scholarly journals Hepatocyte-specific deletion of XBP1 sensitizes mice to liver injury through hyperactivation of IRE1α

2020 ◽  
Author(s):  
Caroline C. Duwaerts ◽  
Kevin Siao ◽  
Russell K. Soon ◽  
Chris Her ◽  
Takao Iwawaki ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Liver Injury ◽  
Er Stress ◽  
Adult Mouse ◽  
Active Form ◽  
Cellular Responses ◽  
Genetic Deletion ◽  
Specific Deletion ◽  
Adult Mouse Liver

AbstractX-box binding protein-1 (XBP1) is a transcription factor that plays a central role in controlling cellular responses to endoplasmic reticulum (ER) stress. Under stress conditions, the transcriptionally active form of XBP1 is generated by unique splicing of Xbp1 mRNA by the ER-resident protein inositol-requiring enzyme-1 (IRE1α). Genetic deletion of XBP1 has multiple consequences: some resulting from the loss of the transcription factor per se, and others related to compensatory upstream activation of IRE1α. The objective of the current study was to investigate the effects of XBP1 deletion in adult mouse liver and determine to what extent they are direct or indirect. XBP1 was deleted specifically from hepatocytes in adult Xbp1fl/fl mice using AAV8-Transthyretin-Cre (Xbp1Δhep). Xbp1Δhep mice exhibited no liver disease at baseline, but developed acute biochemical and histologic liver injury in response to a dietary challenge with fructose for 4 wk. Fructose-mediated liver injury in Xbp1Δhep mice coincided with heightened IRE1α activity, as demonstrated by cJun phosphorylation and regulated IRE1α -dependent RNA decay (RIDD). Activation of eIF2α was also evident, with associated up-regulation of the pro-apoptotic molecules CHOP, BIM and PUMA. To determine whether the adverse consequences of liver-specific XBP1 deletion were due to XBP1 loss or heightened IRE1α activity, we repeated a fructose challenge in mice with liver-specific deletion of both XBP1 and IRE1α (Xbp1Δhep;IRE1αΔhep). Xbp1Δhep;IRE1αΔhep mice were protected from fructose-mediated liver injury and failed to exhibit any of the signs of ER stress seen in mice lacking XBP1 alone. The protective effect of IRE1α deletion persisted even with long-term exposure to fructose. Xbp1Δhep mice developed liver fibrosis at 16 wk, but Xbp1Δhep;IRE1αΔhep mice did not. Overall, the results indicate that the deleterious effects of hepatocyte-specific XBP1 deletion are due primarily to hyperactivation of IRE1α. They support further exploration of IRE1α as a contributor to acute and chronic liver diseases.

scholarly journals Gata2 is required for HSC generation and survival

2013 ◽  
Vol 210 (13) ◽  
pp. 2843-2850 ◽  
Author(s):  
Emma de Pater ◽  
Polynikis Kaimakis ◽  
Chris S. Vink ◽  
Tomomasa Yokomizo ◽  
Tomoko Yamada-Inagawa ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Transcription Factor ◽  
Developmental Stages ◽  
Vascular Endothelial ◽  
Vascular Integrity ◽  
Hematopoietic Stem ◽  
Vascular Endothelial Cadherin ◽  
Umbilical Arteries ◽  
Specific Deletion

Knowledge of the key transcription factors that drive hematopoietic stem cell (HSC) generation is of particular importance for current hematopoietic regenerative approaches and reprogramming strategies. Whereas GATA2 has long been implicated as a hematopoietic transcription factor and its dysregulated expression is associated with human immunodeficiency syndromes and vascular integrity, it is as yet unknown how GATA2 functions in the generation of HSCs. HSCs are generated from endothelial cells of the major embryonic vasculature (aorta, vitelline, and umbilical arteries) and are found in intra-aortic hematopoietic clusters. In this study, we find that GATA2 function is essential for the generation of HSCs during the stage of endothelial-to-hematopoietic cell transition. Specific deletion of Gata2 in Vec (Vascular Endothelial Cadherin)-expressing endothelial cells results in a deficiency of long-term repopulating HSCs and intra-aortic cluster cells. By specific deletion of Gata2 in Vav-expressing hematopoietic cells (after HSC generation), we further show that GATA2 is essential for HSC survival. This is in contrast to the known activity of the RUNX1 transcription factor, which functions only in the generation of HSCs, and highlights the unique requirement for GATA2 function in HSCs throughout all developmental stages.

scholarly journals Unification of Opposites between Two Antioxidant Transcription Factors Nrf1 and Nrf2 in Mediating Distinct Cellular Responses to the Endoplasmic Reticulum Stressor Tunicamycin

Antioxidants ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 4 ◽  
Author(s):  
Yu-ping Zhu ◽  
Ze Zheng ◽  
Shaofan Hu ◽  
Xufang Ru ◽  
Zhuo Fan ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Transcription Factor ◽  
Transcription Factors ◽  
Er Stress ◽  
Target Genes ◽  
Cellular Responses ◽  
Water Soluble ◽  
Heme Oxygenase 1 ◽  
Nuclear Factor ◽  
Activating Transcription Factor

The water-soluble Nrf2 (nuclear factor, erythroid 2-like 2, also called Nfe2l2) is accepted as a master regulator of antioxidant responses to cellular stress, and it was also identified as a direct target of the endoplasmic reticulum (ER)-anchored PERK (protein kinase RNA-like endoplasmic reticulum kinase). However, the membrane-bound Nrf1 (nuclear factor, erythroid 2-like 1, also called Nfe2l1) response to ER stress remains elusive. Herein, we report a unity of opposites between these two antioxidant transcription factors, Nrf1 and Nrf2, in coordinating distinct cellular responses to the ER stressor tunicamycin (TU). The TU-inducible transcription of Nrf1 and Nrf2, as well as GCLM (glutamate cysteine ligase modifier subunit) and HO-1 (heme oxygenase 1), was accompanied by activation of ER stress signaling networks. Notably, the unfolded protein response (UPR) mediated by ATF6 (activating transcription factor 6), IRE1 (inositol requiring enzyme 1) and PERK was significantly suppressed by Nrf1α-specific knockout, but hyper-expression of Nrf2 and its target genes GCLM and HO-1 has retained in Nrf1α−/− cells. By contrast, Nrf2−/−ΔTA cells with genomic deletion of its transactivation (TA) domain resulted in significant decreases of GCLM, HO-1 and Nrf1; this was accompanied by partial decreases of IRE1 and ATF6, rather than PERK, but with an increase of ATF4 (activating transcription factor 4). Interestingly, Nrf1 glycosylation and its trans-activity to mediate the transcriptional expression of the 26S proteasomal subunits, were repressed by TU. This inhibitory effect was enhanced by Nrf1α−/− and Nrf2−/−ΔTA, but not by a constitutive activator caNrf2ΔN (that increased abundances of the non-glycosylated and processed Nrf1). Furthermore, caNrf2ΔN also enhanced induction of PERK and IRE1 by TU, but reduced expression of ATF4 and HO-1. Thus, it is inferred that such distinct roles of Nrf1 and Nrf2 are unified to maintain cell homeostasis by a series of coordinated ER-to-nuclear signaling responses to TU. Nrf1α (i.e., a full-length form) acts in a cell-autonomous manner to determine the transcription of most of UPR-target genes, albeit Nrf2 is also partially involved in this process. Consistently, transactivation of ARE (antioxidant response element)-driven BIP (binding immunoglobulin protein)-, PERK- and XBP1 (X-box binding protein 1)-Luc reporter genes was mediated directly by Nrf1 and/or Nrf2. Interestingly, Nrf1α is more potent than Nrf2 at mediating the cytoprotective responses against the cytotoxicity of TU alone or plus tBHQ (tert-butylhydroquinone). This is also further supported by the evidence that the intracellular reactive oxygen species (ROS) levels are increased in Nrf1α−/− cells, but rather are, to our surprise, decreased in Nrf2−/−ΔTA cells.

scholarly journals Activating transcription factor 6-dependent sestrin 2 induction ameliorates ER stress-mediated liver injury

2017 ◽  
Vol 1864 (7) ◽  
pp. 1295-1307 ◽  
Author(s):  
Kyung Hwan Jegal ◽  
Sang Mi Park ◽  
Sam Seok Cho ◽  
Sung Hui Byun ◽  
Sae Kwang Ku ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Liver Injury ◽  
Er Stress ◽  
Activating Transcription Factor

scholarly journals Depletion of essential isoprenoids and ER stress induction following acute liver-specific deletion of HMG-CoA reductase

2020 ◽  
Vol 61 (12) ◽  
pp. 1675-1686
Author(s):  
Marco De Giorgi ◽  
Kelsey E. Jarrett ◽  
Jason C. Burton ◽  
Alexandria M. Doerfler ◽  
Ayrea Hurley ◽  
...  
Keyword(s):  
Er Stress ◽  
Mevalonate Pathway ◽  
Critical Role ◽  
Cellular Level ◽  
Hmg Coa Reductase ◽  
Biochemical Level ◽  
Genetic Deletion ◽  
Coa Reductase ◽  
Rate Limiting ◽  
Specific Deletion

HMG-CoA reductase (Hmgcr) is the rate-limiting enzyme in the mevalonate pathway and is inhibited by statins. In addition to cholesterol, Hmgcr activity is also required for synthesizing nonsterol isoprenoids, such as dolichol, ubiquinone, and farnesylated and geranylgeranylated proteins. Here, we investigated the effects of Hmgcr inhibition on nonsterol isoprenoids in the liver. We have generated new genetic models to acutely delete genes in the mevalonate pathway in the liver using AAV-mediated delivery of Cre-recombinase (AAV-Cre) or CRISPR/Cas9 (AAV-CRISPR). The genetic deletion of Hmgcr by AAV-Cre resulted in extensive hepatocyte apoptosis and compensatory liver regeneration. At the biochemical level, we observed decreased levels of sterols and depletion of the nonsterol isoprenoids, dolichol and ubiquinone. At the cellular level, Hmgcr-null hepatocytes showed ER stress and impaired N-glycosylation. We further hypothesized that the depletion of dolichol, essential for N-glycosylation, could be responsible for ER stress. Using AAV-CRISPR, we somatically disrupted dehydrodolichyl diphosphate synthase subunit (Dhdds), encoding a branch point enzyme required for dolichol biosynthesis. Dhdds-null livers showed ER stress and impaired N-glycosylation, along with apoptosis and regeneration. Finally, the combined deletion of Hmgcr and Dhdds synergistically exacerbated hepatocyte ER stress. Our data show a critical role for mevalonate-derived dolichol in the liver and suggest that dolichol depletion is at least partially responsible for ER stress and apoptosis upon potent Hmgcr inhibition.

scholarly journals Generation of mouse hepatobiliary organoids from hepatocyte progenitors and cholangiocytes isolated from healthy adult mouse liver

2021 ◽  
Author(s):  
Naoki Tanimizu ◽  
Norihisa Ichinohe ◽  
Yasushi Sasaki ◽  
Tohru Itoh ◽  
Ryo Sudo ◽  
...  
Keyword(s):  
Adult Mouse ◽  
Functional Connection ◽  
Report Generation ◽  
Mouse Hepatocyte ◽  
Functional Connections ◽  
Metabolic Functions ◽  
Small Hepatocytes ◽  
Liver Organoids ◽  
Adult Mouse Liver

Abstract Number of liver organoids have been reported, though it is not clearly shown whether the functional connection between hepatocytes and cholangiocytes is recapitulated in those organoids. Here, we report generation of a hepatobiliary tubular organoid (HBTO) using mouse hepatocyte progenitors called small hepatocytes (SHs) and cholangiocytes. SHs differentiate and form the bile canalicular network in HBTOs and secret metabolites into the canaliculi, which are then transported into the biliary structure. Hepatocytes in the organoid acquire and maintain metabolic functions including albumin secretion and cytochrome P450 activities, over the long term. We provide the step-by-step protocol for induction of HBTO including isolation of cholangiocytes and SHs and co-culture of these two types of cell to generate functional connections between hepatocytes and cholangiocytes.

The effect of baicalein on endoplasmic reticulum stress and autophagy on liver damage

2021 ◽  
pp. 096032712110036
Author(s):  
MC Üstüner ◽  
C Tanrikut ◽  
D Üstüner ◽  
UK Kolaç ◽  
Z Özdemir Köroğlu ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Transcription Factor ◽  
Er Stress ◽  
Liver Damage ◽  
Albino Rats ◽  
Tem Analysis ◽  
Stress Markers ◽  
Activating Transcription Factor 4 ◽  
Activating Transcription Factor ◽  
Wistar Albino Rats

Carbon tetrachloride (CCl4) is a toxic chemical that causes liver injury. CCl4 triggers endoplasmic reticulum (ER) stress and unfolded protein response (UPR). UPR triggers autophagy to deal with the damage. The aim of this study was to investigate the effect of baicalein, derived from Scutellaria baicalensis, on CCl4-induced liver damage concerning ER stress and autophagy. Two groups of Wistar albino rats (n = 7/groups) were treated with 0.2 ml/kg CCl4 for 10 days with and without baicalein. Histological and transmission electron microscopy (TEM) analysis, autophagy, and ER stress markers measurements were carried out to evaluate the effect of baicalein. Histological examinations showed that baicalein reduced liver damage. TEM analysis indicated that baicalein inhibited ER stress and triggered autophagy. CCl4-induced elevation of C/EBP homologous protein (CHOP), glucose-regulating protein 78 (GRP78), activating transcription factor 4 (ATF4), activating transcription factor 6 (ATF6), inositol requiring enzyme 1 (IRE1), pancreatic ER kinase (PERK), and active/spliced form of X-box-binding protein 1 (XBP1s) ER stress markers were decreased by baicalein. Baicalein also increased the autophagy-related 5 (ATG5), Beclin1, and Microtubule-associated protein 1A/1B-light chain 3-phosphatidylethanolamine-conjugated form (LC3-II) autophagy marker levels. In conclusion, baicalein reduced the CCl4-induced liver damage by inhibiting ER stress and the trigger of autophagy.

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