized cell line. In primary and established glioma cells, TIMM44 depletion, using the lentiviral shRNA strategy or the CRISPR/Cas9 knockout (KO) method, robustly inhibited cell viability, proliferation and migration. Moreover, TIMM44 silencing/KO resulted in mitochondrial complex I inhibition, ATP depletion, mitochondrial membrane potential reduction, oxidative stress and DNA damage, and eventually provoked apoptosis. Conversely, ectopic overexpression of TIMM44 augmented glioma cell proliferation and migration. TIMM44 upregulation in glioma is possibly due to increased TIMM44 transcriptional machinery by the transcription factor GATA3 in a YME1L (YME1 Like 1 ATPase)-dependent manner. In vivo, the growth of subcutaneous glioma xenografts was suppressed after intratumoral injection of TIMM44 shRNA adeno-associated virus (AAV). TIMM44 depletion, ATP reduction, oxidative injury and apoptosis were detected in TIMM44 shRNA AAV-injected glioma xenografts. Moreover, the intracranial growth of TIMM44 KO glioma cells in the mouse brain was largely inhibited. Together, overexpressed TIMM44 could be a novel and promising therapeutic target of human glioma.

COX-2 Expression in Hepatocytes Improves Mitochondrial Function after Hepatic Ischemia-Reperfusion Injury

Cyclooxygenase 2 (COX-2) is a key enzyme in prostanoid biosynthesis. The constitutive hepatocyte expression of COX-2 has a protective role in hepatic ischemia-reperfusion (I/R) injury (IRI), decreasing necrosis, reducing reactive oxygen species (ROS) levels, and increasing autophagy and antioxidant and anti-inflammatory response. The physiopathology of IRI directly impacts mitochondrial activity, causing ATP depletion and being the main source of ROS. Using genetically modified mice expressing human COX-2 (h-COX-2 Tg) specifically in hepatocytes, and performing I/R surgery on the liver, we demonstrate that COX-2 expression has a beneficial effect at the mitochondrial level. Mitochondria derived from h-COX-2 Tg mice livers have an increased respiratory rate associated with complex I electron-feeding pathways compared to Wild-type (Wt) littermates, without affecting complex I expression or assembly. Furthermore, Wt-derived mitochondria show a loss of mitochondrial membrane potential (ΔΨm) that correlates to increased proteolysis of fusion-related OPA1 through OMA1 protease activity. All these effects are not observed in h-COX-2 Tg mitochondria, which behave similarly to the Sham condition. These results suggest that COX-2 attenuates IRI at a mitochondrial level, preserving the proteolytic processing of OPA1, in addition to the maintenance of mitochondrial respiration.

Targeting Mitochondrial Oxidative Phosphorylation Eradicates Acute Myeloid Leukemic Stem Cells

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy characterized by multiple cytogenetic and molecular abnormalities, with a very poor prognosis. Current treatments for AML often fail to eliminate leukemic stem cells (LSCs), which perpetuate the disease. LSCs exhibit a unique metabolic profile, especially dependent on oxidative phosphorylation (OXPHOS) for energy production. Whereas, normal hematopoietic stem cells (HSCs) and leukemic blasts rely on glycolysis for adenosine triphosphate (ATP) production. Thus, understanding the regulation of OXPHOS in LSCs may offer effective targets for developing clinical therapies in AML. This review summarizes these studies with a focus on the regulation of the electron transport chain (ETC) and tricarboxylic acid (TCA) cycle in OXPHOS and discusses potential therapies for eliminating LSCs.

Coupling to Pam16 differentially controls the dual role of Pam18 in protein import and respiratory chain formation

The presequence translocase (TIM23 complex) imports precursor proteins into the mitochondrial inner membrane and matrix. The presequence translocase-associated motor (PAM) provides a driving force for transport into the matrix. The J-protein Pam18 stimulates the ATPase activity of the mitochondrial Hsp70 (mtHsp70). Pam16 recruits Pam18 to the TIM23 complex to ensure protein import. The Pam16-Pam18 module also associates with components of the respiratory chain, but the function of the dual localization of Pam16-Pam18 is largely unknown. Here, we show that disruption of the Pam16-Pam18 heterodimer causes redistribution of Pam18 to the respiratory chain supercomplexes, where it forms a homodimer. Redistribution of Pam18 decreases protein import into mitochondria but stimulates mtHsp70-dependent assembly of respiratory chain complexes. We conclude that coupling to Pam16 differentially controls the dual function of Pam18. It recruits Pam18 to the TIM23 complex to promote protein import but attenuates the Pam18 function in the assembly of respiratory chain complexes.

QiShenYiQi Pills Attenuates Ischemia/Reperfusion-Induced Cardiac Microvascular Hyperpermeability Implicating Src/Caveolin-1 and RhoA/ROCK/MLC Signaling

Aims: Coronary microvascular hyperpermeability is an important contributor to ischemia or reperfusion (I/R) injury. However, the effective strategy for this insult remains limited. This study aimed to explore the protective effect of the compound Chinese medicine QiShenYiQi Pills (QSYQ) against coronary microvascular hyperpermeability after cardiac I/R with focusing on the underlying mechanism.

Methods and Results: Male Sprague-Dawley rats under anesthesia were subjected to occlusion of left coronary anterior descending artery followed by reperfusion. QSYQ was administrated 90 min before ischemia initiation. Human cardiac microvascular endothelial cells (HCMECs) underwent hypoxia or reoxygenation (H/R) challenge with QSYQ administrated 1 h prior to hypoxia. QSYQ exhibited effects on attenuating microvascular damage and albumin leakage after I/R injury, showing a role in maintaining endothelial junctions, caveolae, and collagen in basement membrane (BM) of microvessels. Study using HCMECs disclosed that QSYQ protected endothelial barrier from impairment by H/R, attenuating the decline of respiratory chain complex I and ATP synthase, activation of Src/caveolin-1 and increase of RhoA/ROCK/p-MLC, MMP-9, and CTSS. PP2, a Src inhibitor, partially imitated the effect of QSYQ.

Conclusions: The QSYQ was able to prevent I/R-induced cardiac microvascular hyperpermeability via a mechanism involving Src/caveolin-1 and RhoA/ROCK/MLC signaling.

Recent Advances in Understanding the Structural and Functional Evolution of FtsH Proteases

The FtsH family of proteases are membrane-anchored, ATP-dependent, zinc metalloproteases. They are universally present in prokaryotes and the mitochondria and chloroplasts of eukaryotic cells. Most bacteria bear a single ftsH gene that produces hexameric homocomplexes with diverse house-keeping roles. However, in mitochondria, chloroplasts and cyanobacteria, multiple FtsH homologs form homo- and heterocomplexes with specialized functions in maintaining photosynthesis and respiration. The diversification of FtsH homologs combined with selective pairing of FtsH isomers is a versatile strategy to enable functional adaptation. In this article we summarize recent progress in understanding the evolution, structure and function of FtsH proteases with a focus on the role of FtsH in photosynthesis and respiration.

Targeting Mitochondrial Protein Expression as a Future Approach for Cancer Therapy

Extensive metabolic remodeling is a fundamental feature of cancer cells. Although early reports attributed such remodeling to a loss of mitochondrial functions, it is now clear that mitochondria play central roles in cancer development and progression, from energy production to synthesis of macromolecules, from redox modulation to regulation of cell death. Biosynthetic pathways are also heavily affected by the metabolic rewiring, with protein synthesis dysregulation at the hearth of cellular transformation. Accumulating evidence in multiple organisms shows that the metabolic functions of mitochondria are tightly connected to protein synthesis, being assembly and activity of respiratory complexes highly dependent on de novo synthesis of their components. In turn, protein synthesis within the organelle is tightly connected with the cytosolic process. This implies an entire network of interactions and fine-tuned regulations that build up a completely under-estimated level of complexity. We are now only preliminarily beginning to reconstitute such regulatory level in human cells, and to perceive its role in diseases. Indeed, disruption or alterations of these connections trigger conditions of proteotoxic and energetic stress that could be potentially exploited for therapeutic purposes. In this review, we summarize the available literature on the coordinated regulation of mitochondrial and cytosolic mRNA translation, and their effects on the integrity of the mitochondrial proteome and functions. Finally, we highlight the potential held by this topic for future research directions and for the development of innovative therapeutic approaches.

Neurogenic Hypertension Mediated Mitochondrial Abnormality Leads to Cardiomyopathy: Contribution of UPRmt and Norepinephrine-miR- 18a-5p-HIF-1α Axis

Aims: Hypertension increases the risk of heart disease. Hallmark features of hypertensive heart disease is sympathoexcitation and cardiac mitochondrial abnormality. However, the molecular mechanisms for specifically neurally mediated mitochondrial abnormality and subsequent cardiac dysfunction are unclear. We hypothesized that enhanced sympatho-excitation to the heart elicits cardiac miR-18a-5p/HIF-1α and mitochondrial unfolded protein response (UPRmt) signaling that lead to mitochondrial abnormalities and consequent pathological cardiac remodeling. Methods and Results: Using a model of neurogenic hypertension (NG-HTN), induced by intracerebroventricular (ICV) infusion of Ang II (NG-HTN; 20 ng/min, 14 days, 0.5 μl/h, or Saline; Control, 0.9%) through osmotic mini-pumps in Sprague-Dawley rats (250-300 g), we attempted to identify a link between sympathoexcitation (norepinephrine; NE), miRNA and HIF-1α signaling and UPRmt to produce mitochondrial abnormalities resulting in cardiomyopathy. Cardiac remodeling, mitochondrial abnormality, and miRNA/HIF-1α signaling were assessed using histology, immunocytochemistry, electron microscopy, Western blotting or RT-qPCR. NG-HTN demonstrated increased sympatho-excitation with concomitant reduction in UPRmt, miRNA-18a-5p and increased level of HIF-1α in the heart. Our in silico analysis indicated that miR-18a-5p targets HIF-1α. Direct effects of NE on miRNA/HIF-1α signaling and mitochondrial abnormality examined using H9c2 rat cardiomyocytes showed NE reduces miR-18a-5p but increases HIF-1α. Electron microscopy revealed cardiac mitochondrial abnormality in NG-HTN, linked with hypertrophic cardiomyopathy and fibrosis. Mitochondrial unfolded protein response was decreased in NG-HTN indicating mitochondrial proteinopathy and proteotoxic stress, associated with increased mito-ROS and decreased mitochondrial membrane potential (ΔΨm), and oxidative phosphorylation. Further, there was reduced cardiac mitochondrial biogenesis and fusion, but increased mitochondrial fission, coupled with mitochondrial impaired TIM-TOM transport and UPRmt. Direct effects of NE on H9c2 rat cardiomyocytes also showed cardiomyocyte hypertrophy, increased mitochondrial ROS generation, and UPRmt corroborating the in vivo data. Conclusion: In conclusion, enhanced sympatho-excitation suppress miR-18a-5p/HIF-1α signaling and increased mitochondrial stress proteotoxicity, decreased UPRmt leading to decreased mitochondrial dynamics/OXPHOS/ΔΨm and ROS generation. Taken together, these results suggest that ROS induced mitochondrial transition pore opening activates pro-hypertrophy/fibrosis/inflammatory factors that induce pathological cardiac hypertrophy and fibrosis commonly observed in NG-HTN.

The Role of Mitochondria in Optic Atrophy With Autosomal Inheritance

Optic atrophy (OA) with autosomal inheritance is a form of optic neuropathy characterized by the progressive and irreversible loss of vision. In some cases, this is accompanied by additional, typically neurological, extra-ocular symptoms. Underlying the loss of vision is the specific degeneration of the retinal ganglion cells (RGCs) which form the optic nerve. Whilst autosomal OA is genetically heterogenous, all currently identified causative genes appear to be associated with mitochondrial organization and function. However, it is unclear why RGCs are particularly vulnerable to mitochondrial aberration. Despite the relatively high prevalence of this disorder, there are currently no approved treatments. Combined with the lack of knowledge concerning the mechanisms through which aberrant mitochondrial function leads to RGC death, there remains a clear need for further research to identify the underlying mechanisms and develop treatments for this condition. This review summarizes the genes known to be causative of autosomal OA and the mitochondrial dysfunction caused by pathogenic mutations. Furthermore, we discuss the suitability of available in vivo models for autosomal OA with regards to both treatment development and furthering the understanding of autosomal OA pathology.

Mitochondrial Quality Control Strategies: Potential Therapeutic Targets for Neurodegenerative Diseases?

Many lines of evidence have indicated the therapeutic potential of rescuing mitochondrial integrity by targeting specific mitochondrial quality control pathways in neurodegenerative diseases, such as Parkinson's disease, Huntington's disease, and Alzheimer's disease. In addition to ATP synthesis, mitochondria are critical regulators of ROS production, lipid metabolism, calcium buffering, and cell death. The mitochondrial unfolded protein response, mitochondrial dynamics, and mitophagy are the three main quality control mechanisms responsible for maintaining mitochondrial proteostasis and bioenergetics. The proper functioning of these complex processes is necessary to surveil and restore mitochondrial homeostasis and the healthy pool of mitochondria in cells. Mitochondrial dysfunction occurs early and causally in disease pathogenesis. A significant accumulation of mitochondrial damage resulting from compromised quality control pathways leads to the development of neuropathology. Moreover, genetic or pharmaceutical manipulation targeting the mitochondrial quality control mechanisms can sufficiently rescue mitochondrial integrity and ameliorate disease progression. Thus, therapies that can improve mitochondrial quality control have great promise for the treatment of neurodegenerative diseases. In this review, we summarize recent progress in the field that underscores the essential role of impaired mitochondrial quality control pathways in the pathogenesis of neurodegenerative diseases. We also discuss the translational approaches targeting mitochondrial function, with a focus on the restoration of mitochondrial integrity, including mitochondrial dynamics, mitophagy, and mitochondrial proteostasis.

A Conserved Mitochondrial Chaperone-Protease Complex Involved in Protein Homeostasis

Mitochondria are essential organelles involved in cellular energy production. The inner mitochondrial membrane protein stomatin-like protein 2 (SLP-2) is a member of the SPFH (stomatin, prohibitin, flotilin, and HflK/C) superfamily and binds to the mitochondrial glycerophospholipid cardiolipin, forming cardiolipin-enriched membrane domains to promote the assembly and/or stabilization of protein complexes involved in oxidative phosphorylation. In addition, human SLP-2 anchors a mitochondrial processing complex required for proteolytic regulation of proteins involved in mitochondrial dynamics and quality control. We now show that deletion of the gene encoding the Trypanosoma brucei homolog TbSlp2 has no effect on respiratory protein complex stability and mitochondrial functions under normal culture conditions and is dispensable for growth of T. brucei parasites. In addition, we demonstrate that TbSlp2 binds to the metalloprotease TbYme1 and together they form a large mitochondrial protein complex. The two proteins negatively regulate each other's expression levels by accelerating protein turnover. Furthermore, we show that TbYme1 plays a role in heat-stress resistance, as TbYme1 knock-out parasites displayed mitochondrial fragmentation and loss of viability when cultured at elevated temperatures. Unbiased interaction studies uncovered putative TbYme1 substrates, some of which were differentially affected by the absence of TbYme1. Our results support emerging evidence for the presence of mitochondrial quality control pathways in this ancient eukaryote.

Acetylation in Mitochondria Dynamics and Neurodegeneration

Mitochondria are a unique intracellular organelle due to their evolutionary origin and multifunctional role in overall cellular physiology and pathophysiology. To meet the specific spatial metabolic demands within the cell, mitochondria are actively moving, dividing, or fusing. This process of mitochondrial dynamics is fine-tuned by a specific group of proteins and their complex post-translational modifications. In this review, we discuss the mitochondrial dynamics regulatory enzymes, their adaptor proteins, and the effect of acetylation on the activity of fusion and fission machinery as a ubiquitous response to metabolic stresses. Further, we discuss the role of intracellular cytoskeleton structures and their post-translational modifications in the modulation of mitochondrial fusion and fission. Finally, we review the role of mitochondrial dynamics dysregulation in the pathophysiology of acute brain injury and the treatment strategies based on modulation of NAD⁺-dependent deacetylation.

Mitochondrial Phospholipid Homeostasis Is Regulated by the i-AAA Protease PaIAP and Affects Organismic Aging

Mitochondria are ubiquitous organelles of eukaryotic organisms with a number of essential functions, including synthesis of iron-sulfur clusters, amino acids, lipids, and adenosine triphosphate (ATP). During aging of the fungal aging model Podospora anserina, the inner mitochondrial membrane (IMM) undergoes prominent morphological alterations, ultimately resulting in functional impairments. Since phospholipids (PLs) are key components of biological membranes, maintenance of membrane plasticity and integrity via regulation of PL biosynthesis is indispensable. Here, we report results from a lipidomic analysis of isolated mitochondria from P. anserina that revealed an age-related reorganization of the mitochondrial PL profile and the involvement of the i-AAA protease PaIAP in proteolytic regulation of PL metabolism. The absence of PaIAP enhances biosynthesis of characteristic mitochondrial PLs, leads to significant alterations in the acyl composition of the mitochondrial signature PL cardiolipin (CL), and induces mitophagy. These alterations presumably cause the lifespan increase of the PaIap deletion mutant under standard growth conditions. However, PaIAP is required at elevated temperatures and for degradation of superfluous CL synthase PaCRD1 during glycolytic growth. Overall, our study uncovers a prominent role of PaIAP in the regulation of PL homeostasis in order to adapt membrane plasticity to fluctuating environmental conditions as they occur in nature.

Redox-Mediated Regulation of Mitochondrial Biogenesis, Dynamics, and Respiratory Chain Assembly in Yeast and Human Cells

Mitochondria are double-membrane organelles that contain their own genome, the mitochondrial DNA (mtDNA), and reminiscent of its endosymbiotic origin. Mitochondria are responsible for cellular respiration via the function of the electron oxidative phosphorylation system (OXPHOS), located in the mitochondrial inner membrane and composed of the four electron transport chain (ETC) enzymes (complexes I-IV), and the ATP synthase (complex V). Even though the mtDNA encodes essential OXPHOS components, the large majority of the structural subunits and additional biogenetical factors (more than seventy proteins) are encoded in the nucleus and translated in the cytoplasm. To incorporate these proteins and the rest of the mitochondrial proteome, mitochondria have evolved varied, and sophisticated import machineries that specifically target proteins to the different compartments defined by the two membranes. The intermembrane space (IMS) contains a high number of cysteine-rich proteins, which are mostly imported via the MIA40 oxidative folding system, dependent on the reduction, and oxidation of key Cys residues. Several of these proteins are structural components or assembly factors necessary for the correct maturation and function of the ETC complexes. Interestingly, many of these proteins are involved in the metalation of the active redox centers of complex IV, the terminal oxidase of the mitochondrial ETC. Due to their function in oxygen reduction, mitochondria are the main generators of reactive oxygen species (ROS), on both sides of the inner membrane, i.e., in the matrix and the IMS. ROS generation is important due to their role as signaling molecules, but an excessive production is detrimental due to unwanted oxidation reactions that impact on the function of different types of biomolecules contained in mitochondria. Therefore, the maintenance of the redox balance in the IMS is essential for mitochondrial function. In this review, we will discuss the role that redox regulation plays in the maintenance of IMS homeostasis as well as how mitochondrial ROS generation may be a key regulatory factor for ETC biogenesis, especially for complex IV.

Returning to the Fold for Lessons in Mitochondrial Crista Diversity and Evolution

Cristae are infoldings of the mitochondrial inner membrane jutting into the organelle's innermost compartment from narrow stems at their base called crista junctions. They are emblematic of aerobic mitochondria, being the fabric for the molecular machinery driving cellular respiration. Electron microscopy revealed that diverse eukaryotes possess cristae of different shapes. Yet, crista diversity has not been systematically examined in light of our current knowledge about eukaryotic evolution. Since crista form and function are intricately linked, we take a holistic view of factors that may underlie both crista diversity and the adherence of cristae to a recognizable form. Based on electron micrographs of 226 species from all major lineages, we propose a rational crista classification system that postulates cristae as variations of two general morphotypes: flat and tubulo-vesicular. The latter is most prevalent and likely ancestral, but both morphotypes are found interspersed throughout the eukaryotic tree. In contrast, crista junctions are remarkably conserved, supporting their proposed role as diffusion barriers that sequester cristae contents. Since cardiolipin, ATP synthase dimers, the MICOS complex, and dynamin-like Opa1/Mgm1 are known to be involved in shaping cristae, we examined their variation in the context of crista diversity. Moreover, we have identified both commonalities and differences that may collectively be manifested as diverse variations of crista form and function.

Reduction in mitochondrial oxidative stress mediates hypoxia-induced resistance to cisplatin in human transitional cell carcinoma cells

Tumor hypoxia is known to promote the acquisition of more aggressive phenotypes in human transitional cell carcinoma (TCC), including drug resistance. Accumulating evidence suggests that mitochondria play a central role in the chemoresistance of TCC. However, the role of mitochondria in the hypoxia-induced drug resistance in TCC remains elusive. The present study investigated the function of mitochondria in the drug resistance using a TCC cell line under hypoxic conditions. In vitro hypoxia (0.1% O₂, 48 h) was achieved by incubating TCC cells in air chamber. Mitochondrial events involving hypoxia-induced drug resistance were assessed. Hypoxia significantly reduced the cisplatin-induced apoptosis of TCC cells. Additionally, hypoxia substantially decreased the level of mitochondrial reactive oxygen species (ROS) generated by cisplatin treatment. Analogously, elimination of mitochondrial ROS significantly rescued cells from cisplatin-induced apoptosis. Hypoxia enhanced mitochondrial hyperpolarization, which was not related to ATP production or the reversal of ATP synthase activity. The mitochondrial DNA (mtDNA) amplification efficiency data illustrated that hypoxia significantly prevented oxidative damage to the mitogenome. Moreover, transmission electron microscopy revealed that cisplatin-induced disruption of the mitochondrial ultrastructure was abated under hypoxic conditions. Notably, depletion of mtDNA by ethidium bromide abrogated hypoxia-induced resistance to cisplatin. Taken together, the present study demonstrated that TCC cells exposed to hypoxic conditions rendered mitochondria less sensitive to oxidative stress induced by cisplatin treatment, leading to enhanced drug resistance.

Mitochondrial ATP-Dependent Proteases-Biological Function and Potential Anti-Cancer Targets

Cells must eliminate excess or damaged proteins to maintain protein homeostasis. To ensure protein homeostasis in the cytoplasm, cells rely on the ubiquitin-proteasome system and autophagy. In the mitochondria, protein homeostasis is regulated by mitochondria proteases, including four core ATP-dependent proteases, m-AAA, i-AAA, LonP, and ClpXP, located in the mitochondrial membrane and matrix. This review will discuss the function of mitochondrial proteases, with a focus on ClpXP as a novel therapeutic target for the treatment of malignancy. ClpXP maintains the integrity of the mitochondrial respiratory chain and regulates metabolism by degrading damaged and misfolded mitochondrial proteins. Inhibiting ClpXP genetically or chemically impairs oxidative phosphorylation and is toxic to malignant cells with high ClpXP expression. Likewise, hyperactivating the protease leads to increased degradation of ClpXP substrates and kills cancer cells. Thus, targeting ClpXP through inhibition or hyperactivation may be novel approaches for patients with malignancy.

Homozygous missense mutation in UQCRC2 associated with severe encephalomyopathy, mitochondrial complex III assembly defect and activation of mitochondrial protein quality control

The mitochondrial respiratory chain (MRC) complex III (CIII) associates with complexes I and IV (CI and CIV) into supercomplexes. We identified a novel homozygous missense mutation (c.665G>C; p.Gly222Ala) in UQCRC2 coding for structural subunit Core 2 in a patient with severe encephalomyopathy. The structural data suggest that the Gly222Ala exchange might result in an altered spatial arrangement in part of the UQCRC2 subunit, which could impact specific protein-protein interactions. Accordingly, we have found decreased levels of CIII and accumulation of CIII-specific subassemblies comprising MT-CYB, UQCRB, UQCRQ, UQCR10 and CYC1 subunits, but devoid of UQCRC1, UQCRC2, and UQCRFS1 in the patient's fibroblasts. The lack of UQCRC1 subunit-containing subassemblies could result from an impaired interaction with mutant UQCRC2^Gly222Ala and subsequent degradation of both subunits by mitochondrial proteases. Indeed, we show an elevated amount of matrix CLPP protease, suggesting the activation of the mitochondrial protein quality control machinery in UQCRC2^Gly222Ala fibroblasts. In line with growing evidence, we observed a rate-limiting character of CIII availability for the supercomplex formation, accompanied by a diminished amount of CI. Furthermore, we found impaired electron flux between CI and CIII in skeletal muscle and fibroblasts of the UQCRC2^Gly222Ala patient. The ectopic expression of wild-type UQCRC2 in patient cells rescued maximal respiration rate, demonstrating the deleterious effect of the mutation on MRC. Our study expands the phenotypic spectrum of human disease caused by CIII Core protein deficiency, provides insight into the assembly pathway of human CIII, and supports the requirement of assembled CIII for a proper accumulation of CI.

The pyruvate kinase activator mitapivat reduces hemolysis and improves anemia in a β-thalassemia mouse model

Anemia in β-thalassemia is related to ineffective erythropoiesis and reduced red cell survival. Excess free heme and accumulation of unpaired α-globin chains impose substantial oxidative stress on β-thalassemic erythroblasts and erythrocytes, impacting cell metabolism. We hypothesized that increased pyruvate kinase activity induced by mitapivat (AG-348) in the Hbbth3/+ mouse model for β-thalassemia would reduce chronic hemolysis and ineffective erythropoiesis through stimulation of red cell glycolytic metabolism. Oral mitapivat administration ameliorated ineffective erythropoiesis and anemia in Hbbth3/+ mice. Increased ATP, reduced reactive oxygen species production, and reduced markers of mitochondrial dysfunction associated with improved mitochondrial clearance suggested enhanced metabolism following mitapivat administration in β-thalassemia. The amelioration of responsiveness to erythropoietin resulted in reduced soluble erythroferrone, increased liver Hamp expression, and diminished liver iron overload. Mitapivat reduced duodenal Dmt1 expression potentially by activating the pyruvate kinase M2-HIF2α axis, representing a mechanism additional to Hamp in controlling iron absorption and preventing β-thalassemia-related liver iron overload. In ex vivo studies on erythroid precursors from patients with β-thalassemia, mitapivat enhanced erythropoiesis, promoted erythroid maturation, and decreased apoptosis. Overall, pyruvate kinase activation as a treatment modality for β-thalassemia in preclinical model systems had multiple beneficial effects in the erythropoietic compartment and beyond, providing a strong scientific basis for further clinical trials.

Cache Domain Containing 1 Is a Novel Marker of Non-Alcoholic Steatohepatitis-Associated Hepatocarcinogenesis

Simple Summary

The aim of the present study was to discover novel early molecular biomarkers of liver neoplasms which arise in non-alcoholic steatohepatitis (NASH) Stelic Animal Model (STAM) mice. Significant increase of lipid deposits, hepatocyte ballooning, fibrosis, and incidences and multiplicities of hepatocellular adenomas and carcinomas were detected in the livers of 18-week-old STAM mice. From the results of proteome analysis of STAM mice hepatocellular carcinomas, significant elevation of a novel protein, cache domain-containing 1 (CACHD1) was found. Furthermore, we observed CACHD1-positive foci in STAM mice livers, which number, area, and cell proliferation index within the foci were significantly elevated. Results of immunohistochemical and in vitro functional analysis indicated that CACHD1 may become a useful early biomarker and potential molecular target in NASH-associated hepatocarcinogenesis, which is involved in control of cell proliferation, autophagy and apoptosis.

Abstract

In the present study, potential molecular biomarkers of NASH hepatocarcinogenesis were investigated using the STAM mice NASH model, characterized by impaired insulin secretion and development of insulin resistance. In this model, 2-days-old C57BL/6N mice were subjected to a single subcutaneous (s.c.) injection of 200 μg streptozotocin (STZ) to induce diabetes mellitus (DM). Four weeks later, mice were administered high-fat diet (HFD) HFD-60 for 14 weeks (STAM group), or fed control diet (STZ group). Eighteen-week-old mice were euthanized to allow macroscopic, microscopic, histopathological, immunohistochemical and proteome analyses. The administration of HFD to STZ-treated mice induced significant fat accumulation and fibrosis development in the liver, which progressed to NASH, and rise of hepatocellular adenomas (HCAs) and carcinomas (HCCs). In 18-week-old animals, a significant increase in the incidence and multiplicity of HCAs and HCCs was found. On the basis of results of proteome analysis of STAM mice HCCs, a novel highly elevated protein in HCCs, cache domain-containing 1 (CACHD1), was chosen as a potential NASH-HCC biomarker candidate. Immunohistochemical assessment demonstrated that STAM mice liver basophilic, eosinophilic and mixed-type altered foci, HCAs and HCCs were strongly positive for CACHD1. The number and area of CACHD1-positive foci, and cell proliferation index in the area of foci in mice of the STAM group were significantly increased compared to that of STZ group. In vitro siRNA knockdown of CACHD1 in human Huh7 and HepG2 liver cancer cell lines resulted in significant inhibition of cell survival and proliferation. Analysis of the proteome of knockdown cells indicated that apoptosis and autophagy processes could be activated. From these results, CACHD1 is an early NASH-associated biomarker of liver preneoplastic and neoplastic lesions, and a potential target protein in DM/NASH-associated hepatocarcinogenesis.

Cells Lacking PA200 Adapt to Mitochondrial Dysfunction by Enhancing Glycolysis via Distinct Opa1 Processing

The conserved Blm10/PA200 proteins are proteasome activators. Previously, we identified PA200-enriched regions in the genome of SH-SY5Y neuroblastoma cells by chromatin immunoprecipitation (ChIP) and ChIP-seq analysis. We also found that selective mitochondrial inhibitors induced PA200 redistribution in the genome. Collectively, our data indicated that PA200 regulates cellular homeostasis at the transcriptional level. In the present study, our aim is to investigate the impact of stable PA200 depletion (shPA200) on the overall transcriptome of SH-SY5Y cells. RNA-seq data analysis reveals that the genetic ablation of PA200 leads to overall changes in the transcriptional landscape of SH-SY5Y neuroblastoma cells. PA200 activates and represses genes regulating metabolic processes, such as the glycolysis and mitochondrial function. Using metabolic assays in live cells, we showed that stable knockdown of PA200 does not change basal respiration. Spare respiratory capacity and proton leak however are slightly, yet significantly, reduced in PA200-deficient cells by 99.834% and 84.147%, respectively, compared to control. Glycolysis and glycolytic capacity show a 42.186% and 26.104% increase in shPA200 cells, respectively, compared to control. These data suggest a shift from oxidative phosphorylation to glycolysis especially when cells are exposed to oligomycin-induced stress. Furthermore, we observed a preserved long and compact tubular mitochondrial morphology after inhibition of ATP synthase by oligomycin, which might be associated with the glycolytic change of shPA200 cells. The present study also demonstrates that the proteolytic cleavage of Opa1 is affected, and that the level of OMA1 is significantly reduced in shPA200 cells upon oligomycin-induced mitochondrial insult. Together, these findings suggest a role for PA200 in the regulation of metabolic changes in response to selective inhibition of ATP synthase in an in vitro cellular model.

The mitochondrial unfolded protein response and its diverse roles in cellular stress

Mitochondrial function is centrally involved in many cellular processes, such as energy production, metabolism of nucleotides, amino acids, and lipids, calcium buffering, and regulation of cell death. Multiple mechanisms are engaged under conditions of mitochondrial dysfunction to restore cellular and, subsequently, systemic functions. The mitochondrial unfolded protein response is a homeostatic mechanism that has attracted a lot of interest recently and has been described in several organisms, including humans. The mitochondrial unfolded protein response serves as a first-line-of-defence mechanism against stress to restore mitochondrial proteostasis and functions. Here, we discuss the canonical mechanisms via which the mitochondrial unfolded protein response is activated under stress and examine recent evidence that links the response with other processes that promote survival and the recovery of the mitochondrial network (i.e. the integrated stress response and mitophagy).

Ubiquitination of Intramitochondrial Proteins: Implications for Metabolic Adaptability

Mitochondria are constantly subjected to stressful conditions due to their unique physiology and organization. The resulting damage leads to mitochondrial dysfunction, which underlies many pathophysiological conditions. Hence, constant surveillance is required to closely monitor mitochondrial health for sound maintenance of cellular metabolism and thus, for viability. In addition to internal mitochondrial chaperones and proteases, mitochondrial health is also governed by host cell protein quality control systems. The ubiquitin-proteasome system (UPS) and autophagy constitute the main pathways for removal of damaged or superfluous proteins in the cytosol, nucleus, and from certain organelles such as the Endoplasmic Reticulum (ER) and mitochondria. Although stress-induced ubiquitin-dependent degradation of mitochondrial outer membrane proteins has been widely studied, mechanisms of intramitochondrial protein ubiquitination has remained largely elusive due to the predominantly cytosolic nature of UPS components, separated from internal mitochondrial proteins by a double membrane. However, recent research has illuminated examples of intramitochondrial protein ubiquitination pathways and highlighted their importance under basal and stressful conditions. Owing to the dependence of mitochondria on the error-prone process of protein import from the cytosol, it is imperative that the cell eliminate any accumulated proteins in the event of mitochondrial protein import deficiency. Apparently, a significant portion of this activity involves ubiquitination in one way or another. In the present review article, following a brief introduction to mitochondrial protein quality control mechanisms, we discuss our recent understanding of intramitochondrial protein ubiquitination, its importance for basal function of mitochondria, metabolic implications, and possible therapeutic applications.

Palmitoylated CKAP4 regulates mitochondrial functions through an interaction with VDAC2 at ER-mitochondria contact sites

Cytoskeleton-associated protein 4 (CKAP4) is a palmitoylated type II transmembrane protein localized to the endoplasmic reticulum (ER). Here, we found that knockout (KO) of CKAP4 in HeLaS3 cells induces the alteration of mitochondrial structures and increases the number of ER-mitochondria contact sites. To understand the involvement of CKAP4 in mitochondrial functions, the binding proteins of CKAP4 were explored, enabling identification of the mitochondrial porin voltage-dependent anion-selective channel protein 2 (VDAC2), which is localized to the outer mitochondrial membrane. Palmitoylation at Cys100 of CKAP4 was required for the binding between CKAP4 and VDAC2. In CKAP4 KO cells, the binding of inositol trisphosphate receptor (IP3R) and VDAC2 was enhanced, the intramitochondrial Ca2+ concentration increased and the mitochondrial membrane potential decreased. In addition, CKAP4 KO decreased the oxidative consumption rate, in vitro cancer cell proliferation under low-glucose conditions and in vivo xenograft tumor formation. The phenotypes were not rescued by expression of a palmitoylation-deficient CKAP4 mutant. These results suggest that CKAP4 plays a role in maintaining mitochondrial functions through the binding to VDAC2 at ER-mitochondria contact sites and that palmitoylation is required for this novel function of CKAP4.This article has an associated First Person interview with the first author of the paper.

Quality control of the mitochondrial proteome

Mitochondria contain about 1,000-1,500 proteins that fulfil multiple functions. Mitochondrial proteins originate from two genomes: mitochondrial and nuclear. Hence, proper mitochondrial function requires synchronization of gene expression in the nucleus and in mitochondria and necessitates efficient import of mitochondrial proteins into the organelle from the cytosol. Furthermore, the mitochondrial proteome displays high plasticity to allow the adaptation of mitochondrial function to cellular requirements. Maintenance of this complex and adaptable mitochondrial proteome is challenging, but is of crucial importance to cell function. Defects in mitochondrial proteostasis lead to proteotoxic insults and eventually cell death. Different quality control systems monitor the mitochondrial proteome. The cytosolic ubiquitin-proteasome system controls protein transport across the mitochondrial outer membrane and removes damaged or mislocalized proteins. Concomitantly, a number of mitochondrial chaperones and proteases govern protein folding and degrade damaged proteins inside mitochondria. The quality control factors also regulate processing and turnover of native proteins to control protein import, mitochondrial metabolism, signalling cascades, mitochondrial dynamics and lipid biogenesis, further ensuring proper function of mitochondria. Thus, mitochondrial protein quality control mechanisms are of pivotal importance to integrate mitochondria into the cellular environment.

Mitochondrial unfolded protein response, mitophagy and other mitochondrial quality control mechanisms in heart disease and aged heart

Mitochondria are involved in crucial homeostatic processes in the cell: the production of adenosine triphosphate and reactive oxygen species, and the release of pro-apoptotic molecules. Thus, cell survival depends on the maintenance of proper mitochondrial function by mitochondrial quality control. The most important mitochondrial quality control mechanisms are mitochondrial unfolded protein response, mitophagy, biogenesis, and fusion-fission dynamics. This review deals with mitochondrial quality control in heart diseases, especially myocardial infarction and heart failure. Some previous studies have demonstrated that the activation of mitochondrial quality control mechanisms may be beneficial for the heart, while others have shown that it may lead to heart damage. Our aim was to describe the mechanisms by which mitochondrial quality control contributes to heart protection or damage and to provide evidence that may resolve the seemingly contradictory results from the previous studies.

Resveratrol protects retinal ganglion cells against ischemia induced damage by increasing Opa1 expression

Loss of idiopathic retinal ganglion cells (RGCs) leads to irreversible vision defects and is considered the primary characteristic of glaucoma. However, effective treatment strategies in terms of RGC neuroprotection remain elusive. In the present study, the protective effects of resveratrol on RGC apoptosis, and the mechanisms underlying its effects were investigated, with a particular emphasis on the function of optic atrophy 1 (Opa1). In an ischemia/reperfusion (I/R) injury model, the notable thinning of the retina, significant apoptosis of RGCs, reduction in Opa1 expression and long Opa1 isoform to short Opa1 isoform ratios (L-Opa1/S-Opa1 ratio) were observed, all of which were reversed by resveratrol administration. Serum deprivation resulted in reductions in R28 cell viability, superoxide dismutase (SOD) activity, Opa1 expression and induced apoptosis, which were also partially reversed by resveratrol treatment. To conclude, results from the present study suggest that resveratrol treatment significantly reduced retinal damage and RGC apoptosis in I/R injury and serum deprivation models. In addition, resveratrol reversed the downregulated expression of Opa1 and reduced SOD activity. Mechanistically, resveratrol influenced mitochondrial dynamics by regulating the L-Opa1/S-Opa1 ratio. Therefore, these observations suggest that resveratrol may exhibit potential as a therapeutic agent for RGC damage in the future.

Target verification of artesunate-related antiviral drugs: Assessing the role of mitochondrial and regulatory proteins by click chemistry and fluorescence labeling

Human cytomegalovirus (HCMV) infection is associated with serious pathology such as transplant rejection or embryonic developmental defects. Antiviral treatment with currently available drugs targeting viral enzymes is often accompanied with severe side effects and the occurrence of drug-resistant viruses. For this reason, novel ways of anti-HCMV therapy focusing on so far unexploited small molecules, targets and mechanisms are intensively studied. Recently, we described the pronounced antiviral activity of the artesunate-related class of trioxane compounds, comprising NF-κB/signaling inhibitors like the trimeric derivative TF27, which proved to be highly active in a nanomolar range both in vitro and in vivo. Here, we extend this analysis by presenting further TF27/artesunate-derived antiviral compounds designed for their specific use in target verification by click chemistry applied in fluorescence labeling and tag affinity strategies. Our main findings are as follows: (i) compounds TF27, BG95, AC98 and AC173 exert strong inhibitory activity against HCMV replication in cultured primary human cells, (ii) autofluorescence activity could be quantitatively detected for BG95 and AC98, and confocal fluorescence imaging revealed accumulation in mitochondria, (iii) postulated cellular targets including mitochondrial proteins were down-regulated upon TF27 treatment, (iv) a click chemistry-based protocol of target enrichment was established, and (v) mass spectrometry-based proteomic analysis, using proteins from HCMV-infected fibroblasts covalently interacting with AC173, revealed a refined list of targets. Combined, data strongly suggest a complex mode of antiviral drug-target interaction of artesunate-related compounds, now highlighting potential roles of mitochondrial, NF-κB pathway proteins, exportins and possibly more. This strategy may further promote antiviral drug development on the basis of pharmacologically optimized trioxane derivatives.

Regulation of mitochondrial plasticity by the i-AAA protease YME1L

Mitochondria are multifaceted metabolic organelles and adapt dynamically to various developmental transitions and environmental challenges. The metabolic flexibility of mitochondria is provided by alterations in the mitochondrial proteome and is tightly coupled to changes in the shape of mitochondria. Mitochondrial proteases are emerging as important posttranslational regulators of mitochondrial plasticity. The i-AAA protease YME1L, an ATP-dependent proteolytic complex in the mitochondrial inner membrane, coordinates mitochondrial biogenesis and dynamics with the metabolic output of mitochondria. mTORC1-dependent lipid signaling drives proteolytic rewiring of mitochondria by YME1L. While the tissue-specific loss of YME1L in mice is associated with heart failure, disturbed eye development, and axonal degeneration in the spinal cord, YME1L activity supports growth of pancreatic ductal adenocarcinoma cells. YME1L thus represents a key regulatory protease determining mitochondrial plasticity and metabolic reprogramming and is emerging as a promising therapeutic target.

Mitochondria as intracellular signaling platforms in health and disease

Mitochondria, long viewed solely in the context of bioenergetics, are increasingly emerging as critical hubs for intracellular signaling. Due to their bacterial origin, mitochondria possess their own genome and carry unique lipid components that endow these organelles with specialized properties to help orchestrate multiple signaling cascades. Mitochondrial signaling modulates diverse pathways ranging from metabolism to redox homeostasis to cell fate determination. Here, we review recent progress in our understanding of how mitochondria serve as intracellular signaling platforms with a particular emphasis on lipid-mediated signaling, innate immune activation, and retrograde signaling. We further discuss how these signaling properties might potentially be exploited to develop new therapeutic strategies for a range of age-related conditions.

An Overview on ATP Dependent and Independent Proteases Including an Anterograde to Retrograde Control on Mitochondrial Function; Focus on Diabetes and Diabetic Complications

Mitochondria are the central power stations of the cell involved with a myriad of cell signalling pathways that contribute for whole health status of the cell. It is a well known fact that not only mitochondrial genome encodes for mitochondrial proteins but there are several other mitochondrial specific proteins encoded by nuclear genome which regulate plethora of cell catabolic and anabolic process. Anterograde pathways include nuclear gene encoded proteins and their specific transport into the mitochondria and regulation of mitochondrial homeostasis. The retrograde pathways include crosstalk between the mitochondria and cytoplasmic proteins. Indeed, ATP dependent and independent proteases are identified to be very critical in balancing anterograde to retrograde signalling and vice versa to maintain the cell viability or cell death. Different experimental studies conducted on silencing the genes of these proteases have shown embryonic lethality, cancer cells death, increased hepatic glucose output, insulin tolerance, increased protein exclusion bodies, mitochondrial dysfunction, and defect in mitochondrial biogenesis, increased inflammation, Apoptosis etc. These experimental studies included from eubacteria to eukaryotes. Hence, many lines of theories proposed these proteases are conservative from eubacteria to eukaryotes. However, the regulation of these proteases at gene level is not clearly understood and still research is warranted. In this review, we articulated the origin and regulation of these proteases and the cross talk between the nucleus and mitochondria vice versa, and highlighted the role of these proteases in diabetes and diabetic complications in human diseases.

A salvage pathway maintains highly functional respiratory complex I

Regulation of the turnover of complex I (CI), the largest mitochondrial respiratory chain complex, remains enigmatic despite huge advancement in understanding its structure and the assembly. Here, we report that the NADH-oxidizing N-module of CI is turned over at a higher rate and largely independently of the rest of the complex by mitochondrial matrix protease ClpXP, which selectively removes and degrades damaged subunits. The observed mechanism seems to be a safeguard against the accumulation of dysfunctional CI arising from the inactivation of the N-module subunits due to attrition caused by its constant activity under physiological conditions. This CI salvage pathway maintains highly functional CI through a favorable mechanism that demands much lower energetic cost than de novo synthesis and reassembly of the entire CI. Our results also identify ClpXP activity as an unforeseen target for therapeutic interventions in the large group of mitochondrial diseases characterized by the CI instability.

Maintenance and quality control of the mitochondrial respiratory chain complexes responsible for bulk energy production are unclear. Here, the authors show that the mitochondrial protease ClpXP is required for the rapid turnover of the core N-module of respiratory complex I, which happens independently of other modules in the complex.

Mitochondrial Proteases: Multifaceted Regulators of Mitochondrial Plasticity

Mitochondria are essential metabolic hubs that dynamically adapt to physiological demands. More than 40 proteases residing in different compartments of mitochondria, termed mitoproteases, preserve mitochondrial proteostasis and are emerging as central regulators of mitochondrial plasticity. These multifaceted enzymes limit the accumulation of short-lived, regulatory proteins within mitochondria, modulate the activity of mitochondrial proteins by protein processing, and mediate the degradation of damaged proteins. Various signaling cascades coordinate the activity of mitoproteases to preserve mitochondrial homeostasis and ensure cell survival. Loss of mitoproteases severely impairs the functional integrity of mitochondria, is associated with aging, and causes pleiotropic diseases. Understanding the dual function of mitoproteases as regulatory and quality control enzymes will help unravel the role of mitochondrial plasticity in aging and disease.