bims-mikwok Biomed News
on Mitochondrial quality control
Issue of 2020‒11‒01
fourteen papers selected by
Avinash N. Mukkala
University of Toronto

  1. Cell Death Discov. 2020 ;6 107
    Craig JE, Miller JN, Rayavarapu RR, Hong Z, Bulut GB, Zhuang W, Sakurada SM, Temirov J, Low JA, Chen T, Pruett-Miller SM, Huang LJ, Potts MB.
      Mitochondria are vital organelles that coordinate cellular energy homeostasis and have important roles in cell death. Therefore, the removal of damaged or excessive mitochondria is critical for maintaining proper cellular function. The PINK1-Parkin pathway removes acutely damaged mitochondria through a well-characterized mitophagy pathway, but basal mitochondrial turnover occurs via distinct and less well-understood mechanisms. Here we report that the MEKK3-MEK5-ERK5 kinase cascade is required for mitochondrial degradation in the absence of exogenous damage. We demonstrate that genetic or pharmacological inhibition of the MEKK3-MEK5-ERK5 pathway increases mitochondrial content by reducing lysosome-mediated degradation of mitochondria under basal conditions. We show that the MEKK3-MEK5-ERK5 pathway plays a selective role in basal mitochondrial degradation but is not required for non-selective bulk autophagy, damage-induced mitophagy, or restraint of mitochondrial biogenesis. This illuminates the MEKK3-MEK5-ERK5 pathway as a positive regulator of mitochondrial degradation that acts independently of exogenous mitochondrial stressors.
    Keywords:  Mitophagy; Stress signalling
  2. Cell Physiol Biochem. 2020 Oct 30. 54(6): 1101-1114
    Rodríguez-Graciani KM, Chapa-Dubocq XR, MacMillan-Crow LA, Javadov S.
      BACKGROUND/AIMS: Structural and functional alterations in mitochondria, particularly, the inner mitochondrial membrane (IMM) plays a critical role in mitochondria-mediated cell death in response to cardiac ischemia-reperfusion (IR) injury. The integrity of IMM can be affected by two potential intra-mitochondrial factors: i) mitochondrial matrix swelling, and ii) proteolytic cleavage of the long optic atrophy type 1 (L-OPA1), an IMM-localized dynamin-like GTPase engaged in the regulation of structural organization and integrity of the mitochondrial cristae. However, the relationship between these two factors in response to oxidative stress remains unclear. Here, we elucidated the effects of cardiac IR injury on L-OPA1 cleavage and OMA1 activity.METHODS: Langendorff-mode perfused isolated rat hearts were subjected to 25-min of global ischemia followed by 90-min reperfusion in the presence or absence of XJB-5-131 (XJB, a mitochondria-targeting ROS scavenger) and sanglifehrin A (SfA, a permeability transition pore inhibitor).
    RESULTS: XJB in combination with SfA increased post-ischemic recovery of cardiac function and reduced mitochondrial ROS production at 30- and 60-min reperfusion and affected mitochondrial swelling. L-OPA1 levels were reduced in IR hearts; however, neither XJB, SfA, and their combination prevented IR-induced reduction of L-OPA1 cleavage. Likewise, IR increased the OMA1 enzymatic activity, which remained unchanged in the presence of XJB and/or SfA.
    CONCLUSION: IR-induced cardiac and mitochondrial dysfunctions are associated with OMA1 activation and L-OPA1 cleavage. However, XJB, SfA, and their combination do not prevent these changes despite improved heart and mitochondria function, thus, suggesting that different mechanisms can be implicated in L-OPA1 processing in response to cardiac IR injury.
    Keywords:  Cardiac ischemia-reperfusion; Mitochondria; Optic atrophy type 1 protein; Reactive oxygen species; Mitochondrial swelling; Permeability transition pores
  3. Biomed Pharmacother. 2020 Oct 23. pii: S0753-3322(20)31089-1. [Epub ahead of print]132 110897
    Zhao Y, Guo R, Li L, Li S, Fan G, Zhao X, Wang Y.
      BACKGROUND: Mitochondrial quality control, regulated by mitochondrial dynamics and mitophagy, has been regarded as pivotal process to induce segregation of mitochondria during myocardial ischemia/reperfusion (I/R) injury. However, few works revealed the regulation of mitochondrial quality control by therapeutic agents. Tongmai formula (TM) is a clinically used botanical drug for treating cardiovascular diseases, which mechanism is unveiled. Thus, in this study, we investigated the pharmacological effects of TM on modulating mitochondrial quality control during cardiac injury.METHODS: Rats subjected to myocardial I/R injury and neonatal rat ventricular myocytes (NRVMs) exposed to hypoxia/reoxygenation (H/R) were used to simulate cardiac injury during myocardial ischemia/reperfusion process. Morphological examination, histopathological examination, echocardiography, and immunohistochemistry were used to determine the cardiac injury after I/R injury. Biochemical indices in serum were estimated by the enzyme-linked immunosorbent assays (ELISA). 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1) was used for mitochondrial membrane potential (ΔΨm) evaluation. 2',7'-dichlorofluorescin diacetate (DCFH-DA) was used for intracellular reactive oxygen species (ROS) evaluation. Mitochondria in NRVMs were labeled by tetramethylrhodamine methyl ester (TMRM) for mitochondrial morphosis imaging and estimation. Western blotting was used for cytochrome c (CYCS), apoptosis inducing factor (AIF) and mitofusin 2 (Mfn2) contents evaluation. Immunochemistry fluorescence was used for dynamin related protein 1 (Drp1) expression measurement.
    RESULTS: TM treatment markedly decreased myocardium infarct size. It also significantly improved left ventricular contractile function and alleviated cardiomyocytes apoptosis, as well as reduced the production of cardiac troponin T, creatine kinase, lactate dehydrogenase, malondialdehyde and elevated glutathione and superoxide dismutase. Intriguingly, we found that mitochondrial membrane potential loss and mitochondrial permeability transition pore (mPTP) opening were recovered after TM treatment. It also down-regulated cytochrome c and apoptosis inducing factor contents after myocardial I/R injury. In vitro study showed that TM treatment reduced intracellular ROS content and recovered ΔΨm in NRVMs after H/R injury. We also observed that TM could reduce the expression level of Drp1, while increased Mfn2 in NRVMs after H/R injury, which indicates that TM may regulate mitochondrial dynamics during H/R injury of NRVMs.
    CONCLUSIONS: TM exhibited cardiac protective effect on ischemic myocardium of rats after reperfusion and improved mitochondrial quality control through mitochondrial dynamics in NRVMs after H/R injury.
    Keywords:  Mitochondrial dynamics; Mitochondrial morphosis; Mitochondrial quality control; Myocardial ischemia/reperfusion; Tongmai formula
  4. Int J Mol Sci. 2020 Oct 28. pii: E8007. [Epub ahead of print]21(21):
    Esteca MV, Severino MB, Silvestre JG, Palmeira Dos Santos G, Tamborlin L, Luchessi AD, Moriscot AS, Gustafsson ÅB, Baptista IL.
      The high capacity of the skeletal muscle to regenerate is due to the presence of muscle stem cells (MuSCs, or satellite cells). The E3 ubiquitin ligase Parkin is a key regulator of mitophagy and is recruited to mitochondria during differentiation of mouse myoblast cell line. However, the function of mitophagy during regeneration has not been investigated in vivo. Here, we have utilized Parkin deficient (Parkin-/-) mice to investigate the role of Parkin in skeletal muscle regeneration. We found a persistent deficiency in skeletal muscle regeneration in Parkin-/- mice after cardiotoxin (CTX) injury with increased area of fibrosis and decreased cross-sectional area (CSA) of myofibres post-injury. There was also a significant modulation of MuSCs differentiation and mitophagic markers, with altered mitochondrial proteins during skeletal muscle regeneration in Parkin-/- mice. Our data suggest that Parkin-mediated mitophagy plays a key role in skeletal muscle regeneration and is necessary for MuSCs differentiation.
    Keywords:  differentiation; mitochondria; mitophagy; satellite cells
  5. Int J Mol Sci. 2020 Oct 23. pii: E7887. [Epub ahead of print]21(21):
    Chen YC, Sheu JJ, Chiang JY, Shao PL, Wu SC, Sung PH, Li YC, Chen YL, Huang TH, Chen KH, Yip HK.
      This study tested whether circulatory endothelial progenitor cells (EPCs) derived from peripheral arterial occlusive disease (PAOD) patients after receiving combined autologous CD34+ cell and hyperbaric oxygen (HBO) therapy (defined as rejuvenated EPCs) would salvage nude mouse limbs against critical limb ischemia (CLI). Adult-male nude mice (n = 40) were equally categorized into group 1 (sham-operated control), group 2 (CLI), group 3 (CLI-EPCs (6 × 105) derived from PAOD patient's circulatory blood prior to CD34+ cell and HBO treatment (EPCPr-T) by intramuscular injection at 3 h after CLI induction) and group 4 (CLI-EPCs (6 × 105) derived from PAOD patient's circulatory blood after CD34+ cell and HBO treatment (EPCAf-T) by the identical injection method). By 2, 7 and 14 days after the CLI procedure, the ischemic to normal blood flow (INBF) ratio was highest in group 1, lowest in group 2 and significantly lower in group 4 than in group 3 (p < 0.0001). The protein levels of endothelial functional integrity (CD31/von Willebrand factor (vWF)/endothelial nitric-oxide synthase (eNOS)) expressed a similar pattern to that of INBF. In contrast, apoptotic/mitochondrial-damaged (mitochondrial-Bax/caspase-3/PARP/cytosolic-cytochrome-C) biomarkers and fibrosis (Smad3/TGF-ß) exhibited an opposite pattern, whereas the protein expressions of anti-fibrosis (Smad1/5 and BMP-2) and mitochondrial integrity (mitochondrial-cytochrome-C) showed an identical pattern of INBF (all p < 0.0001). The protein expressions of angiogenesis biomarkers (VEGF/SDF-1α/HIF-1α) were progressively increased from groups 1 to 3 (all p < 0.0010). The number of small vessels and endothelial cell surface markers (CD31+/vWF+) in the CLI area displayed an identical pattern of INBF (all p < 0.0001). CLI automatic amputation was higher in group 2 than in other groups (all p < 0.001). In conclusion, EPCs from HBO-C34+ cell therapy significantly restored the blood flow and salvaged the CLI in nude mice.
    Keywords:  angiogenesis; critical limb ischemia; endothelial progenitor cells; hyperbaric oxygen therapy; nude mice
  6. J Exp Biol. 2020 Oct 27. pii: jeb227801. [Epub ahead of print]223(Pt 20):
    Chung DJ, Schulte PM.
      Temperature is a critical abiotic factor shaping the distribution and abundance of species, but the mechanisms that underpin organismal thermal limits remain poorly understood. One possible mechanism underlying these limits is the failure of mitochondrial processes, as mitochondria play a crucial role in animals as the primary site of ATP production. Conventional measures of mitochondrial performance suggest that these organelles can function at temperatures much higher than those that limit whole-organism function, suggesting that they are unlikely to set organismal thermal limits. However, this conclusion is challenged by recent data connecting sequence variation in mitochondrial genes to whole-organism thermal tolerance. Here, we review the current state of knowledge of mitochondrial responses to thermal extremes and ask whether they are consistent with a role for mitochondrial function in shaping whole-organism thermal limits. The available data are fragmentary, but it is possible to draw some conclusions. There is little evidence that failure of maximal mitochondrial oxidative capacity as assessed in vitro sets thermal limits, but there is some evidence to suggest that temperature effects on ATP synthetic capacity may be important. Several studies suggest that loss of mitochondrial coupling is associated with the thermal limits for organismal growth, although this needs to be rigorously tested. Most studies have utilized isolated mitochondrial preparations to assess the effects of temperature on these organelles, and there remain many untapped opportunities to address these questions using preparations that retain more of their biological context to better connect these subcellular processes with whole-organism thermal limits.
    Keywords:  CTmax; Mitochondria; Performance; Respiration; Temperature; Thermal tolerance
  7. Int J Mol Med. 2020 Oct 22.
    Yu X, Sun Y, Cai Q, Zhao X, Liu Z, Xue X, Fu J.
      Bronchopulmonary dysplasia (BPD), also known as chronic lung disease, is one of the most common respiratory diseases in premature new‑born humans. Mitochondria are not only the main source of reactive oxygen species but are also critical for the maintenance of homeostasis and a wide range of biological activities, such as producing energy, buffering cytosolic calcium and regulating signal transduction. However, as a critical quality control method for mitochondria, little is known about the role of mitophagy in BPD. The present study assessed mitochondrial function in hyperoxia‑exposed alveolar type II (AT‑II) cells of rats during lung development. New‑born Sprague‑Dawley rats were divided into hyperoxia (85% oxygen) and control (21% oxygen) groups. Histopathological and morphological properties of the lung tissues were assessed at postnatal days 1, 3, 7 and 14. Ultrastructural mitochondrial alteration was observed using transmission electron microscopy and the expression of the mitophagy proteins putative kinase (PINK)1, Parkin and Nip3‑like protein X (NIX) in the lung tissues was evaluated using western blotting. Immunofluorescence staining was used to determine the co‑localisation of PINK1 and Parkin. Real‑time analyses of extracellular acidification rate and oxygen consumption rate were performed using primary AT‑II cells to evaluate metabolic changes. Mitochondria in hyperoxia‑exposed rat AT‑II cells began to show abnormal morphological and physiological features. These changes were accompanied by decreased mitochondrial membrane potential and increased expression levels of PINK1‑Parkin and NIX. Increased binding between a mitochondria marker (cytochrome C oxidase subunit IV isoform I) and an autophagy marker (microtubule‑associated protein‑1 light chain‑3B) was observed in primary AT‑II cells and was accompanied by decreased mitochondrial metabolic capacity in model rats. Thus, mitophagy mediated by PINK1, Parkin and NIX in AT‑II cells occurred in hyperoxia‑exposed new‑born rats. These findings suggested that the accumulation of dysfunctional mitochondria may be a key factor in the pathogenesis of BPD and result in attenuated alveolar development.
  8. J Biol Chem. 2020 Oct 25. pii: jbc.RA120.015893. [Epub ahead of print]
    Stafford JD, Yeo CT, Corbett JA.
      Environmental factors, such as viral infection, are proposed to play a role in the initiation of autoimmune diabetes. In response to encephalomyocarditis virus (EMCV) infection, resident islet macrophages release the pro-inflammatory cytokine IL-1β, to levels that are sufficient to stimulate inducible nitric oxide synthase (iNOS) expression and production of micromolar levels of the free radical nitric oxide in neighboring β-cells. We have recently shown that nitric oxide inhibits EMCV replication and EMCV-mediated β-cell lysis and that this protection is associated with an inhibition of mitochondrial oxidative metabolism. Here we show that the protective actions of nitric oxide against EMCV infection are selective for β-cells and associated with the metabolic coupling of glycolysis and mitochondrial oxidation that is necessary for insulin secretion. Inhibitors of mitochondrial respiration attenuate EMCV replication in β-cells, and this inhibition is associated with a decrease in ATP levels. In mouse embryonic fibroblasts (MEFs), inhibition of mitochondrial metabolism does not modify EMCV replication or decrease ATP levels. Like most cell types, MEFs have the capacity to uncouple the glycolytic utilization of glucose from mitochondrial respiration, allowing for the maintenance of ATP levels under conditions of impaired mitochondrial respiration. It is only when MEFs are forced to utilize mitochondrial oxidative metabolism for ATP generation that mitochondrial inhibitors attenuate viral replication. In a β-cell selective manner, these findings indicate that nitric oxide targets the same metabolic pathways necessary for glucose stimulated insulin secretion for protection from viral lysis.
    Keywords:  beta cell; diabetes; glucose metabolism; mitochondria; nitric oxide; plus-stranded RNA virus; virus replication
  9. Curr Opin Physiol. 2020 Oct;17 197-206
    Carvalho EJ, Stathopulos PB, Madesh M.
      Mitochondrial calcium (mCa2+) homeostasis also plays a key role in the buffering of cytosolic calcium (cCa2+) and calcium transported into the mitochondrial matrix regulates cellular metabolism, migration and cell fate decisions. Recent work has highlighted the importance of mCa2+ homeostasis in regulating cellular function. The discovery of the mCa2+ uptake complex has shed new light on the role of mCa2+ dynamics in cytoskeletal remodeling, mitochondrial shape and motility in cellular dynamics. Here we attempt to decipher the vast landscape of calcium regulatory effects of the mitochondria, the underlying mechanisms and the dynamics that control cellular function.
  10. PLoS One. 2020 ;15(10): e0240866
    Hjortbak MV, Grønnebæk TS, Jespersen NR, Lassen TR, Seefeldt JM, Tonnesen PT, Jensen RV, Koch LG, Britton SL, Pedersen M, Jessen N, Bøtker HE.
      INTRODUCTION: Aerobic capacity is a strong predictor of cardiovascular mortality. Whether aerobic capacity influences myocardial ischemia and reperfusion (IR) injury is unknown.PURPOSE: To investigate the impact of intrinsic differences in aerobic capacity and the cardioprotective potential on IR injury.
    METHODS: We studied hearts from rats developed by selective breeding for high (HCR) or low (LCR) capacity for treadmill running. The rats were randomized to: (1) control, (2) local ischemic preconditioning (IPC) or (3) remote ischemic preconditioning (RIC) followed by 30 minutes of ischemia and 120 minutes of reperfusion in an isolated perfused heart model. The primary endpoint was infarct size. Secondary endpoints included uptake of labelled glucose, content of selected mitochondrial proteins in skeletal and cardiac muscle, and activation of AMP-activated kinase (AMPK).
    RESULTS: At baseline, running distance was 203±7 m in LCR vs 1905±51 m in HCR rats (p<0.01). Infarct size was significantly lower in LCR than in HCR controls (49±5% vs 68±5%, p = 0.04). IPC reduced infarct size by 47% in LCR (p<0.01) and by 31% in HCR rats (p = 0.01). RIC did not modulate infarct size (LCR: 52±5, p>0.99; HCR: 69±6%, p>0.99, respectively). Phosphorylaion of AMPK did not differ between LCR and HCR controls. IPC did not modulate cardiac phosphorylation of AMPK. Glucose uptake during reperfusion was similar in LCR and HCR rats. IPC increased glucose uptake during reperfusion in LCR animals (p = 0.02). Mitochondrial protein content in skeletal muscle was lower in LCR than in HCR (0.77±0.10 arbitrary units (AU) vs 1.09±0.07 AU, p = 0.02), but not in cardiac muscle.
    CONCLUSION: Aerobic capacity is associated with altered myocardial sensitivity to IR injury, but the cardioprotective effect of IPC is not. Glucose uptake, AMPK activation immediately prior to ischemia and basal mitochondrial protein content in the heart seem to be of minor importance as underlying mechanisms for the cardioprotective effects.
  11. Cell Death Differ. 2020 Oct 27.
    Huang J, Xie P, Dong Y, An W.
      Hepatic ischemic reperfusion injury (IRI) is a common complication of liver surgery. Although an imbalance between mitochondrial fission and fusion has been identified as the cause of IRI, the detailed mechanism remains unclear. Augmenter of liver regeneration (ALR) was reported to prevent mitochondrial fission by inhibiting dynamin-related protein 1 (Drp1) phosphorylation, contributing partially to its liver protection. Apart from phosphorylation, Drp1 activity is also regulated by small ubiquitin-like modification (SUMOylation), which accelerates mitochondrial fission. This study aimed to investigate whether ALR-mediated protection from hepatic IRI might be associated with an effect on Drp1 SUMOylation. Liver tissues were harvested from both humans and from heterozygous ALR knockout mice, which underwent IRI. The SUMOylation and phosphorylation of Drp1 and their modulation by ALR were investigated. Hepatic Drp1 SUMOylation was significantly increased in human transplanted livers and IRI-livers of mice. ALR-transfection significantly decreased Drp1 SUMOylation, attenuated the IRI-induced mitochondrial fission and preserved mitochondrial stability and function. This study showed that the binding of transcription factor Yin Yang-1 (YY1) to its downstream target gene UBA2, a subunit of SUMO-E1 enzyme heterodimer, was critical to control Drp1 SUMOylation. By interacting with YY1, ALR inhibits its nuclear import and dramatically decreases the transcriptional level of UBA2. Consequently, mitochondrial fission was significantly reduced, and mitochondrial function was maintained. This study showed that the regulation of Drp1 SUMOylation by ALR protects mitochondria from fission, rescuing hepatocytes from IRI-induced apoptosis. These new findings provide a potential target for clinical intervention to reduce the effects of IRI during hepatic surgery.
  12. Autophagy. 2020 Oct 28. 1-16
    Watzlawik JO, Hou X, Truban D, Ramnarine C, Barodia SK, Gendron TF, Heckman MG, DeTure M, Siuda J, Wszolek ZK, Scherzer CR, Ross OA, Bu G, Dickson DW, Goldberg MS, Fiesel FC, Springer W.
      Mitochondrial dysfunction is an early, imminent event in neurodegenerative disorders including Parkinson disease (PD) and Alzheimer disease (AD). The enzymatic pair PINK1 and PRKN/Parkin recognize and transiently label damaged mitochondria with ubiquitin (Ub) phosphorylated at Ser65 (p-S65-Ub) as a signal for degradation via the autophagy-lysosome system (mitophagy). Despite its discovery in cell culture several years ago, robust and quantitative detection of altered mitophagy in vivo has remained challenging. Here we developed a sandwich ELISA targeting p-S65-Ub with the goal to assess mitophagy levels in mouse brain and in human clinical and pathological samples. We characterized five total Ub and four p-S65-Ub antibodies by several techniques and found significant differences in their ability to recognize phosphorylated Ub. The most sensitive antibody pair detected recombinant p-S65-Ub chains in the femtomolar to low picomolar range depending on the poly-Ub chain linkage. Importantly, this ELISA was able to assess very low baseline mitophagy levels in unstressed human cells and in brains from wild-type and prkn knockout mice as well as elevated p-S65-Ub levels in autopsied frontal cortex from AD patients vs. control cases. Moreover, the assay allowed detection of p-S65-Ub in blood plasma and was able to discriminate between PINK1 mutation carriers and controls. In summary, we developed a robust and sensitive tool to measure mitophagy levels in cells, tissue, and body fluids. Our data strongly support the idea that the stress-activated PINK1-PRKN mitophagy pathway is constitutively active in mice and humans under unstimulated, physiological and elevated in diseased, pathological conditions. Abbreviations: Ab: antibody; AD: Alzheimer disease; AP: alkaline phosphatase; CV: coefficient of variation; ECL: electrochemiluminescence; KO: knockout; LoB: Limit of Blank; LoD: Limit of Detection; LoQ: Limit of Quantification; MSD: meso scale discovery; PD: Parkinson disease; p-S65-PRKN: phosphorylated PRKN at serine 65; p-S65-Ub: phosphorylated ubiquitin at serine 65; Std.Dev.: standard deviation; Ub: ubiquitin; WT: wild type.
    Keywords:  Alzheimer disease; PINK1; PRKN; Parkin; Parkinson disease; autophagy; mitophagy; ubiquitin
  13. Front Physiol. 2020 ;11 554904
    Gherardi G, Monticelli H, Rizzuto R, Mammucari C.
      Recently, the role of mitochondrial activity in high-energy demand organs and in the orchestration of whole-body metabolism has received renewed attention. In mitochondria, pyruvate oxidation, ensured by efficient mitochondrial pyruvate entry and matrix dehydrogenases activity, generates acetyl CoA that enters the TCA cycle. TCA cycle activity, in turn, provides reducing equivalents and electrons that feed the electron transport chain eventually producing ATP. Mitochondrial Ca2+ uptake plays an essential role in the control of aerobic metabolism. Mitochondrial Ca2+ accumulation stimulates aerobic metabolism by inducing the activity of three TCA cycle dehydrogenases. In detail, matrix Ca2+ indirectly modulates pyruvate dehydrogenase via pyruvate dehydrogenase phosphatase 1, and directly activates isocitrate and α-ketoglutarate dehydrogenases. Here, we will discuss the contribution of mitochondrial Ca2+ uptake to the metabolic homeostasis of organs involved in systemic metabolism, including liver, skeletal muscle, and adipose tissue. We will also tackle the role of mitochondrial Ca2+ uptake in the heart, a high-energy consuming organ whose function strictly depends on appropriate Ca2+ signaling.
    Keywords:  aerobic metabolism; mitochondria; mitochondrial calcium uniporter (MCU); mitochondrial calcium uptake; systemic metabolism
  14. Redox Biol. 2020 Oct 08. pii: S2213-2317(20)30950-2. [Epub ahead of print]37 101745
    Rao J, Cheng F, Zhou H, Yang W, Qiu J, Yang C, Ni X, Yang S, Xia Y, Pan X, Zhang F, Lu L, Wang X.
      Nogo-B is an endoplasmic reticulum-residential protein with distinctive functions in different diseases. However, it remains unclear the role of Nogo-B in liver sterile inflammatory injury. This study aims to elucidate the functions and mechanisms in liver ischemia and reperfusion injury (IRI). The Nogo-B expression and liver function were analyzed in biopsy/serum specimens from 36 patients undergoing ischemia-related hepatectomy and in a mouse model of liver IRI. Human specimens were harvested prior to ischemia and post-reperfusion. The Nogo-B knockout (Nogo-BKO) and myeloid-specific Nogo-B knockout (Nogo-BMKO) mice were used to analyze the function and mechanism of Nogo-B in a mouse model of liver IRI. In human specimens, the Nogo-B expression was positively correlated with higher levels of serum transaminase (sALT) and severe histopathological injury at one day post-hepatectomy. Moreover, Nogo-B is mainly expressed on macrophages in normal and ischemic liver tissues from human and mice. Unlike in controls, the Nogo-BKO or Nogo-BMKO livers was protected against IRI, with reduced reactive oxygen species (ROS) production and liver inflammation in ischemic livers. In parallel in vitro studies, Nogo-B deficiency reduced M1 macrophage polarization and inhibited proinflammatory cytokines (TNF-α, IL-6, MCP-1 and iNOS) in response to LPS or HMGB-1 stimulation. Mechanistic studies showed that Nogo-B bound to MST1/2, increased MST1/2, LAST1, and YAP phosphorylation, leading to reduced YAP activity. Interestingly, disruption of macrophage YAP abolished Nogo-B deficiency-mediated cytoprotective effects in vitro and in vivo. Thus, YAP is crucial for the regulation of macrophage Nogo-B-triggered liver inflammation. Nogo-B promotes macrophage-related innate inflammation and contributes to IR-induced liver injury by activating the MST-mediated Hippo/YAP pathway, which provides a potential therapeutic target for clinical management in liver IRI.
    Keywords:  Hepatic ischemia/reperfusion injury; Hippo/YAP signaling; Inflammation; MST1/2; Macrophage; Nogo-B