bims-mikwok 2022-06-19 papers

bims-mikwok

Biomed News

on Mitochondrial quality control

Issue of 2022‒06‒19
seventeen papers selected by
Avinash N. Mukkala, University of Toronto

Dynamic rearrangement and autophagic degradation of mitochondria during spermiogenesis in the liverwort Marchantia polymorpha.
The Role of PTEN-L in Modulating PINK1-Parkin-Mediated Mitophagy.
Structure of the second phospho-ubiquitin binding site in parkin.
Parkin: A potential target to promote healthy aging.
The influence of age, sex, and exercise on autophagy, mitophagy, and lysosome biogenesis in skeletal muscle.
OMA1 mediates local and global stress responses against protein misfolding in CHCHD10 mitochondrial myopathy.
An Overview on Mitochondrial-Based Therapies in Sepsis-Related Myocardial Dysfunction: Mitochondrial Transplantation as a Promising Approach.
Loss of hepatic DRP1 exacerbates alcoholic hepatitis by inducing megamitochondria and mitochondrial maladaptation.
Empagliflozin attenuates cardiac microvascular ischemia/reperfusion injury through improving mitochondrial homeostasis.
Mitotherapy in doxorubicin induced cardiotoxicity: A promising strategy to reduce the complications of treatment.
Mitofusin 2 positively regulates Ca2+ signaling by tethering the sarcoplasmic reticulum and mitochondria in rat aortic smooth muscle cells.
Effects of 4-Oxo-2-nonenal on biochemical properties of bovine heart mitochondria.
SLC25A47 is a novel determinant of hepatic mitochondrial function implicated in liver fibrosis.
FUNDC2 promotes liver tumorigenesis by inhibiting MFN1-mediated mitochondrial fusion.
Mitochondrial complex I dysfunction alters the balance of soluble and membrane-bound TNF during chronic experimental colitis.
Assessment of Mitochondrial Function and Oxygen Consumption Measured During Ex Vivo Normothermic Machine Perfusion of Injured Pig Kidneys Helps to Monitor Organ Viability.
Downregulation of thrombomodulin contributes to ischemia-reperfusion injury in mice with steatotic liver.

Cell Rep. 2022 Jun 14. pii: S2211-1247(22)00761-6. [Epub ahead of print]39(11): 110975

Dynamic rearrangement and autophagic degradation of mitochondria during spermiogenesis in the liverwort Marchantia polymorpha.

Takuya Norizuki, Naoki Minamino, Miyuki Sato, Hirokazu Tsukaya, Takashi Ueda.

  Mitochondria change their morphology in response to developmental and environmental cues. During sexual reproduction, bryophytes produce spermatozoids with two mitochondria in the cell body. Although intensive morphological analyses have been conducted, how this fixed number of mitochondria is realized remains poorly understood. Here, we investigate how mitochondria are reorganized during spermiogenesis in Marchantia polymorpha. We find that the mitochondrial number is reduced to one through fission followed by autophagic degradation during early spermiogenesis, and then the posterior mitochondrion arises by fission of the anterior mitochondrion. Autophagy is also responsible for the removal of other organelles, including peroxisomes, but these other organelles are removed at distinct developmental stages from mitochondrial degradation. We also find that spermiogenesis involves nonautophagic organelle degradation. Our findings highlight the dynamic reorganization of mitochondria, which is regulated distinctly from that of other organelles, and multiple degradation mechanisms operate in organelle remodeling during spermiogenesis in M. polymorpha.

Keywords:  CP: Plants; Marchantia polymorpha; autophagy; dynamin-related protein; mitochondria; mitochondrial fission; mitophagy; nonautophagic degradation; organelle reorganization; peroxisome; spermiogenesis

DOI:  https://doi.org/10.1016/j.celrep.2022.110975
Neurotox Res. 2022 Jun 14.

The Role of PTEN-L in Modulating PINK1-Parkin-Mediated Mitophagy.

Mohamed A Eldeeb, Mansoore Esmaili, Marwa Hassan, Mohamed A Ragheb.

  An inherent challenge that mitochondria face is the continuous exposure to diverse stresses which increase their likelihood of dysregulation. In response, human cells have evolved sophisticated quality control mechanisms to identify and eliminate abnormal dysfunctional mitochondria. One pivotal mitochondrial quality control pathway is PINK1/Parkin-dependent mitophagy which mediates the selective removal of the dysfunctional mitochondria from the cell by autophagy. PTEN-induced putative kinase 1 (PINK1) is a mitochondrial Ser/Thr kinase that was originally identified as a gene responsible for autosomal recessive early-onset Parkinson's disease (PD). Notably, upon failure of mitochondrial import, Parkin, another autosomal-recessive PD gene, is recruited to mitochondria and mediates the autophagic clearance of deregulated mitochondria. Importantly, recruitment of Parkin to damaged mitochondria hinges on the accumulation of PINK1 on the outer mitochondrial membrane (OMM). Normally, PINK1 is imported from the cytosol through the translocase of the outer membrane (TOM) complex, a large multimeric channel responsible for the import of most mitochondrial proteins. After import, PINK1 is rapidly degraded. Thus, at steady-state, PINK1 levels are kept low. However, upon mitochondrial import failure, PINK1 accumulates and forms a high-molecular weight > 700 kDa complex with TOM on the OMM. Thus, PINK1 functions as sensor, tagging dysfunctional mitochondria for Parkin-mediated mitophagy. Although much has been learned about the function of PINK1 in mitophagy, the biochemical and structural basis of negative regulation of PINK1 operation and functions is far from clear. Recent work unveiled new players as PTEN-l as negative regulator of PINK1 function. Herein, we review key aspects of mitophagy and PINK1/Parkin-mediated mitophagy with highlighting the role of negative regulation of PINK1 function and presenting some of the key future directions in PD cell biology.

Keywords:  Mitochondrial quality control; Mitophagy; Neurodegeneration; PINK1; PTEN-L; Parkin; Protein degradation; Protein quality control

DOI:  https://doi.org/10.1007/s12640-022-00475-w
J Biol Chem. 2022 Jun 08. pii: S0021-9258(22)00555-5. [Epub ahead of print] 102114

Structure of the second phospho-ubiquitin binding site in parkin.

Rayan Fakih, Véronique Sauvé, Kalle Gehring.

Parkin and PINK1 regulate a mitochondrial quality control system that is mutated in some early onset forms of Parkinson's disease. Parkin is an E3 ubiquitin ligase and regulated by the mitochondrial kinase PINK1 via a two-step cascade. PINK1 first phosphorylates ubiquitin, which binds a recruitment site on parkin to localize parkin to damaged mitochondria. In the second step, PINK1 phosphorylates parkin on its ubiquitin-like domain (Ubl) domain, which binds a regulatory site to release ubiquitin ligase activity. Recently, an alternative feed-forward mechanism was identified that bypasses the need for parkin phosphorylation through the binding of a second phospho-ubiquitin (pUb) molecule. Here, we report the structure of parkin activated through this feed-forward mechanism. The crystal structure of parkin with pUb bound to both the recruitment and regulatory sites reveals the molecular basis for differences in specificity and affinity of the two sites. We use isothermal titration calorimetry measurements to reveal cooperativity between the two binding sites and the role of linker residues for pUbl binding to the regulatory site. The observation of flexibility in the process of parkin activation offers hope for the future design of small molecules for the treatment of Parkinson's disease.

DOI: https://doi.org/10.1016/j.jbc.2022.102114
J Physiol. 2022 Jun 12.

Parkin: A potential target to promote healthy aging.

Jean-Philippe Leduc-Gaudet, Sabah Na Hussain, Gilles Gouspillou.

  Parkin is an E3 ubiquitin ligase mostly known for its role in regulating the removal of defective mitochondria via mitophagy. However, increasing experimental evidence that Parkin regulates several other aspects of mitochondrial biology in addition to its role in mitophagy has emerged over the past two decades. Indeed, Parkin has been shown to regulate mitochondrial biogenesis and dynamics and mitochondrial-derived vesicle formation, suggesting that Parkin plays key roles in maintaining healthy mitochondria. While Parkin is commonly described as a cytosolic E3 ubiquitin ligase, Parkin was also detected in other cellular compartments, including the nucleus, where it regulates transcription factors and acts as a transcription factor itself. New evidence also suggests that Parkin overexpression can be leveraged to delay aging. In D. melanogaster, for example, Parkin overexpression extends lifespan. In mammals, Parkin overexpression delays hallmarks of aging in several tissues and cell types. Parkin overexpression also confers protection in various models of cellular senescence and neurological disorders closely associated with aging, such as Alzheimer's and Parkinson's diseases. Recently, Parkin overexpression has also been shown to suppress tumor growth. In this review, we discuss newly emerging biological roles of Parkin as a modulator of cellular homeostasis, survival, and healthy aging, and we explore potential mechanisms through which Parkin exerts its beneficial effects on cellular health. Abstract figure legend Parkin: A potential target to promote healthy aging Illustration of key aspects of Parkin biology, including Parkin function and cellular localization and key roles in the regulation of mitochondrial quality control. The organs and systems in which Parkin overexpression was shown to exert protective effects relevant to the promotion of healthy aging are highlighted in the black rectangle at the bottom of the Figure. This article is protected by copyright. All rights reserved.

Keywords:  Parkin; aging-related disorders; health span; healthy aging; lifespan; mitochondrial quality control; senescence

DOI:  https://doi.org/10.1113/JP282567
Skelet Muscle. 2022 Jun 11. 12(1): 13

The influence of age, sex, and exercise on autophagy, mitophagy, and lysosome biogenesis in skeletal muscle.

Matthew Triolo, Ashley N Oliveira, Rita Kumari, David A Hood.

  BACKGROUND: Aging decreases skeletal muscle mass and quality. Maintenance of healthy muscle is regulated by a balance between protein and organellar synthesis and their degradation. The autophagy-lysosome system is responsible for the selective degradation of protein aggregates and organelles, such as mitochondria (i.e., mitophagy). Little data exist on the independent and combined influence of age, biological sex, and exercise on the autophagy system and lysosome biogenesis. The purpose of this study was to characterize sex differences in autophagy and lysosome biogenesis in young and aged muscle and to determine if acute exercise influences these processes.METHODS: Young (4-6 months) and aged (22-24 months) male and female mice were assigned to a sedentary or an acute exercise group. Mitochondrial content, the autophagy-lysosome system, and mitophagy were measured via protein analysis. A TFEB-promoter-construct was utilized to examine Tfeb transcription, and nuclear-cytosolic fractions allowed us to examine TFEB localization in sedentary and exercised muscle with age and sex.
RESULTS: Our results indicate that female mice, both young and old, had more mitochondrial protein than age-matched males. However, mitochondria in the muscle of females had a reduced respiratory capacity. Mitochondrial content was only reduced with age in the male cohort. Young female mice had a greater abundance of autophagy, mitophagy, and lysosome proteins than young males; however, increases were evident with age irrespective of sex. Young sedentary female mice had indices of greater autophagosomal turnover than male counterparts. Exhaustive exercise was able to stimulate autophagic clearance solely in young male mice. Similarly, nuclear TFEB protein was enhanced to a greater extent in young male, compared to young female mice following exercise, but no changes were observed in aged mice. Finally, TFEB-promoter activity was upregulated following exercise in both young and aged muscle.
CONCLUSIONS: The present study demonstrates that biological sex influences mitochondrial homeostasis, the autophagy-lysosome system, and mitophagy in skeletal muscle with age. Furthermore, our data suggest that young male mice have a more profound ability to activate these processes with exercise than in the other groups. Ultimately, this may contribute to a greater remodeling of muscle in response to exercise training in males.

Keywords:  Aging; Autophagy; Lysosomes; Mitophagy; Muscle; Sex differences; TFEB

DOI:  https://doi.org/10.1186/s13395-022-00296-7
J Clin Invest. 2022 Jun 14. pii: e157504. [Epub ahead of print]

OMA1 mediates local and global stress responses against protein misfolding in CHCHD10 mitochondrial myopathy.

Mario K Shammas, Xiaoping Huang, Beverly P Wu, Evelyn Fessler, Insung Song, Nicholas P Randolph, Yan Li, Christopher Ke Bleck, Danielle A Springer, Carl Fratter, Ines A Barbosa, Andrew F Powers, Pedro M Quirós, Carlos Lopez-Otin, Lucas T Jae, Joanna Poulton, Derek P Narendra.

  Mitochondrial stress triggers a response in the cell's mitochondria and nucleus, but how these stress responses are coordinated in vivo is poorly understood. Here, we characterize a family with myopathy caused by a dominant p.G58R mutation in the mitochondrial protein CHCHD10. To understand the disease etiology, we developed a knock-in mouse model and found that mutant CHCHD10 aggregates in affected tissues, applying a toxic protein stress to the inner mitochondrial membrane. Unexpectedly, survival of CHCHD10 knock-in mice depended on a protective stress response mediated by OMA1. The OMA1 stress response acted both locally within mitochondria, causing mitochondrial fragmentation, and signaled outside the mitochondria, activating the integrated stress response through cleavage of DELE1. We additionally identified an isoform switch in the terminal complex of the electron transport chain as a component of this response. Our results demonstrate that OMA1 is critical for neonatal survival conditionally in the setting of inner mitochondrial membrane stress, coordinating local and global stress responses to reshape the mitochondrial network and proteome.

Keywords:  Cell Biology; Cell stress; Genetics; Mitochondria; Proteases

DOI:  https://doi.org/10.1172/JCI157504
Can J Infect Dis Med Microbiol. 2022 ;2022 3277274

An Overview on Mitochondrial-Based Therapies in Sepsis-Related Myocardial Dysfunction: Mitochondrial Transplantation as a Promising Approach.

Behnaz Mokhtari, Rana Yavari, Reza Badalzadeh, Ata Mahmoodpoor.

Sepsis is defined as a life-threatening organ failure due to dysregulated host response to infection. Despite current advances in our knowledge about sepsis, it is still considered as a major global health challenge. Myocardial dysfunction is a well-defined manifestation of sepsis which is related to worse outcomes in septic patients. Given that the heart is a mitochondria-rich organ and the normal function of mitochondria is essential for successful modulation of septic response, the contribution of mitochondrial damage in sepsis-related myocardial dysfunction has attracted the attention of many scientists. It is widely accepted that mitochondrial damage is involved in sepsis-related myocardial dysfunction; however, effective and potential treatment modalities in clinical setting are still lacking. Mitochondrial-based therapies are potential approaches in sepsis treatment. Although various therapeutic strategies have been used for mitochondrial function improvement, their effects are limited when mitochondria undergo irreversible alterations under septic challenge. Therefore, application of more effective approaches such as mitochondrial transplantation has been suggested. This review highlights the crucial role of mitochondrial damage in sepsis-related myocardial dysfunction, then provides an overview on mitochondrial-based therapies and current approaches to mitochondrial transplantation as a novel strategy, and proposes future directions for more researches in this field.

DOI: https://doi.org/10.1155/2022/3277274
Hepatology. 2022 Jun 13.

Loss of hepatic DRP1 exacerbates alcoholic hepatitis by inducing megamitochondria and mitochondrial maladaptation.

Xiaowen Ma, Allen Chen, Luma Melo, Ana Clemente-Sanchez, Xiaojuan Chao, Ali Reza Ahmadi, Brandon Peiffer, Zhaoli Sun, Hiromi Sesaki, Tiangang Li, Xiaokun Wang, Wanqing Liu, Ramon Bataller, Hong-Min Ni, Wen-Xing Ding.

BACKGROUND & AIMS: Increased megamitochondria formation and impaired mitophagy in hepatocytes have been linked to the pathogenesis of alcohol-associated liver disease (ALD). This study aims to determine the mechanisms by which alcohol consumption increases megamitochondria formation in the pathogenesis of ALD.APPROACH & RESULTS: Human alcoholic hepatitis (AH) liver samples were used for electron microscopy (EM), histology, and biochemical analysis. Liver-specific dynamin-related protein 1 (DRP1, gene name DNM1L, an essential gene regulating mitochondria fission) knockout (L-DRP1 KO) mice and wild-type (WT) mice were subjected to chronic plus binge alcohol feeding. Both human AH and alcohol-fed mice had decreased hepatic DRP1 with increased accumulation of hepatic megamitochondria. Mechanistic studies revealed that alcohol feeding decreased DRP1 by impairing transcription factor EB-mediated induction of DNM1L. L-DRP1 KO mice had increased megamitochondria and decreased mitophagy with increased liver injury and inflammation, which were further exacerbated by alcohol feeding. Seahorse flux and unbiased metabolomics analysis showed alcohol intake increased mitochondria oxygen consumption and hepatic NAD+, acylcarnitine, and ketone levels, which were attenuated in L-DRP1 KO mice, suggesting that loss of hepatic DRP1 leads to maladaptation to alcohol-induced metabolic stress. RNA-seq and q-PCR analysis revealed increased gene expression of the cGAS-STING-Interferon pathway in L-DRP1 KO mice regardless of alcohol feeding. Alcohol-fed L-DRP1 KO mice had increased cytosolic mtDNA and mitochondrial dysfunction leading to increased activation of cGAS-STING-Interferon signaling pathways and liver injury.
CONCLUSION: Alcohol consumption decreases hepatic DRP1 resulting in increased megamitochondria and mitochondrial maladaptation that promotes AH by mitochondria-mediated inflammation and cell injury.

DOI: https://doi.org/10.1002/hep.32604
Cardiovasc Diabetol. 2022 Jun 15. 21(1): 106

Empagliflozin attenuates cardiac microvascular ischemia/reperfusion injury through improving mitochondrial homeostasis.

Rongjun Zou, Wanting Shi, Junxiong Qiu, Na Zhou, Na Du, Hao Zhou, Xinxin Chen, Li Ma.

  BACKGROUND: Empagliflozin has been reported to protect endothelial cell function, regardless of diabetes status. However, the role of empagliflozin in microvascular protection during myocardial ischemia reperfusion injury (I/R) has not been fully understood.METHODS: Electron microscopy, western blots, immunofluorescence, qPCR, mutant plasmid transfection, co-immunoprecipitation were employed to explore whether empagliflozin could alleviate microvascular damage and endothelial injury during cardiac I/R injury.
RESULTS: In mice, empagliflozin attenuated I/R injury-induced microvascular occlusion and microthrombus formation. In human coronary artery endothelial cells, I/R injury led to adhesive factor upregulation, endothelial nitric oxide synthase inactivation, focal adhesion kinase downregulation, barrier dysfunction, cytoskeletal degradation and cellular apoptosis; however, empagliflozin treatment diminished these effects. Empagliflozin improved mitochondrial oxidative stress, mitochondrial respiration and adenosine triphosphate metabolism in I/R-treated human coronary artery endothelial cells by preventing the phosphorylation of dynamin-related protein 1 (Drp1) and mitochondrial fission 1 protein (Fis1), thus repressing mitochondrial fission. The protective effects of empagliflozin on mitochondrial homeostasis and endothelial function were abrogated by the re-introduction of phosphorylated Fis1, but not phosphorylated Drp1, suggesting that Fis1 dephosphorylation is the predominant mechanism whereby empagliflozin inhibits mitochondrial fission during I/R injury. Besides, I/R injury induced Fis1 phosphorylation primarily by activating the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) pathway, while empagliflozin inactivated this pathway by exerting anti-oxidative effects.
CONCLUSIONS: These results demonstrated that empagliflozin can protect the microvasculature by inhibiting the DNA-PKcs/Fis1/mitochondrial fission pathway during myocardial I/R injury.

Keywords:  Empagliflozin; Endothelial dysfunction; Microvascular injury; Mitochondria; ischemia/reperfusion injury

DOI:  https://doi.org/10.1186/s12933-022-01532-6
Life Sci. 2022 Jun 08. pii: S0024-3205(22)00401-5. [Epub ahead of print] 120701

Mitotherapy in doxorubicin induced cardiotoxicity: A promising strategy to reduce the complications of treatment.

Farshid Maleki, Mona Salimi, Reza Shirkoohi, Mohsen Rezaei.

  AIMS: Doxorubicin is a potent and broad-spectrum antineoplastic medication prescribed for both solid and hematological malignancies. Despite its value, the clinical use of doxorubicin is limited due to cardio-oncologic complication and cardiotoxic adverse effect. Among the mechanisms proposed for its toxicity, mitochondrial dysfunction has gained more attention. Therefore, if damaged mitochondria are replaced by normal efficient mitochondria, cardiac toxicity is expected to be reduced or improved. In this way, we have studied the efficiency of transplantation of freshly isolated rat liver mitochondria in neonatal rat cardiomyocytes that have been damaged by doxorubicin.MATERIALS AND METHODS: For this purpose, isolated mitochondria were characterized using mitochondrial complex II, membrane potential and swelling evaluations, and also fluorescence and electron microscopy. Afterward, the effect of mitotherapy on the damaged cardiomyocytes was investigated by using annexin V/PI staining, MTT, ROS, MMP, lipid peroxidation, GSH and ATP evaluations.
KEY FINDINGS AND SIGNIFICANCE: Transplanted mitochondria could remarkably enter the neonatal rat cardiomyocytes. Addition of mitochondria to the damaged cardiomyocytes, significantly increased cell viability by reducing the level of reactive oxygen species and lipid peroxidation, increasing of ∆Ψ, ATP and GSH contents and decreasing of apoptotic and necrotic cell death. Our results showed that mitotherapy has a significant restorative effect on cardiotoxicity induced by doxorubicin, which promises a better future to reduce the complications of cancer treatment.

Keywords:  Cancer; Cardiotoxicity; Doxorubicin; Mitochondria; Oxidative stress

DOI:  https://doi.org/10.1016/j.lfs.2022.120701
Am J Physiol Cell Physiol. 2022 Jun 15.

Mitofusin 2 positively regulates Ca2+ signaling by tethering the sarcoplasmic reticulum and mitochondria in rat aortic smooth muscle cells.

Sou Inagaki, Yoshiaki Suzuki, Keisuke Kawasaki, Rubii Kondo, Yuji Imaizumi, Hisao Yamamura.

  Mitochondria buffer cytosolic Ca2+increases following Ca2+ influx from extracellular spaces and Ca2+ release from intracellular Ca2+ store sites under physiological circumstances. Therefore, close contact of mitochondria with the sarcoplasmic reticulum (SR) is required for maintaining Ca2+ homeostasis. Mitofusin 2 (Mfn2) localizes in both mitochondrial and SR membranes, and is hypothesized to optimize the distance and Ca2+ transfer between these organelles. However, the physiological significance of Mfn2 in vascular smooth muscle cells (VSMCs) is poorly understood. In the present study, the role of Mfn2 in the physical and functional couplings between SR and mitochondria was examined in rat aortic smooth muscle cells (rASMCs) by confocal and electron microscope imaging. When Mfn2 was knocked-down using siRNA in rASMCs, the mean distance between these organelles was extended from 16.2 to 21.6 nm. The increase in the cytosolic Ca2+ concentration ([Ca2+]cyt) induced by 100 nM arginine vasopressin (AVP) was not affected by Mfn2 siRNA knockdown, whereas cytosolic Ca2+ removal was slower after Mfn2 knockdown. Following the AVP-induced [Ca2+]cyt increase, mitochondrial Ca2+ uptake and Ca2+ refill into the SR were attenuated by Mfn2 knockdown. In addition, Mfn2-knockdown cells exhibited a loss of mitochondrial membrane potential (ΔΨmito) and lower ATP levels in mitochondria. Moreover, Mfn2 knockdown inhibited cell proliferation. In contrast, Mfn2 overexpression increased ΔΨmito and cell growth. This study strongly suggests that Mfn2 is responsible for SR-mitochondria Ca2+ signaling by tethering mitochondria to SR, thereby regulating ATP production and proliferation of VSMCs.

Keywords:  calcium; mitochondria; mitofusin; sarcoplasmic reticulum; smooth muscle

DOI:  https://doi.org/10.1152/ajpcell.00274.2021
Food Sci Nutr. 2022 Jun;10(6): 1830-1840

Effects of 4-Oxo-2-nonenal on biochemical properties of bovine heart mitochondria.

Anand Mohan, Deepak Kafle, Rakesh K Singh, Yen-Con Hung.

  The effects of lipid peroxidation products 4-Hydroxy-2-nonenal (4-HNE) and 4-oxo-2-nonenal (4-ONE) were evaluated using bovine heart mitochondria. Oxygen consumption rate (OCR), ultrastructure, antioxidant activity, and membrane permeability were examined to compare their effects on isolated mitochondria from beef cardiac muscle. For the mitochondrial morphology, the final concentration of mitochondria and 4-ONE or 4-HNE in the reaction tube were 10 mg/ml and 1 mM, respectively. For the OCR experiment, mitochondria (2.5 mg/ml) were incubated with 0.20 mM ONE or in a Clark electrode chamber at 25°C. Mitochondrial membrane permeability was determined by incubating 0.5 mg/ml of mitochondrial protein with either 0.05 mM ONE or HNE or ethanol control at pH 5.6 and 7.4 at 25°C. Transmission electron microscopy (TEM) revealed that the size of 4-ONE treated mitochondria at pH 7.4 increased (p < .05), as did permeability (p < .05), unlike ethanol controls. However, mitochondria incubated with 4-ONE at pH 5.6 showed a decrease in volume (p < .05). Incubating mitochondria with 4-ONE at pH 5.6 and pH increased oxygen consumption rate 7.4 caused less oxygen consumption than either 4-HNE treatment or ethanol control. The hydrogen peroxide assay (H2O2), ferric reducing antioxidant properties (FRAP), and 2,2'-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS.+) assays revealed that 4-ONE is a more potent inhibitor of the endogenous antioxidant system of mitochondria than 4-HNE (p < .05).

Keywords:  4‐Hydroxy‐2‐nonenal; 4‐oxo‐2‐nonenal; antioxidant properties; lipid oxidation; mitochondria; oxygen consumption

DOI:  https://doi.org/10.1002/fsn3.2799
J Hepatol. 2022 Jun 14. pii: S0168-8278(22)00364-6. [Epub ahead of print]

SLC25A47 is a novel determinant of hepatic mitochondrial function implicated in liver fibrosis.

Nadia Bresciani, Hadrien Demagny, Vera Lemos, Francesca Pontanari, Xiaoxu Li, Yu Sun, Hao Li, Alessia Perino, Johan Auwerx, Kristina Schoonjans.

  BACKGROUND & AIMS: Transporters of the SLC25 mitochondrial carrier superfamily bridge cytoplasmic and mitochondrial metabolism by channeling metabolites across mitochondrial membranes and are pivotal for metabolic homeostasis. Despite their physiological relevance as gatekeepers of cellular metabolism, most of the SLC25 family members remain uncharacterized. We undertook a comprehensive tissue distribution analysis of all Slc25 family members across metabolic organs and identified SLC25A47 as a liver-specific mitochondrial carrier.METHOD: We used a murine loss-of-function model to unravel the role of this transporter in mitochondrial and hepatic homeostasis. We performed extensive metabolic phenotyping and molecular characterization of newly generated Slc25a47hep-/- and Slc25a47-Fgf21hep-/- mice.
RESULTS: Slc25a47hep-/- mice displayed a wide variety of metabolic abnormalities, as a result of sustained energy deficiency in the liver originating from impaired mitochondrial respiration in this organ. This mitochondrial phenotype was associated with an activation of the mitochondrial stress response (MSR) in the liver, and the development of fibrosis, which was exacerbated upon feeding a high-fat high-sucrose diet. The MSR induced the secretion of several mitokines, amongst which FGF21 played a preponderant role on systemic physiology. To dissect the FGF21-dependent and -independent physiological changes induced in Slc25a47hep-/- mice, we generated a double Slc25a47-Fgf21hep-/- mouse model and demonstrated that several aspects of the hypermetabolic state were driven by hepatic secretion of FGF21. On the other hand, the metabolic fuel inflexibility observed in Slc25a47hep-/- mice could not be rescued with the genetic removal of Fgf21.
CONCLUSION: Collectively, our data place SLC25A47 at the center of mitochondrial homeostasis, which upon dysfunction triggers robust liver-specific and systemic adaptive stress responses. The prominent role of SLC25A47 in hepatic fibrosis identifies this carrier, or its transported metabolite, as a potential target for therapeutic intervention.
LAY SUMMARY: SLC25A47 is a liver-specific mitochondrial carrier. Slc25a47hep-/- mice are unable to maintain mitochondrial homeostasis in hepatocytes and show impaired mitochondrial respiration resulting in chronic energy deficiency, mitochondrial stress, and fibrosis in hepatocytes. Hepatic mitochondrial stress is characterized by the secretion of the mitokine FGF21 which drives a strong and systemic hypermetabolic state impacting whole-body physiology.

Keywords:  FGF21; Fibrosis; Liver; Metabolism; Mitochondrial solute carriers; Mitochondrial stress response

DOI:  https://doi.org/10.1016/j.jhep.2022.05.040
Nat Commun. 2022 Jun 17. 13(1): 3486

FUNDC2 promotes liver tumorigenesis by inhibiting MFN1-mediated mitochondrial fusion.

Shuaifeng Li, Shixun Han, Qi Zhang, Yibing Zhu, Haitao Zhang, Junli Wang, Yang Zhao, Jianhui Zhao, Lin Su, Li Li, Dawang Zhou, Cunqi Ye, Xin-Hua Feng, Tingbo Liang, Bin Zhao.

Mitochondria generate ATP and play regulatory roles in various cellular activities. Cancer cells often exhibit fragmented mitochondria. However, the underlying mechanism remains elusive. Here we report that a mitochondrial protein FUN14 domain containing 2 (FUNDC2) is transcriptionally upregulated in primary mouse liver tumors, and in approximately 40% of human hepatocellular carcinoma (HCC). Importantly, elevated FUNDC2 expression inversely correlates with patient survival, and its knockdown inhibits liver tumorigenesis in mice. Mechanistically, the amino-terminal region of FUNDC2 interacts with the GTPase domain of mitofusin 1 (MFN1), thus inhibits its activity in promoting fusion of outer mitochondrial membrane. As a result, loss of FUNDC2 leads to mitochondrial elongation, decreased mitochondrial respiration, and reprogrammed cellular metabolism. These results identified a mechanism of mitochondrial fragmentation in cancer through MFN1 inhibition by FUNDC2, and suggested FUNDC2 as a potential therapeutic target of HCC.

DOI: https://doi.org/10.1038/s41467-022-31187-6
Sci Rep. 2022 Jun 15. 12(1): 9977

Mitochondrial complex I dysfunction alters the balance of soluble and membrane-bound TNF during chronic experimental colitis.

Ainize Peña-Cearra, Miguel Angel Pascual-Itoiz, Jose Luis Lavín, Miguel Fuertes, Itziar Martín-Ruiz, Janire Castelo, Ainhoa Palacios, Diego Barriales, Asier Fullaondo, Ana M Aransay, Hector Rodríguez, Juan Anguita, Leticia Abecia.

Inflammatory bowel disease (IBD) is a complex, chronic, relapsing and heterogeneous disease induced by environmental, genomic, microbial and immunological factors. MCJ is a mitochondrial protein that regulates the metabolic status of macrophages and their response to translocated bacteria. Previously, an acute murine model of DSS-induced colitis showed increased disease severity due to MCJ deficiency. Unexpectedly, we now show that MCJ-deficient mice have augmented tumor necrosis factor α converting enzyme (TACE) activity in the context of chronic inflammation. This adaptative change likely affects the balance between soluble and transmembrane TNF and supports the association of the soluble form and a milder phenotype. Interestingly, the general shifts in microbial composition previously observed during acute inflammation were absent in the chronic model of inflammation in MCJ-deficient mice. However, the lack of the mitochondrial protein resulted in increased alpha diversity and the reduction in critical microbial members associated with inflammation, such as Ruminococcus gnavus, which could be associated with TACE activity. These results provide evidence of the dynamic metabolic adaptation of the colon tissue to chronic inflammatory changes mediated by the control of mitochondrial function.

DOI: https://doi.org/10.1038/s41598-022-13480-y
Transpl Int. 2022 ;35 10420

Assessment of Mitochondrial Function and Oxygen Consumption Measured During Ex Vivo Normothermic Machine Perfusion of Injured Pig Kidneys Helps to Monitor Organ Viability.

James P Hunter, Letizia Lo Faro, Kaithlyn Rozenberg, Fungai Dengu, Anne Ogbemudia, Annemarie Weissenbacher, John F Mulvey, Laura Knijff, Kishore Gopalakrishnan, Rutger J Ploeg.

  Donor kidney assessment may improve organ utilisation. Normothermic Machine Perfusion (NMP) has the potential to facilitate this advance. The mechanism of action is not yet determined and we aimed to assess mitochondrial function during NMP. Anaesthetised pigs (n = 6) had one kidney clamped for 60 min. The healthy contralateral kidney was removed and underwent NMP for 8 h (healthy control (HC), n = 6). Following 60 min warm ischaemia the injured kidney underwent HMP for 24 h, followed by NMP for 8 h (n = 6). Mitochondria were extracted from fresh tissue for analysis. Injured kidneys were analysed as two separate groups (IMa, n = 3 and IMb, n = 3). Renal resistance was higher (0.39ï, ± 0.29 vs. 1.65ï, ± 0.85; p = 0.01) and flow was lower (55ï, ± 28 vs. 7ï, ± 4; p = 0.03) during HMP in IMb than IMa. NMP blood flow was higher in IMa versus IMb (2-way ANOVA; p < 0.001) After 60 min NMP, O2 consumption was significantly lower in IMb versus IMa (p ≤ 0.002). State-3 respiration was significantly different between the groups (37ï, ± 19 vs. 24ï, ± 14 vs. 10ï, ± 8; nmolO2/min/mg; p = 0.049). Lactate levels were significantly lower in IMa versus IMb (p = 0.028). Mitochondrial respiration levels during NMP may be suggestive of kidney viability. Oxygen consumption, renal blood flow and lactate can differentiate severity of kidney injury during NMP.

Keywords:  ischemia/reperfusion injury; kidney; mitochondria; normothermic machine perfusion; preservation

DOI:  https://doi.org/10.3389/ti.2022.10420
Hepatol Res. 2022 Jun 17.

Downregulation of thrombomodulin contributes to ischemia-reperfusion injury in mice with steatotic liver.

Megumi Yamaguchi, Hirotaka Tashiro, Shintaro Kuroda, Sho Okimoto, Tsuyoshi Kobayashi, Takao Hinoi, Hideki Ohdan.

  AIM: Ischemia-reperfusion (IR) injury is one of the most critical complications commonly associated with liver surgery, including liver transplantation. Steatotic livers are particularly vulnerable to IR injury. However, the underlying mechanisms of this increased susceptibility have not fully been understood. In the present study, we used heterogeneous thrombomodulin (TM)-knockout (KO) (TM+/- ) mice, which express about 50% functional activity of TM as compared with wild type, to investigate whether dysregulation of TM enhances IR injury in steatotic livers.METHODS: Steatotic livers were induced using choline-deficient diets (CDD) in mice. The biological activity of TM was assessed using the productivity of protein C. Susceptibility to IR injury was compared between steatotic livers and non-steatotic livers and also assessed in TM-KO mice. We investigated whether recombinant TM (rTM) and the lectin-like domain of TM (rTM-D1) ameliorated IR injury in steatotic livers.
RESULTS: Protein C activity was significantly decreased to less than 20% in CDD-fed mice compared with mice with non-steatotic livers. Steatotic livers showed exaggerated IR injury compared with non-steatotic livers. Recombinant TM (rTM) and the lectin-like domain of TM (rTM-D1), which has anti-inflammatory effects, ameliorated IR injury in steatotic livers. TM+/- mice showed increased susceptibility to IR injury, and rTM ameliorated the increased IR injury in TM+/- mice.
CONCLUSION: We conclude that downregulation of TM increases susceptibility to hepatic IR injury in steatotic livers and that rTM ameliorates hepatic IR injury through anti-inflammatory action. This article is protected by copyright. All rights reserved.

Keywords:  HMGB1; ischemia-reperfusion injury; lectin-like domain thrombomodulin; steatotic liver

DOI:  https://doi.org/10.1111/hepr.13802