HIF-1α triggers ER stress and CHOP-mediated apoptosis in alveolar epithelial cells, a key event in pulmonary fibrosis

Delbrel, Eva; Soumaré, Abdoulaye; Naguez, Adnan; Label, Rabab; Bernard, O.; Bruhat, Alain; Fafournoux, Pierre; Tremblais, Geoffrey; Marchant, Dominique; Gille, Thomas; Bernaudin, Jean-François; Callard, P; Kambouchner, Marianne; Martinod, Emmanuel; Valeyre, Dominique; Uzunhan, Y.; Planès, Carole; Boncoeur, Émilie

doi:10.1038/s41598-018-36063-2

Cited by 120 publications

(87 citation statements)

References 41 publications

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“…Despite the fact that previous studies reported the hypoxia-related induction of BIP expression [ 7 , 60 , 61 , 62 ], we found that BiP mRNA levels were reduced after a 12 h exposure to hypoxia. Furthermore, the significant accumulation of apoptotic CHOP ( DDIT3) mRNA was observed only in cells exposed to hypoxia for 24 h. Although CHOP accumulation and the potential induction of an apoptotic response were observed in some hypoxia experiments (including lung endothelial cells) [ 63 , 64 ], these protein and mRNA levels were much lower than those observed during ER stress [ 19 ]. Furthermore, we did not observe the accumulation of XBP1s that could have suggested the UPR-related activation of IRE1 signaling.…”

Section: Discussionmentioning

confidence: 99%

IRE1 Endoribonuclease Activity Modulates Hypoxic HIF-1α Signaling in Human Endothelial Cells

2020

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While the role of hypoxia and the induction of the hypoxia inducible factors (HIFs) and the unfolded protein response (UPR) pathways in the cancer microenvironment are well characterized, their roles and relationship in normal human endothelium are less clear. Here, we examined the effects of IRE1 on HIF-1α protein levels during hypoxia in primary human umbilical vein endothelial cells (HUVECs). The results demonstrated that HIF-1α levels peaked at 6 h of hypoxia along with two of their target genes, GLUT1 and VEGFA, whereas at up to 12 h of hypoxia the mRNA levels of markers of the UPR, IRE1, XBP1s, BiP, and CHOP, did not increase, suggesting that the UPR was not activated. Interestingly, the siRNA knockdown of IRE1 or inhibition of IRE1 endonuclease activity with 4µ8C during hypoxia significantly reduced HIF-1α protein without affecting HIF1A mRNA expression. The inhibition of the endonuclease activity with 4µ8C in two other primary endothelial cells during hypoxia, human cardiac microvascular endothelial cells and human aortic endothelial cells showed the same reduction in the HIF-1α protein. Surprisingly, the siRNA knockdown of XBP1s during hypoxia did not decrease the HIF1α protein levels, indicating that the IRE1-mediated effect on stabilizing the HIF1α protein levels was XBP1s-independent. The studies presented here, therefore, provide evidence that IRE1 activity during hypoxia increases the protein levels of HIF1α in an XBP1s-independent manner.

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Section: Discussionmentioning

confidence: 99%

IRE1 Endoribonuclease Activity Modulates Hypoxic HIF-1α Signaling in Human Endothelial Cells

2020

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“…Thus, the increased severity of pulmonary fibrosis in old mice was associated with increased numbers of profibrotic monocyte-derived alveolar macrophages. Chronic activation of the integrated stress response (ISR) during aging has been linked to the development of pulmonary fibrosis (33)(34)(35)(36). We treated young mice with a small molecule inhibitor of the integrated stress response, ISRIB (25 mg/kg via intraperitoneal injections) or vehicle daily starting at day 7 after instillation of bleomycin, when acute lung injury is largely resolved and active fibrogenesis has begun, and continued until harvest at day 28 ( Figure 3A).…”

Section: Resultsmentioning

confidence: 99%

Resetting proteostasis with ISRIB prevents pulmonary fibrosis

Watanabe

Markov

et al. 2020

Preprint

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Aging is among the most important risk factors for the development of pulmonary fibrosis. We found that a small molecule that specifically inhibits translational inhibition induced by activation of the integrated stress response (ISRIB) attenuated the severity of pulmonary fibrosis in young and old mice. The more severe fibrosis in old compared to young mice was associated with increased recruitment of pathogenic monocyte-derived alveolar macrophages. Using genetic lineage tracing and transcriptomic profiling we found that ISRIB modulates stress response signaling in alveolar epithelial cells resulting in decreased apoptosis and decreased recruitment of pathogenic monocyte-derived alveolar macrophages. These data support multicellular model of fibrosis involving epithelial cells, pathogenic monocyte-derived alveolar macrophages and fibroblasts.Inhibition of the integrated stress response in the aging lung epithelium ameliorates pulmonary fibrosis by preventing the prolonged recruitment of monocyte-derived alveolar macrophages.

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“…The proapoptotic, ER-stress-related transcription factor CHOP is present at low levels under physiological conditions but is highly upregulated in response to ER stress [ 15 , 21 ], hypoxia [ 26 , 27 ], or DNA damage [ 28 ], which may also lead to misfolded protein accumulations and UPR activation [ 26 – 28 ]. CHOP expression is mainly regulated at the transcriptional level [ 29 ].…”

Section: Discussionmentioning

confidence: 99%

Regulation and role of the ER stress transcription factor CHOP in alveolar epithelial type-II cells

et al. 2019

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Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by type-II alveolar epithelial cell (AECII) injury and fibroblast hyperproliferation. Severe AECII endoplasmic reticulum (ER) stress is thought to underlie IPF, but is yet incompletely understood. We studied the regulation of C/EBP homologous protein (CHOP), a proapoptotic ER-stress-related transcription factor (TF) in AECII-like cells. Interestingly, single or combined overexpression of the active ER stress transducers activating transcription factor-4 (Atf4) and activating transcription factor-6 (p50Atf6) or spliced x-box-binding protein-1 (sXbp1) in MLE12 cells did not result in a substantial Chop induction, as compared to the ER stress inducer thapsigargin. Employing reporter gene assays of distinct CHOP promoter fragments, we could identify that, next to the conventional amino acid (AARE) and ER stress response elements (ERSE) within the CHOP promoter, activator protein-1 (AP-1) and c-Ets-1 TF binding sites are necessary for CHOP induction. Serial deletion and mutation analyses revealed that both AP-1 and c-Ets-1 motifs act in concert to induce CHOP expression. In agreement, CHOP promoter activity was greatly enhanced upon combined versus single overexpression of AP-1 and c-Ets-1. Moreover, combined overexpression of AP-1 and c-Ets-1 in MLE12 cells alone in the absence of any other ER stress inducer was sufficient to induce Chop protein expression. Further, AP-1 and c-Ets-1 were upregulated in AECII under ER stress conditions and in human IPF. Finally, Chop overexpression in vitro resulted in AECII apoptosis, lung fibroblast proliferation, and collagen-I production. We propose that CHOP activation by AP-1 and c-Ets-1 plays a key role in AECII maladaptive ER stress responses and consecutive fibrosis, offering new therapeutic prospects in IPF. Key messages Overexpression of active ER stress sensors Atf4, Atf6, and Xbp1 does not induce Chop . AP-1 and c-Ets-1 TFs are necessary for induction of the ER stress factor Chop . AP-1 and c-Ets-1 alone induce Chop expression in the absence of any ER stress inducers. AP-1 and c-Ets-1 are induced in AECII under ER stress conditions and in human IPF. Chop expression alone triggers AECII apoptosis and consecutive profibrotic responses. Electronic supplementary material The online version of this article (10.1007/s00109-019-01787-9) contains supplementary material, which is available to authorized users.

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HIF-1α triggers ER stress and CHOP-mediated apoptosis in alveolar epithelial cells, a key event in pulmonary fibrosis

Cited by 120 publications

References 41 publications

IRE1 Endoribonuclease Activity Modulates Hypoxic HIF-1α Signaling in Human Endothelial Cells

IRE1 Endoribonuclease Activity Modulates Hypoxic HIF-1α Signaling in Human Endothelial Cells

Resetting proteostasis with ISRIB prevents pulmonary fibrosis

Regulation and role of the ER stress transcription factor CHOP in alveolar epithelial type-II cells

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