Inhibition of eIF2α Dephosphorylation Protects Hepatocytes from Apoptosis by Alleviating ER Stress in Acute Liver Injury

Objectives. Protein kinase R-like ER kinase (PERK)/eukaryotic initiation factor 2 alpha (eIF2α) is an important factor along the main pathways for endoplasmic reticulum (ER) stress-mediated apoptosis. In this study, we investigated the effects of eIF2α phosphorylation on hepatocyte apoptosis and the ER stress mechanisms in acute liver injury. Methods. eIF2α phosphorylation and apoptosis under ER stress were monitored and measured in male BALB/c mice with acute liver injury and human hepatocyte line LO2 cells. Results. Carbon tetrachloride (CCl4) administration triggered ER stress and hepatocyte apoptosis, as well as eIF2α phosphorylation in mice. Inhibition of eIF2α dephosphorylation, as the pretreatment with 4-phenylbutyric acid (chemical chaperone, ER stress inhibitor), mitigated CCl4-induced intrahepatic ER stress, apoptosis, and liver injury. In an ER stress model of LO2 cells induced by thapsigargin (disrupting ER calcium balance), inhibition of eIF2α dephosphorylation reduced ER stress and apoptosis, while PERK knockdown reduced eIF2α phosphorylation and exacerbated ER stress and apoptosis. Conclusions. eIF2α phosphorylation is one of the mechanisms employed by ER stress for restoring cellular homeostasis. Inhibition of eIF2α dephosphorylation mitigates hepatocyte apoptosis by alleviating ER stress in acute liver injuries.

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Chronic Carbon Tetrachloride Applications Induced Hepatocyte Apoptosis in Lipocalin 2 Null Mice through Endoplasmic Reticulum Stress and Unfolded Protein Response

International Journal of Molecular Sciences ◽

10.3390/ijms21155230 ◽

2020 ◽

Vol 21 (15) ◽

pp. 5230

Author(s):

Erawan Borkham-Kamphorst ◽

Ute Haas ◽

Eddy Van de Leur ◽

Anothai Trevanich ◽

Ralf Weiskirchen

Keyword(s):

Endoplasmic Reticulum ◽

Carbon Tetrachloride ◽

Liver Injury ◽

Er Stress ◽

Stress Responses ◽

Protein Glycosylation ◽

Initiation Factor ◽

Wild Type ◽

Hepatocyte Apoptosis ◽

Unfolded Protein

The lack of Lipocalin (LCN2) provokes overwhelming endoplasmic reticulum (ER) stress responses in vitro and in acute toxic liver injury models, resulting in hepatocyte apoptosis. LCN2 is an acute phase protein produced in hepatocytes in response to acute liver injuries. In line with these findings we investigated ER stress responses of Lcn2−/− mice in chronic ER stress using a long-term repetitive carbon tetrachloride (CCl4) injection model. We found chronic CCl4 application to enhance ER stress and unfolded protein responses (UPR), including phosphorylation of eukaryotic initiation factor 2α (eIF2α), increased expression of binding immunoglobulin protein (BiP) and glucose-regulated protein 94 (GRP94). IRE1α/TRAF2/JNK signaling enhanced mitochondrial apoptotic pathways, and showed slightly higher in Lcn2−/− mice compared to the wild type counterparts, leading to increased hepatocyte apoptosis well evidenced by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. Hepatocyte injuries were confirmed by significant high serum alanine transaminase (ALT) levels in CCl4-treated Lcn2−/− mice. Lcn2−/− mice furthermore developed mild hepatic steatosis, supporting our finding that ER stress promotes lipogenesis. In a previous report we demonstrated that the pharmacological agent tunicamycin (TM) induced ER stress through altered protein glycosylation and induced high amounts of C/EBP-homologous protein (CHOP), resulting in hepatocyte apoptosis. We compared TM-induced ER stress in wild type, Lcn2−/−, and Chop null (Chop−/−) primary hepatocytes and found Chop−/− hepatocytes to attenuate ER stress responses and resist ER stress-induced hepatocyte apoptosis through canonical eIF2α/GADD34 signaling, inhibiting protein synthesis. Unexpectedly, in later stages of TM incubation, Chop−/− hepatocytes resumed activation of IRE1α/JNK/c-Jun and p38/ATF2 signaling, leading to late hepatocyte apoptosis. This interesting observation indicates Chop−/− mice to be unable to absolutely prevent all types of liver injury, while LCN2 protects the hepatocytes by maintaining homeostasis under ER stress conditions.

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4-Phenylbutyric acid improves free fatty acid-induced hepatic insulin resistance in vivo

Endocrine Connections ◽

10.1530/ec-21-0248 ◽

2021 ◽

Vol 10 (8) ◽

pp. 861-872

Author(s):

Sandra Pereira ◽

Jessy Moore ◽

Jia-Xu Li ◽

Wen Qin Yu ◽

Husam Ghanim ◽

...

Keyword(s):

Insulin Resistance ◽

Protein Kinase ◽

Er Stress ◽

Mitogen Activated Protein Kinase ◽

Hepatic Insulin Resistance ◽

Initiation Factor ◽

Fibroblast Growth Factor 21 ◽

Chemical Chaperone ◽

Fetuin A ◽

Phenylbutyric Acid

Plasma free fatty acids (FFAs) are elevated in obesity and can induce insulin resistance via endoplasmic reticulum (ER) stress. However, it is unknown whether hepatic insulin resistance caused by the elevation of plasma FFAs is alleviated by chemical chaperones. Rats received one of the following i.v. treatments for 48 h: saline, intralipid plus heparin (IH), IH plus the chemical chaperone 4-phenylbutyric acid (PBA), or PBA alone and a hyperinsulinemic-euglycemic clamp was performed during the last 2 h. PBA co-infusion normalized IH-induced peripheral insulin resistance, similar to our previous findings with an antioxidant and an IκBα kinase β (IKKβ) inhibitor. Different from our previous results with the antioxidant and IKKβ inhibitor, PBA also improved IH-induced hepatic insulin resistance in parallel with activation of Akt. Unexpectedly, IH did not induce markers of ER stress in the liver, but PBA prevented IH-induced elevation of phosphorylated eukaryotic initiation factor-2α protein in adipose tissue. PBA tended to decrease circulating fetuin-A and significantly increased circulating fibroblast growth factor 21 (FGF21) without affecting markers of activation of hepatic protein kinase C-δ or p38 mitogen-activated protein kinase that we have previously involved in hepatic insulin resistance in this model. In conclusion: (i) PBA prevented hepatic insulin resistance caused by prolonged plasma FFA elevation without affecting hepatic ER stress markers; (ii) the PBA effect is likely due to increased FGF21 and/or decreased fetuin-A, which directly signal to upregulate Akt activation.

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Inhibiting alpha subunit of eukaryotic initiation factor 2 dephosphorylation protects injured hepatocytes and reduces hepatocyte proliferation in acute liver injury

Croatian Medical Journal ◽

10.3325/cmj.2019.60.532 ◽

2019 ◽

Vol 60 (6) ◽

pp. 532-544

Author(s):

Guimei Chen ◽

Xuemei Yang ◽

Yihuai He ◽

Yongjing Tang ◽

Rendong Tian ◽

...

Keyword(s):

Liver Injury ◽

Acute Liver Injury ◽

Initiation Factor ◽

Alpha Subunit ◽

Hepatocyte Proliferation ◽

Eukaryotic Initiation Factor ◽

Eukaryotic Initiation Factor 2 ◽

Initiation Factor 2

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Dynamin-related protein 1 deficiency accelerates lipopolysaccharide-induced acute liver injury and inflammation in mice

Communications Biology ◽

10.1038/s42003-021-02413-6 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Lixiang Wang ◽

Xin Li ◽

Yuki Hanada ◽

Nao Hasuzawa ◽

Yoshinori Moriyama ◽

...

Keyword(s):

Liver Disease ◽

Liver Injury ◽

Er Stress ◽

Disease Progression ◽

Acute Liver Injury ◽

Mitochondrial Dynamics ◽

Mitochondrial Fission ◽

Mitochondrial Fusion ◽

Related Protein ◽

Liver Disease Progression

AbstractMitochondrial fusion and fission, which are strongly related to normal mitochondrial function, are referred to as mitochondrial dynamics. Mitochondrial fusion defects in the liver cause a non-alcoholic steatohepatitis-like phenotype and liver cancer. However, whether mitochondrial fission defect directly impair liver function and stimulate liver disease progression, too, is unclear. Dynamin-related protein 1 (DRP1) is a key factor controlling mitochondrial fission. We hypothesized that DRP1 defects are a causal factor directly involved in liver disease development and stimulate liver disease progression. Drp1 defects directly promoted endoplasmic reticulum (ER) stress, hepatocyte death, and subsequently induced infiltration of inflammatory macrophages. Drp1 deletion increased the expression of numerous genes involved in the immune response and DNA damage in Drp1LiKO mouse primary hepatocytes. We administered lipopolysaccharide (LPS) to liver-specific Drp1-knockout (Drp1LiKO) mice and observed an increased inflammatory cytokine expression in the liver and serum caused by exaggerated ER stress and enhanced inflammasome activation. This study indicates that Drp1 defect-induced mitochondrial dynamics dysfunction directly regulates the fate and function of hepatocytes and enhances LPS-induced acute liver injury in vivo.

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The Potential Role of Protein Kinase R as a Regulator of Age-Related Neurodegeneration

Frontiers in Aging Neuroscience ◽

10.3389/fnagi.2021.638208 ◽

2021 ◽

Vol 13 ◽

Author(s):

Nicolás W. Martinez ◽

Felipe E. Gómez ◽

Soledad Matus

Keyword(s):

Protein Kinase ◽

Pathological Process ◽

Translation Initiation Factor ◽

Initiation Factor ◽

Protein Kinase R ◽

Eukaryotic Translation ◽

Neurodegenerative Process ◽

Age Related ◽

Initiation Factor 2

There is a growing evidence describing a decline in adaptive homeostasis in aging-related diseases affecting the central nervous system (CNS), many of which are characterized by the appearance of non-native protein aggregates. One signaling pathway that allows cell adaptation is the integrated stress response (ISR), which senses stress stimuli through four kinases. ISR activation promotes translational arrest through the phosphorylation of the eukaryotic translation initiation factor 2 alpha (eIF2α) and the induction of a gene expression program to restore cellular homeostasis. However, depending on the stimulus, ISR can also induce cell death. One of the ISR sensors is the double-stranded RNA-dependent protein kinase [protein kinase R (PKR)], initially described as a viral infection sensor, and now a growing evidence supports a role for PKR on CNS physiology. PKR has been largely involved in the Alzheimer’s disease (AD) pathological process. Here, we reviewed the antecedents supporting the role of PKR on the efficiency of synaptic transmission and cognition. Then, we review PKR’s contribution to AD and discuss the possible participation of PKR as a player in the neurodegenerative process involved in aging-related pathologies affecting the CNS.

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Inhibition of Endoplasmic Reticulum Stress Attenuated Ethanol-Induced Exosomal miR-122 and Acute Liver Injury in Mice

Alcohol and Alcoholism ◽

10.1093/alcalc/agz058 ◽

2019 ◽

Vol 54 (5) ◽

pp. 465-471 ◽

Cited By ~ 5

Author(s):

Sheng Wang ◽

Jiajie Luan ◽

Xiongwen Lv

Keyword(s):

Endoplasmic Reticulum ◽

Liver Injury ◽

Endoplasmic Reticulum Stress ◽

Er Stress ◽

Acute Liver Injury ◽

Hepatosomatic Index ◽

Intragastric Administration ◽

Alcoholic Liver Injury ◽

Therapy Strategy ◽

Related Proteins

ICR mice received ethanol (5 g/kg) by intragastric administration, showing an increase in hepatosomatic index and ALT. These effects were accompanied by increased expression of ER stress-related proteins and exosomal miR-122, PBA intervention can attenuate these changes induced by ethanol provides a potential therapy strategy for acute alcoholic liver injury.

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Viral host-range factor C7 or K1 is essential for modified vaccinia virus Ankara late gene expression in human and murine cells, irrespective of their capacity to inhibit protein kinase R-mediated phosphorylation of eukaryotic translation initiation factor 2

Journal of General Virology ◽

10.1099/vir.0.015347-0 ◽

2009 ◽

Vol 91 (2) ◽

pp. 470-482 ◽

Cited By ~ 33

Author(s):

S. Backes ◽

K. M. Sperling ◽

J. Zwilling ◽

G. Gasteiger ◽

H. Ludwig ◽

...

Keyword(s):

Translation Initiation Factor ◽

Initiation Factor ◽

Late Gene Expression ◽

Protein Kinase R ◽

Eukaryotic Translation ◽

Modified Vaccinia Virus Ankara ◽

Initiation Factor 2 ◽

Eukaryotic Translation Initiation ◽

Viral Host Range ◽

Translation Initiation Factor 2

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Tumour necrosis factor α up-regulates protein kinase R (PKR)-activating protein (PACT) and increases phosphorylation of PKR and eukaryotic initiation factor 2-α in articular chondrocytes

Biochemical Society Transactions ◽

10.1042/bst0300886 ◽

2002 ◽

Vol 30 (6) ◽

pp. 886-889 ◽

Cited By ~ 13

Author(s):

S. J. Gilbert ◽

V. C. Duance ◽

D. J. Mason

Keyword(s):

Protein Kinase ◽

Tumour Necrosis ◽

Cartilage Degradation ◽

Initiation Factor ◽

Tumour Necrosis Factor Α ◽

Protein Kinase R ◽

Initiation Factor 2 ◽

Factor Α ◽

Necrosis Factor

Our previous analysis of the genes regulated in cartilage at the onset of spontaneous osteoarthritis in the guinea pig knee revealed up-regulation of the gene for protein kinase R (PKR)-activating protein (PACT), which encodes the cellular activator of the protein kinase, PKR. PACT and PKR are upstream components of a number of signal transduction and gene transcription pathways used by pro-inflammatory cytokines. We have investigated the role of PACT and PKR in articular cartilage degradation using cytokine treatment of bovine primary chondrocytes and cartilage explants. Tumour necrosis factor α increased expression of PACT protein after 3 h of treatment. Furthermore, increased phosphorylation of PKR and eukaryotic initiation factor 2-α was observed. The known role of PKR in cytokine-induced signalling pathways, together with our data showing cytokine regulation of PACT and PKR in chondrocytes, reveals a novel mechanism of cartilage degradation that may be important in the pathogenesis of arthritic diseases.

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Human Cytomegalovirus Protein pUL38 Induces ATF4 Expression, Inhibits Persistent JNK Phosphorylation, and Suppresses Endoplasmic Reticulum Stress-Induced Cell Death

Journal of Virology ◽

10.1128/jvi.02307-08 ◽

2009 ◽

Vol 83 (8) ◽

pp. 3463-3474 ◽

Cited By ~ 90

Author(s):

Baoqin Xuan ◽

Zhikang Qian ◽

Emi Torigoi ◽

Dong Yu

Keyword(s):

Endoplasmic Reticulum ◽

Cell Death ◽

Er Stress ◽

Human Cytomegalovirus ◽

Initiation Factor ◽

Α Subunit ◽

Unfolded Protein ◽

Initiation Factor 2 ◽

The Unfolded Protein Response ◽

Protein Response

ABSTRACT The endoplasmic reticulum (ER) is a key organelle involved in sensing and responding to stressful conditions, including those resulting from infection of viruses, such as human cytomegalovirus (HCMV). Three signaling pathways collectively termed the unfolded protein response (UPR) are activated to resolve ER stress, but they will also lead to cell death if the stress cannot be alleviated. HCMV is able to modulate the UPR to promote its infection. The specific viral factors involved in such HCMV-mediated modulation, however, were unknown. We previously showed that HCMV protein pUL38 was required to maintain the viability of infected cells, and it blocked cell death induced by thapsigargin. Here, we report that pUL38 is an HCMV-encoded regulator to modulate the UPR. In infection, pUL38 allowed HCMV to upregulate phosphorylation of PKR-like ER kinase (PERK) and the α subunit of eukaryotic initiation factor 2 (eIF-2α), as well as induce robust accumulation of activating transcriptional factor 4 (ATF4), key components of the PERK pathway. pUL38 also allowed the virus to suppress persistent phosphorylation of c-Jun N-terminal kinase (JNK), which was induced by the inositol-requiring enzyme 1 pathway. In isolation, pUL38 overexpression elevated eIF-2α phosphorylation, induced ATF4 accumulation, limited JNK phosphorylation, and suppressed cell death induced by both thapsigargin and tunicamycin, two drugs that induce ER stress by different mechanisms. Importantly, ATF4 overexpression and JNK inhibition significantly reduced cell death in pUL38-deficient virus infection. Thus, pUL38 targets ATF4 expression and JNK activation, and this activity appears to be critical for protecting cells from ER stress induced by HCMV infection.

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