bims-unfpre 2024-08-18 papers

bims-unfpre

Biomed News

on Unfolded protein response

Issue of 2024–08–18
eight papers selected by
Susan Logue, University of Manitoba

UPF3B modulates endoplasmic reticulum stress through interaction with inositol-requiring enzyme-1α.
Megakaryocyte maturation involves activation of the adaptive unfolded protein response.
Endoplasmic reticulum associated degradation preserves neurons viability by maintaining endoplasmic reticulum homeostasis.
Activation of PERK/eIF2α/ATF4/CHOP branch of endoplasmic reticulum stress response and cooperation between HIF-1α and ATF4 promotes Daprodustat-induced vascular calcification.
Mycoplasma hyopneumoniae inhibits the unfolded protein response to prevent host macrophage apoptosis and M2 polarization.
The mammalian Ire1 inhibitor, 4µ8C, exhibits broad anti- Aspergillus activity in vitro and in a treatment model of fungal keratitis.
Inhibition of TFEB deacetylation in proximal tubular epithelial cells (TECs) promotes TFEB activation and alleviates TEC damage in diabetic kidney disease.
ER-phagy drives age-onset remodeling of endoplasmic reticulum structure-function and lifespan.

Cell Death Dis. 2024 Aug 13. 15(8): 587

UPF3B modulates endoplasmic reticulum stress through interaction with inositol-requiring enzyme-1α.

XingSheng Sun, Ruqin Lin, Xinxia Lu, Zhikai Wu, Xueying Qi, Tianqing Jiang, Jun Jiang, Peiqiang Mu, Qingmei Chen, Jikai Wen, Yiqun Deng.

The unfolded protein response (UPR) is a conserved and adaptive intracellular pathway that relieves the endoplasmic reticulum (ER) stress by activating ER transmembrane stress sensors. As a consequence of ER stress, the inhibition of nonsense-mediated mRNA decay (NMD) is due to an increase in the phosphorylation of eIF2α, which has the effect of inhibiting translation. However, the role of NMD in maintaining ER homeostasis remains unclear. In this study, we found that the three NMD factors, up-frameshift (UPF)1, UPF2, or UPF3B, were required to negate the UPR. Among these three NMD factors, only UPF3B interacted with inositol-requiring enzyme-1α (IRE1α). This interaction inhibited the kinase activity of IRE1α, abolished autophosphorylation, and reduced IRE1α clustering for ER stress. BiP and UPF3B jointly control the activation of IRE1α on both sides of the ER membrane. Under stress conditions, the phosphorylation of UPF3B was increased and the phosphorylated sites were identified. Both the UPF3BY160D genetic mutation and phosphorylation at Thr169 of UPF3B abolished its interaction with IRE1α and UPF2, respectively, leading to activation of ER stress and NMD dysfunction. Our study reveals a key physiological role for UPF3B in the reciprocal regulatory relationship between NMD and ER stress.

DOI: https://doi.org/10.1038/s41419-024-06973-3
Genes Cells. 2024 Aug 13.

Megakaryocyte maturation involves activation of the adaptive unfolded protein response.

M Faiz, M L Kalev-Zylinska, C Dunstan-Harrison, D C Singleton, M P Hay, E C Ledgerwood.

  Endoplasmic reticulum stress triggers the unfolded protein response (UPR) to promote cell survival or apoptosis. Transient endoplasmic reticulum stress activation has been reported to trigger megakaryocyte production, and UPR activation has been reported as a feature of megakaryocytic cancers. However, the role of UPR signaling in megakaryocyte biology is not fully understood. We studied the involvement of UPR in human megakaryocytic differentiation using PMA (phorbol 12-myristate 13-acetate)-induced maturation of megakaryoblastic cell lines and thrombopoietin-induced differentiation of human peripheral blood-derived progenitors. Our results demonstrate that an adaptive UPR is a feature of megakaryocytic differentiation and that this response is not associated with ER stress-induced apoptosis. Differentiation did not alter the response to the canonical endoplasmic reticulum stressors DTT or thapsigargin. However, thapsigargin, but not DTT, inhibited differentiation, consistent with the involvement of Ca2+ signaling in megakaryocyte differentiation.

Keywords:  IRE1α; XBP1; calcium; endoplasmic reticulum (ER) stress; megakaryopoiesis; unfolded protein response (UPR)

DOI:  https://doi.org/10.1111/gtc.13151
Front Neurosci. 2024 ;18 1437854

Endoplasmic reticulum associated degradation preserves neurons viability by maintaining endoplasmic reticulum homeostasis.

Shuangchan Wu, Pingting Liu, Marija Cvetanovic, Wensheng Lin.

  Endoplasmic reticulum-associated degradation (ERAD) is a principal quality-control mechanism responsible for targeting misfolded ER proteins for cytosolic degradation. Evidence suggests that impairment of ERAD contributes to neuron dysfunction and death in neurodegenerative diseases, many of which are characterized by accumulation and aggregation of misfolded proteins. However, the physiological role of ERAD in neurons remains unclear. The Sel1L-Hrd1 complex consisting of the E3 ubiquitin ligase Hrd1 and its adaptor protein Sel1L is the best-characterized ERAD machinery. Herein, we showed that Sel1L deficiency specifically in neurons of adult mice impaired the ERAD activity of the Sel1L-Hrd1 complex and led to disruption of ER homeostasis, ER stress and activation of the unfold protein response (UPR). Adult mice with Sel1L deficiency in neurons exhibited weight loss and severe motor dysfunction, and rapidly succumbed to death. Interestingly, Sel1L deficiency in neurons caused global brain atrophy, particularly cerebellar and hippocampal atrophy, in adult mice. Moreover, we found that cerebellar and hippocampal atrophy in these mice resulted from degeneration of Purkinje neurons and hippocampal neurons, respectively. These findings indicate that ERAD is required for maintaining ER homeostasis and the viability and function of neurons in adults under physiological conditions.

Keywords:  ER stress; ER-associated degradation; Purkinje neuron; hippocampal neuron; neurodegeneration

DOI:  https://doi.org/10.3389/fnins.2024.1437854
Front Pharmacol. 2024 ;15 1399248

Activation of PERK/eIF2α/ATF4/CHOP branch of endoplasmic reticulum stress response and cooperation between HIF-1α and ATF4 promotes Daprodustat-induced vascular calcification.

Andrea Tóth, Gréta Lente, Dávid Máté Csiki, Enikő Balogh, Árpád Szöőr, Béla Nagy, Viktória Jeney.

  Introduction: Vascular calcification is accelerated in patients with chronic kidney disease (CKD) and increases the risk of cardiovascular events. CKD is frequently associated with anemia. Daprodustat (DPD) is a prolyl hydroxylase inhibitor for the treatment of CKD-associated anemia that enhances erythropoiesis through the activation of the hypoxia-inducible factor 1 (HIF-1) pathway. Studies showed that DPD promotes osteogenic differentiation of human aortic smooth muscle cells (HAoSMCs) and increases aorta calcification in mice with CKD. HIF-1 activation has been linked with endoplasmic reticulum (ER) stress; therefore, here we investigated the potential contribution of ER stress, particularly activating transcription factor 4 (ATF4), to the pro-calcification effect of DPD. Methods: Here, we used an adenine-induced CKD mouse model and HAoSMCs as an in vitro vascular calcification model to study the effect of DPD. Results: DPD treatment (15 mg/kg/day) corrects anemia but increases the expression of hypoxia (Glut1, VEGFA), ER stress (ATF4, CHOP, and GRP78), and osteo-/chondrogenic (Runx2, Sox9, BMP2, and Msx2) markers and accelerates aorta and kidney calcification in CKD mice. DPD activates the PERK/eIF2α/ATF4/CHOP pathway and promotes high phosphate-induced osteo-/chondrogenic differentiation of HAoSMCs. Inhibition of ER stress with 4-PBA or silencing of ATF4 attenuates HAoSMC calcification. DPD-induced ATF4 expression is abolished in the absence of HIF-1α; however, knockdown of ATF4 does not affect HIF-1α expression. Conclusion: We concluded that DPD induces ER stress in vitro and in vivo, in which ATF4 serves as a downstream effector of HIF-1 activation. Targeting ATF4 could be a potential therapeutic approach to attenuate the pro-calcific effect of DPD.

Keywords:  ATF4; Daprodustat; chronic kidney disease (CKD); endoplasmic reticulum stress; hypoxia-inducible factor 1; prolyl hydroxylase inhibitor; vascular calcification

DOI:  https://doi.org/10.3389/fphar.2024.1399248
Infect Immun. 2024 Aug 12. e0005124

Mycoplasma hyopneumoniae inhibits the unfolded protein response to prevent host macrophage apoptosis and M2 polarization.

Tong Liu, Yujuan Zhang, Huanjun Zhao, Qi Wu, Jiuqing Xin, Qiao Pan.

  Enzootic pneumonia caused by Mycoplasma hyopneumoniae (M. hyopneumoniae) has inflicted substantial economic losses on the global pig industry. The progression of M. hyopneumoniae induced-pneumonia is associated with lung immune cell infiltration and extensive proinflammatory cytokine secretion. Our previous study established that M. hyopneumoniae disrupts the host unfolded protein response (UPR), a process vital for the survival and immune function of macrophages. In this study, we demonstrated that M. hyopneumoniae targets the UPR- and caspase-12-mediated endoplasmic reticulum (ER)-associated classical intrinsic apoptotic pathway to interfere with host cell apoptosis signaling, thereby preserving the survival of host tracheal epithelial cells (PTECs) and alveolar macrophages (PAMs) during the early stages of infection. Even in the presence of apoptosis inducers, host cells infected with M. hyopneumoniae exhibited an anti-apoptotic potential. Further analyses revealed that M. hyopneumoniae suppresses the three UPR branches and their induced apoptosis. Interestingly, while UPR activation typically drives host macrophages toward an M2 polarization phenotype, M. hyopneumoniae specifically obstructs this process to maintain a proinflammatory phenotype in the host macrophages. Overall, our findings propose that M. hyopneumoniae inhibits the host UPR to sustain macrophage survival and a proinflammatory phenotype, which may be implicated in its pathogenesis in inducing host pneumonia.

Keywords:  Mycoplasma hyopneumoniae; antiapoptosis; cytokines; polarization; unfolded protein response

DOI:  https://doi.org/10.1128/iai.00051-24
bioRxiv. 2024 Aug 08. pii: 2024.08.08.607189. [Epub ahead of print]

The mammalian Ire1 inhibitor, 4µ8C, exhibits broad anti- Aspergillus activity in vitro and in a treatment model of fungal keratitis.

Manali M Kamath, Emily M Adams, Jorge D Lightfoot, Becca L Wells, Kevin K Fuller.

Objective: The fungal unfolded protein response consists of a two-component relay in which the ER-bound sensor, IreA, splices and activates the mRNA of the transcription factor, HacA. Previously, we demonstrated that hacA is essential for Aspergillus fumigatus virulence in a murine model of fungal keratitis (FK), suggesting the pathway could serve as a therapeutic target. Here we investigate the antifungal properties of known inhibitors of the mammalian Ire1 protein both in vitro and in a treatment model of FK.
Methods: The antifungal activity of Ire1 inhibitors was tested against conidia of several A. fumigatus isolates by a microbroth dilution assay and against fungal biofilm by XTT reduction. The influence of 4μ8C on hacA mRNA splicing in A. fumigatus was assessed through gel electrophoresis and qRT-PCR of UPR regulatory genes. The toxicity and antifungal profile of 4μ8C in the cornea was assessed by applying drops to uninfected or A. fumigatus -infected corneas 3 times daily starting 4 hours post-inoculation. Corneas were evaluated daily through slit-lamp imaging and optical coherence tomography, or at endpoint through histology or fungal burden quantification via colony forming units.
Results: Among six Ire1 inhibitors screened, the endonuclease inhibitor 4μ8C displayed the strongest antifungal profile with an apparent fungicidal action. The compound both blocked conidial germination and hyphal metabolism of A. fumigatus Af293 in the same concentration range that blocked hacA splicing and UPR gene induction (60-120 µM). Topical treatment of sham-inoculated corneas with 0.5 and 2.5 mM 4μ8C did not impact corneal clarity, but did transiently inhibit epithelialization of corneal ulcers. Relative to vehicle-treated Af293-infected corneas, treatment with 0.5 and 2.5 mM drug resulted in a 50% and >90% reduction in fungal load, respectively, the latter of which corresponded to an absence of clinical signs of infection or corneal pathology.
Conclusion: The in vitro data suggest that 4μ8C displays antifungal activity against A. fumigatus through the specific inhibition of IreA. Topical application of the compound to the murine cornea can furthermore block the establishment of infection, suggesting this class of drugs can be developed as novel antifungals that improve visual outcomes in FK patients.

DOI: https://doi.org/10.1101/2024.08.08.607189
FASEB J. 2024 Aug 31. 38(16): e23884

Inhibition of TFEB deacetylation in proximal tubular epithelial cells (TECs) promotes TFEB activation and alleviates TEC damage in diabetic kidney disease.

Xiaoyu Li, Yaozhi Zhang, Huixia Chen, Yang Wu, Yongming Chen, Siqiao Gong, Yonghan Liu, Huafeng Liu.

  The inhibition of the autophagolysosomal pathway mediated by transcription factor EB (TFEB) inactivation in proximal tubular epithelial cells (TECs) is a key mechanism of TEC injury in diabetic kidney disease (DKD). Acetylation is a novel mechanism that regulates TFEB activity. However, there are currently no studies on whether the adjustment of the acetylation level of TFEB can reduce the damage of diabetic TECs. In this study, we investigated the effect of Trichostatin A (TSA), a typical deacetylase inhibitor, on TFEB activity and damage to TECs in both in vivo and in vitro models of DKD. Here, we show that TSA treatment can alleviate the pathological damage of glomeruli and renal tubules and delay the DKD progression in db/db mice, which is associated with the increased expression of TFEB and its downstream genes. In vitro studies further confirmed that TSA treatment can upregulate the acetylation level of TFEB, promote its nuclear translocation, and activate the expression of its downstream genes, thereby reducing the apoptosis level of TECs. TFEB deletion or HDAC6 knockdown in TECs can counteract the activation effect of TSA on autophagolysosomal pathway. We also found that TFEB enhances the transcription of Tfeb through binding to its promoter and promotes its own expression. Our results, thus, provide a novel therapeutic mechanism for DKD that the alleviation of TEC damage by activating the autophagic lysosomal pathway through upregulating TFEB acetylation can, thus, delay DKD progression.

Keywords:  Trichostatin A; acetylation; diabetic kidney disease; transcription factor EB; tubular epithelial cells

DOI:  https://doi.org/10.1096/fj.202302634R
bioRxiv. 2024 Aug 08. pii: 2024.08.07.607085. [Epub ahead of print]

ER-phagy drives age-onset remodeling of endoplasmic reticulum structure-function and lifespan.

Ekf Donahue, N L Hepowit, B Keuchel, A G Mulligan, D J Johnson, M Ellisman, R Arrojo E Drigo, J MacGurn, K Burkewitz.

The endoplasmic reticulum (ER) comprises an array of structurally distinct subdomains, each with characteristic functions. While altered ER-associated processes are linked to age-onset pathogenesis, whether shifts in ER morphology underlie these functional changes is unclear. We report that ER remodeling is a conserved feature of the aging process in models ranging from yeast to C. elegans and mammals. Focusing on C. elegans as an exemplar of metazoan aging, we find that as animals age, ER mass declines in virtually all tissues and ER morphology shifts from rough sheets to tubular ER. The accompanying large-scale shifts in proteomic composition correspond to the ER turning from protein synthesis to lipid metabolism. To drive this substantial remodeling, ER-phagy is activated early in adulthood, promoting turnover of rough ER in response to rises in luminal protein-folding burden and reduced global protein synthesis. Surprisingly, ER remodeling is a pro-active and protective response during aging, as ER-phagy impairment limits lifespan in yeast and diverse lifespan-extending paradigms promote profound remodeling of ER morphology even in young animals. Altogether our results reveal ER-phagy and ER morphological dynamics as pronounced, underappreciated mechanisms of both normal aging and enhanced longevity.

DOI: https://doi.org/10.1101/2024.08.07.607085